STRENGTHENING BEHAVIOR 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 i n Go-free Fe-Ni-Mn maraging steels. Marked changes in tensile properti es occurred as a function of ageing time and temperature, and alloy co mposition. As the amount of Mn and Ti increased, strength increased dr astically but suffered from severe embrittlement. The strengthening be haviour of aged specimens was explained by the well-known Orowan mecha nism. There was no evidence of second phase precipitation and no segre gation of Mn along grain boundaries, which have been suggested as the proofs for the explanation of the embrittlement phenomena by many rese archers. It is proposed that the combined amount of (Mn + Ti) should b e 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 elongati on (18.8%) was obtained after ageing Fe-20.8Ni-2.13Mn-0.8 Ti alloy for 1 h at 450 degrees C.