After pickling the surface of continuous casting billet, it was found that there were mesh cracks on the surface of the billet, and the depth was up to 5mm. What causes the mesh cracks? The main reasons are:
(1) The surface of the high temperature casting billet absorbs the copper of the mold, and the copper becomes a liquid and then permeates along the austenite grain boundary.
(2) The selective oxidation of iron on the surface of the billet causes the residual elements in the steel (such as Cu, Sn, etc.) to remain on the surface and penetrate along the grain boundaries to form cracks. The results show that Cu, Sn, Sb and other elements are enriched in the crack zone, Cu content in steel is greater than 0.1%, and the crack is aggravated. With the increase of Al content in steel, the network cracks are aggravated.
How could we prevent to generate mesh crack ?
(1) The surface of the crystallizer is plated with Cr or Ni to increase the hardness.
(2) Suitable secondary cooling water.
(3) Control the residual elements in the steel such as Cu< 0.2%,Mn/S>40.
