Calcium aluminate in A529 steel

Calcium aluminate in A529 steel

Figure 1: Oxide inclusions found in A529 furnace tap sample: calcium aluminate. SEM, scale bar: 20 µm.

Inclusion name: Calcium aluminate
Record No.: 790
Inclusion formula: CaO x 2Al2O3
Inclusion type (Macro/Micro/Nano): Macro
Inclusion type (Exogenous/Indigenous): Indigenous
Inclusion classification: Oxide
Inclusion composition in weight %: No data
Sample: A529 furnace tap sample, high strength low alloy (HSLA) steel
Steel composition in weight %: 0.10% C, 0.64% Mn, 0.01% P, 0.05% S, 0.13% Si, 0.31% Cu, 0.10% Ni, 0.04% Cr.
Note: The cleanliness of high strength low alloy (HSLA) steel was assessed qualitatively and quantitatively. The determination of inclusion type and inclusion morphology were carried out using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED) method allowing in-situ examination of inclusion morphology by analytical techniques such as SEM/EDS.
CaO x 2Al2O3 phase was found to crystallize as thin lathes in an aluminate matrix having similar composition corresponding to CaO x 2Al2O3. This observation is in good agreement with literature. Presence of MgO in calcium aluminate inclusions often indicates exogenous sources since calcium containing deoxidizers are generally magnesium free. Calcium inclusions with high MgO content most likely originate from magnesia refractories by erosion or by reaction between slag and refractories. However, the raw material charged into the EAF for making the current steel samples is mainly scrap steel containing trace MgO, therefore this may contribute to the trace MgO detected in the inclusions. The strong influence of refractory composition on calcium aluminate inclusions emphasizes the importance of a thorough knowledge on details of specific steelmaking practice while assessing inclusion’s origin.
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