Research On Non-preheating Welding Technique For HQ785T1 HSLA Steel

The current welding method which enable to avoid cold crack during in high strength low alloy steel is preheating.Aim at this status,two kinds of non-preheating welding technique were brought forward in this paper.The HQ785T1 steel with 28mm thichness was welded with these methods. There was much research on the crack sensitivity of different strength levels low-alloy electrodes and austenitic HCr20NilOMn7Mo wire on the HQ785T1 steel.The organization and performance of the welded joint was also researched.The results indicated that the method of using low strength wire of HS-50 in backing weld, equal strength wire of HS-80 in cosmetic weld, could effectively improve cold cracking susceptibity of the joints, achieve the purpose of non-preheat welding on the HQ785T1 steel with 28mm thichness. Compared with equal matching weld joint, the static strength of strength mis-matched joints of double V groove was related with the relative thickness of HS-50 weld.When the relative thickness of HS-50 weld did not exceed 50%, the static strength of joints kept intact, and the tensile test specimen should broke in soften zone on joints; When the relative thickness of HS-50 weld was 58%, the static strength of joints would unchange, but the tensile test specimen should broke in weld.The static strength of strength mis-matched joints of single bevel groove was related with root gap.With the different of root gap, the static strength should slightly fluctuation,and it was up to the technology requirements of the base metal.The method of using austenitic HCr20NilOMn7Mo wire in backing weld, low strength wire of HS-50 in transition weld, low strength wire of HS-50 in cosmetic weld, by controlling heat input, could effectively improve cold cracking susceptibity of the joints, achieve the purpose of non-preheat welding on the HQ785T1 steel with 28mm thichness.In order to avoid cold crack,the input of HCr20NilOMn7Mo weld should be less than 1.1 kJ/mm,and the input of HS-50 weld should be less than 0.9 kJ/mm. Compared with equal matching weld joint, the static strength of organization mis-matched joints of double V groove hadn't been reduced.