[en] The temperature-dependent plane-specific diffraction elastic constants (DEC) of ferrite in a high-strength quenched and tempered structural steel, S690QL1 (Fe–0.16C–0.2Si–0.87Mn–0.33Cr–0.21Mo (wt.%)), have been determined with a high degree of precision. For this purpose, in situ tensile tests have been carried out at different temperatures in a high-energy synchrotron X-ray diffractometer. The data reported are of considerable significance, since they allow an accurate determination of the residual stress states from the measured local d-spacings between lattice planes