P/M components experience considerable changes during heat treatment that include changes in mechanical properties, in dimensions, in magnitude and sense of residual stresses, and in metallurgical phase composition. Since the quality assurances criteria that all heat-treated P/M components must meet include prescribed minimum mechanical properties and compliance with dimensional tolerances, it is necessary for P/M producers to be able to accurately predict these changes in order to take appropriate measures to prevent their harmful effects and insure the production of good quality parts. Satisfactory response to heat treatment is often gauged by the ability of the component to be heat treated to a desired microstructure, hardness and strength level without undergoing cracking, distortion or excessive dimensional changes.
Other than the reversible changes caused by thermal expansion and contraction, metallic components experience permanent dimensional changes during heat treatment.