Effect of different welding wires on microstructure and low temperature impact toughness of welded joint of X65M steel pipe

As an important engineering material, LSAW pipes are widely used in steel structures, pipelines and pile foundation. Based on economic considerations, Algerian customer required steel sheet raw material to meet not only API 5L 45th PSL2 specification, but also high impact toughness at −29 ℃, without additional metal element Ni. In order to obtain welded joint of X65M grade steel with good low temperature impact toughness, four internal and external welding design schemes with different chemical composition were adopted to conduct welding process test on X65M pipeline steel. The macrostructure of weld and heat-affected zone was analysed with optical microscop, and hardness and toughness were tested by hardness tests and multi-temperature impact tests. The test results show that MnNiTiB, MnMoNiTiB+MnMoTiB and MnMoNiTiB internal and external welding programmes meet technical requirements of single welding seam and heat-affected zone with impact energy greater than 49 J and average value greater than 61 J at −29 ℃. Among them, MnMoNiTiB scheme has the largest surplus. In terms of economy, the MnNiTiB plan meets technical requirements, and price is the lowest among the four schemes.