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Duplex steel flanges and stainless steel flanges (such as 304, 316 and other austenitic stainless steel flanges) are mainly reflected in the material composition, organization, performance characteristics and application scenarios. The following is a specific comparison:
I. Material composition and organizational structure
Characteristics Duplex steel flanges Stainless steel flanges (austenitic, for example)
Main components - ferrite + austenitic duplex organization (about 50% each)
- Containing chromium (Cr: 22% ~ 25%), molybdenum (Mo: 3% ~ 5%), nitrogen (N: 0.15% ~ 0.3%)
- Nickel (Ni: 4%~8%, lower than austenitic stainless steel) - mono austenitic organization
- Contains chromium (Cr: 18%~20%), nickel (Ni: 8%~12%)
- Molybdenum (Mo: 0% ~ 3%, some grades such as 316L contains molybdenum)
Organizational structure Duplex organization (ferrite + austenite) coexist, both the advantages of a single austenitic organization, toughness, but lower strength
Second, mechanical properties comparison
Characteristics Duplex steel flange Stainless Steel Flanges
Strength and hardness - Yield strength of the austenitic stainless steel is about twice the yield strength (eg, 2205 Duplex steel yield strength of ≥450MPa, and 316L is only ≥205MPa). Harder and more wear resistant - Harder and more wear resistant - Yield strength of 2205 duplex ≥ 450 MPa compared to 316L ≥ 205 MPa)
- Higher hardness and better wear resistance - Lower strength but better plasticity and toughness, easy to machine and shape
Toughness and brittleness - Toughness better than pure ferritic stainless steels but lower than austenitic stainless steels
- Lower risk of brittleness at low temperatures (better than ferritic stainless steels) - Excellent toughness, not easily brittle at low temperatures
Processing properties - Cold working is more difficult (easier to harden), need to control the machining process
- Welding needs to pay attention to heat input to avoid tissue degradation - Excellent processing performance, good weldability, suitable for complex structure manufacturing
Third, the difference in corrosion resistance
Characteristics Duplex steel flanges Stainless steel flanges
Resistance to pitting and crevice corrosion - Containing high chromium, molybdenum, nitrogen, high resistance to pitting corrosion index (PREN) (eg, 2205 duplex PREN ≈ 32, higher than the PREN ≈ 25 of 316L)
- Suitable for corrosive media containing chloride ions (Cl-) - Austenitic stainless steels (e.g. 316L) are more resistant to corrosion, but are prone to pitting and stress corrosion in high Cl- environments
Stress Corrosion Cracking (SCC) - Duplexes have a significantly better SCC resistance than austenitic stainless steels due to the reduction of stress concentrations (especially in Cl- environments) environment) - Austenitic stainless steel is prone to SCC under high stress + Cl- environment (e.g. 304/316L in seawater environment need to be careful)
Uniform corrosion Resistance to acid and alkali corrosion is comparable to austenitic stainless steel, but is more suitable for oxidation - reduction mixed environment Strong resistance to uniform corrosion, suitable for neutral or weakly corrosive environments
IV, Application Scenario Comparison
Scenario Duplex Steel Flanges Stainless Steel Flanges
Chemical and Ocean Engineering - Desalination, Salt Chemical Industry, Petroleum Extraction (H₂S/Cl-containing media)
- High corrosive and high stress environment (such as pressure vessels, pipeline connections) - Food medicine, chemical containers (non-high Cl-environment)
- General corrosive liquid transportation (e.g. water, weak acids)
Energy industry - circulating water systems in nuclear power plants, offshore wind turbines - conventional piping in thermal power stations, heat exchangers
Cost & Economics - Costs are higher than for normal stainless steels (e.g. 316L) but lower than for super austenitic stainless steels
- Better long-term corrosion resistance and lower overall cost - Lower cost (e.g. 304), suitable for low corrosion scenarios
V. Other key differences
Magnetism
Duplex: weakly magnetic due to the ferrite phase.
Austenitic stainless steels: usually non-magnetic (trace magnetism may occur after processing).
Heat treatment requirements
Duplex steels: solution treatment (fast cooling at high temperatures) is required to keep the duplex organization in balance and avoid precipitation of embrittled phases.
Austenitic stainless steel: heat treatment to eliminate stress or improve machinability, the process is relatively simple.
Summarize: how to choose?
Priority selection of duplex steel flange: need to meet the high strength, high corrosion resistance (especially anti-Cl- corrosion), anti-stress corrosion scenarios, such as ocean engineering, chemical high-pressure pipeline.
Priority is given to stainless steel flanges: high requirements for processing performance and toughness, or weak corrosive environments (e.g., atmosphere, fresh water), such as architectural decoration and food equipment.