Austenitic stainless steels possessing good corrosion resistance have recently found growing applications as a constructional material. In this instance, increasing strength properties, which are typically quite low, is of great interest. Due to the low stacking fault energy, strain hardening of alloyed austenite is efficient for increasing tensile strength without impairing ductility seriously. In addition, certain grades are unstable, so that cold working creates strain‐induced martensite that enhances strengthening. Grain size refinement to micrometer scale or even finer can also increase the yield strength, still providing good ductility. In the present paper dislocation and phase transformation strengthening and thereby properties achievable in temper rolled austenitic stainless steels are discussed. Strengthening by the reversion annealing is also described and excellent results achievable are shown. Finally, the effect of bake hardening through the static strain ageing is presented. Long‐term research work in various projects indicates that the current knowledge of strengthening of austenitic stainless steels is close to the industrial utilisation.

The effects of chemical composition, cold rolling and subsequent annealing parameters on the reversion of strain-induced martensite to austenite were investigated in three experimental Mn and Si-free Cr-Ni austenitic stainless steels and two commercial Type 301 and Type 301LN grades by optical and electron microscopy, X-ray diffraction and magnetic measurements. Hardness and tensile tests were performed to determine the mechanical properties achieved. In cold rolling, completely martensitic structure could be obtained in the experimental heats, but only partially in 301 and 301LN grades at reasonable reductions. Upon annealing, in 301LN the reversion took place by the nucleation and growth mechanism, and submicron austenite grains were formed within a few seconds at temperatures above 700°C. In the other steels, reversion took place by the shear mechanism, and ultra-fine grains were formed by the recrystallization of austenite at temperatures of 900°C or above. Partial reversion resulted in an excellent combination of yield strength and elongation in 301LN, and also in 301 such ones were attained in the reverted structure even before any profound formation of submicron grains.

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The yield strength in austenitic stainless steels can be improved by cold rolling. Recently, it has been realized that a considerable further increase can be achieved through static strain ageing (SSA). The effect of SSA in four austenitic stainless steel grades was studied. The test materials were formerly cold rolled to three different reductions of 15%, 30% and 40%. Subsequently, the steels were aged at temperature range between 160 and 400 °C with ageing times from 15 to 15000 seconds. Owing to SSA, increments over 200 MPa in yield strength were observed, while elongation decreased only slightly or even improved by 1 to 2%-units. The influence of ´-martensite on the strength increase was apparent. The maximum strength increase with relatively small drop of elongation was achieved in the steels cold rolled to 30% reduction while approximately 50% of ´- martensite was formed. However, a small increase in the yield strength was detected even in steels cold rolled to 15% reduction and containing 0 to 2% of ´-martensite only. Therefore, SSA seems also to take place in the austenite phase. To clarify the reason for improvement of the ductility in the instance of strengthening, work hardening rates were determined and found to differ considerably between aged and non-aged structures. The activation energy of the SSA process determined was found to be almost equal to the activation energy of carbon and nitrogen diffusion in the austenite phase. A mechanism resembling the Suzuki effect was suggested as the main mechanism of the SSA process.