JP2862185B2 - High strength cold rolled steel sheet with excellent press formability after laser welding - Google Patents
High strength cold rolled steel sheet with excellent press formability after laser weldingInfo
- Publication number
- JP2862185B2 JP2862185B2 JP2248341A JP24834190A JP2862185B2 JP 2862185 B2 JP2862185 B2 JP 2862185B2 JP 2248341 A JP2248341 A JP 2248341A JP 24834190 A JP24834190 A JP 24834190A JP 2862185 B2 JP2862185 B2 JP 2862185B2
- Authority
- JP
- Japan
- Prior art keywords
- steel sheet
- rolled steel
- laser welding
- strength
- low
- 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.)
- Expired - Fee Related
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
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- Laser Beam Processing (AREA)
Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は、レーザー溶接後のプレス成形性に優れた高
強度冷延鋼板に関し、より詳しくは、引張り強さ60kgf/
mm2以上の複合組織高強度冷延鋼板に関するものであ
る。The present invention relates to a high-strength cold-rolled steel sheet excellent in press formability after laser welding, and more specifically, to a tensile strength of 60 kgf /.
The present invention relates to a high-strength cold-rolled steel sheet having a composite structure of 2 mm or more.
（従来の技術及び解決しようとする課題） 近年、例えば、自動車業界において自動車のボディな
どをプレス加工により成形する際、プレス加工前に、種
々の鋼板を組合せ、それらの端面にレーザー照射して突
合せ溶接を行うことにより、一般にブランク材と呼ばれ
るプレス加工用の素板を製作し、その後、プレス加工を
行って異種材料の一体成形を行う方法が実用化され始め
ている。(Prior Art and Problems to be Solved) In recent years, for example, in the automobile industry, when an automobile body or the like is formed by press working, various steel plates are combined before press working, and the end faces thereof are irradiated with a laser and butt-joined. A method of manufacturing a blank for press working, generally called a blank material, by performing welding, and then performing press working to integrally form a dissimilar material has begun to be put into practical use.
この方法は、鋼板の歩留り向上、板厚、材料強度の適
材適所の使用、製品の見栄え向上などを目的として行わ
れており、これまでには、軟鋼板を中心に自動車のパネ
ル類の部材に対して適用が進められている。This method has been used for the purpose of improving the yield of steel sheets, using the right material in the right place with the appropriate thickness and material strength, and improving the appearance of products. The application is in progress.
一方、自動車の軽量化要求への高まりを背景として、
バンパー、ドアガードバー等の強度部材に対して高強度
冷延鋼板が使用されるに至っているが、このような高強
度冷延鋼板をプレス加工する際に、予め難成形部位にの
み、より成形性のよい鋼板をレーザー溶接してブランク
材を製作し、その後プレス加工を行う方法が検討されて
いる。On the other hand, against the background of increasing demand for lighter vehicles,
High-strength cold-rolled steel sheets have been used for high-strength members such as bumpers and door guard bars. A method of producing a blank material by laser welding a good steel plate and then performing a press working is being studied.
一般に、引張り強さ60kgf/mm2以上の高強度冷延鋼板
を得るためには、従来は、析出強化、加工強化、及びマ
ルテンサイト等の低温変態生成物の形成による組織強
化、又はこれらの種々の組合せによる強化方法が用いら
れている。In general, in order to obtain a strength of 60 kgf / mm 2 or more high strength cold rolled steel sheet tensile is conventionally precipitation strengthening, processing strengthening, and tissue strengthening by the formation of low-temperature transformation products such as martensite, or these various Are used.
ここに、析出強化や加工強化による高強度鋼はフェラ
イトの延性を著しく劣化させるので、成形性も著しく劣
るが、その組織をフェライトと低温変態生成物からなる
複合組織とすることによって高延性を得ることができる
ことが知られている。Here, high-strength steel by precipitation strengthening or work strengthening significantly deteriorates the ductility of ferrite, so that formability is also extremely poor, but high ductility is obtained by making its structure a composite structure consisting of ferrite and low-temperature transformation products. It is known that it can.
既に、本発明者らも先に、マルテンサイト等の低温変
態生成物の炭素濃度をできるだげ高め、延性の優れたフ
ェライト体積を増すことによって、極めて延性の優れる
高強度冷延鋼板が得られることを提案した（特願昭60-2
79575号）。Already, the present inventors have also earlier, by increasing the carbon concentration of low-temperature transformation products such as martensite as much as possible, and by increasing the ferrite volume with excellent ductility, a high-strength cold-rolled steel sheet with extremely excellent ductility can be obtained. (Japanese Patent Application No. 60-2)
79575).
しかし、かゝる高強度冷延鋼板であっても、レーザー
溶接し、その後プレス加工を行う場合においては、溶接
部近傍の熱影響部（以下「HAZ」と称する）の軟化によ
り著しく成形性が低下するという改善の余地があること
が見い出された。すなわち、前述したような高強度冷延
鋼板のレーザー溶接の適用においては、素材の延性が優
れるのみならず、溶接後の成形性の低下が少ないことが
強く要求されるのである。However, even in the case of such high-strength cold-rolled steel sheets, when laser welding is performed and then press working is performed, the heat-affected zone (hereinafter referred to as “HAZ”) in the vicinity of the welded portion is significantly reduced in formability. It has been found that there is still room for improvement, which is lower. That is, in the application of laser welding of a high-strength cold-rolled steel sheet as described above, it is strongly required that not only the material be excellent in ductility but also that the formability after welding be small.
本発明は、かゝる要求に要請に応えるべくなされたも
のであって、延性に優れると共に、レーザー溶接等の溶
接後の成形性にも優れる高強度複合組織冷延鋼板を提供
することを目的とするものである。The present invention has been made to meet such a demand, and has an object to provide a high-strength composite structure cold-rolled steel sheet having excellent ductility and excellent formability after welding such as laser welding. It is assumed that.
（発明が解決しようとする課題） 本発明者らは、前記課題を解決するために、延性に優
れると共にレーザー溶接後の成形性にも優れる高強度複
合組織冷延鋼板を得るべく更に研究した結果、複合組織
冷延鋼板において低温変態生成物が非常に硬い場合に
は、それが微細且つ場一に分散していても、レーザー溶
接した場合に溶接部近傍の熱影響部（HAZ）において低
温変態生成物の焼戻しによる軟化のため、プレス加工時
にHAZにひずみが集中し、最終的にHAZで破断が生じるこ
とにより、著しく成形性が低下することを究明した。(Problems to be Solved by the Invention) In order to solve the above-mentioned problems, the present inventors have further studied to obtain a high-strength composite microstructure cold-rolled steel sheet having excellent ductility and excellent formability after laser welding. If the low-temperature transformation product is extremely hard in a cold rolled steel sheet with a composite structure, even if it is fine and in-situ dispersed, the low-temperature transformation in the heat-affected zone (HAZ) in the vicinity of the welded part can be achieved by laser welding. Due to the softening of the product due to tempering, strain was concentrated in the HAZ during the press working, and finally the breakage occurred in the HAZ.
そこで、本発明者らは、この成形性の低下を防止し得
る方策について鋭意研究を重ねた結果、複合組織高強度
鋼板において、レーザー溶接後にHAZで軟化を生じない
鋼板であれば、成形性の低下率は軟鋼板をレーザー溶接
した場合と同等であり、その実現のためには、低温変態
生成物の硬度とフェライトの硬度の比、及びその低温変
態生成物の体積比率を所定の範囲に規制することによ
り、可能であることを見い出し、ここに本発明に至った
ものである。Therefore, the present inventors have conducted intensive studies on measures that can prevent this decrease in formability, and as a result, in a composite structure high-strength steel sheet, if the steel sheet does not cause softening in HAZ after laser welding, the formability is reduced. The rate of decrease is equivalent to the case of laser welding mild steel, and in order to achieve this, the ratio of the hardness of the low-temperature transformation product to the hardness of the ferrite and the volume ratio of the low-temperature transformation product are restricted to predetermined ranges. As a result, the present inventors have found out that the present invention is possible, and have reached the present invention.
すなわち、本発明は、マルテンサイト等の低温変態生
成物の硬度HVMとフェライトの硬度HVFの比が次式（１） 5.96−0.0201×TS≧HVM/HVF≧2.28−0.0061×TS ……（１） （但し、TS:当該鋼板の引張り強さ） を満足し、かつ、その低温変態生成物の体積比率Ｖ
M（％）が次式（２） −274.0＋70lnTS≦ＶM ……（２） を満足することを特徴とするレーザー溶接後のプレス成
形性に優れたフェライト及び低温変態生成物により構成
される引張り強さ60kgf/mm2以上の複合組織高強度冷延
鋼板を要旨とするものである。また、レーザー溶接以外
に他の高エネルギービームによる溶接法も可能である。That is, according to the present invention, the ratio of the hardness HV M of the low-temperature transformation product such as martensite to the hardness HV F of the ferrite is given by the following formula (1): 5.96−0.0201 × TS ≧ HV M / HV F ≧ 2.28-0.0061 × TS ... (1) (where TS: tensile strength of the steel sheet) and the volume ratio V of the low-temperature transformation product
M (%) satisfies the following equation (2) −274.0 + 70 lnTS ≦ V M (2) Tensile composed of ferrite excellent in press formability after laser welding and low-temperature transformation product A gist is a composite structure high-strength cold-rolled steel sheet having a strength of 60 kgf / mm 2 or more. In addition to the laser welding, other high energy beam welding methods are also possible.
以下に本発明を更に詳細に説明する。 Hereinafter, the present invention will be described in more detail.
（作用） 本発明の複合組織高強度冷延鋼板は、以下の方法によ
り得ることができる。(Action) The composite structure high-strength cold-rolled steel sheet of the present invention can be obtained by the following method.
まず、種々の強度を有する鋼を造塊又は連続鋳造によ
りスラブとし、これを通常の方法で無間圧延し、酸洗を
して冷間圧延した後、連続焼鈍によりAc1点以上の２相
域温度に加熱して焼鈍を施し、強制空冷し、次いで水焼
入れなどによって常温まで冷却し焼入れする。このよう
にして、鋼板の延性を高めるために、延性の高いフェラ
イト相と低温変態生成物を得る。ここで低温変態生成物
とはマルテンサイト又はベイナイト又はこれらの混合物
からなる生成物をいう。First, a slab of steel having various strengths is formed by ingot casting or continuous casting, and this is rolled in a usual manner without rolling, pickled and cold-rolled, and then subjected to continuous annealing to obtain a two-phase region of one or more Ac points. The steel is annealed by heating to a temperature, forcibly air-cooled, and then cooled to room temperature by water quenching or the like and quenched. In this way, a ferrite phase having high ductility and a low-temperature transformation product are obtained in order to increase the ductility of the steel sheet. Here, the low-temperature transformation product refers to a product composed of martensite, bainite, or a mixture thereof.
この場合に、低温変態生成物の体積比率ＶM（％）が
次式（２）を満足するように調整することが必要であ
る。In this case, it is necessary that the volume of the low-temperature transformation product ratio V M (%) is adjusted so as to satisfy the following equation (2).
−274.0＋70lnTS≦ＶM ……（２） ここで、ＶMが上式の左辺の値以下である場合には、
所定の引張り強度を得ようとすると第２相の硬さが著し
く硬くなり、鋼板の局部伸びが低下し、加工性が悪くな
る。−274.0 + 70lnTS ≦ V M (2) Here, when V M is equal to or less than the value on the left side of the above equation,
In order to obtain a predetermined tensile strength, the hardness of the second phase becomes extremely hard, the local elongation of the steel sheet decreases, and the workability deteriorates.
この後、適時効処理を施す。この適時効処理によって
焼戻しを行い、前述の焼入れを行った冷間圧延鋼板の低
温変態生成物の硬さを調整する。Thereafter, an appropriate aging treatment is performed. Tempering is performed by this appropriate aging treatment, and the hardness of the low-temperature transformation product of the quenched cold-rolled steel sheet is adjusted.
すなわち、この適時効処理によって、低温変態生成物
の硬度HVMとフェライトの硬度HVFの比が次式（１）を満
足するように調整することが必要である。That is, it is necessary to adjust the ratio of the hardness HV M of the low-temperature transformation product to the hardness HV F of the ferrite by the appropriate aging treatment so as to satisfy the following expression (1).
5.96−0.0201×TS≧HVM/HVF≧2.28−0.0061×TS ……（１） ここで、HVM/HVFが上式の右辺の値以上であると、後
述するレーザー溶接した場合に溶接部近傍の熱影響部
（HAZ）において低温変態生成物の焼戻しによる軟化が
生じるため、プレス加工時にHAZにひずみが集中し、著
しく成形性が低下する。他方、左辺の値より小さいと、
所定の強度の高強度鋼板を得ることができない。5.96−0.0201 × TS ≧ HV M / HV F ≧ 2.28−0.0061 × TS (1) Here, if HV M / HV F is equal to or more than the value on the right side of the above equation, welding is performed when laser welding described later is performed. Since the low-temperature transformation product is softened by tempering in the heat-affected zone (HAZ) near the part, strain is concentrated on the HAZ during press working, and the formability is significantly reduced. On the other hand, if it is smaller than the value on the left side,
A high-strength steel plate having a predetermined strength cannot be obtained.
かくして、延性に優れると共にレーザー溶接後の成形
性の低下の少ない引張り強さ60kgf/mm2以上の高強度複
合組織冷延鋼抜を得ることができる。Thus, it is possible to obtain a high-strength composite structure cold-rolled steel having excellent ductility and a small decrease in formability after laser welding and a tensile strength of 60 kgf / mm 2 or more.
この高強度冷延鋼板をレーザー溶接する場合の溶接条
件は、鋼板の板厚によって任意に選択すればよいが、そ
の際、形成される溶接ビードの幅（ｂ）は、溶接可能で
ある限り小さいことが望ましい。特に限定されるもので
はないが、溶接ビード幅（ｂ）は2.20t（但し、t:鋼板
の板厚）以下が好ましい。これは、溶接ビードの輻
（ｂ）が2.20t以上では、レーザー溶接した場合に溶接
部近傍の熱影響部（HAZ）の幅が底くなり、熱ひずみの
問題が生じるためである。The welding conditions for laser welding this high-strength cold-rolled steel sheet may be arbitrarily selected depending on the thickness of the steel sheet. At this time, the width (b) of the weld bead formed is as small as possible to be welded. It is desirable. Although not particularly limited, the weld bead width (b) is preferably equal to or less than 2.20 t (where t is the thickness of the steel sheet). This is because when the radiation (b) of the weld bead is 2.20 t or more, the width of the heat-affected zone (HAZ) near the welded portion becomes lower when laser welding is performed, which causes a problem of thermal distortion.
更に、その溶接方法はレーザー溶接ばかりでなく、電
子ビーム、プラズマビーム等の被照射体に熱を付与する
高エネルギービームによる溶接であれば、同等の効果を
得ることができる。Furthermore, the same effect can be obtained if the welding method is not only laser welding but also welding using a high energy beam that applies heat to an irradiation target such as an electron beam or a plasma beam.
なお、本発明は高強度冷延鋼板に関するものである
が、前述の組織条件を満足する鋼板であれば、熱延鋼板
であっても何ら問題はない。Note that the present invention relates to a high-strength cold-rolled steel sheet, but there is no problem even if a hot-rolled steel sheet is used as long as the steel sheet satisfies the above-described structural conditions.
次に本発明の実施例を示す。 Next, examples of the present invention will be described.
（実施例） 第１表に種々の冷延鋼板の特性を示す。また、第１図
に本発明鋼と比較鋼のレーザー溶接ビード付近の硬度分
布を示す。(Example) Table 1 shows the characteristics of various cold-rolled steel sheets. FIG. 1 shows the hardness distribution near the laser weld bead of the steel of the present invention and the comparative steel.
第１表より明らかなように、比較鋼はいずれも高強度
と溶接後の優れた成形性がともに得られていない。一
方、本発明鋼はいずれも高強度でかつ溶接後の成形性が
優れている。As is clear from Table 1, none of the comparative steels obtained high strength and excellent formability after welding. On the other hand, each of the steels of the present invention has high strength and excellent formability after welding.
例えば、第１図に示すように、比較鋼No.4は、HAZで
軟化し、母材の硬度に戻る硬度分布であるのに対し、本
発明鋼No.5はHAZで軟化を生じていない。このため、プ
レス成形した場合、比較鋼No.4ではHAZの軟化領域にひ
ずみが集中して成形性が著しく低下する。一方、本発明
鋼No.5ではHAZにひずみが集中せず、成形性の低下率も
小さくなる。For example, as shown in FIG. 1, comparative steel No. 4 has a hardness distribution softened by HAZ and returns to the hardness of the base material, whereas steel No. 5 of the present invention does not soften by HAZ. . For this reason, when press-forming, in the comparative steel No. 4, strain concentrates in the softening region of the HAZ, and the formability is significantly reduced. On the other hand, in the steel No. 5 of the present invention, the strain is not concentrated on the HAZ, and the reduction rate of the formability is small.
これを確かめるため、第２図に示すJIS5号引張り試験
片を製作し引張試験を行った。To confirm this, a JIS No. 5 tensile test piece shown in FIG. 2 was manufactured and subjected to a tensile test.
第３図に母材の伸びに対するレーザー溶接材の伸びの
低下率を示す。同図より、比較鋼No.2、No.4、No.6、N
o.8は著しくその成形性が低下しているのに対し、本発
明鋼No.3、No.5、No.7、No.9は比較鋼No.1の軟鋼板と同
程度の低下率を示し、その成形性の著しい低下は見られ
ないことがわかる。FIG. 3 shows the reduction rate of the elongation of the laser welding material with respect to the elongation of the base material. From the figure, the comparative steel No. 2, No. 4, No. 6, N
o.8 markedly reduced its formability, while the steels of the present invention No.3, No.5, No.7 and No.9 had the same reduction rate as the mild steel sheet of comparative steel No.1 And it can be seen that no significant decrease in the moldability was observed.
（発明の効果） 以上詳述したように、本発明によれば、低温変態生成
物の体積比率と共に延性の高いフェライトとの硬度比を
調整することにより、延性に優れると共にレーザー溶接
等の溶接後の成形性に優れる引張り強さ60kgf/mm2以上
の高強度複合組織冷延鋼板を得ることができる。 (Effects of the Invention) As described above in detail, according to the present invention, by adjusting the volume ratio of the low-temperature transformation product and the hardness ratio with ferrite having high ductility, the ductility is excellent and the post-welding such as laser welding is performed. It is possible to obtain a high-strength composite structure cold-rolled steel sheet having a tensile strength of 60 kgf / mm 2 or more, which is excellent in formability.
第１図は本発明鋼と比較鋼のレーザー溶接ビード付近の
硬度分布を示す図、 第２図はレーザー溶接材の引張り試験を行う場合のJIS5
号引張り試験片の摸式図、 第３図は引張り試験における母材の伸びに対するレーザ
ー溶接材の伸びの低下率を示す図である。FIG. 1 is a diagram showing a hardness distribution near a laser weld bead of the steel of the present invention and a comparative steel, and FIG. 2 is a JIS5 diagram for performing a tensile test of a laser welded material.
FIG. 3 is a schematic view of a tensile test piece, and FIG. 3 is a view showing a reduction rate of elongation of a laser welded material with respect to elongation of a base material in a tensile test.
───────────────────────────────────────────────────── フロントページの続き (58)調査した分野(Int.Cl.6，ＤＢ名) C22C 38/00 - 38/60 B23K 26/00 310──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. 6 , DB name) C22C 38/00-38/60 B23K 26/00 310
Claims (2)
HVMとフェライトの硬度HVFの比が次式（１） 5.96−0.0201×TS≧HVM/HVF≧2.28−0.0061×TS ……
（１） （但し、TS:当該鋼板の引張り強さ） を満足し、かつ、その低温変態生成物の体積比率Ｖ
M（％）が次式（２） −274.0＋70 1nTS≦ＶM ……（２） を満足することを特徴とするレーザー溶接後のプレス成
形性に優れたフェライト及び低温変態生成物により構成
される引張り強さ60kgf/mm2以上の複合組織高強度冷延
鋼板。1. Hardness of low-temperature transformation product such as martensite
The ratio of HV M to ferrite hardness HV F is given by the following formula (1): 5.96−0.0201 × TS ≧ HV M / HV F ≧ 2.28−0.0061 × TS ……
(1) (however, TS: tensile strength of the steel sheet) is satisfied, and the volume ratio V of the low-temperature transformation product is satisfied.
M (%) is constituted by ferrite and low-temperature transformation products excellent in press formability after laser welding, characterized by satisfying the following formula (2): -274.0 + 701nTS ≦ V M (2) tensile strength of 60 kgf / mm 2 or more complex structure and high-strength cold-rolled steel sheet.
ネルギービームによる溶接法である請求項１に記載の複
合組織高強度冷延鋼板。2. The high-strength composite structure high-strength cold-rolled steel sheet according to claim 1, wherein the welding method is a welding method using another high energy beam instead of laser welding.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2248341A JP2862185B2 (en) | 1990-09-18 | 1990-09-18 | High strength cold rolled steel sheet with excellent press formability after laser welding |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2248341A JP2862185B2 (en) | 1990-09-18 | 1990-09-18 | High strength cold rolled steel sheet with excellent press formability after laser welding |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04128341A JPH04128341A (en) | 1992-04-28 |
| JP2862185B2 true JP2862185B2 (en) | 1999-02-24 |
Family
ID=17176647
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2248341A Expired - Fee Related JP2862185B2 (en) | 1990-09-18 | 1990-09-18 | High strength cold rolled steel sheet with excellent press formability after laser welding |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2862185B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3198976B2 (en) | 1997-05-21 | 2001-08-13 | 日本電気株式会社 | PRINTING SYSTEM, CHARGING METHOD FOR PRINTING SYSTEM, AND RECORDING MEDIUM CONTAINING RECORDING CONTROL PROGRAM FOR PRINTING SYSTEM |
-
1990
- 1990-09-18 JP JP2248341A patent/JP2862185B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04128341A (en) | 1992-04-28 |
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