原奥氏体晶粒尺寸对珠光体钢组织及韧性的影响

探索了奥氏体晶粒尺寸对珠光体等温转变组织特征以及对韧性性能的影响规律.研究表明,在相同等温转变温度下,珠光体片层间距无明显变化,随奥氏体晶粒尺寸的增加,先共析铁素体量减少而珠光体团尺寸增加.珠光体断裂韧性受控于裂纹前沿塑性影响区尺寸(1～2)δc,其中δc为临界裂纹张开位移,当原奥氏体晶粒大于(1～2)δc时,裂纹扩展阻力主要来自穿越珠光体片层α、θ相的颈缩、破断.当原奥氏体晶粒尺寸接近或小于(1～2)δc时,裂纹主要沿晶界、珠光体团界、α+θ片层界面扩展,通过扩展路径发生多次弯折消耗能量,随原奥氏体晶粒尺寸增加,准静态断裂韧度J变化幅度较小.而冲击韧性缺口前沿塑性影响区远大于原奥氏体晶粒,大角度晶界将促使裂纹的转折而提高扩展阻力,提高裂纹前沿塑性区大角度晶界密度有利于提高冲击功,冲击韧性A随晶粒尺寸的增加显著下降.

Effect of Prior Austenite Grain Size on Microstructure and Toughness of Pearlitic Steel

The effect of prior austenite grain size on the pearlitic microstructure and toughness was investigated.Experimental results,showed that the interlarnellar spacing had no obvious change under the same isothermal transformation temperature.The proeutectoid ferrite percentage decreased and the pearlitic colony size increased with the increase of the prior austenite grain size.The fracture toughness was controlled by the microplasticity zone ((1-2)δc) at the crack tip,and the δc was opening displacement of critical crack.If prior austenite grain size was larger than (1-2)δc,the majority of crack propagation resistance came from necking and breaking of the pearlitic lamellar α and θ phase.If prior austenite grain size was close to or less than (1-2)δc,crack propagation mainly went through the grain boundaries,pearlitic colony boundaries and α+θ larnellar interface,which caused high crack tortuosity.The crack propagation resistance came from the crack deflection and branching.And the quasi-static fracture toughness J had small changes with the increase of prior austenite grain size,While the front microplasticity zone of the impact toughness notch was much larger than the prior austenite grain size.High angle grain boundary in the microplasticity zone would cause the crack deflection and branching,which increased the crack growth resistance.Improving high angle grain boundary density of the plastic zone was beneficial to improve the impact toughness,and the impact toughness decreased significantly with the increase of prior austenite grain size.