Peculiarities of Revealing and Estimation of Austenitic Grain in Structural Alloyed Steels

Abstract

Purpose. Establishing effective and correct techniques for detecting the grain structure in structural medium-carbon steels taking into account the recommendations of modern standards (ДСТУ ISO, ASTM, ГОСТ) with the aim of reliably determining the austenitic grain size and putting into operation of metal with the well-known and required, according to the normative technical documentation (technical requirements, drawings) quality.
 Research methods. Metallographic analysis of microstructure and evaluation of the austenitic grain size were carried out by comparing the image revealed on polished and etched using various chemical reagents microsections of heat-treatable steel 40KHN2МА-Ш with etalon of scale of standard.
 Results. Studies of structural alloyed steel 40ХН2МА-Ш found that the most effective etchant reagent, which best detects initial austenitic grain boundaries in medium-carbon alloyed steels, is a standard reagent - a saturated aqueous solution of picric acid. As a result of etching in this reagent, a visible image of the grain structure is formed in the form of a clear contrast of light areas of the grain body and dark lines of the grain boundaries, which allows a correct comparison of the structure with the images of the standards on the scales.
 Scientific novelty. On the example of heat- treatable steel 40ХН2МА-Ш, the ways of further development of ideas regarding the choice of an effective chemical reagent are considered for the purpose of detecting and forming a visible grain structure in accordance with the requirements of methodical standards in structural medium-carbon steels, proper and reliable estimation of austenitіс grain size using standard scale.
 Practical value. A correct procedure for detecting the initial austenite grain is proposed, which allows to reliably determine the grain size and quality from this parameter of various structural steels including for the production of responsible parts of aircraft and spacecraft.