Among the many types of stainless steel, austenitic stainless steel and ferritic stainless steel are the two most common categories. They have significant differences in microstructure, performance, and application areas. In this article, we will take a deeper look at the difference between austenitic stainless steel and ferritic stainless steel.
Definition Of Austenitic Stainless Steel And Ferritic Stainless Steel:
- Austenitic stainless steel: Austenitic stainless steel is an alloy steel with austenite structure as the main component, usually containing more than 18% chromium and more than 8% nickel. Typical austenitic stainless steels are 304 and 316 stainless steels.
- Ferritic stainless steel: Ferritic stainless steel is mainly composed of ferrite structure, usually containing 12% to 18% chromium and almost no nickel. Typical ferritic stainless steels include 430 and 446 stainless steels.
Mechanical Properties:
Strength and hardness:
- Austenitic stainless steel: It has high ductility and low strength and hardness.
- Ferritic stainless steel: Compared with austenitic stainless steel, ferritic stainless steel has higher yield strength and hardness, but poor ductility.
Corrosion resistance:
- Austenitic stainless steel: In most environments, especially those containing chloride ions, austenitic stainless steel exhibits excellent corrosion resistance. This is mainly due to its high chromium and nickel content.
- Ferritic stainless steel: Ferritic stainless steel has low corrosion resistance, especially in chloride-containing environments, and is prone to pitting. However, in specific acidic environments and high-temperature oxidation conditions, its corrosion resistance is better than austenitic stainless steel.
Welding performance:
- Austenitic stainless steel: Due to its good plasticity and toughness, austenitic stainless steel has excellent welding performance. Good mechanical properties and corrosion resistance can be maintained after welding.
- Ferritic stainless steel: Due to its low ductility and high hardness, ferritic stainless steel is prone to cracks during welding and has poor welding performance. Especially when welding thick plates, the heat-affected zone of the weld is prone to embrittlement.
Intergranular corrosion resistance:
- Austenitic stainless steel: During high temperature welding, chromium carbide may precipitate at the grain boundaries, causing austenitic stainless steel to be susceptible to intergranular corrosion under certain conditions. To avoid this problem, low-carbon or ultra-low-carbon austenitic stainless steels such as 304L and 316L are usually used.
- Ferritic stainless steel: Ferritic stainless steel has a low carbon content and its microstructure is not prone to chromium carbide precipitation, so it has good intergranular corrosion resistance. Ferritic stainless steel has advantages in welding applications because it does not undergo sensitization during welding.
Physical Properties:
Density and thermal expansion coefficient:
- Austenitic stainless steel: The density is relatively high, about 7.93 g/cm³, and the thermal expansion coefficient is high. This means that in high temperature environments, the dimensional changes of austenitic stainless steel will be more significant.
- Ferritic stainless steel: The density is relatively low, about 7.75 g/cm³, and the thermal expansion coefficient is low.
Thermal conductivity and resistivity:
- Austenitic stainless steel: The thermal conductivity is poor, but the resistivity is high.
- Ferritic stainless steel: has good thermal conductivity, but its resistivity is low.
Magnetism：
- Austenitic stainless steel: due to its face-centered cubic structure, it is usually non-magnetic or only very weakly magnetic.
- Ferritic stainless steel: due to its body-centered cubic structure, ferritic stainless steel is usually magnetic.
Chemical Properties:
Anti-oxidation properties：
- Austenitic stainless steel: exhibits excellent anti-oxidation properties at both room temperature and high temperature.
- Ferritic stainless steel: Ferritic stainless steel has better oxidation resistance at high temperature than austenitic stainless steel, especially in an environment exceeding 600°C.
Acid and alkali resistance：
- Austenitic stainless steel: exhibits good corrosion resistance in most acid and alkali environments and is suitable for chemical industry and other fields.
- Ferritic stainless steel: In some strong acid environments, ferritic stainless steel may show better corrosion resistance than austenitic stainless steel, but its acid and alkali resistance is generally weaker.
Application Areas:
- Austenitic stainless steel: widely used in food processing equipment, chemical equipment, nuclear power plant components, building decoration and other fields.
- Ferritic stainless steel: suitable for heat exchangers, automobile exhaust systems, household appliance parts, architectural decoration and other fields.
Material Cost:
- Austenitic stainless steel: Due to the high content of nickel and chromium, the cost of austenitic stainless steel is relatively high.
- Ferritic stainless steel: Ferritic stainless steel has no or only a small amount of nickel, so its cost is relatively low.
Austenitic stainless steel and ferritic stainless steel each have unique properties and advantages. When choosing stainless steel materials, you should choose the appropriate stainless steel materials according to your needs.
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