Volume 57, Issue 1

Submerged arc welded heat resistant 2.25Cr-1Mo-0.25V weld metals are increasingly used for hydrocrackers and thick-walled pressure vessels in the petrochemical industry. They are exposed to high pressures and temperatures of more than 450 °C. In order to satisfy the high demands with respect to strength and toughness, they are typically subjected to a post-welding heat treatment at temperatures in the range of 691 – 719 °C. During heat treatment, a large number of changes take place in the weld's microstructure. These changes can partly be observed during a light microscope examination. Etching studies described in the literature are mostly concerned with determining phase fractions in multi-phase steels. This work shows how selective etching and precipitation etching allow for contrasting various microstructural features. While the etching solutions Klemm I, aqueous sodium metabisulfite, and picric acid are suitable for revealing the former austenitic grain structure, the dendritic solidification structure of samples in as-welded condition can be contrasted using color etching techniques according to LePera, Klemm I, and Beraha I. For an identification of changes in the shape of dendrites, it is recommended to perform picric acid etching. Color etchings according to Klemm I and LePera are recommended for revealing larger carbides, as they provide a good contrast between the carbides which appear bright, while the surrounding microstructure is colored.

The aim of this study is the optimal preparation of the surfaces of nickel bicrystals to be used in thermal grooving experiments. For this purpose, it must be ensured that the surface is smooth, flat and distortion-free in the region around the grain boundary. We will present different approaches to the preparation of a nickel bicrystal, namely mechanical, chemical and electrolytic polishing as well as ion cross-section milling. The different preparation methods will be evaluated and compared with regard to the requirements for the prepared surface and their advantages and disadvantages. In order to evaluate the quality of the prepared surface, images will be obtained using optical light microscopy, scanning electron microscopy, laser scanning microscopy and atomic force microscopy. It was found that broad ion beam milling was the only method to satisfactorily meet all the criteria for the prepared surface.

In this contribution, some aspects of fractography are discussed, arguably the failure analysts' most potent analytical tool in metallurgical failure analyses. The characterisation of fracture surfaces is indispensable when it comes to getting to the bottom of things in regards to component failures. When machine parts or entire assemblies fail by fracture of individual members, the fracture surface contains the data that tells the failure analyst about the history of the failed component, and hopefully will also shed some light on the exact failure mode that eventually lead to fracture. That makes fractography, the art of reading fracture surfaces, so valuable. This applies to all material classes, i. e. metals, ceramics, and plastics alike. This paper, however, focuses on failures of metallic components only. When there is no fracture surface in a failed part, one is produced by forcing open cracks or other imperfections that might be suitable for this purpose. Once this is achieved, the failure analyst will open his or her toolset of macro- and microfractographic analysis equipment. It is not exaggerated to say that the scanning electron microscope (SEM) revolutionised the art of microfractography from the early 1960 s on. In this paper, a number of examples for this are given.