Transverse cracks at corners of continuous casting slabs

MADNESS OF SUBMERGED ARC WELDING DEFECTS OF REINFORCED CORNER BARS

Submerged arc welding (SAW) is the most widely used welding process for the manufacture of reinforced corner bars due to its high welding speed and good welding performance. It is also the main welding method for thick steel plates. But the high deposition rate of the metal requires high levels of welding quality control and trust in the welding operator’s ability. In this article, we will discuss the madness of SAW defects of reinforced corner bars.

Submerged Arc Welding (SAW) is a process in which no contact occurs between the metal and the electrode that is used to generate and transfer the heat energy. A metallic powder called flux is scattered and suspended in the arc in order to shield the molten weld pool vicinity, allowing the molten metal to cool and solidify. The process is commonly used in industrial applications and is known for its quick welding rate and strong bonding strength.

Although this process has a large array of advantages to offer, such submerged arc welding of the corner bars can have the risk of generating defects due to improper welding techniques and joint design. A weld defect that arises from improper welding techniques and joint design is known as a Longitudinal Crack. This is a crack type defect found along the weld in the direction of welding. This defect is mostly caused by a weld with low welding current which results in an insufficient thermal fusion and undercut at the root side. In addition, the weld bead can also be insufficient in size which could also lead to such defects.

Another defect caused by SAW is the Breaks in Slag. This defect is considered to be a defect that occurs when the slag layer between the weld layers breaks. This may be caused due to gas pockets trapped in the weld which leads to an insufficient slag cover, inadequate welding beads and inadequate surfacing of the corner bars.

Finally, the weld may have Porosity due to the trapped gas. Porosity refers to a defect of small holes closely located together that can be found in a weld. This defect is generally caused due to the presence of gas pockets or moisture which is not able to escape the weld pool.

In conclusion, submerged arc welding of corner bars exhibits a variety of defects due to its higher deposition rate, improper welding techniques and joint design. Care must be taken to ensure that the welders understand the basics of SAW process, and that good welding techniques are adhered to.

Longitudinal cracks are common problems in the corner parts of continuous casting billets, and they are a great challenge to the product quality of the steel mills.

The main causes of longitudinal cracks in the corner parts of continuous casting billets include: (1) The percentage of nonmetallic inclusions in the slag is too high and exceeds the standard; (2) The wall thickness of the corner part of the billet is uneven; (3) The surface of the billets at the corner parts is not smooth and wavy; (4) The pouring speed of the molten steel is not uniform, resulting in unequal cooling of the billet corners; (5) Excessive local temperature drop in the corner part of the billet.

To solve this problem, we must first analyze and determine the causes of the cracking of the corner parts of the continuous casting billets. We need to strengthen the cleaning and purification of molten steel, reduce the non-metallic inclusion content, strengthen the evenness of the billet cooling, and keep the temperature at the corner parts not too high or too low. At the same time, we must pay attention to the surface treatment of the corner parts of the billet and strive to achieve smooth and wavy surface.

In addition, it is also necessary to adjust the speed at which the corners of the billets are pulled and cooled. It is best to slow down the speed of the solidification and cooling process at the corner parts of the billet to make them uniform in temperature which will greatly reduce the longitudinal cracking at the corner parts of the billet.

In short, in order to reduce the longitudinal cracks at the corner parts of the continuous casting billet, the slag cleaning should be enhanced, and the surface treatment, cooling and temperature control should be strengthened. With such improved techniques, all steel mills can produce better quality steel billet products.