Steel construction

 

(57) Abstract:

The invention relates to metallurgy, in particular to the development of structural steel for the manufacture of billets used in cold landing fasteners. The proposed structural steel containing carbon, manganese, silicon, boron, vanadium, aluminum, titanium, nitrogen and iron in the following ratio, wt. % : carbon 0,18 - 0,24, manganese 0,90 - 1,30, silicon 0,17 - 0,37, boron 0,0005 - 0,0050, vanadium 0,01 - 0,08, aluminum 0,02 - 0,06, titanium 0.01 to 0.04, nitrogen 0,005 -0,015 and iron - rest, provided that the content of the elements satisfies the following relations: , the Technical result of the invention is to increase the hardenability characteristics and ensuring end-to-end hardenability thermonuclear workpieces with a diameter up to 25 mm 2 table.

The invention relates to the field of metallurgy, in particular to the development of high-strength structural steel intended for billets used in cold landing fasteners.

Known structural steel containing, wt.%: carbon 0.06-0.30, si 0.17-1.0, manganese 0.8-2.0, vanadium, 0.01 to 0.25, the nitrogen of 0,005 0,040, boron 0.001-0.008, aluminum from 0.005 to 0.10, titanium 0.005-0.015, the rest of the iron [1]. Not contrazione border element content, which does not allow for residual stability properties of steel.

Closest to the technical essence and the achieved effect to the proposed steel is a steel containing, in wt.%: carbon 0.06-0.30, si 0.17-1.0, manganese 0.8-2.0, boron 0.001-0.008, vanadium, 0.01 to 0.25, aluminum, 0.005-0.10, titanium 0,005-0,015, nitrogen from 0.005 to 0.40, the rest of the iron [2].

The disadvantages of the known steel are the broad limits of variation of carbon, manganese, which does not allow to obtain a stable level of mechanical properties. In the analyzed composition is not taken into account the protection factor sconce from binding in the nitrides that when industrial output level of nitrogen in the steel will not allow to receive high characteristics of its hardenability.

The objective of the invention is to increase the hardenability characteristics and ensuring end-to-end hardenability thermolysine steel with a diameter up to 25 mm

This object is achieved in that the proposed steel containing carbon, manganese, silicon, boron, vanadium, aluminum, titanium, nitrogen and iron contains components in the following ratio, wt.%:

Carbon - 0.18 - 0.24

Manganese - 0.90 - 1.30

Silicon - 0,17 - 0,37

Bor - 0.0005 - 0.0050

Vanadium - 0,01 - 0,08

Al is s elements satisfies the following relationships:

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Impurities: phosphorus 0.025%, Nickel up to 0.20%, copper up to 0.20%.

Given the combination of alloying elements allow you to get in the proposed steel rod with a diameter up to 25 mm), after thermolysine (tempering temperature of not less than 920oC followed by tempering temperature not lower than 620oC) a homogeneous fine structure of martensite leave with a favorable combination of strength and ductility.

Carbon and carbonitrides 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. While vanadium manages the processes in the austenitic region (determines the tendency to grain growth of austenite (up to 950oC) stabilize the structure during thermomechanical processing, increases the temperature of recrystallization and, consequently, affects the character -- transformation. Vanadium also contributes to the hardening stage when thermolysine. The upper limit of the content of carbon (0.24%), vanadium (0.08%) due to the need to ensure the required level of ductility of steel, and the lower (respectively, 0.18%, 0.01%) - obespechenie solid solution, on the other hand, as an element of substantially increasing the stability of the supercooled austenite and increases the hardenability of steel. The upper levels of manganese (1.30%) is determined by the need to ensure the required level of ductility of steel, and the lower (0.90%), the need to ensure the required level of strength and hardenability of the steel.

Silicon belongs to territooriumil elements. The lower limit for silicon (0.17%) caused by the deoxidation of steel. The silicon content higher 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 content of boron (0.0050) is determined by considerations of ductility of steel, and the lower (0.0005) - 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 content data items (0.01 and 0.02, respectively) is determined by the requirement to ensure the hardenability of steel, and the upper level (0.06 and 0.04) - requirement to provide sadanori 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.

To ensure complete bonding of nitrogen in the nitride type TiN and AIN 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.

Relations 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 introduction of new components - vanadium, aluminium and titanium, as well as ratios:

Analysis of patent and scientific and technical information not found solutions with the same set of features, which would reach a similar effect - enhancing characteristics of the hardenability of steel.

The following are examples of implementation of the invention within the scope of the claims.

In experimental conditions in 60-kg open induction furnace smelted 10 heats experience what it was forged on tutuncu section 70 x 70 mm They are then rolled in a sheet with a thickness of 14 mm From the sheet made of billet samples of size 14 x 14 x 300 mm, which were heat treated in a laboratory furnaces of the type of snz in the following modes: quenching from 950oC with a holding time of 50 minutes and cooled in water. Vacation at a temperature of 630oC with a holding time of 30 minutes. The thickness of the workpiece and the cooling during hardening provided through hardenability blanks.

The mechanical characteristics were determined on a tangential samples. Tensile test at room temperature were performed on samples of type 1, GOST 1497-84, on the test machine "INSTRON-1185" with registration strain deformation. The loading rate of the sample is 5 mm/min was Determined characteristics of strengthbandof 0.2and plasticity .

Average values were calculated according to the results of the test at least three samples per pixel. The significance of differences of average values of the analyzed values were assessed using student's criterion, calculated as follows:

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where M1and M2- average values compared;

S21and S22- - dispersion medium; t0,kr Characterization of hardenability (critical diameter D50) was performed by the method of mechanical hardening cylindrical samples with a diameter of 25.0 mm and a length of 100 mm, shoulder, according to GOST 5657. Before manufacture of sample blanks were heat treated in a chamber furnace at the following mode: normalization, 950oC , 1 h, air. Tested on two sample for smelting. Hardening of the samples was carried out with a water jet in a special unit. In connection with the need to prevent oxidation and decarburization of the end of the sample in direct contact with a jet of water during hardening, heating the samples in a chamber furnace (without protective atmosphere) was performed in special glasses. The end of the sample was placed on a special graphite plate. The sample was heated in a furnace to a temperature of 950oC. the Duration of heating of the sample on the quenching temperature was 30 - 50 minutes. Deviations from the set temperature quenching did not exceed 5oC. Exposure of the sample at a temperature of quenching after heating was 30 minutes drive Time from the moment of extraction of the sample from the furnace before cooling does not exceed 5 seconds. The sample was kept under running water until completely cooled (about 15 to 20 minutes). Was temperaturesensitive two diametrically opposite the site to a depth 0.50.1 mm. The site was sosotoyalas with abundant cooling water. The roughness of the ground was rougher 7th cleanliness class according to GOST 2789. Not permitted prizhogi, causing structural changes in the metal. Curve hardenability steel measuring the hardness began at a distance of 1.5 mm from the hardened end face in the axial direction. The first 16 measurements from the end of the sample produced with an interval of 1.5 mm, and then through a 3 mm. If at a certain distance from the end of the sample, the hardness does not change, then the measurements were made after one interval, and then stopped the test. To ensure internal fixation measurement of hardness was specially designed and manufactured device. If necessary, repeated changes of hardness on the surface on which the measurements were taken, the area was pereshlifovyvat. The depth of metal removal when re-grinding was 0.1-0.2 mm Hardness was determined according to Rockwell (HRC) in accordance with the requirements of GOST 9013. For each pair of points lying at the same distance from the end of the sample at two opposite sites, positively average hardness.

Mechanical properties are presented in table 2.

Sources of information

1. USSR author's certificate N 601321, C 22 C 38/12, 06.02.1976,

2. USSR author's certificate N 605854, C 22 C 38/14, 1978 (prototype)e

Steel containing carbon, manganese, silicon, boron, vanadium, aluminum, titanium, nitrogen and iron, characterized in that it contains components in the following ratio, wt.%:

Carbon - 0,18 - 0,24

Manganese - 0,90 - 1,30

Silicon - 0,17 - 0,37

Bor - 0,0005 - 0,0050

Vanadium - 0,01 - 0,08

Aluminum - 0,02 - 0,06

Titanium - 0.01 to 0.04)

Nitrogen - 0,005 - 0,015

Iron - Rest

provided that the content of the elements satisfies the following relationships:

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