Effect of Nb Content on the Abnormal Grain Growth in 20MnCr5 Hot‐Rolled Bar

In the present article, the abnormal grain growth behavior of 20MnCr5 hot‐rolled bars with microalloying of 0.0198 wt% niobium low‐Nb steel (LNb) and 0.0241 wt% niobium high‐Nb steel (HNb) are investigated after heat treatment at 960 °C for 4 h. The radius of the hot‐rolled bars is 22.5 mm and the results show that the mixed grain region in LNb hot‐rolled bar is with a radius ranging from 9.5 to 22.5 mm, while the mixed grain region in HNb hot‐rolled bar is with a radius of 20 to 22.5 mm. The main precipitates are AlN and NbC, particles, and their composite precipitates. In LNb and HNb, the precipitates in outer region 1 are larger than those in inner region 3, and the number density is less. In the same region, the particle size of precipitates in LNb is larger than that in HNb, and the number density is much lower. Therefore, the mixed grains appear near the outer region of the experimental steels, and the mixed grain phenomenon of LNb is more serious than that of HNb.