Segregation of boron in the temperature range of lower hot ductility of microalloy steels

The distribution of boron in 2.25Cr-1.0Mo steels cooled at 15 ℃ /s from 1320 ℃ to 1000 ℃,900 ℃,800 ℃ and then quenched after holding for 10 s was investigated by particle tracking autoradiography(PTA).The effect of the segregation of boron on hot ductility of the steel was discussed.The experimental results show that boron segregates to austenite grain boundaries as cooled to different experimental temperatures,and the concentration of boron at grain boundaries reaches its maximum at about 900 ℃.The precipitations containing boron are not observed in the steel containing boron of 0.00075 wt%.As cooled to 900 ℃ and 800 ℃,a small amount of precipitations containing boron in grain and grain boundaries are observed in the steel containing 0.0035 wt% boron.Large number of precipitations containing boron distribute in grain and grain boundaries at 1000 ℃ in the steel containing boron of 0.0081 wt%.The number of the precipitation increases as the temperature decreases,and when cooling to 800 ℃,most of the boron segregated to grain boundary are precipitated.It is also found that the segregation of boron to grain boundaries,which retards the formation of ferrite,enhances hot ductility of micro-alloy steels.