Comparison Of 304 And 316: General-Purpose Vs Molybdenum-Containing Corrosion-Resistant Austenitic Stainless Steel

304 and 316 are representative general-purpose and molybdenum-containing austenitic stainless steels, with the core difference being the addition of molybdenum (2.00-3.00%) in 316 and higher nickel content. Molybdenum significantly improves pitting and crevice corrosion resistance in chloride environments, making them suitable for different corrosion environment levels.

Core Parameter Comparison

Parameter	304 Stainless Steel	316 Stainless Steel
Chemical Composition (wt%)	C≤0.08, Si≤1.00, Mn≤2.00, P≤0.045, S≤0.030, Cr=18.00-20.00, Ni=8.00-10.50, 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 ≥515MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness ≤201HB	Tensile Strength ≥515MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness ≤217HB
Service Temperature	-196℃ to 870℃ (continuous service)	-196℃ to 870℃ (continuous service)
Equivalent Grades	SUS304 (JIS), EN 1.4301, UNS S30400	SUS316 (JIS), EN 1.4401, UNS S31600

Key Performance Differences: 1. Corrosion resistance: 316's molybdenum addition enhances resistance to pitting, crevice corrosion and chloride corrosion (pitting resistance equivalent PREN≈25), while 304's PREN≈18, which is poor in chloride environments. 2. Low-temperature performance: Both can work stably at -196℃, but 316's higher nickel content improves low-temperature toughness slightly. 3. High-temperature performance: 316's molybdenum addition improves high-temperature oxidation resistance in corrosive atmospheres, more suitable for high-temperature corrosive environments. 4. Cost: 316 is 30-40% more expensive than 304. 5. Formability: Both have excellent formability, but 316's higher alloy content increases deformation resistance slightly.

Applicable Scenario Distinction: 304 is suitable for low-corrosion environments, such as fresh water pipelines, indoor decorative parts, food processing equipment (dry or low-salt), medical equipment and indoor storage tanks. 316 is suitable for medium-corrosion environments, such as marine hardware, chemical equipment (weak acid/alkali), seawater pipelines, food processing machinery (saline food) and coastal engineering components.

Practical Q&A

Q1: Why is 316 more suitable for coastal areas than 304? A1: Coastal atmospheric environments contain high chloride ions; 316's molybdenum forms a more stable passivation film, which can resist chloride ion erosion, with a service life of 5-8 years; 304 will rust within 1-2 years in coastal areas.

Q2: Can 304 replace 316 in food processing? A2: Only suitable for dry or low-salt food processing (such as flour, grain); not suitable for saline or acidic food (such as seafood, pickles) processing, as it is prone to rust and contaminates food; 316 is the standard material for corrosive food contact scenarios.

Q3: What is the difference in welding materials between 304 and 316? A3: 304 uses ER308L welding wire, while 316 uses ER316L welding wire; the latter has matching molybdenum content to ensure corrosion resistance of the weld area.

Q4: What is the corrosion rate difference between 304 and 316 in seawater? A4: In static seawater, 304's corrosion rate is >0.5mm/year, while 316's corrosion rate is <0.1mm/year, which can meet long-term service requirements in seawater environments.

Q5: How to select between 304 and 316? A5: Choose 304 if cost is a priority and the environment is low-corrosion (dry, fresh water); choose 316 if chloride corrosion resistance is required, even if the cost is higher.