Influence of Test Method, Microstructure, and Microalloy Additions on Austenite Grain Size of Heat Treated SAE 1045 Steel

The austenite grain size (AGS) developed immediately before final cooling by quenching or other means is known to exert a substantial effect on the resistance to fracture in the final part. SAE 1045 steels containing Al, V, and V+Nb and a non-microalloyed steel were preconditioned by various thermomechanical treatments and then assessed for AGS by several methods defined in ASTM E112. Test results show that the microalloys present, the test method selected to evaluate the AGS, and the condition of the steel prior to conducting the grain size tests all have substantial effects on the measured AGS. The results demonstrate that for a meaningful AGS specification and test result, it is necessary to specify the precondition of the steel, the test method, and the test conditions.