Microstructure and mechanical properties of welded joint between high nitrogen stainless steel and 675 high strength steel

According to the principle of “low strength matching”,pulse MIG welding experiments of high nitrogen stainless steel and 675 high strength steel with 13.5 mm thickness were carried out with ER307Mo stainless steel wire.The results showed that the welded joint with good formation and better performance could be obtained when the welding speed was 5 mm/s,the wire feeding speed was 5.5～6.0 m/min,the welding current was 155～166 A,and the arc voltage was 19.6～20.3 V.Microstructure of the weld was mainly composed of austenite and ferrite,of which ferrite precipitated from the austenite grain boundary.The lateral heat affected zone of high nitrogen stainless steel was dominated by massive austenite,while that of 675 high strength steel was dominated by martensite.The tensile strength of welded joint was about 730 MPa,which was 71% of the strength of high nitrogen stainless steel base material.The fracture form of welded joint was ductile fracture,and no obvious cleavage fracture was found.Highlights:(1)According to the principle of “under matching”,ER307Mo stainless steel welding wire was used to weld high nitrogen stainless steel and 675 high strength steel,and a well-formed welded joint was obtained.(2)The microstructure and mechanical properties of the weld were analyzed.The weld zone was mainly composed of austenite and ferrite distributed on the austenite matrix.The tensile strength of the joint reached 731 MPa,which was 71% of the base material of high nitrogen steel.