Microstructure and Mechanical Properties of YAG Laser Welded Spheroidal Graphite Cast Iron

Cast iron welding improves the performance of joints using welding rods for cast iron. However, such rods are more than twice as expensive as those for mild steel. The authors found that when spheroidal graphite cast iron is melted and rapidly solidified, spherical graphite nodules aggregate and moved to the surface. If the spherical graphite nodules in the fusion zone moved to the surface, the carbon concentration may reduce, thereby suppressing the generation of ledeburite. In this study, by irradiating with YAG laser, I-type butt-welded joints were fabricated using L materials (with an average spherical graphite nodule diameter of 52 µm) specimen without groove width. Ferrite and pearlite matrices joints were undermatch joints. Applying PWHT (Post Weld Heat Treatment) restored the joint strength to more than 90% that of the base metal. The impact value as-welded joint dropped to less than 15% of that for the base metal. However, it could be recovered up to about 40% of that for the base metal by PWHT. Ferrite matrix joints after PWHT exhibited similar level impact values as the as-welded pearlite matrix joints. Moreover, the surface of spheroidal graphite cast iron with different numbers and size of spherical graphite nodules was irradiated with YAG laser. As the result, at irradiation feed rates above 100 cm/min L materials specimen exhibited a much lower hardness in the fusion zone than S materials (with an average spherical graphite nodule diameter of 27 µm) specimen. The spherical graphite nodules in the fusion zone moved to the surface during rapid melting by laser irradiation. In the S materials specimen studied, more ledeburite, martensite and retained austenite formed near the fusion boundary than with the L materials specimen.