The transverse cracks on the surface of continuous casting billet are located at the trough of the vibration mark on the inner arc surface of the billet, which is usually hidden and invisible. After pickling, it can be found that the crack depth is up to 7mm and the width is 0.2mm. The crack is located in the ferrite network region, which is the primary austenite grain boundary. And there are small particles (such as AlN) precipitation on the grain boundary. In particular, C-MN-Nb (V) steel is more sensitive to cracks. Causes of transverse cracks:
(1) Vibration marks are too deep.
(2) The increase in the content of A1 and Nb in the steel promotes the precipitation of particles (A1N) at the grain boundary and induces transverse cracks.
(3) The casting billet is straightened at the brittleness temperature of 700 ~ 900℃.
(4) Secondary cooling is too strong.
Measures to prevent transverse cracks on the surface of continuous casting billet:
1) The use of high frequency (200 ~ 400 times/min) small vibration spoke (2 ~ 4mm) is an effective way to reduce the depth of the vibration mark.
2) The secondary cooling zone adopts stable weak cooling, and the surface temperature of the billet is greater than 900℃ when straightening.
3) The mould liquid level is stable, and the protective slag has good lubrication performance and low viscosity.
