Damage functions, represented here as multigroup cross sections for neutron-induced radiation damage production, were derived for irradiation of two A 350-series ferritic steels at temperatures of 510 and 430°F (266 and 221°C), representing the PM-2A and SM-1A reactor pressure vessels. The functions were derived using the SAND-II computer code with the neutron spectra and resulting increases in transition temperature from a series of irradiations in different reactor locations. The derived damage functions effected a best correlation of available data and on that basis are considered good through comparison of total fluence values determined both from experimental measurements and from the damage-function calculation technique. Trends are suggested for the magnitude of damage function cross-section values as a function of energy at low vs elevated temperatures. However, the present experimental data are not sufficiently definitive to draw positive conclusions about the specific contributions of neutrons of all energy levels to the neutron embrittlement process.