Microstructural characterisation of artificially aged and service-exposed ASTM A204 Grade C steel reveals changes in the cementite particles of pearlite and microstructure. The ageing temperatures were chosen to be high enough to replicate the service degradation but below A c1 to avoid austenitisation in the inter-critical regime. Tensile testing of artificially aged materials shows a decrease in the ultimate tensile strength (UTS) along with an increase in elongation. On the other hand, service-exposed material resulted in an increase in UTS and a decrease in elongation. The softening of pearlite due to spheroidisation of cementite and segregation of alloying elements towards grain boundaries were responsible for the lower UTS of the artificially aged samples. Whereas, the increase in UTS in the service-exposed sample was attributed to the formation of nano-sized carbides inside ferrite grains, hence strengthening the steel matrix. © 2020 Institute of Materials, Minerals and Mining.