Comparison Of 904L And 316 Stainless Steel: Ultra-High Corrosion-Resistant Vs Standard Corrosion-Resistant Austenitic Grade

904L and 316 are both austenitic stainless steels, with the core difference being corrosion resistance level (ultra-high vs standard) determined by alloying elements (high nickel-copper-molybdenum vs standard nickel-molybdenum). 904L is suitable for strong acid harsh environments, while 316 is suitable for medium corrosion environments. This comparison clarifies the selection balance between corrosion resistance requirements and cost.

Core Parameter Comparison

Parameter	904L Stainless Steel	316 Stainless Steel
Chemical Composition (wt%)	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	C≤0.08, Si≤1.00, Mn≤2.00, P≤0.045, S≤0.030, Cr=16.00-18.00, Ni=10.00-14.00, Mo=2.00-3.00, Fe=Balance
Mechanical Properties (Annealed)	Tensile Strength ≥490MPa, Yield Strength ≥215MPa, Elongation ≥35%, Hardness ≤250HB	Tensile Strength ≥515MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness ≤217HB
Service Temperature	-196℃ to 450℃ (continuous service)	-196℃ to 870℃ (continuous service)
Equivalent Grades	SUS904L (JIS), EN 1.4539, UNS N08904	SUS316 (JIS), EN 1.4401, UNS S31600

Key Performance Differences: 1. Corrosion resistance: 904L has high nickel (23-28%), molybdenum (4-5%) and copper (1-2%), PREN ≥32, excellent resistance to strong acids (sulfuric acid, phosphoric acid) and mixed acids; 316's PREN ≈25, suitable for medium corrosion environments. 2. High-temperature performance: 316's service temperature (870℃) is 420℃ higher than 904L (450℃), better high-temperature oxidation resistance. 3. Cost: 904L is 2-3 times more expensive than 316, belonging to high-end corrosion-resistant materials. 4. Formability: Both have good formability, but 904L's high alloy content increases deformation resistance, requiring higher stamping force. 5. Weldability: Both have good weldability, but 904L requires strict control of heat input to avoid intergranular corrosion.

Applicable Scenario Distinction: 904L is suitable for strong acid harsh corrosion environments, such as sulfuric acid production equipment (10-80% concentration), phosphoric acid storage tanks, chemical fertilizer plants, and pickling equipment. 316 is suitable for medium corrosion environments, such as chemical pipelines (weak acid/alkali), marine hardware, food processing machinery, and heat exchangers (industrial water).

Practical Q&A

Q1: Why is 904L suitable for sulfuric acid environments? A1: Its high nickel and copper content can form a stable passivation film in sulfuric acid (concentration 10-80%, temperature ≤80℃); copper can promote the dissolution of metal ions, inhibiting the anodic corrosion reaction, which 316 cannot achieve.

Q2: Can 316 replace 904L in weak acid environments? A2: Yes. In weak acid environments (such as 5% hydrochloric acid, room temperature), 316 can meet corrosion resistance requirements, and its cost is much lower than 904L; 904L is only necessary in strong acid environments.

Q3: What welding materials are used for 904L? A3: Use ERNiCrMo-4 welding wire; control welding heat input ≤150J/mm to avoid overheating; post-weld passivation treatment with nitric acid is required to improve corrosion resistance.

Q4: What is the service life difference between 904L and 316 in sulfuric acid environments? A4: In 50% sulfuric acid (60℃), 904L's service life is ≥10 years, while 316 will be severely corroded (corrosion rate >1mm/year) and can only be used for ≤6 months.

Q5: How to select between 904L and 316? A5: Choose 316 if the environment is medium corrosion (weak acid/alkali, chloride) and cost is a concern; choose 904L only if strong acid (sulfuric acid, phosphoric acid) harsh corrosion resistance is required, regardless of cost.