Open Access Conference Proceedings

Secondary phase’s precipitation is dangerous for stainless steel. The most important secondary phases for stainless steels with carbon amount higher than 0.2 % are carbides (especially M23C6). Most dangerous secondary phase for stainless steels with smaller amount of carbon and high chromium content (for example 25% of Cr) is sigma phase (σ). Secondary phases absorb chromium from neighbouring areas. This mechanism is very danger for technological treatment of stainless steels (welding, heating above 300 °C). Fundamental property of stainless steel is corrosion resistance for working conditions. Aim of the work was to analyse influence of sigma phase precipitation on the intergranular corrosion resistance for X2CrNiMoN25-7-4 super duplex stainless steel. High chromium amount induce precipitation of high chromium sigma phase and it cause changes of the material intergranular corrosion resistance. Very low carbon amount (about 0.02%) prevents carbides precipitation and well described sensitization caused with carbides do not occurs in this case. Heat treatment parameters for performed analysis have to initiate different amount of sigma phase precipitation. Results of performed analysis confirm conservative opinion about sigma phase influence on the intergranular corrosion resistance. Some additional and not described jet results concerning influence of sigma phase precipitation on the intergranular corrosion achieved. On the basis of achieved results, specific case, when sigma phase increase intergranular corrosion of X2CrNiMoN25-7-4 super duplex stainless steel was revealed. The paper describe mechanism of intergranular corrosion resistance improve for X2CrNiMoN25-7-4.

Keywords: Intergranular corrosion, sigma phase, sensitization, Huey test

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