Current status of research on the formation and control of longitudinal cracks on the surface of continuous casting billets

Continuous casting technology is one of the core technologies of the steel industry,and its ingot quality directly affects the quality and production efficiency of steel products.However,as a serious ingot quality defect,longitudinal cracks on the surface of continuous casting ingots have long troubled steel companies.This paper will explore the formation mechanism,influencing factors and current control research status of longitudinal cracks on the surface of continuous casting ingots.

Formation Mechanism of Longitudinal Cracks on Surface of Continuous Casting Ingot

The formation of longitudinal cracks on the surface of continuous casting billets is mainly due to uneven heat transfer and unstable billet shell growth during the initial solidification stage of molten steel.Specifically,its formation mechanism includes the following aspects:

Influence of steel composition:Too high content of P,S and other elements in steel will significantly reduce the high temperature strength and plasticity of steel and increase the tendency of longitudinal cracks.In addition,when the carbon content is in the peritectic region,the volume shrinkage of molten steel near the solidification point is large,which aggravates the uneven solidification of the billet shell and leads to the generation of longitudinal cracks on the surface of the billet.

Influence of continuous casting parameters:Improper settings of continuous casting parameters such as mold cooling intensity,pulling speed,and superheat will lead to uneven heat transfer in the mold,affecting the uniform growth of the billet shell.In particular,when the stress generated by the friction between the crystallizer and the billet shell is too large,it will cause internal cracks and even rupture the billet shell.

Influence of mold slag performance:The physical and chemical properties of mold slag have an important influence on the heat transfer between molten steel and the crystallizer.Poor melting performance of mold slag,too thick or too thin liquid slag layer will lead to uneven thickness of slag film,making the shell too thin locally,reducing strength,and increasing the probability of longitudinal cracks.

Influence of equipment factors:Equipment factors such as misalignment between the nozzle and the crystallizer,fluctuation of the crystallizer liquid level,unreasonable size and immersion depth of the submerged nozzle can also lead to the formation of longitudinal cracks on the surface of the ingot.

Factors affecting longitudinal cracks on the surface of continuous casting billet

There are many factors affecting the longitudinal cracks on the surface of continuous casting billets,mainly including the following aspects:

Molten steel composition and quality:The content of elements such as P,S,C in the steel and the composition at the end point of converter smelting have a significant impact on the generation of longitudinal cracks on the surface of the ingot.

Continuous casting process parameters:The settings of continuous casting parameters such as mold cooling intensity,pulling speed,superheat,and mold taper directly affect the heat transfer and solidification process of the ingot,and thus affect the generation of surface longitudinal cracks.

Protection slag properties:The melting properties of the protection slag,the thickness of the liquid slag layer and the distribution of the slag film structure have an important influence on the generation of longitudinal cracks on the surface of the casting.

Equipment factors:Equipment factors such as the alignment of the nozzle and the crystallizer,the stability of the crystallizer liquid level,the size of the submerged nozzle and the immersion depth are also important factors affecting the occurrence of longitudinal cracks on the surface of the casting.

Current status of research on control of longitudinal cracks on the surface of continuous casting slabs

In view of the formation mechanism and influencing factors of longitudinal cracks on the surface of continuous casting billets,domestic and foreign scholars and enterprises have conducted a lot of research and practice,and proposed a series of effective control measures:

Optimize the composition of molten steel:By adjusting the content of elements such as P,S,and C in steel,the high-temperature strength and plasticity of steel can be improved and the tendency of longitudinal cracks can be reduced

Reasonable setting of continuous casting parameters:According to the characteristics of steel grade and production conditions,reasonable setting of continuous casting parameters such as mold cooling intensity,pulling speed,superheat,etc.,to ensure uniform heat transfer and stable growth of the ingot.

Select appropriate protective slag:According to the solidification characteristics of the steel grade,select protective slag with good melting and lubrication properties to form a stable slag film structure to protect the billet shell from thermal and mechanical stress.

Optimize equipment conditions:ensure that the nozzle is aligned with the crystallizer,the liquid level in the crystallizer is stable,the size and immersion depth of the submerged nozzle are reasonable,etc.,to reduce the impact of equipment factors on longitudinal cracks on the surface of the ingot.

Adopt advanced detection technology:Use advanced non-destructive testing technology and data analysis methods to conduct real-time monitoring and early warning of longitudinal cracks on the surface of the ingot,and promptly discover and deal with potential quality problems.

In summary,the formation and control of longitudinal cracks on the surface of continuous casting billets is a complex and important topic.By deeply studying its formation mechanism and influencing factors and taking effective control measures,the probability of longitudinal cracks on the surface of casting billets can be significantly reduced,and the quality and production efficiency of steel products can be improved.With the advancement of science and technology and the improvement of processes,it is believed that the control problem of longitudinal cracks on the surface of continuous casting billets will be more effectively solved in the future.