Castability and Inclusions in a Low Sulfur Ca‐Treated Peritectic Steel for Two Deoxidation Techniques

Abstract

Liquid inclusions are important to avoid nozzle clogging during continuous casting of steel. To minimize clogging tendency at a Brazilian steelworks for a low‐sulphur Ca‐treated peritectic steel, deoxidation technique is changed from only Al addition as deoxidant to Fe–Si ferroalloy followed by Al addition, reducing the amount of Al by 20 wt%. Calcium treatment procedure is not changed. According to steelworks data, clogging occurrences are drastically reduced with this process change. In this context, quenched steel samples are collected from the tundish before and after the aforementioned process change. Nonmetallic inclusions characterization is manually performed using scanning electron microscope. For both conditions—before and after the industrial process changes—the inclusions are typically globular ones. However, before the changes, the inclusion modification is not complete because the core of the inclusions is composed by polygonal spinel. After the changes, the inclusions become homogeneous. Computational thermodynamics is applied to calculate the castability windows; they show that the amount of calcium dissolved in liquid steel is too low before the process changes, and this fact explains the blockage of the tundish nozzles, which is observed at steelworks, due to the deposition of high melting point spinel inclusions.

Sliver defects in an ultra-low carbon Al-killed steel caused by low steel level in the tundish

“…Moreover, this sequence presented a TO average of 36.0 ppm per heat (see Table 1) in the tundish. In a recent research [31] made with the same continuous casting reactor used in the present work, the authors found 38.7 ppm per heat, as the TO average in the tundish for an appropriate castability of an Al-killed steel grade.…”

Formation and Prevention of Nozzle Clogging during the Continuous Casting of Steels: A Review

“…-Large inclusions show a large deposition rate. cleanliness improvement experiment -Lowering the oxidation potential -Reducing REM inclusions before CC -Preventing the reoxidation of steel during CC [110] cleanliness improvement experiment -Optimization of refining slag -Improving the soft stirring operation to reduce the steel-slag desulfurization [111] liquid modification of inclusions experiment -Al 2 O 3 modification by Ca treatment [1] liquid modification of inclusions experiment -Replacement Al deoxidation by Si-Al deoxidation to form liquid inclusions after Ca treatment [112] inclusion modification experiment -Increasing Al/Ti ratio in ULC steels to lower the oxidation of Ti [54] inclusion modification experiment -Controlling the liquid fraction of inclusions larger than 20% [113] fluid flow control simulation -Employing a parabolic curve shaped SEN bottom to guide the liquid steel flow in the SEN [114] fluid flow control and coating material experiment -Application the annular step SEN with carbon free liner combined with a multi layer porous upper nozzle [115] fluid flow control simulation -Controlling the internal flow of nozzles by designed chambers or deflectors to decrease the inclusion deposition [116] surface treatment and fluid flow control experiment and simulation -Anticlogging nozzles by applying selected purified raw materials, type of graphite, surface treatment, and new structure for internal flow control of SEN [70] Base material experiment -Changing alumina-graphite nozzles to alumina, zirconia, and zirconia-graphite nozzles to reduce the refractory-steel interactions [117] Coating material experiment -Application of an Al 2 O 3 plasma coated Al 2 O 3carbon nozzle [118] protective coating material experiment -Employing CaO-ZrO 2 -C nozzles to form liquid phase by the reaction of CaO in the coat with Al 2 O 3 [119] coating treatment experiment -CaTiO 3 coating of alumina-graphite SENs [120] coating experiment -Using yttria-stabilized zirconia (YSZ) [121] treatment containing CaTiO 3 coated nozzles to form liquid phase by the reaction between Al 2 O 3 and CaTiO 3 .…”

Influence of Calcium Treatment and Electromagnetic Stirring on Ridging in Dual‐Stabilized Ferritic Stainless Steels

“…[ 18,19 ] Clogging problems can be prevented by transforming the solid alumina and spinel into liquid inclusions that do not attach themselves to the SEN. An efficient way of achieving this is to use calcium treatment. [ 18,20–25 ] Li et al [ 26–28 ] have shown that a small amount of Ca in Al‐killed Ti‐bearing 11Cr stainless steel effectively modifies Al 2 O 3 –TiO x inclusions into liquid oxide inclusions and reduces the stability of the spinel by modifying the solid alumina into liquid calcium aluminate.…”