Effect of Thermal Cycle on Properties of Welding Heat Affected Zone

In this report T-T-T diagram and CCT-Curve from austenitizing temperature 1200•Ž were researched and then effects of preheat temperatures and welding thermal cycle on properties of heat affected zone were clarified to investigate weldagility of 21/4 Cr-1Mo steel and also we carried out a restraind crack test to investigate crack sensitivity of the steel. The results of experiments are summarized as follows : (1) As shown in Fig. 1 T-T-T diagram have two noses at A1 and Ar' transformation ranges. (2) A1 transformation rate in CCT-Curve (Fig. 2) is suppressed remarkably. (3) With raising preheat temperature, maximum hardness in the heat affected zone decreases and toughness improves. (4) Welding heat affected zone which is hardened by the first pass at the range of preheat temperature 200•`300•Ž is heated over the A1 transformation temperature by following welding thermal cycle and its mircostructure is refined. (5) According to results of restrained weld cracking sensitivity test, crack in the weld zone is vented by preheating to 200•`300•Ž.