Austenitic SS 347

Austenitic SS 347

A columbium/tantalum stabilized version of stainless steel is 347 stainless steel equivalent to type 304 and it is austenitic chromium-nickel steel with the addition of Columbium and Tantalum. As compared 321 vs 347 Stainless steel is slightly improved corrosion resistant  to type 321 stainless steel in strongly oxidizing environments.

Alloy 347 stainless steel is a type with columbium(niobium)/tantalum stabilized austenitic chromium-nickel type which was developed to provide improved intergranular-corrosion resistance to type 18-8 alloy. SS 347 stainless steel is a slightly improved version of stainless steel with better corrosion resistance than any other alloys of stainless steel especially in strongly oxidizing environments as it contains columbium (niobium) and tantalum. 

347 stainless steel composition

The columbium content in AISI 347 Stainless steel type makes it immune to chromium carbide precipitation. This type of grade is recommended in applications where welding cannot be further annealed or in applications where the usual service temperature is 800° – 1600° F.

Here’s a detailed table showing SS 347 chemical composition in detail.
Cr Ni C Mn P Si Fe S Nb (Cb)
SS 347H MIN % 17 9 0.04 9 0.32
MAX % 20 13 0.1 13 0.04 1 BALANCE 0.03 1
SS 347 MIN % 17 9 9 0.32
MAX % 20 13 0.08 13 0.04 1 BALANCE 0.03 1

Grade 347 stainless steel or UNS S34700 stainless steel grade is slightly better in corrosion resistance when compared to type 321 in strongly oxidizing environments. SS 347 has columbium to stabilize it which is preferred in aqueous and low-temperature environments as it has good resistance capabilities to intergranular attacks. 

347 SS composition is also stabilized with niobium with corrosion resistance abilities similar to 304/304L. SS 347 is commonly used in the 800° – 1500° F temperatures where it is stabilized against chromium carbide precipitation by adding niobium, which results in the precipitation of niobium carbides. 

SS 347 Steel is excellent in intergranular corrosion resistance after it is exposed to this temperature range, and it resists oxidation up to 1500°F and comes with higher creep and stress rupture properties than the type SS 304 or SS 304L. Type SS 347 also has good low-temperature toughness and in annealed conditions, it is non-magnetic. 

Stainless steel 347 is recommended in the working temperature range of 2100° – 2250° F (1149° – 1232° C) and ideal in applications like forging, upsetting and other hot work processes. This alloy is not recommended under temperatures below 1700° F (927° C). To re-attain the maximum corrosion resistance, the material needs to be water quenched or completely annealed after working. 

347 Grade stainless steel properties

SS 347 or UNS S34700 can be considered for applications where intermittent heating is between 800ºF (427ºC) and 1650ºF (899ºC), or for welding applications where post-weld annealing is prevented. 347 stainless steel properties are superior when compared to SS 304. Talking about SS 347 mechanical properties, SS 347 needs higher initial forces. Stainless steel 347 is a bit tougher and ductile can be easily stamped, blanked, spun, and drawn.

Grade Density
Melting Point Elastic Modulus
Mean Co-eff of Thermal
Thermal Conductivity (W/m.K) Specific Heat(0-100°C)
SS 347/347H 7.96 1454°C 190-210 0-100°C at 100°C ( J/g.K)
17.3 16.3 0.5
General Specification
SS 347 S34700 BS EN NO NAME 2338 SUS 347
347S31 58G 1.455 X6CrNiNb 8-10

Grade 347 Stainless steel alloy is good in nitric solutions which are the most diluted organic acids at moderate temperatures, at lower temperatures Grade 347 is recommended in pure phosphoric acid and up to 10% diluted solutions at higher temperatures. Alloy 347 stainless steel can resist polythionic acid stress corrosion cracking when used in hydrocarbon service.

Type 347 Stainless steel is commonly used for equipment fabrications, which is good in services under extreme corrosive conditions and it is frequently used in petroleum refining industries. 

Most common applications suggested by many 347 stainless steel sheet suppliers are:
  • High-temperature chemical processes
  • Heat exchanger tube
  • High-temperature steam service
  • High-pressure steam pipes
  • Radiant superheaters
  • Boiler tubes
  • Heavy-duty exhaust systems
  • General refinery piping