JP5245376B2 - Alloyed hot dip galvanized steel sheet using steel sheet for galvannealed alloy with excellent bake hardenability - Google Patents

Description

  The present invention relates to a steel plate for alloying hot dip galvanizing having bake hardenability (hereinafter referred to as BH (Bake Hardenability)), and more specifically, as a P-containing high strength alloying hot dip galvanizing steel plate, The present invention relates to a steel plate applicable as an inner and outer plate for automobiles.

  Alloyed hot-dip galvanized steel sheets are extremely used in automobiles, home appliances, building materials and the like because they are excellent in coating adhesion, coating corrosion resistance, weldability, and the like. An alloyed hot-dip galvanized steel sheet forms a Zn-Fe alloy by coating hot-dip zinc on the surface of the steel sheet and immediately holding it at a temperature equal to or higher than the melting point of zinc and diffusing Fe from the steel sheet into the zinc. However, since the alloying speed varies greatly depending on the composition and structure of the steel sheet, the control thereof requires a considerably advanced technique. On the other hand, steel sheets for automobiles that are pressed into complex shapes are required to have very high formability, and in recent years, alloyed hot dip galvanizing has been applied due to an increase in demand for rust prevention performance of automobiles. Increasing cases.

  In recent years, in the automobile field, it has been necessary to increase the strength of plated steel sheets in order to ensure the function of protecting passengers in the event of a collision and to reduce the weight for the purpose of improving fuel efficiency.

  In order to increase the strength of the steel sheet without deteriorating workability, it is effective to add elements such as Si, Mn, and P. However, since addition of Si tends to cause non-plating, currently Mn, Steel plates that have been strengthened by the addition of P are most often used.

  Furthermore, a technique for improving dent resistance while securing workability by imparting BH properties that increase the strength in the paint baking process after pressing is also used.

  However, the steel sheet to which P is added is known to have a problem that streak defects are likely to occur. There are no problems with streak defects when machining, welding, or painting, but many consumers do not like the appearance defect. In particular, a steel sheet having BH is used for a part having a strict appearance such as a door or a hood, so that generation of a streak defect becomes a big problem.

  As a method for producing the surface appearance of the P-containing alloyed hot-dip galvanized steel sheet, for example, Patent Document 1 proposes a technique for attaching sulfur or a sulfur compound to the surface. In this production method, sulfur or sulfur is used. Since a facility for applying the compound is required, it is not possible to employ it when there is no space. In addition, there is a problem that the production cost increases due to the installation of the coating equipment.

  Further, Patent Document 2 proposes a technique for defining ferrite grains having a crystal grain size of 15 μm or less to 70 area% or less in the surface layer portion within 50 μm in the thickness direction from the surface of the hot-rolled sheet. This is merely a description of a phenomenon that generally occurs when the hot rolling finishing temperature is maintained at Ar3 + 20 ° C. or higher. In other words, this is a proposal of a manufacturing method in which the hot rolling finishing temperature is manufactured at Ar3 transformation point + 20 ° C. or higher. . This increase in the hot rolling finishing temperature causes a problem that the production cost increases because it is necessary to use a large amount of energy of the heating furnace.

  Similarly, Patent Document 3 proposes a manufacturing method in which the hot-rolling finishing temperature is manufactured at an Ar3 transformation point + 30 ° C. or higher, but the increase in the hot-rolling finishing temperature requires the use of a large amount of energy in the heating furnace. As a result, the production cost increases.

Japanese Patent Laid-Open No. 11-50220 JP 2001-316663 A Japanese Patent No. 3339615

In view of the above situation, the present invention is excellent in bake hardenability that can suppress generation of surface defects such as streak patterns without installing new equipment and without increasing production costs in the hot rolling process. Another object of the present invention is to provide a galvannealed steel sheet using a P-containing high-strength galvannealed steel sheet.

  As a result of examining various means for suppressing the occurrence of streak pattern defects without installing new equipment and reducing the productivity of the hot rolling process, the present inventor has reduced C, N, Al, etc. Defines the amount of C, N, Ti, Nb added to the steel sheet to which P and Mn are added, and adds one or more of Cu, Ni, Cr, Mo, Sn to the surface such as streaks The inventors have found that the occurrence of defects can be suppressed and have reached the present invention.

  That is, the gist of the present invention is as follows.

(1) In mass%,
C: 0.0001 to 0.015%,
Si: 0.001 to 0.45%,
Mn: 0.20% or more,
Mn: 0.20 to 2.8% ,
P: 0.02 to 0.2%
Al: 0.0005 to 0.05%
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
In addition,
Cu: 0.005 to 0.1%,
Ni: 0.005 to 0.1%,
Cr: 0.005 to 0.1%,
Mo: 0.005 to 0.1%,
Sn: 0.005-0.1%
Among them, the acid-soluble Ti content of the steel sheet containing one or more kinds in total of 0.3% or less and the balance Fe and inevitable impurities is represented by the following formula (1) ([% X] is expressed by mass%. the alloy galvannealed steel plate you satisfies the condition given by the content) of the alloy element X expressed in Al: 0.05 to 0.5 wt%, Fe: contains 7 to 15 wt%, further,
Cu: 0.001 to 0.15 mass%,
Ni: 0.001 to 0.15 mass%,
Cr: 0.001 to 0.15 mass%,
Mo: 0.001 to 0.15 mass%,
Sn: 0.001-0.15 mass%
An alloyed hot-dip galvanized steel sheet excellent in appearance, characterized in that an alloyed hot-dip galvanized layer containing one or more of these, the balance being Zn and inevitable impurities is formed.
[% C] × 4 + [% N] × 48 / 14−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14−0.002% (1)

(2) By mass%
C: 0.0001 to 0.015%,
Si: 0.001 to 0.45%,
Mn: 0.20 to 2.8% ,
P: 0.02 to 0.2%
S: 0.015% or less,
Al: 0.0005 to 0.05% or less,
Ti: 0.002 to 0.10%,
Nb: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
In addition,
Cu: 0.005 to 0.1%,
Ni: 0.005 to 0.1%,
Cr: 0.005 to 0.1%,
Mo: 0.005 to 0.1%,
Sn: 0.005-0.1%
Among them, the acid-soluble Ti content of the steel sheet containing one or more kinds in total of 0.3% or less and the balance Fe and inevitable impurities is represented by the following formula (2) ([% X] is expressed in mass%. the alloy galvannealed steel plate you satisfies the condition given by the content) of the alloy element X expressed in Al: 0.05 to 0.5 wt%, Fe: contains 7 to 15 wt%, further,
Cu: 0.001 to 0.15 mass%,
Ni: 0.001 to 0.15 mass%,
Cr: 0.001 to 0.15 mass%,
Mo: 0.001 to 0.15 mass%,
Sn: 0.001-0.15 mass%
An alloyed hot-dip galvanized steel sheet excellent in appearance, characterized in that an alloyed hot-dip galvanized layer containing one or more of these, the balance being Zn and inevitable impurities is formed.
[% C] × 4 + [% N] × 48/14 − [% Nb] × 48 / 93−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14− [ % Nb] × 48 / 93-0.002%
(2)

(3) The alloyed hot-dip galvanized steel sheet further contains B: 0.0002 to 0.003% by mass% as an additional component, as described in (1) or (2) above Alloyed hot-dip galvanized steel sheet with excellent appearance.

(4) The alloyed hot dip galvanizing steel sheet further contains 0.0001 to 0.01% in total of one or more of Ce, La, Nd, Pr, and Sm as an additional component in mass%. The galvannealed steel sheet having excellent appearance according to any one of (1) to (3) above .

(5) X-ray diffraction intensities Iζ and IΓ of d = 1.26 and d = 1.222 of the steel plate for alloying hot dip galvanizing according to any one of (1) to (4) and a Si standard plate The ratio of Iζ / ISi and IΓ / ISi to the X-ray diffraction intensity ISi of d = 3.13 is Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004. Alloyed hot-dip galvanized steel sheet.

  The present invention makes it possible to provide a steel sheet to be plated that can produce a P-containing high-strength galvannealed steel sheet that has excellent workability, has BH properties, and can suppress the occurrence of surface defects such as streaks. It is extremely important to contribute to industrial development.

  Hereinafter, the present invention will be described in detail. First, the reason why the range of each component is limited in the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

  C: C is an element that increases the strength of the steel, and it is effective to contain 0.0001% or more. However, if it is excessively contained, the strength is excessively increased and the workability is lowered, so the upper limit content is 0.8. 015%. In particular, when high workability is required, the C content is preferably 0.010% or less.

  Si: Si is also an element that improves the strength of the steel and contains 0.001% or more. However, if excessively contained, workability and hot dip galvanizing properties are impaired, so the upper limit is made 0.45%. In particular, when high workability is required, the Si content is 0.10% or less.

  Mn: Mn is added in an amount of 0.2% or more as a solid solution strengthening element. The reason why the Mn content is 0.2% or more is that if Mn is less than 0.2%, it is difficult to ensure the required tensile strength. The upper limit is not particularly limited, but if the amount added is excessive, cracking of the slab is likely to occur and spot weldability is also deteriorated, so 2.8% is desirable. More preferably, it is 0.2 to 1.8% from the balance of strength, workability and cost.

  P: P is added in an amount of 0.02% or more as an element that increases the strength without significantly impairing the workability of the steel sheet, particularly the elongation. The reason why the P content is 0.02% or more is that it is difficult to ensure the required tensile strength when P is less than 0.02%. The upper limit is not particularly limited, but if added excessively, grain boundary embrittlement due to grain boundary segregation becomes significant, so 0.2% or less is desirable. More preferably, it is 0.02 to 0.1% from the balance of strength, workability and cost.

  S: Since S is an element that lowers the hot workability and corrosion resistance of steel, it is preferably as small as possible, and the upper limit content is 0.015%. However, it is costly to reduce the amount of S of the ultra-low carbon steel as in the present invention, and surface defects such as streaks are liable to occur if S is excessively reduced, so hot workability and corrosion resistance. It is sufficient to reduce S to a necessary level. Desirably, it is 0.008 to 0.015%.

  Al: Al needs to contain 0.0005% or more as a deoxidizing element of steel. However, if excessively contained, a coarse intermetallic compound is formed and workability is impaired, so the upper limit content is 0. .05%. As will be described later, by reducing the amount of Al added, it is possible to suppress surface defects caused by alumina clusters and to obtain an galvannealed steel sheet having a better appearance. In order to suppress surface defects caused by alumina clusters and obtain a better appearance, it is desirable that the amount of Al added is 0.008% or less.

  Ti: Addition of 0.002% or more is necessary to fix C and N in steel as carbides and nitrides. On the other hand, even if added over 0.10%, the effect is no longer saturated, but the alloy addition cost only increases unnecessarily, so the upper limit content is 0.10%. Since excessive solute Ti may impair the workability and surface quality of the steel sheet, it is more preferably 0.050% or less.

In the present invention, for the purpose of further imparting BH properties, the acid-soluble Ti content is within the range satisfying the following formula (1) ([% X] is the content of alloy element X expressed in mass%): To do.
[% C] × 4 + [% N] × 48 / 14−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14−0.002% (1)
This is because if the acid-soluble Ti content is in the above range, BH properties can be imparted while securing non-aging at room temperature.

  Here, the acid-soluble Ti is Ti that can be dissolved when the steel sheet is dissolved in an acid. Specifically, it refers to Ti dissolved in 20% by mass sulfuric acid when steel is dissolved in heated 20% by mass sulfuric acid. This includes Ti dissolved in steel and Ti existing as intermetallic compounds such as carbides, nitrides and sulfides. On the other hand, since Ti oxide does not dissolve in acid, Ti present as oxide is not included in acid-soluble Ti.

  Here, the acid-soluble Ti is Ti that can be dissolved when the steel sheet is dissolved in an acid. Specifically, it refers to Ti dissolved in 20% by mass sulfuric acid when steel is dissolved in heated 20% by mass sulfuric acid. This includes Ti dissolved in steel and Ti existing as intermetallic compounds such as carbides, nitrides and sulfides. On the other hand, since Ti oxide does not dissolve in acid, Ti present as oxide is not included in acid-soluble Ti.

  In the present invention, since Mn content is high and S content is low, S is almost observed as MnS. Therefore, most Ti compounds are observed as carbides, nitrides, and oxides. On the other hand, most of the compounds of C and N are Ti compounds, and the others are dissolved in Fe. Therefore, by controlling the acid-soluble Ti content, the amount of solid solution C + the amount of solid solution N We have found that it is possible to control the value.

  BH properties increase as the value of solute C amount + solute N amount increases, but if the value of solute C amount + solute N amount becomes too large, yield point elongation (YP-El) occurs during molding. Therefore, the acid-soluble Ti content needs to be in a range that satisfies the formula (1).

  If the acid-soluble Ti content is less than {[% C] × 4 + [% N] × 48 / 14−0.006%}, the fixation of C in the steel is insufficient, and solid solution C and solid solution N YP-El due to the fixed dislocation is likely to be generated. Specifically, since YP-El after artificial aging exceeds 0.2%, non-aging property at room temperature cannot be secured, so [% C] × 4 + [% N] × 48 / 14−0.006% ≦ [% Ti].

  Further, when the acid-soluble Ti content exceeds {[% C] × 4 + [% N] × 48 / 14−0.002%}, C in the steel is fixed, and dislocations generated by processing are fixed. Since it becomes difficult to apply BH of 29 MPa or more, [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14−0.002%.

  N: N increases the strength of the steel while lowering the workability, so the upper limit is made 0.004%, and when high workability is particularly required, it is more preferably 0.003% or less. More preferably, the content is 0.002% or less. N is preferably as little as possible, but reducing it to less than 0.0005% requires excessive cost, so the lower limit content is made 0.0005%.

In the present invention, one or more of Cu, Ni, Cr, Mo, and Sn are added for the purpose of suppressing generation of streak pattern defects. Cu, Ni, Cr, Mo, and Sn contained in the steel are iron oxide layers mainly composed of FeO, Fe ₃ O _{4 and the} like formed during slab heating, hot rolling or after hot rolling (scale It is not included in the layer), and it is concentrated at the interface between the scale layer and the steel sheet, thereby suppressing the occurrence of streak defects. The reason why the addition of Cu, Ni, Cr, Mo, and Sn to suppress the generation of streak defects is as follows.

  1. Cu, Ni, Cr, Mo, Sn is concentrated at the scale / steel sheet interface to improve scale adhesion, thus preventing scale peeling of the hot-rolled sheet and suppressing unevenness of the steel sheet surface due to scale peeling. Prevents streak defects.

  2. Cu, Ni, Cr, Mo, Sn is concentrated at the scale / steel plate interface, and by forming a barrier layer, the concentration of P on the surface during subsequent cold rolling and annealing is suppressed, and the uneven concentration of P Prevents streak pattern defects that occur due to crystallization.

  3. Cu, Ni, Cr, Mo, and Sn concentrated on the surface of the steel sheet when the hot-rolled scale is generated suppress the generation of streak defects caused by the reaction rate difference by homogenizing the plating alloying reaction.

  The effect of suppressing the generation of streak defects can be seen when Cu, Ni, Cr, Mo, or Sn is added in an amount of 0.005% or more. However, these elements are expensive, and even if added over 0.1%, the effect is saturated, so the upper limit of the amount added is 0.1%. Further, if one or more of Cu, Ni, Cr, Mo, Sn is added in a total of more than 0.3%, a pattern due to surface concentration of these metals is generated, so the upper limit of the amount added is set to 0. 3%. Desirably, the total of the addition amount of one or more of Cu, Ni, Cr, Mo, and Sn is set to ½ to 5 times the addition amount of P.

  In the present invention, in addition to the above, as an additional component, Nb can be added under the above Ti addition in order to fix C and N in the steel as carbides and nitrides. In order to sufficiently exhibit the C and N fixing effect, addition of 0.002% or more is necessary. Even if Nb is added in excess of 0.10%, the effect is no longer saturated, but the cost only increases unnecessarily, so the upper limit content is 0.10%. Excessive Nb addition raises the recrystallization temperature of the steel sheet and lowers the productivity of the hot dip galvanizing line.

Further, in the present invention, for the purpose of imparting BH property to the steel added with Nb, the acid-soluble Ti content is expressed by the following formula (2) ([% X] is the content of the alloy element X expressed by mass%). ).
[% C] × 4 + [% N] × 48/14 − [% Nb] × 48 / 93−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14− [ % Nb] × 48 / 93-0.002%
(2)
This is because if the acid-soluble Ti content is in the above range, BH properties can be imparted while securing non-aging at room temperature.

  If the content of acid-soluble Ti is less than {[% C] × 4 + [% N] × 48/14 − [% Nb] × 48 / 93−0.006%}, the fixing of C in the steel becomes insufficient. YP-El due to dislocations fixed by solute C is likely to be generated. Specifically, since YP-El after artificial aging exceeds 0.2%, room temperature non-aging cannot be ensured.

  Further, when the acid-soluble Ti content exceeds {[% C] × 4 + [% N] × 48/14 − [% Nb] × 48 / 93−0.002%}, C in the steel is fixed. Since it becomes difficult to fix dislocations generated by processing, it becomes difficult to apply BH of 29 MPa or more.

  In the present invention, the steel sheet may further contain 0.0002 to 0.003% of B as an additional component, and this is intended to improve secondary workability. If the B content is less than 0.0002%, the secondary workability improvement effect is not sufficient, and even if added over 0.003%, the effect is no longer saturated, and the moldability is reduced. Therefore, when adding B, the range is made 0.0002 to 0.003%. In particular, when high deep drawability is required, the amount of B added is more preferably 0.0015% or less.

  In the present invention, one or more of Ce, La, Nd, Pr, and Sm can be added to the steel sheet as an additional component in a total amount of 0.0001 to 0.01%. Ce, La, Nd, Pr, and Sm are elements used for deoxidation, and the addition amount of Al can be reduced by adding one or two or more in a total of 0.0001 to 0.01%. Become. In the low carbon steel to which P is added, it becomes easy to generate alumina inclusions, and the amount of alumina clusters becomes very large. Therefore, one or two or more of Ce, La, Nd, Pr, and Sm are added in a total amount of 0.0. By adding 0001 to 0.01% and reducing the amount of Al added, it becomes possible to suppress surface defects caused by alumina clusters and obtain an alloyed hot-dip galvanized steel sheet having a good appearance. In order to deoxidize steel by reducing the addition amount of Al, the addition amount of one or more of Ce, La, Nd, Pr, and Sm needs to be 0.0001% or more. Addition of 0.0001% or more of Ce, La, Nd, Pr, or Sm makes it possible to reduce the amount of Al added to 0.008% or less and prevent the alumina cluster from becoming coarse. can do. However, if it exceeds 0.01%, not only will the cost be increased, but the oxides of these metals become inclusions in the steel sheet, which tends to cause surface defects after press working, so the amount added is 0.01% in total. % Or less.

  Ce, La, Nd, Pr, and Sm can be added using a single metal, but it can also be added using an alloy containing Ce, La, Nd, Pr, and Sm such as misch metal.

  In the present invention, O in the steel sheet is not particularly limited, but O generates oxide inclusions and impairs the workability, corrosion resistance, and appearance of the steel. .

  In addition to the above components, the steel sheet of the present invention may contain other alloy elements for the purpose of further improving the corrosion resistance and hot workability of the steel sheet itself, or as an inevitable impurity from secondary materials such as scrap. Even if other alloy elements are contained, it does not depart from the scope of the present invention. Examples of such alloy elements include W, Co, Ca, Y, V, Zr, Ta, Hf, Pb, Zn, Mg, Ta, As, Sb, and Bi.

In the present invention, the alloyed hot-dip galvanized steel sheet contains Al: 0.05 to 0.5 mass%, Fe: 7 to 15 mass%,
Cu: 0.001 to 0.1% by mass,
Ni: 0.001 to 0.1% by mass,
Cr: 0.001 to 0.1% by mass,
Mo: 0.001 to 0.1% by mass,
Sn: 0.001 to 0.1% by mass
Among them, an alloyed hot-dip galvanized layer containing one or two or more of them, the balance being Zn and inevitable impurities is formed.

  In the present invention, the reason why the Al composition of the galvannealed layer is limited to 0.05 to 0.5% by mass is that when it is less than 0.05% by mass, Zn-Fe alloying proceeds too much during the alloying treatment. This is because a brittle alloy layer develops too much at the iron interface and the plating adhesion deteriorates. If it exceeds 0.5 mass%, the Fe—Al—Zn-based barrier layer is formed too thick and alloying occurs during the alloying treatment. This is because the desired iron content plating cannot be obtained because it does not progress. Desirably, it is 0.1-0.3 mass%.

  The reason why the Fe composition is limited to 7 to 15% by mass is that if it is less than 7% by mass, a soft Zn—Fe alloy is formed on the plating surface and press formability is deteriorated. This is because a brittle alloy layer develops too much at the iron interface and the plating adhesion deteriorates. Desirably, it is 9-12 mass%.

Furthermore, in this invention, in order to suppress generation | occurrence | production of a streak pattern defect, 1 type, or 2 or more types of Cu, Ni, Cr, Mo, Sn is contained in an alloying hot-dip galvanization layer. Cu, Ni, Cr, Mo, and Sn contained in steel are contained in an iron oxide layer mainly composed of FeO, Fe ₃ O _{4 and the} like formed during slab heating, hot rolling, or after hot rolling. Is not included, and the generation of streak pattern defects is suppressed by concentrating at the interface between the scale layer (iron oxide layer) and the steel sheet. The reason why the addition of Cu, Ni, Cr, Mo, and Sn to suppress the generation of streak defects is as follows.

  1. Cu, Ni, Cr, Mo, Sn is concentrated at the scale / steel sheet interface to improve scale adhesion, thus preventing scale peeling of the hot-rolled sheet and suppressing unevenness of the steel sheet surface due to scale peeling. Prevents streak defects.

  2. Cu, Ni, Cr, Mo, Sn is concentrated at the scale / steel plate interface, and by forming a barrier layer, the concentration of P on the surface during subsequent cold rolling and annealing is suppressed, and the uneven concentration of P Prevents streak pattern defects that occur due to crystallization.

  3. Cu, Ni, Cr, Mo, and Sn concentrated on the surface of the steel sheet when the hot-rolled scale is generated suppress the generation of streak defects caused by the reaction rate difference by homogenizing the plating alloying reaction.

  In other words, streak defects cause differences in the plating alloying reaction due to non-uniformity of the steel sheet surface during hot rolling, cold rolling, and annealing, resulting in slight differences in the plating adhesion amount and Fe content in the plating layer. It is thought that this phenomenon appears as a difference between the two.

  Therefore, after hot rolling, one or more of Cu, Ni, Cr, Mo, Sn concentrated at the interface between the scale layer and the steel sheet remain on the steel sheet surface after cold rolling and annealing, and plating and alloys By diffusing into the plating layer in the process of forming, an alloyed hot-dip galvanized steel sheet having a good appearance can be obtained.

  The effect of suppressing the generation of streak defects can be seen by adding 0.001% or more of Cu, Ni, Cr, Mo, and Sn in the plating layer. However, these elements are expensive and the effect is saturated even if added in excess of 0.15%, so the upper limit of the content in the plating layer is 0.15%. Moreover, in order to make an element with a small addition amount in a steel sheet contain more than 0.15% in a plating layer having an Fe composition of 7 to 15% by mass, a large amount is concentrated in Fe diffusing into the plating layer. However, for this purpose, a great amount of cost is required for scale generation and scale removal. Therefore, the content in the plating layer is preferably 2 to 50 times the product of the steel sheet addition amount and the Fe composition in the plating layer.

Next, the alloyed hot-dip galvanized layer will be described. In the present invention, the alloyed hot dip galvanized layer is a plated layer mainly composed of an Fe—Zn alloy in which Fe in steel can diffuse during Zn plating by an alloying reaction. This plating layer forms alloy layers called ζ phase, δ ₁ phase, and Γ phase due to the difference in Fe content. Among them, the ζ phase has a high coefficient of friction because it is soft to be plated and easily adheres to the press mold, and tends to cause plate breakage when severe pressing is performed. Further, since the Γ phase is hard and brittle, plating peeling called powdering is liable to occur during processing. Therefore, press workability and plating adhesion can be improved by reducing the ζ phase and the Γ phase as much as possible and making the plating layer a δ ₁ phase. Here, it is known that a hard and brittle phase called Γ ₁ phase is also present in the plating layer. However, since the Γ phase and the Γ ₁ phase cannot be distinguished from the X-ray diffraction intensity, the Γ phase And Γ ₁ phase are combined and treated as Γ phase.

  Specifically, the ratio between the X-ray diffraction intensity Iζ and IΓ of d = 1.26 and d = 1.222 indicating the ζ phase and the Γ phase and the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate. Let Iζ / ISi and IΓ / ISi be Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.

  The reason why Iζ / ISi is limited to 0.004 or less is that when Iζ / ISi is 0.004 or less, the amount of ζ phase is extremely small, and the press workability is not deteriorated.

  Further, the reason why IΓ / ISi is limited to 0.004 or less is that when IΓ / ISi is 0.004 or less, the Γ phase is extremely small, and the plating adhesion is not deteriorated.

  As a manufacturing process of the steel sheet of the present invention, a manufacturing process of a normal hot-rolled steel sheet (hot strip) or a cold-rolled steel sheet (cold strip) may be applied.

  Since the steel sheet of the present invention can be applied to a normal hot dip galvanized steel sheet production line to obtain an alloyed hot dip galvanized steel sheet having excellent workability, formability and plating adhesion, there is no particular restriction on the manufacturing process. . A process may be selected as appropriate in consideration of cost and productivity.

The steel sheet of the present invention contains one or more of Pb, Sb, Si, Mg, Mn, Co, Ca, Li, Ti, Be, Bi, and rare earth elements in a hot dip galvanizing bath or galvanizing, or Even if it mixes, the effect of this invention is not impaired, and depending on the quantity, corrosion resistance may be improved. There are no particular restrictions on the amount of galvannealed coating, but it is preferably 20 g / m ² or more from the viewpoint of corrosion resistance and 150 g / m ² or less from the viewpoint of economy.

  In the present invention, the method for producing a plated steel sheet is not particularly limited, and a normal non-oxidizing furnace type hot dipping method can be applied. Although the alloying treatment conditions are not particularly defined, a treatment temperature range of 460 to 550 ° C. and a treatment time range of 5 to 60 seconds is appropriate in actual operation.

  In the present invention, the thickness of the steel sheet does not impose any restrictions on the present invention, and the present invention can be applied as long as it is a commonly used sheet thickness. Furthermore, the steel sheet of the present invention is sufficiently effective whether it is a cold-rolled steel sheet or a hot-rolled steel sheet manufactured by a normal process, and the effect does not change greatly depending on the history of the steel sheet. . Moreover, the hot rolling conditions, the cold rolling conditions, the annealing conditions, etc. may be selected according to the dimensions of the steel sheet and the required strength, depending on the hot rolling conditions, the cold rolling conditions, the annealing conditions, etc. The effect of the steel sheet of the present invention is not impaired.

  Of course, it is of course possible to apply various types of upper plating, especially electroplating, on the galvannealed steel sheet obtained by using the steel sheet of the present invention in order to improve the paintability and weldability. And does not depart from the present invention. Further, it is of course possible to add various treatments to the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention. For example, chromate treatment, phosphate treatment, and phosphate treatment properties can be achieved. Even if the treatment for improving, the lubricity improving treatment, the weldability improving treatment, the resin coating treatment, etc. are performed, it does not depart from the scope of the present invention, and various types are added depending on the required additional characteristics. Can be applied.

The steel sheet of the present invention is a high-strength steel sheet (300, 340, 400, 440 N / mm ² grade) having a performance satisfying a tensile strength of 300 N / mm ² or more.

  Hereinafter, the present invention will be described specifically by way of examples.

[Example 1]
A slab having the composition shown in Table 1 was heated to 1100 ° C. to form a 4 mm hot-rolled steel strip at a finishing temperature of 920 to 940 ° C. and wound at 680 to 720 ° C. After pickling and cold rolling to obtain a 0.8 mm cold rolled steel strip, an alloyed hot dip galvanized steel sheet was produced using an in-line annealing continuous hot dip galvanizing facility.

In plating, the annealing atmosphere was 5% hydrogen + 95% nitrogen mixed gas, the annealing temperature was 780 to 820 ° C., and the annealing time was 90 seconds. The molten zinc bath was molten zinc containing 0.12% Al, and the basis weight of zinc was adjusted to 50 g / m ² with a gas wiper. The alloying was heated using induction heating type heating equipment so that the Fe content in the alloyed hot dip galvanizing was 11 to 12.5%. The Al content during plating of the galvannealed steel sheet thus obtained was 0.15 to 0.25%.

  Moreover, the X-ray diffraction intensity measurement results of the plated layer of the obtained galvannealed steel sheet were as follows: d = 1.26, d = 1.222 X-ray diffraction intensity Iζ, IΓ and Si standard plate d = 3 .13 X-ray diffraction intensity ISi ratio, Iζ / ISi, IΓ / ISi were Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.

  As an index of workability, tensile tests on each alloyed hot-dip galvanized steel sheet were performed, and tensile strength, elongation, and Rankford value (r values; average r values of 0 °, 45 °, and 90 °) were measured. A tensile strength of 340 MPa or more was accepted.

  BH properties are as follows. First, 2% tensile pre-strain is applied in the rolling direction, the load is once unloaded, a heat treatment equivalent to coating baking at 170 ° C. for 20 minutes is performed, and then a tensile test is performed again. It evaluated by calculating | requiring a raise, and 29 Mpa or more was set as the pass.

  The room temperature non-aging property was measured by measuring YP-El after artificial aging at 100 ° C. × 1 hr, and 0.2% or less was accepted.

As for the appearance, the entire length of the coil was visually observed, the occurrence of the streak pattern was evaluated according to the following classification, and ○ was accepted. Here, the streak pattern refers to a part that appears to have a different color tone due to a difference in the plating alloying reaction, and counts those having a width of 1 mm or more and a length of 100 mm or more.
○: The length of the portion where the streaks are mixed is less than 0.3% of the total length,
Δ: The length of the portion mixed with the streak pattern is 0.3% or more and less than 3% of the total length,
X: The length of the part in which the streaks are mixed is 3% or more of the total length.

The amounts of Cu, Ni, Cr, Mo, and Sn in the plating were obtained by dissolving the plating with hydrochloric acid containing an inhibitor and then adding aqua regia to completely dissolve it, and measuring by ICP. Evaluation evaluated the content of 1 type, or 2 or more types of Cu, Ni, Cr, Mo, Sn in a plating layer with the following classification | category, and made (circle) the pass.
○: Content of 0.001% or more and 0.15% or less,
Δ: Content exceeding 0.15%,
X: Content is less than 0.001%.

  The results are shown in Table 1. In Nos. 42, 43, and 44, the addition amount of Cu, Ni, Cr, Mo, and Sn was outside the range of the present invention, so that a streak pattern was generated and the appearance was unacceptable. No. 45 was insufficient in tensile strength because the amount of P added was outside the range of the present invention. Nos. 46 and 47 were insufficient in tensile strength because the addition amounts of P and Mn were outside the scope of the present invention. In addition, in Nos. 45, 46, and 47, since the addition amount of P is outside the range of the present invention, the presence or absence of addition of Cu, Ni, Cr, Mo, and Sn does not affect the appearance.

  The products of the present invention other than these were P-containing high-strength galvannealed steel sheets having excellent appearance and BH properties.

[Example 2]
A slab having the composition shown in Table 2 was heated to 1100 ° C. to form a 4 mm hot-rolled steel strip at a finishing temperature of 920 to 940 ° C. and wound at 680 to 720 ° C. After pickling and cold rolling to obtain a 0.8 mm cold rolled steel strip, an alloyed hot dip galvanized steel sheet was produced using an in-line annealing continuous hot dip galvanizing facility.

In plating, the annealing atmosphere was 5% hydrogen + 95% nitrogen mixed gas, the annealing temperature was 780 to 820 ° C., and the annealing time was 90 seconds. The molten zinc bath was molten zinc containing 0.12% Al, and the basis weight of zinc was adjusted to 50 g / m ² with a gas wiper. The alloying was heated using induction heating type heating equipment so that the Fe content in the alloyed hot dip galvanizing was 11 to 12.5%. The Al content during plating of the galvannealed steel sheet thus obtained was 0.15 to 0.25%.

  Moreover, the X-ray diffraction intensity measurement results of the plated layer of the obtained galvannealed steel sheet were as follows: d = 1.26, d = 1.222 X-ray diffraction intensity Iζ, IΓ and Si standard plate d = 3 .13 X-ray diffraction intensity ISi ratio, Iζ / ISi, IΓ / ISi were Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.

  As an index of workability, a tensile test of each alloyed hot-dip galvanized steel sheet was performed, and tensile strength, elongation, and Rankford value (r values; average r values of 0 °, 45 °, and 90 °) were measured. A tensile strength of 340 MPa or more was accepted.

  BH properties are as follows. First, 2% tensile pre-strain is applied in the rolling direction, the load is once unloaded, a heat treatment equivalent to coating baking at 170 ° C. for 20 minutes is performed, and then a tensile test is performed again. It evaluated by calculating | requiring a raise, and 29 Mpa or more was set as the pass.

  The room temperature non-aging property was measured by measuring YP-El after artificial aging at 100 ° C. × 1 hr, and 0.2% or less was accepted.

Surface defects after press working were evaluated by a ball head overhang test. Test conditions are shown below.
・ Sample drawing width: 200 × 200mm
・ Mold: Ball head punch with radius 60mm, Dies with beads
・ Pressing load: 60t
-Overhang speed: 30 mm / min
-Oil coating: anti-rust oil coating The surface defect was evaluated by performing 1,000 ball head overhang tests, and evaluated according to the following classification, with a pass.
○: The occurrence rate of cracks due to non-metallic inclusions is less than 0.5%,
(Triangle | delta): The crack generation rate resulting from a nonmetallic inclusion is 0.5% or more and less than 3%,
X: The occurrence rate of cracks due to non-metallic inclusions is 3% or more.

As for the appearance, the entire length of the coil was visually observed, the occurrence of the streak pattern was evaluated according to the following classification, and ○ was accepted. Here, the streak pattern refers to a part that appears to have a different color tone due to a difference in the plating alloying reaction, and counts those having a width of 1 mm or more and a length of 100 mm or more.
○: The length of the portion where the streaks are mixed is less than 0.3% of the total length,
Δ: The length of the portion mixed with the streak pattern is 0.3% or more and less than 3% of the total length,
X: The length of the part in which the streaks are mixed is 3% or more of the total length.

The amounts of Cu, Ni, Cr, Mo, and Sn in the plating were obtained by dissolving the plating with hydrochloric acid containing an inhibitor and then adding aqua regia to completely dissolve it, and measuring by ICP. Evaluation evaluated the content of 1 type, or 2 or more types of Cu, Ni, Cr, Mo, Sn in a plating layer with the following classification | category, and made (circle) the pass.
○: Content of 0.001% or more and 0.15% or less,
Δ: Content exceeding 0.15%,
X: Content is less than 0.001%.

  The results are shown in Table 2. In No. 26, the addition amount of Ce and La is 0.0001% or less, and since the addition amount of Al is large, the alumina cluster is increased and the surface defects after press working are rejected, and Cu, Ni, Cr Since the amount of addition of Mo and Sn was outside the range of the present invention, streaks were generated and the appearance was not acceptable. In No. 27, the addition amount of Cu, Ni, Cr, Mo, and Sn was outside the range of the present invention, so that a streak pattern was generated and the appearance was rejected. No. 28 had an insufficient tensile strength because the amount of P added was outside the range of the present invention. Nos. 29 and 30 were insufficient in tensile strength because the addition amounts of P and Mn were outside the range of the present invention. In addition, numbers 28, 29, and 30 have an addition amount of P outside the range of the present invention, so the presence or absence of addition of Cu, Ni, Cr, Mo, and Sn does not affect the appearance.

  In addition, in No. 24, since the addition amounts of Ce and La were 0.01 or more, the REM oxide became a cluster and the surface defect after press working was rejected, but the appearance was acceptable. In No. 25, the addition amount of Ce and La is 0.0001% or less, and since the addition amount of Al is large, the alumina cluster is increased and the surface defects after press working are rejected, but the appearance is acceptable. there were.

  The products of the present invention other than these were P-containing high-strength galvannealed steel sheets having suppressed appearance of surface defects after press working, excellent appearance, and BH properties.

[Example 3]
A slab having the composition shown in Table 3 was heated to 1100 ° C. to form a hot-rolled steel strip of 4 mm at a finishing temperature of 920 to 940 ° C., and wound at 680 to 720 ° C. After pickling, cold-rolled into a 0.8mm cold-rolled steel strip, then alloyed hot-dip galvanized steel sheet using a vertical hot-dip plating machine capable of simulating the CGL thermal cycle and atmosphere Manufactured. In plating, the annealing atmosphere was 5% hydrogen + 95% nitrogen mixed gas, the annealing temperature was 800 to 840 ° C., and the annealing time was 90 seconds. The molten zinc bath was made of molten zinc containing Al, and the basis weight of zinc was adjusted to 50 g / m ² by gas wiping. The alloying was heated using induction heating system heating equipment, and the heating temperature and heating time were changed to produce plated steel sheets having different Fe contents. Various changes were also made to the Al concentration in the plating bath to produce plated steel sheets having different Al contents in the alloyed hot dip galvanizing.

  The tensile strength was measured by performing a tensile test of each alloyed hot-dip galvanized steel sheet, and confirmed that the tensile strength was 300 MPa or more.

  The Fe content and Al content during plating were measured by ICP after dissolving the plating layer with hydrochloric acid containing an inhibitor. The amounts of Cu, Ni, Cr, Mo, and Sn in the plating were obtained by dissolving the plating with hydrochloric acid containing an inhibitor and then adding aqua regia to completely dissolve it, and measuring by ICP.

  X-ray diffraction is the ratio of the X-ray diffraction intensity Iζ and IΓ of d = 1.26 and d = 1.222 indicating the ζ phase and the Γ phase to the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate. Iζ / ISi and IΓ / ISi were measured.

  The obtained plated steel sheet was examined for press formability and plating adhesion.

As for press formability, a bead pull-out test was conducted in order to investigate the sliding property of plating in press working. Test conditions are shown below.
・ Sample drawing width: 30mm
-Mold: Square bead with one side shoulder R1mmR (convex part is 4x4mm) convex, the other side is concave shape with shoulder R1mmR-Pressing load: 800, 1000kg
・ Pullout speed: 200mm / min
・ Oil coating: anti-rust oil coating Press formability was evaluated according to the following classification, and ◎ and ○ were accepted.
◎: Pulled out with a pressing load of 1000 kg,
○: Pulled out at a pressing load of 800 kg, but broken at a load of 1000 kg,
X: Fracture at a pressing load of 800 kg.

For plating adhesion, the test piece with adhesive tape (cellophane tape) previously applied to the compression side was bent into a V shape so that the bending angle was 60 °, and after bending back, the adhesive tape was peeled off and peeled off. The width of the plating was measured and evaluated according to the following classification, and ◎ and ○ were regarded as acceptable.
(Double-circle): The peeling width of a plating layer is 1.5 mm or less,
○: peeling width of the plating layer is more than 1.5 mm, 3 mm or less,
(Triangle | delta): The peeling width of a plating layer is more than 3 mm and 5 mm or less,
X: The peeling width of the plating layer is more than 5 mm.

The alloyed hot-dip galvanized steel sheet was prepared for several tens of sheets at different locations in the longitudinal direction and the width direction of the coil, and the appearance was evaluated. As for the appearance, the number of samples in which portions (patterns) that appear to differ in color tone due to the difference in the plating alloying reaction were evaluated according to the following classification, and ○ was accepted.
○: The number of samples mixed with the pattern is 0,
Δ: The number of samples mixed with the pattern is 1 or 2,
X: The number of samples mixed with the pattern is 3 or more.

  The evaluation results are as shown in Table 4. Nos. 1 and 26 failed in press formability because Fe% and Iζ / ISi in the plating were outside the scope of the present invention. In Nos. 5 and 30, since the Fe% and IΓ / ISi in the plating are out of the range of the present invention, the plating adhesion was rejected. In Nos. 6 and 31, Al% during plating and IΓ / ISi were out of the range of the present invention, so that the plating adhesion was unacceptable.

  The products of the present invention other than these were P-containing high-strength galvannealed steel sheets excellent in press formability and plating adhesion.

Claims (5)

% By mass
C: 0.0001 to 0.015%,
Si: 0.001 to 0.45%,
Mn: 0.20% or more,
Mn: 0.20 to 2.8% ,
P: 0.02 to 0.2%
Al: 0.0005 to 0.05%
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
In addition,
Cu: 0.005 to 0.1%,
Ni: 0.005 to 0.1%,
Cr: 0.005 to 0.1%,
Mo: 0.005 to 0.1%,
Sn: 0.005-0.1%
Among them, the acid-soluble Ti content of the steel sheet containing one or more kinds in total of 0.3% or less and the balance Fe and inevitable impurities is represented by the following formula (1) ([% X] is expressed by mass%. the alloy galvannealed steel plate you satisfies the condition given by the content) of the alloy element X expressed in Al: 0.05 to 0.5 wt%, Fe: contains 7 to 15 wt%, further,
Cu: 0.001 to 0.15 mass%,
Ni: 0.001 to 0.15 mass%,
Cr: 0.001 to 0.15 mass%,
Mo: 0.001 to 0.15 mass%,
Sn: 0.001-0.15 mass%
An alloyed hot-dip galvanized steel sheet excellent in appearance, characterized in that an alloyed hot-dip galvanized layer containing one or more of these, the balance being Zn and inevitable impurities is formed.
[% C] × 4 + [% N] × 48 / 14−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14−0.002% (1) % By mass
C: 0.0001 to 0.015%,
Si: 0.001 to 0.45%,
Mn: 0.20 to 2.8% ,
P: 0.02 to 0.2%
S: 0.015% or less,
Al: 0.0005 to 0.05% or less,
Ti: 0.002 to 0.10%,
Nb: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
In addition,
Cu: 0.005 to 0.1%,
Ni: 0.005 to 0.1%,
Cr: 0.005 to 0.1%,
Mo: 0.005 to 0.1%,
Sn: 0.005-0.1%
Among them, the acid-soluble Ti content of the steel sheet containing one or more kinds in total of 0.3% or less and the balance Fe and inevitable impurities is represented by the following formula (2) ([% X] is expressed in mass%. the alloy galvannealed steel plate you satisfies the condition given by the content) of the alloy element X expressed in Al: 0.05 to 0.5 wt%, Fe: contains 7 to 15 wt%, further,
Cu: 0.001 to 0.15 mass%,
Ni: 0.001 to 0.15 mass%,
Cr: 0.001 to 0.15 mass%,
Mo: 0.001 to 0.15 mass%,
Sn: 0.001-0.15 mass%
An alloyed hot-dip galvanized steel sheet excellent in appearance, characterized in that an alloyed hot-dip galvanized layer containing one or more of these, the balance being Zn and inevitable impurities is formed.
[% C] × 4 + [% N] × 48/14 − [% Nb] × 48 / 93−0.006% ≦ [% Ti] ≦ [% C] × 4 + [% N] × 48 / 14− [ % Nb] × 48 / 93-0.002%
(2) 3. The alloying excellent in appearance according to claim 1, wherein the steel sheet for galvannealing further contains, as an additional component, B: 0.0002 to 0.003% by mass% . 4. Hot dip galvanized steel sheet. The alloyed hot dip galvanized steel sheet further contains 0.0001 to 0.01% in total of one or more of Ce, La, Nd, Pr, and Sm as an additional component in mass%. An alloyed hot-dip galvanized steel sheet excellent in appearance according to any one of claims 1 to 3 . Plating d = 1.26 galvannealed steel plate according to any one of claims 1 to 4, d = 1.222 in the X-ray diffraction intensity Aizeta, the IΓ and Si standard plate d = 3.13 The alloyed hot-dip galvanized steel sheet with excellent appearance, characterized in that the ratios Iζ / ISi and IΓ / ISi to X-ray diffraction intensity ISi are Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004 .