ASTM EN DIN GB JIS Standard Hastelloy X Round Bar /Bright Bar / Nickel Alloy Rod

Hastelloy X (UNS N06002) is a nickel-chromium-iron-molybdenum alloy that is widely recognized as one of the most versatile solid-solution strengthened superalloys available on the global market. This alloy maintains exceptional oxidation resistance at temperatures up to 1200°C and offers outstanding high-temperature strength and stress-rupture properties above 790°C. It is particularly valued for its excellent resistance to carburizing and nitriding atmospheres, making it a preferred material for extreme environment applications across aerospace, industrial heating, and power generation industries. The round bars and bright bars manufactured from Hastelloy X provide designers and engineers with reliable performance in the most demanding thermal and corrosive conditions.

1. Chemical Composition

The chemical composition of Hastelloy X is carefully balanced to deliver its signature high-temperature performance. The precise elemental formulation creates a robust austenitic matrix that maintains structural integrity under thermal stress while forming protective oxide layers that resist various corrosive environments.

Table 1: Chemical Composition of Hastelloy X (Weight %)

This specific combination of elements delivers three crucial performance characteristics: the high nickel content provides the fundamental resistance to oxidation and carburization; the chromium contribution enables exceptional oxidation resistance by forming tenacious Cr₂O₃ surface scales; and the molybdenum and tungsten additions deliver solid-solution strengthening that enhances high-temperature creep rupture strength-1.

2. Physical Properties

The physical properties of Hastelloy X make it particularly suitable for applications involving rapid thermal cycling and high thermal gradients. Its moderate thermal expansion coefficient and density provide designers with advantageous characteristics for high-temperature structural components.

Table 2: Physical Properties of Hastelloy X

The melting range of 1295-1381°C defines the safe upper-temperature limit for applications, while the density of 8.28 g/cm³ makes it lighter than many comparable high-temperature alloys, providing advantageous strength-to-weight ratios in rotating components.

3. Mechanical Properties

Hastelloy X maintains impressive mechanical properties across a wide temperature spectrum, retaining significant strength at elevated temperatures where most structural alloys would rapidly deteriorate. This performance profile makes it particularly valuable for applications requiring sustained loading at high temperatures.

Table 3: Typical Mechanical Properties of Hastelloy X (Solution Annealed Condition)

The high temperature capability of Hastelloy X is demonstrated by its retention of approximately 36% of its room temperature tensile strength at 900°C, a temperature where most steels and standard stainless alloys have completely lost their structural integrity. The exceptional elongation properties at elevated temperatures (often exceeding 40%) provide crucial damage tolerance in thermal cycling applications, allowing for stress redistribution without crack formation.

4. Standard Specifications

Hastelloy X round bars and bright bars are produced under various international standards to ensure consistent quality, performance, and dimensional accuracy. These specifications govern the manufacturing process, chemical composition, mechanical properties, testing requirements, and dimensional tolerances.

Table 4: Standard Specifications for Hastelloy X Round Bar

The ASTM B572 standard is the primary specification for Hastelloy X rod and bar products, covering chemical, mechanical, and dimensional requirements. The DIN 2.4665 designation is commonly referenced in European applications, while GB/T 15007 defines the Chinese equivalent as NS3102 (also known historically as GH4090). For aerospace applications, AMS 5754 imposes additional rigorous requirements for quality assurance, traceability, and testing to ensure reliability in critical components.

5. Manufacturing Process

The production of Hastelloy X round bars employs sophisticated manufacturing techniques to ensure optimal microstructure and mechanical properties:

• Melting Practice: High-quality Hastelloy X is typically produced using Vacuum Induction Melting (VIM) followed by Electroslag Remelting (ESR) or Vacuum Arc Remelting (VAR). This double-melt approach significantly reduces impurities, gases, and harmful elements while improving chemical homogeneity and solidification structure.

• Hot Working: The converted ingots are then forged or hot-rolled at temperatures ranging from 1150°C to 1000°C into round bars. Controlled deformation processes refine the as-cast structure, achieve uniform grain size (typically ASTM 4-6), and enhance density through reduction of microporosity.

• Heat Treatment: All Hastelloy X products undergo solution annealing at temperatures between 1150°C and 1180°C, followed by rapid cooling (water quench or forced air). This critical process dissolves secondary phases and carbides, producing a uniform single-phase austenitic microstructure that optimizes corrosion resistance, ductility, and high-temperature performance.

• Surface Finishing: For bright bars, additional processing includes turning and polishing to achieve superior surface finish with precise dimensional tolerances. This typically results in smooth, oxide-free surfaces with roughness values of Ra ≤ 0.6μm, ideal for precision applications.

6. Key Features and Advantages

Hastelloy X round bars offer several distinct advantages that make them the material of choice for extreme environment applications:

• Exceptional High-Temperature Strength: Hastelloy X maintains impressive load-bearing capability and creep resistance at temperatures up to 1200°C, significantly outperforming standard stainless steels and many other nickel-based alloys in the 800-1100°C range.

• Outstanding Oxidation Resistance: The alloy exhibits superior oxidation resistance in both oxidizing (air) and reducing environments up to 1200°C. The high chromium content forms a continuous, adherent Cr₂O₃ scale that protects the underlying material from further degradation, even during thermal cycling.

• Excellent Corrosion Resistance: Hastelloy X demonstrates remarkable resistance to various corrosive media, including hot sulfur-bearing gases, carburizing atmospheres, and combustion products. It effectively resists attack by weak acids, alkalies, and salts, particularly in chloride-containing environments.

• Good Fabrication Characteristics: Unlike many high-temperature alloys, Hastelloy X offers good formability and excellent weldability using common techniques such as GTAW (TIG), GMAW (MIG), and SMAW (stick welding). Post-weld heat treatment is generally not required for most applications.

7. Applications

Hastelloy X round bars are specified across multiple industries where materials must withstand extreme temperatures and corrosive environments:

• Aerospace Industry: Jet engine combustion chambers, flame holders, afterburner components, tail pipes, and turbine seals routinely utilize Hastelloy X due to its ability to maintain structural integrity in high-stress, high-temperature environments.

• Industrial Gas Turbines: The alloy is extensively used in combustion liners, transition ducts, nozzle rings, and hot gas path components where temperatures can exceed 1000°C during continuous operation.

• Heat Treatment Equipment: Radiation tubes, retorts, muffles, furnace rolls, and heat treatment baskets benefit from the alloy's resistance to oxidation, carburization, and thermal cycling.

• Power Generation: Nuclear reactor components, superheater supports, boiler components, and waste incineration systems employ Hastelloy X for its long-term stability at elevated temperatures.

• Chemical Processing: Pyrolysis tubes, reformer components, high-temperature reactors, and heat exchanger tubing in petrochemical applications utilize the alloy's corrosion resistance under demanding conditions.

8. Comparison with Similar Alloys

Hastelloy X occupies a unique position in the family of high-temperature alloys, offering a balanced combination of high-temperature strength, oxidation resistance, and fabricability that differs from other commonly specified materials:

While Inconel 625 offers superior corrosion resistance in aqueous environments, Hastelloy X provides better performance in high-temperature oxidizing and carburizing atmospheres. Compared to Haynes 230, Hastelloy X generally offers better fabricability and weldability while maintaining comparable high-temperature performance up to 1000°C. Against Inconel 617, Hastelloy X demonstrates superior oxidation resistance but lower strength at the very highest temperature extremes (above 1000°C).

This balanced property profile makes Hastelloy X particularly valuable for applications requiring both excellent high-temperature capability and relative ease of fabrication without complex post-weld heat treatment requirements.

Conclusion

Hastelloy X round bars and bright bars represent a premium solution for engineering challenges involving extreme temperatures and corrosive environments. With its carefully balanced chemical composition, well-established manufacturing protocols, and comprehensive standardization across international specifications, this alloy continues to be the material of choice for critical applications in aerospace, power generation, and industrial processing. The combination of exceptional high-temperature strength, outstanding oxidation resistance, and excellent fabricability ensures that Hastelloy X remains a versatile and reliable option for designers and engineers facing the most demanding material selection challenges.

When sourcing Hastelloy X round bars, it is essential to work with qualified suppliers who can provide full material traceability, including chemical certification and heat treatment records, to ensure compliance with the required specifications and end-use application requirements.