The austenite reversion in a Cu-containing 3.5wt.%Ni high-strength low-alloy(HSLA)steel with intercritical heat treatment was investigated by electron back-scatter diffraction(EBSD),transmission electron microscopy(TEM)and atom probe tomography(APT).It was found that the reverted austenite was formed predominantly located at prior austenite grain boundaries(PAGBs),martensite packet or block boundaries and martensite lath boundaries(LBs)during intercritical tempering at 675℃ for 1 h.The reverted austenite was rich in austenite stabilizers Ni,Mn,Cu and C.Cu-rich precipitates were also detected by TEM distributed at PAGBs and martensite LBs as well as in ferritic matrix.C-rich precipitates,which were simultaneously enriched with austenite stabilizers Ni and carbide formers Cr and Mo,were found by APT.Since austenite reversion and formation of alloyed carbides are both triggered by initial C segregation,there is a competitive diffusion of austenite stabilizers and carbide formers during the further proceeding of austenite reversion and carbide precipitation,leading to the formation of paraequilibrium C-rich precipitates.On the other hand,Cu precipitation is greatly associated with the clustering and segregation of austenite stabilizers Ni and certainly Cu,which inevitably induces a competitive diffusion of the related atoms in participating in austenite reversion and Cu precipitation.As a result,no Cu-rich precipitates are detected in and around the reverted austenite.