(19)
(11)EP 3 417 081 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
31.03.2021 Bulletin 2021/13

(21)Application number: 17753570.5

(22)Date of filing:  27.01.2017
(51)International Patent Classification (IPC): 
C22B 9/193(2006.01)
B22D 7/06(2006.01)
B22D 23/10(2006.01)
(86)International application number:
PCT/SE2017/050073
(87)International publication number:
WO 2017/142455 (24.08.2017 Gazette  2017/34)

(54)

A MOULD FOR THE MANUFACTURING OF MOULD STEELS IN AN ELECTRO SLAG REMELTING PROCESS

GUSSFORM ZUR HERSTELLUNG VON FORMSTÄHLEN IN EINEM ELEKTROSCHLACKEUMSCHMELZVERFAHREN

MOULE POUR LA FABRICATION D'ACIERS DE MOULE DANS UN PROCÉDÉ DE REFUSION DE LAITIER ÉLECTROCONDUCTEUR


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 16.02.2016 SE 1650203

(43)Date of publication of application:
26.12.2018 Bulletin 2018/52

(73)Proprietor: Uddeholms AB
683 85 Hagfors (SE)

(72)Inventor:
  • SJÖQVIST PERSSON, Eva
    683 92 Hagfors (SE)

(74)Representative: Zacco Sweden AB 
P.O. Box 5581
114 85 Stockholm
114 85 Stockholm (SE)


(56)References cited: : 
WO-A1-99/20804
JP-A- H0 613 651
US-A1- 2013 336 353
GB-A- 536 470
US-A- 4 953 177
  
  • DATABASE WPI Week 201016 Thomson Scientific, London, GB; AN 2010-B96540 XP002787050, -& CN 201 400 710 Y (JIANGSU HUAJIU SPECIAL STEEL TOOL CO LTD) 10 February 2010 (2010-02-10)
  • DATABASE WPI Week 201036 Thomson Scientific, London, GB; AN 2010-F82585 XP002787051, -& CN 201 459 215 U (UNIV CHONGQING ARTS & SCI) 12 May 2010 (2010-05-12)
  • HOLZGRUBER W: 'Overview of 50 Years of Development in Electroslag Remelting in Austria' BERG- UND HUTTENMäNNISCHE MONATSHEFTE vol. 161, 2016, pages S2 - S11, XP035884436
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

TECHNICAL FIELD



[0001] The invention relates to a mould for the manufacturing of mould steels in an Inertgas Electro Slag Remelting (IESR) or a Pressurized Electro Slag Remelting (PESR) process.

BACKGROUND ART



[0002] Mould steels are used for making moulds and dies for the manufacturing of light metal or plastic articles. Electro Slag Remelting (ESR) is commonly used in order to minimize segregation and to reduce the amount of non metallic inclusions of the remelted material. The cleanliness and homogeneity of ESR ingots result in improved mechanical properties as compared to conventionally cast material. The conventional ESR is performed without isolation of the atmosphere.

[0003] Various moulds for electroslag remelting are known from CN201400710 and GB536470.

[0004] In recent years the protective gas methods Inertgas Electro Slag Remelting (IESR) and Pressurized Electro Slag Remelting (PESR) have gained a considerable interest, since these methods eliminate the risk of picking up hydrogen and oxygen from the atmosphere and result in a further reduction of the amount of non metallic inclusions in the remelted material. However, it has now been recognized, that large ingots produced by IESR and PESR do not have the same high cleanliness as compared to smaller ingots. This problem is important, in particular for ingots having diameters exceeding 1000 mm, in particular in view of the increased demand for large sized moulds and dies.

SUMMARY OF THE INVENTION



[0005] The general objective of the present invention is to provide a mould for the manufacturing of large sized mould steel ingots with an improved cleanliness and/or an improved microstructure in an Inertgas Electro Slag Remelting (IESR) or in a Pressurized Electro Slag Remelting (PESR) process.

[0006] Another object is to provide an IESR or PESR apparatus comprising the improved large size mould. A further object is to provide a steel ingot obtainable with the inventive IESR or PESR and thereby having an improved cleanliness and/or an improved microstructure.

[0007] These objects are achieved by the means of the invention as defined in the independent claims.

BRIEF DESCRIPTION OF THE DRAWINGS



[0008] In the following, the invention will be described in more detail with reference to the preferred embodiments and the appended drawings.

Fig. 1 is a schematic drawing of the cross section of a conventional mould having a diameter of 1250 mm and having an area of 0.39 m2.

Fig. 2 is a schematic drawing of one embodiment of the present invention showing the cross section of an elliptical mould having the same area as the conventional mould.


DETAILED DESCRIPTION



[0009] The invention is defined in the claims.

[0010] The present inventor has surprisingly found that the cleanliness of the refined mould steel can be influenced by changing the shape of the mould. By replacing the conventional round mould nowadays used in IESR and PESR by a mould having an improved shape, it is possible to further improve the cleanliness and the microstructure of the remelted ingot.

[0011] The inventive mould comprises a non-rectangular and non-circular inner copper sleeve having a width, w, of 1000-2500 mm and a thickness, t, of 700-1250 mm, wherein the short sides in the thickness direction of the copper sleeve at least partly have sections with curved surfaces and wherein the long sides in the width direction at least partly have sections with curved surfaces.

[0012] The invention will be described in detail with reference to the attached drawings.

[0013] Figure 1 discloses the cross section of a conventional mould having a diameter, d, of 1250 mm and an area of 0.39 m2.

[0014] Figure 2 discloses the cross section of an inventive mould having the same area as the conventional mould but having an elliptical shape. The thickness of the mould was chosen to be 800 mm, wherein the width of the elliptical mould was 1953 mm.

[0015] Both figures relate to the size of the inner sleeve of the mould, which size, except for the solidification shrinkage, corresponds to the size of the remelted ingot.

[0016] According to the invention, the mould can have different shapes. However, the short sides, in the thickness direction of the copper sleeve, as well as the long sides, in the width direction, both have, at least partly, sections with curved surfaces.

[0017] The short sides and the long sides may have sections that are straight.

[0018] The short sides may optionally be provided with straight sections, which are positioned in the mid portions of the short sides, i.e. at t/2. The short sides may be designed to have a constant radius of curvature (arc shaped) or having a variable radius of curvature (e.g. oval-, elliptical- or super elliptical- shaped). The radius of curvature can extend to any desired point up to the position w/4.

[0019] The long sides may have only one straight section or more than one straight section on each side. Two straight sections may be formed on each long side, in particular in the sections w/8 to w/2 and may have a smooth transition at w/2.

[0020] The mid thickness of the mould at w/2 may be the same as the thickness at the quarter thickness of the mould at w/4 from each short side of the mould. However, it is normally preferred, that the mid thickness of the mould at w/2 is at least 10 mm thicker than the quarter thickness at w/4 of the mould from each short side of the mould. The thickness at w/2 may be 20, 40, 60, 80, 100, 120, 140, 160 or 180 mm larger than the thickness at w/4.

[0021] The sections with curved surfaces of the short sides can have a constant or a variable radius of curvature. The short sides may have a constant or variable radius of curvature up to the position w/4. The mould can have an oval, elliptical or super-elliptical form and/or the width of the mould, w, may be at least 1.1 times larger than the thickness, t, preferably w>1.2t.

[0022] The size of the mould can be freely varied within the ranges set out in claim 1. The width can be restricted to 2400, 2300, 2200, 2100, 2000, 1900, 1800, 1700, 1600, 1500, 1400, 1300, 1200 or 1100 mm. The thickness can be restricted to 1200, 1150, 1000, 950, 900, 850, 800 or 750 mm. The width is always larger than the thickness.

Example



[0023] A plastic mould steel was produced by conventional EAF steelmaking followed by ladle metallurgy, vacuum degassing and casting into electrodes having suitable diameters for the remelting in the respective PESR. The moulds are schematically shown in Figures 1 and 2. The remelting was performed with the same type of slag based on CAF-CaO-Al2O3 under argon protective atmosphere. Samples were taken from the centre of the forged and heat treated material at the same height of the respective ingot. The samples were cut, cold mounted, grinded and polished and thereafter subjected to examination in a Light Optical Microscope (LOM). The number of inclusions per mm2 in the respective ingot was examined. Only inclusions larger than 8 µm were counted.

[0024] It was found, that the number of inclusions per mm2 could be reduced by changing the thickness of the mould. The reason for this result is presently not fully understood and the inventor does not wish to be bound by any theory. However, it would appear, that the positive result may be influenced by a number of factors such as a different turbulent flow in the slag and in the molten pool, a less deep metal pool and/or by more favourable solidification conditions, leading to a reduction of the solidification time of the ingot and a reduced amount or complete absence of equiaxed crystals in the remelted ingot.

Industrial applicability



[0025] The invention is particularly suited for the manufacturing of large sized dies in hot work tool steel for die casting of light alloys as well as for the manufacturing of large sized plastic mould steel moulds used for the moulding of plastics articles.


Claims

1. A mould for the manufacturing of mould steels in an inert gas or a pressurized electro slag re-melting process, characterized in that the mould comprises a non-rectangular and non-circular inner copper sleeve having a width, w, of 1000-2500 mm and a thickness, t, of 700-1250 mm, wherein the short sides in the thickness direction of the copper sleeve, at least partly, have sections with curved surfaces and wherein the long sides in the width direction, at least partly, have sections with curved surfaces.
 
2. A mould according to claim 1, wherein the curved surfaces of the short sides have a constant radius of curvature.
 
3. A mould according to claim 1, wherein the curved surfaces of the short sides have a variable radius of curvature and, optionally, straight sections.
 
4. A mould according to any of the preceding claims, wherein the mid thickness of the mould at w/2 is the same as the thickness at the quarter thickness of the mould at w/4 from both short sides of the mould.
 
5. A mould according to any of the preceding claims, wherein the mid thickness of the mould at w/2 is at least 10 mm thicker than the quarter thickness at w/4 of the mould from both short sides of the mould.
 
6. A mould according to claim 3, wherein the mould has an oval, elliptical or super-elliptical form.
 
7. A mould according to any of the preceding claims, wherein the mould has a width of 1500 - 2000 mm and/or a thickness of 800 - 1050 mm.
 
8. A mould according to any of the preceding claims, wherein the long sides have at least one straight section.
 
9. A mould according to any of the preceding claims, wherein the inner copper sleeve does not have any welding seams.
 
10. An Inertgas Electro Slag Remelting or a Pressurized Electro Slag Remelting apparatus characterized in that it is provided with a mould according to any of the preceding claims.
 
11. An ESR remelted tool steel ingot for making moulds or dies, characterized in that the steel ingot is obtainable with an apparatus as defined in claim 10, wherein the steel ingot is non-rectangular and non-circular and has a width, w, of 1000 - 2500 mm and a thickness, t, of 700 - 1250 mm and wherein the short sides in the thickness direction of the ingot, at least partly, have sections with curved surfaces and wherein the long sides in the width direction, at least partly, have sections with curved surfaces.
 


Ansprüche

1. Gussform zur Herstellung von Formstählen in einem Inertgas oder einem druckbeaufschlagten Elektroschlackeumschmelzverfahren, dadurch gekennzeichnet, dass die Gussform eine nicht-rechteckige und nicht-kreisförmige innere Kupferhülse umfasst mit einer Breite, w, von 1000-2500 mm und einer Dicke, t, von 700-1250 mm, wobei die kurzen Seiten in der Dickenrichtung der Kupferhülse zumindest teilweise Abschnitte mit gekrümmten Oberflächen aufweisen, und wobei die langen Seiten in der Breitenrichtung zumindest teilweise Abschnitte mit gekrümmten Oberflächen aufweisen.
 
2. Gussform nach Anspruch 1, wobei die gekrümmten Oberflächen der kurzen Seiten einen konstanten Krümmungsradius aufweisen.
 
3. Gussform nach Anspruch 1, wobei die gekrümmten Oberflächen der kurzen Seiten einen variablen Krümmungsradius und eventuell gerade Abschnitte aufweisen.
 
4. Gussform nach einem der vorgehenden Ansprüche, wobei die mittlere Dicke der Gussform bei w/2 die gleiche ist wie die Dicke bei einem Viertel der Dicke der Gussform bei w/4 von beiden kurzen Seiten der Gussform.
 
5. Gussform nach einem der vorgehenden Ansprüche, wobei die mittlere Dicke der Gussform bei w/2 mindestens 10 mm dicker als ein Viertel der Dicke bei w/4 der Gussform von beiden kurzen Seiten der Gussform.
 
6. Gussform nach Anspruch 3, wobei die Gussform eine ovale, elliptische oder super-elliptische Form aufweist.
 
7. Gussform nach einem der vorgehenden Ansprüche, wobei die Gussform eine Breite von 1500 - 2000 mm und/oder eine Dicke von 800 - 1050 mm aufweist.
 
8. Gussform nach einem der vorgehenden Ansprüche, wobei die langen Seiten mindestens einen geraden Abschnitt aufweisen.
 
9. Gussform nach einem der vorgehenden Ansprüche, wobei die innere Kupferhülse keine Schweißnähte aufweist.
 
10. Inertgaselektroschlackeumschmelzvorrichtung oder druckbeaufschlagte Elektroschlackeumschmelzvorrichtung, dadurch gekennzeichnet, dass sie mit einer Gussform nach einem der vorgehenden Ansprüche vorgesehen ist.
 
11. ESR-umgeschmolzener Werkzeugstahlrohblock zur Herstellung von Gussformen oder Matrizen, dadurch gekennzeichnet, dass der Stahlrohblock mit einer Vorrichtung nach Anspruch 10 erreichbar ist, wobei der Stahlrohblock nicht-rechteckig und nicht-kreisförmig ist und eine Breite, w, von 1000 - 2500 mm und eine Dicke, t, von 700 - 1250 mm aufweist, und wobei die kurzen Seiten in der Dickenrichtung des Rohblocks zumindest teilweise Abschnitte mit gekrümmten Oberflächen aufweisen, und wobei die langen Seiten in der Breitenrichtung zumindest teilweise Abschnitte mit gekrümmten Oberflächen aufweisen.
 


Revendications

1. Moule pour la fabrication d'aciers de moule dans un gaz inerte ou un procédé de refusion de laitier électroconducteur sous pression, caractérisé en ce que le moule comprend un manchon intérieur en cuivre non rectangulaire et non circulaire ayant une largeur, w, de 1000 à 2500 mm et une épaisseur, t, de 700 à 1250 mm, dans lequel les côtés courts dans la direction d'épaisseur du manchon en cuivre ont, au moins en partie, des sections avec des surfaces incurvées, et dans lequel les côtés longs dans la direction de largeur ont, au moins en partie, des sections avec des surfaces incurvées.
 
2. Moule selon la revendication 1, dans lequel les surfaces incurvées des côtés courts ont un rayon de courbure constant.
 
3. Moule selon la revendication 1, dans lequel les surfaces incurvées des côtés courts ont un rayon de courbure variable et, éventuellement, des sections droites.
 
4. Moule selon l'une quelconque des revendications précédentes, dans lequel l'épaisseur moyenne du moule à w / 2 est la même que l'épaisseur au quart d'épaisseur du moule à w / 4 des deux côtés courts du moule.
 
5. Moule selon l'une quelconque des revendications précédentes, dans lequel l'épaisseur moyenne du moule à w / 2 est au moins 10 mm plus épaisse que le quart d'épaisseur à w / 4 du moule des deux côtés courts du moule.
 
6. Moule selon la revendication 3, dans lequel le moule a une forme ovale, elliptique ou super-elliptique.
 
7. Moule selon l'une quelconque des revendications précédentes, dans lequel le moule a une largeur de 1500 à 2000 mm et / ou une épaisseur de 800 à 1050 mm.
 
8. Moule selon l'une quelconque des revendications précédentes, dans lequel les côtés longs ont au moins une section droite.
 
9. Moule selon l'une quelconque des revendications précédentes, dans lequel le manchon intérieur en cuivre ne comporte aucun cordon de soudure.
 
10. Dispositif de refusion de laitier électroconducteur à gaz inerte ou de refusion de laitier électroconducteur sous pression, caractérisé en ce qu'il est pourvu d'un moule selon l'une quelconque des revendications précédentes.
 
11. Lingot d'acier à outils refondu ESR pour fabriquer des moules ou des matrices, caractérisé en ce que le lingot d'acier peut être obtenu avec un dispositif tel que défini dans la revendication 10, dans lequel le lingot d'acier est non rectangulaire et non circulaire et a une largeur, w, de 1000 - 2500 mm et une épaisseur, t, de 700 à 1250 mm, et dans lequel les côtés courts dans la direction d'épaisseur du lingot ont, au moins en partie, des sections avec des surfaces incurvées, et dans lequel les côtés longs dans la direction de largeur ont, au moins en partie, des sections avec des surfaces incurvées.
 




Drawing








Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description