Effect of Normalizing Pre-Treatment on Microstructure of Laser Hardened Ductile Iron

Abstract

We adjusted the pearlite content of ductile iron matrixin by normalizing, finding that the microstructures of laser hardened ductile iron with different pearlite content and distribution were quite different. According to their microstructure characteristics, there are three types: ⑴pearlite transformation type; ⑵ pearlite and ferrite transformation type; ⑶ferrite transformation type. We also studied the microhardness of different ductile iron laser hardened layers and the phase around the graphite ball. The results showed that under the appropriate laser treatment process (laser output power of 1kw, spot diameter of 5.2mm, scan speed of 16mm / s), ledeburite shell, with the hardness up to HV0.11070, formed around the graphite ball in the surface layer of ductile iron hardened layer. Outside the ledeburite was the carbon diffusion zone with hardness of HV0.1850. It was composed by the plate martensite of large needle and large amount of residual austenite. In the hardened layer of ferrite transformation type, martensite formed out around the ledeburite shell or graphite ball.