JPS5942728B2 - 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 of manufacturing a composite roll for hot rolling steel.

Generally, in the rough stand used in hot rolling steel, the rolled material is at a high temperature, and the rolling speed is slow, so the thermal effect is extremely large.

Therefore, the rolls used there develop cracks due to thermal fatigue, and in severe cases, the cracks progress and breakage accidents occur.

As a countermeasure to these problems, the outer shell is made of ama-daitrol material, which has good biting properties and wear-resistant amacite C, and contains 1.4 to 2.5% of spheroidal graphite steel. Alternatively, a composite roll with an inner shell made of spheroidal graphite cast iron can be used to prevent the occurrence of cracks due to the above-mentioned thermal fatigue, and to prevent accidents by stopping the cracks that occur at the boundary between the inner shell and the outer shell. Efforts have been made to prevent this from occurring.

However, when the material of the inner shell is spherical graphite steel, defects such as remelting at the boundary between the inner shell and the outer shell or near the outer shell are likely to occur, and a shrinkage cavity is generated in the center of the inner shell. There are various problems, and there are cases where the accident resistance is insufficient.Also, when the inner shell is made of spheroidal graphite cast iron, it does not have the problems of spheroidal graphite steel, but it has the disadvantage of poor toughness.

Incidentally, to explain the heat treatment of the conventional composite roll described above in detail with reference to FIG.
The first material is held at a temperature of 1020°C for 10 to 20 hours, subjected to diffusion heat treatment to strengthen it, and then cooled to below 600°C.
In Figure B, annealing is performed at a temperature of 700 to 800°C to form pearlite granules, and then cooling to below 600°C.
850°~920°C to ensure sufficient hardness in Figure C
The material is heated to a temperature of 500 to 600° C., then cooled to a temperature of 600° C. or higher, and then heat treated in the first stage at a temperature of 500 to 600° C. to stabilize the strain and structure.

Note that in this process, the annealing treatment at a humidity of 700° to 800° C. may be omitted.

The present invention solves the problems and drawbacks of rolls and composite rolls as explained above, and the composite roll has a toughened outer shell made of ama daitro roll material and an excellent toughness of the inner shell made of spheroidal graphite cast iron. This is a method for manufacturing composite rolls.

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 of amaranthite roll material containing 1.4 to 2.5% C, and this outer shell is solidified. After, C3, 0-3.7%, Si1, 5-2.5
%, Mn 0.2-1.0%, Ni 3%, Cr0.
4% or more, Mo 1% or more, Mg 0.02-0.1%
, a roll-shaped material made by casting an inner shell of spheroidal graphite cast iron consisting of the remainder Fe and unavoidable impurities into the hollow part of the outer shell and completely welding the outer shell and inner shell is heated to a temperature of 950° to 1020°C, After cooling to 600℃, then 780℃
After reheating at a temperature of 840°C for at least 10 hours, it is air cooled to at least 500°C.

Hereinafter, the 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, C1 is added to the outer shell.
, 4 to 2.5% is used because it has excellent wear resistance and good biting properties of steel materials, but the C content is 1.4%. If the content is less than 2.5%, the wear resistance will be extremely poor, and if the content exceeds 2.5%, it will become too hard and cannot be made tougher.

Next, the components and component ratios of the inner shell made of ductile cast iron will be explained.

C is an element that requires an appropriate amount to improve strength and toughness, but if the content is less than 30%, a structure with little graphite and a lot of cementite will result, causing problems in casting and deteriorating toughness. If the content exceeds 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 if its content is less than 1.5%, the degree of graphitization will be low, the amount of cementite will increase, and the strength will deteriorate, and casting problems are likely to occur. Moreover, if the content exceeds 25%, graphitization will be promoted and the strength will deteriorate, resulting in brittleness.

Therefore, the Si content is set to 1.5 to 2.5%.

Mn combines with S and prevents the negative effects of S, but if the content is less than 0.2%, the effect is small and low Mn
Moreover, although Mn easily increases the hardness of the material, if it is contained in an amount exceeding 1.0%, the material becomes brittle.

Therefore, the Mn content is set to 0.2 to 1.0%.

Mi is an element that toughens the material and increases its hardness without making it brittle, but if the content exceeds 3%, the structure of the material tends to become thermally unstable bainite and is not economical.

Therefore, the Ni content is set to less than 3%.

Cr is an element that promotes crystallization of cement.
If the content exceeds 4%, the amount of cementite becomes too large and the toughness decreases.

Therefore, the Cr content is set to 0.4% or less.

Mo, like Ni, 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 1.0% or less.

Mg is an element that makes graphite spheroidal, but the content is 0.0
If the content is less than 2%, no effect will be observed, and if the content exceeds 0.1%, casting defects will likely occur.

Therefore, the Mg content is set to 0.02 to 0.1%.

In addition, in the method for manufacturing a composite roll according to the present invention, the outer shell made of ama daitro roll material having the above ingredients and proportions and the inner shell made of spheroidal graphite cast iron having the above ingredients and proportions are in a completely welded state. There is no possibility of peeling off.

In the method for manufacturing a composite roll according to the present invention, the above components,
The heat treatment of a roll-shaped material in which an outer shell made of ama daitro roll material with the above-mentioned composition ratio and an inner shell made of spheroidal graphite cast iron with the above-mentioned composition ratio are welded and integrated will be described.

That is, by holding the roll-shaped material at 950° to 1020°C for usually 10 to 20 hours, the outer shell made of amadite material is subjected to diffusion heat treatment to strengthen it, and at the same time, the crystallized cementite in the inner shell made of ductile cast iron is strengthened. to improve toughness.

If the heating temperature is less than 950°C and the holding time is less than 10 hours, the outer shell and inner shell cannot be strengthened, and
If the heating time exceeds 1020° C. and the holding time exceeds 20 hours, this effect will not be diminished, and it is rather uneconomical.

Next, after this diffusion heat treatment, the temperature was once lowered to 600°C or lower, and then the temperature was again raised to 780°C to 840°C for 10 hours or less to strengthen the outer shell and the inner shell made of spheroidal graphite cast iron. Promote more.

Thereafter, the temperature is lowered to 500°C or less by air cooling.

To explain this further, cooling to a temperature below 600'C after diffusion heat treatment at a temperature of 950° to 1020°C is because recrystallization occurs due to transformation when cooling to a temperature below 680°C, which is the transformation point, and the net form is formed. When the cementite is destroyed and reheated above the transformation point, the net-like cementite disappears.

Therefore, the temperature of such materials must be below the transformation point.

Normally, it depends on the size of the roll, but it is air-cooled at 500℃ or less.
If the roll is 00φ or less, it has passed through the transformation point all the way to the center.

Also, keeping it at a temperature of 780'-840°C for 10 hours or less and then cooling it to 500°C or less does not mean that 100% transformation is completed by passing through the humidity of 680°C.
Furthermore, as the temperature decreases, transformation progresses, but this changes depending on the amount of alloy.

This is to obtain as much pearlite as possible at as low a temperature as possible, and to keep the maximum temperature of the other parts of the roll (near the center) to 680°C or less.

To explain this heat treatment process with reference to FIG. 2, the roll-shaped material is heated to 950'C to 1020C for 10-2
Hold for 0 hours and perform diffusion heat treatment to bring the temperature to below 600°C, then heat treat to hold at a temperature of 780°-8゛4.0°C for several hours to 10 hours, and then air cool to bring the temperature to below 500°C. Reduce to temperature.

The criteria for heating to a temperature of 780° to 840° C. and holding it for 10 hours in this heat treatment step will be explained.

That is, C1.85%, Si0.52%, Mn0.86%
Nip, 35%, Cr1.10%, Mo 0.36%,
An outer shell of amadite material consisting of Po, 025%, 80.010%, Fe balance and unavoidable impurities is cast into a hollow shape by centrifugal casting, and the hollow part of this outer shell is filled with C3, 48%, S.
i2.20%, Mn 0.43%, Ni 1.56%, C
rO, 14%, Mo0.15%, Po, 043%, so
, oos, Mg 0.045%, balance Fe and unavoidable impurities, an inner shell of spheroidal graphite cast iron was cast and completely welded to produce a roll-shaped material.

The dimensions of this roll were 500φ x 1600# in the body, and the thickness of the outer shell was 70 mm.

The roll-shaped material thus produced was held at a temperature of 980°C for 20 hours to perform diffusion heat treatment, and then the third
As shown in the figure, the heat treatment temperature was maintained for 10 hours and then air cooled.

Then, a test piece was taken at a position 30 mm from the boundary between the inner shell and the outer shell to the inner shell.

Test results All test pieces have a tensile strength of 50-55
kg7Bli'.

In addition, the offshore temperature is 7800 to 840℃ as shown in Figure 3.
For example, those in the temperature range of 760℃, 860℃
It can be seen that this temperature is much better than that at temperatures of .

From this, the inner shell of ductile cast iron is 780°~84°
Heat treatment held at 0° C. for several hours to 10 hours is most effective for increasing toughness, and a composite roll having accident resistance can be produced by air cooling after this heat treatment.

In addition, in the method for manufacturing a composite roll according to the present invention, a hollow outer shell is cast by centrifugal force casting using an adamite roll material containing 4 to 2.5% C1, and after this outer shell has solidified, After, C3, 0~3.7%, Si1.5~2.5%Mn 0.
2-1.0%, Ni3% or more f1Cr0.4% or less, Mo
1% or less, Mg 0.02-0.1%, balance Fe and unavoidable impurities.Inner shell of spheroidal graphite cast iron is cast into the hollow part of outer shell, and the outer shell and inner shell are completely welded. The material is heated to a temperature of 950 to 1020°C, then cooled to a temperature of 600°C, and then heated to a temperature of 780 to 8°C.
After reheating at a temperature of 40°C for 10 hours, and air cooling to 500°C or less, a composite roll that can be fully used for practical purposes can be manufactured.
Strain relief heat treatment may be performed after air cooling to 00°C or less, but performing this strain relief heat treatment is a matter of course in terms of heat treatment, and must be carried out in the manufacturing method of the composite roll according to the present invention. It's not a thing.

If this strain relief heat treatment is to be performed, the purpose is to completely transform a small amount of untransformed structure remaining and to eliminate strain, and the temperature is 500 to 600℃.
This is done by reheating to a temperature of

However, according to the method for manufacturing a composite roll according to the present invention, it can of course be used satisfactorily as a roll for hot rolling of steel without performing strain relief heat treatment.

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

Example 500φ x 16001 roll cylinder product dimensions outer shell thickness 7
A roll material of 0 to 89 mm was subjected to diffusion heat treatment at 980°C for 15 hours, then air-cooled after being held at 820°C for 8 hours, and the surface of the roll body was heated to 500°C.

Then, to further complete the metamorphosis, heat at 550°C for 10
Heat treatment was performed to remove time distortion.

This roll was used as a rough triple roll for bar rolling and obtained twice the performance of the conventional C1.5% Adamite roll.

It was successfully used without any accidents and was disposed of due to its small diameter. Three sets are currently in use using the same manufacturing method.

In addition, six other stands are expected to be scrapped.

As explained above, since the method for manufacturing a composite roll according to the present invention has the above structure, it is possible to strengthen the outer shell made of adamite roll material, and at the same time, it is possible to strengthen the outer shell made of adamite roll material. It is also possible to promote the improvement of the toughness of the inner shell, which makes it difficult for cracks to develop due to thermal fatigue caused by hot rolling of steel, so it is possible to obtain an excellent composite roll without roll breakage accidents. .

[Brief explanation of the drawing]

FIG. 1 is a heat treatment process diagram in a conventional composite roll manufacturing method, FIG. 2 is a heat treatment process diagram in a composite roll manufacturing method according to the present invention, and FIG. 3 is a graph showing the relationship between heat treatment temperature and stiffness. .

Claims (1)

[Claims] An Adamite roll material containing 4 to 2.5% of I C1° is cast into a hollow shell by centrifugal force casting, and after the outer shell is solidified, an adamite roll material containing 4 to 2.5% of C3,0 to 3. 7%, Si1.5-2.5%, Mn 0
．． 2-1.0%, Ni 3% or less, CrO, 4% or less, M
A roll shape in which an inner shell of spheroidal graphite cast iron consisting of o1% or less, Mg 0.02 to 0.1%, and the balance Fe and unavoidable impurities is cast into a hollow part of an outer shell to completely weld the outer shell and inner shell. The material is heated to a temperature of 950 to 1020°C, then once cooled to 600°C or less, and then heated to a temperature of 780 to 84°C.
A method for manufacturing a composite roll, which comprises reheating at a temperature of 0°C for 10 hours or less, and then air cooling to 500°C or less.