Control of Oxygen, Nitrogen and Hydrogen in Induction Melted Steels

Bradken (Formerly AG Anderson Ltd) continues to make an effort geared towards producing castings free of non-metallic inclusions, with gas control and removal remaining a critical aspect of the production process. This paper discusses various outcomes produced through different gas control and removal methods at the Bradken (Formerly AG Anderson Ltd) foundry. The paper also highlights the importance of gas removal and control in furnace to reduce gas related defects in steel castings.

Bradken (Formerly AG Anderson Ltd) experienced high amounts of gas inclusions in carbon and low alloy steels in the early 90s. They used a melting and pouring practice that includes medium frequency induction furnaces and lip pour ladles ranging from 600 to 4,000 lb. The furnaces were lined with a spinel bond fused alumina-based refractory, while the ladles were lined with fused alumina-based castable refractory materials. A project was undertaken in 1997 to reduce gas porosity in steel castings. Various potential sources of gases in steel castings were addressed.

It was found that insufficient or inefficient deoxidation was the main cause of gas porosity in steel castings. Extensive projects were carried out to determine the filter blockage factor for aluminum deoxidized steels. It was determined that additions of aluminum in excess of 0.05% would reduce the filter blockage factor of ceramic filters from 25 to 10 lbs./sq. Inch. In order to increase the filter blockage factor, the amount of aluminum used for deoxidation must be drastically reduced, and another additional final deoxidizer was needed. When a combination of 0.05% titanium and 0.02% aluminum was used, the filter blockage factor increased to 45 lbs./sq. inch.

Gas control in steel castings is crucial in ensuring high-quality results. While controlling gases is more challenging in induction melting furnaces, continuous efforts to reduce gas-related defects must be made. The final deoxidizer, whether titanium or aluminum, is just a part of the solution. The study also revealed that it is always better to scrap a casting in its early stage than a partially machined one to avoid tooling damage caused by filter breakage.

Bradken's technical group continues to identify defect-free, high-quality steel castings through their efforts to control and remove gases.