| In order to investigate the effect of cooling rate on the formation of δ-ferrite in type 304 stainless steel. Gleeble experiment. TIG welding and laser surface melting were carried out. The transformation mechnism of δ-ferrite to austenite was studied by interrupted quenching experiment of unidirectional solidification. Transformation of δ-ferrite to austenite in the 1400 and 1160℃ range has the profound effect on δ-ferrite content. δ-ferrite content was about 74% at the final solidification, which decreased to about 8% at room temperature. As the cooling rate increased from 0.5 to 9.7×10³C/s, δ-ferrite content increased from 3 to 20%, but the further increase in cooling rate from 9.7×10³ to 3.3×10⁴C/s decreased δ-ferrite content from 20 to 9.7%. With increasing the cooling rate, δ-ferrite morphology changed from vermicular ferrite, lacy ferrite and to euteetic ferrite with concurrent decrease in the δ-ferrite content. |
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