AISI 904L Super-Austenitic Stainless Steel: Propriedades, Fabricação & Applications Guide

AISI 904L is a super-austenitic stainless steel engineered for extreme corrosion resistance—far beyond standard alloys like 316L. Its high nickel and molybdenum content makes it a top choice for harsh environments, from chemical processing to desalination. Este guia quebra suas principais especificações, Traços de desempenho, and real-world uses to help you select it for high-corrosion projects.

1. Visão geral do material & Principais especificações

Understanding 904L’s unique composition and standards is critical to leveraging its full potential. Abaixo está um colapso claro de suas propriedades essenciais.

Composição química & Padrões

As a904L super austenitic grade, isso é904L chemical composition se destaca: 904L high nickel content 23–28 % e904L high molybdenum 4–5 % (far more than 316L’s 2–3% molybdenum). These elements create a protective layer against corrosion. It adheres to global standards:

• 904L UNS N08904 (Sistema de numeração unificada)
• 904L EN 1.4539 equivalente (Padrão europeu para desempenho correspondente)
• 904L ASTM A240 / 904L ASME SA-240 (para placas, folhas, e tiras)

Físico & Propriedades mecânicas

904L delivers reliable strength while prioritizing corrosion resistance. As principais métricas estão organizadas na tabela abaixo:

A chemical plant in Germany uses904L ASTM A240 plates for sulfuric acid tanks—they rely on the 220 MPa yield strength to handle tank pressure and corrosive fluid.

2. Resistência à corrosão & Desempenho ambiental

904L’s biggest advantage is its industry-leading corrosion resistance. Its904L PREN 34–36 (Número equivalente de resistência ao pitting) is far higher than 316L’s PREN of ~24, meaning it resists pitting and crevice corrosion in harsh fluids.

Principais traços resistentes à corrosão

• Pitting & Crevice Corrosion: It has exceptional 904L pitting corrosion resistance and a high 904L crevice corrosion threshold (resists attack in tight gaps, Por exemplo, heat exchanger gaskets).
• Stress Corrosion Cracking: It offers 904L chloride stress corrosion cracking immunity—even in high-chloride environments like seawater or brine.
• Resistência química: It handles 904L sulfuric acid corrosion (resists 50% sulfuric acid up to 60 ° c), 904L phosphoric acid resistance (ideal for fertilizer plants), e 904L nitric acid performance (resists dilute nitric acid).
• Água do mar & Brine: O 904L seawater corrosion rate is ≤0.01 mm/year, and it resists 904L brine corrosion (common in desalination plants).

904L vs 316L corrosion comparison: 316L fails in 10% sulfuric acid after 6 meses, while 904L shows no corrosion after 5 anos. A Saudi desalination plant switched from 316L to 904L for piping—leaks dropped by 90%.

3. Propriedades de alta temperatura & Resistência a oxidação

While 904L is known for corrosion resistance, it also performs well in moderate high-temperature environments (though it’s not designed for extreme heat like 310S).

Características críticas de alta temperatura

• Resistência a oxidação: It resists rust up to 400 ° c-904L oxidation resistance up to 400 ° c makes it suitable for warm chemical processes (Por exemplo, 350 °C sulfuric acid evaporation).
• Força de fluência: 904L creep rupture data shows it can last 10,000+ horas em 300 °C under light stress. Para tarefas mais curtas, 904L short-time tensile at 350 ° c is ~350 MPa.
• Limites de serviço: O 904L continuous service temperature é 400 ° c, e o 904L intermittent service limit é 450 ° c. Beyond this, oxidation and strength decline.
• Thermal Shock Resistance: 904L thermal shock resistance is good—it handles moderate temperature changes (Por exemplo, de 300 °C to room temperature) sem quebrar.

Um estudo de caso: A U.S.. power plant used904L flue-gas desulfurization (FGD) componentes (operando em 350 ° c). Depois 8 anos, no corrosion or deformation occurred—unlike the previous 316L components that failed every 2 anos.

4. Tratamento térmico & Controle de microestrutura

Proper heat treatment ensures 904L maintains its corrosion resistance and microstructure stability.

Processos essenciais de tratamento térmico

• Recozimento da solução: Heat to 1050–1150 °C, Segure por 30 a 60 minutos, Em seguida, a água (o 904L water quench requirement is critical to dissolve carbides and prevent sensitization). This step ensures 904L carbide precipitation avoidance.
• Trabalho quente: Usar 1150–900 ° C. as the 904L hot working range for forging or rolling. Isso mantém o material dúctil e evita rachaduras.
• Trabalho frio: 904L cold working strain hardening is moderate—cold forming (Por exemplo, flexão) increases strength but may require annealing to restore ductility.

Outras considerações

• Risco de fase sigma: 904L sigma phase formation kinetics is slow—no brittle sigma phase forms even after long-term heating at 300–400 °C.
• Alívio do estresse residual: Heat to 450–500 °C to reduce stresses from welding or forming. Esse 904L residual stress relief doesn’t affect corrosion resistance.
• Microestrutura: It has a pure austenitic structure—904L duplex phase absence ensures no brittle phases form.

5. Soldagem, Fabricação & Diretrizes de usinagem

Welding and machining 904L require simple adjustments to preserve its corrosion resistance.

Dicas de soldagem

• Metal de enchimento: Usar 904L filler metal ER385 (904L) (for TIG welding) ou 904L MIG wire 904L—matching the base metal’s composition is critical to avoid corrosion in the weld.
• Pré -aquecer & Post-Weld Care: 904L no preheat required for most thicknesses. After welding, perform 904L post-weld cleaning passivation (with nitric acid) to restore the protective oxide layer.
• Soldabilidade: 904L weldability rating is “excellent”—it has strong 904L hot cracking resistance and works for 904L dissimilar welding to duplex stainless steel (Por exemplo, in offshore structures).

Usinagem & Formação

• Velocidades & Feeds: 904L machining speeds and feeds should be 15–20% lower than carbon steel. Por exemplo, use 60–80 m/min speed with 904L tool life with coated carbide (TiAlN coatings last 2x longer than uncoated tools).
• Formabilidade: 904L formability deep drawing works well for parts like chemical reactor heads—use lubrication to avoid scratching the surface (scratches can lead to corrosion).
• Controle de distorção: Usar 904L distortion control techniques (Por exemplo, aperto durante a soldagem, resfriamento lento) to keep parts true to size.

6. Formulários de produto, Tamanhos & Cadeia de mantimentos

904L is available in a wide range of forms to fit high-corrosion projects.

Formulários comuns do produto

• Pratos & Folhas: 904L stainless steel plate thickness chart ranges from 3 mm para 200 mm; 904L sheet gauge sizes (16 medir para 1/2 polegada) are ideal for pharmaceutical equipment.
• Tubos & Tubos: 904L seamless pipe ASTM A312 (for high-pressure chemical piping) e 904L welded tube dimensions (for low-pressure seawater lines).
• Barras & Acessórios: 904L round bar stock (10 mm para 300 mm diâmetro), 904L angle iron sizes (20×20 mm a 100×100 mm), e 904L threaded rod grades (Nota 1 for general use).
• Formulários especializados: 904L coil slit widths (10 mm para 1250 mm), 904L hollow bar suppliers (Para peças leves), 904L custom forgings (Por exemplo, reactor nozzles), e 904L clad plate suppliers (for cost-effective large structures).

Dicas da cadeia de suprimentos

Work with global suppliers who stock904L seamless pipe ASTM A312 e904L clad plate suppliers—these forms have longer lead times. Para projetos urgentes, prioritize suppliers with local inventory of common sizes.

7. Aplicações do setor & Estudos de caso

904L’s corrosion resistance makes it a top choice for industries handling harsh fluids. Here are key use cases:

• Processamento químico: 904L chemical process reactors (for sulfuric/phosphoric acid), 904L sulfuric acid storage tanks, e 904L phosphoric acid evaporators.
• Water Treatment: 904L seawater heat exchangers e 904L desalination plant piping (resist high chloride levels).
• Poder & Industrial: 904L flue-gas desulfurization (FGD) componentes e 904L scrubber systems (remove sulfur from exhaust gases).
• Usos especializados: 904L pharmaceutical equipment (meets hygiene standards) e 904L paper mill bleach washers (resist chlorine-based bleaches).

Um exemplo real: A Brazilian fertilizer plant replaced 316L with 904L for phosphoric acid evaporators—maintenance costs dropped by 70%, and evaporator lifespan increased from 3 anos para 12 anos.

Perspectiva da tecnologia YIGU

Na tecnologia Yigu, we recommend 904L for clients facing extreme corrosion. Nós fonte904L ASTM A240 pratos e904L seamless pipe ASTM A312 de moinhos certificados, ensuring PREN 34–36 compliance. For chemical and desalination clients, we prioritize post-weld passivation to maximize corrosion resistance. Our team advises on filler metal selection (ER385) to avoid weld failures. While 904L costs more than 316L, its 5–10x longer lifespan makes it cost-effective for high-corrosion projects.

Perguntas frequentes

1. When should I choose 904L over 316L?
   Choose 904L if your project involves high chlorides (seawater/brine), sulfuric/phosphoric acid, or crevice-prone parts (trocadores de calor). Its 904L PREN 34–36 e chloride stress corrosion cracking immunity outperform 316L. Use 316L for milder environments (Por exemplo, processamento de alimentos) to save cost.
2. Eu preciso de tratamento térmico pós-soldado (Pwht) for 904L?
   Não-904L no preheat required and PWHT is unnecessary. Em vez de, perform 904L post-weld cleaning passivation (com 20% ácido nítrico) to remove weld scale and restore the protective oxide layer. This step is critical to maintain corrosion resistance.
3. Can 904L be used in high-temperature applications (Por exemplo, 600 ° c)?
   No—904L’s continuous service temperature é 400 ° c. Above this, its oxidation resistance and strength decline. Para 600 °C+ applications, choose 310S (resists up to 1100 ° c) or 347H (better creep strength). 904L is designed for corrosion, not extreme heat.