Synthetic Slag for Secondary Steelmaking...

Synthetic Slag for Secondary Steelmaking Synthetic slag consists of prepared mixture of several individual oxides which is used during secondary steelmaking to assist the steel treatment in the ladle from the viewpoint of effective refinement. Synthetic slag practice is normally used to obtain clean steels and also for the desulphurization of the liquid steel. Secondary steelmaking is a critical quality control step between the primary steelmaking and the continuous casting of the liquid steel. A key feature for success with the secondary steelmaking processes is the slag control. Use of synthetic slag which is specifically designed to have the required chemical composition and physical properties helps in the slag control. The  desirable properties of the synthetic slag include (i) slag is to have high sulphide capacity, (ii) it is to be basic in nature, (iii) it is to be fluid to obtain faster reaction rates, and (iv) it is not to cause excessive refractory wear. The secondary steelmaking slag is in liquid form in the ladle and floats on the surface of liquid steel which is usually at temperature of 1,600 deg or higher. It acts like a sponge to absorb the impurities consisting mainly of sulphur and non-metallic inclusions. The design of the slag is a critical step impacting the efficiency of the steel refining processes during the secondary steelmaking. Slag regime in secondary steelmaking significantly influences the final quality of the produced steel, particularly with respect to the achieved desulphurization of steel. One of the possibilities for influencing the slag regime is the application of synthetic slags to the ladle slag, formed from slag-making additions during the liquid steel tapping. Synthetic slag practice during secondary steelmaking maximizes the efficiency of the steel refining process by (i) improving steel quality, (ii) improving productivity,...

Selection of Coal for inclusion in Coal Blend in Coke Making Sep26

Selection of Coal for inclusion in Coal Blend in Coke Making...

Selection of Coal for inclusion in Coal Blend in Coke Making Blending of coals is necessary from economical point of view by reducing the percentage of high cost, prime or hard coking coals and replacing it with medium or soft coking coals. In some coke oven plants even a small percentage of non-coking or steam coals have also been used in the blend. Selection of a proper coal blend for use in by product coke ovens is always a big challenge for the coke producer since the blend has to meet the following requirements. It is to meet the requirement of crushing during coal preparation. All the components of the coals are neither be over crushed or under crushed. The sized coal blend for charging the coke ovens is to meet the requirements of density, flow, and the size fractions. It is to have necessary coking and caking properties for producing coke of quality which meets the quality requirements of blast furnace (BF) coke. The three basic quality requirements of BF coke are (i) to provide heat for the endothermic reactions taking place in the blast furnace, (ii) to act as a reducing agent by producing the necessary reduction gases, and (iii) to provide a permeable support in the BF for the iron bearing burden. It is to provide safe pushing performance in coke ovens. It must not put excessive pressure on coke oven walls during the process of coking and damage them. It should meet the yield requirements not only of BF coke but also of coke oven gas. A proper coal blend will not produce excessive nut coke and coke breeze. It is to be economical. In view of the above varied types of requirements, the decisions regarding coal blends are not...

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)...

Coking coals

Coking coals  Coking coals because of their special characteristics are suitable for carbonizing to produce blast furnace (BF) coke. Coking coal is also known as metallurgical coal. Fig 1 shows coking coal.  Fig 1 Coking or Metallurgical coal  Important properties required technically to produce good coke are Good coking and caking properties such as fluidity, dilatation and crucible swelling number etc. Appropriate rank indicated by reflectance value (MMR) Properties important for commercial as well as BF operation such as total moisture, ash etc. Properties which affects the properties of hot metal and steel such as percentage of sulphur and phosphorus. Modern coke making practice involves carbonization of a blend of coking coals. Coking coals in blended form are carbonized in a coke oven battery to produce metallurgical grade coke which is suitable for the operation of a blast furnace. Each plant uses its own blend based on the facilities available. In some of the Japanese plants coal blends consists of up to 20 different coals ranging in quality from coals with very high coking properties to coals with almost zero coking properties. The blended coking coal should have desirable coking properties for producing coke of required properties for BF operation. Quality requirement of coking coals Total moisture – It is limited to 10% maximum in as received condition. High moisture creates handling problem and lowers available carbon. Ash – It is limited to 10% maximum in air dried condition. High ash content reduces BF productivity and increases coke rate in the furnace. Volatile matter (VM) – The volatile matter in coking coals ranges from 20% to 35% in air dried sample. High volatile matter reduces the yield of metallurgical coke in coke oven battery but improves the coke oven gas generation. Sulphur – In coking coals sulphur is...