Carburizing Process and Carburizing Steels...

Carburizing Process and Carburizing Steels  Carburizing is one of the most widely used surface hardening processes. It has been in use for a long time. The process involves diffusing carbon into a low carbon steel to form a high carbon steel surface. Carburizing process is also referred to as case hardening or case carburizing process. It is a heat treatment process that produces a surface which is resistant to wear, while maintaining toughness and strength of the core. The carburizing process has evolved with advancements in heat treatment techniques that have improved the hardness and durability of products like carbon steel wire springs and carbon steel forgings. Carburizing is a heat treatment process in which steel absorbs carbon liberated when the steel is heated between 850 deg C to 950 deg C in the presence of a carbon bearing material, such as charcoal or carbon monoxide, with the intent of making the steel harder. The heated steel at this temperature has austenitic structure which has got high solubility for carbon and which is a stable structure. Depending on the amount of time and temperature, the affected area can vary in carbon content. Longer carburizing times and higher temperatures typically increase the depth of carbon diffusion. When the steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard via the transformation from austenite to martensite while the core remains soft and tough as a ferritic and/or pearlitic microstructure. The typical carburizing process cycle including the quenching and tempering steps is shown in Fig 1. Fig 1 Typical carburizing cycle including the quenching and tempering step  Carburized steel consists of a composite material, where the carburized surface is hard but the unaffected core is softer and ductile. Compressive residual stresses are formed in...