JPS6032688B2 - Manufacturing method of composite roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a composite roll, and more specifically,
The present invention relates to a method for manufacturing a composite roll that can prevent 8.0 and metal breakage.

Generally, in hot rolling of steel using cast iron rolls, cracks occur in the roll body due to thermal fatigue, and the cracks may propagate and lead to breakage accidents.

The same thing happens with composite rolls, that is, when a crack that occurs in the outer shell of the composite roll reaches the boundary with the inner shell, it leads to a breakage accident. In addition, in the past, when manufacturing cast iron composite rolls, 3
Strain relief heat treatment is performed at a temperature of 000 to 700q0, but the strength of the inner shell made of spheroidal graphite cast iron is almost the same as as cast, so the rolling load during hot rolling and Cracks caused by thermal fatigue may accumulate and cause the roll to break.

The purpose of the present invention is to prevent body breakage and metal breakage in the above-mentioned conventional composite rolls. Specifically, by making the inner shell of a cast iron composite roll highly rutted, it is possible to prevent rolling loads and heat. This is a method for manufacturing composite rolls that can prevent accidents caused by breakage or breakage of the roll body and metal parts due to cracks caused by fatigue. The manufacturing method of the composite roll according to the present invention is characterized in that the outer shell is cast into a hollow shape by centrifugal force casting using cast iron roll material, and after the cast outer shell is solidified, the hollow part of the outer shell is C
3.0-3.7%, Sil. 5-2.5%, Mno. 2
~1.0%, Nj 3% or less, Cro. 4% or less, Mol
% or less, Mg 0.02 to 0.1%, the remainder unavoidable impurities and Fe, and the roll-shaped material is cast as an inner shell and completely welded.
In the heat treatment of heating to a temperature of ℃ and then air cooling or water cooling, the spherical graphite casting of the roll inner shell is heated to a temperature of 780o to 840℃.
The purpose is to provide a temperature difference between the roll surface and the inside so that the temperature range is regulated to qo.

For this operation, rapid heating and a roll surface of 840
Shorten the holding time in the temperature range of o~960oo,
Depends on how to speed up the subsequent cooling. Next, a method for manufacturing a post-coating roll according to the present invention will be explained in detail.

In the method for manufacturing a composite roll according to the present invention, the outer shell of the composite roll is made of commonly used materials, such as chilled roll material, grain roll material, and spheroidal graphite cast iron roll material.

This is because heat resistance and wear resistance are required for hot rolling of steel. Then, using any of these materials, a hollow outer shell is cast by deep casting, and after casting, an inner shell is cast into the hollow outer shell. Spheroidal graphite cast iron is used for this inner shell, and its components and proportions are C3
．． 0-3.7%, Sil. 5-2.5%, Mno. 2~
1.0%, Ni 3% or less, Cro. 4% or less, Mol%
The material is composed of 0.02 to 0.1% Mg, the balance being unavoidable impurities, and Fe, and will be specifically explained below.

That is, C is an element necessary for improving strength and toughness, but if the C content is less than 3.0%, a structure with less graphite and more cementite will occur, causing problems in casting, and poor toughness. When the content exceeds 3.7%, graphitization progresses rapidly and sufficient strength cannot be obtained, resulting in brittleness.

Therefore, the C content is set to 3.0 to 3.7%. Si is an element that affects graphitization, and its content is 1.5%.
If the content is less than 2.5%, graphitization will be poor and the amount of cementite will be large, resulting in poor strength and casting problems.If the content exceeds 2.5%, the matrix will become brittle and the toughness will be poor.

Therefore, the Si content is set to 1.5 to 2.5%. Mn combines with S and prevents the harmful effects of S, but when its content is 0
．． If it is less than 2%, the effect is small and it is difficult to obtain a low Mn molten metal, and Mn increases hardness, but 1.0
If the content exceeds 5%, the amount of cementite will increase, and the matrix will also become too hard and brittle.

Therefore, the Mn content is set to 0.2 to 1.0%. Ni is an element that strengthens the material and increases its hardness without making it brittle, but if it is contained in an amount exceeding 3%, it tends to become thermally unstable bainite and is not economical.

Therefore, Ni should be 3% or less. Cr is an element that promotes the crystallization of cementite, and if it is contained in an amount exceeding 0.4%, cementite becomes too large and the sea bream quality deteriorates. Therefore, the Cr content is set to 0.4% or less. Like Ni, Mo is an element that increases the hardness of the material without making it brittle, but if it is contained in an amount exceeding 1.0%, it is not very effective and is not economical.

Therefore, the Mo content is set to 1% or less. Mg is an element that makes graphite spheroidal, but its effect is not recognized when the content is less than 0.02%, and when it is contained more than 0.1%, casting defects are likely to occur. .

Therefore, the Mg content is set to 0.02 to 0.1%. Since the inner shell with such components and proportions is completely welded to the outer shell, the outer shell and inner shell will never separate.

The heat treatment in the method for manufacturing a composite roll according to the present invention will be explained.

In the method for manufacturing a composite roll according to the present invention, a roll-shaped material consisting of an inner shell having the above-described components and component ratios and an outer shell made of the above-mentioned material is heated to a temperature of 0 to 960 oo, and then air-cooled. Alternatively, the outer shell is cooled with water to impart desired wear resistance and hardness, and the inner shell's spheroidal graphite cast iron is controlled to a temperature range of 7,800 to 8,400 C to impart rice grain properties to it.

In this case, the outer shell becomes austenitic at 800 qo or more and transforms into pearlite, habenite, or martensite upon cooling.

Regarding this transformation from austenite, the cooling rate,
It varies depending on the alloy components and is determined depending on the intended use of each roll. Furthermore, after the heat treatment, it is common to carry out strain relief, but it goes without saying that the temperature at which strain relief is applied is also important, since it also affects the base. The reason why the roll surface temperature is set to 840o to 960oo is because a temperature lower than 840qo cannot impart sufficient hardness and wear resistance to the outer shell.
This is because if the temperature exceeds 840 degrees, there is no need for a higher temperature, and it becomes difficult to keep the temperature of the inner shell below 840 degrees.

In addition, the spheroidal graphite cast iron inside the roll is heated to 780o~840℃.
The temperature range of c3.32%, Sjo. 95%, Mno. Spot %, Ni
3.27%, Crl. 15%, Moo. 27%, P.O.
058%, SO. After the outer shell is solidified by centrifugal casting of the outer shell material consisting of 0.15% balance Fe, C3 is poured into the hollow part of the outer shell.
．． 45%, Si2.16%, Mno. 41%, Nio.
87, Cro. 20%, MOO. 13%, P.O. 045
%, SO. The inner shell material was cast, completely welded, and cooled.

In this case, the thickness of the outer shell is 4 mm. After maintaining the temperature at the temperature shown in Figure 1 for a period of time, a test piece was taken at a position three distances from the boundary between the inner and outer shells to the inner shell. The tensile strength was all 50-55 [9/th]. Also, the elongation is 7800
The elongation is 2.6 to 3% within the temperature range of ~8400°, and is 2% or less at temperatures below 780° and over 840q0. As is clear from this, the toughness of the inner shell becomes extremely excellent by heating to a temperature range of 7,800 to 840 oo. Furthermore, the material of the spheroidal graphite cast iron roll (within the range of ingredients and ingredient ratios used in the manufacturing method of the composite roll according to the present invention)
When heated to a temperature of 780° to 8403° and cooled, the matrix structure becomes a two-phase mixed structure of ferrite and pearlite. That is, at this temperature, the matrix is not completely austenite, but consists of ferrite and austenite. This is because of the coexistence of austenite, and upon subsequent cooling, austenite transforms into pearlite.

The thus obtained two-phase mixed structure of ferrite and pearlite has relatively high hardness and excellent strength, and also has high elongation.

This is because the ferrite portion inhibits the crack development process. At temperatures below 780 qo, the base pearlite becomes granular, resulting in lower hardness and slightly lower strength.

However, the elongation is smaller than that of ferrite and pearlite two-phase structures. Moreover, at a temperature exceeding 84,000, the base becomes completely austenite, and the properties are reduced by subsequent cooling to become completely pearlite. In this case, the hardness is high and the strength is excellent, but the elongation is low. Furthermore, elongation is important for the accident resistance of the roll, and the relationship between elongation and heating temperature is as shown in FIG. moreover,
In the method for manufacturing a composite roll according to the present invention, creating a temperature difference between the roll surface and the inside is achieved by rapid heating, holding time, and cooling rate, but what is particularly important is the temperature raising and holding operations. It is.

For example, 450? 700 rolls (outer shell thickness 6 m)
After preheating to qo, the surface temperature was heated to 90,000 at a heating rate of 300°C'Hr and held for 10 minutes.
When cooling at 00oC/Hr to 2500C/Hr, the maximum temperature is 825q at a position 6 ribs from the roll surface.
It becomes ○. In this case, the outer shell material once becomes austenite, and its properties change depending on the subsequent cooling rate and alloy component content, but also change depending on the heating temperature.

That is, even if other conditions are the same, heating to a high temperature results in high hardness, and heating to a low temperature results in low hardness. According to the method of manufacturing a composite roll according to the present invention, there is a temperature difference between the vicinity of the roll and the inside, so even within the outer shell, the hardness of the inside is lower than that of the surface. This is not a problem when actually using the roll. Next, an example of the method for manufacturing a composite roll according to the present invention will be described.

Example C3.20%, Sio. 28%, Mno. 26%, Ni
3.25%, Crl. 26%, Moo. 24%, P.O.
067%, SO. 010%, the remainder being Fe, the outer shell of chilled roll material is cast into a hollow shape by centrifugal casting and solidified. 4
7%, Nil. 25%, Cro. 17%, Moo. 15
%, PO. 042%, SO. 010%, M Liu. 042%
An inner shell of spheroidal graphite cast iron made of the remainder of Fe is cast and completely welded to the outer shell.

The dimensions of the roll (body) at this time were 3700 x 800 sleeves, and the thickness of the outer shell was 45 ribs. The roll-shaped material made in this way was preheated to 750 qo, held for 3 hours, heated to 880°C at a heating rate of 40 pC/Hr, held for 5 minutes, and cooled in the air to below 600°C. (cooling rate: 150°C'Hr) and held at a temperature of 55,000°C for 5 hours to remove strain. As a result, the shore hardness of the arm surface was ~70, and the strength of the inner shell of spheroidal graphite cast iron was uneven. 8k
9/Iso, elongation was 2.9%. This roll was used in a small angle finishing stand, and it had good wear resistance with no breakage accidents. As explained above, since the method for manufacturing a composite roll according to the present invention has the above configuration, even if cracks occur in the roll body due to thermal fatigue during hot rolling of steel, To manufacture a composite roll having an inner shell having excellent toughness that eliminates the occurrence of breakage accidents due to propagation of cracks, and further having an outer shell having excellent wear resistance. It is something that can be done.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heat treatment temperature and elongation in the method for manufacturing a composite roll according to the present invention. Blind drawing

Claims (1)

[Claims] 1. Using cast iron roll material, the outer shell is cast into a hollow shape by centrifugal force casting, and after the cast outer shell is solidified, the hollow part of the outer shell is filled with 0.3 to 3.7% C and 1.5 to 1.5% Si. 2.5%, Mn
0.2 to 1.0%, Ni 3% or less, Cr 0.4% or less,
A roll-shaped material made of spheroidal graphite cast iron consisting of Mo1% or less, Mg0.02-0.1%, and the remainder unavoidable impurities and Fe is cast as an inner shell and completely welded to 840° to 96°.
In the heat treatment of heating to a temperature of 0°C and then cooling with air or water, the maximum heating temperature of the spheroidal graphite cast iron of the roll inner shell is set to 7.
A method for manufacturing a composite roll, characterized in that the temperature range is from 80° to 840°C.