The grade has nitrogen addition to provide strength and avoid common corrosion problems in the austenitic 300 series. The microstructure of the grade comprises of ferritic phase surrounding the austenitic phase.
Ferritic alloys have higher strength and better corrosion cracking resistance while austenitic grades have better machining properties and general corrosion resistance, pertaining to the difference in the content of iron, carbon and other alloying elements. The duplex grade 2205 combines the properties of both the phases. Therefore, it can be argued that 2205 is the most widely used duplex stainless steel. It has outstanding fatigue strength along with double the yield strength of austenitic grades, which allows the grade to be used in various dynamic applications. It can be sectioned, fabricated and weighed as per the designer’s consideration. Localized as well as uniform resistance to corrosion is provided in environments from moderate to severe corrosion conditions.
The localized corrosion like pitting and crevice corrosion performance of the grade is better than grades, 316L and 317L of 300 series. The grade also has lower thermal expansion comparatively. Hence, during welding, there is little to no expansion of the base metal at the heat affected zone and the grade also demonstrate enhanced welding properties. Balanced welding properties are maintained even at the heavier sections of the grade. The excellent ductility and the composition of 2205 are the key elements to forge the grade as per the needs of the application. Hot forming as well as cold forming can be suitably done on the grade.
Hot forming needs to be carefully and uniformly done in the range 950-1150°C. At this range, the matrix becomes soft and is easily formed. Below this temperature, the grade becomes more prone to austenitic structure than ferritic, moreover, if the shape is not uniform, the corners may be cooler than other areas resulting in the formation of cracks. Also, there might be a formation of intermetallic phases below 930°C. The intermetallic phases in the grade severely deteriorate the grade's corrosion resistance, mechanical and welding properties. It needs to be completely annealed so as to restore its properties and use it in applications. The grade has very high strength and work-hardening rate due to which cold forming requires higher forces. Even allowances are required for the spring-back of the grade due to its strength. The grade 2205 makes its way in most of stainless steel applications because of its varying properties and versatility stemming from its two-phase structure.
