JP4724406B2 - Method for producing hot-pressed high-strength steel members with low residual stress - Google Patents
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Description
本発明は、鋼板を加熱してプレス加工を行なうホットプレス成形をした後、次工程でトリミング、ピアシング等の後加工を行なうことによって引張強さが９８０ＭＰａ以上の高強度鋼製部材を製造する方法に関するもので、例えば自動車の足回り、シャーシ、メンバー、衝突安全用補強部材等に用いられる高強度部材として有効に活用できる。 The present invention relates to a method for producing a high strength steel member having a tensile strength of 980 MPa or more by performing post-processing such as trimming and piercing in the next step after hot-press forming in which a steel plate is heated and pressed. For example, it can be effectively used as a high-strength member used for automobile undercarriages, chassis, members, collision safety reinforcing members and the like.
近年、地球環境保全に向けた自動車軽量化ニーズ、衝突安全性の向上ニーズ等に伴い、プレス成形によって製造される鋼製部材にも引張強度で９８０ＭＰａ以上の高強度化が強く望まれている。しかし、素材としての鋼板の高強度化はプレス成形性の低下を招き、複雑な形状の製作が困難となる。具体的には、延性低下による破断、スプリングバックによる寸法精度の劣化という問題等である。このため、高強度鋼板を用いてのプレス加工による複雑な形状の製作は容易ではない。 In recent years, with the need for weight reduction of automobiles for environmental protection and the need for improvement of collision safety, a steel member manufactured by press molding is strongly desired to have a tensile strength of 980 MPa or more. However, increasing the strength of a steel sheet as a raw material causes a decrease in press formability, making it difficult to manufacture complex shapes. Specifically, there are problems such as breakage due to reduced ductility and deterioration of dimensional accuracy due to springback. For this reason, it is not easy to produce a complicated shape by press working using a high-strength steel plate.
そこで、最近注目されつつある技術としてホットプレス（熱間プレス）がある。本技術は、例えば特開２００２−２８２９５１号公報（特許文献１）に開示されているように、鋼板を加熱してプレス加工する方法であり、鋼板が高温ゆえに、軟質、高延性となり、複雑な形状も寸法精度良く成形可能である。加えて、加熱時にオーステナイトが生成する温度域まで昇温しておけば、プレス加工後の冷却、あるいは、プレス加工時の金型内で冷却することにより、所望の材質を得ることが可能であり、すなわち、冷却速度を高めることにより、硬化相であるマルテンサイトを生成し、高強度部材を得ることが可能である。 Therefore, there is a hot press (hot press) as a technology that has been attracting attention recently. This technique is a method of heating and pressing a steel plate as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-282951 (Patent Document 1). Since the steel plate is hot, it becomes soft and highly ductile, and is complicated. The shape can also be molded with dimensional accuracy. In addition, if the temperature is raised to a temperature range where austenite is generated during heating, it is possible to obtain a desired material by cooling after pressing or by cooling in a mold during pressing. That is, by increasing the cooling rate, it is possible to produce martensite which is a cured phase and obtain a high strength member.
しかし、このようなマルテンサイト組織を含む高強度部材は、水素を起因とする水素脆化が懸念され、特に、プレス成形後の次工程でトリミングやピアシング等の後加工を行なうと、非常に高い残留応力が発生し、特に４００ＭＰａを超える場合は、耐水素脆化特性を大きく劣化させてしまう。このような問題に対して、従来技術として、レーザートリムやレーザーピアスといったレーザー加工を利用する方法や、先にトリミングやピアシングを行ない、その後に加熱してプレスするといった先加工という方法がある。 However, high strength members containing such a martensite structure are concerned with hydrogen embrittlement due to hydrogen, and are particularly high when post-processing such as trimming and piercing is performed in the next process after press molding. Residual stress occurs, and particularly when it exceeds 400 MPa, the hydrogen embrittlement resistance is greatly deteriorated. In order to deal with such problems, there are conventional methods of utilizing laser processing such as laser trimming and laser piercing, and methods of prior processing in which trimming and piercing are performed first, followed by heating and pressing.
しかしながら、レーザー加工は、装置が非常に高価で、かつ生産効率の観点から適用が難しく、また、先加工は、その後の加熱やプレスで、先加工部の寸法精度、形状精度が低下するという問題に加え、Ａｌめっき鋼板等のスケールガード鋼板を使用したとしても、先加工断面の表面にスケールが生成するという問題がある。 However, laser processing is very expensive and difficult to apply from the viewpoint of production efficiency, and pre-processing is a problem that the dimensional accuracy and shape accuracy of the pre-processed part are reduced by subsequent heating and pressing. In addition, even if a scale guard steel plate such as an Al-plated steel plate is used, there is a problem that scale is generated on the surface of the pre-processed cross section.
また、トリミングを伴う加工に関した技術として、特開平５−１３８４３１号公報（特許文献２）では、金属板のトリミングやスリッティングの際、切断機とその前または後のピンチロールとの間の金属板に直接通電し、金属板端部を加熱する方法が開示されている。この方法によると、せん断による加工硬化の低減、あるいは、せん断により発生した加工硬化の除去が可能であり、次工程での割れを減らすことが可能である。また、残留応力に関しては言及されていないが、金属端部の残留応力緩和にも寄与すると考えられる。しかしながら、この方法では、生産効率が低下するのみならず、加熱された部分の材質が変化してしまい、高強度部材としての要求特性を均一に満足することが不可能となる。 In addition, as a technique related to processing involving trimming, Japanese Patent Laid-Open No. 5-138431 (Patent Document 2) discloses a metal between a cutting machine and a pinch roll before or after the trimming or slitting of a metal plate. A method of directly energizing the plate and heating the end of the metal plate is disclosed. According to this method, work hardening due to shearing can be reduced, or work hardening generated by shearing can be removed, and cracks in the next process can be reduced. Moreover, although it is not mentioned regarding a residual stress, it is thought that it contributes also to the residual stress relaxation of a metal edge part. However, this method not only reduces the production efficiency, but also changes the material of the heated portion, making it impossible to uniformly satisfy the required characteristics as a high-strength member.
本発明は、ホットプレス後に、トリミングまたはピアシング等の後加工を施して製造する、９８０ＭＰａ以上の引張強度を有し、かつ、残留応力の低い高強度鋼製部材の製造方法を提供することを目的とする。 An object of the present invention is to provide a method for producing a high-strength steel member having a tensile strength of 980 MPa or more and low residual stress, which is produced by performing post-processing such as trimming or piercing after hot pressing. And
本発明者らは、上記のような課題を克服するために、ホットプレスで成形した部材を、種々の条件でトリミングやピアシングを行ない、残留応力の測定、加工部端面の性状調査を実施した。その結果、部材全域の高強度を確保しつつ、かつ、残留応力の上昇を抑制し、加えて、加工部端面のスケール生成を抑制するためには、従来のようにプレス時に下死点で保持して金型で焼き入れするのではなく、プレスはクランクプレス等を用いて短時間で行ない、部材がオーステナイト域中にある間にトリミングやピアシング等の後加工を実施し、その後冷却することが有効であることを見出した。 In order to overcome the above-described problems, the present inventors performed trimming and piercing on members molded by hot pressing under various conditions, measured residual stress, and investigated the properties of the end face of the processed part. As a result, while maintaining high strength in the entire area and suppressing the increase in residual stress, in addition to suppressing the scale formation on the end face of the processed part, it is held at the bottom dead center during pressing as in the past. Rather than quenching with a mold, the press can be performed in a short time using a crank press, etc., and post-processing such as trimming and piercing can be performed while the member is in the austenite region, and then cooled. I found it effective.
本発明は、上記知見に基づいてなされたもので、その要旨とするところは以下の通りである。
（１）鋼板をＡｃ3 変態点以上１３００℃以下の温度に加熱した後、Ａｒ3 変態点＋２０℃以上の温度でホットプレスし、引き続きＡｒ3 変態点以上の温度で、部材をプレス下死点で保持して金型で焼き入れずに、部材がオーステナイト域中にある間に、トリミングまたはピアシングの後加工を施し、ホットプレス時のサイクルを、１０回／分以上とし、その後冷却するが、前記冷却の速度を１０℃／秒以上１０００℃／秒以下の速度で冷却し、９８０ＭＰａ以上の引張強度を有し、かつ、残留応力が４００ＭＰａ以下で、マルテンサイト組織の面積率が６０％以上である部材を得ることを特徴とする残留応力の低いホット
プレス高強度鋼製部材の製造方法。
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) After heating the steel plate to a temperature not lower than the Ac 3 transformation point and not higher than 1300 ° C., hot pressing is performed at a temperature not lower than the Ar 3 transformation point + 20 ° C., and then the member is pressed at the bottom dead center at a temperature not lower than the Ar 3 transformation point. While being held in the mold and not quenched with a mold, while the member is in the austenite region , after trimming or piercing is performed, the cycle at the time of hot pressing is set to 10 times / minute or more, and then cooled, The cooling rate is 10 ° C./second or more and 1000 ° C./second or less, the tensile strength is 980 MPa or more, the residual stress is 400 MPa or less, and the area ratio of the martensite structure is 60% or more. A method for producing a hot-pressed high-strength steel member with low residual stress, characterized by obtaining a member.
（２）後加工部端面のスケール厚みが５０μｍ以下であることを特徴とする前記（１）記載の残留応力の低いホットプレス高強度鋼製部材の製造方法にある。 (2) The method for producing a hot-pressed high-strength steel member with low residual stress according to (1), wherein the scale thickness of the end face of the post-processed portion is 50 μm or less.
本発明により、９８０ＭＰａ以上の引張強度を有し、かつ、残留応力が４００ＭＰａ以下で、後加工部端面のスケール厚みが５０μｍ以下の高強度鋼製部材の製造が可能であり、自動車等の耐水素脆化特性に優れた部品として有効で工業的価値が高い。 According to the present invention, it is possible to produce a high-strength steel member having a tensile strength of 980 MPa or more, a residual stress of 400 MPa or less, and a scale thickness of the end face of the post-processed part of 50 μm or less, Effective as a component with excellent embrittlement characteristics and high industrial value.
以下に、本発明を更に詳細に説明する。
本発明の製造方法は、図１に示すように、大きく４工程に分けられる。第１工程は加熱工程、第２工程は高温域でのプレス工程、第３工程はトリミングやピアス等の後加工工程、第４工程は冷却工程である。
Hereinafter, the present invention will be described in more detail.
The manufacturing method of the present invention is roughly divided into four steps as shown in FIG. The first step is a heating step, the second step is a press step in a high temperature range, the third step is a post-processing step such as trimming or piercing, and the fourth step is a cooling step.
まず、第１工程の加熱についてであるが、６００℃程度の加熱でもプレス成形性は向上する。しかし、９８０ＭＰａ以上の高強度を得るためには、加熱時にオーステナイト組織とし、第４工程である冷却時にマルテンサイト組織を得る必要があるため、下限をＡｃ3 変態点以上の温度とした。Ａｃ3 変態点温度は、鋼板２を構成する化学成分によって異なるが、おおよそ８００℃程度である。一方、過度の加熱は、鋼板組織の粗粒化、スケールの増加、加熱コストの上昇を招くため、上限は１３００℃とした。なお、加熱方法には特段の限定はないが、例えば加熱炉１を用いて均一に速く効率良く加熱可能な装置を使用することが好ましい。また、目的とする部材強度によっては、加熱時にフェライト相が残存していても問題ない。
First, regarding the heating in the first step, the press formability is improved by heating at about 600 ° C. However, in order to obtain a high strength of 980 MPa or more, it is necessary to obtain an austenite structure at the time of heating and a martensite structure at the time of cooling, which is the fourth step. Therefore, the lower limit is set to a temperature equal to or higher than the Ac 3 transformation point. The Ac 3 transformation point temperature is about 800 ° C., although it varies depending on the chemical components constituting the
第２工程のプレスは、次工程でのトリミングやピアス等の後加工を部材組織がオーステナイト域中で実施する必要があることを考慮すると、加熱後なるべく短い時間でプレスを開始し、終了するが必要であるため、プレス成形のサイクルを１０回／分以上に限定した。尚、プレス成形のサイクルとは、プレス成形機に鋼板をセットしてから、成形が完了し、次の鋼板をセットするまでと定義する。また、プレス成形の開始温度は、第３工程での温度を確保するため、Ａｒ3 変態点＋２０℃以上とし、好ましくはＡｒ3 変態点＋５０℃以上とすることが好適である。 In consideration of the fact that the member structure needs to be subjected to post-processing such as trimming and piercing in the next step in the austenite region, the press in the second step starts and ends in as short a time as possible after heating. Since it is necessary, the press molding cycle was limited to 10 times / minute or more. The cycle of press forming is defined as the time from setting a steel plate to the press forming machine until the completion of forming and setting the next steel plate. In order to secure the temperature in the third step, the press molding start temperature is Ar 3 transformation point + 20 ° C. or higher, preferably Ar 3 transformation point + 50 ° C. or higher.
第３工程のトリミングやピアス等の後加工工程は、本発明において、制御すべき最も重要な工程であり、この工程をＡｒ3 変態点以上の温度域で実施することにより、部材の高強度を確保しつつ、残留応力の上昇を抑制することが可能である。ここで、温度の下限をＡｒ3 変態点に限定する理由は、Ａｒ3 変態点未満の温度域、すなわちフェライト組織が生成した後でトリミングやピアス等の後加工工程を行なった場合、残留応力の上昇は抑制可能であるが、マルテンサイト組織分率が低下し、ゆえに部材の強度が低下してしまうからである。また、Ａｒ3 変態点以上の温度域から先に冷却し、その後、トリミングやピアス等の後加工工程を行なうと、部材の高強度は確保できるが、残留応力は大きく上昇してしまうので、本発明の順序に限定する。なお、符号３はシャーを示す。 The post-processing step such as trimming and piercing in the third step is the most important step to be controlled in the present invention. By carrying out this step in the temperature range above the Ar 3 transformation point, the high strength of the member is increased. It is possible to suppress an increase in residual stress while ensuring. The reason for limiting the lower limit of the temperature Ar 3 transformation point, the temperature range of Ar less than 3 transformation point, i.e., the ferrite structure makes a processing step after such trimming and piercing After generating, the residual stress The increase can be suppressed, but the martensite structure fraction decreases, and therefore the strength of the member decreases. In addition, if cooling is first performed from the temperature range above the Ar 3 transformation point and then a post-processing step such as trimming or piercing is performed, the high strength of the member can be ensured, but the residual stress increases greatly. Limited to the order of the invention. Reference numeral 3 denotes a shear.
第４工程での冷却は、冷却後に得られる鋼組織中のマルテンサイト組織の分率を高くするために、冷却速度は高い方が好ましい。１０℃／秒未満の冷却速度では、マルテンサイト組織の分率が減り所望する強度を得られなくなるため、冷却速度は１０℃／秒以上と限定した。一方、１０００℃／秒超にすることは操業上困難なため、上限を１０００℃／秒とした。また、冷却による形状悪化を抑制するために、冷却媒体（金型、水槽等）４を用いる。例えば第２工程で使用した金型と同一形状の金型を利用して冷却することも有効である。 In the fourth step, the cooling rate is preferably high in order to increase the fraction of the martensite structure in the steel structure obtained after cooling. At a cooling rate of less than 10 ° C./second, the martensite structure fraction decreases and the desired strength cannot be obtained, so the cooling rate is limited to 10 ° C./second or more. On the other hand, since it is difficult for the operation to exceed 1000 ° C./second, the upper limit was set to 1000 ° C./second. Moreover, in order to suppress shape deterioration due to cooling, a cooling medium (mold, water tank, etc.) 4 is used. For example, it is also effective to cool using a mold having the same shape as the mold used in the second step.
次に、ミクロ組織についてであるが、冷却後に得られる鋼の面積率最大の相をマルテンサイトとする理由は、９８０ＭＰａ以上、好ましくは、１２００ＭＰａ、更には１５００ＭＰａ以上の高い引張強度を得るためであり、そのためには硬質相であるマルテンサイト相を６０％以上、好ましくは８０％以上、更に好ましくは９５％以上１００％以下の量を素地とすることが好ましい。ただし、ここで言う面積率１００％とは、当然鋼中に不可避的不純物や介在物が存在し、厳密には１００％とはならないが、光学顕微鏡での観察ではこれらの不可避的不純物や介在物が認識できないレベルの大きさで存在するので１００％とした。 Next, as for the microstructure, the reason why the maximum area ratio of the steel obtained after cooling is martensite is to obtain a high tensile strength of 980 MPa or more, preferably 1200 MPa, or even 1500 MPa or more. For this purpose, the martensite phase, which is a hard phase, is preferably used in an amount of 60% or more, preferably 80% or more, more preferably 95% or more and 100% or less. However, the area ratio of 100% mentioned here naturally has unavoidable impurities and inclusions in the steel, and strictly speaking, it is not 100%. However, these unavoidable impurities and inclusions are observed by observation with an optical microscope. Is 100% because it exists at a level that cannot be recognized.
その他の残部組織として、フェライト、パーライト、ベイナイトの１種又は２種以上を面積率の合計で４０％以下含有しても良い。残留応力が４００ＭＰａを超える場合は、耐水素脆化特性を大きく劣化させてしまうので、４００ＭＰａ以下と規定する。なお、残留応力はトリミング等後加工部端面の測定値であり、Ｘ線残留応力測定装置を用いて測定した値と定義する。 As other remaining structures, one or more of ferrite, pearlite, and bainite may be contained in a total area ratio of 40% or less. When the residual stress exceeds 400 MPa, the hydrogen embrittlement resistance is greatly deteriorated, so it is defined as 400 MPa or less. The residual stress is a measured value of the end surface of the post-processed part such as trimming, and is defined as a value measured using an X-ray residual stress measuring apparatus.
また、加工部端面のスケール厚みを５０μｍ以下に限定した理由は、これより厚いスケールが生成した場合、部材の塗装や取り付け前に、スケール除去の工程を必要とするためである。なお、部材全体のスケール生成を抑制するためには、ＡｌめっきやＺｎめっき等のスケールガード鋼板を使用することが有効であるが、たとえこのようなスケールガード鋼板を使用しても、加工部端面はめっきがないため、スケールが生成してしまう。 Moreover, the reason why the scale thickness of the end face of the processed part is limited to 50 μm or less is that when a scale thicker than this is generated, a scale removing step is required before painting or attaching the member. In order to suppress scale formation of the entire member, it is effective to use a scale guard steel plate such as Al plating or Zn plating, but even if such a scale guard steel plate is used, the end face of the processed part Since there is no plating, scale is generated.
加工部端面のスケール厚みを５０μｍ以下とするためには、加熱、ホットプレスの後に、加工する、すなわち後加工が有効であり、かつ、その後の室温までの冷却速度を１０℃／ｓｅｃ以上とすることが好ましい。ここで、加工部端面とは、トリミング等の後加工で得られる加工端部の垂直断面をいう。 In order to set the scale thickness of the processed part end face to 50 μm or less, processing is performed after heating and hot pressing, that is, post-processing is effective, and the subsequent cooling rate to room temperature is set to 10 ° C./sec or more. It is preferable. Here, the end surface of the processed portion refers to a vertical cross section of the processed end portion obtained by post-processing such as trimming.
次に、実施例により本発明をさらに詳細に説明する。
表１に、オーステナイト組織から冷却してマルテンサイト組織とすることで、引張強度９８０ＭＰａ以上が得られる３種類の鋼板、すなわち、鋼種Ａは０．２３％Ｃ−０．２３％Ｓｉ−１．３％Ｍｎ系、鋼種Ｂは０．１８％Ｃ−０．２１％Ｓｉ−１．２％Ｍｎ系、鋼種Ｃは０．１２％Ｃ−０．２２％Ｓｉ−１．３％Ｍｎ系を用いて、ホットプレス、端面トリミング試験を実施した。鋼種ＡのＡｃ3 変態点温度は８２５℃であり、Ａｒ3 変態点温度は５６０℃であり、鋼種ＢのＡｃ3 変態点温度は８３０℃であり、Ａｒ3 変態点温度は５６５℃であり、鋼種ＣのＡｃ3 変態点温度は８３５℃であり、Ａｒ3 変態点温度は５７０℃である。なお、板厚は全て１．６ｍｍで実施し、加熱にはボックス電気炉を、プレスにはハット形状金型を、トリミングにはシャーを、冷却には水をそれぞれ使用した。
Next, the present invention will be described in more detail with reference to examples.
In Table 1, three types of steel sheets that can obtain a tensile strength of 980 MPa or more by cooling from an austenite structure to a martensite structure, that is, steel type A is 0.23% C-0.23% Si-1.3. % Mn series, steel grade B is 0.18% C-0.21% Si-1.2% Mn series, steel grade C is 0.12% C-0.22% Si-1.3% Mn series , Hot press, and end face trimming test were conducted. The Ac 3 transformation point temperature of steel type A is 825 ° C, the Ar 3 transformation point temperature is 560 ° C, the Ac 3 transformation point temperature of steel type B is 830 ° C, and the Ar 3 transformation point temperature is 565 ° C, The Ac 3 transformation point temperature of steel type C is 835 ° C, and the Ar 3 transformation point temperature is 570 ° C. The plate thickness was all 1.6 mm, a box electric furnace was used for heating, a hat-shaped mold was used for pressing, a shear was used for trimming, and water was used for cooling.
このようにして得られた部材の引張強度、トリミング端面の残留応力、マルテンサイトの面積率、トリミング端面のスケール厚みを測定した結果を表２に示す。引張強度はＪＩＳ １３Ｂ号試験片で評価し、残留応力はＸ線残留応力測定装置を用いて測定した。また、マルテンサイトの面積率とトリミング端面のスケール厚みは光学顕微鏡を用いて測定した。 Table 2 shows the results of measuring the tensile strength, the residual stress of the trimming end face, the martensite area ratio, and the scale thickness of the trimming end face of the member thus obtained. The tensile strength was evaluated with a JIS 13B test piece, and the residual stress was measured using an X-ray residual stress measuring apparatus. The area ratio of martensite and the scale thickness of the trimming end face were measured using an optical microscope.
Ｎｏ．１、２、８、９、１４、１５は本発明の条件を満たしており、引張強度９８０ＭＰａ以上、トリミング端面の残留応力４００ＭＰａ以下、マルテンサイトの面積率６０％以上、トリミング端面のスケール厚み５０μｍ以下を満足している。
一方、Ｎｏ．３、４、６、１０、１２、１６、１８、２０は、残留応力は４００ＭＰａ以下、トリミング端面のスケール厚み５０μｍ以下は満足しているが、引張強度９８０ＭＰａ以上、マルテンサイトの面積率６０％以上は満足していない。
No. 1, 2, 8, 9, 14, and 15 satisfy the conditions of the present invention, the tensile strength is 980 MPa or more, the residual stress of the trimming end surface is 400 MPa or less, the martensite area ratio is 60% or more, and the scale thickness of the trimming end surface is 50 μm or less. Is satisfied.
On the other hand, no. 3, 4, 6, 10, 12, 16, 18, and 20 are satisfied with a residual stress of 400 MPa or less and a scale thickness of the trimming end face of 50 μm or less, but a tensile strength of 980 MPa or more and a martensite area ratio of 60% or more. Is not satisfied.
この理由は、Ｎｏ．３、４、１０、１６については、プレス速度が遅く時間を要し、トリミング温度がＡｒ3 変態点以下であったため、フェライト組織が生成して強度が低下し、所望の引張強度が得られなかったためである。Ｎｏ．６、１２、１８については、加熱温度がＡｃ3変態点以下であったため、加熱時に十分オーステナイト組織とならず、冷却後のマルテンサイト組織面積率が低くなり、所望の引張強度が得られなかったためである。Ｎｏ．２０については、冷却速度が遅かったため、マルテンサイト組織面積率が低くなり、所望の引張強度が得られなかったためである。 The reason for this is that no. For 3, 4, 10, and 16, since the press speed was slow and time was required, and the trimming temperature was below the Ar 3 transformation point, the ferrite structure formed and the strength decreased, and the desired tensile strength could not be obtained. This is because. No. For 6, 12, and 18, the heating temperature was below the Ac 3 transformation point, so that the austenite structure was not sufficiently obtained during heating, the martensite structure area ratio after cooling was low, and the desired tensile strength was not obtained. It is. No. For No. 20, because the cooling rate was slow, the martensite structure area ratio was low, and the desired tensile strength could not be obtained.
また、Ｎｏ．５、１１、１７はトリミングを冷却後に室温で実施したために、マルテンサイト組織面積率、引張強度、トリミング端部表面のスケール厚みは満足するものの、残留応力が高くなり４００ＭＰａを超えた。Ｎｏ．７、１３、１９は、先にトリミングをした後、加熱、プレスを実施したため、トリミング端面のスケール厚みが５０μｍを超えた。また、トリミング部の形状精度も低下した。 No. In Nos. 5, 11, and 17, trimming was performed at room temperature after cooling, so the martensite structure area ratio, tensile strength, and scale thickness of the trimming end surface were satisfactory, but the residual stress increased and exceeded 400 MPa. No. Nos. 7, 13, and 19 were subjected to heating and pressing after trimming first, so that the scale thickness of the trimming end face exceeded 50 μm. In addition, the shape accuracy of the trimming part also decreased.
以上の結果から、Ａｃ3 変態点以上１３００℃以下の温度に加熱した鋼板を、ホットプレスし、プレス部材温度がＡｒ3 変態点以上の温度でトリミングまたはピアシング等の後加工を施し、その後、冷却することで、９８０ＭＰａ以上の引張強度を有し、かつ、残留応力が４００ＭＰａ以下で、後加工部端面のスケール厚みが５０μｍ以下で、マルテンサイト組織の面積率が６０％以上である鋼製高強度部材の製造が可能である。 From the above results, the steel sheet heated to a temperature not lower than the Ac 3 transformation point and not higher than 1300 ° C. is hot-pressed, subjected to post-processing such as trimming or piercing at a temperature of the pressing member temperature not lower than the Ar 3 transformation point, and then cooled. By doing so, the steel has high tensile strength having a tensile strength of 980 MPa or more, a residual stress of 400 MPa or less, a scale thickness of the end face of the post-processing part of 50 μm or less, and an area ratio of the martensite structure of 60% or more. The member can be manufactured.
１ 加熱炉
２ 鋼板
３ シャー
４ 冷却媒体（金型、水槽等）
特許出願人 新日本製鐵株式会社
代理人 弁理士 椎 名 彊 他１
1
Patent applicant: Nippon Steel Corporation
Attorney Attorney Shiina and others 1
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| JP4840089B2 (en) * | 2006-11-08 | 2011-12-21 | 住友金属工業株式会社 | Manufacturing method of molded products |
| KR100842710B1 (en) | 2007-03-13 | 2008-07-01 | 학교법인 선목학원 | Oil cooling die which has function of preventing heat deformation and manufacturing method for machine parts using the same |
| JP4845813B2 (en) * | 2007-06-01 | 2011-12-28 | アイシン高丘株式会社 | Press working equipment in die quench method |
| JP5499847B2 (en) * | 2009-05-29 | 2014-05-21 | 新日鐵住金株式会社 | Manufacturing method of panel assembly |
| JP5609172B2 (en) * | 2010-03-11 | 2014-10-22 | Ｊｆｅスチール株式会社 | High temperature sliding test equipment |
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| JP6082451B2 (en) | 2015-03-18 | 2017-02-15 | 株式会社神戸製鋼所 | Steel sheet for hot pressing and manufacturing method thereof |
| JP6424841B2 (en) * | 2016-01-13 | 2018-11-21 | Ｊｆｅスチール株式会社 | Method of manufacturing molded member |
| JP7338573B2 (en) * | 2020-07-06 | 2023-09-05 | Ｊｆｅスチール株式会社 | Shearing blade, shearing mold, shearing method for metal plate, and method for manufacturing pressed parts |
| KR102412624B1 (en) * | 2020-12-24 | 2022-06-24 | 현대제철 주식회사 | Hot stamping component and method of manufacturing the same |
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