| In this paper,Q235 steel and 304 stainless steel were diffusion bonded.Microstructure and mechanical properties were studied and the conclusions are summarized as follows:(1)Sound joint was obtained by diffusion bonding in the following parameters:the vacuum was 0.6 Pa,the pressure was about 20～25MPa,the temperature was about 950～1000℃ and the bonding time lasted for 30 minutes.(2)Results of the tensile tests showed that the fracture was occurred on the side of Q235 base metal,which was away from the bonded joint.The tensile strength of the specimens was 430 MPa and the elongation was about 27.7%.Results of the impact toughness showed that the impact energy was 118 J,which was not less than that of the Q235 base metal.Results of the 180 degrees bending tests showed that no cracks existed on the surface of the joint.Results of the high frequency fatigue tests showed fracture also occurred on the Q235 base metal which was far away from the interface.At 2×106cycles,fatigue strength of the fatigue specimens on the survival rate of 50%and 95%were 187.33 MPa and 175.06 MPa,respectively.(3)Microstructure and component analysis were studied by OM,SEM,EDS,EBSD,XRD,EPMA,TEM and results showed that grain refinement was occurred at both sides of the interface.Carbon-poor region was observed near the interface of Q235 the width of which was 100μm The element of carbon diffused from Q235 to 304 stainless steel and the chromium diffused from 304 stainless steel to Q235 near the interface,which resulted in the formation of carbon-poor region above.The interface consisted of(Fe,Cr)xCy transition layer the width of which was 1μm.(4)Results of microhardness and nanoindentation showed that the interface hardness was the highest hardness of the ferrite at the carbon poor region was higher than the Q235 base metal due to the solid solution strengthening of Cr. |
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