SU956575A1 - Method for reducing crack-prone steel - Google Patents

Description

The invention relates to ferrous metallurgy, in particular to the smelting of crack-sensitive structural steel in an electric arc furnace, in particular for subsequent electroslag remelting.

Known smelting of crack-sensitive structural steels of grades 50Г, 40ХН, 40Х, 45, 40 in 25 tons of arc-burning furnaces for subsequent electroslag remelting with replacement of metal deoxidation with aluminum by deoxidation and microalloying of steel in the ladle with titanium. To do this, TiV grade ferrotitanium with a titanium content of at least 60% and a aluminum to titanium ratio of not more than 0.07 fl is placed on the bottom of the ladle.

In this method, an extremely deficient, high-grade ferrotitanium is used, which does not allow for an expansion of the production volume of cracked feelings of grit steels by this technology.

Also known additive silicocalcium fraction of not more than 50 mm per slag in the smelting of steel in the main arc furnaces 2j.

The addition of lump silicocalcium to slag in a working arc furnace LEADS to a fly of calcium in the region

effects on slag electric arcs, since calcium is an element that has a high vapor pressure at steelmaking temperatures. As a result, the beneficial use of calcium as a deoxidizing agent is reduced.

Closest to the proposed technical essence and achievable

The result is a method of deoxidizing steel, smelted in an electric arc furnace for subsequent electroslag remelting, including pre-deoxidation of metal with a piece of ferro-syrup, a deoxidation of slag with coke powders and high-grade ferrosilicon and the final deoxidation of steel with silico calcysm and a. .

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Aluminum is injected onto iron rods 0.7 kg / t, silicocalcium with a particle size of not more than 50 mm 1.0 kg / t. Silikokaltsy prisyvayut under the stream of metal.

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The disadvantages of this method of steel deoxidation are the need for a special fracture of silicocalcium into powder, which is associated with an explosion hazard, especially when grinding in

30 ball mill silicocalcous grades SK20-30 with a calcium content of more than 20%, as well as use of silicocalcium with a particle size of not more than 50 mm, i.e., for the additive in the bucket. the containing fraction and the fine fraction, which is partly removed from the ladle by heat flows. As a result, the beneficial use of calcium is reduced. The deoxidation of steel with aluminum in the amount of 0.7 kg / t causes the formation of aluminum nitrides in the metal, which are the main reason for the occurrence of cracks in electroslag ingots obtained from raw steel deoxidized with a significant amount of aluminum. In addition, a disadvantage of the steel deoxidation process is the small amount of silicocalcium used for the final deoxidation of the metal in the ladle, since such an amount of silicocalus does not prevent the formation of aluminum nitrides in the steel due to the interaction of calcium with the metal nitrogen. The purpose of the invention is to increase the efficiency of use of calcium and reduce scrap: electroslag ingots along longitudinal cracks. The goal is achieved by the method of deoxidation of sensitive steel, melted in an electric arc furnace for the subsequent electroslag remelting, including preliminary metal deoxidation by lump ferrosilicon , slag deoxidation with coke powders and high-grade ferrsilicium powders and final steel deoxidation with silicocalcium and aluminum - during the production process, first unit release of the smelting is applied to the disconnected furnace to the silicosilicate refining slag, particle size up to 20 mm in the amount of 10-20% of its total consumption equal to 1.5-3.0 kg / the remaining amount of silicocalcium in pieces of size 20-100 mm input with intensity feeding 2-4 kg / ton to the steel-teeming ladle to the metal stream during the first third melt draining and at the same time dying - steel with aluminum in the amount of 0.10, 3 kg / t, while the aluminum is evenly distributed along the height of the ladle research from its bottom is within 1 / 8-1 / 3 of its height. The addition of a silicocalcium fraction less than 20 mm to the refining slag in the disconnected furnace ensures a high degree of deoxidation of the final refining slag. Due to this, during the introduction of silicocalcium with a grain size of 20-100 mm, the silicocalcium is removed from the small fraction of the fine fraction, which increases the useful use of calcium. Simultaneous deoxidation of steel by a ladle with silicocalcium- and aluminum contributes to the reduction of calcium inhibition. As a result, favorable conditions are created for the interaction of calcium with metal nitrogen. This reduces the likelihood of the formation of aluminum nitrides in steel, which is one of the main causes of longitudinal cracks in electroslag ingots. Deoxidation of steel with aluminum before deoxidizing it with silicocalcium increases the likelihood of the formation of adverse nitrides. Deoxidation of steel with aluminum after deoxidizing it with silicocalcium reduces the beneficial use of calcium. Processing steel calcium increases its plasticity. This is favorably reflected in the resistance of the metal to the occurrence of cracks. The introduction of silicocalcium and aluminum into the ladle during the discharge of the first third of the melt promotes a better mixing of metal deoxidizing elements and averaging their content in steel. The consumption of silicocalcium less than 1.5 kg / t does not provide / a fair reduction of waste of electroslag ingots along longitudinal cracks. The use of silicocalcium in an amount of more than 3 kg / ton is not rational, since when silicocalcium contains 70-75% silicon, the silicocalcium treatment of the metal in the ladle increases the silicon content in it by more than 0.150, 20%, and this limits the use of high-grade ferrosilicon powder for deacidification slag in an electric arc furnace. Additive before smelting to refining slag in the switch-off furnace silicocalcium in the amount of less than 10% of its total consumption does not ensure deoxidation of the refined slag to its content of ferrous oxide less than 0.5%. Additive on refined slag in the disconnected silicocalc furnace in the amount of more than 20% of its total consumption is not feasible, since it reduces the amount of silicocalcium consumed for the steel processing in the ladle. The introduction of silicocalcium with a particle size of less than 20 mm into the pouring ladle leads to the removal of fine fractions and reduces the useful use of calcium. The introduction of silicocalcium with a grain size of more than 100 mm into the pouring ladle is not rational, since it increases the time for the melting of silicocalcium, which shortens the time of interaction of calcium with steel. The lower limit of the intensity of introducing silicocalcium into the casting ladle {2 kg / ton, min) is determined by the need to add the total amount of silicocalcium for a time not exceeding the duration of the drain of one third of the heat. The introduction of silicocalcium into the ladle with an intensity of more than 4 kg / t-min leads to a decrease in the temperature of the slag-metal melt and is associated with the danger of the formation of a slag-like conglomerate of silicocalcium. Deoxidation of steel in a ladle with aluminum in an amount of less than 0.1 kg / t does not provide for obtaining the necessary austenite grain in steel of 6-8 points, and deoxidation with aluminum in an amount of more than 0.3 kg / ton is uneconomical and increases the probability of formation of unfavorable aluminum nitrides. . The location of aluminum at a distance of less than 1/8 of its height from the bottom of the bucket is impractical, since the first portions of metal and slag cools down more than the next; and aluminum dissolves slowly in them, which is associated with the danger of slagging. Placing aluminum at a distance of more than 1/3 of its height from the bottom of the ladle does not ensure effective mixing and uniform distribution of aluminum in steel. The relevance of using the invention in the smelting of crack-sensitive structural steels of grades 12-20ХНЗА, ЗОХГСА, 40ХН, 45, 40, etc. in electric arc furnaces with a capacity of 25-200 tons is determined by the ability, as experienced melts show, to significantly reduce and even completely eliminate the rejection of electroslag ingots of these steels due to a defect longitudinal crack. This eliminates the need to use deficient ferrotitanium of TiV grade with an actual titanium content of 70% and an aluminum: titanium ratio of not more than 0.07 in smelting cracking steel. Example 1. At smelting in 25 t of an arc furnace, steel 20ХНЗА.metal at the beginning of the refined period is preliminarily deoxidized with lumpy 45% ferrosilicon at the rate of 0.15% silicon. Refining slag, built-in lime 25 kg / t, fire chimney and fluorspar 5 kg each are sieved with coke powders 1-3 kg / t and 65% ferrosilicon 3-5 kg / t. Before releasing the smelting into a shut-off furnace, the silicon skincare grade SKZA with a grain size of up to 20 mm in an amount of 10% of its total consumption of 3 kg / t, ie, 0, 3 kg / t or 7.5 kg per smelting, is squeezed onto the refining slag with a grain size of up to 20 mm and the slag is mixed wood rake. At the time of the first third melt production, the remaining silicocalcium with a particle size of 20-100 mm in the amount of 2.7 kg /, t, i.e. 67.5 kg per smelting, with a flow rate of 4 kg / t, min, t. e.-silicocalcium is introduced in 40 s. The duration of the entire release is 2.5 minutes. Simultaneously with the introduction of silicocalcium, the steel in the ladle is deoxidized with aluminum in the amount of 0.3 kg / t, i.e. 7.5 kg for smelting, for which the pig aluminum in pieces of not more than 4 kg, mounted on the rod, is fixed on the side of the ladle so that the aluminum pieces are evenly spaced in height from the bottom to the bottom of the ladle. 1/4 of the bucket height. Steel is poured into consumable electrodes with a section of -370 x 370 mm in a semi-continuous casting plant. After electroslag remelting of electrodes, the reject of ingots with a cross section of 550 X 550 mm and a weight of 5.5 tons of steel 20KhNZASH due to a defect, the longitudinal crack decreases from 20 to 2%. P me R 2. In the course of smelting in 100 tons of an arc furnace, the ZOHGSA steel metal at the beginning of the refining period is preliminarily deoxidized with lumpy 45% ferrosilicon on the basis of 0.20% silicon. Refining slag, built from lime 25 kg / t, fireclay bo and fluorspar 5 kg / t, is squeezed with coke powders 1-3 kg / t and 65% ferromilicate 3-5 kg / t. Before the release of the melt, they sit down on the refining slag in the switched-off silicocalic furnace with a particle size of up to 20 mm in the amount of 15% of its total consumption equal to 2.5 kg / t, i.e. 0.37 kg / ton or 37 kg for smelting, and the slag is mixed with a wooden paddle. The time of the first third melt production is introduced into the steel casting ladle on the metal stream, the remaining silicocalcium with a particle size of 20-100 mm in an amount of 2.13 kg / ton or 213 kg per heat, with a feed rate of 2.5 kg / t-min. those. silicone salts are introduced in 52 seconds. The duration of the entire issue is 4 minutes. Simultaneously, with the introduction of silicocalcium, the steel in the ladle is deoxidized with aluminum in the amount of 9.15 kg / t, i.e. 15 kg for smelting, for which the pig aluminum in pieces of not more than 4 kg, mounted on rods, is fixed on board the ladle so that the aluminum pieces are evenly spaced in height from the bottom of the ladle within 1 / 6-1 / 3 of height bucket. The steel is siphoned into bars weighing 6.5 tons and rolled onto pavement VIIe electrodes with a cross section of 370 x 370 mm. After electroslag remelting of electrodes, the marriage of bars with a cross section of 550 x X 550 mm and weight of 5.5 tons has become ZOHGSSASH due to a longitudinal crack defect decreases from 10 up to 1%. Example 3. When melting in 200 tons of arc furnace steel 40X metal at the beginning of the refining period before

Claims (1)

Claim The method of deoxidation of crack-sensitive steel # smelted in an electric arc furnace for subsequent electroslag remelting, including preliminary deoxidation of the metal with lump ferrosilicon, slag deoxidation with coke powders and high percent ferrosilicon, and the final deoxidation of steel with silicocalcium and aluminum in the process of heating , in order to increase the efficiency of calcium use and reduce the rejection of electroslag ingots along longitudinal cracks, they are snapped off before releasing the smelting a cured oven for refining silica-calcium slag with a grain size of up to 20 mm in an amount of 10-20% of its total consumption; equal to 1.5-3.0 kg / t, the remaining amount of silicocalcium in pieces ^- with a grain size of 20-100 mm is introduced with a feed rate of 2-4 kg / t * min into the steel pouring ladle on a metal stream during the discharge of the first third of the heat and at the same time steel is deoxidized aluminum in an amount of 0.1-0.3 kg / t, while aluminum is placed evenly along the height of the bucket at a distance from the bottom of the bucket within 1 / 8-1 / 3. its heights.