Nb对转K2弹簧钢中MX析出相的影响

采用Thermo-Calc热力学软件,对转K2弹簧钢在400~1600℃存在的平衡析出相及Nb、V在奥氏体相中的固溶规律进行了计算,探讨了各合金元素含量对析出相析出规律的影响,并利用碳萃取复型与透射电镜(TEM)分析了Nb含量对析出相的影响.结果表明:转K2弹簧钢中平衡析出相主要为MX、M₇C₃、M₃C₂和AlN;Nb能显著提高MX相的稳定性.TEM分析表明,析出相尺寸变化范围为几纳米到100纳米以上,形态多呈近似球形或圆片状;随Nb含量增加,从低温铁素体中析出的细小颗粒所占比例显著增大,未溶解碳氮化物比例也有所增大,总体而言析出相平均颗粒尺寸得到细化;大颗粒析出相为富Nb的碳化物,而小颗粒为富V的碳化物,这与热力学计算结果相一致.

Effect of Nb on the precipitated phases of MX in switch K2 spring steel

Equilibrium precipitated phases in switch K2 spring steel in the temperature range of 400 to 1600℃ and the solubilities of Nb and V in austenite were calculated by using the thermodynamic software Thermo-Calc to investigate the effect of alloying element content on the equilibrium precipitated phases.Then,the effect of Nb content on the precipitated phases was analyzed by carbon extraction replica and transmission electron microscopy(TEM).It is shown that the main equilibrium precipitated phases in switch K2 spring steel are MX,M₇C₃,M₃C₂ and AlN,and the stability of MX phase can be significantly improved by adding Nb.TEM results reveal that the precipitated phases are spherical or disc-shaped,and their sizes range from several nanometers to more than 100nm.With the content of Nb increasing,the proportion of fine particles which precipitated from low-temperature phase ferrite increases dramatically,and the proportion of undissolved carbonitride also increases,overall the average particles size is refined.The large precipitates are Nb-rich carbides,while the small ones are V-rich carbides,which is in accordance with the results of thermodynamic calculations.