| ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ KAWASAKI STEEL TECHNICAL REPORT No.6 ( September 1982 ) ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ |
| Effects of Chemical Composition and Structure of Hot Rolled High Strength Steel Sheets on the Formability of Flash Butt Welded Joints
Masatoshi Shinozaki, Toshiyuki Kato, Toshio Irie, Hiroshi Hashimoto |
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Synopsis : To clarify the factors required of high strength steels for wheel rim use, formability of flash butt welded joints in three types of hot rolled high strength sheet steels, i.e., solid solution hardened steel, precipitation hardened steel and dual phase steel was investigated. Formability in stretch-flanging is closely related to changes in the hardness and microstructure of the weld. It is impaired by localized fracture due to softening at the heat affected zone or weld interface in dual phase steels and precipitation hardened steels having low alloy content. To avoid softening precipitation hardened steel, the carbon equivalent should be raised in proportion to tensile strength in the newly proposed equation for Ceq [FBW]. Formability in bending is deteriorated by two types of defects, i.e., penetrator crack and hook crack. The former is caused by oxides generated at the weld interface during welding. It can be suppressed by controlling Si and Mn contents to maintain the Mn/Si ratio in an adequate range of 4 to 23. Hook crack can be suppressed by lowering the amount of sulfide inclusions. |
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