The influence of the cooling rate immediately before hot working on the flow stress and microstructure of δ ferrite-austenite duplex stainless steel (25 % Cr duplex stainless steel) was investigated by a hot compression test at 1,000 – 1,200 °C with various strain rates (0.1 to 10.0 s-1). In spite of the fact that the compression temperature was the same, the condition of rapid cooling immediately before the hot compression test greatly reduced the maximum flow stress σmax and work-hardening coefficient n values. In addition, the stable stress at a slow strain rate of 0.1 s-1 under the rapid cooling condition gradually increased with increasing compression strain. The microstructure just after the compression test was investigated by EBSD (Electron Back Scatter Diffraction Patterns). As a result of a detailed crystal orientation analysis, it was found that supercooled δ ferrite produced by rapid cooling immediately before the hot compression test influenced the decrease in σmax and n. Furthermore, a slow strain rate condition promoted the strain induced austenite phase transformation from the supercooled δ ferrite phase during the hot compression test, and because the increased austenite phase during the hot compression test is harder than the δ ferrite phase, stable stress gradually increased together with progress of the austenite transformation.Keywords: duplex stainless steel, flow stress, hot compression test
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