セミキルド厚鋼板の内部欠陥について

抄録

The extent of internal defects, which lay at the top of the semikilled mild steel plate, was measured by ultrasonic testing of the liquid-holding method. Samples were selected from plates of the same size which were rolled from ingots of the same type.
The extent (area) of the defects seemed to have some relation to manufacturing conditions.
Studying the relation, the following results were obtained:
(1) The extent of defects is low for the first and last poured ingots, but is high for those poured between.
(2) The extent of defects has a linear relation to the pouring temperature, i. e. the higher the temperature, the higher the extent of defects.
(3) Pouring speed does not affect the extent of defects.
(4) Ingots, charged into a soaking pit inversely, show the same tendency as (1) as to extent of defects, however, except for the first poured, the extent of defects is lower than. for usual charging.
(5) Too large cropping of slabs after slabbing greatly increases the extent of defects.. This is caused by the oxidation of the shrinkage pipe.
(6) Too short track time disturbs the relation shown in (1) and increases the average extent of defects.
(7) These defects seem to be caused by the scum remaining near the top surface of the ingot.