A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Introduction <s> Abstract Plasma nitriding treatments are approved to reduce wear occurring in the field of hot forging applications. But there are demands for a further optimization of the processes in order to achieve adapted properties for differently loaded forging tools. This work presents the influence of main process parameters on the wear behavior of dies. The focused steel material of this work is DIN-X38CrMoV5-1 (1.2343), a standard hot forming tool steel. The influence of nitriding parameters like temperature, nitrogen flow and time on the nitriding depth, hardness and crack sensitivity has been investigated. Comparative application tests show the influence of different surface treatments on the wear behavior and lifetime of forging tools in an industrial environment. <s> BIB001 </s> A State-of-the-art overview - Recent development in low friction and wear-resistant coatings and surfaces for high-temperature forming tools <s> Introduction <s> Machining difficult-to-machine materials such as alloys used in aerospace, nuclear and medical industries are usually accompanied with low productivity, poor surface quality and short tool life. Despite the broad use of the term difficult-to-machine or hard-to-cut materials, the area of these types of materials and their properties are not clear yet. On the other hand, using cutting fluids is a common technique for improving machinability and has been acknowledged since early 20th. However, the environmental and health hazards associated with the use of conventional cutting fluids together with developing governmental regulations have resulted in increasing machining costs. The aim of this paper is to review and identify the materials known as difficult-to-machine and their properties. In addition, different cutting fluids are reviewed and major health and environmental concerns about their usage in material cutting industries are defined. Finally, advances in reducing and/or eliminating the use of conventional cutting fluids are reviewed and discussed. <s> BIB002
The ever increasing demand for quality, flexibility, productivity and environmental performance has introduced new machining and forming technologies, including near net shape production, high speed machining, hard turning, micromanufacturing, dry machining and environmentally conscious machining. The successful implementation of many of these processes demands high performance from the forming tools. The tools have to resist rough conditions, such as the cyclic contact with the rapid-heated materials at temperatures above 1000°C, abrasive wear by hard particles like scale and oxides, in combination with adhesive wear by high pressure loading BIB001 . In some forming processes, the severe adhesion between the mould and the working materials becomes a major difficulty for demoulding without applying releasing agents or lubricants. Therefore the production of materials that exhibit low wear rate and low coefficient of friction (CoF) over a wider range of working conditions is a big challenge in modern industrial tribological systems. This technical challenge is relevant not only to metal forming but also to industrial processes including tooling, aerospace parts and assemblies like propulsion bearing and fasteners and moving assemblies for hypersonic aircraft, missiles and nuclear industries. In order to improve the performance of the tools, an ideal tool material should combine properties like high hardness, good toughness and chemical stability. Moreover, the material has to cope with thermal loading by being more refractory, or by generating less heat during machining (i.e. reducing both shear and frictional energies), and/or by taking away the generated heat rapidly. With this regard, monolithic tool materials are being replaced by coated tools to enhance their performance. The coatings form a barrier between the tool and the work piece, preventing the tool material from being exposed. This reduces the diffusion rate and lowers the chemically and thermally induced tool wear such as adhesion and oxidation. Coatings can also improve the tools behaviour by altering the coefficient of friction, and increasing the hot hardness, resulting in lower abrasion rate BIB002 .