Einfluss unterschiedlicher Oberflächenzustände vor dem Plasmanitrieren auf Eigenschaften und Zerspanungsverhalten des Schnellarbeitsstahls S 6‐5‐2

Surface states and wear behavior of drills of ground, sandblasted and plasmanitrided samples and drills made of AISI M2 high speed steel In the present work the effect of different surface conditions on plasma nitriding response of AISI M2 high speed steel was investigated. The plasma nitriding of ground and sandblasted samples and drills was performed at temperatures of 400°C and 500°C for two gas mixtures: 5 vol.% N₂ and 76 vol.% N₂ in hydrogen. Surface layers were characterized before and after plasma nitriding concerning the microstructure, roughness, microhardness, chemical composition, phase composition and residual stress states. Machining tests were carried out with drills during which drilling forces and flank wear have been measured. A significant effect of the surface state prior to nitriding on residual stress states and the properties of the nitrided layer and untreated core has been observed. Thinner nitrided layers on ground and sandblasted samples were attributed to high compressive residual stress states and a stress affected diffusion of nitrogen and carbon. In the machining tests, sandblasted drills exhibited the best performance. Lower nitrogen concentrations in the gas atmosphere without the formation of a compound layer gave the lowest drill flank wear for sandblasted surfaces while higher nitrogen concentrations led to a reduction of drilling forces and torque.     

Effect of fluctuation and modification on microstructure and impact toughness of 20 wt.% Cr hypereutectic white cast iron. Einfluss durch Partikelzugaben und Modifikationen auf die Mikrostruktur und die Kerbschlagzähigkeit von übereutektischem weißen Gusseisen mit 20 Gew.‐% Cr

In the present study, Fe‐Cr‐C hypereutectic high chromium white cast iron were prepared from industry‐grade materials and subjected to the treatment of modification using Fe‐Si‐RE alloy, aluminum and a self‐made intermediate alloy, fluctuation (ferroalloy powder), and the combination of the fluctuation and the modification respectively. The structures of the treated alloy were investigated by means of the optical microscopy (OM). The impact toughness of the specimens was also examined. The fractographs of the samples were examined by scanning electron microscopy (SEM). The results showed that, with the addition of fluctuation or modifying agents, the primary carbides were refined and the impact toughness of the alloys was improved, especially with the combination of them.