| Effects of niobium addition and reverted austenite on the tempering characteristics of martensitic Fe-16Cr-5Ni-0.06C(in weight percent) stainless steels were investigated over the temperature range from 400 to 680℃. Tempering stages of these steels can be divided into three distinct regions, namely 1) region I (up to 440℃) : mechanical poperties remained constant, 2) region II (500-620℃) : strength abruptly dropped and ductility increased with increasing temperature resulting from the formation of reverted austenite and 3) region III (above 620℃) : strength increased and ductility decreased again with increasing temperature due to the martensitic transformation of reverted austenite during cooling. In Nb-free alloy (M1), hardness and strength were dropped rapidly after the reversion of austenite started. On the contrary, the strength drop in Nb-containing alloy (M2) was rather gradual, meaning that the softening effect due to the formation of reverted austenite was compensated by the solid-solution hardening and the precipitation hardening of NbC. Moreover, the Nb addition not only improved mechanical properties but affected the formation of reverted austenite. |
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