Metastable bcc-Cu precipitation behavior and its effect on microstructure and strengthening of as-cast Fe–B alloy containing 3 wt% copper content

The metastable bcc-Cu precipitation behavior, with particular focus on effect of metastable bcc-Cu on microstructural evolution and strengthening is investigated by experiment and calculation simulation in an as-cast Fe–B alloy containing 3 wt% Cu content. The results show that the metastable bcc-Cu precipitates with the size of 3 to 5 nm can precipitate from the α-Fe (pearlite). During the precipitation process, the metastable bcc-Cu can act as the highly effective heterogeneous nuclei of pearlitic ferrite, which results in the formation of abnormal pearlite. Additionally, the existence of bcc-Cu will lead to the refinement of abnormal pearlitie, the dissolution of abnormal pearlitic cementite, and the strengthening of pearlite. The microstructural evolution process can be essentially described as: L (liquid phase) → γ (austenite), L → γ + M₂B(boride), γ → P(normal pearlite), γ → P + bcc-Cu₁ (the first precipitates), γ → P + P*(abnormal pearlite) + bcc-Cu₂ (the second precipitates) + bcc-Cu₁, and γ → M (martensite). Moreover, the calculation simulation analyses are in good agreement with the experimental results. (paper)