Project Description
S44600 / AISI 446 / SUH446 Stainless Steel Seamless Tube
S44600 — designated as AISI 446 under the AISI system and SUH446 under JIS — is a high-chromium ferritic stainless steel engineered for sustained high-temperature oxidation resistance. With a chromium content of 23.0–27.0% and near-zero nickel, this grade delivers exceptional scaling resistance in continuous service up to 1095°C (2000°F), making it a cost-effective alternative to nickel-rich austenitic grades like 310S in oxidizing environments where creep strength is not the limiting factor.
As a EAF + LF + VD steelmaker with optional ESR refining, Fushun Steel Tube supplies S44600 as seamless tubes in hot-rolled, cold-drawn, and cold-rolled conditions. The fully ferritic microstructure at room temperature delivers excellent resistance to sulfur-bearing atmospheres, oxidizing flue gases, and molten non-ferrous metals. For procurement teams seeking a reliable, long-service-life tube material in high-temperature oxidizing environments — without the nickel surcharge — S44600 is a proven choice. Contact us for a free quote with your target dimensions.
Typical Applications
S44600 tubes are specified where sustained oxidation resistance at elevated temperatures is the primary requirement. Common downstream products and components include:
- Radiant tubes and recirculation tubes in industrial heat-treating furnaces
- Burner nozzles and combustion chamber liners in oil and gas-fired heaters
- Boiler baffles, tube sheets, and flue gas ducting liners
- Glass mold plunger tubes and gob distributor sleeves
- Heat exchanger tubes in chemical and petrochemical process plants
- Recuperator tubes and air preheater components
- Kiln furniture support tubes in ceramic and brick manufacturing
- Molten zinc and aluminum handling tubes in galvanizing and die-casting lines
- Thermocouple protection tubes (oxidizing atmosphere)
- Sulfur recovery unit (SRU) tail gas piping components
In all these applications, the key value proposition of 446 is its chromium-rich oxide scale that remains adherent and protective well beyond the temperature limits of conventional austenitic stainless steels. Tell us your specifications and we will match the optimal manufacturing route to your service conditions.
Product Image
S44600 / AISI 446 stainless steel seamless tubes are supplied in hot-rolled, cold-drawn, or cold-rolled conditions with surface finishes tailored to end-use requirements. The high-chromium ferritic microstructure ensures uniform oxidation resistance throughout the wall thickness.
Specifications & Standards
S44600 / 446 / SUH446 is recognized across multiple international standards frameworks, with coverage in both tube-specific and general product standards:
Tube & Pipe Standards
- ASTM A268/A268M — Seamless and welded ferritic/martensitic stainless steel tubing for general service
- ASTM A511/A511M — Seamless stainless steel mechanical tubing (supplementary requirement for S44600)
- ASTM A554 — Welded stainless steel mechanical tubing (when welded form is acceptable)
General Product Standards
- ASTM A276/A276M — Stainless steel bars and shapes (covers 446 for bar reference)
- JIS G4312 — Heat-resisting steel bars and wire rods (SUH446)
- AMS 5645 — Steel, corrosion/heat resistant, bars, forgings, and rings (27Cr)
Fushun Steel Tube primarily supplies S44600 under ASTM A268 for general-service seamless ferritic tubing, with options to certify to ASTM A511 for mechanical tubing applications. For all orders, standard delivery conditions include full chemical analysis and mechanical property verification per the applicable standard. Request a sample with the destination standard you require.
Available Sizes & Delivery
Fushun Steel Tube produces S44600 seamless tubes through hot-rolling followed by optional cold-drawing or cold-rolling for tighter dimensional control:
| Process Route | OD Range | WT Range | Length |
|---|---|---|---|
| Hot-rolled seamless | 32–325 mm | 3.5–40 mm | Up to 12 m |
| Cold-drawn seamless | 6–168 mm | 0.8–15 mm | Up to 12 m (fixed or random) |
| Cold-rolled precision | 6–89 mm | 0.5–10 mm | Up to 10 m |
Delivery Information
- Ready stock (common sizes)
- Approximately 7 days from order confirmation
- Custom/non-standard specifications
- MOQ 2–3 tons; lead time approximately 25–35 days
- Small trial orders
- Accepted for special grades and first-article qualification
- Volume orders
- Negotiable pricing and scheduled delivery upon inquiry
We maintain buffer stock of S44600 semi-finished hollows to reduce lead times on repeat orders. Contact us with your OD × WT × length requirements for an availability check.
Chemical Composition
The S44600 grade is defined by its high chromium content, which drives the formation of a dense, protective chromium-oxide scale at elevated temperatures. Compositional limits vary slightly between standards:
| Element | ASTM A268 / AISI 446 | JIS G4312 SUH446 |
|---|---|---|
| Carbon (C) | 0.20 max | 0.20 max |
| Manganese (Mn) | 1.50 max | 1.50 max |
| Silicon (Si) | 1.00 max | 1.00 max |
| Phosphorus (P) | 0.040 max | 0.040 max |
| Sulfur (S) | 0.030 max | 0.030 max |
| Chromium (Cr) | 23.0–27.0 | 23.0–27.0 |
| Nitrogen (N) | 0.25 max | — |
| Nickel (Ni) | Residual only | 0.60 max |
The near-absence of nickel is a defining economic advantage of this grade. With a fully ferritic structure, S44600 is immune to chloride stress-corrosion cracking — in sharp contrast to 304 and 316 austenitic grades — while also resisting sulfur attack in reducing flue gas environments.
Manufacturing Process
Fushun Steel Tube produces S44600 tubes using an integrated steelmaking and pipe-making route. The melt is prepared in an EAF with LF refining and VD treatment to control gas content and inclusion cleanliness. For applications demanding superior micro-cleanliness — such as thin-wall tubes used in critical furnace atmospheres — an optional ESR step is available. Ingots or continuous-cast rounds are then pierced and hot-rolled into seamless tube hollows.
For standard industrial applications, hot-rolled tubes are supplied in the annealed condition. Where tighter dimensional tolerances or smoother surface finish are required, the hot-rolled hollows undergo cold-drawing or cold-rolling to achieve precision tolerances of ±0.05 mm on wall thickness. Post-forming annealing at 760–830°C restores the fully ferritic microstructure and relieves work-hardening stresses. The entire process is backed by our ISO 9001 quality management system.
Mechanical Properties
S44600 is supplied in the annealed condition as standard. As a ferritic stainless steel, it does not respond to martensitic hardening and exhibits moderate strength with good ductility:
| Property | Metric | Imperial |
|---|---|---|
| Tensile Strength (min) | 485 MPa | 70 ksi |
| Yield Strength — 0.2% Offset (min) | 275 MPa | 40 ksi |
| Elongation in 50 mm (min) | 20% | 20% |
| Hardness (max) | HB 201 / HRB 92 | HB 201 / HRB 92 |
| Modulus of Elasticity | 200 GPa | 29.0 × 106 psi |
| Density | 7.74 g/cm³ | 0.280 lb/in³ |
Higher strength levels up to approximately 550 MPa tensile can be achieved through cold-working for applications where elevated yield strength is required. However, cold-work strengthening may partially anneal at sustained service temperatures above 500°C. Contact us for a free quote if your application requires specific mechanical property targets.
Heat Treatment
The heat treatment of S44600 is critical to achieving a uniform ferritic microstructure free of embrittling phases. The standard practice involves full annealing with controlled cooling:
| Treatment | Temperature Range | Holding Time | Cooling Method |
|---|---|---|---|
| Annealing | 760–830°C (1400–1525°F) | 1 hour per 25 mm of section thickness | Air cool or water quench |
| Stress Relieving | 540–650°C (1000–1200°F) | 1–2 hours | Air cool |
Rapid cooling through the 540–400°C range is recommended after annealing to minimize exposure to the 475°C embrittlement temperature window. Similarly, prolonged exposure in the 650–950°C range should be avoided to prevent sigma-phase formation, which can embrittle the material at room temperature. Fushun Steel Tube's controlled furnace systems and documented heat treatment records ensure every batch meets the required microstructure requirements before dispatch.
Surface Finish & Tolerances
S44600 tubes are available in multiple surface finish grades depending on manufacturing route and end-use requirements. Hot-rolled tubes are supplied with a black oxidized surface — suitable for furnace fabrication where internal surface quality is secondary to mechanical integrity. For more demanding applications, cold-drawn and cold-rolled tubes are delivered in a bright, smooth finish with surface roughness Ra typically below 1.6 µm.
Our precision tube capability — via cold-rolling — achieves OD tolerances of ±0.05 mm and wall thickness tolerances of ±0.03 mm on smaller diameters. For stainless steel tubes used in heat exchanger bundles, additional pickling and passivation treatments remove surface scale and enhance the natural corrosion resistance. Optional mechanical polishing to 400 grit or finer is available for exposed architectural or food-contact applications.
Quality Assurance & Testing
Every S44600 tube shipment is supported by a comprehensive quality control workflow aligned to ISO 9001 and EN 10204 certification requirements:
Raw Material Inspection
- 100% ladle chemistry verification by optical emission spectrometry (OES)
- Billet/bloom surface inspection and conditioning
- Macro-etch evaluation of cast structure on sample sections
In-Process Control
- Hot-working temperature monitoring and pass reduction tracking
- Wall thickness monitoring via ultrasonic gauging during cold-drawing
- Intermediate anneal verification — hardness and grain size
Finished Product Testing
- 100% hydrostatic test or eddy current (ET) non-destructive testing per ASTM A450/A450M
- Tensile testing at room temperature per ASTM A370
- Flattening and flaring tests on sample pieces from each heat
- Dimensional inspection — OD, WT, length, straightness on every tube
- Intergranular corrosion testing (Practice E of ASTM A763) when specified
- Metallographic examination — grain size and phase distribution
EN 10204 3.1 certificates are standard; 3.2 certificates with third-party witness are available on request.
Packing & Shipping
S44600 stainless steel tubes are packed to prevent mechanical damage and surface contamination during transit. Small-bore tubes (OD < 60 mm) are bundled with steel straps and wrapped in waterproof polyethylene sheeting before being secured in wooden crates. Larger-diameter tubes are individually capped at both ends with plastic end protectors and loaded into open-top containers with dunnage separation between layers.
Standard export packing includes vapor-phase corrosion inhibitor (VCI) paper interleaving between contact surfaces. Each bundle carries a weatherproof tag showing heat number, grade, dimensions, and net weight. Shipment is primarily by sea freight in 20- or 40-foot containers from major Chinese ports; air freight is available for urgent shipments upon request.
Frequently Asked Questions
What sizes of S44600 stainless steel tube do you supply?
Seamless tubes in OD 6–325 mm, WT 0.5–40 mm, lengths up to 12 m. Hot-rolled covers the upper OD range; cold-drawn and cold-rolled deliver precision tolerances in the 6–168 mm OD band.
What is the maximum continuous service temperature for 446 stainless steel?
S44600 withstands continuous exposure up to 1095°C (2000°F) in clean oxidizing atmospheres. Intermittent service is rated to approximately 1065°C (1950°F). Performance degrades in reducing or carburizing environments.
Can I order a small quantity for initial testing?
Yes. We accept trial orders with a minimum of 2–3 tons for non-stock specifications. For ready-stock sizes, even single tubes can be supplied. Contact us with your material specification for availability.
How does 446 compare to 310S for furnace tubes?
S44600 offers comparable or better oxidation resistance at significantly lower material cost due to zero nickel content. However, 310S (austenitic) retains higher creep strength above 900°C and avoids the 475°C embrittlement zone. The choice depends on whether the limiting factor is oxidation or creep in your specific application.
Is the 475°C embrittlement issue a concern for 446 tubes in service?
475°C embrittlement — caused by alpha-prime phase precipitation — can reduce room-temperature ductility in ferritic stainless steels after prolonged exposure in the 400–540°C range. It does not affect high-temperature properties and is generally not a concern when the tubes remain at service temperature. If your tubes will experience frequent thermal cycling through this range, we recommend evaluating this factor with your design team.
