Method for the production of continuously cast billets rolled 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 particularly complex form. The technical result is getting directly into the mill stream (without additional spheroidizing annealing) patterns of long steel products 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, perform steel containing, wt.%: carbon 0,08-0,34, manganese 0,90-1,4, silicon of 0.01 to 0.15, boron 0,0005-0,0050, chrome from 0.005 to 0.40, vanadium, 0.005 to 0.08%, aluminum 0,02-0,06%, titanium 0.01 to 0.04%, sulfur of 0,005 0,020, nitrogen 0,005-0,015, calcium, 0,001-0,010%, iron and inevitable impurities else, and Ti/48+Al/27-N/140,6.10-3; Mn+5,0C2.0; Ca/S0,065, lead to the release of the melt, secondary treatment, during which the steel alloyed with titanium and boron in the degasser, conduct continuous casting of steel, then hot rolling and regulated cooling. 3 C.p. f-crystals.

The invention relates to the field of metallurgy is ocaproce fasteners particularly complex form.

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 steel from blending until ready rolled it takes a long processing, comprising the following operations: smelting, 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.

The known method is rogatko, 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 increased procedimenti and method of manufacturing it rolled, providing directly into the mill stream (without additional spheroidizing annealing). The technical result is to obtain spheroidizing patterns rolled guaranteeing the rational conditions of cold massive forming geometrically-complex high-strength fasteners, as well as elevated values of characteristics of hardenability.

The technical result is achieved in that in the method of production of long steel products, including steel smelting in the electric furnace, the production of metal, secondary treatment, continuous casting, hot rolling, continuous casting, cooling, smelted steel in the following ratio, wt.%:

Uomini of 0.2-0.6%

Titanium 0.01 to 0.04%

Sera of 0,005 0,020

Nitrogen 0,005-0,015

Calcium 0,001-0,010

Iron and inevitable impurities Else

And

(Ti/48)+(Al/27)+(N/14)(0,610-3MP+5,Z,0 (Ca/S)0,065

hot rolling starting at a temperature of 900-950º C and finished at a temperature of 740-850, with the deformation in the last passes of at least 20% and spend the regulated cooling in the temperature range of 730-600C with speeds 5-20C/min With the release of the melt perform deoxidation and alloying in the bucket, at the stage of secondary treatment carry out alloying steel with titanium and boron in the degasser, in continuous casting protect streams of metal with argon.

Given the combination of alloying elements (p. 1) allow to get in the proposed steel (finished product diameter up to 25 mm) after 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 carbonitrides (vanadium) elements are introduced into the composition of the steel to ensure the fine is knosti. While vanadium manages the processes in the austenitic region (determines the tendency to grain growth of austenite, stabilizes the structure during thermomechanical processing, increases the temperature of recrystallization and, consequently, affects the character --transformation. Vanadium also contributes to hardening of the steel during thermolysine. The upper limit of carbon content (0,34%), vanadium (0,08%) due to the need to ensure the required level of ductility of steel, and the bottom respectively of 0.08%, 0.005% and provide the required strength level of the steel.

Manganese and chromium are 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 1.40% and chromium of 0.40% 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 territooriumil elements. The lower limit for silicon 0,07% caused by the deoxidation of steel. The silicon content higher than 0.37% of blagopri is emoti 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 to 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 ductility of steel. The upper limit (0,020%) due to the necessity of obtaining the.

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 protection boron from tying it in nitrides and decrease characteristics of the hardenability of steel.

Ratios

(Ti/48)+(Al/27)+(N/14)0,610-3Mn+5,0C2,0 (Ca/S)0,065

define storage conditions in more than 50% of the effective Bohr that provides the specified characteristics of the hardenability of steel.

Below is an example of the method.

Smelting boron steel containing carbon 0,17%, manganese 1,10%, silicon of 0.10% boron 0,0031%, chromium of 0.25%, vanadium of 0.02%, aluminum 0,031%, titanium 0,021%, sulfur 0,008%, nitrogen 0,008%, calcium 0,0011% produce 150-ton electric arc furnaces (EAF) using the mixture of 100% DRI pellets, allowing for the mass fraction of nitrogen before the release of the DSP is not more of 0.003% and a low content of non-ferrous impurities. Pre-alloying metal to manganese and silicon are produced in the bucket for the production of particleboard. After the release was made metal blowing argon through the bottom vent block, during which the steel rascals the 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 produce guidance 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, vanadium 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 machine radial type in the ingot sizes 300360 mm with a speed of extrusion of 0.6-0.7 m/min, protecting the metal from oxidation by the use of top slag mixtures in the tundish and the mould, protective pipes, submersible glasses and a flow of argon. It also ensures bottom measuring the length of the received continuous cast billet was cooled furnaces controlled cooling. Hot rolling of long products start at a temperature of 900-950º C and finished at a temperature of 740-850, with the deformation in the last passes of at least 20%. After rolling is used in the temperature range 600-S modes regulated cooling of rental with 5 speed-20C/min

The execution ratio of the alloying elements helped to ensure that the content of the “effective” boron in steel level 0,0020% and through-hardenability of the workpiece diameter 22 mm

(Ti/48)+(Al/27)+(N/14)=0,00216 aluminum 0,031%, titanium 0,021%, nitrogen 0,008%,

MP+5.0 s=2,05; carbon 0,19%, manganese 1,10%

(Ca/S)=was 0.138, sulfur 0,008%, calcium 0,0011%.

The introduction of the proposed method of production of long-rolled products from boron steel of high hardenability providing directly into the mill stream (without additional spheroidizing annealing) patterns of 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 is erod 0,08-0,34

Manganese 0,90-1,40

Silicon 0,01-0,15

Bor 0,0005-0,0050

Chrome from 0.005 to 0.40

Vanadium is 0.005 to 0.08

Aluminum 0,02-0,06

Titanium 0,01-0,04

Nitrogen 0,005-0,015

Sera of 0,005 0,020

Calcium 0,001-0,010

Iron Rest

when performing ratio: Ti/48+Al/27-N/140,610-3; Mn+5,0C2,0; Ca/S0,065, where Ti - ti, Al - aluminum, N - nitrogen, Mn - manganese, CA - calcium, S - sulfur, C - carbon, hot-rolling start at 900-950º C and ends at 850-S with the degree of deformation in the last passes of at least 20% and spend the regulated cooling in the temperature range of 730-600C with a cooling rate of 5-20 ° C/min

2. The method according to p. 1, characterized in that in the production of melt perform deoxidation and alloying in the bucket.

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

4. The method according to p. 1, wherein during the continuous casting protect streams of metal with argon.

 

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