Duplex stainless steel is becoming more and more common. They can be produced in all major steel mills. The reasons for its general application are as follows: higher strength leads to weight saving, stronger corrosion resistance, especially stress corrosion cracking, high price stability and relatively cheap price.
However, even with these advantages, the market share of global duplex stainless steel is still limited. The purpose of this paper is to provide a simple guidance for this kind of stainless steel. The advantages and disadvantages will be described.
Principle of duplex stainless steel
The idea of duplex stainless steel can be traced back to 1920s, and was first made in 1930 in Avesta, Sweden (Avesta). However, in the past 30 years, duplex stainless steel has only been reused. This is mainly due to the progress of steelmaking technology, especially in controlling nitrogen content.
Standard austenitic stainless steels such as 304 (1.4301) and 430 ferritic stainless steel are relatively easy to make. From their names, they are mainly composed of one phase, namely austenite or ferrite. Although these types are applicable to a wide range of applications, there are some important technical shortcomings in the two types:
Austenite low strength (200MPa, 0.2%PS) under the condition of solid solution annealing, low stress corrosion cracking, ferrite low strength (slightly higher than austenite, 250MPa, 0.2%PS), poor thick section weldability and poor toughness at low temperature. In addition, the high nickel content of austenitic stainless steel leads to price fluctuation, which is unfavorable for many end users.
The basic idea of duplex stainless steel is to produce the chemical composition of the mixture that causes the ferrite and austenite to be approximately equal. This balance phase provides the following:
Higher strength – the current dual phase brand 0.2%PS has a range of 400-550MPa. This may cause the section thickness to be reduced, thereby reducing the weight. This advantage is particularly important for applications such as pressure vessels and tanks, as well as structural applications such as bridges; thick section weldability is not as simple as austenite, but better than ferrite; good toughness is better than ferrite, especially at low temperatures, as low as minus 50 degrees Celsius, extending to zero below zero. 80 degrees Celsius; stress corrosion cracking – standard austenitic steel is particularly prone to corrosion. The important applications include: hot-water tank, brewing tank, processing plant, swimming pool structure.
Source: China Duplex Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)