What Is The Difference Between Stainless Steel And Duplex Stainless Steel
stainless steel is a name given to any steel that is stainless. To qualify as stainless, the material must have a minimum of 10% chromium in the content. There are ferritic and austenitic stainless steel grades. These come in the 400 series and 300 series respectively. The ferritic steels are magnetic and the austenitic steels are non-magnetic. They have different metallurgic microstructures. The duplex steels have both ferritic and austenitic phases in the metallurgic microstructure and have the best of both ferritic and austenitic steel grades together. The duplex steels are both strong and corrosion resistance. The modern duplex grades are used in place of more traditional and expensive metal material. There are three major categories of duplex steel such as standard duplex, super duplex and lean duplex grades.
The stainless steels can handle corrosion to certain extent but not very good at handling highly corrosive agents. Grades such as the 316 austenitic stainless steels can handle high concentrations of chlorides but cannot handle acids. The duplex grades have better corrosion resistance to chlorides, acids, reducing agents and oxidizing agents. The corrosion resistance of the different duplex grades is better than most austenitic stainless steels. In extremely corrosive applications such as acid production plants, much versatile materials such as the hastelloys are used.
The pickling and passivation processes improve the corrosion resistance or materials. The pickling method involves the surface treatment of any metal to remove impurities. The removal of inorganic contaminants and stains is important for pipes and tubes before being used in sensitive applications such as food grade applications and chemical applications. The passivation is a process through which the material surface is made inactive. The iron and oxides from the surface are removed by an acid bath. The passivation method is much useful for products that are to be used in acidic applications and applications with other oxidizing agents. Usually, the metals are pickled, machined and then passivated to get the best result and to fully cleanup the surface.
The stainless steels are definitely cheaper than the duplex grades. The stainless steels are readily available in the market and are used for many applications. They could be machined, cut, formed and welded with ease. The duplex steel grades are not readily available in the market. They have to be specified and ordered because they are not as common as the stainless steels. Also the prices of the duplex steels are higher due to the higher alloying content in the composition. The duplex steel grades have specific welding procedures such as preheating to a definite temperature before welding and post weld heat treating after welding. However, for applications that require strength, corrosion resistance and high temperature resistance, regardless of the higher prices, the duplex steels are much suitable.
|EUROPE EN||BRITISH BS||AISI||DIN||SS||TYPICAL COMPOSITION (%)|
|1.4362||X2CrNiN23-4||2327||0.03 ×||22||4||0.4||0.4 Cu|
|1.4501||318S13||0.03 ×||24||6||3||0.5 W|
|1.4507||0.03 ×||24||6||3||1.0 Cu|
|AUSTENITIC STAINLESS STEEL||FERRITIC STAINLESS STEEL||MARTENSITIC STAINLESS STEEL||DUPLEX STEEL|
|Room Temp. Strength||M/H||M||VH||H|
|Strength at Temperature||H||L/M||-||H|
|GRADES||TEMPERATURE||YOUNG'S MODULUS||THERMAL EXPANSION COEFFICIENT||SPECIFIC HEAT CAPACITY||THERMAL CONDUCTIVITY|
|C||F||GPA||10−6K1||J KG−1 K−1||WM−1 K−1|
Duplex stainless Steel:
Austenitic Stainless Steel:
Precipitation Hardened Stainless Steel:
Martensitic Stainless Steel:
Ferritic Stainless Steel: