309 grade is an austenitic stainless steel developed for use in high temperature corrosion resistance applications. The alloy resists oxidation up to 1900°F (1038°C) under non-cyclic conditions. Frequent thermal cycling reduces oxidation resistance to approximately 1850°F (1010°C).

Because of its high chromium and low nickel content,  309 grade can be utilized in sulfur containing atmospheres up to 1832°F (1000°C). The alloy is not recommended for use in highly carburizing atmospheres since it exhibits only moderate resistance to carbon absorption. Alloy 309 can be utilized in slightly oxidizing, nitriding, cementing and thermal cycling applications, albeit, the maximum service temperature must be reduced.

When heated between 1202 – 1742°F (650 – 950°C) the alloy is subject to sigma phase precipitation. A solution annealing treatment at 2012 – 2102°F (1100 – 1150°C) will restore a degree of toughness.

309S is the low carbon version of the alloy. It is utilized for ease of fabrication. 309H is a high carbon modification developed for enhanced creep resistance. It most instances the grain size and carbon content of the plate can meet both the 309S and 309H requirements.

309 can be easily welded and processed by standard shop fabrication practices.

Available forms:  Coils, Sheets, Strips, Welded Tubes, Profiles

Chemical Analysis

Chemical Compositions*

Element % Present (in product form)
C, H, P, L TW2)
Carbon (C) 0.20 0.20
Silicon (Si) 1.50 – 2.00 1.50 – 2.50
Manganese (Mn) 2.00 2.00
Phosphorous (P) 0.045 0.045
Sulfur (S) 0.015 0.030
Chromium (Cr) 19.00 – 21.00 19.00 – 21.00
Nickel (Ni) 11.00 – 13.00 11.00 – 13.00
Nitrogen (N) 0.11
Iron (Fe) Balance Balance

Mechanical properties (at room temperature in annealed condition)

Product Form
C, H, P L TW*
Thickness a or diamter d (mm) a ≤ 12 d ≤ 25 a=25
Hardness HB max. 1) 2) 3) 216
Proof Strength3) Rp0.2 N/mm2 190 230
Rp1.0 N/mm2 230 270
Tensile Strength Rm N/mm2 500 – 720 min. 550
Elongation min. in % Long Products 401)
Flat Products 0.5 ≤ a/d ˂ 3 404)5) 304)5)6)
3 ≤ a/d 404)5) 304)5)6)

Usage Areas

  • Boiler baffles
  • Furnace components
  • Oven linings
  • Fire box sheets
  • Other high temperature containers