It seems like we have been talking about stainless steels for weeks …. and well, it actually is 2 months but we’ll just call it weeks! Hopefully you’ve been here the whole time. Diligently paying attention and taking notes. Seriously tho, thank you for watching and please subscribe if you find these videos interesting! Click this little mmi button right here.
This is the last of our series on the basics of the various types within the family of alloys classified as “stainless steels“. Today we’ll be discussing Nitrogen Strengthened Austenitic and Duplex Stainless Steels
First up is a category that has the austenitic type structure but these alloys have higher strengths achieved by using Nitrogen and higher levels of Manganese in the chemistry. All these types are non-magnetic. Various grades were developed and made popular with the proprietary name”Nitronic”. Three of the most popular are Nitronic 40, Nitronic 50 and Nitronic 60.
All have strengths nearly double those of the 300 series in the annealed condition.
Nitronic 40 (aka 21-6-9) is made in two variations depending on the carbon content. UNS S21900 has .point 08 % maximum carbon and UNS S21904 is restricted to .point 04 maximum carbon. In ASTM standards, the grades are designated as XM-10 and XM-11. AMS 5656 requires the low carbon version.
Nitronic 50 has a 55,000 psi minimum yield strength in annealed bar form and with up to 3 % Molybdenum for higher corrosion resistance,it is used where strength and corrosion performance are both important: For example in marine applications like boat shafting. Generic designation assigned to this alloy chemistry is UNS S20910. ASTM grade designation is XM-19 and this grade is found in many ASTM standards. A typical aerospace specification would be AMS 5764 for bar material.
Nitronic 60, aka UNS S21800, in addition to having high yield strength, is very resistant to galling. Galling is the type of wear when rubbing surfaces want to bond to each other. The ASTM grade designation is UNS21800. AMS 5848 would be an applicable aerospace standard for bar material.
Nitronic grades with the suffix “HS” indicate an even higher strength version that requires special processing at the producing steel mill. Proprietary named “Nitronic” alloys require the brand name product. UNS or ASTM grade designations are generic. Like the difference in Tylenol and Acetaminophen at the drugstore. Specifications …. as always….are key to determine the complete requirements.
Our second category, Duplex and Super Duplex stainless steels contain both austenite and ferrite in roughly equal proportions. Chemical compositions are balanced to achieve high strength, high corrosion resistance, stress corrosion resistance. The mixed structure has the best attributes of each and are most often found used in highly corrosive petrochemical applications. There is a response to a magnet due to the ferrite in the structure.
A common example of this type is grade “2205” , aka UNS S32205 can also be certified as UNS S31803 (which permits a wider range of some elements) . The UNS designation is used in ASTM standards and like the other types we have discussed in the entire series is in many. Other UNS designations for Duplex stainless …..S32550,S32750,S32950,S32977.
Other common Duplex grades found in ASTM standards
Ferralium 255 UNS S32550
2507 UNS S32750
Duplex alloys are commonly certified to NACE standards for use in the petrochemical industry.
So, we’ve reached the end of the road with our discussion on the basics of stainless steels. We’ve talked about austenitics, matensitics, ferritics, semit-austenitics, PH grades, Nitrogen Strengthened austenitics, and duplex stainless steels. Those have been discussed in our first 7 videos. For our previous videos, in case you missed them, not sure how….click here. If you have made it this far, please subscribe b/c you obviously find this captivating enough to make it to the end. Thank you for tuning in and come back next week where we’ll start on a new type of metal!