High-strength steel of high hardenability

 

The invention relates to metallurgy, in particular to the development of high-strength structural steel, intended for the manufacture of welded structures for various purposes. The proposed steel contains components in the following ratio, wt.%: carbon 0,14-0,20; manganese 1,10-1,50; silicon 0,15-0,35; Bor 0,0010-0,0050; molybdenum 0,45-0,55; aluminum 0,03-0,06; titanium 0.01 to 0.04; nitrogen 0,005-0,015; calcium 0,001-0,010; sulfur of 0,005 0,020; iron - rest. With:;Mn+3,0Mo2,7.The technical result of the invention is to increase hardenability characteristics of the claimed steel and ensuring end-to-end hardenability thermoelectric sheets with thickness up to 40 mm and rolled diameter up to 50 mm 2 table.

The invention relates to the field of metallurgy, in particular to the development of high-strength structural steel, intended for the manufacture of welded structures for various purposes.

Known structural steel, containing (wt.%): carbon 0,08-0,20%, silicon of 0.2-0.6%, manganese 1,2-2,0%, calcium is 0.0002-to 0.060%, nitrogen from 0.005 to 0.025%, boron 0,0005-0,0050%, aluminum 0,010-to 0.060%, titanium from 0.01 to 0.10%, yttrium 0,0001-0,050%, the rest of the iron [1]. The disadvantage of this steel allstargame elements, which does not allow for sufficient stability properties of steel.

Closest to the technical essence and the achieved effect to the proposed steel is a steel containing (wt.%): the carbon of 0.12-0.20%, si of 0.1-0.5%, manganese 1.0 to 1.6%, and nitrogen 0,015-0,030%, boron 0.003 to 0.01%, and calcium of 0.005 to 0.3%, aluminum of 0.02 to 0.08%, the rest of the iron [2].

The disadvantage of steel is a relatively low content of the elements, which increases the stability of austenite. The absence of titanium, with a high nitrogen does not take into account protection factor of boron from binding in the nitrides that when industrial output level of nitrogen in the steel will not provide the required characteristics of hardenability.

The objective of the invention is to increase the hardenability characteristics, and ensuring end-to-end hardenability thermoelectric sheets in thicknesses up to 40 mm and rolled diameter up to 50 mm

The problem is solved by the fact that the proposed steel containing carbon, manganese, silicon, nitrogen, calcium, aluminum, boron, iron, further comprises molybdenum, titanium and sulfur in the following ratio, wt.%:

The carbon 0,14-0,20

Manganese, Mn 1,10-1,50

Silicon, Si 0,15-0,35

Boron, In 0,0010-0,0050

Molybdenum, Mo 0,45-0,55

Aluminum, Al 0,03-0,06

Titanium, Ti 0,01-0,04

Nitrogen, N 0,005-0,015

�//img.russianpatents.com/chr/8805.gif">2,7

Impurities include phosphorus to 0.025%, copper up to 0.20%.

Given the combination of alloying elements allow you to get in the proposed steel (sheet thickness up to 40 mm and rolled diameter up to 50 mm) after thermolysine (tempering temperature of not less than 920°C, followed by tempering temperature not lower than 620°C) homogeneous fine structure of martensite leave with a favorable combination of strength and ductility.

Carbon is introduced into the composition of this steel to ensure strength and hardenability. The upper limit of carbon content (0,21%) due to the need to ensure the required level of ductility of steel, and the lower to 0.16% by providing the required strength level of the steel.

Manganese and molybdenum 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 contents of these elements (respectively 1,50% MP, 0,55% Mo) is determined by the need to ensure the required level of ductility of steel, and the lower - 1,10% MP, 0,45% Mo - the need to ensure the required level of strength, procon technology deoxidation of steel. The silicon content higher than 0,35% 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 (0.03 and 0.01 respectively) is determined by the requirement to ensure the hardenability of steel, and the upper level (0.06 and 0.03 in) 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.

Sulfur determines the level of ductility of steel. The upper limit is caused by the necessity of obtaining a given level of ductility and toughness of steel, and the lower limit issues-tech production.

Calcium is an element, modi is the ductility and toughness of steel, and the lower limit issues-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:

, Mn+3,0Mo2,7,

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

Ratios

, Mn+3,0Mo2,7

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 of molybdenum, titanium and sulfur and ratios:

, MP+3,0Mo2,7.

Thus, the proposed solution meets the criterion of "novelty".

Analysis of patent and scientific and technical information not found solutions with the same set of features, which was achieved shodn meets the criterion of "substantial differences".

The following are examples of implementation of the present invention, not excluding other in the scope of the claims.

In experimental conditions produced 10 of the bottoms experienced steel, whose chemical composition is given in table 1. Procurement of samples of size 1414300 mm were heat treated in a laboratory furnaces of the type of snz in the following modes: quenching from 950°C with a holding time of 50 minutes and cooled in water. Vacation at a temperature of 630°C 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 I, 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 strengthinand0.2and plasticity -and. 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 �8826.gif">

where M1and M2- average values compared; S21and S22the dispersion medium; t0.05KR() is a critical value of the student test at a significance level of 0.95 and the number of degrees of freedom. 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, 950°C, 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 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 950°C. the Duration of heating of the sample to the quenching temperature was 30-50 minutes. Deviations from the specified temperature after extraction of the sample from the furnace before cooling does not exceed 5 C. The sample was kept under running water until completely cooled (about 15-20 min). The temperature of cooling water at (20±5)°C. For measuring the hardness along the length of the tempered sample was sosotoyalas two diametrically opposite the site to a depth (0,5±0,1) mm Ground 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 accurate fixation of the measurement of hardness was specially designed and manufactured device. If necessary, re-measuring the hardness at the site at which 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 sootvetstvuetopredelennyj sites calculated average hardness. Mechanical properties are presented in table 2. As can be seen from table 2, the proposed steel in comparison with the known higher hardenability characteristics.

SOURCES of INFORMATION

1. USSR author's certificate No. 1052558, With 22 38/4, 04.06.1982,

2. USSR author's certificate No. 773125, With 22 38/06, 26.03.1979, (prototype).

Claims

High-strength steel of high hardenability, containing carbon, manganese, silicon, nitrogen, calcium, aluminum, boron and iron, characterized in that it further comprises molybdenum, titanium and sulfur in the following ratio, wt.%:

Carbon 0,14-0,20

Manganese 1,10-1,50

Silicon 0,15-0,35

Bor 0,0010-0,0050

Molybdenum 0,45-0,55

Aluminum 0,03-0,06

Titanium 0,01-0,04

Nitrogen 0,005-0,015

Calcium 0,001-0,010

Sera of 0,005 0,020

Iron Rest

and

MP+3,0Mo2,7.

 

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4 ex, 1 tbl

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21 cl, 1 dwg, 9 tbl, 5 ex

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2 tbl, 1 ex

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5 tbl

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