Patent ID: 10689724

Abstract:
There is provided a steel sheet with strain induced transformation type composite structure having a predetermined chemical composition in which a microstructure at the ¼ thickness of the steel sheet includes, by area ratio, 50% to 85% of a polygonal ferrite, 3% to 10% of a residual austenite, 5% to 47% of bainite and 1% or less of a fresh martensite and a tempered martensite in total and satisfies the equation of 0.01<Ex.C/fsd≤0.015, the microstructure includes 1×1016 pieces/cm3 or more of precipitates containing TiC, an average grain diameter of the residual austenite 1.0 μm to 5.0 μm at an equivalent circle diameter, an average of closest distances of the austenite is 3.0 μm to 10.0 μm, and an average diameter of the precipitates is 3 nm or less.