JPH042649B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy chilled roll whose used layer requires wear resistance, such as a hot rolling roll, which is intended to further improve the wear resistance by subjecting the used layer to a specific heat treatment. The wear resistance of the layer used in a hot rolling roll (hereinafter, the layer used in the present invention refers to the outer layer of a composite roll, the outer layer of a single roll, and the sleeve layer of an assembled roll) is determined by both the carbide and the matrix. As a general rule, the higher the hardness of both, the better the wear resistance. Conventionally, cementite or Cr double carbide has been used as the carbide, but recently, in order to achieve even higher hardness, the applicant has previously filed a patent application for materials containing W and V carbides. It was proposed as No. 83283 and Japanese Patent Application No. 134045-1983. On the other hand, regarding the base, in terms of high hardness,
Martensite is judged to be the best, but it is generally difficult to obtain a uniform martensite base, and there is a tendency for some to become pearlite or for residual austenite to remain. Therefore, even if the carbide has high hardness, the desired wear resistance cannot be obtained if the base has pearlite with low hardness or if retained austenite in an untransformed structure remains. The present invention utilizes conventional chilled roll materials (Japanese Patent Application No. 56-83283, Japanese Patent Application No. 57-83, which have already achieved high hardness).
No. 134045), it was made to have a martensite base with even higher hardness and uniformity, and to provide even more excellent wear resistance. That is,
The present invention was able to achieve the objective by applying a specific heat treatment to the above-mentioned conventional method.The feature of the present invention is that the roll-used layer contains chemical components in weight percent, C. ; 3.0-4.2% Si; 0.1-2.0% Mn; 0.3-2.0% P; 0.01-0.5% or less S; 0.1% or less Ni; 0.2-4.0% Cr; 0.2-18.0% Mo; 0.1-6.0% W; 2.0 Using a chilled alloy consisting of ~10.0% Fe and impurities, the chilled material was heated and held at a temperature of 850 to 1050°C, then cooled at a cooling rate of 100 to 1000°C/Hr, and then The heat treatment is performed at a temperature of 560° C. for 1 to 50 hours, and another feature is that the chemical components contain 30% or less of V. The present invention will be explained in detail below. The chemical composition of the alloy constituting the chilled alloy material used in the roll layer of the present invention and the reason for its limitation will be described. C: 3.0 to 4.2% C dissolves into the base, hardens the martensite of the base, and forms carbides. If it is less than 3.0%, the amount of carbide will be small and the wear resistance will be poor. on the other hand
If it exceeds 4.2%, primary carbides crystallize and become brittle, and wear resistance also deteriorates. Si: 0.1-2.0% Si has a deoxidizing effect on molten metal and improves castability. If the content is less than 0.1%, no effect can be expected, and in practice it is difficult to reduce the content below 0.1%.
However, if it exceeds 2.0%, it will dissolve into the ferrite and make the material brittle, which is undesirable. Mn: 0.3 to 2.0% Mn removes the harmful effects of S and improves the hardenability of the material. If it is less than 0.3%, no results are expected, and if it exceeds 2.0%, it is not preferable because it causes a decrease in the toughness of the material. P; 0.01-0.5% P is generally known as an impurity element, but
It has the effect of improving seizure resistance. In order to improve this seizure resistance, 0.5% is sufficient, and more content is not preferable because it makes the material brittle. The lower the P content, the higher the toughness of the material (although the seizure resistance is lower), but it is economically disadvantageous to set it to less than 0.01%. S: 0.1% or less S is an impurity element and deteriorates the toughness of the material, so it should be kept at 0.1% or less. Note that setting it below 0.005% is disadvantageous in terms of cost, and due to Mn
The harmful effects of S below 0.005% are eliminated. Ni: 0.2-4.0% Ni is an element that increases hardenability and is necessary to obtain a uniform martensite base. Due to its necessity, it should be set at 0.2% or more. On the other hand, if it exceeds 4.0%, the martensite transformation point becomes too low and residual austenite tends to remain. Cr; 0.2 to 18.0% Cr increases the hardenability of the matrix and hardens the carbide. Also, if it is contained in a large amount, the eutectic point can be lowered to a low C.
% side to reduce segregation and refine carbides. For the above reasons, it is set at 0.2% or more, and the upper limit is set at 18.0% or less as a condition to prevent the formation of (FeCr) ₂₃ C ₆ carbide. Mo: 0.1 to 6.0% Mo has the property of improving hardenability without significantly changing the martensitic transformation temperature.
If it is less than 0.1%, this effect cannot be obtained, and if it exceeds 6.0%, residual austenite tends to remain like Ni. Moreover, if it exceeds 6.0%, the amount of Mo carbides increases and becomes brittle, which is also disadvantageous in terms of cost. W; 2.0 to 10.0% W mainly forms carbides. This carbide has extremely high hardness and is effective in improving wear resistance at high temperatures. If it is less than 2.0%, the amount of W carbide is small and the effect is small. On the other hand, if it exceeds 10.0%, it is not preferable because it deteriorates the toughness of the material and reduces heat crack resistance. In addition, especially when manufacturing by centrifugal casting, W tends to segregate due to the difference in specific gravity, but in that case, the above-mentioned Cr is effective in preventing segregation. V: 3.0% or less In addition to forming highly hard carbides, V has the effect of improving the shape of double carbides containing W into lumps.
Improves the toughness of the material and improves crack resistance. Therefore, since the material quality is improved by adding V, it is preferable to include it, but in that case, 3.0%
The effect is saturated even if it exceeds 3.0%, so it should be 3.0% or less. Next, the heat treatment means implemented in the present invention will be explained. FIG. 1 shows a thermal curve of heat treatment according to the present invention. In the figure, A is for the purpose of austenitization and precipitation of carbides. Conventionally, low-temperature heat treatment (below 550°C) was performed for the purpose of stabilizing the structure and eliminating distortion, but untransformed structures tend to remain in this low-temperature heat treatment. The reason for this is that due to the non-uniformity of the alloying elements in the matrix, there are localized areas with a low martensitic transformation point. Therefore, when heat treatment is performed at, for example, 600° C. for the purpose of transforming retained austenite, martensite that has already been generated is tempered, resulting in a decrease in hardness. In the present invention, in order to reduce the alloy content of austenite by precipitating carbides in the area where alloying elements are concentrated, and to make the austenite uniform, the temperature is raised to the austenite region. 1000℃
temperature. The reason why the holding temperature is limited to the above-mentioned holding temperature is as follows. For example, in the case of the material of sample 2 described later, the holding temperature and martensitic transformation start point (hereinafter referred to as Ms point)
changes as follows. (Holding temperature) Ms point 800℃ 170℃ 850〃 140〃 900〃 100〃 950〃 70〃 1000〃 50〃 1050〃 30〃 1100〃 -10〃 According to the above, the Ms point is as high as 170℃ at 800℃ However, since the amount of austenite is small, the hardness is low. On the other hand, at 1100°C, the Ms point drops too much and retained austenite tends to remain. Therefore, the temperature of A is 850~850 for the material components used in the present invention.
1050℃ is suitable. Note that a holding time of 10 minutes to 10 hours is appropriate. For B in Figure 1, it is sufficient to provide a cooling rate that is sufficient to suppress pearlite transformation, and in the case of the material of sample 2,
150℃/Hr or more is sufficient. Generally, for the materials used in the present invention, a range of 100° C./Hr to 1000° C./Hr is appropriate from the viewpoint of the need to suppress pearlite transformation and operational problems. Regarding C in FIG. 1, the temperature needs to be lower than D described later. At this time, if the temperature is lowered to around room temperature, there will be no problem with the material, but cracking will likely occur, so it is preferable to keep the temperature at just below D. D in FIG. 1 is particularly important. This D needs to be 560°C or lower because it is not aimed at pearlite transformation which causes a decrease in hardness. According to the material of sample 2, depending on the holding temperature and time of D, Ms
The points change as follows. (Holding temperature/time) (Ms point) 560℃×5Hr 230℃ 500〃×50〃 205〃 500〃×12〃 160〃 500〃×1〃 120〃 450〃×8〃 110〃 400℃×15Hr 90℃ 350〃×7〃 60〃 (Note) Austenitization, cooling conditions: 950℃×
4Hr, 300°C/Hr An increase in the Ms point is advantageous in terms of preventing cracking and preventing retained austenite, and from the above test results, the appropriate holding temperature range for D is 400 to 560°C. Further, the holding time is a problem in terms of work, that is, if it is too long, it is disadvantageous in terms of cost, and from the above test results, it is preferably 1 to 50 hours. The characteristics of the material are determined by the thermal curves A to D in Figure 1, but from the viewpoint of residual stress as a roll and stabilization of the structure, the thermal curves shown in E in Figure 1 are further determined. Heat treatment (e.g. holding temperature 300-560
It is desirable to add a holding time of 2 to 20 hours). Next, examples of the present invention will be listed together with comparative examples. <Example> Γ roll dimensions (body); 420φ x 700 Γ casting method; horizontal centrifugal casting (inner layer; tough cast iron) Γ chemical composition (weight %, balance Fe and impurities/outer layer only)

[Table] Γ heat treatment (A); 950℃×4Hr (B); 400℃/Hr (D); 500℃×20Hr (E); 520℃×15Hr Γ hardness (Hs) (shell surface) Sample 1 Sample 2 Hs 86.2 91.3 Γ Microscopic structure (according to sample 2) Figure 2 (x50), Figure 3 (x400) <Comparative example> (Patent application No. 56-83283) Roll dimensions, casting method, and chemical composition are as in the example Same Γ heat treatment 520℃ x 10 hours (strain relief heat treatment; equivalent to E in Example) Γ hardness (Hs) (body surface) Sample 1 Sample 2 Hs 84.3 88.2 Γ Microscopic structure (according to sample 2) Fig. 4 (×50 ), FIG. 5 (×400) As a result of studying the above examples and comparative examples, the following was found. Even though the chemical compositions of both materials are the same, in the case of the comparative example, only a low-temperature strain relief heat treatment was applied, so as is clear from the micrographs in Figures 4 and 5, the austenite is non-uniform and inevitably remains. Austenite tends to remain. As a result, the hardness was low, and the residual austenite was transformed during rolling use, making it more likely that wear and surface roughness would occur. In addition, due to the transformation of retained austenite (due to heat load during rolling and changes in temperature), breakage accidents sometimes occurred during use. On the other hand, in the example, as is clear from the micrographs in Figures 2 and 3, the austenite was homogenized, uniform transformation occurred throughout, and residual austenite was almost eliminated ( However, constant temperature treatment aimed at raising the Ms point, that is, D is required.) As a result,
The increase in hardness is clear even when compared with the comparative example, and the wear resistance and roughness resistance are also improved. Several sets of rolls from the example and comparative example are currently in use, and the average lifespan of the example is 1.8
It turns out to be twice as large. As described above, the present invention can be applied to a chilled alloy material having a specific chemical composition in the roll layer by increasing the temperature.
After holding at a temperature of 850-1050℃, 100-1000℃/
By performing a specific heat treatment of cooling at a cooling rate of 1 hour and then holding at a temperature of 400 to 560 degrees Celsius for 1 to 50 hours, it is possible to achieve In contrast, we were able to provide a product with a martensite base with even higher hardness and uniformity and even greater wear resistance, resulting in extremely significant improvements in its rolling performance and service life. The layer used in the roll of the present invention is as defined at the beginning, but to add an explanation of the roll example in particular when it is used as the outer layer of a composite roll, the outer layer can be formed horizontally, inclinedly, or vertically. Although centrifugal force casting is also possible, vertical centrifugal force casting is most preferred from the standpoint of preventing segregation. The inner layer material may be FC, DCI, graphite steel, or cast steel, but FC is usually sufficient since the stand has a relatively light load. Furthermore, in centrifugal force casting, the toughness of the inner layer material tends to deteriorate as the outer layer material melts into the inner layer, so providing an intermediate layer between the outer layer and the inner layer will further improve the soundness.

[Brief explanation of drawings]

FIG. 1 shows the thermal curve of heat treatment according to the present invention, and FIG.
3 and 3 are micrographs of the layer using a roll according to the present invention, and FIGS. 4 and 5 are the same photographs of the comparative example.

Claims (1)

[Claims] 1 The chemical components in the layer used in the roll are in weight percent: C; 3.0 to 4.2% Si; 0.1 to 2.0% Mn; 0.3 to 2.0% P; 0.01 to 0.5% or less S; 0.1% or less Ni; 0.2 to 4.0% Cr; 0.2 to 18.0% Mo; 0.1 to 6.0% W; 2.0 to 10.0% A chilled alloy consisting of the balance Fe and impurities is used, and the chilled material is heated and maintained at a temperature of 850 to 1050°C. A method for manufacturing an alloy chilled roll having excellent wear resistance, which comprises cooling at a cooling rate of 100 to 1000°C/Hr, and then performing heat treatment at a temperature of 400 to 560°C for 1 to 50Hr. 2 The chemical components in the layer used in the roll are C; 3.0 to 4.2% Si; 0.1 to 2.0% Mn; 0.3 to 2.0% P; 0.01 to 0.5% or less S; 0.1% or less Ni; 0.2 to 4.0% Cr; 0.2 ~18.0% Mo; 0.1 to 6.0% W; 2.0 to 10.0% V; 3.0% or less After using a chilled alloy consisting of the balance Fe and impurities, raising the temperature of the chilled material and holding it at a temperature of 850 to 1050°C A method for manufacturing a chilled alloy roll having excellent wear resistance, which comprises cooling at a cooling rate of 100 to 1000°C/Hr, and then performing heat treatment at a temperature of 400 to 560°C for 1 to 50Hr.