AOD Refining

Stainless, duplex and nickel alloys can only be refined in an AOD or VOD vessel. The ability to refine and readily control gas contents does not exist when dead melting in an induction furnace.

Goodwin carries out refining in an AOD vessel which removes volatile trace elements and metalloids, reduces carbon and sulphur; it produces a cleaner metal by removing non-metallic inclusions. The 'blow' can purge the melt of gases and metallic oxides to lower levels than are attainable by vacuum induction melting. Nitrogen can be added or removed at will.

Austenitic and Duplex Stainless Steels:

AOD refining allows close compositional control and the economic reduction of sulphur and carbon to very low levels. In normal induction melting the essential nitrogen is added via expensive nitrogen bearing ferro-alloys, in the AOD the nitrogen is added through the tuyeres as a gas. This is a very economical process route.

Super Nickel Alloys (alloy 825, 625, Has B-2, C276):

In super nickel alloys AOD refining results in properties in thicker sections which approach or match those in the thinner sections. The tensile properties are improved and the elongation properties can be increased by 100% compared with air or VIM melted materials. Nitrogen can be removed in the AOD process which is essential to minimise the risk of embrittling the alloy.

NACE requirements for AOD processing:

The American International standard NACE MR-0175 specification for materials resistant to Sulphide Stress Cracking (sour service) mandates AOD refining for certain materials. Including super nickel Ni-Cr-Mo alloys and the 29Ni20CrMoCu alloy CN7M.

The Castings Development Centre (CDC), the UK research organisation, recommends AOD refining of CA6NM (13Cr4Ni) in order to meet the NACE hardness requirements.

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