Abstract
Alloying element like boron, even in small addition, is well known to improve hardenability of steels. Its application can improve mechanical properties of steels and reduce alloying costs. Despite these benefits is not easy to cast boron steels, mainly in dynamical solidification process like continuous casting, due to their crack susceptibility1,2. The strategy of using Phase-Field simulation of the solidification process is based on its proved capacity of predicting realistic microstructure that emerge during solidification under conditions even far from equilibrium3-5. Base on this, some comparative simulations were performed using a three component dilute alloy in a two dimensional domain under unconstrained (isothermal) and constrained (directional) solidification. Simulation results suggested two fragile mechanisms: one related to a deep dendritic primary arms space and other due to the remelting of this region at low temperature. Both resulted mainly from the high boron segregation in interdendritic regions.
Highlights
Phase-Field model is an approach based on the concept introduced by Gibbs and Van der Waals, which states that solid-liquid interface has a physical dimension of nanometer magnitude[3,6,7]
Developments of Phase-Field models can be addressed to Van der Waals who perceived that the addition of gradient term in free energy functional has an effect of creating interface with certain thickness[6]
As far as the rate of solidification is small, solute concentration should approach the values given by phase diagrams
Summary
Phase-Field model is an approach based on the concept introduced by Gibbs and Van der Waals, which states that solid-liquid interface has a physical dimension of nanometer magnitude[3,6,7]. Phase-Field models of solidification of three component alloys without convection in liquid or solid state tension effects are composed by four diffusion equations: one for the order parameter; one for temperature and two for the solutes. In that case and considering the analytical solution of Equation 8, simplified to describe the equilibrium of pure and isotropic material without noise in an one dimension domain, it is possible to relate these parameters to the interfacial tension (σ) and interface thickness (2λ) as follows[11]: ξ0
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