0001]The present invention is, automobiles, ships, bridges, construction machinery, used in various plants, etc., the surface layer grain refining hot shearing method and the surface layer grain refining hot shearing of the carbon content of 0.15 mass% or more of the steel plate on parts.
BACKGROUND
[0002]Automotive Conventionally, ships, bridges, construction machinery, the metal material used for the various plants, etc. (steel sheet), shearing by the punch and the die is often subjected. In recent years, from the viewpoint of safety and weight reduction proceeds strength of various members, "Press Technology", pp Vol.46Nanba7,36-41 (hereinafter, referred to as "Non-Patent Document 1") is disclosed and it has as substantially performed simultaneously to a heat treatment and press forming, quenching press molding a high strength member is performed.
[0003]
　For typical cold pressed product, after press forming, shearing is performed, such as piercing and trimming. However, when the shearing after molded to quench pressed product, it is remarkably shortened life of the shearing tool for high member hardness. Further, there is a concern that delay due to the residual stress in the shearing unit breakdown occurs. Therefore, for the quench pressed product, often a laser cutting rather than shearing takes place.
[0004]
　However, since the laser cutting is costly, method (e.g., JP 2009-197253 JP (hereinafter, refer to as "Patent Document 1")) to perform the heat treatment after shearing, before simultaneously quenching and hot press by performing shearing, a method of reducing the residual stress in the shearing unit (e.g., JP 2005-138111 JP (hereinafter, referred to as "Patent Document 2"), JP 2006-104526 JP (hereinafter, "Patent Document 3 "hereinafter), JP 2006-83419 JP (hereinafter) rEFERENCE" Patent Document 4 "), a method of reducing the hardness by gradual cooling rate of the shearing unit (e.g., JP 2003-328031 No. (hereinafter, referred to as "Patent Document 5")), the method of processing to soften only the shearing scheduled portion by performing a local electric heating (e.g., "CIRP Annal s-Manufacturing Technology "57 (2008), p.321-324 (hereinafter" referred to Non-Patent Document 2 ")), and by controlling the surface layer structure of the shearing surface of the high strength steel sheet, improved delayed fracture resistance technique according to the shearing (JP 2012-237041 JP (hereinafter, "Patent Document 6" hereinafter) reference) and the like have been proposed heretofore.
Summary of the Invention
Problems that the Invention is to Solve
[0005]
　The method disclosed in Patent Documents 1 to 6 and the method disclosed in Non-Patent Document 2, a number of challenges exist. The method disclosed in Patent Document 1 is a method can be used only to a specific material, also, since it is a method of shearing the hardenability has been material, the problem of tool life decreases can not be solved.
[0006]
　The method disclosed in Patent Documents 2 to 4, can reduce the residual stress in the shearing section due to the deformation resistance of the steel sheet, thermal stress caused with tool ware, the nonuniformity of the mold contact during hardening and, it is impossible to reduce the residual stresses caused by the transformation of the steel sheet. Therefore, when the ductility of the hot shearing unit is low, problems delayed fracture occurs can not be solved. Further, there is no description of how to improve the hot shearing of ductility.
[0007]
　The method disclosed in Patent Document 5, although shearing portion of the steel sheet is believed to allow improvement of ductility does not cure, by the amount to slow the cooling rate machining time increases, the cost increases. Further, the method disclosed in Non-Patent Document 2, it is necessary to prepare a mold having a resistance heating apparatus for newly shearing, the cost is increased.
[0008]
　The method disclosed in Patent Document 6 is excellent has the effect of improving the delayed fracture resistance, shearing initiation temperature is defined to 400 ° C. ~ 900 ° C. regardless the material and the cooling rate of the workpiece. Therefore, depending on the material and processing conditions of the workpiece may happen that the shearing in a temperature range of occurrence of delayed fracture (low temperature side). Conversely, large amount of thermal expansion when shearing at a high temperature more than necessary so delayed fracture does not occur, a large dimensional change upon returning to room temperature. As a result, dimensional errors of the workpieces is increased. Therefore, in line with the actual hot shear conditions, if precisely controlled shearing temperature on the low temperature side, there remains a possibility that the delayed fracture can be suppressed machining accuracy of the workpiece while further improved.
[0009]
　Patent Document 6 discloses that delayed fracture does not occur when the surface of the shear section there is fine ferrite. However, for example, Table 1 steel component A8 and A9 in results obtained at a Table 5 Conditions In Test No. 36-40 using steel A8 with the same heating condition retention in the embodiment, the same shearing temperature cooling rate in some cases be processed delay varies tissue destruction occurs. Incidentally, were similar even results using steel A9 in Table 5.
[0010]
　The present invention is to solve the above problems, without increasing the machining time and new steps, to prevent the delayed fracture occurring hot shearing unit, and the object is to increase the working accuracy of a product, providing a surface layer grain refining hot shearing method for solving the problem, and an object thereof is to provide a surface layer grain refining hot shearing parts that meet these requirements.
Means for Solving the Problems
[0011]
　The present inventors have intensively studied a technique for solving the above problems. As a result, the temperature (shearing start temperature) to initiate the shearing, is set in a proper range based on equivalent plastic strain in the surface layer of the shearing part, even higher residual stresses in the shearing section is present , it found that delayed fracture does not occur.
[0012]
　That is, the equivalent plastic strain amount is the temperature at the time of processing of the processing unit, is affected by tissue before processing (or ferrite or austenite), the tissue changes after processing in accordance with the equivalent plastic strain in the processing unit and the processing temperature different. For how different, the composition of the steel sheet, the pressing conditions and temperature history associated therewith contributes if the pressing is carried out before processing. All factors considered to processing temperature also delayed fracture in high residual stresses in the shearing section by optimizing is present dimensional accuracy without occurrence of these have found conditions to improve.
[0013]
　In particular, a carbon content of 0.15 mass% or more, considering the cold workability after shearing cooling, preferably, mechanical structure carbon content of not more than 0.48 mass%, defined by JIS G 4051 in use carbon steel, if approximately 500 ° C. or less is measured Ar3 point during cooling, that the present invention can be applied, S17C of JIS G 4051, S25C, S35C and was confirmed by cold rolled steel S45C.
[0014]
　The present invention has been made based on the above findings and has as its gist is as follows.
[0015]
　A first aspect of the present invention, after the carbon content is 0.15 mass% or more of the steel sheet was subjected to austenite by heating and held in a range of Ac3 ~ 1400 ° C., shearing installed into a mold was carried out, in hot shearing method by quenching quenching process, the temperature for initiating the shearing surface layer grain refining to temperature (℃) plus Ar3 to 30 ~ 140 ° C. of the steel plate measured in advance providing hot shearing method.
[0016]
　A second aspect of the present invention, after the carbon content is 0.15 mass% or more of the steel sheet was subjected to austenite by heating and held in a range of Ac3 ~ 1400 ° C., shearing installed into a mold was carried out, in hot shearing method by quenching quenching process, the temperature for initiating the shearing, the coefficient of 40-60 to the equivalent plastic strain in the surface layer of the shearing part to Ar3 of the steel plate measured in advance providing a surface layer grain refining hot shearing methods to adding a value calculated as multiplied by a temperature (° C.).
[0017]
　A third aspect of the present invention, the considerable plastic strain in the surface layer of the shearing portion 5 to the plate thickness of the steel plate to the inside of the steel plate in the normal direction of the shear plane from the shear plane of the shearing unit in the range of 20%, and is calculated as the average of the equivalent plastic strain amount of the a plate 20-50% of the thickness of the steel plate from the lower surface in the thickness direction of the steel sheet shearing portion of the burr side region providing a second surface layer grain refining hot shearing method according to aspects of the present invention.
[0018]
　A fourth aspect of the present invention, the considerable plastic strain in the surface layer of the shearing part, the steel sheet temperature calculated by numerical simulation performed based on the stress-strain diagrams of 500 ~ 800 ° C., the second aspect of the present invention or provide shearing method between the surface layer grain refining heat according to the third aspect.
[0019]
　A fifth aspect of the present invention, the equivalent plastic strain in the surface layer of the shearing unit, is calculated based on the yield function of Mises the following formula (1), second through fourth one of the present invention 1 It provides a shearing method between the surface layer grain refining heat according to aspect.
[0020]
[Number 1]

[0021]
　A sixth aspect of the present invention, the steel sheet after contacting the mold to the start of the shearing of the steel sheet within 3 seconds, the surface layer grain refining hot shearing according to the first or second aspect of the present invention to provide a method.
[0022]
　A seventh aspect of the present invention, the performing rapid cooling, to provide a first or surface layer grain refining hot shearing method according to a second aspect of the present invention by contacting the steel sheet into the mold.
[0023]
　An eighth aspect of the invention, the water jetted from the holes formed in the steel sheet contact portion of the mold, performing the rapid cooling by being passed through a groove provided on the steel plate contact portion, the first of the present invention It provides a shearing method between the surface layer grain refining heat by 1 or the second aspect.
[0024]
　A ninth aspect of the present invention, between the shearing and the heating of the steel plate, performing press molding without breaking to the steel sheet, the surface fine Kanetsu according to the first or second aspect of the present invention providing between shearing method.
[0025]
　A tenth aspect of the present invention, the surface layer in the range of 100μm to the inside of the steel sheet in the normal direction of the shear plane from the fracture surface at a shear cross-processed portion of the carbon content is 0.15 mass% or more of the steel sheet, ferrite phase and consists of a balance, the balance grain size 3μm following bainite phase, martensite phase, having at least one phase of the retained austenite phase, and cementite and generating unavoidable inclusions, the average of the ferrite phase particle size is an at 3μm or less, and comprises 5% or more of aspect ratio of 3 or more grains in number, yet outside the martensite generating unavoidable inclusions of the 100 [mu] m, or bainite and martensite, and generates providing a surface layer grain refining hot shearing parts consisting of unavoidable inclusions.
[0026]
　An eleventh aspect of the present invention, the number density of the cementite in the surface layer is 0.8 or / Myuemu3 less, and the maximum length of the cementite is 3μm or less, the surface fine according to the tenth aspect of the present invention providing Tsubukanetsu between shearing parts.
[0027]
　A twelfth aspect of the present invention, EBSD (electron backscatter diffraction) the bainite phase is measured by observation and martensite phase and the area ratio in the surface layer which is the sum of residual austenite phase is 10-50%, providing a tenth or surface layer grain refining hot shearing part according to the eleventh aspect of the present invention.
[0028]
　A thirteenth aspect of the present invention, after the carbon content is 0.15 mass% or more of the steel sheet was subjected to austenite by heating and held in a range of Ac3 ~ 1400 ° C., shearing installed into a mold was carried out, manufactured by by quenching quenching process, and, Ar @ 3 to 30 ~ 140 ° C. was added the temperature (℃) and has been surface grain refinement of the steel sheet temperature to initiate the shearing is measured in advance providing hot shearing parts.
[0029]
　A fourteenth aspect of the present invention, after the carbon content is 0.15 mass% or more of the steel sheet was subjected to austenite by heating and held in a range of Ac3 ~ 1400 ° C., shearing installed into a mold It was carried out, manufactured by by quenching quenching process, and the temperature for starting the shearing is the surface coefficient of equivalent plastic strain amount to 40-60 of the shearing part to Ar3 of the steel plate measured in advance to provide a temperature (℃) and has been surface comminuted hot shearing parts plus the value calculated as multiplied.
The invention's effect
[0030]
　The surface grain refining hot shearing method and surface grain refining hot shearing component of the present invention, without increasing the processing time and the new step to suppress delayed fracture in the sheared section, excellent dimensional accuracy it is possible to provide a workpiece.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031]
Is a schematic view showing an aspect of piercing shearing by FIG 1A] punch and die.
It is a schematic view showing the FIG. 1B] embodiment of the trim shearing by the punch and the die.
It shows an aspect of the shearing portion of FIG. 2 steel.
3 is a diagram showing the relationship between the temperature history and the Ar3 point.
It is a diagram showing a state before shearing of the hot shearing apparatus used in FIG. 4A] Test A.
Is a diagram showing a state during shearing of the hot shearing apparatus used in FIG. 4B] Test A.
It is a diagram showing a state after shearing of the hot shearing apparatus used in FIG. 4C] Test A.
[5] was observed by the replica method using a transmission electron microscope of the comparative example, it illustrates the surface of inclusions shearing unit (replica method, transmission electron microscope image).
It is a diagram showing a region averaging FIG 6A] equivalent plastic strain.
[FIG 6B] is a diagram actually shows the region in which microstructure is formed in the hot shearing the shearing unit.
An example of FIG. 7 metallographic structure it obtained according to Example 1 (EBSD image).
8 is an example of inclusions of the metallic structure obtained in Example 1 (a replica method, transmission electron microscope image).
It is a diagram illustrating a bending state of the hot shearing apparatus used in FIG 9A] Test B.
Is a diagram illustrating a shearing state of the hot shearing apparatus used in FIG. 9B] Test B.
DESCRIPTION OF THE INVENTION
[0032]
First Embodiment
[0033]
　Hereinafter, the surface layer grain refining hot shearing method and the surface layer grain refining hot shearing component of the first embodiment of the present invention will be described in detail.
[0034]
　First, it describes common shearing, described shearing portion of the shearing shear workpiece.
[0035]
　Figure 1A, as shown in FIG. 1B, by the punch 2 is lowered with respect to the steel plate 1 installed on the die 3, punching shearing or trimming shearing takes place. Shearing unit 8 of this time, the steel sheet 1, as shown in FIG. 2, the sagging 4 formed by being pushed entirely by (a) the steel sheet 1 is punched 2, (b), the punch 2 and the die 3 clearance steel 1 (gap between the punch 2 and the die 3) is drawn, the shearing surface 5 formed by being locally stretched, broken steel plate 1 drawn in (c) of the punch 2 and the die 3 clearance a fracture surface 6 formed Te, formed by a burr 7 produced on the rear surface of the (d) steel plate 1.
[0036]
　Also in the following description of the embodiments, the same reference numerals refer to like elements, a detailed description thereof will be omitted.
[0037]
　Further, in the present embodiment, using the term "surface of the shearing part", which refers to a region of up to 100μm shear plane normal direction from the surface of the shearing unit.
[0038]
　Hereinafter, first, described findings of the present inventors for hot shearing, next describes the surface grain refining hot shearing method was found based on the findings, and finally by the processing method for forming surface comminuted hot shearing parts will be described together with the action of the working method.
[0039]
　In hot shearing of the present embodiment using the steel plate of high carbon region of 0.15 wt%. The transformation start temperature (Ae3 point) in the state diagram from austenite to ferrite of the steel sheet is 800 ~ 900 ° C.. The portion was large plastic deformation in a state of austenite does not occur martensite transformation even quenched Suppose transformed into ferrite. Accordingly, if rapid cooling after processing in the temperature range of austenite single phase relative to the phase diagram, substantially all become ferrite surface layer of the large shearing portion of the plastic deformation, it portion not plastically deformed other than the martensite Become. However, dimensional accuracy is deteriorated due to the thermal strain when the processing temperature is high. Further, there is a problem that variation in occurrence of the processing in the temperature range where austenite and ferrite are mixed relative to the state diagram delay due to ferrite plastically deformed breakdown occurs.
[0040]
　Accordingly, the present inventors have experimentally performed the shearing at different temperatures (shearing start temperature) to initiate shearing after the steel sheet was soaked. Note that the shearing start temperature, embed a thermocouple centrally 3 ~ 5 mm spaced apart position from the shearing position in the thickness direction of the steel sheet, the temperature was measured at the shearing start. Steel sheet and the temperature is heat removal touching the mold is lowered, the steel sheet was from contacting the mold until shearing starts within 3 seconds.
[0041]
　In the present embodiment, the "mold" refers to a die 3 and the pad 9 to be used at the time of shearing (see Figure 4A). Furthermore, "after contacting the mold to the steel sheet" means from the time of contacting the steel plate 1 to either the third or pad 9.
[0042]
　As a result, there is a temperature range in which dimensional precision is improved without causing delayed fracture in shearing of the steel plate (fracture surface), this temperature range the inventors that different with the components of the processing conditions and the steel sheet is found It was. Further, the present inventors to control the cooling of the steel sheet before shearing was also found together can affect the dimensional accuracy of the delayed fracture and processing components of shearing section (fracture surface).
[0043]
　Furthermore, proper temperature to the fine bainite and martensite in addition to fine ferrite as described below the shearing initiation temperature, and residual austenite are applied to obtain the knowledge decreases further cementite.
[0044]
　Fine ferrite organization, in general, higher toughness than the martensitic structure. Therefore, the fine ferrite structure of high toughness if present surface layer of the shearing part, the delayed fracture is suppressed.
[0045]
　The shearing initiation temperature in consideration of the temperature change in hot shearing to determine the proper temperature range by further performing calculations on the magnitude of the shearing strain.
[0046]
　First, heating the steel sheet to 950 ° C., when it is installed on a four pointed needles a steel sheet held 90 seconds (hereinafter, sometimes referred to as "pin support") was measured transformation temperature after cooling in. Temperature measurements were conducted by a thermocouple embedded in the steel sheet.
[0047]
　Measured Ar3 point is not a hypothetical cooling rate 0 as in a state diagram, the temperature at which begins to transform to BBC crystal structure of ferrite or the like from the austenite structure is FCC crystal in the cooling rate of a finite.
[0048]
　Ar3 point This was measured, the transformation temperature from austenite indicated by the state diagram to the ferrite (Ae3 point) were significantly different from 200 ~ 300 ° C.. Further, when the surface contact state in the mold (some degree baked does not fall but the cooling rate is faster than the pin support) was measured Ar3 point at about 400 ° C. lower than the Ae3 point, i.e. the pin support It was low about 100 ° C. as compared.
[0049]
　It Ar3 point is lower than the Ae3 point is common general knowledge in the field of metallic materials. However, it is not clear for the quantitative differences. The attempt of the present inventors, in hot shearing became apparent that appears as a very large difference as described above.
[0050]
　For reference, it shows the results of measurement of the Ar3 point at the measuring method (pin support) in FIG. Steel plate was mainly used as a thickness of 1.5mm. Thick plate range of the steel sheet used for processing is about 0.5 mm ~ 3.0 mm. Incidentally, the Ar3 point because it is transformation start temperature from austenite to ferrite need not include shearing and hardening the (rapid cooling) step to the measurement. Therefore, in the graph of FIG. 3 it does not include quenching process.
[0051]
　In Figure 3, initially, when the cooling rate was 7 ° C. / s, the cooling rate is rapidly decreased from the start of cooling after the elapse of 50 seconds. The temperature of the steel plate cooling rate of the steel is equal to or less than 1 ° C. / s (about 680 ° C.) is identified as transformation temperature (Ar @ 3 points). When Ar3 point measurement, but steel is cool to room temperature, actually shearing is started at a temperature higher than the Ar3 point, then quenching step.
[0052]
　In the present embodiment defines the Ar3 temperature measured in the actual processing of the plate installation conditions using the same method as in the case of pin support described above as "measured (of steel) Ar3 '. Cooling rate during the measurement is approximately 5 ° C. / s from 30 ° C. / s about (cooling state) and is often made.
[0053]
　Incidentally, if you know the implementation to appropriate hot shearing conditions the experiment as a preliminary test, in actual mass production process steps, soaking temperature control of suitable steel, and the steel sheet at the mold by performing the time management until shearing start, necessarily prepared mold with embedded thermocouples, it may not operate by measuring the surface temperature of the steel sheet is sheared at shearing start for each shearing. In the case of operation by measuring the surface temperature of the steel sheet production process, a radiation thermometer just before hot-sheared it may measure the surface temperature of the steel sheet.
[0054]
　Then, since the plastic deformation caused by shearing as described above is associated with shearing of the tissue, the present inventors performed derivation of plastic strain of shearing vicinity Numerical. Here, plastic strain was evaluated as the equivalent plastic strain.
[0055]
　Since the actual processing is processed at a higher than Ar3 temperature measured area, as a premise of the calculation, the numerical value of the mechanical properties such as deformation resistance of the steel sheet is the value of the austenite. The temperature dependence of the mechanical properties of the austenite after heating the hot tensile test (steel 22MnB5 equivalent steel widely used in hot stamping to a temperature of at least Ac3 point, allowed to cool to a predetermined temperature, the tensile subsequently tested using the measured values ​​in the conduct). Such a temperature dependence such as "Hongsheng Liu, Jun Bao, Zhongwen Xing, Dejin Zhang, Baoyu Song, and Chengxi Lei;" Modeling and FE Simulation of Quenchable High Strength Steels Sheet Metal Hot Forming Process ", Journal of Materials Engineering and Performance, Vol. 20 (6), 2011, pp.894-pp.902 "(hereinafter," may be referred to as non-Patent Document 3 ") are described in, without practitioner actually measured It can also be used such reference values.
[0056]
　Plastic strain obtained by the numerical calculation was smaller with distance from the largest surface the surface of the shearing surface. Furthermore, it was found that the region of 100% or more of equivalent plastic strain in the case if the shearing unit at a predetermined temperature range occurs, actually microstructure occurs region coincide.
[0057]
　The value obtained by numerical calculation is feared variation due analyst. Therefore, we steels plurality Street analysts, performs numerical calculations in software, the area equivalent plastic strain occurs more than 100% in the direction normal to the shear plane of the shearing portion of the (distance) and microstructure the temperature range of shear plane normal to the direction of the area (distance) coincide resulting got approximately 30 ~ 140 ° C. is a temperature range higher results than were measured Ar @ 3.
[0058]
　Here, higher than plus Ar3 to 140 ° C. as measured temperature (hereinafter, may be referred to as "Ar3 + 140 ° C. greater than") in the temperature range is the shear plane normal to the direction of the shearing part obtained by calculation towards a region equivalent plastic strain of about 100% occurs is greater than the actual fine area of ​​shearing of the workpiece. Analysis of the structure of the tissue in the fine region, the majority were ferrite and carbides. On the other hand, other than the surface layer is martensite.
[0059]
Ferrite and martensite volume is different from the difference of the solid-solution state of the crystal structure and elemental. Therefore, wide surface which is formed on microstructure region of shearing section, and the majority of Microstructure and composed of ferrite, increases the border area of ​​fine ferrite and martensite. As a result, the dimensional accuracy of the workpiece is deteriorated. Furthermore, so that the shearing start temperature given the heat distortion dimensional accuracy of the higher workpiece is deteriorated.
[0060]
　Also, less shearing starting temperature plus Ar3 to 30 ° C. as measured temperature (hereinafter, it may be referred to as "Ar3 + 30 below ° C.") In the case of, from a region where more than 100% of the equivalent plastic strain occurs in fact of the smaller fine area. Further, since the area of ​​100% or more of equivalent plastic strain occurs decreases, the actual microstructure region smaller than the region is very small. In yet measured Ar @ 3 + 30 below ℃ temperature and a portion of the austenite under the influence of internal heat distribution begins to transform to ferrite, such ferrite plastically deformed by shearing. As a result, it was also found to increase the risk of residual stresses on the surface of the shearing portion of the workpiece is excessive delayed fracture.
[0061]
　On the other hand, shearing starting temperature austenite if Ar @ 3 + 30 ° C. than is to shearing previously steel sheet to initiate transformation to ferrite, that the residual stress of the shearing unit of a ferrite becomes excessive is avoided.
[0062]
　Based on the above findings, the surface layer grain refining hot shearing method according to the present embodiment is constituted as follows.
[0063]
　First, briefly described shearing device used for the test. As shown in FIG. 4A, the shearing device 10 includes a third steel sheet 1 is placed, is placed on top of the die 3, the pad 12 for pressing the steel plate 1 installed on the die 3, the interior of the pad 12 It is disposed, and a punch 2 punching the predetermined range of the steel sheet 1 by being inserted into the hole 14 of the die 3.
[0064]
　First, the carbon content by heating the steel sheet 1 of 0.15 wt% to a range of high Ac3 ~ 1400 ° C. than shearing initiation temperature in the range of Ar3 + 30 ℃ ~ Ar3 + 140 ℃, the soaking treatment after applying, placed on the die 3 (refer to FIG. 4A).
[0065]
　Thereafter, as shown in FIG. 4B, after holding the steel sheet 1 on the die 3 in the pad 12, to shearing a steel plate 1 by the punch 2. Incidentally, it starts shearing of the steel plate 1 a steel plate 1 within three seconds after placed on the die 3. Range by installing a steel plate 1 to the die 3 by controlling the time (shearing start time) until the start of shearing, the temperature of the steel sheet 1 during shearing of Ar3 + 30 ℃ ~ Ar3 + 140 ° to control to.
[0066]
　As shown in FIG. 4C, the punch 2 with punched predetermined range of the steel sheet 1, the punched steel plate 1 enters is baked, workpiece which is shearing is formed by being quenched by the die 3 and the pad 12 .
[0067]
　Thus the surface layer grain refining hot shearing method and surface grain refining hot shearing part formed by the processing method of the present embodiment (hereinafter sometimes referred to as "workpieces") a description of the operation of the .
[0068]
　The shearing unit 8 of the thus processed component formed by (steel), the surface layer in the range inside of 100μm steel plate in the normal direction of the shear plane 5, a ferrite phase forming at least a portion of the fracture face and consists of a balance, the balance has a bainite phase, martensite phase, residual austenite phase, and cementite and generation unavoidable inclusions. Further, the ferrite phase and the bainite phase formed on the surface layer of the shearing unit 8, martensite, residual austenite phase has an average particle size of 3 [mu] m or less. Further, the surface layer of the shearing unit 8 includes 5% or more the aspect ratio of 3 or more particles in% by number. Incidentally, other than the surface layer of the shearing unit 8 generates unavoidable inclusions and martensite, or a mixed structure of martensite and bainite and produce unavoidable inclusions.
[0069]
　That is, the processing component, because formed by shearing a steel plate 1 which has been heated to Ar3 point + 30 ℃ ~ 140 ℃, shearing unit 8 (fracture surface 6) (see FIG. 2) surface layer on a fine ferrite structure of martensite site organization, bainite, residual austenite structure is formed. Indeed shown in FIG. 6B what the steel plate 1 was sheared. As shown in FIG. 6B, but shear plane 5 toward fine structure 11 from fracture surfaces 6 in the shearing unit 8 is formed on the surface layer, particularly fine structure from the surface to 100μm approximately depth in fracture surface 6 is formed It is.
[0070]
　Fine ferrite organization, in general, higher toughness than the martensitic structure. Therefore, the fine ferrite structure of high toughness due to the presence in the surface layer shearing unit 8 (fracture surface 6), the occurrence of delayed fracture shearing unit 8 by delayed fracture (fracture surface 6) is suppressed.
[0071]
　Moreover, as described below, the processing component of the present embodiment, the shearing unit 8 surface which is formed in a fine martensitic structure of (fracture surface 6), bainitic structure, the residual austenite structure, shearing unit 8 it is possible to suppress the occurrence of delayed fracture in (fracture surface 6).
[0072]
　It shows the surface layer of the structure photographs of the shearing part obtained by EBSD of this embodiment in FIG. 7 for reference.
[0073]
　7, the black portion is bainite phase, martensite phase or the residual austenite phase. Crystal grains shown in the picture there is also more than the aspect ratio of 3, but does not occur destruction delay for reasons which will be described later.
[0074]
　Here, the term "particle size" as the area of ​​each crystal grain of ferrite when observed in cross section along the thickness direction of the steel sheet in the normal direction of the shear plane, was replaced with a circle of the same area It means the diameter circle, i.e. a circle converted diameter (equivalent circle diameter).
[0075]
　The surface layer of the shearing unit 8 is not a single-phase fine ferrite phase, bainite phase or martensite phase, retained austenite phase is present. Generally, bainite phase or martensite phase present in a ferrite phase, residual austenite phase to trap diffusible hydrogen that cause delayed fracture. Therefore, if the presence of these phases in fine ferrite phases, an effect of suppressing delayed fracture.
[0076]
　Further, the bainite phase or martensite phase, residual austenite phase because the site for trapping the diffusible hydrogen becomes less and fine 3μm further increase, further delayed to suppress the fracture.
[0077]
Meanwhile, cementite is small the effect of trapping the diffusible hydrogen, less the better as it can become a starting point of delayed fracture.
[0078]
　The particle size is 3μm or less and a fine bainite phase and martensite phase, a ferrite having an aspect ratio in the rest configuration of the residual austenite phase exceeds 3 it was inevitable that appears. It was analyzed by transmission electron microscopy, since ferrite aspect ratio exceeds 3, there is little plastic deformation, or a small state, not intended to be drawn in terms of the plastic deformation as described in Patent Document 6, a delay It did not adversely affect the resistance of destruction. Its While details of the action is unknown, bainite phase or martensite phase as described above, the presence of the aspect ratio of 3 or more ferrite structure in a rest configuration in the residual austenite phase is essential.
[0079]
　Also for these tissues, it is necessary to adjust the shearing temperature Ar3 + 30 ℃ ~ Ar3 + 140 ℃. Steel some since a cooling rate being cooled tissue above the processing temperature is generated transformation nuclei to other phases to non martensite joined by working strain appropriate amount but remain austenite already it is conceivable that. In this case, either the transformation to which phase cooling rate contributes.
[0080]
　Ar3 + 140 fast cooling rate if ℃ greater, austenite becomes undercooled state (temperature is lower than the temperature range Ownership may be present) during cooling if subjected to any processing strain which can not be transformed into martensite . Austenite is easily transformed into a fine ferrite structure in such a case.
[0081]
　On the other hand, if less Ar @ 3 + 140 ° C. degrees, can not be transformed to ferrite, the grain that does not be transformed into martensite occurs at further processing strain effect of. Such a grain becomes bainite. In addition, there is also a grain of work strain is transformed to less martensite. Additionally, transformation to such uneven three phases induces a carbon enrichment of some austenite, such austenite becomes residual austenite to a stable even at room temperature. Since these phases occur between fine ferrite grains, itself also becomes 3μm or less and fine.
[0082]
　Incidentally, in order to further stably form the these tissues, it is preferable that the steel sheet be within 3 seconds time-to-sheared starting from contact with the mold. Produce scale on the surface of the steel sheet If the time until the shearing start is more than 3 seconds, because the contact of the steel sheet and the mold is not uniform. If uneven heat due uneven contact is Shojire, variation occurs in the cooled state of the shearing unit.
[0083]
　Moreover, the distribution of the surface layer of cementite fracture surface upon shearing the steel sheet of Patent Document 6 Ar3 point + 140 ° C. of greater than 5. Patent Document 6, also encompasses the case of Ar @ 3 + 140 ° C. greater because not set only the temperature region of the shearing start temperature merely 400 ℃ ~ 900 ℃. In that case, for example, as shown in FIG. 5, the number density of cementite C (black portion excluding the circle) is 0.8 pieces / [mu] m 3 or more, the maximum length is more than 3 [mu] m.
[0084]
　On the other hand, in the case of the present embodiment, as shown in later test result (Fig. 8), the surface layer of the fracture surface of the steel sheet, cementite number density of (black portion excluding the circle) is 0.8 pieces / [mu] m 3 less and, and its maximum length is 3μm or less. According to the inventors experience, the number of cementite is small, and it becomes a starting point of fracture delay cementite itself in case the size smaller does not occur substantially to this extent.
[0085]
　Further, as shown in FIG. 7, the inside 100μm range of the steel sheet in the normal direction of the shear plane from the fracture surface at a shear cross processed portion of the steel plate, as measured by EBSD (electron backscatter diffraction) observation the bainite, summed area ratio of martensite or retained austenite phase is 10-50%.
[0086]
　According to this also the inventors experience, the total area fraction of those phases is less than 10%, can not be sufficiently performed occlusion of diffusible hydrogen, the risk of delayed fracture is increased. On the other hand, if the total area fraction of those phases is more than 50%, decreases the effect of improving the toughness by fine ferrite in the proportion of fine ferrite in the surface layer of the fracture surface is reduced, the risk of delayed fracture is increased. The total area fraction of those phases is not necessarily lost effect immediately present invention if outside this range, and more preferred if it is within this range.
[0087]
　A method of quenching a steel plate 1 after shearing Mold as in the present embodiment (the die 3, the pad 12) is not limited to quenching by contact with the steel sheet 1, for example, water directly to the steel plate 1 or one which is contacted quenched steel plate 1. As a method of contacting the water to the steel plate 1, a method of passing the cooling water and the like in the groove formed in the steel sheet contact portion of the mold.
[0088]
　Further, it is possible to form the case even, machining parts that dimensional accuracy by suppressing the delayed fracture of workpiece like the shearing section of the present embodiment performs shearing after press molding.
[0089]
Second Embodiment
[0090]
Described surface layer grain refining hot shearing method according to a second embodiment of the present invention. The same components as in the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted. Further, the surface layer grain refining shearing part formed by a surface layer comminution hot shearing method of the present embodiment is the same as the first embodiment described the effects thereof will be omitted.
[0091]
　We area and fine ferrite equivalent plastic strain of about 100% in the shear plane normal to the direction of the shearing unit occurs, martensite, the area of ​​the bainite residual austenite structure is resulting shearing surface normal direction (distance) It found that matching the temperature range may be set temperature range was added to Ar3 of measuring the value obtained by multiplying the coefficient of 40-60 to the equivalent plastic strain in the surface layer of the shearing part (℃) as shearing starting temperature It was.
[0092]
　In the present embodiment as the equivalent plastic strain in the surface layer of the shearing part, it was considered suitable to use the following values.
[0093]
As shown in FIG. 6A, the shear plane 5 of the shearing unit 8 to the inside of the steel plate 1 in the normal direction of the shear plane 5, in the range of 5-20% of the thickness H of the steel sheet 1, and shearing unit 8 from burr 7 side of the lower surface 12 in the thickness direction of the steel sheet 1, the average value of the plastic strain amount obtained by calculation in a region in the range of 20-50% of the thickness H of the steel sheet 1 a (the thick line frame) It was used as the equivalent plastic strain in the surface layer of the shearing unit.
[0094]
　By setting this way regions A, it was found that the equivalent plastic strain amount is less affected difference analysts and analysis conditions are obtained. This value is considered to be a reasonable numbers as the equivalent plastic strain amount as described below, may be used the values ​​of other correction distortion in accordance with the calculation means.
[0095]
　Incidentally, the equivalent plastic strain in the surface layer of the processed part was used the values ​​obtained by calculation of the temperature range of 500 ℃ ~ 800 ℃. In this region was confirmed to be equivalent plastic strain in the surface layer becomes substantially constant.
[0096]
　Equivalent reason for providing a lower limit of 40 to the coefficient to be multiplied to the plastic strain amount is by considering the difference in coefficient due steels, the error of the numerical calculations. By repeating the experiment and numerical calculation, out of range even be fine ferrite of this factor, martensite, bainite, and residual austenite organization appears to give 40 as a lower limit of the coefficient appearing in a higher probability.
[0097]
　The reason why providing the 60 limit the coefficient multiplied to the equivalent plastic strain amount is because the dimensional accuracy of the workpiece and the processing temperature is too high to deteriorate. This density difference is large between the surface layer other than the portions temperature but becomes the the wider area of ​​the surface layer of the microstructure higher adjacent, presumably because dimensional accuracy is deteriorated further after cooling the heat distortion is also increased.
[0098]
　On the other hand, the difference between the working part dimensions and part design dimensions, generally if they fit within the range of -0% + 5% of the design dimensions, there is no problem substantially lowered failure rate of the product to the extent economically acceptable . Therefore, we determined these limits as a result of trial and error.
[0099]
　Measured Ar3 point of the steel sheet, by installing a steel sheet in a mold which is actually used, in advance, it should be measured by the temperature drop history thermocouple. Embedding a thermocouple in the mold, the thermocouple sensor unit, it is desirable to direct contact with the steel plate of the sheared material. This measured Ar3 point is because different depending on the cooling rate of the steel sheet. Incidentally, as illustrated in FIG. 3, the measured Ar3 point is widely known to be measured as the point at which the rate of decrease in temperature is different. Later tests A, also in the B using this method.
[0100]
　In the present embodiment, it is important to calculate the equivalent plastic strain of shearing unit. The hot shearing is inevitable that transforms to shearing during or immediately after the metal structure occurs, it is impossible to measure the equivalent plastic strain. Therefore, by performing the shearing simulation by FEM (Finite Element Method) analysis, corresponding calculates the plastic strain.
[0101]
　In the simulation of the shearing, changes occur in the steep plastic strain. Therefore, the calculation result of the shearing part surface of the plastic strain is likely to occur differences due analyst and analysis conditions. To reduce the effect of such analyst and analysis conditions, it sets the FEM analysis region constant, it is desirable to calculate and average the equivalent plastic strain in the region.
[0102]
　The present inventors have found through trial and error, and set its area. Figure 6A, shows a region averaging the equivalent plastic strain. As shown in FIG. 6A, corresponding area A (the thick frame) averaging the plastic strain is inward from shear plane 5 of the steel plate 1 in the normal direction of the shear plane 5 of the shearing unit 8, of the steel plate 1 plate from 5 to 20% of the thickness H (see FIG. 4), and from the lower surface 12 of the shearing portion of the burr 7 side in the thickness direction of the steel sheet 1, in the range of 20-50% of the thickness H of the steel sheet 1 It has been set.
[0103]
　Further, in the simulation, since the temperature change is changed sequentially, the shearing start temperature set by the temporary, corresponding to calculated plastic strain based on this, on the basis of the equivalent plastic strain is calculated, starting true shearing it is necessary to perform the repetitive calculations that determine the temperature. Such a calculation is costly.
[0104]
　The present inventors have calculated at several levels, it is clear that can be approximated by performing numerical simulation once based on the stress-strain diagram in either a steel sheet temperature of 500 ~ 800 ° C. It was.
[0105]
　Incidentally, as a premise of the calculation, the numerical value of the mechanical properties such as rigidity of the steel plate at that time in case of processing at higher measured Ar3 temperature region was the value of the austenite.
[0106]
　Incidentally, when the simulation, particularly without considering the anisotropy, by calculating the equivalent plastic strain by yield function of Mises assuming an isotropic, without any particular problem, it is possible to calculate the shearing start temperature It was.
[0107]
　Equivalent plastic strain increment d?-P by yield function of Mises, when taking material coordinate system x, y, a z, is represented by the following formula, the equivalent plastic strain is given as the integral of this increment.
[0108]
[Number 2]

[0109]
　As described above, in the processing method according to the present embodiment, by shearing the steel sheet calculated shearing start temperature, the surface layer in the tissue, such as fine ferrite of shearing portion is formed, shearing section (fracture the occurrence of delayed fracture cross-section) is suppressed, it can be a shearing start temperature to suppress the thermal strain or the like by within a predetermined range to ensure the dimensional accuracy of the machined parts.
[0110]
　In particular, for the corresponding calculated plastic strain amount, setting the predetermined coverage area A in the sheared section, it was possible to calculate the small equivalent plastic strain amount of error.
[0111]
Further, in corresponding simulations FEM for calculating a plastic strain amount, the temperature change is changed sequentially correspond to calculate the plastic strain amount based on provisional shearing start temperature, the true shearing start temperature based on this iterative calculations that determined it was necessary. However, in the present embodiment, since it is possible approximated only by numerical simulation once based on the stress-strain diagram in either a steel sheet temperature of 500 ~ 800 ° C., calculation is simplified.
[0112]
　Further, by calculating the equivalent plastic strain by yield function of Mises assuming an isotropic, it is simplified even more calculations.
[0113]
　The method of calculating the equivalent plastic strain amount as described in the surface layer grain refining hot shearing method of the second embodiment, the calculation of the equivalent plastic strain amount in the surface layer grain refining hot shearing method of the first embodiment it is possible to apply.
Example
[0114]
　Next, a description will be given of an embodiment of the present invention, processing conditions in the embodiment is an example of employing the processing conditions for confirming the workability and effects of the present invention, the present invention relates to the machining condition the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various processing conditions.
[0115]
(Test A)
[0116]
　Using shearing device 10 shown in FIGS. 4A ~ Figure 4C, the pads to a high strength steel sheet of the steel types A ~ C of compositions shown in Table 1 1 (200 mm × 150 mm) after installation in the die 3, on the steel plate 1 12 hold the steel sheet 1 in the pad 12 to approximate the punch 2 from above with when shearing the steel plate 1 by the punch 2 (width 65 mm) simultaneously. Shearing steel sheet 1 is rapidly cooled by the mold (die 3 and the pad 12). The processing conditions are shown in Table 2. In addition, clearance of the punch 2 and the die 3 was set to 0.15mm.
[0117]
　The holding time of the steel plate 1 to the die 3 with the exception of the comparative example abuts to start shearing was 3 seconds 0.5 seconds. Table 2 shearing initiation temperature in is the temperature obtained in the range of the holding time.
[0118]
　Thickness of the steel sheet used in the examples was 1.5 mm. Incidentally, the steel sheet thickness of the scope of the present invention is about 3mm from 0.5 mm.
[0119]
Measured Ar3 point of each steel sheet, the steel sheet was heated to 950 ° C. in shearing device placed and cooled in contact with the top of the mold, the temperature decreases up (room temperature was determined by measuring the temperature history at that time previously, the cooling rate of the steel sheet was considered Ar3 point to a temperature equal to or less than 1 ° C. / sec.).
[0120]
　For equivalent estimate of plastic strain, finite element steel plate with Dassault Systemes (DS) Ltd. Abaqus / Standard is a commercial software the shearing simulation as input the deformation resistance during a 750 ° C. It was carried out by law simulation. In this case, using the yield function of Mises, the analysis region in the vicinity of the tool tip was 0.02 mm × 0.04 mm quadrilateral completely integral element. Also, it was remeshing every punch indentation 0.05 mm. Fracture is defined by the ductile fracture model of Hancock & Mackenzie, was the rigidity of satisfying the condition element with 0. Model parameters of ductile fracture was fitted based on actually observed shear plane ratio in certain conditions. Steel sheet shear plane 5 in the normal direction of the shear plane 5 with 10% thickness H of the steel sheet 1, and the burr 7 side of the lower surface 12 of the shearing unit 8 in the thickness direction of the steel sheet 1 in the shearing unit 8 1 with an average equivalent plastic strain at 30% of the area a of the plate thickness H (see FIG. 6A).
[0121]
　Further, to evaluate the length of the scrap 16 punched out of the processed as dimensional accuracy (see FIG. 4 (C)). If resulted error of dimensions, the length of the scrap 16 after processing should be 65 mm. Thus, in Table 2, the error of the length of the scrap 16 after processing was divided by 65, described converted into percentage (× 100) value as the dimension error.
[0122]
[Table 1]

[0123]
[Table 2]

[0124]
　The test was carried out each Example, Comparative Example triplicate. It is to be noted that the presence or absence of delayed fracture, even once delayed fracture if occurred, was evaluated that there is a delayed fracture. In addition, the size error, was defined as the average value of three times.
[0125]
　In Examples 1-6, the shearing unit are generated in the delayed fracture in (fracture surface) is suppressed, and it can be seen that the dimensional accuracy of the workpiece is improved.
[0126]
　The microstructure in the range of the fracture surface of 100 [mu] m of shearing unit in the first embodiment, FIG. 7 (EBSD, microstructure image) and will be described with reference to FIG. 8 (transmission electron microscopy image of the extraction replica specimen).
[0127]
As shown in FIG. 7, EBSD analysis results, by transmission electron microscopy of EDS (characteristic X-ray energy dispersive spectroscopy) and electron diffraction analysis, ferrite, bainite, martensite, residual austenite, alloy elements other than cementite and iron It was confirmed that it is constituted by inclusions derived.
[0128]
　Specifically, FIG. 7, embedding a cross-sectional sample of Example 1 along the thickness direction of the steel sheet in the normal direction of the shear plane at a shear cross processing unit to a hard resin, polished, microstructure by EBSD after electropolishing it is an image, FIG. 8 SPEED method: in which a sample of example 1 was prepared and observed transmission electron microscope by (potentiostatic Etching by electrolytic Dissolution nonaqueous solvent controlled potential electrolysis method) the extraction replica method using.
[0129]
　As shown in FIG. 7 (EBSD microstructure image), the surface layer of the fracture surface in the region of 100μm in a direction normal to the shear plane from the fracture surface, ferrite (Fig. 7, portions other than black) particle size of the F is 3μm or less very small and, martensite, bainite, residual austenite (Figure 7, black portion) the particle size of BMA was also 3μm or less. Further, this range, the ratio grain also seen that the aspect ratio exceeds 3 was about 6% by the number.
[0130]
　It was similar in microstructure in any of Examples 2-6. Here, upon identification of the microstructure was taken about five points the field of randomly 8.0 × 20 [mu] m in 100μm range from the surface of the fracture surface per Example.
[0131]
　Further, as shown in FIG. 8, cementite (black portion excluding circular) in Example 1 the proportion of C is found to be very small. Number density of cementite in Example 1 is 0.8 pieces / [mu] m 3 a, and the maximum length of the observed cementite were 3μm or less. Here, it is determined by five photographs a view of 9.5 × 7.5 [mu] m at random from the surface of the shearing unit per one of the conditions for distribution of cementite. It was similar in both of Examples 2-6.
[0132]
　On the other hand, in Comparative Examples 1-5, a mixed structure (Comparative Examples 1 and 2) of the bainite and martensite containing no ferrite or became ferrite single phase (Comparative Examples 3-5). Inclusions in Comparative Examples 1 and 2 was not almost the same cementite hardly observed and 8, 0.8 units / [mu] m as in FIG. 5, Comparative Examples 3-5 3 very high number density cementite greatly exceeding (Fig. 5, reference black portion excluding circular) C was observed.
[0133]
Incidentally, other than the shearing starting temperature was the same as in Example 1, the die 3 and the pad 9 experiments in which the retention time until the shearing starts after cooling in contact with (also referred to as a mold) and 3.5 seconds went. Machining start temperature at this time was also Ar @ 3 + 30 ° C. or higher, but delayed fracture occurs once of which was repeated three times. The resulting product of shearing face surface occurrence of the observed where delayed fracture of shearing portion surface of the free products tissue, in the range of 100μm from the shear plane, the ferrite grain size is 3μm or less and very small, Martens site, bainite, the particle size of the residual austenite was 3μm or less. Further, the ratio grain also seen that the aspect ratio exceeds 3 was approximately 7% number.
[0134]
　However, the tissue of the surface layer of the shearing portion of the workpiece that delayed fracture is generated in a range of 100μm from the shear plane, although the ferrite grain diameter was there at about 5 [mu] m, martensite, bainite, and the particle size of the residual austenite It was 5μm. Further, the surface layer of the shearing part, crystal grains having an aspect ratio of more than 3 also seen, this ratio was approximately 7% number%.
[0135]
(Test B)
[0136]
　Shearing device 20 includes a die 3 that is the hole 24 for venting deformation bending bottom surface of the hole 22 and the hole 22 for the molding forming the steel plate 1 is installed, to be inserted into the hole 22 the punch 2 to cause bending deformation to the steel plate 1, and a movable mold 26 for forming a hole (shearing) in a predetermined range of the steel sheet 1 by being inserted into the hole portion 24 after bending deformation is incorporated into the punch 2 provided.
[0137]
To simulate a press forming without fracture of the steel sheet, shearing device 20, after the setting of the steel plate 1 on the die 3, were molded steel plate 1 heated by first driving the punch 2 to the hat-shaped ( see Fig. 9A). This was tested for performing punching of a diameter of 20mm steel plate 1 by the movable mold 13 (see FIG. 9B).
[0138]
　The steel plate 1 the time from contact with the movable mold 26 to the shearing start was about 0.5 seconds 0.1 seconds with the exception of the comparative example.
[0139]
　Clearance of the punch 2 and the die 3 and 0.15 mm, were identified Ar3 measured from the thermal history after hat shaped. Calculation of equivalent plastic strain were the same as in Test A. The processing conditions shown in Table 3 was employed.
[0140]
　The evaluation test method B is also the same as Test A.
[0141]
　Incidentally, the dimensional accuracy in the test B was evaluated by the diameter of punched hole after processing. If resulted error dimension, punching hole diameter of the steel plate 1 after the processing should be 20 mm. Than this, in Table 3 is the execution result of this test, the error of the vent hole diameter after processing was divided by 20, describes converted into percentage (× 100) value as the dimension error.
[0142]
[table 3]

[0143]
In Examples 7-10, it can be seen that the occurrence of delayed fracture is suppressed in the shearing section (fracture surface).
[0144]
　Further, Table 3 in Examples 7-10 In the surface shear cross processed portion of a microstructure (100 range μm from the surface), the Examples 1-6 (FIG. 7 (microstructure) and 8 (inclusions) ) as well as contained ferrite, bainite, martensite, residual austenite, the inclusions from the alloy elements other than cementite and iron. Microstructure and inclusions of Examples 7-10 were the same as in Examples 1-6.
[0145]
　Microstructure of Comparative Examples 6-11, inclusions were similar to Comparative Example 1-5. That is, Comparative Examples 6-8 are mixed structure of bainite and martensite which does not contain ferrite, Comparative Examples 9-11 was a ferrite single phase. Cementite in Comparative Examples 6-8 were hardly observed, Comparative Examples 9 to 11, 0.8 pieces / [mu] m 3 cementite very high number density greatly exceeding were observed.
[0146]
　Incidentally, disclosure of 2013 May 9, Japanese Patent Application No. 2013-099243, filed on, the entirety of which is incorporated herein by reference.
Industrial Applicability
[0147]
　As described above, according to the present invention, in the hot shearing of the steel sheet, without increasing the processing time and the new step, it is possible to prevent delayed fracture occurring hot shearing unit. Accordingly, the present invention has high applicability in the steel sheet processing technology industry.

WE CLAIM

The steel sheet of the carbon content is more than 0.15 mass%, after the heat-holding to austenitizing range of Ac3 ~ 1400 ° C., subjected to shearing by installing the mold, to quenching treatment by rapid cooling in hot shearing method, temperature for starting the shearing, temperature (℃) surface comminuted hot shearing method according to plus Ar3 to 30 ~ 140 ° C. of the steel plate measured in advance.
[Requested item 2]
The steel sheet of the carbon content is more than 0.15 mass%, after the heat-holding to austenitizing range of Ac3 ~ 1400 ° C., subjected to shearing by installing the mold, to quenching treatment by rapid cooling in hot shearing method, temperature for starting the shearing, the value calculated as multiplied by the coefficients of the equivalent plastic strain amount to 40-60 of the surface layer of the shearing part to Ar3 of the steel plate measured in advance In addition temperature (℃) surface comminuted hot shearing method according to.
[Requested item 3]
The equivalent plastic strain in the surface layer of the shearing unit, a plate a range of 5-20% of the thickness of the steel plate from the shear plane of the shearing portion on the inner side of the steel plate in the normal direction of the shearing surface, and the shear surface grain refining of claim 2 wherein calculating the average value of the equivalent plastic strain in the region is a plate 20-50% of the thickness of the steel sheet in the thickness direction of the steel plate from the lower surface of the burr side of the processing unit hot shearing method.
[Requested item 4]
The equivalent plastic strain in the surface layer of the shearing part, the surface layer grain refining hot shear according to claim 2 or 3 steel sheet temperature calculated by numerical simulation performed based on the stress-strain diagrams of 500 ~ 800 ° C. processing method.
[Requested item 5]
The equivalent plastic strain in the surface layer of the shearing part, the surface layer grain refining hot shearing method according to any one of claims 2 to 4, calculated on the basis of the yield function of Mises the following formula (1) .
[Number 1]

[Requested item 6]
　Within 3 seconds claim 1 or 2 surface layer grain refining hot shearing method according to the steel starts to shearing of the steel plate from contact with the mold.
[Requested item 7]
Surface grain refining hot shearing method according to claim 1 or 2 performs the rapid cooling by contacting the steel sheet into the mold.
[Requested item 8]
Water ejected from holes formed in the steel sheet contact portion of the mold, between the surface layer grain refining heat according to claim 1 or 2 performs the rapid cooling by being passed through a groove provided on the steel plate contact portion shear processing method.
[Requested item 9]
Between the shearing and the heating of the steel sheet, the surface layer grain refining hot shearing method according to claim 1 or 2 performs press forming without fracture on the steel plate.
[Requested item 10]
　Surface layer in the range of 100μm to the inside of the steel sheet in the normal direction of the shear plane from the fracture surface at a shear cross-processed portion of the carbon content is 0.15 mass% or more of the steel sheet is composed of a ferrite phase and the balance, the balance being bainite phase of crystal grain size is 3μm or less, the martensite phase, at least one phase of the retained austenite phase, and has a cementite and generating unavoidable inclusions, the average particle diameter of the ferrite phase is a by 3μm or less, and includes more than 5% the aspect ratio of 3 or more grains in number, surface configured further outside the martensite generating unavoidable inclusions of the 100 [mu] m, or bainite and martensite, and generates unavoidable inclusions grain refining hot shearing parts.
[Requested item 11]
The number density of the cementite in the surface layer is 0.8 pieces / [mu] m 3 or less, and the surface layer grain refining hot shearing component of claim 10, wherein the maximum length of the cementite is 3μm or less.
[Requested item 12]
EBSD (electron backscatter diffraction method) surface fine according to claim 10 or 11 area ratio is 10-50% in the surface layer which is the sum of the bainite phase and martensite phase and residual austenite phase is measured by observing Tsubukanetsu between the shearing parts.
[Requested item 13]
The steel sheet of the carbon content is more than 0.15 mass%, after the heat-holding to austenitizing range of Ac3 ~ 1400 ° C., subjected to shearing by installing the mold, to quenching treatment by rapid cooling manufactured by and temperature (℃) and has been surface comminuted hot shearing parts plus Ar3 to 30 ~ 140 ° C. of the steel sheet temperature to initiate the shearing is measured in advance.
[Requested item 14]
The steel sheet of the carbon content is more than 0.15 mass%, after the heat-holding to austenitizing range of Ac3 ~ 1400 ° C., subjected to shearing by installing the mold, to quenching treatment by rapid cooling manufactured by, and the temperature for starting the shearing is a value calculated as multiplied by the coefficients of the equivalent plastic strain amount to 40-60 of the surface layer of the shearing part to Ar3 of the steel plate measured in advance In addition temperature (℃) and has been surface comminuted hot shearing parts.