The developed microstructures and their deformation behavior were studied in a high-strength low-alloy steel subjected to tempforming, i.e., tempering followed by large-strain rolling at temperatures of 823 K or 923 K. Tempforming has been recently proposed as an advanced treatment for low-alloy steels in order to substantially increase their impact toughness at low temperatures. However, the mechanical properties, especially the fatigue behavior, of tempformed steels have not been studied in sufficient detail. The present study, therefore, is focused on the strengthening mechanisms of the tempformed steel, placing particular emphasis on the low-cycle fatigue behavior. Tempforming resulted in a lamellar-type microstructure with a high dislocation density and dispersed Cr