JP4696656B2 - High tensile alloyed hot dip galvanized steel sheet with excellent plating adhesion - Google Patents

Description

  The present invention relates to a high-tensile hot-dip galvanized steel sheet suitable for use in automobiles, building materials, home appliances, and the like, and particularly relates to improving plating adhesion after alloying.

In recent years, the use of high-tensile steel sheets has been increasing for the use of automobiles, building materials, home appliances, and the like. In particular, from the viewpoint of global environmental protection, there is a demand for improved automobile fuel consumption. From the viewpoint of reducing the weight of automobile bodies, and from the viewpoint of improving collision safety of automobile bodies, the use of high-tensile steel plates for automobile bodies is required. It is increasing rapidly.
As a high-tensile steel plate suitable for an automobile body, for example, Patent Document 1 includes C: 0.007% or less, Si: 0.2 to 1.0%, Mn: 0.2 to 1.5%, and further, P, Al, and Ti in appropriate amounts. A high-strength cold-rolled steel sheet for deep drawing having an excellent strength-ductility balance is proposed. However, since the steel sheet described in Patent Document 1 contains a large amount of Si in particular, a Si oxide film is formed on the steel sheet surface during annealing, and when hot dip galvanizing is applied, the plating properties deteriorate, and a partial It is known that so-called non-plating occurs in which molten zinc does not adhere to the steel sheet surface. Moreover, in the hot-dip galvanized steel sheet using such a high-tensile steel sheet as an original sheet, even if non-plating does not occur and it can be plated, an oxide film is generated at the interface between the plating layer and the ground iron. It is known that the plating adhesion is lowered due to this, and there is a problem in practical use.

Further, in a hot-dip galvanized steel sheet in which an oxide film is generated at such an interface, the oxide film becomes a barrier layer and the Fe—Zn alloying reaction is delayed, so that an alloying treatment at a high temperature is required. For this reason, there is a problem that a large amount of the Γ phase, which is the hardest and most brittle among the Fe—Zn alloy phases, is generated, and the plating adhesion during bending is significantly reduced.
For example, Patent Document 2 discloses a reduction zone hydrogen after rapid oxidation with an oxidation zone combustion air ratio of 0.95 to 1.10 and an average oxidation rate in the oxidation zone excluding the pretropical zone of 30 liters / sec or more. There has been proposed a method for producing a high-Si high-tensile hot-dip galvanized steel sheet with good plating adhesion, which is annealed in an atmosphere having a concentration of 10% or less and hot-dip galvanized. According to the technique described in Patent Document 2, since annealing in the oxidation zone does not concentrate Si oxide on the steel sheet surface, only Fe oxide is generated and easily reduced in the reduction zone. It is said that the plating adhesion after hot dip galvanizing treatment can be improved and the appearance can be made uniform.

Further, in Patent Document 3, when hot dip galvanizing is performed on a Si-containing high-strength steel plate containing 0.2% or more of Si, 0.1 to 1000 mg / m ^{2 of} sulfur or a sulfur compound is attached as an S amount, or as a preheating step. Film uniformity after plating in a weakly oxidizing atmosphere followed by annealing at a temperature of 680 ° C or higher in a non-oxidizing atmosphere containing hydrogen and then dipping in a molten zinc bath containing at least 0.05 to 0.30% Al In addition, a method for producing a Si-containing high-strength hot-dip galvanized steel sheet excellent in adhesion has been proposed. According to the technique described in Patent Document 3, a Si-containing high-strength hot-dip galvanized steel sheet having a good surface appearance and excellent plating film uniformity and adhesion is obtained, and no alloying unevenness occurs. It is said that an alloyed hot-dip galvanized steel sheet having excellent powdering resistance can be obtained.
Japanese Patent Publication No. 3-51778 Japanese Patent No. 2587724 Japanese Patent Laid-Open No. 11-50223

  However, when a steel sheet having a high Si content is used as the plating base plate of the hot dip galvanized steel sheet, the oxidation rate on the steel sheet surface is greatly reduced with the increase of the Si content in the steel. Depending on such a technique, oxidation does not proceed and it is difficult to secure a sufficient amount of oxide necessary for suppressing the surface concentration of Si. Therefore, there has been a problem that non-plating occurs or a significant delay in alloying occurs when alloying is performed.

In addition, even when the technique described in Patent Document 3 uses a steel sheet having a high Si content as a plating base plate of a hot dip galvanized steel sheet, the wettability with the hot dip zinc cannot be sufficiently improved, and non-plating is performed. However, the present situation is that the delay in alloying has not been completely eliminated.
The present invention has been made in view of the problems of the prior art, and uses a high-strength steel plate containing Si and further containing Mn and Al as a plating base plate, which has excellent plating surface appearance and excellent plating adhesion. The purpose is to propose a high-tensile alloyed hot-dip galvanized steel sheet.

In order to achieve the above-described problems, the present inventors diligently studied various factors affecting the plating adhesion of the high-tensile alloyed hot-dip galvanized steel sheet. As a result, by adjusting the Al balance in the plating layer and the amount of Γ phase in the plating layer (Fe-Zn alloy layer) to an appropriate range, or further in the plating layer, S, Se, Cl, Br, Na, It has been newly added that, by containing one or more elements selected from K in total at least 1 mg / m ² per side, plating properties are improved and plating adhesion is greatly improved. I found it.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) An alloyed hot-dip galvanized steel sheet formed by forming a plating layer on the steel sheet surface, wherein the steel sheet is mass%, C: 0.25% or less, Si: 0.1-3.0%, Mn: 0.5-3.0% , Al: a high-tensile steel plate having a composition containing 0.01 to 3.0%, the plating layer contains 7 to 15 mass% Fe, and the following formula (1) A value = Al (g / m ² ) − in the plating layer (Fe in coating layer (g / m ² ) x Al in steel plate (mass% )) / 100-Zn in plating layer (g / m ² ) × 0.0012 (1)
The γ-phase fluorescence X-ray diffraction intensity I (Γ1.22) (cps) of the Γ-phase satisfying the A value of 0.04 to 0.20 and the crystal lattice spacing d of 1.22Å depending on the Fe content (2) Or (3) Fe in the plating layer: 7 mass% or more and less than 8 mass%
200 ≦ I (Γ1.22) ≦ 600 (2)
Fe in the plating layer: 8 mass% or more and 15 mass% or less
Max [3000 cps, {Fe (mass%) × C value + 200−8 × C value} × 3] ≧ I (Γ1.22) ≧ {Fe (mass%) × C value + 200−8 × C value} (3)
Where Max [α, β]: the larger of α and β
Fe (mass%): Fe content in the plating layer
C value = 200: (when the Si content in the steel sheet is less than 0.375 mass%)
= 75 / Si content in steel sheet: (When the Si content in the steel sheet is 0.375 mass% or more and 3 mass% or less)
A high-strength galvannealed steel sheet with excellent plating adhesion, characterized by satisfying
(2) In (1), the plating layer contains one or more elements selected from S, Se, Cl, Br, Na, and K in total at least 1 mg / m ² per side. A high-strength galvannealed steel sheet characterized by:

  According to the present invention, even when a high-strength steel plate containing alloy elements such as Si, Mn, and Al is used as a plating base plate, a high-tensile alloyed hot-dip galvanized steel plate having good plating appearance and plating adhesion can be easily obtained. In addition, there is a remarkable industrial effect that it can be manufactured at low cost.

In the present invention, a high-tensile steel plate is used as a plating original plate that is a material to be plated. The high-tensile steel plate to be used is a steel plate having a composition including C: 0.25 mass% or less, Si: 0.1 to 3.0 mass%, Mn: 0.5 to 3.0 mass%, and Al: 0.01 to 3.0 mass%.
Next, the reasons for limiting the composition of the high-tensile steel plate used as the plating original plate will be described. Hereinafter, mass% in the composition is simply expressed as%.

C: 0.25% or less C is a useful element that contributes to increasing the strength of steel, and further has an action of promoting the generation of a retained austenite phase (hereinafter also referred to as a residual γ phase) that improves the strength-ductility balance. Such an effect is remarkably exhibited when the content is 0.05% or more. On the other hand, the content exceeding 0.25% deteriorates the weldability. For this reason, C was limited to 0.25% or less.

Si: 0.1-3.0%
Si is a useful element that contributes to increasing the strength of steel, and needs to be contained in an amount of 0.1% or more to ensure strength. On the other hand, if the content exceeds 3.0%, it is difficult to improve the plating adhesion even if the Al balance and the Γ phase content in the plating layer are adjusted to appropriate amounts. For this reason, Si was limited to the range of 0.1 to 3.0%.

Mn: 0.5-3.0%
Mn is a useful element that contributes to increasing the strength of steel and needs to be contained in an amount of 0.5% or more in order to ensure strength. On the other hand, if the content exceeds 3.0%, the strength-ductility balance and weldability are adversely affected, and even if the Al balance and the Γ phase content in the plating layer are adjusted to appropriate amounts, it is difficult to improve plating adhesion. For this reason, Mn was limited to the range of 0.5 to 3.0%.

Al: 0.01-3.0%
Al is an element added in a complementary manner to Si, and in order to refine crystal grains, it is necessary to contain 0.01% or more. However, if it exceeds 3.0%, strength-ductility balance and weldability are required. In addition to adverse effects, it is difficult to improve plating adhesion. For this reason, Al was limited to the range of 0.1 to 3.0%.

  Since Si, Mn, and Al are elements that form an oxide film on the surface of the steel sheet during annealing and adversely affect non-plating and plating adhesion, the present invention is limited to the above-described range. In addition, you may contain elements other than these in the high tension steel plate used as a plating original plate by this invention as needed. For example, in order to adjust the strength-ductility balance, Cr: 1% or less, Mo: 1% or less, Nb: 0.2% or less, Ti: 0.2% or less Also good.

  Cr, Mo, Nb, and Ti all have an effect of adjusting the strength-ductility balance. Further, Cr, Mo, and Nb have a function of promoting so-called internal oxidation in which Si and Al are oxidized not on the steel sheet surface but on the inside, and have an effect of suppressing oxidation of Si and Al on the steel sheet surface. Such an effect becomes remarkable when Cr: 0.01% or more, Mo: 0.01% or more, Nb: 0.005% or more, Ti: 0.005% or more. On the other hand, if the Cr content exceeds 1%, the Cr itself is concentrated on the surface to lower the plating adhesion and adversely affect the weldability. For this reason, it is preferable to limit Cr to 1% or less. Further, if the Mo content exceeds 1%, the production cost increases, which is economically disadvantageous. For this reason, it is preferable to limit Mo to 1.0% or less. Moreover, since containing Nb exceeding 0.2% leads to an increase in cost, Nb is preferably limited to 0.2% or less. Moreover, the content of Ti exceeding 0.2% lowers the plating adhesion. For this reason, Ti is preferably limited to 0.2% or less.

In order to promote the formation of the residual γ phase, one or more selected from Cu: 0.5 or less, Ni: 1.0% or less, and B: 0.01% or less may be contained.
Cu, Ni and B all have a function of promoting the formation of a residual γ phase, and Cu further has a function of promoting the internal oxidation of Si and Al, and oxidation of Si and Al on the steel sheet surface. Can be selected and contained as necessary. Such an effect becomes remarkable when Cu: 0.01% or more, Ni: 0.01% or more, and B: 0.0005% or more. On the other hand, the content exceeding Cu: 0.5% and Ni: 1.0% raises the manufacturing cost and is economically disadvantageous. Therefore, it is preferable to limit to Cu: 0.5% or less and Ni: 1.0% or less. Further, if the content exceeds B: 0.01%, the plating adhesion deteriorates, so B is preferably limited to 0.01% or less.

The balance other than the above components is Fe and inevitable impurities. As unavoidable impurities, P: 0.1% or less and S: 0.2% or less are acceptable.
P deteriorates weldability, surface quality, etc., further deteriorates plating adhesion in the case of non-alloying, raises the alloying temperature in the case of plating alloying, lowers the ductility and alloying at the same time In order to reduce the adhesion of the plating layer, it is preferable to reduce it as much as possible, but 0.1% is acceptable. Further, since a large amount of S deteriorates weldability, it is preferable to reduce it as much as possible, but it is acceptable up to 0.2%.

  The hot-dip galvanized steel sheet of the present invention is an alloyed hot-dip galvanized steel sheet formed by forming a plating layer on the surface of a high-tensile steel sheet having the above-described composition. The plated layer formed on the surface of the galvannealed steel sheet of the present invention contains 7 to 15 mass% Fe, and is composed of the balance Zn and inevitable impurities. When the Fe content in the plating layer is less than 7 mass%, a large amount of soft ζ phase is generated on the surface of the plating layer, and the slidability during processing is lowered. Also, plating appearance defects such as alloying irregularities are likely to occur. On the other hand, when the Fe content in the plating layer exceeds 15 mass%, a hard and brittle Γ phase is formed at the base metal interface in the plating layer, and the plating adhesion deteriorates. For this reason, in this invention, Fe content in a plating layer was limited to 7-15 mass%.

  In addition to Zn, the plating layer may contain Pb, Sb, and Ni added in a small amount in the plating bath without any problem in plating characteristics. Similarly, there is no problem even if Fe eluted in the plating bath is mixed into the plating layer. In addition, it is preferable that the composition of a plating layer uses the method of melt | dissolving a plating layer and analyzing the obtained liquid by ICP (Inductively Coupled Plasma) or an atomic absorption method. The method for dissolving the plating layer is not particularly limited. For example, 20 mass% NaOH-10 mass% triethanolamine aqueous solution 195 cc and 35 mass% hydrogen peroxide solution 7 cc are mixed immediately before use, and the plated steel sheet is immersed in the mixed solution. And a method of dissolving a plating layer, a method of immersing a plated steel sheet in a 5 mass% HCl aqueous solution mixed with 0.05 mass% inhibitor, and the like.

In the present invention, the plating adhesion amount is preferably 20 to 90 g / m ² per side. When the coating weight is less than 20 g / m ² , the corrosion resistance is lowered. On the other hand, when it is more than 90 g / m ² , the adhesion is lowered and it is easy to peel off during bending. More preferably, it is 30 to 50 g / m ² .
Further, the plating layer formed on the surface of the galvannealed steel sheet of the present invention is a plating layer satisfying an A value defined by the following formula (1) of 0.04 to 0.20. A value = Al in plating layer (g / m ² ) − (Fe in plating layer (g / m ² ) × Al in steel sheet (mass%) )) / 100-Zn in plating layer (g / m ² ) × 0.0012 (1)
The A value is an index that represents the amount of Fe—Al alloy layer in the initial stage of plating, and is an amount that represents the amount of Al in diffusion Fe from the base material from the amount of Al (g / m ² ) in the plating layer. Fe in layer (g / m ² ) x Al in steel plate (mass% )) / 100 and a value obtained by subtracting Zn (g / m ² ) × 0.0012 in the plating layer, which is an amount representing the amount of Al dissolved in Zn. If the A value is less than 0.04, the amount of Al incorporated into the plating layer is small, and a Γ phase is easily formed, making it difficult to ensure good plating adhesion. On the other hand, if the A value exceeds 0.20, the amount of Al incorporated into the plating layer is too large, and alloying of the plating layer is too delayed to ensure good plating adhesion. For this reason, in this invention, A value defined by (1) Formula was limited to the range of 0.04-0.20.

The plated layer formed on the surface of the alloyed hot-dip galvanized steel sheet of the present invention has an A value adjusted within the above-described range and further has a Γ-phase fluorescence X-ray diffraction intensity I (Γ1) having a crystal lattice spacing d of 1.22Å. .22) A plating layer in which (cps) satisfies the following formula (2) or the following formula (3) according to the Fe content in the plating layer.
Fe in the plating layer: 7 mass% or more and less than 8 mass%
200 ≦ I (Γ1.22) ≦ 600 (2)
Fe in the plating layer: 8 mass% or more and 15 mass% or less
Max [3000 cps, {Fe (mass%) × C value + 200−8 × C value} × 3] ≧ I (Γ1.22) ≧ {Fe (mass%) × C value + 200−8 × C value} (3)
Where Max [α, β]: the larger of α and β
Fe (mass%): Fe content in the plating layer
C value = 200: (when the Si content in the steel sheet is less than 0.375 mass%)
= 75 / Si content in steel sheet: (When the Si content in the steel sheet is 0.375 mass% or more and 3 mass% or less)
In the present invention, the amount of Γ phase in the plating layer is used as an indicator of plating appearance and plating adhesion. The amount of Γ phase generated in the plating layer is easily measured by the Γ phase with a crystal lattice spacing d of 1.22Å, so the fluorescent X-ray diffraction intensity I (Γ1.22) (cps) of the Γ phase with d = 1.22Å is used as an index. It was. Note that I (Γ1.22) (cps) uses a value obtained as follows.

For example, after degreasing the plated steel plate and shearing it to a size of width 25 x length 100 mm, it is bonded to a cold-rolled steel sheet of the same size with an epoxy adhesive so that the bonding area is 25 x 13 mm and the adhesive thickness is 2 mm And bake and harden at 170 ° C. for 30 minutes. Then, it is pulled with a tensile tester, and the plating layer is peeled off at the interface between the plating layer and the steel plate. The cold-rolled steel sheet with the peeled plating layer attached is punched out to a size of 15 mmφ, and the X-ray diffraction strength is measured from the peel interface side. X-ray diffraction intensity is measured using the θ-2θ method under the following conditions: X-ray tube: Cu
Tube voltage: 50kV
Tube current: 250mA
From the result of X-ray diffraction obtained, the X-ray diffraction intensity I (Γ1.22) (cps) of the Γ phase having a crystal lattice spacing d of 1.22Å in the plating layer is obtained. Note that cps means the number of counts per 1 s.

  A large I (Γ1.22) means that a large amount of Γ phase is generated in the plating layer. In the present invention, the amount of Γ phase in the plating layer is limited to an appropriate range. If I (Γ1.22) is less than the lower limit of the formula (2) or (3), a large amount of ζ phase is generated, resulting in poor alloying, resulting in uneven alloying and poor plating appearance. Become. On the other hand, if I (Γ1.22) exceeds the upper limit of the formula (2) or (3), a large amount of Γ phase is generated and the plating adhesion is poor. Depending on the Fe content in the plating layer, when I (Γ1.22) satisfies the formula (2) or (3), the plating appearance and plating adhesion are improved.

  In addition, when the Fe content in the plating layer is 8 mass% or more, the generation of the Γ phase is affected by the Si content in the steel sheet, and when the Si content is large, the generation tends to be suppressed. This phenomenon corresponds to a change in the threshold value for I (Γ1.22) in accordance with the Si content in the steel sheet in equation (3). The C value corresponds to the change in the threshold according to the Si content. The influence of the Si content in the steel sheet on the C value is shown in FIG. When the Si content in the steel sheet is less than 0.375 mass%, the inhibitory effect on the Γ phase formation is saturated and the C value is constant. When the Fe content in the plating layer is less than 8 mass%, if I (Γ1.22) is less than 200, the degree of alloying is low, which is equivalent to non-alloying, and if the Fe content is less than 8 mass%, Since I (Γ1.22) does not exceed 600, I (Γ1.22) is limited to the range of 200 to 600 as shown in Equation (2).

Moreover, the plating layer formed on the surface of the galvannealed steel sheet of the present invention is composed of one or more elements selected from S, Se, Cl, Br, Na, and K on one side in total. It is preferable to contain 1 mg / m ² or more per unit. As a result, the A value falls within the above-described range, and I (Γ1.22) further satisfies the above-described expression (2) or (3), and the plating appearance and plating adhesion are remarkably improved. The method for incorporating these elements into the plating layer is not particularly limited. For example, these elements are previously attached to the surface of the plating original plate that is the material to be plated, and then recrystallized and annealed to perform hot dip galvanizing treatment. It is preferable. These elements are taken into the plating layer during the alloying process. For the adhesion of these elements to the plating original plate, for example, a method of applying an aqueous solution of a chemical containing these elements to the surface of the plating original plate with a roll coater or the like and drying is preferable. Also, instead of the coating method, these elements can be mixed in a trace amount in the atmosphere of the annealing furnace. Alternatively, the gas containing these elements is sprayed on the surface of the steel plate in the annealing furnace immediately before the plating treatment, and plating is performed as it is. It is good also as the method of processing.

  In addition, as a chemical | medical agent of S, Na, and Cl, sodium sulfate, ammonium sulfate, iron (III) sulfate, ammonium iron (II) sulfate, iron iron (III) sulfate, sodium hydrogen phosphate, iron chloride (II), iron chloride (III ), Sodium chloride, sodium thiosulfate and the like. Examples of the K, Br, and Se agents include potassium sulfate, ammonium sulfate, potassium selenate, potassium hydrogen phosphate, iron (II) bromide, iron (III) bromide, potassium bromide, potassium chloride, and the like. .

The analysis of the content of the element in the plating layer formed on the surface of the galvannealed steel sheet of the present invention is performed as follows in the present invention.
A method is used in which the plating layer is dissolved with a dilute acid or an alkaline aqueous solution, and the obtained liquid is quantified by ICP or atomic absorption method. The method for dissolving the plating layer is not particularly limited. The above-described method for dissolving the plating layer can be similarly applied.

Next, an example of the result of investigating the influence of the presence or absence of S in the plating layer on the plating adhesion is shown in FIG. A slab having a composition of 0.15% C-0.6 to 1.5% Si-1.5% Mn-0.01% P-0.004% S-0.03Al is heated to 1200 ° C x 60min and hot rolled to a thickness of 3.2mm. The hot-rolled steel sheet. Next, these hot-rolled steel sheets were pickled to remove the black scale, and then cold-rolled to obtain 1.6 mm-thick cold-rolled steel sheets. These cold-rolled steel plates were used as plating base plates, and an aqueous ammonium sulfate solution was applied to the surface so that the surface was 50 mg / m ^{2 on} one side in terms of S and dried. In addition, it experimented also when not apply | coating ammonium sulfate aqueous solution. These steel sheets were subjected to a hot dip galvanizing treatment in a continuous hot dip galvanizing line having a direct fire type (DFF) heating furnace, and then subjected to an alloying treatment. The hot dip galvanizing treatment was performed under the conditions of Al content in the plating bath: 0.13% and bath temperature: 470 ° C. Moreover, the alloying process was 460-580 degreeC. About the obtained steel plate, I (Γ1.22), which is an index of the amount of Γ phase generated in the plating layer, was measured using an X-ray diffraction method. Moreover, Fe content, Al content, and S content in the plating layer were measured by chemical analysis. The relationship between the obtained I (Γ1.22) and the Fe content in the plating layer is shown in FIG.

  From FIG. 1, all of the plating layers containing S are within the scope of the present invention (not shown) with an A value of 0.08 to 0.10, and I (Γ1.22) is the expression (2) or (3) of the present invention. ) Expression is satisfied, and the plating adhesion is good (black ○, black Δ, black □). On the other hand, all the plating layers not containing S have an A value of 0.02 to 0.038, which is out of the range of the present invention, and I (Γ1.22) is less than the lower limit of the formula (2) or (3) of the present invention. The plating adhesion is poor (◯, Δ, □). Thus, it can be seen that by containing an element such as S in the plating layer, a plating layer with significantly good plating adhesion can be obtained stably.

  Below, the preferable manufacturing method of the hot dip galvanized steel plate of this invention is demonstrated. The steel material (slab) having the above-described high-tensile steel composition is heated and hot-rolled, and then the black scale is removed by pickling or the like, followed by cold-rolling to obtain a cold-rolled steel sheet having a predetermined thickness. . Next, it is preferable to subject these cold-rolled steel sheets to recrystallization annealing, subsequently to hot-dip galvanizing treatment, and after forming a predetermined amount of plating layer, to alloying treatment to obtain alloyed hot-dip galvanized steel plates. The recrystallization annealing, hot dip galvanizing treatment and alloying treatment are preferably performed using a continuous hot dip galvanizing line. The heating zone of the continuous hot dip galvanizing line may be either direct flame heating or non-oxidation heating. The atmosphere in the heating zone is preferably an oxidizing atmosphere and the dew point is preferably 0 ° C. or higher. The soaking zone is preferably a reducing atmosphere. Thereby, it becomes easy to incorporate elements such as S into the plating layer. When the dew point is less than 0 ° C., elements such as S do not adhere to the steel sheet and are easily released into the heating zone. The soaking zone is preferably a reducing atmosphere.

  In the present invention, the amount of Al added in the plating bath, the plating bath temperature, and the plating processing time are adjusted in the hot dip galvanizing process so that the A value that is the Al balance in the plating layer is within the range of the present invention. Is preferred. Moreover, the production amount of the Γ phase can be adjusted by adjusting the alloying temperature in the alloying treatment. In the present invention, the alloying temperature is adjusted so that I (Γ1.22) satisfies the formula (2) or (3).

  In order to adjust the A value and I (Γ1.22) in the plating layer within the range of the present invention, in the present invention, each element such as S, Cl, Na, K, Se, and Br is included in the plating layer. It is more preferable to contain a predetermined amount. For this purpose, it is preferable to apply an aqueous solution of a chemical agent containing these elements to the surface of the plating original plate and dry it, and then to perform recrystallization annealing, followed by hot dip galvanizing treatment and alloying treatment. As a result, Si, Mn, Al, etc. can be selectively oxidized and concentrated on the surface during recrystallization annealing, and oxides of these elements can be prevented from growing in the form of a film on the steel sheet surface during recrystallization annealing. In addition, during heating in the hot dip galvanizing treatment, film formation of oxides of oxidizable elements such as Si, Mn, and Al can be suppressed. As a result, the growth of oxide scale is promoted on the surface, and the oxide scale is reduced during the subsequent heating in a reducing atmosphere, and as a result, the surface is activated and the reactivity of the surface is improved. For this reason, Al added to the plating bath at the time of plating sufficiently reacts on the surface of the ground iron and is taken into the plating layer.

  As a result, Si is fixed as an oxide on the outermost surface layer of the steel, so that even in high-tensile steel sheets with high Si content, the substantial Si activity in the outermost layer part that is involved in plating adhesion is greatly reduced. As the Γ phase generation amount increases and the alloying reaction is accelerated, the alloying process can be performed at a relatively low temperature, the Γ phase generation amount can be easily adjusted, and the plating adhesion can be easily achieved. Can be improved.

  Next, the present invention will be described in more detail based on examples.

  A steel material (slab) having the composition shown in Table 1 was heated in a heating furnace at 1260 ° C. for 60 minutes, and hot rolled into a 2.8 mm thick hot-rolled steel sheet and wound at 580 ° C. Thereafter, the black scale was removed by pickling, and then cold rolled to form a cold-rolled steel sheet having a thickness of 1.6 mm. An aqueous solution of the type of chemicals shown in Table 2 was applied to the surface of these cold-rolled steel sheets by a roll coater method and dried. The amount of drug applied was changed by changing the concentration of the aqueous solution. Next, these steel sheets were subjected to recrystallization annealing at 830 ° C., hot dip galvanizing treatment and alloying treatment in a continuous hot dip galvanizing line having a direct-fired heating furnace to obtain alloyed hot dip galvanized steel sheets. . In addition, the hot dip galvanizing treatment was performed by using a plating bath temperature: 460 ° C., a plating bath: hot dip zinc added with an Al amount shown in Table 2, and the adhesion amount of the plating layer was adjusted by gas wiping to an amount shown in Table 2. The alloying treatment temperature was set to the temperature shown in Table 2.

  In addition, content of the element contained in the plating layer is obtained by immersing the plated steel sheet in a mixed solution of 195cc of 35mass% NaOH-10mass% triethanolamine aqueous solution and 7cc of 35mass% hydrogen peroxide solution, Each element of the obtained liquid was quantified by the ICP method and calculated as the content per unit area of one side. Moreover, A value defined by (1) Formula was computed from content of each obtained element. Further, I (Γ1.22) was measured in the same manner as in the fluorescent X-ray diffraction method described above for the Γ phase generation amount in the plating layer. Moreover, about the obtained galvannealed steel sheet, the appearance of plating was visually examined, and when there was no unplating, the appearance of plating was judged as ◯ (good), and when there was no plating, the appearance of plating was judged as poor (x). did. In addition, the presence or absence of uneven appearance due to alloying delay during the alloying treatment was also considered.

  Moreover, about the obtained galvannealed steel plate, plating adhesiveness was investigated. The plating adhesion was obtained by applying a cellophane tape to the obtained galvannealed steel sheet and bending the cellophane tape surface by 90 °. The cellophane tape surface after bending at 90 ° was irradiated with fluorescent X-rays, and the Zn count number was measured as an index of the amount of peeling per unit length. If the Zn count is 0 to 500 counts, rank 1; if it exceeds 500 to 1000 counts, rank 2; if it exceeds 1000 to 2000 counts, rank 3; if it exceeds 2000 to 3000 counts, rank 4 and 3000 counts The super case was ranked 5. Rank 1 has good peel resistance and rank 5 is inferior. The case of ranks 1 and 2 was evaluated as good (◯, Δ) for plating adhesion, and the case of rank 3 or higher was evaluated as defective (x).

  The obtained results are shown in Table 2.

  In any of the present inventions, peeling of the plating layer is small, and the plating adhesion is excellent even though a high-strength steel plate containing a large amount of Si, Mn, and Al is used as the plating base plate. On the other hand, in comparative examples that are outside the scope of the present invention, plating adhesion and / or plating appearance are deteriorated.

It is a graph which shows the relationship between the amount of (GAMMA) phase production | generation which affects plating adhesiveness, and Fe content in a plating layer. It is a graph which shows the influence of Si content in the steel plate which acts on C value.

Claims (2)

An alloyed hot-dip galvanized steel sheet formed by forming a plating layer on the steel sheet surface, wherein the steel sheet is mass%, C: 0.25% or less, Si: 0.1-3.0%, Mn: 0.5-3.0%, Al: A high-tensile steel plate having a composition containing 0.01 to 3.0%, wherein the plating layer contains 7 to 15 mass% Fe, and the A value defined by the following formula (1) satisfies 0.04 to 0.20, and the crystal lattice Plating adhesion characterized in that the fluorescent X-ray diffraction intensity I (Γ1.22) (cps) of the Γ phase with an interval d of 1.22Å satisfies the following formula (2) or (3) depending on the Fe content: High strength alloyed hot dip galvanized steel sheet with excellent resistance.
A value = Al (g / m ² ) in plating layer-(Fe (g / m ² ) in plating layer) Al in steel plate (mass% )) / 100-Zn in plating layer (g / m ² ) × 0.0012 (1)
Fe in the plating layer: 7 mass% or more and less than 8 mass%
200 ≦ I (Γ1.22) ≦ 600 (2)
Fe in the plating layer: 8 mass% or more and 15 mass% or less
Max [3000 cps, {Fe (mass%) × C value + 200−8 × C value} × 3] ≧ I (Γ1.22) ≧ {Fe (mass%) × C value + 200−8 × C value} (3)
Where Max [α, β]: the larger of α and β
Fe (mass%): Fe content in the plating layer
C value = 200: (when the Si content in the steel sheet is less than 0.375 mass%)
= 75 / (Si content in steel sheet): (When Si content in steel sheet is 0.375 mass% or more and 3 mass% or less) The plating layer contains one or more elements selected from S, Se, Cl, Br, Na, and K in total at least 1 mg / m ² per side. 1. A high-strength galvannealed steel sheet according to 1.

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