Nitrogen in CA6NM

[gieter]

What is the maximum amount of N that can be tolerated in CA6NM?

Apart from possible porosity problems due to the solubility, N is an austenite stabilisor. I expect the more nitrogen, the more retained austenite. From what percentage is this becoming a problem?

A close match to CA6NM: DIN/SEW X4CrNi13.4, 1.4313 even specifies a minimum of 0.02% N, but doesn't state a maximum.

Thanks for any help on this subject,

 

[metengr]

Are you sure about this being a minimum? Typically, values are reported as maximum, unless a range is given. Also, I checked various sources, and nitrogen is not listed as an alloy element for CA-6NM castings supplied under ASTM A 743 or A 487. There are cases where nitrogen and manganese are intentionally used to allow nickel to be reduced saving cost, and I believe this would be for austenitic grades of steel castings. CA-6NM is considered a martensitic grade, and I would be concerned with adding nitrogen because it is an austenite stabilizer. In most cases, changes in alloy elements for castings would have to be by agreement between the purchaser and the vendor.

 

[gieter]

Metengr,

I double checked on the 1.4313 material: according to the Euronorm (EN10088-1,2&3, EN10028-7, EN10272) this is the specified composition:
C<=0.05, Si<=0.70, Mn<=1.50, P<=0.040, S<=0.015, Cr=12.0-14.0, Ni=3.50-4.50, Mo=0.30-0.70 and indeed N>=0.020 without a maximum specified.
Mechanical properties (EN10088-2):
QT780 Rp0.2>=630MPa, Rm=780-980MPa, A5>=15%
QT900 Rp0.2>=800MPa, Rm=900-1100MPa, A5>=11%

 

[metengr]

gieter;
It looks like there is some difference in the stated chemical composition for CA-6NM as reported below from ASTM versus your values above. Just curious, what is the specified heat treatment for the 1.4313 material?

CA-6NM
12 Chromium,4 Nickel

C 0.06% Max
Mn 1.00% Max
Si 1.00% Max
P 0.04% Max
S 0.03% Max
Cr 11.5-14.0%
Ni 3.5-4.5%
Mo 0.40-1.0%


Mechanical
CA-6NM 12 Chromium, 4 Nickel
UTS [MPa]
110 [755]
YS
80 [550]

Elongation in 2" gage - 15%

RA - 35%

Heat treatment:

Heat to 1850ºF [1010ºC] minimum, air cool to 200ºF [95ºC] or lower prior to any optional intermediate temper and prior to the final temper. The final temper shall be between 1050ºF [565ºC] and 1150ºF [620ºC].

 

[metengr]

gieter;
For what it is worth, I decided to check on one of the web sites I frequent and found the 1.4313 material with some analyses information provided. The nitrogen content is listed at 0.02% by mass. I would presume a melter would shoot for 0.02% N.

http://www.metallograf.de/start-eng.htm?werkstoffkartei-eng/4313/4313.htm

 

[arunmrao]

gieter,
CA6NM being a martensitic alloy,it will be better to have Nitrogen levels at lower levels. However,since ASTM does not specify Nitrogen content,it is a factor,we have never considered while producing castings.

Else your concerns regarding higher level of retained austenite or gas porosityare true.

Just curious,how do you propose to add Nitrgen in the melt?

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[gieter]

Metengr, Arunmrao,

To be quite honnest the question arose because we did cast a heavy sectioned piece (430 mm) in a CA6NM-like alloy and accidentally had 0.077% of Nitrogen in the melt due to a mix-up of ingredients.

I contacted CTI UK and they calculated a maximum solubility of 0.14%. They couldn't say anything on the effect on mechanical properties.

Metengr,

On your question on the heat treatment: I found the alloy on the internet and apart from the QT780 and QT900 I don't have anymore details on the HT. I chould have mentioned that for what I found 1.4313 is not a casting alloy.

For now I'm a bit more at ease that the risk of N causing porosities is limited and I promise to come back to you with more results as I have them (in some weeks).