Annealing, normalizing, quenching, and tempering; the TTT diagram concept that explains why cooling rate controls whether steel becomes pearlite, bainite, or martensite; and the case-hardening processes that put a hard, wear-resistant surface over a tough core.
Two parts machined from the identical bar of steel can end up with dramatically different hardness, strength, and toughness depending only on the heat treatment each one receives afterward — because heat treatment changes microstructure, not composition or shape. This module builds that structure-property connection from the ground up: how annealing and normalizing soften and refine a structure, how quenching suppresses diffusion to force martensite formation, how the TTT diagram explains the cooling-rate/microstructure relationship behind hardenability, and how tempering trades some of that as-quenched hardness back for the toughness a real part needs.
By the end of this module you should be able to explain why a gear is carburized or induction-hardened rather than through-hardened, and why alloying elements that shift a steel's TTT nose to the right make thick sections easier to through-harden with a milder quench. Module 11's fatigue content and Module 13's failure analysis both return to the surface condition and residual stress state that heat treatment establishes here.