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,...

Calcium in Steels

Calcium in Steels Calcium (Ca) (atomic number 20 and atomic weight 40.08) has density of 1.54 gm/cc. Melting point of Ca is 842 deg C and boiling point is 1484 deg C. Ca additions are made during steel making for refining, deoxidation, desulphurization, and control of shape, size and distribution of oxide and sulphide inclusions . Ca is not used as alloying element since its solubility in steel is very low. Further it has a high vapour pressure since it boiling point is lower than the temperature of the liquid steel. It has a high reactivity and hence special techniques are necessary for its introduction and retention  of even a few parts per million in the liquid steel. Advantages directly attributable to Ca treatment include greater fluidity, simplified continuous casting and improved cleanliness (including reduction in nozzle blockage), machinability, ductility and impact strength in the final product. Available forms Ca is added to steel in the stabilized forms of calcium silicon (CaSi), calcium manganese silicon (CaMnSi), calcium silicon barium (CaSiBa) and calcium silicon barium aluminum (CaSiBaAl) alloys or as calcium carbide (CaC2). Elemental Ca is difficult and dangerous to add to liquid steel. CaSi in steel sheath (also called cored wire) is the most commonly used addition agent for Ca addition. The cored wire is injected into the liquid steel with help of wire injection system. It has higher recovery of Ca in steel than the virgin Ca / CaSi lumps addition into the ladle. The CaSi cored wire contains 4.5 % of iron (Fe) and 55 % to 65 % of Si. Ca content is usually in three ranges of 28 % to 31 %, 30 % to 33 %, and 32 % to 34 %. It contains around 1 % carbon (C)...

People Strategy for Excellence...

People Strategy for Excellence An organization is as good as the people who work in it. The continual success journey of the organization depends on the expertise, talent, interpersonal skills, and proactivity of its people. People are the lifeline of the organization. People strategy plays a very important role for the organization in its path  for achieving excellence. People are always necessary to the organization since they provide inspiration, creativity, vision and motivation that keeps the organization alive. They provide the skills and competencies necessary to make an organization work. And above all they provide the labour for the production of the goods and services that the organization supplies to its customers. People are a major and often the most important resource that the organization has. People and the intelligent use of their knowledge are the major determinants for the success for the  organization. The organization aiming for success through excellence develops and implements  its people strategy in a manner to attract, retain and fully engage its people and to ensure that they are empowered. Right type of people strategies are needed for making people of the organization to appreciate and to rely on each other for becoming ‘active citizens’ of the organization. With proper people strategies, people become committed to high performance and continuous improvement. They operate with high efficiency and with principles of fairness and integrity all the time.  They have opportunities to grow. They feel cared for since their efforts are recognized and appreciated. They feel proud of the organization they work in, the products and services they deliver and that they are making a positive contribution to the environment around them. Proper people strategies focus on the right combination and type of people and the level of performance required to...

Failure Analysis Dec16

Failure Analysis

Failure Analysis Failures of equipment components and assemblies, or structures in industry can cause loss of life, unscheduled shutdowns, increased maintenance and repair costs, and damaging litigation disputes. To prevent future recurrence of the problem caused by the failures ,it is essential to carry out an investigation in each failure. The conducting of an  investigation for a failure is known as failure analysis.  Failure analysis is a process of collecting and analyzing data and it is carried out to determine the causes or factors that have led to the undesired loss of functionality or failures of equipment components and assemblies, or structures. It is a multilevel process that includes physical investigation. The normal scope of a failure analysis is to find the failure mechanism and the most probable cause of the failure. The term failure mechanism is normally described as the metallurgical, chemical, mechanical, or tribological process leading to a particular failure mode. Failures of the equipment components and assemblies, or structures occur as a result of some sort of a mistake causing a weak link in the chain of the continuous process of engineering, design, manufacturing, and operation. The cause of a failure can be any one or more of the following. Fault in design Defects in material Deficiencies during processing and manufacturing Defects in assembly or installation Off-design or unintended service conditions Deficiencies in maintenance (neglect and procedures etc.) Improper operation Major steps while conducting a failure analysis are given in Fig 1. Fig 1 Majors steps in failure analysis The main principle of a failure analysis is to preserve evidence and the necessary information from the subject part or assembly in the as-received condition and the same is captured before anything is done to alter its condition. Further during failure analysis...

Hydrogen in Steels

Hydrogen in Steels  Hydrogen (H) (atomic number 1 and atomic weight 1.008) is a colourless gas. It has a density of 0.0899 gm/litre. Melting point of H is – 259.2 deg C and boiling point is -252.8 deg C. The phase diagram of the Fe-H  is given at Fig 1. Fig 1 Fe-H phase diagram  H in steels is considered as an undesirable impurity which is quite harmful in certain applications. It is always a source of various problems within steel production because of its generally detrimental effects on processing characteristics and service performance of steel products. Just a few parts per million of H dissolved in steel is sufficient to do the harm. Hence where necessary, it should be avoided or removed as required. Source of hydrogen There are multiple sources identified for H to enter into steel by any of several routes. In the primary steel making furnace, source of H is water which enter the furnace through wet scrap, flux materials, ferro alloys and refractory materials which are not fully dried. Water dissociates on contact with liquid steel and produces H which is absorbed by the steel bath. This H generally get removed by the purging action of the carbon (C) boil, but some can remain in the steel. Contact between the liquid steel and moisture in refractory materials  of the steel teeming ladles and/or humid air can cause pick up of H by the liquid steel. The hydrophilic calcium oxide (CaO) in the slag and decomposition of refractory binders which are required for sufficient thermal shock resistance, also account for H entering into the steel. Dissociation of water vapour (equation given below) contained in furnace gases generated during the steel making practices employing the combustion of hydrocarbon fuels produces H...