Duplex stainless steels have become more common. They are on offer by virtually all of the duplex stainless steel pipe for many reasons:
Higher strength resulting in weight saving
Greater corrosion resistance particularly stress corrosion cracking
Better price stability
You will discover a conference with reference to duplex every 2-three years where many highly technical papers are presented. There is lots of marketing activity surrounding these grades. New grades are now being announced frequently.
Yet, in spite of all this interest, the ideal estimates for global market share for duplex are between 1 and 3%. The objective of this information is to supply a straightforward help guide to this steel type. The advantages and disadvantages will likely be described.
The concept of duplex stainless steels extends back for the 1920s with all the first cast being made at Avesta in Sweden in 1930. However, it is actually only in the last three decades that duplex steels have started to “take off” in the significant way. This is mainly because of advances in steelmaking techniques particularly with respect to control over nitrogen content.
Grade 430 features a predominance of ferritisers so is ferritic in structure. Grade 304 becomes austenitic mainly by using about 8% nickel. To arrive at a duplex structure with about 50% for each phase, there needs to be an equilibrium in between the austenitisers along with the ferritisers. This explains why the nickel content of duplex steels is usually below for austenitics.
In several of the recently developed grades, nitrogen and manganese are being used together to create the nickel content to suprisingly low levels. This has an effective effect on price stability.
At the moment, we have been still quite definitely within the development phase of duplex steels. Therefore, each mill is promoting its own particular brand. It can be generally agreed that there are lots of grades. However, this is probably going to continue until the “winners” emerge.
The range of duplex steels enables them to be matched for corrosion resistance with all the special steel section. There is absolutely no single way of measuring corrosion resistance. However, it can be simple to use the Pitting Resistance Equivalent Number (PREN) as a method of ranking the grades.
Stainless-steel structures in pools are known to be prone to SCC. The use of standard austenitic stainless steels like 304 and 316 is forbidden with this application. The best steels to use for this purpose would be the high nickel austenitic steels including the 6% Mo grades. However, in some cases, duplex steels such as 2205 (1.4462) and also the superduplex grades can be regarded.
The attractive blend of high strength, wide variety of corrosion resistance, moderate weldability would seem to offer great prospect of enhancing the market share of duplex stainless steels. However, it is important to be aware of the limitations of duplex stainless steels and why they are always apt to be “niche players”.
The main advantage of high strength immediately is a disadvantage when thinking about formability and machinability. The top strength also comes along with lower ductility than austenitic grades. Therefore, any application requiring an increased level of formability, for example, a sink, is ruled out for duplex grades. Even when the dexopky10 is adequate, higher forces have to make up the material, for example in tube bending. There is one exception towards the normal rule of poorer machinability, grade 1.4162.
The metallurgy of duplex stainless steels is much more complex than for duplex stainless steel tube. For this reason 3 day conferences might be devoted simply to duplex! This factor means they are harder to produce at the mill and to fabricate.