Oxygen Blowing Lance and its Role in Basic Oxygen Furnace Oct10

Oxygen Blowing Lance and its Role in Basic Oxygen Furnace...

Oxygen Blowing Lance and its Role in Basic Oxygen Furnace In the basic oxygen furnace (BOF) steel making a water-cooled lance is used for injecting a high velocity (super-sonic) stream of oxygen onto the liquid bath for its refining. The velocity or momentum of the oxygen jet results in the penetration of the liquid slag and metal to promote oxidation reactions over a relatively small area. The velocity of the oxygen jet and the penetration characteristics are functions of the nozzle (lance tip) design. The top-blowing lance oxygen jet of the BOF converter works as the source of feeding oxygen and energy for stirring of the liquid metal in the bath. Major in-furnace phenomena of a BOF converter that involve the top-blowing lance oxygen jet are formation of a cavity as a result of physical interaction between the oxygen jet and liquid metal, stirring of liquid metal, generation of spitting and dust, and post combustion of CO gas generated by decarburization and reaction with oxygen. For the optimization of BOF converter operation and control the above phenomena, different devices and improvements have been made and applied to the design and operation of top-blowing lance. Examples of these include the employment of Laval nozzles capable of converting pressure energy to jet kinetic energy with high efficiency in order to promote stirring of liquid metal, and the use of a multi-hole lance that enables high-speed oxygen feeding while suppressing generation of spitting and dust by dispersing of the oxygen jet. With the introduction of combined blowing in the BOF converters, the role of top-blowing lance jets as the source of energy for stirring liquid metal iron declined and flexibility in design and operation has been enhanced significantly. The main reason for blowing oxygen into the liquid...

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)...

Secondary Cooling Technology in Continuous Casting Process Jul31

Secondary Cooling Technology in Continuous Casting Process...

Secondary Cooling Technology in Continuous Casting Process  A wide range of steel grades ranging from ultra low carbon (ULC) and low carbon grades to high carbon and different grades of special steels are required to be cast in continuous casting machine (CCM). The casting of these grades is to be achieved while maximizing CCM output. Consistent production of prime quality cast steel product requires increased operational and maintenance flexibility in the CCM for maintaining optimum casting parameters can be maintained. This flexibility is needed both for every element as well as control system of CCM. While the strand is continuously withdrawn at the casting speed, solidification of steel continues beneath the mould through the different zones of cooling having a series of water sprays. The secondary cooling system consists of these different zones, each responsible for a segment of controlled cooling of the solidifying strand as it progresses through the CCM. The sprayed medium is either water or a combination of air and water (mist spray cooling). Mist spray cooling provides the following advantages. Uniform cooling Less water requirement Reduced surface cracking Product quality in a CCM is considerably influenced by temperature variations during strand cooling in secondary cooling zone. Hence secondary cooling zone has a very important function for the maintenance of a correct temperature parameter and is crucial to the quality of the cast steel product. Since the quality of steel depends on the behavior of the surface temperature and the solidification of steel front in time, it is to a large extent defined by the intensity of the water sprays. Improper cooling conditions can have detrimental impact on stress distribution in solidified shell. First of all, overcooling can lead to the formation of cracks. Moreover, there must be a smooth transition...