Method for the production of continuously cast billets rolled with spheroidizing structure of boron steel for cold massive forming of high-strength fasteners

 

(57) Abstract:

The invention relates to the field of metallurgy, in particular to the production of long-rolled products of boron steel for cold massive forming of high-strength fasteners. The technical result of the invention is to provide a structure of the rolled that provide sustainable conditions for cold massive forming geometrically-complex high-strength fasteners while providing increased performance hardenability of steel. To achieve a technical result smelted steel in the following ratio, wt.%: carbon 0,17-0,34, manganese 0,90-1,40, silicon 0,01-0,20, chrome from 0.005 to 0.40, boron 0,0005-0,0050, titanium 0.01 to 0.04, sulfur of 0,005 0,020, aluminum 0,02-0,06, calcium 0,001-0,010, nitrogen 0,005-0,015, iron and inevitable impurities rest when performing ratio N/(Ti+0,5 Al+10B)0,21; Ca/S0,065, on the issue of the melt rascist and alloyed in the bucket deoxidizers and alloying elements with low nitrogen content, at the stage of secondary treatment carry out doping of titanium and boron in the degasser, then poured into the metal stream protection of the metal from contact with air. After casting, the ingot is cooled and subjected to hot rolling, which nicholaou deformation calibration. After cold deformation spend spheroidizing annealing by high-speed heating to temperature ANDC1+(10-30)With and regulated cooling to 730-650S with a speed of 0.5-1.0 s/m, and further cooling in a heat chamber at room temperature 100-200C. 3 C.p. f-crystals.

The invention relates to the field of metallurgy, in particular to the production of continuously cast billets rolled with spheroidizing structure of boron steel for cold massive forming of high-strength fasteners.

Known structural steel containing, wt.%: carbon 0.06 to 0,30%, silicon of 0.17 to 1.0%, manganese 0,8-2,0%, vanadium from 0.01 to 0.25%, nitrogen of 0.005-0.040% for boron 0,001-0,.008%, aluminum from 0.005 to 0.10%, titanium 0,005-0,015%, the rest of the iron (USSR author's certificate No. 601321, With 22 38/12, 06.02.1976 year).

The most important requirement of rolled steel from boron steel for cold massive forming of high-strength fasteners particularly complex form, is, on the one hand, the high technological plasticity and low coefficient of strain hardening in the state of delivery and, on the other hand, the ability to provide the specified level of consumer properties after the final heat strengthening. This is e operations: production, hot rolling, spheroidizing annealing, calibration. The task of providing the necessary mechanical properties and performance of technological plasticity and low coefficient of strain hardening of the metal in the state of delivery currently successfully resolved through a number of techniques used at different stages of steel making.

A known method for the production of long products, including boron steel smelting, production of metal casting, hot rolling, cooling... (patent DE 3434744 A1, 03.04.1986, With 21 D 8/06, claims).

The closest analogue is a well-known method for the production of long steel products, including steel smelting in the electric furnace, the production of metal, secondary treatment, continuous casting, hot rolling of continuously cast billets, cooling (EN 2156313 C1, 21 D 8/02, 20.09.2000,).

The basis of the invention is the task of the development of steel of high hardenability. The technical result of the invention is to improve the hardenability and receiving patterns of the rolled guaranteeing the rational conditions of cold massive forming geometrically-complex high-strength fasteners.

For DOS is repaci, the production of metal, secondary treatment, continuous casting, hot rolling, continuous casting, cooling, smelted steel in the following ratio of components

Carbon 0,17-0,34

Manganese 0,90-1,40

Silicon 0,01-0,20

Chrome from 0.005 to 0.40

Bor 0,0005-0,0050

Titanium 0,01-0,04

Sera of 0,005 0,020

Aluminum 0,02-0,06

Calcium, 0,001-0,010

Nitrogen 0,005-0,015

Iron and inevitable impurities Else

When performing correlations: {N/(Ti+0,5 Al+10V)}0,21; (Ca/S)0,065 hot rolling starting at a temperature of 950-900C and end 850-S with the degree of deformation in the last passes of at least 20%, followed by cold deformation calibration with deformation rate of 20-25% and spheroidizing annealing speed by heating to a temperature of AC1+10-30C and regulated cooling in the temperature range of 730-650C at a rate of 0.5 to 1.0 C/min, and further cooling in a heat chamber at room temperature 100-200C.

With the release of the melt perform deoxidation and alloying in the bucket deoxidizers and alloying elements with low nitrogen content; at the stage of secondary treatment carry out doping of boron steel in the vacuum degasser; in continuous casting exercise is the returns in the proposed steel (finished product diameter up to 25 mm), after his thermolysine (quenching from a temperature of at least S with subsequent tempering temperature not lower than C) homogeneous fine structure of martensite leave with a favorable combination of strength and ductility.

Carbon and carbidopa elements are introduced into the composition of this steel to ensure a fine grain structure, which will increase as the level of its strength, and to provide a given level of ductility. The upper limit of carbon content (0,34%) due to the need to ensure the required level of ductility of steel, and the bottom respectively of 0.17% by providing the required strength level of the steel.

Manganese and chromium is used, on the one hand, as a solid solution hardeners, on the other hand, as elements, greatly increasing the stability of the supercooled austenite and increases the hardenability of steel. The upper level of the manganese content of 1.30% and chromium of 0.35% is determined by the need to ensure the required level of ductility of steel, and the bottom of 0.90% and 0.005%, respectively, of the need to ensure the required level of strength and hardenability of the steel.

Silicon belongs to ferry Omnia above 0,37% will adversely affect the characteristics of ductility of steel.

Boron contributes to a sharp increase in the hardenability of steel. The upper limit of the boron content is determined by considerations of ductility of steel, and the lower the need to ensure the required level of hardenability.

Aluminum and titanium are used as deoxidizers and protect the boron from binding in the nitrides, which contributes to a sharp increase in the hardenability of steel. So the lower level of the contents of these elements (0.02 and 0.01 respectively) is determined by the requirement to ensure the hardenability of steel, and the upper level of 0.06 and 0.04) requirement provide a given level of ductility of steel.

Nitrogen is an element that participates in the formation of carbonitrides, while lower levels (0,005%) is determined by the requirement to provide a given level of strength, and the upper level (0,015%) requirement provide a given level of ductility and hardenability.

Calcium is an element, modifying nonmetallic inclusions. The upper limit (0,010%), as in the case of sulfur caused by the necessity of obtaining a given level of ductility and toughness of steel, and the lower (0,001%) limit issues-tech production.

Sulfur determines the level of plasticity was the lower limit (0,005%) questions-tech production.

To ensure complete bonding of nitrogen in the nitride type TiN and AlN as the result of reactions

[Ti]+[N]=TiN [Al]+[N]=AlN

requires the following ratios of elements: otherwise protected boron from tying it in nitrides and decrease characteristics of the hardenability of steel.

Ratios

define storage conditions in more than 50% effective boron, which provides a set of characteristics of the hardenability of steel.

Comparative analysis of the prototype allows us to conclude that the claimed composition differs from the known.

Therefore, the claimed set of characteristics meets the criterion of "substantial differences".

Below is an example implementation of the present invention, not excluding other in the scope of the claims.

Smelting boron steel containing carbon 0,22%, manganese of 1.20%, si 0,10%, chromium of 0.25%, boron 0,0022%, titanium of 0.025%, sulfur 0,008%, aluminum 0,04%, calcium 0,0015%, nitrogen 0,007%, produce 150-ton electric arc furnaces (EAF) using the mixture of 100% DRI pellets, allowing for the mass fraction of nitrogen prior to release from particleboard no more than 0,003%, and low sodium release from particleboard. After the release was made metal blowing argon through the bottom vent block, during which the steel raskalyaetsya aluminum. After that, the metal is fed to the Assembly of complex processing of steel (AKOS), on which there is a possibility of heating the metal to the required temperature, flushing it with argon through bottom vent unit, dosed additives necessary ferroalloys and steel flux-cored wire with various fillers. On the AKOS is pointing refining slag additive lime and fluorspar, deoxidizing slag granulated aluminum alloying metal aluminum content 0,050%, lapping metal content of manganese, heating up to the temperature optimum for further processing. After processing Agos metal is exposed to the vacuum processing on portions of the degasser. During degassing is the final adjustment of the chemical composition. At this stage secondary treatment metal legarrette titanium and boron, which allows efficient use of these elements. After degassing the metal is processed by the silicocalcium and transferred to the casting process. The casting is on chetyrehluchevoy MNRS radially the use of top slag mixtures in the tundish and the mould, protective pipes, submersible glasses and a flow of argon. It also provides for obtaining a low content of nitrogen and oxygen and purity of the metal non-metallic inclusions. After casting and cut-to-length the length of the received continuous cast billet was cooled furnaces controlled cooling. Hot rolling of long products start at a temperature of 950-900 ° C and finished at a temperature of 850-S deformation in the last passes of at least 20%. Followed by pickling hot-rolled steel in sulfuric acid solution (concentration of 180-200 g/l) at a temperature of 80C for 30 min, followed by the application podmazochnaja coverage. Followed by cold deformation calibration with deformation of 20-25% and spheroidizing annealing, including high-speed induction in microtechno temperature range (ACl+10-30C) of cold metal followed by controlled cooling in the temperature range 650-S with velocities of 0.5-1.0 C/min, and further cooled in a heat chamber at room temperature 100-200S, which reduces the duration of the process of spheroidizing 5-10 times.

The execution ratio of the alloying elements allowed to provide content “affectioni 0,04%, Bor 0,0022%, nitrogen 0,007%,

sulfur 0,008%, calcium 0,0015%.

The introduction of the proposed method of production of long-rolled products from boron steel of high hardenability provides obtaining the structure of the rolled guaranteeing the rational conditions of cold massive forming geometrically-complex high-strength fasteners.

1. Method for the production of long steel products, including steel smelting in the electric furnace, the production of metal, secondary treatment, continuous casting, hot rolling of continuously cast billets and cooling, characterized in that the smelted steel in the following ratio, wt.%:

Carbon 0,17-0,34

Manganese 0,90-1,40

Silicon 0,01-0,20

Chrome from 0.005 to 0.40

Bor 0,0005-0,0050

Titanium 0,01-0,04

Sera of 0,005 0,020

Aluminum 0,02-0,06

Calcium 0,001-0,010

Nitrogen 0,005-0,015

Iron Rest

when performing ratio N/(Ti+(0,5 Al+10B)of 0.21, Ca/S0,065, where N is nitrogen, Ti - titanium, boron, Al - aluminum, CA - calcium, S - sulfur, hot rolling start at about 950-900 ° C and ends at 850-S with the degree of deformation in the last passes of at least 20%, followed by cold deformation calibration with deformation rate of 20-25% and spheroidize in the temperature range of 730-650S and further cooling in a heat chamber at room temperature 100-200C.

2. The method according to p. 1, characterized in that are used deoxidizers and alloying elements with low nitrogen content.

3. The method according to p. 1, characterized in that at the stage of secondary treatment carry out doping with boron and titanium in the degasser.

4. The method according to p. 1, wherein during the continuous casting protect stream of metal from contact with air.

 

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