Effect of Chemical Composition on the Formability of Flash Butt Welded Joints in Hot-rolled High-strength Steel Sheets

Abstract

A study has been made of the formability of flash-butt welded joints in three types of hot-rolled high-strength sheet steels, solid solution hardened steel, precipitation hardened steel and dual phase steel, to clarify the factors which are required to high strength steels for wheel rim use.
Formability in stretch-flanging depends strongly on the hardness and microstructure at the weld. It is impaired by localized fracture due to the softening at heat affected zone or weld interface in dual phase steels and precipitation hardened steels having low alloy content. To avoid the softening in precipitation hardened steel, the carbon equivalent should be raised in proportion to the tensile strength in newly proposed equation; Ceq [FBW].
Formability in bending is deteriorated by two types of defects, penetorator crack and hook crack. The former is caused by oxides generated at weld interface during welding. It is suppressed by controlling Si and Mn content to maintain Mn/Si in an adequate range, 423. The hook crack can be suppressed by lowering the amount of sulfide inclusions.