Strengthening Dual Phase Steel Welds by Shot Peening

초록

The softening of the weld zone of dual phase steel (600 MPa) due to welding and its strengthening mechanism linked with shot peening (SP) was investigated. SP was performed on the welded test-piece taken from the steel at the pressure of 0.6 MPa. Hardness of peening medium was about 850Hv and its size was 8Oμm in diameter. The microstructure of weld zone (base metal, heat-affected zone and weld metal) of specimen was examined before SP since rapid heating and cooling at this zone caused grain growth and phase transformation. The results showed that after SP, grains of surface were refined with exposure time increased, and at the exposure time of 5s, weak hardened layer is generated. With the increase in expose time, grains of surface experienced much more severe plastic deformation and subsequently grain size was refined significantly. It was reported that nano-sized grains in Fe were formed by the transformation of the dense dislocation wall and dislocation tangles transformed into grain boundaries when the size of peening medium was small.

키워드