Surface Cracking on Continuously Cast Nickel-microalloyed Steel Billet
Surface cracking on the billet is one of the most serious defects in the production of continuously cast nickel-microalloyed steel. Such defects can lead to a range of problems, including reduced strength, poor formability and weldability, and decreased fatigue life. As a result, it is important to gain an understanding of the mechanism of surface cracking in order to minimize and/or eliminate such defects.
The most common cause of surface cracking on continuously cast nickel-microalloyed steel billet is the rapid cooling process during the casting process. As the billet moves through the process, whether it is in the molds or outside the molds, it cools at a much faster rate than what the alloy is designed for. This rapid cooling causes the alloy to undergo a transformation from austenite to martensite, which is a higher temperature crystal and more brittle. This transformation from austenite to martensite causes the microstructure to shrink due to the decrease in volume, resulting in surface cracking.
One way to minimize surface cracking is by controlling the cooling rate during the casting process. This can be done by using lower casting speeds, or using cooling methods such as water sprays or cooling fans. By controlling the cooling rate, it is possible to reduce the amount of transformation from austenite to martensite and thus reduce surface cracking.
Another way to minimize surface cracking is to optimize the chemical composition of the alloy. This can be done by altering the amount and type of alloying elements used, as well as adjusting the carbon and manganese content. The goal of optimizing the chemical composition is to minimize the martensite transformation and thus minimize the risk of surface cracking.
Finally, the use of technological innovations can also help to reduce surface cracking. For example, the use of oscillating molds or bloom casters can help reduce the solidification rate and thus minimize surface cracking. In addition, the use of coreless induction furnaces or twin roll strip casters can also help control the cooling rate of the billet.
In conclusion, surface cracking on continuously cast nickel-microalloyed steel billet is a serious defect that can lead to a range of problems. It is important to gain an understanding of the causes of surface cracking in order to minimize the defect. Such measures include controlling the cooling rate during the casting process, optimizing the chemical composition of the alloy, and using technological innovations such as oscillating molds or coreless induction furnaces. By following these measures, it is possible to significantly reduce the risk of surface cracking.
