JP4959245B2 - Method for producing high-strength metal member - Google Patents
Method for producing high-strength metal member Download PDFInfo
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- JP4959245B2 JP4959245B2 JP2006188730A JP2006188730A JP4959245B2 JP 4959245 B2 JP4959245 B2 JP 4959245B2 JP 2006188730 A JP2006188730 A JP 2006188730A JP 2006188730 A JP2006188730 A JP 2006188730A JP 4959245 B2 JP4959245 B2 JP 4959245B2
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- 229910052751 metal Inorganic materials 0.000 title claims description 63
- 239000002184 metal Substances 0.000 title claims description 63
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 92
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 85
- 238000010438 heat treatment Methods 0.000 claims description 76
- 229910000831 Steel Inorganic materials 0.000 claims description 45
- 239000010959 steel Substances 0.000 claims description 45
- 230000006698 induction Effects 0.000 claims description 31
- 238000000034 method Methods 0.000 claims description 15
- 239000010960 cold rolled steel Substances 0.000 claims description 9
- 238000012360 testing method Methods 0.000 description 68
- 230000000171 quenching effect Effects 0.000 description 45
- 238000010791 quenching Methods 0.000 description 40
- 238000000465 moulding Methods 0.000 description 32
- 239000000463 material Substances 0.000 description 20
- 238000009826 distribution Methods 0.000 description 15
- 238000000635 electron micrograph Methods 0.000 description 10
- 239000013078 crystal Substances 0.000 description 8
- 230000005291 magnetic effect Effects 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 238000003825 pressing Methods 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 230000008859 change Effects 0.000 description 5
- 239000010419 fine particle Substances 0.000 description 5
- 229910000975 Carbon steel Inorganic materials 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 239000010962 carbon steel Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 238000010008 shearing Methods 0.000 description 2
- 238000005452 bending Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000003302 ferromagnetic material Substances 0.000 description 1
- 238000007542 hardness measurement Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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- Heat Treatment Of Articles (AREA)
Description
本発明は、高強度金属部材及びその製造方法に関し、特に、低炭素金属部材を用いた高強度金属部材の製造方法に関する。 The present invention relates to a high-strength metal member and a method for producing the same, and more particularly to a method for producing a high-strength metal member using a low-carbon metal member.
特許文献１〜３には、冷間でプレス成形を行った後に、焼き入れ処理を行い、それにより、鋼材の強度を上げる技術が開示されている。
ところで、鋼材に熱処理を施すことにより、結晶粒が微細化し、それにより、鋼材の強度が向上することは一般に知られている。また、このときの結晶粒の微細化を促すためには、鋼材に含まれる炭素含有量が０．１０質量％以上でなければならないことも、よく知られている。それよりも少ないと、結晶粒の微細化現象が生じにくく、熱処理しても鋼材の強度は、ほとんど向上しないか、逆に、結晶粒が粗大化して強度の低下を招く。このため、特許文献１では、０．１８〜０．２８質量％、特許文献３では、０．１０〜０．３０質量％というように、いずれも炭素含有量は、０．１０質量％以上の数値となっている。 By the way, it is generally known that the heat treatment of the steel material makes the crystal grains finer, thereby improving the strength of the steel material. It is also well known that the carbon content contained in the steel material must be 0.10 % by mass or more in order to promote the refinement of crystal grains at this time. If it is less than that, the crystal grain refinement phenomenon hardly occurs, and the strength of the steel material is hardly improved even after heat treatment, or conversely, the crystal grains become coarse and the strength is lowered. Therefore, in Patent Document 1, the carbon content is 0.10 % by mass or more, such as 0.18 to 0.28 % by mass , and Patent Document 3 in which 0.10 to 0.30 % by mass . It is a numerical value.
一方、特許文献４は、プレス成形前に、従来一般に行われている焼き入れ処理、すなわち、誘導加熱部（コイル）もワークも動かさずに行う焼き入れ処理を施し、その後プレス成形する技術であるが、該特許文献４には、炭素含有量０．０５質量％と０．０３質量％の鋼材の試験片（プレス成形前）を焼き入れした実験結果が第１０図及び第１１図に掲載されている。第１０図では引張強度を比較しているが、炭素含有量０．０５質量％の試験片は、焼き入れ処理をしていない部分に対し、焼き入れ処理した部分の引張強度が１０〜２０％程度上がっている。これに対し、炭素含有量０．０３質量％の試験片は、焼き入れ処理していない部分と焼き入れ処理した部分との引張強度の差がほとんどない。第１１図の最大荷重についても同様のことが言え、炭素含有量０．０５質量％の試験片では、焼き入れ処理により１０〜２０％程度強度が上がっているのに対し、炭素含有量０．０３質量％の試験片では、焼き入れ処理していない部分と焼き入れ処理した部分とで大きな差異はない。 On the other hand, Patent Document 4 is a technique in which a quenching process that is generally performed before press molding, that is, a quenching process that does not move the induction heating unit (coil) and the workpiece is performed, and then press molding is performed. However, in Patent Document 4, experimental results obtained by quenching steel specimens (before press molding) with carbon contents of 0.05 mass% and 0.03 mass% are shown in FIGS. 10 and 11. ing. In FIG. 10, the tensile strength is compared, but the test piece having a carbon content of 0.05 % by mass has a tensile strength of 10 to 20% in the portion subjected to quenching treatment compared to the portion not subjected to quenching treatment. It has risen to some extent. On the other hand, the test piece having a carbon content of 0.03 % by mass has almost no difference in tensile strength between a portion that has not been quenched and a portion that has been quenched. The same can be said for the maximum load in FIG. 11. In the test piece having a carbon content of 0.05 % by mass , the strength was increased by about 10 to 20% by the quenching process, whereas the carbon content was reduced to about 0.1%. In the 03 % by mass test piece, there is no significant difference between the part that has not been quenched and the part that has been quenched.
以上のことから明らかなように、炭素含有量０．１０質量％未満の鋼材について強度を上げることを目的として熱処理することは、現在実施されているとはいえない。特許文献４においては、確かに、０．１０質量％未満の、炭素含有量０．０５質量％の鋼材が、１０〜２０％程度の強度向上を示す旨が示されているが、炭素含有量が少ないため、炭素含有量０．１０質量％以上のものと比較すれば、強度の変化率は低い。炭素含有量０．０３質量％のものに至っては、熱処理しても、強度がほとんど変化しないデータしか示されていない。 As is clear from the above, it cannot be said that heat treatment for the purpose of increasing the strength of a steel material having a carbon content of less than 0.10 % by mass is currently performed. In Patent Document 4, it is shown that a steel material having a carbon content of less than 0.10 % by mass and having a carbon content of 0.05 % by mass exhibits an improvement in strength of about 10 to 20%. Therefore, the rate of change in strength is low as compared with the carbon content of 0.10 % by mass or more. In the case of a carbon content of 0.03 % by mass, only data whose strength hardly changes even after heat treatment is shown.
本発明は上記に鑑みなされたものであり、炭素含有量の少ない低炭素金属部材、中でも、炭素含有量０．１０質量％未満の低炭素金属部材、さらには、炭素含有量０．０５質量％未満、０．０３５質量％未満の低炭素金属部材であっても、熱処理により熱処理前と比較して強度が向上した高強度金属部材を製造する方法を提供することを課題とする。 The present invention has been made in view of the above, and a low carbon metal member having a low carbon content, particularly a low carbon metal member having a carbon content of less than 0.10 % by mass , and a carbon content of 0.05 % by mass. It is an object of the present invention to provide a method for producing a high-strength metal member whose strength is improved by heat treatment as compared with that before heat treatment even if it is less than 0.035 % by mass .
上記課題を解決するため、請求項１記載の本発明は、自動車用の冷間圧延鋼板又は熱間圧延鋼板からなる炭素含有量０．１０質量％未満、厚さ１．２ｍｍ以下の低炭素金属部材を、冷間でプレス成形を行って断面係数の高い部位を形成し、しかる後、誘導加熱部に対して相対的に所定の移動速度で移動させながら加熱した後、急冷する誘導加熱による熱処理を施すことを特徴とする高強度金属部材の製造方法を提供する。
請求項２記載の本発明は、前記プレス成形により、断面係数の高い部位を形成し、該断面係数の高い部位に隣接した部位に前記熱処理を施す請求項１記載の高強度金属部材の製造方法を提供する。
請求項３記載の本発明は、前記炭素含有量が０．０５質量％未満の低炭素金属部材を用いる請求項１記載の高強度金属部材の製造方法を提供する。
請求項４記載の本発明は、前記炭素含有量が０．０３５質量％未満の低炭素金属部材を用いる請求項３記載の高強度金属部材の製造方法を提供する。
請求項５記載の本発明は、前記熱処理を施す工程では、前記移動速度が、５〜３０ｍｍ／ｓｅｃの範囲に設定されていることを特徴とする請求項１記載の高強度金属部材の製造方法を提供する。
In order to solve the above problems, the present invention according to claim 1 is a low carbon metal having a carbon content of less than 0.10% by mass and a thickness of 1.2 mm or less, comprising a cold rolled steel plate or a hot rolled steel plate for automobiles. The member is cold-formed to form a portion having a high section modulus, and then heated while moving at a predetermined moving speed relative to the induction heating unit, and then rapidly cooled by induction heating. A method for producing a high-strength metal member is provided.
The present invention according to claim 2 is a method for producing a high-strength metal member according to claim 1, wherein a portion having a high section modulus is formed by the press molding, and the heat treatment is performed on a portion adjacent to the portion having the high section modulus. I will provide a.
According to a third aspect of the invention provides a method of producing a high strength metal member according to claim 1, wherein the carbon content using low carbon metal member is less than 0.05 wt%.
The present invention according to claim 4 provides the method for producing a high strength metal member according to claim 3 , wherein the low carbon metal member having a carbon content of less than 0.035 % by mass is used.
The present invention is claimed in claim 5, wherein, in the step of performing the heat treatment, the moving speed is, the method of producing a high strength metal member according to claim 1, wherein the set in the range of 5 to 30 mm / sec I will provide a.
本発明では、低炭素金属部材に、プレス成形などの内部応力を高める加工処理を施し、その後、熱処理を施す。これにより、低炭素金属部材、中でも、炭素含有量０．１０質量％未満、さらには、炭素含有量０．０５質量％未満、０．０３５質量％未満の低炭素金属部材であっても、強度が向上し、熱処理前の強度の１．４〜４倍程度になった高強度金属部材が得られる。 In the present invention, the low carbon metal member is subjected to a processing treatment for increasing internal stress such as press molding, and then subjected to a heat treatment. Thereby, even if it is a low carbon metal member, especially a low carbon metal member with a carbon content of less than 0.10 % by mass , or even a carbon content of less than 0.05 % by mass or less than 0.035 % by mass , And a high-strength metal member having a strength of about 1.4 to 4 times the strength before heat treatment is obtained.
本発明で用いる低炭素金属部材としては、自動車のボディーなどに用いられる安価で加工性のよい圧延鋼板が適する。自動車用圧延鋼板には、冷間圧延鋼板と熱間圧延鋼板があるが、そのいずれも含む。しかしながら、この自動車用圧延鋼板は、炭素含有量が低いため、そのまま熱処理を行っただけでは、上記したように焼き入れ効果が得られない。例えば、後述の試験例で用いた熱間圧延鋼板（住友金属工業（株）製）の炭素含有量は０．０４質量％、冷間圧延鋼板（住友金属工業（株）製）の炭素含有量は０．０２質量％であり、このまま熱処理しただけでは焼き入れ効果は得られないが、本発明によれば、このような炭素含有量の少ない鋼材でも好適な焼き入れ効果が得られる。 As the low carbon metal member used in the present invention, an inexpensive and highly workable rolled steel plate used for an automobile body is suitable. Rolled steel sheets for automobiles include cold rolled steel sheets and hot rolled steel sheets, both of which are included. However, since this rolled steel sheet for automobiles has a low carbon content, it is not possible to obtain a quenching effect as described above only by performing the heat treatment as it is. For example, the carbon content of the hot-rolled steel sheet (manufactured by Sumitomo Metal Industries, Ltd.) used in the test examples described later is 0.04 % by mass , and the carbon content of the cold-rolled steel sheet (manufactured by Sumitomo Metal Industries, Ltd.). 0.02 % by mass , and it is not possible to obtain a quenching effect only by heat treatment as it is, but according to the present invention, a suitable quenching effect can be obtained even with such a steel material having a low carbon content.
本発明で適用可能な低炭素金属部材には、炭素含有量０．１０質量％未満のもの、さらには、０．０５質量％未満のものが含まれる。また、後述の試験例で示したように、炭素含有量０．０４質量％以下、さらには、０．０３５質量％未満のものにも本発明は好適に用いることができる。すなわち、「鋼」は、通例、炭素含有量０．０３５質量％以上の鉄として定義されるが、本発明によれば、「鋼」の概念に含まれない０．０３５質量％未満の低い金属でも強化可能である。本発明では、炭素含有量の低いものでも強度を上げるという焼き入れ効果を得ることが可能であるため、使用目的にもよるが、炭素含有量がより低い、より安価な材料を用いることで、自動車等の製造コストの低減を図ることができる。さらに言えば、本発明は、このように炭素含有量が低くても強度を上げることができるため、従来のように、鋼材成分の均質性の高い材料を用いなくてもよく、より安価な材料、例えば、炭素含有量の多い部分や少ない部分が混在していている、品質面で劣る材料を用いても、強度を向上させることができる。この結果、材料の有効利用を図ることができ、リサイクル性が向上する。 Low carbon metal members applicable in the present invention include those having a carbon content of less than 0.10 % by mass , and further those having a carbon content of less than 0.05 % by mass . Moreover, as shown by the below-mentioned test example, this invention can be used suitably also for carbon content 0.04 mass% or less and also less than 0.035 mass% . That is, “steel” is usually defined as iron having a carbon content of 0.035 % by mass or more, but according to the present invention, a low metal of less than 0.035 % by mass not included in the concept of “steel”. But it can be strengthened. In the present invention, since it is possible to obtain a quenching effect of increasing the strength even with a low carbon content, depending on the purpose of use, by using a cheaper material with a lower carbon content, The manufacturing cost of automobiles and the like can be reduced. Furthermore, since the present invention can increase the strength even if the carbon content is low as described above, it is not necessary to use a material with high homogeneity of steel components as in the prior art, and a cheaper material. For example, the strength can be improved even when a material having inferior quality in which a portion having a high carbon content or a portion having a small carbon content is mixed is used. As a result, the material can be effectively used and the recyclability is improved.
本発明における低炭素金属部材の加工処理は、冷間で行われ、低炭素金属部材の熱処理部周辺部位の内部応力を高めることができる加工手段であればよく、例えば、冷間で（常温で）、低炭素金属部材に塑性変形を与える加工が挙げられる。典型例としては、プレス成形が挙げられる。プレス成形の種類は限定されるもではなく、使用目的に合わせて、曲げ加工、絞り加工、深絞り加工などが用いられ、加工処理対象の低炭素金属部材は、板状のもの、パイプ状のもののいずれも含む。プレス成形以外にも、ロール成形による圧延加工などを適用することもできる。 The processing of the low carbon metal member in the present invention is performed in a cold manner, and any processing means that can increase the internal stress in the peripheral portion of the heat treatment portion of the low carbon metal member may be used. ), A process of giving plastic deformation to the low carbon metal member. A typical example is press molding. The type of press molding is not limited, and bending, drawing, deep drawing, etc. are used according to the purpose of use, and the low carbon metal members to be processed are plate-like or pipe-like. Including any of them. In addition to press forming, rolling processing by roll forming can also be applied.
熱処理方法は任意であるが、好ましくは、高周波焼き入れ（誘導加熱）を用いて行う。また、熱処理の際には、熱処理装置の加熱部（誘導加熱装置の場合には、誘導加熱部を構成するコイル）に対し、熱処理対象の上記低炭素金属部材を、相対的に所定の移動速度で移動させながら加熱した後、急冷することが好ましい。誘導加熱部を構成するコイルの磁力が処理対象である低炭素金属部材に作用するが、誘導加熱部と低炭素金属部材を相対移動させることにより、磁力の影響を受ける部位が時間と共に変化していき、熱処理された部分全体に磁力の影響が及ぶ。この磁力は、加熱している低炭素金属部材をせん断変形させる力として作用するが、せん断変形は、プレス成形などによって内部応力を高めた低炭素金属部材において、均一に生じるわけではない。すなわち、内部応力の高い部位（断面係数の高い部位）におけるせん断変形よりも、この内部応力の高い部位（断面係数の高い部位）に対して隣接した部位に形成されている、相対的に内部応力の低い部位（断面係数の低い部位）におけるせん断変形の方が大きくなる。逆に言えば、断面係数の低い部位では、誘導加熱部のコイルの磁力によりせん断変形しやすいが、断面係数の高い部位ではせん断変形しにくい。 The heat treatment method is arbitrary, but is preferably performed using induction hardening (induction heating). Further, during the heat treatment, the low-carbon metal member to be heat-treated is relatively moved at a predetermined moving speed with respect to the heating part of the heat treatment apparatus (in the case of the induction heating apparatus, the coil constituting the induction heating part). It is preferable to rapidly cool after heating while being moved by. The magnetic force of the coil that constitutes the induction heating unit acts on the low carbon metal member that is the object of processing, but by moving the induction heating unit and the low carbon metal member relatively, the part affected by the magnetic force changes with time. The entire heat-treated part is affected by magnetic force. This magnetic force acts as a force for shearing the heated low carbon metal member, but the shear deformation does not occur uniformly in the low carbon metal member whose internal stress is increased by press molding or the like. That is, rather than shear deformation at a site with a high internal stress (a site with a high section modulus), a relatively internal stress is formed at a site adjacent to the site with a high internal stress (a site with a high section modulus). The shear deformation at a portion with a low (a portion with a low section modulus) is greater. In other words, the portion having a low section modulus is likely to be sheared by the magnetic force of the coil of the induction heating unit, but the portion having a high section modulus is less likely to be sheared.
プレス成形などの内部応力を高める加工処理を行うと、結果として、低炭素金属部材に、断面係数の高い部位が一部に生じ、それに隣接する部位には相対的に断面係数の低い部位が生じる。例えば、断面係数の高い部位（折り曲げ部など）が複数箇所に形成されていれば、その間の部位（すなわち、断面係数の高い部位に隣接する部位）は、相対的に断面係数の低い部位となる。そのことが、誘導加熱時にけるせん断変形を生じにくい部位と生じやすい部位を作る要因となるのであるが、この点が、後述の試験例で示すように、低炭素金属部材であるにも拘わらず、せん断変形を生じやすい部位において結晶粒が微細化され、強度が高まっている理由と考えられる。すなわち、断面係数の高い、せん断変形を生じにくい部位が、いわば、磁力の反力に耐える固定端の如く機能し、隣接するせん断変形を生じやすい部位における金属組織の結晶粒の粗大化を抑制し、微細化を促すものと考えられる。 When processing that increases internal stress such as press molding is performed, as a result, a low carbon metal member has a part with a high section modulus, and a part with a relatively low section modulus is generated at a part adjacent to the part. . For example, if a portion having a high section modulus (such as a bent portion) is formed at a plurality of locations, a portion in between (that is, a portion adjacent to a portion having a high section modulus) is a portion having a relatively low section modulus. . This is a factor that creates a site that is less likely to cause shear deformation during induction heating and a site that is more likely to occur, but this point is a low-carbon metal member, as shown in the test examples described later. This is considered to be the reason why the crystal grains are refined and the strength is increased at the site where shear deformation is likely to occur. In other words, the part with a high section modulus that is difficult to cause shear deformation functions as a fixed end that can withstand the reaction force of magnetic force, and suppresses the coarsening of the crystal grains of the metal structure in the adjacent part that is prone to shear deformation. It is thought that it promotes miniaturization.
なお、プレス成形などの内部応力を高める加工処理を行った低炭素金属部材に、上記のようなせん断変形を生じさせるためには、熱処理装置の加熱部（誘導加熱装置の場合には、誘導加熱部を構成するコイル）は、移動速度５〜３０ｍｍ／ｓｅｃの範囲に設定することが好ましい。より好ましい移動速度は、１０〜１８ｍｍ／ｓｅｃの範囲である。 In order to cause the above-described shear deformation in a low-carbon metal member that has been subjected to processing that increases internal stress such as press molding, the heating section of the heat treatment apparatus (in the case of induction heating apparatus, induction heating is used). The coil constituting the part is preferably set to a moving speed in the range of 5 to 30 mm / sec. A more preferable moving speed is in the range of 10 to 18 mm / sec.
また、本発明では、上記のように熱処理によって低炭素金属部材にせん断変形を生じさせることを利用しているが、かかるせん断変形を生じさせるには、低炭素金属部材は、厚さ２．６ｍｍ以下、さらには、厚さ１．２ｍｍ以下の厚みの薄い材料を用いることが好ましい。加工性、強度等を考慮すると、より好ましい厚みは、０．３５〜１．２ｍｍの範囲である。 Further, in the present invention, the low-carbon metal member is used to generate shear deformation by heat treatment as described above. To generate such shear deformation, the low-carbon metal member has a thickness of 2.6 mm. Hereinafter, it is further preferable to use a thin material having a thickness of 1.2 mm or less. In consideration of workability, strength, etc., a more preferable thickness is in the range of 0.35 to 1.2 mm.
（試験例）
住友金属工業（株）製の冷間圧延鋼板（ＳＰＣ鋼板）及び熱間圧延鋼板（ＳＰＨ鋼板）を４０ｃｍ角に切り出し、これにプレス成形、熱処理を施して試験片を製作した。プレス成形は、３００Ｔプレス機を用いて行い、４０ｃｍ角の各試験片を厚み方向に２ｋｇｆ／ｍｍ２でプレスした。熱処理は、高周波焼き入れ（誘導加熱）を用いた。具体的には、９５０〜１０００℃を目標温度として２分間加熱した後、水冷した。加熱の際には、誘導加熱装置の誘導加熱部を構成するコイルを所定の速度で試験片に対して移動させた。移動速度は、試験片の片側のみにおいてコイルを移動させて加熱した片面焼き入れの場合は、１６ｍｍ／ｓｅｃに設定し、試験片の両側にコイルを配置し、移動させながら加熱した両面焼き入れの場合は、１２ｍｍ／ｓｅｃに設定した。プレス成形時、熱処理時のその他の加工処理条件は、各試験片とも同じである。
(Test example)
A cold rolled steel plate (SPC steel plate) and a hot rolled steel plate (SPH steel plate) manufactured by Sumitomo Metal Industries, Ltd. were cut into 40 cm squares, and subjected to press molding and heat treatment to produce test pieces. The press molding was performed using a 300T press, and each 40 cm square test piece was pressed at 2 kgf / mm 2 in the thickness direction. For the heat treatment, induction hardening (induction heating) was used. Specifically, the mixture was heated for 2 minutes at a target temperature of 950 to 1000 ° C. and then cooled with water. During heating, the coil constituting the induction heating unit of the induction heating apparatus was moved with respect to the test piece at a predetermined speed. The moving speed is set to 16 mm / sec in the case of single-side quenching in which the coil is moved only on one side of the test piece, the coil is placed on both sides of the test piece, In this case, it was set to 12 mm / sec. Other processing conditions during press molding and heat treatment are the same for each test piece.
なお、以下の説明及び図面中に示す試験片記号中、「ＳＰＣ」は、冷間圧延鋼板（ＳＰＣ鋼板）からなることを示し、「ＳＰＨ」は、熱間圧延鋼板（ＳＰＨ鋼板）からなることを示す。また、「ＳＰＣ」又は「ＳＰＨ」の記号の次のかっこ書きは各試験片の厚みを示しており、例えば、（ｔ１．０）は厚み１．０ｍｍという意味である。かっこ書きで示した厚みの後に続く記号のうち「Ｎ」はプレス成形及び熱処理のいずれも施していない試験片であることを意味し、「Ｐ」はプレス成形を施したことを意味し、「ＳＨ」は、試験片の片面のみを熱処理したことを意味し、「ＤＨ」は、試験片を両面から熱処理したことを意味する。
各試験片の化学組成は次表のとおりである。
The chemical composition of each test piece is as shown in the following table.
図１は、上記各試験片のいくつかの例を示す図である。図１（ａ）は、ＳＰＣ（ｔ１．２）の鋼板をプレスしないで片面焼き入れした試験片（ＳＰＣ（ｔ１．２）−ＳＨ）を、図１（ｂ）は、ＳＰＣ（ｔ１．２）の鋼板をプレスしないで両面焼き入れした試験片（ＳＰＣ（ｔ１．２）−ＤＨ）を、図１（ｃ）は、ＳＰＣ（ｔ１．０）の鋼板をプレスした後、両面焼き入れした試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ）を、図１（ｄ）は、ＳＰＣ（ｔ１．０）の鋼板をプレスした後、片面焼き入れした試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＳＨ）を、図１（ｅ）は、ＳＰＨ（ｔ１．２）の鋼板をプレスした後、両面焼き入れした試験片（ＳＰＨ（ｔ１．２）−Ｐ−ＤＨ）を、図１（ｆ）は、ＳＰＨ（ｔ１．２）の鋼板をプレスした後、片面焼き入れした試験片（ＳＰＨ（ｔ１．２）−Ｐ−ＤＨ）を、それぞれ示す。図中、「Hardening region」は、焼き入れした部分の中で硬度測定を行った部位を示し、「Non-hardening region」は、試験片の中で焼き入れしなかった部分において硬度測定を行った部位を示す。 FIG. 1 is a diagram showing some examples of the test pieces. FIG. 1 (a) shows a test piece (SPC (t1.2) -SH) that is single-side quenched without pressing a steel plate of SPC (t1.2), and FIG. 1 (b) shows SPC (t1.2). Fig. 1 (c) shows a test piece obtained by pressing both sides of the steel plate without pressing the steel plate (SPC (t1.2) -DH), and Fig. 1 (c) shows a test piece obtained by pressing both sides of the steel plate after SPC (t1.0). (SPC (t1.0) -P-DH) is a test piece (SPC (t1.0) -P-) in which FIG. 1 (d) shows a single-side quenching after pressing a steel plate of SPC (t1.0). FIG. 1 (e) shows a test piece (SPH (t1.2) -P-DH) which was pressed on a steel plate of SPH (t1.2) and then hardened on both sides, and FIG. After pressing a steel plate of SPH (t1.2), a single-side quenched test piece (SPH (t1.2) -P-DH) Each show. In the figure, “Hardening region” indicates the portion where hardness was measured in the quenched portion, and “Non-hardening region” was measured in the portion that was not quenched in the test piece. Indicates the site.
また、図２（ａ）〜（ｆ）として示した図は、それぞれ、図１（ａ）〜（ｆ）のＡ−Ａ’、Ｂ−Ｂ’、Ｃ−Ｃ’、Ｄ−Ｄ’、Ｅ−Ｅ’、Ｆ−Ｆ’における断面図である。この断面図から明らかなように、図１（ｃ）〜（ｆ）、図２（ｃ）〜（ｆ）ではプレス成形の影響によって形状が変化しており、残留応力が生じていることがわかる。 2A to 2F are respectively AA ′, BB ′, CC ′, DD ′, and E of FIGS. 1A to 1F. It is sectional drawing in -E 'and FF'. As is clear from this cross-sectional view, the shapes in FIGS. 1 (c) to (f) and FIGS. 2 (c) to (f) change due to the influence of press forming, and it is understood that residual stress is generated. .
各試験片のビッカーズ硬度の測定結果の一例を図３に示す。ビッカーズ硬度は、「Hardening region (H. region)」と、「Non-hardening region (N.H. region)」の各部分で、試料表面から０．１ｍｍおきに厚み方向に測定したものである。この図から、ＳＰＣ（ｔ１．０）の鋼板についてプレス成形後、両面から焼き入れしたＳＰＣ（ｔ１．０）−Ｐ−ＤＨと、焼き入れしなかったＳＰＣ（ｔ１．０）−Ｐ−Ｎとの間で、大きな差があることがわかる。これに対し、プレス成形を施していない、ＳＰＣ（ｔ１．２）の鋼板において、両面から焼き入れしたＳＰＣ（ｔ１．２）−ＤＨと、焼き入れしなかったＳＰＣ（ｔ１．２）−Ｎとの間では大きな差はないことがわかる。ここで、深さ方向に得られた硬度は、いずれも、ほぼ一定の値を示すと考えられる。そこで、深さ方向についての平均硬度を計算し、各試験片の平均ビッカーズ硬度を求め、次表に示した。
表２から明らかなように、プレス成形を行っていないＳＰＣ（ｔ１．２）の試験片の場合、両面及び片面のいずれの焼き入れ処理を行っても、硬度がほとんど変化しないことがわかる。一般に、鉄鋼材に焼き入れ処理すると硬度が増加することが知られているが、プレス成形を行っていないＳＰＣ（ｔ１．２）の試験片では、それに反し、硬度が上がっていない。これは、炭素含有量が０．０２質量％と極めて低いためと考えられる。 As is apparent from Table 2, in the case of the SPC (t1.2) test piece that was not press-molded, it was found that the hardness hardly changed even if the quenching treatment was performed on both sides or one side. In general, it is known that the hardness increases when the steel material is quenched, but the hardness of the SPC (t1.2) test piece not subjected to press molding is not increased. This is considered because the carbon content is as extremely low as 0.02 % by mass .
これに対し、炭素含有量がＳＰＣ（ｔ１．２）と同じ０．０２質量％しか含まれていないがプレス成形を施したＳＰＣ（ｔ１．０）の試験片の場合には、焼き入れ処理前後で硬度が約１．５〜１．８倍程度に上がっており、炭素含有量が低くても焼き入れ処理前にプレス成形を施すことにより、炭素含有量０．１０質量％以上の炭素鋼と同様の焼き入れ効果が得られることがわかる。また、上記表から、炭素含有量０．０４質量％のＳＰＨ（ｔ１．２）の試験片も、焼き入れ処理前後で、硬度が約１．４〜１．７倍程度に向上したことがわかる。なお、上記試験では、試験片を両面焼き入れした場合と片面焼き入れした場合について測定しているが、両面焼き入れと片面焼き入れとの間では、硬度変化の顕著な差は見られなかった。 On the other hand, in the case of a test piece of SPC (t1.0) subjected to press molding, although the carbon content is only 0.02 % by mass same as SPC (t1.2), before and after quenching treatment With a carbon steel having a carbon content of 0.10 % by mass or more by applying press molding before quenching even if the carbon content is low, It turns out that the same quenching effect is acquired. Further, from the above table, it is understood that the hardness of the SPH (t1.2) test piece having a carbon content of 0.04 % by mass is improved by about 1.4 to 1.7 times before and after the quenching treatment. . In the above test, the case where the test piece was subjected to double-side quenching and single-side quenching was measured, but there was no significant difference in hardness change between double-side quenching and single-side quenching. .
次に、各試験片について引張試験を行った。試験は、島津製作所製の精密万能試験機（ＡＧ−２５０ｋＮＧ）を使用し、ロードレンジ（感度）を１０ｋＮ、クロスヘッド移動速度を５ｍｍ／ｍｉｎに設定して行った。結果を図４及び図５に応力−ひずみ曲線で示す。図４は、冷間圧延鋼板（ＳＰＣ鋼板）に関する試験結果であり、図５は、熱間圧延鋼板（ＳＰＨ鋼板）に関する試験結果である。 Next, the tensile test was done about each test piece. The test was performed using a precision universal testing machine (AG-250 kNG) manufactured by Shimadzu Corporation, setting the load range (sensitivity) to 10 kN and the crosshead moving speed to 5 mm / min. The results are shown in FIGS. 4 and 5 as stress-strain curves. FIG. 4 shows test results for cold-rolled steel plates (SPC steel plates), and FIG. 5 shows test results for hot-rolled steel plates (SPH steel plates).
図４から明らかなように、プレス成形及び熱処理のいずれも行っていない試験片（ＳＰＣ（ｔ１．０）−Ｎ、ＳＰＣ（ｔ１．２）−Ｎ）の引張り強さ（応力）約３００ＭＰａに対し、プレス成形のみ又は熱処理のみを行った試験片は、引張り強さの点でほとんど差がないか、若干低下している。これに対し、プレス成形と両面焼き入れを行った試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ）、及びプレス成形と片面焼き入れを行った試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＳＨ）は、いずれも約５６０〜６００ＭＰａに上昇し、引張り強さ（応力）が、約１．８〜２倍になっており、伸びは約１５％程度に減少していた。なお、請求項で定義した「強度」とは、この引張り強さ（応力）を意味する。本発明では、炭素含有量の低い低炭素金属部材を用いているため、１．４倍以上の強度上昇が実現できれば十分であるが、プレス成形条件、熱処理条件、材料によっては、熱処理前の４倍の強度を持たせることも可能である。但し、本発明は、低炭素金属部材の強度を上げる技術に関するものであり、公知の炭素鋼を用いた技術のように、大幅な強度上昇を期待するものではない。従って、用途にもよるが、例えば、自動車のボディーに用いる鋼板であれば、１．４〜２倍の強度上昇が図れれば十分であり、この範囲の強度であれば、本発明を適用することによって、炭素含有量のより少ない、あるいは不均質な安価な材料を用いて実現できる。 As is clear from FIG. 4, the tensile strength (stress) of the test pieces (SPC (t1.0) -N, SPC (t1.2) -N) which were not subjected to press molding or heat treatment was about 300 MPa. The specimens subjected to only the press molding or only the heat treatment have little difference in the tensile strength or are slightly lowered. On the other hand, a test piece (SPC (t1.0) -P-DH) subjected to press molding and double-side quenching, and a test piece (SPC (t1.0) -P--) subjected to press molding and single-side quenching. SH) rose to about 560 to 600 MPa, the tensile strength (stress) was about 1.8 to 2 times, and the elongation was reduced to about 15%. The “strength” defined in the claims means this tensile strength (stress). In the present invention, since a low carbon metal member having a low carbon content is used, it is sufficient if an increase in strength of 1.4 times or more can be realized. However, depending on press molding conditions, heat treatment conditions, and materials, 4 before heat treatment is sufficient. It is also possible to have double strength. However, the present invention relates to a technique for increasing the strength of a low-carbon metal member, and does not expect a significant increase in strength unlike a technique using a known carbon steel. Therefore, depending on the application, for example, a steel plate used for an automobile body is sufficient if the strength can be increased by 1.4 to 2 times. If the strength is within this range, the present invention is applied. This can be realized by using an inexpensive material with a lower carbon content or a non-homogeneity.
図５においても、プレス成形及び熱処理のいずれも行っていない試験片（ＳＰＨ（ｔ１．２）−Ｎ）の引張り強さ（応力）約３５０ＭＰａに対し、プレス成形のみを行った試験片（ＳＰＨ（ｔ１．２）−Ｐ）は、引張り強さの点でほとんど差がないか、若干低下している。これに対し、プレス成形と両面焼き入れを行った試験片（ＳＰＨ（ｔ１．２）−Ｐ−ＤＨ）、及びプレス成形と片面焼き入れを行った試験片（ＳＰＨ（ｔ１．２）−Ｐ−ＳＨ）は、約５９０〜６２０ＭＰａに上昇しており、伸びは約１５％程度に減少していた。 Also in FIG. 5, the test piece (SPH (SPH (t1.2) -N) subjected to only press molding is applied to the tensile strength (stress) of about 350 MPa of the test piece (SPH (t1.2) -N) which is not subjected to either press molding or heat treatment. t1.2) -P) is almost the same in terms of tensile strength or slightly decreased. On the other hand, a test piece (SPH (t1.2) -P-DH) subjected to press molding and double-side quenching, and a test piece (SPH (t1.2) -P--) subjected to press molding and single-side quenching. SH) increased to about 590 to 620 MPa, and the elongation decreased to about 15%.
以上の試験例から、炭素含有量の少ない低炭素金属部材であっても、プレス成形と熱処理を施すことにより、炭素鋼と同様の強度上昇を達成できることがわかった。次に、炭素含有量が少ないにも拘わらず、このような強度上昇が生じるメカニズムを調べるため、プレス成形と両面焼き入れを行った部位を有する炭素含有量０．０２質量％の試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ）について、部分的に電子顕微鏡写真をとって金属組織の様子を調べた。電子顕微鏡写真をとった部位は、図６において、「Ｎｏ．１フレーム」として示した平面図のａ〜ｅ点である。なお、図６は、「Ｎｏ．１フレーム」と「Ｎｏ．２フレーム」として示した２つの試験片の平面図と、幅の広い端部側における断面図とをそれぞれ示している。「Ｎｏ．１フレーム」と「Ｎｏ．２フレーム」は、いずれも、同じ材料から加工され、平面から見た際には、幅の狭い端部方向に向かうに従って、内方に曲がる円弧状部を有すると共に、外側縁部付近は、各断面図に示したように、所定の角度曲げられるようにプレス成形されたものである。また、プレス成形した際に同じ大きさで、線対称の同形状となるように形成されている。「Ｎｏ．１フレーム」と「Ｎｏ．２フレーム」との違いは、前者が、幅の広い端部側から幅の狭い端部側へと誘導加熱部を移動させて焼き入れされたものであるのに対し、後者が、その逆方向、すなわち、幅の狭い端部側から幅の広い端部側へと誘導加熱部を移動させて焼き入れされたものであるという点である。なお、この焼き入れ方向の違いによる硬度への影響については後述する。ここでは、「Ｎｏ．１フレーム」を用いて行った硬度測定、金属組織の様子についてまず説明する。 From the above test examples, it was found that even a low carbon metal member having a low carbon content can achieve the same strength increase as carbon steel by performing press molding and heat treatment. Next, in order to investigate the mechanism of such an increase in strength even though the carbon content is small, a test piece (SPC having a carbon content of 0.02 % by mass having a portion subjected to press molding and double-side quenching is used. Regarding (t1.0) -P-DH), an electron micrograph was partially taken to examine the state of the metal structure. The parts taken by the electron micrograph are points a to e in the plan view shown as “No. 1 frame” in FIG. FIG. 6 shows a plan view of two test pieces shown as “No. 1 frame” and “No. 2 frame” and a cross-sectional view on the wide end side, respectively. Both “No. 1 frame” and “No. 2 frame” are processed from the same material, and when viewed from a plane, an arcuate portion that bends inward toward the narrow end portion is formed. In addition, as shown in each cross-sectional view, the vicinity of the outer edge is press-molded so as to be bent at a predetermined angle. Moreover, when it press-molds, it is the same magnitude | size and it forms so that it may become the same shape of line symmetry. The difference between “No. 1 frame” and “No. 2 frame” is that the former is quenched by moving the induction heating unit from the wide end side to the narrow end side. On the other hand, the latter is the one that is quenched by moving the induction heating portion in the opposite direction, that is, from the narrow end portion side to the wide end portion side. The influence on the hardness due to the difference in the quenching direction will be described later. Here, the hardness measurement performed using the “No. 1 frame” and the state of the metal structure will be described first.
図７は、「Ｎｏ．１フレーム」において、焼き入れを開始した部位（ａ点）を０ｍｍとして、焼き入れを行った部位の長手方向に沿って、ａ点からの距離と硬度との関係を詳細に調べた図である。図７に示したように、焼き入れ開始点のａ点の硬度は１０８ＨＶであった。これに対し、誘導加熱部がさらに移動していった部位は、ａ点の硬度よりも上がっており、ａ点から２０ｍｍ〜２３０ｍｍの範囲では、１５０〜２４０ＨＶと高くなっていた。但し、硬度が最も高かったのは、１５０〜１８０ｍｍの範囲であった。 FIG. 7 shows the relationship between the distance from point a and the hardness along the longitudinal direction of the part where quenching was performed, with the part (point a) where quenching was started 0 mm in “No. 1 frame”. It is the figure investigated in detail. As shown in FIG. 7, the hardness at the point a of the quenching start point was 108 HV. On the other hand, the part where the induction heating part further moved was higher than the hardness at the point a, and was as high as 150 to 240 HV in the range of 20 mm to 230 mm from the point a. However, the hardness was highest in the range of 150 to 180 mm.
電子顕微鏡写真をとった部位ａ〜ｅ点の位置は次のとおりである。すなわち、ａ点を基準として、ａ点から６０ｍｍ離れた位置がｂ点、ａ点から９０ｍｍ離れた位置がｃ点、ａ点から１５０ｍｍ離れた位置がｄ点、ａ点から１８０ｍｍ離れた位置がｅ点である。各点における電子顕微鏡写真が図８〜図１２であるが、金属の結晶粒子の直径が１０μｍ以下の微細粒については黒色のインクで塗りつぶして示した。まず、図８では、微細粒の分布率が３９％であり、黒く塗りつぶされた微細粒は、大きな結晶粒子の中に点在しているに過ぎない。これに対し、図９のｂ点では、微細粒が群になって現れ、さらに、隣接する微細粒群同士がつながっているように分布しており、微細粒の分布率が５３％になっている。図１０のｃ点になると、微細粒群同士のつながっている面積がより大きくなり、分布率が５８％となっている。さらに、図１１のｄ点では、微細粒の分布率が７８％、図１２のｅ点では、微細粒の分布率が９３％と、硬度に比例して高くなっている。 The positions of the points a to e taken in the electron micrograph are as follows. That is, with respect to point a, the position 60 mm away from point a is b point, the position 90 mm away from point a is c point, the position 150 mm away from point a is d point, and the position 180 mm away from point a is e Is a point. The electron micrographs at each point are shown in FIGS. 8 to 12, and fine particles having a metal crystal particle diameter of 10 μm or less are filled with black ink. First, in FIG. 8, the distribution ratio of fine grains is 39%, and the fine grains painted black are only scattered in large crystal grains. On the other hand, at the point b in FIG. 9, fine grains appear as a group, and the fine grains are distributed so that adjacent fine grain groups are connected to each other, and the distribution ratio of the fine grains is 53%. Yes. At the point c in FIG. 10, the area where the fine particle groups are connected to each other is larger, and the distribution rate is 58%. Further, at point d in FIG. 11, the distribution rate of fine particles is 78%, and at point e in FIG. 12, the distribution rate of fine particles is 93%, which is higher in proportion to the hardness.
すなわち、これらの電子顕微鏡写真から、炭素含有量が０．０２質量％と極めて低いにも拘わらず、金属組織の微細化現象が起こっていることがわかる。炭素含有量がこのように低いと、通常は、焼き入れ処理しても金属組織が粗大化するだけであるが、プレス成形を行うことにより生じる残留応力の影響によって、粗大化が抑え込まれ、微細化が促進されるものと考えられる。 That is, it can be seen from these electron micrographs that the metal structure has been refined despite the extremely low carbon content of 0.02 % by mass . When the carbon content is low in this way, the metal structure is usually coarsened even by quenching, but the coarsening is suppressed by the influence of residual stress caused by press forming, It is thought that miniaturization is promoted.
その一方、硬度が最も高かったのは、上記のように１５０〜１８０ｍｍの範囲である。この試験片は、図６及び図１４の断面図に示したように、平板状の鋼板の一方の側縁の近辺を斜めに折り曲げた傾斜片Ａとなるようにプレス成形したものであり、プレス成形した段階で、焼き入れする前の焼き入れ予定の部位（以下、単に、「焼き入れ部位」）Ｂより、外側の傾斜片Ａを含む部分の断面係数Ｚ３は、焼き入れ部位Ｂにおける断面係数Ｚ１よりも高くなっている。図６に示した試験片のうち「Ｎｏ．１フレーム」は、図６の左側の幅広の端部から右側の幅狭の端部へと誘導加熱部のコイルを移動して加熱しているが、２００〜２３０ｍｍの範囲で焼き入れした部分は、丁度、図１４の傾斜片Ａに相当する。これに対し、硬度の最も高い１５０〜１８０ｍｍの範囲の焼き入れ部位Ｂは、ほとんどが図１４の平板部Ｃの中に位置し、傾斜片Ａよりも、相対的に、断面係数の低い、磁力によるせん断変形を生じやすい部位に相当する。従って、この断面係数の低い部位の方が、プレス成形によって断面係数の高くなった傾斜片Ａを含む部位よりも、熱処理により硬度が高くなることがわかる。しかしながら、誘導加熱部のコイルを移動させた場合、図７に示したように、平板部Ｃの中に位置しながら、２０〜１５０ｍｍまでの部位と、１５０〜１８０ｍｍまでの部位とでは、硬度が大きく異なっている。この点については、誘導加熱部のコイルの移動方向が関連し、移動開始端よりも移動終了端の方が、試験片に蓄えられた熱の影響によって、微細化がより促進されるものと予想される。 On the other hand, the hardness was highest in the range of 150 to 180 mm as described above. As shown in the cross-sectional views of FIGS. 6 and 14, this test piece is press-formed so as to be an inclined piece A in which the vicinity of one side edge of a flat steel plate is bent obliquely. The section modulus Z3 of the portion including the inclined piece A outside the portion to be quenched (hereinafter simply referred to as “quenched portion”) B before being quenched at the molded stage is the section modulus at the quenched portion B. It is higher than Z1. Among the test pieces shown in FIG. 6, the “No. 1 frame” is heated by moving the coil of the induction heating unit from the wide end on the left side in FIG. 6 to the narrow end on the right side. The part quenched in the range of 200 to 230 mm corresponds to the inclined piece A in FIG. On the other hand, most of the hardened portion B in the range of 150 to 180 mm with the highest hardness is located in the flat plate portion C of FIG. 14 and has a relatively low section modulus than the inclined piece A. Corresponds to a site where shear deformation is likely to occur. Therefore, it can be seen that the portion having a lower section modulus has higher hardness due to heat treatment than the portion including the inclined piece A having a higher section modulus by press molding. However, when the coil of the induction heating unit is moved, as shown in FIG. 7, the hardness of the part up to 20 to 150 mm and the part up to 150 to 180 mm is located in the flat plate part C. It is very different. Regarding this point, the moving direction of the coil of the induction heating unit is related, and it is expected that the movement end end is more accelerated than the movement start end due to the heat stored in the test piece. Is done.
一方、図６の「Ｎｏ．２フレーム」において、焼き入れを開始した部位（ａ’点）を０ｍｍとして、焼き入れを行った部位の長手方向に沿って、ａ’点からの距離と硬度との関係と直径が１０μｍ以下の微細粒の分布率をまとめて示したのが図１３である。 On the other hand, in the “No. 2 frame” of FIG. 6, the part (a ′ point) where quenching was started was set to 0 mm, and the distance and hardness from the point a ′ along the longitudinal direction of the part subjected to quenching were determined. FIG. 13 shows the relationship between the above and the distribution ratio of fine grains having a diameter of 10 μm or less.
図１３から、測定距離１００ｍｍ以降において、硬度の高い部分（特に、１３０〜２００ｍｍ付近）が生じているが、これと微細粒の分布率が対応していることがわかる。すなわち、ａ’点では分布率３４％、ｂ’点では分布率４３％であるが、測定距離１００ｍｍ付近のｃ’点では分布率９７％になり、ｄ’点では６２％、ｅ’点では５６％と、硬度の高い範囲では、微細粒の分布率は高くなっており、上記した「Ｎｏ．１フレーム」と同様の傾向であった。 From FIG. 13, it can be seen that a portion with high hardness (particularly around 130 to 200 mm) occurs after the measurement distance of 100 mm, and this corresponds to the distribution ratio of fine particles. That is, the distribution rate is 34% at the point a ′ and the distribution rate 43% at the point b ′, but the distribution rate 97% at the point c ′ near the measurement distance of 100 mm, 62% at the point d ′, and 62% at the point e ′. In the high hardness range of 56%, the distribution ratio of fine grains was high, which was the same tendency as the “No. 1 frame” described above.
図１５及び図１６は、誘導加熱部であるコイルの移動方向（焼き入れ方向）と微細化が促進される部位（強度が向上する部位）との関連を検証するため、硬度と断面係数比との関係を調べた図である。図１５が、図６の「Ｎｏ．１フレーム」の試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ−Ｎｏ．１）に関するデータで、図１６が、図６の「Ｎｏ．２フレーム」の試験片（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ−Ｎｏ．２）のデータである。硬度のデータは、図１５は図７に示したデータと同じであり、図１６は図１３に示したデータと同じである。なお、ビッカース硬度（ＨＶ）と引張り強さ（ＭＰａ）は、換算可能な対応関係を有するため、図１５及び図１６の左側の縦軸には、両方の値を示した。 15 and 16 show hardness and a section modulus ratio in order to verify the relationship between the moving direction (quenching direction) of the coil, which is the induction heating unit, and the part where the miniaturization is promoted (part where the strength is improved). FIG. FIG. 15 shows data relating to the test piece (SPC (t1.0) -P-DH-No. 1) of “No. 1 frame” in FIG. 6, and FIG. 16 shows the data of “No. 2 frame” in FIG. It is the data of a test piece (SPC (t1.0) -P-DH-No. 2). The hardness data is the same as the data shown in FIG. 7 in FIG. 15, and FIG. 16 is the same as the data shown in FIG. Since Vickers hardness (HV) and tensile strength (MPa) have a convertible correspondence, the vertical axis on the left side of FIGS. 15 and 16 shows both values.
また、断面係数は、図１４に示したように、試験片の中で傾斜片Ａを含む焼き入れ部Ｂよりも外側の部位の断面係数をＺ３、焼き入れ部位Ｂにおける断面係数をＺ１、試験片全体の断面係数をＺ２としたときに、Ｚ３／Ｚ１及びＺ２／Ｚ１の各比を求め、測定距離との関係で、図１５及び図１６にそれぞれにプロットした。 Further, as shown in FIG. 14, the section modulus of the portion outside the quenched portion B including the inclined piece A in the test piece is Z3, and the section modulus at the quenched portion B is Z1, as shown in FIG. When the section modulus of the entire piece was Z2, the ratios of Z3 / Z1 and Z2 / Z1 were determined and plotted in FIGS. 15 and 16 in relation to the measurement distance.
図１５から明らかなように、幅広の端部側から幅狭の端部側へと誘導加熱部を移動させて加熱した場合の硬度及び引張り強さ（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ−Ｎｏ．１）は、Ｚ２／Ｚ１の比のグラフに対応している。つまり、Ｚ２／Ｚ１の比の高い部位が現れる測定距離１７０ｍｍから１８０ｍｍ付近において、硬度も高くなっている。一方、幅狭の端部側から幅広の端部側へと誘導加熱部を移動させて加熱した場合の硬度及び引張り強さ（ＳＰＣ（ｔ１．０）−Ｐ−ＤＨ−Ｎｏ．２）は、図１６から明らかなように、Ｚ３／Ｚ１の比のグラフに対応しており、Ｚ３／Ｚ１の比の高い範囲である測定距離１００ｍｍ以降において、硬度の高い部分（特に、１３０〜２００ｍｍ付近）が生じている。 As is apparent from FIG. 15, the hardness and tensile strength (SPC (t1.0) -P-DH-) when the induction heating unit is moved from the wide end side to the narrow end side and heated. No. 1) corresponds to a graph of the ratio Z2 / Z1. That is, the hardness is high in the vicinity of a measurement distance of 170 mm to 180 mm where a portion having a high ratio of Z2 / Z1 appears. On the other hand, the hardness and tensile strength (SPC (t1.0) -P-DH-No. 2) when the induction heating unit is moved from the narrow end to the wide end are heated. As is clear from FIG. 16, this corresponds to the graph of the ratio of Z3 / Z1, and after the measurement distance of 100 mm, which is a high range of the ratio of Z3 / Z1, there is a portion with high hardness (particularly around 130 to 200 mm). Has occurred.
すなわち、図１５及び図１６から、試験片の形状に拘わらず、誘導加熱部のコイルの移動開始端よりも移動終了端に近い方が硬度が高くなっており、微細化の促進に、試験片に蓄えられていく熱が大きく影響していることがわかる。 That is, from FIGS. 15 and 16, regardless of the shape of the test piece, the hardness is higher near the movement end than the movement start end of the coil of the induction heating unit. It can be seen that the heat stored in is greatly affected.
より詳細には、図６の「Ｎｏ．１フレーム」のように、幅広の端部側から幅狭の端部側へ焼き入れした場合、幅広端寄りの部位（主に、０〜１５０ｍｍまでの部位）は、本来、せん断変形が生じやすい形状であるが、面積が大きいことから熱が逃げやすい。この結果、温度の上昇が抑えられ、加熱によるせん断変形が十分には生じにくい。そのため、微細化が促進されない。その一方、２００ｍｍ以降の部位では、断面係数が高くなっているため、せん断変形が生じにくいが、面積が小さく熱はたまりやすい。これに対し、両者の間の１５０〜１８０ｍｍの熱処理部は、断面係数が低くくて、熱処理部以外の周辺部位は断面係数が高く、熱によるせん断変形が生じやすい。また、熱もたまりやすいことから、微細化が促進されると考えられる。 More specifically, as shown in “No. 1 frame” in FIG. 6, when quenching from the wide end side to the narrow end side, the portion closer to the wide end (mainly from 0 to 150 mm). The part) is originally in a shape that tends to cause shear deformation, but heat is likely to escape because of its large area. As a result, an increase in temperature is suppressed and shear deformation due to heating is hardly generated. Therefore, miniaturization is not promoted. On the other hand, since the section modulus is high at a portion of 200 mm or more, shear deformation is unlikely to occur, but the area is small and heat tends to accumulate. On the other hand, the heat treatment part of 150 to 180 mm between them has a low section modulus, and the peripheral part other than the heat treatment part has a high section coefficient, and shear deformation due to heat tends to occur. Moreover, since heat tends to accumulate, it is considered that miniaturization is promoted.
一方、図６の「Ｎｏ．２フレーム」のように、幅狭の端部側から幅広の端部側へ焼き入れした場合、幅狭端寄りの部位（主に、０〜１００ｍｍまでの部位）は、本来、面積が小さく熱がたまりやすいが、断面係数が高くなっているため、せん断変形が生じにくく、微細化が生じにくい。幅広端寄りの２００ｍｍ以降の部位は、本来、せん断変形が生じやすい形状であるが、面積が大きいことから焼き入れ方向の移動終了端付近であっても、逃げる熱の方が多く、十分な熱量が確保されず、微細化しにくい。これに対し、１００〜２００ｍｍの範囲では、面積が大きくなってきているが、２００ｍｍ以降の部位よりも面積は小さく、また、焼き入れ方向では、コイルの移動範囲のほぼ中間以降となるため、たまる熱の方が勝り、これに断面係数が低くなっていることが加味されてせん断変形が生じやすく、微細化が促進されると考えられる。 On the other hand, when quenching from the narrow end side to the wide end side as shown in “No. 2 frame” in FIG. 6, the part closer to the narrow end (mainly part from 0 to 100 mm). Originally, the area is small and heat tends to accumulate, but since the section modulus is high, shear deformation hardly occurs and miniaturization hardly occurs. The portion of 200 mm or more near the wide end is originally in a shape that tends to cause shear deformation, but since the area is large, there is more heat to escape even near the end of movement in the quenching direction, and a sufficient amount of heat. Is not secured and is difficult to miniaturize. On the other hand, in the range of 100 to 200 mm, the area has become larger, but the area is smaller than the part after 200 mm, and in the quenching direction, it is after the middle of the moving range of the coil. Considering that heat is superior and that the section modulus is low, shear deformation is likely to occur and miniaturization is promoted.
また、幅広の端部から幅狭の端部へと移動させた場合には、硬度分布が断面係数比Ｚ２／Ｚ１の変化に対応し、逆方向へ移動させた場合の硬度分布が断面係数比Ｚ３／Ｚ１の変化に対応している。従って、試験片の一端が狭くて他端が広いような形状の場合、誘導加熱部の移動方向をいずれの方向にするかによって、移動方向に対応する断面係数比Ｚ２／Ｚ１又はＺ３／Ｚ１を利用し、どの位置で断面係数比が高くなるかを特定すれば、加熱する前に、より高硬度化される部位を知ることができる。例えば、自動車用シートのフレーム部品として使用する際、熱処理前の鋼材の各断面係数比を利用することにより、熱処理後に硬度が高くなる部位をフレーム中のどの位置に設定するか容易に判断することができる。 Further, when moving from the wide end to the narrow end, the hardness distribution corresponds to the change in the section modulus ratio Z2 / Z1, and the hardness distribution when moved in the opposite direction is the section coefficient ratio. This corresponds to the change of Z3 / Z1. Therefore, in the case where the end of the test piece is narrow and the other end is wide, the section modulus ratio Z2 / Z1 or Z3 / Z1 corresponding to the moving direction is set depending on which direction the moving direction of the induction heating unit is set. If it is used and the position at which the section modulus ratio becomes high is specified, it is possible to know the part to be hardened before heating. For example, when using it as a frame part of an automobile seat, it is easy to determine which position in the frame to set the part where the hardness increases after heat treatment by using the ratio of each section modulus of the steel material before heat treatment Can do.
本発明によれば、上記各試験例から明らかなように、炭素含有量の低い低炭素金属部材であっても、プレス成形などの内部応力を高める部位を形成する加工処理と熱処理（焼き入れ処理）とを組み合わせることで、金属部材の強度を上げることができる。従って、本発明は、自動車のボディーなどに用いられる炭素含有量の低い冷間圧延鋼板や熱間圧延鋼板の強化に好適に用いられる。その結果、バンパーなどに用いられるレインフォースメントの省略、あるいは使用数・使用箇所の低減を図ることができ、ボディーの軽量化に資する。また、炭素含有量が低くても強度を高めることができるため、炭素含有量が均質でない素材、例えば、炭素含有量が０．１０質量％以上である部位とそうでない部位とが混在していたり、他の構成成分も一様でないような素材であったとしても、全体として強度の向上を図ることができ、本発明は、自動車のボディー等に限らず、各種の用途に適用可能である。 According to the present invention, as is clear from each of the above test examples, processing and heat treatment (quenching treatment) for forming a portion that increases internal stress, such as press molding, even for a low carbon metal member having a low carbon content. ) Can be used to increase the strength of the metal member. Therefore, the present invention is suitably used for strengthening cold-rolled steel sheets and hot-rolled steel sheets with low carbon content used for automobile bodies and the like. As a result, the reinforcement used in bumpers and the like can be omitted, or the number and locations of use can be reduced, contributing to weight reduction of the body. In addition, since the strength can be increased even if the carbon content is low, a material whose carbon content is not homogeneous, for example, a site where the carbon content is 0.10 % by mass or more and a site where the carbon content is not so are mixed. Even if the other components are not uniform, the strength can be improved as a whole, and the present invention is not limited to the body of an automobile and can be applied to various uses.
本発明は、低炭素金属部材について強度を上げるものであるが、低炭素金属部材としては、上記に例示したもののほか、低炭素ステンレス鋼などが挙げられる。また、本発明は、実質的に炭素を含んでいない金属部材をも対象とし、プレス成形などの内部応力を高める部位を形成する加工処理と熱処理（焼き入れ処理）とを組み合わせることによって、それらについても強度を高めることができる。実質的に炭素を含んでいない金属部材には、例えば、アルミニウム等がある。但し、アルミニウムのような非磁性体金属の場合には、誘導加熱時の磁力が、ワークをせん断変形させる力として作用しない。そこで、アルミニウムなどの場合には、熱処理前に、シート状、薄板状、テープ状などの強磁性体を一体化させた複合材に加工するなどの前処理を施した後、熱処理を行うようにする必要がある。 Although this invention raises an intensity | strength about a low carbon metal member, in addition to what was illustrated above, low carbon stainless steel etc. are mentioned as a low carbon metal member. In addition, the present invention is also intended for metal members that do not substantially contain carbon, and by combining a processing process for forming a portion that increases internal stress such as press molding and a heat treatment (quenching process), Can also increase the strength. Examples of the metal member that does not substantially contain carbon include aluminum. However, in the case of a nonmagnetic metal such as aluminum, the magnetic force at the time of induction heating does not act as a force for shearing the workpiece. Therefore, in the case of aluminum or the like, heat treatment is performed after pre-treatment such as processing into a composite material in which ferromagnetic materials such as sheets, thin plates, and tapes are integrated before heat treatment. There is a need to.
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| US9279166B2 (en) * | 2009-11-06 | 2016-03-08 | Johnson Controls Technology Company | Seat structural component tailored for strength |
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