摘要
Influence of the N/C ratio on the microstructure and properties of new-generation high-strength weathering steels was investigated using calculation of phase diagram(CALPHAD)and experiments.The microstructures of weathering steels containing different N/C ratios were predicted by a CALPHAD approach,and only three phases were predicted in these steels within the rolling temperature range of 850-1050℃.The precipitation fraction of VN/V(C,N)in creases with increasing N/C ratio.Microstructures of the four tested steels were all experimentally determined to contain bainite,ferrite,and VN precipitates after air cooling to room temperature.The bainite fraction increases with in creasing N/C ratio,and it is 85%in the steel containing 0.038% N and 0.032% C,The results of the tensile tests and impact tests demonstrated that the yield strength and tensile strength of the steel containing 0.038%N and 0.032%C are greater than 550 and 650 MPa,respectively,and the elongation is greater than 24%,which satisfies the design objectives for mechanical properties.The impact toughness values of the four steels at 0,-20,and-40℃ are all greater than 24 J.With increasing N/C ratio,the bainite fraction and the precipitation fraction of VN/V(C,N)increase,resulting in increasing yield strength and tensile strength.
