Refractories,Flux and Ferroalloys

Ferroalloy Ferroalloy refers to various alloys of iron with a high proportion of one or more other elements such as manganese, aluminium, or silicon. Impart distinctive qualities to steel. In the production of steel, ferro alloys are used for deoxidation, introduction of the alloying elements in the steel. Ferroalloys are usually classified into two groups namely (i) Bulk ferroalloys and (ii) Noble or special ferroalloys.

Trends and Drivers Ferroalloys are produced generally by two methods : in a blast furnace or in an electric arc furnace. More commonly, ferroalloys are produced by carbothermic reactions It is also possible to produce some ferroalloys by direct reduction processes. For example, the Krupp-Renn process is used in Japan to produce ferronickel. With increase in production of Steel there has been a huge demand for Ferro Alloys.

Table 2 Factors influencing optimization of Ferroalloy usage Ferro alloys constitute one of the most expensive inputs to steelmaking In a typical Integrated Steel Plant, it amounts to 7-10% of the cost of saleable steel. Thus optimization of Ferro Alloys usage is very important Table 2 Factors influencing optimization of Ferroalloy usage

New and Emerging Technologies Recently, the eventual role of oxides and other inclusions in ferroalloys has been raised to debating. Even small oxide inclusions can promote nucleation of acicular ferrite in low carbon grades and hinder grain growth thus leading to grain refinement. Typical such particles are for instance Ti and Ce oxides A novel potential product might be master alloys which could carry nanoparticles into liquid steel before solidification. Several techniques have been proposed to prepare master alloy e.g. Mix nano- powder with alloy powder and make pellets, briquettes or cored wire

2) by adding nano powder in liquid ferroalloy in casting and rapid solidification as well as by controlled generation. Improved knowledge of thermodynamics, kinetics and mechanisms of precipitates formation and phase transformations in different steels has been as basis to create new steel grades. Heat treatment processes have strongly evolved as well e:g Thermo-mechanical controlled rolling process (better mechanical properties in steels with less alloying) Cheaper and faster process route

Case Study Optimal Usage of Ferro Alloys: Rolling of C-20(RC) grade in TMT Fe 500D(25 mm). Reduced usage of FeMn by approximately 2T/heat. Approximate Savings(cost transportation + labour + Intangibles not including) = Similarly in future we can restrict the usage of costly Fev, FeNb

Refractories in Steel Making Refractories are broadly defined as materials that have been engineered to withstand high temperatures and often highly corrosive environments. Refractory materials are modified continuously to meet the evolving needs of the steel industry As new advantageous processes and procedures are adopted, refractory modifications or new developments are required.

Refractory Selection Productivity Energy Efficiency Manufacturing Cost Labour Cost

Trends and Drivers The trends and drivers are as varied as the materials and applications for which the refractories are used. Manufacturing cost reductions Production of “clean steel” Other drivers include limiting the amount of landfilled refractory material and the need to measure high-temperature refractory properties in models used to design steelmaking vessels. A general shift to monolithic, including castable, refractories is ongoing, and this trend is expected to continue until all refractory linings are based on cast-in-place technology.

Refractory in BOF and Steel Ladle MgO-C is universal choice for slag zone in carbon grades and ULC grades of steel Metal zone can be: Preferably carbon containing Basic brick lining of carbon bonded MgO, Dolo, Alumina-Magnesia For C sensitive steel grades – low carbon MgO-C, AMC, fired Alumina-Magnesia spinel, spinel based LCC /ULCC For SS grades, fired or low carbon dolo/dolo-mag is preferred Dolo lining reacts with acidic slag generated h SS making process & produces dense C2S/C3S layer Special care needed against “hydration” and “dusting” for β to g -C2S inversion while cooling <6000

Refractories for Secondary Steel making ladles Alumina Magnesia Carbon (AMC) Widely used in bottom and metal zone wall Resin bonded bricks with Alumina , Alumina Magnesia spinel and graphite Trial with fired spinel brick with encouraging result has been reported Improved characteristics of AMC/ spinel bricks Graphite reduces wetting by slag & steel, thereby, reduces infiltration High thermal shock resistance of high alumina bricks further improved by graphite due to its high thermal conductivity Magnesia in AMC bricks forms spinel with Al2O3 at decarburised hot face resulting in volume growth, densifies hot face that reduces slag infiltration, joint wear and further carbon oxidation. Alumina Magnesia spinels trap cations, e.g.,Mn2+, Fe2+ etc. from the infiltrating slag into the spinel structure making slag less corrosive

AluMag Spinel castable Refractories for RH - Degasser RH-Degasser Snorkel Direct bonded MagChrome Upper vessel Direct bonded MagChrome High fired MagChrome (Co-clinkered, Fused grain) Lower vessel Tabular Alumina – AluMag Spinel castable

New and Emerging Technologies Moving away from the standard “single-component” materials to multi- component composite materials Magnesia-graphite refractories (with and without metallic additions) have been used successfully in steelmaking vessel barrels and slag lines. Castable refractories, including self-flow types, are increasingly used to line low wear areas of steelmaking vessels Magnesia-based tundish linings have emerged as an alternative to sprayed magnesia linings. New refractory placement techniques such as shotcreting have been found to provide superior properties over gunable or ramable materials

Six refractory-related materials R&D topics present the greatest opportunities: Submerged entry nozzles that resist accretion Dewatering of monolithics Castable development Refractory recycling/landfill reduction High-temperature properties measurement Refractory wear gauge for steelmaking vessels

metal will take care of itself Take care of slag, metal will take care of itself

Flux in Steel Making In metallurgy, a flux (derived from Latin fluxus meaning “flow”) is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes are often referred to as acid, basic, or neutral Fluxes may have more than one function at a time. Limestone is used as a slag former. Dolomite is used as a slag former, slag modifier and as a refractory material. High calcium and dolomitic  lime mostly used in BOF and EAF.  Lime is particularly effective in removing phosphorus, sulphur, and silica, and, to a lesser extent, manganese.

FLUX MATERIALS Calcined Lime, Calcined Dolomite, Aux. Flux. Presently calcined dolomite being used along with Lime (70:30) for increased MgO level. AUX. FLUX Flourspar, Bauxite, Manganese Ore. Used for Slag Conditioning. Essential due to extensive use of Dolomite. Cost and Availability limits use of Spar. Blend of Bauxite, Mn Ore, Mill Scale Retained slag practice also practiced.

Dolomite and dolomitic lime are used for their magnesia content.   The BIS (IS: 10345 – 1982) has prescribed the under mentioned guidelines for flux limestone for use in steel plants: Limestone is considerably less expensive than lime because it is not calcined; however, lime is far more difficult to handle and reacts readily with water Dolomite and dolomitic lime are used for their magnesia content. Fluorspar is a neutral flux often used as an additive in steel- making slags to improve fluidity  

Trends and Drivers There is also a trend to production of lower silicon hot metal and lower hot metal manganese requirements which results in lower flux consumption in steelmaking. During pretreatment of hot metal in desulphurization plant lime is used. Fettling of the vessel lining as well as patching is done with dolomite based compounds Finer flux injection pneumatically in some combined blowing converters. Refining Mode operation vs Flux optimization mode.

Present (Present) Present (Present) (Present)

Present (Present) Present (Present) (Present)

Present

New and Emerging Technologies New slag functions such as foaming to provide a blanket over the bath to achieve post combustion of gases and allow adequate heat transfer might redefine flux requirements The direct ironmaking processes will use coal in preference to coke which will increase the sulfur burden on the process. Use of coals of lower grade than present metallurgical coals might require alteration of flux practices Disposal of LD slag is also becoming a problem and effective ways are evolving. Utilization of lime injection technology is being addressed by the electric arc furnace shops.

Thank You