Abstract This investigation focuses on the dependence of stable crack growth resistance, as measured by the short-rod fracture toughness test, on secondary void-initiating particles such as AlN and Ti-based grain-refining precipitates in a variety of high-strength steels with tempered martensitic microstructures. The model developed by Ritchie and Thompson is modified to illustrate the significant amounts of toughening that can result from the refinement of secondary particles. Analysis of the data suggests that material strength is a predominant factor in increasing the short-rod fracture toughness relative to linear-elastic measures of initiation fracture toughness, but the extent of toughening is limited by the size and number density of secondary particles in the microstructure. The variation in estimates of secondary microvoid initiation and growth strains with precipitate size reinforce the notion that primary fracture at non-metallic inclusions and secondary fracture at smaller particles occur as sequential processes with a degree of concurrence that is dependent on the state of precipitation in both particle dispersions. Toughening in this connection is maximized by increases in microvoid growth strain that result from decreases in the size and areal number density of secondary void-initiating particles. Finally, the occurrence of transient instabilities during crack extension in short-rod specimens is explained with a phenomenological model that relates crack growth stability to natural variations in the dispersion of secondary void-initiating particles in the microstructure.

中文翻译：

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二次空洞起始粒子对高强钢稳态裂纹扩展性能的影响

摘要 本研究的重点是通过短杆断裂韧性试验测量的稳定裂纹扩展阻力对各种高强度钢中二次空洞起始颗粒（如 AlN 和 Ti 基晶粒细化沉淀物）的依赖性。回火马氏体显微组织。对 Ritchie 和 Thompson 开发的模型进行了修改，以说明二次颗粒细化可能导致的大量增韧。数据分析表明，相对于起始断裂韧度的线弹性测量，材料强度是增加短杆断裂韧度的主要因素，但韧化程度受微观结构中次级颗粒的尺寸和数量密度的限制. 二次微孔起始和生长应变随沉淀物尺寸的变化，强化了这样一种观点，即非金属夹杂物处的一次断裂和较小颗粒处的二次断裂是作为连续过程发生的，具有一定程度的并发性，这取决于两者的沉淀状态。颗粒分散体。在这方面，由于二次空隙引发颗粒的尺寸和面数密度的降低，微孔生长应变的增加使增韧最大化。最后，用现象学模型解释了短棒试样裂纹扩展过程中瞬态不稳定性的发生，该模型将裂纹扩展稳定性与微观结构中二次空隙起始粒子分散的自然变化联系起来。