The Young's modulus (E) of variously heat-treated alloys containing 11.6%Al was measured by longitudinal vibration method at room temperature. The specimen containing much martensite by quenching showed very low Young's modulus. On tempering, however, it showed various different Young's moduli according to the tempering temperatures and the rates of cooling from those temperatures. The tempering reaction is very active at temperatures above 350° but not below 300°. On tempering at above 400°, the alloy finally showed very high Young's modulus, and the tempering curve, which E on the ordinate and the tempering duration on the abscissa, showed a maximum and a minimum values in the initial range. On tempering at just 400°, after passing this maximum and minimum E increased rapidly to the saturation value. On tempering at above 500°, the maximum was missing and after passing the minimum E increased rapidly to the saturation value. These phenomena were explained as follows : The increase of E up to the maximum (at the begining) is due to the release of quenching stress in martensite (β'). The next decrease of E up to the minimum is due to the change of residual structure into martensite. The final increase of E up to the saturation value is due to the decomposition of martensite into pearlite.
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