JPH08218123A - Heat treatment method of complex sleeve - Google Patents

Abstract

PURPOSE: To improve the mechanical property of an inner layer material by forcedly cooling from the inner surface of a sleeve, too in a quenching process, at the time of executing the heat treatment to the sleeve of a complex sleeve combining type roll composed of austenitic materix structure. CONSTITUTION: The heat treatment is executed to the complex sleeve composed of the austenitic matrix structure so as to transform the outer layer into martenstic matrix structure and the inner layer into pearlitic matrix structure. In this method, at the quenching and cooling process, while rotating the sleeve 2, the forcedly cooling is executed not only from the outer surface but also from the inner surface with high pressure air from holes 6 formed in the steel pipe 5 set at the inside of the sleeve 2. By this method, the martensitic transformation at the outer layer is promoted and the internal stress is reduced and also, the mechanical property of the inner layer material can be improved, and while maintaining the high sttrength of the complex sleeve, the crack of the sleeve at the time of producing and during using the rolling accompanied with complexing can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a composite sleeve, which is applied to manufacture a composite sleeve assembly type roll for rolling.

[0002]

2. Description of the Related Art Generally, as a rolling roll, as shown in FIG. 5, an integrated type and a sleeve assembly type roll for the purpose of reducing the roll cost are widely used. That is, FIG. 5 is an explanatory view showing the structure of a conventional composite sleeve. As shown in this figure, the most required property of the sleeve 2 of the roll body 1 is abrasion resistance, and it is effective to make the matrix structure of the outer layer 3 hard martensite. Therefore,
Materials with good hardenability are widely adopted. on the other hand,
It is also necessary to prevent accidents such as cracks during use, and it is often a composite type with an inner layer 4 of a pearlite matrix structure that has few internal defects and excellent toughness, and has both wear resistance and accident resistance. By the way, as a heat treatment for making this sleeve into a martensitic matrix structure, quenching is generally performed in the actual situation.

[0003]

In order to sufficiently exhibit wear resistance, it is desired that the matrix structure be completely martensite. Generally, the martensitic transformation requires a sufficient quenching and cooling rate to prevent the pearlite transformation. However, since the sleeve applied to the steel rolling roll has a large diameter and a large wall thickness, it is difficult to secure the quenching and cooling rate necessary for the complete martensitic transformation. Therefore, a method of increasing the quenching temperature may be carried out, but the high-temperature quenching treatment coarsens the pearlite matrix structure of the inner layer, so that mechanical properties such as toughness are remarkably deteriorated.

On the other hand, as shown in FIG. 6, since the martensitic transformation is accompanied by a remarkable volume expansion, internal stress is generated in the composite sleeve having a pearlite structure without expansion as an inner layer. That is, compressive stress is generated in the outer layer where the martensite transformation expands, and tensile stress occurs in the inner layer where the martensite transformation does not expand. Further, in the sleeve assembly type roll, since the sleeve is fitted on the shaft (arbor) by shrink fitting, a tensile shrink fitting stress is generated on the inner surface of the sleeve. Therefore, on the inner surface of the sleeve, the tensile stress due to the martensitic transformation of the outer layer during heat treatment and the tensile stress due to shrink fitting remain, and the tensile stress such as thermal stress during rolling is applied. It has a problem that cracks occur.

[0005]

In order to solve the above problems, as a result of intensive development by the inventors, as a result of forced cooling from the inner and outer surfaces of the sleeve during quenching and cooling of the composite sleeve. The present invention provides a method for manufacturing a composite sleeve assembling roll, which maintains the high hardness of the composite sleeve and eliminates the sleeve cracking during the manufacturing and during the rolling and the use. The gist of the invention is to heat-treat a sleeve made of an austenite matrix structure to transform the outer layer of the sleeve into a martensite matrix structure and the inner layer of the sleeve into a pearlite matrix structure. In the process, not only the outer surface of the sleeve but also the inner surface of the sleeve is forcibly cooled to promote martensitic transformation of the outer layer, reduce internal stress, and improve mechanical properties of the inner layer material.

[0006]

In the present invention, the outer layer is limited to a material having a martensitic matrix structure because it is the hardest and effective means in terms of wear resistance as compared with pearlite and bainite. Also, the reason why the inner layer is limited to the material having a pearlite matrix structure is that expansion does not occur due to the martensite transformation expansion of the outer layer, but the inner layer of the pearlite matrix structure shrinks relatively with the martensite transformation expansion of the outer layer. Since tensile stress is generated, cracking may occur,
According to the heat treatment method of the present invention, the stress can be reduced, which is effective as a practical technique.

In the heat treatment of the composite sleeve of the present invention, that is, in the quenching and cooling process, the following effects are brought about by the forced cooling from the outer surface and the inner surface of the sleeve. The first is to promote the outer layer martensite transformation. The forced cooling from the inner surface of the sleeve naturally increases the cooling rate of the entire sleeve and promotes the martensitic transformation to the inside of the outer layer.

Secondly, the tensile stress generated in the inner layer (in particular, the inner surface of the sleeve) can be reduced. In the quenching and cooling process, the stress generated on the inner surface of the sleeve is the transformation stress due to the outer layer martensite transformation expansion and the thermal stress caused by the temperature difference (temperature distribution) between the outer and inner surfaces of the sleeve. The martensitic transformation expansion is governed by the thickness of the outer layer, while the thermal stress is the temperature distribution from the outer surface to the inner surface (cross-sectional direction) of the sleeve at the time of changing from the plastic region to the elastic region during the quenching and cooling process. Depends on By the forced cooling from the inner surface of the sleeve, the temperature difference between the outer and inner surfaces is reduced, and the generation of thermal stress is significantly reduced.

Thirdly, the mechanical properties of the inner layer are improved.
The pearlite structure is a layered structure of ferrite and cementite. Generally, the smaller the (layered) spacing between ferrite and cementite, the smaller the structure, and the more the mechanical properties improve. Forced cooling from the inner surface of the sleeve makes the pearlite structure fine and improves mechanical properties.

[0010]

Next, an embodiment of the method for forcibly cooling the outer and inner surfaces of the sleeve in the sleeve quenching and cooling process according to the present invention will be described. First, a sleeve body was manufactured with the dimensions and components shown in Table 1. (That is, in this embodiment, the inner layer of the sleeve is made of graphite cast steel and the outer layer is made of high chromium adamite.) Next, the sleeve was heated in a heat treatment furnace to 950 to 1000 ° C. to be an austenite structure and heated. rear,
It is extracted from the heat treatment furnace and quenched and cooled. Quenching of the outer surface of the sleeve is shown in FIG. FIG. 1 is an explanatory view showing an embodiment of inner surface cooling according to the present invention. As is generally done, while rotating a sleeve, a fan (fan) or MIS is provided.
While cooling by T (spray), the inner surface of the sleeve is cooled naturally by the conventional method, whereas in the present invention, as shown in FIG. 50mm processed hole 6 formed in
The steel pipe 5 for cooling the inner surface of the sleeve was set inside the sleeve 2, and forced cooling was performed by the high-pressure (about 5 kg / cm ² ) Air. The quenching of the outer surface of the sleeve and the forced cooling of the inner surface of the sleeve were performed up to 450 ° C in order to prevent the pearlite transformation of the outer layer, and then naturally cooled in the air, and the tempering was performed at 500 to 550 ° C.

[0011]

[Table 1]

FIG. 2 shows the temperature transition during the quenching and cooling process. On the outer surface, the average cooling rate from 950 to 450 ° C. is 70 to 80 ° C./min, while on the inner surface of the sleeve, 950.
Up to ~ 600 ℃ is 40 ~ 50 ℃ / min, 600 ~ 450
The cooling rate up to ° C is 15 to 20 ° C / min. The average cooling rate of the inner surface of the sleeve in the conventional method is 950 to
The rate was 10 to 15 ° C / minute up to 450 ° C. in this way,
The inner surface of the sleeve is forcibly cooled and the cooling rate is 950-6
The reason for limiting the temperature to 00 ° C to 40 to 50 ° C / min and the temperature to 600 to 450 ° C to 15 to 20 ° C / min is that if the cooling rate is further increased, a part of bainite structure appears and a perfect pearlite structure is formed. This is because it does not happen. On the contrary, when the cooling speed is slowed down, the temperature difference from the outer surface becomes large, and the effect of reducing residual stress, which is the gist of the invention, does not occur.

FIG. 3 shows a comparison of temperature distributions between the cooling method according to the present invention and the conventional method. In the comparative example shown in FIG. 3 (B) as compared with the inner surface cooling method of the present invention shown in FIG. 3 (A). It can be seen that there is a large temperature difference between the outer surface and the inner surface of the sleeve, especially during cooling. FIG. 4 is a diagram showing a comparison of stress distributions between the present invention and a conventional method. According to the inner surface cooling of the present invention shown in FIG. 4 (A), compared with the method in the comparative example shown in FIG. 4 (B). It can be seen that the residual stress on the inner surface of the sleeve is reduced. Therefore, in the conventional method, cracks originated from the inner surface of the sleeve.

[0014]

EFFECTS OF THE INVENTION According to the heat treatment method of the present invention, while maintaining the high hardness of the composite sleeve, the cracking of the sleeve during the production and during the rolling use accompanying the compounding is eliminated, and the wear resistance is high. It is possible to manufacture sleeve assembly type rolls, which is highly valuable as a practical technology.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of inner surface cooling according to the present invention,

FIG. 2 is a diagram showing an inner surface cooling rate according to the present invention,

FIG. 3 is a diagram showing a comparison of temperature distributions in a cooling method according to the present invention and a conventional method,

FIG. 4 is a diagram showing a comparison of stress distributions of the present invention and a conventional method due to cooling;

FIG. 5 is an explanatory view showing a structure of a conventional composite sleeve,

FIG. 6 is an expansion / contraction state diagram of the inner and outer layers of the composite sleeve during heat treatment.

[Explanation of symbols]

 1 Roll Main Body 2 Sleeve 3 Sleeve Outer Layer 4 Sleeve Inner Layer 5 Sleeve Inner Surface Cooling Steel Pipe 6 Hole Formed in Cooling Steel Pipe

Claims (1)

[Claims] 1. A heat treatment method for a composite sleeve in which a sleeve made of an austenite matrix structure is heat treated to transform an outer layer of the sleeve into a martensite matrix structure and an inner layer of the sleeve into a pearlite matrix structure, and a quenching and cooling step. Thus, by forcibly cooling not only the outer surface of the sleeve but also the inner surface of the sleeve, the martensitic transformation of the outer layer is promoted, and the internal stress is reduced and the mechanical properties of the inner layer material are improved. Heat treatment method for composite sleeve.