Air-hardening, martensitic forging steels with medium manganese content

  Overview of different forging steels IEHK Figure 1: Overview of different forging steels

Quenching and tempering (Q&T) steels and precipitation-hardening ferritic-pearlitic (AFP) steels are the state of the art in the forging industry. The conventional Q&T-steels have the problem that the forging is followed by a cost intensive three-step heat treatment. On the contrary, AFP steels can be hardened directly utilizing the forging heat whilst exhibiting inferior mechanical properties in comparison to Q&T steels. An attractive substitute for these steel grades are bainitic steels with the dispensability of additional heat treatments subsequent to forging and similar low alloying costs as Q&T steels. The difficulty with bainitic steel grades is the necessity for an exact temperature control in order to acquire the desired microstructure, which is challenging in particular for components of complex geometry.

The diffusion controlled phase transformation can be significantly suppressed by the addition of manganese, whereby promoting martensitic microstructures. These materials have comparable properties to Q&T-steels despite the much shorter process route. Moreover, an exact temperature control is not necessary.

In a joint research project, several alloying-concepts are developed and optimized with special focus on the cyclic behavior. The research focus lies on the microstructure and precipitation control including the characterization of the micro- and nanostructure with respect to the mechanical properties.