The full transcript for the above video is found here. In this video we are trying to answer the following questions: What is austenitic stainless steel? What grades are considered austenitic stainless steel? Can austenitic stainless steels be heat treated? What does 18-8 stand for? What’s the difference between austenitic and ferritic stainless steels?
Continuing our series on stainless steels, this video is focused on the most commercially popular Austenitic types or grades. In this video we will discuss 303 or 303S, 303 Se, 304, 304L, 316, 317 and 317L.
From our introduction to stainless steels video you know that Chrome is primarily what makes these “stainless” steels corrosion resistant or, it helps make stainless STAINLESS. Other elements also affect the properties of the commercial standard alloys. Well what are those other elements Michael? I am so glad you asked. In addition to answering that, there’s a little additional terminology along with the elemental descriptions that apply here….. When you see a suffix of “L”, it indicates a low carbon version of the grade. This is NOT to be confused with the alloy steel connotation of something lie 11L17 or 11L37 both of which mean LEAD. In our discussion of stainless steel HERE, the “L” again, means LOW CARBON. A suffix of F indicates a free machining version as does “S” for Sulfur added or “Se” for Selenium added. Whenever we mention a %, we mean percent by weight. So in a 18% Cr alloy, there would be 18 pounds of Cr in 100 pounds of metal.
When Chrome is added to iron it tends to stabilize a ferritic structure. Molybdenum is also a ferrite stabilizing element. Nickel and Manganese act to stabilize an austenitic structure and are present in various proportions in all the austenitics. Other elements present promote either austenite or ferrite in the metallurgical structure. In this case, the balance in the chemical composition assures the austenitic structure.
In this family of standard grades, type 304 is the most popular of the “18-8” grades. Now, do you remember what 18-8 stands for? In this case, I’ll tell you 🙂 18% nominal Chrome content and 8% nominal nickel content. General corrosion performance is very good. The low carbon 304 “L” grade is recommended for applications involving welding or heat cycles above 900 deg. F.
Type 303 (or sometimes shown as 303S) has .15 % minimum Sulfur added which aids in the machining characteristics but with some loss of corrosion performance. 303 Se substitutes Selenium for S to Achieve the improved machining with less impact on some other properties but is much less commonly used and much more costly. In case you ever need to BUY any 303Se (I know a guy). It’s a secret, me.
Type 316 has 2-3% Molybdenum which raises the corrosion performance, particularly in chloride environments. Nickel content is increased to keep the austenitic structure.
317 has yet higher Cr, Ni and 3-4% Molybdenum for another step higher in corrosion performance. 317 “L” versions are suited for welding applications more so than regular straight grade 317.
Additional alloy grades exist for specialized applications. In general, higher Cr and Ni for high temperature applications. Nitrogen strengthened alloys in the 200 series or “Nitronic” grades. For any additional information, see future videos or comment below and ask any questions you might have.
A word of caution here about specifications. Basic grade definitions are frequently modified by restricting chemistry further by adding requirements and testing to verify conformance to that specification. So the grade or type is only the beginning of the requirements that may apply to a metal you buy. If you ARE buying metal and have questions, Michlin Metals is here to help.
I hope you have enjoyed this video. Make sure to subscribe and don’t forget to check out all our previous videos as well. Thank you and stay tuned! Michael Michlin Metals – Out!