Origin of the lathy ferrite in AISI 304 stainless steel during directional solidification

• The solidification path of AISI 304 stainless steel has been investigated.
• The mechanism of three-phase reaction was confirmed as peritectic not eutectic.
• The retained delta-ferrite is the result of incomplete peritectic reaction.

The solidification path has been revealed and the mechanism of three-phase reaction in 18-8 austenitic stainless steel has been clarified using directional solidification and liquid quenching. It is found that primary delta-ferrite precipitates from the melt at the initial stage of solidification. With the decrease in the melt temperature, it is confirmed that austenite is formed through peritectic transformation rather than eutectic reaction. After peritectic reaction, partial delta-ferrite is retained since peritectic reaction is incomplete and delta-ferrite and peritectic austenite is enveloped by the surrounded liquid. At the final stage of solidification, the rest of liquid transforms into austenite directly. Experimental evidences have been presented to account for the solidification details.