Nb-Ti微碳深冲双相钢的连续冷却转变规律

通过连续冷却实验研究了Nb-Ti微碳深冲双相钢在不同冷却速率下的显微组织变化规律。并结合显微组织、热膨胀曲线以及实验钢的硬度值绘制出实验钢的CCT曲线。结果表明,实验钢的CCT曲线由铁素体、珠光体与贝氏体区组成,其中铁素体和贝氏体的区域较大,覆盖冷却速度范围较广。实验冷却速率下未出现马氏体组织。在0.5～1℃/s的慢冷速下,组织由铁素体和珠光体组成;当冷速增加至3℃/s时,贝氏体开始出现,珠光体消失。当冷速在5～10℃/s范围内时,获得铁素体+贝氏体双相组织;当冷速大于10℃/s时,铁素体相变消失,此时为纯贝氏体转变。热处理过程中若想获得一定量的马氏体组织,退火温度宜设置在820～900℃双相区较低温度范围,使合金元素充分富集于少量奥氏体中,在随后冷却过程中此奥氏体转变为马氏体组织。

Continuous cooling transformation of Nb-Ti micro-carbon deep drawing dual-phase steel

The microstructures of Nb-Ti micro-carbon deep-drawing dual-phase steel at different cooling rates were studied by continuous cooling test,and CCT curve of the tested steel basing on the microstructures,the thermal expansion curves and the hardness values was determined.The results show that the CCT curve of the experimental steel is composed of ferrite,pearlite and bainite regions,among which the ferrite and bainite occupy a larger area for cooling.The martensitic transformation does not occur at the experimental cooling rate.The microstructure is composed of ferrite and pearlite at a slow cooling rate of 0.5-1℃/s.As the cooling rate increases to 3℃/s,bainite microstructure begins to appear and pearlite disappears.When the cooling rate is 5-10℃/s,the dual-phase microstructure of ferrite and bainite can be obtained.When the cooling rate is over 10℃/s,the ferrite transformation disappears,then pure bainite transformation occurs.To obtain a certain amount of martensite during heat treatment,the annealing temperature should be set between 820-900℃,so the alloy elements can be fully enriched in a small amount of austenite,which is conducive to the formation of martensite in the subsequent cooling process.