1. INNGANGUR
1.4762 ryðfríu stáli—also known as X10CrAlSi25 in DIN/EN parlance and AISI 446 or UNS S44600 in American standards—represents a ferritic alloy optimized for high-temperature service.
It combines elevated chromium, Ál, and silicon levels to achieve exceptional oxidation resistance and thermal stability.
Í þessari grein, we analyze 1.4762 from metallurgical, vélrænt, Efni, economic, environmental, and application-oriented perspectives.
2. Söguleg þróun & Standardization
Originally developed in the 1960s to address premature failure in furnace components, 1.4762 emerged as a cost-effective alternative to nickel-based alloys.
- DIN to EN Transition: First standardized as DIN X10CrAlSi25, it later migrated into EN 10088-2:2005 as grade 1.4762 (X10CrAlSi25).
- ASTM Recognition: The AISI/ASTM community adopted it as AISI 446 (UNS S44600) under ASTM A240/A240M for pressure-vessel and high-temperature sheet and plate.
- Global Availability: Today, major steel producers in Europe and Asia supply 1.4762 in forms ranging from sheet and strip to tubes and bars.
3. Efnasamsetning & Metallurgical Foundations
The exceptional high-temperature performance of 1.4762 stainless steel stems directly from its finely tuned chemistry.
In particular, elevated chromium, aluminum and silicon levels combine with stringent limits on carbon, nitrogen and other impurities to balance oxidation resistance, creep strength and fabricability.
| Element | Nominal Content (wt %) | Virka |
|---|---|---|
| Cr | 24.0–26.0 | Forms a continuous Cr₂O₃ scale, the primary barrier against high-temperature attack. |
| Al | 0.8–1.5 | Promotes formation of dense Al₂O₃ under cyclic heating, reducing scale spallation. |
| Og | 0.5–1.0 | Enhances scale adhesion and improves resistance to carburizing atmospheres. |
C. |
≤ 0.08 | Kept low to minimize chromium carbide precipitation at grain boundaries. |
| Mn | ≤ 1.0 | Acts as a deoxidizer in steelmaking and controls austenite formation during processing. |
| P. | ≤ 0.04 | Restricted to avoid phosphide segregation, which embrittles ferritic steels. |
| S | ≤ 0.015 | Kept minimal to reduce sulfide inclusions, thereby improving ductility and toughness. |
| N | ≤ 0.03 | Controlled to prevent nitride precipitation that could impair creep resistance. |
Alloy Design Philosophy.
Transitioning from earlier ferritic grades, engineers increased Cr above 24 % to secure a robust passive film in oxidizing gases.
Meanwhile, the addition of 0.8–1.5 % Al represents a deliberate shift: alumina scales adhere more strongly than chromia when parts cycle between 600 ° C og 1 100 ° C..
Silicon further augments this effect, stabilizing the mixed oxide layer and guarding against carbon ingress that can embrittle components in hydrocarbon-rich environments.
4. Physical & Vélrænni eiginleika 1.4762 Ryðfríu stáli
Physical Properties
| Eign | Value |
|---|---|
| Þéttleiki | 7.40 g/cm³ |
| Melting Range | 1 425–1 510 ° C. |
| Hitaleiðni (20 ° C.) | ~ 25 W·m⁻¹·K⁻¹ |
| Specific Heat Capacity (20 ° C.) | ~ 460 J·kg⁻¹·K⁻¹ |
| Stuðull hitauppstreymis | 11.5 × 10⁻⁶ K⁻¹ (20–800 °C) |
| Mýkt (20 ° C.) | ~ 200 GPA |
- Þéttleiki: At 7.40 g/cm³, 1.4762 weighs slightly less than many austenitic grades, thereby reducing component mass without sacrificing rigidity.
- Hitaleiðni & Heat Capacity: With a conductivity near 25 W·m⁻¹·K⁻¹ and heat capacity around 460 J·kg⁻¹·K⁻¹,
the alloy absorbs and distributes heat efficiently, which helps prevent hot spots in furnace linings. - Thermal Expansion: Its moderate expansion rate demands careful allowance in assemblies operating between room temperature and 800 ° C.; neglecting this can induce thermal stresses.
Room-Temperature Mechanical Properties
| Eign | Specified Value |
|---|---|
| Togstyrkur | 500–600 MPa |
| Ávöxtunarstyrkur (0.2% Offset) | ≥ 280 MPA |
| Elongation at Break | 18–25 % |
| Hörku (Brinell) | 180–220 HB |
| Charpy Impact Toughness (−40 °C) | ≥ 30 J. |
Elevated-Temperature Strength & Skríða mótspyrna
| Hitastig (° C.) | Togstyrkur (MPA) | Ávöxtunarstyrkur (MPA) | Creep Rupture Strength (100 000 h) (MPA) |
|---|---|---|---|
| 550 | ~ 300 | ~ 150 | ~ 90 |
| 650 | ~ 200 | ~ 100 | ~ 50 |
| 750 | ~ 150 | ~ 80 | ~ 30 |
Fatigue and Thermal Cycling Behavior
- Low-Cycle Fatigue: Tests reveal endurance limits around 150 MPa at 20 °C for 10⁶ cycles. Þar að auki, the ferritic matrix’s fine grain structure delays crack initiation.
- Thermal Cycling: The alloy resists scale spallation through hundreds of heating–cooling cycles between ambient and 1 000 ° C., thanks to its alumina-enriched oxide layers.
5. Tæring & Oxidation Resistance
High-Temperature Oxidation Behavior
1.4762 achieves outstanding scale stability by forming a duplex oxide structure:
- Inner Alumina (Al₂O₃) Layer
-
- Formation: Between 600–900 °C, aluminum diffuses outward to react with oxygen, yielding a thin, continuous Al₂O₃ layer.
- Benefit: Alumina adheres tenaciously to the substrate, greatly reducing scale spallation under thermal cycling.
- Outer Chromia (Cr₂O₃) and Mixed Oxide
-
- Formation: Chromium at the surface oxidizes to Cr₂O₃, which overlays and reinforces the alumina.
- Synergy: Together, the two oxides slow further oxidation by limiting oxygen ingress and metal outward diffusion.
Aqueous Corrosion Resistance
Although ferritic steels generally trail austenitics in chloride environments, 1.4762 performs respectably in neutral to mildly acidic media:
| Environment | Behavior of 1.4762 |
|---|---|
| Fresh Water (pH 6–8) | Passive, minimal uniform corrosion (< 0.02 mm/y) |
| Dilute Sulfuric Acid (1 wt %, 25 ° C.) | Uniform attack rate ~ 0.1 mm/y |
| Chloride Solutions (NaCl, 3.5 wt %) | Pitting resistance equivalent to PRE ≈ 17; no cracking up to 50 ° C. |
6. Fabrication, Suðu & Hitameðferð
Suðu
- Aðferðir: Tig (GTAW) and plasma welding are preferred to minimize heat input and avoid grain coarsening.
Use of matching filler metal (T.d., ER409Cb) or 309L for dissimilar joints. - Precaution: Preheat to 150–200°C for thick sections (>10 mm) to reduce cooling rates and prevent martensitic transformation, which can cause cracking.
Post-weld annealing at 750–800°C improves ductility.
Forming and Machining
- Cold Forming: Good ductility allows moderate bending and rolling, though work hardening is less pronounced than in austenitic steels.
Springback must be accounted for in tooling design. - Hot Working: Forge or roll at 1000–1200°C, with rapid cooling to avoid sigma phase formation (which embrittles the alloy at 800–900°C).
- Vinnsla: Moderate machinability due to its ferritic structure; use high-speed steel (HSS) tools with positive rake angles and abundant coolant to manage chip evacuation.
Hitameðferð
- Glitun: Stress relief at 700–800°C for 1–2 hours, fylgt eftir með loftkælingu, to eliminate residual stresses from fabrication and restore dimensional stability.
- No Hardening: As a ferritic steel, it does not harden via quenching; strength improvements rely on cold working or alloy modifications (T.d., adding titanium for grain refinement).
7. Surface Engineering & Protective Coatings
To maximize service life in aggressive thermal environments, engineers employ targeted surface treatments and coatings on 1.4762 ryðfríu stáli.
Pre-Oxidation Treatments
Before placing components into service, controlled pre-oxidation creates a stable, tightly adherent oxide:
- Ferli: Heat parts to 800–900 °C in air or oxygen-rich atmosphere for 2–4 hours.
- Niðurstaða: A uniform Al₂O₃/Cr₂O₃ duplex scale forms, reducing initial mass gain by up to 40 % during the first 100 h of service.
- Benefit: Engineers observe a 25 % drop in scale spallation during rapid thermal cycles (800 °C ↔ 200 ° C.), thereby extending maintenance intervals.
Diffusion Aluminizing
Diffusion aluminizing infuses extra aluminum into the near-surface region, building a thicker alumina barrier:
- Technique: Pack cementation—components sit in a mixture of aluminum powder, activator (NH₄Cl), and filler (Al₂O₃)—at 950–1 000 °C for 6–8 h.
- Performance Data: Treated coupons exhibit 60 % less oxidation mass gain at 1 000 °C over 1 000 h compared to untreated material.
- Consideration: Apply a post-coat grit blast (Ra ≈ 1.0 µm) to optimize coating adherence and minimize thermal stresses.
Ceramic and Metallic Overlays
When service temperatures exceed 1 000 °C or when mechanical erosion accompanies oxidation, overlay coatings provide additional protection:
| Overlay Type | Typical Thickness | Service Range (° C.) | Key Advantages |
|---|---|---|---|
| Al₂O₃ Ceramic | 50–200 µm | 1 000–1 200 | Exceptional inertness; thermal barrier |
| NiCrAlY Metallic | 100–300 µm | 800–1 100 | Self-healing alumina scale; good ductility |
| High-Entropy Alloy | 50–150 µm | 900–1 300 | Superior oxidation resistance; tailored CTE |
Emerging Smart Coatings
Cutting-edge research focuses on coatings that adapt to service conditions:
- Self-Healing Layers: Incorporate microencapsulated aluminum or silicon that release into cracks, reforming protective oxides in situ.
- Thermochromic Indicators: Embed oxide pigments that change color when critical temperatures are exceeded, enabling visual inspection without dismantling.
- Nano-Engineered Topcoats: Utilize nanostructured ceramic films (< 1 µm) to provide both oxidation resistance and wear protection with minimal added weight.
8. Applications of 1.4762 Ryðfríu stáli
Furnace and Heat Treatment Equipment
- Radiant tubes
- Retorts
- Furnace muffles
- Annealing boxes
- Heating element supports
Petrochemical Industry
- Reformer tubes
- Ethylene cracking furnace components
- Catalyst trays and supports
- Heat shields in carburizing/sulfidizing environments
Power Generation and Incineration Systems
- Superheater tubes
- Exhaust gas ducts
- Boiler linings
- Flue gas channels
Metal and Powder Processing
- Sintering trays
- Slag guides
- Support grids
- High-temperature fixtures
Glass and Ceramic Manufacturing
- Kiln furniture
- Burner nozzles
- Thermal insulation hardware
Automotive and Engine Applications
- Heavy-duty exhaust manifolds
- EGR modules
- Turbocharger housings
9. 1.4762 vs. Alternative High-Temperature Alloys
Below is a comprehensive comparison table that consolidates the performance characteristics of 1.4762 ryðfríu stáli against alternative high-temperature alloys: 1.4845 (AISI 310S), 1.4541 (Aisi 321), Og Inconel 600.
| Eign / Criteria | 1.4762 (Aisi 446) | 1.4845 (AISI 310S) | 1.4541 (Aisi 321) | Inconel 600 (UNS N06600) |
|---|---|---|---|---|
| Structure | Járn (BCC) | Austenitic (FCC) | Austenitic (Stöðug) | Austenitic (Ni-base) |
| Main Alloying Elements | Cr ~25%, Al, Og | Cr ~25%, Ni ~20% | Cr ~17%, Ni ~9%, Af | Ni ~72%, Cr ~16%, Fe ~8% |
| Max Continuous Use Temperature | ~950 °C | ~1 050 °C | ~870 °C | ~1 100 °C |
| Oxidation Resistance | Framúrskarandi (Cr₂O₃ + Al₂O₃) | Mjög gott (Cr₂O₃) | Gott | Framúrskarandi |
| Carburization Resistance | High | Miðlungs | Lágt | Very High |
Thermal Fatigue Resistance |
High | Miðlungs | Miðlungs | Framúrskarandi |
| Creep Strength @ 800 ° C. | Miðlungs | High | Lágt | Very High |
| Stress Corrosion Cracking (Scc) | Resistant | Susceptible in chlorides | Susceptible in chlorides | Highly resistant |
| Cold Workability | Limited | Framúrskarandi | Framúrskarandi | Miðlungs |
| Suðuhæfni | Miðlungs (preheat needed) | Framúrskarandi | Framúrskarandi | Gott |
| Fabrication Complexity | Miðlungs | Easy | Easy | Moderate to complex |
| Kostnaður | Lágt | High | Miðlungs | Very High |
| Best Application Fit | Oxidizing/carburizing air, furnace parts | Pressurized high-temp components | Formed, welded lower-temp parts | Critical pressure & tæring, >1000 ° C. |
10. Niðurstaða
1.4762 ryðfríu stáli (X10CrAlSi25, Aisi 446) marries economical alloy design with outstanding high-temperature oxidation and creep performance.
From a metallurgical standpoint, its carefully tuned Cr-Al-Si chemistry underpins stable protective scales.
Mechanically, it retains sufficient strength and ductility up to 650 °C for most industrial applications.
Environmentally, its high recyclability aligns with sustainability goals, while its cost advantage over nickel alloys appeals to budget-constrained projects.
Looking ahead, innovations in nanoscale reinforcement, additive manufacturing,
and intelligent coatings promise to push its performance envelope even further, ensuring that 1.4762 remains an authoritative choice for high-temperature service.
At Þetta, we stand ready to partner with you in leveraging these advanced techniques to optimize your component designs, material selections, and production workflows.
ensuring that your next project exceeds every performance and sustainability benchmark.
