J. Phys. IV France
Volume 115, June 2004
Page(s) 251 - 258

J. Phys. IV France
115 (2004) 251
DOI: 10.1051/jp4:2004115030

Press formability YAG laser welded TRIP/DP tailored blanks

A. Nagasaka1, K.I. Sugimoto2, M. Kobayashi2, K. Makii3 and S. Ikeda3

1  Department of Mechanical Engineering, Nagano National College of Technology, 716 Tokuma, Nagano 381-8550, Japan
2  Department of Mechanical Systems Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
3  Materials Research Laboratory, Kobe Steel, Ltd., 5-5 Takatsukadai, 1-chome, Nishi-ku, Kobe, Hyogo 651-2271, Japan

In the present work, to improve the press formability of the combination of the TRIP steel and ferrite-martensite dual-phase (DP) steel, the mechanical properties and press formability (stretch-formability) of YAG laser welded TRIP/DP tailored blanks were investigated. An as-cold-rolled sheet steel with the chemical composition of (0.1-0.3)C-1.5Si-1.5Mn (mass%) was used in this study. For comparison, 0.14C-0.22Si-1.78Mn (mass%) DP steel was also prepared. The quenched DP steel is called MDP0, and the tempered MDP0 steel is called MDP4. For butt welding, the blank obtained after the heat treatment was cut using a fine cutter, and YAG laser processing equipment was used. The press formability was evaluated from the maximum stretch-height ( $H_{\max}$). Tensile tests and stretch forming tests have been conducted for laser butt welded joints obtained from the combination of the different steel. The $H_{\max}$ value of the MDP0 steel was not controlled at the strength level of the DP steel, and was not different from the $H_{\max}$ value of the MDP4 steel. It is thought that this was assisted to TRIP of the TDP steel because the tensile strength of the TDP steel is consequentially lower than that of the MDP0 steel. High ductility and the high stretch-formability were able to be secured by the high strength TRIP/DP tailored blanks.

© EDP Sciences 2004