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The high temperature of annealing may result in oxidation of the metal's surface, resulting in scale. If scale must be avoided, annealing is carried out in a special atmosphere, such as with endothermic gas (a mixture of carbon monoxide, hydrogen gas, and nitrogen gas). Annealing is also done in forming gas, a mixture of hydrogen and nitrogen.
Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally ...
Tempering at even higher temperatures, between 540 and 600 °C (1,004 and 1,112 °F), will produce excellent toughness, but at a serious reduction in strength and hardness. At 600 °C (1,112 °F), the steel may experience another stage of embrittlement, called "temper embrittlement" (TE), which occurs if the steel is held within the temperature ...
The steel is then re-quenched to 'fix' the temper at the desired level. A talented smith or metalworker can fine-tune the performance of a steel tool or item to precisely what is required based solely on careful observation of temper colours. A visual representation of this process may make the concept easier to understand.
Common heat treatment processes include annealing, precipitation strengthening, quenching, and tempering: [32] Annealing process softens the metal by heating it and then allowing it to cool very slowly, which gets rid of stresses in the metal and makes the grain structure large and soft-edged so that, when the metal is hit or stressed it dents ...
Differential tempering (also called graded tempering, selective tempering or local tempering) is the inverse of differential hardening, to ultimately produce similar results. Differential tempering begins by taking steel that has been uniformly quenched and hardened, and then heating it in localized areas to reduce the hardness.
The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or spheroidite and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel.
The rate of the microscopic mechanisms controlling the nucleation and growth of recrystallized grains depend on the annealing temperature. Arrhenius-type equations indicate an exponential relationship. Critical temperature. Following from the previous rule it is found that recrystallization requires a minimum temperature for the necessary ...
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