The applications of stainless steels may be meeting in chemical industry, food industry, civil building, but present an increased interest also in machine constructions or household.This paper highlight the structural modifications obtained after temperature variations for AISI 321 stainless steel. The modifications of structure and proprieties can be induced by heat treatments applied to semi-products before or after the obtaining of final parts, but also by heating at regimes which respect the exploitation conditions of part. In the experiments, it is applied quenching to put into solution, with modification of final treatment temperature and maintaining time, aiming the dissolution of complex carbides and in this mode an easy processing. The treatment parameters were chosen, after the determination of alloying elements by AISI 321 samples, by optic spectrometry. The dilatometric analysis aimed to highlight the structural modifications, specific to thermal fatigue phenomenon, due to temperatures variations.

The paper presents a study about the structural modifications induced by heat treatment at the stainless steels, like AISI 321 and AISI 304, frequently used in industrial applications. The principal characteristic of these steels is their bigger corrosion resistance, conferred by chrome and nickel.The addiction of other elements is made for the improvement of corrosion resistance in humid environments (molybdenum and cooper), mechanical characteristics at low and high temperatures (tungsten, molybdenum, niobium and cobalt). The necessary condition to obtaining a high corrosion resistance is that all chrome content to be in forms of solid solution. The precipitation of carbides from solid solution causing a decrease under 12% of chrome content, the structure become bi-phase and the corrosion resistance decrease. For the improvement of machinability may be applied an annealing, with respect of all the treatment parameters, obtaining a micro-hardness decrease.The heating for annealing was made in an electric furnace, type UTTIS, with fixed hearth. The imposed heating speed was 10°C/minute. The decrease of micro-hardness by annealing, permit an easy processing for high alloy steels.