Estimation of the Formed Position of the Surface Cracks on the Slab in the Continuous Caster

Abstract

When surface cracks on continuously cast slab were observed by a microscope, internal oxidation layers were sometimes present along the cracks. Attention was paid to these layers which are called subscales for the estimation of the formed position of the surface cracks in the continuous caster.
First, the subscale was formed on the test sample in the laboratory under the cooling condition of the continuously cast slab. Second, some kinds of cracks on the continuously cast slabs were collected, observed by a microscope and compared with the subscale of the former samples.
The results are summarized as follows.
(1) The thickness of the subscale for the formed position in the continuous caster was calculated by the combination of the internal oxidation theories and the cooling curve of the slab.
(2) The formed position of five kinds of cracks were considered as follows.
(i) The small longitudinal crack was formed in the mold and enlarged in secondary cooling zone.
(ii) The horizontal crack had the initiation point of crack existing in the secondary cooling zone and was enlarged at the unbending point.
(iii) The star crack and C-crack were formed in the mold or just under the mold.
(iv) The edge crack was formed at the unbending point.