Visco Elasticity

In the welding of steels, the crystal structure around the heat-affected-zone (HAZ) differs from that of the surrounding metal, presenting an area that is structurally weaker. Stress relaxation consists of heating the HAZ uniformly and letting it cool at a defined rate, thereby altering the crystal structure in pursuit of a more uniform steel with homogeneous properties.

For example, weld repairs to railway track components run the risk of developing Martensite, a brittle structure, because of the composition of the base steels used. Post-heating the weld and slowly cooling it converts the Martensite to less brittle structures, thereby reducing the risk of stress cracking in the neighbourhood of the weld, an action that is crucial to maintaining rail safety.

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Another technique uses vibratory stress relief to do the job.

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