AISI 309Cb Stainless Steel Plate | 309Cb China steel mill-Direct Supply
What is AISI 309Cb Stainless Steel Plate?
As a professional China steel mill-Direct Supply and stainless steel plate supplier, SHH STEEL is pleased to present AISI 309Cb Stainless Steel Plate.
AISI 309Cb (UNS S30940), also known as 309Cb, is a niobium (columbium)-stabilized version of the heat-resisting austenitic stainless steel 309. It contains approximately 22–24% chromium and 12–15% nickel, with intentional niobium addition to stabilize the grade against intergranular corrosion. This stabilization allows the material to maintain good corrosion resistance after welding or exposure to the sensitization temperature range, while retaining the excellent high-temperature oxidation resistance characteristic of the 309 family.
AISI 309Cb is particularly suitable for welded high-temperature equipment such as furnace components, radiant tubes, heat-treatment fixtures, kiln parts and petrochemical process equipment operating in oxidizing atmospheres where resistance to intergranular attack is also required.
SHH STEEL supplies AISI 309Cb as true China steel mill-Direct Supply, sourcing directly from major Chinese stainless steel mills. This model delivers competitive mill pricing, consistent quality, complete heat traceability and reliable delivery. SHH STEEL offers AISI 309Cb in plate and sheet form across a practical range of thicknesses and surface finishes suitable for elevated-temperature service.
AISI 309Cb is frequently compared with a240 309s, a240 310s, a240 310h, a240 321, a240 347 and a240 304l when selecting stabilized or high-temperature grades. SHH STEEL provides technical support to help customers choose the most appropriate material.
Material Specification
| Specification Element | Requirement | SHH STEEL Compliance |
|---|---|---|
| Grade | AISI 309Cb / UNS S30940 | Confirmed |
| Related Standards | ASTM A240, ASME SA240, related high-temperature specs | Available |
| Product Form | Plate, Sheet | Available |
| Delivery Condition | Solution Annealed | Standard |
| Thickness Range | 1 mm – 80 mm (thicker available on request) | Custom sizes supported |
| Width | Up to 2000–3000 mm | Available |
| Length | Up to 12000 mm or cut-to-length | Available |
| Surface Finish | No.1, 2B, and others on request | Available |
| Certification | EN 10204 3.1 / Mill Test Certificate | Available |
SHH STEEL can supply AISI 309Cb dual-certified to ASTM A240 / ASME SA240 when required by the project.
Chemical Composition
Typical Chemical Composition of AISI 309Cb (UNS S30940):
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Silicon (Si) | ≤ 1.00 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 22.00 – 24.00 |
| Nickel (Ni) | 12.00 – 15.00 |
| Niobium (Nb/Cb) | 10 × C min – 1.10 max |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
The intentional niobium (columbium) addition is the key stabilizing element in AISI 309Cb. Niobium combines preferentially with carbon to form stable niobium carbides, thereby preventing chromium carbide precipitation at grain boundaries and providing excellent resistance to intergranular corrosion after welding. Combined with high chromium and nickel, the grade delivers outstanding high-temperature oxidation resistance. SHH STEEL carefully controls the niobium-to-carbon ratio to ensure effective stabilization.
Mechanical Properties
Annealed Condition (typical values)
| Property | Value |
|---|---|
| Tensile Strength | ≥ 515 MPa (75 ksi) |
| Yield Strength (0.2%) | ≥ 205 MPa (30 ksi) |
| Elongation (in 50 mm) | ≥ 40% |
| Hardness | ≤ 217 HB |
At elevated temperatures, AISI 309Cb retains useful strength and excellent oxidation resistance. The niobium stabilization also helps maintain corrosion performance after high-temperature exposure. For applications requiring higher creep strength, related grades such as a240 310h may be considered. SHH STEEL supplies material with consistent high-temperature properties.
Physical Properties Density is approximately 7.90 g/cm³. The grade is non-magnetic in the annealed condition. Melting range is approximately 1400–1450°C.
Material Comparison
| Grade | Stabilization | Cr (%) | Ni (%) | Weldability & IGC | Oxidation Resistance | Typical Preference |
|---|---|---|---|---|---|---|
| AISI 309S | Low carbon | 22–24 | 12–15 | Excellent | Very Good | Welded high-temperature service |
| AISI 309Cb | Niobium (Cb) | 22–24 | 12–15 | Excellent | Very Good | Stabilized high-temp welded service |
| AISI 310S | Low carbon | 24–26 | 19–22 | Excellent | Excellent | Severe high-temperature service |
| AISI 321 | Titanium | 17–19 | 9–12 | Excellent | Good | Stabilized moderate high-temp service |
| AISI 347 | Niobium | 17–19 | 9–13 | Excellent | Good | Stabilized welded service |
| AISI 304L | Low carbon | 18–20 | 8–12 | Excellent | Good | General welded constructions |
AISI 309Cb is selected when both excellent high-temperature oxidation resistance and stabilization against intergranular corrosion are required. Compared with a240 309s, the niobium addition provides additional protection in the heat-affected zone. For more severe high-temperature service, SHH STEEL recommends a240 310s or a240 310h. Stabilized grades such as a240 321 or a240 347 are often considered for lower-temperature welded applications.
Corrosion Resistance
AISI 309Cb provides excellent resistance to oxidation and scaling in air and oxidizing atmospheres at elevated temperatures up to approximately 1000–1100°C in continuous service (depending on conditions). The niobium stabilization ensures good resistance to intergranular corrosion after welding or exposure to the sensitization temperature range.
At room temperature it offers good resistance to atmospheric corrosion and many mild chemical environments. In sulfur-containing or highly carburizing atmospheres, performance may be limited. For the most demanding high-temperature oxidizing service, SHH STEEL recommends a240 310s. In chloride-rich aqueous environments, a240 316l or a240 2205 should be considered.
Weldability
AISI 309Cb has excellent weldability due to niobium stabilization. Matching or appropriate niobium-bearing filler metals are recommended. The stabilization effectively prevents intergranular corrosion in the heat-affected zone, making post-weld annealing generally unnecessary for most applications.
SHH STEEL recommends proper welding procedures and post-weld cleaning to achieve optimum high-temperature and corrosion performance. This combination of high-temperature capability and as-welded corrosion resistance is the main advantage of AISI 309Cb over non-stabilized grades.
Heat Treatment
AISI 309Cb is normally supplied in the solution-annealed condition by SHH STEEL.
Recommended solution annealing temperature range is 1040–1150°C, followed by rapid cooling. Proper annealing ensures that niobium is available for effective stabilization and optimizes both room-temperature ductility and high-temperature oxidation resistance. SHH STEEL controls heat treatment to ensure consistent quality for elevated-temperature service.
Surface Finishes
| Finish | Description | Typical Use / Keywords |
|---|---|---|
| No.1 | Hot-rolled, annealed and pickled | AISI 309Cb No.1 – most common for industrial high-temp plate |
| 2B | Cold-rolled, annealed, pickled, skin-passed | AISI 309Cb 2B – thinner plates |
| Special | Ground or custom finishes | AISI 309Cb Special – on request |
SHH STEEL regularly supplies AISI 309Cb in No.1 finish, which is the preferred condition for most high-temperature plate applications.
Tolerances
Dimensional tolerances for AISI 309Cb Stainless Steel Plate supplied by SHH STEEL generally conform to ASTM A480 practices.
Typical available size range is thickness 1 mm – 80 mm, width up to 2000–3000 mm, and length up to 12000 mm or cut-to-length. SHH STEEL provides precise dimensional control and can support tighter tolerances when required.
Equivalent Material Grades
| Grade / Designation | Standard / UNS | Notes |
|---|---|---|
| AISI 309Cb | — | — |
| UNS S30940 | — | Unified Numbering System |
| ASTM A240 Type 309Cb | ASTM A240 | When dual certified |
| Related Nb-stabilized 309 | EN / JIS / GB | Approximate national equivalents |
Related grades for comparison include a240 309s, a240 310s, a240 310h, a240 321, a240 347 and a240 304l.
Applications
AISI 309Cb is selected for welded high-temperature applications requiring both excellent oxidation resistance and resistance to intergranular corrosion. Typical applications of AISI 309Cb include:
| Industry / Sector | Typical Components / Equipment (with keywords) |
|---|---|
| Heat Treatment & Furnaces | AISI 309Cb furnace components, radiant tubes, fixtures, trays |
| Industrial Heating | AISI 309Cb kiln parts, muffles, supports and retorts |
| Power Generation | AISI 309Cb high-temperature ducting and structural parts |
| Petrochemical & Refining | AISI 309Cb furnace linings, process equipment and welded parts |
| Chemical Processing | AISI 309Cb high-temperature vessels and welded components |
| General High-Temperature Service | AISI 309Cb equipment operating in oxidizing atmospheres |
SHH STEEL supplies AISI 309Cb for these elevated-temperature welded applications with consistent quality. For related industry solutions, see our energy industry, petrochemical industry and equipment manufacturing pages. Supporting services include steel cutting services and steel welding services.
Why Choose SHH STEEL
SHH STEEL is a China steel mill-Direct Supply specializing in stainless steel plate and sheet. By working directly with major Chinese stainless steel mills, SHH STEEL supplies AISI 309Cb with the following advantages:
- Genuine China steel mill-Direct Supply pricing
- Consistent quality and complete heat traceability
- Full Mill Test Certificates (EN 10204 3.1)
- Niobium-stabilized material optimized for welded high-temperature service
- Flexible dimensions and surface finishes (including AISI 309Cb No.1 and AISI 309Cb 2B)
- Technical support for selection among 309S, 309Cb, 310S, 321, 347 and related grades
- Value-added services including steel cutting services, steel welding services and worldwide shipping service
For more information about our company and full product range, please visit China steel Mill Agent-SHH STEEL.
FAQ
- What is the main advantage of AISI 309Cb over AISI 309S?The niobium (columbium) addition provides additional stabilization against intergranular corrosion, offering extra protection in the heat-affected zone after welding. SHH STEEL recommends 309Cb when maximum resistance to intergranular attack in high-temperature welded service is required.
- How does AISI 309Cb compare with AISI 321 or 347?AISI 309Cb offers significantly higher chromium and nickel contents and superior high-temperature oxidation resistance, while 321 and 347 are stabilized grades primarily used at lower temperatures. SHH STEEL can help select the appropriate grade based on service temperature and environment.
- What is the density of AISI 309Cb?Approximately 7.90 g/cm³. SHH STEEL provides material certificates confirming physical and mechanical properties.
- Does SHH STEEL supply dual-certified ASTM A240 / AISI 309Cb material?Yes, SHH STEEL commonly supplies dual-certified material upon request.
Conclusion
AISI 309Cb Stainless Steel Plate is a niobium-stabilized high-chromium, high-nickel austenitic grade that combines excellent high-temperature oxidation resistance with superior resistance to intergranular corrosion after welding. It is an outstanding choice for welded furnace components, radiant tubes, heat-treatment equipment and petrochemical process equipment operating in oxidizing atmospheres.
As a professional China steel mill-Direct Supply, SHH STEEL provides high-quality AISI 309Cb Stainless Steel Plate with competitive pricing, full certification and complete technical support.
Contact SHH STEEL today for stock availability, surface finish options (including AISI 309Cb No.1 and AISI 309Cb 2B), or a competitive quotation.
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