V对高碳钢连续冷却时组织转变的影响

THE EFFECTS OF V ON PHASE TRANSFORMATION OF HIGH CARBON STEEL DURING CONTINUOUS COOLING

通过在Gleeble1500热模拟试验机上的模拟加热和冷却实验,研究了连续冷却条件下不同含量的V对高碳钢组织转变的影响,并测定了相关力学性能.实验结果表明:V的加入降低了高碳钢珠光体转变温度,推迟了珠光体转变的CCT曲线,细化了珠光体片层,增加了高碳钢珠光体组织的强度和硬度,从V降低珠光体转变开始温度和降低珠光体团长大速率两个方面分析了V降低珠光体平均转变温度的原因.实验还观察到在1℃/s冷速下高碳钢原奥氏体晶界上存在少量铁素体,加入0.1%V对晶界铁素体的析出有抑制作用,而加入0.2%V到0.3%V则促进铁素体在晶界明显析出,相关力学性能的测定表明晶界铁素体的出现改善了高碳钢塑性.

Interlamellar spacing is one of the most fundamental parameters to characterize the pearlite microstructure and its mechanical properties,the influence of some alloying elements on interlamellar spacing in high carbon steels has been extensively studied in the past.Unfortunately,few studies refer to the influence of vanadium.In this paper,the effects of different amounts of vanadium on phase transformation in high carbon steels during continuous cooling has been investigated on Gleeblel500 thermo-mechanical simulator,and the mechanical properties relevant to these effects have been measured.The results show that by the way of adding vanadium to the high carbon steel,the pearlite transformation temperature is depressed,the CCT curves of this transformation are postponed so that the interlamellar spacing is reduced,leading to the increase of the pearlite hardness and strength in the high carbon steel.There are two reasons why vanadium can depress the average temperature of pearlite transformation：firstly,vanadium depresses the start temperature of this transformation, secondly,it lowers the velocity of pearlite nodule growing.It is also found that ferrite appears on the austenite grain boundaries of the high carbon steel,introducing 0.1%vanadium into the high carbon steel can somewhat restrain the ferrite formation,nevertheless by the way adding 0.2%or 0.3% vanadium,the ferrite formation on the austenite grain boundaries is apparently promoted.Evidently, the ferrite formation on austenite grain boundaries is beneficial to the improvement of ductility of high carbon steels as confirmed in this paper.