Volume 59, Issue 2

Using the example of the high-alloy austenitic steel 1.4828 (X15CrNiSi20-12), which is typically used for high-temperature applications, this paper will demonstrate how the performance characteristics of semi-finished products are impacted by the condition of a material after production and processing. For this purpose, samples of a cost-effective as-cast condition and a comparatively expensive as-forged condition were studied in a comparative approach. The microstructure was examined by means of light optical as well as scanning electron microscopy, hardness values were determined, and the corrosion behavior was characterized by electrochemical investigations. The comparative studies show that despite an almost identical chemical composition, both the as-fabricated and as-processed conditions of a material have a decisive impact on the performance characteristics, particularly on corrosion behavior.

The metastable austenitic steel X6CrNi-Nb18-10 (AISI 347) will partly transform to α‘-martensite under mechanical loading at room temperature. In order to determine the influence of loading conditions on deformation-induced martensitic transformation, a thorough surface preparation is required for the samples to be analyzed, ensuring that a martensite-free sample surface is achieved prior to mechanical loading. In this paper, two preparation techniques were compared, focusing in particular on the final preparation step, which is polishing. Measurements using electron backscatter diffraction (EBSD) have revealed that large α‘-martensite volume fractions of more than 20 % are present on the prepared sample surface after vibratory polishing. However, they can be removed almost completely by electrolytic polishing and chemical etching respectively.

Failure analysts are sometimes surprised to find well-known metallurgical failure mechanisms at work in completely unexpected places. This contribution is an eloquent example for just such an incidental convergence of well-known failure mechanism and fabrication process where it was not reported to have previously occurred. Liquid Metal Embrittlement (LME) was observed in Narrow Gap Welds (NGW) produced for Welding Procedure Qualification (WPQ). The embrittling liquid metal was copper in this case. It is believed to have originated from copper backing used for weld pool protection. It was recommended to replace copper backing with ceramic weld pool protection.