Optimisation of Thermal Processes with Plasma Nitriding on Vanadis 4 High Speed Steel

Abstract

Vanadis 4 steel is a tool steel processed by powder metallurgy (PM). Its main alloying elements are Cr, V and Mo. Through the application of a design of experiments with six factors and eight experiments, the parameters of the process related to the thermal treatment of these steels are deliberately varied. Those thermal parameters related to the destabilisation of austenite were analysed: the cooling method in quenching, tempering and the application of an ionic nitriding treatment. Through XRD, the percentage and types of precipitated crystalline phases were determined, and, through SEM-EDX, the microstructure was revealed. At the same time, through a pin-on-disc test, those factors with a significant influence on resistance to wear were determined. It has been concluded that, in order to increase resistance to wear, treatments of destabilisation of the austenite at 900 °C with oil quenching, tempering at 550 °C for 4 h and a subsequent treatment of plasma nitriding would be very favourable. This tempering favours a second destabilisation of the austenite and its transformation into martensite, as well as the joint precipitation of type M7C3 and MC carbides. The thickness of the nitrided layer exceeds 100 microns and generates a fully adhesive wear mechanism.

PBF-EB of Fe-Cr-V Alloy for Wear Applications

“…The EBSD inverse pole figures (IPF) demonstrate that there is no significant preferential crystallographic orientation for the main phases, and thus, no texture or orientation along the build direction which might arise in PBF-EB microstructures (see Figure 6 ). This is mainly reasoned by the in situ heat treatment during PBF-EB and the vanadium-rich carbides that act as obstacles against grain growth [ 38 ]. The M 7 C 3 carbides seem to be distributed inhomogeneously in the matrix both in the case of size and orientation.…”

Processing of Niobium-Alloyed High-Carbon Tool Steel via Additive Manufacturing and Modern Powder Metallurgy

“…Tempering of such alloys is carried out at a high temperature, usually around 550 • C. At this temperature, precipitation of fine carbides, mostly M 6 C, MC or M 2 C types, occurs [7,8]. In higher-chromium steels, chromium-based M 7 C 3 or M 23 C 6 carbides could precipitate [9]. Due to related changes in austenite composition, i.e., a decrease in carbon content in austenite, which causes an increase in the "martensite start" and "martensite finish" temperatures, the retained austenite transforms to martensite upon cooling from the tempering temperature.…”