中文摘要：

X70管线钢在用常规方法焊接时,焊接热影响区的晶粒容易粗化,造成焊接接头强度和韧性下降。采用间隙宽度为4 mm的焊剂带约束电弧超窄间隙焊接方法,对14 mm厚的管线钢进行单道多层焊接工艺试验,获得了根焊、填充焊、盖面焊的工艺参数。试验了加填充条、背面衬陶瓷衬垫的方法,可以得到良好的单面焊双面成型的根焊焊道。这种方法焊接线能量约为0.6 k J/mm;焊缝组织主要为细小的针状铁素体;热影响区未出现严重粗化;焊缝硬度比较高,高出母材30%左右;低温冲击韧性良好,韧脆转变温度约为-40℃。

英文摘要：

In the conventional welding for X70 pipeline steel, the grains in heat affected zone easily coarsen,which can cause the strength and toughness of the welded joint decreased. A series of ultra-narrow gap welding for X70 pipeline steel with 4mm gap width was made to study the welding process parameters of root welding, filling welding and cosmetic welding. The thickness of X70 pipeline steel was 14 mm.The results indicate that the ultra-narrow gap welding with filler wire and ceramic liner backing can be used to get good root weld bead with both sides formation in a single pass. The welding line energy of this welding method is 0.6 KJ/mm; the weld microstructure is mainly acicular ferrite; heat affected zone does not generate serious coarsening. The hardness of weld seam is higher than that of the matrix metal by about 30%. The welded joint has good low temperature impact toughness, and the ductile-brittle transition temperature is about-40℃.