Abstract
The microscopic structure and chemical composition of streak seams in the experimentally prepared 5 ton killed steel-ingot (200-500g/t Al were added) were investigated, then the mechanism or process of the seams-occurrence were researched. The results obtained were as follows.
(i) Mn-silicate type of seams found very rarely in the bottom or surface of the ingots were the reaction-products between refractory materials and [Mn], [MnO] or [Fe].
(ii) Al2O3 type-seams found in the interior of ingots were almost Al2O3 crystal and high Al2O3 type-seams containing 65-70% Al2O3 had Al2O3 crystals precipitated on the matrix of Mn-Fe-Al-silicate.
(iii) Al2O3 type and high Al2O3 type-seams originated from the oxidation of [Al] by the air and the reduction of eroded refractory particle by [Al].
(iv) Al2O3 type and high Al2O3 type-seams already grew in the metals of runner brick at the hottom pouring. They happened in the narrow metal independently of the theories of the cedimental crystal or the segregation at ring ghost in the large ingot.
(v) The maximum length of the seams coagulated by the effect of cedimental crystal were calculated under some assumptions. They wese about 2-3mm when the forging ratio of ingots were 10-20. But by the observation of seams-distribution in ingot, the effect of cedimental crystal was rather thought to prevent the floating up of the macro-scopic inclusions in the mold.
The effect of the cooling velocity of mold-bottom on the floating up of macroscopic inclusions poured into the mold (top poured), the relation between the demension of the ladle or nozzle and the poured stream-condition of molten steel and so on are now being studied.
