Laser cladding of High strength steels for rolling mill applications

Details

Supervisors

Jacques, Pascal

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

Laser cladding is an additive manufacturing technology through which a material in form of powder or wire is deposited and melted into a substrate achieving a metallurgical bond between the substrate and the cladding material. One promising use of this technology is the production of High-Speed-Steel (HSS) work rolls for steel manufacturing, in which the high performance HSS alloy is deposited on top of the cheaper substrate made of low alloy steel. This aims at producing longer lasting rolls that will eventually result in cheaper lifetime operating costs for the steel manufacturer. Despite the vast adoption of the laser cladding technology, many challenges still exist. Among all, the formation of cracks during and after the cladding process of HSS is a main concern for the applicability of this technology to work rolls for steel manufacturing, which needs to sustain thermal fatigue during service. Recent findings highlight that the main source of cracking during laser cladding of HSS is correlated to the high level of residual stresses that build up in the material during the thermal cycle of the cladding process. However, a clear correlation between laser power, cladding speed and the metallurgical behavior of the alloy is still missing. This master thesis investigates the formation of internal stresses in a HSS through a resource-friendly 1-dimensional analytical mechanical model parameterized on experimental data. The main finding shows that, while capturing the nature of residual stress during the cladding process, the model provided an overestimated stress values compared to experimental measurements carried out by X-Ray Diffraction. Despite that, the great contribution of the martensite transformation was successfully showcased by the model. Indeed, these findings confirmed that martensite transformation is the major contributor to the build up of internal stresses that eventually lead to the cracking of the deposited material. Since the model does not include the influence of the process parameters (cladding power, scanning speed and powder deposition rate, pre-heating, e.g.), a more complex model is needed to fully coupled the modelling results with process parameters.