Next-Generation High-Strength Sheet Steel Utilizing Transformation-Induced Plasticity (TRIP) Effect

摘要

An outline description is made of the elongation increase mechanism, manufacturing principles, production-line operating examples, formability, weldability, and fatigue strength of next-generation high-strength sheet steel utilizing the transformation-induced plasticity (TRIP) effect. Hot-rolled and cold-rolled sheets with tensile strengths of 590 to 980 N/mm~2 were produced from the next-generation high-strength TRIP steel and- were proved to have a better combination of strength and elongation than conventional high-strength steels, The new high-strength TRIP steel was found to have very good stretchability near the plane-strain state and to yield high deep drawability in the TZP test. Since deformation on the punch shoulder occurs in the plane-strain state, TRIP increases the fracture strength, thereby improving the deep drawability of the steel. The spot weld strength of the new steel is comparable to that of conventional high-strength steels, and its fatigue strength is higher than that of dual-phase steel, which is claimed to have the highest fatigue strength for the same tensile strength.