Surface crack and its formation mechanism of horizontal continuous casting billets produced with copper scrap were analyzed.With decreasing in diameters of the billets

surface crack which is mainly distributed into the upper of the billets is increased.The major crack with relatively round-obtuse tip and a little sharp tip are in range of 0.3～0.5 mm in depth

and the deepest crack reaches 4 mm

meanwhile

intergranular crack around crack tip can be observed.There exists inclusion including SiO2 and Al2O3 in crack.Formation mechanism of crack on the billets was analyzed based on solidification theory.It is believed that surface crack on the billets is mainly related to the incorrect secondary cooling process.Through using annular feed-water injector in secondary cooling process

surface crack is eliminated

improving greatly the quality of the billets.