RU2186857C1 - Method for manufacture of round section rolled products - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: method involves providing manganese and silicon ladle deoxidation of metal with following blending blasting; providing ultimate aluminum deoxidation. Aluminum consumption is determined from expression: Q $\genfrac{}{}{0ex}{}{\text{sk}}{\text{A1}}$ = 0.307x[C] -3.021x[Si]+0.582x[Mn]-30.438x[N] +0.327, Q $\genfrac{}{}{0ex}{}{\text{k}}{\text{A1}}$ =-1.728x[C]-1.538x[Si]+1.746x[Mn]-0.713x[N]+0.792, where Q $\genfrac{}{}{0ex}{}{\text{sk}}{\text{A1}}$ , Q $\genfrac{}{}{0ex}{}{\text{k}}{\text{A1}}$ are amount of aluminum consumed for deoxidation of semikilled steel and killed steel, respectively, kg/t; [C],[Si], [Mn], [N] are content of carbon, silicon, manganese and nitrogen in metal after blending blasting, %; 0.307, 3.021, 0.582, 30.438, 0.327, 1.728, 1.538, 1.746, 0.713, 0.792, are empirical coefficients obtained by experimentation; pouring metal in graded ingot molds; producing rolled products of 5.5-20 mm diameter; intensified cooling of rolled products with water till obtaining required average weight temperature of rolled product determined from expression: T= 10.74xDrp+82.86x[Si]+717.21, where T is average weight temperature of rolled product, C; Drp is diameter of rolled product, mm; Si is content of silicon in metal after pouring in graded ingot molds; 10.74, 82.86, 717.21 are empirical coefficients obtained by experimentation; providing air cooling of formed coils of rolled products. EFFECT: increased quality of rolled products by reduced surface defects and nonmetallic inclusions, and increased yield. 2 tbl, 1 ex

Description

 The invention relates to the field of ferrous metallurgy, and in particular to methods for the production of rolled round section from low carbon steel, and can be used in metallurgical plants.

 A known method of deoxidation of carbon steel containing 0.45-0.80% carbon, including deoxidation of the molten metal in the furnace with manganese, subsequent deoxidation in the ladle with silicon and aluminum supplied in the amount of 60-130 g / t of steel, the final deoxidation in the mold with aluminum, supplied in batches with an increase for every 0.01% of the actual decrease in carbon content by 2 g / t of steel, while the ratio of the total amount of aluminum introduced into the ladle and the mold to the silicon introduced into the ladle is maintained in the ratio 1: (15-80), getting prok that round section and accelerated cooling with water (A.S. 607846, class C 21 C 7/06, publ. 25.05.78.).

 The known method does not provide high quality steel for non-metallic inclusions, since it contains a significant amount of poorly removable undeformable silicates and corundum up to 100 microns in size, which significantly reduce the plastic properties of rolled products, and additional deoxidation with aluminum in the mold reduces the uniformity of the physicochemical properties of the metal, which reduces the yield strength of rolled products and increases the tendency to aging. The method does not allow you to adjust the number of non-metallic inclusions depending on the level of oxidation of the molten metal and to most fully remove them and, as a result, regulate the temperature of the end of accelerated cooling of the rolled metal depending on the chemical composition of the metal, in particular on the silicon content to obtain the desired macro- and microstructure at the ready rental.

The closest analogue to the present invention is a method for producing round rolled products, including steel smelting in open-hearth furnaces with metal melt blowing with oxygen and deoxidation in the furnace with ferromanganese 5-10 minutes before the metal is released, subsequent deoxidation of the metal in the ladle with 45% ferrosilicon and aluminum, casting varietal metal in the mold, heating the ingots to rolling is rolled round section obtaining such wire rod with a diameter greater than 5 mm, the cooling water temperature, rolling end 1050-1070 ^o C to 620-670 ^o C. y accelerated cooling and subsequent air cooling of individual turns of the dissolved wire rod riot on the conveyor belt (Vanchikov V.A., Smolyarenko D.A., Grekov E.A. et al. Interrelation of technological parameters of steelmaking and quality of metal products. - M.: Metallurgy 1979, p. 170-179).

 Signs of an analogue that coincide with the essential features of the present invention: deoxidation of metal with manganese, silicon and aluminum, casting of metal into high-quality molds, production of rolled products with a diameter of 5.5-20 mm, accelerated cooling of rolled products with water and subsequent air cooling of formed coils of rolled products.

 The known method does not provide the desired technical result for the following reasons.

 The deoxidation of the metal in the furnace by manganese leads to its unstable assimilation, due to the fact that manganese supplied to the furnace in large quantities helps to quickly establish the equilibrium of the deoxidation reaction in local volumes, leading to a high content of manganese and a low oxygen content in these volumes, which leads to unstable oxygen content in the metal volume. In addition, the presence of oxidizing slag in the furnace excludes the possibility of regulating the deoxidation process, and in the absence of special mixing methods, it can lead to a significant “waste” of manganese, and the chemical composition of the metal sample before it is released into the ladle is incorrect due to the heterogeneity of the melt. Subsequent deoxidation of the metal in the ladle with ferrosilicon and aluminum with an unknown oxygen content does not allow to accurately determine the consumption of silicon and aluminum to obtain the required level of metal oxidation. This leads to the formation of a significant amount of non-metallic inclusions in the form of aluminum oxides and brittle silicates, which reduce the mechanical properties of the finished product.

The high content of brittle silicates significantly affects the thermal conductivity of the metal, which with accelerated cooling with water from the temperature of the end of rolling 1050-107 ^o C to 620-670 ^o C, as well as the regulated cooling temperature without taking into account the specific level of oxidation, estimated, for example, by the silicon content, leads to an uneven hardened surface layer. Subsequent air cooling, the uneven size of the hardened layer does not allow to obtain the required properties of the finished product due to the high number of surface defects and non-metallic inclusions.

The basis of the invention is the task of improving the method of production of rolled steel by optimizing process parameters depending on the specific chemical composition of the metal. The expected technical result is the provision of the optimal value of the hardened surface layer after accelerated cooling, which allows to reduce surface defects and non-metallic inclusions and increase the yield. The technical result is achieved by the fact that in the known method for the production of round rolled products, including the production of ladle and deoxidation of metal with manganese, silicon and aluminum, casting metal into high-quality molds, obtaining rolled products with a diameter of 5.5-20 mm, accelerated cooling of rolled steel with water and subsequent air cooling of the formed coils of rolled products, according to the invention, the metal is deoxidized with manganese and silicon in a ladle, followed by averaging, neutral gas, and aluminum deoxidation is carried out after averaging, blowing at its expense, for semi-calm or quiet steel, respectively, determined by the expression:
Q _Al ^ps = 0.307 • [C] -3.021 • [Si] + 0.582 • [Mn] -30.438 • [N] +0.327,
Q _Al ^sp = -1.728 • [C] -1.538 • [Si] + 1.746 • [Mn] -0.713 • [N] +0.792,
where Q _Al ^ps , Q _Al ^sp - aluminum consumption during deoxidation of semi-quiet and mild steel, respectively, kg / t;
[C], [Si], [Mn], [N] - the content of carbon, silicon, manganese and nitrogen in the metal after an average blow,%;
0.307, 3.021, 0.582, 30.438, 0.327, 1.728, 1.538, 1.746, 0.713, 0.792 - empirical coefficients obtained experimentally, while accelerated cooling of the rolled water with lead to obtain the desired mass-average temperature, determined from the expression
T = 10,74 • D _ave + 82,86 • Si + 717,21,
where T is the average bulk temperature of the rolled product, ^o C;
D _CR - diameter, mm;
Si is the silicon content in the metal after it is cast into varietal molds;
10.74, 82.86, 717.21 - empirical coefficients obtained experimentally.

Empirical coefficients obtained experimentally allow, depending on the specific chemical composition of the metal, to optimize the necessary consumption of aluminum supplied to the ladle for deoxidation, and to obtain the necessary level of metal oxidation, which leads to a decrease in the amount of aluminates and aluminosilicates, thereby improving the castability of steel, and subsequent averaging purge leads to the removal of the resulting non-metallic inclusions in the slag phase. In the case of regulated deoxidation by aluminum, spherical nonmetallic inclusions are converted to spheroidal and, as a result, to a decrease in the kinematic viscosity of the melt, which makes it possible to reduce the temperature of the metal fed to the casting by 20–40 ^° C, which improves its spillability and provides dense ingots with a low content of non-metallic inclusions. Removing a significant amount of deoxidation products during averaging purge results in a metal with a low content of non-deformable non-metallic inclusions on a silicon basis. Accelerated water cooling to obtain the optimum mass-average temperature depending on the silicon content in the finished metal and on the diameter of the rolled metal leads to a decrease in structural heterogeneity over the cross section, which is explained by the effect of supercooled surface layers on the stability and decomposition kinetics of austenite of the inner layers. The optimum mass average temperature of the rolled product for a specific level of metal oxidation allows stabilizing the hardenability by non-metallic inclusions to stabilize the hardenability and thereby guarantee the optimum uniform tempered surface layer, which leads to the desired properties under conditions of further air cooling of the rolled product.

 Example.

Smelting of low carbon steel grades 3ps and 3sp was carried out in a 300-ton two-shaft steelmaking unit using scrap metal, pig iron, and the bath was purged with oxygen. Upon reaching a temperature of the metal melt of 1630 ^o With a carbon content of 0.11%, the metal was released into the bucket. During the release of metal from the furnace into the ladle, the metal was preliminarily deoxidized with manganese and silicon by supplying 3.3 tons of ferromanganese and 1.3 tons of ferrosilicon to produce semi-quiet steel, and 3.5 tons of ferromanganese and 2.5 tons of ferrosilicon were fed to produce mild steel with simultaneous purging of the metal with nitrogen. After the metal was discharged into the ladle and the furnace slag was removed, an averaging purge was carried out at the metal refining unit with neutral gas (nitrogen) for three minutes, after which a sample was taken to determine the metal chemical composition.

 The chemical composition of the metal after averaging purge is presented in table 1.

Then, the final deoxidation of metal by aluminum in the bucket was carried out by feeding an aluminum wire rod at its flow rate, determined from the expression:
Q ^ps _Al = 0.307 • 0.16-3.021 • 0.06 + 0.582 • 0.39-30.438 • 0.0045 + 0.327 = 0.285 ct / t,
Q ^sp _Al = -1.728 • 0.15-1.538 • 0.22 + 1.746 • 0.58-0.713 • 0.005 + 0.792 = 1.2 kg / t.

 After entering the aluminum wire rod, the metal was averaged by purging with a neutral gas (nitrogen) for three minutes. Then the metal was poured into a high-grade mold and, during the casting, samples were taken to determine the chemical composition of the finished metal. The chemical composition of the finished metal is presented in table 2.

The obtained ingots were heated in heating wells to a temperature of 1300 ^° C. The ingots were rolled to obtain a square billet with a side of a square of 124 mm. After examining the preforms and cleaning their surface defects, the preforms were heated in a methodical heating furnace to a temperature of 1235 ^o C and fed to a small-sized wire mill to obtain a wire rod with a diameter of 10 mm

The finished wire rod from a temperature of the end of rolling equal to 930 ^o C was subjected to accelerated cooling with water in an accelerated cooling unit to obtain the optimum mass-average temperature, determined from the expression:
Tps = 10.74 • 10 + 82.86 • 0.08 + 717.21 = 831 ^o C,
Tsp = 10.74 • 10 + 82.86 • 0.22 + 717.21 = 843 ^o C.

 Then the wire rod was fed to the coiler and the formed coils were air-cooled on a plate conveyor.

 The proposed method allows, due to obtaining the optimum level of oxidation, to reduce metal defiling by surface defects and the number of non-metallic inclusions. This made it possible to reduce the sorting of workpieces by 30% during visual inspection of them on the racks before feeding a fine-grained wire mill to the heating furnace and by 50% rejection of metal by non-metallic inclusions while monitoring the macrostructure of the metal. The method provides the desired macro- and microstructure and increases the yield compared to the closest analogue by 10-15%.

Claims (1)

A method for the production of round rolled products, including the production of metal and manganese, silicon and aluminum into the ladle and deoxidation, casting of metal into high-quality molds, the production of rolled products with a diameter of 5.5-20 mm, the accelerated cooling of the rolled products with water and the subsequent air cooling of the rolled coils, characterized in that the metal is deoxidized with manganese and silicon in the ladle, followed by averaging by neutral gas, and the deoxidation by aluminum is carried out after averaging, at its flow rate, for semi-quiet or quiet oynoy steel respectively defined from expressions
Q ^ps _Al = 0.307 • [C] -3.021 • [Si] + 0.582 • [Mn] -30.438 • [N] +0.327,
Q ^sp _Al = -1.728 • [C] -1.538 • [Si] + 1.746 • [Mn] -0.713 • [N] +0.792,
where Q ^ps _Al , Q ^sp _Al - aluminum consumption during deoxidation of semi-quiet or mild steel, respectively, kg / t;
[C], [Si], [Mn], [N] - the content of carbon, silicon, manganese and nitrogen in the metal after an average blow,%;
0.307, 3.021, 0.582, 30.438, 0.327, 1.728, 1.538, 1.746, 0.713, 0.792 - empirical coefficients obtained experimentally,
while accelerated cooling of the water with a lead to obtain the required mass-average temperature determined from the expression
T = 10,74 • D _ave + 82,86 • [Si] +717,21,
where T is the required mass average temperature of the rolled product, ^o C;
D _CR - diameter, mm;
Si is the silicon content in the metal after it is cast into varietal molds;
10.74, 82.86, 717.21 - empirical coefficients obtained experimentally.

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