JP5014807B2 - Steel sheet for hot press - Google Patents
Steel sheet for hot press Download PDFInfo
- Publication number
- JP5014807B2 JP5014807B2 JP2007005691A JP2007005691A JP5014807B2 JP 5014807 B2 JP5014807 B2 JP 5014807B2 JP 2007005691 A JP2007005691 A JP 2007005691A JP 2007005691 A JP2007005691 A JP 2007005691A JP 5014807 B2 JP5014807 B2 JP 5014807B2
- Authority
- JP
- Japan
- Prior art keywords
- steel
- steel sheet
- scale
- strength
- hot
- 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
Landscapes
- Metal Rolling (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、プレス成形と焼き入れによる部材の強度向上を同時に行う熱間プレス用鋼板、特に自動車ボデーの骨格部品、補強部品や足回り部品などの製造に使用される熱間プレス用鋼板に関する。 The present invention relates to a steel sheet for hot pressing that simultaneously improves the strength of a member by press forming and quenching, and more particularly, to a steel sheet for hot pressing used for manufacturing a frame part, a reinforcing part, a suspension part, and the like of an automobile body.
近年、地球環境の観点から自動車の軽量化が強く望まれている。ボデー等の鋼板が使用される部品では、高強度鋼板を採用し鋼板の板厚を薄くして軽量化が図られている。しかしながら、鋼板の高強度化は部品製造時の加工性、プレス成形性の低下を招き、特にスプリングバック等により製品精度の確保がより難しくなっている。 In recent years, weight reduction of automobiles has been strongly desired from the viewpoint of the global environment. In a part using a steel plate such as a body, a high strength steel plate is adopted to reduce the thickness of the steel plate and reduce the weight. However, increasing the strength of the steel sheet causes a decrease in workability and press formability at the time of manufacturing the parts, and in particular, it is more difficult to ensure product accuracy due to springback and the like.
これらの課題解決のために、これまで加工性に優れた鋼板の開発や製品精度を高める加工方法が提案されているが、自動車に適用される鋼板の高強度化もさらに進み、特に引張り強度（ＴＳ：Ｔｅｎｓｉｌｅ Ｓｔｒｅｎｇｔｈ）が１１８０ＭＰａを越える高強度鋼板においては、上記の加工性、製品精度の観点から適用可能な部品に制限があるのが実情である。 In order to solve these problems, the development of steel plates with excellent workability and processing methods that improve product accuracy have been proposed so far. However, the strength of steel plates applied to automobiles has further increased, especially tensile strength ( In a high-strength steel sheet having a TS (Tensile Strength) exceeding 1180 MPa, there is a limit to the parts that can be applied from the viewpoints of the above workability and product accuracy.
近年、鋼板の高強度化と加工性、製品精度を同時に満足する手法として熱間プレス工法（プレスクエンチ工法）が実用技術として使用されるようになってきた。例えば特許文献１に開示されている。これは、鋼板を約８００℃以上のオーステナイト域まで加熱した後、プレス成形し、同時に成形後の冷却により焼き入れを行い高強度の材質を得るものである。この熱間プレス工法により成形時の割れ発生等の加工性が改善され、かつ、比較的良好な製品精度を有する部品の製造が可能となり、加えてプレス成形時に導入される残留応力も減少するため、引張り強度で１１８０ＭＰａを超える高強度鋼板で問題となる遅れ破壊の感受性も低下するが、以下の不具合が残った。 In recent years, the hot press method (press quench method) has come to be used as a practical technique as a method of simultaneously satisfying the high strength, workability, and product accuracy of steel sheets. For example, it is disclosed in Patent Document 1. In this method, the steel sheet is heated to an austenite region of about 800 ° C. or higher, then press-formed, and simultaneously quenched by cooling after forming to obtain a high-strength material. This hot press method improves the workability such as cracking during molding and makes it possible to manufacture parts with relatively good product accuracy. In addition, the residual stress introduced during press molding is reduced. Although the sensitivity of delayed fracture, which is a problem with high-strength steel sheets with a tensile strength exceeding 1180 MPa, also decreases, the following problems remain.
上述のように、熱間プレス工法（プレスクエンチ工法）では、鋼板を約８００℃以上まで加熱するため、鋼板表面が酸化し鉄酸化物、いわゆるスケールが生じることとなる。鋼板表面にこのようなスケールが存在した状態でプレス成形が実施された場合、成形によりスケールが剥離し金型部内に残存し、次サンプルのプレス成形時の押し込み傷の原因となるため、金型内を清掃する必要が生じ生産性を阻害する場合がある。このため、熱間プレス工法においては、加熱時に生成されるスケールはプレス成形時に導入される加工ひずみに対して、密着性を具備することが望まれている。また、スケールが残存した状態で、次工程で塗装する場合に塗膜との密着性が低いため、結果として耐食性の低下を招くため、プレス成形後、塗装前の工程としてショットブラストに代表されるスケール除去工程が必要となる。 As described above, in the hot press method (press quench method), the steel plate is heated to about 800 ° C. or higher, so that the surface of the steel plate is oxidized to produce iron oxide, so-called scale. When press molding is performed with such a scale on the surface of the steel sheet, the scale peels off due to molding and remains in the mold part, causing indentation scratches during press molding of the next sample. It may be necessary to clean the interior, which may hinder productivity. For this reason, in the hot press method, it is desired that the scale generated during heating has adhesion to the processing strain introduced during press molding. In addition, when coating is performed in the next process with the scale remaining, the adhesion to the coating film is low, resulting in a decrease in corrosion resistance. As a result, after press molding, the process before coating is represented by shot blasting. A scale removal process is required.
このような課題に対して、鋼板にメッキによる表面処理を施すことで、スケール生成を抑制し、スケール除去工程を設定せずとも塗装性、耐食性を確保することが可能となることが特許文献２に記載あるが、メッキを施すことにより、コストアップは避けられないのが実情である。 For such a problem, it is possible to suppress the generation of scale and to ensure the paintability and corrosion resistance without setting the scale removal step by applying a surface treatment to the steel sheet by plating. However, the actual situation is that an increase in cost cannot be avoided by plating.
また、自動車の製造における部品同士の接合は通常、スポット溶接が使用されているが、熱間プレスに使用されている鋼板は、焼入れ後の強度と焼き入れ性を確保するため添加成分が多いので、スポット溶接部は高硬度化され、スポット溶接部の接合の信頼性（破断形態）を低下させている。 In addition, spot welding is usually used for joining parts in the manufacture of automobiles, but steel sheets used for hot pressing have many additional components to ensure strength and hardenability after quenching. In addition, the spot welded portion is increased in hardness, and the reliability (breaking form) of the joint of the spot welded portion is lowered.
すなわち、熱間プレス工法に使用される鋼板において、メッキの施されていない鋼板で熱間プレス・焼き入れ後の部品強度とスケール密着性、スポット溶接部の品質が考慮された鋼板は未だ無い状況である。 In other words, in the steel plate used for the hot press method, there is still no steel plate that has not been plated, and has not been considered for the strength and scale adhesion of parts after hot pressing and quenching, and the quality of spot welds. It is.
本発明者らは、上記のような課題を克服し、熱間プレス・焼き入れ後の部品強度、スケール密着性、スポット溶接部の品質を満足する熱間プレス用鋼板を提供することを目的とするものである。 It is an object of the present invention to provide a hot press steel sheet that overcomes the above-described problems and satisfies the requirements of component strength after hot pressing and quenching, scale adhesion, and quality of spot welds. To do.
本発明の要旨は以下の通りである。 The gist of the present invention is as follows.
（１） 質量％にて、
Ｃ ：０．１５〜０．３％、
Ｓｉ：０．０５〜０．５％、
Ｍｎ：０．５〜３．０％、
Ｐ ：０．００５〜０．１％、
Ｓ ：０．０２％以下
Ａｌ：０．０１〜３．０％、
Ｎ ：０．０１％以下、
Ｃｒ：０．０５〜０．５％、
Ｂ：０．０００２〜０．０１％、
を含有し、残部が鉄および不可避的不純物からなる鋼で、下記式（Ａ）、（Ｂ）を満足し、かつ、熱間圧延、酸洗、圧延率が２０〜６０％である冷間圧延を施された未焼鈍材であり、プレス焼入れ後の引張り強度が１１８０ＭＰａ以上となることを特徴とする熱間プレス用鋼板。
０．５≦ （Ｃｒ／Ｓｉ） ≦１．５ ・ ・ ・（Ａ）
０．３５≧ Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｒ／２０＋４×Ｂ＋２×Ｐ＋４×Ｓ
・ ・ ・（Ｂ）
(1) In mass%
C: 0.15-0.3%
Si: 0.05 to 0.5%,
Mn: 0.5 to 3.0%
P: 0.005-0.1%,
S: 0.02% or less Al: 0.01-3.0%,
N: 0.01% or less,
Cr: 0.05 to 0.5%,
B: 0.0002 to 0.01%
Steel, the balance of which is iron and inevitable impurities, satisfying the following formulas (A) and (B), and hot rolling, pickling, and cold rolling with a rolling rate of 20 to 60% A steel sheet for hot pressing, which is an unannealed material that has been subjected to heat treatment and has a tensile strength of 1180 MPa or more after press quenching.
0.5 ≦ (Cr / Si) ≦ 1.5 (A)
0.35 ≧ C + Si / 30 + Mn / 20 + Cr / 20 + 4 × B + 2 × P + 4 × S
(B)
（２）更に、質量％にて
Ｔｉ：０．００２〜０．５％、
を含有し、残部が鉄および不可避的不純物からなる鋼であることを特徴とする前記（１）に記載の熱間プレス用鋼板。
(2) Further, in mass% Ti: 0.002 to 0.5%,
The steel sheet for hot pressing as described in (1) above, wherein the balance is steel composed of iron and inevitable impurities.
本発明の熱間プレス用高強度鋼板は、熱間プレス・焼き入れ後の部品強度を確保すると同時にスケール密着性、スポット溶接品質に優れた鋼板を提供することができ、本発明の鋼板により製造された部材を使用すれば自動車製造における信頼性の向上、ひいては自動車の軽量化、安全性向上に大きく貢献できるものと考えられ、産業上の寄与は大きい。 The high-strength steel sheet for hot pressing according to the present invention can provide a steel sheet excellent in scale adhesion and spot welding quality while ensuring the strength of parts after hot pressing and quenching, and is manufactured by the steel sheet according to the present invention. It is considered that the use of such a member can greatly contribute to the improvement of reliability in automobile manufacturing, and consequently to the reduction in weight and safety of automobiles, and the industrial contribution is great.
本発明者らは、熱間プレス・焼き入れ後の部品強度およびスケール密着性、スポット溶接特性を満足するために様々な添加成分、添加量、また、添加成分相互の影響について調査を行った。 The present inventors have investigated various additive components, additive amounts, and the influence of additive components in order to satisfy the parts strength and scale adhesion after hot pressing and quenching, and spot welding characteristics.
スケール密着性について調査したところ、鋼中のＣｒ、Ｓｉの添加量比率（Ｃｒ／Ｓｉ）が影響を及ぼし、この比率が特定の範囲内にあれば密着性が良好であることを見出した。 As a result of investigating the scale adhesion, it was found that the ratio of Cr and Si added in the steel (Cr / Si) has an effect, and if this ratio is within a specific range, the adhesion is good.
加えて、熱間圧延、酸洗後の鋼板に対して冷間圧延を行い、その後に連続焼鈍を施さない、すなわち未焼鈍材において密着性が良好であり、その圧延率が２０〜６０％の条件で、さらに密着性が向上することも判明した。次にスポット溶接性について調査したところ、熱間プレス・焼き入れした鋼板をスポット溶接した場合、溶接部の熱履歴によって、母材の強度に対して溶接部及び熱影響部の強度が変化するため、接合強度を評価した場合、スポット溶接部の破断形態は、溶接部（ナゲット）が残らない剥離破断やナゲットが残存するナゲット外破断を呈する場合があることが判明した。そして、鋼中にＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎ、Ｃｒ、Ｂ、Ｔｉを含有する場合において、これらの中でＣ、Ｓｉ、Ｍｎ、Ｃｒ、Ｂ、Ｐ、Ｓが所定の関係式を満たした場合にスポット溶接部の破断形態がナゲット外破断を呈しやすくなることを見い出した。 In addition, hot rolling, cold rolling is performed on the steel plate after pickling, and then continuous annealing is not performed, that is, adhesion is good in an unannealed material, and the rolling rate is 20 to 60%. It was also found that the adhesion was further improved under the conditions. Next, when the spot weldability was investigated, when the hot-pressed and hardened steel plate was spot-welded, the strength of the welded part and the heat-affected zone changes with respect to the strength of the base metal due to the thermal history of the welded part. When the joint strength was evaluated, it was found that the fracture form of the spot welded part may exhibit a peeling rupture in which the welded part (nugget) does not remain or an external nugget rupture in which the nugget remains. And when C, Si, Mn, P, S, Al, N, Cr, B, Ti are contained in the steel, among these, C, Si, Mn, Cr, B, P, S are predetermined. It has been found that when the relational expression is satisfied, the fracture form of the spot welded portion tends to exhibit a nugget-out fracture.
以上の知見を元に鋼板の添加成分を最適化し、かつ相互の添加量比を所定の範囲にすることで、所望の特性を有する熱間プレス用鋼板が得られる。 Based on the above knowledge, a steel sheet for hot pressing having desired characteristics can be obtained by optimizing the additive components of the steel sheet and setting the mutual additive amount ratio within a predetermined range.
以下に本発明を詳細に説明する。 The present invention is described in detail below.
まず、以下に鋼の各成分を、所定の範囲に限定する理由について述べる。 First, the reason why each component of steel is limited to a predetermined range will be described below.
Ｃは、熱間プレス、焼き入れ後の部品強度に影響を及ぼす重要な元素であり、０．１５％未満では、十分な強度が確保できない。また、０．３％を超えるとスポット溶接時の破断形態を劣化させると同時に部品製造における打抜き時のクラック発生の起点となるセメンタイトを増加させ遅れ破壊を生じやすくするため、０．１５〜０．３％とした。 C is an important element that affects the strength of parts after hot pressing and quenching, and if it is less than 0.15%, sufficient strength cannot be secured. Further, if it exceeds 0.3%, the fracture form at the time of spot welding is deteriorated, and at the same time, the cementite that becomes the starting point of crack generation at the time of punching in the manufacture of parts is increased to easily cause delayed fracture. 3%.
Ｓｉは、熱間プレス、焼き入れ性、スケール密着性に影響する元素であり、かつセメンタイト析出を抑制する元素であるが、０．０５％未満では十分な効果を得ることができない。また、０．５％を超えるとその効果は飽和し、コストがかかり経済的に不利となる。 Si is an element that affects hot pressing, hardenability, and scale adhesion, and is an element that suppresses cementite precipitation. However, if it is less than 0.05%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.5%, the effect is saturated, which is costly and disadvantageous economically.
Ｍｎは、熱間プレス、焼き入れ性に影響する元素であり、鋼板の強度上昇に有効である。しかし、０．５％未満ではこの効果が得られないので、下限値を０．５％とした。また、３．０％を超えるとＰ、Ｓとの共偏析を助長し、スポット溶接部の脆化を招くため３．０%を上限値とする。 Mn is an element that affects hot press and hardenability, and is effective in increasing the strength of the steel sheet. However, this effect cannot be obtained at less than 0.5%, so the lower limit was set to 0.5%. Further, if it exceeds 3.0%, co-segregation with P and S is promoted and the spot welded portion becomes brittle, so 3.0% is made the upper limit.
Ｐは、粒界偏析による粒界破壊の助長をする元素であり、低い方が望ましいが、０．００５％未満にしようとすると、製造工程における製鋼でのコスト上昇を招くため好ましくない。また０．１％を超えると粒界破壊の助長、スポット溶接部の脆化を招くため、上限を０．１％とする。 P is an element that promotes intergranular fracture due to intergranular segregation, and a lower value is desirable. However, if it is attempted to make it less than 0.005%, it is not preferable because it causes an increase in the cost of steelmaking in the production process. On the other hand, if it exceeds 0.1%, intergranular fracture will be promoted and spot welds will become brittle, so the upper limit is made 0.1%.
Ｓは、ＭｎＳ等の非金属介在物を生成し打抜き性を劣化させたり、熱間脆性やスポット溶接部の脆化を助長する元素であり、低い方が望ましいが、極低化は製造コスト上好ましくないため０．０２％以下とする。 S is an element that generates non-metallic inclusions such as MnS and degrades punchability, or promotes hot embrittlement and embrittlement of spot welds. A lower value is desirable, but extremely low is an increase in manufacturing cost. Since it is not preferable, it is made 0.02% or less.
Ａｌは、脱酸のため０．０１％以上を添加するが、添加量が増加するとアルミナ等の介在物が増加し、打抜き面の粗大クラック発生の要因となるため上限を３．０％とした。 Al is added in an amount of 0.01% or more for deoxidation. Increasing the addition amount increases inclusions such as alumina, which causes generation of coarse cracks on the punched surface, so the upper limit was made 3.0%. .
Ｎは、添加量が多くなると粗大化合物を生成するため、打抜き面の粗大クラックの発生を招いたり、後述のＢと結合してＢＮを生成し、Ｂ添加の効果を低下させるため、添加は少ない方が望ましい。特に０．０１％を越えるとその影響が顕著となるため、上限を０．０１％とした。また少ない方が望ましいが、０．０００５％未満にするには製造コスト上好ましくないため、下限値を０．０００５％とすることが好ましい。 Since N produces a coarse compound when the amount of addition increases, it causes the occurrence of coarse cracks on the punched surface, or forms BN by combining with B described later, thereby reducing the effect of B addition, so the addition is small. Is preferable. In particular, when the content exceeds 0.01%, the effect becomes significant, so the upper limit was made 0.01%. Moreover, although it is desirable that the content is less, it is not preferable in view of manufacturing cost to make it less than 0.0005%, so the lower limit value is preferably made 0.0005%.
Ｃｒは、鋼板の焼き入れ性、スケール性能に影響する元素であり、熱間プレス、焼き入れ後の強度やスケール密着性確保のために必要である。しかし、０．０５％未満ではこれらの効果が得られないため、下限値を０．０５％とした。また、多量の添加は焼き入れ性が飽和するだけでなく、スケール密着性を悪化させ、遅れ破壊感受性を高める恐れがあるため、０．５％を上限とする。 Cr is an element that affects the hardenability and scale performance of the steel sheet, and is necessary for ensuring the strength and scale adhesion after hot pressing and quenching. However, since these effects cannot be obtained if the content is less than 0.05%, the lower limit is set to 0.05%. Moreover, addition of a large amount not only saturates the hardenability but also deteriorates the scale adhesion and increases the delayed fracture susceptibility, so the upper limit is made 0.5%.
Ｂは、焼き入れ性を向上させるのに有効な元素である。このような効果を有効にするためには、０．０００２％以上の添加が必要ある。しかし、過多に添加してもその効果は飽和するので、０．０１％を上限とした。 B is an element effective for improving the hardenability. In order to make such an effect effective, 0.0002% or more must be added. However, the effect is saturated even if added excessively, so 0.01% was made the upper limit.
Ｔｉは、強炭化物生成元素であり、析出物や介在物を生成させて熱間プレス、焼き入れした部材の強度を確保するとともにＮを固定することによりＢとの結合を防止し、Ｂの焼入れ性の効果を十分発揮させる。この効果を発揮させるには、０．００２％以上の添加が必要となる。しかし、過剰に添加すると、粗大析出または晶出物が生成するために、打抜き面の粗大クラックの発生の要因となるため、０．５％を上限とする。 Ti is a strong carbide-forming element, which generates precipitates and inclusions to ensure the strength of the hot-pressed and quenched members and prevents N from being bonded by fixing N and quenching B Fully demonstrate the effects of sex. In order to exert this effect, 0.002% or more must be added. However, if excessively added, coarse precipitates or crystallized substances are formed, which causes generation of coarse cracks on the punched surface, so 0.5% is made the upper limit.
さらに本発明においては、上記各成分の添加量が下記式（Ａ）、（Ｂ）を満足することが重要となる。
０．５≦ （Ｃｒ／Ｓｉ） ≦１．５ ・ ・ ・（Ａ）
０．３５≧ Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｒ／２０＋４×Ｂ＋２×Ｐ＋４×Ｓ
・ ・ ・（Ｂ）
式（Ａ）の値が０．５未満あるいは１．５を超えると熱間プレス、焼き入れ後のスケール密着性が低下する。好ましくは、０．９から１．２の範囲がさらに良好なスケール密着性が得られる。本発明者らは、実験室にて鋼中成分としてＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎ、Ｃｒ、Ｂ、Ｔｉを含有する鋼板において、これらの中でＳｉ、Ｃｒの量を変化させた種々の成分組成を有する鋼板を用いて、熱間プレス、焼き入れを行い、スケールの挙動を調査した。加熱は、大気中にて９３０℃×３ｍｉｎとし、その後、平板金型により焼き入れした。その結果、鋼中のＣｒ、Ｓｉの添加量比率（Ｃｒ／Ｓｉ）が０．５以上、１．５以下の場合、スケール密着性は良好であった。このスケールの状態を調査したところ、スケールと鋼板の界面にＦｅＣｒ２Ｏ４、（Ｆｅ、Ｍｎ、Ｃｒ）２ＳｉＯ４が存在することがわかった。
Furthermore, in the present invention, it is important that the amount of each component added satisfies the following formulas (A) and (B).
0.5 ≦ (Cr / Si) ≦ 1.5 (A)
0.35 ≧ C + Si / 30 + Mn / 20 + Cr / 20 + 4 × B + 2 × P + 4 × S
(B)
When the value of the formula (A) is less than 0.5 or exceeds 1.5, the scale adhesion after hot pressing and quenching decreases. Preferably, the range of 0.9 to 1.2 provides better scale adhesion. In the steel sheet containing C, Si, Mn, P, S, Al, N, Cr, B, and Ti as components in steel in the laboratory, the inventors changed the amounts of Si and Cr. Using the steel plates having various component compositions, hot pressing and quenching were performed, and the behavior of the scale was investigated. Heating was performed at 930 ° C. × 3 min in the air, and then quenched with a flat plate mold. As a result, when the ratio of Cr and Si in the steel (Cr / Si) was 0.5 or more and 1.5 or less, the scale adhesion was good. When the state of this scale was investigated, it was found that FeCr 2 O 4 , (Fe, Mn, Cr) 2 SiO 4 was present at the interface between the scale and the steel plate.
これに対し、鋼中のＣｒ、Ｓｉの添加量比率（Ｃｒ／Ｓｉ）が０．５未満では、スケールと鋼板の界面にはＦｅ２ＳｉＯ４が存在した。また、鋼中のＣｒ、Ｓｉの添加量比率（Ｃｒ／Ｓｉ）が１．５を超えるとスケールと鋼板の界面にはＦｅＣｒ２Ｏ４が存在した。スケール密着性が向上する理由は明確ではないが、鋼中のＣｒ、Ｓｉの添加量比率（Ｃｒ／Ｓｉ）によってスケールと鋼板界面に生成される酸化物が異なることから、ＦｅＣｒ２Ｏ４、（Ｆｅ、Ｍｎ、Ｃｒ）２ＳｉＯ４の酸化物がスケールと鋼板界面に存在することにより、スケールと鋼板との間の整合性が向上したものと推察される。 On the other hand, when the addition ratio of Cr and Si in the steel (Cr / Si) was less than 0.5, Fe 2 SiO 4 was present at the interface between the scale and the steel plate. Further, when the addition ratio of Cr and Si in the steel (Cr / Si) exceeded 1.5, FeCr 2 O 4 was present at the interface between the scale and the steel plate. The reason why the scale adhesion improves is not clear, but since the oxide generated at the interface between the scale and the steel sheet differs depending on the ratio of Cr and Si in the steel (Cr / Si), FeCr 2 O 4 , ( The presence of the oxide of Fe, Mn, Cr) 2 SiO 4 at the interface between the scale and the steel plate is presumed to improve the consistency between the scale and the steel plate.
次に式（Ｂ）の値が０．３５を超えるとスポット溶接部のピール試験（ＪＩＳ Ｚ３１４４）にて破断形態を評価した場合、スポット溶接部の破断形態が、溶接部（ナゲット）が残らない剥離破断する場合が多くなるため（Ｂ）式の上限を０．３５とした。式（Ｂ）が成り立つ場合、すなわち、Ｃ、Ｓｉ、Ｍｎ、Ｃｒ、Ｂ、Ｐ、Ｓの添加量が本発明に従う場合には、破断形態はナゲット外破断あるいは、一部ナゲット内破断であることが判明した。これは、Ｃ、Ｓｉ、Ｍｎ、Ｃｒ、Ｂ、は、溶接部および熱影響部の強度を高めるため、またＰ、Ｓは、溶接時の入熱により粒界への偏析を生じやすくなるため、過剰に添加されると溶接部を脆化させ、剥離破断の傾向となるものと考えられる。剥離破断は溶接部の接合強度が母材の強度より低くなる場合もあるため、部品の性能の信頼性を損なう可能性もある。このため、部品性能の信頼性を確保するためには、上記式（Ｂ）を満足することが重要となる。式（Ｂ）を満足する場合、破断形態は一部ナゲット内破断もしくは、ナゲット外破断となり、溶接部（ナゲット）が一方の鋼板に残存する破断形態となる。さらに式（Ｂ）の値が０．３３以下にすればナゲット外破断となる確率が多くなり、溶接部品質の観点からもより好ましい。 Next, when the value of the formula (B) exceeds 0.35, when the fracture form is evaluated by a peel test (JIS Z3144) of the spot welded part, the welded part (nugget) does not remain as the fractured form of the spot welded part. Since there are many cases of peeling and breaking, the upper limit of the formula (B) is set to 0.35. When the formula (B) is satisfied, that is, when the addition amount of C, Si, Mn, Cr, B, P, and S is in accordance with the present invention, the fracture mode is a nugget fracture or a partial nugget fracture. There was found. This is because C, Si, Mn, Cr, B increase the strength of the welded part and the heat affected zone, and P and S tend to segregate to the grain boundary due to heat input during welding. If it is added excessively, it is considered that the welded portion becomes brittle and tends to peel and break. In the case of peeling fracture, since the joint strength of the welded portion may be lower than the strength of the base material, the reliability of the performance of the component may be impaired. For this reason, in order to ensure the reliability of component performance, it is important to satisfy the above formula (B). When the formula (B) is satisfied, the fracture mode is a partial fracture in the nugget or an external nugget fracture, and a fracture mode in which the welded portion (nugget) remains in one of the steel plates. Furthermore, if the value of the formula (B) is 0.33 or less, the probability of fracture outside the nugget increases, which is more preferable from the viewpoint of welded part quality.
本発明の高強度鋼板の製造方法は、その各種条件が、用途や必要特性に応じて、適宜選択され得るものである。 In the method for producing a high-strength steel sheet according to the present invention, various conditions can be appropriately selected according to the use and required characteristics.
例えば、以下の方法に従って高強度鋼板を製造することができる。まず、転炉で上記成分組成の範囲で調整された鋼を溶製し、連続鋳造法によりスラブとなす。このスラブを高温状態のまま、あるいは、室温まで冷却した後、加熱炉に挿入し、１０００〜１２５０℃の温度範囲で仕上げ圧延を行い、７００℃以下の温度で巻き取って熱延鋼板とする。次いで、酸洗、冷間圧延を行い冷延鋼板となし、熱間プレス用鋼板となる。冷間圧延後に通常の連続焼鈍を実施せず未焼鈍のままで熱間プレス用鋼板とすることで、スケール密着性が向上する。この理由は定かではないが、圧延によるひずみの導入により、熱間プレス工法での加熱工程においてスケールが生成する際に、鋼板中のＦｅの拡散速度が変わることで酸化の速度が変化することが密着性向上に影響しているものと推定している。このため、連続焼鈍を施した場合、冷間圧延工程で導入されたひずみが焼鈍により除去されるため、密着性向上効果が無くなる。また、冷間圧延工程における圧延率は、２０〜６０％にすることでスケール密着性がさらに向上することが確認された。この効果は、圧延率２０％未満では認められず、また６０％を超えるとその効果は飽和し、かつ加工硬化により鋼板の強度が高くなり、切断等が困難になるため、６０％を上限とする。 For example, a high-strength steel plate can be manufactured according to the following method. First, steel adjusted in the range of the above-mentioned component composition is melted in a converter and made into a slab by a continuous casting method. After this slab is kept in a high temperature state or cooled to room temperature, it is inserted into a heating furnace, finish-rolled in a temperature range of 1000 to 1250 ° C., and wound at a temperature of 700 ° C. or less to obtain a hot-rolled steel sheet. Next, pickling and cold rolling are performed to form a cold-rolled steel sheet, which becomes a hot-press steel sheet. Scale adhesiveness improves by making it the steel plate for hot press, without performing normal continuous annealing after cold rolling, and leaving unannealed. The reason for this is not clear, but due to the introduction of strain due to rolling, when the scale is generated in the heating process in the hot press method, the rate of oxidation may change due to the change in the diffusion rate of Fe in the steel sheet. It is estimated that it has an effect on improving adhesion. For this reason, when continuous annealing is performed, the strain introduced in the cold rolling process is removed by annealing, so that the effect of improving adhesion is lost. Moreover, it was confirmed that the scale adhesion is further improved by setting the rolling rate in the cold rolling step to 20 to 60%. This effect is not recognized when the rolling rate is less than 20%, and when it exceeds 60%, the effect is saturated, and the strength of the steel sheet increases due to work hardening, and cutting becomes difficult. To do.
次に実施例について述べる。 Next, examples will be described.
表１に示す成分組成の鋼を転炉で溶製し、常法に従い連続鋳造でスラブとした。これらのスラブを加熱炉中で１１４０℃〜１２５０℃の温度で加熱し、８１０℃〜８８０℃の仕上げ温度で熱間圧延を行い、６００℃〜６６０℃にて巻き取り、熱延鋼板（板厚：２．０ｍｍ）とした。そして、一部のものについては、酸洗後に冷間圧延の圧延率を変化させて冷延鋼板とし、さらに一部のものには冷間圧延後に連続焼鈍を施した。上記の鋼板を用い、加熱炉にて９３０℃×３ｍｉｎの条件にて加熱を行い、ハット形状品の熱間プレスを実施し、部材引張り強度１４７０ＭＰａクラスの部品を作成した。（ハット形状：幅１００ｍｍ、長さ：３００ｍｍ、高さ：６０ｍｍ）部品強度の評価は熱間プレス後の引張り強度が１４７０ＭＰａ以上を合格とした。スケール密着性の評価は、常温近くまで冷却後、金型より取り出し、スケールでの剥離状態を目視により評価、スケール剥離のないものを合格とした。さらに、このプレス品より、評価サンプルを切り出し、熱間プレス・焼き入れ後の引張り強度、スポット溶接品質を評価した。引張り試験は、ＪＩＳ Ｚ ２２０１に従って実施した。スポット溶接品質として破断形態評価は、ＪＩＳ Ｚ ３１４４に従うピール試験によって行った。溶接には、定置式スポット溶接機を使用し、加圧力：４．４ｋＮ、通電時間：０．３ｓ、保持時間：０．０８ｓとし、電流値は、各鋼種にてナゲット径が４√ｔ（ｔ：板厚ｍｍ）の大きさになるように設定した。スポット溶接品質の評価はその破断形態がＡ：剥離破断、Ｂ：ナゲット内破断、Ｃ：ナゲット外破断、で区分し、ナゲットが残るＢ、Ｃを合格とした。結果を表２に示した。 Steels having the component compositions shown in Table 1 were melted in a converter and slabs were obtained by continuous casting according to a conventional method. These slabs are heated in a heating furnace at a temperature of 1140 ° C. to 1250 ° C., hot-rolled at a finishing temperature of 810 ° C. to 880 ° C., wound up at 600 ° C. to 660 ° C., and hot rolled steel sheet (sheet thickness) : 2.0 mm). And about some things, the rolling rate of the cold rolling was changed after pickling, and it was set as the cold-rolled steel plate, and also the continuous annealing was given to some ones after cold rolling. Using the above steel plate, heating was performed in a heating furnace under the condition of 930 ° C. × 3 min, and the hat-shaped product was hot-pressed to produce a part having a member tensile strength of 1470 MPa class. (Hat shape: width 100 mm, length: 300 mm, height: 60 mm) In the evaluation of the component strength, the tensile strength after hot pressing was 1470 MPa or more. Evaluation of scale adhesion was taken out from the mold after cooling to near normal temperature, and the peeled state on the scale was evaluated visually, and the one without scale peeling was regarded as acceptable. Furthermore, an evaluation sample was cut out from this press product, and the tensile strength and spot welding quality after hot pressing and quenching were evaluated. The tensile test was performed according to JIS Z 2201. The fracture form evaluation as spot welding quality was performed by a peel test according to JIS Z 3144. For the welding, a stationary spot welder is used, the applied pressure is 4.4 kN, the energization time is 0.3 s, the holding time is 0.08 s, and the current value is 4√t ( t: plate thickness mm). The evaluation of spot welding quality was classified into A: peeling fracture, B: fracture in nugget, C: fracture outside nugget, and B and C in which the nugget remained were regarded as acceptable. The results are shown in Table 2.
表２の結果から、本発明鋼の範囲では、焼き入れ後の引張り強度が約１４７０ＭＰａ程度以上となっており、所望の部品引張り強度を有することが確認された。これに対し、本発明の範囲から外れた場合には、引張り強度が低くなった。また、本発明鋼の範囲では、スケール密着性も良好となるが、本発明の範囲から外れた場合、スケール密着性は劣位であった。さらに、本発明鋼の範囲では、スポット溶接時の破断形態を満足するが、本発明の範囲から外れた場合には、剥離破断の傾向を呈し、本発明鋼が所望の特性を満足することがわかる。 From the results shown in Table 2, the tensile strength after quenching was about 1470 MPa or more in the range of the steel of the present invention, and it was confirmed that the desired component tensile strength was obtained. On the other hand, when it was outside the scope of the present invention, the tensile strength was low. Moreover, in the range of this invention steel, scale adhesiveness also becomes favorable, but when it remove | deviated from the range of this invention, scale adhesiveness was inferior. Furthermore, in the range of the steel of the present invention, the fracture mode at the time of spot welding is satisfied, but when it is outside the range of the present invention, the tendency of peeling fracture is exhibited and the steel of the present invention satisfies the desired characteristics. Recognize.
Claims (2)
Ｃ ：０．１５〜０．３％、
Ｓｉ：０．０５〜０．５％、
Ｍｎ：０．５〜３．０％、
Ｐ ：０．００５〜０．１％、
Ｓ ：０．０２％以下
Ａｌ：０．０１〜３．０％、
Ｎ ：０．０１％以下、
Ｃｒ：０．０５〜０．５％、
Ｂ：０．０００２〜０．０１％、
を含有し、残部が鉄および不可避的不純物からなる鋼で、下記式（Ａ）、（Ｂ）を満足し、かつ、熱間圧延、酸洗、圧延率が２０〜６０％である冷間圧延を施された未焼鈍材であり、プレス焼入れ後の引張り強度が１１８０ＭＰａ以上となることを特徴とする熱間プレス用鋼板。
０．５≦ （Ｃｒ／Ｓｉ） ≦１．５ ・ ・ ・（Ａ）
０．３５≧ Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｒ／２０＋４×Ｂ＋２×Ｐ＋４×Ｓ
・ ・ ・（Ｂ） In mass%
C: 0.15-0.3%
Si: 0.05 to 0.5%,
Mn: 0.5 to 3.0%
P: 0.005-0.1%,
S: 0.02% or less Al: 0.01-3.0%,
N: 0.01% or less,
Cr: 0.05 to 0.5%,
B: 0.0002 to 0.01%
Steel, the balance of which is iron and inevitable impurities, satisfying the following formulas (A) and (B), and hot rolling, pickling, and cold rolling with a rolling rate of 20 to 60% A steel sheet for hot pressing, which is an unannealed material that has been subjected to heat treatment and has a tensile strength of 1180 MPa or more after press quenching.
0.5 ≦ (Cr / Si) ≦ 1.5 (A)
0.35 ≧ C + Si / 30 + Mn / 20 + Cr / 20 + 4 × B + 2 × P + 4 × S
(B)
Ｔｉ：０．００２〜０．５％、
を含有し、残部が鉄および不可避的不純物からなる鋼であることを特徴とする請求項１に記載の熱間プレス用鋼板。 Furthermore, in mass% Ti: 0.002 to 0.5%,
The steel sheet for hot pressing according to claim 1, wherein the steel is made of iron and inevitable impurities.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007005691A JP5014807B2 (en) | 2007-01-15 | 2007-01-15 | Steel sheet for hot press |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007005691A JP5014807B2 (en) | 2007-01-15 | 2007-01-15 | Steel sheet for hot press |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2008169452A JP2008169452A (en) | 2008-07-24 |
| JP5014807B2 true JP5014807B2 (en) | 2012-08-29 |
Family
ID=39697825
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2007005691A Active JP5014807B2 (en) | 2007-01-15 | 2007-01-15 | Steel sheet for hot press |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP5014807B2 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5421062B2 (en) * | 2008-10-23 | 2014-02-19 | 株式会社神戸製鋼所 | Hardened steel plate and high strength member |
| JP5316025B2 (en) * | 2009-01-28 | 2013-10-16 | Ｊｆｅスチール株式会社 | Die quench steel plate with excellent hot punchability |
| JP5316026B2 (en) * | 2009-01-28 | 2013-10-16 | Ｊｆｅスチール株式会社 | Die quench steel plate with excellent hot punchability |
| JP5316027B2 (en) * | 2009-01-28 | 2013-10-16 | Ｊｆｅスチール株式会社 | Die quench steel plate with excellent hot punchability |
| EP2527481B1 (en) * | 2009-12-30 | 2014-12-17 | Hyundai Steel Company | Quenched steel sheet having excellent hot press formability, and method for manufacturing same |
| US9353424B2 (en) * | 2013-03-14 | 2016-05-31 | Nippon Steel & Sumitomo Metal Corporation | High strength steel sheet excellent in delayed fracture resistance and low temperature toughness, and high strength member manufactured using the same |
| WO2017163098A1 (en) * | 2016-03-25 | 2017-09-28 | Arcelormittal | Process for manufacturing cold-rolled and welded steel sheets, and sheets thus produced |
| WO2019003449A1 (en) | 2017-06-30 | 2019-01-03 | Ｊｆｅスチール株式会社 | Hot-pressed member and method for manufacturing same, and cold-rolled steel sheet for hot pressing |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3896061B2 (en) * | 2002-10-07 | 2007-03-22 | 新日本製鐵株式会社 | Steel sheet with excellent curability after hot forming and method of using the same |
| JP2004337923A (en) * | 2003-05-15 | 2004-12-02 | Sumitomo Metal Ind Ltd | Manufacturing method of steel for hot forming |
| JP2005262232A (en) * | 2004-03-16 | 2005-09-29 | Nippon Steel Corp | Hot forming method |
-
2007
- 2007-01-15 JP JP2007005691A patent/JP5014807B2/en active Active
Also Published As
| Publication number | Publication date |
|---|---|
| JP2008169452A (en) | 2008-07-24 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5206244B2 (en) | Cold rolled steel sheet | |
| JP5598157B2 (en) | Steel sheet for hot press excellent in delayed fracture resistance and collision safety and method for producing the same | |
| JP5014807B2 (en) | Steel sheet for hot press | |
| WO2012157581A1 (en) | Hot stamp molded article, method for producing hot stamp molded article, energy absorbing member, and method for producing energy absorbing member | |
| JP2005126733A (en) | Steel sheet for hot press having excellent hot workability, and automotive member | |
| JP4254663B2 (en) | High strength thin steel sheet and method for producing the same | |
| CN110042321B9 (en) | HPF molded member having bendability and method for producing same | |
| EP2768989B1 (en) | High strength hot dip galvanised steel strip | |
| TWI460292B (en) | Ferritic stainless steel | |
| JP2017512247A (en) | Steel plate products, steel parts manufactured from these steel plate products, and automobile bodies | |
| EP2653582A1 (en) | Hot-dip zinc-plated steel sheet and process for production thereof | |
| JP4495064B2 (en) | Steel sheet for hot press | |
| KR20120087185A (en) | High strength hot dip galvanised steel strip | |
| JP6606897B2 (en) | Steel plate for heat treatment, method for producing the same, and hot stamped product | |
| JP4317491B2 (en) | Steel sheet for hot press | |
| JP4987272B2 (en) | Manufacturing method of high-strength parts and high-strength parts | |
| JP5692305B2 (en) | Thick steel plate with excellent heat input welding characteristics and material homogeneity, and its manufacturing method | |
| JP4984933B2 (en) | Hot rolled steel sheet for tailored blanks and tailored blanks | |
| JP4551300B2 (en) | Manufacturing method of high strength parts | |
| JP6417977B2 (en) | Steel plate blank | |
| JP5549618B2 (en) | High strength steel plate for spot welding with a tensile strength of 980 MPa or more | |
| JP5929556B2 (en) | Method for producing continuous cast slab and method for producing high-strength cold-rolled steel sheet | |
| JP4551169B2 (en) | Manufacturing method of high strength parts | |
| JPH10251794A (en) | Hot rolled steel plate for structural purpose, excellent in press formability and surface characteristic, and its production | |
| JP6179609B2 (en) | Manufacturing method of thick high-strength steel sheet with excellent cold workability |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20090217 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20110830 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20111019 |
|
| 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: 20120529 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20120606 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150615 Year of fee payment: 3 |
|
| R151 | Written notification of patent or utility model registration |
Ref document number: 5014807 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R151 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150615 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150615 Year of fee payment: 3 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150615 Year of fee payment: 3 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |