What is the impact of slag protection on the quality of continuous casting billets?
Release time:
2020-07-30
Crystallizer Protective Slag Added to the surface of the steel in the mold, Protective Slag The quality mainly affects the surface quality of the billet.
（ 1) Longitudinal cracks on the surface of the slab: Longitudinal cracks originate from the uneven thickness of the main shell in the meniscus region of the crystallizer. The liquid slag on the steel surface cannot flow evenly and distribute around the billet, resulting in uneven thickness of the solidified shell. Thin parts of the shell are prone to stress concentration, and cracks will occur when the stress exceeds the high-temperature strength of the solidified shell.
Indicates that the liquid slag layer on the crystallizer surface is maintained at 5 ~ 15 mm can significantly reduce longitudinal cracks on the surface of the billet. Longitudinal cracks are also related to slag viscosity (), melting speed (tf), and withdrawal speed (V). It is pointed out that the larger the /tf ratio, the smaller the longitudinal crack index. For example, when the slag temperature is 1300, /tf=1, the longitudinal crack index is 6, /tf=2, and the longitudinal crack index is 0. Some believe that the continuous casting slab Protective Slag The film is uniform, the heat transfer is stable, the lubrication is good, and the cracks are significantly reduced.
（ 2) Slag inclusion: Slag inclusion can be divided into surface slag inclusion and subcutaneous slag inclusion. The sizes of slag inclusions vary. From a few millimeters to more than ten millimeters, the depth of surface slag inclusion varies. The included slag will seriously damage the surface quality of the product and must be removed before heat treatment.
The crystallizer shell is included in the slag, which is an important source of slag inclusions. For example, slag spots are formed on the surface of the shell, where the thermal conductivity is poor and the condensed shell is thin, forming a high-temperature “hot spot”, which is one of the reasons for steel leakage from the crystallizer shell.
The slag inclusions on the surface of the slab are mainly anorthite and anorthite, among which The A12O3 content is greater than 20%, and the melting points are 1550 and 1590 respectively, which easily causes slag inclusion. In the crystallizer, the liquid level fluctuates too much, the submerged nozzle is inserted too shallow, and the rotation of the liquid level will involve the slag.
The efficient energy-saving technology of steelmaking and continuous casting flame cutting was selected as a key project to promote the scientific and technological achievements of the Ministry of Science and Technology. This technology has been successfully applied in many steelmaking enterprises, reversing the previous situation of high coal gas consumption, large cutting gap, rough cutting section, high oxygen pressure, large workshop dust, high noise, large environmental pollution, frequent tool damage, and high labor intensity of workers. It shows great energy-saving and emission-reduction capabilities and good environmental protection effects. This technology has the following characteristics:
1. Advanced technology: When cutting, the flame is concentrated, and the cutting speed is fast. The cutting section is smooth, the upper edge is not broken, the lower edge has less slag, and the yield is high. Automation is possible, and both cutting and continuous casting can be achieved.
2. Steel saving: The gap between cutting billets and slabs can be maintained at about 3 mm, and the cutting loss per ton of steel can be reduced by more than 0.5 kg.
3. Energy saving: The gas pressure and oxygen pressure of the energy-saving continuous casting cutting nozzle are 1/2-1/3 and 1/2 of other cutting nozzles respectively, saving more than 50% gas and 40-50% oxygen, and can be automatically cut off and ignited during cutting.
More about Protective Slag For questions, please contact Luoyang Turner High Temperature Instrument Co., Ltd.
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