Effects of quenching and aging on the structure and Young's modulus of the 45NKhT elinvar are studied. The as-quenched alloy has a decreased elastic modulus, and this effect becomes more pronounced with increasing quenching temperature. Aging leads to the recovery of the modulus. The temperature range of the stability of Young's modulus is found to be virtually independent of the heat treatment conditions used in this study. The contributions of structural and magnetoelastic factors to the modulus defect are estimated. The conditions of the decomposition of supersaturated solid solution by continuous or discontinuous mechanisms are considered. The extent of the modulus recovery is shown to be virtually independent of the decomposition mechanism.