Effect of Ni and Cr Addition on Transformation and Properties of Low-Carbon Bainitic Steels

Four low-carbon bainitic steels with different nickel (Ni) and chromium (Cr) contents were designed to analyze the influences of Ni and Cr on bainitic transformation, microstructure and properties by metallographic method and dilatometry. The results showed that compared to the base steel, the kinetics of bainitic transformation in Ni or Cr addition steels was retarded. In addition, single Cr addition increased the amount of bainitic transformation in spite of the retarded transformation kinetics, while single Ni addition decreased the amount of bainitic transformation. Combined addition of Ni and Cr further reduced the kinetics of bainitic transformation. Moreover, individual Ni and Cr addition or composite addition of Ni and Cr improved the strength by refining bainite microstructure, carbide precipitation and martensite, but the total elongation decreased at the same time. Steel with composite addition of Ni and Cr presented the best product of strength and elongation. The work provided reference for the composition design of low-carbon bainitic steels.