Correlating Macroetch Results to Microstructural Examinations in Steel Products

Macroetch evaluation of ingots, billets and forgings have been conducted for many years on steel product. This trend continues today, however, there has been an increase in macroetch evaluations of non-ferrous alloys in recent years. In addition, common ASTM specifications that govern this evaluation are being invoked to accommodate different alloys, geometrical shapes and updated processing methods. There have been changes to ASTM E381 in recent years regarding the “Standard Method of Macroetch Testing of Steel Bars, Billets, Blooms, and Forgings” to address frequent structural interpretation questions. Other specifications, like ASTM A604, govern additional macroetch evaluation criteria. Improvements in preparation techniques and digital photography have caused some to question what some of the macroetch features indicate about the underlying microstructure. Debates regarding specification criteria versus how the material behaves in service have been raised in recent years, particularly in regard to segregation and dendritic structures. This presentation discusses the correlation between common macroetch features and their microstructural counterparts. Different carbon steel and stainless steel alloys are investigated with common defects presented for each alloy family. Preparation methodologies employed have a large impact on what macroetch indications are visible and will be discussed in the presentation as well.

Keywords: macroetch, microstructure, defects, microscopy, ingot, billet, forging.