Q-P process is one of the latest techniques for heat treatment of high-strength steels with increased silicon levels. It is believed to be based on diffusion and migration of carbon between martensite and untransformed austenite, where the latter becomes enriched with carbon, and therefore becomes thermodynamically stable. However, the question remains whether much of the carbon partitioning in the Q-P process might be the result of the competing bainitic transformation induced by arrested quenching below the Ms temperature. This paper explores the use of dilatometry for identifying the products of austenite decomposition during Q-P processing of medium-carbon 42SiCr low-alloy steel.