Study of phase formation in metal injection moulding through real time neutron diffraction

The sintering of metal injection moulded stainless steel was investigated using in situ neutron diffraction with different sintering temperatures, from 1270 deg. C up to 1390 deg. C, with sintering profiles that were based on those used in industry. The production of an unwanted high temperature phase, δ-ferrite, was observed during sintering and is seen to be retained in the final product after sintering. Ferrite production during sintering acts to speed up the sintering process by forming in the grain pores but is unwanted in the final product as it is a soft and malleable phase. The ferrite that was formed at high temperature was observed to not completely disappear during cooling as a result of the coexistence of dual high temperature phases delta-ferrite and gamma-austenite during the high temperature soak. This suggests the segregation of the alloying elements between the two phase which changes the composition of the phase grains and allows the ferrite to exist during cooling, resulting in the unwanted phase in the final product.