• CN:11-2187/TH
  • ISSN:0577-6686

›› 1980, Vol. 16 ›› Issue (3): 1-17.

• 论文 •    下一篇

钢的回火与强度塑性的配合

周惠久   

  1. 西安交通大学
  • 发布日期:1980-06-01

TEMP ERING OF STEELS AND THE BALANCE BETWEEN THEIR STRENGTH AND DUCTILITY

Zhou Huijiu   

  1. Xian Jiao-Tong University
  • Published:1980-06-01

摘要: 淬火后回火是最常用的热处理工艺之一。然而,钢的强度与塑性常常随回火温度——时间参量的发言改变而向相反的方向变化。必须指出,这些强度与塑性值通常是由光滑试样单向拉力试验得来的,一个机械零件的实际承载能力或寿命往往既不单纯取决于材料的强度,也不单纯取决于塑性,而是根据服役条件决定于两者的合理配合。本文提供了几种结构钢淬火成为金属马氏体后回火对某些机械性能参量影响的研究结果。这些参量更接近于表征一些典型钢种的实际承载能力或服役寿命。它们包括:一次加载时的失效抗力:带有不同应力集中直至一个实际裂纹的极限拉伸强度,缺口敏感度,断裂韧性和冲击韧性。循环加载下的失效抗力:光滑与缺口试样的疲劳极限,过载持久寿命,重复冲击持久寿命,裂纹产生的应力循环次数及裂纹扩展速率。试验结果表明,几乎所有这些参量均在一定的回火温度下出现高峰、低谷或饱和拐点,它们反映了给定材料的强度与塑性之间的一种适当的配合关系,当服役条件改变时这些转折回火温度则向一定的方向转移,要求新的配合。从而为选择回火温度提供一些依据。通过回火转变的高压电镜薄膜透射研究,显示了不同回火温度下所发生的组织变化,为这些表征参量的变化提供了部分内在的联系数。

Abstract: Quenching followed by tempering is one of the most popular heat treating processes for steels. But it is usually observed that the strength and ductility of steels vary according to temperature-time parameter of tempering in opposite ways. It should be noted that these conventional strength and ductility values are obtained from unidirectional tension tests with smooth specimens. The actual load carrying capacity or service life of a machine part, however, does not follow closely with either strength or ductility of the material uniquely, but is determined by a suitable combination of strength and ductility according to service conditions.This paper presents results of investigations on the effect of tempering upon some of the parameters which more nearly characterize the load carrying capacity and service life of a few constructional steels quenched to fully martensitic structure. These parameters include:Resistance against fracture under monotonic loading-ultimate tensile strength of notched specimens with various stress concentrations right up to an actual crack and notch sensitivity factor, fracture toughness and impact toughness;Resistance against fracture under cyclic loading-endurance limit of smooth and notched specimen and endurance life due to over loading, endurance life due to repeated impact. Stress cycles for crack initiation and rate of crack propagation.Experimental results obtained show that nearly all of these parameters exhibit some peak, valley or saturation values at certain tempering temperatures, each corresponding to a suitable balance between strength and ductility of the steel prescribed conditions, This might throw some light on the selection of tempering temperature.Thin film electron-micrographs taken by a high voltage TEM reveal the structural changes which occur at different tempering temperatures. An, analysis of these changes provides some evidences for the above observations.