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DIM360 (Ver 1.5 21 Nov 2005) - 1100000/0 1710000/0
0841410
EUROPEAN PATENT APPLICATION
published in accordance with Art. 158(3) EPC
A1
19980513
EP
96925205.5
19960709
19980209
ru
en
en
95110850
19950711
RU
95110851
19950711
RU
95110852
19950711
RU
19980513
199820
19980513
199820
6
6C 22C 38/24 A
de
LEGIERTER KONSTRUKTIONSSTAHL
en
ALLOYED CONSTRUCTION STEEL
fr
ACIER ALLIE DE CONSTRUCTION
Fedchun, Vladimir Alexeevich
02274160
N.74218-WA
ul. Energgeticheskaya, 4-5
Moscow 111116
RU
Aslibekyan, Felix Surenovich
02274170
N.74218-WA
Leninsky prospekt, 22-51
Moscow 117071
RU
Prokofiev, Vladimir Konstantinovich
02274200
N.74218-WA
ul. Shabolovka, 52-18
Moscow 117419
RU
Fedchun, Vladimir Alexeevich
ul. Energgeticheskaya, 4-5
Moscow 111116
RU
Aslibekyan, Felix Surenovich
Leninsky prospekt, 22-51
Moscow 117071
RU
Prokofiev, Vladimir Konstantinovich
ul. Shabolovka, 52-18
Moscow 117419
RU
Allen, William Guy Fairfax
00027654
J.A. KEMP & CO. 14 South Square Gray's Inn
London WC1R 5LX
GB
DE
FR
GB
IT
SE
RU9600184
19960709
ru
WO9703217
19970130
199706
19970130
000000
Alloyed construction steel containing carbon, silicon, manganese, chromium, vanadium and iron, and containing in addition a plasticity-enhancing and nitration-boosting chemical element, the relative proportions of components being (wt. %):
Carbon | 0.10-0.63
Silicon | 0.20-1,20
Manganese | 0.40-0.60
Chromium | 0.60-3.00
Plasticity-enhancing and nitration-boosting chemical element | 0.40-1.50
Vanadium | 0.15-0.35
Iron | Rem.
The plasticity-enhancing and nitration-boosting chemical element used is copper or germanium.

Scope of Application
The invention pertains to metallurgy, in particular, compositions of steels used for fabrication of critical parts for machine-building industry.

Previous Technology Level
The alloyed construction steel with the composition (wt. %) shown below is known:
Carbon | 0.4 max
Silicon | 0.56-1.5
Manganese | 0.30-2.0
Chromium | 0.71-3.0
Vanadium | 0.21-1.0
Aluminum | 0.3 max
Iron | Rem.
(JP, A, # 52-27584) |
This steel does not offer the required complex of properties, especially plasticity, elimination of intercrystalline brittleness and boosted nitration process.
Also known is the alloyed construction steel that has the following components, wt. %:
Carbon | 0.30-0.45
Manganese | 0.30-0.60
Silicon | 0.17-0.37
Chromium | 1.50-2.50
Vanadium | 0.20-0.50
Germanium | 0.20-0.80
Iron | Rem.
(SU, A, # 926060) |
The advantage of this steel is low strength at satisfactory plasticity across the cross section of the part made thereof following both traditional hardening methods and low-temperature nitration. Besides, there is a likelihood of temper brittleness typical of nitrided steels that are currently used.
The alloyed construction steel that contains carbon, silicon, manganese, chromium, molybdenum, nickel, vanadium and iron in proportions shown below (wt. %) is the closest from the point of view of the technological content and result sought:
Carbon | 0.27-0.34
Silicon | 0.17-0.60
Manganese | 0.30-0.60
Chromium | 2.30-2.70
Molybdenum | 0.20-0.30
Nickel | 0.12-0.30
Vanadium | 0.06-0.12
Iron | Rem.
(Steel 30X3MΦ, GOST 4543-71. Alloyed construction steel, grades and specifications).
The disadvantage of this steel are low yield and hardness, slow rate of saturation during nitrating and presence of scarcely available molybdenum arid nickel that results in high production costs. Besides, there is a likelihood of temper brittleness typical of nitrided steels that are currently used.

Disclosure Of The Invention
This invention is based on the objective to ensure high physical and mechanical properties of steel combined with high plasticity across the cross section of the part made thereof, following both traditional hardening techniques (quenching, tempering) and low-temperature nitration at 470-520°C, with minimum tendency for temper brittleness, as well as fabrication cost reduction.
The nature of the invention lies in the fact that, besides carbon, silicon, manganese, chromium, vanadium and iron, the alloyed construction steel additionally contains a chemical element that enhances plasticity and boosts the nitration process. The content of components is as follows, wt. %:
Carbon | 0.10-0.63
Silicon | 0.20-1.20
Manganese | 0.40-0.60
Chromium | 0.60-3.00
Plasticity-enhancing and nitration-boosting chemical element | 0.40-1.50
Vanadium | 0.15-0.35
Iron | Rem.
Also, either copper or germanium are used as the chemical element that enhances plasticity and boosts the nitration process.
The copper content is 0.40-0.80 wt. %, provided the silicon/copper ratio is 1.5-2.5.
The germanium content is 0.60-1.50 wt. %, provided the silicon content is 0.20-0.40 wt. %.
The combination of essential features described above is aimed at achieving the technical result sought and is related to it through cause and consequence, as it makes it possible to:
- ensure superior strength and hardness properties of the alloyed construction steel that has high plasticity across the entire cross section of the part made thereof, due to the chemical composition of the steel, shown above;
- boost the nitration process and ensure high plasticity across the cross section of parts;
- bring the steel making cost down by eliminating scarcely available components.
Besides, the invention may be used commercially in various industries for fabrication of critical parts and components.
Thus, a conclusion may be drawn that the technical invention claimed meets the requirements of its patentability.

The Best Way to Exercise The Invention
An experimental batch of alloyed construction steel is produced in an induction furnace. This experimental batch is then used to fabricate blanks that are to be exposed to quenching for 20 minutes at 890°C and to oil cooling and tempering for 3 hrs at 200°C and air cooling.
Standard mechanical properties are to be determined, i.e.: ultimate tensile strength σ_B, yield point σ_{0.2}, elongation δ, reduction ψ, impact strength KCV^{+20} and Rockwell hardness, HRC, as well as surface hardness HV, layer thickness up HV-400, comparative wear resistance, fatigue strength of nitrided samples σ_{-1}, endurance strength of nitrided samples σ^k_{-1} and impact strength of nitrided samples KCV^{+20}.
Table 1 shows steel compositions which use copper as the plasticity-enhancing and nitration-boosting the element; Table 2 contains steel compositions in which germanium is used as the plasticity-enhancing and nitration-boosting element. Mechanical properties of steels listed in Table 1 are shown in Table 3; operational properties of steels included in Table 1, after nitration, are described in Table 4; mechanical properties of steels listed in Table 2 are summarized in Table 5 and operational properties of steels included in Table 2, after nitration, are included in Table 6.

Commerical Use
Use of the alloyed construction steel in question will help to ensure superior physical and mechanical properties combined with high plasticity across the entire cross section of the part made thereof, with minimum tendency for temper brittleness, and reduce the steel making cost by 30-40%.

Table 1
Component | Composition, mass %
| 1 | 2 | 3 | Prototype
Carbon | 0.10 | 0.35 | 0.63 | 0.30
Silicon | 0.80 | 0.90 | 1.20 | 0.27
Manganese | 0.40 | 0.50 | 0.60 | 0.45
Chromium | 0.60 | 1.80 | 3.00 | 2.50
Chemical element that enhances plasticity and boosts | 0.40 | 0.50 | 0.80 | -
nitration - copper | 0.15 | 0.25 | 0.35 | 0.09
Vanadium | Rem. | Rem. | Rem. | Rem.
Iron | | | |
Silicon Copper | 2.0 | 1.8 | 1.5 | -

Table 2
Component | Composition, mass %
| 1 | 2 | 3 | Prototype
Carbon | 0.10 | 0.35 | 0.63 | 0.30
Silcon | 0.20 | 0.29 | 0.40 | 0.27
Manganese | 0.40 | 0.50 | 0.60 | 0.45
Chromium | 0.60 | 1.80 | 3.00 | 2.50
Chemical element that enhances plasticity and boosts | 0.60 | 1.02 | 1.50 | -
nitration - germanium | 0.15 | 0.20 | 0.35 | 0.09
Vanadium | Rem. | Rem. | Rem. | Rem.
Iron | | | |

Table 6
Steel | Nitration conditions | Nitrided layer depth, mm | Surface hardness HV, N/mm^2 | Comparative wear resistance, | Fatigue strength σ_{-1}, N/mm^2 | Endurance strength N/mm^2
Offered | | | | | |
1 | 500°C 36 hrs | 0.98 | 580 | 1.02 | 530 | 1420
2 | 500°C 36 hrs | 0.87 | 7800 | 1.31 | 890 | 2320
3 | 500°C 36 hrs | 0.74 | 7950 | 1.28 | 780 | 2200
Prototype | 500°C 36 hrs | 0.40 | 7150 | 1.18 | 620 | 1300
1. Alloyed construction steel containing carbon, manganese, chromium, vanadium and iron, characterized by containing, in addition, a chemical element that enhances plasticity and boosts the nitration process, the component ratio being (wt/%):
Carbon | 0.10-0.63
Silicon | 0.20-1.20
Manganese | 0.40-0.60
Chromium | 0.60-3.00
Plasticity-enhancing and nitration-boosting chemical element | 0.40-1.50
Vanadium | 0.15-0.35
Iron | Rem.
2. Alloyed construction steel according to claim 1, characterized by the use of copper or germanium or as the plasticity-enhancing and nitration-boosting chemical element.
3. Alloyed construction steel according to claims 1 and 2, characterized in that the copper content is 0.40-0.80 wt.%, provided the silicon copper ratio is maintained at 1.5-2.5.
4. Alloyed construction steel according to claims 1 and 2, characterized in that the germanium content is 0.60-1.50 wt.%, provided the silicon content is 0.20-0.40 wt.%.