Influence of Partitioning Effects on the Retained Austenite Content and Properties of Martensitic Stainless Steel

The effect of a quenching and partitioning (Q&P) heat treatment with a quenching temperature (T_Q) range from 20 to 190 °C is investigated for two martensitic stainless tool steels X40Cr14 and “X25CrN13”, focusing on microstructural evolution, hardness, and toughness. The influence on the retained austenite (RA) content, when replacing part of carbon with nitrogen, is of core interest. The amount of RA is analyzed by X-ray diffraction and is additionally proved with electron backscatter diffraction, and the RA content is thermodynamically calculated. Subsequently, the effect of the microstructure on toughness and hardness is investigated. For both steels, the toughness maximum is reached in the region of the RA maximum. The “X25CrN13” attains higher toughness at higher RA contents. Higher RA contents do not benefit X40Cr14. Furthermore, the effect of double tempering at higher tempering temperatures after Q&P on the steels is investigated. Besides RA contents and hardness, dilatometer curves are used to evaluate the formation of fresh martensite in the microstructure. The secondary hardness maximum of “X25CrN13” is reached at 500 °C and that of X40Cr14 is at 480 °C. For double tempering temperature at 520 °C, T_Q has little effect on toughness, and “X25CrN13” shows better values.