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Conventionally melted iron contains 4-10 PPM of free oxygen, which makes it difficult to cast quality parts. Deoxidized iron contains close to 1 PPM free oxygen – minimizes casting surface and sub-surface defects.

Why Deoxidize Molten Iron?

April 10, 2023
Very small quantities of free-oxygen atoms have a profound effect on molten iron, and it’s up to executives and managers to grasp the big picture.

Foundries are reluctant to try new technology. Ferrous foundry operators maintain a tolerance for slag-filled ladles containing iron with small amounts of free oxygen – not believing that may affect the quality of the whole mass of molten metal. Conventionally melted iron contains 4-10 PPM of free oxygen, which changes the iron into a material that is more difficult to cast into perfect castings.

Deoxidized iron contains close to 1 PPM free oxygen. Very low levels of free oxygen produced by deoxidation leads to no precipitated, nano-sized oxides in the cast iron – so no oxides remain to turn into the unwanted surface and sub-surface casting defects.

Iron deoxidation is a process based in science and demonstrated at a few foundries that produces precisely what is claimed, and still it may be difficult to accept all the benefits attributed to deoxidized iron.

Many ferrous foundry metallurgists and operators maintain their out-of-date perceptions of cast iron, so the appeal must also be made to foundry executives – who should be eager to understand how:
-  Coke-fired cupola melting furnaces can operate in compliance with environmental regulations; and,
-  Greenhouse gases can be cut in half, or nearly eliminated;
-  Environmental targets can be met;
-  Slag formation is undesirable and can be entirely avoided;
-  No oxidation losses during the melt cycle are possible;
-  1.0% casting scrap rates are possible;
-  Energy consumed in the casting process can be reduced manyfold.

Now those foundry CEOs can recognize that all the big issues their businesses must resolve can be addressed with technology available today. Their role is simply to initiate the changes.

One-percent casting scrap rates can be attained at any ferrous foundry that recognizes that free oxygen contained in the molten iron is the major cause for casting scrap – and deals with it. Most of these foundries don't realize the intolerable levels of free oxygen in their molten iron, and even fewer realize the adverse effects on their foundry operation. One-percent casting scrap rates cannot be reached when excess free-oxygen atoms exists in molten iron.

Melt cycles, in electric furnace and in cupolas, can achieve full recovery of all ingredients, alloys, and metallics. Whatever is intended to be melted can be done in a manner that no oxidation losses occur during the melt cycle. This is far different from what occurs today.

Executive action

The CEO that impresses this fact upon his team can reach all these targets quite easily.

  Oxidation during the melt cycle must be prevented or countered, and it is, but few foundries have adopted the available technology and products.

  Slag formation must be prevented. The CEO must emphasize slag formation is a by-product of oxidation, and that oxidation must be (and has been shown) to be easily prevented. The executive must make sure all technologists are on-board, knowing how to stop oxidation.

  In cupola operations, the CEO must insist the iron oxide produced on the surface of the descending molten iron droplets is instantly chemically reduced and does not spread throughout the furnace. The CEO must prove to all that slag produced during the cupola operation can be reduced over 80%, and the possibility of eliminating limestone additions exists (as demonstrated in deoxidized cupola operations.)

  The CEO must require reduced coke rates; near 6% coke rates has been demonstrated by deoxidized cupola operations.

GHG and other effects

Cupola operations today, utilizing 9-12% coke rates, can be altered to cut greenhouse gas production nearly in-half. Low coke rates near 6% are possible in all cupolas. Efficient cupola operation will prove to generate less GHG per unit of molten iron, compared to coal-fired or gas-fired process electricity generation. The CEO must firmly resist efforts to switch to EF melting.

CEOs will agree poorly operated cupola melting operations produce excess GHGs but can aggressively state properly operated cupola melting operations produce the benchmark for GHG / unit molten iron when all melting methods are compared. The startling revelation is that cupola melting will produce lower GHG levels than EFs, comparing apples to apples.

Sharp executives will realize that the metallurgical improvements possible when free-oxygen atoms are eliminated in molten iron is the vision of the future. When deoxidized, cast iron or ductile iron will almost become new grade of iron.

Deoxidized cast iron is very clean, with no slag forming from within the molten metal mass. Its strength improves nearly 25% with deoxidation. Its metallurgical characteristics are unsurpassed. Precipitated graphite is optimized. Its machinability sets the benchmark. Its fluidity is incomparable to conventionally melted iron.

  Base ductile iron deoxidized before magnesium treatment is also extremely clean, with no slag forming in the molten metal. It’s as-cast elongation is unsurpassed reaching 22% elongation without annealing heat treatments. Properly deoxidized iron’s cover slag contacting the molten mass will be iron oxide-free.

Tensile strength exceeds 100,000 psi, coupled with the elevated elongation results. Graphitic nodule size and distribution are optimized. Adding materials to produce graphite nucleation sites is not necessary or wanted.

  Carbide-forming tendencies with elevated residual alloys (e.g., chrome) are nearly nil in ductile iron that has been deoxidized prior to treatment. Its machinability establishes the benchmark rating, as is casting fluidity due to the metal’s cleanliness.

  Deoxidized base iron de-sensitizes the effect of carbide-forming elements such as chrome in ductile iron. Chrome levels near 0.30% have been reported as carbide-free, with 20% as-cast ductility. This de-sensitizing affect allows frag-steel substitution for P&S metallic scrap in the EF charge. This new technology is mostly unknown by ductile iron producers today.

An 18-year-veteran ductile iron lab technician and a long-time pipe-fittings foundry operator reported that as-cast elongation levels nearing 20% had never before been achieved without substituting the frag-steel in the cupola charge with P&S, to reduce chrome contamination levels. The as-cast elongation levels for an entire melt campaign neared or exceeded the 20% mark. This suggests the seriousness of the changes being discovered for metallurgical responses within the ductile iron matrix due to deoxidation.

Controlling interactions

The role of the oxygen atom has proven to be very complex. Deoxidation is exposing the far-reaching and unwanted interactions for oxygen atoms in molten iron – and that news must be emphasized to all ferrous foundry technologists.

The CEO can point out that alloys commonly added to enhance tensile strength (e.g., copper) can be eliminated due to the pure base iron's improved tensile strength, as-cast. And the CEO also can indicate that many ductile-iron foundries automatically add copper to every heat, as insurance, to meet physical strength requirements. Eliminating copper additions produces easy-to-calculate big savings.

Magnesium alloy treatment also can be reduced since all oxygen present in the base iron readily combines with magnesium added in the treatment, creating MgO, which is inert and does not contribute too nodularity. Because no free oxygen is present in deoxidized iron, less magnesium is needed to produce the nodularity desired. Typically, 15% or more magnesium treatment alloy can be saved.

In conventional ductile iron, magnesium's spectrographic analysis includes both the combined magnesium in the form of MgO, and the free magnesium needed for nodularity. In deoxidized iron, no MgO is present, which reduces the minimum-level spectrographic magnesium needed for perfect nodularity.

The CEO will point out base ductile iron deoxidation eliminates all iron oxide contacting the molten iron and therefore cuts-off the supply of free-oxygen atoms to the treated ductile iron, substantially extending fade time, which provides needed flexibility to foundry operators.

Show some energy

Overall, for EF melting, eliminating oxidation losses saves the energy required to produce the lost alloys; saves the energy lost to the furnace roof refractories and surroundings due to the friendly cover slag no-iron oxide barrier; saves the energy expended during repeated and near continuous bath chemistry correction periods; and saves energy consumed by oxidation reactions. Energy per unit of melted iron on an overall basis is substantially less due to the more efficient and predictable operation that occurs when oxidation irregularities are eliminated.

The CEO also must highlight that reducing casting scrap rates correlates directly with energy savings. Example: a 2% reduction in casting scrap means 2% less energy needed per unit of metal produced.

As for energy requirements in cupola melting, reducing the coke rate, eliminating alloy oxidation losses, reducing slag formation, reducing refractory erosion, elongating cupola campaign life, and stabilizing iron chemistry all contribute to huge reductions in energy per unit of melted iron.

Cupola deoxidation is the only technology that can save the energy and GHGs needed to prevent the forced switchover from cupola melting to EF melting. In fact, deoxidation takes the cupola from an excess GHG generator role and establishes cupola melting as the preferred, lowest GHG producer.

In summary, it’s up to the CEOs now to make ferrous foundry operators aware of the proven deoxidation technology available to make iron melting more efficient. Iron deoxidation will improve the foundry’s bottom line substantially, improve its the long-term prospects significantly, and contribute to a cleaner environment.

Ron Beyerstedt is the president of Mastermelt LLC. Contact him at [email protected]