SUS321 vs. SUS347 stainless steel: Differences
SUS321 vs. SUS347 stainless steel: Differences
What is SUS347 stainless steel?
SUS347 is an austenitic stainless steel material, belonging to the 18Cr-9Ni-Nb type stainless steel, conforming to the standard JIS G4311-2019. In the solution-treated state, it exhibits excellent corrosion resistance and mechanical properties. 347 stainless steel has superior high-temperature stress rupture and creep resistance properties compared to 304 stainless steel. It is widely used in aerospace, power generation, chemical, petrochemical, food, and paper manufacturing industries.
What are the equivalent materials for SUS321 stainless steel?
SUS321 stainless steel has several equivalents across standards, with the most direct being AISI 321 (USA), UNS S32100 (USA), and EN/DIN 1.4541 / X6CrNiTi18-10 (Europe), plus BS 321S31 (UK) and Chinese standards like 0Cr18Ni10Ti, all being titanium-stabilized grades offering similar corrosion resistance, especially after welding.
SUS321 vs. SUS347 stainless steel: Differences
321 and 347 stainless steels both exhibit superior high-temperature creep and stress rupture properties compared to 304/304L. Their maximum continuous service temperature can reach approximately 900°C to 925°C. Due to the inherent stability of niobium carbide, 347 stainless steel generally performs slightly better in maintaining mechanical strength and creep resistance at high temperatures. This is particularly relevant in certain extreme high-temperature and high-pressure applications (such as nuclear power or supercritical boilers).
Chemical Composition of 347 and 321 Stainless Steel
| Element | Grade 347 Stainless Steel | Grade 321 Stainless Steel |
|---|---|---|
| C | 0.08 | 0.08 |
| Mn | 2.00 | 2.00 |
| Si | 0.75 | 0.75 |
| P | 0.045 | 0.045 |
| S | 0.030 | 0.030 |
| Cr | 17.0-19.0 | 17.00 – 19.00 |
| Ni | 9.0-13.0 | 9.00 – 12.00 |
| Mo | – | – |
| N | – | 0.1 |
Mechanical Properties of 321 vs 347 Stainless Steel:
| Mechanical Property | 321 Stainless Steel | 347 Stainless Steel |
|---|---|---|
| Tensile Strength (MPa) | 515 – 730 | 515 – 655 |
| Yield Strength (0.2% offset) (MPa) | ≥205 | ≥205 |
| Elongation (%) | ≥40 | ≥40 |
| Hardness (Brinell HB) | ≤217 (Annealed) | ≤217 (Annealed) |
Physical Properties of 321 vs 347 Stainless Steel:
| Physical Property | 321 Stainless Steel | 347 Stainless Steel |
|---|---|---|
| Density (g/cm³) | 7.93 | 7.96 |
| Melting Point (°C) | Approx. 1400 | Approx. 1400 |
| Coefficient of Thermal Expansion | 16.5 x 10^-6 /°C | 16.5 x 10^-6 /°C |
| Thermal Conductivity (W/m·K) | 16.3 (100°C) / 21.5 (500°C) | 16.3 (100°C) / 21.5 (500°C) |
| Young's Modulus (GPa) | 193 | 193 |
| Electrical Resistivity (μΩ·cm) | 72 (20°C) / 86 (500°C) | 72 (20°C) / 86 (500°C) |
SUS321 vs. SUS347 stainless steel: High temperature resistance
SUS321 and SUS347 are both titanium (Ti) or niobium (Nb) stabilized austenitic stainless steels, designed for high-temperature applications. SUS347, due to the addition of niobium (Nb), can withstand higher temperatures and stresses, with a continuous service temperature exceeding 980°C, and exhibits greater creep resistance than 321 at high temperatures. It is commonly used in demanding environments such as aerospace, boilers, and high-temperature heat exchangers.
| Property | SUS321 (AISI 321 / EN 1.4541) | SUS347 (AISI 347 / EN 1.4550) |
|---|---|---|
| Stabilizing Element | Titanium (Ti ≥ 5 × C%) | Niobium + Tantalum (Nb + Ta ≥ 10× C%) |
| Maximum Continuous Service Temperature | Up to 870–900°C | Up to 900–925°C |
| Resistance to Sensitization (450–850°C) | Very good (Ti prevents Cr carbide formation) | Excellent (Nb stabilizes weld metal effectively) |
| Oxidation Resistance | Excellent up to ~900°C | Excellent up to ~900–925°C |
What is the difference between SS 347 and 316?
347 is a niobium-stabilized austenitic steel, which prevents welding sensitization through the formation of NbC and exhibits excellent resistance to intergranular corrosion. However, in chloride-containing environments, its PREN is approximately 23–25, and its resistance to pitting and crevice corrosion is lower than that of 316 (PREN approximately 25–27), which contains 2–3% Mo. Therefore, 347 is more suitable for high-temperature conditions without strong chlorides, while 316 offers significantly better resistance to localized corrosion in chloride/acidic media such as seawater and acids/alkalis.
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