Which method is commonly used to strengthen steel and cast iron alloys?

Quenching is a heat treatment process that involves heating the metal to a high temperature and then rapidly cooling it, usually by immersion in water, oil, or air. This rapid cooling alters the microstructure of the steel or cast iron, transforming its properties significantly. It increases hardness and strength, making the material less ductile and more brittle. The resulting structure, known as martensite, is crucial in applications where high strength is required.

In contrast, while annealing is another method used on metals primarily to relieve stress, improve ductility, and refine the grain structure, it does not typically enhance strength to the same extent as quenching. Sintering is a process used to form solid shapes from powders, which is more common in the production of ceramics or metal matrix composites rather than strengthening alloys. Forging is a manufacturing process that deforms the material into a desired shape and can improve strength, but it does so through mechanical work rather than a thermal treatment method like quenching.