Microstructures and mechanical properties of laser-arc hybrid welded API-X70 linepipe steel

Abstract

Microstructures and mechanical properties for welded joints of API X70 grade steel, using LAHW(Laser-Arc Hybrid Welding) with the combination of 2kW laser power and 1.2kW GMAW power, were investigated and compared with those of SAW(submerged arc welding) joints. In the hybrid welding experiments, the deepest penetration was obtained when the distance between laser and arc was 6.5mm. The microstructure of LAHW joint exhibited more finer than that of SAW joint. Impact absorbed energy of CGHAZ and weld deposit in the LAHW joint were 55.3J and 45.3J of minimum value at - 20 °C, respectively. The low carbon TMCP type steel used for both LAHW and SAW showed softening behaviour in the HAZ adjacent to base metal, which was known to be closely related with the SOHIC(stress oriented hydrogen induced cracking). Comparing hardness on ICHAZ, softening ratio of ICHAZ/base metal in the LAHW was measured as 0.94 which was higher than the ratio of 0.86 in SAW. By suppressing softening in the ICHAZ region, the SSCC resistance of low carbon TMCP steel welded joints could be improved.Microstructures and mechanical properties for welded joints of API X70 grade steel, using LAHW(Laser-Arc Hybrid Welding) with the combination of 2kW laser power and 1.2kW GMAW power, were investigated and compared with those of SAW(submerged arc welding) joints. In the hybrid welding experiments, the deepest penetration was obtained when the distance between laser and arc was 6.5mm. The microstructure of LAHW joint exhibited more finer than that of SAW joint. Impact absorbed energy of CGHAZ and weld deposit in the LAHW joint were 55.3J and 45.3J of minimum value at - 20 °C, respectively. The low carbon TMCP type steel used for both LAHW and SAW showed softening behaviour in the HAZ adjacent to base metal, which was known to be closely related with the SOHIC(stress oriented hydrogen induced cracking). Comparing hardness on ICHAZ, softening ratio of ICHAZ/base metal in the LAHW was measured as 0.94 which was higher than the ratio of 0.86 in SAW. By suppressing softening in the ICHAZ region, the SSCC resista...