TECHNICAL FIELD
[0001] The present disclosure relates to a steel component and in particular to a steel
component having excellent wear resistance. Further, the present disclosure relates
to a method of producing the steel component.
BACKGROUND
[0002] Carbon steel, a steel containing a high concentration of carbon, has high hardness
and is therefore widely used as a material for textile machinery components, bearing
components, machine blades, and other steel components that require wear resistance.
[0003] In typical steel component production, a cold-rolled steel sheet as a raw material
is worked into a component shape, followed by quenching treatment and tempering treatment.
While quenching treatment increases hardness and reduces toughness, subsequent tempering
treatment may improve toughness. However, there is a problem that tempering treatment
reduces hardness.
[0004] Therefore, various technologies have been proposed to further increase the hardness
of steel components and achieve better wear resistance.
[0005] For example, in Patent Literature (PTL) 1, a technology is described for improving
formability and wear resistance in a steel sheet having a ferrite-cementite microstructure
by increasing the grain size of ferrite, spheroidizing carbides (mainly cementite)
of appropriate particle size, and reducing pearlite microstructure.
[0006] Further, in PTL 2, a technology is described for improving wear resistance of a cold-rolled
steel sheet by annealing the steel sheet under specific conditions to make the metal
microstructure a pearlitic microstructure, which is a layered microstructure of hard
cementite and soft ferrite.
[0007] In PTL 3, a technology is described for improving wear resistance of a steel sheet
by precipitating coarse Nb, Ti carbides having an equivalent circular diameter of
0.5 µm or more in the ferrite phase matrix microstructure.
[0008] In PTL 4, a technology is described for improving wear resistance of steel by precipitating
coarse carbides having a particle size of 2 µm or more in the matrix microstructure.
[0009] In PTL 5, a technology is proposed to improve a spheroidization rate of carbides
such as cementite and to improve toughness of a steel sheet containing C: 0.5 mass%
to 0.7 mass% by bringing the steel sheet to an annealing finishing state in a stage
immediately before final quenching and tempering.
[0010] In PTL 6, a technology is proposed to produce a soft high-carbon steel sheet having
excellent blanking properties by increasing the number density of generated voids
in the material by bringing the material to an annealing finishing state in a stage
immediately before final quenching and tempering.
[0011] In PTL 7, a technology is proposed to improve impact toughness and wear resistance
in a high-carbon steel sheet by controlling the formation of cementite, not including
niobium, titanium, or vanadium carbides, and by achieving desired values for the spheroidization
rate and number density of cementite.
[0012] In PTL 8, a technology is proposed to improve toughness by adjusting the particle
size of cementite, not including niobium, titanium, or vanadium carbides, and the
grain size of retained austenite and prior austenite, by bringing the material to
an annealing finishing state in a stage immediately before final austempering, and
further, by obtaining a bainitic microstructure instead of a martensitic tempered
microstructure obtainable in a typical heat treatment of quenching and tempering.
CITATION LIST
Patent Literature
SUMMARY
(Technical Problem)
[0014] According to conventional technologies, such as those proposed in PTL 1 to 8, there
is some improvement in the hardness and wear resistance of steel. However, the inventors
have found that steel components produced from conventional steel material may not
have sufficient wear resistance in actual use.
[0015] In view of the circumstances described above, it would be helpful to provide a steel
component having excellent wear resistance.
(Solution to Problem)
[0016] As a result of studies, the inventors arrived at the following discoveries.
- (1) When a steel component is actually used, temperature rises due to friction with
other parts. For example, when a steel component is used as a textile machinery component,
such as a knitting needle, the steel component is constantly exposed to friction with
fibers, resulting in a rise in temperature.
- (2) Accordingly, to achieve excellent wear resistance in actual use, not only inhibiting
static wear caused by abrasion between materials, but also inhibiting softening of
the steel sheet due to the rise in temperature during friction is necessary.
- (3) To improve the wear resistance of a steel component, carbides containing at least
one of Nb, Ti, or V need to be precipitated in the steel. Among the carbides, coarse
carbides have an effect of inhibiting static wear. For example, in the case of a textile
machinery component, the presence of coarse carbides may reduce the amount of abrasion
caused by fibers and foreign matter such as grit attached to fibers.
- (4) On the other hand, among the carbides, fine carbides have an effect of inhibiting
softening of a steel sheet caused by rising temperature during friction. That is,
the presence of fine carbides inhibits a hardness reduction caused by the recovery
of dislocation microstructure when temperature rises due to friction. Further, in
a steel in which fine carbides are present, prior austenite grains are refined during
quenching and tempering, which increases a grain boundary strengthening effect and,
as a result, further inhibits hardness reduction caused by dislocation microstructure
recovery.
- (5) To obtain the effects described above, the average particle sizes of coarse and
fine carbides, respectively, need to be controlled within specific ranges.
[0017] The present disclosure is based on the discoveries described above, and primary features
of the present disclosure are as described below.
- 1. A steel component comprising a chemical composition containing (consisting of),
in mass%,
C: 0.6 % to 1.25 %,
Si: 0.10 % to 0.55 %,
Mn: 0.20 % to 2.0 %,
P: 0.0005 % to 0.05 %,
S: 0.01 % or less,
Al: 0.001 % to 0.1 %,
N: 0.001 % to 0.009 %,
Cr: 0.05 % to 0.55 %, and
at least one of Ti: 0.05 % to 1.0 %, Nb: 0.1 % to 0.5 %, or V: 0.01 % to 1.0 %,
with the balance being Fe and inevitable impurity,
wherein the average grain size of prior austenite grains is 25 µm or less,
further comprising carbides containing at least one of Nb, Ti, or V, wherein
among the carbides, the average particle size of particles having a particle size
of 0.1 µm or more is 0.15 µm to 2.5 µm, and
among the carbides, the average particle size of particles having a particle size
less than 0.1 µm is 0.005 µm to 0.05 µm.
- 2. The steel component according to aspect 1, wherein the chemical composition further
contains, in mass%, at least one selected from the group consisting of:
Sb: 0.1 % or less,
Hf: 0.5 % or less,
REM: 0.1 % or less,
Cu: 0.5 % or less,
Ni: 3.0 % or less,
Sn: 0.5 % or less,
Mo: 1 % or less,
Zr: 0.5 % or less,
B: 0.005 % or less, and
W: 0.01 % or less.
- 3. The steel component according to aspect 1 or 2, wherein the steel component is
any one of a component for textile machinery, a bearing component, or a blade for
machinery.
- 4. A method of producing a steel component, the method comprising:
heating a steel slab comprising the chemical composition according to aspect 1 or
2 under a set of conditions including: a slab heating temperature of 1,100 °C or more
and a holding time of 1.0 h or more;
processing the heated steel slab into a hot-rolled steel sheet under a set of conditions
including a finishing start temperature of Ac3 or more;
cooling the hot-rolled steel sheet under a set of conditions including: a time from
end of hot rolling to start of cooling of 2.0 s or less, an average cooling rate of
25 °C/s or more, and a cooling stop temperature of 640 °C to 720 °C;
coiling the cooled hot-rolled steel sheet;
applying, to the hot-rolled steel sheet after coiling, first annealing under a set
of conditions including: an annealing temperature of 650 °C or more and 720 °C or
less, and an annealing time of 3 h or more;
applying, to the hot-rolled steel sheet after the first annealing, a cycle applied
twice or more of cold rolling at a rolling ratio of 15 % or more and second annealing
at an annealing temperature of 600 °C to 800 °C and a heating rate of 50 °C/h or more;
final cold rolling at a rolling ratio of 30 % or more; and
applying, to the cold-rolled steel sheet:
machining into a component shape, and
heat treatment including quenching under a set of conditions including: a quenching
temperature of 700 °C or more and 950 °C or less and a holding time of 1.0 min or
more to 60 min or less, and tempering under a set of conditions including: a tempering
temperature of 100 °C to 400 °C and a holding time of 20 min or more to 3 h or less.
(Advantageous Effect)
[0018] The present disclosure provides a steel component having excellent wear resistance.
The steel component according to the present disclosure exhibits excellent wear resistance
not only under static conditions, but also under conditions where temperature rises
due to friction, and is therefore suitable for use for various applications including
components for textile machinery, bearing components, and blades for machinery.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In the accompanying drawings:
FIG. 1 is a schematic diagram illustrating shape of a wear test piece;
FIG. 2 is a schematic diagram of a wear test apparatus; and
FIG. 3 is a schematic diagram illustrating shape of the wear test apparatus used for
Examples.
DETAILED DESCRIPTION
[0020] A detailed description is provided below. The present disclosure is not limited to
the following embodiments. Further, as described above, the present disclosure focuses
on carbides containing at least one of Nb, Ti, or V. Therefore, in the following description,
"carbides containing at least one of Nb, Ti, or V" may simply be referred to as "carbides".
[Chemical composition]
[0021] The cold-rolled steel sheet according to the present disclosure has the chemical
composition described above. The reasons for the above limitations are described below.
Hereinafter, "%" as a unit of content indicates "mass%" unless otherwise specified.
C: 0.6 % to 1.25 %
[0022] C is an element necessary to improve hardness after quenching and tempering. Further,
C is an element necessary to form cementite and carbides of elements such as Nb, Ti,
V, and the like. To produce the required carbides and to obtain hardness and wear
resistance after quenching and tempering, C content needs to be 0.6 % or more. The
C content is therefore 0.6 % or more. The C content is preferably 0.7 % or more. On
the other hand, when the C content exceeds 1.25 %, hardness increases excessively
and embrittlement occurs. When the C content exceeds 1.25 %, surface scale becomes
firm during heating, resulting in deterioration of surface characteristics, and the
surface becomes prone to cracking during subsequent cold rolling, as well as cracking
when quenching, resulting in reduced wear resistance. The C content is therefore 1.25
% or less. The C content is preferably 1.20 % or less.
Si: 0.10 % to 0.55 %
[0023] Si is an element that has an effect of increasing strength through solid solution
strengthening, and an increase in strength also improves wear resistance. To achieve
this effect, Si content is 0.10 % or more. The Si content is preferably 0.12 % or
more. On the other hand, when the Si content is excessive, coarse ferrite is formed
on the steel sheet surface during hot working, which inhibits the formation of carbides
necessary for improving wear resistance in subsequent working. The Si content is therefore
0.55 % or less. The Si content is preferably 0.50 % or less. The Si content is more
preferably 0.45 % or less.
Mn: 0.20 % to 2.0 %
[0024] Mn is an element having an effect of improving hardness by promoting quenching and
inhibiting temper softening. In order to inhibit temper softening, inhibiting the
formation of C as cementite or delaying dislocation recovery is necessary, and Mn
has both of these effects. Further, not only during tempering, Mn also has an effect
of inhibiting dislocation recovery caused by friction heat during use of a steel component.
To achieve these effects, Mn content is 0.20 % or more. The Mn content is preferably
0.25 % or more. On the other hand, when the Mn content exceeds 2.0 %, a banded microstructure
is formed due to Mn segregation. In particular, abnormal grain growth and microstructure
nonuniformity are likely to occur at MnS segregations, which inhibit carbide formation
and are a cause of cracking and shape defects during component machining. The Mn content
is therefore 2.0 % or less. The Mn content is preferably 1.95 % or less.
P: 0.0005 % to 0.05 %
[0025] The addition of a small amount of P increases hardness through solid solution strengthening
and thus improves wear resistance. To achieve this effect, P content is 0.0005 % or
more. The P content is preferably 0.0008 % or more. On the other hand, when the P
content exceeds 0.05 %, the strength of grain boundaries decreases and embrittlement
occurs. The P content is therefore 0.05 % or less. The P content is preferably 0.045
% or less.
S: 0.01 % or less
[0026] S consumes Mn by forming sulfides with Mn, and therefore reduces hardenability. As
hardenability decreases, strength of steel decreases, resulting in lower wear resistance.
S content is therefore 0.01 % or less. From the viewpoint of improving wear resistance,
the lower the S content, the better, and therefore a lower limit of S content is not
particularly limited and may be 0 %. However, excessive reduction leads to increased
production costs, and therefore from the viewpoint of industrial production, the S
content is preferably 0.0005 % or more. The S content is more preferably 0.001 % or
more.
Al: 0.001 % to 0.1 %
[0027] Al is an element necessary for deoxidation during steelmaking. Al content is therefore
0.001 % or more. On the other hand, an excess of Al results in the formation of coarse
nitrides. The nitrides are often formed on the surface of steel, and promote formation
of cracks and voids initiating from the nitrides, thus reducing wear resistance. Al
content is therefore 0.1 % or less. The Al content is preferably 0.08 % or less. The
Al content is more preferably 0.06 % or less.
N: 0.001 % to 0.009 %
[0028] The addition of a small amount of N may form fine nitrides and improve toughness
by refining grain size. To achieve these effects, N content is 0.001 % or more. On
the other hand, an excess of N combines with Al to form coarse nitrides. The nitrides
are often formed on the surface of steel, and promote formation of cracks and voids
initiating from the nitrides, thus reducing wear resistance. The N content is therefore
0.009 % or less. The N content is preferably 0.008 % or less.
Cr: 0.05 % to 0.55 %
[0029] Cr is an element that has an effect of increasing hardenability of steel and improving
hardness, and therefore the addition of Cr improves wear resistance. To achieve these
effects, Cr content is 0.05 % or more. The Cr content is preferably 0.12 % or more.
On the other hand, an excess of Cr causes formation of coarse Cr carbides and Cr nitrides,
and voids forming around the Cr carbides and Cr nitrides results in reduced performance
of steel components. Further, as a result of the formation of Cr carbides, the formation
of carbides effective in improving wear resistance is inhibited. The Cr content is
therefore 0.55 % or less. The Cr content is preferably 0.95 % or less.
[0030] The chemical composition described above contains at least one element selected from
the group consisting of Ti: 0.05 % to 1.0 %, Nb: 0.1 % to 0.5 %, and V: 0.01 % to
1.0 %.
Ti: 0.05 % to 1.0 %
[0031] Ti is an element that has an effect of forming fine carbides and inhibiting both
static wear and thermal wear. Further, Ti has an effect of improving wear resistance
by refining prior austenite grains during quenching and inhibiting dislocation recovery.
When Ti is added, in order to obtain these effects, Ti content is 0.05 % or more.
The Ti content is preferably 0.015 % or more. On the other hand, excessive addition
of Ti causes carbides to become coarser than necessary, and the carbides become initiation
points for voids and cracking, which reduces the workability of steel sheets when
worked into component shapes. The Ti content is therefore 1.0 % or less. The Ti content
is preferably 0.9 % or less.
Nb: 0.1 % to 0.5 %
[0032] Nb is an element that has an effect of forming fine carbides and inhibiting both
static wear and thermal wear. Further, Nb has an effect of improving wear resistance
by refining prior austenite grains during quenching and inhibiting dislocation recovery.
When Nb is added, in order to obtain these effects, Nb content is 0.1 % or more. On
the other hand, excessive addition of Nb causes carbides to become coarser than necessary,
and the carbides become initiation points for voids and cracking, which reduces the
workability of steel sheets when worked into component shapes. The Nb content is therefore
0.5 % or less. The Nb content is preferably 0.45 % or less.
V: 0.01 % to 1.0 %
[0033] V is an element that has an effect of forming fine carbides and inhibiting both static
wear and thermal wear. Further, V has an effect of improving wear resistance by refining
prior austenite grains during quenching and inhibiting dislocation recovery. When
V is added, to obtain these effects, V content is 0.01 % or more. On the other hand,
excessive addition of V causes carbides to become coarser than necessary, and the
carbides become initiation points for voids and cracking, which reduces the workability
of steel sheets when worked into component shapes. The V content is therefore 1.0
% or less. The V content is preferably 0.95 % or less.
[0034] The cold-rolled steel sheet according to an embodiment of the present disclosure
has a chemical composition consisting of the above components, with the balance being
Fe and inevitable impurity.
[0035] Further, according to another embodiment of the present disclosure, the chemical
composition described above contains at least one selected from the group consisting
of Sb: 0.1 % or less, Hf: 0.5 % or less, REM: 0.1 % or less, Cu: 0.5 % or less, Ni:
3.0 % or less, Sn: 0.5 % or less, Mo: 1 % or less, Zr: 0.5 % or less, B: 0.005 % or
less, and W: 0.01 % or less.
Sb: 0.1 % or less
[0036] Sb is an effective element for improving corrosion resistance, but when added in
excess, a rich Sb layer is formed under scale generated during hot rolling, causing
surface defects (scratches) on the steel sheet after hot rolling. Sb content is therefore
0.1 % or less. A lower limit of the Sb content is not particularly limited. From the
viewpoint of increasing the effect of Sb addition, the Sb content is preferably 0.0003
% or more.
Hf: 0.5 % or less
[0037] Hf is an effective element for improving corrosion resistance, but when added in
excess, a rich Hf layer is formed under scale generated during hot rolling, causing
surface defects (scratches) on the steel sheet after hot rolling. Hf content is therefore
0.5 % or less. A lower limit of the Hf content is not particularly limited. From the
viewpoint of increasing the effect of Hf addition, the Hf content is preferably 0.001
% or more.
REM: 0.1 % or less
[0038] REM (rare earth metals) are elements that improve strength of steel. However, excessive
addition of REM may retard refinement of carbides, promote non-uniform deformation
during cold working and degrade surface characteristics. REM content is therefore
0.1 % or less. A lower limit of the REM content is not particularly limited. From
the viewpoint of increasing the effect of REM addition, the REM content is preferably
0.005 % or more.
Cu: 0.5 % or less
[0039] Cu is an effective element for improving corrosion resistance, but when added in
excess, a rich Cu layer is formed under scale generated during hot rolling, causing
surface defects (scratches) on the steel sheet after hot rolling. Cu content is therefore
0.5 % or less. A lower limit of the Cu content is not particularly limited. From the
viewpoint of increasing the effect of Cu addition, the Cu content is preferably 0.01
% or more.
Ni: 3.0 % or less
[0040] Ni is an element that improves strength of steel. However, excessive addition may
promote non-uniform deformation during cold working and degrade surface characteristics.
Ni content is therefore 3.0 % or less. A lower limit of the Ni content is not particularly
limited. From the viewpoint of increasing the effect of Ni addition, the Ni content
is preferably 0.01 % or more.
Sn: 0.5 % or less
[0041] Sn is an effective element for improving corrosion resistance, but when added in
excess, a rich Sn layer is formed under scale generated during hot rolling, causing
surface defects (scratches) on the steel sheet after hot rolling. Sn content is therefore
0.5 % or less. A lower limit of the Sn content is not particularly limited. From the
viewpoint of increasing the effect of Sn addition, the Sn content is preferably 0.0001
% or more.
Mo: 1 % or less
[0042] Mo is an element that improves strength of steel. However, excessive addition of
Mo may retard the spheroidization of carbides, promote non-uniform deformation during
cold working, and degrade surface characteristics. The Mo content is therefore 1 %
or less. A lower limit of the Mo content is not particularly limited. From the viewpoint
of increasing the effect of Mo addition, the Mo content is preferably 0.001 % or more.
Zr: 0.5 % or less
[0043] Zr is an effective element for improving corrosion resistance, but when added in
excess, a rich Zr layer is formed under scale generated during hot rolling, causing
surface defects (scratches) on the steel sheet after hot rolling. Zr content is therefore
0.5 % or less. A lower limit of the Zr content is not particularly limited. From the
viewpoint of increasing the effect of Zr addition, the Zr content is preferably 0.01
% or more.
B: 0.005 % or less
[0044] B is an element that has an effect of improving hardenability and may be added. However,
when B content exceeds 0.005 %, surface cracking is likely to occur during quenching.
The B content is therefore 0.005 % or less. A lower limit of the B content is not
particularly limited. From the viewpoint of increasing the effect of B addition, when
B is added, the B content is preferably 0.0001 % or more.
W: 0.01 % or less
[0045] W is an element that has an effect of improving hardenability and may be added. However,
when W content exceeds 0.01 %, surface cracking is likely to occur during quenching.
The W content is therefore 0.01 % or less. A lower limit of the W content is not particularly
limited. From the viewpoint of increasing the effect of W addition, when W is added,
the W content is preferably 0.001 % or more.
Average grain size of prior austenite grains: 25 µm or less
[0046] A grain boundary strengthening effect is improved by refining prior austenite grains.
As a result, dislocation recovery during frictional heat generation is inhibited,
and therefore hardness may be maintained even under a hot environment, improving wear
resistance. To achieve the effect, the average grain size of prior austenite grains
is 25 µm or less.
[Carbides]
[0047] The steel component according to the present disclosure contains carbides including
at least one of Nb, Ti, or V. Conventionally, cementite has been used to improve wear
resistance, but carbides containing at least one of Nb, Ti, or V are harder than cementite,
and therefore precipitation of carbides containing at least one of Nb, Ti, or V is
able to improve wear resistance more than conventionally.
[0048] As mentioned previously, among the carbides, coarse carbides have the effect of inhibiting
static wear, while fine carbides have the effect of inhibiting wear at elevated temperatures
caused by friction. Therefore, by appropriately controlling particle sizes of coarse
carbides and fine carbides, respectively, the wear resistance of steel components
in actual use may be effectively improved.
[0049] According to the present disclosure, among carbides containing at least one of Nb,
Ti, or V, carbides having a particle size of 0.1 µm or more are defined as coarse
carbides and carbides having a grain size of less than 0.1 µm are defined as fine
carbides.
• Coarse carbides
[0050] The coarse carbides act to inhibit static wear. For example, in the case of a textile
machinery component such as a knitting needle, the presence of the coarse carbides
may reduce wear caused by abrasion with fibers and foreign matter such as grit attached
to the fibers. However, when the average particle size of the coarse carbides is less
than 0.15 µm, resistance to static wear is not exhibited. The average particle size
of the coarse carbides is therefore 0.15 µm or more. On the other hand, when the carbides
become too coarse, the opportunity for the carbides to function as resistance is reduced,
and therefore the effect of resistance to wear saturates. The average particle size
of the coarse carbides is therefore 2.5 µm or less. The number density of the coarse
carbides is not particularly limited. The higher the number density, the better, and
250/mm
2 or more is preferred. The coarse carbides may be present at crystal grain boundaries
or within crystal grains.
• Fine carbides
[0051] The fine carbides stabilize dislocation microstructure and help prevent dislocation
recovery when temperature rises due to frictional heat. Accordingly, by precipitating
the fine carbides, softening due to frictional heat may be inhibited and wear resistance
under a hot environment may be improved. The effect of inhibiting dislocation recovery
increases with a smaller average particle size of the fine carbides. The average particle
size of the fine carbides is therefore 0.05 µm or less. On the other hand, excessively
fine carbides lead to excessive hardness and embrittlement. The average particle size
of the fine carbides is therefore 0.005 µm or more. The fine carbides are more effective
when formed within crystal grains than at crystal grain boundaries. The number density
of the fine carbides is not particularly limited. The higher the number density, the
greater the effect, and 0.11/µm
2 or more is preferred.
[0052] Further, the microstructure of the steel component according to the present disclosure
is not particularly limited. Desired properties are obtainable as long as the conditions
described above are met. Typically, the microstructure of the steel component according
to the present disclosure may consist of tempered martensite, cementite, and carbides
containing at least one of Nb, Ti, or V. The cementite and the carbides containing
at least one of Nb, Ti, or V are preferably spheroidized. Specifically, the spheroidization
ratio of the carbides, defined by the following expression using average major axis
length La and average minor axis length Lb of the carbides, is preferably 0.71 or
more.

[0053] La is obtained by dividing the sum of the major axis length of all carbides in a
100 µm
2 range by the number of such carbides. Further, Lb is obtained by dividing the sum
of the minor axis length of all carbides in a 100 µm
2 range by the number of such carbides.
[Sheet thickness]
[0054] The sheet thickness of the cold-rolled steel sheet is not particularly limited and
may be any thickness. The sheet thickness is preferably 0.1 mm or more. The sheet
thickness is more preferably 0.2 mm or more. Further, an upper limit of the sheet
thickness is not particularly limited. The sheet thickness is particularly 2.5 mm
or less. The sheet thickness is more preferably 1.6 mm or less. The sheet thickness
is even more preferably 0.8 mm or less. When the sheet thickness is 0.2 mm or more
and 0.8 mm or less, the cold-rolled steel sheet is particularly suitable for use as
a material for knitting needles and the like.
[Method for producing cold-rolled steel sheet]
[0055] The following describes a method for producing a cold-rolled steel sheet according
to an embodiment.
[0056] The cold-rolled steel sheet may be produced by performing the following processes
in sequence, starting with a steel slab having the chemical composition described
above.
- (1) Heating
- (2) Hot rolling
- (3) Cooling
- (4) Coiling
- (5) First annealing
- (6) Cold rolling
- (7) Second annealing
- (8) Final cold rolling
- (9) Machining and heat treatment
[0057] The processes (6) and (7) above are applied two or more times. The following describes
each of the processes.
(1) Heating
[0058] First, a steel slab having the chemical composition described above is heated. A
method for producing the steel slab is not particularly limited, and any method may
be used. For example, composition adjustment of the steel slab may be performed by
a blast furnace converter steelmaking process or by an electric furnace steelmaking
process. Further, for example, casting from molten steel into a slab may be done by
continuous casting or by blooming.
Slab heating temperature: 1,100 °C or more
Holding time: 1.0 h or more
[0059] In the heating, the steel slab is heated under a set of conditions including: a slab
heating temperature of 1,100 °C or more and a holding time of 1.0 h or more, in order
to homogenize the steel microstructure and to allow some carbides in the steel to
be solid-dissolved and the rest to be precipitated.
[0060] Some C combined with Nb, Ti, V to form the coarse carbides needs to be precipitated
at the slab heating stage described above, while other undissolved carbides are dissolved
at the slab heating stage in order to precipitate to desired dimensions at a later
annealing stage. When the slab heating temperature is lower than 1,100 °C or when
the holding time is shorter than 1 h, coarse Nb, Ti, V carbides are not precipitated,
and later, coarse Nb, Ti, V carbides to increase resistance to static wear are not
obtainable. On the other hand, when the slab heating temperature is too high, Nb,
Ti, V solid-solubilize, decreasing a precipitation amount, and therefore the slab
heating temperature is preferably 1,380 °C or less.
(2) Hot rolling
[0061] The heated slab is then hot rolled to obtain a hot-rolled steel sheet. In the hot
rolling, rough rolling and finishing rolling may be performed according to conventional
methods.
Finishing start temperature: Ac3 or more
[0062] When the finishing start temperature of the hot rolling is less than Ac3, stretched
ferrite is formed in the steel sheet after hot rolling, and this stretched ferrite
remains in the finally obtainable cold-rolled steel sheet. As a result, the formation
of carbides at grain boundaries and within grains, which is effective in improving
wear resistance, is inhibited. The finishing start temperature of the hot rolling
is therefore Ac3 or more. An upper limit of the finishing start temperature is not
particularly limited. The finishing start temperature is preferably 1,200 °C or less.
[0063] The Ac3 temperature (°C) is obtained by the following Formula (1).

[0064] Here, the element symbols denote the content in mass% of the respective elements,
and the content of any element not contained is assumed to be 0.
(3) Cooling
Time from end of hot rolling to start of cooling: 2.0 s or less
[0065] The hot-rolled steel sheet is then cooled. When a long time elapses between the end
of hot rolling and the start of cooling, coarse ferrite grains are formed in a surface
layer of the steel sheet and remain until later processing. As a result, the precipitation
of carbides to grain boundaries and into grains, which is effective in improving wear
resistance, is inhibited. The time between the end of hot rolling and the start of
cooling is therefore 2.0 s or less. In view of the above, the shorter the time between
the end of hot rolling and the start of cooling, the better, and therefore a lower
limit is not particularly limited. However, from an industrial production viewpoint,
the time may be 0.5 s or more, or even 0.8 s or more.
Average cooling rate: 25 °C/s or more
[0066] Similarly, when the average cooling rate during the cooling is less than 25 °C/s,
coarse ferrite grains are formed in a surface layer of the steel sheet, and precipitation
of carbides that are effective in improving wear resistance is inhibited. The average
cooling rate in the cooling is therefore 25 °C/s or more. An upper limit of the average
cooling rate is not particularly limited. When the cooling rate is excessively high,
volume expansion caused by transformation during subsequent coiling results in a poor
coiling shape. Therefore, from the viewpoint of achieving a good coiling shape, the
average cooling rate is preferably 160 °C/s or less. The average cooling rate is more
preferably 150 °C/s or less.
Cooling stop temperature: 640 °C to 720 °C
[0067] When the cooling stop temperature is too high during the cooling, a non-uniform microstructure
consisting of abnormally coarse portions and fine portions is formed, which inhibits
subsequent carbide formation. The cooling stop temperature is therefore 720 °C or
less. On the other hand, when the cooling stop temperature is too low, coiling shape
defects occur due to volume expansion caused by transformation during coiling. As
a result, non-uniform strain is introduced into the steel sheet during subsequent
cold rolling, and therefore carbides of the desired particle size are not obtained,
and wear resistance is not improved. The cooling stop temperature is therefore 640
°C or more.
(4) Coiling
[0068] After the cooling is stopped, the cooled hot-rolled steel sheet is coiled. At this
time, the coiling temperature is not particularly limited. The coiling temperature
is preferably 600 °C to 700 °C.
(5) First annealing
[0069]
Annealing temperature: 650 °C or more and 720 °C or less
Annealing time: 3 h or more
[0070] The hot-rolled steel sheet after the coiling is subjected to the first annealing
under a set of conditions including: an annealing temperature of 650 °C or more and
720 °C or less, and an annealing time of 3 h or more. The microstructure of the hot-rolled
steel sheet after the coiling is a pearlitic microstructure lined with plate-like
cementite and ferrite. When the microstructure is pearlitic, strain is not introduced
stably during subsequent cold rolling, and the cold-rolled steel sheet may be defective
in shape. Accordingly, breaking up the pearlitic microstructure and spheroidizing
the carbides is necessary. However, the pearlitic microstructure is stable to heat,
and therefore tends to maintain plate shapes. The plate-like microstructure needs
to be broken up by holding at a high temperature for a long time to increase interface
area. The first annealing is therefore performed at a temperature of 650 °C or more
for 3 h or more. After the first annealing, further cold rolling and second annealing
helps to break up plate-like cementite. On the other hand, when the annealing temperature
is higher than 720 °C, microstructure change proceeds preferentially from one portion,
resulting in a mixed microstructure of coarse and fine microstructures, and ultimately
carbides of the desired size are not obtained, and wear resistance is not improved.
An upper limit of the annealing time is not particularly limited. An excessively long
annealing time reduces productivity and also saturates the effect. Therefore, the
annealing time is preferably 20 h or less.
[0071] Prior to the first annealing, the hot-rolled steel sheet is preferably pickled.
(6) Cold rolling
(7) Second annealing
[0072] Cold rolling is an important process for improving wear resistance, as the plate-like
carbides broken up in the first annealing process are further broken up and dispersed
throughout the steel sheet, and dispersed at the desired dimensions by the second
annealing process. Plate-like carbides formed after hot rolling and coiling are stable,
and therefore tend to remain until later stages of production. Plate-like carbide
formation may cause void formation and cracking. Further, wear progresses unilaterally
in portions of the microstructure where carbide formation does not occur due to not
being dispersed throughout the steel sheet.
[0073] Therefore, in order to precipitate carbides having a particle size effective for
improving wear resistance, the hot-rolled steel sheet after the first annealing is
subjected to two or more cycles of cold rolling and second annealing. The cold rolling
is used to break up the plate-like carbides formed in the steel sheet, and the second
annealing is used to distribute the carbides of the desired dimensions throughout
the steel sheet. To achieve these effects, the rolling ratio in the cold rolling is
15 % or more and the annealing temperature in the second annealing is 600 °C or more.
On the other hand, when the annealing temperature is higher than 800 °C, prior austenite
grains in the finally obtained microstructure become coarser, resulting in decreased
wear resistance during friction heat generation. The annealing temperature is therefore
800 °C or less.
[0074] When the heating rate in the second annealing is too slow, local coarsening of the
carbides occurs, and the fine carbides necessary to inhibit the softening of the steel
sheet as temperature rises during friction are not obtained. The heating rate is therefore
50 °C/h or more. An upper limit of the heating rate is not particularly limited. The
heating rate is preferably 200 °C/s or less.
[0075] Although a higher rolling ratio in the cold rolling is better, when the rolling ratio
is 65 % or more, the shape of a resulting cold-rolled steel sheet may become unstable.
The rolling ratio is therefore preferably less than 65 %.
[0076] The number of cycles of the cold rolling and the second annealing is two or more.
Two or more cycles of the cold rolling and the annealing refines the microstructure
and distributes carbides throughout the steel sheet to achieve the final desired carbide
sizes. A large number of cycles is preferable to consistently obtain good steel sheet
shape and thickness accuracy, and an upper limit of the number of cycles is not particularly
limited. However, when the number of cycles exceeds five, the effect saturates, and
therefore the number of cycles is preferably five or less.
(8) Final cold rolling
Rolling ratio: 30 % or more
[0077] After the cycle of the cold rolling and the second annealing is performed two or
more times as described above, final cold rolling at a rolling ratio of 30 % or more
is further applied. According to the final cold rolling at a rolling ratio of 30 %
or more, the fine carbides are produced during final quenching and tempering, which
improves wear resistance during frictional heat generation. Further, final cold rolling
at a rolling ratio of 30 % or more refines prior austenite grain size, and therefore
further improves wear resistance. The larger the rolling ratio in the final cold rolling,
the better, but the shape of the steel sheet may become unstable when the rolling
ratio is 65 % or more. The rolling ratio is therefore preferably less than 65 %.
[0078] Further, the final cold-rolled steel sheet may be subjected to further optional surface
treatment.
(9) Machining and heat treatment
[0079] The resulting cold-rolled steel sheet is then machined into component shapes and
heat-treated to produce the final steel component. The method of machining is not
particularly limited and any method may be applied. The machining may be, for example,
at least one of blanking, cutting work, drawing, bending, or polishing.
[0080] The heat treatment includes quenching under a set of conditions including: a quenching
temperature of 700 °C or more and 950 °C or less and a holding time of 1.0 min or
more to 60 min or less, and tempering under a set of conditions including: a tempering
temperature of 100 °C to 400 °C and a holding time of 20 min or more to 3 h or less.
The quenching and tempering conditions are important to control carbide particle size
and prior austenite grain size, in order to obtain excellent wear resistance.
[0081] In order to produce the fine carbides, the quenching temperature (heating temperature
during quenching) needs to be high. The quenching temperature is therefore 700 °C
or more. The quenching temperature is preferably 720 °C or more. On the other hand,
when the quenching temperature is too high, prior austenite grain size increases and
wear resistance decreases. The quenching temperature is therefore 950 °C or less.
The quenching temperature is preferably 920 °C or less.
[0082] In order to produce carbides of the desired dimensions during the quenching, holding
at the heating temperature for 1.0 min or more is necessary. The holding time is therefore
1.0 min or more. On the other hand, when the holding time exceeds 60 min, prior austenite
grains become coarser and wear resistance decreases. The holding time is therefore
60 min or less. Cooling in the quenching process is preferably performed by cooling
to room temperature using oil or other coolant.
[0083] In order to improve hardness and obtain high wear resistance, tempering temperature
needs to be low. The tempering temperature is therefore 400 °C or less. The tempering
temperature is preferably 380 °C or less. On the other hand, when the tempering temperature
is too low, the fine carbides do not grow to the desired dimensions. Further, hardness
becomes too high and the material is embrittled. The tempering temperature is therefore
100 °C or more. The tempering temperature is preferably 130 °C or more.
[0084] When the holding time during the tempering is less than 20 min, the fine carbides
do not grow to the desired dimensions, and hardness increases too much, causing embrittlement,
and therefore the holding time is 20 min or more. On the other hand, when the holding
time exceeds 3 h, the fine carbides become too coarse to achieve the desired dimensions.
The holding time is therefore 3 h or less.
[0085] The heat treatment may be performed after the machining or during the machining.
[0086] According to the above method, a steel component having excellent wear resistance
may be produced. Applications of the steel component are not particularly limited.
The steel component is particularly suitable for applications requiring wear resistance,
such as components for textile machinery, bearing components, and blades for machinery.
EXAMPLES
[0087] Steels having the chemical compositions listed in Table 1 were melted in a converter
and made into steel slabs by continuous casting. Each steel slab was then heated,
hot rolled, cooled, coiled, first annealed, cold rolled, second annealed, and finally
cold rolled in sequence to produce a cold-rolled steel sheet having a final sheet
thickness of about 0.4 mm. Each process was carried out under the conditions listed
in Tables 2 and 3. The cycle of cold rolling and second annealing was applied a number
of times listed in Table 3. The cold-rolled steel sheets were then subjected to heat
treatment consisting of quenching and tempering under the conditions listed in Table
3 to obtain samples. In the Examples, the process of machining to a component shape
was omitted.
[0088] For each sample, the average grain size of prior austenite grains, the average particle
size of the coarse carbides, and the average particle size of the fine carbides were
measured by the following procedures.
(Prior austenite grain size)
[0089] Test pieces for microstructure observation were taken from the samples obtained.
For each test piece, after polishing a rolling direction cross section (L-section)
of the test piece for microstructure observation, final polishing was performed with
colloidal silica, and electron backscatter diffraction (EBSD) measurements were performed
to identify prior austenite grain boundaries. After identifying prior austenite grain
boundaries, individual grain sizes and the number of grains were determined, and the
equivalent circular diameter was calculated and used as the average grain size. The
evaluation results are listed in Table 4.
(Coarse carbides)
[0090] Test pieces for carbide observation were taken from the samples obtained. For each
test piece, after polishing a rolling direction cross section (L-section) of the test
piece for carbide observation, the polished surface was corroded with 1 vol% to 3
vol% nital solution to reveal the microstructure. The surface of the test piece for
carbide observation was then imaged using scanning electron microscopy (SEM) at a
magnification of 3,000× to obtain a microstructure image. The particle size of each
carbide containing at least one of Nb, Ti, or V in the microstructure image obtained
was measured by a cutting method, and the average particle size of the carbides was
calculated. Nb, Ti, V carbides were identified using SEM energy dispersive X-ray spectroscopy
(EDS) analysis. Elemental mapping was performed with respect to the observed fields
of view to separate cementite from other carbides, and the other carbides were considered
to be Nb, Ti, V carbides. The evaluation results are listed in Table 4. The column
was left blank (-) when no coarse carbides were observed.
(Fine carbides)
[0091] Test pieces for carbide observation were taken from the samples obtained, thinned
to a thickness of about 70 µm, and then observation samples were prepared by electropolishing.
For each observation sample, carbides containing at least one of Nb, Ti, or V were
observed by transmission electron microscopy (TEM) at 150,000× to 250,000× magnification
and analyzed by TEM-EDS. The diameter of each carbide was determined by the cutting
method, and the arithmetic mean of the obtained diameters was calculated to obtain
the average particle size of the fine carbides. The evaluation results are listed
in Table 4. The column was left blank (-) when no fine carbides were observed.
(Wear resistance)
[0092] The wear resistance of the resulting steel sheets after quenching and tempering was
evaluated under the following two conditions.
[0093] First, the wear resistance under static conditions, where temperature rise due to
friction hardly occurs, was evaluated using the following procedure.
[0094] From each test piece, a wear test piece 10 was taken having the shape illustrated
in FIG. 1. Each of the wear test pieces 10 was provided with four holes 11 for threading.
[0095] Wear tests were conducted using the wear test pieces 10 and a wear test apparatus
20 illustrated in FIG. 2. Specifically, an amount of wear was measured by running
a yarn S fed from a yarn unwinder 21 for 100,000 m per hole with the yarn S in contact
with the side of the hole 11 of the wear test piece 10. Full dull polyester knitting
yarn was used as the yarn S. The running speed of the yarn S was 5 m/min. Further,
the tension of the yarn was adjusted to 10 ± 2 N/cm using a tension regulator 22.
[0096] As illustrated in FIG. 3, a groove 12 was formed by wear at a point where the hole
11 was in contact with the yarn. After running the yarn 100,000 m, the running was
stopped and a depth d (wear depth) of the groove 12 was measured using optical microscopy.
[0097] The same test was performed on each of the four holes 11 and the average of the four
wear depths obtained was taken as the wear depth of the wear test piece 10. When the
wear depth was less than 490 µm, the wear resistance was judged to be good (O), and
when 490 µm or more, wear resistance was judged to be poor (X). The evaluation results
are listed in Table 4.
[0098] Next, in order to evaluate wear resistance under conditions with a temperature increase
caused by friction, the same procedure was used as in the static condition test above,
except that the yarn running speed was set to 180 m/min, and wear resistance was evaluated
using the same criteria. The evaluation results are listed in Table 4.
[Table 1]
[0099]
Table 1
Steel sample ID |
Chemical composition (mass%) * |
Ac3 |
Remarks |
C |
Si |
Mn |
P |
S |
Al |
N |
Cr |
Ti |
Nb |
V |
Other |
A |
0.95 |
0.22 |
0.71 |
0.018 |
0.0010 |
0.002 |
0.003 |
0.40 |
- |
0.11 |
- |
- |
748 |
Conforming steel |
B |
0.90 |
0.24 |
0.81 |
0.010 |
0.0030 |
0.003 |
0.003 |
0.50 |
0.07 |
0.10 |
- |
- |
773 |
Conforming steel |
C |
0.68 |
0.21 |
1.05 |
0.015 |
0.0100 |
0.004 |
0.005 |
0.55 |
0.01 |
0.08 |
0.04 |
- |
769 |
Conforming steel |
D |
0.79 |
0.22 |
0.90 |
0.010 |
0.0020 |
0.003 |
0.002 |
0.40 |
0.08 |
0.21 |
002 |
- |
786 |
Conforming steel |
E |
0.95 |
0.25 |
0.55 |
0.031 |
0.0100 |
0.002 |
0.001 |
0.44 |
- |
0.11 |
- |
- |
763 |
Conforming steel |
F |
0.88 |
0.24 |
0.77 |
0.028 |
0.0022 |
0.030 |
0.002 |
0.55 |
- |
0.10 |
- |
- |
773 |
Conforming steel |
G |
0.95 |
0.44 |
0.61 |
0.042 |
0.0026 |
0.002 |
0.006 |
0.32 |
0.10 |
- |
- |
- |
818 |
Conforming steel |
H |
1.18 |
0.15 |
0.70 |
0.017 |
0.0080 |
0.020 |
0.003 |
0.55 |
0.38 |
- |
0.30 |
Mo:0.01 |
880 |
Conforming steel |
I |
1.11 |
0.3 |
0.86 |
0.018 |
0.0020 |
0.040 |
0.002 |
0.41 |
- |
- |
0.06 |
Ni:0.01, Cu:0.01 |
748 |
Conforming steel |
J |
0.80 |
0.5 |
0.81 |
0.022 |
0.0030 |
0.003 |
0.001 |
0.20 |
- |
0.18 |
0.00 |
Sb:0.005, Sn:0.002, Hf0.001, REM:0.001, Zr:0.003, B:0.001, W:0.001 |
779 |
Conforming steel |
K |
0.530 |
0.51 |
0.38 |
0.016 |
0.0030 |
0.003 |
0.001 |
0.22 |
0.05 |
0.18 |
0.05 |
- |
842 |
Comparative steel |
L |
1.52 |
0.24 |
0.66 |
0.012 |
0.0040 |
0.004 |
0.002 |
0.09 |
0.04 |
0.22 |
0.06 |
- |
714 |
Comparative steel |
M |
0.88 |
0.07 |
0.58 |
0.012 |
0.0050 |
0.002 |
0.003 |
0.31 |
0.04 |
0.27 |
0.9 |
- |
765 |
Comparative steel |
N |
0.90 |
0.68 |
0.55 |
0.014 |
0.0080 |
0.002 |
0.002 |
0.28 |
0.05 |
0.38 |
0.42 |
- |
797 |
Comparative steel |
O |
0.91 |
0.21 |
0.17 |
0.013 |
0.0100 |
0.003 |
0.002 |
0.44 |
0.82 |
0.12 |
0.02 |
- |
1092 |
Comparative steel |
P |
1.11 |
0.24 |
2.22 |
0.016 |
0.0030 |
0.003 |
0.004 |
0.50 |
0.41 |
0.19 |
0.03 |
- |
849 |
Comparative steel |
Q |
0.68 |
0.25 |
1.23 |
0.08 |
0.0100 |
0.004 |
0.004 |
0.51 |
0.3 |
0.2 |
0.03 |
- |
927 |
Comparative steel |
R |
0.79 |
0.30 |
1.00 |
0.023 |
0.0300 |
0.005 |
0.003 |
0.47 |
0.11 |
0.29 |
0.08 |
Mo:0.03 |
808 |
Comparative steel |
S |
0.90 |
0.41 |
0.69 |
0.033 |
0.0060 |
0.16 |
0.005 |
0.49 |
0.78 |
0.24 |
002 |
- |
1156 |
Comparative steel |
T |
0.90 |
0.20 |
0.58 |
0.027 |
0.0030 |
0.003 |
0.022 |
0.50 |
0.07 |
0.14 |
0.01 |
- |
790 |
Comparative steel |
U |
0.95 |
0.40 |
1.88 |
0.028 |
0.0030 |
0.007 |
0.002 |
0.03 |
0.13 |
0.5 |
0.07 |
- |
786 |
Comparative steel |
V |
0.92 |
0.33 |
0.77 |
0.011 |
0.0010 |
0.003 |
0.003 |
0.92 |
0.04 |
0.38 |
0.61 |
- |
760 |
Comparative steel |
W |
0.99 |
0.28 |
0.45 |
0.042 |
0.0020 |
0.003 |
0.006 |
0.38 |
0.01 |
- |
- |
- |
776 |
Comparative steel |
X |
0.70 |
0.25 |
0.40 |
0.039 |
0.0080 |
0.004 |
0.005 |
0.29 |
- |
- |
1.1 |
- |
803 |
Comparative steel |
Y |
1.25 |
0.49 |
0.61 |
0.015 |
0.0003 |
0.002 |
0.003 |
0.30 |
- |
- |
- |
- |
733 |
Comparative steel |
* The balance being Fe and inevitable impurity |
[Table 2]
[0100]
Table 2
No. |
Steel sample ID |
Ac3 |
Heating |
Hot rolling |
Cooling |
First annealing |
Remarks |
Slab heating temp. |
Holding time |
Finishing start temp. |
Time to start * |
Cooling rate |
Cooling stop temp. |
Annealing temp. |
Annealing time |
°C |
°C |
h |
°C |
s |
°C/s |
°C |
°C |
h |
1 |
A |
748 |
1108 |
1.0 |
1010 |
1.3 |
50 |
685 |
700 |
6 |
Example |
2 |
B |
773 |
1180 |
2.0 |
1120 |
1.5 |
30 |
700 |
705 |
4 |
Example |
3 |
C |
769 |
1220 |
1.5 |
1190 |
1.4 |
30 |
690 |
695 |
8 |
Example |
4 |
D |
786 |
1190 |
6.0 |
1110 |
1.0 |
50 |
690 |
680 |
6 |
Example |
5 |
E |
763 |
1220 |
4.0 |
1200 |
1.5 |
45 |
685 |
710 |
10 |
Example |
6 |
F |
773 |
1250 |
4.5 |
1180 |
2.0 |
60 |
690 |
720 |
15 |
Example |
7 |
G |
818 |
1310 |
3.0 |
1230 |
1.7 |
105 |
690 |
720 |
6 |
Example |
8 |
H |
880 |
1370 |
6.0 |
1305 |
0.9 |
90 |
705 |
700 |
6 |
Example |
9 |
I |
748 |
1200 |
2.0 |
1090 |
1.5 |
40 |
685 |
730 |
10 |
Example |
10 |
J |
779 |
1150 |
4.0 |
1015 |
1.5 |
85 |
680 |
660 |
12 |
Example |
11 |
K |
842 |
1270 |
3.0 |
1050 |
1.0 |
30 |
690 |
680 |
4 |
Comparative Example |
12 |
L |
714 |
1160 |
4.5 |
1080 |
2.0 |
28 |
690 |
690 |
5 |
Comparative Example |
13 |
M |
765 |
1130 |
2.0 |
1050 |
1.8 |
85 |
700 |
700 |
6 |
Comparative Example |
14 |
N |
797 |
1180 |
4.0 |
1100 |
1.9 |
55 |
705 |
680 |
6 |
Comparative Example |
15 |
O |
1092 |
1200 |
3.0 |
1120 |
1.5 |
65 |
710 |
690 |
6 |
Comparative Example |
16 |
P |
849 |
1280 |
5.0 |
1200 |
2.0 |
60 |
700 |
700 |
8 |
Comparative Example |
17 |
Q |
927 |
1290 |
4.0 |
1210 |
1.5 |
70 |
680 |
710 |
10 |
Comparative Example |
18 |
R |
808 |
1170 |
3.5 |
1090 |
2.0 |
50 |
650 |
690 |
8 |
Comparative Example |
19 |
S |
1156 |
1290 |
1.0 |
1210 |
1.8 |
50 |
700 |
660 |
8 |
Comparative Example |
20 |
I |
790 |
1080 |
2.5 |
1000 |
1.5 |
55 |
690 |
650 |
6 |
Comparative Example |
21 |
U |
786 |
1140 |
3.0 |
1060 |
1.8 |
25 |
680 |
700 |
6 |
Comparative Example |
22 |
V |
760 |
1160 |
3.5 |
1080 |
2.0 |
30 |
680 |
690 |
8 |
Comparative Example |
23 |
W |
776 |
1130 |
4.5 |
1050 |
2.0 |
70 |
650 |
680 |
8 |
Comparative Example |
24 |
X |
803 |
1120 |
4.0 |
1040 |
1.8 |
65 |
640 |
680 |
10 |
Comparative Example |
25 |
Y |
733 |
1100 |
5.0 |
1100 |
1.5 |
50 |
680 |
680 |
6 |
Comparative Example |
26 |
C |
769 |
990 |
8.0 |
1040 |
1.5 |
30 |
690 |
700 |
5 |
Comparative Example |
27 |
C |
769 |
1390 |
5.0 |
1110 |
1.8 |
41 |
700 |
700 |
8 |
Example |
28 |
C |
769 |
1180 |
0.5 |
1010 |
2.0 |
40 |
660 |
710 |
10 |
Comparative Example |
29 |
C |
769 |
1100 |
3.0 |
760 |
1.0 |
25 |
640 |
680 |
12 |
Comparative Example |
30 |
F |
773 |
1210 |
4.0 |
1180 |
5.0 |
38 |
700 |
720 |
4 |
Comparative Example |
31 |
F |
773 |
1190 |
5.0 |
1120 |
1.5 |
10 |
690 |
660 |
9 |
Comparative Example |
32 |
F |
773 |
1180 |
8.0 |
1010 |
0.9 |
40 |
610 |
680 |
8 |
Comparative Example |
33 |
F |
773 |
1100 |
1.0 |
1000 |
1.8 |
55 |
730 |
710 |
3 |
Comparative Example |
34 |
D |
786 |
1110 |
4.0 |
1060 |
1.5 |
60 |
680 |
620 |
5 |
Comparative Example |
35 |
D |
786 |
1180 |
8.0 |
1020 |
2.0 |
49 |
690 |
750 |
4 |
Comparative Example |
36 |
D |
786 |
1200 |
3.0 |
1080 |
1.7 |
34 |
710 |
700 |
1 |
Comparative Example |
37 |
D |
786 |
1110 |
5.5 |
1305 |
1.6 |
90 |
690 |
700 |
5 |
Comparative Example |
38 |
D |
786 |
1150 |
5.5 |
1090 |
1.5 |
50 |
700 |
690 |
4 |
Comparative Example |
39 |
D |
786 |
1200 |
9.0 |
1070 |
1.0 |
40 |
660 |
710 |
8 |
Comparative Example |
40 |
D |
786 |
1210 |
6.0 |
1050 |
1.3 |
45 |
680 |
720 |
9 |
Comparative Example |
41 |
C |
769 |
1230 |
4.5 |
1030 |
1.5 |
48 |
700 |
680 |
10 |
Comparative Example |
42 |
G |
818 |
1210 |
6.0 |
1090 |
1.7 |
40 |
680 |
710 |
6 |
Comparative Example |
43 |
G |
818 |
1105 |
4.0 |
1100 |
1.6 |
30 |
650 |
720 |
4 |
Comparative Example |
44 |
G |
818 |
1310 |
8.5 |
1040 |
1.0 |
25 |
690 |
700 |
7 |
Comparative Example |
45 |
G |
818 |
1150 |
5.0 |
990 |
2.0 |
48 |
640 |
720 |
5 |
Comparative Example |
46 |
I |
748 |
1350 |
6.0 |
1070 |
1.2 |
70 |
710 |
700 |
10 |
Comparative Example |
47 |
I |
748 |
1230 |
8.0 |
1050 |
1.1 |
100 |
670 |
690 |
12 |
Comparative Example |
48 |
I |
748 |
1210 |
6.0 |
1000 |
2.0 |
50 |
690 |
720 |
8 |
Comparative Example |
49 |
C |
769 |
1150 |
3.5 |
990 |
1.4 |
45 |
690 |
695 |
6 |
Comparative Example |
* Time from end of hot rolling to start of cooling |
[Table 3]
[0101]
Table 3
No. |
Cold rolling and second annealing |
Cold rolling |
Quenching |
Tempering |
Remarks |
Cold rolling |
Second annealing |
No. of cycles |
Rolling ratio |
Quenching temp. |
Holding time |
Tempering temp. |
Holding time |
Rolling ratio |
Annealing temp. |
Heating rate |
% |
°C |
°C/h |
Times |
% |
°C |
min |
°C |
min |
1 |
48 |
680 |
120 |
3 |
35 |
810 |
100 |
250 |
60 |
Example |
2 |
50 |
690 |
100 |
3 |
40 |
770 |
5.0 |
200 |
120 |
Example |
3 |
55 |
680 |
110 |
2 |
30 |
830 |
15.0 |
300 |
120 |
Example |
4 |
20 |
700 |
140 |
3 |
35 |
850 |
15.0 |
290 |
60 |
Example |
5 |
44 |
710 |
190 |
2 |
30 |
780 |
250 |
280 |
30 |
Example |
6 |
35 |
690 |
90 |
3 |
32 |
800 |
200 |
180 |
20 |
Example |
7 |
55 |
730 |
100 |
5 |
35 |
750 |
250 |
170 |
150 |
Example |
8 |
32 |
780 |
130 |
3 |
30 |
910 |
5.0 |
200 |
100 |
Example |
9 |
40 |
725 |
80 |
4 |
35 |
900 |
100 |
210 |
110 |
Example |
10 |
35 |
700 |
100 |
2 |
40 |
850 |
15.0 |
300 |
60 |
Example |
11 |
37 |
710 |
150 |
3 |
30 |
760 |
450 |
190 |
80 |
Comparative Example |
12 |
30 |
680 |
100 |
3 |
35 |
760 |
100 |
230 |
60 |
Comparative Example |
13 |
35 |
700 |
100 |
2 |
30 |
780 |
100 |
200 |
30 |
Comparative Example |
14 |
40 |
680 |
80 |
2 |
35 |
800 |
200 |
260 |
30 |
Comparative Example |
15 |
25 |
710 |
70 |
4 |
30 |
810 |
200 |
280 |
45 |
Comparative Example |
16 |
30 |
720 |
120 |
4 |
30 |
780 |
300 |
300 |
60 |
Comparative Example |
17 |
35 |
700 |
150 |
3 |
30 |
780 |
300 |
260 |
80 |
Comparative Example |
18 |
30 |
690 |
50 |
3 |
35 |
800 |
100 |
250 |
80 |
Comparative Example |
19 |
35 |
720 |
180 |
4 |
30 |
820 |
15.0 |
260 |
60 |
Comparative Example |
20 |
40 |
680 |
90 |
3 |
30 |
820 |
15.0 |
280 |
90 |
Comparative Example |
21 |
45 |
700 |
110 |
4 |
30 |
800 |
15.0 |
300 |
90 |
Comparative Example |
22 |
50 |
720 |
110 |
3 |
35 |
810 |
200 |
240 |
50 |
Comparative Example |
23 |
55 |
750 |
130 |
2 |
30 |
790 |
15.0 |
250 |
60 |
Comparative Example |
24 |
35 |
750 |
100 |
3 |
35 |
780 |
100 |
260 |
45 |
Comparative Example |
25 |
30 |
750 |
150 |
4 |
35 |
780 |
300 |
280 |
50 |
Comparative Example |
26 |
38 |
710 |
130 |
3 |
40 |
800 |
100 |
190 |
70 |
Comparative Example |
27 |
40 |
770 |
150 |
2 |
30 |
910 |
5.0 |
280 |
60 |
Example |
28 |
35 |
800 |
90 |
3 |
35 |
810 |
600 |
240 |
120 |
Comparative Example |
29 |
20 |
630 |
110 |
2 |
30 |
850 |
15.0 |
250 |
100 |
Comparative Example |
30 |
35 |
690 |
120 |
2 |
30 |
770 |
100 |
300 |
20 |
Comparative Example |
31 |
30 |
700 |
120 |
2 |
35 |
800 |
160 |
240 |
30 |
Comparative Example |
32 |
28 |
730 |
150 |
3 |
40 |
820 |
35.0 |
160 |
70 |
Comparative Example |
33 |
29 |
710 |
200 |
4 |
30 |
920 |
15.0 |
210 |
90 |
Comparative Example |
34 |
19 |
700 |
160 |
3 |
35 |
900 |
100 |
280 |
30 |
Comparative Example |
35 |
25 |
750 |
190 |
3 |
40 |
800 |
300 |
210 |
60 |
Comparative Example |
36 |
20 |
660 |
60 |
5 |
55 |
810 |
600 |
300 |
50 |
Comparative Example |
37 |
10 |
700 |
110 |
4 |
30 |
900 |
15.0 |
180 |
60 |
Comparative Example |
38 |
30 |
580 |
80 |
2 |
40 |
850 |
25.0 |
200 |
90 |
Comparative Example |
39 |
50 |
810 |
150 |
2 |
35 |
880 |
15.0 |
260 |
80 |
Comparative Example |
40 |
45 |
800 |
130 |
1 |
35 |
750 |
400 |
300 |
100 |
Comparative Example |
41 |
40 |
790 |
190 |
3 |
25 |
830 |
300 |
210 |
70 |
Comparative Example |
42 |
20 |
700 |
100 |
3 |
40 |
670 |
450 |
220 |
150 |
Comparative Example |
43 |
50 |
710 |
100 |
3 |
30 |
970 |
5.0 |
200 |
60 |
Comparative Example |
44 |
45 |
730 |
80 |
2 |
35 |
810 |
0.5 |
190 |
100 |
Comparative Example |
45 |
42 |
800 |
80 |
2 |
40 |
830 |
800 |
280 |
70 |
Comparative Example |
46 |
48 |
780 |
120 |
2 |
50 |
900 |
15.0 |
410 |
90 |
Comparative Example |
47 |
38 |
720 |
130 |
3 |
45 |
880 |
35.0 |
240 |
5 |
Comparative Example |
48 |
34 |
690 |
120 |
5 |
35 |
850 |
200 |
250 |
200 |
Comparative Example |
49 |
25 |
680 |
40 |
3 |
35 |
760 |
100 |
230 |
80 |
Comparative Example |
[Table 4]
[0102]
Table 4
No. |
Steel sample ID |
Prior austenite grain size |
Average particle size of coarse carbides |
Average particle size of fine carbides |
Wear resistance |
Remarks |
Wear test (1) (Running speed 5 m/min) |
Wear test (2) (Running speed 180 m/min) |
µm |
µm |
µm |
µm |
Evaluation |
µm |
Evaluation |
1 |
A |
15 |
0.5 |
0.005 |
420 |
O |
455 |
O |
Example |
2 |
B |
12 |
0.3 |
0.010 |
430 |
O |
456 |
O |
Example |
3 |
C |
12 |
0.3 |
0.023 |
420 |
O |
457 |
O |
Example |
4 |
D |
18 |
0.8 |
0.011 |
440 |
O |
450 |
O |
Example |
5 |
E |
15 |
0.5 |
0.016 |
440 |
O |
451 |
O |
Example |
6 |
F |
10 |
1.0 |
0.020 |
430 |
O |
461 |
O |
Example |
7 |
G |
13 |
1.2 |
0.010 |
415 |
O |
446 |
O |
Example |
8 |
H |
15 |
0.4 |
0.009 |
455 |
O |
468 |
O |
Example |
9 |
I |
20 |
0.3 |
0.008 |
450 |
O |
450 |
O |
Example |
10 |
J |
14 |
0.6 |
0.009 |
440 |
O |
460 |
O |
Example |
11 |
K |
28 |
0.1 |
- |
510 |
X |
495 |
X |
Comparative Example |
12 |
L |
20 |
2.4 |
0.050 |
530 |
X |
550 |
X |
Comparative Example |
13 |
M |
18 |
0.8 |
0.011 |
500 |
X |
520 |
X |
Comparative Example |
14 |
N |
18 |
0.1 |
0.004 |
515 |
X |
505 |
X |
Comparative Example |
15 |
O |
15 |
0.3 |
0.021 |
480 |
O |
505 |
X |
Comparative Example |
16 |
P |
25 |
0.1 |
0.004 |
505 |
X |
520 |
X |
Comparative Example |
17 |
Q |
12 |
0.3 |
0.010 |
515 |
X |
515 |
X |
Comparative Example |
18 |
R |
15 |
0.2 |
0.030 |
520 |
X |
520 |
X |
Comparative Example |
19 |
S |
10 |
0.1 |
0.011 |
500 |
X |
515 |
X |
Comparative Example |
20 |
I |
10 |
0.3 |
0.023 |
510 |
X |
520 |
X |
Comparative Example |
21 |
U |
15 |
0.1 |
0.008 |
495 |
X |
510 |
X |
Comparative Example |
22 |
V |
18 |
0.1 |
0.004 |
505 |
X |
510 |
X |
Comparative Example |
23 |
W |
15 |
0.1 |
0.003 |
500 |
X |
515 |
X |
Comparative Example |
24 |
X |
18 |
2.8 |
0.010 |
520 |
X |
525 |
X |
Comparative Example |
25 |
Y |
25 |
0.1 |
0.001 |
525 |
X |
550 |
X |
Comparative Example |
26 |
C |
15 |
- |
0.028 |
490 |
X |
479 |
O |
Comparative Example |
27 |
C |
13 |
1.5 |
0.005 |
480 |
O |
472 |
O |
Example |
28 |
C |
10 |
- |
0.021 |
495 |
X |
471 |
O |
Comparative Example |
29 |
C |
17 |
3.2 |
0.001 |
500 |
X |
552 |
X |
Comparative Example |
30 |
F |
15 |
- |
0.003 |
510 |
X |
521 |
X |
Comparative Example |
31 |
F |
13 |
- |
0.002 |
515 |
X |
520 |
X |
Comparative Example |
32 |
F |
10 |
- |
0.002 |
510 |
X |
539 |
X |
Comparative Example |
33 |
F |
14 |
- |
0.001 |
530 |
X |
545 |
X |
Comparative Example |
34 |
D |
10 |
- |
0.015 |
500 |
X |
501 |
X |
Comparative Example |
35 |
D |
18 |
1.5 |
- |
480 |
O |
536 |
X |
Comparative Example |
36 |
D |
19 |
- |
0.005 |
490 |
X |
478 |
O |
Comparative Example |
37 |
D |
20 |
4.2 |
0.005 |
515 |
X |
480 |
O |
Comparative Example |
38 |
D |
18 |
4.0 |
0.005 |
495 |
X |
532 |
X |
Comparative Example |
39 |
D |
38 |
1.0 |
0.008 |
500 |
X |
515 |
X |
Comparative Example |
40 |
D |
18 |
2.7 |
- |
520 |
X |
546 |
X |
Comparative Example |
41 |
C |
15 |
2.8 |
- |
515 |
X |
551 |
X |
Comparative Example |
42 |
G |
15 |
0.9 |
0.002 |
480 |
O |
563 |
X |
Comparative Example |
43 |
G |
40 |
1.1 |
0.013 |
540 |
X |
525 |
X |
Comparative Example |
44 |
G |
15 |
1.0 |
0.001 |
480 |
O |
571 |
X |
Comparative Example |
45 |
G |
35 |
1.3 |
0.042 |
525 |
X |
530 |
X |
Comparative Example |
46 |
I |
18 |
1.5 |
0.092 |
475 |
X |
522 |
X |
Comparative Example |
47 |
I |
14 |
0.6 |
0.002 |
480 |
O |
491 |
X |
Comparative Example |
48 |
I |
19 |
0.8 |
0.061 |
470 |
O |
555 |
X |
Comparative Example |
49 |
C |
13 |
2.2 |
- |
420 |
O |
528 |
X |
Comparative Example |
REFERENCE SIGNS LIST
[0103]
- 10
- wear test piece
- 11
- hole
- 12
- groove
- 20
- wear test apparatus
- 21
- yarn unwinder
- 22
- tension adjuster
- 23
- yarn winder
- S
- yarn
- d
- wear depth