Dry corrosion of metals - Industrial cases: oxidation, carburation

Many industrial processes require materials to be brought to temperatures in excess of 500°C. As with use at ambient temperature, the choice of these materials is the result of a compromise between economic (lowest cost), technical (mechanical strength, hardness, deformability, machinability, weldability, mass, etc.) and aesthetic (design, visual appearance) considerations. High-temperature use does, however, give rise to additional constraints. These include creep, microstructural stability and high-temperature corrosion (or dry corrosion).

In many applications, increasing working temperatures improves yields (energy conversion) and/or reduces environmental nuisances (energy consumption, CO ₂ emissions). It does, however, lead to increased corrosion and thus a reduction in plant service life. Materials therefore need to be adapted to the maximum operating temperature.

Virtually all environments of technological interest contain sufficient chemically reactive gaseous species for almost all metals to become thermodynamically unstable, and thus to be transformed into oxides, chlorides, nitrides, carbides, sulfides... The rate of corrosion then depends on the product formed, the nature of which is determined by complex interactions between the composition, microstructure and surface morphology of the alloy, the thermochemistry of the environment and the reaction temperature. The resulting dry corrosion consists, on the one hand, of a reduction in the thickness of the material, often the primary cause of the limited service life of the installation, and, on the other, of the dissolution of oxygen, nitrogen or carbon in the alloy, resulting in internal corrosion that also degrades mechanical strength and thus contributes to the breakage of parts.

Here, we describe the main types of dry corrosion encountered in practice, and the relative performance of the main metallic materials available, i.e. Fe-, Ni-, Cr- or Co-based metals, whether raw or coated.