JP5935844B2 - Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same - Google Patents
Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same Download PDFInfo
- Publication number
- JP5935844B2 JP5935844B2 JP2014162839A JP2014162839A JP5935844B2 JP 5935844 B2 JP5935844 B2 JP 5935844B2 JP 2014162839 A JP2014162839 A JP 2014162839A JP 2014162839 A JP2014162839 A JP 2014162839A JP 5935844 B2 JP5935844 B2 JP 5935844B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- steel sheet
- cold
- rolled steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 239000010960 cold rolled steel Substances 0.000 title claims description 25
- 230000003111 delayed effect Effects 0.000 title claims description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 229910000831 Steel Inorganic materials 0.000 claims description 104
- 239000010959 steel Substances 0.000 claims description 104
- 238000001816 cooling Methods 0.000 claims description 29
- 238000000137 annealing Methods 0.000 claims description 26
- 239000002244 precipitate Substances 0.000 claims description 21
- 239000000463 material Substances 0.000 claims description 19
- 238000010438 heat treatment Methods 0.000 claims description 18
- 238000005096 rolling process Methods 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 14
- 229910052758 niobium Inorganic materials 0.000 claims description 14
- 238000005098 hot rolling Methods 0.000 claims description 8
- 238000005097 cold rolling Methods 0.000 claims description 7
- 238000004804 winding Methods 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 2
- 238000003466 welding Methods 0.000 description 39
- 239000006104 solid solution Substances 0.000 description 29
- 230000000694 effects Effects 0.000 description 27
- 239000002184 metal Substances 0.000 description 23
- 229910052751 metal Inorganic materials 0.000 description 23
- 238000000034 method Methods 0.000 description 23
- 230000008569 process Effects 0.000 description 13
- 238000012360 testing method Methods 0.000 description 13
- 239000001257 hydrogen Substances 0.000 description 12
- 229910052739 hydrogen Inorganic materials 0.000 description 12
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 10
- 238000005728 strengthening Methods 0.000 description 8
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 7
- 239000010953 base metal Substances 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000013078 crystal Substances 0.000 description 5
- 230000006872 improvement Effects 0.000 description 5
- 230000009467 reduction Effects 0.000 description 5
- 230000007423 decrease Effects 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910001563 bainite Inorganic materials 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- 238000007545 Vickers hardness test Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000003610 charcoal Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000004993 emission spectroscopy Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000007542 hardness measurement Methods 0.000 description 1
- 238000009616 inductively coupled plasma Methods 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- LDOXGBXBUUGDFT-UHFFFAOYSA-M pentane-2,4-dione tetramethylazanium chloride Chemical compound [Cl-].C[N+](C)(C)C.C(C)(=O)CC(C)=O LDOXGBXBUUGDFT-UHFFFAOYSA-M 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 229910052720 vanadium Inorganic materials 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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、自動車、電機等に用いて好適な板厚0.4mm以上3.0mm以下の冷延鋼板に関し、特には、引張強さが980MPa以上のレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板およびその製造方法に関する。 The present invention relates to a cold-rolled steel sheet having a thickness of 0.4 mm or more and 3.0 mm or less that is suitable for use in automobiles, electric machines, etc., and in particular, excellent delayed fracture resistance of a laser welded part having a tensile strength of 980 MPa or more. The present invention relates to a cold-rolled steel sheet and a manufacturing method thereof.
近年、地球環境保全の観点から自動車の燃費向上が重要になっており、車体の軽量化が進められている。これに対しては、使用する鋼板を高強度化し、板厚を薄くすることが、最も有効な手段である。また、乗員の安全性向上技術も重要な課題であり、これに対しても、使用する鋼板の高強度化が有効な対策となる。このような鋼板の高強度化を目的として、従来、熱間圧延とその後の連続焼鈍条件を厳格に管理するとともに、鋼板中にCやMnなど種々の合金元素を添加することが行われてきた。 In recent years, improvement in fuel efficiency of automobiles has become important from the viewpoint of global environmental protection, and weight reduction of the vehicle body has been promoted. For this, the most effective means is to increase the strength of the steel sheet used and to reduce the thickness. In addition, occupant safety improvement technology is also an important issue. Against this, increasing the strength of the steel sheet used is an effective measure. For the purpose of increasing the strength of such steel sheets, conventionally, hot rolling and subsequent continuous annealing conditions have been strictly controlled, and various alloy elements such as C and Mn have been added to the steel sheets. .
一方、冷延鋼板が自動車用部材として用いられる際には、成形加工の後、鋼板同士を溶接により接合し、所望の形状に仕上げる方法が一般的である。このため、車体構造として優れた安全性を確保するには、冷延鋼板母材のみならず溶接金属と溶接熱影響部を含む領域についても、優れた機械的特性が必要となる。 On the other hand, when a cold-rolled steel sheet is used as a member for an automobile, a method is generally employed in which the steel sheets are joined together by welding and finished into a desired shape after forming. For this reason, in order to ensure excellent safety as the vehicle body structure, excellent mechanical characteristics are required not only for the cold-rolled steel sheet base material but also for the region including the weld metal and the weld heat affected zone.
一般に、鋼板を高強度化して板厚を薄くすると、自動車構造としての剛性が低下することが問題となるが、これを克服する手段の一つとして、一般的なスポット溶接(点溶接)ではなく、連続溶接を適用することが挙げられる。例えば、レーザ溶接法は、溶接精度が高く、小入熱で深い溶け込みが得られるため、母材への熱影響を最小限に抑えることが可能である。また、ファイバー伝送による遠隔操作が容易であるため、自動車用部材の自動連続溶接法として、その適用が拡大している。特に近年、自動車用部材のプレス成形の負荷を軽減できることから、事前にレーザ溶接で異鋼種を接合した後、プレス成形をするテーラードブランク技術の利用が増加している。 Generally, if the steel plate is made stronger and the plate thickness is made thinner, there is a problem that the rigidity of the automobile structure decreases, but as a means of overcoming this, instead of general spot welding (spot welding) Applying continuous welding. For example, the laser welding method has high welding accuracy and can obtain deep penetration with a small heat input, so that it is possible to minimize the heat effect on the base material. Moreover, since remote control by fiber transmission is easy, the application is expanding as an automatic continuous welding method of the member for motor vehicles. Particularly in recent years, since the load of press molding of automobile members can be reduced, the use of tailored blank technology for press molding after joining different steel types by laser welding in advance is increasing.
しかしながら、一般的にレーザ溶接法は、急熱急冷で鋼板を溶融凝固することを特徴とするため、溶接金属および溶接熱影響部のミクロ組織がマルテンサイト組織となり、母材と比較して硬度が高くなって脆化し易い。また、従来のスポット溶接法と比較しても、溶接金属および溶接熱影響部の硬化は顕著である。 However, in general, the laser welding method is characterized by melting and solidifying the steel sheet by rapid heating and quenching, so that the microstructure of the weld metal and the weld heat affected zone becomes a martensite structure, and the hardness is higher than that of the base metal. Elevated and easily brittle. Further, even when compared with the conventional spot welding method, the hardening of the weld metal and the weld heat-affected zone is remarkable.
さらに、レーザ溶接では、従来のスポット溶接法とは異なり、溶接時に鋼板の表面および裏面の溶融部が大気環境に曝されるため、湿度、温度などの溶接環境や、溶接前の鋼板表面性状によっては、溶接時に水素が溶接金属中に混入し易く、またその後の冷却が極めて早いため、再び水素が溶接金属中から環境に放出されにくいという特徴がある。そのため、レーザ溶接による溶接部の水素量は、従来のスポット溶接による溶接部の水素量よりも高くなる傾向にある。
また、溶接金属に混入した水素は、時間の経過とともに溶接金属ごく近傍の溶接熱影響部にも拡散し、溶接熱影響部の脆化も助長する。
Furthermore, in laser welding, unlike the conventional spot welding method, the welded portion of the steel sheet surface and back surface is exposed to the atmospheric environment during welding, so depending on the welding environment such as humidity and temperature, and the steel sheet surface properties before welding. Is characterized in that hydrogen is easily mixed into the weld metal during welding and the subsequent cooling is extremely fast, so that hydrogen is not easily released from the weld metal to the environment again. Therefore, the amount of hydrogen in the welded part by laser welding tends to be higher than the amount of hydrogen in the welded part by conventional spot welding.
In addition, hydrogen mixed in the weld metal diffuses into the weld heat affected zone in the vicinity of the weld metal with time, and promotes embrittlement of the weld heat affected zone.
このように、著しく硬化し、かつ水素が混入した溶接金属および溶接熱影響部を含む鋼板に対して、テーラードブランクのような成形加工を施す場合には、水素脆化により、溶接金属とその近傍の溶接熱影響部を起点とする遅れ破壊と呼ばれる脆性破壊が発生し易いという問題がある。 As described above, when a forming process such as a tailored blank is applied to a steel plate including a weld metal and a weld heat-affected zone, which is hardened and mixed with hydrogen, the weld metal and the vicinity thereof are formed by hydrogen embrittlement. There is a problem that a brittle fracture called a delayed fracture starting from the weld heat affected zone is likely to occur.
この点、特許文献1〜5には種々の高強度鋼板が提案されているが、十分な経済性や生産性の下、引張強さ:980MPa以上の高強度化とレーザ溶接部の耐遅れ破壊特性の十分な改善とを両立するには至っていないのが現状である。 In this regard, various high-strength steel sheets have been proposed in Patent Documents 1 to 5, but with sufficient economic efficiency and productivity, high tensile strength: 980 MPa or more and delayed fracture resistance of laser welds. At present, it has not been possible to achieve both sufficient improvement in characteristics.
本発明は、上記の現状に鑑み開発されたものであって、製造コストの増大や生産性の低下を招くことなく、引張強さが980MPa以上であるレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板を、その有利な製造方法とともに提供することを目的とする。 The present invention has been developed in view of the above-described present situation, and has excellent delayed fracture resistance of a laser welded portion having a tensile strength of 980 MPa or more without causing an increase in manufacturing cost or a decrease in productivity. An object is to provide a cold-rolled steel sheet together with its advantageous production method.
さて、発明者らは、上記の課題を達成するため、鋼板の化学成分、製造方法およびミクロ組織を決定する各種要因に関して鋭意研究を行い、以下の知見を得た。
(1) 引張強さ:980MPa以上を達成するには、鋼板の化学組成を厳密に調整し、さらにTiとNの質量%比(Ti/N)を適正に制御することが重要である。
というのは、Ti/Nを適正に制御することで、TiNの生成による結晶粒微細化強化と析出強化が発現し、さらには焼鈍過程で固溶状態のNbを確保することが可能となって、これにより発現する加熱時の再結晶進行を遅延させる効果が、鋼板の高強度化に寄与するからである。
Now, in order to achieve the above-mentioned problems, the inventors have conducted intensive research on various factors that determine the chemical composition, manufacturing method and microstructure of the steel sheet, and obtained the following knowledge.
(1) Tensile strength: In order to achieve 980 MPa or more, it is important to strictly adjust the chemical composition of the steel sheet and to properly control the mass% ratio (Ti / N) of Ti and N.
This is because by properly controlling Ti / N, grain refinement strengthening and precipitation strengthening due to the formation of TiN are manifested, and it is possible to secure Nb in a solid solution state during the annealing process. This is because the effect of delaying the progress of recrystallization during heating, which is manifested thereby, contributes to increasing the strength of the steel sheet.
(2) 優れたレーザ溶接部の耐遅れ破壊特性を達成するには、レーザ溶接における溶接金属および溶接熱影響部の過度の硬化および脆化を抑制することが重要である。そのためには、溶接金属および溶接熱影響部において、固溶Nを極力低減すること、および結晶粒を微細化することに加えて、溶接金属および溶接熱影響部中の固溶Bを極力低減することが重要になる。
ここで、溶接金属および溶接熱影響部中の固溶Bの低減には、鋼板中に、実質的にBを含ませないことが有効である。鋼板中にBが存在すると、溶接の加熱時に固溶し、その後の冷却過程で焼入れ性が増大し、溶接金属および溶接熱影響部における過度な硬度上昇と脆化を招くことになる。
また、鋼中にNbが固溶状態で存在すると、溶接時の冷却過程の低温域でNbCを形成し、溶接熱影響部の軟化を防止することができる。さらに、鋼中にNbがNbCとして存在すると、このNbCが拡散性水素のトラップサイトとして作用し、水素による遅れ破壊を抑制することができる。
(2) To achieve excellent delayed fracture resistance of laser welds, it is important to suppress excessive hardening and embrittlement of the weld metal and weld heat affected zone in laser welding. For that purpose, in the weld metal and the weld heat affected zone, in addition to reducing the solid solution N as much as possible and making the crystal grains finer, the solid solution B in the weld metal and the weld heat affected zone is reduced as much as possible. It becomes important.
Here, in order to reduce the solute B in the weld metal and the weld heat affected zone, it is effective that the steel sheet does not substantially contain B. If B is present in the steel sheet, it dissolves at the time of heating during welding, and the hardenability increases in the subsequent cooling process, leading to an excessive increase in hardness and embrittlement in the weld metal and weld heat affected zone.
Moreover, when Nb exists in a solid solution state in steel, NbC can be formed in a low temperature region during the cooling process during welding, and softening of the weld heat affected zone can be prevented. Further, when Nb is present as NbC in the steel, this NbC acts as a trapping site for diffusible hydrogen, and delayed fracture due to hydrogen can be suppressed.
(3) 上記のような効果を有効に発現させるには、焼鈍後の冷延鋼板中のTiおよびNbの存在状態を適正に制御することが必要である。
また、所望とするTiおよびNbの存在状態を得るには、鋼板の成分組成およびTi/Nを厳密に調整した上で、製造条件、特に熱間圧延条件および焼鈍条件を適正に制御することが重要である。
本発明は、上記の知見に基づき、さらに検討を加えた末に完成されたものである。
(3) In order to effectively exhibit the effects as described above, it is necessary to appropriately control the presence of Ti and Nb in the cold-rolled steel sheet after annealing.
In addition, in order to obtain the desired state of Ti and Nb, it is necessary to precisely control the manufacturing conditions, particularly hot rolling conditions and annealing conditions, after strictly adjusting the component composition and Ti / N of the steel sheet. is important.
The present invention was completed after further studies based on the above findings.
すなわち、本発明の要旨構成は次のとおりである。
1.質量%で、
C:0.05〜0.15%、
Si:0.05〜2.0%、
Mn:1.2〜3.5%、
P:0.05%以下、
S:0.005%以下、
Al:0.01〜0.1%、
Nb:0.010〜0.070%、
Ti:0.005〜0.040%および
N:0.0005〜0.0065%
を含有するとともに、TiとNの質量比:Ti/Nが2.5以上7.5以下であり、さらにBの混入を0.0003%以下に抑制し、残部がFeおよび不可避的不純物からなる鋼組成を有し、
鋼中のTiのうち70%以上が析出物として存在する一方、鋼中のNbのうち15%以上65%以下が固溶Nbとして存在し、
引張強さが980MPa以上であることを特徴とするレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板。
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.05 to 0.15%,
Si: 0.05-2.0%,
Mn: 1.2 to 3.5%
P: 0.05% or less,
S: 0.005% or less,
Al: 0.01 to 0.1%,
Nb: 0.010 to 0.070%,
Ti: 0.005-0.040% and N: 0.0005-0.0065%
In addition, the mass ratio of Ti and N: Ti / N is 2.5 or more and 7.5 or less, further mixing of B is suppressed to 0.0003% or less, and the balance is made of Fe and inevitable impurities. Having a steel composition,
While 70% or more of Ti in steel exists as precipitates, 15% or more and 65% or less of Nb in steel exists as solute Nb,
A cold-rolled steel sheet excellent in delayed fracture resistance of a laser weld, wherein the tensile strength is 980 MPa or more.
2.前記鋼板が、さらに質量%で、
Cr:0.01〜1.0%、
Mo:0.01〜1.0%、
Cu:1.0%以下、
Ni:1.0%以下および
V:0.1%以下
から選んだ1種または2種以上を含有することを特徴とする前記1に記載のレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板。
2. The steel sheet is further mass%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
Cu: 1.0% or less,
1. Cold rolling excellent in delayed fracture resistance of the laser welded portion according to 1 above, containing one or more selected from Ni: 1.0% or less and V: 0.1% or less steel sheet.
3.前記1または2に記載の鋼組成を有する鋼素材を、Tsを下記式(1)で示される温度とするとき、(Ts−50)℃以上(Ts+200)℃以下の温度域に加熱し、仕上圧延終了温度:850℃以上の熱間圧延を施した後、650℃以下の温度で巻取り、ついで、冷間圧延を施した後、700℃以上900℃以下の温度域に加熱し、その後の冷却過程において、平均冷却速度5℃/s以上50℃/s以下で200℃以上450℃以下の温度域まで冷却し、該温度域で30s以上600s以下の時間保持する連続焼鈍を行うことにより、
鋼中のTiのうち70%以上が析出物として存在する一方、鋼中のNbのうち15%以上65%以下が固溶Nbとして存在し、また引張強さが980MPa以上である冷延鋼板を得ることを特徴とするレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板の製造方法。
記
Ts(℃)=6770/[2.26−log10{[%Nb]×
([%C]+0.86[%N])}]−273 ・・・(1)
ここで、[%Nb]、[%C]および[%N]は、それぞれ鋼中のNb、CおよびNの含有量(質量%)を示す。
3. When the steel material having the steel composition described in 1 or 2 is set to a temperature represented by the following formula (1), Ts is heated to a temperature range of (Ts-50) ° C. or higher and (Ts + 200) ° C. or lower to finish. Rolling end temperature: after hot rolling at 850 ° C. or higher, after winding at a temperature of 650 ° C. or lower, then after cold rolling, heated to a temperature range of 700 ° C. or higher and 900 ° C. or lower, In the cooling process, by cooling to a temperature range of 200 ° C. or more and 450 ° C. or less at an average cooling rate of 5 ° C./s or more and 50 ° C./s or less, and performing continuous annealing for 30 hours or more and 600s or less in the temperature range ,
While 70% or more of Ti in steel is present as precipitates, 15% to 65% of Nb in steel is present as solute Nb, and a cold-rolled steel sheet having a tensile strength of 980 MPa or more. A method for producing a cold-rolled steel sheet excellent in delayed fracture resistance of a laser weld.
Ts (° C.) = 6770 / [2.26-log 10 {[% Nb] ×
([% C] +0.86 [% N])}]-273 (1)
Here, [% Nb], [% C] and [% N] indicate the contents (mass%) of Nb, C and N in the steel, respectively.
本発明によれば、製造コストの増大や生産性の低下を招くことなく、引張強さ:980MPa以上のレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板を得ることができる。
また、本発明の冷延鋼板を用いることにより、自動車などの鋼構造物作製時の製造効率や自動車搭乗者に対する安全性を向上でき、さらには燃費向上に伴う環境負荷の軽減に大きく寄与することができる。
ADVANTAGE OF THE INVENTION According to this invention, the cold rolled steel plate excellent in the delayed fracture resistance of the laser weld part of tensile strength: 980 MPa or more can be obtained, without causing the increase in manufacturing cost or the fall of productivity.
In addition, by using the cold-rolled steel sheet of the present invention, it is possible to improve the production efficiency when manufacturing a steel structure such as an automobile and the safety for passengers of the automobile, and further contribute greatly to the reduction of the environmental load accompanying the improvement of fuel consumption. Can do.
以下、本発明を具体的に説明する。
まず、本発明において、鋼材の成分組成を前記の範囲に限定した理由について説明する。なお、鋼材の成分組成における元素の含有量の単位はいずれも「質量%」であるが、以下、特に断らない限り単に「%」で示す。
C:0.05〜0.15%
Cは、鋼を強化する上で最も重要な元素であり、高い固溶強化能を有する。このような効果を得るには、Cの0.05%以上の含有を必要とする。一方、C量が0.15%を超えると、母材中のマルテンサイト相が増加して著しく硬化し、穴拡げ性が劣化する。さらには、レーザ溶接を行う場合に溶接金属および溶接熱影響部が著しく硬化し、レーザ溶接部の耐遅れ破壊特性が劣化する。このため、C量は0.05〜0.15%の範囲に限定する。好ましくは0.06〜0.13%の範囲である。
Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel material is limited to the above range in the present invention will be described. In addition, although the unit of element content in the component composition of steel materials is “mass%”, hereinafter, unless otherwise specified, it is simply indicated by “%”.
C: 0.05 to 0.15%
C is the most important element for strengthening steel and has a high solid solution strengthening ability. In order to acquire such an effect, 0.05% or more of C is required. On the other hand, if the amount of C exceeds 0.15%, the martensite phase in the base material is increased and markedly hardened, and the hole expandability deteriorates. Further, when laser welding is performed, the weld metal and the weld heat affected zone are significantly hardened, and the delayed fracture resistance of the laser weld is deteriorated. For this reason, C amount is limited to 0.05 to 0.15% of range. Preferably it is 0.06 to 0.13% of range.
Si:0.05〜2.0%
Siは、脱酸材として作用する、製鋼上、必要な元素である。また、Siは、鋼に固溶して固溶強化により鋼板を高強度化する効果を有する。このような効果を得るためには、Siの0.05%以上の含有を必要とする。一方、Si量が2.0%を超えると、溶接金属および溶接熱影響部が脆化し、耐遅れ破壊特性が低下する。このため、Si量は、0.05〜2.0%の範囲に限定する。好ましくは0.10〜1.60%の範囲である。
Si: 0.05-2.0%
Si is a necessary element in steelmaking that acts as a deoxidizing material. Moreover, Si has the effect of increasing the strength of a steel sheet by solid solution in steel and solid solution strengthening. In order to obtain such an effect, it is necessary to contain 0.05% or more of Si. On the other hand, if the amount of Si exceeds 2.0%, the weld metal and the weld heat affected zone become brittle, and the delayed fracture resistance deteriorates. For this reason, Si amount is limited to 0.05 to 2.0% of range. Preferably it is 0.10 to 1.60% of range.
Mn:1.2〜3.5%
Mnは、比較的安価に鋼の焼入れ性を増加させる効果を有し、引張強さ:980MPa以上の母材強度を確保するには、Mn量を1.2%以上とすることが必要である。一方、Mn量が3.5%を超えると、母材のミクロ偏析が大きくなり、この偏析部にレーザ溶接を行うと、過度の硬度上昇を招き、遅れ破壊の発生を助長する。このため、Mn量は、1.2〜3.5%の範囲に限定する。好ましくは1.3〜3.3%の範囲である。
Mn: 1.2 to 3.5%
Mn has the effect of increasing the hardenability of steel at a relatively low cost, and in order to ensure the base material strength of tensile strength: 980 MPa or more, the Mn content needs to be 1.2% or more. . On the other hand, if the amount of Mn exceeds 3.5%, the microsegregation of the base material becomes large. When laser welding is performed on this segregated portion, an excessive increase in hardness is caused and the occurrence of delayed fracture is promoted. For this reason, the amount of Mn is limited to the range of 1.2 to 3.5%. Preferably it is 1.3 to 3.3% of range.
P:0.05%以下
Pは、固溶強化能が大きい元素であるが、Mnとともにミクロ偏析を助長する。このため、P量が0.05%を超えると、母材が脆化するだけでなく、粒界偏析部が遅れ破壊の発生起点となり易くなる。従って、Pは0.05%を上限として、可能な限り低減することが望ましい。ただし、過度のP低減は精錬コストを高騰させ経済的に不利となるため、Pの下限は0.005%程度とすることが望ましい。
P: 0.05% or less P is an element having a large solid solution strengthening ability, but promotes microsegregation together with Mn. For this reason, if the amount of P exceeds 0.05%, not only the base material becomes brittle, but also the grain boundary segregation part tends to be the starting point of delayed fracture. Therefore, it is desirable to reduce P as much as possible with 0.05% as the upper limit. However, excessive P reduction raises the refining cost and is economically disadvantageous, so the lower limit of P is preferably about 0.005%.
S:0.005%以下
Sは、粒界に偏析して熱間圧延時の延性を低下させるため、0.005%を上限として可能な限り低減することが望ましい。
S: 0.005% or less S is segregated at the grain boundary to lower the ductility during hot rolling, so it is desirable to reduce 0.005% as much as possible.
Al:0.01〜0.1%
Alは、脱酸剤として作用し、鋼板の溶鋼脱酸プロセスにおいて、最も汎用的に用いられる元素である。また、鋼中の固溶Nを固定してAlNを形成することで、固溶Nによる脆化を抑制する効果を有する。このような効果を得るには、Alの0.01%以上の含有を必要とする。一方、Al量が0.1%を超えると、スラブ製造時の表面割れを助長する。このため、Al量は、0.01〜0.1%の範囲に限定する。好ましくは0.02〜0.07%の範囲である。
Al: 0.01 to 0.1%
Al acts as a deoxidizer and is the most widely used element in the molten steel deoxidation process for steel sheets. Moreover, it has the effect which suppresses the embrittlement by solid solution N by fixing solid solution N in steel and forming AlN. In order to obtain such an effect, it is necessary to contain 0.01% or more of Al. On the other hand, if the Al content exceeds 0.1%, surface cracks during slab production are promoted. For this reason, the amount of Al is limited to the range of 0.01 to 0.1%. Preferably it is 0.02 to 0.07% of range.
Nb:0.010〜0.070%
Nbは、冷間圧延後の焼鈍加熱において、固溶Nbとして存在することにより、ソリュートドラッグ効果を発現し、冷間圧延で生成した加工組織の再結晶を遅延することにより、焼鈍後の鋼板を高強度化する重要な元素である。また、熱間圧延および焼鈍工程で生成するNbCは、母材、溶接金属および溶接熱影響部のミクロ組織を微細化して、靱性を改善するだけでなく、溶接時に混入した拡散性水素のトラップサイトとして作用し、耐遅れ破壊特性の向上に寄与する。このような効果を得るためには、Nbの0.010%以上の含有が必要である。一方、Nb量が0.070%を超えると、粗大な炭窒化物が析出し、スラブ製造時の表面割れを助長するとともに、破壊の起点となることがある。このため、Nb量は、0.010〜0.070%の範囲に限定する。好ましくは0.015〜0.060%の範囲である。
Nb: 0.010 to 0.070%
Nb is present as a solid solution Nb in the annealing heating after cold rolling, thereby producing a solution drag effect, and delaying the recrystallization of the processed structure generated by cold rolling, thereby allowing the steel plate after annealing to It is an important element for increasing strength. NbC produced in the hot rolling and annealing processes not only improves the toughness by refining the microstructure of the base metal, weld metal and weld heat affected zone, but also traps diffusible hydrogen trapped during welding. It contributes to the improvement of the delayed fracture resistance. In order to obtain such an effect, it is necessary to contain 0.010% or more of Nb. On the other hand, when the Nb content exceeds 0.070%, coarse carbonitride precipitates, which may promote surface cracking during slab production and may be a starting point for fracture. For this reason, the amount of Nb is limited to a range of 0.010 to 0.070%. Preferably it is 0.015 to 0.060% of range.
Ti:0.005〜0.040%
Tiは、本発明において重要な合金元素であり、固溶Nを固定してTiNを形成することにより、母材、溶接金属および溶接熱影響部における結晶粒の粗大化を抑制する効果を有するとともに、固溶Nの低減により脆化を抑制する効果を有する。また、TiNの形成により、熱間圧延および焼鈍工程において、Nb窒化物の生成抑制を介して所定量の固溶Nbを確保し、焼鈍後の鋼板を高強度化するのに有効に寄与する。このような効果を得るためには、Tiの0.005%以上の含有が必要である。一方、Ti量が0.040%を超えると、非常に硬くて脆いTiCが析出し、脆化を助長する。このため、Ti量は0.005〜0.040%の範囲に限定する。好ましくは0.010〜0.035%である。
Ti: 0.005-0.040%
Ti is an important alloying element in the present invention, and has the effect of suppressing the coarsening of crystal grains in the base metal, the weld metal and the weld heat affected zone by fixing solid solution N to form TiN. , It has the effect of suppressing embrittlement by reducing the solid solution N. In addition, the formation of TiN effectively contributes to securing a predetermined amount of solid solution Nb through suppressing the formation of Nb nitride in the hot rolling and annealing processes, and increasing the strength of the steel sheet after annealing. In order to obtain such an effect, it is necessary to contain 0.005% or more of Ti. On the other hand, if the amount of Ti exceeds 0.040%, very hard and brittle TiC precipitates and promotes embrittlement. For this reason, Ti amount is limited to 0.005 to 0.040% of range. Preferably it is 0.010-0.035%.
N:0.0005〜0.0065%
Nは、不可避的不純物として鋼中に含まれるが、Tiを適量添加することにより、TiNを形成し、溶接の際に溶接金属および溶接熱影響部における結晶粒の粗大化を抑制する効果を発現する。このような効果を得るためには、N量を0.0005%以上とする必要がある。一方、N量が0.0065%を超えると、固溶Nの増大により、耐時効性が著しく低下する。このため、N量は0.0005〜0.0065%の範囲に限定する。好ましくは0.0010〜0.0060%である。
N: 0.0005 to 0.0065%
N is contained in steel as an unavoidable impurity, but by adding an appropriate amount of Ti, TiN is formed, and the effect of suppressing the coarsening of crystal grains in the weld metal and weld heat affected zone during welding is expressed. To do. In order to obtain such an effect, the N content needs to be 0.0005% or more. On the other hand, when the N content exceeds 0.0065%, the aging resistance is remarkably lowered due to an increase in the solid solution N. For this reason, N amount is limited to 0.0005 to 0.0065% of range. Preferably it is 0.0010 to 0.0060%.
また、本発明では、上記した成分組成とするとともに、TiとNの質量%比:Ti/Nを適正に制御することが重要である。
Ti/N:2.5以上7.5以下
Ti/Nを上記の範囲内に制御することで、TiNの生成による結晶粒微細化強化と析出強化が発現する。また、Nb窒化物の生成抑制を介して、焼鈍過程で適正量の固溶Nbを確保することが可能となり、これにより発現する加熱時の再結晶進行を遅延させる効果が、鋼板の高強度化に寄与する。また、レーザ溶接による溶接金属および溶接熱影響部においては、固溶Nの低減および結晶粒の微細化に寄与し、溶接金属および溶接熱影響部の脆化を防止する。
ここで、Ti/Nが2.5未満になると、鋼板中の固溶Nが増加し、脆化を助長する。一方、Ti/Nが7.5を超えると、非常に硬くて脆いTiCが鋼板中に生成し、延性の低下、ひいては脆化が顕著になる。このため、Ti/Nは2.5〜7.5の範囲に限定する。好ましくは3.0〜7.0の範囲である。
In the present invention, it is important to control the mass ratio of Ti and N: Ti / N appropriately with the above-described component composition.
Ti / N: 2.5 or more and 7.5 or less By controlling Ti / N within the above range, grain refinement strengthening and precipitation strengthening due to the formation of TiN appear. In addition, an appropriate amount of solute Nb can be ensured in the annealing process through the suppression of Nb nitride formation, and the effect of delaying the recrystallization progress during heating, which increases the strength of the steel sheet. Contribute to. Moreover, in the weld metal and weld heat affected zone by laser welding, it contributes to the reduction of solid solution N and the refinement of crystal grains, and prevents the weld metal and weld heat affected zone from becoming brittle.
Here, when Ti / N is less than 2.5, the solid solution N in the steel sheet increases and promotes embrittlement. On the other hand, when Ti / N exceeds 7.5, very hard and brittle TiC is generated in the steel sheet, and the ductility is lowered and the embrittlement becomes remarkable. For this reason, Ti / N is limited to the range of 2.5-7.5. Preferably it is the range of 3.0-7.0.
さらに、本発明の冷延鋼板では、Bの混入を0.0003%以下に抑制することが不可欠である。というのは、鋼中に0.0003%を超えるBが混入すると、レーザ溶接による溶接金属および溶接熱影響部に固溶Bが生成して過度の硬化を招いて脆化を助長し、耐遅れ破壊特性を劣化させるからである。このため、本発明の冷延鋼板では、Bの混入を0.0003%以下、好ましくは0.0002%以下に抑制する。 Furthermore, in the cold-rolled steel sheet of the present invention, it is indispensable to suppress B contamination to 0.0003% or less. This is because if more than 0.0003% B is mixed in the steel, solid solution B is generated in the weld metal and weld heat affected zone by laser welding, causing excessive hardening and promoting embrittlement. This is because the destructive characteristics are deteriorated. For this reason, in the cold-rolled steel sheet of the present invention, the B content is suppressed to 0.0003% or less, preferably 0.0002% or less.
以上、基本成分について説明したが、本発明では、必要に応じて、Cr、Mo、Cu、NiおよびVのうちから選んだ1種または2種以上を含有させることができる。
Cr:0.01〜1.0%
Crは、鋼の強度向上に寄与する元素である。このような効果を得るためには、Crの0.01%以上の添加が必要である。一方、Cr量が1.0%を超えると、過度な強度上昇により脆化を助長するだけでなく、経済的に不利になる。このため、Cr量は、0.01〜1.0%の範囲とする。好ましくは0.03〜0.8%の範囲である。
As mentioned above, although the basic component was demonstrated, in this invention, the 1 type (s) or 2 or more types selected from Cr, Mo, Cu, Ni, and V can be contained as needed.
Cr: 0.01 to 1.0%
Cr is an element that contributes to improving the strength of steel. In order to obtain such an effect, it is necessary to add 0.01% or more of Cr. On the other hand, if the amount of Cr exceeds 1.0%, not only does it promote embrittlement due to an excessive increase in strength, but it becomes economically disadvantageous. For this reason, the Cr content is in the range of 0.01 to 1.0%. Preferably it is 0.03 to 0.8% of range.
Mo:0.01〜1.0%
Moは、鋼の強度向上に寄与する元素である。このような効果を得るためには、Moの0.01%以上の添加が必要である。一方、Mo量が1.0%を超えると、過度な強度上昇により脆化を助長するだけでなく、経済的に不利になる。このため、Mo量は、0.01〜1.0%の範囲とする。好ましくは0.03〜0.8%の範囲である。
Mo: 0.01 to 1.0%
Mo is an element that contributes to improving the strength of steel. In order to obtain such an effect, it is necessary to add 0.01% or more of Mo. On the other hand, if the amount of Mo exceeds 1.0%, not only does it promote embrittlement due to an excessive increase in strength, but it becomes economically disadvantageous. For this reason, Mo amount is taken as 0.01 to 1.0% of range. Preferably it is 0.03 to 0.8% of range.
Cu:1.0%以下
Cuは鋼の強度向上に寄与する元素であるが、Cu量が1.0%を超えると熱間脆性を生じて鋼板の表面性状を劣化させる。このため、Cu量は1.0%以下とする。
Cu: 1.0% or less Cu is an element that contributes to improving the strength of steel. However, if the amount of Cu exceeds 1.0%, hot brittleness is caused and the surface properties of the steel sheet are deteriorated. For this reason, the amount of Cu shall be 1.0% or less.
Ni:1.0%以下
Niは、鋼の強度向上に寄与する元素であるが、Ni量が1.0%を超えるとその効果は飽和し、経済的に不利になる。このため、Ni量は1.0%以下とする。
Ni: 1.0% or less Ni is an element that contributes to improving the strength of steel. However, if the amount of Ni exceeds 1.0%, the effect is saturated and economically disadvantageous. Therefore, the Ni content is 1.0% or less.
V:0.1%以下
Vは、鋼の強度向上に寄与する元素であるが、V量が0.1%を超えると母材延性を劣化させる。このため、V量は0.1%以下とする。
V: 0.1% or less V is an element that contributes to improving the strength of steel. However, if the amount of V exceeds 0.1%, the base metal ductility is deteriorated. For this reason, the amount of V is made into 0.1% or less.
本発明の鋼板における成分組成のうち、上記以外の成分はFeおよび不可避的不純物である。 Among the component compositions in the steel sheet of the present invention, components other than those described above are Fe and inevitable impurities.
以上、本発明の鋼板における成分組成について説明したが、本発明では、TiおよびNbの鋼中における存在形態を適正に制御することが極めて重要である。
鋼中に析出物として存在するTiの割合:70%以上
焼鈍過程においては、Ti析出物により組織が微細化され、最終的に得られる冷延鋼板の穴拡げ性が向上する。また、焼鈍後の冷延鋼板中にTiが析出物として存在すると、溶接の際の溶接熱履歴による溶接熱影響部の結晶粒の粗大化が抑制され、溶接部の破断強度が向上する。このような効果を得るためには、鋼中のTiのうち70%以上が析出物として存在する必要がある。好ましくは75%以上である。また、鋼中に析出物として存在するTiの割合の上限は特に規定されるものではないが、100%となると固溶Nの残存により靭性が大きく劣化することから、100%未満とすることが好ましく、98%未満とすることがより好ましい。
なお、析出物の形態は、TiNの単独、もしくはTiNと他の析出物との複合析出物が主であるが、Ti酸化物あるいはTi炭化物が、全体のTi系析出物個数の10%未満であれば、混入してもその影響は無視できる。
As mentioned above, although the component composition in the steel plate of this invention was demonstrated, in this invention, it is very important to control the presence form in steel of Ti and Nb appropriately.
Ratio of Ti present as precipitates in steel: 70% or more In the annealing process, the structure is refined by Ti precipitates, and the hole expandability of the finally obtained cold rolled steel sheet is improved. Moreover, when Ti exists as a precipitate in the cold-rolled steel sheet after annealing, coarsening of the crystal grains in the weld heat affected zone due to the welding heat history during welding is suppressed, and the fracture strength of the weld zone is improved. In order to obtain such an effect, 70% or more of Ti in the steel needs to be present as precipitates. Preferably it is 75% or more. Further, the upper limit of the ratio of Ti present as precipitates in the steel is not particularly specified, but when it becomes 100%, the toughness is greatly deteriorated due to the remaining solid solution N, so it may be made less than 100%. Preferably, it is less than 98%.
The form of the precipitate is mainly TiN alone or a composite precipitate of TiN and other precipitates, but Ti oxide or Ti carbide is less than 10% of the total number of Ti-based precipitates. If there is, the effect is negligible even if mixed.
鋼中に固溶Nbとして存在するNbの割合:15%以上65%以下
Nbが固溶状態で存在すると、焼鈍過程においては、加熱時の再結晶抑制効果により、鋼の高強度化に有効に寄与するとともに、溶接熱影響部の軟化を抑制する効果を有する。
このような効果を得るためには、鋼中のNbのうち15%以上が固溶Nbとして存在する必要がある。好ましくは20%以上である。
一方、鋼中に固溶Nbとして存在するNbの割合が65%を超えると、上記の効果が飽和するうえ、鋼中のNbCが減少して、拡散性水素のトラップサイトとしての作用が弱まり、耐遅れ破壊特性が低下する。このため、鋼中に固溶Nbとして存在するNbの割合は65%以下とする必要がある。好ましくは60%以下である。
なお、固溶Nb以外の鋼中におけるNbの存在形態としては、NbCといったNb炭化物やNb炭窒化物などが挙げられる。
Ratio of Nb present as solid solution Nb in steel: 15% or more and 65% or less When Nb is present in a solid solution state, it is effective in increasing the strength of steel in the annealing process due to the effect of suppressing recrystallization during heating. While contributing, it has the effect of suppressing softening of the weld heat affected zone.
In order to obtain such an effect, 15% or more of Nb in steel needs to exist as solute Nb. Preferably it is 20% or more.
On the other hand, when the ratio of Nb existing as solid solution Nb in the steel exceeds 65%, the above effect is saturated, NbC in the steel is reduced, and the action as a diffusible hydrogen trap site is weakened. Delayed fracture resistance decreases. For this reason, the ratio of Nb which exists as solid solution Nb in steel needs to be 65% or less. Preferably it is 60% or less.
In addition, as a presence form of Nb in steel other than solid solution Nb, Nb carbide, Nb carbonitride, etc., such as NbC, are mentioned.
次に、本発明の製造方法について説明する。なお、製造条件における鋼板の温度は、鋼板の表面温度を意味するものとする。 Next, the manufacturing method of this invention is demonstrated. In addition, the temperature of the steel plate in manufacturing conditions shall mean the surface temperature of a steel plate.
上記した成分組成の溶鋼を転炉、電気炉等の公知の方法で溶製し、連続鋳造法または造塊−分塊圧延法等の公知の方法で、所定寸法のスラブ等の鋼素材とする。なお、溶鋼に、取鍋精錬や真空脱ガス等の処理を付加しても良いことは言うまでもない。
ついで、得られた鋼素材を、直ちにまたは一旦冷却し、(Ts−50)℃以上(Ts+200)℃以下の温度域に加熱し、仕上圧延終了温度:850℃以上にて熱間圧延を施した後、650℃以下で巻取って熱延鋼板とする。
なお、Tsは次式(1)により定義される。
Ts(℃)=6770/[2.26−log10{[%Nb]×
([%C]+0.86[%N])}]−273 ・・・(1)
ここで、[%Nb]、[%C]および[%N]は、それぞれ鋼中のNb、CおよびNの含有量(質量%)を示す。
The molten steel having the above component composition is melted by a known method such as a converter or an electric furnace, and is made into a steel material such as a slab having a predetermined size by a known method such as a continuous casting method or ingot-bundling rolling method. . It goes without saying that treatments such as ladle refining and vacuum degassing may be added to the molten steel.
Subsequently, the obtained steel material was immediately or once cooled, heated to a temperature range of (Ts-50) ° C. or higher and (Ts + 200) ° C. or lower, and finished with a finish rolling at a temperature of 850 ° C. or higher. Then, it winds at 650 degrees C or less, and is set as a hot rolled sheet steel.
Ts is defined by the following equation (1).
Ts (° C.) = 6770 / [2.26-log 10 {[% Nb] ×
([% C] +0.86 [% N])}]-273 (1)
Here, [% Nb], [% C] and [% N] indicate the contents (mass%) of Nb, C and N in the steel, respectively.
加熱温度:(Ts−50)℃以上(Ts+200)℃以下
鋼素材の溶製時に晶出した粗大なNbを含む炭窒化物は、鋼板の高強度化に寄与しない上、レーザ溶接時に侵入する水素のトラップサイトとしても十分には作用しない。このため、粗大なNb系晶出物は、熱間圧延前の加熱段階で、一旦鋼中に固溶させて、その後の圧延、冷却、焼鈍等の過程で、再度、微細なNb炭化物や炭窒化物として析出させることが重要である。
ここに、この加熱温度が(Ts−50)℃未満では、加熱が十分ではないためにNb系晶出物が十分に鋼中に固溶せず、焼鈍後の強度が不足する。一方、(Ts+200)℃を超えると、上記の効果が飽和する上、Ti晶出物が完全に固溶して、焼鈍後に適正量のTiを析出物として存在させることが困難となる。また、加熱のための燃料費の増加とともにスケールオフ増大による歩留まり低下のため、経済的に不利である。従って、加熱温度は(Ts−50)℃以上(Ts+200)℃以下とする。好ましくは(Ts−20)℃以上(Ts+170)℃以下である。
Heating temperature: (Ts-50) ° C. or more and (Ts + 200) ° C. or less Carbonitride containing coarse Nb crystallized during melting of the steel material does not contribute to high strength of the steel sheet, and hydrogen penetrates during laser welding. It does not work well as a trap site. For this reason, the coarse Nb-based crystallized material is once dissolved in steel in the heating stage before hot rolling, and then again in the process of rolling, cooling, annealing, etc., again with fine Nb carbides and charcoal. It is important to deposit as nitride.
If the heating temperature is less than (Ts-50) ° C., the heating is not sufficient, so that the Nb-based crystallized substance does not sufficiently dissolve in the steel, and the strength after annealing is insufficient. On the other hand, when the temperature exceeds (Ts + 200) ° C., the above effect is saturated, and the Ti crystallized product is completely dissolved, and it becomes difficult to make an appropriate amount of Ti present as a precipitate after annealing. In addition, it is economically disadvantageous because the yield decreases due to an increase in scale-off as the fuel cost for heating increases. Accordingly, the heating temperature is set to (Ts-50) ° C. or higher and (Ts + 200) ° C. or lower. Preferably, it is (Ts−20) ° C. or higher and (Ts + 170) ° C. or lower.
仕上圧延終了温度:850℃以上
仕上圧延終了温度が850℃未満になると、圧延効率が低下するだけでなく、圧延荷重が増大し、圧延機への負荷が大きくなる。このため、仕上圧延終了温度は850℃以上とする。
Finish rolling end temperature: 850 ° C. or more When the finish rolling end temperature is less than 850 ° C., not only the rolling efficiency is lowered, but also the rolling load is increased and the load on the rolling mill is increased. For this reason, finish rolling finish temperature shall be 850 degreeC or more.
巻取り温度:650℃以下
熱延鋼板の巻取り温度が650℃を超えると、巻取り中に析出するNbCが過度に粗大化するため、脆化し易く、破壊の起点となり易い。このため、熱延鋼板の巻取り温度は650℃以下とする必要がある。好ましくは620℃以下である。なお、熱延鋼板の巻取り温度の下限は特に規定する必要はないが、過度の温度低下は製造効率を低下させるため、400℃程度とすることが好ましい。
Winding temperature: 650 ° C. or less When the winding temperature of the hot-rolled steel sheet exceeds 650 ° C., NbC precipitated during winding is excessively coarsened, so that it easily becomes brittle and tends to be a starting point of fracture. For this reason, the coiling temperature of a hot-rolled steel sheet needs to be 650 degrees C or less. Preferably it is 620 degrees C or less. Note that the lower limit of the coiling temperature of the hot-rolled steel sheet does not need to be specified in particular.
ついで、得られた熱延鋼板に冷間圧延を施し、冷延鋼板とする。ここに、冷間圧延の条件は特に規定する必要はないが、焼鈍後に所望の強度を確保するには、総圧下率を30%以上とすることが好ましい。一方、圧延機への過度の負荷を避けるためには、総圧下率を80%以下とすることが好ましい。 Next, the obtained hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet. Here, the conditions for cold rolling need not be specified, but in order to ensure a desired strength after annealing, the total rolling reduction is preferably 30% or more. On the other hand, in order to avoid an excessive load on the rolling mill, the total rolling reduction is preferably 80% or less.
そして、上記のようにして得られた冷延鋼板について、以下の条件で連続焼鈍を施す。
連続焼鈍における加熱温度:700℃以上900℃以下
連続焼鈍における加熱温度が700℃未満であると、オーステナイトの逆変態が不十分となり、その後の冷却時に生成する硬質のマルテンサイトもしくはベイナイトの量が不十分となり、所望の強度が得られない。一方、900℃を超えると、オーステナイト粒の粗大化が顕著になり、母材の穴拡げ性および溶接熱影響部の靭性が劣化する。このため、連続焼鈍における加熱温度は、700℃以上900℃以下とする。好ましくは720℃以上880℃以下である。
And about the cold-rolled steel plate obtained as mentioned above, continuous annealing is given on the following conditions.
Heating temperature in continuous annealing: 700 ° C. or more and 900 ° C. or less When the heating temperature in continuous annealing is less than 700 ° C., the reverse transformation of austenite becomes insufficient, and the amount of hard martensite or bainite generated during subsequent cooling is insignificant. It becomes sufficient and the desired strength cannot be obtained. On the other hand, when it exceeds 900 ° C., coarsening of austenite grains becomes remarkable, and the hole expansibility of the base metal and the toughness of the weld heat affected zone deteriorate. For this reason, the heating temperature in continuous annealing shall be 700 degreeC or more and 900 degrees C or less. Preferably they are 720 degreeC or more and 880 degrees C or less.
なお、加熱後の保持時間は特に規定する必要はないが、均一な温度分布と安定したミクロ組織を確保するには15s以上保持することが好ましい。一方、長時間の保持は、製造効率の低下だけでなく、オーステナイト粒の粗大化を招くため、保持時間は600s以下とすることが好ましい。 The holding time after heating is not particularly required, but is preferably held for 15 seconds or more in order to ensure a uniform temperature distribution and a stable microstructure. On the other hand, holding for a long time not only lowers the production efficiency but also causes coarsening of austenite grains, so the holding time is preferably 600 s or less.
平均冷却速度:5℃/s以上50℃/s以下
加熱後の冷却過程における平均冷却速度が5℃/s未満であると、冷却中に軟質のフェライト相が過剰に生成して所望の強度を確保し難くなるだけでなく、冷却の途中でNbが過度に再析出するため、所望量の固溶Nbを確保することが困難になる。また、冷却の途中に粗大なフェライト相やパーライト相が生成し、強度が低下する。一方、焼鈍後の平均冷却速度が50℃/sを超えると、鋼板形状の確保が困難になる。このため、焼鈍処理後の平均冷却速度は、5℃/s以上50℃/s以下とする。好ましくは7℃/s以上45℃/s以下である。
Average cooling rate: 5 ° C./s or more and 50 ° C./s or less If the average cooling rate in the cooling process after heating is less than 5 ° C./s, a soft ferrite phase is excessively generated during cooling, and the desired strength is obtained. Not only is it difficult to ensure, but also Nb reprecipitates excessively during cooling, making it difficult to secure a desired amount of solid solution Nb. Further, a coarse ferrite phase or pearlite phase is generated during the cooling, and the strength is lowered. On the other hand, if the average cooling rate after annealing exceeds 50 ° C./s, it becomes difficult to ensure the shape of the steel sheet. For this reason, the average cooling rate after annealing treatment shall be 5 degrees C / s or more and 50 degrees C / s or less. Preferably they are 7 degrees C / s or more and 45 degrees C / s or less.
冷却停止温度:200℃以上450℃以下
冷却停止温度を200℃未満とすると、鋼板の搬送速度を極端に低下させることになるため、製造効率の面で好ましくない。一方、450℃を超える温度で冷却を停止すると、冷却停止後に比較的軟質のベイナイト相が過剰に生成して所望の強度を確保し難くなるだけでなく、冷却停止後にNbが過度に再析出するため、所望量の固溶Nbを確保することが困難になる。また、フェライトなどの軟質の組織が過度に生成し、強度が不足する。このため、冷却停止温度は200℃以上450℃以下とする。好ましくは230℃以上420℃以下である。
Cooling stop temperature: 200 ° C. or higher and 450 ° C. or lower If the cooling stop temperature is lower than 200 ° C., the conveyance speed of the steel sheet is extremely reduced, which is not preferable in terms of production efficiency. On the other hand, when the cooling is stopped at a temperature exceeding 450 ° C., not only is a relatively soft bainite phase generated excessively after the cooling is stopped and it becomes difficult to secure a desired strength, but Nb is excessively re-deposited after the cooling is stopped. Therefore, it becomes difficult to secure a desired amount of solid solution Nb. In addition, a soft structure such as ferrite is excessively generated and the strength is insufficient. For this reason, cooling stop temperature shall be 200 degreeC or more and 450 degrees C or less. Preferably they are 230 degreeC or more and 420 degrees C or less.
冷却停止温度域における保持時間:30s以上600s以下
冷却停止温度域における保持時間が30s未満であると、鋼板内の温度、材質の均一性が低下する。一方、冷却停止温度域における保持時間が600sを超えると、製造効率が低下する。このため、冷却停止温度域における保持時間は、30s以上600s以下とする。
Holding time in the cooling stop temperature region: 30 s or more and 600 s or less When the holding time in the cooling stop temperature region is less than 30 s, the temperature and the uniformity of the material in the steel sheet are lowered. On the other hand, when the holding time in the cooling stop temperature region exceeds 600 s, the manufacturing efficiency is lowered. For this reason, the holding time in the cooling stop temperature region is set to 30 s or more and 600 s or less.
表1に示す成分組成となる鋼を、転炉で溶製後、取鍋精錬を行い、連続鋳造により鋼スラブとした。ついで、鋼スラブに、表2に示す条件で熱間圧延を施し、熱延鋼板とした。その後、これらの熱延鋼板に、表2に示す条件で冷間圧延、連続焼鈍を施し、冷延鋼板を得た。 Steel having the component composition shown in Table 1 was melted in a converter and then smelted in a ladle and made into a steel slab by continuous casting. Subsequently, the steel slab was hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled steel sheet. Thereafter, these hot-rolled steel sheets were subjected to cold rolling and continuous annealing under the conditions shown in Table 2 to obtain cold-rolled steel sheets.
かくして得られた冷延鋼板について、以下の要領で、(1)析出物の抽出残渣分析、(2)引張試験、および(3)レーザ溶接試験を実施した。 The cold-rolled steel sheet thus obtained was subjected to (1) precipitate residue analysis, (2) tensile test, and (3) laser welding test in the following manner.
(1)析出物の抽出残渣分析
上記のようにして得られた各冷延鋼板から電解抽出用試験片を採取し、該試験片について、AA系電解液(アセチルアセトンテトラメチルアンモニウムクロライドのエタノール溶液)を用いた電解処理を実施し、ろ過により残渣を抽出した。
抽出した残渣について、純水で100mlに定容して、高周波誘導結合プラズマ(Inductively Coupled Plasma)発光分光法によりTi量を測定し、測定したTi量を析出物として存在するTi量とした。また、同様に、抽出した残渣中のNb量を測定し、この測定したNb量を、試験片中に含有される全Nb量から差し引くことで、固溶Nb量を算出した。
かくして算出した析出物として存在するTi量および固溶Nb量をそれぞれ、試験片中に含有される全Ti量およびNb量で除することで、鋼中に析出物として存在するTiの割合および鋼中に固溶Nbとして存在するNbの割合を求めた。これらの評価結果を表3に示す。
(1) Extraction residue analysis of precipitates Samples for electrolytic extraction were collected from each cold-rolled steel sheet obtained as described above, and AA electrolyte solution (ethanol solution of acetylacetone tetramethylammonium chloride) was used for the test pieces. The residue was extracted by filtration.
The extracted residue was made up to a volume of 100 ml with pure water, and the amount of Ti was measured by high frequency inductively coupled plasma emission spectroscopy. The measured amount of Ti was defined as the amount of Ti present as a precipitate. Similarly, the amount of Nb in the extracted residue was measured, and the amount of solid solution Nb was calculated by subtracting the measured amount of Nb from the total amount of Nb contained in the test piece.
By dividing the Ti amount and solid solution Nb amount present as precipitates thus calculated by the total Ti amount and Nb amount contained in the test piece, respectively, the ratio of Ti present as precipitates in the steel and the steel The ratio of Nb existing as solid solution Nb was determined. These evaluation results are shown in Table 3.
(2)引張試験
圧延方向に対して直角方向からJIS5号引張試験片を採取し、JIS Z 2241(2011)に準拠して、引張強さ(TS)および全伸び(El)を測定した。これらの評価結果を表3に示す。なお、ここでは、TS≧980MPa、El≧13%以上となるものを良好と判定した。
(2) Tensile test A JIS No. 5 tensile test piece was taken from the direction perpendicular to the rolling direction, and the tensile strength (TS) and total elongation (El) were measured according to JIS Z 2241 (2011). These evaluation results are shown in Table 3. Here, it was determined that TS ≧ 980 MPa and El ≧ 13% or more were good.
(3)レーザ溶接試験
上記のようにして得られた冷延鋼板を用い、発振機としてNdYAGレーザ、シールドガスとしてアルゴンを用い、レーザ出力4.5kW、溶接速度5.5m/minの溶接条件で、レーザ溶接を実施した。この際、1.6mmt×45mmw×90mmLの同一鋼板2枚を突合せ、90mmLが溶接線となるようにレーザ溶接を実施した。
レーザ溶接後、得られたサンプルを用いて、レーザ溶接部のエリクセン試験および断面試験を以下の要領で実施した。
(3) Laser welding test Using the cold-rolled steel sheet obtained as described above, NdYAG laser as the oscillator, argon as the shielding gas, laser power of 4.5 kW and welding speed of 5.5 m / min. Laser welding was performed. At this time, two identical steel plates of 1.6 mmt × 45 mmw × 90 mmL were butted together and laser welding was performed so that 90 mmL became a weld line.
After the laser welding, an Erichsen test and a cross-sectional test of the laser welded part were performed as follows using the obtained sample.
・エリクセン試験
上記のようにして得られたサンプルを、レーザ溶接後直ちに25℃、湿度60%の恒温恒湿槽で保管し、24時間経過後取り出した。
そして、遅れ破壊特性の試験として、JIS Z 2247(2006)に準拠し、エリクセン試験を実施した。具体的には、サンプルの溶接線中央にポンチが接するようにして、ポンチを押し込み、亀裂が発生した時のくぼみの深さを測定しエリクセン値とした。ここでは、エリクセン値が5mm以上のものを、レーザ溶接部の耐遅れ破壊特性に優れると判断した。
Erichsen test The sample obtained as described above was stored in a constant temperature and humidity chamber at 25 ° C and 60% humidity immediately after laser welding, and taken out after 24 hours.
Then, an Erichsen test was conducted as a test for delayed fracture characteristics in accordance with JIS Z 2247 (2006). Specifically, the punch was pushed in such a way that the punch was in contact with the center of the weld line of the sample, and the depth of the dent when a crack occurred was measured to obtain an Erichsen value. Here, it was judged that an Erichsen value of 5 mm or more is excellent in delayed fracture resistance of a laser welded portion.
・断面試験
レーザ溶接後、溶接ビードに垂直に切り出した溶接部断面を研磨した後、ナイタール腐食し、硬度測定用試験片とした。
JIS Z 2244(2009)に準拠し、試験力0.9807Nで、鋼板表面から0.4mm下方位置において、鋼板表面と平行に0.25mmピッチで一方の母材から、溶接熱影響部、溶接金属、溶接熱影響部および他方の母材までビッカース硬度試験を実施し、ビッカース硬度の最大値がHV500未満のものをレーザ溶接部の耐遅れ破壊特性に優れると判断した。
これらの評価結果を表3に併記する。
-Sectional test After laser welding, the welded section cut out perpendicular to the weld bead was polished, and then subjected to Nital corrosion to obtain a specimen for hardness measurement.
In accordance with JIS Z 2244 (2009), at a test force of 0.9807 N, at a position 0.4 mm below the steel sheet surface, from one base metal at a 0.25 mm pitch parallel to the steel sheet surface, the weld heat affected zone, weld metal The Vickers hardness test was carried out on the weld heat affected zone and the other base metal, and it was judged that those having a maximum value of Vickers hardness of less than HV500 were excellent in the delayed fracture resistance of the laser weld zone.
These evaluation results are also shown in Table 3.
表3に示したとおり、発明例ではいずれも、母材の引張強さが980MPa以上であるとともに、エリクセン値が5mm以上で、かつビッカース硬度の最大値がHV500未満という優れたレーザ溶接部の耐遅れ破壊特性が得られた。また、発明例ではいずれも、母材の全伸びが13%以上であった。
一方、比較例は、母材の引張強さおよび全伸び、ならびにレーザ溶接試験におけるエリクセン値およびビッカース硬度の最大値のうちの少なくとも1つが十分なものとは言えなかった。
As shown in Table 3, in all of the inventive examples, the tensile strength of the base material is 980 MPa or more, the Erichsen value is 5 mm or more, and the maximum value of Vickers hardness is less than HV500. Delayed fracture characteristics were obtained. In all the inventive examples, the total elongation of the base material was 13% or more.
On the other hand, in the comparative example, it could not be said that at least one of the tensile strength and total elongation of the base material and the maximum value of Erichsen value and Vickers hardness in the laser welding test was not sufficient.
Claims (3)
C:0.05〜0.15%、
Si:0.05〜2.0%、
Mn:1.2〜3.5%、
P:0.05%以下、
S:0.005%以下、
Al:0.01〜0.1%、
Nb:0.010〜0.070%、
Ti:0.005〜0.040%および
N:0.0005〜0.0065%
を含有するとともに、TiとNの質量比:Ti/Nが2.5以上7.5以下であり、さらにBの混入を0.0003%以下に抑制し、残部がFeおよび不可避的不純物からなる鋼組成を有し、
鋼中のTiのうち70%以上が析出物として存在する一方、鋼中のNbのうち15%以上65%以下が固溶Nbとして存在し、
引張強さが980MPa以上であることを特徴とするレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板。 % By mass
C: 0.05 to 0.15%,
Si: 0.05-2.0%,
Mn: 1.2 to 3.5%
P: 0.05% or less,
S: 0.005% or less,
Al: 0.01 to 0.1%,
Nb: 0.010 to 0.070%,
Ti: 0.005-0.040% and N: 0.0005-0.0065%
In addition, the mass ratio of Ti and N: Ti / N is 2.5 or more and 7.5 or less, further mixing of B is suppressed to 0.0003% or less, and the balance is made of Fe and inevitable impurities. Having a steel composition,
While 70% or more of Ti in steel exists as precipitates, 15% or more and 65% or less of Nb in steel exists as solute Nb,
A cold-rolled steel sheet excellent in delayed fracture resistance of a laser weld, wherein the tensile strength is 980 MPa or more.
Cr:0.01〜1.0%、
Mo:0.01〜1.0%、
Cu:1.0%以下、
Ni:1.0%以下および
V:0.1%以下
から選んだ1種または2種以上を含有することを特徴とする請求項1に記載のレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板。 The steel sheet is further mass%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
Cu: 1.0% or less,
2. One or more selected from Ni: 1.0% or less and V: 0.1% or less are contained. Cooling excellent in delayed fracture resistance of laser welds according to claim 1 Rolled steel sheet.
鋼中のTiのうち70%以上が析出物として存在する一方、鋼中のNbのうち15%以上65%以下が固溶Nbとして存在し、また引張強さが980MPa以上である冷延鋼板を得ることを特徴とするレーザ溶接部の耐遅れ破壊特性に優れた冷延鋼板の製造方法。
記
Ts(℃)=6770/[2.26−log10{[%Nb]×
([%C]+0.86[%N])}]−273 ・・ ・(1)
ここで、[%Nb]、[%C]および[%N]は、それぞれ鋼中のNb、CおよびNの含有量(質量%)を示す。 When the steel material having the steel composition according to claim 1 or 2 is heated to a temperature range of (Ts-50) ° C. or higher and (Ts + 200) ° C. or lower when Ts is set to a temperature represented by the following formula (1), Finishing rolling finish temperature: after hot rolling at 850 ° C. or higher, winding at a temperature of 650 ° C. or lower, then cold rolling, and then heating to a temperature range of 700 ° C. or higher and 900 ° C. or lower, in the course of cooling, by performing the average to a cooling rate of 5 ° C. / s or higher 50 ° C. / s or less at 200 ° C. or higher 450 ° C. or less of the temperature range is cooled, continuous annealing for holding 30s or 600s following time temperature range ,
While 70% or more of Ti in steel is present as precipitates, 15% to 65% of Nb in steel is present as solute Nb, and a cold-rolled steel sheet having a tensile strength of 980 MPa or more. A method for producing a cold-rolled steel sheet excellent in delayed fracture resistance of a laser weld.
Ts (° C.) = 6770 / [2.26-log 10 {[% Nb] ×
([% C] +0.86 [% N])}]-273 (1)
Here, [% Nb], [% C] and [% N] indicate the contents (mass%) of Nb, C and N in the steel, respectively.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2014162839A JP5935844B2 (en) | 2014-08-08 | 2014-08-08 | Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same |
PCT/JP2015/003882 WO2016021170A1 (en) | 2014-08-08 | 2015-07-31 | Cold-rolled steel sheet having excellent delayed fracture resistance for laser welds, and manufacturing method therefor |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2014162839A JP5935844B2 (en) | 2014-08-08 | 2014-08-08 | Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same |
Publications (2)
Publication Number | Publication Date |
---|---|
JP2016037651A JP2016037651A (en) | 2016-03-22 |
JP5935844B2 true JP5935844B2 (en) | 2016-06-15 |
Family
ID=55263466
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP2014162839A Active JP5935844B2 (en) | 2014-08-08 | 2014-08-08 | Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same |
Country Status (2)
Country | Link |
---|---|
JP (1) | JP5935844B2 (en) |
WO (1) | WO2016021170A1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP6705249B2 (en) * | 2016-03-29 | 2020-06-03 | 日本製鉄株式会社 | Method for manufacturing press-formed product made of tailored blank material |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH09176781A (en) * | 1995-12-22 | 1997-07-08 | Nkk Corp | Refined 60 kilo class steel excellent in weldability and galvanizing crack resistance and its production |
JP5162836B2 (en) * | 2006-03-01 | 2013-03-13 | 新日鐵住金株式会社 | High-strength cold-rolled steel sheet excellent in hydrogen embrittlement resistance of welds and method for producing the same |
JP4926814B2 (en) * | 2007-04-27 | 2012-05-09 | 新日本製鐵株式会社 | High strength steel plate with controlled yield point elongation and its manufacturing method |
-
2014
- 2014-08-08 JP JP2014162839A patent/JP5935844B2/en active Active
-
2015
- 2015-07-31 WO PCT/JP2015/003882 patent/WO2016021170A1/en active Application Filing
Also Published As
Publication number | Publication date |
---|---|
JP2016037651A (en) | 2016-03-22 |
WO2016021170A1 (en) | 2016-02-11 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP6787466B2 (en) | Manufacturing method of high-strength galvanized steel sheet and manufacturing method of high-strength member | |
JP6620474B2 (en) | Hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, and methods for producing them | |
EP2832889B1 (en) | Low yield ratio high-strength steel plate having superior strain aging resistance, production method therefor, and high-strength welded steel pipe using same | |
EP2832890B1 (en) | Low yield ratio high-strength steel plate having superior strain aging resistance, production method therefor, and high-strength welded steel pipe using same | |
JP5928654B2 (en) | Thick and high toughness high strength steel sheet and method for producing the same | |
CN109154045B (en) | Plated steel sheet and method for producing same | |
JP6234845B2 (en) | High strength galvannealed steel sheet with excellent bake hardenability and bendability | |
JP6303782B2 (en) | Hot-rolled steel sheet and manufacturing method thereof | |
JP4855553B2 (en) | High-strength ultra-thick H-section steel and its manufacturing method | |
JP2005126733A (en) | Steel sheet for hot press having excellent hot workability, and automotive member | |
WO2006009299A1 (en) | Steel for welded structure excellent in low temperature toughness of heat affected zone of welded part, and method for production thereof | |
JP2010215958A (en) | High-strength cold-rolled steel sheet superior in bending workability and delayed fracture resistance, and manufacturing method therefor | |
JP2007016296A (en) | Steel sheet for press forming with excellent ductility after forming, its forming method and automotive parts using the steel sheet for press forming | |
KR101445465B1 (en) | High-strength hot-dip galvanized steel sheet with excellent processability and spot weldability and process for producing same | |
JP7440799B2 (en) | Steel plate and its manufacturing method | |
CN113166884A (en) | Steel material having excellent toughness in weld heat affected zone and method for producing same | |
JP5935843B2 (en) | Cold-rolled steel sheet with excellent spot weldability and method for producing the same | |
JP2006110713A (en) | High strength component manufacturing method and high strength components | |
JP6417977B2 (en) | Steel plate blank | |
JP2015086411A (en) | High strength hot rolled steel sheet excellent in material quality stability and weldability and manufacturing method therefor | |
JP2009228079A (en) | Zn-Al-Mg BASED STEEL SHEET HAVING EXCELLENT HOT DIP METAL EMBRITTLEMENT CRACK RESISTANCE AND METHOD FOR PRODUCING THE SAME | |
JP5391606B2 (en) | High-strength cold-rolled steel sheet with excellent weldability and manufacturing method thereof | |
JP2005133181A (en) | High-strength cold-rolled steel sheet and manufacturing method therefor | |
JP2018003114A (en) | High strength steel sheet and manufacturing method therefor | |
JP5935844B2 (en) | Cold-rolled steel sheet with excellent delayed fracture resistance of laser welds and method for producing the same |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
A975 | Report on accelerated examination |
Free format text: JAPANESE INTERMEDIATE CODE: A971005 Effective date: 20151215 |
|
A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20160209 |
|
A521 | Request for written amendment filed |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20160229 |
|
TRDD | Decision of grant or rejection written | ||
A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20160412 |
|
A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20160425 |
|
R150 | Certificate of patent or registration of utility model |
Ref document number: 5935844 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |