Technical field
[0001]
The present disclosure relates to a method of producing hardened moldings, a method of manufacturing hot pressing steel material, and a hot press steel material.
BACKGROUND
[0002]
The vehicle body component to form a vehicle body, and light weight and high strength are required. As a method of increasing the strength of the body component, that after heating the material e.g. at 950 ° C., and a cooling press at the same time (also referred to as hot press or press quenching) hot stamping the quenching is known.
Summary of the Invention
Problems that the Invention is to Solve
[0003]
　However, in such a vehicle body components, although the tensile strength is high, there is a tendency that toughness decreases with increasing the strength, can also occur if the strength requirements can not be maintained.
[0004]
　The present disclosure aims to provide a method for producing hardened molded article can increase the toughness while ensuring the strength of the quench moldings, a method of manufacturing hot pressing steel material, and a hot press steel material to.
Means for Solving the Problems
[0005]
　Method for producing a hardened molded article which solves the above described problems, after austenitized by heating blanking the steel to a temperature higher than Ac3 transformation point, and the first heat treatment step of martensite transformation or bainite transformation is cooled, after austenite by heating the steel material was first heat treatment step to a temperature above the Ac3 transformation point, with a second heat treatment step of martensitic transformation by cooling, wherein the first heat treatment step or after heating the steel in at least one step of the second heat treatment step to a temperature above the Ac3 transformation point, and molded at a temperature higher than the Ar3 transformation point it is completed.
Effect of the invention
[0006]
　The present embodiment, while ensuring the strength toughness highly hardened molded article is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007]
[1] Figure 1 is a diagram showing a manufacturing method of quenching the molded article according to the present embodiment.
FIG. 2 is a diagram showing a bumper according to the first embodiment.
FIG. 3 is a diagram showing the temperature history of the bumper according to the first embodiment.
[4] FIG. 4 is an explanatory view illustrating a modified test of the bumper in the first embodiment.
FIG. 5 is a diagram showing test results of the first embodiment.
FIG. 6 is a diagram showing an M-bumper according to the second embodiment.
[7] FIG. 7 is a diagram showing test results of the second embodiment.
[8] FIG. 8 is a diagram showing a center pillar according to the third embodiment.
[9] FIG. 9 is a diagram showing test results of the third embodiment.
DESCRIPTION OF THE INVENTION
[0008]
　Hereinafter, an embodiment with reference to FIGS. 1-9.
　Figure 1 is an explanatory diagram showing a manufacturing method 10 for quenching the molded article according to the present embodiment. This figure, the manufacturing process for molding the hardened molded article 14 of the hat-shaped cross section of a steel plate blank 12 is a flat plate-like steel is shown.
[0009]
　Steel blank 12 is cut rolled steel strip to a predetermined size, formed by so-called blanking. Steel blank 12 is a flat plate shape.
[0010]
　The steel blank 12, the volume fraction of the hard phase is less than 90%. The hard phase, martensite, bainite and the like. Specifically, the steel plate blank 12 is mainly composed of hard phase consisting of at least one tissue of martensite and bainite structure, and more specifically, the volume fraction of the martensite structure which constitutes the hard phase 50% more than 90% or less. To include a phase other than the hard phase in the steel plate blank 12, it is possible to suppress the rolled punching of the strip is facilitated, and the wear of the blade portion of the mold for performing punching.
[0011]
　To facilitate cutting of the steel strip, the volume fraction of the martensite structure of the steel plate blank 12 preferably 90% or less. Further, the volume fraction of the martensite structure of the steel plate blank 12 to 80% or less, and more preferably 70% or less.
[0012]
　Steel used as the steel sheet blank 12, by mass%, C: 0.3% or more and 0.8% or less, Si: 0.001% or more and 2.0% or less, Mn: 0.5% to 3.0% or less , P: 0.05% or less, S: 0,01% or less, sol. Al: 0.001% to 1.0% or less, N: 0.01% or less, B: 0.01% or less containing as a chemical composition, it is preferred that the balance being Fe and impurities. Further, the chemical composition, instead of a part of Fe, Ti, Nb, V, Cr, Mo, Cu, may contain one or more selected from the group consisting of Ni.
[0013]
　Steel used as the steel plate blank 12 is preferably one carbon content is 0.8 wt% or less than 0.3 mass% containing, steel sheet blank 12 of the present embodiment, the amount of carbon contained 0.3 wt% and 0.8 mass% or less.
[0014]
　If the amount of carbon C is too small, it can be a less intense effect of quenching not much product. Therefore, in the present embodiment, the amount of carbon contained in the steel sheet blank 12 was 0.3 mass% or more.
[0015]
　On the other hand, when the amount of carbon C is too large, the poor too hard toughness products. Therefore, in the present embodiment, the amount of carbon contained in the steel sheet blank 12 of 0.8 wt% or less, the amount of carbon contained in the steel sheet blank 12, and a 0.3 wt% 0.8 wt% or less.
[0016]
　Further, in order to ensure more strength 1800MPa, it is preferable that the C content is 0.25 mass% or more. To stably obtain a higher strength is preferably set to 0.30 percent. Considering the toughness after quenching, C content is more preferably 0.60 mass% or less, more preferably 0.50 mass% or less.
[0017]
　Si is preferably controlled to a range of 0.001 mass% to 2.0 mass%. Si, without deteriorating the ductility to suppress the formation of carbides during cooling from the austenite phase to be transformed into low-temperature transformation phase, or to improve ductility, an element having an effect of increasing the strength after quenching is there. Si content is less than 0.001 wt% it is difficult to obtain the above effect. Therefore, Si content is preferably 0.001 mass% or more.
[0018]
　Incidentally, when the Si content more than 0.05 wt%, the ductility is further improved. Therefore, Si content is more preferably 0.05 mass% or more. On the other hand, the Si content is 2.0 mass percent, the effect of the action on the economic disadvantage saturated, deterioration of the surface properties is remarkable. Therefore, Si content is preferably 2.0 mass% or less. More preferably not more than 1.5 mass%.
[0019]
　Mn is preferably controlled to a range of 0.5 mass% to 3.0 mass%. Mn enhances the hardenability of steel, in order to ensure by the strength after quenching stable and is an element that is very effective. However, the Mn content is less than 0.5 wt%, the effect is insufficient even in the rapid cooling conditions, such as in the present embodiment, highly be ensured tensile strength of at least 1200MPa in strength after quenching it is difficult to. Therefore, Mn content is preferably 0.5 mass% or more. Incidentally, when the Mn content more than 1.0 mass%, it is possible to secure a tensile strength of at least 1350MPa in strength after quenching. Therefore, Mn content is more preferably 1.0 mass% or more. On the other hand, Mn content is 3.0 mass percent, becomes uneven structure of the band-like structure, the deterioration of the impact properties is remarkable. Therefore, Mn content is preferably 3.0 mass% or less. It is more preferable that the content of Mn in terms of alloy cost, etc. 2.5 wt% or less.
[0020]
　P is preferably controlled to 0.05 mass% or less. P is generally is an impurity which is inevitably contained in the steel, the solid solution strengthening, it may actively be contained since it has an effect of improving the strength. However, P content resistance weldability occurs with member and other members of the present embodiment is significantly in excess 0.05%. The risk of brittle fracture increases when aimed at the more high-strength 2500MPa. Accordingly, P content is preferably 0.05 mass% or less. P content is more preferably at most 0.02 mass%. To obtain the above effects more reliably, it is preferable that the P content is 0.003 mass% or more.
[0021]
　S is preferably controlled to 0.01% by mass or less. S is an impurity which is inevitably contained in the steel combines with Mn and Ti is deposited to produce a sulfide. When the deposition amount is excessively increased surface of the deposit and the main phase is preferably as low because it can be a starting point of fracture. S content is its adverse effect becomes significant at greater than 0.01 wt%. Thus, S content is preferably not more than 0.01 mass%. More preferably 0.003 mass% or less, more preferably not more than 0.0015 mass%.
[0022]
　sol. Al is preferably controlled in a range of 0.001 mass% to 1.0 mass%. Al is an element having an effect of consolidation steel by deoxidation of steel and also an element having an effect of improving the yield of carbonitride-forming elements such as Ti. sol. Al content is difficult to obtain the above effect is less than 0.001 mass%. Therefore, sol. Al content is preferably 0.001 mass% or more. More preferably not less than 0.015 mass%. On the other hand, sol. The Al content is more than 1.0 mass%, with a decrease in weldability becomes significant, oxide inclusions deterioration of surface properties is significantly increased. Therefore, sol. Al content is preferably 1.0 mass% or less. More preferably not more than 0.080 mass%.
[0023]
　N is preferably controlled to 0.01% by mass or less. N is an impurity which is inevitably contained in the steel, preferably as low from the viewpoint of weldability. N content lowers the weldability becomes significant at greater than 0.01 wt%. Therefore, N content is preferably not more than 0.01 mass%. More preferably not more than 0.006 mass%.
[0024]
　B is preferably controlled to 0.01% by mass or less. B is an element having an effect of improving the low temperature toughness. Therefore, it may be contained B. However, when the content exceeds 0.01 mass%, hot workability is degraded, the hot rolling becomes difficult. Therefore, B content is preferably not more than 0.01 mass%. Incidentally, in order to obtain the effect of the action more reliably, B content that is more preferably set to 0.0003% by mass or more.
[0025]
　Other additive elements
　Ti, Nb, V, Cr, Mo, Cu, and Ni, to improve the hardenability of steel, and strength may be added as required in order to stably secure after quenching.
[0026]
　(First heat treatment step)
　so that when the molded article 14 quenching from this steel plate blank 12 are treated with a first heat treatment step 20. The first heat treatment step 20 includes a heating step 22 of heating the steel sheet blank 12, and a cooling step 24 for cooling the heated steel sheet blank 12.
[0027]
　In the heating step 22, austenitizing and heated above Ac3 transformation point to the steel plate blank 12 in the heating furnace 26. The heating furnace 26, a high-frequency heating furnace or a resistance heating furnace, gas furnace or an infrared heating furnace and the like.
[0028]
　The heat treatment heating temperature for heating the steel sheet blank 12 in the heating step 22, it is preferably less than or equal to Ac3 transformation point + 0.99 ° C. Ac3 transformation point + 50 ℃ or more of the steel plate blank 12. In this embodiment, the constant temperature of the heat treatment the heating temperature Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ or less.
[0029]
　Here, austenitizing transformation temperature (Ac3), the carbides in solution, i.e. varies with the chemical composition after dissolution. In other words, austenitizing transformation point by dissolution of carbides varies.
[0030]
　When heated in a short time carbides large amount of material (C content high material), since the carbide remains dissolved, it is necessary to set a high heat treatment heating temperature. Therefore, the steel sheet blank 12 of the present embodiment where the carbon content was 0.3 wt% to 0.8 wt% or less containing, it is desirable that the heat treatment the heating temperature Ac3 transformation point + 50 ℃ or higher.
[0031]
　On the other hand, when the heat treatment the heating temperature is too high, the austenite grain size becomes larger. Martensite set identification which is transformed from high austenite grain size toughness is lowered. Therefore, it is desirable that the heat treatment the heating temperature and the Ac3 transformation point + 150 ℃ or less.
[0032]
　At this time, the crystal grains standing furnace time when heating the steel plate blank 12 is too long it may be affected toughness coarse. Therefore, the heating time at the high temperature of the steel sheet blank 12, it is desirable to make the steel plate blank 12 is within 20 minutes after reaching the heat treatment the heating temperature of the target, it is more preferably within 400 seconds.
[0033]
　In the present embodiment, (soaking time after reaching the target of the heat treatment the heating temperature) standing furnace time from reaching the heat treatment the heating temperature of the target to take out from the heating furnace of a steel plate blank 12 is heated step 22 400 and within seconds.
[0034]
　Cooling step 24, the steel plate blank 12 became heated austenite structure in the heating step 22 is cooled by the cooling device 28 martensitic transformation or to bainite transformation to. That is, the cooling rate of the cooling by the cooling device 28, the steel plate blank 12 is martensite transformation or the speed of bainite transformation, quenching of the critical cooling rate or faster. The cooling rate at this time is determined by the composition of the steel plate blank 12. As the cooling device 28, the accelerated cooling equipment, gas type cooling device using a cooling device and water cold type and the like.
[0035]
　It is possible to form a hot-pressed steel material 30 suitable for hot pressing carried out in a later step by the first heat treatment step 20. In this case, by treatment in each step 22, 24 described above with reference to the steel plate blank 12 described above, the hot press steel 30 carbon amount is less 0.8 wt% 0.3 wt% containing .
[0036]
　Further, if the processing in each step 22, 24 described above with reference to the steel plate blank 12 described above, hot press steel material 30 to be formed, the sum of the volume fraction of martensite and bainite and nearly 100% Become. However, if the sum of the volume fraction of martensite and bainite is 80% or more, less undissolved carbides in the next heating step, hot press steel material 30 having excellent toughness compared with conventional products obtained it has been confirmed to be. Thus, hot press steel material 30, martensite structure and the sum of the volume fraction of bainite is 80% or more, the remainder is assumed to be pearlite structure or the like made of ferrite or ferrite and cementite.
[0037]
　(Second heat treatment step)
　Then, processing the hot-press steel 30 which is an example of a flat blank in the second heat treatment step 40. The second heat treatment step 40 includes a heating step 42 of heating the first heat treatment step 20 for hot pressing steel 30 formed by, by forming a hot-pressed steel material 30 that has been heated, molded upon completion and a molding quenching step 44 of cooling.
[0038]
　In the heating step 42 of the second heat treatment step 40, austenitizing and heated above Ac3 transformation point in a heating furnace 46 the hot press steel material 30 formed by the first heat treatment step 20. The heating furnace 46, and a heating furnace of the same type as the heating furnace 26 described above. The as heat treatment heating temperature for heating the hot press steel material 30 in the heating step 42 of the second heat treatment step 40, it is desirable that the high temperature and Ac3 transformation point + 80 ° C. or less than Ac3 transformation point. Therefore, in this embodiment, the constant temperature of the hot and Ac3 transformation point + 80 ° C. or less than Ac3 transformation point to a heat treatment heating temperature.
[0039]
　In the second heat treatment step 40, the result of the first heat treatment step 20, for forming a hot-pressed steel material 30 in which the carbon C is dispersed finely, without increasing too much temperature against Ac3 transformation point carbides it is possible to dissolve easily, also resulting in easy austenite transformation. Further, in order to obtain a final product having excellent toughness, controlled (maintained) the austenite grain size in granules. Therefore, the heat treatment the heating temperature in the second heat treatment step 40 to a high temperature and Ac3 transformation point + 80 ° C. or less than Ac3 transformation point. Heat treatment temperature range of the second heat treatment step 40 is the low temperature range compared with the heat treatment the heating temperature of the first heat treatment step 20.
[0040]
　Here, there is a possibility that the effect on the toughness of the final product and the crystal grain standing furnace time when heating the hot press steel material 30 is too long coarsened exits. Therefore, the heating time of the hot press steel material 30, it is desirable to make hot press steel material 30 is within 20 minutes after reaching the heat treatment the heating temperature of the target, to be within 400 seconds more preferable.
[0041]
　In the present embodiment, the soaking time in the hot press steel material 30 is heated step 42 after reaching the stationary furnace time (target of the heat treatment the heating temperature from reaching the heat treatment the heating temperature of the target to take out from the heating furnace ) is within 400 seconds.
[0042]
　In molding quenching process 44 of the second heat treatment step 40, a hot press steel 30 which is heated from the high temperature Ac3 transformation point in the heating step 42 is molded and pressed by a die 48 at a temperature above Ar3 transformation point. Thereby forming a hot-pressed steel material 30 in a hat-shaped cross section.
[0043]
　Molding Upon completion, the heat of the hot-press steel 30 is cooled deprive the mold 48, to form a molded article 14 hardened by martensite transformation. Specifically, the mold is closed 48 to the point of forming a predetermined shape maintaining the temperature above Ar3 transformation point, forming a shaped article 14 hardened by quenching takes heat in the mold 48 immediately after the to.
[0044]
　Here, the boundaries of the temperature switch to single-phase austenite is A3 transformation point. Strictly speaking, the temperature switch to austenite single phase heated is Ac3. Then, the steel austenite single phase is cooled, not an austenite single phase temperature is Ar @ 3. Therefore, at the time of molding by pressing a mold 48, a temperature higher than the Ar3 transformation point.
[0045]
　The second heat treatment step 40 hardened molded article 14 obtained through the is mainly a martensite structure, the volume fraction of martensite is 50% or more. To the higher strength of the hardened molded article 14, martensite volume fraction of 70% or more, preferably 80% or more, more preferably, the volume fraction of martensite of 90% or more to.
[0046]
　As the quenching molded article 14, automobile bumper reinforcement, a center pillar, A-pillar, Rufureiru, side sill, and a structural member for the purpose of deformation inhibiting sip suppressed to small deformation during a collision, such as a frame. In these quenching the molded article 14, since no brittle fracture at the time of collision, it is possible to increase the strength (versus crashworthiness) for motor vehicle collision, a high-strength vehicle body while reducing the weight by thinning realizable.
[0047]
　Here, the measurement method of the volume fraction of each tissue is as follows.
　From the measurement target product, taking samples with a cut surface taken along the rolling direction and the thickness direction (hereinafter referred to as "L section").
　Then, the L cross-section of the sample was polished and nital etching, and expressed by corrosion of grain boundaries of L cross-section.
　Next, the electron back scattering pattern analyzer (EBSD device) with a scanning electron microscope, of the L cross-section of the sample, 500X area (200μm × 200mμ) located thickness T × 1/4 from the surface of the sample It is observed in the double. Then, the observation screen, determine the area ratio of the tissue to observe the screen. Then, define the area ratio of each tissue and the volume fraction of each tissue.
[0048]
　Incidentally, in the observation screen, the identification of each organization, carried out as follows.
　Ferrite structure, bainite structure, and martensite structure, using the EBSD measurement results analysis software OIMAnalysis version 7.2.1, displays a measuring point having a BCC crystal structure to identify the value of the crystal orientation distribution and Image Quality the Map . Austenitic structure (residual including austenitic structure) displays the measuring points with the FCC crystal structure to identify the same manner.
[0049]
　(Function and Effect)
　illustrating operations and effects of the manufacturing method of quenching the molded article according to the present embodiment.
　In the present embodiment, the steel strip by blanking to form a steel plate blank 12, quenching the steel plate blank 12 in the first heat treatment step 20.
[0050]
　Here, when the quenching the steel strip, prone to cracking, etc. and the payout at the time when winding the steel strip being quenched.
[0051]
　Specifically, as the winding of the pickling line, it is a belt winding using a belt wrapper, a grip windings wound by bitten the tip of the strip to the mandrel of the tension reel. Steel strip which has been hardened is, because of the high yield stress, can not be belt winding. In addition, when you grip winding a steel strip which has been hardened, there is a possibility that a crack is a part that caught the mandrel. Moreover, when the payout is to flatten the steel strip in the leveler, the strip which is hardened in and risk of cracking during leveler passing plate, it may not be possible to modify the flat failure. If the flat is too bad, there may not grasp in the transfer robot to be introduced to the press.
[0052]
　In contrast, in the present embodiment, quenching the steel plate blank 12 that blanking a steel strip in the first heat treatment step 20. Accordingly, or flat hot press steel 30 being quenched by the first heat treatment step 20 in the leveler, without bent or wound, can be treated in the next step, to suppress unexpected cracking can.
[0053]
　In the first heat treatment step 20 prior to performing this quenching, it is desirable to plastic working at plastic working step the steel plate blank 12 is subjected to hot press or cold press. In this case, performing plastic working was combined with mold properly cooled with a cooling medium such as clamping and or cooling water in the first heat treatment step 20 first quenching of the shape.
[0054]
　If predetermined shape intermediate molded article is not flat after the first tempering, when setting the intermediate product in the mold at hot working after, easy positioning of the punch on the basis of a predetermined shape in addition to become possible, the deformation load by pressing it is expected that the growing molding properties by being dispersed.
[0055]
　In the plastic working process may be a cold working at hot working. In terms of reducing the step, the plastic working process is a hot working, it is preferable that the first quenching the while clamping in hot working.
[0056]
　Then, in the heating step 22 of the first heat treatment step 20, the martensitic transformation or to bainite transformation after which it attained a complete solid-solution of carbide once austenitizing the steel plate blank 12. Accordingly, the steel plate blank 12 as compared with the case where ferrite pearlite, in the molding quenching process 44 of the second heat treatment step 40, a hot press steel 30 in a state austenite grain size (hereinafter γ grain size) is small can be formed, it is possible to enhance the tissue toughness.
[0057]
　In the first heat treatment step 20, after austenitized by heating the steel sheet blank 12 to a temperature higher than Ac3 transformation point, thereby martensite transformation or bainite transformation is cooled.
[0058]
　At this time, the first quench in the first heat treatment step 20, desired to obtain a hot press steel material 30 having high percentage of martensite or bainite. Therefore, quenching start to start cooling, it is desirable to make all of the steel plate blank 12 and austenitic structure.
[0059]
　Therefore, in this embodiment, it is made higher than the Ac3 transformation point the heating temperature by the heating furnace 26, to austenite by heating the steel sheet blank 12 to a temperature higher than Ac3 transformation point. Therefore, even if the steel sheet blank 12 from the furnace 26 until the start of cooling is taken out steel sheet blank 12 is cooled, the quenching at the beginning to start the rapid cooling, maintaining the steel sheet blank 12 into austenite it can. Thus, it is possible to obtain a hot-press steel 30 high proportion of martensite or bainite.
[0060]
　Then, even the hot-press steel 30 when heated in the second heat treatment step 40, in a case where carbides in hot pressed steel material 30 prior to heating is not completely lost, carbide can be dissolved in a short time carbides from the particle size is fine. This allows loss of residual carbides at the start of the molding quenching process 44 of the second heat treatment step 40. Furthermore, it is possible to increase the toughness achieving grain refining of γ grain size by heating in the second heat treatment step 40. As a result of the second heat treatment step 40, since the hardened molded article 14 is martensitic, the strength of the hardened molded article 14 to be formed can be enhanced.
[0061]
　Specifically, when using high-carbon material to increase the strength of the final molded article, even if heating is finished undissolved carbides is likely to remain. It can also increase the heating temperature attempt to complete solid solution carbides and or longer heating time, which leads to coarsening of γ grain size. In that case, the martensite structure which is transformed from coarse γ particle size toughness is lowered, and the result of the residual carbides exist mismatch between the main phase occurs, the final molded article becomes brittle characteristics.
[0062]
　Such brittle characteristics when forming a vehicle body component in the final molded article such, when destroy before with the best material strength may occur with the final molded article material for example during a collision deformation. In this case, not obtained design characteristics aim always, a design change is forced.
[0063]
　In the manufacturing method of quenching the molded product of the present embodiment, the two or more austenitizing heat treatment at a first heat treatment step 20 and the second heat treatment step 40, the phase transformation process from two or more austenite to hard phase carry out the door. Thus, it is possible to it is possible to generate a martensitic transformation from loss and fine-grained γ grain size of residual carbides, obtaining a hardened molded article 14 of a high toughness.
[0064]
　That is, it is possible to obtain a quenching molded article 14 having high toughness while ensuring the strength.
[0065]
　In such quenching article producer method obtained in quenching the molded article 14, while having the above material strength 1.8 GPa, even stress multiaxiality high deformation field such as collision deformation, a brittle It does not occur early break. In other words, both high strength and high toughness aim exactly was confirmed.
[0066]
　In the present embodiment, by quenching in the first heat treatment step 20 to form a hot-press steel 30, the molded article quenching by pressing the hot press steel 30 in the second heat treatment step 40 It has been described the case of forming a 14, but is not limited thereto.
[0067]
　For example, in the first heat treatment step 20 for the first quenching after heating the steel sheet blank 12 to a temperature above the Ac3 transformation point, cooled with clamping by the mold at a temperature above the Ar3 transformation point, press molding and goods.
[0068]
　Here, in the first quench in the first heat treatment step 20, when simply quench the flat steel plate blank 12, there is a fear that cooling unevenness is lowered flatness occur. Moreover, further quenching the steel plate blank 12 is not flat, cooling unevenness is further increased.
[0069]
　Therefore, in the first heat treatment step 20, after heating the steel sheet blank 12 to a temperature higher than Ac3 transformation point, if cooled while clamping the mold at a temperature above the Ar3 transformation point, it is possible to suppress the cooling plaques .
[0070]
　Further, by the first heat treatment step 20 at the first predetermined shape of the press-molded product in quenching, it is possible to perform the second heat treatment step 40 stably.
[0071]
　The cooling is, the heat of the steel plate blank 12 from mold cooling to take a mold, direct cooling is desirable to cool out the refrigerant from the mold.
[0072]
　The first press-molded product obtained by molding in the heat treatment step 20 without pressing or the like in the second heat treatment step 40 may be performed only quenching in the press-molded product. Further, the steel plate blank 12 in the first heat treatment step 20 is press-molded, and may also be performed press or the like in the second heat treatment step 40.
[0073]
　Also, the case of performing the first heat treatment step 20 consisting of the heating step 22 and the cooling step 24 once has been described as an example, but the invention is not limited to, performing a first heat treatment step 20 a plurality of times it may be. In this case, in each of the first heat treatment step 20, a heat treatment, a heating temperature of Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ less, the high temperature and from the final heat treatment the heating temperature Ac3 transformation point in the final heat treatment step 40 Ac3 transformation point + it is preferable to 80 ° C. or less.
[0074]
　Although heating the steel blank 12 Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ below in the heating step 22 of the first heat treatment step 20, it is not limited thereto, the steel sheet blank 12, Ac3 transformation it may be heated above the point.
[0075]
　Here, Ac3 transformation point can be determined from the composition of the steel sheet by the following equation (1).
[0076]
　Ac3 (℃) = 910-203 × √C (mass%) + 44.7 × Si (mass%) - 30 × Mn (mass%) - 11 × Cr (mass%) + 700 × S (mass%) + 400 × Al (mass%) + 50 × Ti (% by mass) · (formula 1)
[0077]
　C: Carbon, Si: silicon, Mn: manganese, Cr: Chromium, S: Sulfur, Al: aluminum, Ti: Titanium
[0078]
　Ac3 transformation point obtained by this equation (1) shows the temperature of the case of heating at a slower heating rate (e.g., 3 ° C. / sec (per Celsius 3 degrees) following heating rate). However, in the production line, in order to improve productivity, it has been made to be heated at a faster heating rate.
[0079]
　Therefore, in order to improve productivity, it is desirable to heat in the first heat treatment to the steel plate blank 12 in the heating step 22 step 20 20 ° C. / sec (per 20 degrees Celsius) or more heating rate, other in embodiments, to set the heating rate in the heating step 22 of the first heat treatment step 20 to 20 ° C. / sec or higher.
[0080]
　In this case, Ac3 transformation point is departing from temperature determined by equation (1). This divergence is, if you set the heating rate to 20 ° C. / sec or more, has been found on the record to be a calculation result + about 20 ° C. by (Equation 1).
[0081]
　Therefore, in the manufacturing line in this embodiment, the heat treatment the heating temperature for heating the steel sheet blank 12 in the heating step 22, defined in the Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less in the range in the formula (1) described above It shall be set.
[0082]
　Although it is heating the hot press steel 30 temperature and the Ac3 transformation point + 80 ° C. or less than Ac3 transformation point in the second heat treatment step 40, it is not limited thereto, hot pressing steel material 30, Ac3 may be heated to the transformation point or higher.
[0083]
　Here, the Ac3 transformation point sought the aforementioned (Equation 1), the case of heating by as described above, a slow heating rate (e.g., 3 ° C. / sec (per Celsius 3 degrees) following heating rate) shows the temperature, in the manufacturing line, in order to improve productivity, it has been made to be heated at a faster heating rate.
[0084]
　Therefore, in order to improve productivity, it is desirable to heat in the second heat treatment heating step 42, the steel plate blank 12 20 ° C. / sec (per 20 degrees Celsius) steps 40 or more heating rate, other in embodiments, to set the heating rate in the heating step 42 of the second heat treatment step 40 to 20 ° C. / sec or higher.
[0085]
　In this case, the Ac3 transformation point, as described above, when deviates from temperature determined by equation (1), the deviation width, set the heating rate to 20 ° C. / sec or higher, calculation result of (Equation 1) + to be approximately 20 ℃ has been found on the track record.
[0086]
　Therefore, in the manufacturing line in this embodiment, the heat treatment the heating temperature for heating the hot press steel material 30 in the heating step 42 of the second heat treatment step 40, defined by Ac3 transformation point + 20 ° C. In the above equations (1) It shall be set in the range of Ac3 transformation point + 100 ° C. or less.
[0087]
　Then, the steel plate blank 12 is the amount of carbon contained is 0.3 wt% to 0.8 wt% or less, it is not limited thereto, the steel sheet blank 12, the amount of carbon containing 0.3 or it may be greater than percent by weight less than or 0.8 wt%.
[0088]
　The first heat treatment step 20 may not be performed. In this case, it is possible organization of the steel material used in the second heat treatment step 40 to obtain the effect described above, if bainite or martensite structure. At this time, if the sum of the volume fraction of martensite and bainite in the steel material used in the second heat treatment step 40 is 80% or more, excellent toughness compared to conventional products.
[0089]
　Furthermore, the apparatus having receiving the delivery of hot pressing steel material 30 described above (steel obtained by martensite transformation or bainite transformation after the steel plate blank 12 were austenitized) to implement only the second heat treatment step 40 it may be. In this case, when the hot press steel material 30 that has been delivered is not molded, quenched and pressed by the second heat treatment step 40 to form a molded article 14.
[0090]
　When the hot press steel material 30 that has been delivered is molded, it hardened only may be performed without pressing or the like in the second heat treatment step 40. Further, even when the hot press steel material 30 that has been delivered is molded, in the second heat treatment step 40 may be performed press.
Example
[0091]
　Table 1 is a table showing the chemical compositions of the steel sheet used in the following examples have been shown SteelA ~ SteelD.
[0092]
[Table 1]

[0093]
　(First embodiment)
　using SteelA (cold rolled steel) material having a thickness 1.4 mm, verify the effect of the two heat treatment using a mold for forming a bumper cross-sectional shape model 50 as shown in FIG. 2 did. Figure 3 shows the temperature history at the time of molding the bumper cross-sectional shape model 50.
[0094]
　In the first thermal processing step (corresponding to a first heat treatment step 20 of the embodiment), was held for about 5 minutes isothermally heated to 1000 ° C. in order to complete solid solution for molding material of the carbide, the press die perform molding by introducing within was quenched by cooling to room temperature by using a contact heat transfer by the mold.
[0095]
　Then, the second heat treatment step (corresponding to a second heat treatment step 40 of the embodiment), was heated to about 900 ° C. immediately above the Ac transformation point, while molding press decided immediately poured into a mold by cooling with a mold was manufactured hardened bumper sectional shape model 50 (example 1).
[0096]
　As a comparative example, was maintained for about 5 minutes isothermally heating the same SteelA material to about 950 ° C., subjected to molding and introduced into a press mold, bumper sectional shape model 50 is cooled in the mold was manufactured (comparative example 1).
[0097]
　Further, after about 5 minutes and kept isothermally heated to about 950 ° C. in a similar manner using the low SteelD material amount of carbon C, subjected to molding and introduced into a press mold, and cooled at a mold bumper It was manufactured sectional shape model 50 (Comparative example 2).
[0098]
　Next, with respect to these three bumper sectional shape model 50, as shown in FIG. 4, in addition a static load from the hat top and compared the deformation resistance and the stroke curve of the bumper cross-sectional shape model 50. Figure 5 shows the results.
[0099]
　In the bumper cross-sectional shape model 50 of Comparative Example 1 of the heat treatment once using the same materials as in Example 1 (hot stamp Normal process), stroke rupture and the load at 8.5mm is rapidly lowered. In contrast, after the fine γ subjected to two austenitization heat treatment, the bumper cross-sectional shape model 50 of Example 1 aimed at higher toughness by martensitic transformation, without breaking the stroke until 17mm than maintaining high deformation load.
[0100]
　Further, deformation load of the bumper cross-sectional shape model 50 of Example 1 is higher than that of low carbon content SteelD (Comparative Example 2), and SteelD (Comparative Example 2) as well as plastic deformation to a high stroke maintain it can be seen that.
[0101]
(Example 2)
　using a thickness 2.3 mm SteelB material (hot-rolled steel sheet), to verify the effect of the two heat treatment using a mold for forming a M-shaped bumper 52 shown in FIG.
[0102]
　In the first thermal processing step (corresponding to a first heat treatment step 20 of the embodiment), was held approximately 6 minutes to heat the materials to put to 935 ° C. in a gas furnace, a flat mold top removed material Place the parts, immediately covered with a mold of the plate from the material an upper and quenched with a flat plate state by taking heat in molds.
[0103]
　Then, after about 2.5 minutes was put in a gas furnace set the material was quenched to 860 ° C. held by the first thermal processing, was charged into a press mold and taken out immediately, molded at a temperature above Ar3 transformation point and quenched with processed hardened (corresponding to a second heat treatment step 40 of the embodiment), was manufactured M-shaped bumper 52 (example 2).
[0104]
　For comparison, Example 2 and after the SteelB the same material and held for about 6 minutes and heated to the charged 950 ° C. in a gas furnace, and molded by introducing into the press die, M-shaped bumper 52 hardened was manufactured (comparative example 3).
[0105]
　Next, the bending these three points by R150 indenter with two M-shaped bumper 52 is set to a dynamic hydraulic test machine set to span 800mm bending with speed 9km / h (hour 9km), the load at that time stroke curves were compared in terms similar to the first embodiment. The test results are shown in Figure 7.
[0106]
　Similarly to the first embodiment, whereas the Comparative Example 3 is reduced load by breaking a stroke of about 60 mm, Example 2 was performed twice austenitizing heat treatment is not reduced sudden load, abrupt it can be seen that showed stable load characteristic without load change.
[0107]
(Example 3)
　Similarly the second embodiment, using SteelC (cold rolled steel) material having a thickness of 1.6 mm, the effect of two heat treatment using a mold for molding the center pillar 54 shown in FIG. 8 It was verified. In the first round heat treatment step (corresponding to a first heat treatment step 20 of the embodiment), the material hardening in the second round heat treatment step (corresponding to a second heat treatment step 40 of the embodiment), molding and simultaneously It was hardening.
[0108]
　In first thermal processing step, after holding for about 5 minutes and heated to put the material in the gas oven 950 ° C., placed on the flat portion of the die top surface removed material, immediately dies of the plate from the material an upper covered and hardened in a state of flat plate by taking heat in molds.
[0109]
　Then, after maintaining the first thermal approximately 2 minutes to put the material was hardened in a gas furnace set at 870 ° C. at step immediately taken out to molding at a temperature higher than the Ar3 transformation point and put into the press die by quenching with quenching was fabricated center pillar 54 (example 3).
[0110]
　Further, as a comparison, the SteelC material of the same material as in Example 3 was held for about 5 minutes and heated to the charged 950 ° C. in a gas furnace, and simultaneously hardened molded and put into the press die, the center pillar 54 was manufactured (comparative example 4).
[0111]
　Then, to manufacture a closing plate which is cut to fit than 440MPa grade cold rolled steel sheet 1.4mm to the outer shape of the center pillar 54, and a closed cross section by closing the rear opening portion of the center pillar 54 in the closing plate. Joining the center pillar 54 and the closing plate is carried out in φ6WR type electrode shape nugget diameter 4.5√T, at a pitch 30 mm, it was fabricated center pillar 54. Example twice heat treatment 3 and once the same fabrication conditions also with Comparative Example 4 of the heat treatment.
[0112]
　Then, these two center pillar 54 is set to drop tower impact testing machine with support spacing 600 mm, subjected to three-point bending by φ100 indenter at a speed 25km / h (hour 25km), the load-stroke curve at that time It was compared in the same viewpoint as the first embodiment. The test results are shown in Figure 9.
[0113]
　Similar to the first and second embodiments, the load rapidly decreases and the base material fracture occurs once Comparative Example 4 In stroke 60mm heat treatment. However, in Example 3 was subjected to two rounds of austenitizing heat treatment, the stroke rather than reduction of sudden load to greater than 90 mm, it can be seen that performance than Comparative Example 4 is good.
[0114]
　Austenitizing at a temperature higher than Ac3 transformation point two or more times than the respective examples, and the manufacturing method of quenching performed molded at a temperature higher than Ar3 transformation point, than the austenitizing and quenching with one of a hot stamping, high it was confirmed that the molded article having excellent deformation properties in toughness is obtained.
[0115]
　It is a description of the code below.
The method of manufacturing 10 hardened molded article
12 steel blank
(steel) 14 hardened molded article
30 for hot pressing steel
40 final heat treatment step
50 the bumper cross-sectional shape model
52 M-shaped bumper
54 center pillar
　«note»
　from this specification, the following aspects are conceptualized.
　That is, the first aspect,
　after austenitized by heating blanking the steel to a temperature higher than Ac3 transformation point, and the first heat treatment step of martensite transformation or bainite transformation is cooled,
　the first heat treatment step after austenite by heating the went steel to a temperature above the Ac3 transformation point, and a second heat treatment step of martensitic transformation by cooling,
　with a
　of the first heat treatment step or the second heat treatment step after heating the steel in at least one step to a temperature above the Ac3 transformation point, the production method of the molded completed quenched molded article at a temperature above the Ar3 transformation point.
　The second aspect,
　the first heat treatment the heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ less,
　heating the steel in the second heat treatment step the second heat treatment the heating temperature, quenching method for producing a molded article according to a first aspect of the high temperature and Ac3 transformation point + 80 ° C. or less than Ac3 transformation point to.
　The third aspect,
　the first heat treatment the heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less, which is defined by equation (1),
　wherein the a second heat treatment heating temperature for heating the steel at a second heat treatment step, the formula (1) by the Ac3 according to a first aspect of the transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less quenching the molded article defined in Production method.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by mass)
　fourth aspect,
　the heating rate of the first heat treatment step, 20 ° C. / sec is more described in the third aspect of the quenching moldings Production method.
　The fifth aspect,
　the heating rate of the second heat treatment step, the third aspect or quenching method for producing a molded article according to the fourth embodiment is 20 ° C. / sec or higher.
　The sixth embodiment,
　the first heat treatment the heating time after reaching the first heat treatment the heating temperature in the step until the end of the heating in the first heat treatment step, a second aspect is within 400 seconds quenching method for producing a molded article according to any of embodiments of the fifth aspect of.
　The seventh embodiment,
　the heating time after reaching the second heat treatment the heating temperature before terminating the heating at the second heat treatment step in the second heat treatment step, the second aspect is within 400 seconds quenching method for producing a molded article according to any of embodiments of the sixth aspect of.
　Eighth aspect,
　wherein the steel material, quenching method for producing a molded article according to any of embodiments of the first aspect seventh aspect the carbon content is 0.8 wt% or less than 0.3 wt%.
　Ninth aspect,
　steel is processed by the first heat treatment step, the production of hardened molded article according the first aspect volume fraction of the hard phase is less than 90% in any of the embodiments of the eighth aspect Method.
　Tenth aspect,
　the second heat treatment step the molded article obtained through the quenching according the first aspect the volume fraction of martensite is 50% or more to any of embodiments of the ninth aspect manufacturing method of a molded article.
　11th aspect,
　the first heat treatment the cooling quenching method for producing a molded article according to any of embodiments of the first aspect eighth aspect which is performed in a state where the mold clamping the steel process.
　A twelfth aspect is
　blanking after austenitized by heating at a temperature higher than ranking the steel the Ac3 transformation point, hot manufacturing method of a press steel material to martensite transformation or bainite transformation is cooled.
　A thirteenth aspect is
　after heating the steel material to a temperature above the Ac3 transformation point, hot manufacturing method of a press steel material according to a twelfth aspect of cooling by molding at a temperature higher than the Ar3 transformation point.
　Aspect of the fourteenth,
　the 12th aspect or hot manufacturing method of a press steel material according to a thirteenth aspect and less Ac3 transformation point + 0.99 ° C. Ac3 transformation point + 50 ℃ than the heating temperature of the steel material.
　15 embodiment,
　the heating temperature of the steel product, the formula (1) by the Ac3 according to the twelfth aspect or the thirteenth aspect and transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. The following hot press steel material defined Production method.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
　16 embodiment,
　the temperature rising rate during the heating, production of hot-press steel according to the fifteenth aspect is 20 ° C. / sec or higher Method.
　17 embodiment,
　the heating temperature in the heating time after reaching the hot manufacturing method of a press steel material as set forth in the 14th aspect is within 400 seconds in any of the aspects of the sixteenth embodiment.
　18 embodiment,
　the steel, a method of manufacturing hot press steel according twelfth aspect the carbon content is 0.3 wt% to 0.8 wt% in one embodiment of the seventeenth aspect .
　19 embodiment,
　the steel is hot manufacturing method of a press steel material according to any of embodiments of the twelfth aspect eighteenth aspect volume fraction of the hard phase is less than 90%.
　20th aspect,
　wherein the cooling is quenching method for producing a molded article according to any of embodiments of the first aspect eighth aspect which is performed in a state where the mold clamping the steel material.

　21 embodiment,
　the carbon content of 0.3 wt% to 0.8 wt% or less even in martensite and bainite volume fraction sum of 80% or more of hot-press steel.
　22 embodiment,
　the hot press steel according to a twenty-first aspect is a flat blank.
　23 embodiment,
　the hot press steel according to a twenty-first aspect is a press-molded product.
　24 embodiment,
　after forming at a temperature higher than the austenite to Ar3 transformation point by heating the hot press steel according to a temperature above the Ac3 transformation point to any of embodiments of the 23rd aspect from a 21 aspect, cooled quenching method for producing a molded article to martensite transformation to.
　25 embodiment,
　after heating the martensite and bainite volume fraction of the sum of 80% or more of the molded article to a higher heat treatment the heating temperature than Ac3 transformation point austenitization, quenching to martensite transformation by cooling manufacturing method of a molded article.
　26 embodiment,
　the molded article production method of hardening the molded article according to the 25th aspect is a hardened molded article.
　27 embodiment,
　the heat treatment the heating temperature is twenty-fifth aspect or quenching method for producing a molded article according to the 26th aspect is less temperature and Ac3 transformation point + 80 ° C. from the Ac3 transformation point.
　28 embodiment,
　the heat treatment the heating temperature is, the formula (1) being defined Ac3 transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less in
　the 25 aspect or manufacturing method of quenching the molded article according to 26 embodiment .
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
　29 embodiment,
　the temperature rising rate during heating to the heat treatment the heating temperature is, quenching molding according to the 28 embodiment is 20 ° C. / sec or higher method of manufacturing the goods.
　30th aspect,
　the heating time after reaching the heat treatment the heating temperature is within 400 seconds
　hardening method for producing a molded article according to any aspect of the 29th aspect from a 25 aspect.
　
　In addition, the present specification, the following other aspects are conceptualized.
　First other embodiment,
　after austenitized by heating the steel above Ac3 transformation point, and the first heat treatment step of martensite transformation or bainite transformation to cool,
　was first heat treatment step steel the after austenitized by heating to above Ac3 transformation point, and a second heat treatment step of martensitic transformation by cooling,
　comprising a,
　in at least one step of the first heat treatment step or the second heat treatment step method for producing a hardened molded article for molding the steel material at a temperature not lower than Ar3 transformation point.
　Second other embodiment,
　the first heat treatment the heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ or less,
　in the second heat treatment step the second heat treatment the heating temperature, Ac3 quenching method for producing a molded article according to the first other embodiment of the transformation point or higher Ac3 transformation point + 80 ° C. or less to heat the steel material.
　Third other embodiment,
　the first heat treatment the heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less, which is defined by the formula (1) ,
　according to the first other embodiment to the second heat treatment the heating temperature for heating the steel in the second heat treatment step, the formula (1) being defined Ac3 transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less manufacturing method of quenching the molded article.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
　4th other embodiments,
　heating rate of the first heat treatment step, according to a third another aspect is 20 ° C. / sec or higher manufacturing method of quenching the molded article.
　Another aspect of the fifth,
　the heating rate of the second heat treatment step, a third other aspects or quenching method for producing a molded article according to a fourth other embodiment is 20 ° C. / sec or higher .
　Another aspect of the sixth,
　the first heat treatment step at heating time after reaching the first heat treatment the heating temperature before terminating the heating in the first heat treatment step is within 400 seconds quenching method for producing a molded article according to any of embodiments of another aspect 5 of the fifth from the second other aspects.
　Another aspect of the seventh,
　the second heat treatment step at heating time after reaching the second heat treatment the heating temperature before terminating the heating at the second heat treatment step is within 400 seconds quenching method for producing a molded article according to any one of the sixth aspect of another embodiment from the second other aspects.
　Another aspect of the eighth,
　the steel material, from a first other embodiment the amount of carbon contained is not more than 0.3 mass% to 0.8 mass% in any of the embodiments of the seventh other embodiment quenching method for producing a molded article according.
　Another aspect of the ninth,
　after austenitized by heating the steel above Ac3 transformation point, the production method of the hot press steel to martensite transformation or bainite transformation is cooled.
　Another aspect of the tenth
　molding the steel material heated to above Ac3 transformation point at a temperature above Ar3 transformation point, the ninth method of hot-press steel according to another aspect manufacture cooling.
　11 other aspects,
　a method of manufacturing a ninth other embodiment or tenth other embodiment of the hot press steel to not more than Ac3 transformation point + 0.99 ° C. Ac3 transformation point + 50 ℃ than the heating temperature of the steel product .
　Twelfth another aspect,
　the heating temperature of the steel product, other aspect or the 10 other aspects of the ninth to Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less, which is defined by the formula (1) hot manufacturing method of a press steel material according to.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
　other aspects of the thirteenth,
　the temperature rising rate during the heating, the heat of paragraph 12 of another embodiment is 20 ° C. / sec or higher production method between press for steel.
　14 other embodiments,
　the heating time after reaching the heating temperature is 11 how other aspects of the hot press steel according to another embodiment of the thirteenth production is within 400 seconds .
　Another aspect of the fifteenth,
　the steel material, the ninth other embodiment the amount of carbon contained is not more than 0.3 mass% to 0.8 mass% in any of the embodiments of the fourteenth other embodiment hot manufacturing method of a press steel material according.
　Another aspect of the sixteenth,
　the carbon content of 0.3 wt% to 0.8 wt% or less even in martensite and bainite volume fraction sum of 80% or more of hot-press steel.
　Another aspect of the seventeenth,
　after molding at hot temperature steel material is heated to above Ac3 transformation point austenitized above Ar3 transformation point press according to another embodiment of the sixteenth, martensitic transformation by cooling quenching method for producing a molded article to be.
　18 of another embodiment,
　martensite and after the sum of the volume fraction of the bainite structure by heating 80% of the molded article to heat treatment the heating temperature higher than Ac3 transformation point to austenite, martensite and cooled method for producing a hardened molded article to transform.
　Another aspect of the nineteenth,
　wherein the molded article, the 18 method of hardening the molded article according to another aspect manufacturing a hardened molded article.
　Another aspect of the twentieth,
　the heat treatment the heating temperature is, quenching method for producing a molded article according to the eighteenth other aspect or the 19 other aspect is Ac3 transformation point + 80 ° C. or less than Ac3 transformation point.
　Another aspect of the twenty-first,
　the heat treatment the heating temperature is to another aspect of another embodiment or the 19 of the 18 to Ac3 transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less, which is defined by the formula (1) quenching method for producing a molded article according.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by mass)
　another aspect of the twenty-second,
　heating rate when heating to the heat treatment the heating temperature is 21 another embodiment is 20 ° C. / sec or higher quenching method for producing a molded article according to.
　Another aspect of the 23,
　the heating time after reaching the heat treatment the heating temperature is, quenching from the 18 other embodiments are within 400 seconds according to any of embodiments of the other aspects of the 22 manufacturing method of a molded article.
　2016 November 25 discloses a the Japanese Patent Application No. 2016-229472 filed on days, entirely incorporated herein by reference.
　Further, all documents described herein, patent applications and technical standards, each individual publication, to the same extent as if the patent and technical standards are incorporated by reference marked specifically and individually, It incorporated by reference herein.

The scope of the claims
[Requested item 1]
　After austenite by heating the blanking and steel material to a temperature higher than Ac3 transformation point, and the first heat treatment step of martensite transformation or bainite transformation is cooled,
　the steel the Ac3 transformation point was first heat treatment step after austenite by heating to higher temperatures, a second heat treatment step of martensitic transformation by cooling,
　comprising a
　steel in at least one step of the first heat treatment step or the second heat treatment step Ac3 after heating to above the transformation temperature, the production method of the molded completed quenched molded article at a temperature above the Ar3 transformation point.
[Requested item 2]
　The first heat treatment heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 50 ℃ above Ac3 transformation point + 150 ℃ below,
　a second heat treatment for heating the steel in the second heat treatment step the heating temperature, quenching method for producing a molded article according to claim 1, high-temperature and Ac3 transformation point + 80 ° C. or less than Ac3 transformation point.
[Requested item 3]
　The first heat treatment heating temperature for heating the steel in the first heat treatment step, with the Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less, which is defined by equation (1),
　in the second heat treatment step a second heat treatment heating temperature for heating the steel material, quenching method for producing a molded article according to claim 1, Ac3 transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less, which is defined by equation (1).
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
[Requested item 4]
　The heating rate of the first heat treatment step, hardening method for producing a molded article according to claim 3 is 20 ° C. / sec or higher.
[Requested item 5]
　The heating rate of the second heat treatment step, hardening method for producing a molded article according to 20 ° C. / sec or higher in claim 3 or claim 4.
[Requested item 6]
　The heating time after reaching the first heat treatment the heating temperature before terminating the heating in the first heat treatment step in the first heat treatment step, of claims 2 5 is within 400 seconds quenching method for producing a molded article according to any one.
[Requested item 7]
　The heating time after reaching the second heat treatment the heating temperature before terminating the heating at the second heat treatment step in the second heat treatment step, of claims 2 6 is within 400 seconds quenching method for producing a molded article according to any one.
[Requested item 8]
　The steel, quenching method for producing a molded article according to any one of claims 1 to 7 carbon content is 0.8 wt% or less than 0.3 wt%.
[Requested item 9]
　The steel is processed in the first heat treatment step, the manufacturing method of hardening the molded article as claimed in any one of claims 8 volume fraction of the hard phase is less than 90%.
[Requested item 10]
　The second heat treatment step the through-obtained molded article manufacturing method of hardening the molded article as claimed in any one of claims 9 volume fraction of martensite is 50% or more.
[Requested item 11]
　Wherein the cooling of the first heat treatment step quenching method for producing a molded article as claimed in any one of claims 8 to be performed while clamping the steel material.
[Requested item 12]
　After austenite by heating the blanking and steel material to a temperature higher than Ac3 transformation point, the production method of the hot press steel to martensite transformation or bainite transformation is cooled.
[Requested item 13]
　After heating the steel material to a temperature above the Ac3 transformation point, hot manufacturing method of a press steel material according to claim 12, cooled by molding at a temperature higher than the Ar3 transformation point.
[Requested item 14]
　Hot manufacturing method of a press steel material according to claim 12 or claim 13 or less Ac3 transformation point + 0.99 ° C. Ac3 transformation point + 50 ℃ than the heating temperature of the steel material.
[Requested item 15]
　The heating temperature of the steel material, manufacturing method of hot-press steel according to claim 12 or claim 13, Ac3 transformation point + 70 ℃ above Ac3 transformation point + 170 ° C. or less, which is defined by equation (1).
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
[Requested item 16]
　The heating rate during heating, hot manufacturing method of a press steel material according to claim 15 is 20 ° C. / sec or higher.
[Requested item 17]
　The heating time from reaching the heating temperature, hot manufacturing method of a press steel material according to any one of claims 16 claim 14 is within 400 seconds.
[Requested item 18]
　The steel is hot manufacturing method of a press steel material according to claims 12 to any one of claims 17 carbon content is not more than 0.3 mass% to 0.8 mass%.
[Requested item 19]
　The steel is hot manufacturing method of a press steel material according to any one of claims 12 to claim 18 volume fraction of the hard phase is less than 90%.
[Requested item 20]
　The cooling quenching method for producing a molded article according to any one of claims 1 to claim 8 which is carried out while clamping the steel material.
[Requested item 21]
　Carbon content of 0.3 wt% to 0.8 wt% or less even in martensite and bainite volume fraction sum of 80% or more of hot-press steel.
[Requested item 22]
　Hot press steel according to claim 21 which is a flat blank.
[Requested item 23]
　Hot press steel according to claim 21 which is a press-molded product.
[Requested item 24]
　After molding at a temperature higher than the austenite to Ar3 transformation point by heating the hot press steel according to a temperature above the Ac3 transformation point to any one of claims 23 claim 21, martensitic transformation by cooling quenching method for producing a molded article to be.
[Requested item 25]
　After martensite and austenite sum of the volume fraction of bainite structure by heating 80% of the molded article to a higher heat treatment the heating temperature than Ac3 transformation point, the production method of hardening the molded article to martensite transformation by cooling .
[Requested item 26]
　The molded article production method of hardening the molded article according to claim 25 which is a quenching moldings.
[Requested item 27]
　The heat treatment heating temperature, quenching method for producing a molded article according to claim 25 or claim 26 high temperature and is less than Ac3 transformation point + 80 ° C. from the Ac3 transformation point.
[Requested item 28]
　The heat treatment heating temperature, quenching method for producing a molded article according to claim 25 or claim 26 and wherein (1) being defined Ac3 transformation point + 20 ° C. or higher Ac3 transformation point + 100 ° C. or less.
　Equation (1) Ac3 (℃) = 910-203 × √C ( wt%) + 44.7 × Si (wt%) - 30 × Mn (wt%) - 11 × Cr (wt%) + 700 × S (wt% ) + 400 × Al (wt%) + 50 × Ti (% by weight)
[Requested item 29]
　Heating rate when heating to the heat treatment the heating temperature is, quenching method for producing a molded article according to claim 28 is 20 ° C. / sec or higher.
[Requested item 30]
　The heat treatment the heating time from reaching the heating temperature, quenching method for producing a molded article according to any one of claims 29 claim 25 is within 400 seconds.