Effect of conventional and subzero treating on the mechanical properties of aged martensitic Fe–12 wt.% Ni–X wt.% Mn alloys

Fe–Ni–Mn maraging alloys are suffering from sever embrittlement after aging. Mechanism of the embrittelement has not been well understood yet. Segregation of Mn atoms or formation of Austenite particles at prior Austenite grain boundaries (PAGBs) have been reported as embrittelement mechanisms while it remains controversial now. For better understanding of embrittelement behavior, effect of subzero treating after aging, double aging and modification of alloy composition on the mechanical properties and fracture behavior were investigated. Alloys of chemical compositions Fe–11.9 wt.% Ni–6.3 wt.% Mn and Fe–10.5 wt.% Ni–5.8 wt.% Mo–3 wt.% Mn were studied. Double solution annealing was performed at 1223 and 1093 K for 3.6 ks followed by water quenching. After aging at 723 K for 0.9 ks (under aging) and 172.8 ks (over aging), tensile properties of specimens heat treated conventionally and cryogenically were measured. Double aging was done at 623 K for 3.6 ks followed by a step aging at 753, 783 and 803 K. Aging behavior and tensile properties of Fe–10.5 wt.% Ni–5.8 wt.% Mo–3 wt.% Mn were investigated after aging at 773 K. Results showed that alloy modification yields reasonable tensile properties while subzero treatment and double aging couldn’t improve tensile properties. An insight toward more investigation of the embrittelement mechanism was made on the basis of this study.