Volume 56, Issue 1

Metallurgical analysis is widely used in the field of heat treatment of metals to ensure the quality of the treatments carried out on a wide variety of industrial parts and treatments carried out. It is therefore a valuable tool for subcontractors of the heat treatment industry to monitor their production and treatment response on various parts. Through different examples, we will present actual cases that involve in particular automotive parts. We show that there is a strong interdependence between material and heat treatment, one being related to each other, a successful treatment depends both on the metallurgical quality of the material and the production quality of the heat treatment process. We will discuss the type of treatments like: vacuum hardening or under protective atmosphere, surface induction hardening, carburizing, nitriding and brazing.

For the assessment of the precipitation state in aluminum-based alloys by transmission electron microscopy (TEM), the sample must have an orientation in the [100] direction of the matrix. TEMs equipped with objective lenses that are optimized for high resolution are mostly characterized by limited sample tilt angles. The required crystal orientation must thus be taken into account during sampling. A favorably oriented grain was chosen in a coarse-grained material using electron backscatter diffraction and prepared in a suitable direction applying the in-situ lift-out method in the focused ion beam device. After that, the final correction of the orientation in the TEM amounts to less than 12°.

A prerequisite for the successful optimization of a heat treatment for high-alloyed steels is the knowledge about the present initial microstructure. The metallographic preparation and characterization of the initial microstructure poses a challenge, especially for blackplate, due to its low thickness. In this article, a method is presented which facilitates the handling of blackplate during metallographic preparation. With a precise knowledge of the initial microstructure, tests for the optimization of a heat treatment for such blackplate can also be performed. An optimization of the heat treatment process is particularly important for energy and resource efficient manufacturing processes. In this work, a preparation method was developed which allows winding blackplate to hollow cylinders to determine the optimized heat treatment parameters with the help of a quenching and deformation dilatometer. It will be shown that the two methods presented are an efficient but yet reliable way to optimize heat treatment processes of blackplate via laboratory tests.

A number of fuel gas supply pipes or feeder lines of heavy-duty gas turbine engines for power generation were found cracked in two sister engines of a power plant, this after approximately 100 000 operating hours. Cracks originated from the outer diameter (OD) of the feeder pipes, at the fusion line of the fillet weld that joined the subject pipes to the main burner bodies. The incident components failed by high cycle fatigue (HCF) fracture. The failure mechanism is purely mechanic. No evidence of corrosion or any other contributing mechanism was found. Design, manufacture, such as welding and coating, burner assembly, and burner installation are all unrelated to the failure. The root cause of the failure is excessive dynamic service loading.