Mechanical properties of high-speed tool steel recycled from grinding chips by field-assisted sintering

In the metal working industry, masses of grinding waste are generated every year that are disposed by landfill or combustion. In order to establish a circular economy, the recovery of the subtracted metallic portion is crucial. In particular, the introduction of high-alloyed tool steel chips as a secondary raw material for powder metallurgical processes is of interest from an economical and ecological point of view. Since the grinding waste consists not only of metallic chips but also of cooling lubricant and non-metallic abrasive particles, separation of the metallic grinding chips from the contaminations is a prerequisite for the recycling of the steel. Cleaned high-speed tool steel grinding chips that still contain non-metallic particles were compacted to cylindrical discs by field-assisted sintering technology (FAST). The residual non-metallic inclusions give rise to concerns regarding the mechanical properties of the recycled steel. Therefore, mechanical properties of the FAST-recyclate in heat-treated condition were assessed by static compression testing, pressure swelling testing, and cyclic bending testing. The resulting static and cyclic mechanical properties are compared to reference samples conventionally produced by hot isostatic pressing of pristine gas atomized powder. It was found that the static compressive properties of the recycled tool steel do not deviate significantly from those of the reference material. However, residual non-metallic inclusions lead to premature failure during both cyclic testing.