Preliminary Evaluation of Fatigue in Carburized, Conventionally and Intensively Quenched Steels

摘要

Steels subjected to carburizing, quenching and tempering are widely used for components that require hardness and superficial mechanical resistance together with good core toughness. Intensive quenching is a method that includes advantages of crack prevention when subjected to severe cooling, increased mechanical resistance and improvement in fatigue performance, among others, when high compressive residual stresses at the surface of steel parts are achieved and fine grains at their core are provided.If the cooling rate is sufficiently high, low-hardenability, killed plain carbon steels may be used instead of higher-cost, low alloy steels because after intensive quenching compressive residual stresses are formed at the surface of steel parts. The objective of this work is to compare carburized non-killed AISI 1020 steel samples, which were not modified by Al to make fine grains that were subsequently conventionally and also intensively quenched. For comparison, carburized AISI 8620 samples were conventionally quenched. After quenching, all steel samples were compared metallurgical and mechanical analyses.The results of this study showed that when the same carburized non-killed AISI 1020 steel was compared with samples that were subjected to the two quenching methods, intensive quenching was superior with respect to mechanical and metallurgical properties. When comparing the different steels, it was found that samples of intensively quenched non-killed AISI 1020 steel yielded grain sizes which were three times greater than those obtained with conventionally quenched AISI 8620. Therefore the benefits of intensive quenching are overcome by this fact. These results show that plain carbon steels must be modified by Al to make fine grains.