Microstructure and properties of joints of 600 MPa grade ultrafine grained steel obtained by friction welding

13mm diameter bars of 600MPa grade ultra-fine grain steel were welded by friction welding. Experimental results show that ultra-fine grain steel has good weldability of friction welding when the friction welding process parameters were properly controlled. Ultra-fine grain steel friction welding joint was mainly composed of four zones: welding seam, thermo-mechanically affected zone (TMAZ), heat affected zone(HAZ) and base material. The grain size was about 9-11 μm in the HAZ, which was slightly larger than the one of the base metal. Mechanical properties results showed that joint strength of the ultrafine-grained steel friction welding was up to 715 MPa with 22% elongation and 68% contraction ratio of cross section, and impact toughness was about 98 J. Meanwhile typical ductile fracture was obtained for this kind of joint.