Influence of Martensite Fraction on Tensile Properties of Quenched and Partitioned (Q&P) Martensitic Stainless Steels

By means of a simplified quenching and partitioning (Q&P) processing with quench temperature equal to room temperature, austenite fractions of 56, 43, and 24 vol% are stabilized in the microstructures of Q& P-processed Fe-Cr-C, Fe-Cr-C-Co, and Fe-Cr-C-N stainless steels, respectively. The mechanical stability of austenite is quantified by tensile tests at temperatures between 20 and 200 degrees C. In agreement with the Q&P concept, the stability of austenite is found to be highest for the steel with the highest martensite fraction. The carbon enrichment of austenite in a specimen of the Fe-Cr-C steel processed to have 82 vol% martensite is estimated by X-ray diffraction measurement of the austenite lattice parameter. The results indicate that only about 12% of the carbon contained in the martensite has partitioned into the austenite. The formation of tempering carbides is one of the mechanisms behind the significant deviation of the carbon enrichments from the full partitioning assumption.