Cold-rolled steel for deep drawing

 

The invention relates to metallurgy, namely the composition of the 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; niobium from 0.005 to 0.060; 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 minimum titanium content is calculated from the ratio of (Ti)min= 3,43(N)+2,4(S), where (Ti), (N) and (S) - content of titanium, nitrogen and sulfur, wt.%. The optimum content of niobium in steel is determined from the ratio oforwhere (C) and (Nb) - the content of carbon and niobium, respectively, wt.%. The technical result is to increase stanoevska steel regardless of the mode of heat treatment and application of protective coatings, as well as increased corrosion resistance. 2 C.p. f-crystals, 1 table.

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 KOR the protective coatings, for example, after hot-dip galvanizing, stampability of this steel is not high. In addition, due to increased aluminum content and a corresponding increase of the heterogeneity of the structure of the corrosion resistance of cold-rolled sheet of such steel in aqueous environments containing chlorine 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 not high. 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, cream the components, 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

Niobium 0,01-0,15

Phosphorus (0,005-0,015) or (0,05-0,1)

1,5 sulfur +3,43 nitrogen + 6 carbonTitan1,5 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, increase corrosion resistance and durability of the finished product.

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, niobium, oxygen, and iron, according to the invention, appointed by the p>

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

Niobium from 0.005 to 0.060

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, with a minimum titanium content is calculated from the relation

where (Ti), (N) and (S) - content of titanium, nitrogen and sulfur, respectively, wt.%.

also the fact that it contains niobium in an amount which is determined from the relation

or in the amount determined from the relation

where (C) and (Nb) - the content of carbon and niobium, respectively, wt.%.

The invention consists in that to ensure the highest stanoevska steels with a carbon content of not more than 0,006% is required microalloying steels titanium together with niobium 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 consider necessary the 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 control over the content of oxygen in steel, which is an inevitable impurity, the total element content-deoxidizers and relationships the aluminum content to the oxygen content. 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 carloine 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 elements above the upper limits of the claims leads to the necessity of increasing the number microeconomic elements that may degrade the quality of the surface, deterioration of 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, the CLA content of phosphorus is due to the fact, 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 a factor that has a positive effect on the corrosion of steel. The increase in the titanium content is above the upper limit leads to a higher cost of steel. In addition, high concentrations of titanium may degrade the quality of the surface.

When used as microeconomic elements titanium together with niobium possible depending on the requirements of consumers receiving steels of different levels of strength. When assigning the content of niobium in accordance with the expression (2) it is not enough for a full carbon sequestration, which partially remains in solid solution is lower content of niobium is a significant strengthening of the original cold-rolled sheet, which will adversely affect stanoevska. At higher content of niobium than in accordance with the expression (2) corresponds to expression (3)), the effect of hardening when drying will not, however stampability will be very high, especially if the titanium content corresponds to the expression (1). Further increase in the content of niobium in comparison with the upper limit of expression (3) does not have a significant impact on the stampability, however, leads to a significant rise in prices of metal products.

Examples of embodiment of the invention.

Two 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 the project 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 steel, and corrosion tests of cold-rolled metal.

Has been tested with the following options steels.

Option 1 - steel containing 0,004% carbon 0,009% silicon, 0.14% of manganese, a 0.012% phosphorus, to 0.007% sulfur, 0.03% aluminum, 0,045% titanium, 0.025% niobium, 0,003% nitrogen, 0,004% oxygen, iron and inevitable impurities, with the ratio of Al/O=7,5, total content of aluminum and titanium - 0,075%, the titanium content exceeds the minimum acceptable value in accordance with the claims of 0.045%>0,027%, the content of niobium is within the limits prescribed by p. 2 claims: 0,005%<0.025% of<0,031, you have the option fully meets p. 2 claims.

Option 2 - steel containing 0,004% carbon, 0,008% silicon, 0,13% manganese, 0,010% phosphorus, to 0.007% sulfur, to 0.04% aluminum, 0.04% of titanium, a 0.04% niobium, 0,004% nitrogen, 0,004% oxygen, iron and inevitable impurities, with the ratio of Al/O=10, the total content of aluminum and titanium to 0.08%, the titanium content exceeds the minimum acceptable value in accordance with the claims 0,04%>0,0305%, the content of niobium netvue p. 3 claims.

Mechanical testing of 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, for control was 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 g 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 is operatsii 2%;

2) the samples were placed in a furnace heated to a temperature of 17010C, and kept for 20 minutes;

3) the samples were tested for tensile strength, determining the value of the NR 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).

Relevant requirements also predstavlennoi details in the drying process of the paint coating.

As a method of corrosion testing of samples of cold rolled steel was used the method of 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.

For steel option 1 mechanical properties meet the requirements to become a category hoods SIA, while ensuring maximum value: NR effect and the finished product made from such steel will have increased strength and satisfactory corrosion resistance. For steel option 2 mechanical properties correspond to the category hoods VOSV with satisfactory corrosion resistance.

That is, the use of this proposal significantly increases stampability cold rolled steel for deep drawing, in particular after continuous annealing and when applied xt-align:center; margin-top:2mm;">Claims

1. Cold-rolled steel for deep drawing, containing carbon, silicon, manganese, sulfur, phosphorus, aluminum, nitrogen, titanium, niobium, 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

Niobium from 0.005 to 0.060

The oxygen of 0.001-0.005

Iron and inevitable impurities Else

the total content of aluminum and titanium is 0,07-0,12%, the ratio of aluminum content to the oxygen content is not less than 5.0, with a minimum titanium content calculated from the relation

(Ti)min=3,43(N)+2,4(S)

where (Ti),(N) and (S) - content of titanium, nitrogen and sulfur, respectively, wt.%.

2. Cold-rolled steel for deep drawing under item 1, characterized in that it contains niobium in amounts

0,005%(Nb)7,75(C)

where (C) and (Nb) - the content of carbon and niobium, respectively, wt.%.

3. Cold-rolled steel for deep drawing under item 1, characterized in that it contains niobium in an amount which is determined from the relation

7,75 ()<(Nb)

 

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2 tbl, 1 ex

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1 dwg, 1 tbl

FIELD: ferrous metallurgy; motor-car industry; production of steels intended for manufacture of items of a complex configuration with the help of cold sheet stamping.

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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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