Revealing prior-austenite grain boundaries and martensitic structure of as-quenched aisi 4140 steel treated by plasma electrolysis

Abstract

The determination of prior-austenite grain size has been the subject of metallurgical research efforts for many years. Metallurgical laboratories are often required to perform prior-austenite grain size determinations on martensitic steel components that have been heat treated. Although these methods may occasionally be mandated by material or procedural speciffcations, they are typically not preferred because they have a tendency of altering the as-received microstructure. These processes can also be labour-intensive and costly. The goal of this work is to chemically etch and identify the prior austenite grain size and martensitic structure of AISI 4140 steel treated by plasma electrolysis. Polished samples were immersed in 60% HCl, 30% HNO3, 5% HF, 5% H2O for 5 seconds then immersed in 5% picric acid, 5% HCl, 90% ethanol to reveal microstructures. Finally, the grain boundary and lath martensitic structure were revealed.