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High Temperature Austenitic And Ferritic Stainless Steel By yaang.com

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Yaang high temperature stainless steels have been specifically designed for temperatures up to 1150 °C. This has been achieved by the addition of a number of important alloying elements in the steel – ensuring superior performance across a wide spectrum of high-temperature applications. 

High temperature austenitic stainless steels grades

High temperature austenitic stainless steels are commonly employed in a number of applications where the temperature exceeds 550°C.

Typical applications for high temperture austenitic stainless steels grades:

  • equipment and components within the iron, steel and other metallurgical industries
  • engineering industry
  • energy conversion plants
  • cement industry

An important consideration at high temperatures is that creep strength is usually the primary dimensioning factor. This means that by choosing the right material, you not only extend the lifetime of your application, but can also specify a thinner material for overall savings in cost.

High temperature ferritic stainless steels grades

The main alloying element in the ferritic grades is chromium. Its positive effect on the scaling resistance is enhanced by silicon and aluminium.

Ferritic steel grades 4713 and 4724 are best suited for temperatures between 550°C and 850°C. The higher alloyed 4736, 4742, 4762 grades can be applied at temperatures up to 1150°C showing excellent resistance against reducing sulphur attacks and molten metals.
 
Due to their ferritic structure, the ferritic steels show lower strength at temperatures exceeding 600°C, but are more resistant to thermal shocks than high temperature austenitic stainless steels. With the thermal conductivity higher and the thermal expansion lower than the respective values for austenitic steels, equal thermal shocks will result in lower thermal stresses in the ferritic material. In these terms, ferrites allow greater tolerances for design and operation. 

High temperature ferritic grades are mainly used in high temperature applications with sulphurous atmospheres and/or at low tensile loads.

Typical applications for ferritic high temperature grades:

  • installations within chemical, power and metalworking industries
  • furnace technology

Grade properties

High temperature austenitic steels are mainly optimised for oxidation and high temperature corrosion resistance. However, they also have good mechanical properties, in part due to their austenitic structure and in part to certain alloying elements we employ. 

High temperature ferritic stainless steels have broadly the same mechanical properties as their austenitic counterparts at room temperature. However, when subjected to high temperatures (> 600°C), it is possible for the creep strength to drop to just a quarter of the value an austenitic heat resistant steel would show in the same environment.

Weldability

Welding of austenitic high temperature grades

High temperature constructions are frequently exposed to thermal fatigue due to variations in temperature. For this reason it is very important to design the welded joint without notches. Furthermore it is important that welds have oxidation resistance and creep strength compatible with the parent material. Autogenous welding of thin material is possible if full penetration can be achieved. Fillet welds without full penetration should be avoided due to risk of thermal fatigue. Optimal design would call for welds to be located in low stress areas of the equipment being fabricated.

Corrosion resistance

The resistance of a material to high-temperature corrosion is in many cases dependent on its ability to form a protective oxide layer. In a reducing atmosphere, when such a layer cannot be created (or maintained), the corrosion resistance of the material will be determined by the alloy content of the material.

For a comparison of chemical and mechanical properties of common austenitic and ferritic grades of stainless steel according to ASTM A240, see our website: www.yaang.com.

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Stainless Steel

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