Comparison Of SUS304 And SUS316: General-Purpose Vs Molybdenum-Containing Corrosion-Resistant Austenitic Stainless Steel

SUS304 and SUS316 are representative general-purpose and molybdenum-containing austenitic stainless steels, with the core difference being the addition of molybdenum (2.00-3.00%) in SUS316 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	SUS304 Stainless Steel	SUS316 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	EN 1.4301, UNS S30400, AISI 304	EN 1.4401, UNS S31600, AISI 316

Key Performance Differences: 1. Corrosion resistance: SUS316's molybdenum addition enhances resistance to pitting, crevice corrosion and chloride corrosion (pitting resistance equivalent PREN≈25), while SUS304's PREN≈18, poor in chloride environments. 2. Low-temperature performance: Both can work at -196℃, but SUS316's higher nickel content improves low-temperature toughness slightly. 3. High-temperature performance: SUS316's molybdenum addition improves high-temperature oxidation resistance in corrosive atmospheres, more suitable for high-temperature corrosive environments. 4. Cost: SUS316 is 30-40% more expensive than SUS304. 5. Formability: Both have excellent formability, but SUS316's higher alloy content increases deformation resistance slightly.

Applicable Scenario Distinction: SUS304 is suitable for low-corrosion environments, such as fresh water pipelines, indoor decorative parts, food processing equipment (dry or low-salt), and medical equipment. SUS316 is suitable for medium-corrosion environments, such as marine hardware, chemical equipment (weak acid/alkali), seawater pipelines, and food processing machinery (saline food).

Practical Q&A

Q1: Why is SUS316 more suitable for coastal areas than SUS304? A1: Coastal atmospheric environments contain high chloride ions; SUS316's molybdenum forms a more stable passivation film, which can resist chloride ion erosion, with a service life of 5-8 years; SUS304 will rust within 1-2 years in coastal areas.

Q2: Can SUS304 replace SUS316 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; SUS316 is the standard material for corrosive food contact scenarios.

Q3: What is the difference in welding materials between SUS304 and SUS316? A3: SUS304 uses ER308L welding wire, while SUS316 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 SUS304 and SUS316 in seawater? A4: In static seawater, SUS304's corrosion rate is >0.5mm/year, while SUS316's corrosion rate is <0.1mm/year, which can meet long-term service requirements in seawater environments.

Q5: How to select between SUS304 and SUS316? A5: Choose SUS304 if cost is a priority and the environment is low-corrosion (dry, fresh water); choose SUS316 if chloride corrosion resistance is required, even if the cost is higher.