Strengthening behaviour and embrittlement phenomena in Fe-Ni-Mn-(Ti) maraging alloys

The effects of manganese and titanium on the mechanical properties of Fe-20Ni-(1.0–3.5)Mn-(0–1.0)Ti maraging steels were studied in order to investigate the strengthening behaviour and embrittlement phenomena in Co-free Fe-Ni-Mn maraging steels. Marked changes in tensile properties occurred as a function of ageing time and temperature, and alloy composition. As the amount of Mn and Ti increased, strength increased drastically but suffered from severe embrittlement. The strengthening behaviour of aged specimens was explained by the well-known Orowan mechanism. There was no evidence of second phase precipitation and no segregation of Mn along grain boundaries, which have been suggested as the proofs for the explanation of the embrittlement phenomena by many researchers. It is proposed that the combined amount of (Mn+Ti) should be controlled to below 3.5 wt.% in order to avoid severe embrittlement in Fe-20Ni-Mn-Ti maraging alloys, where the amount of Ti is held to 1.0 wt.%. The best combination of yield strength (1371 MPa) and elongation (18.8%) was obtained after ageing Fe-20.8Ni-2. 13Mn-0.8 Ti alloy for 1 h at 450 °C.