Effect of Cold Reduction Ratio and Annealing Temperature on Microstructure and Mechanical Property of Added Phosphorus High Strength Nb-IF Steel

Abstract

Hot rolled added phosphorus high strength IF steel was used to study the effect of cold reduction ratio and annealing temperature on the microstructures and mechanical properties of experimental steel. The experimental results showed that the recrystallization has finished under 840°C to 880°C annealing temperature followed 65% to 75% cold reduction ratio. Under 600°C coiling temperature, 840°C annealing temperature and 65% to 75% cold reduction ratio, the yield strength, tensile strength ,elongation percentage, yield point elongation, the plastic strain ratio and strain hardening exponent were approximate 240MPa, 410MPa, 36.0%, 1.6%, 0.26 and 1.9. Under 650°C coiling temperature, 860°C annealing temperature and 65% to 75% cold reduction ratio, and that were approximate 240MPa, 415MPa, 35.0%, 2.0%, 0.24 and 1.9. Under 700°C coiling temperature, 880°C annealing temperature and 65% cold reduction ratio, and that were approximate 190MPa, 380MPa, 35.0%, 0.8%, 0.26 and 2.0. Therefore, the suggested the optimal coiling temperature6 is 600°C, cold reduction ratio is 65% to 75%, annealing temperature is 840 °C, and it obtains optimally match of high strength and punching property.