Steel Quench Hardening: The Martensite Transformation Front

Plunge a red-hot steel bar into water, oil or still air and watch its microstructure actually compute itself: a radial finite-difference heat-conduction model drives real temperatures inward ring by ring, and every ring's coldest-reached temperature feeds the Koistinen-Marburger equation to decide how much austenite has transformed into hard, brittle martensite. Carbon content sets both the martensite-start temperature and the achievable hardness ceiling, the quenchant sets how fast heat leaves the surface, and bar radius sets how far that heat has to travel from the core — reproducing the "mass effect" that keeps the centre of a thick part soft even after a severe water quench. Live readouts track elapsed time, surface and core temperature, average martensite fraction and estimated Rockwell-C hardness as the transformation front sweeps inward.