Transformation behaviour of laser processed Fe-5% Cr,Fe-5% Ni and Fe-6% Cr-2% Ni alloys

The effects of rapid cooling, of the order of 10⁴? C sec^?1, achieved through the laser surface alloying process, on the transformation behaviour of Fe-5% Cr, Fe-5% Ni and Fe-6% Cr-2% Ni alloys have been investigated. The solidification structures and microstructures were characterized by optical and transmission electron microscopy. The significant findings are that Fe-5% Cr alloy undergoes a massive transformation to ferrite while Fe-5% Ni and Fe-6% Cr-2% Ni alloys undergo a transformation to a structure consisting of both ferrite and martensite. The substructures of ferrite and martensite were observed to contain essentially dislocations. These alloys also exhibited two carbide precipitations namely epsilon carbide and cementite. Solidification studies revealed that cellular solidification structures were present in 5% Ni and 6% Cr-2% Ni alloys with a cell spacing of 3 Μm but no solidification structures were observed in 5% Cr alloy. The influence of nature of solute and cooling rate on solidification behaviour, transformation mode and morphology of structures have been discussed.