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Post-weld heat treatment (PWHT) is carried out to improve fracture toughness and to remove residual stress in the heat-affected zone (HAZ). There are some problems, such as a toughness decrease and stress-relief cracking (SRC) in the coarse-grained HAZ subject to the effect of the tempering treatment. Therefore, in this paper, the effect of the heating rate and heat input on PWHT embrittlement under applied stresses of 0, 98, 196, and 294 MPa (0, 10, 20, and 30 kg/mm2), applied to simulate residual stress in the welded HAZ of chromium-molybdenum (Cr-Mo) steel was evaluated using the crack-opening displacement (COD) fracture toughness test and observation of the fracture surfaces. The fracture toughness of welded HAZ decreased with an increase in the heating rate under no stress, but it improved with an increase in the heating rate under stress. Applied stress in welded HAZ during PWHT assisted precipitation of oversaturated alloying elements in the structure, so grain boundary failure from the welding heat input was barely evident at a heat input of 10 kJ/cm and a heating rate of 600°C/h, but it appeared at an applied stress of 294 MPa at 30 kJ/cm and 220°C/h and of 196 MPa at 40 kJ/cm and 60°C/h.
weldments, post-weld heat treatment, PWHT embrittlement, residual stress, heating rate, heat input, COD fracture toughness test, welded HAZ, grain boundary failure
Associate professor, Chonbuk National University, Chonju,
Professor, Chonbuk National University, Chonju,