CD Laboratory for Mobility and Diffusion of Metallic and Non-Metallic Elements during Production and Finishing of High Strength Steel Sheets

Physical and chemical processes on the surface of high-strength steel strip are at the centre of research activities. The understanding gained here will subsequently contribute to optimised steel production.

Targeted laboratory tests and simulations are used to gain a comprehensive understanding of the surface of high-strength steel strips in particular. The production of high-strength and ultra-high-strength steel grades has made physicochemical surface processes for these steel strips increasingly important. These steels must not only become harder, more resistant and easier to process, but also have a flawless surface. There are many production steps on the way from the ingot of cast steel to the galvanised steel sheet.

During production, certain elements, some of which are undesirable, accumulate in the steel alloys. In the context of research activities, particular attention is paid to the elements hydrogen and oxygen. These diffuse from the surface into the steel alloy during some production steps.

In particular, the so-called grain boundary oxidation is analysed. In this process, oxygen atoms diffuse along the grain boundaries of the material grains into the steel alloy and oxidise the material along the diffusion path. This can also be significantly influenced by the diffusion of metallic and non-metallic alloy components to the grain boundaries (segregation). Based on the analysis, this effect, which occurs in particular during the hot rolling of steel strips, is subsequently modelled and thus made accessible for simulation. Furthermore, the pickling of oxide layers - caused by the production process - often leads to an irregular surface, which is caused in particular by these grain boundary oxides. The processes that play a role in this are being researched by the partner at TU Wien.

Hydrogen, in turn, can diffuse into the steel alloy during wet-chemical cleaning steps and galvanising. In the case of high-strength steels, this can lead to brittle fractures in the material. Therefore, as part of the development work, a highly sensitive, non-invasive measurement method is being developed that enables the measurement of hydrogen in steel.

The assessment of the effects of these processes on the further processing and utilisation of the steel grades is just as much a goal of the activity as the expansion of the understanding of their physicochemical principles.