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. © 2014 The Japan Institute of Metals and Matenals.