JPS60116723A - Heat treatment of roll for rolling - Google Patents

Abstract

PURPOSE:To obtain efficiently a roll for rolling whose inner part is resistant to breakage and whose surface is hard and resistant to abrasion by ferritizing a diffusion-annealed roll for rolling by cooling, austenitizing by elevating the temp., and then hardening the surface by rapid heating. CONSTITUTION:The roll for rolling which is diffusion-annealed to remove a remaining strain is ferritized by slow cooling to <= transformation point A1. Then the roll is slowly heated to a temp. close to the transformation temp. A3 not to generate a plastic strain, and is austenitized. Then the surface is rapidly heated to a quenching temp. and hardened. Although the vicinity of the surface is transformed by a CCT curve into primary sorbite which is fine pearlite or fine primary troostite from austenite, the inner part is only transformed into pearlite. Accordingly, the roll for rolling whose surface is hard resistant to abrasion and whose inner part is soft and resistant to breakage can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat treatment method for a mill roll, and more particularly to an improvement in a heat treatment method for an integral mill roll, which is suitable for application to rolling work rolls formed by casting.

Rolls used for hot or cold rolling are required to have contradictory properties: the surface should be hard and wear resistant, and the inner surface should be soft and break resistant. In order to meet this requirement, conventional methods have been adopted, such as the inlay method that changes the inner surface roughness, the shrink-fitting method that integrates the two after casting them separately, or the heat treatment method that heat-treats them after casting. .

Among these, the □ heat treatment method has conventionally used, for example, the ingredients shown in Table 1 below, the shape shown in Figure 1, and the dimensions of each part being 1350 u
φ, same length J21-209011111, outside of left end @
! 0x-1030 days φ, same length β, 2-1180n, right end 4 diameter Da = 670nφ, same length 15-780m, and hardness is about 50 on Shore hardness. As shown in Figure 2, when performing heat treatment on steel, there is a known method in which the temperature is raised to a temperature T1 higher than the A3 transformation point, diffusion annealing is performed, the furnace temperature is lowered to the quenching temperature T2, and then the quenching is performed. ing.

(Unit: %) However, although such conventional heat treatment methods yield good results in terms of removing residual strain generated during the casting stage, they do not improve the hardness distribution in the radial direction of the roll after heat treatment. , as shown in Figure 3, it is difficult to obtain properties that gradually change from the surface to the center, making it difficult to achieve both desired breakage resistance and abrasion resistance.
In particular, there was a problem in that it was difficult to maintain breakage resistance.

The present invention has been made in view of such conventional problems, and the roll is sufficiently soft on the center side in the radial direction and has good breakage resistance, while the surface side is sufficiently hard and has good wear resistance. The object of the present invention is to provide a method for heat treatment of a rolling roll, which makes it possible to obtain a rolling roll having the following properties.

The present invention provides a heat treatment method for an integrated rolling roll, comprising:
A procedure of diffusion annealing the rolling roll, a procedure of lowering the temperature to below the A1 transformation point to ferrite the structure after the diffusion annealing, and after the ferrite,
The procedure is to gradually raise the temperature to around the A3 transformation point to austenite the structure, and after the austenite formation, rapid heating is performed at a furnace temperature increase rate such that a predetermined temperature distribution is obtained in the radial direction of the rolling roll. The above object has been achieved by adopting a configuration including a step of quenching the rolling roll after the rapid heating reaches the desired temperature distribution in the radial direction of the roll.

The present invention makes it possible to optimally adjust the hardness distribution in the radial direction of the roll by controlling heat treatment of heating and cooling so that a predetermined temperature gradient is created in the radial direction of the roll during quenching.
This makes it possible to maintain sufficient breakage resistance on the center side of the roll in the radial direction, and to achieve both abrasion resistance on the same surface side.

The present invention will be explained in detail below.

In the present invention, first, in order to remove residual strain generated during casting, a rolling roll is heated to a temperature higher than the A3 transformation point, the structure is changed to austenite, and diffusion annealing is performed.

Thereafter, the temperature is lowered to below the A1 transformation point by slow cooling, and the structure is once converted into ferrite. For these procedures, temperature settings or heating/cooling rates are set based on known knowledge.

Next, the temperature is gradually increased and heated to around the A3 transformation point while avoiding plastic strain in the structure, and after the structure is austenitized again, rapid heating is performed to create a temperature gradient in the radial direction of the roll. It is something.

Furnace temperature increase rate a ('C/hr) in this eternal heating treatment
The holding temperature T (° C.) and the holding time X (hr) can be determined by, for example, a simulation temperature distribution calculation using the difference method, taking into consideration conditions such as furnace heating capacity, generated thermal stress, and cooling rate.

For this calculation, equation (1), which is a one-dimensional heat conduction equation in the cylindrical coordinate radius direction, was converted into (2
) can be used.

Here, the conversion temperature φ and the heat content H are defined by equation (3).

However, in the above equations (1) to (3), ρ is density, Cp is specific heat, k is thermal conductivity, kd is standard thermal conductivity, T is temperature,
r is radius and t is time.

When equation (3) is differentiated and expressed for the surface, interior, and center, Qi of equation (6) becomes equations (4), (5), and (6), respectively.
is the heat flow to the surface point l, which is expressed by equation (7) in the furnace and equation (8) during cooling.

However, here φco is the overall heat exchanger yield in the furnace, T.

is the furnace gas temperature, Tc is the cooling medium (water, air) temperature, α
is the heat transfer coefficient during cooling.

Using the above equation, the temperature distribution in the heat treatment furnace and in the roll radial direction during quenching can be calculated, and the above-mentioned parameter a
, T, and X can be determined.

Parameters a, T determined in this way.

After rapid heating is carried out using
By performing quenching and treatment, a characteristic can be obtained in which the cooling rate is high near the surface, but the cooling rate decreases at an accelerating rate toward the inside.

As a result, the metal structure near the surface changes from austenite to primary nrubite, which is a fine structure of pearlite, or to primary troostite, which has a finer structure of pearlite, in the so-called continuous cooling transformation II (OCT curve), but the metal structure inside Since the structure only changes from austenite to pearlite, the hardness after quenching is different, and it is possible to adjust the hardness distribution to the intended one.

As a result, it is possible to manufacture a rolling work roll that is hard on the surface and has excellent abrasion resistance, and is soft (and has excellent breakage resistance) on the inside.Examples of the present invention will now be described.

In this example, a rolling work roll having the same composition as shown in Table 1 was heat-treated in a conventional batch-type heat-treating furnace in a heat-treating pattern as shown in FIG. In the figure, 12 shows the procedure of heating to a temperature T8 higher than the '10SA3 transformation point and performing a diffusion annealing treatment, and 12 shows the procedure of slowly cooling the structure after the diffusion treatment to a temperature T4 below the A1' transformation point. Steps for converting into ferrite, Step 1: After 14 is turned into ferrite, the temperature is gradually raised to a temperature Ts (=800° C.) near the A3 transformation point to turn the structure into austenite, 1
Step 6 is a step of further rapidly heating the rolling work roll to temperature T at a heating rate such that a predetermined temperature distribution is obtained in the radial direction of the rolling work roll after the austenitization; The procedure is to hold the temperature for X hours until the target temperature distribution is reached in the direction 20, and the procedure is to perform quenching after the temperature is held at 20.

Here, the temperature increase rate a (°C/hr), holding temperature T (°C), and holding time X (11r), which are the parameters during the rapid heating operation before quenching, are obtained from the simulation temperature distribution calculation using the difference method described above. , can be determined from the temperature distribution during quenching that provides the desired cooling rate in the radial direction.

Calculated heating rate a, holding temperature T, and holding time X
The optimum range of is not shown in equations (9) to 11).

40≦a≦80 ('C,/hr) −(9)950≦
T≦11oo (℃) ... (1o) 0≦X≦10
(hr) ・=(11) Here, in equation (9), the temperature increase rate a is above 40'CZ 1rJJ because it is 40°C.
/'hrJ: J, the reason is that there is no difference in the temperature distribution in the radial direction, and even if quenching is performed as it is, there is no difference in hardness. Note that this a is defined in To in the above-mentioned equation (7) by the following equation.

To-ax time +800 - (12) This a is, in order to maximize the hardness difference in the roll radial direction,
The higher the temperature, the better, but if the temperature is raised above 80°C by 1 hour, the generated thermal stress will increase and there is a risk of cracking, so the upper limit is 80'C/l+r&! It is best to keep it to a minimum.

In addition, in equation (10), the holding temperature T is set at 950°C or higher because the temperature rises above the transformation point Ac5JX of the working material, and also because it is the lowest temperature that can create a temperature gradient in the radial direction. This is because it is a condition. The reason why the temperature is 1100° C. or lower is that if the temperature is 1100° C. or higher, the temperature gradient becomes too large, increasing the risk of distortion, cracking, etc. due to thermal stress.

Furthermore, the reason why the holding time X is set to 10 br or less in equation (11) is that if the holding time is held for 10 hr or more, the temperature distribution in the radial direction becomes uniform and no temperature difference is established. Regarding the lower limit of the holding time It may be set to zero if it can be reached.

From the range of formulas 9) to (11) above, the temperature increase rate a-
80℃/11r, holding temperature T-1040℃, holding time X
After selecting the value of -3 hr and performing heat treatment based on the procedure shown in FIG. 4 above, the hardness distribution of the work roll was measured, and the hardness distribution shown in FIG. 6 was obtained.

As is clear from the figure, the shore hardness of most of the central part in the radial direction of the roll is suppressed to about 30, providing sufficient breakage resistance, and the hardness increases rapidly from around 300 inches in the radial direction of the roll. The Shore hardness of the outermost surface increased to 55, confirming that sufficient wear resistance was obtained.

The reason why a is set to 80℃/hr here is to improve the efficiency of heat treatment, and the reason why the temperature is set to 1040℃ is because if there is a large amount of Or, microcracks will occur if the surface temperature exceeds 1030℃. This is because the danger arises and the stress value continues to increase due to the temperature gradient becoming large. Also,
The reason for setting X to 3 hr is that, as shown in Figure 5, in order to make the cooling rate during quenching 6°C/win up to a depth of around 100+am, the furnace temperature of 1040°C is maintained for 3 hr and the cooling rate at a depth of 10
This is because the concentration at zero temperature needs to be 940°C.

In this example, the roll is non-linear in the radial direction! l
! ! Although rapid heating was performed so that the hardness distribution, that is, the hardness sharply increases only near the surface, the shape of the hardness distribution curve is not particularly limited to the shape shown in FIG.

As explained above, according to the present invention, the center side of the roll in the radial direction is sufficiently soft and has good breakage resistance compared to the conventional roll, while the surface side is sufficiently hard and has a durability equal to or higher than that of the conventional roll. The effect of providing wear resistance is obtained.

Furthermore, since the heat treatment time is shortened, it also contributes to energy saving and high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an example of the shape of a rolling work roll, Fig. 2 is a temperature temporary line diagram showing an example of a conventional heat treatment method for a rolling work roll, and Fig. 3 is a diagram showing the above-mentioned rolling work roll. A hardness-depth diagram showing the hardness distribution in the radial direction of the roll after heat treatment according to the conventional example, FIG. 4 is a temperature-vi interval diagram corresponding to FIG. The diagram in FIG. 5 shows O in 4 in the same example.
FIG. 6 is a hardness-depth diagram corresponding to FIG. 3 showing the hardness distribution in the radial direction of the roll after heat treatment. Agent Takaya Ron (and 1 other person) Fig. 1 W Ray 92-4 ----- Tsukasa 1 ----- Key λ32 Fig. 2 Time M 113 m Roll table number call Fig. 4 Time cry flight

Claims (1)

[Claims] (1) A heat treatment method for an integrated rolling roll, which includes the following steps: diffusion annealing the rolling roll; after the diffusion annealing, lowering the humidity to below the A1 transformation point to turn the structure into ferrite; After ferritizing, As
There are two methods: one is to gradually raise the temperature to near the transformation point to austenitize the structure, and the other is to rapidly heat the material after the austenitization process by using a furnace at an easy-to-rise rate to obtain a predetermined temperature distribution in the radial direction of the rolling rolls. A method for heat treating a roll, comprising: - and quenching after the roll has reached a desired temperature distribution in its radial direction by the rapid heating.