In situ observation on microstructural development of high-speed steel during carbon partitioning process

Quenching–partitioning–tempering (Q–P–T) process was applied to treat high-speed steel. Microstructural development and properties were studied using high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, X-ray diffraction and a drop hammer impact toughness tester. The results of impact toughness test showed that the impact absorption energy increased to 16.2–20.1 J along the Q–P–T process, namely 56–93% higher than that of traditional Q–T approach (10.4 J). The results of in situ HRTEM showed that the interface of martensite/austenite (α/γ) migrated from martensite towards austenite with the increase of holding time, which led to a reduction of retained austenite. One of the migration planes was (110)_α/(111)_γ. The cementite precipitation and slight decomposition of retained austenite were observed during carbon partitioning process.