Lord Fin Tube--Ferritic and Martensitic Stainless Steel Tubing
ASTM A268 Ferritic and Martensitic Stainless Steel Tubing: Complete Guide
ASTM A268/ASME SA268 specifications cover various grades of stainless steel tubing designed for general corrosion-resistant and high-temperature service. These specifications include both seamless and welded ferritic and martensitic stainless steel tubing, providing solutions for diverse industrial applications.
Ferritic Stainless Steel Tubing
Ferritic stainless steels are characterized by their high chromium content (typically 15-30%) and low carbon content. This composition provides excellent corrosion resistance, good oxidation resistance, and stress corrosion cracking resistance. They are generally more cost-effective due to the absence of nickel.
Ferritic Stainless Steel Tubing Key Characteristics:
- Chromium content: 15%-30%
- Generally does not contain nickel
- May include small amounts of Mo, Ti, Nb
- High thermal conductivity
- Low thermal expansion coefficient
- Good oxidation resistance
- Excellent resistance to stress corrosion
- Used for air, water vapor, water, and oxidation acid corrosion parts
Ferritic Stainless Steel Tubing Common Grades (ASTM A268):
| Grade | C (max) | Mn (max) | P (max) | S (max) | Si (max) | Cr (%) | Ni (%) | UTS (MPa) | YS (MPa) | Elongation (%) |
|---|---|---|---|---|---|---|---|---|---|---|
| TP405 | 0.08 | 1.0 | 0.04 | 0.03 | 1.0 | 11.5-14.5 | 0.75 | 415 min | 205 min | 20 min |
| TP409 | 0.08 | 1.0 | 0.04 | 0.02 | 1.0 | 10.5-11.75 | 0.5 | 380 min | 170 min | 20 min |
| TP430 | 0.12 | 1.0 | 0.04 | 0.03 | 1.0 | 16.0-18.0 | 0.75 | 450 min | 205 min | 20 min |
| TP439 | 0.03 | 1.0 | 0.04 | 0.03 | 1.0 | 17.0-19.0 | 0.75 | 450 min | 205 min | 20 min |
| TP444 | 0.025 | 1.0 | 0.04 | 0.03 | 1.0 | 17.5-19.5 | 1.00 | 450 min | 205 min | 20 min |
Ferritic Stainless Steel Tubing Applications:
Ferritic stainless steel tubing is commonly used in automotive exhaust systems, heat exchangers, furnace parts, and other applications requiring excellent corrosion resistance and thermal properties. Their resistance to stress corrosion cracking makes them ideal for chloride-containing environments.
Martensitic Stainless Steel Tubing
Martensitic stainless steels contain higher levels of carbon, which allows them to be hardened by heat treatment. This makes them suitable for applications requiring high strength and hardness. However, they are generally less corrosion-resistant than ferritic grades.
Martensitic Stainless Steel Tubing Key Characteristics:
- Similar to ferritic but can be hardened by heat treatment
- Chromium content: typically around 12%-18%
- Ferromagnetic properties
- Can be hardened by heat treatment
- Sensitive to notch-brittleness on slow cooling to ordinary temperatures
- Used in applications requiring increased hardness and strength
Martensitic Stainless Steel Tubing Common Grades (ASTM A268):
| Grade | C (max) | Mn (max) | P (max) | S (max) | Si (max) | Cr (%) | Ni (%) | UTS (MPa) | YS (MPa) | Elongation (%) |
|---|---|---|---|---|---|---|---|---|---|---|
| TP410 | 0.15 | 1.0 | 0.04 | 0.03 | 1.0 | 11.5-13.5 | 0.5 | 485 min | 275 min | 20 min |
| TP429 | 0.12 | 1.0 | 0.04 | 0.03 | 1.0 | 14.0-16.0 | 0.5 | 380 min | 205 min | 20 min |
| TP434 | 0.12 | 1.0 | 0.04 | 0.03 | 1.0 | 16.0-18.0 | 0.75 | 450 min | 205 min | 20 min |
| TP436 | 0.12 | 1.0 | 0.04 | 0.03 | 1.0 | 16.0-18.0 | 0.75 | 450 min | 205 min | 20 min |
| TP442 | 0.2 | 1.0 | 0.04 | 0.03 | 1.0 | 18.0-23.0 | 0.5 | 450 min | 205 min | 20 min |
| TP446 | 0.2 | 1.0 | 0.04 | 0.03 | 1.0 | 23.0-27.0 | 0.75 | 450 min | 205 min | 20 min |
| UNS S41500 | 0.05 | 1.0 | 0.04 | 0.03 | 1.0 | 11.5-14.5 | 0.5-1.5 | 515 min | 345 min | 20 min |
Martensitic Stainless Steel Tubing Applications:
Martensitic stainless steel tubing is widely used in cutlery, surgical instruments, valves, pump shafts, and other applications requiring high strength, hardness, and moderate corrosion resistance. Their ability to be heat-treated makes them suitable for components that require specific mechanical properties.
Ferritic Stainless Steel Advantages
- Excellent corrosion resistance
- Good stress corrosion cracking resistance
- Lower cost (no nickel content)
- Good oxidation resistance
- High thermal conductivity
- Low thermal expansion
Martensitic Stainless Steel Advantages
- High strength and hardness
- Can be heat treated
- Good wear resistance
- Moderate corrosion resistance
- Good mechanical properties
- Suitable for high-stress applications
ASTM A268 Stainless Steel Tubing Selection
ASTM A268/ASME SA268 tubing includes several grades of tubing, each tailored to different operational environments and mechanical requirements. Ferritic stainless steels, with high chromium content and typically no nickel, offer excellent resistance to stress corrosion and oxidation, making them ideal for applications like automotive exhaust systems and heat exchangers. Martensitic stainless steels, known for their ability to be hardened by heat treatment due to higher carbon content, are preferred in applications that demand high strength and hardness, such as in cutlery and valves.
When selecting between ferritic and martensitic stainless steel tubing under ASTM A268 specifications, consider factors such as corrosion environment, mechanical requirements, thermal conditions, and budget constraints. Ferritic grades generally offer better corrosion resistance at a lower cost, while martensitic grades provide superior strength and hardness through heat treatment.
