ＨＹ系高張力鋼溶接金属の低温割れに関する基礎的研究 Ｖ ＨＹ系高張力鋼溶接部の相変態挙動による拘束応力の緩和現象について

Abstract

This study was done to develop the possibility of sound welding of higher grade HY-type of steel having a low lower critical stress, utilizing transformation expansion of weldment including weld metal and the heat-affected zone.The restraint stresses in root pass welded joint of various strength steels such as SM41, HT60, HT80, HY130 and HY150 were quantitatively evaluated utilizing the RRC test under the restraint intensity of 9.8 and 29.4 kN/mm.mm by GTA welding with filler wire. On the other hand, transformation expansion of welded joint was measured by dilatometric technique. Then the relationship between the restraint stress and the transformation expansion was quantitatively investigated.Consequently, the final value of the restraint stress reduced with an increase in strength of base steel, namely in the order of SM41, HT60, HT80, HY130 and HY150 under the same restraint intensity. For example, the final restraint stress in SM41, HY130 and HY150 was about 490, 216 and 147 MPa, respectively, in the restraint intensity of 9.8 kN/mm·mm. Reducing the restraint stress was attributed to transformation expansion of welded joint. The increase of transformation expansion was much effective for reducing the final restraint stress in HY130 and HY150 weldments in comparison with the other weldments. The transformation temperatures of HY130 and HY150 weldments were lower than those of other weldments, so that not only large transformation expansion but also low transformation temperature were very useful to reduce the final restraint stress. In addition, these results suggested that the crackfree weldments of HY130 and HY150 steels may be completed by developing the higher alloy filler wire having high expansion coefficient and low transformation temperature during cooling after welding.