Method for manufacturing compression-processed product

Abstract

[Problem] To provide a method for manufacturing a compression-processed product in which the size of gaps formed between non-metal inclusions and a matrix included in a steel material is appropriately controlled in consideration of a deformation phenomenon occurring in the non-metal inclusions and the matrix in compression processing. [Solution] A method for manufacturing a compression-processed product in which a steel material containing non-metal inclusions is subjected to multiple iterations of compression processing, wherein the rolling reduction rate for the steel material in each of the multiple iterations of the compression processing is set to within a range not greater than an upper limit rolling reduction rate, the upper-limit rolling reduction rate corresponding to a target gap area ratio in relationship information derived in advance from the relationship between the rolling reduction rate in a compression process performed on a target steel containing non-metal inclusions and the gap area ratio of gaps formed between the non-metal inclusions and a matrix by the compression process, the target gap area ratio being the target value of the gap area ratio after completion of the plurality of compression processes performed on the steel.

Description

Manufacturing method of compressed processed products

[0001] The present invention relates to a method for producing a compressed product.

[0002] Steel inevitably contains foreign matter known as nonmetallic inclusions due to the manufacturing process. In steel products, such as bearing parts, manufactured through rolling or forging, gaps can form around nonmetallic inclusions. These gaps are thought to arise at the interface between the nonmetallic inclusions and the parent phase due to differences in deformability between the two. These gaps can promote crack initiation and serve as crack initiation sites within bearing parts that are subject to rolling fatigue during use. Specifically, the raceway surface on which the rolling elements roll during use is subjected to repeated contact loads. If these gaps exist in this affected area, they can promote crack initiation within the bearing part and serve as crack initiation sites. These cracks can reach the raceway surface, leading to spalling and subsequent failure of the bearing part. Therefore, methods for reducing the gaps around nonmetallic inclusions have been proposed to improve the lifespan of steel products, such as bearing parts.

[0003] Patent Document 1 describes a method of forging in which the forging temperature and the amount of depression of a die having an annular convex mold satisfy a predetermined relationship so that a predetermined hydrostatic stress is obtained in the forging process for producing the raceway surface of a thrust ball bearing.The method of producing the raceway surface of a thrust ball bearing in Patent Document 1 is said to be able to eliminate voids that occur around inclusions when rolling a steel bar, thereby making it possible to bring the inclusions into close contact with the base material.

[0004] Patent No. 6665737

[0005] The method of Patent Document 1 is targeted at a forging process in which a die is pressed against the steel to form rolling grooves. It only specifies conditions under which a certain level of hydrostatic stress can be applied to a steel part or a raw material during the forging process. In other words, it does not take into consideration deformation phenomena of nonmetallic inclusions and the parent phase that occur during compression processes such as rolling and ring rolling. Therefore, the method of Patent Document 1 cannot be applied to processes that involve such deformation phenomena. Furthermore, 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 gaps between the inclusions and the parent phase can be closed.

[0006] The present application aims to provide a method for manufacturing a compression-processed product that appropriately controls the size of the gap formed between the non-metallic inclusions and the parent phase, taking into consideration the deformation phenomenon of the non-metallic inclusions and the parent phase contained in the steel material during compression processing.

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

[0008] (1) A method for manufacturing a compressed product in which a steel material containing non-metallic inclusions is subjected to a plurality of compression processes, wherein a rolling reduction rate for the steel material in each of the plurality of compression processes is set within a range equal to or less than an upper limit rolling reduction rate, and the upper limit rolling reduction rate is a rolling reduction rate corresponding to a target gap area rate, which is a target value for the gap area rate after the completion of the plurality of compression processes of the steel material, in relationship information obtained in advance from the relationship between the gap area rate of gaps formed between the non-metallic inclusions and a parent phase by compression processing of the target steel material containing the non-metallic inclusions and the rolling reduction rate in the compression processing.

[0009] (2) The method for producing a compressed product according to (1) above, wherein the compression is rolling or ring rolling.

[0010] (3) The method for manufacturing a compressed product described in (1) or (2) above, characterized in that the relationship information is obtained by using CAE analysis to obtain multiple gap area ratios of gaps formed when a model of a target steel material is compressed, with the reduction ratio being changed, and based on multiple relationships between the gap area ratios and the reduction ratios.

[0011] (4) The method for producing a compressed product according to (3) above, wherein the relationship information is an approximation curve for the multiple relationships between the gap area ratio and the rolling reduction ratio.

[0012] (5) The method for producing a compressed product according to (4) above, wherein the approximation curve is a linear function.

[0013] (6) A method for manufacturing a compressed product described in any one of (1) to (5) above, characterized in that the relationship information is relationship information obtained based on the relationship between the gap area ratio of the gap formed by the compression processing first performed on the target steel material and the rolling reduction ratio.

[0014] (7) The method for producing a compressed product according to any one of (1) to (6), wherein the gap area ratio is a value calculated by the following formula [1]: Gap area ratio (%) = gap cross-sectional area / non-metallic inclusion cross-sectional area × 100 [1]

[0015] (8) The method for producing a compressed product according to (7) above, wherein the gap cross-sectional area and the non-metallic inclusion cross-sectional area are cross-sectional areas of a cross section passing through the non-metallic inclusion, the cross-sectional area being a cross section taken along a steel material thickness direction-steel material supply direction.

[0016] (9) A method for manufacturing a compressed product according to any one of (1) to (8) above, characterized in that the rolling reduction is a ratio of the amount of reduction in thickness in a target compression processing pass to the initial thickness of the steel material before the compression processing.

[0017] (10) The method for producing a compressed product according to any one of (1) to (9) above, characterized in that the compressed product is processed into the shape of a rolling part after the completion of the compression processing.

[0018] According to one aspect of the embodiment, it is possible to provide a method for manufacturing a compression-processed product in which the size of the gap formed between the non-metallic inclusions and the parent phase is appropriately controlled, taking into consideration the deformation phenomenon of the non-metallic inclusions and the parent phase contained in the steel material during compression processing.

[0019] Fig. 1 is a schematic diagram showing a cross section of a steel material including non-metallic inclusions and surrounding gaps. Fig. 2 is a schematic diagram showing rolling processing. Fig. 3 is a graph showing an example of an approximation curve for the relationship (plot) between the gap area ratio and the reduction ratio obtained by rolling analysis processing. Fig. 4 is a schematic diagram of a ring rolling mill that performs ring rolling. Fig. 5 is a graph showing the relationship between the gap area ratio and the reduction ratio obtained by rolling analysis processing and the approximation curve that is the obtained relationship information when the roll diameter is different.

[0020] Hereinafter, an embodiment of a method for manufacturing a compressed product will be described. The method for manufacturing a compressed product of the embodiment is a method for manufacturing a compressed product that can control gaps (voids) between non-metallic inclusions contained in a steel material and the surrounding matrix to a predetermined size range (a target gap area ratio or less). More specifically, when compressing a steel material to a desired thickness or size by multiple compression treatments, the method performs compression treatment by setting a reduction rate in each compression treatment so that the gaps can be controlled to a predetermined size range.

[0021] The compression process includes, for example, rolling and ring rolling. In this embodiment, the case where rolling is performed will be described as an example.

[0022] The compression-processed product manufactured by the manufacturing method of this embodiment can be used to manufacture rolling parts with reduced cracking and an excellent rolling life, such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, crank pins, and piston pins.

[0023] The method for manufacturing a compressed product according to this embodiment includes a step of deriving related information and a processing step. The step of deriving related information is a step of determining related information from the relationship between a gap area ratio, which indicates the size of gaps formed around non-metallic inclusions by rolling, and the reduction ratio in the rolling process. The processing step is a step of determining an upper limit reduction ratio corresponding to a target gap area ratio based on the derived related information, and performing multiple rolling processes (compression processes) at reduction ratios equal to or less than the upper limit reduction ratio to manufacture a compressed product with the desired reduction ratio. Each step will be described in detail below.

[0024] (Relationship information derivation step) The relationship information derivation step is a step of determining in advance, before actual rolling, relationship information between the reduction rate and the gap area ratio for a target steel material. The relationship information is determined from the relationship between the reduction rate and the gap area ratio of gaps formed by initially performing rolling on a steel material before rolling, i.e., a steel material in a state in which gaps have not yet been formed between non-metallic inclusions and the matrix.

[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 nonmetallic inclusions and surrounding gaps. The X axis is the rolling (steel material movement) direction, and the Z axis is the thickness direction (rolling reduction direction) of the steel material. Nonmetallic inclusions L are present in the matrix of the steel material, and gaps (hatched areas) exist between the nonmetallic inclusions and the matrix. The size and shape of the gaps in FIG. 1 are merely examples and are not limited to these. In the rolling process, deformation occurs in the steel material when it passes through rolls. More specifically, the gaps are formed during the rolling process due to the difference in deformability between the matrix and the nonmetallic inclusions.

[0026] In this embodiment, the gap area ratio is a value calculated 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 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 are cross-sections passing through the non-metallic inclusions in the steel material, and can be cross-sectional areas in a thickness direction-rolling direction (steel material feed direction) cross-section of the steel material. Furthermore, when the gap area ratio is calculated by rolling analysis using a computer as described below, the calculation can be performed assuming that the shape of the non-metallic inclusion is spherical. Specifically, the gap cross-sectional area and the non-metallic inclusion cross-sectional area can be calculated in a thickness direction-rolling direction (steel material feed direction) cross-section passing through the center of the spherical non-metallic inclusion. Note that the X-Z cross-section in FIG. 1 is a thickness direction-rolling direction (steel material feed direction) cross-section.

[0027] By performing rolling processing on a steel material at a certain reduction ratio and determining the gap cross-sectional area and non-metallic inclusion cross-sectional area of ​​the steel material after the rolling processing, it is possible to determine the gap area ratio formed at that rolling reduction ratio. Then, by determining the gap area ratio of the gaps formed in the rolling processing at various reduction ratios, it is possible to obtain relevant information.

[0028] The related information can be obtained by using a rolling analysis with a computer. Alternatively, the related information may be obtained by performing a rolling test on an actual steel test piece. In this embodiment, a case where the related information is obtained by using a rolling analysis with a computer will be described.

[0029] The rolling analysis for obtaining the relevant information can be performed using a rolling analysis model that conforms to the known rigid-plastic / elasto-plastic finite element method (FEM). CAE (Computer Aided Engineering) analysis can be used for the rolling analysis. CAE analysis is an analytical method that evaluates (simulates) design problems of a product that is artificially reproduced on a computer. CAE analysis can accurately determine the gap area ratio. CAE analysis is realized by a computer program.

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

[0031] 2 is a schematic diagram of rolling processing to explain a rolling analysis method, in which the X axis corresponds to the rolling direction (stretching direction) of a steel plate (plate model) 11, and the Z axis corresponds to the plate 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 behavior of gap generation around a non-metallic inclusion L when the steel plate 11 is rolled using a pair of upper and lower mill rolls 12.

[0032] Typical parameters to be given to the rolling analysis model include the type of steel, plate thickness, hot or cold conditions (temperature, etc.), type, location and size of nonmetallic inclusions, reduction ratio in rolling treatment, number of times of rolling treatment, physical property data of the material (Young's modulus, Poisson's ratio, stress-strain curve, etc.), roll diameter of rolling rolls, etc. These parameters can be ascertained by analyzing in advance the properties of the steel material used in rolling parts such as bearings.

[0033] The conditions for nonmetallic inclusions set in the rolling analysis model can be conditions that could become the starting point of cracks if nonmetallic inclusions are present in a part or product. Regarding the type of nonmetallic inclusions, the steel material to be rolled is analyzed to identify the type of nonmetallic inclusions contained, and that type of inclusion can be set in the model. Although not limited thereto, nonmetallic inclusions are usually sufficiently hard compared to the parent phase material and can be considered not to deform, so they can be set in the model as rigid bodies.

[0034] Regarding the size of inclusions, the cross section of the steel material in question can be observed under a microscope to check for any nonmetallic inclusions that may be present, and the size of the inclusions to be set for the model can be determined based on that size.

[0035] Regarding the location of the inclusions, the possible locations of the inclusions can be confirmed from the above-mentioned cross-sectional observation, and the location of the inclusions to be set in the model can be determined based on the location. However, for example, when polishing or cutting is performed after rolling to manufacture final parts or products, it is preferable to set the inclusions at a location inside the steel material rather than at a location that will become the surface of the final part or product. This is because it is necessary to control the size of the gap for inclusions located inside the surface of the final part or product. In other words, inclusions located at a location that will be removed by polishing or the like will not cause cracks in the part or product.

[0036] Although not limited thereto, the size of the inclusions can be set to a range of 100 μm or less, for example, and although not limited thereto, the position of the inclusions can be set to a range of 1 mm or less inward in the thickness direction of the steel sheet from the position that will become the surface of the final rolling component or the like.

[0037] The reduction rate is the degree of rolling expressed as a percentage. The reduction rate is R (%), and the thickness of the material before rolling (plate thickness) is h. １ , the thickness of the material after the rolling pass is ２ Then, it can be calculated by the following formula (2): R = (h １ -h ２ ) / h １ ×100 (2)

[0038] However, in this embodiment, the reduction ratio is the ratio of the reduction in thickness in the target pass to the initial thickness of the steel material before rolling. That is, the reduction ratio in this embodiment is reduction ratio R (%) = reduction in thickness in the target pass / initial thickness before rolling × 100. Therefore, for the second and subsequent passes of the multiple rolling passes set based on the relationship information described below, the reduction ratio is calculated based on the initial thickness before rolling. For example, a case will be described in which a steel plate with an initial thickness of 10 mm is rolled at a total reduction ratio of 20%. When rolling is performed four times at a reduction ratio of 5% to achieve a total of 20%, the reduction in thickness in each pass is 10 mm × 5% = 0.5 mm, based on the initial thickness. In this case, the final thickness after the completion of the four rolling passes is 8 mm (= 10 - 0.5 × 4).

[0039] In the rolling analysis described above, necessary specifications are set, and a process of performing a single rolling process on a target steel material is simulated. From the rolling analysis results, the gap cross-sectional area and the nonmetallic inclusion cross-sectional area can be calculated for gaps formed around the nonmetallic inclusions set as the analysis target. From these cross-sectional areas, the gap area ratio formed in the rolling process at a given reduction ratio can be calculated. By performing rolling analysis with variously changed reduction ratios, the gap area ratios corresponding to a plurality of reduction ratios can be calculated.

[0040] In the method of the present embodiment, the relevant information is derived based on a rolling analysis of the first rolling process of the steel material, and the relevant information can be used to set the reduction ratios of the first to nth rolling processes (n is an integer of 2 or more) so that the gap area ratio after all rolling processes are completed is appropriately controlled.

[0041] Next, the relationship information can be an approximate curve (mathematical formula) obtained by performing fitting (curve fitting) on ​​the relationships between the obtained gap area ratios and the reduction ratios. FIG. 3 is a graph showing an approximate curve obtained for the relationship (plot) between the gap area ratio and the 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 a linear function y = 0.61x. Furthermore, the example of FIG. 3 is an example in which the gap area ratios of gaps formed when the steel material is initially reduced at reduction ratios of approximately 2%, approximately 5%, approximately 10%, approximately 20%, and approximately 40% as the first rolling process are obtained. Note that details of the rolling conditions used to obtain the relationship between the gap area ratio and the reduction ratio in FIG. 3 will be described in the examples.

[0042] The approximation curve, which is the relational information, is not limited to a linear function, but can be determined by fitting a function that best fits, such as an n-th order function (n is an integer of 2 or more) or a logarithmic function.

[0043] Furthermore, if a sufficiently accurate approximate curve cannot be obtained, the approximate curve can be determined again by changing the reduction ratio and performing further rolling analysis to increase the number of analysis processes and the number of plots. This completes the step of deriving the relevant information. It is preferable that the specifications of the rolling model are the same as the various conditions when actually performing rolling according to a pass schedule (reduction ratio for multiple rolling passes) determined using the derived relevant information.

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

[0045] The reduction ratio for each pass is determined based on a target gap area ratio. The target gap area ratio is a target value for the size of the gap formed after all of the multiple rolling processes (compression processes) are completed. More specifically, if the gap area ratio is controlled to be equal to or less than the target gap area ratio, the occurrence of cracks caused by the gap can be suppressed. The target gap area ratio can be set appropriately depending on the steel material used, the product to be manufactured, the type of part, etc. For example, in the case of rolling parts, a value of 8 to 9% or less is generally recommended based on past experience, etc.

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

[0047] Then, the reduction ratios of the first to nth rolling processes (passes) to be actually performed are determined within a range equal to or less than the upper limit reduction ratio. For example, if the target gap area ratio is set to 8%, the corresponding reduction ratio is approximately 13% in the example of the relationship information in FIG. 3. Therefore, the upper limit reduction ratio can be set to 13%. In this case, the reduction ratios of each rolling process can be determined with an 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 rolling may exceed the target gap area ratio. In this case, it is not possible to appropriately control the size of the gap formed by rolling.

[0048] The reduction rate for each pass can be set by dividing the desired total reduction rate. Furthermore, the reduction rate for each pass may be set to a reduction rate equal to or less than the upper limit reduction rate. For example, if a rolling process with a total reduction rate of 20% is desired, four rolling processes with a reduction rate of 5% may be performed, or one rolling process with a reduction rate of 10% and two rolling processes with a reduction rate of 5% may be performed. The reduction rate for each pass may be the same as, greater than, or smaller than the reduction rate of any of the passes up to that pass. The reduction rate may be sequentially decreased or increased in multiple rolling processes. Furthermore, the fewer the number of rolling processes, the better the production efficiency, but there is no particular limitation.

[0049] In addition, from the viewpoint of further reducing the gap, it is preferable to set the reduction rate per pass as small as possible. This is because, when the reduction rate in rolling is small, deformation is limited to the surface of the steel material. However, since the elongation deformation in the rolling direction is constrained to the undeformed portion inside the steel material, compressive stress in the elongation direction is more likely to be effective on the surface side of the steel material. Therefore, the larger the reduction rate, the greater the difference in compressive stress acting between the surface side of the steel material and the interior side of the steel material, making it more likely that gaps will be formed. Therefore, when focusing on the surface layer of the steel material, a smaller reduction rate is more effective in suppressing gaps. Specifically, for example, it is desirable to set the reduction rate to 40% or less of the determined upper limit reduction rate.

[0050] In the method of this embodiment, an upper limit reduction rate corresponding to the target gap area ratio is determined based on the relationship information obtained from the first rolling process of the target steel material. Then, the reduction rate for each rolling process can be set to be equal to or lower than the upper limit reduction rate. By performing rolling processing at the set reduction rate, the gap area ratio can be made equal to or lower than the target gap area ratio. In other words, the gap area ratio can be controlled within an appropriate range.

[0051] Here, in the second and subsequent passes of a target steel material, the matrix and inclusions deform while gaps are formed around the nonmetallic inclusions. Furthermore, the inventor's research has revealed that the behavior of the gap area ratio reduction differs for each rolling pass. Therefore, when performing multiple rolling passes to achieve a desired total reduction, it is difficult to predict the behavior of the gap reduction. However, the method of this embodiment makes it possible to appropriately set the reduction ratio for each pass based on the relationship information obtained from the first rolling process. In other words, it is possible to set the reduction ratio for each pass that achieves an appropriate gap area ratio, even without performing prior rolling analysis for, for example, the second or third pass. Therefore, the method of this embodiment has the excellent effect of efficiently designing an appropriate pass schedule.

[0052] According to the method for manufacturing a compressed product of the present embodiment, a compressed product can be manufactured with an appropriate gap area ratio. By determining the relevant information based on a rolling analysis that takes into account the deformation phenomenon of non-metallic inclusions and gaps, and setting the reduction ratio for each pass, it is possible to perform rolling with the gap size appropriately controlled during the rolling process.

[0053] According to the method of this embodiment, a compression-processed product having excellent durability and suppressed crack generation can be manufactured. Therefore, by processing the compression-processed product manufactured by the method of this embodiment into the shape of a rolling part after the completion of the compression (rolling) process, it is possible to manufacture rolling parts and products having excellent life spans and suppressed crack generation.

[0054] As described above, the gap area ratio calculated by rolling analysis is a calculated value obtained by simulation, and therefore may deviate from the actual measured value by approximately 1 to 2%. Since the deviation is small, it can be ignored, but the reduction ratio for multiple rolling processes may be determined taking the deviation amount into consideration. For example, when determining the upper limit reduction ratio, the upper limit reduction ratio may be set to a reduction ratio corresponding to a gap area ratio that is approximately 1 to 2% lower than the target gap area ratio, and the reduction ratio for each pass may be set based on that upper limit reduction ratio. Furthermore, while the method of this embodiment can be used when compressing bearing steel such as SUJ2, the steel material to be processed is not limited to this, and the method can be used for compressing various types of steel material.

[0055] (Other Embodiments) In the above-described embodiment, a case where a rolling process is performed on a steel plate as compression processing has been described, but another embodiment where ring rolling is performed 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 that uses multiple rolls to increase the diameter of a ring-shaped steel material while reducing its wall thickness, thereby obtaining a ring component of desired dimensions. Similar to rolling processing, ring rolling is a processing method that compresses steel material in that the wall thickness decreases as the ring passes between the rolls.

[0056] The ring rolling mill in Figure 4 has a drive roll (main roll) 21 and a driven roll (mandrel) 22. The drive roll 21 rotates when a rotational force is applied from a drive source (not shown). A ring-shaped steel material 20 is held between the drive 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] For this ring rolling, a computer simulation is performed in the same way as for rolling to obtain information on the relationship between the reduction rate and the gap area ratio. Then, based on the relationship information, a reduction rate equal to or lower than the upper limit reduction rate corresponding to the target gap area ratio can be set and multiple runs of processing can be performed. Note that, when used in a rolling part or product, nonmetallic inclusions can be set on the surface that will become the rolling surface of the ring-shaped steel material 20 (the surface where the gap around the inclusions needs to be controlled), and rolling analysis can be performed to obtain the relationship information.

[0058] In the case of ring rolling, one rotation of the ring-shaped steel material is considered to be one compression process (one pass). By setting the reduction rate between the rolls for each rotation using this method and performing compression processes multiple times at that reduction rate, a ring-shaped steel material with a desired total reduction rate can be obtained. The reduction rate for each rotation can be set to an appropriate value by controlling the rotation speed of the drive roll 21 and the movement speed of the driven roll 22 in the diameter expansion direction.

[0059] Even in the case of ring rolling, the method of the embodiment can produce a compressed product in which the gap between the nonmetallic inclusions and the matrix is ​​controlled to an appropriate size. Therefore, by using the compressed product produced by this method, parts and products such as rolling parts with excellent fatigue life can be produced.

[0060] (Example 1) A more specific explanation will be given with an example. Using the relationship information shown in FIG. 3, rolling tests were set up with multiple runs of various reduction ratios. Then, rolling processing using the set reduction ratios was simulated using CAE software, and rolling analysis (CAE analysis) was performed. DEFORM (manufactured by Scientific Forming Technologies Corporation) was used as the CAE software. A plate rolling model was used, in which a 1 mm diameter inclusion was located 1 mm from the surface of a 50 mm thick steel material. The rolling temperature was set to 1000°C. The diameter of the rolling roll was set to 250 mm. Other parameters given to the model were the contact condition (shear friction coefficient) of the non-metallic inclusion L and the parent phase: 0.3, Young's modulus of the plate: 206 GPa, Poisson's ratio of the plate: 0.3, The inclusions and the parent phase were in close contact (no gap), the roll peripheral speed was 12.6 rad / s, and the shear friction coefficient between the rolling roll and the plate model was 0.7. The steel type of the steel used in the plate rolling model was SUJ2, and the inclusions were Al. ２ O ３ The target gap area ratio was set to 8%, and the corresponding upper limit reduction ratio was set to 13% based on the relationship information in Figure 3. The rolling analysis performed when the relationship information shown in Figure 3 was obtained was also performed using the same software, the same rolling conditions, and the same rolling model.

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

[0062]

[0063] In the test examples of Test Nos. 1 and 2, which included passes exceeding the upper limit of the rolling reduction rate of 13%, the gap area ratio after completion of rolling exceeded the target gap area ratio of 8%.

[0064] On the other hand, in the test examples of Test Nos. 3 to 7, in which all passes were performed at a reduction rate equal to or less than the upper limit, all of the test examples were able to produce products with a gap area ratio equal to or less than the target gap area ratio. Test No. 4 achieved the smallest gap area ratio. Test Nos. 6 and 7, in which rolling treatment was performed in intermediate passes at a reduction rate greater than that of the previous passes, also achieved a gap area ratio equal to or less than the target gap area ratio.

[0065] As described above, in this example, the gap area ratio after completion of rolling processing in each pass schedule was determined by rolling analysis using the finite element method (FEM analysis). This rolling analysis using the finite element method is a sufficiently reliable evaluation method, and the obtained gap area ratio is comparable to the value obtained by actual testing. A test that actually confirmed this point will be described. As an actual test, a mixture of SUJ2 powder and alumina particles as inclusions in a mass ratio of 500:1 was sintered to obtain a base material test piece containing inclusions. This base material test piece was rolled from 50 mm to 40 mm in thickness using a roll with a roll diameter of φ870 mm at a roll peripheral speed of 715 mm / s to obtain a test piece for observation. The test piece for observation was cut at the center position in the width direction, and a cut was made at the center 50 mm of the cut surface. ２ Ten alumina particles present within the specimen were observed, and the gap area ratios around the alumina particles were measured. The average value of these gap area ratios (3.7%) was then calculated as the actual gap area ratio. In contrast, a rolling analysis (CAE analysis) was performed under the same conditions using the above-mentioned observation test piece as a plate model, resulting in a calculated gap area ratio of 2.6%. The error in the calculated value relative to the above actual test value (average value) was only about 1.1%, confirming that the gap area ratio can be accurately determined by CAE analysis.

[0066] Example 2: The rolling analysis was similarly performed to obtain the relevant information when the rolling conditions used to obtain the relevant information were changed from those used to obtain the relevant information in Figure 3. That is, the relevant information was obtained when rolling was performed using a mill roll with a different roll diameter than that used in the rolling analysis in Figure 3 (roll diameter 250 mm). The mill roll diameters were 175 mm and 400 mm. Other rolling conditions, rolling models, and software used for the analysis were the same as those in Example 1. By rolling analysis using mill rolls of each diameter, the gap area ratio of gaps formed when rolling was performed once at various reductions was obtained. Then, fitting was performed on multiple relationships (plots) between the obtained gap area ratio and the reduction ratio to obtain the relevant information. The multiple relationships between the gap area ratio and the reduction ratio obtained by the rolling analysis process and the obtained relevant information (formula for the approximate curve) are shown in Figure 5. When the gap area is y and the reduction ratio is x, the relevant information was y = 0.36x when the mill roll diameter was 175 mm. When the rolling roll diameter was 400 mm, the related information was y=0.49x.

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

[0068] 11 Steel plate 12 Rolling roll L Non-metallic inclusion 20 Ring-shaped steel material 21 Driving roll 22 Follower 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 each steel material in the multiple compression processes is set within a range not exceeding an upper limit reduction ratio, and the upper limit reduction ratio is determined from relationship information obtained in advance based on the relationship between the gap area ratio of the gap formed between the non-metallic inclusions and the matrix phase by compression processing on the target steel material containing non-metallic inclusions, and the reduction ratio in that compression processing, and is the reduction ratio corresponding to a target gap area ratio which is the target value of the gap area ratio after completion of multiple compression processes of the steel material. A method for manufacturing a compression processed product, characterized by this.

2. The method for manufacturing a compression processed product according to claim 1, characterized in that 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 gaps formed when the model of the target steel material is compression processed using CAE analysis, by obtaining a plurality of gap area ratios while changing the reduction ratio. The method for manufacturing a compression processed product according to claim 1 or 2, characterized by this.

4. The method for manufacturing a compression processed product according to claim 3, characterized in that the relationship information is an approximate 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, characterized in that the approximate 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 gaps formed by the first compression process performed on the target steel material. The method for manufacturing a compression processed product according to any one of claims 1 to 5, characterized by this.

7. The method for manufacturing a compression processed product according to any one of claims 1 to 6, 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) 8. The method for manufacturing a compression processed product according to claim 7, characterized in that 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 cross-section in the thickness direction - steel material supply direction of the steel material.

9. The method for manufacturing a compression processed product according to any one of claims 1 to 8, 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.

10. The method for manufacturing a compression processed product according to any one of claims 1 to 9, 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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