The "quenching and partitioning" process: background and recent progress

TLDR

A new process concept, “quenching and partitioning” (Q&P), has been proposed recently for creating steel microstructures with retained austenite. The paper reviews the Q&P concept, its thermodynamic basis, and models processing temperatures. The process quenches austenite below the martensite‑start temperature, then partitions carbon into the remaining austenite to stabilize it at room temperature, and is applied to silicon‑containing steels for low‑carbon TRIP sheet and medium‑carbon bar steel, as well as silicon‑containing ductile cast iron. Recent experiments show that Q&P can produce unique and attractive microstructure/property combinations in these steels. The study is funded by NSF (USA), CNPq (Brazil), and EPSRC (UK).

Abstract

A new process concept, "quenching and partitioning" (Q&P) has been proposed recently for creating steel microstructures with retained austenite. The process involves quenching austenite below the martensite-start temperature, followed by a partitioning treatment to enrich the remaining austenite with carbon, thereby stabilizing it to room temperature. The process concept is reviewed here, along with the thermodynamic basis for the partitioning treatment, and a model for designing some of the relevant processing temperatures. These concepts are applied to silicon-containing steels that are currently being examined for low-carbon TRIP sheet steel applications, and medium-carbon bar steel applications, along with a silicon-containing ductile cast iron. Highlights of recent experimental studies on these materials are also presented, that indicate unique and attractive microstructure/property combinations may be obtained via Q&P. This work is being carried out through a collaborative arrangement sponsored by the NSF in the USA, CNPq in Brazil, and the EPSRC in the United Kingdom.