Yoshinobu Ono

Structural Materials. Influence of Welding Heat on Low Yield Strength Steel.

The yield stress of the low yield strength steel (LY100) that is used well as a hysteresis dumper is reduced by coarsing grain in the heat treatment process of steel plate production. Therefore, the yield stress rises, when the steel plates are built up by welding to a member. The test specimen that welded 2 sheets of steel plates by butt welding was prepared, in order to investigate the influence of the welding heat input and the cause on the mechanical properties of the steel plate. Gathering the test pieces according to the distance from the weld line, the tension test, chemical composition analysis, optical microscope and micro Vickers hardness test were performed. Also, the change of the yield stress by means of heat treatment become hot after welding was examined. As a result, it is guessed the cause that the heat input record and the cooling under residual stress refine the grain size at the temperature rise part of vicinity of the weld line. And, the grain is coarsened once again by heat treatment for one hour at 850°C after the welding assembly. Therefore it is possible that the yield stress that have rised at the time of the welding assembly is made lower equal to that of the base material.