JP2010236560A - Method of manufacturing structural member having improved impact absorbing characteristics - Google Patents
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Abstract
Description
本発明は、クラッシュボックスやフロントフレーム等の衝撃吸収特性に優れた自動車構造部材の製造方法に関する。 The present invention relates to a method for manufacturing an automobile structural member having excellent shock absorption characteristics such as a crash box and a front frame.
衝突安全性の面から、車体構造としては、自動車衝突時の衝撃エネルギーを客室以外の構造部材の塑性変形で吸収させ、客室部（以下、キャビンと記す）の変形を最小限に抑えて生存空間を確保する車体構造が、広く一般的に採用されている。この場合、クラッシュボックスやフロントフレーム等の構造部材で衝撃エネルギーをいかに有効に吸収させるかが重要になる。
一般に、自動車構造部材はハット型の閉断面で構成したもので、長手方向（軸方向）に衝撃荷重を受けたとき、蛇腹状に座屈変形することで衝撃エネルギーを吸収するように設計される。この際、衝撃吸収特性を高めるためには、規則正しく蛇腹状の座屈変形を生じさせ、かつ、座屈初期のピーク荷重を下げることが重要である。
From the aspect of collision safety, the vehicle body structure absorbs the impact energy at the time of automobile collision by plastic deformation of structural members other than the passenger cabin, and minimizes the deformation of the passenger cabin (hereinafter referred to as the cabin) to minimize the living space. A vehicle body structure that secures this is widely and generally adopted. In this case, it is important how to effectively absorb the impact energy by a structural member such as a crash box or a front frame.
Generally, an automobile structural member is configured with a hat-shaped closed cross section, and is designed to absorb impact energy by buckling and deforming in a bellows shape when subjected to an impact load in the longitudinal direction (axial direction). . At this time, in order to improve the shock absorption characteristics, it is important to regularly generate bellows-like buckling deformation and lower the peak load at the initial buckling.
例えば、自動車のフロントフレームは基端部をキャビンと、また先端部はクラッシュボックスやバンパー補強部材と固着された状態でフェンダーパネルと平行して配置されている。衝突事故時に自動車が正面衝突した場合、このクラッシュボックスやフロントフレーム先端には衝撃荷重が加わって軸方向に座屈変形を起こすが、衝突初期の荷重は比較的大きくなる傾向がある。そこで、１５ｋｍ／ｈ以下の軽衝突時には座屈初期のピーク荷重を下げてフロントフレームを含むキャビン等の後方に配置された別の構造部材の損傷を防止し（以下、本明細書ではこの要求性能を「ダメージャビリティ」と記す）、かつ、それ以上の高速衝突時ではフロントフレームの衝突面側からキャビン側に向けて順次に塑性変形が進行するよう、規則正しく蛇腹状に座屈変形することが要求されている。 For example, a front frame of an automobile is arranged in parallel with a fender panel in a state where a base end portion is fixed to a cabin and a front end portion is fixed to a crash box or a bumper reinforcing member. When a car collides head-on at the time of a collision accident, an impact load is applied to the front end of the crash box and the front frame to cause buckling deformation in the axial direction, but the load at the beginning of the collision tends to be relatively large. Therefore, at the time of a light collision of 15 km / h or less, the peak load in the initial buckling is lowered to prevent damage to other structural members disposed behind the cabin including the front frame (hereinafter, this required performance is referred to in this specification). Can be buckled and deformed regularly in a bellows shape so that the plastic deformation progresses sequentially from the collision surface side of the front frame toward the cabin during high-speed collisions. It is requested.
従来、上記課題を解決するため、例えば特許文献１に見られるように、潰れビードと呼ばれる変形の端緒を与える窪みを構造部材に配置する対策が取られてきた。特許文献１で提案されている構造部材は、等間隔に構造面で弱い潰れビードを配置してその部位を優先的に変形させて、より低い荷重で対象とする構造部材の初期座屈を誘発させ（ダメージャビリティの性能を付与させ）、かつ、構造部材全体を規則正しく蛇腹状に座屈変形させるものである。
また、特許文献２では、事前に８００〜１１００℃に加熱した鋼板を、プレス成形と同時に所定部位を急冷熱処理（一般にダイクエンチと呼ばれる）して硬化させ、硬質部と軟質部を共存させる手段により、１枚の鋼板から部分毎に強度の異なる構造部材用のＵ字加工品の成形方法が提案されている。
Conventionally, in order to solve the above-described problem, for example, as seen in Patent Document 1, a measure has been taken in which a recess called a crush bead that gives an indication of deformation is arranged in a structural member. The structural member proposed in Patent Document 1 induces initial buckling of the target structural member with a lower load by arranging weak crush beads on the structural surface at equal intervals and preferentially deforming the part. (The ability of damage ability is imparted), and the entire structural member is regularly buckled and deformed in a bellows shape.
Moreover, in patent document 2, the steel plate heated to 800-1100 degreeC in advance is hardened by quenching a predetermined site | part simultaneously with press molding (generally called die quench), and the means to which a hard part and a soft part coexist, A method of forming a U-shaped product for a structural member having a different strength for each portion from a single steel sheet has been proposed.
しかしながら、特許文献１で提案された、いわゆる潰れビードを配置する対策では、複数の潰れビードを設ける必要があることから、低強度の普通鋼板を素材とする場合は問題ないが、高強度普通鋼板を用いて製作する場合はプレス成形が難しく、作業が煩雑になり易いといった問題がある。すなわち、鋼板が高強度化するにつれて鋼板の伸び等の成形性が低下することから、プレス成形で複数の潰れビードを設ける場合には素材に割れを生じ易く、製品形状が制約されたり、あるいは、割れ抑制手段としてのプレス工程の多工程化が附随したりするといった欠点があった。
自動車の衝突安全性の面からみると、延性の低下は衝突時に構造部材の潰れビード等（プレス成形時にひずみが付与された部位）において耐割れ性に悪影響を及ぼす。さらに、プレス成形で潰れビードを形成させるため、車種ごとに対象とする構造部材のサイズや形状も異なることから、保有する金型点数が膨大になり製造コストアップに繋がり易いといった欠点もあった。
However, in the measure proposed by Patent Document 1 for arranging so-called crushed beads, it is necessary to provide a plurality of crushed beads. In the case of manufacturing using, there is a problem that press molding is difficult and the work is likely to be complicated. That is, because the formability such as the elongation of the steel sheet decreases as the steel sheet becomes stronger, when forming a plurality of crushed beads by press molding, the material is likely to crack, and the product shape is restricted, or There is a drawback that a multi-step press process as a means for suppressing cracking is accompanied.
From the standpoint of automobile crash safety, the reduction in ductility adversely affects cracking resistance in a crush bead or the like of a structural member at a collision (a portion to which strain is applied during press molding). Furthermore, since the crushing beads are formed by press molding, the size and shape of the target structural member are different for each vehicle type, so that there is a drawback that the number of molds to be held becomes enormous and the manufacturing cost tends to increase.
また、ダイクエンチを活用して硬質部と軟質部を１枚の鋼板に共存させる特許文献２の対策では、作業の煩雑さ等を大幅に軽減するといった長所を有するが、硬質部で延性の低下を招くことから、衝突時における構造部材の母材割れに対して有効な処置を講じることはできない。
本発明は、これらの現状に鑑みて発明されたものであり、鋼板の高強度化を実施した場合においても製品形状の制約や作業の煩雑性といった問題を伴わず、かつ、プレス成形時や自動車衝突時の母材割れ抑制にも有効な衝撃吸収特性に優れた自動車構造部材の製造方法を提供することを目的とするものである。
In addition, the countermeasure of Patent Document 2 in which a hard part and a soft part coexist on a single steel sheet by utilizing die quenching has the advantage of greatly reducing the complexity of work, but the hard part reduces ductility. Therefore, it is impossible to take an effective measure against the crack of the base material of the structural member at the time of collision.
The present invention has been invented in view of these current situations, and does not suffer from problems such as product shape restrictions and work complexity even when the strength of a steel plate is increased, and is also suitable for press molding and automobiles. It is an object of the present invention to provide a method for manufacturing an automobile structural member having excellent shock absorption characteristics that is effective in suppressing cracking of a base material at the time of a collision.
本発明の衝撃吸収特性に優れた構造部材の製造方法は、その目的を達成するため、Ｃ：０.０８質量％以下、Ｓｉ：１.０質量％以下、Ｍｎ：２.０質量％以下、Ｎｉ：８.０〜１０.５質量％、Ｃｒ：１８.０〜２０.０質量％を含む成分を有し、圧延率が１５〜２５％の冷間調質圧延を実施したオーステナイト系ステンレス調質圧延鋼板を素材としたハット型閉断面構造を有する構造部材の各壁面鋼板に、前記構造部材の長手方向に直角な帯状の低強度部を、前記構造部材の長手方向に所定の間隔を空けて形成することを特徴する。
帯状の低強度部は、当該部分を固溶化熱処理温度まで部分加熱することにより形成することが好ましい。この部分加熱は、レーザー照射やＴＩＧ溶接トーチを用いた照射によりなすことができる。
In order to achieve the object, the method for producing a structural member having excellent shock absorption characteristics according to the present invention includes C: 0.08% by mass or less, Si: 1.0% by mass or less, Mn: 2.0% by mass or less, Austenitic stainless steel having a component containing Ni: 8.0 to 10.5% by mass and Cr: 18.0 to 20.0% by mass and subjected to cold temper rolling with a rolling rate of 15 to 25%. A strip-shaped low-strength portion perpendicular to the longitudinal direction of the structural member is provided at a predetermined interval in the longitudinal direction of the structural member on each wall surface steel plate having a hat-type closed cross-section structure made of textured steel plate. It is characterized by forming.
The band-shaped low-strength part is preferably formed by partially heating the part to the solution heat treatment temperature. This partial heating can be performed by laser irradiation or irradiation using a TIG welding torch.
本発明によれば、車種ごとに異なる製品形状の制約やプレス成形金型点数の増大といった問題がなく、かつ、プレス成形時や自動車衝突時の母材割れ抑制にも有効な衝撃吸収特性に優れたハット型閉断面構造部材を製造できる。 According to the present invention, there are no problems such as restrictions on the product shape that are different for each vehicle type and an increase in the number of press molding dies, and excellent shock absorption characteristics that are effective in suppressing cracking of the base metal during press molding or automobile collision. A hat-type closed cross-section structural member can be manufactured.
本発明者等は、自動車構造部材のうち、高い衝撃吸収特性等が要求される構造部材に好適な素材について種々検討を重ねてきた。その結果、ハット型閉断面形状の構造部材が座屈変形時に母材割れを招くことなく、蛇腹状に塑性変形して自動車衝突時の衝撃エネルギーを効率良く吸収させるためには、高強度と高延性とを兼備したオーステナイト系ステンレス調質圧延鋼板で自動車構造部材を製作することが有効であるとの知見を得た。
なかでも、固溶化熱処理温度まで部分加熱して形成した低強度の部位を、構造部材の長手方向にわたって所定の間隔を空けて形成させた場合、衝撃吸収特性の再現性とダメージャビリティの向上に有効であることを見出した。
以下、本発明で使用するオーステナイト系ステンレス調質圧延鋼板の成分・含有量や調質圧延の冷間圧延率等を個別に説明する。
The inventors of the present invention have made various studies on materials suitable for structural members that require high shock absorption characteristics and the like among automobile structural members. As a result, in order for the hat-shaped closed cross-section structural member to be plastically deformed in a bellows shape without causing cracks in the base material during buckling deformation and to efficiently absorb the impact energy at the time of automobile collision, We have obtained the knowledge that it is effective to manufacture automotive structural members with austenitic stainless temper rolled steel sheet that has both ductility and ductility.
In particular, when low-strength parts formed by partial heating up to the solution heat treatment temperature are formed at predetermined intervals along the longitudinal direction of the structural member, the reproducibility of impact absorption characteristics and the improvement of damageability are improved. I found it effective.
Hereinafter, the components and contents of the austenitic stainless temper rolled steel sheet used in the present invention, the cold rolling rate of temper rolling, and the like will be individually described.
〔成分設計〕
Ｃ：０.０８質量％以下
高強度化に重要な合金成分であり、強度上昇に伴い衝撃吸収特性も向上する。この点、多量のＣを含有することが好ましいが、過剰量のＣはプレス成形性や溶接性に悪影響を及ぼすので０.０８質量％を上限とした。
(Ingredient design)
C: 0.08% by mass or less C is an alloy component important for increasing the strength, and the impact absorption characteristics are improved as the strength is increased. In this respect, it is preferable to contain a large amount of C, but an excessive amount of C adversely affects press formability and weldability, so 0.08 mass% was made the upper limit.
Ｓｉ：１.０質量％以下
脱酸剤として添加される成分であるが、鋼材を固溶強化する作用もある。しかし、過剰な含有はプレス成形性に悪影響を及ぼすので、１.０質量％を上限とする。
Si: 1.0% by mass or less Si is a component added as a deoxidizing agent, but also has an effect of strengthening the solid solution. However, excessive content adversely affects press formability, so 1.0 mass% is the upper limit.
Ｍｎ：２.０質量％以下
高温域でδフェライトの生成を抑制する作用があるが、過剰添加は耐食性にとって好ましくないので２.０質量％を上限とした。
Mn: 2.0% by mass or less Although there is an effect of suppressing the formation of δ ferrite in a high temperature range, excessive addition is not preferable for corrosion resistance, so 2.0% by mass was made the upper limit.
Ｎｉ：８.０〜１０.５質量％
オーステナイト形成に必要な合金成分であり、耐食性向上にも寄与する。本成分系でＮｉ添加の効果を得るためには、８.０質量％のＮｉが必要である。しかし、高価な元素であり、１０.５質量％を超えて添加しても耐食性改善効果は飽和し、経済的にも不利である。
Ni: 8.0 to 10.5% by mass
It is an alloy component necessary for austenite formation and contributes to improvement of corrosion resistance. In order to obtain the effect of adding Ni in this component system, 8.0% by mass of Ni is required. However, it is an expensive element, and even if added in excess of 10.5 mass%, the effect of improving corrosion resistance is saturated, which is disadvantageous economically.
Ｃｒ：１８.０〜２０.０質量％
耐食性向上に必須な元素であり、構造部材の使用箇所によっては高強度普通鋼板で採用されているめっきの省略が可能である。構造部材に必要な耐食性を確実にする上で、Ｃｒ含有量を１８.０質量％以上とした。一方、過剰Ｃｒは、高温域で生成したδフェライトが残留し、加工性に悪影響を与える原因になる。また、オーステナイト組織を維持するため、Ｃｒの増量に見合ってＮｉ添加量も増やす必要があるので経済的にも不利である。したがって、Ｃｒの上限は２０.０質量％とする。
なお、Ｐ、Ｓ、Ｃｕ、Ｍｏ、Ｎｂ、Ｖ、Ｔｉ、Ｍｇ、Ａｌ等の元素が製鋼段階で不可避的に混入する場合があるが、それらの元素は、目的をもって添加されたものではないので、本明細書では不可避的不純物として取り扱うことにする。
Cr: 18.0 to 20.0 mass%
It is an element indispensable for improving corrosion resistance, and depending on the use location of the structural member, it is possible to omit the plating adopted in the high-strength ordinary steel plate. In order to ensure the corrosion resistance necessary for the structural member, the Cr content is set to 18.0% by mass or more. On the other hand, excess Cr causes the δ ferrite generated in the high temperature region to remain, which adversely affects workability. Further, in order to maintain the austenite structure, it is also economically disadvantageous because the amount of Ni added needs to be increased in accordance with the increase in Cr. Therefore, the upper limit of Cr is 20.0 mass%.
In addition, elements such as P, S, Cu, Mo, Nb, V, Ti, Mg, and Al may be inevitably mixed in the steel making stage, but these elements are not added for the purpose. In this specification, it is treated as an inevitable impurity.
調質圧延の冷間圧延率：
本実施の形態のオーステナイト系ステンレス調質圧延鋼板は、熱間圧延を施したオーステナイト系ステンレス熱延鋼板に対して焼鈍および酸洗を実施し、次に所望の板厚にするための中間冷間圧延および中間焼鈍を適当な回数だけ繰返した後、引張強さが７００ＭＰａ以上となるよう、最終工程で調質圧延の冷間圧延率を１５％以上に設定して加工を行って得られたものである。ただし、冷間圧延率を高めるほど鋼板の引張強さは増大するが、延性の低下を招いてプレス成形時や自動車の衝突時に母材割れを引き起こし易くなるため、全伸びが２０％以上を確保できるよう、冷間圧延率は２５％を上限とする。
ここで、「冷間圧延率（％）」は（１−圧延後板厚／圧延素材板厚）×１００により規定される。
Cold rolling ratio of temper rolling:
The austenitic stainless tempered rolled steel sheet of the present embodiment is subjected to annealing and pickling on the hot-rolled austenitic stainless hot rolled steel sheet, and then intermediate cold for making a desired sheet thickness After rolling and intermediate annealing an appropriate number of times, and obtained by processing with the cold rolling rate of temper rolling set to 15% or more in the final step so that the tensile strength is 700 MPa or more It is. However, the higher the cold rolling rate, the greater the tensile strength of the steel sheet. However, the ductility is reduced and it is easy to cause cracking of the base metal at the time of press molding or automobile collision. The upper limit of the cold rolling rate is 25% so that it is possible.
Here, the “cold rolling rate (%)” is defined by (1−post-rolling sheet thickness / rolling material sheet thickness) × 100.
熱処理：
本実施の形態の構造部材は、所定の成分と冷間調質圧延率に調整して得られたオーステナイト系ステンレス調質圧延鋼板をハット型閉断面形状にプレス加工して組み立てるが、自動車衝突時の蛇腹状の座屈変形の基点となる、構造的に弱い部位を等間隔に配置させる。具体的には、ハット曲げを目的としたプレス加工の後に構造部材の長手方向にわたって所定間隔を空けて複数箇所に、例えばレーザー照射やＴＩＧ溶接トーチを用いた照射で固溶化熱処理を加えることにより低強度部位を形成すればよい。
Heat treatment:
The structural member of the present embodiment is assembled by pressing austenitic stainless tempered rolled steel sheet obtained by adjusting to a predetermined component and a cold temper rolling ratio into a hat-shaped closed cross-sectional shape. The structurally weak parts that are the base points of the bellows-shaped buckling deformation are arranged at equal intervals. Specifically, after press working for hat bending, a low temperature is obtained by applying a solution heat treatment at a plurality of locations at predetermined intervals along the longitudinal direction of the structural member, for example, by laser irradiation or irradiation using a TIG welding torch. What is necessary is just to form an intensity | strength site | part.
調質圧延による加工ひずみと金属組織の変態（オーステナイト組織→マルテンサイト組織）によって硬化した鋼板は、１０００℃以上に加熱して急冷すると、オーステナイト組織に戻って軟化する。ただし、１１５０℃以上の温度に過熱した場合はオーステナイト組織中にフェライト組織を生じやすい。したがって、加熱温度範囲は１０００〜１１５０℃が望ましい。また、この適正加熱温度より急冷することでオーステナイト組織が得られるが、この急冷は炭化物析出温度範囲（４５０〜８５０℃）を迅速に冷却し、耐食性に悪影響を及ぼす結晶粒界での炭化物の析出を防止するためである。
冷却方法については水冷、空冷等の手段によって行い、必要な冷却能力に応じてそれらを選定すればよい。
When the steel sheet hardened by deformation due to temper rolling and transformation of the metal structure (austenite structure → martensite structure) is heated to 1000 ° C. or higher and rapidly cooled, it returns to the austenite structure and softens. However, when it is heated to a temperature of 1150 ° C. or higher, a ferrite structure tends to be formed in the austenite structure. Therefore, the heating temperature range is desirably 1000 to 1150 ° C. In addition, an austenite structure can be obtained by rapidly cooling from the proper heating temperature. This rapid cooling rapidly cools the carbide precipitation temperature range (450 to 850 ° C.), and precipitates carbide at grain boundaries that adversely affect corrosion resistance. It is for preventing.
About a cooling method, it may carry out by means, such as water cooling and air cooling, and should just select them according to required cooling capacity.
表１の化学成分を有する鋼板を真空溶解炉で１００ｋｇ溶解し、鍛造、熱間圧延を経て板厚：２.５〜４.０ｍｍの熱延鋼板を製造した。表中のＡが本発明で規定した化学成分の条件を満足するオーステナイト系ステンレス鋼であり、Ｂは比較に用いたフェライト系の普通鋼である。
なお、鋼Ａおよび鋼Ｂともに、残部はＦｅと不可避的不純物からなる。
次に、１１００℃×均熱６０秒→炉冷の焼鈍を施し、酸洗後に冷間圧延し、１０８０℃×均熱６０秒→空冷の仕上げ焼鈍と冷間圧延率：２０％の調質圧延を施して板厚：１.２ｍｍの冷間調質圧延材を得た。比較に用いた素材としては、板厚：１.２ｍｍの冷間圧延焼鈍材を準備した。
プレス成形前の素材による引張試験で得られた機械的性質の調査結果を表２に示す。
100 kg of a steel plate having the chemical components shown in Table 1 was melted in a vacuum melting furnace and subjected to forging and hot rolling to produce a hot rolled steel plate having a thickness of 2.5 to 4.0 mm. A in the table is an austenitic stainless steel that satisfies the conditions of the chemical components defined in the present invention, and B is a ferritic plain steel used for comparison.
Note that the balance of both steel A and steel B is made of Fe and inevitable impurities.
Next, 1100 ° C. × soaking 60 seconds → furnace cooling annealing, pickling and cold rolling, 1080 ° C. × soaking 60 seconds → air cooling finish annealing and cold rolling rate: temper rolling at 20% To obtain a cold-tempered rolled material having a thickness of 1.2 mm. As a material used for comparison, a cold-rolled annealing material having a thickness of 1.2 mm was prepared.
Table 2 shows the survey results of the mechanical properties obtained by the tensile test using the material before press molding.
ハット型閉断面構造部材の閉断面形状を図１に示す。ハット型閉断面構造部材は、表２に示した３種類の鋼板を用いてプレス成形したフランジ付きのＵ字加工品（すなわち、ハット型断面板）１１と平板状の背面板１２をスポット溶接によって接合したものである。
ハット型閉断面構造部材の寸法は、板厚１.２ｍｍ、高さ３００ｍｍ、正四角形閉断面の一辺の長さ７０ｍｍ、フランジ長さ２０ｍｍ、コーナＲ半径５ｍｍである。スポット溶接は３０ｍｍ間隔で実施した。
長手方向の所定間隔ごとに部分加熱して固溶化熱処理を施す手段としては、レーザー照射を用いた。レーザー照射条件は炭素ガスレーザー装置を用い、出力３ｋＷ、走行速度３ｍ／分とした。この実施例では、図２に示すように、ハット型閉断面構造部材の長手方向と直角をなす７０ｍｍ間隔の帯状の部分加熱部（軟化部）２１を複数個設けた。
The closed cross-sectional shape of the hat-type closed cross-section structural member is shown in FIG. The hat-type closed cross-section structural member is formed by spot welding a flanged U-shaped product (that is, a hat-type cross-section plate) 11 and a flat plate-
The dimensions of the hat-type closed cross-section structural member are a plate thickness of 1.2 mm, a height of 300 mm, a length of one side of a regular square closed cross section of 70 mm, a flange length of 20 mm, and a corner R radius of 5 mm. Spot welding was performed at intervals of 30 mm.
Laser irradiation was used as a means for performing a solution heat treatment by partial heating at predetermined intervals in the longitudinal direction. The laser irradiation conditions were a carbon gas laser device, with an output of 3 kW and a traveling speed of 3 m / min. In this embodiment, as shown in FIG. 2, a plurality of band-shaped partial heating portions (softening portions) 21 with a spacing of 70 mm perpendicular to the longitudinal direction of the hat-type closed cross-section structural member are provided.
構造部材に要求される衝撃吸収特性等に関する評価試験は、ハット型閉断面構造部材の一端を固定し、他端面に自動車衝突時に匹敵する速度で落錘を落下させる試験（この試験方法を本明細書中では、以下「落重試験」と記す）を実施し、構造部材の座屈形態や母材割れの発生有無の外観観察、並びに構造部材の衝撃吸収特性の測定を行って評価した。
なお、落重試験は、その概念図を図３に示すように、ハット型閉断面構造部材の軸方向に衝撃荷重を作用させて軸圧潰させた場合のハット型閉断面部材に作用する荷重と変位の関係を調査するための試験方法である。
An evaluation test related to shock absorption characteristics required for structural members is a test in which one end of a hat-type closed cross-section structural member is fixed, and a falling weight is dropped on the other end surface at a speed comparable to that in a car collision (this test method is described in this specification). In the document, the following “falling weight test”) was carried out, and the evaluation was performed by observing the appearance of the buckling form of the structural member and the presence / absence of cracking of the base material, and measuring the impact absorption characteristics of the structural member.
The drop weight test is a conceptual diagram of the load acting on the hat-type closed cross-section member when the impact load is applied to the axial direction of the hat-type closed cross-section structural member and the shaft is crushed as shown in FIG. This is a test method for investigating the relationship of displacement.
実際の落重試験では、ハット型閉断面構造部材３１の長手方向を鉛直にしてロードセル３２を組み込んだ台座３３の上に載せ、１９０ｋｇの落錘３４を５１ｋｍ／ｈの速度で衝突させてハット型閉断面構造部材を軸方向に圧潰させた。なお、ハット型閉断面構造部材を１８０ｍｍ押し潰した後は、落錘が停止するよう、ストッパー３５の高さを調整した。そして、落錘が構造部材に衝突した以降の移動量（以下、変位と記す）は、非接触式変位計（図示せず）を用いて連続測定し、荷重−変位曲線を得た。
In an actual drop test, the hat-shaped closed cross-section
図４は、上記落重試験で測定した、落錘による衝撃荷重が構造部材の軸方向に作用する際の推移を概念的に示した荷重−変位曲線のグラフである。この場合、構造部材は、図５に示すように、長手方向の複数箇所で座屈を生じて蛇腹状に圧潰する。また、この座屈の発生と対応して、荷重−変位曲線上では、複数の荷重ピーク値が周期的に現れる。ここで、任意の変位毎に荷重値を積算して得られる、すなわち図中の荷重−変位曲線内に囲まれた面積が、１８０ｍｍまで圧潰した際に、落重試験に供した構造部材が吸収した衝撃エネルギー量である。ダメージャビリティを評価する指標に対しては、荷重−変位曲線の初期に現れる荷重のピーク値（以下、初期ピーク荷重と記す）を用いた。
上記の落重試験で得られた評価結果を表３に示す。
FIG. 4 is a graph of a load-displacement curve conceptually showing the transition when the impact load due to the falling weight acts in the axial direction of the structural member, measured in the drop weight test. In this case, as shown in FIG. 5, the structural member is buckled at a plurality of locations in the longitudinal direction and crushed into a bellows shape. Corresponding to the occurrence of buckling, a plurality of load peak values appear periodically on the load-displacement curve. Here, it is obtained by integrating the load value for each arbitrary displacement, that is, when the area surrounded by the load-displacement curve in the figure is collapsed to 180 mm, the structural member subjected to the drop weight test absorbs it. The amount of impact energy. As an index for evaluating damage ability, a load peak value (hereinafter referred to as an initial peak load) appearing at an early stage of a load-displacement curve was used.
Table 3 shows the evaluation results obtained in the drop weight test.
表３から明らかなように、本発明例の条件に基づいて構造部材を製作した場合、落重試験による母材割れを生じることなく規則正しく蛇腹状に軸圧潰変形し、衝撃吸収エネルギー量の向上と初期ピーク荷重の低減を兼ね備えた構造部材が得られた。
これに対して、レーザー照射による部分加熱を実施しない比較例１では、図６のような、不安定な座屈形態を呈し、衝撃吸収エネルギー量の低下と初期ピーク荷重の増大を招くことが分かった。冷間調質圧延を行っていない比較例２の場合は、加工ひずみとマルテンサイト化による鋼板の高強度化効果が得られず、鋼板の引張強さが大幅に不足して衝撃吸収エネルギー量の著しい低下を招いた。
As is apparent from Table 3, when a structural member was manufactured based on the conditions of the present invention example, the shaft was deformed in a regular bellows shape without cracking the base material in the drop weight test, and the amount of energy absorbed was improved. A structural member having a reduction in initial peak load was obtained.
On the other hand, in Comparative Example 1 in which partial heating by laser irradiation is not performed, it is found that an unstable buckling form as shown in FIG. 6 is exhibited, resulting in a decrease in the amount of shock absorption energy and an increase in the initial peak load. It was. In the case of Comparative Example 2 in which cold temper rolling is not performed, the effect of increasing the strength of the steel sheet due to work strain and martensite cannot be obtained, and the tensile strength of the steel sheet is greatly insufficient, resulting in an impact absorption energy amount of It caused a significant decline.
また、本発明で規定した化学成分の条件を満足しない鋼種（すなわち、金属組織がフェライト系の普通鋼）をもとに構造部材を製作した比較例３では、衝撃吸収エネルギー量がやや低く、初期ピーク荷重は逆に高くなるとともに、素材の延性不足から、落重試験後の構造部材に母材割れを生じた。ここで、初期ピーク荷重が高めの傾向を示すのは、金属組織の違いから、レーザー照射による部分加熱部では軟化せず、逆に硬化して高強度化作用をもたらしたことが原因である。 Further, in Comparative Example 3 in which a structural member was manufactured based on a steel type that does not satisfy the chemical component conditions defined in the present invention (that is, a ferritic plain steel having a metal structure), the amount of shock absorption energy is slightly low, On the contrary, the peak load increased, and due to insufficient ductility of the material, the base material cracked in the structural member after the drop weight test. Here, the reason why the initial peak load tends to be high is that due to the difference in the metal structure, the partial heating portion by laser irradiation does not soften, but conversely hardens and has an effect of increasing strength.
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| JP2022148375A (en) * | 2021-03-24 | 2022-10-06 | 豊田鉄工株式会社 | Vehicle structural member |
| JP7555868B2 (en) | 2021-03-24 | 2024-09-25 | 豊田鉄工株式会社 | Method for manufacturing a vehicle structural member |
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