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

Steels treated through carburizing, quenching and tempering are broadly used in components that need to have hardness and superficial mechanical resistance together with a good toughness at the core of the component. Intensive quenching is a method that presents some advantages, such as the possibility of avoiding cracking due to extreme cooling, the increase in mechanical resistance and improvement in fatigue performance, among others. Once the cooling rate is very high, it can be used low carbon steels instead of low alloy steel. The present work aims to compare carburized samples that were quenched afterwards. AISI 1020 samples were thermally treated by intensive quenched and only a few were treated by oil quenching. All AISI 8620 samples were treated by conventionally quenched. Once it was done, comparisons were made by metallurgical and mechanical analysis. Results showed that when the same carburized AISI 1020 steel quality was compared with samples that went through different quenching methods, intensive quenching was superior. Examples were higher core hardness and higher mechanical resistance. When comparing different alloys it was found that samples of intensively quenched AISI 1020 presented grain sizes which were three times bigger than for conventionally quenched AISI 8620. Therefore, in a certain way, it has overcome the benefits of intensive quenching such as higher mechanical resistance in the stress-strain testing. Besides this, the difference between Wohler curves is subtle even with this significant difference in grain size.