Processing of M2 powder metallurgy high-speed steel by means of starch consolidation

A study is made of a new method called starch consolidation (SC) for the production of powder metallurgy (P/M) high-speed steel (HSS) components. Samples of a commercial HSS, M2, were shaped by using 1.5, 3.5 and 5 vol% of starch and up to 60 vol% of powder. The high solids loading was made possible by a small addition (0.03 wt%) of dispersant (polyacrylic acid) that stabilized the repulsive forces and provided the desired fluidity to the slurries. After shaping and demoulding, the bending strength of the green bodies was evaluated. Debinding cycles were optimized by comparing the carbon content in argon, in a mixture of N2–5H2 and in pure hydrogen atmospheres at 450 and 600 °C. The three atmospheres caused no significant differences in carbon removal. Best results were achieved from sintering in vacuum with a debinding cycle in H2 up to 600 °C for 30 min. Sintering tests were carried out at 1250 and 1260 °C for 30 min. The heat treatments then performed on the samples showed the best combination of properties: 1250 MPa and 888 HV.