The microstructure of austenitic stainless steel is face-centered cubic austenite, and this structure itself isnon-ferromagnetic. At the same time, because no phase transformation occurs during cooling, itcannot be hardened by heat treatment like martensitic stainless steel; its strength can only be increased by cold working (such as cold rolling or cold drawing).
The key to sustaining this structure isnickel (Ni)and other austenite-forming elements. The classic “18-8” steel (approximately 18% chromium and 8% nickel) is the originator and foundation of austenitic stainless steel.
The 300 series is the most common in daily industrial and consumer applications, and two grades form the basic dividing line:
304: the most widely used benchmark grade.It performs in a balanced way in most mild everyday environments and food-processing environments, and its formability is usually better than that of 316.
316: the advanced choice for corrosion resistance.By adding approximately2%–4% molybdenum (Mo)to the 304 composition, it significantly improves resistance topitting corrosion(especially in chloride-containing environments). Although the two grades are similar in basic characteristics such as being non-magnetic, not hardenable by heat treatment, and easy to form, 316 is superior in corrosion resistance (especially pitting resistance).
There are also low-carbon versions (such as 304L and 316L) to improve corrosion resistance after welding, as well as stabilized grades with added titanium or niobium (such as 321 and 347).
The performance characteristics of austenitic stainless steel are very distinct, and its strengths and weaknesses are almost two sides of the same coin:
Core Advantages
Excellent ductility, toughness, and formability: This is its most prominent advantage, making it easy to perform cold working such as deep drawing and bending. Itmaintains good toughness at low temperaturesand has no obvious ductile-to-brittle transition temperature.
Excellent weldability: Most grades are easy to weld, which laid the foundation for its wide application.
Good corrosion resistance: It has good resistance to oxidizing media and to many organic and inorganic acids.
Inherent Shortcomings
Relatively low strength: Itsyield strength(on the order of about 250 MPa) is significantly lower than that of duplex stainless steel. This means that in the design of pressure-bearing equipment, a larger wall thickness is often required to ensure strength, with corresponding increases in material consumption and cost.
Sensitive to chloride-induced stress corrosion: In warm chloride-containing environments, conventional austenitic stainless steels (such as 304 and 316) have a relatively high risk ofstress corrosion cracking. This is precisely one of the main driving forces behind the development of duplex stainless steel.
Poor hardness and wear resistance: The face-centered cubic structure itself is not very hard, resulting in unsatisfactory wear resistance.
