Different types of 316L i.e 1.4435 vs 1.4404

[tgreenwood]

Could someone please explain the difference of what appears to be two different subtypes of 316L S/S. (DIN 1.4435 and DIN 1.4404) Also, does BPE subgroup of ASME recognize DIN 1.4435 as a Pharmaceutical or Biotech grade? Would a problem occur if a 1.4404 fitting was unknowingly welded to a 1.4435 valve body?
When I am purchasing fittings to modify valves they are usually listed as 316L. I want them to also be DIN 1.4435, will I need to request a certificate or MTR?
Thanks in advance

 

[unclesyd]

It looks like the only difference is that the Din 1.4435 limits the amount of ferrite to <1.0% with a little different chemistry, Cr, Ni, Mo, while there appears no limit on ferrite Din 1.4404.
All my references equate both materials to ASTM specifications for 316 SS corresponding to the component used.
The apparent call out is to minimize the ferrite and possible corrosion associated with it. There should be on problem with the interchange of materials on one component as the welding rod should help with the welding and one side is the right material.

You should always get an MTR with any materials.

Maybe some with the Din specs will jump on board.

 

[tgreenwood]

unclesyd,

Thanks for the information. The limit on ferrite makes sense. In pharma/biotec grade tanks and fittings it seems that the 1.4435 is going to be less likely to corode and is therefore a better material for many applications than the 1.4404. I am surprised that it isn't specified more often. Most specs simply request 316L S/S.
Of course we see more and more requests for Hastelloy and AL6XN as time goes on. Higher price up front, but should have a longer life of use. As I am beginning to understand, there is more than one type of hastelloy as well. I have mostly encountered C276.

 

[Metalguy]

You need to keep in mind that the weld metal itself will probably have 5-10% ferrite, for resistance to weld cracking. What counts is the environment that your parts will see.

The various Hastelloys were developed to suit different severe corrosive conditions-some will dissolve in some acids/conditions where others will be almost unaffected. But in difference environments the reverse is true.

You really have to know what your expected envirn. will be in order to make an intelligent choice.

 

[tedg]

Hi tgreenwood:

Would suggest you visit <

http://www.nidi.org>

the web site of the Nickel Development Institute. Their technical section contains all kinds of detail on your question, and you can
get answers to psecific questions from their metallurgists.

 

[ijzer]

1.4435 has 2.5 to 3% Mo
1.4404 has 2 to 2.5 %Mo

The higher Mo will improve the corrosion resistance (pitting resistance).
Since Mo is a ferrite former , the 1.4435 needs a higher Ni content to balance the structure (Ni is a austenite former).