Weathering steel (WS), which is also called low-alloy steel, is steel with a carbon content of less than 0.2 wt.% to which alloying elements, mostly Cu, Cr, Ni, P, Si, and Mn, add up to no more than 3–5 wt.% [1]. The chemicals in these steel alloys are put together in a way that makes it easy for a rust/iron oxide layer to form quickly and protect the steel underneath from the weather.

The rate of corrosion in WS is so low that bridges made from it can easily last for 120 years with very little maintenance. In reality, weathering steel construction has a lot of other benefits, such as lower overall lifecycle costs and better safety because you don’t need a paint system to protect it and you don’t have to check it as often. Since there is no need for paint, no volatile organic compounds are put into the air, and the building process goes faster. From a material cost and maintenance point of view, the costs of weathering steel bridges are, on average, 5% less than the costs of painted steel bridges. The alloy was first sold in 1933 to keep ore waggons from needing to be painted or repaired in other ways. Over time, it gets a rusty look, called a patina, which is now very popular among architects and can be seen on many famous buildings and monuments, such as the John Deere World Headquarters in Illinois and the Angel of the North monument in the UK. The patina on WS makes it more resistant to corrosion than mild steel and also gives it an attractive look and the ability to heal itself.


WS has better corrosion resistance than other alloys because it has more copper and nickel than other alloys. Other alloying elements, such as Cr, Mn, and P, also help. Copper is important because it helps the protective oxide layer stick to the metal and slows down corrosion.

The steel is left to rust. Because it is made of an alloy, it rusts more slowly than regular steel, and the rust forms a protective coating that slows the rate of corrosion in the future. Research has shown that wet/dry cycling needs to happen over and over again for the best dense and stuck-on rust layer to form. Rainwater should wash the steel surface well, moisture should drain easily, and the surface should dry quickly. Structures need to be free of cracks where water can collect because corrosion would happen there if a protective patina didn’t form. This was shown by a recent study of S355J2W steel motorway bridges in the Czech Republic.

The oxidation process can go on for years before the surface “stabilises” in a steady state with a coating that sticks tightly together. This depends a lot on the weather conditions at the time. Phosphorus and sulphur also play an important role in the formation of the patina layer. Low-soluble sulphates or phosphates form between the base steel and the existing corrosion if the surface is exposed to alternating wet and dry periods. ISO 9223 says that “SO2 pollution in the air makes it possible for a thicker layer of rust to form.” Leygraf and Graedel agree with this statement, but they also think that large amounts of non-metal oxides make the water layer very acidic, which stops the patina from forming. Phosphorus species have also been shown to form a passive protective film over the surface of the steel. This film keeps aggressive ions and water from getting in, which helps a dense patina layer form. Phosphorus, on the other hand, can hurt the grain structure of the alloy and, as a result, the mechanical strength of the steel. To fix this, low levels of boron or carbon are added to bring back the required grain boundaries.


Cor-Ten is one of the best-known types of steel that doesn’t rust. Cor-brand Ten’s name comes from the two things that make it different from carbon steel (CS): its resistance to corrosion (Cor), which comes from the copper in it, and its tensile strength (Ten), which comes from its better mechanical properties. In fact, it is said that Cor-Ten has 30% better mechanical properties and 4–8 times better weather resistance than regular CS.

There are two kinds of Cor-Ten: Cor-Ten A and Cor-Ten B. ASTM standard designation A 242 is for Cor-Ten A (up to 12.7mm thick), and the newer ASTM grades are A 588 for Cor-Ten B. (over 12.7mm thickness). Depending on how thick the steel is, you can weld Cor-Ten with gas shield, spot, or submerged arc welding. When welding, it’s important to use a method that lets the rusting happen the same way as the rest of the structure. In general, Cor-Ten A and B are the same, but Cor-Ten A alloys have more phosphorus to make them more resistant to corrosion.

GradeC [%]Si [%]Mn [%]P [%]S [%]AI [%]Cu [%]Cr [%]Ni [%]
Corten A0.120.25/0.750.20/0.500.07/0.150.0300.015/0.060.25/0.550.50/1.250.65
Grade    Thickness (mm) Strip ProductsPlate ProductsYield Strength RelN/mm²MinimumTensile Strength RmN/mm²MinimumElongation Aso%Minimum
Corten A2-126-1234548520
GradeC [%]Si [%]Mn [%]P [%]S [%]AI [%]Cu [%]V [%]Cr [%]Ni [%]
Corten B0.190.30/0.650.80/1.250.0350.0300.02/0.060.25/0.400.02/0.10.40/0.650.40
GradeThickness (mm) Strip ProductsPlate ProductsYield Strength Rel N/mm²MinimumTensile StrengthRm N/mm²MinimumElongationA50 %Minimum
Corten B2 – 136 – 4034548519


PATINAX is a weathering steel made to the European standard EN 10025-5 and also as a special mill grade. During the weather resistance process, an oxide rust coating is made that is thought to be “virtually impermeable to oxygen”. PATINAX® is mostly used unpainted or uncoated. Its natural weathered rust colour makes it a good choice for bridges, landscaped structures, power line derricks, containers, mine cars, facades, tanks, and steel sculptures. PATINAX comes in several grades, such as PATINAX® 355 (S355J2W) and PATINAX® 355P (S355J2WP), which has a higher phosphorus content and are more resistant to corrosion. There is also PATINAX® 275PK, which is a thinner cold-rolled sheet with a higher phosphorus alloy (S355J2WP).

GradeMax. plate thickness [mm]Grade acc. to EN 10025-5Alloying elementsRe, min [MPa]Rm [MPa]Amin [%]T27 [°C]
PATINAX 355P12.5S355J2WP+NCr Cu P355470-63020-20
PATINAX 35550S355J2W+NCr Cu355 (t≤ 16mm)470-63020-20

Composition of PATINAX 355P

≤0.120.25 – 0.750.20 – 0.500.07 – 0.15≤ 0.0300.50 – 1.250.25 – 0.55≤ 0.65
Steel GradeMinimum yield point ReH MPa *)Tensile strength Rm MPaMinimum elongation A (Lo =5.65√So) %
PANTINAX 355P355470 -63020
Steel GradeMinimum yield point ReH MPa *)Tensile strength Rm MPaMinimum elongation A %
PATINAX 275PK27541025
Weathering fine grain structural steel Heavy platesSteel gradeMaterial No.Material Specification532July 2014
TKSE-Short nameEN-Short name
PATINAX 355S355J2W+N1.8965


≤ 0.160.30 – 0.500.80 – 1.25≤ 0.030≤ 0.0300.40 – 0.650.25 – 0.400.02 – 0.10≤ 0.40
Material thickness mmMinimum yield point ReHMPa*)Tensile strength RmMPaMinimum elongation A(Lo =5.65√So)%
≤ 16355470 – 63020

European Standard Weathering Steels

Specifications for the European EN 10025 Weathering steels are very similar to Cor-Ten and PATINAX, and they are the same in terms of how well they resist corrosion and how strong they are. Cor-Ten A and PATINAX 355P are both the same as EN 10025 S355 J0WP because they both have the same amount of phosphorus (0.20% for Cor-Ten A and 0.3% for PATINAX 355P).

S355 J0WP and PATINAX at 0.15%) to make them less likely to rust. On the other hand, Corten B and PATINAX 355 are the same as European specification EN 10025 S355 J2W and EN 10025 S355 J2W+N, with the same tolerances for vanadium, copper, manganese, aluminium, and chromium. But in the case of EN 10025 S355 J2W+N and PATINAX 355, different combinations of nitrogen-binding elements can be added to the steel to make it have a finer grain structure. For example, 0.02% aluminium, Nb 0.015-0.060%, V 0.02-0.12%, and Ti 0.02-0.10%.

Thickness Range
Corten Axxxxxxxxx
Corten B        x
S355JOWP      xxx
S355JOW       x 
S355J2W+N       xx
PATINAX 355P        x
Thickness Range
Corten Axxx xxxx 
Corten Bxxx x xxx
S355JOWPxxxxx xx 
S355JOW x x     
S355J2W+Nxxxxx xx 
S355J2WP+N       xx
PATINAX 355Pxxx x x  
Thickness Range
Corten A          
Corten Bxxxxxxxxxx
PATINAX 355Pxxxxxxxxxx
Corten AThickness RangeAvailable Widths
 0.6mm to 12mm1000mm, 1250mm, 1500mm, 1800mm, 2000mm, 2500mm
Corten BThickness RangeAvailable Widths
 3mm to 60mm1000mm, 1250mm, 1500mm, 2000mm, 2500mm, 3000mm
S355JOWPThickness RangeAvailable Widths
 2mm to 15mm1000mm, 1140mm, 1250mm, 1310mm, 1400mm, 1500mm, 1800mm, 2000mm, 2500mm
S355JOWThickness RangeAvailable Widths
 2.5mm to 7mm1400mm, 1500mm, 2000mm
S355J2W+NThickness RangeAvailable Widths
 2.5mm to 60mm1000mm, 1100mm, 1250mm, 1500mm, 2000mm, 2500mm, 3000mm
S355J2WP+NThickness RangeAvailable Widths
 12mm to 30mm1000mm, 1500mm, 2000mm
PATINAX 355PThickness RangeAvailable Widths
 3mm to 60mm1000mm, 1250mm, 1500mm, 2000mm, 2500mm, 3000mm

The information above is based on what is readily available from stock. Where there are enough pieces for mill production, the thicknesses and widths that are available vary.


Weathering steel has been used for building structures for more than 50 years, and it has a good track record for being strong and requiring little upkeep. On the market, there are a number of similar products, such as Cor-Ten, PATINAX, and European counterparts. All of these products are equally good at resisting corrosion and having the mechanical/tensile strength that is needed for a wide range of uses, from buildings to bridges. Lakshya International is a Worldwide Supplier of Corten Steel (Weathering Steel) and its products.

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