JP2007131916A - High-strength cold rolled steel sheet for deep drawing and hot dip plated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength cold rolled steel sheet for deep drawing applied to the fields of automobiles, house appliances or the like, particularly, to provide a high-strength cold rolled steel sheet having excellent deep drawability, weld joint efficiency and secondary processing brittleness resistance required for an automobile fuel tank, and to provide a hot dip plated steel sheet having excellent corrosion resistance. <P>SOLUTION: The high strength cold rolled steel sheet for deep drawing having excellent weld joint efficiency and hot dip plated steel sheet contain, by weight, ≤0.010% C, ≤0.10% Si, 1.0 to 3.0% Mn, ≤0.03% P, 0.01 to 0.040% Ti, 0.01 to 0.045% Nb and 0.0010 to 0.0050% B, and contain, as selective elements from the viewpoint of strength and processability, 0.01 to 1.0% Ni and 0.01 to 1.0% Mo. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a deep drawing high strength cold-rolled steel sheet, a hot-dip steel sheet, and a manufacturing method thereof applied to the fields of automobiles, home appliances, and the like, and in particular, deep drawability and welded joint efficiency required for a fuel tank of an automobile. The present invention relates to a high-strength cold-rolled steel sheet having excellent secondary work brittleness resistance, a hot-dip plated steel sheet having excellent corrosion resistance, and a method for producing them.

  In recent years, steel sheets for automobiles have been increased in strength for the purpose of improving fuel efficiency by reducing vehicle body weight. Similarly, steel plates for fuel tanks are required to have excellent formability due to the complexity of fuel tanks due to the lighter tanks and more complicated vehicle body design due to the location of the fuel tanks. In order to satisfy such demands for both formability and high strength, IF (Interstitial Free) steel, in which carbonitride-forming elements such as Ti and Nb are added to ultra-low carbon steel, P, Si, Mn High-strength IF steel added with solid solution strengthening elements such as has been developed.

  However, since IF steel precipitates and fixes C and N as carbides with Ti and Nb, the crystal grain boundary becomes very clean, and secondary processing embrittlement is likely to occur due to grain boundary fracture after forming. There is a point. Furthermore, in the case of high-strength IF steel, there is a problem that secondary work embrittlement is promoted because the intragranular strength is strengthened by the solid solution strengthening element and the relative grain boundary strength is significantly reduced.

  The fuel tank is used by pressing the upper surface and the lower surface separately and joining them together by welding. However, even if the strength of the steel plate is increased, there is a problem that the strength of the welded joint cannot be improved to a height commensurate with the increase in strength of the steel plate. In addition, since the fuel tank is an important safety part, it is necessary to improve the fracture resistance against a collision in winter in a low temperature region.

  Among these problems, several methods have been proposed for the purpose of avoiding secondary work embrittlement. For example, in the disclosed technique disclosed in Patent Document 1, based on Ti-added IF steel, in order to avoid deterioration of secondary work embrittlement resistance due to segregation of grain boundaries, the amount of P addition is reduced as much as possible, and Mn, A technique for manufacturing a high-tensile steel sheet excellent in deep drawability and secondary work brittleness resistance by adding a large amount of Si has been proposed. In addition, the disclosed technique disclosed in Patent Document 2 proposes a technique for increasing grain boundary strength and increasing secondary work brittleness resistance by adding B in addition to Ti and Nb using an ultra-low carbon steel sheet. Has been. In the disclosed technique disclosed in Patent Document 2, the optimum B addition amount is found in consideration of improving the secondary work brittleness resistance and preventing an increase in load during hot rolling due to a delay in recrystallization of austenite grains. ing.

Several proposals have been made for the purpose of improving weldability. For example, in the disclosed technique disclosed in Patent Document 3, an ultra-low carbon steel sheet to which Ti or Nb is added is carburized during annealing to form a martensite or bainite structure on the surface layer, thereby improving spot weldability. Patent Document 4 intends to increase the strength of a spot welded joint by adding Cu to an extremely low carbon steel and widening a heat-affected zone during welding. Patent Document 5 adds Mg to steel, forms Mg oxide and Mg sulfide, and refines the welded part and heat-affected zone by the pinning effect, thereby improving the formability of the welded part. This is a technology for preventing the deterioration of the material.
JP-A-5-59491 JP-A-6-57373 JP-A-7-188777 JP-A-8-291364 JP 2001-288534 A

However, in the disclosed techniques of Patent Documents 1 and 2, workability and secondary work brittleness resistance are good, but the problem that weld joint efficiency is low remains. Since the method described in Patent Document 3 is carburized during annealing, the rate of plate feed, atmospheric gas composition, and temperature are not constant in actual production equipment, so the amount of carburization changes and the material variation between the steel plates to be produced is large. Become. For this reason, it is difficult to produce a stable steel sheet. The method described in Patent Document 4 has a problem in that since a large amount of Cu is added, surface defects due to Cu frequently occur and the yield decreases. Furthermore, the method described in Patent Document 5 is effective in arc welding with a relatively slow cooling rate after welding, but has a drawback that the effect is not recognized in seam welding with a high cooling rate.

  Accordingly, the present invention has been devised in view of the above-described problems, has a tensile strength of 3800 MPa or more and less than 590 MPa, has press formability applicable to automotive steel plates, particularly fuel tanks, and The object is to propose a high-strength cold-rolled steel sheet for deep drawing, a hot-dip steel sheet, and a method for producing them, which are excellent in secondary work brittleness resistance and weld joint efficiency.

  The present inventors have achieved high strength cold-rolled steel sheets and high-strength hot-dip galvanized steel sheets that have excellent press formability and excellent secondary work brittleness resistance and weld joint efficiency, which has been extremely difficult with the prior art. In order to obtain As a result, the amount of addition of P and Si, which are conventional solid solution strengthening elements, is reduced as much as possible, and by utilizing transformation strengthening even in ultra-low carbon steel sheets, the secondary work brittleness resistance can be further improved, and welded joints We found that efficiency could be improved.

  That is, the deep drawing high-strength cold-rolled steel sheet according to Claim 1 of the present invention is, in weight%, C: 0.0005 to 0.010%, Si: 0.10% or less, Mn: 1.0 to 3.0%, P: 0.03% or less, Ti: It contains 0.01 to 0.040%, Nb: 0.01 to 0.045%, B: 0.0010 to 0.0050%, and is characterized by being composed of the balance inevitable impurities.

  The deep drawing high-strength cold-rolled steel sheet according to claim 2 is in weight%, C: 0.0005 to 0.010%, Si: 0.10% or less, Mn: 1.0 to 3.0%, P: 0.03% or less, Ti: 0.01 to It contains 0.040%, Nb: 0.01-0.045%, B: 0.0010-0.0050%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, and the balance consists of inevitable impurities.

  The hot dip plated steel sheet according to claim 3 of the present application is C: 0.0005 to 0.010%, Si: 0.10% or less, Mn: 1.0 to 3.0%, P: 0.03% or less, Ti: 0.01 to 0.040%, Nb:% by weight. It is characterized by containing 0.01 to 0.045%, B: 0.0010 to 0.0050%, and the balance being inevitable impurities.

  The hot-dip galvanized steel sheet according to claim 4 is C: 0.0005-0.010%, Si: 0.10% or less, Mn: 1.0-3.0%, P: 0.03% or less, Ti: 0.01-0.040%, Nb: It contains 0.01 to 0.045%, B: 0.0010 to 0.0050%, Ni: 0.01 to 1.0%, Mo: 0.01 to 1.0%, and the balance consists of inevitable impurities.

  The manufacturing method of the deep drawing high-strength cold-rolled steel sheet according to claim 5 of the present application includes continuous casting, hot rolling, and cold rolling of the molten steel having the composition according to claim 1 or 2 at a temperature of 860 ° C. or less. It is characterized by crystal annealing.

  The manufacturing method of the hot-dip galvanized steel sheet according to claim 6 of the present invention is to continuously cast, hot-roll, and cold-roll the molten steel having the composition according to claim 3 or 4 and to perform recrystallization annealing at a temperature of 860 ° C. or lower. Features.

  According to the present invention, by adding low amounts of P and Si, which are solid solution strengthening elements that have been positively added to conventional high-strength steel sheets, and by specifying Mn, Nb, Ti, and B, conventional carbon It is possible to utilize the bainite structure with ultra-low carbon steel without specially controlling the cooling rate during cooling after annealing the bainite structure that was used only in high-amount steel, and at the same time achieving high strength It has excellent processing characteristics, and has excellent secondary work brittleness resistance and weld joint efficiency. This effect makes it possible to improve fuel efficiency by reducing the weight of automobiles by increasing strength, and in particular, to manufacture fuel tanks that are compatible with lighter fuel tanks and more complicated body designs. Further, the hot-rolled steel sheet is soft and has a merit that the manufacturing cost can be reduced because the strength can be increased after cold-rolling annealing. These effects are extremely large industrially.

  Hereinafter, as the best mode for carrying out the present invention, high-strength cold-rolled steel sheet for deep drawing, hot-rolled steel sheet having press formability and excellent secondary work brittleness resistance and weld joint efficiency, and hot-dip plated steel sheets thereof, and those The manufacturing method will be described in detail. Hereinafter, the mass% in the composition is simply described as%. The joint efficiency means that the strength ratio of the peel strength to the base metal strength is 50% or more, and that a brittle fracture surface does not occur on the fracture surface in a peel test at a temperature of −50 ° C. or less.

  In high-strength cold-rolled steel sheet and hot-dipped steel sheet for deep drawing to which the present invention is applied, in order to improve the weld joint efficiency, the addition amount of P and Si, which are conventional solid solution strengthening elements, is reduced as much as possible. However, material design is based on the concept of improving secondary work brittleness resistance and improving weld joint efficiency by actively utilizing transformation strengthening.

  That is, the steel components constituting the present invention are C: 0.0005 to 0.010%, Si: 0.10% or less, Mn: 1.0 to 3.0%, P: 0.03% or less, Ti: 0.01 to 0.040%, Nb: 0.01 by weight. -0.045%, B: 0.0010-0.0050%, and it is characterized by containing Ni: 0.01-1.0% and Mo: 0.01-1.0% as a selection element from a viewpoint of intensity | strength and workability.

  Next, the reason why the chemical components of the deep drawing high-strength cold-rolled steel sheet and hot-dip steel sheet to which the present invention is applied will be described.

C: 0.0005-0.010%
C is the most basic element that controls the hardenability and strength of steel, and is an extremely important element in the present invention. Although it is a very effective element for generating a low-temperature transformation phase and achieving high strength, if added over 0.010%, it causes a decrease in workability and a decrease in weld joint efficiency. The concentration of C is 0.010% or less. Further, when extremely high workability is required, it is preferable to add at 0.0050% or less. In the method of the present invention, even if the C concentration is lowered, the generation of the low temperature transformation phase is not affected, but if it is less than 0.0005%, it is difficult to ensure the strength. Moreover, since decarburization cost rises at the time of steelmaking, it is necessary to make it 0.0005% or more.

Si: 0.10% or less Si is well known as a solid solution strengthening element and is an element effective for deoxidation. However, in the present invention, the secondary work embrittlement resistance that increases the Si addition amount deteriorates and at the same time the weld joint efficiency is lowered, so the addition amount needs to be suppressed to 0.10% or less.

Mn: 1.0-3.0%
Mn is an element that improves the hardenability and raises the strength of the material by solid solution strengthening, as is the case with Si, and is one of the important elements in the present invention for the purpose of improving secondary work embrittlement resistance. Mn is an extremely effective element for reducing the Ac1 transformation temperature and generating a low-temperature transformation phase by achieving an α + γ phase at the time of annealing even at a normal annealing temperature, thereby achieving high strength. In addition, by forming an α + γ phase at the time of annealing, TiC or C precipitated as NbC is easily re-dissolved, thereby improving secondary work brittleness resistance. For this reason, an addition amount of 1.0% or more is necessary. On the other hand, if the Mn concentration exceeds 3.0%, the workability deteriorates and the desired workability cannot be ensured.

P: 0.03% or less
P is an element contained as an inevitable impurity in steel and is not an element intentionally added. It is well known that P is an element that has little deterioration in workability and is effective for increasing the strength by solid solution strengthening. However, P is segregated at the grain boundary to deteriorate the secondary work embrittlement resistance, and at the same time, solidification segregation occurs in the welded portion and lowers the weld joint efficiency. For this reason, the concentration of P needs to be 0.03% or less. The lower limit of P does not need to be specified, but since the refining cost increases to lower the P concentration to 0.005% or less, the present invention is mainly performed at 0.005 to 0.02%.

Ti: 0.01-0.040%
It is well known that Ti has a strong affinity with N and C, forms carbonitrides during solidification, reduces solid solution N and C in steel, and improves workability. For this reason, this Ti needs to be added at a minimum of 0.01%. On the other hand, when the addition amount increases, the amount of dissolved C disappears and the grain boundary strength decreases, so the upper limit was made 0.040%.

Nb: 0.01-0.045%
Nb improves toughness by refining the structure, and has a strong affinity with N and C as well as Ti, forms carbonitrides during solidification, reduces solid solution N and C in steel, and processes It is well known to increase sex. For this purpose, it is necessary to add at least 0.01%. On the other hand, as the amount added increased, the amount of dissolved C disappeared and the grain boundary strength decreased, so the upper limit was specified as 0.045%.

B: 0.0010-0.0050%
B is known to be an element that segregates at the grain boundaries to increase the grain boundary strength and improve the secondary work brittleness resistance. Also, by adding together with Mn and Ni, the γ phase during annealing acts to suppress ferrite transformation during cooling, promotes the formation of low temperature transformation phase, and is an element necessary for contributing to high strength is there. For this reason, at least 0.0010% is necessary. On the other hand, when the addition amount increases, not only the effect of adding B is saturated, but also the recrystallization temperature is increased and high-temperature annealing is required, leading to an increase in manufacturing cost and further degrading workability. . For this reason, the concentration of B needs to be 0.0050% or less.

Ni: 0.01-1.0%
Ni, like Mn, is an element effective for increasing the strength. In particular, it can be added as a selective element from the above viewpoint because it contributes to increasing the strength by lowering the temperature in the two-phase region during annealing and generating a low-temperature transformation phase. In order to exert these effects, it is preferable to contain 0.01% or more of Ni. However, addition exceeding 1.0% causes an increase in production cost. For this reason, the upper limit was made 1.0%.

Mo: 0.01-1.0%
Mo is an element effective for increasing the strength, like Ni and Mn. In particular, it contributes to high strength through the generation of a low-temperature transformation phase from the two-phase temperature during annealing. In order to exert these effects, it is preferable to contain 0.01% or more of Mo. It also has the effect of improving processability. As a selective element, it can be added from the above viewpoint. However, addition exceeding 1.0% causes an increase in production cost.

  In the present invention, addition of elements such as S, Al, Cr, and Cu other than the above components does not impair the characteristics of the present invention, so it may be added in a normal range.

  The steel having the above steel composition is subjected to hot rolling by using a converter or an electric furnace, and if necessary, vacuum degassing treatment to form a slab. A hot-rolled coil is usually cold-rolled after descaling, adjusted to a predetermined plate thickness, and subjected to annealing. Since the heating temperature of hot rolling does not impair the characteristics of the present invention as many times as necessary, it should be selected within a range that does not hinder the rolling operation, and the characteristics of the present invention are not changed depending on the hot rolling finishing temperature, so it is particularly specified. Although it is not necessary, it is preferably carried out in the range of 800 to 900 ° C. from the viewpoint of operability. The cold rolling rate is preferably about 60 to 80%, which is usually performed.

  Next, the reason why recrystallization annealing is performed at a temperature of 860 ° C. or lower will be described.

  When annealing is performed at a temperature exceeding 860 ° C., the ferrite grain size and the grain size of the low-temperature transformation phase are increased, the secondary work brittleness resistance is lowered, and the weld joint efficiency is lowered. For this reason, the annealing temperature needs to be 860 ° C. or lower. Preferred conditions are in the range of 760 ° C. to 830 ° C. in order to obtain excellent workability, secondary work brittleness resistance and weld joint efficiency. The average cooling rate to 500 ° C. after annealing is preferably 2.5 ° C./second or more. In addition, you may make it perform an overaging process during this cooling. Further, even if hot-dip plating of zinc, Al alloy, Sn, Sn—Zn alloy or the like is performed in the annealing cooling process, the characteristics of the present invention are exhibited.

  Thereafter, the annealed steel sheet and the plated steel sheet are temper-rolled and shipped as necessary. The annealed steel sheet does not impair the characteristics of the present invention even if it is electroplated.

After heating and holding a slab having the steel composition shown in Table 1 at 1200 ° C, a hot rolled steel sheet having a thickness of 3.7 mm was made under conditions of a hot rolling finishing temperature of 850 to 880 ° C and a winding temperature of 600 to 650 ° C, After pickling, annealing was performed under the conditions shown in Table 1, and temper rolling was performed at 1.0%. The steel sheet was examined for tensile properties, r value as an index of deep drawing, secondary work brittleness resistance, and welded joint efficiency.
Hereinafter, the evaluation method will be described.

  As for the tensile properties, JIS No. 5 test pieces were collected so that the tensile direction was parallel to the rolling direction, a tensile test was performed, and tensile strength and elongation were evaluated. TS was 440 MPa or more and the elongation was 35% or more.

The r value was measured by collecting JIS No. 5 tensile specimens parallel to the rolling direction, 45 °, and perpendicularly. Evaluation of r value was performed by the average value of each direction. This average value, when the r value of _r 0, 45 ° direction parallel r values in the rolling direction and _{r 45,} the r value of the direction perpendicular and _{r 90, r = (r 0} + 2 × r 45 + r 90) / 4. The r value was 1.50 or higher.
Secondary work brittleness is as follows: blanking the steel plate to 105φ, cylindrical punching with a punch with an outer diameter of 50φ, placing the throttle cup on a truncated cone of 30 degrees, 5kg weight from 1m height at various temperatures The cup was dropped and evaluated at the lowest temperature at which no cracks occurred in the cup. The weld joint efficiency was evaluated by evaluating the strength and toughness of the welded portion by seam welding two steel plates (plate thickness: 1.2 mm). At that time, the strength of the welded portion was evaluated by the ratio of the shear tensile strength and the tensile strength of the base material (shear tensile strength / base tensile strength). Further, the toughness of the welded portion was obtained by seam welding the steel plates 1a and 1b having the shape shown in FIG. 1 to produce test pieces, and the welded portion 2 was subjected to a peel test at different temperatures. Then, the fracture surface was observed by SEM and evaluated at a temperature at which no brittle fracture surface occurred. These results are shown in Table 2.

  Steel No. 1 is an example within the scope of the present invention in which Mn, Ti, Nb, and B are added. This steel sheet exhibits good workability and has a secondary work brittle temperature as low as −60 ° C. and excellent secondary work brittleness resistance. Moreover, the weld joint strength is also high, and it can be seen that the temperature at which a brittle fracture surface occurs on the peel test fracture surface of the joint is −70 ° C. or less and has excellent joint toughness. Steel No. 2 is an example within the scope of the present invention in which 0.5% of Ni was added. It can be seen that this steel sheet also has excellent workability, excellent secondary work brittleness resistance and weld joint efficiency. Steel No. 3 is an example within the scope of the present invention in which 0.45% of Mo was added. This steel sheet has a high r value of 1.8, which is an index of deep drawability, and it can be seen that workability is improved by adding Mo. Moreover, it turns out that it has the characteristic which was excellent in secondary work brittleness resistance and the welded joint efficiency.

  Steel No. 4 is a comparative example deviating from the scope of the present invention by setting the P concentration to 0.092%. Although this steel sheet has a good r value of 1.63, the secondary work brittleness resistance is inferior at 20 ° C., the peel strength in the weld peel test is low, and the temperature at which the brittle fracture surface in the peel test occurs is 0. The joint strength and joint toughness are both inferior and high, and the object of the present invention cannot be achieved. Steel No. 4 is a comparative example deviating from the lower limit of Ti defined in the present invention by setting the Ti concentration to 0.001%. This steel No. 4 has a tensile strength of 312 MPa, which falls outside the intended strength range of the present invention: 380 to 590 MPa, and cannot achieve the object of the present invention. Steel No. 6 is a comparative example in which the concentration of Mn is 0.80%, which is out of the scope of the present invention. This steel plate also does not provide the intended strength of the present invention. Steel No. 7 is a comparative example in which the C concentration is 0.0180% and deviates from the C concentration range defined in the present invention. This steel plate has a secondary work brittleness resistance of −20 ° C., which is inferior to those of the examples within the scope of the present invention, and the weld joint efficiency is also inferior. Steel No. 8 is a comparative example in which the amount of B deviates from the lower limit of the range of the present invention. The tensile strength of this steel sheet is 354 MPa, which does not reach the strength target of the present invention.

  Steel No. 9 was annealed at a too high temperature, resulting in two-phase annealing, resulting in poor ductility and weld joint efficiency.

After pickling, it was cold-rolled to a thickness of 1.2 mm and annealed at the temperatures shown in Table 3. This steel plate was subjected to Ni plating by 1 g / m ² using a Watt bath and then Sn—Zn plating by a flux method. As the flux, a ZnCl ₂ aqueous solution was applied by roll coating. The bath composition was Sn-7% Zn, the bath temperature was 280 ° C., and the plating adhesion was adjusted to 30 g / m ² on one side by air wiping after plating. After the plating, temper rolling of 1.0% was performed, and further chromium ³⁺ main chromate treatment was performed.
The steel sheet was examined for tensile properties, r value as an index of deep drawing, secondary work brittleness resistance, and welded joint efficiency. The test method was the same as in Example 1. In addition to the above test, the surface of the plating was observed to investigate the presence or absence of non-plating. A score of ◯ indicates that there is no non-plating, and a score of x indicates that no plating is observed. The evaluation results are shown in Table 4.

  Steel No. 1A is an example within the scope of the present invention in which Mn, Ti, Nb, and B are added. This steel sheet exhibits good workability and has a secondary work brittle temperature as low as −60 ° C. and excellent secondary work brittleness resistance. Moreover, the weld joint strength is also high, and it can be seen that the temperature at which a brittle fracture surface occurs on the peel test fracture surface of the joint is −70 ° C. or less and has excellent joint toughness. Steel No. 2A is an example within the scope of the present invention in which 0.5% of Ni was added. It can be seen that this steel sheet also has excellent workability, excellent secondary work brittleness resistance and weld joint efficiency. Steel No. 3A is an example in which 0.45% of Mo was added. It can be seen that this steel has excellent workability, secondary work brittleness resistance and weld joint efficiency as well as a cold-rolled steel sheet.

  Steel No. 4A has a P concentration of 0.092%, which is a comparative example deviating from the P concentration range defined in the present invention. This steel No. 4A shows an excellent r value of 1.73, but the secondary work brittleness resistance is inferior at 20 ° C, and the peel strength in the weld peel test is low, resulting in a brittle fracture surface in the peel test. The temperature is as high as 0 ° C., the joint strength and joint toughness are inferior, and the intended effects of the present invention cannot be obtained. Steel No. 5A is a comparative example with a Ti concentration of 0.005%, which deviates from the Ti concentration range defined in the present invention. This steel No. 5A has a tensile strength of 351 MPa and deviates from the target strength range of the present invention: the range of 380 to 590 MPa, and the intended effects of the present invention cannot be obtained. Steel No. 6A is a comparative example in which the Mn concentration is 0.80%, which is out of the Mn concentration range defined in the present invention. This steel plate also does not have the intended strength of the present invention. Steel No. 7A is a comparative example having a C concentration of 0.0180%, which deviates from the Ti concentration range defined in the present invention. This steel No. 7A has a secondary work brittleness resistance of −20 ° C., which is inferior to the examples within the scope of the present invention, and the weld joint efficiency is also inferior. Steel No. 8A is a comparative example in which the B concentration is 0.0001% and deviates from the lower limit of B defined in the present invention. The tensile strength of this steel No. 8A is 364 MPa, which does not reach the strength target of the present invention. Steel No. 9A has a Ti concentration of 0.085%, which is a comparative example deviating from the upper limit of Ti defined in the present invention. This steel No. 9A has a high secondary work brittleness resistance of −20 ° C., a low weld joint strength, and a brittle fracture surface temperature of 0 ° C., which is inferior in weld toughness. Steel No. 10A has a Si content of 0.60%, which is a comparative example deviating from the Si concentration defined in the present invention. This steel No. 10A is inferior in secondary work brittleness resistance and weld joint efficiency, and in addition, a large number of portions where plating is not formed remain and the plating property is also inferior.

It is a figure which shows the shape of a weld peel test piece.

Explanation of symbols

1a, 1b Steel plate 2 Welded part

Claims (6)

% By weight
C: 0.0005 to 0.010%,
Si: 0.10% or less,
Mn: 1.0-3.0%
P: 0.03% or less,
Ti: 0.01-0.040%,
Nb: 0.01-0.045%,
B: A high-strength cold-rolled steel sheet for deep drawing characterized by containing 0.0010 to 0.0050% and the balance being inevitable impurities. % By weight
C: 0.0005 to 0.010%,
Si: 0.10% or less,
Mn: 1.0-3.0%
P: 0.03% or less,
Ti: 0.01-0.040%,
Nb: 0.01-0.045%,
B: 0.0010-0.0050%,
Ni: 0.01-1.0%,
Mo: A high-strength cold-rolled steel sheet for deep drawing characterized by containing 0.01 to 1.0% and the balance being inevitable impurities. % By weight
C: 0.0005 to 0.010%,
Si: 0.10% or less,
Mn: 1.0-3.0%
P: 0.03% or less,
Ti: 0.01-0.040%,
Nb: 0.01-0.045%,
B: A hot-dip galvanized steel sheet containing 0.0010 to 0.0050% and consisting of the balance inevitable impurities. % By weight
C: 0.0005 to 0.010%,
Si: 0.10% or less,
Mn: 1.0-3.0%
P: 0.03% or less,
Ti: 0.01-0.040%,
Nb: 0.01-0.045%,
B: 0.0010-0.0050%,
Ni: 0.01-1.0%,
Mo: A hot-dip galvanized steel sheet containing 0.01 to 1.0%, the balance being inevitable impurities. A method for producing a high-strength cold-rolled steel sheet for deep drawing, characterized in that the molten steel having the composition according to claim 1 or 2 is continuously cast, hot-rolled, cold-rolled and recrystallized at a temperature of 860 ° C or lower. . A method for producing a hot-dip galvanized steel sheet, comprising: continuously casting, hot rolling, cold rolling the molten steel having the composition according to claim 3 or 4 and performing recrystallization annealing at a temperature of 860 ° C or lower.

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