Automatic Sample Preparation of Austenitic Stainless Steels for Microstructural Analysis
The high ductility of stainless steels presents difficulties during sample preparation. Austenitic steels are soft, ductile, and prone to mechanical deformation. Sectioning the hollow geometries of pipes and tanks can require special considerations as the thin walls may deform under the load of the cutoff wheel. Thin walled samples may undergo hot compression or cold mounting prior to grinding and polishing to make the process easier for the metallographer. When preparing 304 stainless, avoid coarse grinding steps and high pressures as this can result in deep deformation. Some companies will use diamond suspensions to polish the sample, while others will use electrolytic polishing and etching to reveal the microstructure. Electrolytic polishing gives excellent results for checking the microstructure, but is not suited to identify carbides as they will appear washed out or enlarged. Traditional etching can be difficult with stainless steels as they are highly corrosion resistant and require very strong acids to reveal their microstructure. If the stainless steel sample contains a weld, various image analysis programs can be used to measure features of the weld, like throat, penetration, and porosity. This presentation will demonstrate how automatic sample preparation can be used to achieve reproducible results, suitable for microstructural and weld measurement in austenitic stainless steels.