Effect of Prior Austenite Grain Size on Microstructure and Toughness of Pearlitic Steel
LIANG Yu1,2, XIANG Song1,2, LIANG Yilong1,2, YANG Ming 1,2, WEI Zemin1,2, XIONG Hu1,2, LI Jing1,2
1 School of Materials and Metallurgy, Guizhou University, Guiyang 550025; 2 The Key Laboratory for Mechanical Behavior and Microstructure of Materials, Guiyang 550025;
Abstract: The effect of prior austenite grain size on the pearlitic microstructure and toughness was investigated. Experimental results showed that the interlamellar 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 cri-tical 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 lamellar 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.
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2017, Vol. 31 
