JP4696870B2 - High strength steel plate and manufacturing method thereof - Google Patents
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- JP4696870B2 JP4696870B2 JP2005335130A JP2005335130A JP4696870B2 JP 4696870 B2 JP4696870 B2 JP 4696870B2 JP 2005335130 A JP2005335130 A JP 2005335130A JP 2005335130 A JP2005335130 A JP 2005335130A JP 4696870 B2 JP4696870 B2 JP 4696870B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 86
- 239000010959 steel Substances 0.000 title claims description 86
- 238000004519 manufacturing process Methods 0.000 title claims description 12
- 238000001816 cooling Methods 0.000 claims description 60
- 229910000859 α-Fe Inorganic materials 0.000 claims description 48
- 238000005096 rolling process Methods 0.000 claims description 39
- 229910001562 pearlite Inorganic materials 0.000 claims description 37
- 239000002245 particle Substances 0.000 claims description 23
- 238000004804 winding Methods 0.000 claims description 17
- 238000005246 galvanizing Methods 0.000 claims description 13
- 229910052758 niobium Inorganic materials 0.000 claims description 8
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- 238000005266 casting Methods 0.000 claims description 7
- 238000005554 pickling Methods 0.000 claims description 7
- 229910052720 vanadium Inorganic materials 0.000 claims description 7
- 238000005097 cold rolling Methods 0.000 claims description 6
- 238000002844 melting Methods 0.000 claims description 6
- 230000008018 melting Effects 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 238000005098 hot rolling Methods 0.000 description 10
- 230000007704 transition Effects 0.000 description 10
- 238000000034 method Methods 0.000 description 9
- 229910001566 austenite Inorganic materials 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 238000007747 plating Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 238000005728 strengthening Methods 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 4
- 229910001563 bainite Inorganic materials 0.000 description 4
- 239000011701 zinc Substances 0.000 description 4
- 229910052725 zinc Inorganic materials 0.000 description 4
- 229910001335 Galvanized steel Inorganic materials 0.000 description 3
- 229910001567 cementite Inorganic materials 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000008397 galvanized steel Substances 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
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- 238000005204 segregation Methods 0.000 description 2
- 238000010008 shearing Methods 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 241000219307 Atriplex rosea Species 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
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- 239000002131 composite material Substances 0.000 description 1
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- 230000003247 decreasing effect Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
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- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
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Description
本発明は、家電製品、自動車部品等に適用される高強度鋼板の製造方法に関する。 The present invention relates to a method for manufacturing a high-strength steel sheet applied to home appliances, automobile parts and the like.
家電製品や自動車部品へ鋼板を適用するに際しては、剛性、素材の薄肉化による軽量化などの観点から、高強度鋼板の適用が有望と考えられている。そして、プレス成形を伴なう場合には優れた張出し性、伸びフランジ性が素材に要求されることから、高強度鋼板に対しても伸び、伸びフランジ性の高いことが望まれる。
また、成形後の部品特性として、使用環境が寒冷雰囲気である場合には、強度(静的、動的な凹み難さ)や耐衝撃性能に加えて、低温靭性(耐二次加工脆性)が重要であると考えられる。耐二次加工脆性は、素材強度が高く、プレス成形が厳しい部品ほど不利になることから、高強度鋼板に対して特性向上が求められており、このような素材要求に対し、これまでに種々の鋼板及びその製造技術が開示されている。
When applying steel sheets to household appliances and automobile parts, high strength steel sheets are considered promising from the viewpoints of rigidity and weight reduction by thinning the material. And in the case of press forming, since the material is required to have excellent stretchability and stretch flangeability, it is desired to stretch even to high-strength steel sheets and to have high stretch flangeability.
In addition, as a part characteristic after molding, when the usage environment is a cold atmosphere, in addition to strength (static and dynamic dent difficulty) and impact resistance performance, low temperature toughness (secondary work brittleness resistance) It is considered important. Secondary work brittleness is high in material strength and is more disadvantageous for parts with severe press forming. Therefore, improvement in properties is required for high-strength steel sheets. Steel sheets and manufacturing techniques thereof are disclosed.
特許文献１には、伸びフランジ性の優れた低炭素熱延鋼板の製造方法が開示されている。また、特許文献2には、Si添加のフェライト、ベイナイト組織を主体とする高強度熱延鋼板が開示されている。特許文献3には、加工用低炭素熱延高張力鋼板の製造方法が開示されている。
特許文献1に開示された技術によれば、γ域仕上圧延後の急速冷却と250〜540℃の低温巻取りにより、鋼板組織を微細フェライト＋ベイナイト組織とし、引張強度が52〜61kgf/mm2、Elが25〜31%、λが101〜141%の特性を有する熱延鋼板が得られている。このような引張強度が45kgf/mm2（440MPa）級の鋼板では、強度−延性の指標であるTS×El値が16000MPa・%以上であれば張出し性は良好であり、また強度−穴拡げ性の指標であるTS×λ値(λ値：穴拡げ率)が45000MPa・%であれば、伸びフランジ性は好ましい。これに対して特許文献１に記載の鋼板は、TS×λ値は60378〜73539MPa・%と高いことから、強度-伸びフランジ性バランスが良好であるが、TS×El値は14945〜15798MPa・%と低く、強度-伸びバランスは低く、張出し性は好ましくない。また、国内外の寒冷地使用を考慮した場合、耐二次加工脆性の遷移温度（脆性破壊しない最低温度）は-60℃以下が必要と考えられる。しかし特許文献１では、耐二次加工脆性を意図しておらず、良好な低温靭性が得られないと考えられる。 According to the technique disclosed in Patent Document 1, the steel sheet has a fine ferrite + bainite structure by rapid cooling after γ region finish rolling and low temperature winding at 250 to 540 ° C., and the tensile strength is 52 to 61 kgf / mm 2. Thus, a hot-rolled steel sheet having properties of El of 25 to 31% and λ of 101 to 141% is obtained. For steel sheets with a tensile strength of 45 kgf / mm 2 (440 MPa), if the TS × El value, which is an index of strength-ductility, is 16000 MPa ·% or more, the stretchability is good, and the strength-hole expansibility If the TS × λ value (λ value: hole expansion rate) is 45000 MPa ·%, the stretch flangeability is preferable. On the other hand, the steel sheet described in Patent Document 1 has a high TS × λ value of 60378 to 73539 MPa ·%, and thus has a good strength-stretch flange balance, but the TS × El value is 14945 to 15798 MPa ·%. The strength-elongation balance is low, and the overhanging property is not preferable. Considering the use of cold regions in Japan and overseas, the transition temperature of secondary work brittleness resistance (minimum temperature without brittle fracture) is considered to be -60 ℃ or less. However, Patent Document 1 does not intend secondary work brittleness resistance, and it is considered that good low temperature toughness cannot be obtained.
特許文献2に開示された技術によれば、Si添加の低炭素鋼において、仕上圧延後にC、Si、Mn、P量で規定される温度までの急冷と低温巻取り(350超〜500℃)により、TS×El値が17493〜18110MPa・%で、TS×λ値が63700〜77714MPa・%の伸び、伸びフランジ性の良好な複合組織鋼板が得られるとしている。しかし、特許文献２では、マルテンサイトを含むため、良好な耐二次加工脆性は得られないと考えられる。また、表面性状に好ましくないSiを積極的に添加しているため、熱延鋼板の表面外観は低下しているばかりか、自動車用部品に多く使用されている溶融亜鉛めっき鋼板への適用にも好ましくない。 According to the technique disclosed in Patent Document 2, in low carbon steel with Si addition, rapid cooling to a temperature specified by the amount of C, Si, Mn, P after finish rolling and low temperature winding (over 350 to 500 ° C.) According to the above, it is said that a composite steel sheet having a TS × El value of 17493 to 18110 MPa ·%, a TS × λ value of 63700 to 77714 MPa ·%, and a good stretch flangeability can be obtained. However, in Patent Document 2, since martensite is included, it is considered that good secondary work embrittlement resistance cannot be obtained. In addition, since Si, which is not preferable for the surface properties, is actively added, not only the surface appearance of hot-rolled steel sheets has deteriorated, but also for application to hot-dip galvanized steel sheets that are often used in automotive parts. It is not preferable.
特許文献3では、γ域において仕上圧延終了後、20℃/s以上の冷却速度による二段冷却制御により、微細フェライト、パーライト組織を有し、TS×El値が13495〜14582MPa・%の強度鋼板を開示している。しかし特許文献3に記載の鋼板では十分な延性が得られているとは言い難い。また、仕上圧延後の冷却速度も低いため、十分な細粒組織が得られていないと予想されることから、耐二次加工脆性は低いと考えられる。更に、伸びフランジ性を意図していないことから、伸びフランジ成形性が低いと考えられる。
このように従来の技術は、いずれも自動車部品等に適用される高強度鋼板に求められる優れた伸び(TS×El値≧16000MPa・%)、優れた伸びフランジ性(TS×λ値≧45000MPa・%)、そして優れた耐二次加工脆性(遷移温度≦-60℃)が得られていない。
In Patent Document 3, after finishing rolling in the γ region, the steel plate has a fine ferrite and pearlite structure by two-stage cooling control at a cooling rate of 20 ° C./s or more, and has a TS × El value of 13495-14582 MPa ·%. Is disclosed. However, it is difficult to say that the steel sheet described in Patent Document 3 has sufficient ductility. In addition, since the cooling rate after finish rolling is low, it is expected that a sufficient fine-grained structure is not obtained. Therefore, the secondary work brittleness resistance is considered to be low. Furthermore, since stretch flangeability is not intended, it is considered that stretch flangeability is low.
As described above, all of the conventional technologies have excellent elongation (TS × El value ≧ 16000 MPa ·%) and excellent stretch flangeability (TS × λ value ≧ 45000 MPa ·%) required for high-strength steel plates applied to automobile parts and the like. %) And excellent secondary work brittleness resistance (transition temperature ≦ −60 ° C.) has not been obtained.
本発明では、かかる事情に鑑み、上記問題点を解決するためになされたもので、伸び、伸びフランジ性及び耐二次加工脆性に優れた高強度鋼板を得ることを目的とする。 In view of such circumstances, the present invention has been made to solve the above problems, and an object of the present invention is to obtain a high-strength steel sheet excellent in elongation, stretch flangeability and secondary work brittleness resistance.
本発明者らは、上記の課題を解決すべく鋭意研究した。その結果、フェライト、パーライトを主体とする鋼板組織において、伸び、伸びフランジ性及び耐二次加工脆性を向上させるには、これらの組織を微細化することが重要であり、そのためには、所定の鋼成分とともに、これらの組織が形成される熱間仕上圧延後の冷却速度を適正な範囲に制御することが有効であることを見出した。 The present inventors have intensively studied to solve the above problems. As a result, in a steel sheet structure mainly composed of ferrite and pearlite, it is important to refine these structures in order to improve elongation, stretch flangeability and secondary work brittleness resistance. It has been found that it is effective to control the cooling rate after hot finish rolling in which these structures are formed together with the steel components within an appropriate range.
本発明は、以上の知見に基づきなされたもので、その要旨は以下のとおりである。
［1］質量%で、C:0.10〜0．20%、Si≦0.5%、Mn:0.5〜1.2%、P:0.01〜0.1%、S≦0．01%、sol.Al≦0.1%、N≦0．01%を含有し、残部Feおよび不可避的不純物からなり、フェライトの平均粒径が10μm未満であり、パーライトの平均粒径が6μm未満でありかつ、前記フェライトと前記パーライトの合計面積率が95%以上である組織を有することを特徴とする高強度鋼板。
［2］前記［1］において、さらに、質量％で、Nb、Ti、Vの一種または二種以上を合計で0.01〜0.1%含有することを特徴とする高強度鋼板。
［3］前記［1］または［2］に記載の化学成分からなる鋼を溶製し、鋳造した後、Ar3点以上の温度で仕上圧延し、次いで、700〜600℃の一次冷却停止温度までを50〜400℃/sの平均冷却速度で冷却し、次いで、巻取り温度までを50℃/s以下の平均冷却速度で冷却した後、450〜650℃の巻取り温度で巻取ること特徴とする高強度鋼板の製造方法。
［4］前記［1］または［2］に記載の化学成分からなる鋼を溶製し、鋳造した後、Ar3点以上の温度で仕上圧延し、次いで、700〜600℃の一次冷却停止温度までを50〜400℃/sの平均冷却速度で冷却し、次いで、巻取り温度までを50℃/s以下の平均冷却速度で冷却した後、450〜650℃の巻取り温度で巻取り、次いで、酸洗、もしくは酸洗、冷間圧延した後、連続溶融亜鉛めっき処理を行うことを特徴とする高強度鋼板の製造方法。
The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: 0.10 to 0.20%, Si ≦ 0.5%, Mn: 0.5 to 1.2%, P: 0.01 to 0.1%, S ≦ 0.01%, sol.Al ≦ 0.1%, N ≦ 0.01%, consisting of the balance Fe and inevitable impurities, the average grain size of ferrite is less than 10 μm, the average grain size of pearlite is less than 6 μm, and the total area ratio of the ferrite and the pearlite A high-strength steel sheet characterized by having a structure of 95% or more.
[2] The high-strength steel plate according to [1], further containing 0.01% to 0.1% of Nb, Ti, or V in total by mass.
[3] After melting and casting the steel composed of the chemical component according to [1] or [2], finish rolling at a temperature of 3 or more points of Ar, and then a primary cooling stop temperature of 700 to 600 ° C Is cooled at an average cooling rate of 50 to 400 ° C / s, and then cooled to an winding temperature at an average cooling rate of 50 ° C / s or less, and then wound at a winding temperature of 450 to 650 ° C. A method for producing a high strength steel sheet.
[4] After melting and casting the steel composed of the chemical component described in [1] or [2], finish rolling at a temperature of 3 or more points of Ar, and then a primary cooling stop temperature of 700 to 600 ° C. Is cooled at an average cooling rate of 50 to 400 ° C./s, then cooled to an winding temperature at an average cooling rate of 50 ° C./s or less, and then wound at a winding temperature of 450 to 650 ° C. A method for producing a high-strength steel sheet, characterized by performing continuous hot-dip galvanization after pickling, pickling, or cold rolling.
なお、本明細書において、鋼の成分を示す%は、すべて質量%である。 In the present specification, “%” indicating the component of steel is “% by mass”.
本発明によれば、伸び、伸びフランジ性及び耐二次加工脆性に優れた高強度鋼板を得ることができる。このように本発明では、鋼化学成分、熱延後の冷却条件などの製造条件を適正に制御することにより、家電製品、自動車内板部品などに要求される伸び、伸びフランジ性、耐二次加工脆性に優れた鋼板を安定して製造することが可能となり、本発明の自動車、鉄鋼業界における利用価値は大きい。 ADVANTAGE OF THE INVENTION According to this invention, the high strength steel plate excellent in elongation, stretch flangeability, and secondary work brittleness resistance can be obtained. As described above, in the present invention, by appropriately controlling the manufacturing conditions such as the steel chemical composition and the cooling condition after hot rolling, the elongation, stretch flangeability, secondary resistance required for home appliances, automotive interior parts, etc. It becomes possible to stably produce a steel plate excellent in work brittleness, and the utility value of the present invention in the automobile and steel industry is great.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
まず、本発明者らは、伸びフランジ性の向上を目的とし、フェライト、パーライトを主体とする鋼板組織について鋭意検討した。その結果、ブランクのせん断加工の際の、軟質フェライトと硬質なセメンタイトの界面への応力集中によるボイド発生を低減することが伸びフランジ性の向上には重要であることがわかった。そして、ボイド発生を低減するためには、ボイド発生源となる個々のフェライト、パーライトの界面積を低減すること、すなわち、フェライト、パーライトの結晶粒径を減小させることが有効であることが分かった。さらに、このような組織の微細化には、熱間圧延過程におけるオーステナイトからのフェライト、パーライト組織形成に対し、仕上圧延後のランナウトテーブルにおける冷却速度を適正に制御することが有効であることが分かった。また、このようなフェライト、パーライト組織の微細化により、深絞り成形後の耐二次加工脆性も良好な特性が得られることが明らかとなった。 First, for the purpose of improving stretch flangeability, the present inventors diligently studied a steel sheet structure mainly composed of ferrite and pearlite. As a result, it was found that reducing the generation of voids due to stress concentration at the interface between soft ferrite and hard cementite during shearing of the blank is important for improving stretch flangeability. In order to reduce the generation of voids, it has been found effective to reduce the interfacial area of individual ferrite and pearlite that are the source of void generation, that is, to reduce the crystal grain size of ferrite and pearlite. It was. Furthermore, it has been found that such a refinement of the structure is effective in appropriately controlling the cooling rate in the run-out table after finish rolling for the formation of ferrite and pearlite structures from austenite in the hot rolling process. It was. In addition, it has been clarified that the fineness of the ferrite and pearlite structures can provide good secondary work brittleness resistance after deep drawing.
以下にその内容について詳細に説明する。 The contents will be described in detail below.
まず、引張特性、穴拡げ率及び縦割れ遷移温度（耐二次加工脆性）と仕上圧延後の冷却速度との関係を調べるために、C:0.12〜0.15%、Si:0.02〜0.05%、Mn:0.6〜0.75%、P:0.01〜0.02%、S:0.004〜0.006%、sol.Al:0.03〜0.06%、N:0.003〜0.006%を含有し、残部Feおよび不可避不純物からなる成分の鋼を溶製し、スラブに鋳造して、室温まで冷却した後、熱間圧延（スラブ加熱温度:1200℃、仕上温度:840℃、巻取温度：580℃）を行った。なお、前記熱間圧延では、仕上圧延後、650℃までの平均冷却速度を5〜500℃/sまで変化させ、次いで、650℃未満から巻取温度(580℃)までの平均冷却速度は20℃/ｓとした。以上により得られた熱延板について、引張特性、穴拡げ率、縦割れ遷移温度（耐二次加工脆性）を測定し、仕上圧延後の650℃までの平均冷却速度で整理した。得られた結果を図1に示す。 First, in order to investigate the relationship between tensile properties, hole expansion ratio, longitudinal crack transition temperature (secondary work brittleness resistance) and cooling rate after finish rolling, C: 0.12 to 0.15%, Si: 0.02 to 0.05%, Mn : 0.6 to 0.75%, P: 0.01 to 0.02%, S: 0.004 to 0.006%, sol.Al: 0.03 to 0.06%, N: 0.003 to 0.006%, the steel of the component consisting of the balance Fe and inevitable impurities After melting and casting into a slab and cooling to room temperature, hot rolling (slab heating temperature: 1200 ° C., finishing temperature: 840 ° C., winding temperature: 580 ° C.) was performed. In the hot rolling, after finish rolling, the average cooling rate up to 650 ° C. is changed from 5 to 500 ° C./s, and then the average cooling rate from less than 650 ° C. to the coiling temperature (580 ° C.) is 20 It was set to ° C / s. The hot-rolled sheet obtained as described above was measured for tensile properties, hole expansion ratio, longitudinal crack transition temperature (secondary work brittleness resistance), and arranged at an average cooling rate up to 650 ° C. after finish rolling. The obtained results are shown in FIG.
なお、引張特性は圧延方向から採取したJIS5号引張試験片を用いて、引張速度10mm/minにて引張試験を実施し、引張特性を測定し、TS×El値で評価した。伸びフランジ性は日本鉄鋼連盟規格JFS T1001に準拠した穴拡げ率（λ）を測定し、TS×λ値で評価した。また、耐二次加工脆性は図2に示すように、絞り比1.8で深絞り成形した直径50mm、高さ35mmの円筒深絞り成形材を用いて、縦割れ破壊しない最低温度(縦割れ遷移温度Tc)を測定し、寒冷地での使用に適用できる温度として、-60℃以下の場合に特性良好と判定した。また、走査電子顕微鏡組織写真より、フェライト、パーライトの平均結晶粒径を測定した。なお、引張強度が45kgf/mm2(440MPa)級の鋼板において、高い張出し性、高い伸びフランジ性の求められる部品に適用できる特性として、TS×El値が16000MPa・%以上、TS×λ値が45000MPa・%以上の場合に特性良好と判定した。 Tensile properties were measured using a JIS No. 5 tensile specimen taken from the rolling direction at a tensile speed of 10 mm / min, measured for tensile properties, and evaluated by TS × El value. The stretch flangeability was evaluated by measuring the hole expansion rate (λ) in accordance with the Japan Iron and Steel Federation standard JFS T1001 and using TS × λ value. In addition, as shown in Fig. 2, the secondary work brittleness resistance is the lowest temperature (longitudinal crack transition temperature) that does not cause longitudinal cracking failure using a 50mm diameter and 35mm high diameter deep-drawn molded material with a draw ratio of 1.8. Tc) was measured, and when the temperature applicable to use in a cold region was -60 ° C or less, it was determined that the characteristics were good. Moreover, the average crystal grain size of ferrite and pearlite was measured from a scanning electron microscopic structure photograph. In addition, in steel plates with a tensile strength of 45 kgf / mm 2 (440 MPa), the TS × El value is 16000 MPa ·% or more and the TS × λ value is a characteristic that can be applied to parts that require high stretchability and high stretch flangeability. It was determined that the characteristics were good when the pressure was 45000 MPa ·% or more.
図1より、強度-延性、強度-穴拡げ率の指標であるTS×El値、TS×λ値が高く、縦割れ遷移温度Tcが低い値を得るには、平均冷却速度の適正範囲が存在することがわかる。すなわち、平均冷却速度が50℃/s未満では、TS×El値、TS×λ値はそれぞれ16000MPa・%、45000MPa・%より低く、またTcも-60℃より高い。この平均冷却速度範囲（50℃/s未満）にて得られた熱延板の組織を調べたところ、この熱延板の組織は平均粒径が約11μmのフェライトと平均粒径が約8μmのパーライトからなる粗大組織であることがわかった。そして、TS×El値、TS×λ値がそれぞれ16000MPa・%、45000 MPa・%より低く、またTcも-60℃より高くなったのはこの組織に起因すると推定される。一方、平均冷却速度が400℃/sを超えると、TS×λ値は48000MPa・%と高く、Tcは-100℃と低温であるが、TS×El値は16000MPa・%より低く、延性は低下している。これは、冷却速度が高いため、仕上圧延後のオーステナイトからのフェライト変態の際、オーステナイト粒内からの針状フェライト組織の形成が促進され、延性に好ましい等軸フェライトの形成が少なかったためと推定される。
上記に対し、平均冷却速度が50℃/s以上400℃/s以下では、TS×El値、TS×λ値はそれぞれ16000MPa・%、45000MPa・%以上の値が得られており、かつ、Tcは-60℃以下の低温の特性を示しており、より高いTS×El値、TS×λ値、より低いTcが得られていることがわかる。また、この平均冷却速度範囲（50℃/s以上400℃/s以下）にて得られた熱延板の組織を調べたところ、フェライトの平均粒径は2〜7μm、パーライトの平均粒径は1〜5μmと、微細化しており、フェライト組織とパーライト組織が合計面積率で95〜100％形成されていた。以上のことから、平均冷却速度が50℃/s以上400℃/s以下での特性向上は、平均粒径が2〜7μmの微細フェライトと平均粒径が1〜5μmの微細パーライトの組織が合計面積率で95〜100％形成されていることによると推定される。そして、このような微細組織が得られたのは、仕上圧延後の650℃までの急速冷却により、オーステナイトからの微細等軸フェライト、微細パーライトの形成が促進されたためと考えられる。
From Fig. 1, there is an appropriate range of average cooling rate in order to obtain high TS × El and TS × λ values and low longitudinal crack transition temperature Tc, which are indicators of strength-ductility and strength-hole expansion ratio. I understand that That is, when the average cooling rate is less than 50 ° C./s, the TS × El value and the TS × λ value are lower than 16000 MPa ·% and 45000 MPa ·%, respectively, and the Tc is higher than −60 ° C. Examination of the average cooling rate range (50 ° C. / less than s) The hot-rolled sheet obtained by the tissue, this hot-rolled sheet organization ferrite having an average particle diameter of about 11μm average particle size of approximately 8μm It was found to be a coarse structure composed of pearlite. It is estimated that the TS × El value and TS × λ value were lower than 16000 MPa ·% and 45000 MPa ·%, respectively, and that Tc was higher than -60 ° C. On the other hand, when the average cooling rate exceeds 400 ° C / s, TS × λ value is as high as 48000MPa ·%, Tc is as low as -100 ° C, but TS × El value is lower than 16000MPa ·%, and ductility decreases. is doing. This is presumed to be because the formation of acicular ferrite structure from the austenite grains was promoted during the ferrite transformation from austenite after finish rolling due to the high cooling rate, and the formation of equiaxed ferrite preferred for ductility was small. The
In contrast, when the average cooling rate is 50 ° C / s or more and 400 ° C / s or less, the TS × El value and TS × λ value are 16000 MPa ·% and 45000 MPa ·%, respectively, and Tc Indicates a low temperature characteristic of −60 ° C. or lower, and it can be seen that higher TS × El value, TS × λ value, and lower Tc are obtained. Moreover, when the structure of the hot rolled sheet obtained in this average cooling rate range (50 ° C / s or more and 400 ° C / s or less) was examined, the average particle size of ferrite was 2 to 7 µm, and the average particle size of pearlite was It was refined to 1 to 5 μm, and a ferrite structure and a pearlite structure were formed in a total area ratio of 95 to 100%. From the above, the average characteristic improvement in the cooling rate is less 50 ° C. / s or higher 400 ° C. / s, the average particle size average particle size of fine ferrite 2~7μm there is tissue 1~5μm fine pearlite total It is estimated that the area ratio is 95 to 100%. And, such a fine structure was obtained because the rapid cooling to 650 ° C. after finish rolling promoted the formation of fine equiaxed ferrite and fine pearlite from austenite.
よって、本発明においては、フェライトの平均粒径は10μm未満、パーライトの平均粒径は6μm未満とし、かつ、前記フェライトと前記パーライトの合計面積率は95%以上とする。上記のように、フェライトの平均粒径が10μm以上およびパーライトの平均粒径は6μm以上のような粗大組織では、ブランクのせん断加工の際にボイドが発生するなど、充分な伸び、伸びフランジ性及び耐二次加工脆性が得られない。さらに、粒径2μm以上5μm以下のフェライトと、粒径1μm以上3μm以下のパーライトとの合計面積率を70%以上とすることが好ましい。 Therefore, in the present invention, the average particle size of ferrite is less than 10 μm, the average particle size of pearlite is less than 6 μm, and the total area ratio of the ferrite and pearlite is 95% or more. As described above, in coarse structures such as ferrite having an average particle diameter of 10 μm or more and pearlite having an average particle diameter of 6 μm or more, voids are generated during blank shearing, and sufficient elongation, stretch flangeability and Secondary processing brittleness resistance cannot be obtained. Furthermore, it is preferable that the total area ratio of ferrite having a particle diameter of 2 μm or more and 5 μm or less and pearlite having a particle diameter of 1 μm or more and 3 μm or less is 70% or more.
また、上記組織とするために、本発明においては、仕上圧延直後の一次平均冷却速度を50℃/s以上400℃/s以下とする。 In order to obtain the above structure, in the present invention, the primary average cooling rate immediately after finish rolling is set to 50 ° C./s or more and 400 ° C./s or less.
以上の知見に基づき、本発明では、家電製品、自動車内・外板部品などに適用する際に求められる、優れた伸び、伸びフランジ性及び耐二次加工脆性を有する鋼板を安定して製造する技術を完成するに至った。 Based on the above knowledge, the present invention stably manufactures steel sheets having excellent elongation, stretch flangeability and secondary work brittleness resistance required when applied to home appliances, automotive interior / exterior plate parts, and the like. The technology has been completed.
次に、本発明の成分限定理由および製造条件の限定理由について説明する。
(1)化学成分範囲
C:0.10〜0.20%
Cは本発明で意図する熱延時の微細パーライト形成に有効であり、また鋼板の強化の観点から、0.10%以上添加する。Cの添加量が0.20%を超えると、パーライトの粗大化とともに、パーライト体積率の増大により、伸びフランジ性、耐二次加工脆性の低下を引き起こす。よって、C量は0.10以上0.20%以下とする。好ましくは、0.11%以上0.15%以下である。
Next, the reasons for limiting the components of the present invention and the reasons for limiting the production conditions will be described.
(1) Chemical composition range
C: 0.10-0.20%
C is effective for forming fine pearlite during hot rolling intended in the present invention, and is added in an amount of 0.10% or more from the viewpoint of strengthening the steel sheet. When the amount of C exceeds 0.20%, the pearlite becomes coarse, and the pearlite volume fraction increases, which causes a decrease in stretch flangeability and secondary work brittleness resistance. Therefore, the C amount is set to 0.10 or more and 0.20% or less. Preferably, it is 0.11% or more and 0.15% or less.
Si≦0.5%
Siは鋼板の強化に有効な元素であり、適宜添加することが出来る。しかし、Siの添加量が0.5%を超えると、赤スケールの発生による鋼板の表面性状が劣化するため、Si量は0.5%以下とする。
Si ≦ 0.5%
Si is an element effective for strengthening steel sheets and can be added as appropriate. However, if the amount of Si exceeds 0.5%, the surface properties of the steel sheet deteriorate due to the occurrence of red scale, so the Si amount is 0.5% or less.
Mn:0.5〜1.2%
Mnは鋼板の強化に有効な元素であるが、添加量が0.5%未満では鋼板の強化能が小さい。一方、Mn量が1.2%を超えると、連続鋳造時のMn偏析に起因した板厚方向の不均一組織により、耐二次加工脆性、伸びフランジ性が低下する。よって、Mn量は0.5%以上1.2%以下とする。
Mn: 0.5-1.2%
Mn is an element effective for strengthening the steel sheet, but if the addition amount is less than 0.5%, the strengthening ability of the steel sheet is small. On the other hand, if the Mn content exceeds 1.2%, the secondary work brittleness resistance and stretch flangeability deteriorate due to the uneven structure in the thickness direction due to Mn segregation during continuous casting. Therefore, the Mn content is 0.5% or more and 1.2% or less.
P: 0.01〜0.1 %
Pは鋼板の強化に有効な元素であるが、添加量が0.01%未満では鋼板の強化能が小さい。また、Pの添加量が0.1%を超えると、Pのフェライト粒界偏析による粒界脆化により、耐二次加工脆性が著しく悪化する。また、合金化溶融亜鉛めっき処理を施す場合には、めっき密着性が著しく低下する。以上より、P量は0.01%以上0.1%以下とする。
P: 0.01-0.1%
P is an element effective for strengthening the steel sheet, but if the addition amount is less than 0.01%, the strengthening ability of the steel sheet is small. On the other hand, if the addition amount of P exceeds 0.1%, the secondary work embrittlement resistance is remarkably deteriorated due to grain boundary embrittlement due to P ferrite grain boundary segregation. Further, when the alloying hot dip galvanizing treatment is performed, the plating adhesion is remarkably lowered. From the above, the P content is 0.01% or more and 0.1% or less.
S:≦0.01%
Sは0.01%を超えると、MnS生成による伸びフランジ性の低下が顕著となるばかりか、熱間脆性によるスケール表面欠陥の発生が著しくなる。このため、S量は0.01%以下とする。
S: ≦ 0.01%
If S exceeds 0.01%, not only will the stretch flangeability deteriorate due to the formation of MnS, but also the occurrence of scale surface defects due to hot brittleness will become significant. Therefore, the S content is 0.01% or less.
sol.Al≦0.1%
sol.Alは0.1%を超えると表面性状が低下するばかりか、Nと結合してAlNが過剰に形成され、鋼板の延性は著しく低下する。このため、sol.Alは0.1%以下とする。
sol.Al ≦ 0.1%
When sol.Al exceeds 0.1%, not only the surface properties are deteriorated, but also AlN is excessively formed by combining with N, and the ductility of the steel sheet is remarkably lowered. For this reason, sol.Al is made 0.1% or less.
N≦0.01%
Nは0.01%を超えると、Alと結合してAlNが形成され易くなり、鋼板の延性低下が顕著となる。このため、N量は0.01%以下とする。
N ≦ 0.01%
When N exceeds 0.01%, AlN is easily formed by combining with Al, and the ductility of the steel sheet is significantly reduced. Therefore, the N content is 0.01% or less.
本発明で用いる鋼板は、上記の必須含有元素で目的とする特性が得られるが、所望の特性に応じて以下の元素を含有することができる。 The steel sheet used in the present invention can achieve the intended characteristics with the above essential elements, but can contain the following elements depending on the desired characteristics.
Nb、Ti、Vの一種または二種以上の合計：0.01〜0.1%
Nb、Ti、VはCと結合して炭化物を形成し、熱延時のオーステナイトの細粒化に寄与し、オーステナイトから変態するフェライト、パーライトの微細化に有効である。このため、Nb、Ti、Vは一種または二種以上含有することが出来る。含有する場合、Nb、Ti、Vの合計含有量が0.01%未満ではこの効果は小さい。一方、Nb、Ti、Vの合計含有量が0.1%を超えると、Cと結合して炭化物が形成され易くなり、鋼板の延性低下が著しくなる。よって、Nb、Ti、Vを含有する場合、その合計量は0.01%以上0.1%以下とする。好ましくは0.02%以上0.05%以下である。
Total of one or more of Nb, Ti, V: 0.01 to 0.1%
Nb, Ti, and V combine with C to form carbides, contribute to the fine graining of austenite during hot rolling, and are effective in refining ferrite and pearlite transformed from austenite. For this reason, Nb, Ti, and V can contain 1 type, or 2 or more types. When contained, this effect is small when the total content of Nb, Ti and V is less than 0.01%. On the other hand, when the total content of Nb, Ti, and V exceeds 0.1%, it becomes easy to form carbides by combining with C, and the ductility of the steel sheet is significantly reduced. Therefore, when Nb, Ti, and V are contained, the total amount is 0.01% or more and 0.1% or less. Preferably it is 0.02% or more and 0.05% or less.
上記以外の残部はFe及び不可避不純物とする。また、本発明では、本発明の作用効果を害さない微量元素として、例えば、Cr、Moは0.5%以下を含有してもよい。 The remainder other than the above is Fe and inevitable impurities. In the present invention, as a trace element that does not impair the effects of the present invention, for example, Cr and Mo may contain 0.5% or less.
(2)高強度鋼板の製造方法
本発明の高強度鋼板は、まず、上記成分組成を有する鋼を溶製し、鋳造する。特にミクロ偏析などの不均一な組織が発生しなければ、鋳造方法は、造塊法、連続鋳造法のどちらでも良い。次いで、鋳造されたスラブを熱間圧延する。
(2) Method for producing high-strength steel sheet The high-strength steel sheet of the present invention is first prepared by melting and casting steel having the above composition. In particular, as long as a non-uniform structure such as microsegregation does not occur, the casting method may be either an ingot-making method or a continuous casting method. Next, the cast slab is hot-rolled.
熱間圧延は、高温の鋳造スラブをそのまま圧延しても良いし、室温まで冷却されたスラブを再加熱してから圧延しても良い。スラブ加熱する場合、圧延加熱温度が1100℃未満では圧延荷重が高くなるため、圧延が困難となる。また、スラブ加熱温度が1300℃を超えると、一次スケールの過剰な発生による熱延時のスケール欠陥発生し易くなる。このため、スラブの加熱温度は、1100℃以上1300℃以下が好ましい。粗圧延後、仕上圧延し、コイルに巻き取る。仕上圧延の際、Ar3点未満の温度で圧延終了すると、板厚の表層付近に圧延方向に伸長したフェライト粒が形成され、本発明の意図する微細な等軸フェライト粒の形成が困難となり、鋼板の伸び、伸びフランジ性の低下を引き起こす。このため、仕上温度はAr3点以上とする。
仕上圧延後、ランナウトテーブルにおいて高温での滞留時間が長いとフェライト、パーライトが粒成長するため、仕上圧延終了後は急速に冷却（一次冷却と称す）する必要がある。700〜600℃までの温度域での平均冷却速度が50℃/s未満では細粒化効果は小さい。一方、700〜600℃までの温度域での平均冷却速度が400℃/sを超えると、オーステナイト粒内からの針状フェライトの形成が促進され、微細な等軸フェライトが得られない。よって、一次冷却停止温度を700〜600℃とし、仕上圧延終了から一次冷却停止までの温度域の平均冷却速度は50℃/s以上400℃/s以下とする。好ましくは100℃/s以上400℃/s以下である。なお、これは本発明において、最も重要な要件の一つである。
また、上記一次冷却終了後からコイルに巻取るまで（二次冷却と称す）の冷却速度が50℃/sを超えると、コイル巻取過程においてフェライト粒界、粒内へのセメンタイトの析出が促進され、鋼板の延性および伸びフランジ性が低下する。よって、上記一次冷却終了後からコイルに巻取るまでの温度域での平均冷却速度は50℃/s以下とする。好ましくは5℃/s以上30℃/s以下である。
In hot rolling, a high-temperature cast slab may be rolled as it is, or a slab cooled to room temperature may be reheated and then rolled. In the case of slab heating, if the rolling heating temperature is less than 1100 ° C., the rolling load becomes high, so that rolling becomes difficult. Further, when the slab heating temperature exceeds 1300 ° C., scale defects are easily generated during hot rolling due to excessive generation of primary scale. For this reason, the heating temperature of the slab is preferably 1100 ° C. or higher and 1300 ° C. or lower. After rough rolling, it is finish-rolled and wound on a coil. During finish rolling, when rolling is completed at a temperature lower than the Ar 3 point, ferrite grains elongated in the rolling direction are formed in the vicinity of the surface layer of the plate thickness, making it difficult to form fine equiaxed ferrite grains intended by the present invention, Causes the steel sheet to stretch and stretch flangeability. For this reason, the finishing temperature is set at Ar 3 or higher.
After the finish rolling, if the residence time at a high temperature is long on the runout table, ferrite and pearlite grow in grains, and thus it is necessary to rapidly cool (referred to as primary cooling) after finishing rolling. When the average cooling rate in the temperature range from 700 to 600 ° C. is less than 50 ° C./s, the effect of atomization is small. On the other hand, when the average cooling rate in the temperature range from 700 to 600 ° C. exceeds 400 ° C./s, the formation of acicular ferrite from the austenite grains is promoted, and fine equiaxed ferrite cannot be obtained. Accordingly, the primary cooling stop temperature is set to 700 to 600 ° C., and the average cooling rate in the temperature range from the finish rolling to the primary cooling stop is set to 50 ° C./s or more and 400 ° C./s or less. Preferably, it is 100 ° C./s or more and 400 ° C./s or less. This is one of the most important requirements in the present invention.
Also, if the cooling rate from the end of the primary cooling to the coil winding (referred to as secondary cooling) exceeds 50 ° C / s, the precipitation of cementite in the ferrite grain boundaries and grains is accelerated during the coil winding process. As a result, the ductility and stretch flangeability of the steel sheet deteriorate. Therefore, the average cooling rate in the temperature range from the end of the primary cooling to the winding of the coil is 50 ° C./s or less. Preferably, it is 5 ° C./s or more and 30 ° C./s or less.
巻取温度は450℃未満の場合、オーステナイトからのベイナイト形成が進行し、鋼板の延性の低下が大きい。一方、巻取温度が650℃を超えると、パーライト体積率が増大し、伸びフランジ性の低下が顕著となる。このため、巻取温度は450℃以上650℃以下とする。尚、好ましい巻取温度は480〜600℃である。 When the coiling temperature is less than 450 ° C., bainite formation from austenite proceeds, and the ductility of the steel sheet is greatly reduced. On the other hand, when the coiling temperature exceeds 650 ° C., the pearlite volume fraction increases and the stretch flangeability deteriorates significantly. For this reason, the coiling temperature is set to 450 ° C. or higher and 650 ° C. or lower. A preferable winding temperature is 480 to 600 ° C.
熱延鋼板を酸洗した後、または熱延鋼板を酸洗し、冷間圧延した後、目的に応じて適宜連続溶融亜鉛めっき処理を施すことができる。連続溶融亜鉛めっき処理を施しても本発明の目的とする特性は充分に得られる。冷間圧延する場合、焼鈍時のフェライト再結晶の観点から、圧延率は50%以上であれば良い。圧延率が90%を超えると、圧延荷重の増大により、圧延が困難となる。よって、冷間圧延率は50%以上90％以下が好ましい。連続溶融亜鉛めっき処理は、熱延鋼板を酸洗した後に実施する場合は、熱延で得られた微細フェライト、パーライト組織を維持するため、850℃以下の温度で焼鈍した後、溶融亜鉛めっき処理する。冷間圧延後に連続溶融亜鉛めっき処理する場合は、本発明の目的とする微細フェライト、パーライト組織を得るため、焼鈍温度はフェライトの再結晶温度以上880℃以下として焼鈍し、溶融亜鉛めっき処理をする。尚、好ましい焼鈍温度の上限は850℃である。また、前記の溶融めっき処理は、純亜鉛めっき、合金化亜鉛めっき、亜鉛+ニッケル合金めっき、亜鉛+アルミ合金めっきでも良い。
以上により、本発明の目的とする高強度鋼板が得られるが、冷延鋼板の場合、めっき処理を施さない連続焼鈍材やこの連続焼鈍材に電気亜鉛めっき、化成処理、有機系皮膜処理等の表面処理を施しても本発明の目的とする特性を損なうことはない。
After pickling the hot-rolled steel sheet or pickling the hot-rolled steel sheet and cold rolling, continuous hot-dip galvanizing treatment can be appropriately performed depending on the purpose. Even if the continuous hot dip galvanizing treatment is performed, the target characteristics of the present invention can be sufficiently obtained. In the case of cold rolling, the rolling rate may be 50% or more from the viewpoint of ferrite recrystallization during annealing. When the rolling rate exceeds 90%, rolling becomes difficult due to an increase in rolling load. Therefore, the cold rolling rate is preferably 50% or more and 90% or less. When continuous hot-dip galvanizing treatment is performed after pickling the hot-rolled steel sheet, in order to maintain the fine ferrite and pearlite structure obtained by hot-rolling, the hot-dip galvanizing treatment is performed after annealing at a temperature of 850 ° C or lower. To do. In the case of continuous hot dip galvanizing after cold rolling, in order to obtain the objective fine ferrite and pearlite structure of the present invention, the annealing temperature is annealed at a recrystallization temperature of ferrite to 880 ° C. or lower, and hot dip galvanizing is performed. . The upper limit of the preferable annealing temperature is 850 ° C. Further, the hot dipping treatment may be pure zinc plating, alloyed zinc plating, zinc + nickel alloy plating, or zinc + aluminum alloy plating.
As described above, the high-strength steel sheet intended for the present invention can be obtained. In the case of a cold-rolled steel sheet, continuous annealing material that is not subjected to plating treatment or electrogalvanizing, chemical conversion treatment, organic coating treatment, etc. Even if the surface treatment is performed, the target characteristics of the present invention are not impaired.
表1に示す成分の鋼(No.1〜5:本発明鋼、No.6:比較鋼)を溶製し、スラブに鋳造して、室温まで冷却した後、熱間圧延を実施した。熱間圧延はスラブ加熱温度を1200℃、仕上温度を850℃とし、巻取温度を500℃として実施し、板厚2.6mmの熱延鋼板を作製した。尚、仕上圧延後ランナウトテーブルにおいて、600℃までを平均冷却速度200℃/sで冷却し、次いで500℃までを平均冷却速度10℃/sで冷却し、コイルに巻取った。このようにして得られた熱延板について、引張特性、穴拡げ率、耐二次加工脆性、鋼板組織を調査した。 Steels having the components shown in Table 1 (No. 1 to 5: invention steel, No. 6: comparative steel) were melted, cast into slabs, cooled to room temperature, and then hot-rolled. Hot rolling was performed at a slab heating temperature of 1200 ° C., a finishing temperature of 850 ° C., and a coiling temperature of 500 ° C. to produce a hot rolled steel plate having a thickness of 2.6 mm. In the run-out table after finish rolling, the sheet was cooled down to 600 ° C. at an average cooling rate of 200 ° C./s, and then cooled down to 500 ° C. at an average cooling rate of 10 ° C./s and wound on a coil. The hot-rolled sheet thus obtained was examined for tensile properties, hole expansion ratio, secondary work brittleness resistance, and steel sheet structure.
引張特性は圧延方向から採取したJIS5号引張試験片を用いて、引張速度10mm/minにて引張試験を実施して求めた。耐二次加工脆性は図2に示すように、絞り比1.8で深絞り成形した直径50mm、高さ35mmの円筒深絞り成形材を用いて、縦割れ破壊しない最低温度（縦割れ遷移温度；Tc）を測定し、寒冷地での使用に適用できる温度として、-60℃以下の場合に特性良好と判定した。伸びフランジ性は日本鉄鋼連盟規格JFS T1001に準拠した穴拡げ率（λ）を測定し、TS×λ値で評価した。また、鋼板組織は、走査電子顕微鏡組織写真よりフェライト、パーライトの平均結晶粒径とこれらの組織の合計面積率を測定した。 Tensile properties were obtained by conducting a tensile test at a tensile speed of 10 mm / min using JIS No. 5 tensile test specimens taken from the rolling direction. As shown in Fig. 2, the resistance to secondary work brittleness is the lowest temperature (longitudinal crack transition temperature; Tc) that does not cause vertical crack fracture using a deep-drawn cylindrical material with a diameter of 50 mm and a height of 35 mm that is deep-drawn at a draw ratio of 1.8. ) Was measured, and it was determined that the characteristics were good when the temperature was -60 ° C or lower as the temperature applicable for use in a cold region. The stretch flangeability was evaluated by measuring the hole expansion rate (λ) in accordance with the Japan Iron and Steel Federation standard JFS T1001 and using TS × λ value. Moreover, the steel plate structure measured the average crystal grain diameter of ferrite and pearlite and the total area ratio of these structures from the scanning electron microscope structure photograph.
表2に上記により得られた鋼板の特性の結果を示す。 Table 2 shows the results of the characteristics of the steel sheet obtained as described above.
表２より、本発明成分範囲内の本発明例No.1〜5では、フェライト平均粒径は3.5〜4.9μm、パーライト平均粒径は2.1〜2.9μmと微細組織となっており、かつ、これらの微細組織の合計面積率は99.5〜100%となっている。そのため、縦割れ遷移温度Tcは-100〜-125℃の低温特性を有し、またTS×El値は16000MPa・%以上、TS×λ値は45000MPa・%以上の高い値が得られている。本発明例の中でもNo.2は、TS×El値が17480MPa・%、TS×λ値が52900MPa・%と高く、Tcは-125℃と低い特性を有する。本発明例No.2は、粒径2μm以上5μm以下のフェライトと粒径1μm以上3μm以下のパーライトが合計面積率で75％と高く、微細組織が多い事から、より高い特性が得られていると考えられる。以上より、本発明例では、良好な耐二次加工脆性、伸び、伸びフランジ性を有していることがわかる。 From Table 2, the present invention examples Nos. 1 to 5 within the component range of the present invention have a fine structure with an average ferrite particle size of 3.5 to 4.9 μm and an average pearlite particle size of 2.1 to 2.9 μm. The total area ratio of the microstructure is 99.5 to 100%. Therefore, the longitudinal crack transition temperature Tc has a low temperature characteristic of −100 to −125 ° C., the TS × El value is 16000 MPa ·% or higher, and the TS × λ value is 45000 MPa ·% or higher. Among the inventive examples, No. 2 has a TS × El value as high as 17480 MPa ·%, a TS × λ value as high as 52900 MPa ·%, and Tc as low as −125 ° C. Invention Example No. 2 has higher characteristics because ferrite with a particle size of 2 μm or more and 5 μm or less and pearlite with a particle size of 1 μm or more and 3 μm or less is as high as 75% in total area ratio and has a fine structure. it is conceivable that. From the above, it can be seen that the examples of the present invention have good secondary work brittleness resistance, elongation and stretch flangeability.
一方、成分が本発明の範囲外である比較例No.6は、バンド組織が発達しているため、TS×λ値は40216MPa・%と低い。また、Tcは-40℃と高いことから、良好な耐二次加工脆性、伸びフランジ性を兼備していない。 On the other hand, Comparative Example No. 6 having a component outside the scope of the present invention has a low TS × λ value of 40216 MPa ·% because the band structure is developed. Also, Tc is as high as -40 ° C, so it does not have good secondary work brittleness resistance and stretch flangeability.
表1に示す成分の鋼No.1を溶製し、スラブに鋳造した後、室温まで冷却した。鋳造スラブを加熱温度1250℃、仕上温度850℃または750℃で熱間圧延し、圧延後600℃まで平均冷却速度30〜500℃/sで冷却し、次いで600℃から巻取温度まで平均冷却速度20℃/s〜60℃/sで冷却した後、550℃または430℃で巻取処理した。次に、得られた熱延鋼板(板厚2.6mm)の一部は酸洗後、連続溶融亜鉛めっき処理を、他の一部は、酸洗し、板厚1.2mmまで冷間圧延をそれぞれ施した後、連続溶融亜鉛めっき処理を施した。熱延鋼板の連続溶融亜鉛めっきは、730℃で焼鈍した後、460℃の溶融亜鉛めっき浴に浸漬し、520℃でめっきの合金化処理をした。また、冷延鋼板の連続溶融亜鉛めっきは、810℃で焼鈍した後、上記と同様の条件にてめっき処理をし、伸長率1.0％の調質圧延を施した。
以上により得られた熱延鋼板、熱延下地の溶融亜鉛めっき鋼板、冷延下地の溶融亜鉛めっき鋼板のそれぞれについて、引張特性、穴拡げ率、耐二次加工脆性、鋼板組織を調査した。なお、引張特性、穴拡げ率、耐二次加工脆性、鋼板組織の測定方法は実施例1と同様である。
Steel No. 1 having the components shown in Table 1 was melted, cast into a slab, and then cooled to room temperature. The cast slab is hot rolled at a heating temperature of 1250 ° C, a finishing temperature of 850 ° C or 750 ° C, cooled to 600 ° C after cooling at an average cooling rate of 30 to 500 ° C / s, and then from 600 ° C to the winding temperature After cooling at 20 ° C./s to 60 ° C./s, winding treatment was performed at 550 ° C. or 430 ° C. Next, part of the obtained hot-rolled steel sheet (thickness 2.6 mm) is pickled and then subjected to continuous hot-dip galvanizing treatment, and the other part is pickled and cold-rolled to a thickness of 1.2 mm. After the application, a continuous hot dip galvanizing treatment was performed. Continuous hot-dip galvanizing of hot-rolled steel sheets was annealed at 730 ° C, then immersed in a hot-dip galvanizing bath at 460 ° C, and alloyed at 520 ° C. In addition, the continuous hot-dip galvanizing of the cold-rolled steel sheet was annealed at 810 ° C., and was then subjected to a plating treatment under the same conditions as described above, and subjected to temper rolling with an elongation rate of 1.0%.
With respect to each of the hot-rolled steel sheet, hot-rolled base hot-dip galvanized steel sheet, and cold-rolled base hot-dip galvanized steel sheet obtained as described above, the tensile properties, hole expansion rate, secondary work brittleness resistance, and steel sheet structure were investigated. Note that the tensile characteristics, hole expansion ratio, secondary work brittleness resistance, and steel sheet structure measurement methods are the same as in Example 1.
表3に上記により得られた鋼板の特性の結果を示す。 Table 3 shows the results of the characteristics of the steel sheet obtained as described above.
表３より、仕上温度、巻取温度、圧延後の一次冷却速度、二次冷却速度が本発明範囲内にある本発明例No.8〜11では、フェライト平均粒径が4.6〜5.2μm、パーライト平均粒径が2.7〜3.4μmと微細組織となっており、かつ、これらの微細組織の合計面積率は98.0〜100％となっている。そのため、TS×El値は16507〜16600MPa・%、TS×λ値は48018〜48792MPa・%と高く、Tcは-100〜-105℃と低い値が得られている。以上より本発明例では、伸び、伸びフランジ性、耐二次加工脆性は良好であることがわかる。
これに対し、仕上温度、巻取温度、圧延後の一次冷却速度、二次冷却速度のいずれかの条件が本発明範囲外である比較例7、12〜15の場合、良好な伸び、伸びフランジ性、耐二次加工脆性を兼備していない。すなわち、圧延後の一次冷却速度が本発明範囲外にある比較例No.7、12では、TS×El値が15000〜15300MPa・%と低い。比較例No.7ではフェライト平均粒径、パーライト平均粒径が10.3μm、8.2μmと大きいため、また、比較例No.12は針状フェライトの形成促進により、等軸フェライト+パーライトの合計面積率が93％と低いため、伸びが低下したと考えられる。また、二次冷却速度が本発明範囲外にある鋼No.13、巻取温度が本発明範囲外にある鋼No.14においてもTS×El値が14678〜14904MPa・%と低い。鋼No.13ではフェライト粒界、粒内へのセメンタイト析出が多く、等軸フェライト+パーライトの合計面積率が低いことが、また鋼No.14ではベイナイト形成されていることが、伸びが低下した原因と考えられる。更に、仕上圧延温度が本発明範囲外にある比較例No.15は、フェライト、パーライト平均粒径が10.5μm、8.4μmと大きいため、Tcが-30℃と高く、TS×El値、TS×λ値は14800MPa・%、39000MPa・%と低い。
From Table 3, in Example Nos. 8 to 11 in which the finishing temperature, the coiling temperature, the primary cooling rate after rolling and the secondary cooling rate are within the scope of the present invention, the ferrite average particle size is 4.6 to 5.2 μm, and pearlite. The average particle size is 2.7 to 3.4 μm , and the microstructure is fine. The total area ratio of these microstructures is 98.0 to 100%. Therefore, the TS × El value is as high as 16507 to 16600 MPa ·%, the TS × λ value is as high as 48818 to 48789 MPa ·%, and the Tc is as low as −100 to −105 ° C. From the above, it can be seen that the examples of the present invention have good elongation, stretch flangeability, and secondary work brittleness resistance.
On the other hand, in the case of Comparative Examples 7 and 12-15 in which any one of the finishing temperature, the coiling temperature, the primary cooling rate after rolling, and the secondary cooling rate is outside the scope of the present invention, good elongation, stretch flange It doesn't have the property and the secondary processing brittleness. That is, in Comparative Examples No. 7 and 12 where the primary cooling rate after rolling is outside the range of the present invention, the TS × El value is as low as 15000 to 15300 MPa ·%. In Comparative Example No. 7, the average ferrite particle diameter and the average pearlite particle diameter are as large as 10.3 μm and 8.2 μm, and in Comparative Example No. 12, the total area ratio of equiaxed ferrite + pearlite is promoted by the formation of acicular ferrite. Is as low as 93%. Further, in Steel No. 13 where the secondary cooling rate is outside the scope of the present invention and Steel No. 14 where the coiling temperature is outside the scope of the present invention, the TS × El value is as low as 14678 to 14904 MPa ·%. In steel No.13, there was a lot of cementite precipitation in the ferrite grain boundaries and grains, the total area ratio of equiaxed ferrite + pearlite was low, and in steel No.14 that bainite was formed, the elongation decreased. Possible cause. Further, Comparative Example No. 15 in which the finish rolling temperature is outside the scope of the present invention is ferrite, pearlite average particle size is as large as 10.5 μm, 8.4 μm, Tc is as high as −30 ° C., TS × El value, TS × The λ value is as low as 14800 MPa ·% and 39000 MPa ·%.
家電製品、自動車内板部品等を中心に、優れた伸び、伸びフランジ性、耐二次加工脆性が要求される分野に好適である。 It is suitable for fields that require excellent elongation, stretch flangeability, and resistance to secondary work brittleness, mainly for home appliances and automobile interior plate parts.
Claims (4)
フェライトの平均粒径が10μm未満であり、パーライトの平均粒径が6μm未満であり
かつ、前記フェライトと前記パーライトの合計面積率が95%以上である組織を有することを特徴とする伸び、伸びフランジ性及び耐二次加工脆性に優れた高強度鋼板。 In mass%, C: 0.10 to 0.20%, Si ≦ 0.5%, Mn: 0.5 to 1.2%, P: 0.01 to 0.1%, S ≦ 0.01%, sol.Al ≦ 0.1%, N ≦ 0. Contains 01%, consists of the balance Fe and inevitable impurities,
Elongation , stretch flange, characterized in that the average particle size of ferrite is less than 10 μm, the average particle size of pearlite is less than 6 μm, and the total area ratio of the ferrite and the pearlite is 95% or more High-strength steel sheet with excellent workability and secondary work brittleness resistance .
次いで、700〜600℃の一次冷却停止温度までを50〜400℃/sの平均冷却速度で冷却し、
次いで、巻取り温度までを50℃/s以下の平均冷却速度で冷却した後、
450〜650℃の巻取り温度で巻取ること特徴とする請求項1または2に記載の伸び、伸びフランジ性及び耐二次加工脆性に優れた高強度鋼板の製造方法。 After melting and casting steel , finish rolling at a temperature of 3 or more points of Ar,
Next, the primary cooling stop temperature of 700 to 600 ° C is cooled at an average cooling rate of 50 to 400 ° C / s,
Next, after cooling to the coiling temperature at an average cooling rate of 50 ° C./s or less,
The method for producing a high-strength steel sheet excellent in elongation, stretch flangeability and secondary work brittleness resistance according to claim 1 or 2 , wherein winding is performed at a winding temperature of 450 to 650 ° C.
次いで、700〜600℃の一次冷却停止温度までを50〜400℃/sの平均冷却速度で冷却し、
次いで、巻取り温度までを50℃/s以下の平均冷却速度で冷却した後、
450〜650℃の巻取り温度で巻取り、
次いで、酸洗、もしくは酸洗、冷間圧延した後、
連続溶融亜鉛めっき処理を行うことを特徴とする請求項1または2に記載の伸び、伸びフランジ性及び耐二次加工脆性に優れた高強度鋼板の製造方法。 After melting and casting steel , finish rolling at a temperature of 3 or more points of Ar,
Next, the primary cooling stop temperature of 700 to 600 ° C is cooled at an average cooling rate of 50 to 400 ° C / s,
Next, after cooling to the coiling temperature at an average cooling rate of 50 ° C./s or less,
Winding at a winding temperature of 450-650 ° C,
Next, after pickling, pickling, cold rolling,
3. The method for producing a high-strength steel sheet excellent in elongation, stretch flangeability and secondary work brittleness resistance according to claim 1, wherein continuous hot-dip galvanizing treatment is performed.
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| JP5434984B2 (en) * | 2011-08-05 | 2014-03-05 | Ｊｆｅスチール株式会社 | High-strength hot-dip galvanized steel sheet excellent in workability with a tensile strength of 440 MPa or more and its production method |
| JP5927994B2 (en) * | 2012-03-01 | 2016-06-01 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet, method for producing the same and method for producing cold-rolled steel sheet |
| JP2013227656A (en) | 2012-03-30 | 2013-11-07 | Nisshin Steel Co Ltd | Cold rolled steel sheet and method for producing the same |
| JP5618432B2 (en) * | 2013-01-31 | 2014-11-05 | 日新製鋼株式会社 | Cold rolled steel sheet and method for producing the same |
| JP5618431B2 (en) | 2013-01-31 | 2014-11-05 | 日新製鋼株式会社 | Cold rolled steel sheet and method for producing the same |
| CN105051228B (en) * | 2013-03-19 | 2017-04-12 | 杰富意钢铁株式会社 | Full hard cold-rolled steel sheet and process for manufacturing same |
| JP6601286B2 (en) * | 2016-03-15 | 2019-11-06 | 日本製鉄株式会社 | Hot-rolled steel sheet and manufacturing method thereof |
| WO2017169871A1 (en) * | 2016-03-31 | 2017-10-05 | Ｊｆｅスチール株式会社 | Thin steel plate and plated steel plate, hot rolled steel plate manufacturing method, cold rolled full hard steel plate manufacturing method, thin steel plate manufacturing method and plated steel plate manufacturing method |
| KR20240098839A (en) | 2022-12-21 | 2024-06-28 | 주식회사 포스코 | High strength steel shet having high yield ratio and method for manufacturing the same |
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