熔接熱サイクル再現装置による鋼の熱影響部の冶金的研究(第2報)

Abstract

Following the previous study, mechanical and impact properties of the microstructures in weld heat affected zone in structural steels have been studied by means of the synthetic apparatus.Firstly, the effects of the maximum heating temperatures, 500, 650, 750, 900, 1100, 1300 and 1400°C. on the tensile and impact properties of a Mn-Si high strength steels were investigated. The maximum values of tensile and yield strengths were obtained approximately at about 1300°C. of peak temperatures ; but the elongation, the reduction in area and the impact value were found to show more remarkable decrease at higher temperatures over 1300°C.Similarly, from the tests carried on the effects of tempering temperatures, 450, 550 and 650°C. on the tensile and impact properties of five steels, it was found that the tensile and yield strengths were decreased with an increase of tempering temperature, while the elongation, the reduction in area and the impact value were generally increased on the contrary. However, the yield strength was slightly increased by tempering at 450°C.Next, the effects of thermal cycles on tensile properties of five steels were studied. The ductilities as revealed with the values of elongation and reduction in area were decreased with an increase of cooling rates at 540°C., and were closely related to the microstructures of transformation products. From these relations, the critical cooling rate and hardness to preserve a satisfactory ductility were determined for each steel.Finally, from the test results of the small size bead bend test, it was ascertained that elongation or reduction in area of the synthetic round bar tensile specimen were a good indication of the bend ductility of steels.