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In practice and industry, this reduction of Gibbs free energy is termed stress relief. [citation needed] The relief of internal stresses is a thermodynamically spontaneous process; however, at room temperatures, it is a very slow process. The high temperatures at which annealing occurs serve to accelerate this process. [citation needed]
Stress-relieving is a technique to remove or reduce the internal stresses created in metal. These stresses may be caused in a number of ways, ranging from cold working to non-uniform cooling. Stress-relieving is usually accomplished by heating a metal below the lower critical temperature and then cooling uniformly. [21]
[2] [6] The specified holding temperature is one that is at a high enough temperature to relieve high residual stress levels, yet is still below the lower transformation temperature. [ 1 ] [ 2 ] In addition to the reduction of stress, high hold temperatures below the transformation temperature allow for microstructural transformations, therein ...
The amount of relaxation which takes place is a function of time, temperature and stress level, thus the actual effect it has on the system is not precisely known, but can be bounded. Stress relaxation describes how polymers relieve stress under constant strain.
A cryogenic treatment is the process of treating workpieces to cryogenic temperatures (typically around -300°F / -184°C, or as low as −190 °C (−310 °F)) in order to remove residual stresses and improve wear resistance in steels and other metal alloys, such as aluminum.
This is a combination of a large temperature gradient due to low thermal conductivity, in addition to rapid change in temperature on brittle materials. The change in temperature causes stresses on the surface that are in tension, which encourages crack formation and propagation. Ceramics materials are usually susceptible to thermal shock. [2]
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Tempering is sometimes used in place of stress relieving (even heating and cooling of the entire object to just below the A 1 temperature) to both reduce the internal stresses and to decrease the brittleness around the weld. Localized tempering is often used on welds when the construction is too large, intricate, or otherwise too inconvenient ...