The Prediction of Microstructure in Low-chromium Substitutes for Stainless Steels.
J Mater Eng 1988 10(3):181-191
Previous Bureau of Mines research has shown that additions of si and al can partially replace the cr in stainless steels for use in oxidation-resistant applications. Because an austenitic microstructure is desired for optimum mechanical properties, a series of fe-(4 to 12)cr-(8 to 18)ni-(0 to 8)si-(0 to 6)al-1mn-0.05C alloys were metallographically examined to determine the compositions that stabilized this austenitic microstructure and inhibited the formation of ferrite or martensite. A series of fe- 1mn-0.05C-si-al metastable phase diagrams for various cr and ni contents were drawn to provide better predictions of alloy microstructure than does the schaeffler diagram. At the 8- to 10- pct cr level, an austenitic region is formed only when ni is at least 14 pct. An equation was developed to correlate the austenite and/or ferrite content to cr- and ni-equivalent relationships. A second equation was developed to predict the transformation of austenite to martensite. These relationships can be used to predict alloy microstructure for fe-base alloys containing 4 to 12 pct cr.
J. Mater. Eng., V. 10, No. 3, 1988, PP. 181-191