Microstructural morphology and stability of rapidly solidified duplex stainless steel

摘要

The microstructure susceptibility of duplex stainless steel alloy with high ratio of Cr{sub}(eq)/Ni{sub}(eq) to unequilibrium solidification conditions were studied after rapid solidification. Three methods of locally surface melting were used:stationary gas tungsten arc, plasma arc and electron beam arc melting. Applying relatively high cooling rates in the range from 10{sup}1 to 10{sup}3 0{left sup}Cs{sup}(-1) and undercooling of 1.5-13°C, the primary ferrite with second-phase austenite (FA)solidification mode was unchanged, but significant changes in microstructure morphology, such as intercellular austenite, very fine microstructural constituents and increase of volume fraction of retained ferrite were observed. At the critical coolingrate of the order of 10{sup}4 0{left sup}Cs{sup}(-1) and undercooling ΔT>75°C a transformation of solidification mode from FA to single-phase ferrite (F) and developing of ferrite grain structure with Widmanstatten austenite was demonstrated. Based onthese results the partitionless solidification of ferrite and undercooling below the ferrite T{sub}0 curve was suggested. The fact that ferritic solidification was favored, was explained by the chemical composition of the alloy. During the subsequentannealing the obtained microstructures were highly unequilibrium and hence unstable.