50 grades of stainless steel

The BSSA has selected 50 Grades of Stainless Steel as its theme for 2014. Each week throughout the year, we will showcase one grade and illustrate the variety of corrosion resistant, mechanical and physical properties which determine its suitability for a wide range of applications.



Austenitic H grades 304H 316H 321H 1.4948 1.4919 1.4941 S30409 S31609 S32109

The H grade versions of familiar grades like 304, 316 and 321 have a minimum carbon content to produce increased high temperature strength, particularly creep strength.  They must also meet a minimum grain size.

Approximate Compositions: As 304, 316 and 321 but with 0.04-0.08% C (Exact composition ranges vary between EN and ASTM standards).

Compared to 304, 316 and 321 these grades combine the following characteristics:

  • Similar general corrosion resistance
  • Reduced intergranular corrosion resistance
  • Improved high temperature 0.2% proof strength
  • Improved creep strength

Carbon is an important element in stainless steels. It is usually kept low in order to aid weldability, especially in the avoidance of chromium carbide, which gives rise to intergranular corrosion. However, carbon is an important strengthening element. In certain cases, notably at high temperature, strength may take precedence over the risk of intergranular corrosion. The minimum carbon level of 0.04% in the H grades provides this extra strength. Creep strength is enhanced with a large grain size. Therefore, it is usual for standards to specify an ASTM grain size of 7 or coarser for the H grades. H grades are now something of a rarity in general stockholders.

Applications which illustrate these features include:

Heat exchangers, gas boilers, aerospace, exhaust systems, process plant, element tubing, power generation, rocket engine parts, seals, expansion joints.

Find out more about the 50 Grades of Stainless Steel campaign

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