JPS62180019A - Manufacture of composite roll - Google Patents

Abstract

PURPOSE:To obtain tough composite roll having inner layer of large tensile strength, by composing core material of special cast steel having a specified compsn. and specifying heat treating condition after diffusion heat treatment. CONSTITUTION:High Cr material contg. by weight 10-20% Cr is centrifugally cast to hollow-shaped outer layer. After the solidification, special cast steel composed of 0.5-1.0% C, 0.3-0.8% Si, 0.4-0.9% Mn, <=2% Ni, <=0.5% Cr, <=0.4% Mo and the balance Fe is cast as inner layer to roll shape. Roll-shaped body after casting the inner and outer layers is subjected to diffusion heat treatment in which it is heated to 900-1,000 deg.C then cooled to <=600 deg.C. Thereafter, the body is stepwisely held at temps. higher and lower than transformation point i.e. 750-780 deg.C and 680-710 deg.C, next, subjected to granulation heat treatment in which it is cooled to <=600 deg.C then quenched and annealed. In this way, composite roll having inner layer of >=60kg/mm<2> tensile strength is obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a composite roll, and particularly relates to a strong composite roll whose inner layer has a tensile strength of 60 kg/mml or more. Used in the field of composite roles.

[Conventional technology]

In order to improve the productivity of hot rolling, rolling mills have been made larger and faster, and as a result, efforts have been made to make rolling rolls tougher, and composite rolls have come into use.

Attempts are constantly being made to strengthen the inner layer of composite rolls; for example, Japanese Patent Publication No. 11657.59-20417
discloses a composite roll with a strong core material and a method for manufacturing the same.

[Problem that the invention seeks to solve]

The core material of these composite rolls was cast iron or graphite steel, and the tensile strength was less than 60 kg/mm2.

Conventionally, the heat treatment of these composite rolls whose core materials are ductile cast iron or graphite steel is as shown in Fig. 3.
A diffusion heat treatment is carried out by holding at a temperature of 1000°C for 10-20 hours, then air-cooled to below 500°C, and then heated to 500°C.
BH annealing is performed at 00 to 600°C for 10 to 20 hours.

An object of the present invention is to solve the problems of the prior art described above and to provide a method for manufacturing a strong composite roll whose inner layer has a tensile strength of 60 kg/mm2 or more.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, a step of centrifugally casting a high chromium material containing 10 to 20% Cr by weight into a hollow outer layer, and after the outer layer is solidified, an inner layer of C: 05 to 10, Si
: 0.3-0.8%, Mn: 0.4-09%, Ni
Cr: 0.5% or less, Mo: 0.4% or less, with the remainder being Fe and unavoidable impurities. a diffusion heat treatment step in which the roll shaped body is heated to a temperature of 900 to 1000°C and then cooled to 600°C or less, and 750 to 780°C and 680 to 710°C after the diffusion heat treatment;
The temperature was held stepwise at f temperatures above and below the transformation point of
It comprises a granulation heat treatment step of cooling, and a step of quenching and annealing after the vertical specific heat treatment, and the inner layer has a tensile strength of 60 kg/mm2JU or more. This is a method for manufacturing a composite roll.

The reasons for limiting the components of the composite roll of the present invention will be explained. The reason for limiting the amount of Cr in the high chromium material of the outer layer is as follows.

Cr: Currently, the composition range of high chromium rolls generally used as rolling rolls is in the range of 10 to 20% Cr, and if it is less than CrlO%, the amount of carbide is small and wear resistance is poor, and Cr is 20%. If it exceeds this amount, coarse carbides will crystallize and deteriorate the roughness resistance, so it is limited to a range of 10 to 20%.

Next, the reason for limiting the composition of the holding cast steel in the inner layer will be explained.

C: C is an element necessary to improve strength and toughness, but if it is less than 0.05%, the fluidity will deteriorate and defects such as blowholes will easily occur at the boundary between the inner and outer layers, so it is necessary to have a content of 0.5% or more. Further, since C exceeds 10%, cementite crystallizes and the toughness decreases, so C was limited to 05 to 1.0%.

SI: Si needs to be 0.3% or more for deoxidation, but even if it exceeds 0.8%, the deoxidation effect will be saturated and will not change, so Si should be 0.3 to 0.3%.
It was limited to 0.8%.

Mn: Mn combines with S and has the effect of blocking the negative effects of S, but if it is less than 0.4%, the effect is not sufficient, and if it is less than 0.9%
If the Mn exceeds 0.04% to 0.9%, the material becomes brittle.
limited to.

Ni: Ni has the effect of toughening the material without making it brittle, but if it exceeds 2%, it tends to harden and is uneconomical, so Nl was limited to 2% or less.

Cr: Cr is an element that promotes cementite crystallization,
If the content exceeds 0.05%, the toughness decreases, so Cr was limited to 0.05% or less.

MO: MO has the effect of increasing quenching sensitivity, but from an economical point of view, it is limited to 0.04% or less.

After centrifugal casting of the outer layer, when casting the inner layer on the inner surface, it is necessary to completely weld the outer layer and the inner layer.

Next, the heat treatment shown in FIG. 1 will be explained.

First, roll-shaped bodies cast into the inner and outer layers are
Diffusion heat treatment is carried out between the high chromium material of the outer layer and the special cast steel of the inner layer by holding at a temperature of 0°C for usually 10 to 20 hours. If the heating temperature at this time is less than 900°C and the holding time is less than 10 hours, sufficient diffusion effect cannot be given to the outer and inner layers, and if the heating temperature exceeds 1000°C, some of the high chromium material cementite will melt. (1) Diffusion heat treatment was limited to a temperature of 900 to 1000° C., since the holding time exceeds 20 hours, which is uneconomical since the effect is saturated.

■After diffusion heat treatment, it is once cooled to below 600℃, but
The reason why the temperature is limited to 0.degree. C. or lower is that the temperature is completely below the transformation point up to the center of the roll.

After cooling to 600°C or lower, the temperature (750 to 780°C) above and below the transformation point (730°C) was heated for about 8 hours and (680°C).
◎Granulation heat treatment is carried out by holding in a stepwise manner for ~710)℃ x 8 hours. This is to increase the toughness by dispersing it into the fabric.

The roll-shaped body of this example was heated at 760°C for 16 hours at 780°C.
Three types of @granulation heat treatment were performed: 8 hours at 700°C, 8 hours at 700°C, and the tensile strength of the inner layer was investigated. The results are shown in FIG. The results shown in Figure 2 show that the granulation efficiency is best when the temperature is maintained within ±(20~50℃) above and below the transformation point.◎The temperature of the granulation heat treatment is 750~7
The temperature was limited to 80°C and steps from 680 to 710°C.

◎After the granulation heat treatment, it is cooled to 600°C or less, and then ○■ Strain-removal annealing is carried out at a normal temperature of (900 to 1000)°C for about 1 hour.

〔Example〕

φ660mmXJ150 whose target chemical composition is shown in Table 1
A roll material with a thickness of 0 mm, an outer layer thickness of 75 mm, and the rest as an inner layer thickness was subjected to diffusion heat treatment at 950°C for 15 hours.
Then cool to 600°C, then 760°C and 700°C.
Granulation heat treatment was performed by holding each sample at ℃ for 8 hours.

Table 1 Next, it was cooled to 550°C, heated again to 900°C, and heated to 10
After holding for a period of time and quenching with air cooling, the
Distortion removal firing was performed by holding for a certain period of time.

When a test piece was taken from the inner layer of this roll material and a tensile test was performed, the tensile strength was 63 to 70 kg/mm.
It was 2.

In addition, the composite roll of the present invention example of φ750mmXI'2030mm was used as a work roll before the finishing roll of a hot strip mill, and 350,000 tons could be smoothly rolled without any accidents.

〔Effect of the invention〕

As is clear from the above examples, the present invention performs diffusion heat treatment on a composite roll containing limited components at 900 to 1000°C, and
750-780℃ and 680-7 after cooling to below 00℃
By performing stepwise granulation heat treatment at 10℃, cooling to below 600℃, and then quenching and annealing, the tensile strength of the inner layer is increased to 6.
A strong composite roll of 0 kg/mm2 or more could be manufactured.

[Brief explanation of drawings]

Figure 1 is a heat treatment process diagram for high chromium rolls of the present invention;
The figure is a diagram showing the relationship between the granulation heat treatment temperature and the tensile strength of the inner layer of the composite roll, and FIG. 3 is a diagram of the heat treatment process of a conventional high chromium roll.

Claims (1)

[Claims] (1) A step of centrifugally casting a high chromium material containing 10 to 20% Cr by weight into a hollow outer layer, and after the outer layer is solidified, the inner layer is made of C: 0.5 to 1.0, Si:
0.3-0.8%, Mn: 0.4-0.9%, Ni: 2
% or less, Cr: 0.5% or less, Mo: 0.4% or less, with the remainder being Fe and unavoidable impurities. A diffusion heat treatment step in which the body is heated to a temperature of 900 to 1000 °C and then cooled to 600 °C or less, and after the diffusion heat treatment, it is held stepwise at temperatures above and below the transformation point of 750 to 780 °C and 680 to 710 °C, and then 600 °C ℃ or below, and a step of performing quenching and annealing after the granulation heat treatment, and the inner layer has a tensile strength of 60 kg/mm^2 or more. A method for manufacturing a composite roll.