Prevention of scaling by means of recycled process waste gases

Abstract

Abstract. During hot forging of steel materials, the blanks are subjected to various heating processes. During these processes, scale is formed, which can lead to a mass loss of up to 3%. The additional mass required to compensate this material loss for a given forging component has a significant impact on the process emissions, as the production of the billet material has the highest impact on the overall CO₂ footprint of metal forming products [1]. Additionally, descaling operations such as upsetting are required to guarantee forging quality and process stability. At the same time, large quantities of process waste gas are emitted in the production of raw materials and components. These burnt gases have lower oxygen concentration due to the prior chemical combustion reaction. This work addresses the question, whether these burnt gases can be utilized as a forging process atmosphere. This would not only reduce material loss, but would also result in a reuse of the process waste gas. In order to retrofit existing forging infrastructure, a tooling system with a gas-tight enclosure was constructed and realized in a forming press. Defined gas combinations were fed into the enclosure to create an oxygen-reduced atmosphere. First, different gas combinations were investigated in annealing tests. The three most promising ones were then selected for the forging tests. The enclosure contained a heating, transport, forming and collecting unit. The blanks were fed in through a magazine and inductively heated to 1200 °C, formed and cooled under the defined atmosphere. In each atmosphere, 100 components were forged from the material 42CrMo4. Furthermore, it was investigated whether forming under a gas atmosphere has an influence on tool wear as scale can act as an abrasive. The investigations showed that both the surface of the starting material and the oxygen concentration of the atmosphere have a significant influence on scale formation. The amount of scale formed was reduced by up to 74% compared to an oxygen atmosphere. The adhesive layer on the upper dies was reduced with decreasing oxygen concentration. On the lower dies was an increased adhesive build-up.