Comprehensive Guide to 347 Stainless Steel Sheets: Performance, Uses, and Selection

347 stainless steel sheets are a niobium-stabilized austenitic chromium-nickel alloy used where improved resistance to intergranular corrosion and high-temperature strength are required. Commonly identified under UNS S34700 and covered by specifications such as ASTM A240, these sheets balance corrosion resistance with formability and weldability for industrial and architectural applications.

347 Stainless Steel Sheets: Key Properties

Chemical composition and stabilization

347 stainless steel contains chromium (typically about 17–19%) and nickel (about 9–13%), with additions of niobium (also called columbium) to stabilize the alloy against chromium carbide precipitation. Carbon is controlled to low levels to limit sensitization. The niobium binds carbon to form niobium carbides, which reduces the risk of intergranular corrosion when the material is exposed to elevated temperatures during welding or service.

Mechanical and thermal properties

347 sheets exhibit mechanical properties typical of austenitic stainless steels: good ductility, moderate strength in the annealed condition, and retention of toughness at low temperatures. The niobium stabilization improves creep and tensile properties during prolonged exposure to moderately high temperatures (several hundred degrees Celsius), making the material suitable for certain heat-resistant applications.

Corrosion resistance

347 offers strong general corrosion resistance in a wide range of environments due to its chromium content and passive oxide film. The stabilization treatment specifically reduces susceptibility to intergranular corrosion in welded sections. For environments with strong chlorides or extreme oxidizing conditions, comparison with other stainless grades and consideration of corrosion testing per standards (for example NACE guidance on sour environments) is recommended.

Standards, Designations, and Specification Notes

Common designations

347 stainless steel sheets are commonly referred to by the UNS number S34700 and are specified in many national and international standards. The chemical and mechanical requirements for plate, sheet, and strip products are often written to ASTM specifications such as ASTM A240. Consult the applicable specification for thickness, finish, and testing requirements.

Testing and certification

Suppliers and fabricators typically provide material test reports demonstrating compliance with specified standards. Relevant tests include chemical analysis, tensile testing, and surface condition checks. For critical applications, additional nondestructive examination or corrosion testing per regulatory guidance may be requested.

For more detailed standard information, see the ASTM specification for stainless steel plate, sheet, and strip: ASTM A240.

Applications and Fabrication Considerations

Typical applications

Common uses for 347 stainless steel sheets include components subject to moderate heat and corrosive atmospheres: industrial heat exchangers, chemical processing equipment, exhaust and furnace parts, food processing equipment, and architectural panels where weld stability and appearance are important.

Forming, welding, and surface finishes

Sheets in this grade are readily formed using conventional cold and hot working methods. Welding is straightforward; however, niobium stabilization reduces the risk of carbide precipitation in the heat-affected zone. Standard post-weld cleaning and passivation improve corrosion performance and appearance. Surface finishes range from mill bright to polished finishes depending on application and aesthetic requirements.

Comparison with related grades

Grade 347 is often compared with 321 stainless steel. Both are stabilized austenitic grades; 321 uses titanium while 347 uses niobium. The choice between them depends on specific service temperature ranges, fabrication history, and supplier availability. In environments requiring higher chromium or molybdenum content for chloride resistance, duplex or 316-family alloys may be considered instead.

Selection Guidelines and Long-Term Performance

Choosing the right thickness and finish

Select sheet thickness and surface finish based on mechanical loading, corrosion exposure, and aesthetic needs. Thicker sections improve stiffness and longevity in structural uses, while smoother finishes can limit bacterial harboring and ease cleaning in hygienic applications.

Maintenance and inspection

Routine inspection for pitting, crevice corrosion, and stress corrosion cracking is advised in aggressive environments. Proper cleaning, passivation, and avoidance of contaminating iron particles during installation extend service life. For regulated industries, follow guidance from agencies or standards bodies relevant to that sector.

Frequently Asked Questions

What are common uses for 347 stainless steel sheets?

Common uses include heat exchangers, exhaust components, furnace parts, chemical processing equipment, and architectural panels where welded stability and resistance to intergranular corrosion are important.

How does niobium stabilization affect corrosion resistance?

Niobium ties up carbon as niobium carbide, preventing chromium carbide formation along grain boundaries during welding or heat exposure. This reduces sensitization and the associated intergranular corrosion risks.

Are 347 stainless steel sheets suitable for high-chloride environments?

While 347 has good general corrosion resistance, environments with high chloride levels may require alloys with additional molybdenum or duplex microstructures. Corrosion testing and consultation of standards such as those from ASTM or NACE are advisable for such conditions.

What specifications and designations cover 347 stainless steel sheets?

Specifications typically reference UNS S34700 and applicable ASTM sheets and plates standards such as ASTM A240. Material certificates from suppliers should indicate compliance with requested standards and test results.

How should 347 stainless steel sheets be maintained to maximize service life?

Maintain through regular cleaning, appropriate passivation treatments, removal of iron contamination after fabrication, and periodic inspection for localized corrosion. For regulated industries, follow the sector-specific maintenance protocols and inspection schedules.