||The bonding of an S45C steel inserted into copper during cast welding and heat treatment was examined. The interface shear strength was made with a push-out test. After cast welding, a cast-welding layer formed between steel and copper. After marquenching, martempering and austempering heat treatment, there was a cast-welding layer near the steel matrix, an irregular layer near the copper matrix and between of them was a middle layer. Through X-ray diffraction analysis was used to determine that the interface layer consisted of carbon and CuFeO2. Through electron probe X-ray microanalysis (EPMA), it was showed that iron atoms and carbons, mostly, diffused into the copper matrix. The interface shear strengths of the compound casting while with marquenching, martempering, and austempering were 6.29 MPa, 8.23 MPa, and 8.33 MPa, respectively; The fractured region was all happened near S45C steel matrix in the cast welding layer.