AISI 904L Super-Austenitic Stainless Steel: Propriétés, Fabrication & 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. Ce guide décompose ses spécifications clés, traits de performance, and real-world uses to help you select it for high-corrosion projects.

1. Aperçu du matériel & Spécifications clés

Understanding 904L’s unique composition and standards is critical to leveraging its full potential. Vous trouverez ci-dessous une ventilation claire de ses propriétés essentielles.

Composition chimique & Normes

As a904L super austenitic grade, c'est904L chemical composition se démarquer: 904L high nickel content 23–28 % et904L 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 (Système de numérotation unifiée)
• 904L EN 1.4539 équivalent (Norme européenne pour les performances de correspondance)
• 904L ASTM A240 / 904L ASME SA-240 (pour les assiettes, feuilles, et les bandes)

Physique & Propriétés mécaniques

904L delivers reliable strength while prioritizing corrosion resistance. Des mesures clés sont organisées dans le tableau ci-dessous:

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. Résistance à la corrosion & Performance environnementale

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

Traits clés résistants à la corrosion

• Piqûres & Crevice Corrosion: It has exceptional 904L pitting corrosion resistance and a high 904L crevice corrosion threshold (resists attack in tight gaps, Par exemple, heat exchanger gaskets).
• Stress Corrosion Cracking: It offers 904L chloride stress corrosion cracking immunity—even in high-chloride environments like seawater or brine.
• Résistance chimique: It handles 904L sulfuric acid corrosion (resists 50% sulfuric acid up to 60 ° C), 904L phosphoric acid resistance (ideal for fertilizer plants), et 904L nitric acid performance (resists dilute nitric acid).
• Eau de mer & Brine: Le 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 mois, while 904L shows no corrosion after 5 années. A Saudi desalination plant switched from 316L to 904L for piping—leaks dropped by 90%.

3. Propriétés à haute température & Résistance à l'oxydation

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).

Traits critiques à haute température

• Résistance à l'oxydation: It resists rust up to 400 ° C-904L oxidation resistance up to 400 ° C makes it suitable for warm chemical processes (Par exemple, 350 °C sulfuric acid evaporation).
• Force de fluage: 904L creep rupture data shows it can last 10,000+ des heures de 300 °C under light stress. Pour des tâches plus courtes, 904L short-time tensile at 350 ° C is ~350 MPa.
• Limites de service: Le 904L continuous service temperature est 400 ° C, et le 904L intermittent service limit est 450 ° C. Beyond this, oxidation and strength decline.
• Thermal Shock Resistance: 904L thermal shock resistance is good—it handles moderate temperature changes (Par exemple, depuis 300 °C to room temperature) Sans craquer.

Une étude de cas: A U.S. power plant used904L flue-gas desulfurization (FGD) composants (opérant à 350 ° C). Après 8 années, no corrosion or deformation occurred—unlike the previous 316L components that failed every 2 années.

4. Traitement thermique & Contrôle de la microstructure

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

Processus de traitement thermique essentiels

• Recuit de solution: Heat to 1050–1150 °C, tenir 30 à 60 minutes, puis à coucher à l'eau (le 904L water quench requirement is critical to dissolve carbides and prevent sensitization). This step ensures 904L carbide precipitation avoidance.
• Travail chaud: Utiliser 1150–900 ° C as the 904L hot working range for forging or rolling. Cela maintient le matériau ductile et évite la fissuration.
• Travail au froid: 904L cold working strain hardening is moderate—cold forming (Par exemple, flexion) increases strength but may require annealing to restore ductility.

Autres considérations

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

5. Soudage, Fabrication & Directives d'usinage

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

Conseils de soudage

• Métal de remplissage: Utiliser 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.
• Préchauffer & Post-Weld Care: 904L no preheat required for most thicknesses. Après le soudage, perform 904L post-weld cleaning passivation (with nitric acid) to restore the protective oxide layer.
• Soudabilité: 904L weldability rating is “excellent”—it has strong 904L hot cracking resistance and works for 904L dissimilar welding to duplex stainless steel (Par exemple, in offshore structures).

Usinage & Formation

• Vitesses & Aliments: 904L machining speeds and feeds should be 15–20% lower than carbon steel. Par exemple, use 60–80 m/min speed with 904L tool life with coated carbide (TiAlN coatings last 2x longer than uncoated tools).
• Formabilité: 904L formability deep drawing works well for parts like chemical reactor heads—use lubrication to avoid scratching the surface (scratches can lead to corrosion).
• Contrôle de la distorsion: Utiliser 904L distortion control techniques (Par exemple, serrage pendant le soudage, refroidissement lent) to keep parts true to size.

6. Formulaires de produit, Tailles & Chaîne d'approvisionnement

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

Formulaires de produit communs

• Assiettes & Feuilles: 904L stainless steel plate thickness chart ranges from 3 mm à 200 MM; 904L sheet gauge sizes (16 évaluer 1/2 pouce) are ideal for pharmaceutical equipment.
• Tuyaux & Tubes: 904L seamless pipe ASTM A312 (for high-pressure chemical piping) et 904L welded tube dimensions (for low-pressure seawater lines).
• Bars & Raccords: 904L round bar stock (10 mm à 300 diamètre mm), 904L angle iron sizes (20×20 mm à 100×100 MM), et 904L threaded rod grades (Grade 1 for general use).
• Formulaires de spécialité: 904L coil slit widths (10 mm à 1250 MM), 904L hollow bar suppliers (Pour les pièces légères), 904L custom forgings (Par exemple, reactor nozzles), et 904L clad plate suppliers (for cost-effective large structures).

Conseils de chaîne d'approvisionnement

Work with global suppliers who stock904L seamless pipe ASTM A312 et904L clad plate suppliers—these forms have longer lead times. Pour des projets urgents, prioritize suppliers with local inventory of common sizes.

7. Applications de l'industrie & Études de cas

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

• Traitement chimique: 904L chemical process reactors (for sulfuric/phosphoric acid), 904L sulfuric acid storage tanks, et 904L phosphoric acid evaporators.
• Water Treatment: 904L seawater heat exchangers et 904L desalination plant piping (resist high chloride levels).
• Pouvoir & Industriel: 904L flue-gas desulfurization (FGD) composants et 904L scrubber systems (remove sulfur from exhaust gases).
• Utilisations spécialisées: 904L pharmaceutical equipment (meets hygiene standards) et 904L paper mill bleach washers (resist chlorine-based bleaches).

Un vrai exemple: A Brazilian fertilizer plant replaced 316L with 904L for phosphoric acid evaporators—maintenance costs dropped by 70%, and evaporator lifespan increased from 3 des années à 12 années.

Perspective de la technologie Yigu

À la technologie Yigu, we recommend 904L for clients facing extreme corrosion. Nous achetons904L ASTM A240 plaques et904L seamless pipe ASTM A312 des moulins certifiés, 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.

FAQ

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 (échangeurs de chaleur). Its 904L PREN 34–36 et chloride stress corrosion cracking immunity outperform 316L. Use 316L for milder environments (Par exemple, transformation des aliments) to save cost.
2. Ai-je besoin de traitement thermique après le soudage (Pwht) for 904L?
   Non-904L no preheat required and PWHT is unnecessary. Plutôt, perform 904L post-weld cleaning passivation (avec 20% acide nitrique) 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 (Par exemple, 600 ° C)?
   No—904L’s continuous service temperature est 400 ° C. Above this, its oxidation resistance and strength decline. Pour 600 °C+ applications, choose 310S (resists up to 1100 ° C) or 347H (better creep strength). 904L is designed for corrosion, not extreme heat.