Method for manufacturing compressed product

Abstract

To provide a method for manufacturing a compressed product that can appropriately control the size of a gap formed between a non-metallic inclusion and a parent phase, taking into account a deformation phenomenon of the nonmetallic inclusion and the parent phase contained in a steel material in compression.SOLUTION: A method for manufacturing a compressed product of performs a plurality of times of compression on a steel material containing a non-metallic inclusion. A rolling reduction for the steel material in each of the plurality of times of compression is set in a range equal to or less than an upper limit rolling reduction. The upper limit rolling reduction is a rolling reduction corresponding to a target gap area ratio, which is a target value of a gap area ratio after completion of the plurality of times of compression on the steel material, in relationship information obtained in advance from a relationship between a gap area ratio of a gap formed between the non-metallic inclusion and a parent phase by compression on a target steel material containing the non-metallic inclusion and a rolling reduction in the compression.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a compression processed product.

Background Art

[0002] Steel materials inevitably contain foreign substances called non-metallic inclusions due to their manufacturing processes. In steel products such as bearing parts manufactured through rolling or forging, gaps may be formed around the non-metallic inclusions. This gap is considered to occur at the interface between the non-metallic inclusion and the matrix phase due to the difference in deformability between the two. This gap, for example, in a bearing part that undergoes rolling fatigue during use, may promote the generation of cracks and serve as a crack initiation point. That is, during the use of a bearing part, a repeated contact load is applied to the raceway surface where the rolling elements roll. If the aforementioned gap exists in the affected area, it may promote the generation of cracks in the bearing part and serve as a crack initiation point. When this crack reaches the raceway surface, it may lead to peeling and cause damage to the bearing part. Therefore, in order to improve the lifespan of steel products such as bearing parts, methods for reducing the gap around non-metallic inclusions have been proposed.

[0003] In Patent Document 1, a method of forging is described in which forging is performed such that the forging temperature and the pushing amount of a die having an annular convex shape satisfy a predetermined relationship so that a predetermined hydrostatic pressure can be obtained in the forging process of producing the raceway surface of a thrust ball bearing. According to the method for producing the raceway surface of the thrust ball bearing in Patent Document 1, it is stated that the voids generated around the inclusions during the rolling of the bar steel can be crushed, and the inclusions and the base material can be brought into close contact.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The method of Patent Document 1 targets a forging process of pressing a mold to form a rolling groove. And in the forging process, it only stipulates the conditions under which a certain amount of hydrostatic stress or more can be applied to steel parts or blanks. That is, the deformation phenomena of non-metallic inclusions and the matrix phase caused by compression processes such as rolling and ring rolling are not considered. Therefore, the method of Patent Document 1 cannot be applied to processing accompanied by such deformation phenomena. Also, even if the method of Patent Document 1 is formally applied to compression processes such as rolling and ring rolling, it is unclear whether the gap between the inclusions and the matrix phase can be closed.

[0006] An object of the present application is to provide a method for manufacturing a compression processed product that appropriately controls the size of the gap formed between non-metallic inclusions and the matrix phase in a steel material in compression processing, taking into account the deformation phenomena of the non-metallic inclusions and the matrix phase contained in the steel material.

Means for Solving the Problems

[0007] The means for solving the above problems are as follows.

[0008] (1) A method for manufacturing a compression processed product in which a steel material containing non-metallic inclusions is subjected to multiple compression processes, the reduction ratio for the steel material in each of the multiple compression processes is set within the range of not more than the upper limit reduction ratio, the upper limit reduction ratio is the reduction ratio corresponding to the target gap area ratio, which is the target value of the gap area ratio after completion of multiple compression processes of the steel material, in the relationship information obtained in advance from the relationship between the gap area ratio formed between the non-metallic inclusions and the matrix phase by compression processing of the target steel material containing non-metallic inclusions and the reduction ratio in that compression processing. A method for manufacturing a compression processed product, characterized in that.

[0009] (2) The method for manufacturing a compression processed product according to (1) above, characterized in that the compression processing is rolling or ring rolling.

[0010] (3) The relationship information is obtained by calculating the gap area ratios of the gaps formed when the target steel material model is compressed using CAE analysis for a plurality of cases with different reduction ratios, and is the relationship information obtained based on a plurality of relationships between the gap area ratios and the reduction ratios. The manufacturing method of the compressed product according to (1) above is characterized in that.

[0011] (4) The manufacturing method of the compressed product according to (3) above is characterized in that the relationship information is an approximation curve for the plurality of relationships between the gap area ratio and the reduction ratio.

[0012] (5) The manufacturing method of the compressed product according to (4) above is characterized in that the approximation curve is a linear function.

[0013] (6) The manufacturing method of the compressed product according to (1) or (3) above is characterized in that the relationship information is obtained based on the relationship between the gap area ratio and the reduction ratio of the gap formed by the first compression process performed on the target steel material.

[0014] (7) The manufacturing method of the compressed product according to (1) above is characterized in that the gap area ratio is a value obtained by the following formula [1]. Gap area ratio (%) = Gap cross-sectional area / Non-metallic inclusion cross-sectional area × 100 [1]

[0015] (8) The manufacturing method of the compressed product according to (7) above is characterized in that the gap cross-sectional area and the non-metallic inclusion cross-sectional area are cross-sections passing through the non-metallic inclusions and are cross-sectional areas in the cross-section in the thickness direction - steel material supply direction of the steel material.

[0016] (9) The manufacturing method of the compressed product according to (1) above is characterized in that the reduction ratio is the ratio of the amount of thickness reduction in the pass of the target compression process to the initial thickness of the steel material before the compression process.

[0017] (10) The manufacturing method of the compressed product according to (1) above is characterized in that the compressed product is processed into the shape of a rolling part after the completion of the compression process.

Advantages of the Invention

[0018] According to one aspect of the embodiment, a method for manufacturing a compression processed product can be provided that appropriately controls the size of the gap formed between a non-metallic inclusion and the matrix phase in compression processing, taking into account the deformation phenomena of the non-metallic inclusion and the matrix phase contained in the steel material.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0020] Hereinafter, an embodiment of a method for manufacturing a compression processed product will be described. The method for manufacturing a compression processed product according to the embodiment is a method for manufacturing a compression processed product capable of controlling the gap (void) between a non-metallic inclusion contained in a steel material and the surrounding matrix phase within a range of a predetermined size (below the target gap area ratio). More specifically, in the case of compression processing the steel material to a desired thickness or size by a plurality of compression treatments, the reduction ratio in each compression treatment is set so that the above gap can be controlled within a range of a predetermined size, and the compression processing is performed.

[0021] Compression processing includes, for example, rolling processing and ring rolling processing. In this embodiment, as an example, the case of performing rolling processing will be described.

[0022] By using the compression processed product manufactured by the manufacturing method of the present embodiment, for example, it is possible to manufacture a rolling part with excellent rolling life in which the occurrence of cracks is suppressed. Examples of the rolling part include bearings, gears, hub units, continuously variable transmissions, constant velocity joints, crank pins, piston pins, and the like.

[0023] The manufacturing method of the compression processed product of the present embodiment has a relationship information derivation step and a processing step. The relationship information derivation step is a step of obtaining relationship information from the relationship between the gap area ratio indicating the size of the gap formed around the non-metallic inclusions by the rolling process and the reduction ratio in the rolling process. The processing step is a step of obtaining the upper limit reduction ratio corresponding to the target gap area ratio based on the derived relationship information, and performing a plurality of rolling processes (compression processes) at a reduction ratio equal to or lower than the upper limit reduction ratio to manufacture a compression processed product with a desired reduction ratio. Hereinafter, each step will be specifically described.

[0024] (Relationship information derivation step) The relationship information derivation step is a step of obtaining in advance the relationship information between the reduction ratio and the gap area ratio for the target steel material before performing the actual rolling process. The relationship information is obtained from the relationship between the gap area ratio of the gap formed by first performing the rolling process on the steel material before the rolling process, in which no gap has yet been formed between the non-metallic inclusions and the matrix phase, and the reduction ratio.

[0025] First, the gap area ratio will be described with reference to FIG. 1. FIG. 1 is a diagram schematically showing a cross section (X-Z cross section) of a steel material including non-metallic inclusions and the surrounding gap. The X-axis is the rolling (steel material movement) direction, and the Z-axis is the thickness direction (reduction direction) of the steel material. In the matrix phase of the steel material, there are non-metallic inclusions L, and there is a gap (hatched portion) between the non-metallic inclusions and the matrix phase. The size and shape of the gap in FIG. 1 are examples and are not limited thereto. In the rolling process, deformation occurs in the steel material when it passes through the roll. More specifically, the gap is formed during the rolling process due to the difference in deformability between the matrix phase and the non-metallic inclusions.

[0026] In this embodiment, the gap area ratio is a value obtained by the following formula (1). Gap area ratio (%) = Gap cross-sectional area / Non-metallic inclusion cross-sectional area × 100 (1) Here, the gap cross-sectional area is the total cross-sectional area of the gap portions indicated by the diagonal hatching in Fig. 1. The non-metallic inclusion cross-sectional area is the cross-sectional area of the non-metallic inclusion L portion. The gap cross-sectional area and the non-metallic inclusion cross-sectional area can be the cross-sectional areas in the cross-section passing through the non-metallic inclusions of the steel material and in the thickness direction - rolling direction (steel material supply direction) cross-section of the steel material. Further, when obtaining the gap area ratio by rolling analysis using a computer as described later, it can be obtained by assuming the shape of the non-metallic inclusion as a sphere. Specifically, in the cross-section in the thickness direction - rolling direction (steel material supply direction) passing through the center of the spherical non-metallic inclusion, the gap cross-sectional area and the non-metallic inclusion cross-sectional area may be obtained. Note that the XZ cross-section in Fig. 1 is the cross-section in the thickness direction - rolling direction (steel material supply direction).

[0027] By performing rolling treatment on the steel material at a certain reduction ratio and obtaining the gap cross-sectional area and the non-metallic inclusion cross-sectional area for the steel material after the rolling treatment, the gap area ratio formed at that reduction ratio can be obtained. Then, by obtaining the gap area ratios of the gaps formed respectively for the rolling treatments at various reduction ratios, relationship information can be obtained.

[0028] The relationship information can be obtained by using rolling analysis using a computer. Also, it may be obtained by performing a rolling test on an actual steel material test piece. In this embodiment, the case of obtaining the relationship information by rolling analysis using a computer will be described.

[0029] The rolling analysis for obtaining relationship information can be performed using a rolling analysis model that follows the well-known rigid-plastic / elastic-plastic finite element method (FEM). For the rolling analysis, CAE (Computer Aided Engineering) analysis can be used. CAE analysis is an analysis method for evaluating (simulating) design problems of products virtually reproduced on a computer. By means of CAE analysis, the gap area ratio can be accurately obtained. CAE analysis is realized by a computer program.

[0030] For CAE analysis, for example, DEFORM (manufactured by Scientific Forming Technologies Corporation) that adopts the rigid-plastic finite element method can be used. DEFORM is CAE software that simulates all kinds of processing phenomena such as the material flow of metals, the load state on tools, deformation due to heat treatment, and chip prediction during cutting on a computer. Of course, other similar CAE software may also be used.

[0031] Figure 2 is a schematic diagram of rolling processing for explaining the method of rolling analysis. The X-axis corresponds to the rolling direction (elongation direction) of the steel plate (plate model) 11, and the Z-axis corresponds to the thickness direction of the steel plate 11. The rolling direction is the supply direction of the steel material. By performing rolling analysis on this model, it is possible to analyze the gap generation behavior around the non-metallic inclusions L when the steel plate 11 is rolled using a pair of upper and lower rolling rolls 12.

[0032] Typical parameters given to the rolling analysis model include steel grade, plate thickness, hot or cold conditions (temperature, etc.), type, position, and size of non-metallic inclusions, reduction ratio of the rolling process, number of rolling passes, material property data (Young's modulus, Poisson's ratio, stress-strain curve, etc.), roll diameter of the rolling rolls, and so on. These parameters can be grasped by analyzing in advance the properties of the steel materials used for rolling parts such as bearings.

[0033] The conditions of non-metallic inclusions set in the rolling analysis model can be such that when non-metallic inclusions are present in parts or products, they can serve as crack initiation points. Regarding the types of non-metallic inclusions, an analysis can be performed on the steel material to be rolled, the types of non-metallic inclusions contained can be identified, and inclusions of that type can be set in the model. Although not limited, non-metallic inclusions are usually sufficiently hard with respect to the matrix material and can be considered not to deform, and can be set in the model as rigid bodies.

[0034] Regarding the size of inclusions, cross-sectional observation of the target steel material can be performed with a microscope to confirm the possible existence of non-metallic inclusions, and based on their size, the size of the inclusions to be set in the model can be determined.

[0035] Regarding the position of inclusions, the positions where inclusions may exist can be confirmed from the above cross-sectional observation, and based on that position, the position of the inclusions to be set in the model can be determined. However, for example, when manufacturing final parts or products by polishing or cutting after rolling, it is preferable to set the inclusions at positions inside the steel material rather than at the positions on the surface of the final parts or products. This is because it is necessary to control the size of the gap for inclusions inside the position compared to the surface of the final rolling parts, etc. In other words, inclusions at positions that will be removed by polishing, etc. do not cause cracks in parts or products.

[0036] Although not limited, for example, the size of inclusions can be set in the range of 100 μm or less. Also, although not limited, the position of inclusions can be set in the range within 1 mm from the surface position in the thickness direction of the steel plate to the inside for the final rolling parts, etc.

[0037] The reduction ratio represents the degree of rolling work as a percentage. When the reduction ratio is R (%), the thickness (plate thickness) of the material before rolling is h1, and the thickness (plate thickness) of the material after completion of the rolling pass is h2, it can be obtained by the following formula (2). R = (h1 - h2) / h1 × 100 (2)

[0038] However, the reduction ratio in this embodiment is the ratio of the amount of thickness reduction in the target pass to the initial thickness of the steel material before rolling. That is, the reduction ratio of this embodiment is Reduction ratio R(%) = Amount of thickness reduction in the target pass / Initial thickness before rolling × 100 is. Therefore, for the passes after the second pass in the multiple rolling passes set based on the relationship information described later, the reduction ratio is obtained based on the initial plate thickness before rolling. For example, the case of rolling a steel plate with an initial thickness of 10 mm at a total reduction ratio of 20% will be described. When rolling at a reduction ratio of 5% four times to make a total of 20%, the amount of thickness reduction in each pass is 10 mm × 5% = 0.5 mm based on the initial plate thickness. Then, the final plate thickness after the rolling process of the four passes is 8 mm (= 10 - 0.5 × 4).

[0039] In the rolling analysis described above, various specifications are set, and the process of performing one rolling process on the target steel material is simulated. Then, from the rolling analysis result, for the gaps formed around the non-metallic inclusions set as the analysis target, the gap cross-sectional area and the non-metallic inclusion cross-sectional area can be obtained. From these cross-sectional areas, the gap area ratio formed by the rolling process at that reduction ratio can be obtained. By performing rolling analysis while variously changing the reduction ratio, the gap area ratios corresponding to a plurality of reduction ratios can be obtained respectively.

[0040] Here, in the method of this embodiment, relationship information is derived based on the rolling analysis for the first rolling process on the steel material. Using the relationship information, the reduction ratios of the multiple rolling processes from the first to the nth (n is an integer of 2 or more) can be set so that the gap area ratio after all rolling processes is appropriately controlled.

[0041] Next, the relationship information can use an approximate curve (mathematical formula) obtained by fitting (curve fitting) the relationship between the obtained plurality of gap area ratios and reduction ratios. FIG. 3 is a graph showing the approximate curve obtained for the relationship (plot) between the gap area ratio and reduction ratio obtained by the rolling analysis process. In the example of FIG. 3, when the gap area ratio is y and the reduction ratio is x, the relationship information is the linear function y = 0.61x. Also, in the example of FIG. 3, as the first rolling process, it is an example in which the gap area ratios of the gaps formed when the steel material is first reduced at reduction ratios of about 2%, about 5%, about 10%, about 20%, and about 40% are respectively obtained. Details of the rolling conditions when obtaining the relationship between the gap area ratio and reduction ratio in FIG. 3 will be described in the examples.

[0042] The approximate curve, which is the relationship information, is not limited to a linear function and can be obtained by fitting the function that best fits. For example, it may be an n-th order function (n is an integer of 2 or more) or a logarithmic function.

[0043] Also, when a sufficiently fitting approximate curve cannot be obtained, the number of analysis processes can be increased by changing the reduction ratio and performing further rolling analysis to increase the number of plots, and then the approximate curve can be obtained again. The above are the steps for deriving the relationship information. Note that the specifications of the rolling model are preferably common to the conditions during actual rolling with the pass schedule (reduction ratios for multiple rolling processes) determined using the derived relationship information.

[0044] (Processing step) Next, based on the obtained relationship information, the reduction ratios for multiple rolling processes are determined, and rolling processing is performed on the actual target steel material at the determined reduction ratios.

[0045] The reduction ratio of each pass is determined based on the target gap area ratio. The target gap area ratio is the target value of the size of the gap formed after completion of all rolling processes (compression processes) in multiple passes. More specifically, it is the gap area ratio that can suppress the generation of cracks caused by the gap if it is controlled to be equal to or less than the target gap area ratio. The target gap area ratio can be appropriately set according to the steel material used, the product to be manufactured, the type of parts, etc. For example, in the case of rolling parts, generally 8 to 9% or less is recommended based on past empirical rules and the like.

[0046] In the approximate curve of the obtained relationship information, the reduction ratio corresponding to the value of this target gap area ratio is obtained as the upper limit reduction ratio. The upper limit reduction ratio is the upper limit value when setting the reduction ratio of each pass in this method.

[0047] And within the range of not exceeding the upper limit reduction ratio, the reduction ratio of each rolling process (pass) from the first pass to the nth pass actually performed is determined. For example, when the target gap area ratio is 8%, in the example of the relationship information in Figure 3, the corresponding reduction ratio is approximately 13%. Therefore, the upper limit reduction ratio can be set to 13%. In that case, the reduction ratio of each pass of the rolling process can be determined within the upper limit reduction ratio of 13% or less. On the other hand, if the reduction ratio of any pass exceeds the upper limit reduction ratio, the final gap area ratio after the rolling process may exceed the target gap area ratio. Then, the size of the gap formed by the rolling process cannot be appropriately controlled.

[0048] The reduction ratio of each pass can be set by dividing the desired total reduction ratio. Also, the reduction ratio of each pass only needs to be set to a reduction ratio not exceeding the upper limit reduction ratio. For example, when it is desired to perform a rolling process with a total reduction ratio of 20%, it can be a rolling process with a reduction ratio of 5% × 4 passes, or it can be a rolling process with a reduction ratio of 10% × 1 pass and 5% × 2 passes. The reduction ratio of each pass may be the same as, larger than, or smaller than the reduction ratio of any pass before that pass. In multiple rolling processes, the reduction ratio may decrease or increase sequentially. Also, the fewer the number of rolling processes, the better the production efficiency, but it is not particularly limited.

[0049] From the perspective of making the gap smaller, it is preferable to set a smaller reduction ratio per pass. This is because when the reduction ratio is small in rolling, the deformation is limited to the surface of the steel material. However, since the stretching deformation in the rolling direction is restricted by the undeformed part inside the steel material, the compressive stress in the stretching direction is more likely to act on the surface side of the steel material. Therefore, when the reduction ratio is larger, the difference in the compressive stress acting between the surface side and the inside side of the steel material becomes larger, and it becomes easier to form a gap. Thus, focusing on the surface layer of the steel material, setting a smaller reduction ratio is more effective in suppressing the gap. Specifically, for example, it is desirable to set it to 40% or less of the obtained upper limit reduction ratio.

[0050] And in the method of this embodiment, based on the relationship information obtained from the first rolling process for the target steel material, the upper limit reduction ratio corresponding to the target gap area ratio may be determined. And the reduction ratio for each pass can be set to be equal to or less than the upper limit reduction ratio. By performing the rolling process with the set reduction ratio, the gap area ratio can be made equal to or less than the target gap area ratio. That is, the gap area ratio can be controlled within an appropriate range.

[0051] Here, in the passes after the second pass for the target steel material, the matrix phase and inclusions are deformed in a state where gaps are formed around the non-metallic inclusions. And according to the research of the inventor, it has been found that the reduction behavior of the gap area ratio is different for each rolling pass. Therefore, when performing multiple rolling passes to achieve a desired total reduction ratio, it is difficult to predict the reduction behavior of the gap. However, according to the method of this embodiment, based on the relationship information obtained from the first rolling process, the reduction ratio for each pass can be appropriately set. That is, for example, even if no rolling analysis is performed in advance for each pass of the second pass or the third pass, the reduction ratio for each pass that can achieve an appropriate gap area ratio can be set. Therefore, the excellent effect that an appropriate pass schedule can be efficiently designed can be obtained by the method of this embodiment.

[0052] According to the method for manufacturing a compression processed product of the above embodiment, a compression processed product controlled to an appropriate gap area ratio can be manufactured. By obtaining relationship information based on rolling analysis considering the deformation phenomenon in which the non-metallic inclusions and the gap deform, and setting the reduction ratio for each pass, rolling processing can be performed in which the size of the gap in the rolling process is appropriately controlled.

[0053] According to the method of this embodiment, a compression processed product excellent in durability with the occurrence of cracks suppressed can be manufactured. Therefore, by processing the compression processed product manufactured by the method of this embodiment into the shape of a rolling component after the completion of the compression (rolling) processing, a rolling component or product having an excellent life with the occurrence of cracks suppressed can be manufactured.

[0054] As described above, since the gap area ratio obtained by rolling analysis is a calculated value by simulation, it may deviate from the measured value by about 1 to 2%. Although it may be ignored because the deviation amount is small, the reduction ratio for multiple rolling processes may be determined in consideration of the deviation amount. For example, when obtaining the upper limit reduction ratio, the reduction ratio corresponding to a gap area ratio reduced by about 1 to 2% from the target gap area ratio may be set as the upper limit reduction ratio, and the reduction ratio for each pass may be set based on the upper limit reduction ratio. Further, the method of this embodiment can be used, for example, when compression processing bearing steel such as SUJ2, but the steel material to be processed is not limited to this, and it can be used for compression processing of steel materials of various steel types.

[0055] (Other Embodiments) In the above embodiment, the case of performing rolling processing on a steel plate as compression processing has been described. Other embodiments in the case of performing ring rolling as compression processing will be described. FIG. 4 is a schematic diagram of a ring rolling mill that performs ring rolling. Ring rolling is a processing method in which a plurality of rolls are used to increase the diameter while reducing the wall thickness of a ring-shaped steel material to obtain a ring part of a desired dimension. In terms of the wall thickness decreasing when the ring passes between the rolls, it is a processing method in which the steel material is compression processed in the same manner as rolling processing.

[0056] The ring rolling mill of FIG. 4 has a driving roll (main roll) 21 and a driven roll (mandrel) 22. The driving roll 21 rotates by receiving a rotational force from a driving source (not shown). The ring-shaped steel material 20 is held sandwiched between the driving roll 21 and the driven roll 22. By pressing the driven roll 22 toward the ring-shaped steel material 20, the driven roll 22 rotates due to frictional force, and the inner diameter of the ring-shaped steel material 20 can be plastically deformed in the diameter-expanding direction.

[0057] Regarding this ring rolling, a simulation using a computer is performed in the same manner as in the case of rolling to obtain relationship information between the reduction ratio and the clearance area ratio. Then, based on the relationship information, a reduction ratio equal to or less than the upper limit reduction ratio corresponding to the target clearance area ratio is set, and multiple processes can be performed. In addition, when used for rolling parts and products, a non-metallic inclusion may be set on the surface that becomes the rolling surface of the ring-shaped steel material 20 (the surface where the clearance around the inclusion is to be controlled), and a rolling analysis may be performed to obtain the relationship information.

[0058] In the case of ring rolling, one rotation of the ring-shaped steel material may be regarded as one compression process (one pass). If the reduction ratio between the rolls for each rotation is set by this method and multiple compression processes are performed at that reduction ratio, a ring-shaped steel material with a desired total reduction ratio can be obtained. The reduction ratio for each rotation can be set to an appropriate reduction ratio by controlling the rotation speed of the driving roll 21 and the moving speed of the driven roll 22 in the diameter-expanding direction.

[0059] Even in the case of the above ring rolling, according to the method of the embodiment, a compression processed product in which the clearance between the non-metallic inclusion and the matrix is controlled to an appropriate size can be manufactured. Therefore, by using the compression processed product manufactured by this method, parts and products such as rolling parts with excellent fatigue life can be manufactured.

Example

[0060] (Example 1) A specific description will be given with reference to examples. Using the relationship information shown in Figure 3, rolling tests with various reduction ratios changed multiple times were set. Then, the rolling process with the set reduction ratio was simulated using CAE software for rolling analysis (CAE analysis). As the CAE software, DEFORM (manufactured by Scientific Forming Technologies Corporation) was used. A plate rolling model having inclusions with a diameter of 1 mm at a position 1 mm from the surface of a steel material with a thickness of 50 mm was used. The rolling temperature was set at 1000 °C. The diameter of the rolling roll was 250 mm. Other specifications given to the model were as follows: the contact condition (shear friction coefficient) between the non-metallic inclusion L and the matrix: 0.3, Young's modulus of the plate: 206 GPa, Poisson's ratio of the plate: 0.3, the deformation resistance curve σ of the plate: JPEG2025104281000002.jpg9170 The inclusion and the matrix: in close contact (no gap), roll peripheral speed: 12.6 rad / s, shear friction coefficient between the rolling roll and the plate model: 0.7, etc. Also, the steel type of the steel material of the plate rolling model was SUJ2, and the inclusions were Al2O3-based hard inclusions and were treated as rigid bodies. The target gap area ratio was set at 8%, and the corresponding upper limit reduction ratio was set at 13% based on the relationship information in Figure 3. Note that the rolling analysis performed when obtaining the relationship information shown in Figure 3 was also carried out using the same software under the same rolling conditions and the same rolling model.

[0061] Under the above conditions, rolling analysis was performed on the rolling processes with various reduction ratios set as shown in Table 1. By the rolling analysis, the gap area ratio of the inclusions after the rolling process of all passes was obtained. Then, it was confirmed whether the obtained gap area ratio was less than or equal to the target gap area ratio. The reduction ratio (%) of each pass and the gap area ratio (%) after processing in each test example are shown in Table 1 below.

[0062]

Table 1

[0063] In the test examples of Test No. 1 and 2 including passes with an upper limit reduction ratio exceeding 13%, the gap area ratio after the completion of the rolling process exceeded the target gap area ratio of 8%.

[0064] On the other hand, in the test examples of Test No. 3-7 in which all passes were performed at a reduction rate equal to or lower than the upper limit reduction rate, it was possible to manufacture all of them at a clearance area ratio equal to or lower than the target clearance area ratio. Test No. 4 achieved the smallest clearance area ratio. Even for Test No. 6 and 7 in which rolling was performed at a reduction rate larger than that of the previous passes in the middle of the passes, the target clearance area ratio or lower was achieved.

[0065] As described above, in this example, the clearance area ratio after completion of rolling in each pass schedule was obtained by rolling analysis by the finite element method (FEM analysis). This rolling analysis by the finite element method is a highly reliable evaluation method, and the obtained clearance area ratio is also comparable to the value obtained by actual tests. The tests actually confirmed in this regard will be described. As an actual test, a mixture of SUJ2 powder and alumina particles as inclusions was sintered at a mass ratio of 500:1 to obtain a base material test piece containing inclusions. Such a base material test piece was rolled from a thickness of 50 mm to 40 mm at a roll peripheral speed of 715 mm / s using a roll with a roll diameter of φ870 mm to obtain an observation test piece. The observation test piece was cut at the center position in the width direction, and 10 alumina particles existing within 50 mm 2 at the center of the cut surface were observed, and the clearance area ratio around the alumina particles was measured. Then, the average value (3.7%) of these clearance area ratios was calculated as the actually measured value of the clearance area ratio. On the other hand, when the rolling analysis (CAE analysis) under the same conditions was performed using the above-described observation test piece as a plate model, the calculated value of the clearance area ratio was 2.6%. Since the error of the calculated value with respect to the above actual test value (average value) was only about 1.1%, it was confirmed that the clearance area ratio can be accurately obtained by CAE analysis.

[0066] (Example 2) When the rolling conditions for obtaining the relationship information were changed from the rolling conditions when the relationship information in Fig. 3 was obtained, rolling analysis was similarly performed to obtain the relationship information. That is, the relationship information was obtained for the case of rolling with rolling rolls having roll diameters different from those in the case of the rolling analysis in Fig. 3 (roll diameter 250 mm). The roll diameters were 175 mm and 400 mm. Other rolling conditions, rolling models, software used for analysis, etc. were common to Example 1. By performing rolling analysis using rolling rolls of each diameter, the gap area ratio of the gaps formed when rolling is performed once at various reduction ratios was obtained. Then, fitting was performed on a plurality of relationships (plots) between the obtained gap area ratio and the reduction ratio to obtain the relationship information. A plurality of relationships between the gap area ratio and the reduction ratio obtained by the rolling analysis process and the obtained relationship information (mathematical formula of the approximate curve) are shown in Fig. 5. When the gap area was y and the reduction ratio was x, when the roll diameter was 175 mm, the relationship information was y = 0.36x. Also, when the roll diameter was 400 mm, the relationship information was y = 0.49x.

[0067] As shown in Fig. 5, even if the steel type and other conditions of the workpiece are the same, different relationship information is obtained when the roll diameter is different. And due to the change in the relationship information, the upper limit reduction ratio for the same target gap area ratio also changes. Therefore, by this method, the upper limit reduction ratio corresponding to the roll diameter used when performing rolling can be obtained, and the reduction ratio of each rolling pass can be set based on the upper limit reduction ratio.

Explanation of symbols

[0068] 11 Steel plate 12 Rolling roll L Non-metallic inclusions 20 Ring-shaped steel material 21 Driving roll 22 Driven roll

Claims

1. A method for manufacturing a compression processed product by performing multiple compression processes on a steel material containing non-metallic inclusions, wherein the reduction ratio for the steel material in each of the multiple compression processes is set within a range not exceeding the upper limit reduction ratio, and the upper limit reduction ratio is the reduction ratio corresponding to the target gap area ratio, which is the target value of the gap area ratio after completion of multiple compression processes of the steel material, in the relationship information obtained in advance from the relationship between the gap area ratio of the gap formed between the non-metallic inclusions and the matrix phase by compression processing of the target steel material containing non-metallic inclusions and the reduction ratio in that compression processing. A method for manufacturing a compression processed product characterized by this.

2. The method for manufacturing a compression processed product according to claim 1, wherein the compression processing is rolling or ring rolling.

3. The relationship information is relationship information obtained based on a plurality of relationships between the gap area ratio of the gap formed when the model of the target steel material is compression processed using CAE analysis and the reduction ratio, by obtaining a plurality of gap area ratios of the gap formed when the reduction ratio is changed. The method for manufacturing a compression processed product according to claim 1, characterized by this.

4. The method for manufacturing a compression processed product according to claim 3, wherein the relationship information is an approximation curve for the plurality of relationships between the gap area ratio and the reduction ratio.

5. The method for manufacturing a compression processed product according to claim 4, wherein the approximation curve is a linear function.

6. The relationship information is relationship information obtained based on the relationship between the gap area ratio and the reduction ratio of the gap formed by the first compression process performed on the target steel material. The method for manufacturing a compression processed product according to claim 1 or 3, characterized by this.

7. The method for manufacturing a compression processed product according to claim 1, wherein the gap area ratio is a value obtained by the following formula (1). Gap area ratio (%) = Gap cross-sectional area / Non-metallic inclusion cross-sectional area × 100 (1)

8. The method for manufacturing a compression processed product according to claim 7, wherein the gap cross-sectional area and the non-metallic inclusion cross-sectional area are cross-sectional areas in a cross-section passing through the non-metallic inclusions and in the thickness direction of the steel material - the cross-section in the steel material supply direction.

9. The method for manufacturing a compression processed product according to claim 1, wherein the reduction ratio is the ratio of the amount of thickness reduction in the pass of the target compression process to the initial thickness of the steel material before the compression process.

10. The method for manufacturing a compression processed product according to claim 1, characterized in that the compression processed product is processed into the shape of a rolling part after completion of the compression processing.

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