Use of kinetic model for thermal properties of steel at high temperatures

Abstract

Steel thermal properties determination is essential in steel structure temperature prediction for structural fire design or metallurgical evaluation. Thermal properties include specific heat, thermal expansion and heat transfer coefficients. Since the steel thermal properties variation at high temperature may be considered as a chemical process, kinetic theory could be used to explain the variation. To examine this concept, steel specific heat is first considered in this paper. The validity of the kinetic model that successfully applied to steel specific heat can be used to estimate the variation of other steel thermal properties at high temperatures. Complex non-linear equations for steel specific heat computation are provided in design codes. In this paper, it is found that the way steel specific heat varies with temperature during solid state phase transformation is not unique. Instead of using high-order equations, models using simple linear equations and average specific heat for phase transformation are proposed. These models are based on the latent heat principle whereby the latent heat consumed by steel during phase transformation is constant. Furthermore, the proposed simple models can effectively simplify the steel specific heat computation and provide good steel temperature development simulation shown in the case study.