Volume 78, Issue 4

As an additive manufacturing process, powder bed fusion of metals using a laser beam (PBF-LB/M) enables the near-net-shape production of complex components in a single step. In combination with case hardening, it will thus be possible in the future to produce lightweight, functionally integrated transmission components characterized by high-strength surface layers with a sufficiently tough component core. However, the process-related new initial conditions resulting from very high solidification rates in PBF-LB/M may mean that case hardening of PBF-LB/M materials with standard parameters achieves different case hardening results than have been usual in the past. This hypothesis was investigated in the present work using the case hardening steel 20MnCr5 (material number 1.7147) after successful development of industry-relevant PBF-LB/M parameters. Besides the convincing results regarding microstructure, hardness and carbon depth profiles, case hardening with standard parameters led to irregular grain growth due to holding at high temperatures for several hours during carburization.

Determining the phase transition data of technological materials used for example to design heat treatment processes is generally a complex and labor-intensive process if high data fidelity is required. This work presents a method based on the standard Jominy end quench test with additional instrumentation that can generate many temperature histories required for the generation of continuous cooling diagrams at the same time, greatly simplifying the process. This method is applied to a simple 16MnCr5 case hardening steel to show the practical execution. The resulting diagram and microstructure is consistent with more complex test methods, showing good performance of the much simpler test method.

Quenching and partitioning (Q&P) is a heat treatment used to adjust the retained austenite content in the microstructure. Such heat treatment is used mainly for low-alloyed steels. However, the partitioning effect has an influence on higher alloyed steels also, such as martensitic stainless steels. The typical heat treatment for these steels is quenching and tempering (Q&T). In large-scale tools the cooling rate in the inner area is lower than in the peripheral area, and the central region of the tool might not be cooled down completely to room temperature before the tempering step takes place, resulting in a Q&P instead of a Q&T treatment. This article deals with these effects through dilatometric investigation of steels X40Cr14, “X25CrN13” and “X50CrMoN17-1” at two different austenitizing temperatures and two cooling rates, with a variation of the quenching temperature. It was found that partitioning takes place even at slow cooling rates. However, due to partial pearlite formation and pre-carbide precipitation/coarsening, the retained austenite content may be lower than with rapid cooling. Further, autopartitioning was also detected at slow cooling rates.

The use of hydrogen as a climate-friendly energy source is gaining strongly in importance, as it represents the only solution for short- to medium-term decarbonization for some industrial sectors, such as the steel and basic materials industries. Increasing innovation density and scaling of electrolysis is creating a broader range of uses and applications. So-called green hydrogen can be used as a raw material (basic industry), process gas (direct steel reduction), burner gas (heat treatment) or energy carrier (e.g. transport, energy storage). Depending on the application, hydrogen acts in a cryogenic liquid or gaseous state on the materials with which it comes into contact. This gives rise to various technical requirements that need to be controlled. For the application of hydrogen in large-scale and mass production, appropriate materials and processes will have to be developed that can be used economically and scalably. Considerable R&D activities will be required in the future, from the processing of the starting materials, their property adjustment by heat treatment and coating, to manufacturing processes and testing. This article highlights the current status for selected areas and discusses future material requirements and development potential.