Ladle Metallurgy Apr23

Ladle Metallurgy

Ladle Metallurgy After tapping of steel from a primary steelmaking furnace such as BOF, EAF or EOF, molten steel for high quality or specialty applications is subjected to further refining in a number of alternative processes collectively known as ladle metallurgy. Ladle metallurgy is sometimes also called ladle refining or secondary steelmaking. Ladle metallurgy processes are commonly performed in ladles. Tight control of ladle metallurgy is associated with producing high grades of steel in which the tolerances in chemistry and consistency are narrow. The objectives of ladle metallurgy are the following. Homogenization – Homogenization of chemical composition and temperature of liquid steel in the ladle Deoxidization or killing – Removal of oxygen Superheat adjustment – Heating of the liquid steel to a temperature suitable for continuous casting Ferro alloys and carbon additions – Making adjustments in the chemistry of liquid steel. Vacuum degassing – Removal of hydrogen and nitrogen Decarburization – Removal of carbon for meeting the requirement of certain grades of steel. Desulfurization – Reduction of sulfur concentrations as low as 0.002% Micro cleanliness – Removal of undesirable nonmetallic elements Inclusion morphology – Changing the composition of remaining impurities to improve the microstructure of the steel Mechanical properties – Improvement in toughness, ductility, and transverse properties Depending on the types of steel required, one or more of the following ladle metallurgy processes are used. These are (i) rinsing or stirring, (ii) ladle furnace, (iii) ladle injection (iv) ladle refining, (v) degassing processes, (vi) AOD process, and (vii) CAS-OB (Composition adjustment by sealed argon bubbling with oxygen blowing) process. Some of the ladle metallurgy processes are shown in Fig 1. Fig 1 Some of the ladle metallurgy processes  Historical background  The treatment of steel in the ladle started around 45 years ago when the first ladle-to-ladle and ladle-to-ingot mold vacuum...

Steel Hardening by Quenching and Tempering...

 Steel Hardening by Quenching and Tempering Hardening is carried out by quenching steel, which consists of cooling it rapidly from a temperature above the transformation temperature (A?).  The quenching is necessary to suppress the normal breakdown of austenite into ferrite and cementite (pearlite), and to cause a partial decomposition at such a low temperature to produce the new phase called martensite. To achieve this, steel requires a critical cooling velocity, which is greatly reduced by the presence of alloying elements. In such case hardening of steel occurs with mild quenching. Martensite is a supersaturated metastable phase and has body centered tetragonal lattice (bct) instead of bcc. After steel is quenched, it is usually very hard and strong but brittle. Martensite looks needle like under microscope due to its fine lamellar structure. Steel is quenched in water or brine for the most rapid cooling, in oil for some alloy steels, and in air for certain higher alloy steels. Water is one of the most efficient quenching media where maximum hardness is required, but it is liable to cause distortion and cracking of the work piece. Where hardness can be sacrificed, whale, cotton seed and mineral oils are used. These tend to oxidize and form sludge with consequent lowering of efficiency. The quenching velocity of oil is much less than water. To minimize distortion, long cylindrical objects should be quenched vertically, flat sections edgeways and thick sections should enter the bath first. To prevent steam bubbles forming soft spots, a water quenching bath should be agitated. Steel can be hardened by the simple expedient of heating to above the A? transformation temperature, holding long enough to insure the attainment of uniform temperature and solution of carbon in the austenite, and then cooling rapidly (quenching). Complete hardening depends...

Role of Public Relations Management in an Organization...

Role of Public Relations Management in an Organization It is in every organization’s interest to maintain a positive public image. Whether it is a public sector organization or a private sector organization, both types of organizations can only be benefit from proper management of their publics’ perceptions of the organization. Both types of organizations can reap benefits from a positive public image which not only helps to increase confidence in the organization on the behalf of the organization’s publics and key stakeholders but also reinforce trust in the organization’s capabilities towards success. It is often misunderstood that the organizations practice public relations only for the purpose of publicity. But instead, the discipline of public relations (PR) deals with shaping and maintaining the image and reputation of the organization in the eyes of its various publics. It is the deliberate, planned and sustained effort to institute and maintain mutual understanding between the organization and its publics. It uses information to influence opinion for creating and maintaining goodwill. It is the practice of managing communication between the organization and its publics. Publics, in PR terms, are the ones who ever have or ever will form an opinion about the organization. Publics are the interested audiences that are important in some way to an organization including current and potential customers, current and potential employees and management, investors, vendors and suppliers, media, government, and opinion leaders etc. They can be internal within the organization or external to the organization. As an example typical composition of publics of a multinational organization is given in Fig 1. Fig 1 Typical composition of publics in a multinational organization Definition of public relations Public relations activities are planned and sustained to establish and maintain goodwill and mutual understanding between an organization and its publics. Generally there is...

CONARC Process for Steelmaking Apr17

CONARC Process for Steelmaking...

CONARC Process for Steelmaking CONARC process for steelmaking was developed by Mannesmann Demag Huettentechnik (now it is SMS Siemag). The objective for the development of this process was to utilize the benefits of both the conventional top blown converter steelmaking and electric arc furnace (EAF). The name of the process CONARC sums up the fusion of the two processes (CONverter ARCing). The technology of this process is based on the increased use of hot metal in the electric arc furnace and is aimed at optimizing energy recovery and maximizing productivity in such an operation. The process was developed for using any kind and mix of raw materials like hot metal, direct reduced iron (DRI) and scrap to ensure highest quality requirements for the production of all grades and qualities of steels covering a wide range from carbon steels to stainless steels. Depending upon the requirements of the finished products, CONARC process is followed by a ladle furnace or a vacuum degassing unit. Major equipment for the CONARC process The basic equipment of CONARC process consists of two identical refractory lined furnace shells, one slewable electrode structure with one set of electrodes serving both the furnace shells, one electric supply (transformer etc.) for both the shells, and one slewable water cooled top oxygen lance system serving both the shells. Alternatively two stationary top lances, one for each furnace shell for the blowing of oxygen can also be used. Option is available for introducing bottom stirring devices integrated to the bottom of each of the furnace shell. Options are also available to introduce burners and injectors systems in the shell for the injection of fuel, carbon and oxygen as per the process requirements. The other important systems include raw material and flux feeding systems and gas...

Normalizing Process for Steels...

Normalizing Process for Steels Normalizing process for steels is defined as heating the steel to austenite phase and cooling it in the air. It is carried out by heating the steel approximately 50 deg C above the upper critical temperature (AC? for hypoeutectoid steels or Acm in case of hypereutectoid steels, Fig 1) followed by cooling in air to room temperature, or at no greater than 1 bar pressure using nitrogen if the process is being  run in a vacuum furnace. Normalizing temperatures usually vary from 810 deg C to 930 deg C. After reaching the soaking temperature the steel is held at that temperature for soaking. The soaking time depends on the thickness of the work piece and the steel composition. Higher temperatures and longer soaking times are required for alloy steels and larger cross sections. Fig 1 Typical normalizing temperature range for steels In normalizing, steel is uniformly heated to a temperature which causes complete transformation to austenite. Steel is held at this temperature for sufficient time for the formation of homogenous structure throughout its mass. It is then allowed to cool in still air in a uniform manner. Air cooling results into faster cooling rate when compared with the furnace cooling rate. Thus, the cooling time in normalizing is drastically reduced as compared to annealing. Soaking periods for normalizing are usually one hour per 25 mm of thickness of the work piece but not less than 2 hours at the soaking temperature. The mass of the work piece can have a significant influence on the cooling rate and thus on the resulting microstructure. Thin work pieces cool faster and hence are harder after normalizing than the thicker work pieces. This is different than in the case of annealing where the hardness...