JPS5914091B2 - 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 body breakage and metal breakage.

Generally, in hot rolling of steel using cast iron rolls, cracks occur in the roll body due to thermal fatigue, and this crack may develop and lead to a breakage accident.

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, 30
Strain relief heat treatment is performed at a temperature of 0°C to 700°C, but the toughness of the inner shell made of spheroidal graphite cast iron is almost the same as as cast, so rolling during hot rolling is difficult. Cracks may occur due to load or thermal fatigue, resulting in failure of the roll.

The purpose of the present invention is to prevent body breakage and metal breakage in the conventional composite rolls described above. Specifically, by toughening the inner shell of the cast iron composite roll, it is possible to prevent rolling loads and thermal fatigue. This is a method of manufacturing a composite roll that can prevent accidents caused by breakage or breakage of the roll body and metal part due to cracks caused by the occurrence of cracks.

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 casting using cast iron roll material, and after the cast outer shell is solidified, the hollow part of the outer shell is filled with C3. , 0-37%, Si 1.5-2.5, Mn 0.2
~1.0%, Ni 3% or less, cro, 4% or less lMo1
% or less, Mg 0.02 to 0.1%, the remainder unavoidable impurities, and Fe. The roll-shaped material is cast as an inner shell and completely welded to 780°C to 840°C.
It consists of heating to a temperature of

Next, a method for manufacturing a composite 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, ie, tiddle 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 centrifugal 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 component ratios are: C30 to 3.7, Si 1.5 to 2.5, Mn 0.2 to 1.0%, Ni 3% or less, Cr 0.4% or less, Mo 1% or less, Mg 0.02-0.1%.

The remainder consists of inevitable impurities and Fe, which will be specifically explained below.

In other words, an appropriate amount of C is an element necessary to improve 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.
The toughness is also poor, and if the content exceeds 3 or 7, graphitization progresses rapidly and sufficient strength cannot be obtained, resulting in brittleness.

Therefore, the C content is set at 3.0 to 3.7.

Si is an element that affects graphitization, and if its content is less than 1.5%, graphitization will be poor and the amount of cementite will increase, resulting in poor strength and easy casting problems.
．． If the content exceeds 5%, the g and 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 to prevent the harmful effects of S, but if its content is less than 0.2%, its effect is small.

Moreover, it is difficult to obtain a molten metal with a low Mn content, and although Mn easily increases hardness, if it is contained in an amount exceeding 1.0, cementite increases and the matrix becomes too hard and brittle.

Therefore, the Mn content is set to be 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 less than 3%. Cr is an element that promotes the crystallization of cementite, and if it is contained in an amount exceeding 0.4%, the amount of cementite becomes too large and the toughness decreases.

The Cr content shall be 0.4 coefficient 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 MOC content is set to be 1 part or less.

Mg is an element for making graphite spheroidal.

The effect is not recognized when the content is less than 0.02%,
Furthermore, if the content exceeds 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 attached to the outer shell, the outer shell and inner shell never separate.

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 components and component ratios and an outer shell made of the above material is heated to 7808C to 840C and then air-cooled or water-cooled to form an outer shell. It imparts desired wear resistance and hardness as well as toughness to the inner shell material of spheroidal graphite cast iron.

That is, the roll-shaped material is heated to 780°C to 840°C in a heating furnace.
After heating and holding at a temperature of 1 to 10 hours, air cooling or water cooling to a temperature of 600 °C or less,
Strain relief is performed at a temperature of 300°C to 550°C to obtain the desired hardness of the roll body surface and to make the inner shell of the spheroidal graphite cast iron highly tough.

In this case, when heated to a temperature of 780°C to 840°C,
The outer shell once becomes austenite, and its hardness changes depending on the cooling rate, amount of alloy, and strain relief temperature.

Therefore, in order to obtain the desired hardness, it is necessary to select the alloy amount and strain relief temperature, and also consider cooling from a temperature of 780°C to 840°C.

In other words, if the goal is low hardness, low alloys (especially N
i, Mo), high strain relief temperature, 780°C to 840°C
Air cooling is sufficient for cooling from a temperature of Therefore, a fast cooling rate is required.

This roll-shaped material, especially the inner shell of 1 spheroidal graphite cast iron,
Heating to 0°C to 840°C will be explained with reference to FIG.

That is, C3, 32%, Si 0.95%, Mn 0.68%, Ni 3.27%, Cr 1.15%, Mo 0.27% P
An outer shell consisting of 0.058%, 80.015%, and the balance Fe was cast by centrifugal casting, and after the outer shell was solidified, C3,45 and Si2.16 were added to the hollow part of the outer shell.

Mn 0.41%, Ni 0.87%, CrO, 20%.

Mo0.13%, Po, 045%, 80.01%, Mg
An inner shell material consisting of 0.048% balance Fe was cast, completely welded, and cooled.

Incidentally, the thickness of the outer shell is 40m7IL.

Next, the temperature shown in FIG. 1 is 7800C to 840C.
and then from the boundary of the inner shell and outer shell to the inner shell part for 30 minutes.
A test piece was taken at a position of mm.

All expansion forces were 50-55 kg/ma.

The elongation is 2.6% within the temperature range of 780°C to 840°C. ~3%, below 780℃ and 8%
At temperatures above 40°C, the elongation is 2% or less.

As is clear from this, 780°C to 840°
By heating to a temperature range of C, the toughness of the inner shell becomes extremely excellent.

Therefore, when the spheroidal graphite cast iron roll material in the method for manufacturing a composite roll according to the present invention is heated to a temperature of 780° C. to 840° C. and cooled, the base structure becomes a ferrite and pearlite two-phase mixed structure.

That is, at the above temperature, the matrix is not completely austenite, but ferrite and austenite coexist, 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 growth process.

At temperatures below 780°C, the base pearlite is granulated, resulting in lower hardness and a slight decrease in strength.

However, the elongation is smaller than that of the ferrite and pearlite two-phase structure.

Moreover, at temperatures above 840° C., the matrix becomes fully austenitic, and its properties are determined by subsequent cooling.

In the method according to the present invention, the roll material is entirely pearlite within the range of its composition.

In that case, the hardness will be high and the strength will be excellent, but the elongation will be low.

Elongation is important for the accident resistance of rolls, and FIG. 1 illustrates the relationship between elongation and heating temperature.

Next, an example of the method for manufacturing a composite roll according to the present invention will be described.

Example C3, 32%, Si0.95%, Mn0.68%, N
i 3.27%, Cr 1.15'%, Mo0.27
%, PO, 0581%, 80.015%, Fe balance grain roll material outer shell was cast by centrifugal casting, and after solidification, C3, 45%, Si 2.16%, Mn 0.41%
, NiO, 87%, CrO, 20%, Mn 0.1
3 %J'0.045, SO, 010%1Mg 0
．． An inner shell of spheroidal graphite cast iron containing 0.48% Fe and the remainder is cast and completely welded to the outer shell.

Next, it is heated to a temperature of 820°C, held for 75 hours, air cooled to 600°C or less, and further heated to a temperature of 550°C for 5 hours to remove distortion.

The hardness of the shell surface is 65° shore hardness and 55.2k tensile strength.
The g/m melon elongation is 2.7.

This type of roll with roll dimensions (body) of 330φ x 970t was used in an intermediate stand in flat plate rolling.
There was no breakage.

In the past, breakage often occurred.

As explained above, since the method for manufacturing a composite roll according to the present invention has the above-mentioned configuration, cracks due to thermal fatigue do not occur in the roll body even during hot rolling of steel. It is possible to obtain a roll with an inner shell having excellent toughness that prevents cracks from progressing and breakage accidents.

It is possible to manufacture a composite roll that also has an outer shell with excellent wear resistance.

[Brief explanation of drawings]

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. 48-

Claims (1)

[Claims] 1. The outer shell is cast into a hollow shape by centrifugal casting using cast iron roll material, and after the cast outer shell is solidified, the hollow part of the outer shell is filled with C3.0~3.7 and Si1.5~2. 5%, Mn
The inner shell is made of spheroidal graphite cast iron consisting of O,: 2-1.0%, Ni 3% or less, CrO, 4% or less, Mo 1% or less, Mg 0.02-0.1%, the remainder being unavoidable impurities and Fe. 78 pieces of roll-shaped material that has been cast and completely welded
A method for manufacturing a composite roll, which comprises heating to a temperature of 0°C to 840°C and then cooling with air or water.