焊接热输入对F550Z钢焊接接头低温韧性的影响

研究了热输入对海洋钻井平台用550 MPa钢焊接接头组织与低温韧性的影响.结果表明,热输入为15和50 kJ/cm时,对焊缝有热处理作用,组织为针状铁素体加细小弥散的碳化物,其中50 kJ/cm热处理作用较明显.-60℃冲击试验中,热输入为50 kJ/cm时冲击吸收功最高,平均110 J,是其它热输入的2~4倍.熔合线及熔合线2 mm处组织为板条贝氏体加粒状贝氏体.小热输入时,粒状贝氏体含量少并且打乱了板条贝氏体方向,对韧性有利;随着热输入增加,粒状贝氏体逐渐增多且晶粒粗大,低温韧性较差,该区冲击吸收功随热输入增加呈下降趋势.

Effect of heat inputs on low temperature toughness of F550Z steel welding joints

Effect of different heat inputs on microstructure and low temperature toughness of 550 Mpa offshore steel welding joints was studied. The experimental results indicate when the heat input is 15 kJ/cm or 50 kJ/cm,the welding metal experience the effect of heat treatment,and the microstructures are acicular ferrite and fine granular dispersed carbides,especially when the heat input is 50 kJ/cm. In the impact test at -60℃,when the heat input is 50 kJ/cm,the impact energy is the highest, which is 110 J and 2 to 4 times of that obtained under other heat inputs. The microstructure in the fusion line and 2 mm from fusion line are lath bainite and granular bainite. When the heat input is small,a spot of granular bainite disrupt the direction of lath bainite,which is good for low temperature toughness. But the granular bainite increases and gets coarse with the heat input increasing,which leads to bad low temperature toughness. The impact value in these zones decreases with the heat input increasing.