含Nb-Ti微合金钢第三脆性区铸坯缺陷

采用金相显微镜、复型萃取、SEM、TEM对析出物的形貌、尺寸、数量进行统计分析,并利用Gleeble-1500热模拟试验机,系统研究了含Nb-Ti微合金钢第三脆性区的热塑性。结果表明:温度在950~700℃范围内时,断面收缩率最小为25.7%。析出物以TiN、Nb(CN)为主,950℃时粒子尺寸在50nm左右。随着温度的降低,粒子数量密度由51个/μm2增加到580个/μm2,尺寸随之减小。975℃的抗拉强度及临界应力分别为58.3、61.0 MPa。975℃以上,临界应力小于抗拉强度,不易发生沿晶断裂。975℃以下时,晶粒变形临界应力大于抗拉强度,产生沿晶断裂。

Defection in Low Brittle Temperature Zone of Nb-Ti Micro-Alloyed Steel Slab

The morphologies, sizes and quantities of the precipitations in Nb-Ti micro-alloyed steel slab were studied systematically by using metallographic microscope, carbon extraction replicas, SEM and TEM. The hot ductility in low brittle temperature zone of the steel was also tested by Geelble-1500. The results show that when temperature is in the range from 950 to 700??, the lowest value of RA is 25. 7%. The precipitations are mainly TiN and Nb(CN), and their sizes are about 50nm at 950??. With temperature decreasing, the quantity of the particles increases from 51 to 580/??m2 while the size decreases. At 975??, the tensile strength and critical stress are 58. 3 and 61. 0MPa respectively. Over 975??, the critical stress is smaller than the tensile strength, it is difficult to produce inter-granular failure. Under 975??, it is apt to produce inter-granular failure when the critical stress for grain deformation is larger than the tensile strength.