RU2492248C2 - Method of producing boron-containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: for casting boron-containing steel including sulfur in amount of 0.01-0.03 wt %, chromium in amount of 0.15-0.25 wt %, titanium in amount of 0.02-0.045 wt %, after averaging blowing of steel produced in steelmaking unit, steel chemical composition is defined. In case sulfur content exceeds 0.012% slag and line additive are deoxidized at the following ratio: 10³ • (% S-0.012) • 90…110 kg CaO, where S is sulfur content after aforesaid blowing, %; 0.012 is boundary content of sulfur in steel, %; 90…110 CaO is lime consumption per every hundredth of sulfur exceeding 0.012%, kg. Then, slag is removed in steel out-of-furnace treatment in furnace-ladle assy, added are sand manganese-, silicon-, chromium- and molybdenum-bearing ferroalloys, carbon-bearing materials, ferrocalcium,ferrotitanium and ferroboron. After electric heating of steel to 10-15°C above preset temperature, aluminium rods is introduced to steel to produce aluminium content in finished steel approximating to lower limit of grade range, ferrocalcium and sulfur to carry out averaging blowing.

EFFECT: higher yield.

1 ex

Description

The invention relates to the field of metallurgy of steel, and specifically to the production of long products from boron steel.

A known production method, including the smelting of the intermediate in the converter, deoxidation, alloying, input nitride-forming elements, refining with synthetic slag in the ladle during the smelting process and purging the metal with inert gas, boron-containing additives are added to the ladle during the purge process after reducing the amount of iron oxide in the slag to 0.2-2.0 wt.% (USSR No. 918314, IPC С 21 С 7/00, publ. 07.04.1982).

The disadvantages of this method is the insufficient yield of mechanical properties (hardenability), the addition of boron-containing additives when the content of iron oxides in the range of 0.5-2.0% will lead to unstable burnout of boron-containing additives and, accordingly, to the failure to obtain a given chemical composition and, as a result, sorting finished steel by hardenability.

The closest analogue of the claimed invention is a method for the production of boron-containing steel (RU No. 2382086, MPK С21С 7/00, publ. 02.20.2010), which includes steel smelting in a steelmaking unit, its deoxidation, out-of-furnace treatment, ferroboron addition and purging with argon through bottom tuyeres into time of out-of-furnace treatment of steel, out-of-furnace treatment of steel is carried out at the ladle furnace, then an average purge of steel is carried out with argon and the oxidation and temperature of the metal are determined upon arrival at the ladle furnace, calcium is added cored wire comprising, finishing is carried out on the content of chemical elements and steel temperature in the ladle prior to pouring metal impact and ferroboron dopant, carried out together with blowing steel with argon at a rate determined by the relationship:

P _fb = 0.05 × P _FSa -0.169 × O-146.5 × Tprih / Totd + 172.3, where

R _fb - consumption of ferroboron, kg

R _FSa - consumption of calcium-containing flux-cored wire, kg;

O - metal oxidation upon arrival at the installation of the ladle furnace, ppm;

Tprih - metal temperature upon arrival at the ladle furnace, ° С;

Totd is the temperature of the metal in the ladle before it is cast, ° C;

0.05 - the coefficient shows the effect of the consumption of calcium-containing flux-cored wire on the consumption of ferroboron;

0.169 - the coefficient shows the effect of metal oxidation upon arrival at the ladle furnace installation on the consumption of ferroboron;

146.5 - the coefficient shows the influence of the ratio of the temperature of the metal upon arrival at the ladle furnace to the temperature of the metal in the ladle before it is cast

172.3 - coefficient, shows the effect of all unaccounted for technological factors on the consumption of ferroboron.

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

Steel (according to TU 14-101-185-95 "Hot-rolled high-quality strip of steel grades 53G1R and 40G1R" contains not more than 0.03% sulfur), obtained in a known manner, has insufficient yield for mechanical and consumer properties (when the sulfur content in metal less than 0.01% in the manufacture of the finished product from the consumer of strip steel complicates the process of milling the workpiece after hot stamping).

The consumption of boron-containing material, depending only on the consumption of calcium-containing flux-cored wire and the oxidation of the metal upon arrival to the after-furnace treatment, without taking into account the sulfur content, will lead to overgrowing of the channels of the pouring glasses with calcium sulfides (CaS), an increase in the accident rate during casting on high-grade continuous casting machines and a high specific consumption of metal charge.

The basis of the invention, the task is to improve the method, steel production by changing the technology of out-of-furnace treatment, in particular the introduction of chromium, titanium, sulfur.

The expected technical result is to obtain a given chemical composition of steel, to provide the required mechanical and consumer properties, to improve the castability of metal at high-grade continuous casting machines and to increase the yield of mechanical properties and to reduce the specific consumption of the metal charge.

The technical result is achieved in that in a method for the production of boron-containing steel, comprising smelting steel in a steelmaking unit, its deoxidation, out-of-furnace treatment of steel in a ladle furnace, averaging steel purging with argon, determining the chemical composition of the steel and the ferroboron additive, according to the invention, for smelting steel containing sulfur 0.01-0.03%; chromium 0.15-0.25%; titanium 0.02-0.045%, upon receipt, after determining the chemical composition of the steel, the sulfur content in it is more than 0.012%, slag is deoxidized and lime is added in an amount of 10 ³ · (% S - 0.012) · 90 ... 110 CaO, where:% S - sulfur content in steel,%; 0,012 - boundary sulfur content in steel,%; 90 ... 110 CaO - for every hundredth part of sulfur, exceeding 0.012%, in kg, then slag is removed from the ladle furnace and sand is added in the amount of 5.0 ... 8.0 kg / t, after which the chemical composition of the steel is adjusted manganese-, silicon-, chromium- and molybdenum-containing ferroalloys and carbon-containing material are added, ferrocalcium, ferrotitanium and ferroboron are added, the steel is heated 10-15 ° C above the set temperature and an aluminum wire rod is introduced into the steel based on the aluminum content in the finished steel closer to lower limit at the vintage range, ferrocalcium in the amount of 2.0-8.5 kg / t of steel in the form of a flux-cored wire and sulfur in the amount of 0.1-0.5 kg / t of steel in the form of a flux-cored wire with filler sulfur or sulfur pyrite, then carry out averaging purge steel argon.

The essence of the proposed technical solution is to ensure that the finished metal contains aluminum, calcium, sulfur, titanium and boron, which allows to provide the required level of mechanical (hardenability) and consumer properties, to improve the spillability of metal on high-quality continuous casting machines and to increase the yield of mechanical properties and lower specific consumption metal charges.

Introduction to the metal of calcium, which has the greatest deoxidizing ability, allows to obtain the optimal oxidation of the metal, to reduce the formation of undeformed non-metallic inclusions.

A metal containing titanium in the range of 0.02-0.045% reduces the surface energy of austenite grains and increases the stability of supercooled austenite in the supermartensitic temperature region, which allows to obtain the required level of steel hardenability.

The sulfur content in the metal in the range of 0.01-0.03% in the manufacture of the finished product at the consumer from strip steel simplifies the process of milling the workpiece after hot stamping.

Chrome, dissolved in solid iron (content 0.15-0.25%), significantly changes its mechanical properties, increasing strength characteristics.

This method is illustrated by the following example.

Steel grade 35G1R was smelted in a two-shaft steelmaking unit. During the smelting production, 1.0 tons of ferromanganese (FMn78), 2.0 tons of silicomanganese (FeMnSil7), 0.5 tons of ferrochrome (FeCr) and 0.2 tons of pig aluminum (AB86) were added to the ladle. Out-of-furnace melting processing was carried out at the ladle furnace.

After averaging with argon, a metal sample was taken and the temperature and oxidation of the metal were measured with a Celox Multi Lab sensor. The metal contained: carbon 0.274%, silicon 0.11%, manganese 0.955%, sulfur 0.024%, phosphorus 0.015%, chromium 0.189%, nickel 0.034%, copper 0.048%, molybdenum 0.005%, aluminum 0.044%, titanium 0.003%, boron 0.00039%, the temperature of the metal was 1547 ° C, and the oxidation was 16.6 ppm.

To reduce the sulfur content in the metal, lime was added from the ratio

10 ³ · (0,024-0,012) · 100 = 1200 kg

and 300 kg of fluorspar, slag was deoxidized with 150 kg of pig aluminum, the metal was heated to dissolve the lime, and after the lime was completely dissolved and the metal and slag were mixed, a metal sample was taken. The metal contained 0.011% sulfur. The out-of-furnace treatment was stopped, about 60% of the slag was cut out from the steel pouring ladle and sand was added in an amount of 1.0 t. After the sand was added, the metal was heated to a temperature of 1584 ° C. Then, the chemical composition of the steel was adjusted, 450 kg of silicomanganese, 201 kg of 65% ferrosilicon, 150 kg of graphite in the form of cored wire, 100 kg of ferromolybdenum, 200 kg of ferrocalcium in the form of cored wire, 320 kg of ferrotitanium in the form of cored wire and 45 kg of ferroboron were added, conducted an averaging purge and a metal sample was taken. The metal contained: carbon 0.365%, silicon 0.245%, manganese 1.204%, sulfur 0.006%, phosphorus 0.016%, chromium 0.206%, nickel 0.034%, copper 0.048%, molybdenum 0.031%, aluminum 0.012%, titanium 0.039%, boron 0, 00262%, the metal temperature was 1564 ° C, and the oxidation was 1.6 ppm. After obtaining the results of the analysis, the metal was additionally heated at 10 ° С, aluminum was added in the form of a wire rod, in the amount of 15 kg, 1360 kg of ferrocalcium were introduced in the form of flux-cored wire and 45 kg of technical sulfur in the form of flux-cored wire. After the completion of the addition of all deoxidants, an average purge of the metal with argon was carried out for 90 seconds, the metal temperature was measured and a sample was taken. The metal contained: carbon 0.369%, silicon 0.248%, manganese 1.201%, sulfur 0.015%, phosphorus 0.016%, chromium 0.206%, nickel 0.034%, copper 0.048%, molybdenum 0.031%, aluminum 0.022%, titanium 0.041%, boron 0, 00256%, the metal temperature was 1566 ° C, and the oxidation rate was 1.2 ppm.

After obtaining the required chemical composition and conducting an averaging purge, the heat was transferred to a continuous casting machine.

Continuous casting of steel was carried out on a 5-strand high-grade continuous casting machine in billets with a section of 150 × 150 mm. 176.5 tons of high-quality billets were cast, containing 0.379% carbon, 0.24% silicon, 1.194% manganese, 0.016% phosphorus, 0.012% sulfur, 0.195% chromium, 0.034% nickel, 0.048% copper, 0.017% aluminum, 0.039% titanium , 0.0024% boron, 0.007% nitrogen and 0.002% calcium.

With this method of steel production, the required content of chemical elements in the steel is obtained, the content of non-metallic inclusions is reduced, the yield of mechanical properties is increased, production and profit are increased.

Claims (1)

A method of producing boron-containing steel, including smelting steel in a steel-smelting unit, determining the chemical composition of steel, its deoxidation, out-of-furnace treatment of steel at a ladle furnace and averaging steel purging with argon, characterized in that for the smelting of steel containing 0.01-0 sulfur , 03%; chromium 0.15-0.25%; titanium 0.02-0.045%, when a sulfur content of more than 0.012% is obtained in the steel, slag is deoxidized and lime is added in an amount of: 10 ³ · (% S - 0.012) · 90 ... 110 CaO, where% S is the sulfur content in steel ,%; 0,012 - boundary sulfur content in steel,%; 90 ... 110 CaO - for every hundredth part of sulfur, exceeding 0.012%, in kg, then slag is removed at the ladle furnace and sand is added in the amount of 5.0-8.0 kg / t of steel, after which the chemical composition is adjusted they became an additive with manganese, silicon, chromium and molybdenum-containing ferroalloys, carbon-containing material, ferrocalcium, ferrotitanium and ferroboron, then the steel is heated 10-15 ° C above a given temperature and an aluminum wire rod is introduced into the steel based on the calculation of the aluminum content in the finished steel closer to the lower limit at the vintage range, ferrocalcium in the amount of 2.0-8.5 kg / t of steel in the form of a flux-cored wire and sulfur in the amount of 0.1-0.5 kg / t of steel in the form of a flux-cored wire with filler sulfur or sulfur pyrite, then averaging purge steel argon.