Holes - Slab defects

Holes - Slab defects

Figure 1: Holes.

Defect name: Holes
Record No.: 1443
Type of defect (Internal/Surface): Internal, surface
Defect classification: Slab defects
Steel name: Steel
Steel composition in weight %: No data.
Note: For this study we only selected the steel charges which were cast into pipe billets Ø250mm respectively Ø270mm, using all steel grades (carbon, low-alloyed, respectively alloyed) used in making these two types of pipe billets.
The holes are cavities on the external surface or in the under-shell area of the billet at about some tenths of millimeters from the shell surface and they are presented in figure 1.
They have a diametre up to 3mm and a length (depth) that can reach 25 mm. As usually they contain CO, H2, Ar and most of all they are associated with the inclusions. In case that they are superficial and/or few, these are polished (ground). They are determined by: the insufficient deoxidation of steel (gases occurrence: hydrogen, nitrogen, oxygen), the quality and humidity of the casting powder, the quality and homogeneity of its distribution, the variation of the steel level in the mould and the humidity existence in the refractory clay work of the tundish.
Reference: Not shown in this demonstration version.