Short-Time Oxidation Behavior of Low-Carbon, Low-Silicon Steel in Air at 850–1180 °C: II. Linear to Parabolic Transition Determined Using Existing Gas-Phase Transport and Solid-Phase Diffusion Theories

Abstract

Existing gas-phase transport and solid-phase diffusion theories are used to calculate the oxidation kinetics of low carbon and low silicon steel in flowing air at 850–1180 °C. The linear-to-parabolic transition scale thickness derived is proportional to the parabolic rate constant and inversely proportional to the linear rate constant. Calculated parabolic rate constants are consistent with experimental results, whereas calculated linear rate constants are 40% smaller and calculated linear-to-parabolic transition scale thicknesses are 20–40% greater than the experimental results. Introduction of a correction factor cannot simultaneously resolve the discrepancies. Various sources causing the discrepancies are discussed. One important issue identified is that the conditions for deriving the equation for calculating the linear rate constant are different from those in laboratory furnaces. The linear-to-parabolic transition scale thickness derived is also a function of gas composition, gas velocity and sample length. An intrinsic gas-phase mass-transfer factor, independent of gas velocity and sample size, is recommended to express the gas-phase mass-transfer coefficient for calculating the linear rate constant.