×
{pboot:sort scode=} {/pboot:sort}

Electric arc furnace steelmaking

2014-11-20

01 Electric arc furnace(1).jpg

Electric arc furnace steelmaking can be divided into five stages: the collection of raw materials, the preparation before smelting, the melting period, the oxidation period and the reduction period.

 Collection of raw materials

 The scrap steel is the main material of the electric arc furnace steelmaking, the quality of the scrap steel has a direct influence on the quality, cost and productivity of the steel:

 (1) the scrap surface should be clean and rust less, because of the impurities in the scrap steel and other debris will reduce the conductivity of the charge, extend the melting time, but also affect the oxidation of phosphorus removal effect and erosion lining. The corrosion rate of steel and alloy elements can be reduced when the steel is corroded seriously or the oil is contaminated.

 (2) non ferrous metals such as lead, tin, arsenic, zinc, copper, etc. shall not be mixed in scrap steel. The density of lead is large, the melting point is low, and it is insoluble in molten steel. Tin, arsenic and copper, causing hot brittleness.

 (3) stainless steel shall not be mixed with sealed containers, flammable, explosive and toxic to ensure safe production.

 (4) the chemical composition of the scrap steel should be clear, and the content of sulfur and phosphorus should not be too high.

 (5) the scrap size can not be too large (cross-sectional area should not exceed 150mm * 150mm, the maximum length of not more than 350mm). Pig iron in EAF steelmaking is generally used to improve the carbon content of the burden, usually with the amount of not more than 30% of the charge.

 Preparation before smelting

 Batching is an indispensable part in the process of EAF steelmaking, and whether the composition is reasonable or not is related to the normal operation of steelmaking process according to the technical requirements. Reasonable proportioning can shorten smelting time. Ingredients should pay attention to: first, it is necessary to carry out the correct calculation of ingredients and accurately weighing the amount of burden. The two is the size of the burden to match with the proportion, in order to achieve the purpose of good fit, fast. Three kinds of charge should be based on the quality requirements of steel and smelting method with the use of. Four ingredients must comply with the technical requirements.

 The main content of the main elements in the furnace is as follows:

 (1) carbon content. The carbon content in the charge should ensure that there is enough carbon in the oxidation stage to carry out the reaction of carbon and oxygen to achieve the purpose of removing air and removing impurities. Carbon content according to the amount of decarburization melting stage of carbon burning, oxidation and reduction of the amount of carbon during the period of the 3 factors to determine the requirements of melting charge, product specifications and the lower limit of 0.3% ~ 0.4% higher than the amount of carbon steel; but the carbon content is not too high, otherwise it will extend the oxidation time and make molten steel overheating.

 (2) silicon content. Silicon content is generally not greater than 0.8% of the charge, too high will delay the boiling liquid steel.

 (3) manganese content. General steel mix of manganese can not be considered, usually after the removal of manganese content of less than 0.3%, otherwise it will delay the pool boiling.

 Phosphorus and sulfur content in principle, the lower the better. Generally, the phosphorus content should be less than 0.05%.

 In order to make the furnace charge density, charge must be large, medium and small material and reasonable collocation, generally small materials accounted for 15% to 20%, in material accounted for 40% to 50%, accounting for 40% of aniseed.

 Before feeding, the bottom of the furnace should be laid with 1.5% of the material weight, so as to make the molten slag in advance, which is beneficial to the early removal of phosphorus and the reduction of the suction and acceleration of the molten steel.

 Charging should be half of small material into the bottom, the upper and the center of the furnace material into all areas of small aniseed, low carbon steel scrap and refractory material, aniseed placed between the small material, medium material mounted on and around the top of aniseed, aniseed into small material. Where the ingredients used in the electrode block, should be smashed into 50mm ~ 100mm or so, installed in the lower burden.

 In short, the cloth should be: dense and loose, high middle, low around the furnace door, no aniseed; wearing well quickly, do not bypass.

 Melting period

 In the arc furnace steelmaking process, from the beginning of the electricity to the melting of the molten steel is called melting. The melting period accounts for about half of the smelting time, and the power consumption accounts for about 2/3 of the total electricity consumption.

 The melting stage task is under the premise of ensuring the service life of blast furnace, furnace melting temperature quickly with minimal power consumption, and slag made good period for burnt, stable arc, prevent suction and advance to P.

 (1) arc phase. Electric arc furnace and full charge, with the top of the arc was very close, if the input power is too large, too easy to burn out the blast furnace top voltage, so the general choice of intermediate voltage and input transformer rated power of about 2/3.

 (2) drilling stage. This stage is completely surrounded by arc furnace, the heat absorbed almost all the burden, it will not burn the lining, so the use of maximum power, generally wear well time is about 20min, the total melting time of 1/4.

 (3) rising stage. The electrode "wear well" in the end, the bottom has been formed at the bottom of molten pool, oxidation of lime and some elements, which form a layer of slag in liquid steel, surrounded by radiant heat and melting furnace to increase the liquid level, the liquid steel electrode increased gradually increased. At this stage, the maximum power transfer power is still used, and the time is about 1/2 of the total melting time.

 (4) melting the last class. After the charge has been melted more than 3/4, the arc can not be covered by the charge, the 3 electrodes under the high temperature zone has been linked to a piece of time, such as the maximum power supply for a long time, the arc will strongly damage the furnace cover and furnace wall.

 The main task of melting period is melting charge, but in the melting stage is made of slag, the content is an important operation in melting period, if only to satisfy the coverage of liquid steel and arc stability requirements, only 1% to 1.5% of the amount of slag is enough, but in considering the requirements of dephosphorization of molten slag, must have a certain

 Oxidation stage

 1 oxidation of the main tasks

 The main tasks of oxidation are as follows:

 (1) continued oxidation of phosphorus in molten steel. General steel requirements at the end of the oxidation period, the phosphorus content of steel is not higher than 0.015% ~ 0.010%, the high manganese steel due to the high content of phosphorus in ferromanganese, should be controlled lower.

 (2) removal of gases and inclusions. At the end of the oxidation period, the nitrogen content in steel is reduced to 0.004% ~ 0.01%, the hydrogen content in steel is reduced to about 0.00035%, and the total amount of inclusions is not higher than 0.001%.

 (3) the molten steel is heated uniformly and the temperature is higher than the tapping temperature at the end of the oxidation period by 10 DEG C to about 20 DEG C.

 Ore oxidation method is the use of iron ore containing 80% ~ 90% of the high iron oxide into the molten pool, into a low iron oxide (Fe2O3+Fe=3FeO, Fe3O4+Fe=4FeO or Fe3O4=Fe2O3+FeO). Part of the low iron oxide is left in the slag, most of which is used for the oxidation of carbon and phosphorus in the molten steel.

 In order to achieve a good effect of phosphorus removal: the content of FeO in the slag is 12% ~ ~, the R is from 2 to 3, and the fluidity is good.

 Oxidation of carbon: the oxidation of carbon in the process of steelmaking is a very important reaction, and is conducive to the rapid heating of the molten pool, is conducive to the homogenization of the composition of molten steel. Specific steps are as follows:

 FeO=Fe+O, O+C=CO,

 Total response FeO+C=Fe+CO.

 Therefore, the oxidation of the ore method is: the ore into the furnace, in the slag into FeO, and then spread to the molten steel, and distributed in the entire pool. Carbon and oxygen react in the place where the bubble is easy to generate, and generate CO bubble, CO from the reaction zone, rising in the process of rising, and into the furnace gas, resulting in the pool boiling. In order to speed up the decarburization rate, the temperature of the ore in the oxidation period should be greater than 1550.

 In short, the operation of the ore decarburization should be: high temperature, thin slag, batch addition of ore, uniform boiling.

 2 oxidation operation points

 (1) sampling and temperature measurement after melting (no less than 1550 DEG C).

 (2) oxidation, temperature measurement in line with the requirements, good slag condition can be fed in batches, the amount of ore per batch shall not exceed the weight of the material of 1% ~ 2%, the interval between each batch should be greater than 5min.

 (3) the decarburization rate (V) per hour is greater than or equal to 0.06%; C = 0.30% for Delta growingup.

 (4) adjusting slag condition. At the beginning of the oxidation boiling, the slag is required to be R=2 ~ 3, and the slag quantity is controlled from 3% to 4%. In the later stage of oxidation, the slag fluidity should be good, the slag layer should be thin and the slag quantity should be controlled at 2% ~ 3%.

 (5) Interim sampling analysis and control end point carbon. In order to master the degree of oxidation of phosphorus and carbon, the two batches of slag should be sampled and analyzed in time to determine the content of carbon and phosphorus.

 (6) temperature control. Oxidation period is generally a heating stage, the rate of temperature rise and fall according to the situation of steel liquid phosphorus. During the oxidation period, the temperature of the molten steel must be increased to 10 DEG C to C / C, which is greater than the tapping temperature of the steel.

 (7) net boiling. When the chemical composition and temperature appropriate, stop adding ore, adjust slag, let the pool boiling into the natural (5min ~ 10min), the residual oxygen content in molten steel is reduced, and the gas and inclusion of full float, in order to facilitate the reduction period smoothly.

 (8) skimming. Oxidation period, high content of FeO in slag, and a P2O5 period in order to restore the deoxidation and to prevent the return of phosphorus must be slag, slag is the condition of slag temperature is higher than the tapping temperature 10 to 20 DEG C; the slag before carbon, phosphorus and other restrictive components shall comply with the requirements.

 (9) carburizing. If the carbon content is too low to oxidation at the end of the carbon steel surface can be exposed in the slag after the saga pure and dry toner, for carburizing.

 Reduction phase

 During the oxidation period, it is called the reduction period. The main tasks are deoxidation, desulfurization, control of chemical composition, temperature adjustment. The operation process of reduction phase is as follows:

 (1) after the slag is quickly added to the thin slag to cover the steel liquid to prevent inhalation and cooling. M (CaO): m (CaF2) =3: 1.

 (2) thin slag formation after pre deoxidation, adding toner 2.5kg/t ~ 4kg/t to the residue on the surface, after adding the closed door, large input power, the reaction of calcium carbide with calcium oxide powder in the arc zone.

 (3) carbide slag after the formation of 20min ~ 30min, dregs of white, while paying attention to the molten steel carburizing.

please contact: susan@aeaxa.com