JP6205759B2 - High-strength galvannealed steel sheet with excellent plating adhesion - Google Patents

Description

  The present invention relates to a high-strength galvannealed steel sheet, and more particularly to a galvanized steel sheet that can be applied as various members, for example, a strength member for automobiles, as an galvannealed steel sheet excellent in plating adhesion.

  Alloyed hot dip galvanized steel sheets are widely used in automobiles, home appliances, building materials and the like because they are excellent in coating adhesion, post-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, control of the plating structure requires a considerably advanced technique. On the other hand, steel sheets for automobiles that are pressed into a complicated shape are required to have extremely high formability, and in recent years, the demand for rust prevention performance of automobiles has increased. The number of cases applied to industrial steel plates is increasing.

As shown in FIG. 1, the structure of the plated layer of the galvannealed steel sheet is as follows: 1 is a steel plate base material, 2 is a Γ phase (Zn ₁₀ Fe ₃ ), 3 is a δ ₁ phase (Zn ₇ Fe) 4 has a structure in which an intermetallic compound of Fe and Zn is called ζ phase (Zn ₁₃ Fe). Of these, the Γ phase is very hard and brittle and has poor deformability, so it is easily destroyed during processing. For this reason, when pressed into a complicated shape for use in automotive materials, stresses such as compression, tension, and shear are applied to the plating layer, and the plating layer peels off starting from the destruction of the Γ phase at the interface So-called powdering may occur.

In order to make powdering difficult to occur, it is effective to reduce the thickness of the Γ phase.
In order to reduce the thickness of the Γ phase, the degree of alloying may be weakened, that is, the alloying time may be shortened or alloyed at a low temperature in the heating alloying process of the plating layer.

  On the other hand, when the degree of alloying is lowered in order to make the Γ phase thinner, a lot of ζ phase remains on the surface of the plating layer. Since the ζ phase is soft, if the ζ phase is large on the surface of the plating layer, so-called flaking occurs in which the mold bites into the plating layer during press working and the plating layer peels off in a scaly manner.

In order to achieve both powdering resistance and anti-flaking resistance, it is effective to increase both the δ ₁ phase by reducing both the Γ phase and the ζ phase in the plating layer as much as possible. However, it is not easy to control both to an appropriate range, and various methods have been taken so far.

  For example, Patent Document 1 discloses a technique for improving powdering properties by suppressing Γ phase growth by combining rapid heating and rapid cooling during alloying.

  Patent Document 2 discloses that IF (Interstitial Free) steel is used as a base plate, and a small amount of Si and P is added to the steel to promote the diffusion of Zn into the base crystal grain boundary, thereby improving the plating adhesion. An improved steel sheet is disclosed.

Japanese Patent Laid-Open No. 1-29738 JP-A-10-46305

  However, in the technique disclosed in Patent Document 1, although the powdering property is improved if the Γ phase is thinned, the essence of the Γ phase is not changed, so that the plating adhesion cannot be ensured when further hard working is performed. There is a fear. Moreover, in patent document 2, it is a technique limited to the case where IF steel is used as an original plate, and cannot be applied to a high-strength steel plate containing a large amount of Si or Mn from the beginning.

  The present invention solves the problems of the prior art as described above, and allows the structure of the galvannealed layer to be strictly controlled even when a high-strength steel sheet containing Si or Mn is used as the original sheet. It aims at providing the high intensity | strength galvannealed steel plate which can ensure the plating adhesiveness at the time of strong processing.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, by incorporating Ni at a specific concentration in the surface layer region of the steel sheet base material in the alloyed hot-dip galvanized steel sheet, the plating adhesion, particularly It has been found that powdering resistance is improved, powdering hardly occurs even when severe pressing is performed, and plating adhesion can be secured without particularly strictly controlling the thickness of the Γ phase. completed.

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

(1) C: 0.01 to 0.3% by mass,
Si: 0.3 to 2.5% by mass,
Mn: 1.0 to 3.5% by mass,
P: 0.001 to 0.03 mass%,
S: 0.0001 to 0.02 mass%,
Al: 0.005 to 0.1% by mass,
N: 0.0005 to 0.007% by mass
On the steel plate base material, the balance being Fe and inevitable impurities,
Fe: 7 to 15% by mass,
Al: 0.01-1% by mass,
Ni: 0.01 to 10% by mass,
Contain, comprises a plating layer consisting of the remainder Zn and unavoidable impurities, Ri 0.01 to 20% by mass Ni concentration is the mean of the surface layer region within a depth 5μm from the surface of the plate matrix, wherein the steel sheet 5 or more of one or more Si oxides selected from FeSiO ₃ , Fe ₂ SiO ₄ , MnSiO ₃ , Mn ₂ SiO ₄ , SiO ₂ in the surface layer region within a depth of 5 μm from the surface of the base material / μm ² or 1000 / [mu] m ² there be characterized Rukoto less, high strength galvannealed steel sheet excellent in coating adhesion.

(2) It is characterized by containing any one or more of Fe ₃ Ni, FeNi, FeNi ₃ , austenite phase containing Ni in the surface layer region within a depth of 5 μm from the surface of the steel plate base material. The high-strength galvannealed steel sheet having excellent plating adhesion as described in (1) above.

  (3) In the above (1) or (2), the average crystal grain size of the steel plate base material in the surface layer region within a depth of 5 μm from the surface of the steel plate base material is 0.05 μm or more and 3 μm or less. The high-strength galvannealed steel sheet having excellent plating adhesion as described.

( 4 ) The steel plate base material is
Ti: 0.001 to 0.1% by mass,
Nb: 0.001 to 0.1% by mass
The high-strength galvannealed steel sheet having excellent plating adhesion, according to any one of the above (1) to ( 3 ), comprising one or two of the above.

( 5 ) The steel plate base material is
Mo: 0.005 to 0.3% by mass,
Cr: 0.005 to 0.8 mass%,
Cu: 0.005 to 1% by mass,
Ni: 0.005 to 1% by mass
The high-strength galvannealed steel sheet having excellent plating adhesion as described in any one of (1) to ( 4 ) above, comprising one or more of the above.

( 6 ) The steel plate base material is
B: 0.0001 to 0.005 mass%
The high-strength galvannealed steel sheet having excellent plating adhesion as described in any one of (1) to ( 5 ) above.

  The high-strength galvannealed steel sheet of the present invention is based on a high-strength steel sheet containing a large amount of Si and Mn, but it is not necessary to strictly control the alloy scrap structure of the plating scrap, and the plating adhesion during strong processing Therefore, it is possible to provide a high-strength galvannealed steel sheet excellent in plating adhesion, and is extremely effective as an automotive inner plate or a high-strength member.

It is a model drawing which shows an example of the cross-sectional structure of a standard galvannealed steel plate. It is a cross-sectional schematic diagram of the plated steel plate which shows the surface of the steel plate base material in the alloyed hot-dip galvanized steel plate and the position of the surface layer region of the steel plate base material.

  Hereinafter, the present invention will be described in detail.

  First, Ni contained in the surface layer region of the steel sheet base material in the galvannealed steel sheet of the present invention will be described. The alloyed hot-dip galvanized steel sheet of the present invention includes a steel plate base material 5, an alloyed hot-dip galvanized layer 6, a surface 7 of the steel plate base material, a steel plate base material, as shown in the cross-sectional schematic diagram of the plated steel plate of FIG. The surface layer region 8 is formed.

  First, the present inventors diligently studied the plating peeling starting point during strong processing of an alloyed hot-dip galvanized steel sheet when a high-strength steel sheet containing a large amount of Si or Mn was used as a base material. As a result, when the steel plate base material contains a large amount of Si or Mn, the thickness of the Γ phase in the plating layer 6 becomes thin, and plating peeling does not occur in the Γ phase but occurs in the surface region 8 of the steel plate base material 5. From the crack as a starting point, it was found that the crack propagated through the plating layer 6 and led to plating peeling. Furthermore, various methods for suppressing cracks in the surface layer region 8 of the steel plate base material 5 that occur during strong working were studied. As a result, by containing Ni in the surface layer region 8 of the steel plate base material 5 at a specific concentration, the occurrence of cracks in the surface layer region 8 of the steel plate base material 5 can be suppressed at the time of strong processing, and the plating adhesion can be improved. I found that it could be improved. Although the details of the reason why the generation of cracks during strong processing is suppressed by containing Ni in the surface layer region 8 of the steel plate base material 5 are not clear, the surface concentration region of the steel plate base material 5 is increased by increasing the Ni concentration. This is probably because the fracture toughness of 8 itself was improved. In this manner, the occurrence of cracks in the surface layer region of the steel plate base material is suppressed even during strong processing, and as a result, plating adhesion can be ensured.

  In the present invention (1), the Ni concentration in the surface layer region within a depth of 5 μm from the surface of the steel plate base metal is limited to an average range of 0.01 to 20% by mass because the Ni concentration is 0.01% by mass. It is because the effect which improves the plating adhesiveness at the time of a strong process expresses by setting it as the above. Moreover, even if it contains more than 20 mass%, it does not have a bad influence, but it is because the effect which improves the metal-plating adhesiveness at the time of a strong process is saturated, and it becomes disadvantageous in cost. From the viewpoint of plating adhesion and cost, it is preferably in the range of 1 to 15% by mass.

  In order to contain Ni in the surface layer region of the steel plate base material, a method may be used in which Ni is attached to the surface of the steel plate before passing through the CGL, and then heated and diffused in the annealing step of CGL. The method for attaching Ni is not particularly limited, but electroplating, electroless plating, displacement plating and the like are simple and easy to attach. The kind of preliminary plating to be deposited is not particularly limited as long as it contains Ni, and examples thereof include Ni, Ni-P, Ni-B, Ni-Fe, and Ni-Zn.

  The reason why the Ni content is the surface layer region within 5 μm depth from the surface of the steel plate base material is that the region within 5 μm affects the plating adhesion during strong processing. Even if Ni is contained inside the steel plate base material exceeding 5 μm, there is no adverse effect, but there is no effect of improving the plating adhesion during strong working.

  As a method for measuring the Ni concentration in the surface layer region of the steel plate base material, the alloyed hot-dip galvanized layer is dissolved in diluted hydrochloric acid with an inhibitor added, and then the depth direction analysis from the surface of the steel plate base material is performed using high frequency GDS. The Ni concentration is quantified from a calibration curve prepared by measurement of a sample having a known Ni concentration, and an average value from the surface to a depth of 5 μm may be obtained. The depth containing Ni can be measured simultaneously with the Ni concentration by high-frequency GDS measurement. In the case of a steel type in which the steel plate base material contains Ni as a component from the beginning, the Ni component concentration in the steel plate base material is calculated from the average value of the Ni concentration from the surface to a depth of 5 μm obtained by GDS measurement. The subtracted value is defined as the Ni concentration in the surface layer region of the steel plate base material.

  In the present invention, the Fe concentration in the galvannealed layer is limited to the range of 7 to 15% by mass because the spot weldability is inferior if it is less than 7% by mass and exceeds 15% by mass. This is because, since the thickness of the Γ phase becomes too thick, it is difficult to ensure the plating adhesion even in the structure of the present invention. From the viewpoint of securing plating adhesion during strong processing, it is preferably in the range of 8 to 13% by mass.

  The reason why the Al concentration in the plating layer is limited to the range of 0.01 to 1% by mass is that the excess ζ phase in the plating bath is obtained by containing 0.01% by mass or more of Al in the plating layer. This is because the formation of the Γ phase can be suppressed and the Fe concentration in the plating layer can be controlled to a target value. Moreover, when Al is added exceeding 1 mass%, Al will concentrate on the plating layer surface and will deteriorate spot weldability. Therefore, the upper limit of the Al concentration is set to 1% by mass. Preferably it is set as the range of 0.05-0.6 mass%.

  The reason why the Ni concentration in the plating layer is limited to 0.01 to 10% by mass is that the plating layer inevitably contains Ni by containing Ni in the surface layer region of the steel plate base material. By setting the Ni concentration in the surface layer region of the steel plate base material within the range of the present invention, the plating layer contains 0.01 mass% or more of Ni. Further, if Ni is contained in excess of 10% by mass, the corrosion resistance may be deteriorated, so the upper limit was made 10% by mass. From the viewpoint of corrosion resistance, it is preferably 5% by mass or less.

  In order to measure the concentrations of Fe, Al, and Ni in the plating layer, a method of dissolving the plating layer with an acid and chemically analyzing the solution may be used. For example, an alloyed hot-dip galvanized steel sheet cut to 30 mm × 40 mm is dissolved with a 5 mass% HCl aqueous solution to which an inhibitor is added while only the plating layer is dissolved while suppressing elution of the steel sheet base material. A method of quantifying the concentrations of Fe, Al, and Ni from the obtained signal intensity and a calibration curve created from a solution having a known concentration may be used.

The plating adhesion amount is not particularly limited, but is preferably 5 g / m ² or more in terms of single-sided adhesion from the viewpoint of corrosion resistance. Moreover, from the viewpoint of securing plating adhesion at the time of press working for the purpose of automobile use, it is desirable that the amount of adhesion on one side does not exceed 100 g / m ² . On the hot dip galvanized steel sheet of the present invention, for the purpose of improving paintability and weldability, it is possible to apply upper layer plating and various treatments such as chromate treatment, non-chromate treatment, phosphate treatment, lubricity improvement treatment. Even if the weldability improving process is performed, it does not depart from the present invention.

  Below, the reason which has limited the component in steel in this invention (1) is demonstrated.

(C: 0.01 to 0.3% by mass)
C: C is an element that increases the strength of steel, and it is effective to contain 0.01% by mass or more. However, if excessively contained, the strength increases excessively and the workability decreases, so the upper limit is 0.3. Mass%. From the viewpoint of workability and weldability, it is preferably in the range of 0.05 to 0.2 mass%.

(Si: 0.3-2.5% by mass)
Si: Si is an effective element that can improve the strength without reducing ductility, and it is effective to add 0.3% by mass or more. On the other hand, if added over 2.5% by mass, the effect of increasing the strength is saturated and the ductility is lowered, so the upper limit was made 2.5% by mass. Preferably, it is set as the range of 0.5-2.0 mass%.

(Mn: 1.0 to 3.5% by mass)
Mn: Mn is an important element for increasing the strength, and is added by 1.0% by mass or more. However, if it exceeds 3.5 mass%, the slab is likely to crack, and the spot weldability is also deteriorated, so 3.5 mass% is the upper limit. From the viewpoint of strength and workability, it is preferably in the range of 1.5 to 3.0% by mass.

(P: 0.001 to 0.03 mass%)
P: P is an element that increases the strength of steel while reducing workability, so the upper limit is 0.03% by mass. In order to reduce P to less than 0.001% by mass, the scouring cost increases, so the lower limit is made 0.001% by mass. From the balance of strength, workability and cost, 0.005 to 0.02 mass% is preferable.

(S: 0.0001 to 0.02 mass%)
S: S is an element that lowers the hot workability and corrosion resistance of steel. If it exceeds 0.02 mass%, the hot workability and corrosion resistance are deteriorated, so the upper limit is made 0.02 mass%. Moreover, since it is disadvantageous in terms of cost to be less than 0.0001% by mass, the lower limit is set to 0.0001% by mass.
However, since it becomes easy to generate a surface defect when S is reduced too much, it is preferable to set it as 0.001 mass% or more.

(Al: 0.005 to 0.1% by mass)
Al: Al is added as a deoxidizing element of steel, and is added in an amount of 0.005% by mass or more in order to improve the material by suppressing the thinning of the hot rolled material by AlN and the coarsening of crystal grains in a series of heat treatment steps. There is a need. However, if it exceeds 0.1% by mass, the weldability may be deteriorated, so the content is made 0.1% by mass or less. Furthermore, from the viewpoint of reducing surface defects due to alumina clusters, it is more preferable that the amount be 0.08% by mass or less.

(N: 0.0005 to 0.007 mass%)
N: N increases the strength of the steel while lowering the workability, so the upper limit is made 0.007% by mass. In particular, when high workability is required, it is more preferably 0.003% by mass or less, and further preferably 0.002% by mass or less. N is preferably as little as possible, but reducing it to less than 0.0005% by mass requires excessive refining costs, so the lower limit is made 0.0005% by mass.

In the present invention (2), the surface layer region within a depth of 5 μm from the surface of the steel plate base material contains at least one of Fe ₃ Ni, FeNi, FeNi ₃ , and an austenite phase containing Ni. It prescribes. The reason is that the presence of these phases further enhances the effect of improving plating adhesion. Fe ₃ Ni, FeNi, FeNi ₃ , Ni-containing austenite phase nucleates in a granular form as Ni adhering to the surface of the steel sheet base metal interdiffuses with Fe derived from the steel sheet base material in the CGL annealing process However, even after these granular phases remain on the surface of the steel plate base material after forming the alloyed hot-dip galvanized layer, a so-called anchor effect is exhibited even when strong working is applied. Therefore, it is considered that the effect of improving the plating adhesion is further enhanced. Therefore, in the present invention, one or more of Fe ₃ Ni, FeNi, FeNi ₃ , or Ni-containing austenite phase may be contained in the surface layer region within a depth of 5 μm from the surface of the steel plate base material. More preferred.

The surface layer region of the steel plate base material contains at least one of Fe ₃ Ni, FeNi, FeNi ₃ , and austenite phase containing Ni. This indicates that the alloyed hot-dip galvanized layer is diluted with diluted hydrochloric acid. And can be confirmed by analyzing from the surface direction of the steel plate base material using EPMA and EBSD. Since these phases have a high Ni concentration and an fcc structure, the location of the phase is specified by EPMA Ni mapping, and then the area around the region is measured by EBSD to separate the bcc and fcc phases. By displaying, it can be confirmed which of the austenite phases containing Fe ₃ Ni, FeNi, FeNi ₃ and Ni is present.

  In the present invention (3), the average crystal grain size of the steel plate base material in the surface layer region within a depth of 5 μm from the surface of the steel plate base material is defined as 0.05 μm or more and 3 μm or less. This is because the effect of improving the plating adhesion during strong processing is further enhanced. The reason why the plating adhesion is further enhanced by setting the average crystal grain size to 3 μm or less is considered to be because the fracture toughness of the surface layer region itself of the steel plate base material is improved and the propagation of cracks is suppressed. Moreover, it is difficult to make the average crystal grain size of the steel plate base material less than 0.05 μm by a practical process. Therefore, in the present invention, the average crystal grain size of the steel plate base material in the surface layer region within a depth of 5 μm from the surface of the steel plate base material is more preferably 0.05 μm or more and 3 μm or less.

  As a method of measuring the average crystal grain size of the steel plate base material in the surface layer region within a depth of 5 μm from the surface of the steel plate base material, EBSD measurement is performed from the cross-sectional direction, and the depth within 5 μm from the surface of the steel plate base material is analyzed by data analysis. What is necessary is just to obtain the average crystal grain size.

  In order to make the average crystal position diameter 0.05 μm or more and 3 μm or less in the surface layer region within a depth of 5 μm from the surface of the steel plate base material, the method is not particularly limited. A method of forming pinned particles that stops grain growth is mentioned. To form the pinning particles, there are methods such as nitriding, carburizing, and internal oxidation. However, the method may be selected according to the actual process of the manufacturing equipment, and is not particularly limited.

In the present invention (4), one or more selected from the group consisting of FeSiO ₃ , Fe ₂ SiO ₄ , MnSiO ₃ , Mn ₂ SiO ₄ , and SiO ₂ in the surface layer region within a depth of 5 μm from the surface of the steel plate base material. The reason that the number of Si oxides is 5 / μm ² or more and 1000 / μm ² or less is because the effect of improving the plating adhesion is further enhanced by setting the number to 5 / μm ² or more. ^{On the other hand} , if it exceeds 1000 / μm ² , the corrosion resistance after coating of the plating layer may be adversely affected. Therefore, in the present invention, it is more preferable that the Si oxide is present in the range of 5 / μm ^{2 to} 1000 / μm ² .

  The presence of Si oxide in the surface layer region of the steel plate base material further improves the plating adhesion, because the Si oxide is dispersed in the surface layer region of the steel plate base material, the strength increases, This is considered to be because the generation and propagation of cracks from the steel plate base material can be suppressed.

In order to measure the number density of Si oxides, a cross-sectional sample is prepared by FIB processing, and the number of Si oxides in the surface layer region within a depth of 5 μm from the surface of the steel plate base material is measured by TEM observation from the cross-sectional direction. That's fine. At the same time, by performing EDX analysis and diffraction analysis, it is possible to determine whether the type of Si oxide being formed is FeSiO ₃ , Fe ₂ SiO ₄ , MnSiO ₃ , Mn ₂ SiO ₄ , or SiO _2. Can be determined.

  As a method of forming Si oxide in the surface layer region of the steel plate base material, a method of increasing the coiling temperature at the time of hot rolling or annealing in an atmosphere where Si is internally oxidized during the annealing process in CGL is considered. However, it is not limited to any one, and may be appropriately selected according to the actual process of the manufacturing facility.

  Moreover, in this invention (5), 1 type or 2 types of Ti: 0.001-0.1 mass% and Nb: 0.001-0.1 mass% can further be contained in a steel plate base material. .

  Ti and Nb can strengthen steel by precipitating fine nitrides and carbides. Since the strength can be further increased by adding 0.001% by mass or more to the steel, each lower limit is set to 0.001% by mass. On the other hand, if the addition exceeds 0.1% by mass, the ductility decreases, so the upper limit of each was set to 0.1% by mass. In particular, when emphasis is placed on ductility, it is preferably in the range of 0.003 to 0.06 mass%.

  In this invention (6), a steel plate base material is Mo: 0.005-0.3 mass%, Cr: 0.005-0.8 mass%, Cu: 0.005-1 mass%, Ni: 0. The reason why one or more of 0.005 to 1% by mass is contained is that Mo, Cu, Ni, and Cr are elements that further increase the strength. Mo, Cu, Ni, and Cr each exhibit an effect at 0.005 mass% or more. However, since excessive addition of these elements may impair ductility, the upper limit is set to Mo: 0.3% by mass, Cr: 0.8% by mass, Cu: 1% by mass, and Ni: 1% by mass. .

  In the present invention (7), the steel plate base material further contains B in an amount of 0.0001 to 0.005 mass% because the addition of B improves the secondary work brittleness. If the addition amount of B is less than 0.0001% by mass, the effect of improving the secondary work brittleness is not sufficient, and adding more than 0.005% by mass not only saturates the effect but also reduces the moldability. Therefore, it was limited to the range of 0.0001 to 0.005 mass%.

  Next, a method for producing a high-strength galvannealed steel sheet having excellent plating adhesion according to the present invention will be described.

  The slab to be subjected to hot rolling is not particularly limited as long as it is manufactured with a continuous cast slab, a thin slab caster or the like. It is also compatible with processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.

  The finishing temperature of hot rolling is not particularly limited, but is preferably 850 to 970 ° C. from the viewpoint of ensuring the press formability of the steel sheet. There are no particular restrictions on the cooling conditions and coiling temperature after hot rolling. If the coiling temperature is 750 ° C. or lower and the coiling temperature is too low, ear cracks are likely to occur during cold rolling. When Si oxide is formed in the surface layer region of the steel plate base material during winding, the winding temperature is set to 650 ° C. or higher. After performing normal pickling, the rolling reduction during cold rolling may be under normal conditions, and the rolling reduction is preferably 50% or more for the purpose of maximizing workability improvement. On the other hand, performing cold rolling at a rolling rate exceeding 85% requires a large cold rolling load, so it is preferably set to 85% or less.

  As described above, after cold rolling, Ni is adhered to the steel sheet surface. The method is not particularly limited, but methods such as electroplating, displacement plating, electroless plating, and vapor deposition plating are simple and easy to control. Moreover, if the metal to adhere contains Ni, the kind will not be limited, Ni, Ni-P, Ni-B, Fe-Ni, Zn-Ni etc. are mentioned.

Further, the absolute value of the Ni adhesion amount is not particularly limited, but if the adhesion amount is too high, it is disadvantageous in terms of cost, and it is preferably 10 g / m ² or less.

  After Ni is adhered to the steel plate surface, annealing is performed by in-line annealing CGL. As the CGL method, it can be applied to various CGL production such as a total reduction furnace type CGL and a Sendzimir method CGL equipped with a non-oxidation furnace on the entry side, and the CGL method is not particularly limited. Absent. The annealing temperature in CGL is 750 ° C. or higher and 870 ° C. or lower. When the annealing temperature is less than 750 ° C., even if Ni is adhered, diffusion into the steel is insufficient, and Ni is contained in the surface layer region of the steel plate base metal at a predetermined concentration (average 0.01 to 20% by mass). I can't let you. Also, annealing at a temperature exceeding 870 ° C. is not preferable because the load on the equipment is large.

An annealing atmosphere in a reduction furnace of CGL is an atmosphere composed of H ₂ , N ₂ , H ₂ O, O ₂ and unavoidable impurities, and is a logarithm log of the partial pressure of water vapor and the partial pressure of hydrogen (PH ₂ O / PH ₂ ) is preferably controlled in a range of −3 ≦ log (PH ₂ O / PH ₂ ) ≦ 0. In particular, when Si oxide is formed in the surface layer region of the steel plate base material in a CGL reducing furnace, −2 ≦ log (PH ₂ O / PH ₂ ) ≦ 0.

  After annealing, it is immersed in a hot dip galvanizing bath. The temperature of the steel sheet when immersed in the plating bath is not particularly limited, but is preferably 400 ° C or higher and 600 ° C or lower. Below 400 ° C, zinc may solidify near the steel sheet in the hot dip galvanizing bath, and above 600 ° C, zinc may evaporate near the steel plate in the hot dip galvanizing bath, which may impair the surface appearance. Because.

  The components of the hot dip galvanizing bath have an Al concentration of 0.07 to 0.16% by mass. If the Al concentration is less than 0.07% by mass, it is difficult to control the alloying because the formation of the Fe—Al—Zn phase, which has an effect of suppressing an excessive alloying reaction in the bath, is insufficient at the initial stage of plating. Become. If the Al concentration exceeds 0.16% by mass, the amount of Fe—Al—Zn phase formed becomes excessive, so that the alloying reaction is extremely slow and control becomes difficult. Preferably it is 0.10 to 0.14 mass%.

  Although the temperature of a hot dip galvanizing bath is not specifically limited, It is preferable to set it as 440-470 degreeC. If it is less than 440 ° C., the viscosity of the plating bath is high, and it may be difficult to control the amount of plating, and if it exceeds 470 ° C., alloying reaction is likely to occur in the bath, so it is difficult to control alloying of the plating layer. Because there is a possibility of becoming.

  After the steel sheet comes out of the hot dip galvanizing bath, the alloying treatment is performed at 440 ° C. to 580 ° C. after controlling to a predetermined adhesion amount. When the temperature of the alloying treatment is less than 440 ° C., it takes a long time for alloying, and the plating layer drips and the surface appearance is deteriorated. On the other hand, if it exceeds 580 ° C., alloying is too early, and it becomes difficult to control the alloying reaction. Therefore, the temperature of the alloying treatment was limited to 440 ° C to 580 ° C. Preferably it is set to 460-560 degreeC.

  In the present invention, the heating method for the alloying furnace is not particularly limited. As long as the heating temperature can be secured, it may be a width injection heating by a normal gas furnace or a high frequency induction heating. Also, there is no question about the method of cooling from the highest temperature reached after alloying heating. If the heat is shut off by air seal after alloying, an open device is sufficient, and gas cooling that cools more rapidly is possible. Etc. There is no problem.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

A slab having the composition shown in Table 1 is ripened to 1150 to 1250 ° C. and hot-rolled to a finishing temperature of 850 to 970 ° C. to form a hot-rolled steel strip having a thickness of 4 mm. It was wound up at such a temperature. After pickling, cold rolling was performed to form a cold rolled steel strip having a thickness of 1.0 mm, and an adhesion amount of Ni as shown in Table 2 was plated. Thereafter, in CGL, annealing is performed in an atmosphere as shown in Table 2, and the aluminum concentration in the bath is 0.08 to 0.14% by mass and the bath temperature is 460 ° C. so as to be hot dip galvanized. Treatment was performed, and alloying treatment was performed at 460 to 560 ° C.

  As described above, the Ni concentration in the surface region of the steel plate base material was measured using GDS after dissolving the plating layer with hydrochloric acid to which an inhibitor was added.

Regarding the presence or absence of Fe ₃ Ni, FeNi, FeNi ₃ , or Ni-containing austenite phase in the surface layer region of the steel plate base material, the plating layer was dissolved in hydrochloric acid with inhibitor added as described above. Later, the surface direction of the steel plate base material was investigated using EPMA and EBSD.

  As described above, the average crystal grain size in the surface layer region of the steel plate base material was measured by EBSD from the cross-sectional direction, and the average crystal grain size in the surface layer region within a depth of 5 μm from the surface of the steel plate base material was determined by data analysis.

  The measurement of the number density of the Si oxide in the surface layer region of the steel plate base material and the confirmation of the oxide species are as described above, by preparing a cross-sectional sample by FIB processing, and by TEM observation from the cross-sectional direction, the surface of the steel plate base material The number of oxides in the surface region within a depth of 5 μm was measured. Simultaneously, EDX analysis and fraction analysis were performed to identify the type of Si oxide formed.

  As described above, the Fe concentration, Al concentration, and Ni concentration in the plating layer were measured by dissolving only the plating layer with a 5 mass% HCl aqueous solution to which an inhibitor was added, and performing ICP emission analysis on the solution.

  The plating adhesion was evaluated by a powdering test. In the powdering test, a 60-degree V-bending mold was used. Using a mold having a curvature radius of 1 mm at the tip so that the evaluation surface comes to the inside of the bend, bending was performed at 60 degrees, a tape was applied to the inside of the bent portion, and the tape was peeled off. Powdering properties were evaluated from the peeled state of the plating layer peeled off with the tape. Evaluation: ◎◎: Peeling width less than 2 mm, ○: Peeling width of 2 mm or more and less than 3 mm, ◎: Peeling width of 3 mm or more and less than 4 mm, ○: Peeling width of 4 mm or more and less than 5 mm, Δ: Peeling width of 5 mm or more and less than 7 mm : The peeling width was 7 mm or more, and ○ or more was considered acceptable.

The evaluation results are shown in Tables 3 and 4. From Table 3 and Table 4, all the examples of this invention were less than 3 mm of peeling width about plating adhesiveness . On the other hand, the test number 7 of the comparative example which does not satisfy the range of the present invention of the Ni concentration in the surface layer region within 5 μm depth from the surface of the steel plate base material has poor plating adhesion (powdering property). Moreover, test number 25 of the comparative example has high Si content and does not satisfy the component range of the present invention, has poor ductility, is cracked by bending (indicated by *), and has plating adhesion (powdering property). Evaluation was not possible.

1 Steel plate base material 2 Γ phase (Zn ₁₀ Fe ₃ )
3 δ ₁ phase (Zn ₇ Fe)
4 ζ phase (Zn ₁₃ Fe)
5 Steel plate base material 6 Alloyed hot-dip galvanized layer 7 Surface of steel plate base material 8 Surface layer region of steel plate base material

Claims (6)

C: 0.01-0.3 mass%,
Si: 0.3 to 2.5% by mass,
Mn: 1.0 to 3.5% by mass,
P: 0.001 to 0.03 mass%,
S: 0.0001 to 0.02 mass%,
Al: 0.005 to 0.1% by mass,
N: 0.0005 to 0.007% by mass
On the steel plate base material, the balance being Fe and inevitable impurities,
Fe: 7 to 15% by mass,
Al: 0.01-1% by mass,
Ni: 0.01 to 10% by mass,
Contain, comprises a plating layer consisting of the remainder Zn and unavoidable impurities, Ri 0.01 to 20% by mass Ni concentration is the mean of the surface layer region within a depth 5μm from the surface of the plate matrix, wherein the steel sheet 5 or more of one or more Si oxides selected from FeSiO ₃ , Fe ₂ SiO ₄ , MnSiO ₃ , Mn ₂ SiO ₄ , SiO ₂ in the surface layer region within a depth of 5 μm from the surface of the base material / μm ² or 1000 / [mu] m ² there be characterized Rukoto less, high strength galvannealed steel sheet excellent in coating adhesion. The surface layer region within a depth of 5 μm from the surface of the steel plate base material contains at least one of Fe ₃ Ni, FeNi, FeNi ₃ , and an austenitic phase containing Ni. A high-strength galvannealed steel sheet with excellent plating adhesion as described in 1.   3. The plating adhesion according to claim 1, wherein an average crystal grain size of the steel plate base material in a surface region within a depth of 5 μm from the surface of the steel plate base material is 0.05 μm or more and 3 μm or less. High strength alloyed hot dip galvanized steel sheet. The steel plate base material
Ti: 0.001 to 0.1% by mass,
Nb: 0.001 to 0.1% by mass
One or characterized by containing two, according to any one of claims 1 to 3 high strength galvannealed steel sheet excellent in coating adhesion of the. The steel plate base material
Mo: 0.005 to 0.3% by mass,
Cr: 0.005 to 0.8 mass%,
Cu: 0.005 to 1% by mass,
Ni: 0.005 to 1% by mass
One or characterized by containing two or more, according to any one of claims 1-4, high strength galvannealed steel sheet excellent in coating adhesion of the. The steel plate base material
B: 0.0001 to 0.005 mass%
The characterized in that it contains, according to any one of claims 1 to 5 a high strength galvannealed steel sheet excellent in coating adhesion.

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