SS347H and SS321 are austenitic stainless steels, primarily characterized by high-temperature corrosion resistance and weld stability, and are widely used in chemical, energy, aerospace, and food processing industries. HT PIPE is a leading stockist and global exporter with over 16 years of expertise in international trade. We supply pipes, plates, round bars, and a comprehensive range of pipe fittings, flanges, and valves. Contact us now for free quotes and personalized product information.
SS347H and SS321 Chemical Composition
| Chemical Composition | SS321 | SS347H |
|---|---|---|
| Chromium (Cr) | 17.0%-19.0% | 17.0%-19.0% |
| Nickel (Ni) | 9.0%-12.0% | 9.0%-13.0% |
| Stabilizing Element | Titanium (Ti) ≥5×C% and ≤0.70% | Niobium (Nb) + Tantalum (Ta) ≥8×(C+N)% and ≤1.0% |
| Carbon (C) | ≤0.08% | 0.04%-0.10% |
| Manganese (Mn) | ≤2.0% | ≤2.0% |
| Silicon (Si) | ≤1.0% | ≤0.75% |
| Phosphorus (P) | ≤0.045% | ≤0.03% |
| Sulfur (S) | ≤0.045% | ≤0.03% |
SS347H and SS321 Mechanical Properties
| Mechanical Properties | Test Condition | SS321 | SS347H |
|---|---|---|---|
| Tensile Strength | 20°C (Room Temperature) | ≥515MPa | ≥515MPa |
| Yield Strength | 20°C (Room Temperature) | ≥205MPa (≥550MPa after cold working) | ≥205MPa |
| Elongation | 20°C (Room Temperature) | ≥40% (≈15% after cold working) | ≥40% |
| Hardness | 20°C (Room Temperature) | HB≤201 | HB≤201 |
| Strength Retention Rate | 600°C (High Temperature) | Approximately 80%; strength tends to decrease when used above 800°C for a long time | ≥85%; excellent creep resistance |
| High-Temperature Service Capacity | Long-term high-temperature environment | Withstand intermittent high temperature; titanium oxidation is prone to occur above 800°C | Can serve at 800-900°C for a long time with no obvious strength decay |
| Room Temperature Performance Difference | 20°C (Room Temperature) | Basically consistent with SS347H | Slightly better toughness than SS321 after cold working |
SS347H and SS321 Corrosion Resistance Comparison
Intergranular Corrosion Resistance
SS321: Stabilized with titanium, it effectively inhibits chromium carbide precipitation in the sensitization range of 450-850℃. Tested according to ASTM A262 Practice E standard, the corrosion rate is <0.5mm/year, and it maintains good corrosion resistance after welding.
SS347H: Stabilized with niobium, it has superior resistance to intergranular corrosion. In the 800-1500°F (427-816℃) range, the corrosion rate is lower than SS321, and its resistance to polysulfide stress corrosion cracking is more outstanding.
High-Temperature Oxidation and Media Adaptability
SS321: During continuous service at 800℃, a Cr2O3-TiO2 composite oxide film forms on the surface. After 1000 hours of exposure, the oxidation weight gain is <2mg/cm². It is suitable for media such as dilute nitric acid and acetic acid, but has a higher corrosion rate in reducing acids (such as hydrochloric acid).
SS347H: Offers stronger high-temperature oxidation resistance. It performs better than SS321 in a strong oxidizing environment of 1500°F (816℃). It is suitable for harsh media such as nitric acid production and petroleum refining. Its pitting resistance equivalent (PREN) is slightly higher than SS321.
SS347H and SS321 Comparison of Machining and Welding Performance
Machining Performance
SS321: Titanium increases the material's toughness. The cutting speed needs to be 15-20% lower than 304 stainless steel. Carbide-coated tools are required. It has good cold-working formability, but poor polishing performance, making it unsuitable for decorative applications.
SS347H: Niobium has minimal impact on machinability, its cutting, stamping, and forging properties are similar to 304 stainless steel, requiring no significant adjustments to the machining process. It also exhibits moderate work hardening, resulting in higher efficiency in subsequent machining.
Welding Performance
SS321: Titanium is easily burned off at high temperatures during welding, necessitating inert gas shielded welding. ER321 welding wire is recommended, and the interpass temperature should be controlled at ≤150℃. Solution treatment is recommended after welding thick plates.
SS347H: Niobium exhibits less burn-off during welding, resulting in stronger welding stability. No complex post-weld treatment is required, it can be directly welded. Furthermore, niobium can be transferred through a high-temperature arc, making weld quality easier to control and suitable for welding complex structures.
