钛对铌微合金化钢夹杂物析出行为的影响

采用高频真空感应炉在1 550℃的Ar气氛中冶炼不同钛含量的钛、铌微合金化钢并对其进行热处理。分析了钛加入量对钢的成分、组织结构、钢中典型夹杂物及宏观力学性能的影响。研究结果表明:采用Al脱氧后的钛、铌微合金化钢氧含量降低到0.002 0%左右,合金元素的利用率超过80%。钢中的夹杂物主要有球形或近似球形的Al2O3、SiO2、TiOx及其复合夹杂。(Ti,Nb)(C,N)、NbC、TiC夹杂以氧化物夹杂为核心析出。随着钛合金加入量的增加,钢样中的部分夹杂物形貌由球形发展成长方形。经共聚焦激光扫描高温显微镜热处理过的钢样中析出较多细小的(Ti,Nb)(C,N)夹杂物。随着钛含量的增加,热处理后的钢中小于1μm夹杂物数量急剧增加,尺寸大于1μm的夹杂物的数量呈现减少的趋势。高温在线金相组织分析表明:钢中钛加入量增加,高温奥氏体晶粒变小,钢的组织细化,从而钢的宏观硬度增高。

Effect of Titanium on the Precipitation Behavior of Inclusions in Niobium Microalloyed Steel

Experiments were conducted in a high frequency vacuum induction furnace to smelt titanium and niobium microalloyed steel with different titanium addition at 1 550 ℃ under Ar atmosphere,and then the samples underwent heat treatment.The effect of titanium additive amount on composition,microstructure,typical inclusions and macro mechanical property of the titanium and niobium microalloyed steel were analyzed.The results show oxygen content in the steel microalloyed with titanium and niobium decreases to about 20×10-6 after Al is employed to deoxidize and the utilization rate of titanium exceeds 80%.Inclusions in the steel were mainly sphere shaped or approximate to sphere shaped Al2O3,SiO2,and TiOx based complex inclusions.Cube shaped(Ti,Nb)(C,N) complex inclusions and NbC,TiC inclusions in the steel precipitate around the spherical oxide inclusions.A lot of fine(Ti,Nb)(C,N) precipitations after heat treatment can be seen with confocal laser scanning microscope.After heat treatment,with the increase of titanium content in the steel,inclusions with the size less than 1 μm increase significantly,while the inclusions with the size larger than 1 μm tend to decrease.Heated and held at 1 200 ℃,the austenite grain of the samples became smaller with the increase of titanium addition in the steel.Thus the microstructure was obviously refined in steel,which led to improvement of macro hardness of the steel.