S321 Stainless Steel

S321 Stainless Steel

1. Equivalent Standard Grades: Corresponds to Chinese grade 1Cr18Ni9Ti, U.S. grades 321, S32100, TP321, and Japanese grade SUS321.

2. Material Properties
   2.1 Chemical Composition:

   • Carbon (C) ≤ 0.08%, Silicon (Si) ≤ 1.00%, Manganese (Mn) ≤ 2.00%, Sulfur (S) ≤ 0.030%, Phosphorus (P) ≤ 0.035%, Chromium (Cr): 17.00–19.00%, Nickel (Ni): 9.00–12.00%, Titanium (Ti) ≥ 5×C%.

   • The addition of Ti enhances resistance to intergranular corrosion but makes it unsuitable for decorative components.
     2.2 Corrosion Resistance:

   • Exhibits good corrosion resistance in organic and inorganic acids of varying concentrations and temperatures, particularly in oxidizing media.

   • Prolonged heating in temperature ranges prone to chromium carbide formation may degrade corrosion resistance in harsh environments.

   • Generally comparable to S347 in most environments but slightly inferior to annealed S347 in strongly oxidizing conditions.

3. Mechanical Properties:

   • Tensile strength (σb) ≥ 520 MPa, Yield strength (σ0.2) ≥ 205 MPa, Elongation (δ5) ≥ 40%, Reduction of area (ψ) ≥ 50%, Hardness ≤ 187 HB, ≤ 90 HRB, ≤ 200 HV.

   • Offers better ductility and stress rupture resistance than 304 stainless steel at elevated temperatures.

4. Weldability:

   • Good weldability. Ti addition suppresses chromium carbide formation during welding, reducing intergranular corrosion risks.

   • Requires controlled welding parameters (current, voltage, speed). Common methods include TIG and manual arc welding.

5. Fabrication:

   • Suitable for cold/hot working. Cold working may require intermediate annealing due to significant work-hardening. Hot working temperature: 1000–1150°C.

6. Applications:

   • Structural engineering (beams, bridges, transmission towers), industrial equipment (furnaces, reactors, pipelines), and high-temperature components (427–816°C), such as aircraft engine parts.

7. Post-Weld Heat Treatment:

   • Solution treatment (920–1150°C rapid cooling) is recommended for high-temperature or high-stress applications. Stabilization treatment (850–930°C) may be specified.

8. Non-Destructive Testing (NDT):

   • Ultrasonic and radiographic testing for internal defects. Fluorescent magnetic particle testing (enhanced sensitivity for magnetic zones) and penetrant testing for surface defects.

S347 Stainless Steel

1. Equivalent Standard Grades: 347, S34700, 0Cr18Ni11Nb.

2. Material Properties
   2.1 Chemical Composition:

   • Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.00%, Nickel (Ni): 9.00–13.00%, Silicon (Si) ≤ 1.00%, Phosphorus (P) ≤ 0.045%, Sulfur (S) ≤ 0.030%, Niobium (Nb) ≥ 10×C%, Chromium (Cr): 17.00–19.00%.

   • Nb addition improves resistance to intergranular corrosion.
     2.2 Corrosion Resistance:

   • Excellent resistance in acids, alkalis, and salts, with oxidation resistance up to 800°C.

   • Similar to S321 in most environments but slightly superior in aqueous and low-temperature conditions.

   • Designed for high-temperature applications requiring strong anti-sensitization to prevent intergranular corrosion.

3. Mechanical Properties:

   • Solution-treated: Yield strength ≥ 206 MPa, Tensile strength ≥ 520 MPa, Elongation ≥ 40%, Hardness ≤ 187 HB.

   • Superior high-temperature stress rupture and creep resistance compared to 304 stainless steel.

4. Weldability:

   • Good weldability (TIG, submerged arc welding). Nb minimizes intergranular corrosion, but excessive heat input must be avoided.

5. Fabrication:

   • Similar to S321. Cold working requires attention to work-hardening; hot working temperature: 1050–1200°C.

6. Applications:

   • Aerospace, power generation, chemical/petrochemical industries. Common in high-temperature equipment (boilers, heat exchangers).

7. Post-Weld Heat Treatment:

   • Solution treatment is standard. Stabilization may be added for specific requirements.

8. NDT:

   • Similar to S321. Fluorescent magnetic particle and penetrant testing for surface defects.

Key Differences & Selection Guidelines

• Sensitization Resistance: S347 (with Nb) outperforms S321 (with Ti) in post-weld and high-temperature anti-corrosion.

• Fabrication: S321’s Ti increases cold-working difficulty; S347’s Nb has less impact on workability.

• Cost: S347 is more expensive due to Nb scarcity.

• Summary:

  • S347: Preferred for long-term high-temperature stability and weld reliability (e.g., boilers, aerospace).

  • S321: Cost-effective for moderate/low-temperature applications (e.g., structural components, pipelines).