Impact toughness analysis of Q355/SKH9 HSS laser refrequency welded joint

A new technology called Narrow-gap submerged arc welding was used to make a Q355/SKH9 high speed steel joint for fitness equipment, and an experiment on the impact toughness of a V-notch submerged Arc was conducted. The results show that when the test temperature drops, the joint is affected by less impact energy absorption, and the welded joint forms an obvious gradient impact toughness. There are a large number of tempered lath martensite structures in BM, and different welding thermal cycles are formed inside the HAZ heat treatment. Many tearing edges were formed at the BM and HAZ fracture sites, showing quasi-cleavage fracture. HAZ has excellent toughness, which is better than BM. After tempering, lath martensite and granular bainite obtained stronger impact toughness. BM maintains a relatively stable microhardness and shear strength, and HAZ forms a large gradient variation of microhardness and shear strength. After the welding thermal cycle treatment and later tempering process, more carbide is formed between HAZ matrix and grain boundary, which increases the strength and hardness of HAZ.