Synopsis
Increasing raw material costs, limited natural resources, and environmental sustainability requirements in industrial production processes necessitate the development of more efficient and innovative approaches. Within the scope of the circular economy, the reuse of process wastes has emerged as a key strategy to enhance resource efficiency and support sustainable production. Molybdenum, a critical alloying element in steel production, has strategic importance in terms of recovery due to its high cost and supply challenges. In the literature, no study has been found on the direct use of molybdenum in its metallic form for alloying purposes.
In this study, the usability of high-purity molybdenum waste obtained from coating processes as an alternative to ferro-molybdenum was investigated. Comparative productions were carried out using Fe-Mo and waste molybdenum in 70MoMn10-4 steel grade, and the chemical, microstructural, and mechanical properties of the produced materials were thoroughly evaluated. According to microstructural and mechanical test results, similar tempered martensitic microstructures and mechanical properties were obtained in both productions after quenching and tempering (Q&T) heat treatment. However, due to insufficient dissolution of waste molybdenum used in bulk form, hardness reductions and heterogeneous microstructure formation were observed beyond certain distances in Jominy hardenability tests.
Optical microscopy and SEM-EDS analyses revealed that this situation was caused by undissolved and locally enriched molybdenum regions within the microstructure. To overcome this problem, waste molybdenum was subjected to a crushing-grinding pre-treatment and used in powder form for re-production. The use of molybdenum in powder form improved dissolution kinetics, resulted in more homogeneous microstructure, and produced hardenability curves similar to those obtained with ferro-molybdenum. This study demonstrates that molybdenum waste can be effectively used as an alloying input through appropriate pre-treatment processes and can contribute significantly to sustainable production approaches.
