Model of hydrogen behaviour in enamelling grade steels

A model has been developed of the behaviour of hydrogen in enamelling-grade steels in relation to the delayed defect of blow-off of enamelled surface (fishscaling). The model is based on current theories concerning reversible and irreversible trapping of hydrogen in metallic materials. It leads to the establishment of a free hydrogen parameterC_L which can be used to assess the susceptibility of a steel to fishscaling following the usual enamelling processess. The model can also be used to study the effect of both thermomechanical steelmaking cycles and enamelling processes on resistance to the defect.Nomenclature E_aD Activation energy of hydrogen diffusion through normal lattice - E_s Saddle-point energy - E_B Trap binding energy - E_aT Trap activation energy=E_s+E_B - A Trapping site - B Normal lattice site - v₀ Vibration frequency of hydrogen at a normal lattice site - v₁ Vibration frequency of hydrogen at a trapping site - N_L Density of normal lattice sites for hydrogen - N_T Density of trapping sites for hydrogen - C_L Concentration of hydrogen on lattice sites - C_T Concentration of hydrogen captured on traps - k Probability of trapping=v₀ exp(–E_s/R T) - p Probability of detrapping =v₁N_L exp (–E_aT/R T) - n Fraction of trapping sites occupied with hydrogen atoms among the total trapping sites=C_T/N_T - t Time - T Temperature - R Gas constant