The surface micro cracks of 25 mm hot rolled plate rolled by cast slab of C-Mn steel(0.13~0.20C
1.00~1.60Mn
0.09Cu
0.07As
0.05Sn)have been studied by scanning electron microscope and X-ray energy dispersive spectrometer.Results showed that there was thin oxidizing-decarburizing layer at both sides of surface crack
the crack fractured along grain-boundary and the low-melting-point Cu-As-Sn enriched phases existed at steel matrix near crack.In production practice
as Cu
As
Sn content in steel was respectively controlled ≤0.02%
the surface net cracks of hot rolled plate were basically eliminated.