Strengthening of Fe-36mass%Ni Low Thermal Expansion Alloy by Additions of C, V, Ti, and Cr and the Effect of Reducing Ni on Thermal Expansion

Abstract

Fe 36massNi alloy is well known as invar alloy for its low thermal expansion (LTE) near room temperature. Since its strength is relatively low and thus its application is limited, strengthening of LTE alloy has been a matter of concern for industrial use. It has been reported that the combined additions of V and C are effective for enhancing age hardness of Fe 36massNi alloy without remarkable increase in thermal expansion. However, since worldwide depletion of rare metals such as V has been making it difficult to purchase and pushing their prices up, saving these elements is an urgent issue for steel industry. In addition, more strengthened LTE alloy is still in demand. From these aspects, the effect of substitution of V by Ti and Cr on strength of Fe 0.2massC 36massNi 0.8massV alloy is investigated in this paper. As a result, age hardness reached its maximum when a quarter of V was replaced by Ti. Substitution by Cr by about up to a half of V had little effect on age hardness. Based on these results, an LTE alloy, Fe 0.3massC 36massNi 0.6massV 0.2massTi 0.6massCr, was prepared and its properties were measured. Consequently, the alloy had 70 MPa higher tensile strength than the previously reported for Fe 0.2massC 36massNi 0.8massV alloy. In the viewpoint of saving rare metals, influence of reducing nickel on thermal expansion is also discussed.

Effect of aging on microstructures and properties of Mo-alloyed Fe–36Ni invar alloy

“…VC, NbC and Mo 2 C [13,14,20]. Nakama et al [13] reported that the invar alloy through precipitation of VC and TiC particles in the austenite matrix, together with subsequent 50% cold deformation presented the highest tensile strength of 1100 MPa, which is two times larger than that of the base Fe-36Ni alloy.…”

“…Conventional strengthening methods, such as solid-solution strengthening [10], grain refinement [5], work hardening [8,11] and precipitation hardening [12][13][14][15][16], have been developed in invar alloys, e.g. Fe-36Ni [5,11], Fe-Ni-Co [12,17,18], Fe-Ni-Ti [19] and Fe-Ni-Mo [10,16], etc.…”

Fe–Ni Invar alloy reinforced by WC nanoparticles with high strength and low thermal expansion

“…The strengthening of Invar alloy through the precipitation of MC-type carbides, such as TiC, VC, and Mo 2 C, or intermetallics, such as γ'-type Ni 3 Ti and Ni 3 Al, was reported to be highly effective. Nakama et al reported a Fe-Ni-V-C Invar alloy reaches a tensile strength of 1000 MPa after a combination of solutionization, aging, which produces VC precipitates, and cold working [7,9]; the same author reported the strengthening of Invar alloy containing Ti, V, and C through TiC and VC precipitation, and achieved 1100 MPa tensile strength at peak aging condition [6]. Yahagi et al reported a Fe-Ni-Co-Ti Invar alloy strengthened by the precipitation of γ'-type Ni 3 Ti intermetallics exhibits a tensile strength of 1313 MPa after cold working [10].…”

“…The strengthening of Invar alloy can be achieved primarily through three methods: grain refinement [5], plastic deformation (and severe plastic deformation, SPD) [6], and precipitation hardening [4,[7][8][9]. Vingradov et al [8] reported that the tensile strength of Fe-36Ni Invar alloy can be increased to 912 MPa by refining the grain size to 180 nm using equal channel angular pressing (ECAP).…”

Strengthening of the Fe-Ni Invar Alloy Through Chromium

“…Fe-Ni binary alloy with a Ni content of ~36 wt.% is known as invar alloy, which shows a very low coefficient of thermal expansion (CTE) of almost zero under 100 °C [1,2,3,4]. Such an anomalous thermal expansion effect of the Fe-36Ni alloy is known as the invar effect [5].…”