Steel sheets partnered with quenchable sheet in hot stamping of tailor-welded blanks and its application to separation p
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ORIGINAL ARTICLE
Steel sheets partnered with quenchable sheet in hot stamping of tailor-welded blanks and its application to separation prevention of fractured components Ken-ichiro Mori 1 & Yasutaka Suzuki 2 & Daisuke Yokoo 1 & Michiya Nishikata 1 & Yohei Abe 1 Received: 21 May 2020 / Accepted: 14 September 2020 / Published online: 3 October 2020 # The Author(s) 2020
Abstract The phase transformation and mechanical properties of non-quenchable steels partnered with the quenchable boron steel in hot stamping of tailor-welded blanks were evaluated to produce tailored components with partially balanced strength and ductility. The effect of the forming start temperature after natural air cooling on the phase transformation and mechanical properties for 270 MPa mild steel, non-quenchable steel, 440 MPa high strength steel, and 22MnB5 steel sheets was examined, and the 270 MPa and non-quenchable sheets had enough ductility after hot stamping. Tailored components having a hardness of about 500 HV1 in the high strength zone and a total elongation of about 30% in the high ductility zone were hot-stamped from a tailor-welded blank composed of 22MnB5 and 270 MPa sheets. It was found that the 270 MPa mild steel sheet is sufficient as a partner sheet of tailorwelded blanks. In addition, the safety of hot-stamped components was heightened by welding a 22MnB5 main blank with a 270 MPa steel patch. Even if the main blank is fractured by a collision, the hot-stamped component is not separated by the 270 MPa patch having high ductility. Keywords Hot stamping . Tailor-welded blank . Partner steel sheet . Ductility . Component separation
1 Introduction To heighten the crash safety of automobiles without weight increase, ultra-high strength steel components of body-inwhite have been increasingly produced by hot stamping. In hot stamping, heated quenchable steel sheets are formed and then are quenched by being held with cold dies at the bottom dead centre of a press [1]. The high strength of the components is gained by means of microstructure control through both austenite and martensite transformations, and the heat treatments are included in stamping operations. Die quenching leads to another advantage of small springback of hot-stamped components due to plastic deformation induced by volume expansion of the martensitic transformation during holding at the bottom
* Ken-ichiro Mori [email protected] 1
Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan
2
TOA Industries Co., Ltd., 26-1 Nishishin-machi, Oota 373-0847, Japan
dead centre [2]. Most of steel sheets used for hot stamping are manganese-boron steel 22MnB5, and the tensile strength of the formed components is about 1.5 GPa. The superiority of the high strength for hot stamping is being lowered by the development of new 1.5 GPa ultra-high strength steel sheets used for cold stamping [3], because cold stamping has the advantages of high productivity, conventional and cheaper equipment, no oxidation prevention trea
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