Comparison of F44 (254SMO) and 904L Stainless Steel: High-Corrosion-Resistant Austenitic Stainless Steel

F44 (254SMO) and 904L are both ultra-high corrosion-resistant austenitic stainless steels, with the core difference being alloying elements (molybdenum, nitrogen) and corrosion resistance orientation. F44 focuses on pitting corrosion resistance in high-chloride environments, while 904L focuses on comprehensive corrosion resistance in strong acid environments. Both are suitable for harsh corrosive environments.

Core Parameter Comparison

Parameter	F44 (254SMO) Stainless Steel	904L Stainless Steel
Chemical Composition (wt%)	C≤0.02, Si≤0.80, Mn≤1.00, P≤0.030, S≤0.010, Cr=19.50-20.50, Ni=17.50-18.50, Mo=6.00-6.50, N=0.18-0.22, Fe=Balance	C≤0.02, Si≤1.00, Mn≤2.00, P≤0.045, S≤0.030, Cr=19.00-23.00, Ni=23.00-28.00, Mo=4.00-5.00, Cu=1.00-2.00, Fe=Balance
Mechanical Properties (Annealed)	Tensile Strength ≥650MPa, Yield Strength ≥310MPa, Elongation ≥40%, Hardness ≤280HB	Tensile Strength ≥490MPa, Yield Strength ≥215MPa, Elongation ≥35%, Hardness ≤250HB
Service Temperature	-270℃ to 315℃ (continuous service)	-196℃ to 450℃ (continuous service)
Equivalent Grades	SUS254SMO (JIS), EN 1.4547, UNS S31254	SUS904L (JIS), EN 1.4539, UNS N08904

Key Performance Differences: 1. Pitting corrosion resistance: F44 has high molybdenum (6-6.5%) and nitrogen (0.18-0.22%), pitting corrosion equivalent (PREN) ≥42, excellent resistance to chloride pitting corrosion; 904L's PREN ≥32, slightly worse than F44. 2. Acid corrosion resistance: 904L has high nickel (23-28%) and copper (1-2%), excellent resistance to strong acids (sulfuric acid, phosphoric acid); F44 is suitable for weak acid/high chloride environments. 3. Strength: F44's tensile strength (≥650MPa) is significantly higher than 904L (≥490MPa), with better mechanical properties. 4. High-temperature performance: 904L's service temperature (450℃) is 135℃ higher than F44 (315℃). 5. Cost: F44 is 20-30% more expensive than 904L, both are high-cost ultra-corrosion-resistant materials.

Applicable Scenario Distinction: F44 is suitable for high-chloride harsh environments, such as seawater desalination equipment, marine oil and gas platforms, chloride-containing chemical reactors, and coastal power plant heat exchangers. 904L is suitable for strong acid corrosion environments, such as sulfuric acid production equipment, phosphoric acid storage tanks, chemical fertilizer plants, and pickling equipment.

Practical Q&A

Q1: What is the significance of PREN value for F44 and 904L? A1: PREN (Pitting Resistance Equivalent Number) = Cr + 3.3Mo + 16N (for F44) / Cr + 3.3Mo + 30C + 16N (for 904L); higher PREN means better pitting corrosion resistance; F44's PREN ≥42 is suitable for high-chloride environments, 904L's PREN ≥32 is suitable for general corrosive environments.

Q2: Can 904L be used in seawater immersion environments? A2: It can be used, but its pitting corrosion resistance is worse than F44; in high-flow seawater, it may suffer pitting corrosion after long-term service; F44 is the preferred material for seawater immersion components (service life ≥15 years).

Q3: What welding materials are used for F44 and 904L? A3: F44 uses ERNiCrMo-3 welding wire; 904L uses ERNiCrMo-4 welding wire; both require strict control of welding heat input (≤150J/mm) to avoid intergranular corrosion; post-weld passivation treatment is required.

Q4: Why is 904L suitable for sulfuric acid environments? A4: Its high nickel and copper content can form a stable passivation film in sulfuric acid (concentration 10-80%, temperature ≤80℃), preventing acid corrosion; copper can promote the dissolution of metal ions and inhibit the corrosion reaction.

Q5: How to select between F44 and 904L? A5: Choose F44 if high-chloride pitting corrosion resistance is required (such as seawater, chloride-containing chemicals); choose 904L if strong acid corrosion resistance is required (such as sulfuric acid, phosphoric acid) and cost is moderate.