State of Segregation with Bubble in Continuously Cast Slab of Ultra Low Carbon Steel

The phosphorus segregation adjoined to pin-hole between primary dendrite arms in continuously casting slab of ultra low carbon steel was clarified. The segregation regions of phosphorus were formed in both growth and anti-growth direction of primary dendrite arm based on the pin-hole. The maximum invaded distances of the pin-hole into primary dendrite arms corresponded to the position at fraction solid of 0.2. The critical velocity of interface between liquid and solid for trapping pin-hole was proportional to -1.1 power of pin-hole diameter. The pin-hole was easy to be trapped between primary dendrite arms of ultra low carbon steel, because the amount of shrinkage during solidification per unit temperature was thought to increase with decreasing the carbon concentration.