Stainless Steel 347 - Alloy Composition

Stainless Steel 347 has slightly improved corrosion resistance over type 321 stainless steel in strongly oxidizing environments. Alloy 347 is a columbium(niobium)/tantalum stabilized austenitic chromium-nickel stainless steel which was developed to provide an 18-8 type alloy with improved intergranular-corrosion resistance. Alloy 347 has a slightly improved corrosion resistance over other alloys of stainless steel in strongly oxidizing environments as a result of the addition of columbium (niobium) and tantalum. Columbium-tantalum carbides precipitate within the grains instead of forming at the grain boundaries. Type 347 should be considered for applications requiring intermittent heating between 800ºF (427ºC) and 1650ºF (899ºC), or for welding under conditions which prevent a post-weld anneal.

Nominal Composition in Percentage:

Ni                     11.00

Cr                    18.00

Fe                    Balance

Si                     1.00

Mn                    2.00

C                      0.080

P                      0.045

S                      0.030

Cb+Ta              10 x C


UNS Number:


Other Standard Specifications:

AMS 5512

300 Series—austenitic chromium-nickel alloys

  • Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
  • Type 302—same corrosion resistance as 304, with slightly higher strength due to added carbon.
  • Type 303—free machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with ISO 3506.
  • Type 304—the most common grade; the classic 18/8 (18% chromium, 8% nickel) stainless steel. Outside of the US it is commonly known as "A2 stainless steel", in accordance with ISO 3506 (not to be confused with A2 tool steel).
  • Type 316—the second most common grade (after 304); for food and surgical stainless steel uses; alloy addition of molybdenum prevents specific forms of corrosion. It is also known as marine grade stainless steel due to its increased resistance to chloride corrosion compared to type 304. 316 is often used for building nuclear reprocessing plants.


  0.29 lbs/in

Exceptional Properties:

Toughness, durability, corrosion resistance, weldability, high temperature, high creep and stress rupture properties.