Transverse cracks will affect the finished product rate just after rolling. Increase billet cleanup time, both great harm. The slab temperature is brittle zone of 700-900 ℃. The reason the lower surface cracks is 1050-1100 ℃, transverse cracks on the surface of the reason is the billet surface by a large segment straightening straightening stress. Niobium nitride in the austenite grain boundaries reduces the binding force, the grain boundary precipitation. At this point in the curved section slab junction arc poor, resulting in a lower surface cracks. Vertical cracks and chemical composition, mold cooling water temperature, mold equipment, the chemical composition of the slag, continuous casting machine precision secondary cooling system related. Related prevention measures:
1. Control steel composition. Try to prevent wC is 0.12% -0.16% D36 steel carbon content in the smelting process control method according to the upper limit. Can effectively reduce the cracks. Peritectic reaction zone.
2. Control crystallization temperature constant mold temperature, mold temperature changes effective way to improve is to increase the mold cooling water preheating device. Suppressing the occurrence of cracks when the weather changes. Can also be used after every stop pouring and pouring time is not open when the water temperature is below 20 ℃ mold mold cooling water, to ensure that the temperature of the casting mold fashion.
3. Adjust the crystallization process parameters to adjust the amount of water the size of the mold, according to different copper thickness. By adjusting the amount of water to ensure that the different stages of the same mold cooling intensity.
4. To improve the secondary cooling system, improving the straightening zone temperature, by optimizing the secondary cooling system. Prevent brittle zone billet straightening, can better reduce the likelihood of slab transverse cracks.
5. Strand by strand appearance cleanup and removal of the slab scarfing corner, is an effective means to clean up the slab billet final quality assurance. We can improve the final quality of the slab.