For bar and wire rod applications low carbon steels of the continuous cast bloom have been developed. Aluminum content is controlled, using RH degassing process, from 0.003 to 0.01% not only to minimize Al2O3 inclusion but also to prevent the subsurface blowholes in the bloom section. Nitrogen content is also reduced under 0.003% by the hardblowing of LD process and shrouding during casting.
Comparing the rimmed steel wire rod, this new steel shows the smaller breakage diameter and higher ductility at the high speed continuous wire drawing. At the coldheading test the surface and center of this steel has shown the higher ducidity. At the higher annealing temperature the ferrite grain of this Al-killed steel tends to grow suddenly. Boron addition is effective to the prevention of the abnormal grain growth and brittle behavior of annealed products. Because of the high cleanliness and low segregation of continuous cast bloom, the size and amount of inclusions are smaller and hence the machinability of this steel is not so good. Higher sulphur content is desirable for the higher machinability. The depth of carburization is relatively small. Boron addition increases the austenite grain size and hardenability of carburized products.
