ＨＹ系高張力鋼溶接金属の低温割れに関する基礎的研究 ＩＩＩ ＬＢ‐ＴＲＣ試験法による溶接金属の低温割れ感受性の評価

Abstract

In this study, the effects of hardness and diffusible hydrogen content on the lower critical stresses o f weld metals (LCS) of high strength steels in the strength range 490 to 1950 MPa were evaluated utilizing the LB-TRC test which was newly developed in order to understand the cold cracking characteristics of weld metal.Test beads were laid utilizing SMA welding and GTA welding in which argon and argon-(0.35, 1.0, 2.0, 3.2 Vol.%) hydrogen mixed gases were used as shielding gases. The diffusible hydrogen content range was 0.1 to 9 ml/100 g. Moreover, yield strength of root-pass deposited metal ((σr)y) and fracture stress of LB-TRC tested specimen which had evolved diffusible hydrogen for 10 days at room temperature (σ*F) were measured in order to evaluate the cold cracking susceptibility. σ*F was regarded as the hydrogen-free LCS, so the cold cracking susceptibility of weld metal was evaluated using two parameters such as σcr/(σr)y and (σ*F-σcr)/σ*F.Consequently, the LCS of weld metals of high strength steels decreased rapidly with an increase in the diffusible hydrogen content in the range 0 to 3 ml/100 g. Moreover, cold cracking susceptibility in weld metal increased with an increase in strength level and/or hardness and then especially, weld metals of HY130 and HY150 were most susceptible to cold cracking rather than that of HY180.