Properties of the weld joints of a bake hardening steel (BH steel) for automobile were investigated. In the first experiment, the BH steel was plastically strained followed by Nd:YAG laser welding or TIG welding and subsequent heat treatment (assembly type weld). Then the influence of laser welding and TIG welding on behavior of bake hardening were investigated. In laser welding, the heat-affected zone (HAZ) was narrow and the weld joint fractured in the base metal. In TIG welding, the large softening zone existed in the HAZ, because the plastic strain was released by the heat input of welding. So the weld joint fractured in the HAZ and had a lower strength than the base metal unlike laser welding. Thus laser welding is found to be beneficial to welding of the BH steel. In the second experiment, the BH steel was welded by laser welding followed by plastic deformation and subsequent heat treatment (tailored blank type weld). Then the influence of laser welding on behavior of bake hardening was investigated. The heat treatment resulted in the increment of hardness in both the base metal and weld metal by bake hardening. The increment of hardness by bake hardening (DHVbh) in the weld metal was larger (31.1HV) than in the base metal (18.2HV). This is caused by the difference of the amount of dissolved nitrogen and carbon. The change in the tensile strength of each region corresponded with the change in hardness. Thus, the linear relation between a hardness and a tensile strength was obtained. It is, therefore, possible to quantitatively predict the tensile strength from the hardness. As for the effect of plastic strain on bake hardening, the amount of bake hardening reached a maximum value at the plastic strain of 5% or more.


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    Title :

    Properties of weld joints of bake-hardening steel for automobile


    Additional title:

    Eigenschaften von Schweißverbindungen in Bake-Hardening-Stählen für den Kraftfahrzeugbau


    Contributors:
    Katayama, T. (author) / Matsui, F. (author) / Yoshida, N. (author) / Hirose, A. (author) / Kobayashi, K.F. (author) / Shibata, K. (author) / Sakamoto, H. (author) / Sakurai, H. (author) / Kanamori, K. (author)


    Publication date :

    2004


    Size :

    6 Seiten, 10 Bilder, 2 Tabellen, 3 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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