ASME SA240 348H Stainless Steel Plate | SA240 Type 348H
What is ASME SA240 348H Stainless Steel Plate?
As a professional stainless steel plate supplier and China Mill-Direct Supply / Mill Direct Exporter, SHH STEEL is pleased to present ASME SA240 348H Stainless Steel Plate, also known as SA240 Type 348H.
ASME SA240 Type 348H is the higher-carbon version of the niobium-tantalum stabilized austenitic stainless steel Type 348. While standard Type 348 has a maximum carbon content of 0.08%, Type 348H is deliberately specified with a carbon range of 0.04–0.10%. This controlled higher carbon content provides significantly improved strength at elevated temperatures, particularly above 500°C, while the niobium + tantalum stabilization continues to deliver outstanding resistance to intergranular corrosion after welding or after prolonged exposure to the sensitization temperature range.
Type 348H combines three important attributes: the elevated-temperature strength of the “H” grades, the superior long-term stability of niobium-tantalum stabilization, and the tighter residual element control (especially low cobalt) that distinguishes the 348 family from standard 347. It is therefore selected for high-temperature pressure vessels, boilers, heat exchangers, nuclear components, and special process equipment where higher allowable stresses, sensitization resistance, and residual element restrictions are simultaneously required.
SHH STEEL supplies ASME SA240 348H as true Mill Direct Supply, sourcing directly from major Chinese stainless steel mills. This model delivers competitive mill pricing, consistent quality, full heat traceability, and shorter lead times. We offer thicknesses from 3 mm to 100 mm (thicker plates available on request), widths up to 2000–3000 mm, and lengths up to 12000 mm or cut-to-length. Material is supplied in the solution-annealed condition, most commonly with No.1 finish for pressure vessel applications.
Material Specification
| Specification Element | Requirement | SHH STEEL Compliance |
|---|---|---|
| Primary Standard | ASME SA240 / SA240M | Full compliance |
| Steel Grade | Type 348H (UNS S34809) | Confirmed |
| Product Form | Plate, Sheet | Available |
| Delivery Condition | Solution Annealed | Standard |
| Thickness Range | 3 mm – 100 mm (thicker available) | 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 / ASME Mill Test Certificate | Available |
Chemical Composition
Heat Analysis (Ladle Analysis) according to ASME SA240 Type 348H:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.04 – 0.10 |
| Silicon (Si) | ≤ 0.75 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 17.00 – 19.00 |
| Nickel (Ni) | 9.00 – 13.00 |
| Niobium + Tantalum (Nb + Ta) | ≥ 8 × C% |
| Tantalum (Ta) | ≤ 0.10 |
| Cobalt (Co) | Tightly controlled (typically ≤ 0.20) |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
Product Analysis (typical permissible variations):
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.04 – 0.10 |
| Silicon (Si) | ≤ 0.75 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 16.90 – 19.10 |
| Nickel (Ni) | 8.90 – 13.10 |
| Niobium + Tantalum (Nb + Ta) | ≥ 8 × C% |
| Tantalum (Ta) | ≤ 0.10 |
The controlled carbon range of 0.04–0.10% provides solid-solution strengthening and improved creep strength at elevated temperatures. The minimum niobium + tantalum content of eight times the carbon percentage ensures effective stabilization, while tighter limits on cobalt and tantalum meet special residual element requirements.
Mechanical Properties
Room-Temperature Mechanical Properties (Annealed Condition)
| Property | Value |
|---|---|
| Tensile Strength | ≥ 515 MPa (75 ksi) |
| Yield Strength (0.2%) | ≥ 205 MPa (30 ksi) |
| Elongation (in 50 mm) | ≥ 40% |
| Hardness | ≤ 217 HB / ≤ 95 HRB |
Elevated-Temperature Performance ASME SA240 348H is specifically intended for service at elevated temperatures. The higher carbon content delivers better tensile and yield strength above approximately 500°C and improved long-term creep and stress-rupture properties compared with standard Type 348. It is used in the temperature range where higher ASME allowable stresses are required.
Physical Properties
- Density: 7.93 g/cm³
- Melting Range: approximately 1400–1425°C
- Magnetic: Non-magnetic in the annealed condition
Material Comparison
| Grade | Carbon Content | Stabilization | Primary Advantage | Typical Service Focus |
|---|---|---|---|---|
| SA240 Type 348 | ≤ 0.08% | Nb + Ta | Excellent sensitization resistance + residual control | High-temp welded service with residual limits |
| SA240 Type 348H | 0.04 – 0.10% | Nb + Ta | Higher strength at elevated temperature + residual control | Continuous high-temp service with residual restrictions |
| SA240 Type 347 | ≤ 0.08% | Niobium | Excellent high-temperature stability | General severe high-temp service |
| SA240 Type 347H | 0.04 – 0.10% | Niobium | Higher high-temp strength | Continuous high-temp service |
| SA240 Type 321H | 0.04 – 0.10% | Titanium | High-temp strength (Ti-stabilized) | Elevated-temperature service |
| SA240 Type 304H | 0.04 – 0.10% | None | High-temperature strength (lowest cost) | High-temp, mild corrosion |
When elevated-temperature strength, long-term sensitization resistance, and tight residual element control are all required, ASME SA240 348H is the appropriate choice. It offers the high-temperature strength advantage of the “H” grades while retaining the residual element controls of the 348 family. For general high-temperature service without residual restrictions, astm a240 type 347h stainless steel sheet plate is more commonly used. For applications needing improved chloride resistance, astm a240 type 316ti stainless steel sheet plate should be evaluated.
High-Temperature
High-Temperature Performance and Sensitization
The higher carbon content that gives Type 348H its elevated-temperature strength is effectively managed by niobium-tantalum stabilization. Niobium and tantalum combine preferentially with carbon, greatly reducing the risk of chromium carbide precipitation even during prolonged exposure in the temperature range of 450–850°C. This makes Type 348H particularly suitable for continuous high-temperature service where mechanical strength, microstructural stability, and residual element control are simultaneously required.
Corrosion Resistance
In the properly annealed condition, ASME SA240 Type 348H offers corrosion resistance similar to Type 348 and Type 347 in most atmospheric, fresh-water, and oxidizing environments. Its principal advantage is the excellent resistance to intergranular corrosion after welding or after prolonged high-temperature exposure, thanks to niobium-tantalum stabilization.
Resistance to pitting and crevice corrosion in chloride environments is comparable to 304 and inferior to molybdenum-bearing grades. For combined high-temperature and chloride service, a molybdenum-containing stabilized grade is preferred.
Weldability
ASME SA240 Type 348H can be welded by all standard fusion and resistance welding methods. Matching niobium-stabilized filler metals (E347 / ER347) are recommended to maintain stabilization and high-temperature strength in the weld metal.
Because of the niobium-tantalum stabilization, the grade can normally be used in the as-welded condition without risk of intergranular corrosion. When maximum high-temperature strength of the weld is required, high-carbon matching consumables are preferred.
Heat Treatment
ASME SA240 Type 348H is supplied in the solution-annealed condition. Proper heat treatment is essential to achieve optimum properties.
Recommended Solution Annealing Parameters
- Temperature range: 1040 – 1150°C (typically 1050 – 1120°C)
- Holding (soaking) time: – Plates ≤ 25 mm thick: minimum 10–20 minutes after the entire cross-section has reached the target temperature – Plates 25–50 mm thick: minimum 20–40 minutes – Plates above 50 mm: 30–60 minutes or longer, depending on thickness and furnace loading, to ensure uniform temperature
- Cooling: Rapid cooling is mandatory. Water quenching is strongly preferred for thicker plates to retain the stabilized structure, maximize corrosion resistance, and preserve high-temperature strength capability.
An optional stabilizing treatment at approximately 840–900°C may be applied in special cases to ensure complete niobium/tantalum carbide precipitation, although modern production practices usually make this unnecessary for most applications.
Surface Finishes
| Finish | Description | Typical Use / Keywords |
|---|---|---|
| No.1 | Hot-rolled, annealed and pickled | SA240 348H No.1 – most common for pressure vessel and high-temperature plate |
| 2B | Cold-rolled, annealed, pickled, skin-passed | SA240 348H 2B – thinner plates and general fabrication |
| No.4 | Brushed finish | SA240 348H No.4 – when improved surface appearance is required |
| Special | Ground or custom finishes | SA240 348H Special – on request |
SHH STEEL regularly supplies ASME SA240 348H in No.1 finish for pressure vessel applications and can provide other finishes according to project requirements.
Tolerances
Dimensional tolerances for ASME SA240 348H plate follow ASME SA240 and the referenced ASTM A480 requirements. Thickness, width, length, and flatness are controlled within standard limits. Tighter tolerances can be arranged for specific projects.
Equivalent Material Grades
| Grade / Designation | Standard | Notes |
|---|---|---|
| SA240 Type 348H | ASME SA240 | — |
| A240 Type 348H | ASTM A240 | Essentially identical |
| UNS S34809 | — | Unified Numbering System |
| Related high-carbon 348 | EN / JIS / GB | Approximate national equivalents |
Related grades frequently evaluated with ASME SA240 348H include astm a240 type 348 stainless steel sheet plate, astm a240 type 347h stainless steel sheet plate, astm a240 type 347 stainless steel sheet plate, and astm a240 type 321 stainless steel sheet plate.
Applications
ASME SA240 Type 348H is selected for equipment that requires elevated-temperature strength, long-term resistance to sensitization, and tight residual element control:
| Industry / Sector | Typical Components / Equipment |
|---|---|
| Nuclear | High-temperature components requiring low cobalt |
| Boilers & Pressure Vessels | Superheater tubesheets, headers, high-temperature shells |
| Heat Exchangers | High-temperature shells, channels, tubesheets |
| Power Generation | Boiler components, hot-process piping |
| Chemical & Petrochemical | High-temperature reactors and process equipment |
| Refinery | Hot-service vessels and piping |
| Industrial Furnaces | Structural parts operating at elevated temperature |
| Special High-Temperature Service | Equipment with residual element restrictions |
Why Choose SHH STEEL
SHH STEEL is a China Mill-Direct Supply and Mill Direct Exporter of stainless steel plate. We maintain long-term strategic relationships with major Chinese stainless steel mills and supply ASME SA240 Type 348H with the following advantages:
- Competitive mill-direct pricing
- Consistent quality and complete heat traceability
- Full Mill Test Certificates (EN 10204 3.1 / ASME)
- Flexible thickness, width, and length combinations
- Technical assistance on high-temperature and residual-controlled material selection
- Reliable worldwide logistics and export documentation
FAQ
- What is the main difference between SA240 348 and SA240 348H?The carbon content. Type 348H has a controlled higher carbon range (0.04–0.10%) to improve high-temperature strength, while standard Type 348 has a maximum of 0.08% carbon. Both are niobium-tantalum stabilized with tight residual element controls.
- When should I choose 348H instead of 347H?Choose 348H when the project specification requires low cobalt content or tighter residual element limits in addition to elevated-temperature strength. For general high-temperature service without residual restrictions, 347H is usually sufficient.
- Is ASME SA240 348H suitable for ASME Code pressure vessels?Yes. It is listed in ASME SA240 and can be used for Code-stamped vessels and boilers operating at elevated temperatures when residual element controls are specified.
- Does 348H require special welding procedures?It can be welded with standard austenitic procedures. Matching niobium-stabilized filler metals (E347) are recommended to maintain both stabilization and high-temperature strength in the weld.
- What is the density of SA240 Type 348H?7.93 g/cm³.
Conclusion
ASME SA240 348H Stainless Steel Plate (SA240 Type 348H) is the high-carbon niobium-tantalum stabilized austenitic grade optimized for elevated-temperature strength while retaining excellent resistance to intergranular corrosion and tight residual element control. It is the material of choice when design conditions demand higher allowable stresses at temperature, long-term microstructural stability, and compliance with low-cobalt or special residual requirements.
As a professional China Mill-Direct Supply and Mill Direct Exporter, SHH STEEL provides reliable ASME SA240 Type 348H plate with competitive pricing, full certification, and complete technical support.
Contact SHH STEEL today for stock availability, surface finish options (including SA240 348H No.1 and SA240 348H 2B), or a competitive quotation for your high-temperature stainless steel requirements.
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