The structure and properties of manganese maraging alloys.

The microstruectures of Fe-Mn-Co and Fe-Mn-Co-Mo alloys in various conditions of heat treatment have been studied using optical and thin foil transmission electron microscopy techniques. After homogenizing in the austenite phase field, the structure at room temperature is lath martensite (bcc-alpha-martensite, and cph-epsilon martensite) or lath martensito and retained austenite. The influence of ageing on the matrix structure has been examined in detail by volume fraction phase analysis using X-ray diffraction. The marten-sitic structure can be strengthened by ageing at temperatures in the range 350° - 500°C. The precipitates responsible for this strengtheningwere tentatively identified as fee X - phase and a hexagonal phase(A[3]B typG), Ovcraging in those alloys is mainly due to the reversion of the matrix to austenite. The effect of ageing on the ductility and toughness of the alloys has shown that embrittlement occurs as a resultof ageing in the temperature range between 350°- 500°C, Improvement in toughness of the alloys can be achieved by ageing above the embrittlement range without severely reducing the strength of the alloys.The influence of deformation on the matrix structure both at room temperature and -196°C was also investigated. The relationship between mechanical properties and matrix structure after deformation and deformation and ageing has also been studied. The best combination of strength and toughness was achieved by a deformation and ageing process. This was due to a combination of the precipitate dispersion in a fine substructure.