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Common quenching medium
Common quenching medium
There are 7 things to need consider when choosing an engineering steel grade 

Steelmaking process and refining technology outside furnace

Slagging: The operation of adjusting the composition, alkalinity and viscosity of slag and its reactivity in the production of steel and iron. The aim is to produce metals with the required composition and temperature through slag-metal smelting. For example, the operation of oxygen top blown converter slagging and oxygen blowing is to generate slag with sufficient fluidity and alkalinity to reduce sulfur and phosphorus below the upper limit of planned steel grade, and to minimize the amount of spatter and slag spilt when oxygen blowing.

Steelmaking process and refining technology outside furnace

Slagging: the operation of slagging or slagging in the process of smelting in eAF according to different smelting conditions and purposes. If smelting with single slag method, at the end of oxidation slag must be raked; The original oxidizing slag must be released thoroughly to prevent phosphorus from returning when making reducing slag by double slag method.

Molten pool stirring: supply energy to molten metal pool to make molten metal and molten slag move, so as to improve the kinetic conditions of metallurgical reaction. Molten pool agitation can be realized by means of gas, mechanical and electromagnetic induction.

Electric furnace bottom blowing: N2, Ar, CO2, CO, CH4, O2 and other gases are blown into the furnace according to the process requirements by the nozzle placed at the bottom of the furnace to accelerate the melting and promote the metallurgical reaction process. The bottom blowing process can shorten the smelting time, reduce the power consumption, improve the operation of dephosphorization and desulfurization, increase the amount of residual manganese in steel, and increase the recovery rate of metal and alloy. It can make the composition and temperature of molten steel more uniform, so as to improve the quality of steel, reduce the cost and increase productivity.

Melting period: the melting period of steelmaking is mainly for open hearth and electric hearth steelmaking. Eaf steelmaking is called the melting period from electrification until the furnace charge is completely melted, and open hearth steelmaking is called the melting period from molten iron to the furnace charge is completely melted. The task of melting period is to melt and heat up the charge as soon as possible, and make the slag of melting period.

Steelmaking process and refining technology outside furnace

Oxidation period and decarbonization period: the oxidation period of ordinary power eAF steelmaking, usually refers to the process stage of furnace charge cleaning, sampling and analysis to the raking of oxide slag. There is also thought to be from the beginning of oxygen blowing or ore decarbonization. The main task of oxidation stage is to oxidize carbon and phosphorus in molten steel. Removal of gas and inclusion; The liquid steel is heated evenly. Decarbonization is an important process in oxidation stage. In order to ensure the purity of steel, the requirement of decarbonization is greater than 0.2% or so. With the development of out of furnace refining technology, the oxidation refining of eAF is mostly carried out in ladle or refining furnace.

Refining period: the process operation period during which elements and compounds harmful to the quality of steel are chemically selected into the gas phase or discharged or floated into the slag by slagging and other methods to remove them from the liquid steel.

Reduction period: in the operation of ordinary power eAF steelmaking, the period from slag picking at the end of oxidation to steel drawing is usually called reduction period. Its main task is to make reduction slag for diffusion, deoxidation, desulfurization, chemical composition control and temperature adjustment. At present, the reduction period has been cancelled for high power and super power eAF steelmaking operations.

Out of furnace refining: the process of moving the molten steel initially refined in the furnace (converter, electric furnace, etc.) to another vessel for refining, also called secondary metallurgy. Steelmaking process is therefore divided into primary refining and refining two steps. Primary smelting: the charge is melted, dephosphorized, decarbonized and main alloyed in an oxidizing atmosphere. Refining: degassing, deoxygenation, desulfurization, inclusion removal and composition fine tuning of the initial molten steel in a vacuum, inert gas or reducing atmosphere container. The advantage of a two-step process is that it improves steel quality, reduces smelting time, simplifies the process and reduces production costs. There are many kinds of out of furnace refining, which can be roughly divided into two types: out of furnace refining under atmospheric pressure and out of vacuum refining. According to the different treatment methods, it can be divided into ladle treatment type and ladle refining type.

Liquid steel stirring: Stirring of liquid steel during refining outside the furnace. It can homogenize the composition and temperature of liquid steel and promote metallurgical reaction. Most metallurgical reactions are phase interface reactions where the diffusion rate of reactants and products is the limiting link. Molten steel in the static state, its metallurgical reaction speed is very slow, such as the static molten steel desulfurization in the electric furnace needs 30 ~ 60 minutes; It only takes 3 ~ 5 minutes to desulphurize by stirring liquid steel in furnace refining. In the static state, the inclusions float up and remove slowly. The removal rate of inclusions increases exponentially when the molten steel is stirred, and it is related to the stirring intensity, type, characteristics and concentration of inclusions.

Ladle wire feeding: the method of deep desulphurization, calcium treatment and fine tuning of carbon and aluminum in steel by feeding powder wrapped with iron sheet, such as CA-Si powder, or directly feeding aluminum wire and carbon wire into ladle through wire feeding machine. It also has the function of cleaning molten steel and improving the shape of non-metallic inclusions.

Ladle treatment: Short for ladle treatment type out of furnace refining. It is characterized by short refining time (about 10 ~ 30 minutes), single refining task, no heating device to compensate for the decrease of molten steel temperature, simple process operation and less equipment investment. It has devices for degassing, desulfurization, composition control and inclusion change. Such as vacuum cycle degassing method (RH, DH), ladle vacuum argon blowing method (Gazid), ladle powder spraying method (IJ, TN, SL), etc.

Steelmaking process and refining technology outside furnace

Ladle refining: Short for ladle out of furnace refining. It has the characteristics of longer refining time than ladle treatment (about 60 ~ 180 minutes), with a variety of refining functions, with a heating device to compensate for the reduction of molten steel temperature, suitable for all kinds of high alloy steel and special performance of steel (such as ultra-pure steel) refining. Vacuum oxygen blowing decarbonization method (VOD), vacuum arc heating degassing method (VAD), ladle refining method (ASA-SKF), closed argon blowing composition fine tuning method (CAS), etc. Argon oxygen decarbonization (AOD) is similar.
Inert gas treatment: blowing inert gas into liquid steel, this gas itself does not participate in metallurgical reaction, but each small bubble rising from the liquid steel is equivalent to a “small vacuum chamber” (the partial pressure of H2, N2, CO in the bubble is close to zero), with “gas washing” effect. The principle of out of furnace refining stainless steel is to use different CO partial pressure under the balance between carbon and chromium and temperature. Refining and decarbonization with inert gas oxygenation can reduce the CO partial pressure in the carbon and oxygen reaction, and the carbon content is reduced and chromium is not oxidized at lower temperatures.

Pre-alloying: The operation of adding one or more alloying elements to liquid steel to meet the composition specifications of finished steel is called alloying. In most cases, deoxidation and alloying are carried out at the same time. Part of the deoxidizer added to the steel is consumed by the deoxidization of the steel, which is converted into deoxidization products and discharged. The other part is absorbed by molten steel and has alloying effect. Before the deoxygenation operation is completed, the alloying effect that the alloy added at the same time with deoxidizer is absorbed by molten steel is called prealloying.

Composition control: the operation of ensuring that all components of finished steel conform to standard requirements. Composition control runs through every link from batching to steel production, but the key point is the control of alloying element composition during alloying. High quality steels often require precise composition control in a narrow range; In general, under the premise of not affecting the performance of steel, according to the lower limit control.

Silicon enrichment: at the end of blowing, the silicon content in liquid steel is very low. A certain amount of silicon must be added in the form of alloy material in order to meet the requirements of silicon content in various steel grades. In addition to being used as a deoxidizer, it also increases silicon in molten steel. The amount of added silicon shall be calculated accurately and shall not exceed the allowable range of the smelting steel.

End point control: the control to make the chemical composition and temperature of the metal meet the requirements of the planned steel production at the end point of oxygen smelting and blowing (the end of oxygen blowing). There are two end-point control methods: carburizing method and carbon pulling method.

Drawing: The operation of discharging liquid steel when the temperature and composition of liquid steel meet the specified requirements of the type of steel being made. Attention should be paid to prevent slag from flowing into ladle when drawing steel. Additives used to adjust the temperature, composition and deoxidation of molten steel are added to the ladle or flow during drawing.