309 is a heat resisting stainless steel, lying somewhere between 304 and 310 in the heat resisting spectrum. It is also used as a welding electrode for welding austenitic stainless steel to carbon steel.
Approximate Composition: 23% Cr 13% Ni (Exact composition ranges vary between EN and ASTM standards).
This grade combines the following characteristics:
- Good oxidation resistance up to 1000°C
- Good resistance to sulphurous atmospheres
- Moderate carburising resistance
- Welding consumable for joining stainless steel to carbon steel
Chromium is an important element in determining the heat resistance of stainless steel. With 23% Cr, 309 is significantly better than 304 with only 18% Cr. The nickel content of 13% means that the steel contains a significant amount of ferrite. The comparatively low nickel content makes it better than 310 (20% Ni) for resistance to reducing sulphur-bearing atmospheres.
Its second, quite different application as 309L, is as a welding consumable for joining grades like 304L to carbon steel. The dilution of the 23% Cr 13% Ni composition by the mild steel still gives a satisfactory metallurgical structure quite close to that of grade 304L. It is also routinely used for welding the low Cr ferritic grade 1.4003 to ensure toughness in the weld.
Annealing covers, waste incinerators, glass blowing equipment, nuclear transport flasks, rotary kilns, calciners, furnace anchor bolts.