Effect of weld thermal cycle on low temperature toughness of 09MnNiDR steel heat affected zone

The effect of welding heat cycle on low temperature toughness of the coarse-grained heat affected zone (CGHAZ) and inter-critically reheated coarse-grained heat affected zone (IRCGHAZ) of 09MnNiDR steel was studied by Gleeble-3800. The results show that when the heat input is 15 kJ/cm and the interpass temperature is 150 ℃, the microstructure of CGHAZ is lath martensite and lower bainite. The lower bainite restricts the growth of martensite and improves the low temperature toughness. While IRCGHAZ is continue to maintain the microstructure of CGHAZ. In the impact test at −70 ℃, IRCGHAZ has the better low-temperature impact toughness than CGHAZ. When the heat input is 15 kJ/cm and the interpass temperature is 150 ℃, the impact energy is the highest of 65 . According to the thermal simulation results, the 09MnNiDR steel was welded with the welding heat input of 15 ~22 J/cm and interpass temperature of 150 ℃, the impact energy of heat-affected zone is 101 J at −70 ℃, and the fracture morphology has a large number of isometric dimples, which has good low-temperature toughness. In the tensile test at −70 ℃, the yield strength is 477 MPa, the tensile strength is 607 MPa, and the elongation is 28.5%, showing the better strength and plasticity. Hardness test results show that the hardness of base metal, weld and heat affected zone increase successively, and there is no softening phenomenon.