KR20090123597A - Heat treatment method of press roll - Google Patents

Abstract

PURPOSE: A method for heat-treating a rolling roll is provided to perform the heat-treatment before the annealing heat-treatment and to increase abrasion resistance of the rolling roll. CONSTITUTION: A steel casting roll is processed under the annealing heat-treatment by inserting molten steel into a mold. The annealing heat-treatment is to heat the roll in the room temperature to be 30~100°C higher than one among transformation points, A1,2,3, and maintains the heated roll for fixed hours. The heated annealing temperature is cooled to a preset temperature. The temperature is getting higher after maintain at the preset temperature for fixed hours. The annealing heat-treatment about the rolling roll is performed before the hardening heat treatment.

Description

Heat treatment method of rolling rolls

The present invention relates to a heat treatment method of a rolling roll, and more particularly, to a heat treatment method of a rolling roll for imparting uniform hardness increase to the whole of the rolling roll.

The rolling rolls hot rolled at the hot rolling mill directly affect the quality and manufacturing cost of the hot rolled steel sheet. In particular, the surface roughness and wear damage of the rolling rolls directly affect the surface quality, dimensions and shape of the product. Not only fatigue but also wear resistance is required.

As the rolled roll material has recently been subjected to harsh rolling conditions such as an increase in high-strength steel and an increase in high-temperature rolled materials, and the demand for surface quality, dimensions, and shapes is strict, hot rolled sheets have high wear resistance and roughness resistance. In cast steel rolls (hereinafter referred to as "HSS rolls") and die-rolled steel, adamite cast steel rolls are mainly used.

In order to improve wear resistance, such cast steel rolls have a high heat treatment, and a heat treatment method for forming carbides of high hardness into cells or boundaries is applied.

1 is a cycle diagram of a heat treatment method of a rolling roll according to the prior art, and in FIG. 2, the microstructure of the rolled roll heat treated by the cycle diagram of FIG. 1 is shown as a microscopic photograph of 400 times and 1500 times. .

Conventionally, as shown in Figure 1, the molten steel tapping from an electric furnace or an induction furnace into a centrifugal casting mold is cast, heated to 980 ° C. for a certain time, and then quenched to 525 ° C. to 550 ° C. The heat treatment is performed by reheating to ℃ and cooling to room temperature at a cooling rate of -14 ℃ / h.

However, the rolled roll produced by the conventional heat treatment method as described above has a high surface hardness, but the hardness decreases as it enters the inside. Therefore, in a formal design such as a groove, the size of the rollable product is limited by the hardness deviation of the roll surface portion and the groove bottom portion, and it is difficult to maintain the dimensional accuracy of the product. Groove is a kind of groove formed in a roll for processing a complicated shape of a product or the like.

The present invention is to solve the conventional problems as described above, an object of the present invention is to provide an annealing heat treatment method for rolling rolls to uniformly increase the hardness of the inside and outside of the roll.

The present invention is to solve the conventional problems as described above, the present invention is first performed annealing (annealing) heat treatment before hardening heat treatment of the cast steel roll cast by injecting molten steel from the electric furnace or induction furnace into the mold The annealing heat treatment is a first step of heating the cast steel roll at room temperature to 30 to 100 ° C. higher than any one of A1, 2, and 3 transformation points and maintaining it for a set time, and maintaining at the heated annealing temperature. And a third step of slowly cooling to a temperature to maintain the set time and a third step of maintaining the set temperature at the holding temperature for a set time and then slowly cooling to room temperature.

The heating temperature in the first step is between 900 ~ 1000 ℃, the holding temperature in the second step is between 450 ~ 600 ℃, the cooling rate in the second step and the third step is 14 ~ 22 ℃ / hr .

The holding time in the first step and the second step is characterized in that 0.3 hours per inch of the cast steel roll.

The hardening heat treatment is heated to 900 ~ 1000 ℃ the annealing heat treatment to maintain a set time and quenched to 450 ~ 530 ℃ and then re-heated to 540 ~ 600 ℃ by cooling 14 ~ 22 ℃ / hr Cool to room temperature at speed.

In the present invention, annealing (Annearing) heat treatment is first performed before the heat treatment of the cast steel roll to form a pearlite of a fine structure. Accordingly, as the fine particles of the composite carbide uniformly distributed in the hardening heat treatment are precipitated, tempering hardening occurs in the entire cast steel roll. Since it forms a uniform microstructure on the entire cast steel roll, it not only provides uniform hardness increase in the inside and outside of cast steel roll but also reduces the hardness deviation inside and outside cast steel roll, so it is excellent in wear resistance and wear life when used as a rolling roll. There is an effect that can increase the dimensional accuracy.

Hereinafter, the preferred embodiment of the heat treatment method of the rolling roll according to the present invention will be described in detail.

3 shows a heat treatment method of a rolling roll according to a preferred embodiment of the present invention.

 As shown in the drawing, in the present invention, the molten steel from an electric furnace or an induction furnace is injected into a mold, and the cast steel roll is subjected to mild heat treatment (anneal heat treatment) (a) before hardening heat treatment (austenite heat treatment) (b). It is characterized by performing.

Gravity casting or centrifugally cast cast steel rolls (hereafter used in combination with rolling rolls) have a high carbon content and a high content of carbide forming elements (chromium, molybdenum, tungsten, etc.). , The overall volume of M2C, M3C, M7C3) is high. This means that the kitchen residual stress of the centrifugal cast steel roll is high. Therefore, in order to remove the internal stress generated during the centrifugal casting process, the annealing heat treatment is first performed before the austenite heat treatment. This internal stress removal of the cast steel roll uniformizes, refines and standardizes the structure of the cast cast steel roll.

Annealing heat treatment is the first step of heating the cast steel roll at room temperature of 30 ~ 50 ℃ higher than any one of the A1, 2, 3 transformation point to maintain for a set time, and the slow cooling from the annealing temperature to the holding temperature for a set time And a third step of slowly cooling to room temperature after maintaining the set time at the holding temperature.

In the first step, the heating temperature is different depending on the carbon content of the cast steel roll, and heated to 900 ~ 1000 ℃ to make the pearlite structure austenite structure. In this embodiment, heating to 980 ℃, in this process a uniform austenite structure of a single phase is obtained.

In the second step, cooling is carried out to a holding temperature of 450 to 600 ° C. at a cooling rate of −14 to −22 ° C./hr. If the holding temperature is lower than 450 ℃ it is difficult to remove the internal stress, higher than 600 ℃ is not preferable because the texture is rough and the material is bad. In particular, the present embodiment is cooled to 595 ℃ and maintained at this temperature for a set time so that the transformation is left, which is the transformation of the coarse pearlite to fine pearlite in a short time around 560 ~ 600 ℃ to complete the transformation rapidly Because. Cooling is slow cooling at the above-mentioned cooling rate so that internal stress is removed, but may be furnace cooling or air cooling.

In the first and second stages, the set holding time is proportional to the size of the cast steel roll, which is usually maintained at about 0.3 hours per inch of the cast steel roll. If the holding time is too long, the structure becomes rough and the material of the cast steel roll is poor.

In the third step, the cast steel roll held at the holding temperature for a suitable time is slowly cooled to room temperature at a cooling rate of -14 to -22 ° C / hr. As a result, a fine and uniform pearlite structure from which internal stress is removed is obtained.

This annealing heat treatment improves the structure of the cast steel roll by removing the structure unevenness and the internal stress. That is, since a uniform pearlite structure is formed on the cast steel roll, a uniform and stable austenite structure is secured in the subsequent curing heat treatment.

The curing heat treatment is the first step of heating to 900 ~ 1000 ℃ as in the prior art for a set time and quenching to 450 ~ 530 ℃ and reheating again to 540 ~ 600 ℃ to -14 ~ -30 ℃ / h It consists of a second step of cooling to room temperature at a cooling rate of.

In the first step, the austenite structure stabilized by the above-described annealing heat treatment is obtained, whereby carbides are uniformly distributed in and out of the cast steel roll. These carbides give a uniform increase in hardness to the inside and outside of the cast steel roll during the two stages of quenching and tempering.

More specifically, the hardened steel has a large amount of austenite, and when tempered at 550 ° C., the austenite turns into martensite, and at this time, the fine particles of the uniformly distributed composite carbide in the austenite are precipitated and temper hardened throughout the cast steel roll. It will cause a phenomenon. Tempering temperature is 450 ~ 600 ℃ to increase the hardness and strength, but more than that it is preferable to temper within the above range because the sharp decrease.

Hereinafter, the heat treatment method of the rolling roll according to the present invention will be described in detail in comparison with the conventional method through the embodiment. To help understand the invention, data values according to the present invention and the conventional invention are shown as tables of comparative examples and examples.

4A to 4C show microstructures of the rolling rolls heat treated by the cycle diagram of FIG. And Table 1 below shows the hardness and hardness deviation from the roll surface of the above-described comparative example and Example to the inner depth, Table 2 shows the grain size (Grain Size) of the rolling roll of the prior art and the present invention.

division Conventional The present invention 900 ℃ + Tempering 940 ℃ + Tempering 980 ℃ + Tempering ASTM (Grain Size) 5 8-9 8 7-8

[Comparative Example]

The molten steel from the electric furnace or induction furnace is injected into the centrifugal casting mold to heat the cast steel roll to 980 ° C for a certain time, and then quenched to 525 ° C and reheated to 550 ° C to produce -14 ° C / h. Rolling rolls were manufactured by a heat treatment method of cooling to room temperature at a cooling rate.

EXAMPLE

After pouring molten steel from an electric furnace or induction furnace into a centrifugal casting mold, the cast steel roll is heated to 980 ° C. and maintained for a certain time, and slowly cooled to 595 ° C. at a cooling rate of 22 ° C./hr, and maintained for a predetermined time. After the annealing heat treatment to cool to room temperature at a cooling rate of -14 ℃ / hr, and then the cast steel roll subjected to the annealing heat treatment is heated to any one selected from 900 ℃, 940 ℃, 980 ℃ to maintain a certain time and 525 ℃ After the quenching (quenching) until the reheating to 550 ℃ to give a curing heat treatment to cool to room temperature at a cooling rate of -14 ℃ / h to prepare a rolling roll.

Looking at Table 1 it can be seen that the rolling rolls of the present invention as well as the internal and external hardness is increased uniformly as well as the hardness deviation is reduced compared to the conventional rolling rolls. This can be confirmed in the microstructure shown in FIGS. 4A to 4C.

That is, the grain size decreases in the order of 900 ° C. + Tempering <940 ° C. + Tempering <980 ° C. + Tempering <the conventional heat treatment, and the crystallinity is determined in the order of 980 ° C. + Tempering <940 ° C. + Tempering <900 ° C. + Tempering <the conventional heat treatment. And it can be seen that the volume of precipitated carbide is reduced. In this case, the grain size is a straight line on a tissue photograph that knows the magnification and represents the total number of grains that the lines pass through. The larger the grain size, the finer the tissue, so the hardness is increased.

That is, it can be seen that the heat treatment method of the present invention increases not only the internal and external hardness of the rolling rolls, but also decreases the hardness of the rolling rolls in comparison with the related art.

The rights of the present invention are not limited to the embodiments described above, but are defined by the claims, and those skilled in the art can make various modifications and adaptations within the scope of the claims. It is self evident.

1 is a cycle diagram showing a heat treatment method of a rolling roll according to the prior art.

Figure 2 is a microstructure photograph of 400 times and 1500 times showing the microstructure of the rolling roll heat-treated by the cycle diagram of FIG.

3 is a cycle diagram showing a heat treatment method of a rolling roll according to a preferred embodiment of the present invention.

 4A to 4C are 400 times and 1500 times microscope histological images showing the microstructure of the rolling rolls heat treated by the cycle diagram of FIG. 3.

Claims (4)

Annealing heat treatment is first performed before hardening heat treatment of cast steel rolls by pouring molten steel from an electric furnace or an induction furnace into a mold. The annealing (annealing) heat treatment is the first step of heating the cast steel roll at room temperature 30 ~ 100 ℃ higher than any one of the A1, 2, 3 transformation point to maintain for a set time, A second step of slowly cooling to the holding temperature at the heated annealing temperature and maintaining it for a set time, and a third step of maintaining the set temperature at the holding temperature for a predetermined time and then slowly cooling to room temperature again. . The method of claim 1, The heating temperature in the first step is between 900 ~ 1000 ℃, the holding temperature in the second step is between 450 ~ 600 ℃, the cooling rate in the second step and the third step is 14 ~ 22 ℃ / hr Heat treatment method of a rolling roll, characterized in that.  The method of claim 1, The holding time in the first step and the second step is a heat treatment method of a rolling roll, characterized in that 0.3 hours per inch of the cast steel roll.  The method according to any one of claims 1 to 3, The curing heat treatment is heated to 900 ~ 1000 ℃ the annealing heat treatment the cast steel is maintained for a set time and quenched to 450 ~ 530 ℃ and then reheated to 540 ~ 600 ℃ cooling rate of 14 ~ 22 ℃ / hr Heat treatment method of a rolling roll, characterized in that the cooling to room temperature.

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