共析钢中片状珠光体脆化钢材的机理研究

Research on Embrittlement Mechanisms of Lamellar Pearlite in Eutectoid Steel

观测了片状珠光体钢在不同热处理状态时的显微组织和断口形貌,对比了不同热处理方式对片状珠光体钢组织及性能的影响,借助断裂模型分析了片状珠光体组织容易导致钢材脆断的作用机理,并讨论了影响片状珠光体形成的因素。结果表明,片状珠光体位向明显、区域偏析严重是钢材脆断的重要因素;片状珠光体钢断口组织粗大,解理面呈河流状花样,解理台阶和撕裂棱较少;低温退火很难改善片状珠光体钢的脆性,而高温正火则能显著提高其韧性;片状珠光体内交界面和相界面越多,韧性越强,而提高过冷度减小片间距能增加相界面;共析钢中碳含量处于共析点决定了其冷却过程中易形成片状珠光体组织。

Microstructures and fracture surface morphologies of lamellar pearlite steel were observed, which were in different heat treatment conditions, The comparison were made on microstructures and properties of lamellar pearlite steel affected by different heat treatment methods. The action mechanism why lamellar pearlite microstructure brings about embrittlement fracture of steel easily is analyzed based on fracture model. And the effect factors to form lamellar pearlite was discussed. The results show that： The important factor of embrittlement fracture is considered of the apparent orientation of pearlite lamellar and high region segregation in steel; Observing in microstructures it was found that the fracture surface was coarse, and cleavage face exhibiting river-like configuration, few cleavage steps and tear ridges were found in lamellar pearlite steel; It＇s difficult to reduce the brittleness by low temperature anneal, but toughness could be improved evidently by high temperature normalizing for lamellar pearlite steel. High toughness is in association with more intersecting interfaces and phase boundaries. Intersecting interface can be increased by increase undercooling to reduce interlamellar spacing. Lamellar pearlite is easily formed during cooling of eutectoid steel because of the carbon content locates at eutectoid point.