Standard austenitic steels like 304 (1.4301) and ferritic steel 430 are also relatively easy to manufacture and manufacture. As the name implies, they consist of a single stage, austenite or ferrite. While these types are thinner than a wide range of applications, there are two types of weaknesses in some important techniques:
Austenite - low strength (0.2 MPa at 200 MPa in solution annealed condition), low resistance stress corrosion cracking
Ferrite - low strength (slightly higher than austenitic, 250 MPa 0.2% PS), poor in the thick part of the weldability, poor low temperature toughness
In addition, the high nickel content of the austenitic type causes price volatility which is undesirable for many end users.
The basic idea of duplexes is to produce a chemical composition that results in a roughly equal mixture of ferrite and austenite. This phase of the balance provides the following:
Higher strength - the current duplex for 0.2% PS is 400-550 MPa. This may result in a reduction in the thickness of the portion, and therefore, a reduction in weight. This advantage is particularly significant for applications such as:
Pressure vessels and storage tanks
Ø Structural applications such as bridges
Weldability of the thick part - not so simple, because the austenitic stainless steel, but ferritic stainless steel is much better.
Good toughness - better than low temperature ferritic stainless steels, and better usually down to minus 50 degrees Celsius, stretching to minus 80 degrees Celsius.
Resistance to stress corrosion cracking - Standard austenitic steels are particularly susceptible to this type of corrosion. What kind of application, this advantage is very important include:
O hot water tank
Ø brew cans
O process plant
Ø Swimming pool structure
How the Austenite/Ferrite Balance is Achieved
To
understand how duplex steels work, first compare the composition of two
familiar steels austenitic 304 (1.4301) and ferritic 430 (1.4016).
| Structure | Grade | EN Number | C | Si | Mn | P | S | N | Cr | Ni | Mo |
| Ferritic | 430 | 1.4016 | 0.08 | 1.00 | 1.00 | 0.040 | 0.015 | - | 16.0/18.0 | - | - |
| Austenitic | 304 | 1.4301 | 0.07 | 1.00 | 2.00 | 0.045 | 0.015 | 0.11 | 17.5/19.5 | 8.0/10.5 | - |