Metal injection moulding (Mim) of M2 high speed steel using a polyethylene based binder

In this work we have optimised a MIM process using a wax-HDPE based binder for high-speed steel (M2). Three different kind of feedstock have been prepared. The first feedstock contains the metal powder as received. The second one contains the metal powder treated with stearic acid solution. The last one was prepared adding stearic acid directly to the mixture. The adsorption of stearic acid onto the metal powder surface causes a decrease in the blend viscosity allowing the use of lower injection temperatures. The injected specimens have been treated under different debinding methods based on thermal debinding using as well, solvent debinding in heptane solution and wick debinding. Heating cycle has a strong influence on the formation of cracks in the parts. The removal cycles have been designed by means of thermogravimetric analysis. The best results have been obtained when capillary extraction of the binder by wick powder has been used. The brown parts had a suitable mechanical strength to be handled because of they were presintered until 850degreesC. Sintering was carried out under vacuum atmosphere.