JPS63230824A - Heat treatment for sleeve roll - Google Patents

Abstract

PURPOSE:To prevent breakage accident and also to increase quenching rate, by holding a diffusion-annealed sleeve roll at a temp. in a specific range until respective temps. in the inner and outer layers are equalized and then subjecting the above to rapid heating to apply temp.-rise to the outer layer alone so as to carry out hardening treatment. CONSTITUTION:After a sleeve roll stock for shape rolling whose outer-shell layer is composed of adamite is diffusion-annealed quench-and-temper treatment is applied. In the above heat treatment, the above sleeve roll stock after diffusion annealing is held at a temp. between 500 and 750 deg.C until respective temps. in the inner and outer layers are equalized. Subsequently, rapid cooling is applied to subject only the outer layer of the roll to temp.-rise up to 830-950 deg.C. Then, the roll stock is taken out of a furnace and cooled to undergo hardening treatment. By this method, the difference in temp. between the inner and outer layers is reduced in the hardening stage so as to reduce stress. As a result, the roll stock causes no occurrence of breakage accident in the hardening and subsequent annealing stages and is also increased in quenching rate, and high hardness can be provided by means of heat treatment alone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of heat treating a material for an assembly roll of a sleeve used in hot rolling of section steel.

[Conventional technology]

In recent years, as rolls for hot rolling, assembly type rolls whose arbor can be used repeatedly have become more common, and in particular, assembly type rolls have become common as rolls for rolling section steel.

Furthermore, in recent years, there has been a demand for increasing the hardness of the roll surface from the perspective of improving wear resistance, and material changes such as making the outer shell layer high-alloy adamite or speeding up the quenching speed in the heat treatment process have been carried out. There is.

However, the method using high-alloy adamite for the outer shell layer is uneconomical because it is expensive and requires a large amount of ROM, nickel, and molybdenum.

Furthermore, the method of increasing the hardness by increasing the quenching speed in the heat treatment process has the problem that breakage of the roll frequently occurs during the quenching or tempering process.

As a method for solving the problem of frequent occurrence of breakage water splashes, methods such as Japanese Patent Publication No. 57-48625 and Japanese Patent Application Laid-Open No. 61-79727 have been proposed.

However, the methods described in the above-mentioned publications involve induction heating and placing the steel in a slow cooling box after quenching to reduce stress, which have the following problems.

The induction heating method is a heat treatment method in which only the surface of the first part is heated to the quenching temperature by induction heating, and then quenched.Generally, it is suitable for rolls for rolling shaped steel that require a hardness depth of 50 mm or more. There are problems with grass that it is unsuitable and the equipment is expensive.

In addition, the method of reducing stress by placing the roll in a slow cooling box after quenching is to use a slow cooling box that stores the roll in a way that isolates it from the outside air, thereby reducing the difference in temperature distribution between the inner and outer layers of the roll after quenching. This is a slow cooling method, which ensures careful temperature control after quenching. Further, when heat treating many rolls at once in order to take the rolls in and out of the slow cooling box, it is inevitable that the process after quenching becomes complicated.

[Problem that the invention seeks to solve]

The purpose of the present invention was to solve the above-mentioned problems, and it is possible to prevent breakage accidents during quenching and tempering processes, and to increase the quenching speed from the beginning of heat treatment. It is an object of the present invention to provide a method in which a roll having a higher hardness than the conventional method can be rolled.

[Means for solving problems]

The present invention relates to a method for heat treating a sleeve roll, which performs a quenching treatment after diffusion quenching.

(1) After the diffusion annealing, maintain the temperature between 500°C and 750°C until the temperature of the inner and outer layers becomes equal. (2) After that, rapidly heat the roll to 830°C and only the outer layer.
The characteristic technical means is to perform a quenching treatment after raising the temperature to 950°C.

[Effect]

First, in the heat treatment of a sleeve roll material for rolling shaped steel whose outer shell layer is made of adamite, we have investigated the relationship between the temperature transition from the start of quenching to the beginning of the tempering process and 11.1 loss. Explain the findings obtained.

The roll is first heated to the quenching temperature in a heating furnace,
The entire roll is held uniform at that quenching temperature. After that, the roll is extracted from the furnace for quenching, and the outer surface of the sleeve, which requires high hardness, is forcedly cooled by spraying mist or blast air, and the temperature of the outer surface is reduced to 400 to 58.
When the temperature reaches 0°C, adjust the amount of mist or blast to prevent the roll surface from reheating at the above temperature of 400 to 580°C.
Hold it and change the base organization to bainite.

After that, it is left to cool naturally in the atmosphere until the outer surface temperature reaches 400~400℃.
When the temperature drops to 460° C., it is charged into the furnace again for tempering treatment. Thereafter, the ambient temperature is maintained at the same temperature as the outer surface until the temperature of the inner and outer surfaces becomes uniform, and then tempering is performed.

FIG. 3 shows the temperature changes on the inner and outer surfaces of the roll during the above-mentioned quenching process.

In Fig. 3, the roll is larger at the transition temperature (approximately 500 to 700°C) where it changes from the plastic region to the elastic region! ! There is a large temperature difference. If the entire roll becomes an elastic region under this temperature difference state and the temperature difference decreases after being left to cool in the atmosphere, the inner surface of the roll will experience greater temperature contraction than the outer surface, so there will be tensile stress on the inner surface and compression on the outer surface. Stress is applied, and when the material is charged into a furnace and the temperature of the furnace is raised for tempering,
Roughly, thermal stress is added, and the strength of the base material of the inner surface layer of the roll (
It is estimated that the loss exceeds 40 to 45 kg/mrr+', resulting in 111 losses.

Therefore, if a method can be established to reduce the temperature difference across the roll during the transition period when the roll changes from the plastic region to the elastic region, the stress when the entire roll becomes the elastic region will be reduced, and the residual stress will be reduced. will be reduced.

As a result of various studies from the above viewpoints, the present invention has been completed.

In other words, the stress reduction method for the assembled roll material for rolling section steel in issue I31 is a method of reducing the temperature difference across the entire roll during the transition period when the roll changes from the plastic region to the elastic region, and the method used is as follows. That's right.

In the heat treatment process for the sleeve roll material of the sleeve assembly roll for rolling section steel whose outer layer is made of adamite,
After diffusion annealing, in the middle of quenching heating, from 500℃ to 750℃
The temperature of the inner and outer layers is maintained between 2 and 3 until the temperature of the inner and outer layers becomes equal, and then the ambient temperature of the furnace is rapidly heated, and the outer shell layer of the roll is heated to 850℃.
~950℃, and create a temperature difference between the inner and outer surfaces so that the inner layer, which requires toughness, is at a lower temperature, and furthermore, the temperature of the inner and outer surfaces is uniform in the range of 500℃ to 700℃ during the quenching process. This is a cooling method.

In addition, the holding temperature during quenching heating is 500°C to 750°C.
This was done for the following reasons.

The reason why the holding temperature before rapid heating was limited to 500°C to 750°C is because if the temperature is less than 500°C, the entire roll is in an elastic range and will break due to thermal stress during rapid heating.
If the temperature exceeds ℃, the temperature in the center of the roll in the thickness direction increases during the transition period, and the temperature difference across the roll increases.
This is because the temperature difference will be the same as in the conventional case.

The reason why the quenching temperature of the outer shell layer of the roll was limited to 830°C to 950°C is because if the temperature is less than 830°C, solid solution of cementite into austenite will not proceed, and the austenite region will be small, so the quenching effect will be lost. However, if the temperature exceeds 950°C, the crystal grains will become coarse and the risk of cracking during quenching will increase, so it is limited.

Generally, heat treatment of sleeve roll material for shape steel rolling having an outer layer of adamite is performed first by performing a high temperature diffusion treatment in which the material is heated and held at a high temperature of 1000°C or higher, and then once Ar1
It is cooled to below Ac point, and then heated to above Ac1 point. During the heating process, the temperature of the inner and outer surfaces is scorching by maintaining the temperature at a low temperature in the plastic region or the temperature in the transition region, and then the temperature of the atmosphere in the furnace is rapidly heated.

The temperature transition after the rapid heating of the furnace atmosphere temperature will be explained with reference to FIG. When the ambient temperature of the furnace is rapidly heated after soaking the roll, the outer surface of the roll is first heated by radiant heat from the furnace wall and combustion gas. The inner surface of the roll receives less radiant heat from the furnace wall and the combustion gas, so the temperature rises slower than the outer surface of the roll. In this state, rapid heating is performed until the part of the waste diameter 5 (see FIG. 2) in the thickness direction of the sleeve roll material reaches the quenching temperature.

Thereafter, the roll 1 is taken out of the furnace and set on the roller 2 of a forced cooling device as shown in FIGS. 2(a) and 2(b). When the roller 2 is rotated, the nozzle 3 starts spraying cooling water (mist) atomized with high-pressure air onto the outer surface of the roll 1 and from the nozzle 4 on the inner surface of the roll 1 (7). This mist cooling is performed on the outer surface of the roll from 450℃ to 5℃.
Until the temperature reaches 20℃, the inner surface of the roll is also heated to 450~5℃.
Continue until the temperature reaches 20°C.

When the outer surface temperature of the roll l reaches 450 to 520°C, mist cooling is stopped, and the roll is left until the outer surface of the roll returns to 520 to 580°C due to heat conduction from the inside, as shown in Figure 4. , 1 to prevent further temperature rise.
The surface is kept in the above range of 520 to 580° C. while being blast-cooled until the temperature does not rise even after the blast is stopped.

Thereafter, the roll 1 is lowered from the roller 2 and left to cool in the atmosphere, and when the temperature of the outer surface of the roll has decreased to 400 to 460°C, it is charged into the furnace again for tempering treatment.

Thereafter, the ambient temperature is maintained at the same temperature as the outer surface until the temperature of the inner and outer surfaces becomes uniform, and then tempering is performed.

The temperature change after the roll was taken out of the furnace is described below.

At the start of quenching, as shown in Figure 1, the outer surface of the roll is heated to the quenching temperature of 900°C or higher, and the inner surface of the roll takes time to conduct heat from the outer surface of the roll, and the amount of radiant heat is small. Therefore, the temperature is around 675°C. When the inner and outer surfaces of the roll are cooled for quenching in this state, the entire roll is cooled, and the center of the roll in the thickness direction is also cooled as the temperature of the inner and outer surfaces of the roll decreases, as shown in FIG.
The temperature difference across the roll in the transition zone is reduced. During the subsequent reheating period and holding period of the outer surface of the roll, the temperature difference across the roll does not increase and shifts to the elastic range. Therefore, when the temperature of the entire roll becomes uniform and reaches the elastic range, Residual stress is reduced due to less temperature shrinkage.

Therefore, if the method of the present invention is employed, the residual stress is reduced, so there will be no roll breakage accidents during the air cooling period after quenching, the heating period in the tempering furnace, and during heating for tempering.

〔Example〕

Next, specific examples of the present invention will be described.

A three-sol roll material for shape steel rolling with an outer diameter of 1,520 mmφ, an inner diameter of 760 mmφ, and a length of 2,000 mm with the outer layer of the roll made of adamite was diffusion annealed and soaked at 550°C, then the ambient temperature of the furnace was raised at 220°C/H, and then Hold at 1100°C for 45 minutes, then cool the outer surface of the roll to 600°C at an average cooling rate of 35°C/min, and to 510°C at an average cooling rate of 4.5°C.
/min, and the inner surface of the roll is cooled to 510°C at an average cooling rate of 9°C/min.

After that, the outer surface of the roll was reheated to 550°C, held so as not to rise above that temperature, and then left to cool in the atmosphere.The inner surface of the roll was similarly reheated to 560°C, and held so as not to rise above that temperature. Figure 1 shows the temperature change when the sample was allowed to cool in the atmosphere after being held in a vacuum.

In Fig. 1, the middle point is taken as a representative example of the temperature distribution at the transition period that causes the generation of residual stress, and the temperature distribution in the radial direction at that time is shown in Fig. 4. The case in which this was done is shown in FIG. 6, and it can be seen that the temperature difference across the rolls is reduced compared to that case.

Furthermore, assuming that stress is zero in the case of the temperature distribution shown in Fig. 4, the residual stress distribution when the entire roll becomes an elastic region and the temperature is uniform is shown in Fig. 5, compared to the conventional temperature distribution shown in Fig. 6. Figure 7 shows the residual stress when the entire roll is in an elastic region and the temperature is uniform, assuming that the stress is zero.
It can be seen that the residual stress is significantly reduced compared to that.

Note that in this example, no stuffing was inserted into the inner surface of the sleeve during rapid heating, but depending on the dimensions of the sleeve, it may be preferable to insert an insulating stuffing into the inner surface of the sleeve to lower the temperature of the inner layer of the sleeve. . As the filling material at this time, ceramic wool material is suitable from the viewpoint of workability.

〔Effect of the invention〕

According to the method of the present invention, in the heat treatment of a sleeve roll material for rolling shaped steel whose outer flt layer is adamite, the temperature difference between the inner and outer surfaces from the quenching to the tempering stage can be significantly reduced compared to the conventional method, As a result, thermal stress during quenching and residual stress immediately before tempering can be significantly reduced.

Therefore, if the method of the present invention is applied, there will be no breakage accidents during heat treatment, and the quenching speed of the outer surface can be made faster than before, so expensive Cr can be used.

It is possible to obtain an outer R layer with high hardness by reducing alloying elements such as Ni and Mo.

Furthermore, in the subsequent tempering process, the residual stress is small, so the time required for strain relief is shortened, and the stress on the inner surface of the roll during shrink fitting (shrink fitting stress + tensile residual stress) is small, so the In addition, since the shrink-fitting stress can be increased, the shrink-fitting allowance can be increased, and roll slipping accidents are also reduced.

Furthermore, in the present invention, only the necessary outer shell layer on the outer surface of the roll is heated to the quenching temperature, and unlike conventional methods, the sintering time is unnecessary, resulting in energy savings.

[Brief explanation of the drawing]

Figure 1 is a graph showing the temperature transition in Book 9.1J],
FIG. 2(a) is a top view showing an example of a forced cooling device used in carrying out the method of this invention, FIG. 2(b) is a side view thereof, and FIG. 3 shows temperature changes on the inner and outer surfaces of the roll in the conventional method. 4 is a graph showing the temperature distribution of the roll at point fil1 during the transition sowing period in the present invention, and FIG. 5 is a graph showing the temperature distribution of the roll in the case of the temperature distribution shown in FIG. Figure 6 is a graph showing the temperature distribution of the roll at the midpoint of the transition period in the conventional method. Figure 7 is a graph showing the temperature distribution of the roll at the midpoint of the transition period in the conventional method. 3 is a graph showing the residual stress distribution when the temperature becomes uniform within the range. 1...Sleeve roll material for rolling section steel 2...Roller 3...Spray nozzle for cooling the outer surface 4...Spray nozzle for cooling the inner surface 5...Discard diameter

Claims (1)

[Claims] 1. A method for heat treatment of a sleeve roll in which a hardening treatment is performed after diffusion annealing, wherein after the diffusion annealing, the temperature of the inner and outer layers is maintained between 500°C and 750°C until the temperature becomes equal, and then rapid heating is performed. A method for heat treating a sleeve roll, which comprises heating only the outer layer of the roll to 830°C to 950°C, and then subjecting it to quenching.