With the aim of improving the performance of electron beam welded joints between spheroidal graphite cast iron (FCD700) and mild steel (SS490), we applied insert-type electron beam welding that has a insert metal into the I-type butt welding between FCD700 and SS490. By using pure nickel and austenitic stainless steel (SUS304) as the insert metal, the microstructure and mechanical properties of the welded joints were examined.
Consequently, we found that, with no weld cracks and porosities in the fusion zone, the microstructure of the fusion zone produced by the pure nickel insert-type welding was austenite, while that of the fusion zone produced by the SUS304 insert-type welding was austenite and martensite. The average hardness of the fusion zone produced by the pure nickel insert-type welding and that of the fusion zone produced by the SUS304 insert-type welding were 235 and 393 HV, respectively, showing a decrease in hardening, compared to that of the fusion zone produced by direct welding, 566 HV.
Concerning the insert-type welded joints, the average tensile strength of the pure nickel welded joint was 425 MPa, while that of the SUS304 welded joint was 443 MPa. The average joint efficiency of the SUS304 welded joint against the mild steel base metal was 84%, showing improvement, compared to that of the directly welded joint, 72%. The impact values of the insert-type welded joints showed almost the same values as those of the directly welded joint. Moreover, concerning the insert-type welded joints (welded joints between FCD700 and SS490), the fatigue limit of the pure Ni welded joint and that of the SUS304 welded joint were 266 and 255 MPa, respectively, showing improvement in fatigue strength, compared to the fatigue limit of the directly welded joint (welded joint between FCD700 and SS400), 209 MPa.