Microstructure and properties of friction hydro pillar processed DH36 high strength steel

Friction hydro pillar processing(FHPP) of DH36 high strength steel for ship structures was performed. The microstructure, hardness profile, tensile strength and Charpy impact value of FHPP welded joints were observed and tested. The tensile fracture surface along the FHPP bonding interface was examined by scanning electron microscope. It was verified that the metallurgical bonding between the pillar and DH36 base material can be successfully obtained under optimum welding parameters.The hardening tendency of FHPP weld was obvious and the highest hardness value reached 3.33 GPa. The tensile strength of FHPP welded joints was higher than that of DH36 base material, and the tensile fracture morphology in the interface between pillar and base material presented specific features blending small equiaxed dimples and cleavage fracture. But Charpy impact toughness around the bonding interface was only 37 J ± 5 J which was obviously lower than 205 J of the base metal. The large amounts of upper bainite produced around the bonding interface during FHPP reduced the impact toughness.