As we know, stainless steel can be divided into martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, ferritic-austenitic duplex stainless steel, and precipitation-hardening stainless steel.
Now let’s talk about Austenitic stainless steel.
Basic information
Basic Type: 304 (1.4301)
Often called 18/8 Stainless (because it contains 18% Chromium & 8% Nickel)
Magnetic: Non magnetic.
Cannot be hardened by heat treatment, but is hardenable by cold working – called work hardening.
Excellent corrosion resistance.
Easily fabricated and formed with good cold formability.
Excellent weldability in all thicknesses.
Suitable for both high and low temperatures (Cryogenics at -190C to 8709C).
Features
The most important type of stainless steel is austenitic stainless steel, whose output and consumption account for about 80% of the total stainless steel, with the largest number of steel grades.
There are 47 austenitic stainless steel grades listed in the national standard.
The classic austenitic stainless steel is called 18/8 Stainless, which contains about 18% chromium and 8%~10% nickel. It is the most typical and basic representative steel. Other austenitic stainless steels are developed on the basis of 18-8 steel.
Advantage
Corrosion resistance. Compared with other types of stainless steel, its corrosion resistance is the best one.
Toughness, plasticity, and weldability. It has excellent toughness and plasticity, is easy to carry out various complex cold and hot deformation processing, and has excellent weldability.
Magnetic and thermal conductivity. Pure austenitic stainless steel is non-magnetic, cannot pass phase transformation, and can only be strengthened by cold working. Compared with ferritic steel, its thermal conductivity is low and its coefficient of linear expansion is large.
Disadvantage
Expensive
Localized corrosion
This phenomenon is closely related to intergranular corrosion. After being heated at about 480~850°C (called sensitization), intergranular corrosion will occur in some corrosive environments.
Tips: In the early 1930s, Bein et al. proposed the famous “chromium-poor theory”, which attributed sensitization to the precipitation of chromium-rich carbides at the grain boundary, causing “chromium-poor” in the adjacent area of the grain boundary. The steel in the chromium-poor zone has a tendency to intergranular corrosion. This theory has been confirmed by a large number of experiments, and a consensus has been reached.
What is the difference between austenitic and ferritic stainless steel?
Ferritic stainless steel is magnetic, austenitic stainless steel is non-magnetic.
Ferritic stainless steel has higher hardness and resistance to localized corrosion and chloride stress corrosion than austenitic stainless steel.
Unlike austenitic stainless steel, ferritic stainless steel is sensitive to intergranular corrosion and has high-notch sensitivity. This is the reason for the limited use of ferritic stainless steel.
