Steelmaking

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STEELMAKING

Producing large steel ingots utilizing the best ladle furnace technology.

EQUIPMENT AND CAPABILITIES

The majority of NAF’s ingots are purchased from Ellwood Quality Steels and shipped hot a few hundred yards between the plants. EQS is North America's most reliable producer of high-quality, low-cost carbon, alloy, tool, and martensitic stainless steel ingots. Low carbon stainless ingots are available from Ellwood National Steel and other approved sources.

Every phase of the ASEA-SKF split steelmaking system is highly monitored and closely controlled producing steels with exceptional cleanliness and tight chemistry ranges. The ability to repeat specific alloy content for given grades allows NAF to achieve consistent mechanical property results after heat treatment. The steel cleanliness rivals that achieved only through re-melted refining processes such as ESR and VAR.

The melt shop features a modern 45 nominal ton Ultra High Power Electric Arc Furnace with Eccentric Bottom Tapping (EBT). The ladle furnace steelmaking is accomplished with split ASEA-SKF secondary steelmaking equipment:

  • Two ladle refining units
  • A custom alloy delivery system
  • One ladle vacuum degasser

THE PROCESS

First, scrap is loaded into clam-shell buckets and charged into an ultra-high powered (UHP) eccentric bottom-tapping (EBT) electric arc furnace. After the scrap is melted, carbon and phosphorus are removed under an oxidizing slag. Steel is then bottom tapped slag-free into a preheated ladle. The ladle serves as the refining vessel and is built for both induction stirring and argon bubbling. During tapping, deoxidation and alloy additions are charged into the ladle, followed by a reducing top slag.

The ladle is transferred to the first refining station for alloy adjustment and refining. Arc heating and induction stirring at this step ensures homogeneous mixing and interaction between the steel and slag.

The ladle is then transferred to a vacuum degassing station whereby hydrogen is removed to a level of less than 1ppm. Combined induction stirring and argon gas bubbling are used during vacuum treatment. After vacuum degassing, the ladle may go to the second ladle refining for calcium wire treatment.

Heats are sent to teem at a consistent pre-designated temperature. All ingots are bottom-poured at a controlled rate of rise in big end up, tapered, fluted molds. A teeming car is used to enable faster turnaround and multi-heat ingot pours. Argon shrouding is employed to minimize re-oxidation and the  pick-up of nitrogen and hydrogen.


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