Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being to produce a 5050 mix, although in commercial alloys the ratio may be 4060. Duplex stainless steels have roughly twice the strength compared to austenitic stainless steels and also improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterized by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels.