Filtern
Dokumenttyp
Schlagworte
- KorroPad (2)
- Pitting corrosion (2)
- Corrosion (1)
- Corrosion resistance (1)
- Heat treatment (1)
- Martensitic stainless steel (1)
- Nitrogen (1)
- Polarisation (1)
- Stainless steel (1)
- ThermoCalc (1)
Organisationseinheit der BAM
In the last years, new approaches for the evaluation of the corrosion resistance of stainless steels were developed which allow short term corrosion testing with increased information content. This work analyses the extensive influence of heat treatment on microstructure and the resulting corrosion resistance of the martensitic stainless steels 1.4034 and 1.4021 with advanced methods. Different heat treatments at various austenitization temperatures up to 1100°C and the effect of different cooling rates were evaluated; the last has not yet been studied in literature at all. The resulting corrosion behaviour in relation to the different carbon content in the two used alloys and the applied heat treatment will be presented and discussed. The applied methods of investigation were conventional evaluation of the critical pitting corrosion potential (PP), modified electrochemical potentiodynamic reactivation (mEPR) and the "KorroPad" (KP) technique. The performance of modified EPR and its interpretation were optimized to provide additional information about the general passivation ability and the extent of chromium depletion as result of applied heat treatment. The aim using PP and KP was the correlation between the Parameters of the mEPR with the changes in the pitting corrosion resistance. Furthermore the results will demonstrate the functionality and usability of the short term corrosion test methods mEPR and KP in order to increase their acceptance within the scientific community. The results indicate a surprisingly large influence of both austenitization temperature and cooling rate on the corrosion resistance within all three used test methods, which can explain the different corrosion behaviour of martensitic stainless steels in earlier investigations.
Nickel-free, nitrogen alloyed austenitic stainless-steels, with about 19 wt.-% Mn and 0,8 wt. % N, are an interesting alternative to classic CrNi austenitic stainless steels due to their superior mechanical properties (Rm > 900 MPa, A5 > 50 %, Av > 350 J) in the solution annealed condition. The formation of chromium-rich nitrides during suboptimal heat treatment, processing or application leads to an inhomogeneous distribution of alloying elements in the microstructure, which reduces the corrosion resistance. Consequently, an accurate knowledge of the sensitization behavior is indispensable for the use of nickel-free, high-nitrogen austenitic stainless steels. The relationship between artificial aging, phase formation and corrosion resistance was investigated on the alloys X8CrMnN18-19 (1.3815) and X8CrMnMoN18-19-2 (1.4456), both alloyed with 0,8 wt.-% Nitrogen, in the present work. The microstructural evolution was studied by LM and SEM while the corrosion resistance was characterized with the electrochemical potentiodynamic reactivation (EPR) and the KorroPad indicator-test. Both alloys showed increased corrosion susceptibility within critical aging parameters. Finally, a sensitization diagram was described successfully for both alloys showing the positive effect of molybdenum.