Tailoring Nanocluster Co‐Precipitation Behavior During Pre‐Deformation and Tempering in Ultralow‐Carbon Bainitic Steel

In this study, tailoring nanocluster co‐precipitation behavior in ultralow‐carbon bainitic steel during subsequent tempering treatment were systematically investigated. It can be found that the introduction of cold rolling prior to tempering can significantly promote the enhancement in mechanical property with the yield strength increased by about 600 MPa at the thickness reduction of 90% compared to the undeformed samples, which are mainly attributed to the synergetic strengthening effects of grains refinement, dislocation–precipitate interactions as well as the altered precipitation characteristics of Cu‐rich clusters (CRCs) and carbides‐formed atomic clusters (CFACs). Notably, with the increase of pre‐deformation, the CRCs exhibit the decreased size but the increased number density, whereas the CFACs show the tendency of coarsening along with the reduced number density during the tempering process, reflecting the distinct underlying formation mechanisms governing the precipitation behavior. Based on the combination of transmission electron microscopy observations and atom probe tomography analysis, it reveals that the formation of nanoscale CRCs is derived from the solubility differences and the driving force for solute segregations, whereas the generation of CFACs is originated from strong chemical bonding between interstitial C atoms and metallic elements. Particularly, the pre‐deformation can produce additional nucleation sites and accelerate atomic diffusion to regular the number density and spatial distribution of clusters, thereby improving the mechanical performance of steel. This work provides an in‐depth understanding of precipitation behavior of ultralow carbon bainitic steel under the coupled effects of plastic deformation and heat treatment. It is anticipated to establish a new strategy for tailoring the balance between CRCs strengthening and CFACs‐related contributions and provide theoretical guidance for the design of high‐strength steels.