JP5561601B2 - Steel cutting method - Google Patents

Description

  The present invention relates to a steel cutting method that is optimal for steel cutting used in products such as molds.

  Conventionally, for various cutting tool steels for cutting steel, for example, 3 mass% V-based high-speed tool steel has been proposed, which is improved in strength and wear resistance by enriching hard V carbide. (See Patent Documents 1 and 2). In steel cutting, wet machining using cutting fluid (cutting oil) for cooling and lubrication is performed to ensure the durability of the cutting tool. From the viewpoint of environmental conservation in recent years, The dry processing without using cutting fluid is progressing. Furthermore, in order to shorten the processing time, high-speed cutting with an increased cutting speed is required.

Japanese Patent Laid-Open No. 01-142056 JP 2003-313642 A

  However, in high-speed cutting in which the temperature of the tool work surface rises, if dry machining that places a heavy load on the cutting tool is applied thereto, the wear of the cutting tool is significant. Therefore, even in the cutting tool according to Patent Documents 1 and 2 excellent in strength and wear resistance, the cutting environment at the time of high-speed cutting is generally wet. Therefore, in order to perform high-speed cutting by dry machining, methods for applying various coatings to the tool work surface have been proposed, but even in this case, there is a concern about peeling of the coating, and there is still a problem in improving the tool life. It was.

  An object of the present invention is a steel cutting method that enables high-speed cutting by dry processing without applying a coating process to the work surface of the cutting tool according to Patent Documents 1 and 2 having excellent mechanical characteristics. Is to provide.

  In the cutting tool of Patent Documents 1 and 2, the present inventor does not coat the work surface, so that the V carbide distributed on the work surface is changed to a low melting point oxide during dry cutting. The phenomenon of leaching between steels to be cut was grasped. Moreover, it has been found that the eluate exhibits the same effect as the above-described cutting fluid and can suppress wear of the cutting tool. And in order to express the above oxidation and elution phenomenon, it discovered that there existed a required relationship between the distribution situation of this V carbide | carbonized_material, and cutting conditions, and came to this invention by identifying it.

  That is, according to the present invention, the work surface has a component composition of mass%, C: 1.0 to 1.6%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Cr: 3.0 to 5.0%, one or two of W and Mo (2Mo + W): 15 to 20%, V: 2.0 to 5.0%, the balance being Fe and inevitable impurities, cross section The average length of the MC type carbide in the structure is 0.5 to 1.5 μm, the area ratio of the MC type carbide having a long diameter of less than 2.0 to 5.0 μm in the cross-sectional structure is 1.5% or more, and The steel to be cut is dry-cut at a cutting speed of 90 m / min or more with a cutting tool in which the area ratio of MC type carbide having a major axis of 5.0 μm or more is less than 0 to 1.2% and the hardness is 63 to 70 HRC. This is a steel cutting method. Preferably, the working surface of the cutting tool has an average major axis of MC type carbide in the cross-sectional structure of 0.9 to 1.2 μm, or, further, its component composition is Al: 0.2% or less and / or rare earth One type or two or more types of elements are included in total: 0.2% or less. The rare earth element is preferably Ce. Alternatively, the working surface of the cutting tool has a component composition containing Co: 10% or less.

  According to the present invention, the amount of cutting fluid used can be reduced, and it is possible to suppress wear on the work surface of the cutting tool during high-speed cutting even in dry machining that does not use the cutting fluid itself. Therefore, it is an effective technique that can respond to both sides of shortening the cutting time and environmental conservation.

Example No. It is the optical micrograph of the cross-sectional structure | tissue which 1 work surface has, and its image analysis figure.

  The feature of the present invention is that, when a cutting tool made of 3 mass% V-based high-speed tool steel having excellent strength and wear resistance is used, V carbide is optimally used without coating the work surface. By controlling to a distributed state, the lubrication effect can be obtained because of high-speed cutting and a dry environment. Hereinafter, each component requirement will be described.

(1) As for the cutting tool, the component composition of the work surface is mass%, C: 1.0-1.6%, Si: 0.1-1.0%, Mn: 0.1-1.0%, Cr: 3.0 to 5.0%, one or two of W and Mo (2Mo + W): 15 to 20%, V: 2.0 to 5.0%, the balance being Fe and inevitable impurities .

That is, the cutting tool of the present invention in which the work surface (blade edge) is not coated can be made of high-speed tool steel having the same component composition as the work surface.
C combines with Cr, W, Mo, and V to generate carbides, imparts quenching and tempering hardness, and contributes to improvement in wear resistance, heat resistance, and seizure resistance. If the amount is too large, the toughness is reduced and a huge carbide is formed. Therefore, considering the balance with Cr, W, Mo, V described later, 1.0 to 1.6% by mass (hereinafter simply referred to as%) ). Preferably it is 1.1 to 1.5%.

  Si and Mn are added in an amount of 0.1 to 1.0% for the purpose of deoxidation in the melting step. Preferably it is 0.2 to 0.6%.

  Cr improves hardenability, abrasion resistance, oxidation resistance, high temperature strength, and temper softening resistance by setting an appropriate content. However, if the amount is too large, the high temperature strength and temper softening resistance are lowered, so the content is made 3.0 to 5.0%. Preferably, it is 3.8 to 4.5%.

W and Mo combine with C to form a special carbide of M ₆ C type and contribute to improvement of wear resistance and seizure resistance. Moreover, the secondary hardening action by tempering is large, which contributes to high temperature strength. However, if too much, toughness and hot workability are impaired. Therefore, those 1 type or 2 types are made into 2-20% by (2Mo + W). Preferably, it is 16.5 to 19.5%.

  V combines with C to form hard V carbide and improves the wear resistance of the work surface. And in order to achieve the lubricating effect of this invention, it is the most important element which forms V carbide | carbonized_material which satisfy | filled the below-mentioned distribution form. However, if the amount of V carbide is too large, the hot workability is significantly reduced. Therefore, V of the present invention is set to 2.0 to 5.0%. Preferably, it is 2.5 to 4.6%.

In addition, the above-mentioned cutting tool can add the following elements as a component composition of the work surface.
Al is an optional additive element that has an effect of increasing the absolute amount of V carbides and crystallizing them finely. However, if added in a large amount, oxygen in the steel and non-metallic inclusions are formed and the toughness is deteriorated. Therefore, even when added, the content is made 0.2% or less. Preferably it is 0.02% or more, More preferably, it is 0.1% or more.

  The rare earth element is an optional additive element that has the effect of increasing the absolute amount of V carbides and finely crystallizing them like Al. These effects are further enhanced by the combined addition with Al. However, when it is too much, it combines with S (sulfur) and oxygen in the steel to form inclusions, which causes casting defects. Therefore, even when rare earth elements are added, the total of one or more of them is 0.2% or less. Preferably they are 0.02% or more and / or 0.05% or less. Among rare earth elements, Ce is preferable because it is difficult to oxidize during handling and the above effects can be easily obtained.

  Co is an optional additive element that strengthens the base of the steel material to increase the tempering hardness and improve the heat resistance. When added in a large amount, the toughness decreases, so even when added, the content is made 10% or less. Preferably it is 4.0% or more. It is more desirable that it is 4.5% or more and / or 5.5% or less.

(2) In the cutting tool, the MC type carbide in the cross-sectional structure of the work surface has an average major axis of 0.5 to 1.5 μm, and the MC has a major axis of less than 2.0 to 5.0 μm in the sectional structure. The area ratio of the MC type carbide having the area ratio of the type carbide of 1.5% or more and the major axis of 5.0 μm or more is 0 to less than 1.2%.
As described above, the lubricating effect of the present invention can be obtained by the oxidation and elution behavior of V carbide distributed on the work surface without coating. That is, the V carbide distributed on the working surface of the cutting tool changes to V oxide due to a temperature rise during cutting and melts to act as a lubricant. What is important in this case is the distribution adjustment of V carbides existing in the base of the work surface.

  The above-mentioned lubrication effect is improved by adjusting the particle size of the V carbide in the base, which is responsible for the wear resistance of the work surface, to an optimum size. If the V carbide is too small, the amount of V oxide that plays the direct role of the lubricant is reduced, making it difficult to obtain a sufficient lubricating effect. However, on the other hand, if the V carbide becomes too coarse, not only the toughness of the material itself that constitutes the cutting tool is impaired, but also the tempering hardness and the grindability for machining into the tool shape are reduced, and cutting is performed. Cannot be established as a tool. Therefore, as a result of studying the particle size of V carbide that can maximize the lubrication effect of the present invention while maintaining the mechanical characteristics as these materials, it has been found that there is an optimum narrow range for both of them. It was.

And in the structure observation of the steel of the present invention described above, this V carbide can be distinguished and specified as MC type carbide different from other carbides such as M ₆ C type mainly composed of Mo and W. it can. Therefore, in the present invention, it was possible to specify a particle size effective for the action effect of V carbide with the MC type carbide observed in the cross-sectional structure. That is, the MC type carbide in the cross-sectional structure has an average major axis of 0.5 to 1.5 μm. When the particle size is less than 0.5 μm, the lubricating effect of the present invention is insufficient. And when it exceeds 1.5 micrometers, the process to a cutting tool will become difficult. The average of the major axis is 0.8 μm or more and / or 1.3 μm or less. More preferably, it is 0.9 μm or more and / or 1.2 μm or less.

  Furthermore, among MC type carbides, it is a large carbide that contributes to the lubricating effect of the present invention. Therefore, in the case of the present invention, in the above, after adjusting the particle size distribution of the MC type carbide as a whole, it is important to manage the distribution state separately for a larger MC type carbide. is there. That is, the area ratio of the MC type carbide having a major axis of less than 2.0 to 5.0 μm in the cross-sectional structure is 1.5% or more. When this area ratio is less than 1.5%, the lubricating effect of the present invention is insufficient. However, since the coarse MC-type carbide deteriorates the workability to the cutting tool, the area ratio of the MC-type carbide having a major axis of 5.0 μm or more in the cross-sectional structure is restricted to 1.2% or less. And also about MC type carbide | carbonized_material whose major axis is 2.0-5.0 micrometers, it is desirable that the upper limit of the area ratio shall be 3.5% or less.

(3) The cutting tool has a work surface hardness of 63 to 70 HRC.
If the hardness is too low, the wear of the work surface becomes significant. However, if the hardness is too high, the toughness is lowered, causing breakage. Therefore, the working surface of the cutting tool has a hardness of 63 to 70 HRC.

(4) The cutting speed when cutting the steel to be cut is 90 m / min or higher.
V oxides that act on the lubrication mechanism of the present invention are produced from V carbides and melt due to the temperature rise of the work surface during cutting. If the cutting speed is too slow, the temperature of the work surface does not rise sufficiently, and oxidation of V carbide is unlikely to occur. Therefore, the cutting speed is 90 m / min or more. Preferably, it is 150 m / min or more. The cutting speed at this time is the speed of the work surface (blade edge). And in each cutting tool, such as turning, turning, and a drilling tool, it is the speed of the outermost or outer peripheral blade part.

(5) The cutting environment when cutting the steel to be cut is dry processing that does not use a cutting fluid.
In order to produce the V oxide, oxygen for oxidizing V carbide distributed on the work surface is required. Therefore, in the present invention, the oxygen is supplied from the air by performing dry processing using the atmosphere during the cutting as air. In the case of wet machining using a cutting fluid, the work surface is cut off from the atmospheric environment and a sufficient amount of oxygen is difficult to be supplied.

  As described above, the lubrication mechanism by adjusting the V carbide of the present invention is manifested in a combined environment of dry machining with a cutting tool that does not perform coating, unlike conventional wet machining and coating. .

  In carrying out the cutting methods of the present invention and the comparative example, a sample for evaluating the wear state generated in the cutting tool was prepared using a high-speed tool steel material having the component composition shown in Table 1. First, a 10 kg steel ingot with components adjusted in a vacuum melting furnace was melted. And No. 1 in Table 1 No. 2 steel ingot at 1210 ° C. No. 3 and 6 steel ingots at 1220 ° C. and no. The steel ingot of No. 5 was subjected to homogenization heat treatment at 1170 ° C. Next, these steel ingots were hot forged at 1150 ° C. to obtain steel materials of 25 mm thickness × 25 mm width, annealed at 870 ° C., and then processed into a shape of 10 mm thickness × 20 mm width × 65 mm length. Then, a quenching process by gas cooling from 1190 ° C. was performed, and a tempering process held at 560 ° C. for 1 hour was performed twice to obtain a sample for a wear test described later. Table 1 shows the hardness of the test surface (working surface) of the sample, the average major axis of the MC-type carbide in the cross-sectional structure, and the major axis in the cross-sectional structure of less than 2.0 to 5.0 μm and 5.0 μm or more. The area ratio of MC type carbide is described.

The average major axis of the MC type carbide and the area ratio were measured as follows. First, the test surface was corroded with 10% nital etchant. Next, this corroded surface is observed with an optical microscope with a magnification of 2000 times, and the major axis of each MC type carbide (white particles in FIG. 1) observed in the measurement visual field 5600 μm ² (70 μm × 80 μm) is obtained by image analysis. It was. In the image analysis, MC type carbide having a major axis of 0.15 μm or more was used as an extraction target. Then, this operation was repeated for 7 fields of view, and the average value of these major diameters was obtained. The area ratio of the MC type carbide was expressed as a percentage by dividing the total of individual areas of the target long diameter MC type carbide by the total measurement area of 39200 μm ² (5600 μm ² × 7 fields of view). FIG. 1 is an optical micrograph of a cross-sectional structure of 1 and an image analysis diagram in which the contrast is enhanced.

  In addition to the sample for wear test, a sample for evaluating toughness and grindability was also produced. The toughness evaluation sample is a bending test piece obtained by performing the same quenching and tempering on a 5 mm diameter × 65 mm length steel piece processed from the steel material after the annealing treatment. The evaluation sample of grindability is a test piece of 2 mm thickness × 18 mm width × 50 mm length cut out from the steel material after the above tempering treatment.

  For evaluation of the wear state, an Ogoshi type wear test was conducted. The test conditions were as follows: counterpart material: SCM415, friction distance: 400 m, final load: 6.8 kg, friction speed (corresponding to cutting speed): 118 m / min and 172 m / min, corresponding to actual dry machining. After the test, the width of the wear scar remaining on the test surface was measured to calculate the wear amount.

  The toughness was evaluated by a bending test. The test conditions were a three-point bending test at a load indentation speed of 1 mm / min and a span (test piece support interval): 50 mm, the indentation load at the time of the test piece breakage was measured, and the bending strength was calculated.

  A surface grinder was used for evaluation of grindability. The grinding conditions were as follows: whetstone: 80KV75 manufactured by Noritake Co., Ltd., whetstone speed: 1820 m / min, cutting depth: 5 μm / pass, and number of passes: 10 times. Then, after grinding, the soft material (SKD61 equivalent steel) is ground with the grindstone, and the wear amount of the grindstone transferred to the soft material is measured. ]) (That is, the higher the numerical value, the better the grindability). The above test results are summarized in Table 2.

  Table 2 shows that the MC type carbide on the work surface was optimally adjusted. Nos. 1 to 4 are comparative examples No. 1 having a small amount of MC type carbide having a major axis of less than 2.0 to 5.0 μm in a dry environment with a high friction speed. The amount of wear is kept lower than 5. Comparative Example No. with a large amount of coarse MC type carbide having a major axis of 5.0 μm or more. No. 6 has a low grinding ratio, although the amount of wear is kept low. It is inferior to grindability than 1-4.

  At the same time as the Ogoshi-type wear test, a cutting tool for evaluating the actual cutting situation was also produced from the high-speed tool steel material shown in Table 1. That is, from the steel material after the annealing treatment, it was processed into a chip shape. In this process, in order to exclude the influence of the decarburized layer of the steel material, the inside of the steel material surface was set to be 2 mm or more from the work surface. Then, the same quenching and tempering treatment was performed to finish a lathe tip.

  And these table No.1. A cutting test using a general-purpose lathe was performed using 1 to 6 chips. Cutting conditions are as follows: steel to be cut is S45C (92.6HRB), cutting speed: 94 m / min, cutting distance: 236 m, cutting depth: 0.2 mm (one side 0.1 mm), feed: 0.2 mm / rotation, cutting Dry processing without oil was used. After cutting, the maximum depth of the worn part at the tip of the chip was measured. The results are shown in Table 3.

  From the results in Table 3, No. 1 according to the cutting method of the present invention was obtained. 1-4 is No. which is a comparative example. The maximum wear depth is smaller than 5, and the wear of the cutting tool under dry conditions is suppressed. Comparative Example No. As described above, 6 is inferior in grindability.

  Cutting tools used in the methods of the present invention and comparative examples were prepared using high-speed tool steel materials having the component compositions shown in Table 4. First, a 10 kg steel ingot with components adjusted in a vacuum melting furnace was melted. Next, this steel ingot was hot forged at 1150 ° C. to obtain a steel material of 25 mm thickness × 25 mm width. At this time, no. Steel ingot No. 10 had poor hot workability, and many cracks occurred after forging, making it impossible to produce subsequent cutting tools.

  Subsequently, No. 4 in Table 4 was obtained. About the steel materials of 7-9, after annealing this at 870 degreeC, it processed into the chip shape. In this process, in order to exclude the influence of the decarburized layer of the steel material, the inside of the steel material surface was set to be 2 mm or more from the work surface. Then, a quenching process was performed by gas cooling from 1190 ° C., and a tempering process held at 560 ° C. for 1 hour was performed twice to finish a lathe chip. Table 4 shows the hardness of the work surface of the chip, the average long diameter of the MC type carbide in the cross-sectional structure, and the MC type carbides having a long diameter of less than 2.0 to 5.0 μm and 5.0 μm or more in the cross-sectional structure. Write the area ratio (measurement procedure follows above).

  No. in Table 4 A cutting test using a general-purpose lathe was performed using 7 to 9 chips. Cutting conditions are as follows: steel to be cut is S45C (92.6HRB), cutting speed: 94 m / min, cutting distance: 236 m, cutting depth: 0.2 mm (one side 0.1 mm), feed: 0.2 mm / rotation, cutting Dry processing without oil was used. After cutting, the maximum depth of the worn part at the tip of the chip was measured. The results are shown in Table 5.

  From the results in Table 5, No. 1 according to the cutting method of the present invention was obtained. 7 and 8 are comparative examples. The maximum wear depth is smaller than 9 and wear of the cutting tool under dry conditions is suppressed. This is a comparative example. 9 is because the V content of the tool work surface is low and the amount of V carbide having a major axis of less than 2.0 to 5.0 μm is small.

  The present invention can be applied to cutting using a drill or an end mill having a higher cutting speed in addition to steel cutting using a tap or a hob.

Claims (6)

  The work surface has a component composition of mass%, C: 1.0 to 1.6%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Cr: 3.0 to 5 0.0%, one or two of W and Mo are (2Mo + W): 15-20%, V: 2.0-5.0%, the balance is Fe and unavoidable impurities, MC type in the cross-sectional structure The average major axis of the carbide is 0.5 to 1.5 μm, the area ratio of the MC type carbide having a major axis of less than 2.0 to 5.0 μm in the cross-sectional structure is 1.5% or more and the major axis is 5.0 μm or more. It is characterized in that the steel to be cut is dry-cut at a cutting speed of 90 m / min or more with a cutting tool having an area ratio of MC type carbide of 0 to less than 1.2% and a hardness of 63 to 70 HRC. Steel cutting method.   2. The steel cutting method according to claim 1, wherein the work surface has an average major axis of MC type carbide in the cross-sectional structure of 0.9 to 1.2 μm.   The steel cutting method according to claim 1 or 2, wherein the work surface of the cutting tool contains Al: 0.2% or less in terms of component composition.   The work surface of the cutting tool contains a total of 0.2% or less of one or more rare earth elements in a component composition of mass%. Cutting method.   The steel cutting method according to claim 4, wherein the rare earth element is Ce.   The steel cutting method according to any one of claims 1 to 5, wherein the work surface of the cutting tool contains Co: 10% or less in terms of component composition.