Microstructure analysis of nodular iron 400-12 after laser surface melt hardening

The application of laser surface melt hardening to nodular iron 400-12 causes the material to undergo microstructural changes. A newly created austenite-ledeburite microstructure with the presence of graphite nodules in the melted zone and a martensite-ferrite microstructure with graphite nodules in the hardened zone have been observed. Microscopy of the hardened zone was used to analyze the occurrence of martensite shells around the graphite nodules in ferrite matrix. The size of the shells was later supported by diffusion calculations. The qualitative effects of the changed microstructures were additionally verified by microhardness/depth measurements in the modified layer and microhardness measurements of characteristic microstructures around the graphite nodules in the hardened zone. (C) Elsevier Science Inc., 1996