Alloy 31 (UNS N08031 / 1.4562) Nitrogen-Strengthened Austenitic Corrosion Resistant Alloy

Alloy 31 – UNS N08031 – X1NiCrMoCu 32 28 7 – 1.4562

In the chemical, oil & gas, and environmental protection industries, selecting suitable piping materials often presents a challenging dilemma: conventional stainless steels deliver insufficient corrosion resistance, while pure nickel-based alloys come with high procurement costs. To address this pain point in industrial service, Alloy 31 (UNS N08031) provides a cost-effective material solution.

As a nitrogen-alloyed iron-nickel-chromium-molybdenum austenitic material, it combines corrosion performance close to that of nickel-based alloys with the forming and processing advantages of austenitic stainless steels. It operates stably for long periods in acidic media and high-temperature, high-pressure environments, and is widely adaptable to demanding scenarios including flue gas desulfurization, acid production, and oil & gas extraction.

The comprehensive performance of Alloy 31 stems from its precise multi-element alloy design：

A 30%–32% nickel content stabilizes the austenitic matrix, paired with 26%–28% high chromium content to form a fundamental barrier against oxidation and acid corrosion.6%–7% molybdenum works in synergy with copper to enhance the alloy’s resistance to reducing acids and pitting environments.As the core strengthening element, 0.15%–0.25% nitrogen both boosts matrix strength and inhibits the precipitation of harmful intermetallic phases, without sacrificing the material’s ductility and toughness.

Alloy 31 Chemical Composition,%

UNS N08031 Typical Physical and Mechanical Properties (RT,Annealed)

The single-phase austenitic matrix endows Alloy 31 with stable physical properties:

At ambient temperature, it has a density of 8.05 g/cm³ and a solidus-liquidus temperature range of 1330℃–1370°C. Its room-temperature magnetic permeability is only 1.001, making it essentially non-magnetic.Its thermal conductivity and thermal expansion change gently with rising temperature: thermal conductivity reaches 11.7 W/m·K at 20°C, and the average coefficient of thermal expansion from 20°C to 100°C is 14.3 μm/m·K.Thermal stress remains controllable under temperature cycling conditions, making it particularly suitable for heat exchange equipment and piping applications with large temperature fluctuations.

Alloy 31 (UNS N08031 / 1.4562) Key Performance Features

1. Resistance to multiple complex acidic media

Alloy 31 delivers outstanding performance in sulfuric acid environments, and its tolerance for sulfuric acid systems mixed with chloride impurities far exceeds that of conventional high-alloy stainless steels. It also offers good resistance to wet-process phosphoric acid, low-concentration hydrochloric acid, sulfite slurry and other media, with a critical pitting temperature of 85°C (per ASTM G48 standard). It effectively mitigates the risks of pitting corrosion, crevice corrosion and intergranular corrosion, adapting well to complex production scenarios with alternating media.

2. Stable mechanical properties

In the solution-annealed condition, Alloy 31 has a room-temperature tensile strength of no less than 650 MPa and an elongation at break of over 40%, outperforming common austenitic stainless steels in strength. Its performance degrades gently with increasing temperature, retaining a yield strength of over 125 MPa at 550°C, and is suitable for pressure vessel manufacturing across the temperature range of -196°C to 550°C. It also boasts excellent low-temperature toughness, with an impact energy of over 140 J/cm² at -196°C, fitting special scenarios such as cryogenic storage and transportation.

3. Excellent structural stability

During conventional welding and medium-high temperature service, Alloy 31 maintains a uniform austenitic structure, avoiding corrosion resistance degradation caused by grain boundary precipitation and extending the overall service life of equipment. Compared with high-alloy stainless steels of the same grade, Alloy 31 delivers higher strength while retaining sufficient formability and ductility, withstanding higher pressure loads. This allows for thinner equipment wall thicknesses and lower overall manufacturing costs.

UNS N08031 Heat Treatment

Alloy 31 has good hot and cold workability, and can be formed into various components via forging, rolling, stamping and other processes. Supporting heat treatment processes shall follow relevant specifications to ensure the corrosion resistance and mechanical properties of the final product.

Hot working processes are recommended to be carried out within the temperature range of 1050°C–1200°C. Rapid cooling is required after processing, and supplementary solution treatment is advised to restore the uniform structure and optimal performance of the material.

Cold forming operations shall be performed on solution-annealed blanks. Due to the work hardening effect of the alloy, intermediate annealing is required for large deformation; when cold deformation exceeds 15%, the finished product must undergo final solution treatment to eliminate processing stress and restore corrosion resistance.

The standard solution treatment temperature is 1150°C–1180°C, followed by rapid air cooling or water quenching. The cooling rate from 1150°C to 500°C shall be no less than 150°C/min to maximize the corrosion resistance of the alloy.

Welding

Alloy 31 has good weldability, and can be welded using conventional high-alloy stainless steel processes such as Gas Tungsten Arc Welding (GTAW/TIG) and Plasma Arc Welding (PAW). No preheating is required during construction, and no additional post-weld heat treatment is needed under conventional service conditions.

Typical Application Fields

1.Chemical acid manufacturing: Sulfuric acid production and storage equipment, sulfuric acid heat exchange piping with chloride impurities, wet-process phosphoric acid reactors and concentration units, as well as corrosion-resistant components for hydrochloric acid regeneration systems.

2.Oil & gas extraction and transportation: Gathering pipelines, coiled tubing and downhole tools for sour oil & gas fields. It complies with NACE MR0175/ISO 15156 standards and is suitable for service conditions containing hydrogen sulfide and carbon dioxide.

Pulp & paper and hydrometallurgy: Equipment and piping for pulp bleaching processes, non-ferrous metal slurry leaching and treatment devices, withstanding chlorine-containing and acidic process media.

• Special pressure-bearing and storage & transportation equipment: Hazardous chemical storage and transportation containers, and wide-temperature-range pressure equipment, with relevant hazardous goods transportation and pressure vessel certifications.

C&N supplies a full range of Alloy 31 (UNS N08031) products, covering bars, plates, seamless pipes, fittings, flanges, forgings and custom fabricated parts. All products are manufactured in strict compliance with relevant standards, with rigorous control over chemical composition, mechanical properties and corrosion performance. We can provide supporting services including customized supply and welding process guidance based on customers’ actual service conditions and processing requirements. Please contact us immediately for your inquiries.