||The bonding of an SK3 steel insert to copper during cast welding and heat treatment was studied. The interface shear strength was made with a push-out test. After cast welding, a cast welding layer formed between SK3 steel and copper. After a continuous cooling heat treatment, there was a cast welding layer near the SK3 steel matrix, an irregular layer near the copper matrix, and a middle layer between them. 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 shown that mainly iron atoms and carbons diffused into the copper matrix. The interface shear strengths of the compound casting while with water quenched, oil quenched, air cooled, and furnace cooled, were 23.42, 18.74, 12.29, 13.43, and 8.33 MPa, all of heat treatment fractures in the cast welding layer near the SK3 steel matrix.