White layer formation resulting from machining and its effect on high strength steel

Abstract

[EN] The present report is separated in two parts. The first part which concerns a literature review mainly focuses on finding out the mechanism of white layer formation and the machining parameters affecting its properties as well as its effect on the microstructure of high strength low-alloy steels. As part of an experimental analysis concerning 300M steel, some similar steels white layers features will be discussed; their properties, causes, formation mechanism and the microstructural changes induced to the material. On a second part, an experimental procedure has been led to reveal white layers on 300M steel samples with different machining parameters. All the steps of sample preparation have been followed; from sectioning with an abrasive cutter, hot compression mounting, grinding and polishing to chemical etching. A parallel literature research has been also led to find the best etchant to reveal the desired microstructure of 300M steel. Hypothesized white layers, compared to literature findings, about 1μm thick have been obtained after sample preparation, by optical microscope observations. No appreciable differences have been found between the different observed bright layer thicknesses of different samples with varying cutting parameters. According to literature findings, this phenomenon may be caused by the use of brand new tools on the machining process and cutting parameters used for the diverse samples could be more different between them. Following white layer laboratory traditional detection methods, some innovative non-destructive ways of detecting white layers are also presented to be explored on future studies, as a way of future confirmation of the hypothesized white layers found on the laboratory or the industry.