Abstract

The performance of many metallic components can be markedly improved by developing a surface region, the case, which is harder than that of the underlying region, the core. Case hardening processes, in which the original surface is an integral part of the case, may involve a physical or a chemical change at the surface. Processing may be accomplished through the use of heat or other methods such as plastic deformation or ion implantation. Small atoms, ie, first row elements, deposited in interstitial positions harden metallic components.

The various case hardening processes used for steels are discussed. Carburizing and nitriding, the most common methods employed, and the resultant case-hardened steels are compared.

Metal surface cleaning is the beginning of any metal treatment. The cleaners for metal surfaces may be classified as solvent-based or aqueous. Usage of solvent-based cleaners is declining. Whereas aqueous cleaners may be acidic, neutral, or alkaline, alkaline cleaners are the most widely used. The types of components typically found in an alkaline cleaner for specific types of metals or alloys, together with cleaning temperatures and other conditions of operation, are discussed. The most common mechanisms of soil removal are presented, as well as descriptions of the various cleaner application methods such as spray, immersion, electro- and barrel cleaning.

Metals, important materials for construction and manufacture, corrode in certain environments limiting the lifetime of manufactured metal goods. To protect from corrosion and to confer paint adhesive properties to metal surfaces, chemical pretreatment conversion coatings are widely used.

The most common metal surface treatments are iron, zinc, or chromium phosphating, chromating, and anodizing. An overview of the mechanism of coating formation, process operation and control considerations, coating characteristics, coloring procedures, and important applications for various coatings is given.

Pickling of metals and metal alloys involves the use of chemical cleaning agents to remove oxides from metal surfaces. The oxides may be in the form of corrosion by-products or heat treatment scales. Chemical pickling is an extremely effective and economical method for oxide removal, particularly for intricate shapes not readily cleaned mechanically. The choice of acid or alkali pickling product is generally dictated by the base metal or alloy that is to be cleaned. Sulfuric acid is the most commonly used pickling agent for ferrous metals. Mixtures of acids are often a better choice for nonferrous alloys. Environmental and health concerns are addressed.