Vacuum Oxygen Decarburization Research Articles

A Dynamic Decarburization Model in Vacuum Oxygen Decarburization Process for Ultrapure Ferritic Stainless Steel

A Dynamic Decarburization Model in Vacuum Oxygen Decarburization Process for Ultrapure Ferritic Stainless Steel

A Dynamic Decarburization Model in Vacuum Oxygen Decarburization Process for Ultrapure Ferritic Stainless Steel

A mathematical model incorporating dynamic parameters is proposed to investigate the overall decarburization process during the vacuum oxygen refining (VOD) process for ultrapure ferritic stainless steel. This paper also conducted a precise theoretical calculation of the C‐Cr equilibrium. Moreover, the top‐blowing oxygen distribution is categorized into six directions: [C] oxidation, alloy component oxidation, CO bubble oxidation above the bath surface, bath surface oxidation (FeO), dissolution in the molten steel ([O]), and escape into the exhausted gas. The FeO and Cr2O3 oxide are intermediate product of oxygen to oxidize [C] remaining in the molten steel during the VCD stage. The modified approach of Gibbs free energies determines the critical carbon concentration by the distribution ratio of carbon to the top‐blowing oxygen. The top‐blowing oxygen primarily consumed by CO‐CO2 bubble (49–55%) and Cr2O3 (26–33%). Additionally, the model considered operational aspects, the system's heat balance, and changes in overall metal‐slag conditions during the refining process. The exhausted gas composition and end‐point carbon concentration align well with industrial data. Within a certain range (approximately up to 0.50%), increasing initial carbon concentration can enhance overall decarburization efficiency.

Pumping stations for today's steel degassing requirements

SummaryThis article focuses on the vacuum equipment used in vacuum degassing (VD) and vacuum oxygen decarburization (VOD) processes. Despite harsh process conditions caused by outgassing and the process gases themselves, there are various pumping principles and designs of vacuum pumps that can be used. Through clever pump selection there is an opportunity to realize substantial energy and operating resource savings on the vacuum pumping side. Last but not least, a new pump series will be presented that further contributes to cost reduction through higher efficiency.

The Production Practice of Ultra-pure and Ultra-low-carbon Stainless Steel 07Cr17Ni12Mo2 by LF-VOD+ESR Steelmaking Process

By reasonably controlling the vacuum degree, oxygen supply intensity, oxygen lance position, and other process parameters of Vacuum Oxygen Decarburization (VOD) refining furnace (60t), and according to the blowing situation, combined with the oxygen concentration difference potential, exhaust gas temperature and CO concentration, accurately determine the blowing end point, and then further remove inclusions in steel by Electro-Slag Remelting (ESR), making the end point C less than or equal to 0.06 %, the total content of (As + Sn + Pb + Sb + Bi) is less than or equal to 150 ppm, total oxygen content is less than or equal to 30 ppm. The content of class A, B, C and D inclusions is less than or equal to grade 1.0 and the total inclusion grade is less than or equal to grade 2.0.

Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel

15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, and vacuum casting were studied. The results show that the DS-type inclusions with sizes larger than 20 μm were CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions in vacuum degassing, typical inclusions were spinel or Al2O3. After Ca–Si additions during ladle treatment, typical inclusions were liquid or dual-phase Al2O3–CaO–SiO2–MgO. During the solidification process, due to the segregation of S and the decrease in solubility, the typical inclusions in the final casting became Al2O3–CaO–SiO2–MgO–CaS. For optimal fatigue performance of stainless steel castings, slag and refractory composition control were also necessary because the [Mg] contents mainly come from the slag and lining.

Reduction of harmful effects of nitrogen on the properties of low-carbon steel 08Y by electing a rational amount of nitride-forming elements

Based on the thermodynamic analysis of nitride formation reactions, the advantage of titanium nitride formation and the lowest probability of boron nitride formation are established. Based on the analysis of experimental data, an analytical expression was established to calculate the required amount of titanium additives to neutralize the harmful effects of nitrogen, which also takes into account the concentration of aluminum in steel and prevents the formation of harmful aluminum nitrides. Necessary and sufficient concentrations of boron in steel are calculated to start the nitride formation reaction and to provide a strengthening effect associated with the formation of boron nitrides. Thermodynamic calculations and based on the analysis of the results of previous experimental melts of low-carbon steel, it is shown that the activity of oxygen in the intermediate to obtain particularly low-carbon steel should be such as to ensure the removal of carbon from it to a given limit, as well as the amounts of carbon deoxidized steels from ferroalloys and electrodes when heating steel on ladle-furnace installations, as well as from periclase-carbon lining-stalkovsha (carbon content in the area of the slag belt 10-12%, in the lining of the walls and bottom - 6%). The consumption of aluminum at the outlet of the furnace should be correlated with the degree of peroxidation of the metal, which would be desirable to stabilize and reduce the precipitation of silicomanganese and ring-containing ferroalloys. When organizing the evacuation of steel, reducing the pressure in the vacuum chamber to 100 mbar is theoretically sufficient for the predominant oxidation of carbon in comparison with manganese and silicon in the entire temperature range of the process. When evacuating non-deoxidized aluminum metal, the final carbon content in the metal of 0.01% is achieved even at its initial content of 0.074%. Due to the use of vacuum oxygen decarburization reaction without additional introduction of oxygen in gaseous form or in the form of oxides, it is possible to obtain a low-carbon metal with a guaranteed carbon content of 0.01% in the finished metal and a minimum manganese content of 0.12% and silicon up to 0.02 %, which provides high plastic properties of the metal. Keywords: low carbon steel, nitrides, titanium, boron, aluminum, vacuum carbon deoxidation

Pure steel milling technology and specific features

Determine the technological parameters of smelting and out-of-furnace processing of low-carbon steel. Method. The thermodynamics of nitride formation reactions is considered and the advantage of titanium nitride forma- ?ion, the lowest probability of boron nitride formation is established. Based on the analysis of experimental data, an analytical expression was obtained, which allows to calculate the required amount of titanium additives to neutralize the harmful effects of nitrogen, which also takes into account the concentration of aluminum in steel and prevents the formation of harmful aluminum nitrides. Necessary and sufficient concentrations of boron in steel are calculated to start the nitride formation reaction and to provide the strengthening effect associated with the formation of boron nitrides. Results. Thermodynamic calculations and based on the analysis of the results of previous experimental melts of lowcarbon steel, it is shown that the activity of oxygen in the intermediate to obtain particularly low-carbon steel should be such as to ensure the removal of carbon from it to a given limit, as well as the amounts of carbon deoxidized steels from ferroalloys and electrodes when heating steel on ladle-furnace installations, as well as from periclase-carbon lining of steel ladle (carbon content in the area of the slag belt 10-12%, in the lining of walls and bottoms - 6%). furnaces must be correlated with the degree of metal oxidation, which would be desirable to stabilize and reduce the precipitation of silicomanganese and calcium-containing ferroalloys. Scientific novelty. When organizing the evacuation of steel, reducing the pressure in the vacuum chamber to 100 mbar is theoretically sufficient for the predominant oxidation of carbon in comparison with manganese and silicon in the entire temperature range of the process. When evacuating non-deoxidized aluminum metal, the final carbon content in the metal is 0.01% is achieved even at its initial content of 0.074%. Practical significance. Due to the use of vacuum oxygen decarburization reaction without additional introduction of oxygen in gaseous form or in the form of oxides, it is possible to obtain low-carbon metal with a guaranteed carbon content of 0.01% in the finished metal and a minimum manganese content of 0.12% and silicon up to 0 , 02%, which provides high plastic properties of the metal.

Characteristics and Formation Mechanism of Inclusions in 304L Stainless Steel during the VOD Refining Process

The formation and characteristics of non-metallic inclusions in 304L stainless steel during the vacuum oxygen decarburization (VOD) refining process were investigated using industrial experiments and thermodynamic calculations. The compositional characteristics indicated that two types of inclusions with different sizes (from 1 μm to 30 μm) existed in 304L stainless steel during the VOD refining process, i.e., CaO-SiO2-Al2O3-MgO external inclusions, and CaO-SiO2-Al2O3-MgO-MnO endogenous inclusions. The calculation results obtained using the FactSage 7.1 software confirmed that the inclusions that were larger than 5 μm were mostly CaO-SiO2-Al2O3-MgO; the similarity in composition to the slag indicated that these inclusions originated from the slag entrapment. The CaO-SiO2-Al2O3-MgO-MnO inclusions that were smaller than 5 μm originated mainly from the oxidation reaction with Ca, Al, Mg, Si, and Mn. The changes in the inclusion composition resulting from changes in the Ca, Al, and O contents, and the temperature during the VOD refining process was larger for the smaller inclusions. Generating mechanisms for the CaO-SiO2-Al2O3-MgO-MnO inclusions in the 304L stainless steel were proposed.

Manufacturing of Ø 1,000 Grade Large Diameter Round Bloom and Development of Cost Effective Hot Forging Process Using the Round Bloom

Taewoong is an open die forging company, specialized in the production of hot forged and ring rolled parts. Recently, Taewoong utilized continuous casting facilities that can manufacture O 1,000 grade large diameter round bloom to increase competitiveness of the company. This study focuses installed continuous casting facilities and ring rolling process using manufactured O 1,000 grade round bloom. Constitution of installed facilities was introduced and characteristics of the facilities, EAF (Electric Arc Furnace), LF (Ladle Furnace), VD (Vacuum Degassing), VOD (Vacuum Oxygen Decarburization) and CC (Continuous Casting) were described. Also, ring rolling experiments were performed using manufactured O 1,000 grade round bloom. Hot forging process design was performed to fabricate sound products. Work sequence design was performed using FE analysis software and optimal forging work sequence was derived. With the results, sound forged parts were formed and improvement of competitiveness was verified. Raw material recovery ratio was increased and the number of process and processing time were decreased. The results show utilized continuous cast facilities give opportunity to be a world competitive company by increasing competitiveness of the company.

Characterization of landfilled stainless steel slags in view of metal recovery

The slag samples taken from landfill, which originated from different metallurgical processes, have been characterized in this study. The slags were categorized as electric arc furnace (EAF) slag, argon oxygen decarburization/metal refining process slag and vacuum oxygen decarburization slag based on chromium content and basicity. EAF slags have higher potential in metal recovery than the other two slags due to its higher iron and chromium contents. The size of the iron-chromium-nickel alloy particles varies from a few μm up to several cm. The recoveries of large metal particles and metal-spinel aggregates have potential to make the metal recovery from landfilled slags economically viable.

Degradation of low‐carbon MgO‐C refractory by high‐alumina stainless steel slags in VOD ladle slagline

AbstractA new type of low‐carbon magnesia carbon refractory (LCMCR) substituting for MgO‐Cr2O3 refractory was successfully used in vacuum oxygen decarburization (VOD) ladle slagline, and the composition and microstructure of the used LCMCR were investigated. The results indicated that the decarburizing reaction (MgO‐C reaction) in the LCMCR under the VOD refining condition (high temperature, low pressure) was inhibited due to the low carbon content in the MgO‐C refractory and the dense layer formed between slag and original layer. The dense layer prevented the penetration of the external O2 into the LCMCR inside because of the lower permeability of this layer, and thus, the direct burnout of the C in the LCMCR was substantially restrained. On the other hand, the large size crystal and the ultra‐low inclusions (SiO2 and Fe2O3) content of the fused magnesia in the LCMCR made the magnesia more slag resistance, because the grain boundary in magnesia had higher slag penetration resistance and the contact area between the slag and the magnesia was reduced. The two aspects of the inhibited decarburizing reaction and the high quality magnesia synthetically contributed to the high slag resistance of the LCMCR.

Variation and optimization of acid-dissolved aluminum content in stainless steel

As a key step in secondary refining, the deoxidation process in clean stainless steel production is widely researched by many scholars. In this study, vacuum oxygen decarburization (VOD) deoxidation refining in a 40-t electric arc furnace + VOD + ingot casting process was analyzed and optimized on the basis of Al deoxidation of stainless steel and thermodynamic equilibrium reactions between the slag and steel. Under good stirring conditions in VOD, the deoxidation reaction reaches equilibrium rapidly, and the oxygen activity in the bulk steel is controlled by the slag composition and Al content. A basicity of 3–5 and an Al content greater than 0.015wt% in the melt resulted in an oxygen content less than 0.0006wt%. In addition, the dissolved oxygen content decreased slightly when the Al content in the steel was greater than 0.02wt%. Because of the equilibrium of the Si–O reaction between the slag and steel, the activity of SiO2 will increase while the Si content increases; thus, the Si content should be lowered to enable the formation of a high-basicity slag. A high-basicity, low-Al2O3 slag and an increased Si content will reduce the Al consumption caused by SiO2 reduction.

Comparison of the chemical corrosion resistance of magnesia-based refractories by stainless steelmaking slags under vacuum conditions

This study evaluates commercially available magnesia–chromite, magnesia–carbon and magnesia–doloma bricks for their use in a Vacuum Oxygen Decarburisation ladle. The corrosion behaviour of these bricks by stainless steelmaking slags is, therefore, investigated through crucible tests in a vacuum induction furnace at elevated temperatures (1650 and 1750°C) and low oxygen partial pressures (5.3 and 3.0×10−11atm). The results reveal that magnesia–carbon bricks are severely corroded due to the high dissolution of MgO, while magnesia–chromite and magnesia–doloma refractories exhibit an excellent corrosion resistance. The MgO enrichment in the slag is believed to be the reason of the low wear rate of the MgO–doloma refractories. Rebonded and direct-bonded MgO–chromite refractories show similar corrosion resistance against the slags because of the ‘secondary chromite inactivation’. Decreasing the slag basicity enhances the dissolution of MgO into the slag, thereby increasing the corrosion of the magnesia-based refractories.

Development of High Nitrogen Stainless Steel for Cryogenic Applications

Austenitic stainless steels are extensively used as structural materials for various aerospace systems. Nitrogen containing stainless steels have special role due to their austenite stabilization tendency down to subzero temperatures, improved strength and resistance to sensitization. Primary processing of nitrogen containing cryogenic grade stainless steel 202 has been carried out through two different melting routes viz. (1). conventional melt route of electric arc furnace (EAF) melting followed by vacuum oxygen decarburization (VOD) & vacuum degassing (VD) and other one through (2). vacuum induction melting (VIM) followed by ESR. Chemical analysis and macrostructure analysis was carried out on the samples drawn from these billets. Homogenization and thermomechanical processing parameters were selected and the same were followed for the ingots made through both the melt routes. Mechanical properties evaluation (including tensile properties at subzero temperature of 77K) and micro structure characterization of the products realised from all the two melt routes were carried out. It is observed that, both the melt routes could result in achieving the required aerospace quality of alloy with respect to the chemical composition, metallurgical and mechanical properties. This paper confirms that any of the melt routes studied herein can be adopted according to availability of the facilities. The process development and characterization of the steels processed by conventional EAF+ VD & VOD and VIM+ESR melt routes is presented in this paper.

Development and Characterization of 15Cr-5Ni-1W Martensitic Precipitation Hardening Stainless Steel for Aerospace Applications

15Cr-5Ni-1W precipitation hardening (PH) stainless steel is a martensitic PH stainless steel finding extensive use in semi-cryo engine applications. The alloy was developed through Vacuum Induction Melting (VIM) + Electro slag refining (ESR) under argon cover route. The alloy contains heavy elements like Mo, Nb, V and W totalling ~ 2 % by weight. Since the alloy is martensitic, stringent gas levels were also specified. Hence it was a challenging task to realise it without any segregation and stringent gas levels. The alloy was successfully melted through two different melt routes – (C). Electric Arc melting followed by Vacuum Oxygen decarburization (VOD) - vacuum degassing (VD) followed by secondary melting by ESR and also by melt route (V) vacuum induction melting (VIM) + ESR route. It was then forged into bars, rods and rings. The samples from the alloy were subjected to two different heat treatment cycles. Both the heat treatment cycles involved hardening at 1000°C for 2 hrs followed by air cooling to room temperature. In one of the cycle, sub-zero heat treatment at-70 °C was done prior to tempering while in the other cycle; direct tempering was carried out after hardening operation. Tempering was carried out at 2 different temperatures of 490 and 500 °C to achieve the specified mechanical properties. It was found that the alloy could meet the specified strength and ductility with both the heat treatment cycles mentioned above. However samples subjected to subzero heat treatment showed marginally higher strength with slight compromise in ductility. The alloy also exhibited similar impact toughness in both the heat treatment conditions. Delta ferrite was also found to be within 2% for both the heat treatment cycles employed in this study. The alloy also exhibited excellent strength and ductility at elevated temperature of 500 °C with just 25% reduction in yield strength compared to room temperature yield strength without much change in ductility.

Assimilation of High-Strength Austenitic Corrosion Resistant Nitrogen-Containing Steel Melting Technology Using Large-Capacity Equipment

A technology is developed for production of high-strength austenitic nitrogen-containing steel, including melting of intermediate product in a basic arc furnace, ladle vacuum-oxygen decarburization, and furnace ladle treatment. Use of contemporary large metallurgical units and the developed technology makes it possible to assimilate industrial production of high-strength austenitic nitrogen-containing steel with provision of a prescribed chemical composition and product quality corresponding to required specifications.

Vacuum oxygen decarburization (VOD) of stainless steel

AbstractHigh costs for vacuum generation and maintenance can be overcome by replacing steam ejector pumps with mechanical vacuum pumps, initially for the vacuum degassing (VD) process but later also for the vacuum oxygen decarburization (VOD) process. Initial concerns about the technical suitability of mechanical pumps for vacuum processing of large heat weights have proven unfounded. There is no real technical upper limit. With detailed knowledge about the vacuum process mechanical vacuum pumps can be successfully engineered for any heat weight where a steam ejector pump would previously have been selected. In fact, suction speed of mechanical vacuum pumps can be ideally controlled to fit the various phases of vacuum processing. This article will show how mechanical vacuum pumps contribute to significant cost reduction and to the possibility of automation of decarburisation, thereby achieving better process control.

Manufacture of Specialty Stainless Steels through Triplex Route at Mukand

Specialty stainless steels designed with higher levels of Chromium, Nickel and Molybdenum than the general austenitic grades AISI 304 and AISI 316 have distinctly superior corrosion resistance properties. The commercial production of such high alloyed stainless steels came with advent of improved steel melting, refining and casting technologies. These technological improvements made it possible to produce such steels with low carbon levels and close control of chemical composition necessary to achieve the desired phase balance and avoid formation of undesirable intermetallic phases. Further, ability to achieve low sulphur levels combined with freedom from undesirable level of tramp elements improved the hot workability characteristics. Thermodynamic aspects of steelmaking and refining in Vacuum Oxygen Decarburization ( VOD) process for manufacture of specialty grades 904L (24% Ni, 20% Cr, 4% Mo, 1.2%Cu) , 317LM ( 19% Cr, 14.5% Ni, 4% Mo,) , 2205 ( 22.5% Cr, 5% Ni, 3% Mo) at Mukand through the Triplex process route ( Ultra High Power Furnace Oxygen Top and Bottom Blown Convertor VOD) are outlined. The effects of undesirable intermetallic phases, particularly sigma phase, on mechanical and corrosion properties are discussed. Application areas for such specialty grades are reviewed. Keywords: High alloyed Stainless steels, triplex process, sigma phase, intermetallic phases, tramp elements, hot workability, corrosion properties, vacuum oxygen decarburization.

Stainless Steel Processing to Meet Advanced Applications

Stainless steel bar and wire products that cater to the high technology application in defence, nuclear, aerospace, oil field and chemical engineering is an area poised for rapid growth in India. The advancing capabilities of alloy steel plants in India have enabled mastering of techniques to make a wide variety of stainless steels. However, there are increasing challenges to meet the advanced property requirements, which call for a basic understanding on the structure property relationship that are influenced by appropriate alloy design and down-stream processing. The special steel industry cater to a wide variety of stainless steels namely ferritic, martensitic, austenitic and precipitation hardenable categories for meeting requirements of high technology. One of the process for making the primary stainless steels is Vacuum Oxygen Decarburisation process. For advanced applications, the primary melted steel is again secondary refined using electroslagremelting for the management of solidification structures and control of inclusions. In the austenitic grades, the hot forged and hot rolled heat treated steels, careful choice of chemistry controls the delta ferrite content and ensures uniformity of the grain size in the product during deformation processing and heat treatment. In the martensitic stainless steel grades, focus is given to delta ferrite, grain size control and appropriate tempering treatment. In the precipitation hardenable steels grades the aging reactions and hot deformation range have to be optimised for deriving specified mechanical properties. Special grades are produced using non ESR and ESR routes to meet high temperature applications such as turbine blades and bolting. In these grades control of delta ferrite content, carbides, carbo-nitrides in the matrix has a deep influence on the mechanical and sub zero fracture properties. In the ferritic stainless steel grade grain size control is critical. The presentation would bring forth the correlation between the alloy design, processing and properties that were achieved in the products mentioned above to meet some of the challenging requirements.

Modern Vacuum Pumps for the Vacuum Degassing of Steel in Small and Large Vacuum-Degassing Units

This article discusses a new design for Roots pumps and screw pumps which uses hermetically sealed motors. The new pump is easy to maintain, alleviates wear, and increases safety, which makes it more reliable than traditional Roots pumps. The screw vacuum pumps operate within a wide range of pressures. Thanks to the absence of friction in the vacuum chamber and the use of special coatings on the working elements, these units can be used in place of water-ring and rotary vane pumps for the high-vacuum evacuation of gases and vapors of liquids (including aggressive liquids). In this case, the gas being pumped is not contaminated by water vapor or oil. The absence of friction elements in the vacuum chamber means that the unit requires almost no maintenance. The use of standardized pre-equipped modular building blocks reduces fabrication and installation/startup costs, makes the equipment more compact, and saves power, oil, and water compared to other systems. The small size of both types of pumps – which can be used in any configuration – not only shortens delivery times and simplifies spare-parts management but also facilitates equipment assembly or (if necessary) replacement. Attainment of the pumps’ rated productivity is assured by parallel connection of several compact modules. The mechanical pumps can be used for VID, VIM, VD, RH, VIT (vacuum ingot teeming), and VAR (vacuum-arc remelting) units, including units that perform vacuum-oxygen decarburization. The pumps’ design incorporates measures to protect against dust and water-vapor condensation, which can lead to the formation of acidic liquids. The pumps can be used in all types of vacuum processes – including processes that involve the injection of oxygen – while observing existing safety standards. The low inertial mass of the pumps helps them respond rapidly to frequency control, which facilitates the evacuation process. Redundant operation is provided for in all the pumping-unit configurations.