Quenched and tempered steel

Quenched-and-tempered (Q&T) steel is plate hardened by rapid water quenching from austenitizing temperature, then reheated below the transformation point to temper the brittle martensite into tougher tempered martensite. The two-step heat treatment yields high yield strength with retained toughness, the route used for ASTM A553 9 percent nickel cryogenic plate and for high-strength structural plates above the normalized grades. In the IACS UR W11 higher-strength grades, the production route may be normalizing, thermo-mechanical control processing (TMCP), or Q&T; TMCP is preferred for thick hull plate because it reaches the strength and toughness with lower carbon equivalent, which improves weldability. Q&T plate demands controlled heat input during welding to protect the heat-affected zone.