论文部分内容阅读
据报导,对于淬火状态的AISI4340钢采用在1200℃的高温奥氏体化处理以代替870℃的常规热处理,可使断裂韧性增加到二倍,但夏氏冲击能量则减少。本文力求依据K_(1c)和冲击试验间的差异来解释夏氏冲击值和断裂韧性数据的矛盾。文献表明:所观察的特性是与剪切唇能量和应变速率效应无关的,但是,由每种奥氏体化处理所得到的组织对于缺口根部半径对韧性影响所起的反应不一样,通过这一点可对上述现象予以合理的解释。本文对于起这种特性作用的显微组织因素作了讨论。以这些和其它观察结果为基础,可以认为,对超高强度低合金钢来讲,把高温奥氏体化作为一种实际的热处理工序来应用是有问题的。最后,我们认为,材料韧性的评价不应该完全以K_(1c)或只以夏氏冲击能量数值为基础,而尖锐裂纹断裂韧性和圆缺口冲击能量试验两者都是需要的。
It has been reported that for quenched AISI4340 steels, high temperature austenitizing at 1200 ° C instead of conventional heat treatment at 870 ° C results in a doubling of fracture toughness but a reduction in Charpy impact energy. This paper seeks to explain the inconsistency between the Charpy impact value and the fracture toughness data based on the difference between K_ (1c) and the impact test. The literature shows that the observed properties are independent of shear lip energy and strain rate effects, but the organization obtained for each austenitizing treatment does not respond differently to the effect of notch root radius on ductility One point can be a reasonable explanation of the phenomenon. This article discusses the microstructural factors that contribute to this property. Based on these and other observations, it is believed that the application of high-temperature austenisation as an actual heat treatment process is problematic for ultra-high strength low-alloy steels. Finally, we believe that the evaluation of material toughness should not be based solely on Kc (1c) or only on Charpy impact energy values, whereas both the sharp-crack fracture toughness and the notched impact energy test are needed.