Low-cobalt austenitic stainless steels: melting pratices

[MaxKortau]

Hi everyone,

for a range of products for nuclear application (reactor parts) we do need to apply low-cobalt AISI 321 / AISI 321H grades in 2 options (type 1 - cobalt max. 0.2%, type 2 - cobalt max 0.025%, depending on application area and specification requirements)

I heard that the only proven way to guarantee cobalt limitation in austenitic steels is to use a well-sorted, Co-limited scrap as basis material. However, it's being discussed about effect of vacuum use in melting / remelting practice.

Is it actually possible to reduce cobalt in austenitic stainless grades, using VIM or VAR technics?

 

[EdStainless]

No, the Co and Ni are too similar.
There is no refinement technique.
Most Type 2 material is melting using a high fraction of virgin pure Ni.
And exceptionally well sorted scrap.
You need to be exceptionally careful in house with scrap segregation.
Type 2 scrap is valuable.

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P.E. Metallurgy, consulting work welcomed

 

[MadisonCameron]

Max Kortau The advantage of using VIM and VAR is that they allow greater control of the melting process and metal composition. The vacuum environment avoids oxidation and contamination of the metal by air or other impurities, which contributes to the creation of a clean and high-quality material. However, it should be noted that even when using VIM and VAR methods, it is not always possible to achieve the desired level of cobalt content in steel. The effectiveness of these methods depends on many factors, such as the initial cobalt content of the material, smelting and remelting process parameters, and the thoroughness of quality control.

 

[jessieleo99]

The initial material's cobalt content must still be low, as these techniques cannot completely eliminate cobalt if it is already present in high amounts. Using Co-limited scrap is essential to ensure low cobalt levels from the start.

https://powder.samaterials.com/

 

[EdStainless]

VIM and VAR will have zero impact on the Co content.
The issue is not only the feedstock (scrap and virgin charge materials) but the heal left in melt furnace as well.
I used to melt alloys that had to be <0.05% Cr, and that was a real pain.
We ended up using about 75% virgin charge material.

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P.E. Metallurgy, consulting work welcomed