JPS591772B2 - Heat treatment method for composite rolls - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat treating a composite roll for rolling.

Conventionally, many inventions have already been made regarding the manufacturing method of composite rolls for rolling (for example, Japanese Patent Publication No. 53-170
(Refer to Publication No. 88, etc.), both of which are mainly inventions related to methods of constructing an outer shell layer used during rolling and a core layer that improves internal toughness, and deal with the internal residual stress of composite rolls. There are very few such inventions, and there is only one, for example, the invention disclosed in Japanese Patent Publication No. 51-25210.

Therefore, the present invention has thoroughly researched the internal residual stress of composite rolls and determined the influence of transformation stress inside the composite roll, thereby providing a rational method that can contribute to improving the roll's crack resistance. The purpose is to obtain a heat treatment method that is

In order to achieve this objective, the inventor of the present invention has repeatedly conducted experimental research on the internal residual stress of composite rolls, and found that in the heat treatment of composite rolls, the entire inside and outside of the rolls are austenitized as in the past, and the rolls are subjected to heat refining and quenching. By avoiding the method of doing this and austenitizing only the outer shell layer,
It was confirmed that it is possible to prevent phenomena involving large disturbances in the residual stress field due to local transformation stress at the boundary with the core material.

Based on this knowledge, the present invention is characterized in that only the first surface layer is austenitized during heat treatment of a rolling composite roll consisting of two or more layers.

Hereinafter, the present invention will be explained in detail based on the accompanying drawings showing the experimental results.

First, as shown in FIG. 1 of the accompanying drawings, three layers S.

A composite roll test material consisting of B and C was created.

Specifically, as shown in the figure, an intermediate layer B having a wall thickness of t is shrink-fitted onto a core material C having a diameter D1, and an outer shell layer S having a diameter D2 is finally fitted onto the core material C having a diameter D1. Layer B
A three-layer roll shrink-fitted on top was forge-welded to form a composite roll, and in this case, the adhesion between each layer was perfect.

In addition, the chemical components of each layer S, B, and C are as shown in the table.

Next, such test materials were subjected to various heat treatments including the method of the present invention, and the resulting internal residual stress distributions were determined.

The results are shown in Figures 2-5.

That is, first, a composite roll test material consisting of such three layers (D1 = 50 mm, t = 1 mrn, D
2=95 mm), induction hardening was performed, that is, only the first layer S was made into austenite, and the residual stress distribution in this case is shown in FIG.

Looking at this, it can be seen that since no transformation stress is generated in the boundary layer, an extremely smooth residual stress distribution is obtained.

In addition, in the figure, σ2. σ and σ indicate residual stress kgf/− in the axial direction, circumferential direction, and radial direction, respectively.

Next, a test material having the same dimensions was quenched and tempered after the entire inside and outside were austenitized, and the residual stress distribution in this case is shown in FIG.

Looking at this, large disturbances in residual stress due to local transformation stress are recognized in intermediate layer part B, and
It can be seen that a phenomenon similar to the result in the invention according to Publication No. 1-25210 appears.

Furthermore, a similar test piece (57 mm in D, t =
1 mvt, D2 = 100 mm) was slowly cooled after austenitizing the entire inside and outside, and the residual stress distribution in this case is shown in Figure 4.

Looking at this, it can be seen that large disturbances in residual stress due to local transformation stress are still observed in the intermediate layer part B, and furthermore, the surface layer S is a tensile stress region, and when propagating inward to the surface crack. It turns out to be harmful.

Finally, a test piece having the same dimensions was heated to a temperature below the transformation point throughout the inside and outside, and then slowly cooled. The residual stress distribution in this case is shown in FIG.

Looking at this, it can be seen that almost no internal residual stress is generated.

In this way, the disturbance of the residual stress field in the intermediate part B between the outer shell layer S and the core material C1 of the composite roll is caused by the difference in the transformation characteristics of the layer materials constituting each layer, as can be seen from the results in Figure 4. It is clear that this is due to the generation of transformation stress based on .

In this case, the reason why the test material was made into a three-layer material was because
Since the stress generated in layered materials is small, the purpose of research is to interpose materials with completely different transformation characteristics to make the heat treatment effect more noticeable.

Regarding the chemical composition of the outer shell material, intermediate material and heartwood,
As can be seen from the table, the pearlite nose in the middle layer is on the longest side, followed by the surface layer material and then the core material.

In this way, from the results shown in Figures 2 to 4, in order to give a preferable compressive residual stress distribution to the surface layer of the composite roll and not create disturbances in the stress field in the composite intermediate layer, it is necessary to It is characterized by controlled heating by setting the heating temperature and heating time based on the thickness and composition of each layer of the composite roll so that only the inside becomes austenite and the inside does not become austenite. It has been revealed that, as a heating method for this purpose, methods such as induction heating quenching and flame quenching are extremely effective.

Furthermore, in recent years there has been an even stronger demand for increasing the hardening depth of rolling rolls, and for example, the recent trend is to gradually increase the hardening depth, that is, the range of austenitization, even with induction hardening and flame hardening. However, according to the present invention, in the case of composite rolls, quantitative It became clear that certain regulations should be added.

When reheating is performed using a composite roll for weld overlay, more care is required because the overlay outer shell layer is generally thin.

Next, the method of the present invention will be explained based on one embodiment thereof.

In the case shown in Fig. 6, the metamorphosis point AC1 is 7.
10℃, boundary layer B is 720'C, core material C is 730℃, and shows the final temperature distribution state in a composite roll.The temperature of the surface layer S is mostly austenitic, but the boundary layer B and heartwood C each have AC 1 point 7
Since the temperature is below 20°C and 730°C, it is not austenitized.

Note that in order to obtain such a final temperature distribution, the heating temperature and heating time must be set in consideration of the thickness of the surface layer S.

The heat treatment method using such heating temperature and heating time is performed as follows, for example.

First, the composite roll to be heat treated is charged into the furnace,
Uniformly heat the inner and outer layers to 600°C.

Next, the planned heating temperature of the first layer, that is, AC1 of the first layer
The above 600℃ temperature was set in a furnace with an atmosphere set approximately 100℃ higher than the temperature at point
By inserting a composite roll uniformly heated to °C and keeping it heated for a predetermined time, the first layer is heated to AC□ point of the first layer + (
Heat to a temperature of 100°C or higher and 300°C or lower).

This predetermined heating holding time varies depending on the outer diameter Dmm of the first layer and its thickness dma, but the time thr is determined by the following t
f) Derived from the above method: This allows only the first layer to be austenitized, and the internal layers are not austenitized.

Once heated to a predetermined temperature in this manner, it is cooled to impart a predetermined performance and to prevent local transformation stress from occurring at the boundaries between the layers.

As described above, according to the present invention, it is possible to prevent a phenomenon accompanied by a large disturbance of the residual stress field due to local transformation stress at the boundary between the outer shell layer and the core material after heat treatment of a rolling composite roll. Therefore, the crack resistance of the roll during rolling can be improved, and the rolling performance of the composite roll can be dramatically improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the configuration of the composite roll test material used in the experiment of the present invention, Fig. 2 is a residual stress distribution diagram when the surface layer of the composite roll test material is tempered after quenching, and Fig. 3 The figure shows the residual stress distribution diagram when the entire inside and outside of the composite roll test material was uniformly austenitized, then quenched and tempered. Figure 4 is the residual stress distribution diagram when the entire inside and outside of the composite roll test material was uniformly austenitized and then slowly cooled. Residual stress distribution diagram, 5th
The figure is a residual stress distribution diagram when the entire composite roll test material is heated to below the transformation point and then slowly cooled, and FIG. 6 is a final temperature distribution diagram of an example of the present invention. S... Outer shell material (surface layer) 1. B: Intermediate material (boundary layer), C: Heartwood.

Claims (1)

[Claims] In the heat treatment of a rolling composite roll consisting of 12 or more layers, the inner and outer layers are uniformly heated to 600°C in advance, and the uniformly heated roll material is heated to 1 point AC of the first layer + (10
0 to 300°C) per mrn of first layer thickness.
．． Heat treatment is performed by heating for 6 hours to austenitize only the first layer, and performing controlled heating so as not to austenite each layer inside, followed by cooling, so as not to generate local transformation stress at the boundary. A method for heat treatment of composite rolls characterized by: