Composite work roll for cold rolling

Details Composite work roll for cold rolling Composite work roll for cold rolling

1998-12-07

2001-03-27

Rosenbaum, I Cuda (Department: 3726)

Roll or roller

Single annular member, per se

Specific metallic composition

C148S541000

Reexamination Certificate

active

06206814

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a composite work roll used for cold rolling of steel, which is endowed with excellent spalling resistance (breakage resistance) and high abrasion resistance.
BACKGROUND ART
Steel cold (rolling) work rolls have conventionally employed forged steel containing 5-7 wt % Cr. Recent years have seen greater application of so-called semi high-speed steel work rolls containing small amounts of Mo, V, W, etc., such as the work rolls disclosed in Japanese Examined Patent Publication No. 61-11310 and Japanese Examined Patent Publication No. 7-68588.
Such conventional cold (rolling) work rolls are subjected to complex processes involving formation of a steel ingot by electro-slag remelting, followed by quenching and tempering through a forging step. During heat treatment, severe quenching by rapid cooling from high temperature is effected using techniques such as progressive induction heating and water quenching, in order to ensure a high hardness of HS 90 or greater. Electro-slag remelting which has conventionally been applied as a method of forged cold (rolling) work rolls gives a slow solidifying rate, so that the crystal grains or carbides tend to be coarse. Because of quenching cracks which occur during quenching when the crystal grains or carbides are coarse, a prior forging step has been essential to ensure sufficient material strength and ductility. From the standpoint of component design, it has been necessary for the C content to be kept to about 0.9 wt %, and all alloys such as Mo, V and W to be restricted. For these reasons, there has been a limit to the improvement in abrasion resistance of such work rolls.
It is known that roll surface hardness is greatly affected by the compression residual stress of the roll surface. For example, in order to ensure a high hardness it has been proposed to purposely provide a high residual stress, such as indicated in Japanese Unexamined Patent Publication No. 5-169112. Also, since the structure of conventional work rolls is an integral one wherein the roll and axis portions consist of the same component system, the internal material strength of the roll body is very high. As a result, the compression residual stress of roll body portions has been at a very high level of 70 kgf/mm
2
or greater. It is therefore common for severe spalling to occur from defects in the roll interior or cracks produced on the roll surface during rolling, so that improvements in breakage resistance, or spalling resistance, have been desired.
DISCLOSURE OF THE INVENTION
It is one of the objects of the present invention to provide a roll outer layer for cold rolling composite work rolls endowed with excellent abrasion resistance and spalling resistance. Specifically, this object is achieved by means of an outer layer formed around the perimeter of a core material for the cold rolling composite work roll, the cold rolling composite work roll outer layer being characterized by comprising; C: 0.9-1.5 wt %, Si: 0.3-1.0 wt %, Mn: 0.3-1.0 wt %, Cr: 4.0-10.0 wt %, Mo: 2.0-8.0 wt %, V: 0.5-5.0 wt % and the remainder Fe and unavoidable impurities.
It is another object of the invention to ensure excellent abrasion resistance by achieving a finer roll structure through an increased solidifying rate, and realizing high alloy steel which has not been possible by the prior art. Integral work rolls themselves require large steel ingots, making it very difficult to ensure a high solidifying rate. According to the invention, therefore, the work roll is given the composite structure of a roll core material and a roll outer layer so that the molten metal volume can be reduced to facilitate a higher solidifying rate. In other words, the highly abrasive resistant cold rolling composite work roll of the invention is characterized by being a cold rolling composite work roll with an outer layer formed around the perimeter of a core material, wherein the outer layer comprising; C: 0.9-1.5 wt %, Si: 0.3-1.0 wt %, Mn: 0.3-1.0 wt %, Cr: 4.0-10.0 wt %, Mo: 3.0-8.0 wt %, V: 0.5-5.0 wt % and the remainder Fe and unavoidable impurities, is formed around the perimeter of the core material made of cast steel or forged steel by a continuous pouring process for cladding, in order to provide high abrasion resistance.
It is a further object of the invention to provide a means for producing a cold rolling composite work roll with a low compression residual stress of 60 kgf/mm
2
or lower and a Shore hardness of HS 90 or greater, and with excellent spalling resistance, by forming a composite structure wherein low alloy steel with low yield strength is used as the work roll core material, and the components of the work roll outer layer are restricted so that the hardness is not impaired even with high temperature tempering at 500° C. and above. In other words, the cold rolling composite work roll with excellent spalling resistance according to the invention is characterized by being a cold rolling composite work roll endowed with excellent spalling resistance and having an outer layer formed around the perimeter of a core material, wherein the outer layer is formed around the perimeter of the core material by a continuous pouring process for cladding, the core is a low alloy steel comprising; at least 0.3-0.7 wt % C, 0.5-3.0 wt % Cr and 0.1-2.0 wt % Mo, the outer layer comprises C: 0.9-1.5 wt %, Si: 0.3-1.0 wt %, Mn: 0.3-1.0 wt %, Cr: 4.0-10.0 wt %, Mo: 2.0-8.0 wt %, V: 0.5-5.0 wt % and the remainder Fe and unavoidable impurities, and the surface portion of the outer layer has a compression residual stress of 60 kgf/mm
2
or lower and a Shore hardness of HS 90 or greater. The cold rolling composite work roll with excellent spalling resistance according to the invention has a high C content as well as a large amount of Mo useful for secondary hardening, in order to allow tempering at high temperatures of 500° C. and above. Steel ingots obtained by conventional electro-slag remelting have had coarse carbides which are a cause of quenching cracks which occur during quenching, and therefore the upper limit for the C content has been 1 wt %, while the Mo content has been limited to 2 wt % at the most. According to the invention, however, application of the continuous pouring process for cladding produces a finer structure, and makes possible high alloying while preventing formation of coarse carbides.
Furthermore, the outer layer of the cold rolling composite work roll with high abrasion resistance or spalling resistance according to the invention may also contain Ni at 5 wt % or less. The outer layer is also characterized by being composed of M
6
C-based network eutectic carbide, granular MC carbide, tempered martensite and retained austenite, and by having a hardness of HS 90 or greater. In addition, the area ratio of the network eutectic carbide is at least 3 wt %. The crystal grain size of the outer layer is not greater than 150 &mgr;m.


REFERENCES:
patent: 5225007 (1993-07-01), Hattori et al.
patent: 5514065 (1996-05-01), Noda et al.
patent: 44-4903 (1967-03-01), None
patent: 61-11310 (1982-03-01), None
patent: 61-26758 (1986-02-01), None
patent: 7-68588 (1991-05-01), None
patent: 4-141553 (1992-05-01), None
patent: 4-220105 (1992-08-01), None
patent: 5-169112 (1993-07-01), None
Patent Abstracts of Japan, vol. 014, No. 211 (C-0715), May 2, 1990 (May 2, 1990) & JP 02 047241 A (Nippon Steel Corp), Feb. 16, 1990 (Feb. 16, 1990).
Patent Abstracts of Japan, vol. 012, No. 358 (C-531), Sep. 26, 1988 (Sep. 26, 1988) & JP 63 114937 A (Kubota Ltd.), May 19, 1988 (May 19, 1988).
Patent Abstracts of Japan, vol. 008, No. 251 (C 252), Nov. 16, 1984 (Nov. 16, 1984) & JP 59 129757 A (Kubota Tekko KK), Jul. 26, 1984 (Jul. 16, 1984).
Patent Abstracts of Japan, vol. 1995, No. 08, Sep. 29, 1995 (Sep. 29, 1985) & JP 07 126795 A (Yodogawa Steel Works Ltd), May 16, 1995 (May 16, 1995).
Patent Abstracts of Japan, vol. 018, No. 468 (C-1244), Aug. 31, 1994 (Aug. 31, 1994), & JP 06 145888 A (Hitachi Metals Ltd.), May 27, 1994 (May 27, 1994).

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