Volume 50, Issue 11

This paper is related to 16Mo3, a low-alloy steel typical in the manufacture of large welded steel casings of heavy-duty gas turbine engines. The usual practice in manufacturing is to stress relieve these housings after fabrication welding. If, however, weld imperfections are detected by non-destructive testing, weld repairs are performed, followed by additional stress-relief heat treatments. The methods applied were used to detect possible embrittlement by secondary carbide precipitation and to finally draw conclusions on material changes. The critical area of a weld is the heat affected zone. In this area a worsening of the stress condition in connection with a change in carbide precipitation and thus a decrease in creep rupture strength occurs. A concrete alloy composition and heat treatment adapted to the precipitation behavior are important, because they determine the type, amount and distribution of the resulting carbides [1, 2].

There is no method that allows the simultaneous preparation of titanium and aluminum, so that both phases can be investigated by means of scanning electron microscopy (SEM) at the same time. Especially local orientation measurements by electron back scatter diffraction (EBSD) are challenging as they require a very good surface quality. This study deals with the preparation of aluminum/titanium composites, produced by Accumulative Roll Bonding (ARB) as well as with their microstructural analysis emphasing on the metallographic sample preparation. Well established routes of metallographic preparation for aluminum and titanium are facing serious problems such as rounding of edges, arising of deformation layers, blurred layers and oxide layers. This is of particular concern when these routes are applied to Al/Ti multilayered samples without adaption. This study reveals a route for metallographic sample preparation that enables SEM including EBSD analyses of Al/Ti composites for both phases simultaneously.

In this study, the characterization and growth kinetics of chromium carbide layer coated on AISI D3 cold-work tool steel by pack method thermo-reactive diffusion process in solid medium were carried out. Coatings were performed by using ferro-chromium powder as Cr source at 950, 1 000, 1 050 and 1 100 °C for 2 and 4 h. The carbide layers were evaluated based on microstructure, thickness, hardness, energy dispersive X-ray facility and X-ray diffraction analysis. Chromium carbide layer thickness on the coated specimens has been in the 4.2–17 μm range depending on treatment time and temperature. Growth kinetics of the carbide layers were analyzed by measuring the depth of carbide layer as a function of temperature and time. The activation energy was estimated to be 180.13 kJ/mol. The microhardness values of the coating layers are range of 1 200–1 600 HV. Ball rotating micro-abrasion technique was used to carry out wear tests on the thin coating layers.

Two types of non-metallic inclusion stringers were found in so-called upending hook nuts, in the vicinity of an indication on the bore wall's surface, first, manganese sulfides that can be expected in this material, and second, endogeneous oxidic inclusions from the steelmaking process. The latter ones, too, can be expected to an extend in the structural steel that was used to make the hook nuts from. However, they are present in an excessive amount and were causative for the decohesions that produced the reported MT indications. The forging process which was employed to produce the semifinished product used to machine the hook nuts from was unable to fragment and disperse the non-metallic inclusions sufficiently as is usually the case.