What is duplex steel?

　　Dual phase steel is a type of stainless steel with two different grain phases, called austenite and ferrite, present in the microstructure. Austenite and ferrite phases have different atomic structures and show different physical properties. Because each phase of dual phase steel contains about 50% of the phases, it can show the beneficial properties of two material types.

　　These attributes include:

　　Compared to other stainless steel products, the strength is relatively high

　　Compared with ferritic steel products, ductility and toughness have been improved, but these values are still lower than those of austenitic products

　　Excellent corrosion resistance

　　How is dual phase steel manufactured?

　　Like all types of stainless steel, duplex steel is smelted by melting and mixing raw materials containing nickel, iron ore, chromium, molybdenum, and other alloying elements in a furnace. Compared with other stainless steels, duplex steel contains a higher chromium content of about 25%, nickel content is reduced to below 9%, and nitrogen content is very low. The alloy content of dual phase steel is defined within a range, usually specified by its chromium content.

　　The molten dual phase steel mixture solidifies into a completely ferrite solid, but when cooled to room temperature, half of the material undergoes a phase transition from ferrite to austenite.

　　What is the purpose of dual phase steel?

　　High strength, high corrosion resistance, and relatively low alloy content (especially nickel) typically make duplex steel a low-cost choice for high-strength, high corrosion risk applications. They are widely used in pipeline systems, manifolds, risers, etc. in the offshore oil and gas industry, as well as in the form of pipelines and pressure vessels in the petrochemical industry.

　　Although duplex stainless steels have high corrosion resistance and oxidation resistance, they cannot be used at high temperatures due to the formation of brittle phases in ferrite at relatively low temperatures. These stages have a significant impact on the toughness of steel and should be avoided.