IMPROVEMENT IN MECHANICAL PROPERTIES OF Fe-Ni-Mn MARAGING STEEL BY HEAVY COLD ROLLING

Maraging steels are a group of martensitic steels possessing ultra high strength along with good fracture toughness. Conventional 18 wt.% Ni maraging steels are very costly in part because of expensive alloying elements such as Ni and Co. Replacement of Ni by cheaper elements like Mn has been studied by many researchers. Fe–Ni–Mn ternary alloys show good age hardenability formation of nanometer sized intermetallic precipitates such as f.c.t. θ-NiMn during aging. These alloys are ductile in the solution annealed condition but suffer from severe embrittlement after aging by intergranular fracture along prior austenite grain boundaries (PAGBs). Discontinuous coarsening of grain boundary precipitates was found as the main source of embrittlement. In this paper the effect of cold rolling on the mechanical properties of Fe-10Ni-7Mn steel was investigated. Cold rolling for 20%, 40%, 60%, 80% and 90% were carried out on a solution annealed material with subsequent aging at 753 K. Improvements in the tensile properties of the as-deformed and aged alloys were found. Substantial improvement is found at thickness reductions larger than 60%, where severe plastic deformation and ultrafine grain formation are realized.