Laboratory experiments and process modelling of the melting and dissolution of low-density ferro-molybdenum in steel melts

A low-density sintered ferro-molybdenum is presented asa new alloying agent . The paper describes laboratory studies about the dissolution in liquid ir on of briquettes of this alloy and of classical high density ferro-molybden um pieces. It presents further a mathematical model of the melting and diss olution process. During dissolution, an approximately 1mm thick layer infil trated by melt forms on the particle surface. The infiltrated melt solidifi es in the plane where the temperature has reached the eutectic temperature in the system iron-molybdenum. Internal dissolution of alloy material in th e layer is weak, which means that the dissolution proceeds almost exclusive ly from the outer surface of the briquette. Dissolution rate increases with sinking briquette density. The lower molybdenum content per volume in the briquettes which is proportional to the density has the effect that the liq uidus concentration and the liquidus temperature at the solid liquid interf ace decrease in comparison with compact material. This reduces the mass tra nsfer rate and increases the heat transfer rate. The effect is a faster mov ement of the interface. Below a critical density of approximately 5200 kg/m (3) for the alloy considered; the molybdenum concentration on both sides of the interface becomes equal. From this moment, the alloy is liquefied sole ly by melting bf the moving interface. Mass transfer from the interface get s negligible and distribution of the molten alloy into the bulk melt takes place only by the outer mixing process. From the described behaviour it fol lows, that below the critical density the melting rate is solely determined by heat transfer. Since heat transfer is faster than mass transfer, meltin g of alloys with reduced density is correspondingly accelerated. The extrem ely slow dissolution rates of high melting alloys can thus, be overcome by giving the alloy a certain porosity. The mathematical process model describ es the phenomena quantitatively.