In the present work a new process route for martensitic stainless steel X30Cr13 (AISI 420) is pursued. Conventional austenitization or high temperature solution nitriding is followed by unconventional tempering and ‘ultra-low’ temperature gaseous nitriding. Tempering is performed in high vacuum and at higher temperatures than the recommended ones for X30Cr13. The relatively high tempering temperature impairs the corrosion resistance, but is restored by an additional gas nitriding step at temperatures below 380°C, which is considered the lower limit for low temperature surface hardening. Surface hardness values of around 1400-1500 HV were achieved for the surface hardened zone, which neither shows cracks nor spallation. Despite the low temperature, the hardened case has an unprecedented depth of 15-20 m for the adopted temperature range. The microstructural evolution was investigated with reflected light microscopy and X-ray diffraction analysis. Micro-hardness Vickers indentation provides information on the depth dependence of the hardness. Electrochemical polarization is performed by potentiodynamic and potentiostatic tests in order to evaluate the passivity of the material and its resistance to localized corrosion (pitting) and, hence, the overall performance after the full treatment cycle.
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