拡散シミュレーションによる鉄系高炭素箔と鋼材との液相挙動予測

概要

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A plane-to-plane bonding by the rapid reaction with liquid phase enables a simplified forming of hollow or complex steel parts. The time for disappearance of transient liquid is absolutely short if a high-carbon filler material controls the Fe–C eutectic liquid at bonding interfaces. Taking advantage of multi-component diffusion simulation, this paper aims to investigate how the behavior of eutectic liquid depends on the constituent in ferrous high-carbon (FHC) foil. Due to the rapid diffusion of carbon in austenite, the FHC foils with dispersed cementite or graphite failed to maintain a prescribed C composition and was predicted to yield a liquid only in the midst of foil. The monophase cementite (θ) foil, on the other hand, resulted in a liquid layer thicker than the initial foil thickness, and that ensures a dissolution of alloying elements in liquid from joined steels.It was possible to synthesize the monophase θ filler by substituting a part of Fe with Cr. Using the Cr-substituted θ filler, microstructures have been analyzed in the quenched samples during bonding of 0.21C–0.8Mn–0.25Si–0.22Cr steels at 1453K. Although the lowest temperature at which a liquid phase was observed was far lower than the simulation, Mn and Si dissolved in liquid layer have been confirmed. The liquid completely disappeared within 180 s and however, the segregation of Cr would remain severe.