８０及び１００キロ級高張力鋼大入熱溶接ＨＡＺ部の靭性劣化とその改善に関する研究（第３報） 溶接後熱処理による島状マルテンサイトの分解挙動及び靭性の改善に関する検討

Abstract

The decomposition of M-A constituent by PWHT (Post Weld Heat Treatment) and its effects on the toughness have been investigated for the weld CGHAZ (Coarse Grained Heat Affected Zone) of HSLA steels of 780-980 MPa classes.As the PWHT temperature and time were increased, the area of the M-A constituent was decreased for all the steels employed, but dependence of the toughness of the 980 MPa class steels on PWHT parameters was quite different from that of the 780 MPa class steels. For the weld CGHAZ of 780 MPa class steel, the toughness was increased, as the M-A constituent was decomposed into ferrite and cementite by the PWHT. For the weld CGHAZ of 980 MPa class steel, however, embrittlement occurred at PWHT temperatures above 823 K though the toughness was increased with PWHT time at temperature below 623 K.From these results, it can be concluded that the toughness of HSLA steels impaired by the high-heat-input welding can be improved significantly by PWHT at temperature about 623 K.