Volume 58, Issue 4

The resistance of martensitic stainless steels to wear and corrosion is greatly influenced by the martensitic matrix and the presence of carbides. The precipitation of carbides along the grain boundaries will lead to a significant decrease in fracture toughness and furthermore, will increase the risk of intergranular corrosion. With tools made of corrosion-resistant steel castings, this fact is of particular relevance as coarse eutectic carbide precipitates are normally not sufficiently dissolved during conventional austenitization. In this context, the dissolution of carbides will be studied on the basis of systematic heat treatment experiments and observed using light optical microscopy and the resulting microstructure and its impact on the mechanical properties (hardness) will be discussed in the following sections.

Vibratory polishing is a rather straightforward technique for the preparation of microstructures for microscopic examinations which would otherwise be difficult to prepare. This work will present a number of practical application examples. For instance, this technique is well-suited for soft materials, pore analysis, interference layer metallography and scanning electron microscopy (SEM) examinations using electron backscatter diffraction (EBSD) as well as electron channeling contrast imaging (ECCI).

Strip material with a thickness of 0.85 m was austempered in a suitable continuous hardening furnace for the further development of blade body steels used for thin-cutting circular and band saw blades. This work also comprised the search for a rather straightforward metallographic preparation procedure allowing for a reliable identification of the microstructure and microstructural constituents. The prepared microstructure can be revealed using Nital or Beraha and LePera etching solutions. None of the three etchants allows a reliable and reproducible distinction of the microstructural constituents of the extremely fine-grained lower bainite using light-optical techniques. Only the use of the scanning electron microscope at higher magnifications allows a reliable identification of the characteristic bainite fiber bundles. For this examination, etching with Nital is recommended.

Severe scaling caused the guiding pin of two control valves of a smaller industrial steam turbine to seize which thus led to a malfunction. The customer sought clarification on whether the oxidation products are really common scale. This could be confirmed.