SINTER-HARDENING OF NEW PM STEELS: MODULAR FURNACE CONCEPT FOR STRINGENT SINTERING PROCESS CONDITIONS

摘要

The application of new PM materials, in particular high-performance PM steels, has increased dramatically in the last few years. This is in large part due to the markedly improved mechanical properties when compared to conventional PM steels, and especially the better fatigue strength and excellent wear resistance. The alloying elements responsible for this are chromium (Cr) and manganese (Mn), and partially also vanadium (V). When compared to the traditional alloy elements used in PM alloy steels today, such as copper (Cu), nickel (Ni) or molybdenum (Mo), all these elements display a much higher affinity for oxygen (O_2) and therefore the production of fairly stable oxides. Apart from placing far greater demands on the purity of the sintering atmosphere in all the sintering process stages, i.e. for binder removal, sintering and cooling, a substantial increase of the sintering temperature from a thermodynamic point of view, is also necessary. Furnaces for sintering of high-performance PM steels must be constructed to meet these requirements. The belt -conveyor and walking-beam furnaces often used today are only suitable for this to a limited extent. By contrast, a newly developed modular furnace concept meets the most stringent requirements with regard to a stable and pure sintering atmosphere. It is based on a modular roller hearth furnace with multiple zones for process-oriented sinter heat treatment of PM parts. It allows high-temperature sintering up to 1,300℃ and sinter hardening in one pass. The separate zones are designed as individual process modules, which operate as separate functional units oriented to the individual process steps. The design, which is presented in detail, has already proven successful several times in practice and it meets both the most stringent technical and economic demands.