In precision machining you cannot speak generically of “stainless steel”. AISI 304 stainless steel proves it. Let’s find out what it is and what it is used for.
The term “stainless steel” covers many human activities, but when it comes to precision components, distinctions must be made. Rather than “stainless steel”, we should speak of “stainless steels” with different properties and uses.
What material is AISI 304?
AISI 304 is an austenitic stainless steel that is non-magnetic when annealed and slightly magnetic when cold-worked. It cannot be hardened by heat treatment, but it can be hardened by cold working.
What does AISI 304 mean? This steel has a chromium content of 18–20% and a nickel content of 8–11%. Its density is about 7.9 kg/dm³.
On the one hand, AISI 304 does not fear rust and resists oxidation and corrosion thanks to its chromium; on the other, its nickel content improves workability (e.g. bending, welding and machining). This austenitic stainless steel has a very low carbon content, tolerating up to 0.080%. As for the thermal conductivity of AISI 304 stainless steel, the reference value at 20°C is 15 W/(m·K).
AISI 304 vs other stainless steels
The American Iron and Steel Institute identifies various types of steel, all commonly (and loosely) referred to with the AISI prefix. In any case, this is a family of steels with at least 11% chromium (just like AISI 304). AISI 304 is not the only corrosion-resistant stainless steel used in various applications: there are also AISI 430 and AISI 316.
Comparing AISI 430 vs 304, the former is a ferritic steel suited to combustion chambers and furnaces thanks to its considerable thermal stability and high melting temperature. AISI 316, on the other hand, is an austenitic alloy with molybdenum, chromium and nickel, in which the molybdenum increases resistance to corrosion (both electrolytic and intergranular). This is why it is used in the chemical and food sectors.
How can you tell 304 from 316 stainless steel? The difference is molybdenum: AISI 304 contains none, while AISI 316 does. To tell 304 from 316, a special reagent can be applied to a polished area: a change in colour indicates molybdenum. Otherwise, it is AISI 304.
Which is the best stainless steel? The answer depends on the application, but austenitic stainless steel is usually the answer.
Applications of AISI 304
Thanks to its exceptional technical data sheet, AISI 304 stainless steel is one of the most widespread stainless steels. It corresponds to 18-10 food-grade steel used for pans and cutlery. But not only that: AISI 304 is also used in the oil, textile, chemical and pharmaceutical industries, as well as for car trim, architectural decoration and furnishings. It is commonly found in window and door frames, tanks, industrial autoclaves, pollution control devices and more.
Whatever the application, thanks to its chemical stability, AISI 304 stainless steel proves almost everlasting.