Evolution of microstructure and compositions in worn surface and subsurface of 45 (0.45 mass% carbon) steel disc slid against tin-alloy-pin was analyzed by SEM, TEM and SIMS. The mechanical alloying layer and plastic deformation layer were formed in the sliding friction-induced deformation layer (SEIDL) of 45 steel. Ultra-refine and nano grains were detected in the worn surface layer. Elements of Sn, Cu and Sb, originated from the mating tin-alloy-pin, with diffusion depth of 35 mu m, 11 mu m and 4 mu m, respectively, were detected in its SFIDL. Mechanisms accelerating atom diffusion in SEIDL were subsequently propounded. (C) 2013 Elsevier Ltd. All rights reserved.