High Manganese and Aluminum Steels for the Military and Transportation Industry

Abstract

Lightweight advanced high strength steels (AHSS) with aluminum contents between 4 and 12 weight percent have been the subject of intense interest in the last decade because of an excellent combination of high strain rate toughness coupled with up to a 17% reduction in density. Fully austenitic cast steels with a nominal composition of Fe-30%Mn-9%Al-0.9%C are almost 15% less dense than quenched and tempered Cr-Mo steels (SAE 4130) with equivalent strengths and dynamic fracture toughness. This article serves as a review of the tensile and high-strain-rate fracture properties associated mainly with silicon additions to this base composition. In the solution-treated condition, cast steels have high work-hardening rates with elongations up to 64%, room-temperature Charpy V-notch (CVN) impact energies up to 200 J, and dynamic fracture toughness over 700 kJ/m 2 . Silicon additions in the range of 0.59-1.56% Si have no significant effect on the mechanical properties of solution-treated steels but increased the tensile strength and hardness during aging. For steels aged at 530°C to an average hardness of 310 Brinell hardness number, HBW, increasing the amount of silicon from 1.07% to 1.56% decreased the room temperature CVN breaking energy from 92 J to 68 J and the dynamic fracture toughness from 376 kJ/m 2 to 265 kJ/m 2 . Notch toughness is a strong function of phosphorus content, decreasing the solutiontreated CVN impact toughness from 200 J in a 0.006% P steel to 28 J in a 0.07% P steel. For age-hardened steels with 1% Si, increasing levels of phosphorus from 0.001% to 0.043% decreased the dynamic fracture toughness from 376 kJ/m 2 to 100 kJ/m 2 .

On the Grain Growth Kinetics of a Low Density Steel

“…The 1273 and 1323 K (1000 and 1050 °C) conditions exhibit a slightly different behavior, the maximum in the work-hardening is not observed until a later stage of deformation at roughly 0.3 true strain and a lower maximum is obtained, 1970 MPa. The elastic modulus of the alloy is noted to be 155 ± 6 GPa, which is significantly lower than typical Fe-C steels and is typically attributed to the effect of increased Al and Mn on causing solid solution softening as reported in literature by both Bartlett and Van Aken [3] and Field et al [22] for manganese steels. A stress-strain plot of the steel in the as-solution treated two hour condition, is shown in Figure 6a.…”

“…The austenitic alloys, sometimes referred to as Fe-Mn-Al steels, are an attractive alloy system for automotive and cryogenic applications because of their high strength and formability as well as good low temperature toughness [1,5]. The density reduction of these alloys is typically attributed to the elevated additions of aluminum leading to a lattice dilation; with an aluminum content in the range of 5-11 wt.%, a density reduction of about 15% can be obtained with equivalent toughness and strength as compared to conventional Cr-Mo steels in the quenched and tempered condition as reported by Bartlett and Van Aken [3]. The increased Al content (>6 wt.%) has a secondary benefit for the austenitic alloys, age hardening by a low (720-920 K) temperature annealing process is a means to strengthen the steel [3,[6][7][8].…”

“…Low density steels have become a topic of significant interest in both automotive and military applications for vehicle implementation [1][2][3]. These steels are derived from Robert Hadfield's original investigation of a Fe-13Mn-1.2C (in wt.%) steel with elevated toughness, high work hardening, and optimal wear resistance [4].…”

Effect of Niobium Addition on Microstructure and Mechanical Properties of Fe–7Al–0.35C Low-Density Steel

“…Aluminum addition also leads to an improved corrosion resistance [1,8]. Because of their low-density, high specific strength, and good corrosion resistance, these steels are considered potential structural materials in thermal power plants and petrochemical industry [1][2][3][4][5][6][7][8][9][10][11][12][13]. Reducing the weight of an automobile by 10% can hike the fuel economy by 6-8%, and therefore, these materials have applications in the automotive industry [1-4, 10, 11].…”

“…Reducing the weight of an automobile by 10% can hike the fuel economy by 6-8%, and therefore, these materials have applications in the automotive industry [1-4, 10, 11]. Further, they may also have potential defense applications [12]. We have earlier reported properties of Fe-7wt.%Al alloys with carbon addition [5,7].…”