On Prevention of Cracks in Underwater Wet Welds by Postweld Heat Treatment : Study on Improving the Mechanical Properties of Underwater Welded Joints (The 2nd Report)

概要

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The effect of postweld heat treatment (PWHT) on occurrence of underbead cracks and toot cracks in underwater wet welds by gravity welding process is investigated. Lime titama type coated electrodes (D5003) of 4 mm in diameter find SM50A steel base metals of 12 mm in thickness ate used. Alain results obtained are summarized as follows: 1) Underbead cracks occur in HAZ of underwater welds about 5 min after the welding. 2) Occurrence of underbead cracks and root cracks can be prevented by PWHT above 100℃. The critical concentration nf hydrogen in weld metal to prevent the occurrence of cracks C_<τc> is 0.3 ml/100gW.M.. 3) As the condition of PWHT, thf critical time factor τ_c, by which Ike critical concentration of hydrogen C_<τc> is obtained, should be selected. 4) An argorithm to obtain the condition of PWHT (τ_c, t_c) from dimensions of weld (l_0, l) initial concentration of diffusible hydrogen (C_0 = H_w), temperature of treatment (T_h) and critical concentration of hydrogen (C_<wc>) is proposed.
1986-04-01