Duplex Stainless Steel Castings: Duplex Steel History
Duplex stainless steel has many practical uses nowadays ranging from flatware to power plants and transportation, but did you know that it was first used in paper mills?
According to the second edition of The Practical Guidelines For The Fabrication Of Duplex Stainless Steel published by the International Molybdenum Association in London, the first wrought duplex steel was made in Sweden in the 1930s and was first used in sulfite paper processing plants. Finland followed suit and came out with the first duplex steel casting during the same year, and six year afterwards, was granted a patent in France for what would be known as the Uranus 50. This duplex steel prototype became the basis for the AISI (American Iron and Steel Institute) Type 329 that was used for heat exchanger tubes following World War II.
Duplex Stainless Steel Castings: Specifications
The abovementioned duplex steel castings belong to the first generation of stainless steel that corroded easily in its welded condition. Heat weakens the strength of the welded parts of duplex steel, limiting its applications. It was in 1968 when alloying nitrogen with stainless steel was discovered, which marked a breakthrough in the development of duplex stainless steel production forever. The following decade saw the invention of improved duplex grades, specifically, second-generation duplex grades such as lean duplex (2204), standard duplex (2205), Alloy 255, super duplex (2507) and hyper duplex. These duplex steel grades are highly resistant to corrosion caused by strong chemicals like chloride as well as heat, and can be easily fabricated. Most importantly, these grades are affordable for both stainless steel producers and end-users.
Workability Of Duplex Stainless Steel Castings Today
Duplex steel castings today offer a wide range of applications most notably in pollution control (e.g. flue gas desulfurisation, desalination), paper production, chemical processing, transportation, mining and construction.
Good Duplex Stainless Steel Castings, experts say, should be able withstand heat treatment and cool rapidly. These qualities prevent the steel from changing into damaging second phases that will cause it from wearing out easily.