JPS6299442A - Alloy for continuously cast roll - Google Patents

Abstract

PURPOSE:To obtain an alloy for continuously cast roll excellent in heat resistance and wear resistance by limiting C, Si, Mn, Ni and Mo content in a composition of 13Cr alloy steel. CONSTITUTION:The alloy for continuously cast roll has a composition consisting of, by weight, 0.03-0.5% C, 0.1-1% Si, 0.1-1% Mn, 2-3.5% Ni, 12.5-17% Cr, 0.1-0.5% Mo, and the balance Fe with inevitable impurities. When manufacturing a continuously cast roll out of this alloy, there is not necessity for forming the whole of roll barrel, from the external surface to the inside, by use of the alloy of this invention and the application of this alloy to the surface layer part alone suffices.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an alloy for continuous casting rolls.

[Conventional technology]

In continuous casting (hereinafter also referred to as "continuous casting") equipment, the continuous casting rolls that support and guide the slab drawn from the mold directly below the tundish are heat resistant and wear resistant against contact with the high temperature slab. Needless to say, it is necessary to have the strength to withstand the load of the slab, and also because the temperature rise due to the heat effect from the slab and the forced cooling by internal water cooling of the roll and surface water spraying are repeated. It is also required to have excellent thermal shock properties so that cracks do not occur due to temperature changes.

Conventionally, this continuous casting roll is made of Cr-Mo-Fe cast steel and has a body surface coated with 13Cr alloy steel.

[Problem to be solved]

13Cr alloy steel contains precipitation hardening elements, and in the matrix,
It has a structure in which precipitated carbides are dispersed, and therefore 13C
Continuous casting rolls whose roll body surfaces are coated and protected with R-based alloy steel have excellent wear resistance and strength. However, on the other hand, it is not sufficient in terms of thermal shock resistance and toughness, and there is a problem that cracks (heat crank) are likely to occur due to the repeated action of heating by the slab and forced cooling by cooling water. . These cracks tend to propagate along the precipitated carbides dispersed throughout the base, eventually causing a roll breakage accident.

For this reason, in a continuous casting operation, the actual situation is that inspection for initial crack occurrence due to thermal shock in the roll body and control of crack depth must be carried out frequently.

In particular, in recent years, operations have become faster and hotter in response to requests for improved efficiency in continuous casting operations and super hot charging of slabs. As operating conditions become more severe, the occurrence and propagation of cracks in the roll body are accelerated, and wear on the body surface is accelerated, resulting in a decrease in roll life and short-term roll life. In addition to being forced to replace the rolls, a large amount of cost is required for the repair work of the rolls.

In order to address the above-mentioned circumstances, the present invention aims to provide an alloy for continuous casting rolls that has good heat resistance, wear resistance, etc., and improved thermal shock resistance.

[Means and effects for solving the problems] The alloy for continuous casting rolls according to the present invention contains C: 0.03 to 0.5%,
Si: 0.1-1.0%, Mn: 0.1-1.0
%, Ni: over 2.0% and 3.5% or less, Cr:
12.5 to 17.0%, MO: 0.1 to 0.5%, and the remainder substantially consists of Fe.

The alloy of the present invention has excellent not only heat resistance and wear resistance but also thermal shock resistance, and exhibits excellent resistance to crack initiation and propagation under thermal cycle conditions of rapid heating and rapid cooling.

The reasons for limiting the components of the alloy of the present invention are as follows.

C: 0.03 to 0.5% C is a solid solution strengthening element and has the effect of increasing the toughness and strength of the matrix. To obtain this effect, at least 0.
03% is required. However, if added in a large amount, embrittlement due to precipitation of secondary carbides and softening of the matrix due to increase in retained austenite phase will occur, so the upper limit is set at 0.5%.

Si: 0.1 to 1.0% St not only has a deoxidizing effect on the alloy, but also has the effect of improving oxidation resistance by solidly dissolving in the matrix. If it is less than 0.1%, the thermal shock properties will deteriorate due to an increase in the amount of nonmetallic inclusions due to insufficient deoxidation. Further, when added in a large amount exceeding 1.0%, a decrease in thermal shock JIC resistance is observed. Therefore,
It is set to 0.1 to 1.0%.

Mn: 0.1 to 1.0% Mn is an element for deoxidizing and desulfurizing the alloy. If it is less than 0.1%, thermal shock resistance will be impaired due to an increase in the amount of nonmetallic inclusions due to insufficient deoxidation and desulfurization. However, if it exceeds 1.0%, the retained austenite phase increases, resulting in softening of the matrix and reduction in toughness, similar to the case with C. Therefore, it is set to 0.1 to 1.0%.

Ni: more than 2.0% and less than 3.5% Ni is one of the main constituent elements of the alloy of the present invention, and is an element that improves the toughness of the matrix and stabilizes the structure at high temperatures. This effect appears when the addition exceeds 2.0%,
The effect increases with increasing content. However, if added in a large amount, thermal shock resistance deteriorates due to softening of the base and lowering of the transformation point, so the upper limit is set at 3.5%.

Cr: 12.5 to 17.0% Cr is an element that strengthens the matrix as a solid solution and has the effect of improving oxidation resistance and toughness. If the amount added is less than 12.5%, the toughness improvement effect will not be sufficient, and the coexisting N
In relation to the quantitative balance with j, the austenite phase region becomes wider at high temperatures, so retained austenite increases in the matrix structure and the hardness of the matrix decreases. On the other hand, 17.0%
If it exceeds 100%, the ferrite phase in the base structure increases, and the strength and toughness decrease. Therefore, the amount of Cr is 12.5~
It shall be 17.0%.

Mo: 0.1 to 0.5% MO combines with C to form fine carbides, strengthens the matrix, and increases toughness. This effect appears when 0.1% or more is added, and increases as the amount added increases. However, if added in a large amount, the carbides will become coarse and the base will become brittle, so the upper limit is set at 0.5%.

When manufacturing a continuous casting roll made of the alloy of the present invention, it is not necessary to form the entire body of the roll from the outer surface to the inside of the alloy of the present invention, and as shown in FIG. It is sufficient to have a two-layer structure consisting of a surface layer portion (11) and a core portion (12), and apply the present invention alloy only to the surface layer portion (11). This is because the heat resistance, abrasion resistance, thermal shock resistance, etc. of the roll body are issues related to the surface layer.

As a method of manufacturing such a roll body with a multilayer structure, for example, a cylindrical body serving as the core (12) is formed of a suitable other material (e.g., SCM equivalent material), and the outer peripheral surface is welded (
A method of forming a built-up layer made of the alloy of the present invention as the surface layer portion (11) by TIG welding, MIG welding, covered arc welding, etc.) can be applied. Alternatively, the cylindrical body serving as the core is coaxially inserted into a mold having an inner diameter larger than the outer diameter of the cylindrical body, and the alloy of the present invention is placed in the cavity defined by the inner surface of the mold and the outer surface of the cylindrical body. A method in which a surface layer made of the alloy of the present invention is formed in close contact with the outer peripheral surface of a cylindrical body (core part) by casting molten metal, or a method in which a surface layer made of the alloy of the present invention is formed in close contact with the outer peripheral surface of a cylindrical body (core part), or a core layer is formed along the inner surface of the mold by using a centrifugal force casting method. It is also possible to apply a method in which a cylindrical body made of the invention alloy is cast, and then a cylindrical body made of another material is cast inside the cylindrical body. In addition,
Although the illustrated continuous casting roll has a cooling water flow path (30) along the axis of the shaft body (20), it goes without saying that the roll structure is not limited to this.

The alloy of the present invention is a martensitic steel. Its heat treatment includes quenching from a temperature of 900 to 1050°C, and
This is achieved by a tempering treatment at ~700°C. When forming the surface layer of the roll body by overlay welding, heat treatment at 550 to 650° C. may be performed as stress relief treatment after welding.

〔Example〕

A thermal shock test was conducted on each sample material having the component composition shown in Table 1, and the results shown in the right column of the table were obtained.

Perfuming (1) to (9) are examples of the present invention, Perfuming (101) to (1)
13) is a comparative example. Comparative examples (101,) to (113
), (101) is an example of a material equivalent to 13Cr alloy steel used as a conventional overlay material;
) to (113) are examples that contain all of the component elements stipulated in the present invention, but the content of one of the elements (indicated by a line in the table) deviates from the stipulations of the present invention. .

The thermal shock test conditions are as follows.

(1) Preparation of test piece Shape: 35x35x50 (m) cube Heat treatment: Quenching (900-1050°C, water cooling), tempering to 550°C
~700°C).

(2) Test method Diameter at the center of the test surface of the test piece (35X 35.Dragon) 1
After rapidly heating a 51 m circular area to 650° C. as a heating section, the test piece is immersed in water and rapidly cooled, and a thermal cycle is repeated. After repeating this rapid heating and cooling 800 times, the maximum depth (n) of the cracks generated in the test piece was measured using a tarac meter.

As shown in Table 1, the alloy of the present invention is different from the conventional material 13
Cr alloy steel equivalent material (llhlol) and other comparative examples (N1
1102-113), the cracks are slight and they have excellent thermal shock properties.

〔Effect of the invention〕

The alloy of the present invention has the heat resistance and wear resistance necessary for continuous casting rolls, and at the same time has thermal shock resistance that greatly exceeds conventional materials such as 13Cr alloy steel. Therefore, continuous casting rolls in which at least the surface layer of the roll body is made of the alloy of the present invention are subject to repeated heating and cooling. It guarantees greater durability than rolls and contributes to stable and smooth continuous casting operations.

In addition to continuous casting rolls, the alloy of the present invention is also useful as a roll material for high-temperature steel transport rolls, hot rolling rolls, etc. that are connected to a steel heating furnace.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing an example of a continuous casting roll. 10: roll body, 11: surface layer, 20: shaft.

Claims (1)

[Claims] (1) C: 0.03-0.5%: Si: 0.1-1.0
%, Mn: 0.1 to 1.0%, Ni: exceeding 2.0%,
3.5% or less, Cr: 12.5-17.0%, Mo: 0
．． An alloy for continuous casting rolls consisting of 1 to 0.5% Fe and the remainder substantially Fe.