Austenitic steels with higher manganese contents (>15%) have recently been developed for applications requiring low magnetic permeability, low temperature (cryogenic) strength and low temperature toughness. This applications stem from the development of superconducting technologies used in transportation systems and nuclear fusion research and to meet the need for structural materials to store and transport liquefied gases.

For low magnetic permeability, these alloys have lower carbon content than the regular Hadfield steels. The corresponding loss in yield strength is compensated by alloying with vanadium, nitrogen, chromium, molybdenum, and titanium. Chromium also imparts corrosion resistance, as required in some cryogenic applications.

The alloys are used in the heat-treated (solution-annealed and quenched) condition except for those that are age-hardenable. Wrought alloys are available in the hot-rolled condition. The microstructure is usually a mixture of g (face-centered cubic or fcc) austenite and e (hexagonal close-packed, or hcp) martensite.

These alloys are characterized by good ductility and toughness, both especially desirable attributes in cryogenic applications. Further, the ductile-brittle transition is gradual, not abrupt. Because the stability of the austenite is composition dependent, a deformation-induced transformation can occur in service under certain conditions. This is usually undesirable because it is accompanied by a corresponding increase in magnetic permeability.

Additions of sulfur, calcium, and aluminum are made to enhance the machinability of these alloys where required. Because of their lower carbon content, most of these alloys are readily weldable by the shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and electron beam welding (EBW) processes. The composition of the weld metal is similar to that of the base metal and tailored for low magnetic permeability. The phosphorus content is generally maintained below 0.02% to minimize the tendency for hot cracking.

Another class of austenitic steels with high manganese additions has been developed for cryogenic and for marine applications with resistance to cavitation corrosion. These alloys have been viewed as economical substitutes for conventional austenitic stainless steels because they contain aluminum and manganese instead of chromium and nickel. Consequently, these alloys are generally of higher strength but lower ductility than conventional stainless steels such as type 304. The microstructure of these alloys is a mixture of g (fcc) austenite and e (hcp) martensite, and in some cases (especially when the aluminum content exceeds about 5%) a (bcc) ferrite. There is a tendency for an embrittling b-Mn phase to form in the high manganese compositions during aging at elevated temperatures. The result is a significant decrease in ductility. The addition of aluminum to some extent suppresses the precipitation of this compound.