Revealing the Microstructure and Mechanical Properties of Rapidly Quenched and Tempered 51CrV4 Steel Processed Via a Continuous Induction Line

Abstract

This study investigates the microstructural evolution and mechanical response of 51CrV4 spring steel subjected to flash quenching and tempering using a continuous high-speed induction heating line. The steel, supplied as 8 mm thick sheets with a composition of Fe–0.5C–0.9Mn–1Cr–0.16V (wt.%), was processed through rapid austenitisation at 900 °C (~200 °C/s), followed by water quenching and tempering at 300 °C. Rapid induction heat treatment was utilized to produce a hardened surface layer with refined microstructure and balanced mechanical properties. Optical microscopy revealed a uniform, crack-free martensitic layer extending to approximately ~1.2 mm from the surface, while hardness profiling showed a gradient from 590 ± 20 HV at the surface to 240–330 HV in the core. Electron Backscatter Diffraction (EBSD) analysis confirmed a fully martensitic surface structure with refined prior austenite grains (~3.2 µm), and FESEM imaging indicated minimal carbide coarsening, supporting the effectiveness of short-time tempering. These results demonstrate that flash induction processing can produce a hardened shell with retained core ductility. The consistency between EBSD, FESEM, and hardness data validates the process as an energy-efficient, scalable alternative to conventional furnace-based treatments.