Structure–property correlation of EN steel and evaluation of mechanical properties through BIT

The present studies deal with the evaluation of mechanical properties through Ball Indentation Technique (BIT) for En steel, having varying microstructure due to specific heat treatment imparted. Investigations have been carried out on four types of failed shaft materials. The dependence of yield strength (YS), ultimate tensile strength (UTS), strength coefficient (K) and strain hardening exponent (n) values on various microstructural features is studied using the BI technique and the results are validated with the standard conventional test results. It is found that indentation diameters (plastic) measured by linear variable displacement transducer (LVDT) are slightly less than the diameters measured by optical microscope and this is due to pile-up/sink-in of materials surrounding the indentations. So the determination of mechanical properties, using LVDT measured depth, requires addition of correction factor for getting actual contact diameter. This structure–property correlation study clearly proved the effectiveness of the BI set-up to find the small changes in mechanical properties due to heat treatment on the same group of material.