Properties and Uses of Steelmaking Slag...

Properties and Uses of Steelmaking Slag Steelmaking slag is an integral part of the steelmaking process. It is produced during the separation of the liquid steel from impurities in steelmaking furnace and is a non-metallic by-product of steelmaking process. It occurs as a molten liquid melt and is a complex solution of silicates and oxides which solidifies upon cooling. It primarily consists of silicates, alumina silicates, calcium aluminum silicates, iron oxides and crystalline compounds. During steelmaking, slag is produced in the hot metal pretreatment processes (desulphurization, desiliconization, and dephosphorization etc.), in the primary steelmaking processes (basic oxygen furnace, electric arc furnace, and induction furnace), slag formed during the secondary refining processes (this slag is sometimes called ?secondary refining slag? or ?ladle slag?), and slag formed in tundish during continuous casting of steel (also known as tundish slag). The slag generated in the basic oxygen furnace (BOF) and electric arc furnace (EAF) is of basic nature while the slag is of acidic nature in induction furnace because of the use of silica ramming mass as the lining material. Since most of the steel produced in the world is by BOF and EAF processes, hence slag from these processes is discussed in this article. The processing of the steelmaking slag (Fig 1) is normally carried out by (i) solidifying and cooling of the hot liquid slag, (ii) crushing and magnetic separation treatment of the slag to recover the scrap, (iii) crushing and classification of the slag for grain size adjustment to manufacture the slag product, and (iv) aging treatment of the slag product for improving its quality and volumetric stability. These processes are explained below.   Fig 1 Processing of steelmaking slag As steelmaking slag is formed, it is in a molten or red-hot state at...

History of Basic Oxygen Steelmaking Dec16

History of Basic Oxygen Steelmaking...

History of Basic Oxygen Steelmaking  Basic oxygen steelmaking (BOS) is the process of making steel by blowing pure oxygen (O2) in a liquid metal bath contained in a vessel which is known as basic oxygen furnace (BOF), LD converter, or simply converter. The history of steelmaking began in the 19th century, when Reaumur of France in 1772, Kelly of the United States in 1850 and Bessemer of Britain in 1856 discovered how to improve on pig iron by controlling the carbon content of iron alloys, which thus truly become steels. While Reaumur, a chemist, was driven by scientific curiosity, but Kerry and Bessemer being engineers, were responding to the need for larger quantities and better qualities of steel which the industrial revolution, with its looms, steam engines, machines and railroads, had created. This had started a dialectical relationship between science and technology and the basic concepts of refining hot metal (pig iron) by oxidizing carbon (C) in a liquid bath were invented at that time. This was a radical change from the gas-solid reaction in the shaft furnaces, the predecessors of blast furnaces which reduce iron ore with charcoal, or from the puddling of iron which was a forging and refining technology carried out in the solid state and which has no equivalent in the present time. The intensity of innovations which at the second half of the 19th century was impressive and it brought a paradigm shift. Steel making by Bessemer converter came into existence in 1856, the open hearth furnace, which can melt scrap in addition to refining hot metal, was discovered nine years only after the Bessemer converter in 1865, and the basic Thomas converter twelve years later in 1877.  The Thomas converter was using air for the refining of the...

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...

Factors affecting Lining Life of a Basic Oxygen Converter Sep20

Factors affecting Lining Life of a Basic Oxygen Converter...

Factors affecting Lining Life of a Basic Oxygen Converter The life, reliability and costs of lining in a basic oxygen converter are vital for the smooth operations of the steel melting shop utilizing basic oxygen process for steel production.  Higher lining life results into improved availability of the converter which in turn improves its productivity. Three important factors for achieving higher lining life of the basic oxygen converter (Fig 1) are (i) qualities of refractories and their laying pattern in the converter, (ii) operating practices followed, and (iii) monitoring of the lining wear and practices for the maintenance of the refractory lining. Development of improved refractory materials in combination with improved process control and better maintenance during campaigns make it possible to increase the lining life of the basic oxygen converter. Fig 1 Factors affecting lining life of the basic oxygen converter These days without exception, basic oxygen converters are lined with magnesia – carbon (MgO-C) refractories because of their superior properties than other types of converter lining materials. However zoned refractory lining practices are followed by using MgO-C refractories of different qualities in different areas of the converter. The causes of wear of refractories in the basic oxygen converter are either due to chemical reasons or due to the physical reasons. Chemical causes for the wear of the converter lining are mainly due to gaseous materials (oxidizing gases, reducing gases, and water vapour), liquid materials (slag. hot metal, and liquid steel melt), and solid materials (fluxes, and carbon disintegration).  Physical causes for the wear of the converter lining are excessive temperatures (poor dissipation, and hot spots), static mechanical stresses (spalling, and expansion), and dynamic mechanical stresses (abrasion, impact, and vibrations). The key wear mechanisms of the refractory lining of basic oxygen converter can...

Understanding Steel Making Operations  in Basic Oxygen Furnace Mar02

Understanding Steel Making Operations in Basic Oxygen Furnace...

Understanding Steel Making Operations  in Basic Oxygen Furnace  Steel making operation in the basic oxygen furnace (BOF) is also sometimes called basic oxygen steel making (BOS). This is the most powerful and effective steel making technology in the world. Around 71 % of the crude steel is made by this process. BOF process was developed in Austria in the early 1950s at the two Austrian steelworks at Linz and Donawitz and hence the BOF process is also called LD (first letters of the two cities) steel making. There exist several variations on the BOF process. The main are top blowing, bottom blowing, and a combination of the two which is known as combined blowing. The BOF process is autogenous, or self sufficient in energy, converts liquid iron (hot metal) into steel using gaseous oxygen (O2) to oxidize the unwanted impurities in hot metal (HM). The O2 used must be of high purity, usually 99.5% minimum, otherwise the steel may absorb harmful nitrogen (N2). The primary raw materials for the BOF are generally HM (around 80 % or more) from the blast furnace and the remaining steel scrap. These are charged into the BOF vessel. O2 is blown into the BOF at supersonic velocities. It oxidizes the carbon (C) and silicon (Si) contained in the HM liberating great quantities of heat which melts the scrap. There are lesser energy contributions from the oxidation of iron(Fe), manganese (Mn), and phosphorus (P). The flux used in this process is primarily calcined lime ( with CaO content of more than 92 %). This lime is produced by the calcining of limestone with low silica (SiO2) content. The post combustion of carbon monoxide (CO) as it exits the converter also transmits heat back to the bath. The product of...