1192 Ferrous Materials Steels

Typically these materials may be classed as (i) carbon steels (mild steel), (ii) low-alloy steels (1-2% alloy additions), and, (iii) high-alloy steels (stainless steels).

Carbon Steels Carbon steel is by far the most widely used engineering alloy by virtue of its low cost, variability in mechanical properties, formability and ease of fabrication, and suitability for the application of protective coatings and cathodic protection methods.

The corrosion rate of carbon steel, like all materials, depends upon the chemical composition and previous history, that is, mechanical working, heat treatment, welding, surface condition and so forth. In general corrosion takes place when the relative humidity is greater than 60% where upon a liquid-phase may form on the metal surface. Once formed the rate of corrosion will depend upon the nature of the environment as discussed previously (Section 11.4). Table 11.10 presents a list of typical corrosion rates for carbon steels within different types of environments.

TABLE 11.10 Typical Corrosion Rates for Mild Steel in Various Environments

Environment

Corrosion Rate (mm/yr)

Atmospheric

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