This is a review paper of high temperature (greater than 200° C) oxidation of steels with total alloying elements less than 3 wt%. Topics include the iron-oxygen phase diagram, the oxidation mechanism and kinetics as well as the effects of alloying elements, environmental atmospheres, and cold work.

High temperature oxidation of low alloy steels

The oxidation properties of iron have been investigated at temperatures in the range 800–1000° C in oxygen over the pressure range 0.3–760 Torr. A duplex scale consisting of wustite and magnetite was formed during the earliest intervals examined. Hematite grew on the magnetite surface after an induction period which decreased with increasing oxygen pressure; this oxide developed as whiskers and platelets at temperatures less than 860° C and as small grains at higher temperatures. Iron transport occurs through the scale and involves short-circuit diffusion in the hematite layer. The oxidation kinetics obeyed a parabolic law independent of oxygen pressure since multilayer scale growth was directly dependent on the lattice diffusivity of iron and the iron gradient established in the wustite layer.

Kinetics and morphological development of the oxide scale on iron at high temperatures in oxygen at low pressure

High speed steels are used for the manufacture of the work rolls used in hot rolling steel mills. An understanding of the degradation phenomena of work rolls is essential, particularly in fields related to the oxidation of the surface, given the importance of the surface quality of the rolled product at the end of the process and its close relation with the changes experienced by the surface of the rolls. The high temperature oxidation behaviour of a work roll grade high speed steel was studied using gravimetric means under isothermal conditions at 550 and 615 °C in dry air and in a mixture of dry air and water vapour. At both temperatures, the mass gain of the samples exposed to the mixture of dry air and water vapour was considerably higher than that of the samples exposed to dry air. For all the experimental conditions, oxide growth was better described by the parabolic rate law. The composition of the oxide layer was influenced by the oxidant atmosphere, as the layer in the water vapour containing environment included an iron-chromium spinel (M3O4), magnetite and hematite, whereas the layer in the dry air condition consisted of iron–chromium spinel, hematite and vanadium oxide. The effect of composition of the oxidant atmosphere on the rate of oxidation of the steel and the components of the oxide scale is discussed.

High Temperature Oxidation of a Work Roll Grade High Speed Steel

The kinetics of oxidation, the composition of oxide scales, and the morphology of scales were markedly affected by recrystallization of the iron substrate at 500°C. There was little difference in behavior over the temperature range of 600 to 900°C. Whiskers of Fe2O3
formed on the outer surface during oxidation at 800 and 900δC, the orientation of the whiskers being either [001] or [110]
⊥
surface, depending upon the batch of the iron. Different batches of iron from the same supplier exhibited variable oxidation behavior which has been attributed to variations in the thermal stability of the crystal texture in the substrates.

The effect of recrystallization on the oxide scale composition and growth of whiskers during the oxidation of pure iron

Oxidation of nimonic 80A at 800°C in low oxygen pressures

The weight increase curves of pure iron specimens cold-worked by abrasion with SiC and 7-μ diamond paste have been registered as a function of pressure and temperature. The oxidation rate increases with temperature and pressure when the pressure is raised from 0.02 to 0.2 bar. When the pressure is further increased to 1.02 bar at 500 and 625°C the oxidation rate decreases. This decrease is attributed to an orientation of the oxide grains in the α-Fe2O3 surface.

Lennart Jansson

Papers

The effect of the oxygen pressure and the growth of whiskers on the oxidation of pure Fe