Haynes HR-224 Nickel Alloy,Ni–27.5Fe–20Cr–3.8Al alloy，1

### **Introduction to Haynes® HR-224® (UNS N06224) Nickel Alloy** **Haynes® HR-224®** is a nickel-chromium-iron-aluminum alloy specifically engineered for exceptional high-temperature service in highly oxidizing environments. The "HR" likely stands for "High Resistance," reflecting its superior performance against oxidation and carburization. Unlike many conventional nickel-based alloys that rely primarily on chromium for oxidation protection, HR-224 incorporates a significant amount of **aluminum (~3.8%)**, which allows it to form a continuous, protective, and self-healing layer of aluminum oxide (Al₂O₃) on its surface. This alumina scale is significantly more stable and resistant to degradation than the chromia (Cr₂O₃) scale formed by standard alloys, enabling HR-224 to perform reliably at temperatures up to **1260°C (2300°F)**. --- ### **Chemical Composition (Weight %, typical)** The composition is a sophisticated balance of oxidation resistance and microstructural stability. | Element | Minimum | Maximum | Key Function | | :--- | :--- | :--- | :--- | | **Nickel (Ni)** | **Balance** | | Provides the austenitic matrix and overall stability. | | **Chromium (Cr)** | 19.0 | 21.0 | Works synergistically with Al to form a robust, multi-layered oxide scale (Al₂O₃ + Cr₂O₃). | | **Iron (Fe)** | 25.0 | 30.0 | A major constituent that helps control cost and contributes to the alloy's matrix. | | **Aluminum (Al)** | 3.5 | 4.0 | **The key element** for forming the protective, slow-growing Al₂O₃ scale. | | **Cobalt (Co)** | - | 2.0 | Incidental element. | | **Manganese (Mn)** | - | 0.50 | - | | **Silicon (Si)** | - | 0.20 | Kept low to prevent formation of low-melting point phases. | | **Carbon (C)** | - | 0.03 | Kept very low to prevent carbide formation and enhance oxidation resistance. | | **Lanthanum (La)** | 0.005 | 0.1 | A "reactive element" that dramatically improves the adhesion and spallation resistance of the oxide scale. | | **Sulfur (S)** | - | 0.005 | Kept extremely low to improve hot workability and scale adhesion. | ***Key Differentiator:*** The **Ni-Fe-Cr-Al** system with **Lanthanum doping** is the cornerstone of its unparalleled oxidation resistance. --- ### **Physical Properties (Typical)** * **Density:** 7.98 g/cm³ (0.288 lb/in³) * **Melting Range:** ~1350 - 1410 °C (~2460 - 2570 °F) * **Thermal Expansion Coefficient:** 14.5 μm/m·°C (20-1000°C) * **Thermal Conductivity:** ~18.0 W/m·K at 100°C * **Modulus of Elasticity (Young's Modulus):** ~200 GPa (29 x 10⁶ psi) at 21°C --- ### **Mechanical Properties (Typical at Room Temperature, Annealed)** * **Tensile Strength:** ≥ 690 MPa (100 ksi) * **Yield Strength (0.2% Offset):** ≥ 310 MPa (45 ksi) * **Elongation:** ≥ 40% ***High-Temperature Strength:*** While its room-temperature strength is moderate, HR-224 retains useful strength at high temperatures and exhibits excellent resistance to thermal fatigue and creep, which is critical for cyclic applications. --- ### **Key Characteristics and Product Applications** #### **Key Characteristics:** 1. **Exceptional Oxidation Resistance:** Its primary advantage is outstanding resistance to oxidation, significantly outperforming standard chromia-forming alloys like Alloy 600 or 601 at temperatures above 1000°C (1800°F). 2. **Excellent Carburization & Nitridation Resistance:** The stable alumina scale acts as an effective barrier against carbon and nitrogen ingress, making it suitable for carburizing atmospheres. 3. **Good Microstructural Stability:** Resists the formation of detrimental intermetallic phases that can embrittle the alloy during long-term exposure. 4. **Good Fabricability:** It can be fabricated using standard hot and cold working techniques, though its high aluminum content requires specific welding procedures, often using a matching composition filler metal. #### **Primary Applications:** HR-224 is designed for the most demanding high-temperature, oxidizing industrial environments. * **Heat Treating Industry:** * **Radiant Tubes, Muffles, and Retorts:** For carburizing, neutral hardening, and carbonitriding furnaces. * **Furnace Rollers and Belts:** For continuous heat treatment lines. * **Fixture Trays and Baskets:** For holding components during high-temperature processing. * **Petrochemical Processing:** * Components in high-temperature reformers and cracking furnaces. * **Aerospace:** * Certain engine components requiring long-term oxidation resistance. * **Industrial Gas Turbines:** * Combustion system components exposed to high temperatures. --- ### **International Standards** As a specialized, proprietary alloy, its standardization is specific. It is recognized under a Unified Numbering System (UNS) designation and is covered by ASTM specifications. | Product Form | Standard | Designation | Notes | | :--- | :--- | :--- | :--- | | **Plate, Sheet, Strip** | ASTM B844 | UNS N06224 | Standard Guide for Nickel-Chromium-Molybdenum-Iron Alloys for Corrosive Service. (HR-224 is often supplied to this standard's chemistry requirements). | | **Bar & Wire** | *Customer/Proprietary Spec* | UNS N06224 | Typically supplied to customer-specific requirements based on the manufacturer's standard. | | **Welding Consumables** | AWS A5.14 / A5.11 | **ERNiFeCr-Al** (proposed) | Matching composition filler metals are available for GTAW and SMAW processes to maintain oxidation resistance in the weld. | **Note:** "Haynes" and "HR-224" are registered trademarks of **Haynes International, Inc.** This alloy represents a specialized solution for extreme temperatures. For any critical application, consultation with the manufacturer and testing under actual service conditions is strongly recommended.

Packing of Standard Packing: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3261 gallon liquid totes Special package is available on request.