Abstract
To clarify the effect of alloying elements (M) on the grain boundary segregation behavior of boron (B) and carbon (C) in α-iron, the grain boundary segregation of B, C and alloying elements was evaluated thermodynamically for the Fe–B–1.0 at.%M and the Fe–C–1.0 at.%M ternary systems (M: Al, Ti, V, Cr, Mn, Nb, Mo) using the parallel tangent law proposed by Hillert. In this calculation, the Gibbs energies of the liquid phase in the Fe–B–M and Fe–C–M ternary systems were applied to those of the grain boundaries. According to the calculated results, in the Fe–B–M ternary systems, co-segregation of Ti, V, Mn or Nb with B was predicted, while no co-segregation behavior was confirmed in the case of Al, Cr or Mo addition; in the Fe–C–M ternary systems, co-segregation of Ti, V, Nb or Mo with C was predicted, while no co-segregation behavior was confirmed in the case of Al, Cr or Mn addition. These co-segregation tendencies correspond well with the formation tendencies of metal borides or metal carbides. Although the present calculated results were based on the assumption that substitutional elements can diffuse sufficiently in addition to interstitial elements B and C, we proposed an equation for the parallel tangent law under paraequilibrium condition in which no partitioning of substitutional elements occurs.
