Research of quality of high-strength shipbuilding steel with high concentration of calcium

The paper studies the microstructure, presence and qualitative composition of nonmetallic inclusions, mechanical tests of industrial smelting of high-strength shipbuilding steel with calcium concentration in the bucket sample of 0.009% have been performed. Steel with a high concentration of calcium is contaminated with a variety of stitch oxide inclusions, and therefore the mechanical properties of the rolled product are sharply reduced (impact strength, ductility in the Z-direction, fracture quality of technological samples). It is shown that the upper permissible limit of calcium content in steel is within the range 0.004–0.009%, but it is necessary to clarify it performing additional research. To ensure high purity of high-strength shipbuilding steel for non-metallic inclusions, it is vital to observe a strictly regulated technology of aluminum deoxidation and modification by ferrocalcium with obtaining the content of these elements in the metal in the previously recommended limits 0.01–0.02 and 0.002–0.004% respectively.

The effects of deoxidation practice on the quality of thin foil low-carbon steel

In converter steelmaking of AISI 1006 steel for thin foil products, two tapping practices are used with respect to deoxidation: silicon and manganese additions during tapping and aluminum deoxidation after complete tapping (?semikilled practice?) and aluminum deoxidation during tapping, ?fully killed practice?. There is a perception that the semikilled practice may be more economical and result in the same quality as the fully killed practice. In this work, the effects of the tapping practice on steel quality and cost variables were evaluated for thin foils of AISI 1006 steel. Oxygen and aluminum content, aluminum and ferro-alloy yield, the type of alumina inclusions formed, and the quality of the steel during thin foil rolling were evaluated and compared. It is shown that the fully killed practice leads to less reoxidation from slag, lower soluble oxygen, and lower total oxygen at the caster as well as better morphology of the remaining alumina inclusions than the semi-killed practice. Thus, the higher quality of the steel produced via the fully killed tapping deoxidation practice when compared with semi-killed tapping is demonstrated. It is also shown that a complete cost evaluation favors this practice in the case of products rolled for tin foil production.