In 2025, ASTM 347 stainless steel plate (a niobium-stabilized austenitic alloy) typically costs between USD 1.8–4.5 per kg (≈ USD 1,800–4,500 per metric ton) depending on finish, origin, and order volume—China exports tend to cluster at the lower end (~USD 2–4/kg), whereas European or US finished and stocked plates often exceed USD 3.5–5.0/kg at retail.

What Is 347 Stainless Steel and Why It Matters

We, as materials specialists, recognize that 347 stainless steel is a niobium (columbium) and sometimes tantalum-stabilized austenitic chromium-nickel stainless steel. The stabilizers prevent chromium carbide precipitation at grain boundaries during high-temperature service, thus minimizing intergranular corrosion risk . The alloy also exhibits high-temperature oxidation resistance and excellent mechanical stability.

Composition, Standards, Equivalents

The alloy typically contains 17–19 % Cr, 9–13 % Ni, ≤ 0.08 % C, plus niobium (0.2–1 %). It is standardized under ASTM A240 for plates, and known by designations such as UNS S34700, EN/DIN 1.4550, JIS SUS347, etc.

Core Properties and Benefits

We observe that key properties include:

• Intergranular corrosion resistance, stemming from niobium stabilization.

• High-temperature strength and creep resistance (service up to ~816 °C / 1,500 °F without loss of integrity).

• Good weldability, as niobium minimizes sensitization during welding, and post-weld heat treatment is often unnecessary.

Limitations

We must nevertheless note its limitations:

• Cost is higher than more common grades like 304 or 316 due to niobium content.

• Machining is more demanding—machinability ratings are lower (~36 %).

• Not as chloride-resistant as some molybdenum-bearing grades; caution in marine or chloride-rich environments.

Typical Applications

We see frequent use in sectors where both elevated heat and corrosion resistance are essential, including:

• Aerospace: exhaust components, collector rings

• Chemical processing: heat exchangers, reactors

• Boiler and furnace components, power generation hardware

• Oil, gas, energy industries, where cyclic thermal stress is common

Forms and Fabrication Methods

Common forms include plates, sheets, bars, tubes, coils, mesh, filler rods, reflecting broad industrial versatility. Plates commonly are hot-rolled >3mm thick, with a characteristically whitish finish relative to cold-rolled variants. Fabrication processes:

• Hot working (forging, rolling) requires controlled temperature (above ~980 °C), followed by air or water quench.

• Cold working induces rapid hardening; intermediate annealing may be needed.

• Cutting: plasma, laser, water-jet, sawing—with carbide tools for precision.

• Heat treatments: annealing (~1850–2000°F), stress relief (~1470–1600°F), optionally solution treat (~1950–2100°F).

Mechanical Properties Summary

From aggregated technical data:

• Density: ~7.7–8.0 g/cm³

• Tensile strength: ≥ 515 MPa

• Yield strength (0.2 %): ≥ 205 MPa

• Elongation: ≥ 40 %

• Modulus of elasticity: ~190–210 GPa; Impact toughness: Charpy ~60 J longitudinal.

Global Price Comparison Table (2025 Estimates)

We adapt these ranges to reflect the current 2025 market dynamics, balancing currency effects, finish quality, and supply chain factors.

FAQs

Q1: Why is niobium added to 347 stainless steel?
Niobium stabilizes the microstructure during welding or high-temperature service, reducing chromium carbide formation that could otherwise enable intergranular corrosion.

Q2: How does 347 compare to 321 stainless steel?
Both are stabilized grades, but 321 uses titanium while 347 uses niobium; 347 often provides slightly better oxidation resistance and high-temperature performance.

Q3: Can I use 347 stainless steel in marine environments?
While 347 has good general corrosion resistance, it is more susceptible to chloride-induced pitting than molybdenum-bearing grades; caution is advised in harsh marine conditions.

Q4: What surface finish affects the price most?
Finished surfaces (polished, mill-finish) and stocked service-center availability in regions like Europe or the US push prices higher—often above USD 3.5–5/kg—versus basic mill-finish Chinese exports.

Q5: Does 347 require post-weld heat treatment?
Generally not, because niobium stabilization maintains corrosion resistance after welding; however, project-specific thermal cycles should be reviewed case-by-case.