Carbon boil
Carbon boil
(OP)
Recently I came a cross several publications mentioning "carbon boil". As I understand it, it's a foundry furnace treatment used for e.g. stainless steel to lower the carbon content.
My questions:
1. When is it used?
2. How is it initiated, controled and ended?
3. What results may be expected?
4. Are there alternatives (apart from AOD)?
Thanks for any help,
My questions:
1. When is it used?
2. How is it initiated, controled and ended?
3. What results may be expected?
4. Are there alternatives (apart from AOD)?
Thanks for any help,






RE: Carbon boil
It is more of a steelmaking practice than a foundry technique, although I have seen it at larger foundries. In the olden days of open-hearth furnaces, typical C removal rate was 0.12-0.18 wt. % C per hour. Faster rates were obtained by the basic oxygen furnace (BOF) and other top-blown oxygen processes [I think 4x faster]. – The Making, Shaping and Treating of Steel, 9th Edn., p. 374. The oxygen blow also removes excess Mn and Si as slag.
I don’t believe carbon boil has much relevance in stainless steelmaking per se, except as a preparatory steelmaking step. Nearly all SS is made by melting scrap in electric arc furnaces, by either AOD (argon-oxygen) or VOD (vacuum-oxygen) processes. The carbon content is reduced by oxygen blowing, and then the excess oxygen is removed prior to alloying additions. Don’t want to make Cr2O3. C content is determined by analysis rather than visual observation of ‘carbon boil,’ which would be difficult if blowing argon or pulling a vacuum. After removal of the initial, oxidizing slag (which contains P and S impurities as well as CaO, MnO & SiO2), a vacuum is applied or argon is blown through the melt to aid CO and excess O removal. This reduces the amount of CaC2, FeSix or Al needed to deoxidize the melt, minimizing the amount of reducing slag and resulting in a cleaner steel (fewer oxide inclusions). Then, the easily-oxidized Cr is added as FeCr2. [CaC2 can be added to reduce Cr2O3 from slag back into the liquid alloy, but I don’t know if this is much used.]
Hope this helps. My knowledge of steelmaking is rather dated, but the chemistry is unchanged although newer techniques (e.g., methods of applying vacuum) have been adopted.
Ken
RE: Carbon boil
Thanks for the torough explanation.
I can inform you that it actually is used by foundries and even on alloy's you (I certainly) don't expect it: Hadfield Steel. It's also used to make NiCr- and NiCrMo-alloys.
The problem (as always in the foundry world) is that so little can be found on the actual procedures.