Cromium
Cromium
(OP)
In 316 melting process, do you loose cromium? if so what percentage.
Thank you, Mario
Thank you, Mario
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RE: Cromium
Yet I'm not a melt shop metallurgist, so I'd suggest you wait until one of those all-knowing folks answers here, or call your local stainless melting facility.
Good luck!
Lee
RE: Cromium
Thank you, Mario
RE: Cromium
What melting process are you using? How big is your melt, and how long does it take? Are you melting virgin materials only i.e. Fe, FeCr, Ni etc, or do you use a percentage of foundry returns/certified scrap plate? At what point in the melting process is the Cr added? Has the type of furnace lining changed recently? Have you got a new furnaceman?
I hope that gives you a few pointers where to look.
Regarding the other problem - will you get the opportunity to try a pair of controlled melts, identical in every way except for the deoxidation practice?
Best of luck
Chris
RE: Cromium
RE: Cromium
Addind Ti and Al will remove nitrogen from effective participation in the alloy even though it will be there on analysis. Check the ferrite/austenite ratios on good versus bad heats/casts and see how that correlates with shrinkage.
RE: Cromium
There are instances of isolated addition of aluminium causing pinholes. Are you referring to that. My best advise would be to cut off Al addition for one pour and observe the castings. This could nail the culprit.
RE: Cromium
RE: Cromium
Thank you for the help and time.
Mario
RE: Cromium
316 should normally have about 5-10% delta ferrite as cast or as-welded before any subsequent annealing to dissolve the ferrite.
In the above problem I don't suspect gas so this leaves phase balance as the main suspect. I think it's possible the alloy is balanced to solidify austenitically and therefore not having the shrinking phase change in the first metal to solidify to reduce internal volume thus leading to shrinkage in the last volume to solidify.
RE: Cromium
Since austenite is about 4% more dense than ferrite, this can make a big difference on the total shrinkage the casting will undergo in freezing and cooling to room temp.
The freezing front will also reject solute according to the portion of the phase diagram the particular composition falls into.
I think in Mario's case he should try to have
C+N = 0.06%
Mn = 1.8%
Ni = 10.2
Cr = 16.5
Mo = 2.1
Si = 0.4
S = low as possible
RE: Cromium
Iron crystals/grains can exist in several forms, two of which are face-centered cubic (FCC) and body-centered cubic (BCC). In steels (stainless included) the FCC phase is called austenite and the BCC phase is called ferrite. Depending on the chemical composition and some other factors, one or both of the phases may be present.
In the case of stainless steels, most alloys are intended to be either fully austenitic (3xx series) or fully ferritic (most of the 4xx series) when produced by wrought processes. Some alloys have been developed to have a duplex stucture, that is, both austenite and ferrite are present. And as mcguire mentioned previously, normally austenitic alloys like 316 can have small amounts of ferrite (from 5-20%) in the as-cast condition.
FYI, I purposely avoided discussing martensitic (4xx alloys like 410 or 420) or precipitation hardening stainless steels in this discussion for clarity/brevity.
mcguire,
Thanks for the refresher on stainless solidification.
RE: Cromium
RE: Cromium
C 0-.08
Cr 18-21
Cu -
Mn 0-1.5
Mo 2-3
Nb 0
Ni 9-12
P 0-.04
S 0-.04
Si 0-2.0
Fe remainder
Do you have any other suggestions based on this spec.
Thank you, Mario Estupinian
RE: Cromium
Despite all these controls, I still wonder if you can get your shrinkage porosity problem solved. You may neeed to rejig the mold and gating and risering.
RE: Cromium
Heat 1 Heat2 Heat3 Heat 4
C .02 .01 .02 .03
Cr 18.55 18.42 18.64 18.43
Cu .10 .16 .07 .09
Mn .47 .78 .28 .42
MO 2.31 2.31 2.24 2.29
Nb 0 0 0 .18
Ni 9.52 9.54 9.92 9.78
P .02 .02 .02 .02
S .01 .01 .02 .02
Si 1.74 1.93 1.60 1.91
Fe 67.27 66.82 67.20 66.84
Do you think having the Mn this low may do it?
Thank you, Mario
RE: Cromium
They will form TiN and TiC and AlN in the liquid phase if the concentrations are high enough and this will cause propblems with fluidity. This is a more likely contributor to porosity, since it would affect how well the casting is fed.
It also has a powerful effect on ferrite/austenite balance.
Sorry to give you a chemistry for 316 when you wanted CF8M.
They are quite different animals.
RE: Cromium
Thank you, Mario
RE: Cromium
The formula is [Al]x[N]>0.0025% then precipitation.
This formula is based on 409 stainless continuous casting. As Cr increase the solubility decreases, so it's very easy to get precipitation in your alloy. Furthermore these Al and Ti oxides and nitrides like to glom together. I suggest you re-examine your need to put the foo-foo dust in the melt unless it has a very well thought-out reason for being there. You have enough de-oxidation with the Mn/Si/Cr.
RE: Cromium
RE: Cromium
Thanks,
Irina