Identification of intermetallic phases in the structure of austenitic steel with use of Scanning Kelvin Probe Microscopy

Delta ferrite is formed in austenitic steels during the solidification of the alloy and its welds. It can also occur as a stable phase in any temperature range in high-alloy austenitic-ferritic steels. Depending on the amount, it can change into gamma and sigma phases and into ferrite with variable chromium content. The main role of delta ferrite in the welds of austenitic stainless steel is to prevent hot cracking. The minimum content of 5% prevents this phenomenon. However, on the other hand, an increase in the δ-phase content increases the brittle tendency of the weld, which also means a reduction in its impact toughness. In addition, a longer thermal exposure leads to the transformation of ferrite δ into a brittle phase σ, which deteriorates the mechanical properties of the steel [1]. Maintaining the appropriate content of the discussed phase, as well as the possibility of estimating the content, especially with suspected exposure of the construction material to elevated temperatures, is useful for assessments of mechanical properties of the material. The described collection contains the results of topographic imaging and potential mapping of the surface of AISI 317L samples. The aim of the research was to confirm the possibility of observing phase heterogeneity based on the diversified morphology and volta potential values. Measurements were made in the semi-contact imaging mode, synchronously with potential mapping using Kelvin probe microscopy. A conductive, semi-contact CDT-NCHR probe was used. The collection contains 12 images.
[1] A. Padilha, C. Tavares, F. Tavares, M. Martorano, Delta Ferrite Formation in Austenitic Stainless Steel Castings. Materials Science Forum. (2012) 730-732. 10.4028/www.scientific.net/MSF.730-732.733.