Effects of chromium on the microstructure and hot ductility of Nb-microalloyed steel

It is well-known that the surface quality of the niobium microalloy profiled billet directly affects the comprehensive mechanical properties of the H-beam. The effects of chromium on the gamma/alpha phase transformation and high-temperature mechanical properties of Nb-microalloyed steel were studied by Gleeble tensile and high-temperature in-situ observation experiments. Results indicated that the starting temperature of the gamma ->alpha phase transformation decreases with increasing Cr content. The hot ductility of Nb-microalloyed steel is improved by adding 0.12wt% Cr. Chromium atoms inhibit the diffusion of carbon atoms, which reduces the thickness of grain boundary ferrite. The number fractions of high-angle grain boundaries increase with increasing chromium content. In particular, the proportion is up to 48.7% when the Cr content is 0.12wt%. The high-angle grain boundaries hinder the crack propagation and improve the ductility of Nb-microalloyed steel.

Automated summary

Chromium has a significant influence on the gamma/alpha phase transformation and high-temperature mechanical properties of Nb-microalloyed steel. The addition of 0.12wt% chromium can improve hot ductility, reduce the thickness of grain boundary ferrite, increase the number fractions of high-angle grain boundaries, and subsequently enhance the ductility of Nb-microalloyed steel.