Cold-rolled steel for deep drawing

 

The invention relates to ferrous metallurgy, namely the composition of low carbon cold rolled steel, for the manufacture of articles of complex shape, mainly parts of the vehicle, including protective coatings. Declared cold-rolled steel for deep drawing contains components in the following ratio, wt.%: carbon 0,001-0,006; silicon 0,002-0,020; manganese 0,07-0,30; phosphorus of 0,005 0,020; sulfur 0,005-0,010; aluminum 0,015-0,050; nitrogen - 0,002-0,006; titanium 0,02-0,08; the oxygen of 0.001-0.005; iron and inevitable impurities rest. The total content of aluminum and titanium is between 0.07 and 0.12 wt.%, and the ratio of aluminum content to the oxygen content is not less than 5.0. The technical result of the invention is to improve stanoevska steel regardless of the mode of heat treatment and application of protective coatings, as well as increased corrosion resistance. table 1.

The invention relates to ferrous metallurgy, namely the chemical composition of low carbon cold rolled steel, for the manufacture of articles of complex shape, mainly parts of the vehicle, including protective coatings. The main requirements predjuice, and after thermal processing in units of continuous annealing, corrosion resistance, ensuring good adhesion of the protective coating to the steel strip. Recently, the consumers of such steels are increasingly demanding to increased levels of strength characteristics, which is maintained as a result of hardening when drying coatings on finished parts.

Known steel used in the manufacture of cold-rolled structural steel sheet for stamping parts of cars, tractors and agricultural machinery, containing carbon, manganese, copper, aluminum, boron, phosphorus, nitrogen and iron in the following ratio, wt.%:

carbon 0,02-0,07

manganese 0,15-0,30

copper 0,02-0,30

aluminum 0,03-0,07

Bor 0,0005-0,005

phosphorus 0,04-0,10

nitrogen 0,001-0,007

iron rest

(A. C. of the USSR № 1741459, IPC With 22 38/16, publ. 10.11.1995,). Cold-rolled sheet of such steel has a high stampability and corrosion resistance in some environments, in particular, in an aqueous solution of sulfuric acid, however, after the application of protective coatings, for example, after the hot shredding, stampability of this steel is low. In addition, due to increased aluminum content and a corresponding increase GE is among the chloride ions as well as in the atmosphere may be sufficient.

Known steel used in the manufacture of structural sheet for stamping, containing carbon, silicon, manganese, copper, calcium and iron in the following ratio, wt.%:

carbon 0,08-0,12

silicon 0,80-1,50

manganese to 0.55-0.90

copper 0,05-0,50

calcium 0,0005-0,0015

iron rest

the ratio of silicon and carbon is 1,0-1,25 (RF Patent 2061780, IPC With 22 38/16, publ. 10.06.1996 year).

Steel has higher strength and corrosion resistance in some environments. However, the stampability of this steel is low. In addition, in the presence of calcium in steel may be the presence of nonmetallic inclusions having a negative impact on corrosion resistance in some environments, in particular in the atmosphere.

Most similar in chemical composition to the proposed steel is cold rolled steel for deep drawing, containing carbon, silicon, manganese, sulfur, phosphorus, aluminum, chromium, Nickel, copper, nitrogen, niobium, titanium and iron in the following ratio, wt.%:

carbon 0,003-0,015

silicon 0,005-0,02

manganese of 0.05-0.2

sulfur 0,004-0,012

aluminum 0,015-0,06

chrome 0,005-0,04

Nickel 0,004-0,03

copper 0,006-0,05

nitrogen 0,001-0,006

="https://img.russianpatents.com/chr/8804.gif">1,5

sulfur + 3,43 nitrogen + 10 carbon, iron rest

(RF patent 2034088, IPC With 22 38/50, publ. 30.04.1995, prototype).

The disadvantage of this steel can be relatively low stampability after the heat treatment for some modes in units of continuous annealing, and after application of protective coatings. In addition, high concentrations of aluminum may result in reduced corrosion resistance of cold-rolled sheet of such steel.

The technical result of the invention is to improve stanoevska steel regardless of the mode of heat treatment and applying a protective coating, the improvement of corrosion resistance.

The technical result is achieved by the fact that in the known cold-rolled steel for deep drawing, containing carbon, silicon, manganese, phosphorus, sulfur, aluminum, nitrogen, titanium, oxygen and iron, according to the invention, assign the contents of the components in the following ratio, wt.%:

carbon 0,001-0,006

silicon 0,002-0,020

manganese 0,07-0,30

phosphorus of 0,005 0,020

sulfur 0,005-0,010

aluminum 0,015-0,050

nitrogen 0,002-0,006

titanium 0,02-0,08

the oxygen of 0.001-0.005

iron and inevitable impurities else

the total content of aluminum and titanium is 0,07-0,12%, and is in fact, to ensure the highest stanoevska steels with a carbon content of not more than 0,006% is required microalloying steels titanium in such quantity to ensure complete removal of the solid solution impurity introducing carbon and nitrogen. Currently used formulas for calculating the required content microeconomic elements take into account the need to link in the carbides, nitrides and carbosulfan total number present in the steel of carbon, nitrogen and sulfur. At the same time, if there is insufficient degree of raskalennoi steel, for example, when a small amount of added for deoxidation aluminium, part of the titanium can be spent on oxygen and it will not be sufficient for complete removal from the solution the introduction of impurities in the form of particles of relatively large size and high stanoevska. The effect of reducing stanoevska insufficient degree of raskalennoi became increasingly evident during continuous annealing of cold rolled Autodiscover steels. Therefore, a prerequisite for high stanoevska, in addition to regulation of the chemical composition of the main alloying elements, is the control over the content of oxygen in steel, which is of nesb oxygen. The lower oxygen content below 0.001% is impractical, as it does not have a positive influence on properties of steel, but leads to its appreciation. Ensuring relationships the aluminum content to the oxygen content of not less than 5 when the oxygen content is not more than 0.005% indicates a high degree of raskalennoi steel, which has a positive effect on stampability and corrosion resistance. In this case the restriction of the lower limit of the total content of aluminum and titanium of at least 0.07% indicates the presence of titanium steel, which will be effectively used to remove impurities introduction of solid solution. The increase in total content of aluminum and titanium above 0,12% is not advisable as it may lead to deterioration of corrosion resistance, as well as to the increased cost of steel.

The restriction of the lower limit of the content of carbon, nitrogen and sulfur in steel is determined by the capabilities of the existing steelmaking technologies. Further reduction of the content of these elements does not cause a significant improvement of consumer properties, but leads to a significant rise in prices of steel products. The increase in the content of these items is participating items what could degrade surface quality, the deterioration of the adhesion of protective coatings, as well as increases the cost of steel products.

The upper limits of the contents of silicon and manganese are associated with the need to limit terrastone hardening steel, which has a negative effect on stampability. Restriction lower limits of the contents of these elements are mainly driven by economic considerations, so as to further decrease their content does not improve the quality of steel.

Limitation upper limit of the content of phosphorus is due to the fact that when its increased content in steel can cause embrittlement of the grain boundaries. The restriction of the lower limit of the content of phosphorus is dictated by economic considerations, as further reducing its content in the steel does not lead to improved properties.

The minimum aluminum content in the steel is determined by the need for sufficient deoxidation of steel, and the minimum content of the titanium - demand sufficient removal of the solid solution impurity introduction.

Limitation upper limit of the content of alloying elements forming nonmetallic inclusions, in particular aluminum, is the factor gender is auditing the cost of steel. In addition, high concentrations of titanium may degrade the quality of the surface.

Examples of embodiment of the invention.

Four options sverkhnizkochastotnye steels were melted in a 300-ton Converter OJSC “Magnitogorsk iron and steel works”, reflected in the continuous casting of steel in the slab cross-section 2501300 mm, of which hot rolling mill “2000” received strip thickness 2.8 mm, providing the temperature of the end of the rolling 880-900C. Strip after dushirovaniya wound into rolls at a temperature of 710-730C. After pickling and cold rolling the strip with a thickness of 0.8 mm metal part was subjected to heat treatment in bell-type furnaces at a temperature of 700(Below this metal is referred to as cold-rolled), another part of the strips were subjected to processing in galvanizing with zinc coating and conducting nepreryvnogo annealing at a temperature of 850(Below this metal is referred to as galvanized). After training with the degree of compression of 0.8% conducted a comprehensive mechanical testing and cold-rolled, and galvanized metal is:

option 1 - steel containing 0,003% carbon, 0,012% silicon, 0.14% of manganese, to 0.011% phosphorus, 0,008% sulfur, 0.03% aluminum, 0.02 percent titanium, 0,004% nitrogen, 0,004% oxygen, iron and inevitable impurities, with the ratio of Al/O = 7,5 corresponded to the claims, and the total content of aluminum and titanium of 0.05% was lower than in accordance with the claims;

option 2 - steel containing 0,004% carbon, 0,010% silicon, 0.15% of manganese, 0,010% phosphorus, 0,010% sulfur, 0.02% aluminum, 0.05% of titanium, of 0.003% nitrogen, 0.005% oxygen, iron and inevitable impurities, with the ratio of Al/O = 4 does not match the claims, and the total content of aluminum and titanium 0,07% corresponds to the formula of the invention; and

option 3 - steel containing 0.005% carbon, 0,008% silicon, 0.12% of manganese, of 0.014% of the phosphorus to 0.007% sulfur, to 0.06% aluminum, 0.05 to titanium, 0,004% nitrogen, 0,004% oxygen, iron and inevitable impurities, with the ratio of Al/O = 15 and the total content of aluminum and titanium 0,11% correspond to the formula of the invention; option does not match the claims on the content of aluminium;

option 4 - steel, containing 0,004% of carbon, to 0.011% silicon, 0,13% manganese, 0.015% phosphorus, 0.005% of sulfur, 0.03% aluminum, 0.04% of titanium, 0,004% nitrogen, 0,004% oxygen, iron and inevitable impurities, the steel is fully southwest samples of galvanized steel was carried out on an Electromechanical testing machine INSTRON-1185. The size of the sample was 20120 mm

The tests were carried out in semi-automatic mode with a strain gauge longitudinal strain (base strain gauge 12.5 mm). Stretch speed was 10 mm/min.

In the case of curves without physical strain yield stress (which is typical, in particular, IF-steels), the value of the yield strength was determined by the strain gauge readings taking into account the linear section of the diagram expansion (in addition to control, used the analysis of machine diagram expansion).

The rate of hardening was determined in the range deformation from 10 to 17%.

The ratio of the normal plastic anisotropy r was defined by the stop trials (17%) by measuring manually the width of the sample (in three sections).

For samples with a width of 20 mm elongation4was determined on the basis of 80 mm (A80).

Tests to determine the hardening of the steel during the drying of the paint coating (EXT-effect) was performed in the following sequence:

1) the samples were stretched to the deformation rate of 2%, which was determined by an extensometer (base 26 mm); this was determined2- stress at strain of 2%;

2) aivali for 20 minutes;

3) the samples were tested for tensile, determining the value of HV-effect, as the difference between yield strengtht(NR) and2.

The results of the mechanical tests of samples of galvanized steel all variants, as well as the results of the corrosion test samples of cold rolled steel are given in table. Stampability steel was evaluated by the main mechanical characteristics required by normative-technical documentation (NTD) for steels of this class, these include yield strengthttensile strengthin, elongation4coefficient of normal plastic anisotropy r and the coefficient of strain hardening n. Criterion high stanoevska considered the compliance values of the parameters specified requirements steels categories hoods salt (very difficult extraction) and VOSV (very very difficult extraction). Appropriate requirements for the parameters are also presented in the table. The table shows the values of HV-effect characterizing the hardenability of stamped parts in the drying process Lakokraska way alternating immersion of the samples autopistol steel in a solution of 3.5% NaCl with being in it for 10 minutes and subsequent removal by air (50 minutes) in accordance with ASTM G 44-75. Corrosion resistance was evaluated by the weight gain (weight) per unit area of the surface of the sample for 30 cycles of testing. If the value of the weight gain was less than 8 g/m2, the corrosion resistance was considered satisfactory. The test results for the studied variants are also presented in the table.

It is seen that for options 1 and 2 due to a lack of high values of the ratio of aluminum content to the oxygen content and the total content of aluminum and titanium obtained high values of yield strength and low values of relative elongation and coefficients of r and n, which does not allow to consider these steel categories hood salt and VOSV. For steels options 3, 4 mechanical properties correspond to the category hoods VOSV. However, for option 3 received the lowest corrosion resistance, which is associated with increased aluminium content. Thus, only steel version 4, corresponding to the formula of the invention has mechanical properties at the category level hoods VOSV with satisfactory corrosion resistance.

That is, the use of this proposal significantly increases stampability cold the Oia, corrosion resistance cold rolled steel.

Claims

Cold-rolled steel for deep drawing, containing carbon, silicon, manganese, sulfur, phosphorus, aluminum, nitrogen, titanium, oxygen and iron, characterized in that it contains the components in the ratio, wt.%:

Carbon 0,001-0,006

Silicon 0,002-0,020

Manganese 0,07-0,30

Phosphorus of 0,005 0,020

Sulfur 0,005-0,010

Aluminum 0,015-0,050

Nitrogen 0,002-0,006

Titanium 0,02-0,08

The oxygen of 0.001-0.005

Iron and inevitable impurities Else

the total content of aluminum and titanium is 0,07-0,12%, and the ratio of aluminum content to the oxygen content is not less than 5.0.

 

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2 tbl, 1 ex

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1 dwg, 1 tbl

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4 ex, 1 tbl

FIELD: steel making.

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EFFECT: achieved elongation strength at least 800 MPa.

21 cl, 1 dwg, 9 tbl, 5 ex

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SUBSTANCE: proposed method includes production of steel blank, heating it to temperature above As3, deformation in controllable mode at specific reduction processes and at total reduction of 50-60% followed by controllable cooling; proposed steel has the following composition, mass-%: carbon, 0.05-0.9; manganese, 1.25-1.6; silicon, 0.15-0.30; chromium, 0.01-0.1; nickel, 0.3-0.6; molybdenum, 0.10-0.25; vanadium, 0.03-0.10; aluminum, 0.02-0.05; niobium, 0.01-0.06; copper, 0.2-0.4; calcium, 0.001-0.005; sulfur, 0.0005-0.005; phosphorus, 0.005-0.015; the remainder being iron; preliminary deformation of blanks is performed at temperature of 950-850°C at total reduction of 50-60%; then, blank is cooled down to temperature of 820-760°C at rate of cooling of 15°C/s on controllable cooling unit and final deformation is performed additionally at temperature of 770-740°C to required thickness of skelp at total reduction of 60-76%; further cooling is performed at higher rate of 35-55°C/s to temperature of 530-350°C, after which skelp is cooled in jacket to temperature of 150±20°C and then in the air. New stage of the proposed method makes it possible to manufacture tubes of 1067-1420 mm in diameter at thickness of walls of 24-40 mm which are used for sea gas pipe lines working at pressure of up to 19 Mpa.

EFFECT: enhanced strength, ductility and cold resistance; enhanced operational reliability; increased service life.

2 tbl, 1 ex

FIELD: metallurgy, namely cold resistant steels.

SUBSTANCE: cold resistant steel for machines and apparatuses, namely in gas- and oil production industry operating in condition of cold climate. Such steel contains, mass %: carbon, 0.15 - 0.22; manganese, 0.3 - 0.6; silicon, 0.15 - 0.40; vanadium, 0.08 -0.12; titanium, 0.001 - 0.040; niobium, 0.001 - 0.040; aluminum, 0.03 - 0.06; sulfur, 0.010 - 0.020; phosphorus, 0.010 - 0.020; cerium, 0.005 - 0.05; calcium, 0.001 - 0.01; barium, 0.001 - 0.01; iron, the balance.

EFFECT: improved strength and cold resistance of steel.

5 tbl

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