Nitrogen In Type 321 Stainless Steel
Nitrogen In Type 321 Stainless Steel
(OP)
What is the basis for the differences in minimum titanium content in Type 321 stainless? SAE-AMS specifications for aircraft tubing (e.g., AMS-5557) require minimum titanium = 5 x (carbon PLUS NITROGEN). Some comparable ASTM Specifications say the same thing (e.g., A-269) while others say required minimum titanium = 5 x carbon (e.g., A-213). Why the differences? What is the beneficial / detrimental influence of nitrogen?





RE: Nitrogen In Type 321 Stainless Steel
(mcguire will be along shortly I'm sure)
Nick
I love materials science!
RE: Nitrogen In Type 321 Stainless Steel
RE: Nitrogen In Type 321 Stainless Steel
RE: Nitrogen In Type 321 Stainless Steel
321 was designed before they were able to make low carbon 304. It's kind of obsolete now. Some specs linger long after their usefulness, and I can't address why some are 5 x carbon. The most erudite specs call for Ti=5(C+N).
In this grade the titanium combines with the carbon before the carbon can combine with chromium and cause sensitization. Titanium combines preferentially with oxygen, nitrogen, sulfur and then carbon. It's the carbon one is trying to eliminate. ( Sulfur and oxygen are also bad, but this wasn't understood when the grade was designed.) Unfortunately, the nitrogen, which is quite beneficial, has to become TiN before the carbon can become TiC ( actually Ti2CS ).
Modern practice when making this grade of steel is to reduce C and N to as low as possible, around 0.015 each, and then use the minimum titanium to get the four times C+N.
Titanium nitride makes a slaggy residue that is hard to float off and makes surface defects. That is the only bad thing about nitrogen in 321.
Make sure you really want 321 and aren't just following obsolete practice. 304L is the more modern answer and it's cheaper.
RE: Nitrogen In Type 321 Stainless Steel
Does anyone have a familiarity with the Ti requirements of 321 per DIN, JIS, etc.???
Your further comments would be welcome. Thanks!!!
RE: Nitrogen In Type 321 Stainless Steel
RE: Nitrogen In Type 321 Stainless Steel
RE: Nitrogen In Type 321 Stainless Steel
A good portion of the C-130 bleed air ducting, from the nacelles inboard, is 321CRES, insulated. Operating temps in the 600-800+F range.
In service failures of the CRES ducting from stress-corrosion cracking is driving the Air Force to convert existing C-130 pneumatic ducting to Inconel 625.
Also, the Air Force C-141 aircraft utilizes ducting fabricated from AM350 material, and it too is experiencing in-service failures from stress-corrosion cracking. As a result, a portion of flight critical ducting is being reconfigured to utilize Inconel 718 material.
RE: Nitrogen In Type 321 Stainless Steel