LOW-TEMPERATURE FATIGUE-INDUCED MARTENSIT IC-TRANSFORMATION OF A METASTABLE AUSTENITIC STAINLESS-STEEL - OPTIMIZATION OF STRENGTH AND FATIGUE PROPERTIES

The enhancement of the strength of a mestastable austenitic AISI 304 L -type stainless steel by fatigue-induced martensite formation in the t emperature range 103 K to 298 K was investigated. The fatigue tests we re run in closed-loop plastic strain control using a symmetric sinusoi dal wave form (0.2 Hz). Plastic strain amplitudes were in the range 3. 2 x 10(-3) to 1.26 x 10(-2) The increase in strength caused by fatigue -induced martensite formation was measured by subsequent monotonic ten sile tests at room temperature. The fatigue-induced martensite content and, as a consequence, the increase in strength and the residual fati gue life vary strongly with pre-deformation conditions (plastic strain range, test temperature, number of cycles). The cyclic pre-deformatio n conditions can be optimized to achieve the best combination of stren gth and residual fatigue life as required for technical applications.