JPH02185928A - Production of work roll for metal rolling mill - Google Patents

Abstract

PURPOSE:To produce a work roll for a metal rolling mill having superior resistance to cracking by thermal shock by hardening only the surface layer of steel stock having a specified compsn. under specified conditions and by carrying out sub-zero treatment and tempering. CONSTITUTION:Stock is cast in steel contg., by weight, 0.7-1.0% C, 0.15-1.5% Si, 0.15-1.5% Mn, 3.0-6.0% Cr, 3.0-5.0% Mo and <=1.2% V and only the surface layer of the steel stock is heated to the transformation temp. or above and spray-quenched. Sub-zero treatment at <=-30 deg.C and tempering at >=180 deg.C are then carried out. A work roll having improved wear resistance and hardenability is obtd. and satisfactory rolling can be maintained for a long time by using the work roll.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a work roll for a metal rolling mill, and more particularly to a work roll for a rolling mill suitable for metal cold rolling.

[Conventional technology]

On work rolls for metal cold rolling mills, thermal shock is applied to the roll surface due to slips that occur between the roll and the material to be rolled during rolling, or accidents in which the material to be rolled is wrapped around the roll, and the thermal shock is significant. In some cases, cracks occur on the roll surface.

In addition to resistance to thermal shock, work rolls are required to have excellent wear resistance and deep hardening depth in order to maintain good rolling operation.

In order to improve the resistance to thermal shock cracks, it is effective to improve the tempering resistance of the roll itself and to perform tempering at a higher temperature.

Conventional work rolls for metal cold rolling mills have a C: 0.7 to 1.
2%, Cr: 2. , O ~ 6.0%, Mo: 1.0
% or less, v:i, o% or less, the material is forged and then quenched and tempered, but in order to obtain a hardness of Hs 95 or higher, the tempering temperature must be 140°C or lower. there were. (Special Publication No. 47-9897 1 Hitachi Review VoQ65.Mn2 1983-2 "High Hardening Depth Work Roll for Cold Rolling") [Problem to be Solved by the Invention] In the above conventional technology, due to the tempering characteristics of the material, 140
When tempering is performed at a temperature of ℃ or higher, it is difficult to obtain a hardness of Hs95 or higher, and in order to improve resistance to thermal tJl cracking, increasing the tempering temperature decreases the hardness and improves wear resistance and However, there was a drawback that the curing depth decreased.

An object of the present invention is to provide a work roll for a metal rolling mill that combines resistance to thermal shock cracking, high wear resistance, and deep hardening depth.

[Means to solve the problem]

The above purpose is to improve the tempering resistance and.

The material is forged from steel that has been sufficiently added with alloying elements that increase wear resistance and hardening depth. Only the surface layer of the material is heated to a temperature above the transformation point, and after fountain quenching, the material is heated to a temperature below -30℃. This is achieved by subjecting the steel to sub-zero treatment at 180° C. and tempering at 180° C. or higher to obtain a hardness of I-I s 95 or higher.

[Effect]

Regarding the amount of C in the chemical components, if it is less than 0.7%, it is difficult to obtain sufficient hardness, and if it exceeds 1%, large carbides increase and thermal shock resistance decreases.
．． It was made into the range of 7-1.0%.

Cr is an element that combines with C to form carbides, improving wear resistance and increasing hardening depth, but if it is less than 3%, this effect is small, and if it exceeds 6%, large eutectic carbides are formed. 3.0 to 6. to generate and reduce toughness.
It was set to 0%.

Mo improves wear resistance and hardenability, and
Although it is an element that significantly increases tempering resistance, if it is less than 3%, the desired effect cannot be obtained, and if it exceeds 5%, forgeability deteriorates, so it was set at 3.0 to 5.0%.

(2) is an element that contributes to refinement of crystal grains and improvement of wear resistance by forming VC type carbide, but if it exceeds 1.2%, grindability deteriorates, so it was set to 1.2% or less.

Regarding heat treatment, the hardenability is significantly improved due to the effect of Mo, so if the center is heated above the transformation point, there is a risk of breakage due to thermal stress during fountain quenching. Therefore, it is necessary to heat only the surface layer to a temperature above the transformation point, and to heat the inside to a temperature below the transformation point.

No sub-zero treatment, or -30℃ even if sub-zero treatment is performed
At temperatures above 15% or more retained austenite will exist, leading to a decrease in wear resistance and hardening depth, and reducing performance as a work roll for a cold rolling mill. Therefore, the sub-zero treatment temperature was set to below -30℃. .

The tempering temperature is 180°C or higher, preferably 180 to 250°C.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The dimensions of the work roll in this example are a trunk diameter of 440 mm and a trunk length of 1422 mm. Table 1 shows the chemical components of this example and the conventional roll.

Table 1 Chemical composition (wt%) Figure 1 shows the relationship between hardness and tempering temperature up to 200°C. In the case of this example, the quenching temperature was 1060° C., and gradual quenching was performed by fountain cooling while only the surface layer was heated by a low frequency induction heating method. Thereafter, subzero treatment was performed at -50°C, and tempering was performed at various temperatures.

With conventional rolls, the tempering temperature at which hardness of Hs 95 can be obtained is 140°C, but in this example, the tempering temperature is 180°C.
Compared to conventional rolls, the tempering temperature at which the same hardness can be obtained is 40°C higher.

FIG. 2 shows a comparison of resistance to thermal shock cracking between this example and a conventional roll. For the test, material was taken from the roll material after forging, machined, and then quenched.For this example, it was tempered at 180°C, and for the conventional roll, it was tempered at 140°C, and then used for the test. The test method is 80n in diameter.
+m, thickness 40+1101 of the above test piece was 142Or
500g of 7m of 20mm square mild steel material rotated at pm
Water cooling was performed while pressing against a rotating test piece with a load of m.

The crack length on the vertical axis in Figure 2 is the total length of the cracks that occurred on the surface of the test piece, and while the crack length of the conventional material was 64 mm, in the case of the one example, it was 29n++
++, which is less than half of the conventional example, indicating excellent resistance to thermal shock cracks.

Figure 3 shows the hardening depth fit! The results are shown below. If the surface hardness is Hs 95, the depth of the conventional roll is 30m.
m and E-1s 91, whereas in this example Hs
93, which shows little decrease in hardness and is excellent in terms of hardening depth.

Figure 4 shows a comparison of wear resistance. In the test, the sliding surface had a diameter of 1
A test piece of 8 mm was subjected to heat treatment similar to that shown in Fig. 2, and #10
o emery paper J: tl' 500 g (7)
A load was applied to it and it was slid. Conventional roll wear amount is 210
+og, whereas in this example it is 11011+1
; shows that it also has excellent wear resistance.

〔Effect of the invention〕

According to the present invention, when the surface hardness is the same as that of conventional rolls, the tempering temperature can be increased by 40° C. or more, which has the effect of significantly increasing resistance to cracks caused by thermal shock during rolling accidents.

Furthermore, since the wear resistance and hardenability are improved, there is also the effect of maintaining good rolling for a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between tempering temperature and hardness of one embodiment of the present invention, Fig. 2 is a diagram showing resistance to heat vI @ cracks, Fig. 3 is a diagram showing hardening depth measurement results, Fig. 4 The figure is a diagram showing wear resistance. 1. Conventional roll, 2. Roll of the present invention. Figure 1 Figure 3 Input! 10Q 150 Yakimotoshi' [Hiki ('c) 2nd evil 10 20 3Q Emen Riki' et al.

Claims (1)

[Claims] 1, C: 0.7-1.0%, Si 0.15-1.5%,
Mn0.15-1.5%, Cr:3.0-6.0%, M
A material made by forging steel containing O: 3.0 to 5.0% and V: 1.2% or less is heated to a temperature above the transformation point only in the surface layer, and then fountain quenched to -30℃ or below. A method for manufacturing a work roll for a metal rolling mill, characterized by performing sub-zero treatment at a temperature of 180° C. or higher, and further tempering at a temperature of 180° C. or higher.