Modelling of Sintering Atmosphere and Microstructure Development of Chromium Alloyed Steel

Journal article, 2008

In order to take advantage of recent achievements in furnace technology and monitoring equipments, it is necessary to have a rigorous understanding of the chemical reactions that take place inside the sintering furnace. If overlooked, there is a risk for insufficient control of the sintering condition and the outcome will be scatter in PM parts’ final alloying content and mechanical properties. At the same time, end user demands require tight tolerances in product performance for sintered goods. In this study, different mixtures of iron based chromium prealloyed Astaloy CrM powder with the nominal composition of 3 wt.% Cr and 0.5 wt.% Mo were studied. The investigated powder mixtures were the plain powder, admixed with lubricant and admixed with lubricant and graphite (0.45 wt.%). Specimens were sintered in N2 and 10%H2/90%N2 atmospheres at 1120°C. Chemical reactions that are possible to occur in the above mentioned atmospheres and between the aforementioned powders mixtures are thoroughly examined from a thermodynamic point of view. Calculations have been performed to find the equilibrium partial pressures of the atmosphere constituents using a thermodynamic software package, HSC Chemistry 6.0. In addition, by means of modern thermodynamic and kinetic modeling software, JMatPro 4.0, the carbon activity for the alloying systems in question has been calculated. The simulation concept used for microstructural predictions of chromium alloyed sintered steel, developed by Nyborg et al. is applied to the alloying systems studied.