The Effects of Cr and Al Addition on Transformation and Properties in Low-Carbon Bainitic Steels

Three low-carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition is effective for improving the strength of low-carbon bainitic steel by increasing the amount of bainite. However, compared with the base steel, combined addition of Cr and Al has no significant effect on bainitic transformation and properties. In Cr-bearing steel, Al addition accelerates initial bainitic transformation, but meanwhile reduces the final amount of bainitic transformation due to the formation of a high-temperature transformation product such as ferrite. Consequently, the composite strengthening effect of Cr and Al addition is not effective compared with individual addition of Cr in low-carbon bainitic steels. Therefore, in contrast to high-carbon steels, bainitic transformation in Cr-bearing low-carbon bainitic steels can be finished in a short time, and Al should not be added because Al addition would result in lower mechanical properties.