Transformation structures and strengthening mechanisms of laser processed Fe-Cr alloys

The microstructures and microhardness of laser processed Fe-Cr surface alloys were investigated as functions of composition (5 to 50 wt % Cr) and melt penetration depth (100 to 1500 m). The transformation structures were characterized by optical metallography and thin foil transmission electron microscopy. The microstructures were ferritic irrespective of compositions and melt depths. The alloys containing chromium up to 12 % (within the -phase field) exhibited a massive ferritic morphology while the alloys containing chromium more than 12% (beyond the -phase field) showed an equiaxed ferritic morphology. Transmission electron microscopy studies revealed that the substructure of ferrite consisted of dislocations, the dislocation density increased with increased chromium content. Melt depth, unlike composition, did not have a significant effect on the morphology and substructure of ferrite grains. Small amounts of -carbide and M₃C carbide phases were observed in these alloys. Both the carbides were found to decrease with an increase in the chromium of the fusion zone. Microhardness measurements indicated that there was an increase in hardness with an increase in the chromium content of the alloy.