Effect of continuous annealing process parameters on microstructure and properties of 1180 MPa grade Nb-microalloyed dual phase steel with high formability
In order to achieve the goal of energy conservation and emission reduction,automobile bodies are develo-ping towards lightweight and high-quality direction.DH steel has a wide application prospect due to its excellent strength and plasticity performance.The high formability 1180 MPa grade Nb-microalloyed dual phase steel,exhib-iting excellent properties,had been developed through laboratory simulated continuous annealing and characteriza-tion analysis of microstructure and properties.The results of continuous annealing tests reveal that the increase of annealing temperature lead to corresponding rise in the content of martensite and bainite,consequently resulting in enhancement of tensile strength up to 1200 MPa at 870 ℃.As the annealing temperature further increases,the vol-ume fraction of tempered martensite and the bainite increases,resulting in slight decrease in strength.As the over-aging temperature increases,the tensile strength gradually decreases and the elongation increases to 16.2％at 370 ℃.Based on the continuous annealing test results and the feature of industrial production line,DH1180 contin-uous annealing plates was industrially produced.Its microstructure is composed of ferrite,martensite,bainite,and residual austenite(φ(γ)=6.62％),dispersed with nano-scaled(Nb,Ti)C precipitates,showing superior match of strength and plasticity with tensile strength of 1257 MPa and elongation of 15.6％.The development and applica-tion of DH1180 steel provides more possibilities for high-strength steel for automobile.
continuous annealingretained austeniteprecipitatesmicrostructure and propertydual phase steel with high formability
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