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

Abstract

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 -10 Ni -7 Mn 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.

Microstructural Analysis of Co-Free Maraging Steel Aged

“…However, recent studies (Hu et al, 2008;Leitner et al, 2011;Mahmoudi et al, 2011;Mahmudi et al, 2011;Nili-Ahmadabadi, 2008;Schnitzer et al, 2010;Sha et al, 2013) are being conducted in maraging steels without cobalt addition, in order to reduce the production costs of this alloy. Maraging steels are considered expensive due to their materials' preparation and expensive alloy elements such as nickel and cobalt processes.…”

“…Cobalt is used only to minimize the solubility of molybdenum. In the case of maraging steel studied, this element was replaced by chrome, which besides improving the hardenability increases the corrosion resistance (Nili-Ahmadabadi, 2008).…”

Ductility enhancement in ultrafine-grained Fe–Ni–Mn martensitic steel by stress-induced reverse transformation

“…Fig. 1 represents the sequence of mechanical properties improvement from our previous work [16] to this research [29]. In our previous study, the maximum obtained elongation was 2.8% and maximum tensile strength was 1840 MPa for 90% cold rolled and aged sample while in as-annealed and aged condition has a premature fracture with zero ductility.…”

“…The nanostructured materials prepared by severe plastic deformation; receive larger strains that mean they could be the subject of different mechanical behaviors in analogy with conventional coarse-grained alloys [17][18][19][20][21][22][23][24][25][26][27][28]. To understand the origin of improved ductility, it was assumed the combination of cold rolling and wire drawing which leads to a larger strain in comparison with our previous work [16] and activate different deformation systems could be very useful steps to have nanograined materials and study any probable phase transformation. In this paper, we reported that the improvement of ductility in the Fe-10Ni-7Mn (wt.%) wire is likely attributed to ultra-grain refining and non-equilibrium austenite stabilization from bcc-martensite under large strain deformation and transformation of this austenite to -martensite in the nano-grained Fe-10Ni-7Mn (wt.%) martensitic steel during uniaxial tensile testing.…”

“…However, the effect of ECAP and heavy cold rolling on the mechanical properties of aged ultrafine-grained Fe-Ni-Mn alloy was studied with some of the present authors and co-workers. It was shown that the ECAP did not improve ductility while heavy cold rolling changes the brittle fracture to a mixed mode brittle and ductile fracture [15,16]. It is well established that high pressure or ultrahigh straining leads to destabilization of the microstructure in nanostructured metals and alloys, which in turn has some impact on their mechanical properties.…”