Effect of austempering temperature on high cycle fatigue behaviour in nanostructured bainitic steels

The effect of three different austempering temperatures viz. 250 degrees C (NB250), 300 degrees C (NB300) and 350 degrees C (NB350) on high cycle fatigue behaviour of carbide-free nanostructured bainite was investigated. There was an increase in yield strength with a decrease in austempering temperature due to finer bainitic ferrite (BF) and its higher volume fraction compared to retained austenite (RA). However, NB350 showed significant strain hardening compared to NB250 and NB300 due to transformation induced plasticity (TRIP). This also had implications in enhancing its fatigue life at almost all stress levels compared to NB250 and NB300 inspite of having a lower yield strength and tensile strength.

Automated summary

This study investigated the effect of three different austempering temperatures on the high cycle fatigue behavior of carbide-free nanostructured bainite. Lower austempering temperature led to increased yield strength, while NB350 showed significant strain hardening due to transformation induced plasticity, resulting in longer fatigue life compared to NB250 and NB300.