The Elastic Properties of Steel at High Temperatures

Hitherto, investigations into the elastic properties of metals have been confined to comparatively low temperatures. Gray, Dunlop, and Blyth have measured the modulus of rigidity and Young’s modulus for wires up to temperatures of 100° C., and found that both these quantities decrease as the temperature rises. Martens determined the influence of heat on the strength of iron up to temperatures of 600° C., but his experiments were the ordinary tensile tests carried to rupture, and though he also found a substantial diminution of Young’s modulus with rise of temperature, he did not go into the point fully, being mainly concerned with breaking stress and elongation. In the experiments here described the elastic properties of steel and iron have been investigated at higher temperatures, ranging up to 800° C., and for stresses greatly below that required to rupture the material. We have found that as the temperature rises the stress-strain relations undergo a remarkable change, which may best be expressed by saying that what is variously called the “time-effect,” or “elastische nachwirkung,” or “creeping,” increases greatly with the temperature. Steel, at high temperatures, behaves like indiarubber or glass; if it is stressed for a time, and the stress removed, it does not at once recover, but after the immediate elastic recovery there is a slow contraction perceptible for many minutes. Such “creeping” can be detected at ordinary temperatures, but at a red heat it attains a different order of magnitude, becoming (in its total amount) a substantial fraction of the whole deformation.