Metallurgical Processes and Defects in Steel Products...

Metallurgical Processes and Defects in Steel Products Defects in steel products are defined as deviations in appearance, shape, dimension, macro-structure / micro-structure, and/or chemical properties when compared with the specifications given in the technical standards or any other normative documents in force. Defects are detected either through visual inspection or with the help of instruments and equipments. There are four main metallurgical processes for the manufacture of finished steel products where the steel products can pick up defects. The defects picked up during these processes are (i) casting defects, (ii) rolling defects, (iii) forging defects, and (iv) welding defects. (Fig 1).These defects are described below. Fig 1 Metallurgical processes and steel product defects Casting defects Casting is a forming process which converts liquid steel into a solid product. In foundries liquid steel is cast into complex shapes by pouring of liquid steel into a mould in which it sets to the required shape. In steel plants, liquid steel is normally continuously cast in the form of slab (either thick or thin), bloom or billets. Casting defects are defined as those characteristics which create a deficiency or imperfection exceeding quality limits imposed by design and service requirements. Defects in foundry cast steel products There are in general three broad categories of defects in the foundry cast steel products. These are (i) the major or most severe defects which result in scraping or rejection of castings, (ii) intermediate defects which permit salvaging of castings through necessary repairs, and (iii) minor defects which can be easily repaired. Common defects which generally occur in castings are given below. Porosity – It consists of the spherical holes of varying size, with bright walls, usually evenly distributed and formed due to the gases in the liquid steel. The larger holes...

Refractory Lining of a Continuous Casting Tundish Dec23

Refractory Lining of a Continuous Casting Tundish...

Refractory Lining of a Continuous Casting Tundish In the continuous casting (CC) of steels, tundish is a buffer refractory lined vessel which is located between the ladle and the CC mould. The tundish serves the purpose of a reservoir  and a distribution vessel. Over the years, there have been dramatic changes in CC tundish. From a mere reservoir and distribution vessel, the tundish today  is viewed as a steel refining vessel and a totally new field in the process of steel making technology has emerged which is known as tundish metallurgy. Tundish today also fulfills certain metallurgical functions such as feeding of the liquid steel to the mould at a controlled rate, and thermal and chemical homogenization etc. It also focus on the continuous improvement of many quality related parameters such as fluid dynamics, thermal insulation, inclusion floatation and removal, and hydrogen pickup etc. Different refractories associated with tundish include tundish lining materials (both permanent and working lining), dams and weirs, impact pad, flow control system (monoblock stopper or slide gate), pouring stream protection between tundish and mould (shroud or submerged entry nozzle,SEN), tundish nozzle, and seating block. Dams and weirs are made of magnesite (MgO) boards or alumina (Al2O3) bricks. Liquid steel from tundish to mould is fed by nozzle submerged into molten steel in mould. SEN are to be resistant to corrosion and spalling, Nozzle clogging is also important. Isostatic pressed SEN with alumina graphite-fused silica are commonly used. Fig 1 shows typical tundish along with its refractories. Fig 1 Typical tundish along with its refractories The refractory lining design and quality of refractories used for lining have major influence on the operational parameters of CC machines such as super heat requirements, speed of the machine, the phenomenon like initial cold running stopper,...