Corrosion properties of HIPped P/M duplex stainless steels

Corrosion properties of experimental nitrogen-alloyed powder metallurgically (P/M) produced duplex stainless steels (DSSs) were investigated and compared with properties of commercial wrought super duplex and super austenitic stainless steels. P/M DSSs were compacted by the hot isostatic pressing (HIP) method.The effect of manufacturing parameters, alloying, microstructure and different annealing and precipitation heat treatments were evaluated by means of pitting and crevice corrosion tests in 6% FeCl 3 solution. Microstructures and surfaces after corrosion tests were examined using light optical and scanning electron microscopy. Pitting and crevice corrosion resistance of nitrogen-alloyed P/M DSSs in 6% FeCl 3 solution is equal to the corrosion resistance of corresponding wrought DSSs and determined critical pitting and crevice corrosion temperatures (CPT and CCT) correlate well with the Pitting Resistance Equivalent (PRENW). Furthermore, a special pitting resistance equivalent with six variables for nitrogen alloyed P/M DSSs is defined with linear regression analysis. In 6% FeCl 3 solution pitting corrosion initiated mainly at austenite phase or at phase boundaries in standard low-alloyed P/M DSSs, and in the case of high-alloyed P/M DSSs pitting corrosion initiated both at austenite and ferrite phases and also at phase boundaries. The most pronounced detrimental effect of slow air cooling after solution annealing heat treatment was on the pitting corrosion resistance of super DSSs. On the other hand, annealing heat treatment at the temperature around 400°C or at 550°C had practically no effect on the corrosion resistance ofthe studied P/M DSSs in 6% FeCl 3 solution.