Cast analysis of chemical composition

[Martinos]

Hi dudes

I am dealing with problem regarding chemical composition deviations. Our foundry production is based on cast analysis - analyse of the melt before pouring. Chemical composition of each our material is described in customer standards without any deviations mentioned. In some standards the melt analysis is requested, but in some standard the part analysis is requested.

I know there exist some general standards with maximal alloved deviation of chemical elements. Do you know some standard like that in Europe (EN, DIN) or in USA? Now I am in the situation that I have e.g. silicon content requested 1,80 - 2,20 % and I need to know what should I do if melt analysis e.g. 2,25% is?

I will appreciate your experiences regarding this problem as well.

Thank you.

 

[arunmrao]

Please refer ASTM A 703 "Standard Specification for Steel Castings, General Requirements, for Pressure- Containing Parts1".

You can find the suitable tolerances for deviation in results between melt and product analysis. Hope it helps.



"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[mrfailure]

I never apply tolerances such as called out in ASTM A703 unless the product specification references them. I would list the part as nonconforming. In practice, casting houses should consider not sending out product that only meets composition when the tolerance band is applied in my personal opinion.

 

[EdStainless]

There are ones in AMS also (2248 for stainless).
Regardless of product form the standard chemistry applies to the melt. Product or check chemistries only come into play when required by spec or by the customer. And unless they say otherwise the tolerances are perfectly acceptable.
For example when I order flat rolled stainless I require that the check meets the original chemistry restrictions without the use of the added tolerance, because often after I make tubing i am required to provide another check and I want some margin to work with.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

@ failure, I agree with your observations. Quite often foundries encounter problem, while reporting low carbon spec, (0.03%), as they are not equipped with secondary refining techniques.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Martinos]

Thank you dudes for your opinions.

As a clear example I have material GX34CrMnNi20-10-6 (patented by our customer) where the part, not the melt analysis is required.

Our production is based on melt analysis. We check the chemistry right before the pouring (as is common) and we know if the melt is OK or NOK. The manganese content is specified as 9,5 - 10,5%, but customer need sulphur content 0,15 - 0,25% as well (part analysis). The melt analysis is OK, but of course there are strong reactions between Mn, S and O during pouring and the part chemical composiion is unpredictable (regarding Mn and S content). That means my melt analysis has to be "somehow out of spec" regarding Mn content to reach required Mn content in parts.

 

[MagBen]

Normal practice is to test chemistry right before pouring, and these results are certified to specs. Unless a spec. has a special request (< 5% chance) for a final check on the part, no chem. re-check is needed.
we VIM hundred of alloys, none of which ask for an internal recheck after melting. All elements, including Mn, are not changing at pouring vs ingot. some elements (not all) must be re-checked if refining (VAR, ESR) since we know % of these elements will be changed.

Your Mn variation may depend on melting types or your melting practices. Your could develop a reference table, such that you would have a target to shoot at pouring to meet your final chem. obviously the chem. check after melting is more accurate if assuming no segregation.

 

[arunmrao]

Most often, the analysis reported is the melt analysis taken from a sample just before pouring an ingot or a casting.

Product analysis is done, only if the buyer or the inspector finds a nonconformance in the report .

However, high S can definitely cause loss of Mn due to formation of MnS, only solution could be addition of S during last stage of melting operation.

Can you please let us know the application of this patented alloy. (Google search for it does not yield any result).


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Martinos]

Guys,
combination 10% Mn and 0,15 - 0,25% S in the most controversial metallurgic combination I've ever seen.

Here are our alloying practices:
1.) FeS into the furnace at late stage of melting; melting surface is subsequently covered by strong desoxidisers to avoid reactions of Mn and S with oxygen (here is the loss of manganese up-to 1,0% only during pouring)
2.) FeS into the ladle (here is the loss of manganese comparable with the previous practice)

Conclusion: after covering of melting surface with strong desoxidisers to avoid reaction of Mn and S with oxygen we are loosing Mn and S in principle only during pouring. It is atmospheric centrifugal casting on melting line. No possibility to avoid ŕeacions of melt surface with the oxygen during pouring and soldification.

Application of this alloy: it is replacement of standard Cr-Ni heat resistant steel in variable turbine geometry washers and adjusting rings. Our customer developed material like this. Customer is one of the most known turbocharger manufacturers in the world. Many of their materials have suplhur content up-to 0,4%, but are without high manganese content.

 

[tbuelna]

If reaction of the casting charge with oxygen is an issue, there are techniques that can be used to isolate the liquid metal from exposure to oxygen. This is a common problem with casting titanium, so titanium is vacuum cast. Some high performance aluminum or magnesium sand castings use a liquid metal feed system pressurized by inert gas to minimize the effect of oxygen exposure. So you might consider modifying your centrifugal casting process to use a vacuum or an inert gas purge.

 

[EdStainless]

We used to melt alloys with Al and Ti in them. We Ar shielded the melt and then Ar purged and shielded the ladle as well.
We accepted the losses in the actual casting process.
High S, this alloy will have very poor corrosion resistance, and poor high temperature strength, but it will machine easily and have self lubricating properties.

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P.E. Metallurgy, Plymouth Tube