JP4889212B2 - High-strength galvannealed steel sheet and method for producing the same - Google Patents

Description

  The present invention relates to a high-strength galvannealed steel sheet and a method for producing the same. The present invention provides an alloyed hot-dip galvanized steel sheet having excellent powdering resistance, and a method for producing the same, mainly used in the fields of home appliances, building materials, automobiles, and the like.

  In recent years, hot-dip galvanized steel sheets have been used in large quantities in fields such as home appliances, building materials, and automobiles. In particular, alloyed hot-dip galvanized steel sheets that are excellent in terms of economy, rust prevention function, and performance after painting are widely used. ing.

This alloyed hot-dip galvanized steel sheet is usually produced as follows. The steel sheet is heated in a preheating furnace before hot dipping, annealed in a reducing atmosphere of H ₂ + N ₂ with a dew point adjusted to −20 ° C. or lower so as not to cause non-plating, then cooled to around the plating bath temperature, and then Apply hot-dip Zn plating. Then, the hot-dip galvanized steel sheet is heated in a heat treatment furnace at a material temperature of 480 to 600 ° C. for 3 to 30 seconds to form an Fe—Zn alloy plating phase, thereby producing an alloyed hot-dip galvanized steel sheet. .

However, when alloyed hot-dip Zn-plated steel sheets are pressed, if there is a soft alloy phase (ζ phase) in which the Fe content in the plating surface layer is relatively low, due to the adhesion phenomenon between the plating surface layer and the mold surface, etc. Since the slidability between the mold surface and the steel plate is inferior, plating peeling (flaking) or press cracking of the steel plate may occur. When the Fe content in the plating layer is high, a hard Γ, Γ ₁ , δ _1c phase is formed in the vicinity of the interface between the steel plate and the plating layer. Therefore, powdering (powdering) of the plating layer is likely to occur. When this phenomenon occurs, a peeling piece adheres to the mold, and a pressing flaw occurs.

In order to solve such problems, it has been proposed that the alloyed hot-dip galvanized steel sheet with a mild steel sheet as the base material should be a δ _1- based alloy phase with a relatively balanced hardness in the coating layer. Has been.

For example, Patent Document 1 proposes an alloyed hot-dip galvanized steel sheet having a basis weight of 45 to 90 g / m ² / one side and excellent in powdering resistance and flaking resistance. Here, the Fe content in the plating layer is controlled to 8 to 12%, and the Al content is controlled to 0.05 to 0.25%, so that the η and ζ phases do not exist in the coating layer, and the base material and the plating layer The Γ phase of the alloy layer at the interface is set to 1.0 μm or less.

  Further, Patent Document 2 discloses an Al concentration in a plating bath of 0.13 regarding a method for producing an alloyed hot-dip galvanized steel sheet in which an alloying treatment is performed so that the Fe content in a coating layer of a coating is 8 to 12%. In addition, the intrusion plate temperature of the base steel plate is increased as the Al concentration in the bath increases, and the plate temperature on the high-frequency induction heating furnace exit side is controlled within an appropriate range. It has been proposed to produce alloyed hot-dip galvanized steel sheets with excellent ring and flaking resistance.

  Next, a method for improving the powdering resistance of the galvannealed steel sheet is proposed as follows for high-strength steel sheets.

In the alloyed hot-dip galvanized steel sheet proposed in Patent Document 3, the chemical composition of the base steel sheet is C: 0.05 to 0.20%, Si: 0.02 to 0.70%, Mn: 0.50 to 3.0%, P: 0.005 to 0.10%, S: 0.1% or less, sol.Al: 0.10 to 2.0%, N: 0.01% or less, and Si + Al: 0.5% or more and reduction annealing at 750 to 870 ° C, A steel plate that is obtained by retaining at a low temperature of 350 to 550 ° C. for 20 seconds or longer and then performing galvanizing and then alloying at a specific alloying temperature and residence time. When the content of the austenite (γ) phase remains in the interior by 1% by volume or more, the steel sheet as a base material is given high strength with excellent local ductility. And while prescribing the Fe content in the plating layer of the coating to 8 to 15% by mass, the average thickness of the Γ phase in the plating layer is 2 μm or less, the maximum Γ ₁ phase length in the thickness direction is 1.5 μm or less, and By defining the maximum Γ ₁ phase length and Γ phase thickness ratio to 1 or less, the powdering resistance is improved.

The alloyed hot-dip galvanized steel sheet proposed in Patent Document 4 has a chemical composition of a steel sheet as a base material in mass% of C: 0.05 to 0.20%, Si: 0.01 to 1.50%, Mn: 0.5 to 3.0%, P: 0.05% or less, S: 0.01% or less, Al: 0.01 to 2.0%, N: 0.01% or less, Si + Al: 0.5% or more,
After reduction annealing at 780 to 870 ° C, the temperature range from 700 ° C to 550 ° C is cooled at an average cooling rate of 30 ° C / sec or more, and then retained at a low temperature of 350 to 550 ° C for 20 seconds or more. Cool, and attach to the obtained base material one or more of Ni, Cu and Co, and again hold it at 780 to 870 ° C for 5 to 500 seconds to perform reduction annealing, and from the temperature reached at that time It is obtained by cooling to the vicinity of the plating bath temperature, plating, and alloying treatment at 520 ° C or less, and the content of austenite (γ) phase in the base steel sheet is 1% by volume. By remaining as described above, the steel sheet as the base material is given high strength and high ductility satisfying the tensile strength TS (MPa) × elongation El (%) ≧ 20,000. And the Al content in the plating layer of the film is defined as 0.2 to 0.4 mass%, the Fe content is defined as 8 to 15 mass%, and the adhesion amount of Ni, Cu, Co, etc. after the first annealing is increased. By promoting alloying, powdering resistance and flaking resistance are improved.

JP-A-1-68456 JP-A-4-76053 JP 2002-30403 A Japanese Patent Laid-Open No. 2002-47535

  There is a strong demand for alloyed hot-dip galvanized steel sheets, but with regard to steel sheets used as the base material of alloyed hot-dip galvanized steel sheets, many steel sheets that have been made lighter have been developed by increasing their strength. Has been.

  However, alloyed hot-dip galvanized steel sheets that use high-strength steel sheets as the base material rapidly increase the surface pressure applied to the coating layer of the coating during press forming. The press factor has a greater effect on the film peeling behavior than the galvanized steel sheet. Therefore, an alloyed hot-dip galvanized steel sheet using a high-strength steel sheet as a base material is assumed to cause a problem that film damage during press forming becomes large.

  The alloyed hot dip galvanized steel sheet obtained by the alloyed hot dip galvanized steel sheet described in Patent Document 1 and the manufacturing method described in Patent Document 2 relates to the alloyed hot dip galvanized steel sheet using a mild steel plate as a base material. Although it defines the alloy phase of the coating layer of the coating, even when applied to an alloyed hot-dip galvanized steel sheet using a high-strength steel sheet as the base material, almost no effect of improving the powdering resistance during press forming is recognized. It turned out not to be.

  In addition, the alloyed hot-dip galvanized steel sheet proposed in Patent Document 3 and Patent Document 4 as a method for improving powdering of the above-described high-strength steel sheet is a steel type in which the contents of Si and P in the steel are relatively high. Therefore, it is necessary to perform heat treatment with a complex reduction annealing heat pattern for the production. Furthermore, in order to obtain the alloyed hot-dip galvanized steel sheet proposed in these documents, a longer heat treatment time is required for alloying than conventional ones, so a heat treatment furnace having a long furnace length is required, and a new capital investment is required. There is a problem that is necessary.

  The present invention has been made for the purpose of solving such problems, and in particular, an alloyed hot-dip galvanized steel sheet excellent in pressability with improved powdering resistance characteristic of a high-tensile steel sheet and a method for producing the same. Is to provide.

  The inventors first investigated the powdering behavior of an alloyed hot-dip galvanized steel sheet using a high-strength steel sheet as a base material. Under the same forming conditions, even if the plate thickness is the same, the contact surface pressure with the mold increases as the base metal strength increases. Unlike the drop-off form, a film close to the peel-off form by high surface pressure sliding was observed.

  When the base material of the alloyed hot-dip galvanized steel sheet is a mild steel sheet, in order to improve the powdering resistance, the content of Fe in the coating layer of the coating is restricted and the formation amount of the Γ phase is suppressed. It is effective to do. On the other hand, when a high strength steel plate with a yield point (YP) exceeding 350 MPa is used as a base material, it can slide as much as possible against a mold rather than a plating layer with a soft coating that can withstand compressive deformation. A film having such a structure and properties under the idea that it is effective to make a plating layer of a relatively hard coating capable of lowering the dynamic resistance and to increase the adhesion at the interface between the base material and the plating layer. The plating layer was examined.

First, in order to harden the plating layer of the coating, it has been found effective to control the Fe content in the plating layer to 11 mass% or more. In addition, when sliding is applied at a high surface pressure, the convex portion of the surface layer of the coating increases the deformation resistance, and the coating scraped by the sliding increases the amount of powdering. It was found that it is effective to control the surface roughness Ra and the surface waviness Wca to a predetermined value or less with respect to the surface shape.

  Next, in order to increase the adhesive strength at the interface between the base material and the plating layer, in the case of an ultra-low carbon steel plate, by increasing the Al concentration in the plating bath, the alloy in the grain and the grain boundary of the base steel plate The method of increasing the difference in the forming rate and increasing the unevenness at the interface between the steel sheet and the galvannealed layer could be adopted. In addition, a similar technique should be adopted for a high-tensile steel plate based on ultra-low carbon steel. However, in a high-strength steel sheet having a relatively high C content in steel in which C is segregated at grain boundaries, even if the Al concentration in the plating bath is increased, the interface between the steel sheet and the galvannealed alloy layer is increased. Since it was not possible to increase the unevenness, it was difficult to significantly improve the interfacial adhesion strength.

  Steel types having a relatively high C content in steel have such problems. Furthermore, since the high-tensile alloyed hot-dip galvanized steel sheet has a large thickness, there is also a problem that when bending is performed, a shear stress is generated due to the bending back deformation at that time, and the coating is peeled off.

  In order to solve these problems, the present inventors, as a result of various investigations, include 0.02 to 0.2% by mass of Si in the steel of the steel plate as the base material, thereby coating the coating in the alloying process. 530 ° C or less, which promotes the diffusion of Zn in the layer to the grain boundary of the steel plate as the base material, increases the unevenness of the interface between the steel plate and the plating layer, and does not diffuse very much into the grain of the steel plate And found that alloying is an effective means.

  The present invention has been completed based on such new knowledge, and relates to the high-tensile galvannealed steel sheet according to any of the following (1) to (3), The present invention relates to a method for producing a high-tensile alloyed hot-dip galvanized steel sheet as described in 4) or (5). Hereinafter, the present invention (1) to the present invention (5), respectively. These may be collectively referred to as the present invention.

(1) An alloyed hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer on the surface of the steel sheet, wherein the steel sheet is in mass%, C: 0.05 to 0.25%, Si: 0.02 to 0.20%, Mn: 0.5 to 3.0 %, S: 0.01% or less, P: 0.035% or less, and sol.Al: 0.01 to 0.5%, the balance having a chemical composition composed of Fe and impurities, and the alloyed hot-dip galvanized layer is mass% And Fe: 11 to 15% and Al: 0.20 to 0.45%, the balance being the chemical composition consisting of Zn and impurities, and the interfacial adhesion strength between the steel sheet and the galvannealed layer is 20 MPa or more A high-strength galvannealed steel sheet characterized by

  (2) The steel sheet contains, by mass%, Ti: 0.01 to 0.5% and Nb: 0.01 to 0.5%, or Mo: 0 to 1.0%, instead of a part of Fe. The high-tensile galvannealed steel sheet according to (1) above, which has a chemical composition.

  (3) The high-tensile galvannealed steel sheet according to (1) or (2) above, wherein the surface roughness Ra is 0.9 μm or less and the surface waviness Wca is 0.6 μm or less.

(4) After the steel sheet having the chemical composition described in (1) or (2) above is immersed in a hot dip galvanizing bath having an Al concentration of 0.08 to 0.13 % by mass in the bath, the plating layer is attached, A method for producing a high-tensile galvannealed steel sheet, characterized in that alloying is performed at a temperature of 470 to 530 ° C so that the Fe content in the steel is 11 to 15 mass%.

  (5) Using a temper rolling roll having a surface roughness Ra of 3 μm or less and a surface waviness Wca of 0.5 μm or less on the high-tensile alloyed hot-dip steel plate after alloying treatment, 1.47 to 2.94 MN / m The method for producing a high-tensile alloyed hot-dip galvanized steel sheet according to (4) above, wherein temper rolling is performed with a rolling line load.

  The surface roughness Ra and the surface waviness Wca on the surface of the high-tensile hot-dip galvanized steel sheet were measured based on the provisions of JISB 0610. That is, the surface roughness Ra was measured by the centerline average roughness, but a cut-off value of 0.8 mm was adopted. The surface waviness Wca was measured by filtering centerline waviness, and a high-frequency cutoff of 0.8 mm and a low-frequency cutoff of 8 mm were employed.

  According to the present invention, it is possible to provide a high-tensile alloyed hot-dip galvanized steel sheet having excellent powdering resistance and flaking resistance and a method for producing the same.

  This high-tensile alloyed hot-dip galvanized steel sheet has excellent pressability and is suitable as a structural member in fields such as home appliances, building materials and automobiles.

  First, the reason for the regulation of the steel sheet which is the base material for plating the high-tensile hot-dip galvanized steel sheet of the present invention will be described. Hereinafter, “%” for the composition represents “% by mass”.

A. Hereinafter, the chemical composition of the steel sheet according to the present invention will be described in detail with respect to the high-tensile galvannealed steel sheet according to the present invention and its manufacturing method. In the present specification, “%” in the chemical composition of the steel sheet, the alloyed hot-dip galvanized layer and the plating bath represents “% by mass” unless otherwise specified.

(1) Chemical composition of steel plate used as base material C: 0.05-0.25%
C is an element effective for improving strength at low cost. If the C content is less than 0.05%, the effect of improving the strength is not sufficient, so the lower limit of the content is set to 0.05%. A preferred lower limit is 0.10%. On the other hand, if the content exceeds 0.25%, the crack progress at the cut or punched portion increases. For this reason, the upper limit of the content is 0.25%. A preferred upper limit is 0.20%.

Si: 0.02 to 0.20%
In the alloying process, Si promotes the diffusion of Zn in the plating layer of the coating to the grain boundaries of the base steel sheet, and increases the irregularities at the interface between the base material and the plating layer, thereby increasing the base material. It is an important element that increases the interfacial adhesion strength between the steel plate and the plating layer.

  If the Si content is less than 0.02%, the effect of improving the interfacial adhesion strength is not sufficient, so the lower limit of the content is set to 0.02%. A preferred lower limit is 0.04%. On the other hand, if the content exceeds 0.20%, the alloying speed is remarkably reduced, so that it is necessary to lengthen the alloying treatment time, leading to a reduction in productivity and an increase in equipment length. Increasing the alloying treatment temperature in order to shorten the alloying treatment time results in a decrease in operability or a decrease in the interfacial adhesion strength. For this reason, the upper limit of the content is 0.20%. A preferred upper limit is 0.10%.

Mn: 0.5-3.0%
Mn is an element effective for improving the strength of the steel sheet, but if the content is less than 0.5%, the effect of improving the strength is not sufficient, so the lower limit of the content is 0.5%. On the other hand, if the Mn content exceeds 3.0%, the steel sheet becomes brittle, so the upper limit of the content is set to 3.0%. When the Mn content increases, the manufacturing cost of the steel sheet increases, so the preferable upper limit is 2.5%.

P: 0.035% or less
P is an optional additive element. If contained in an amount of 0.02% or more, it is effective for increasing the strength, but if it is contained excessively, the alloying speed will decrease, so it will be necessary to lengthen the alloying treatment time, resulting in reduced productivity and equipment. Causes an increase in length. When the alloying treatment temperature is increased in order to shorten the alloying treatment time, the operability is lowered or the interfacial adhesion strength is lowered. For this reason, content of P shall be 0.035% or less. A preferable content is 0.025% or less.

  Even if P is not contained, it is not necessary to positively add P when the strength is sufficiently increased by other alloy components. In this case, the lower limit of P is not limited.

S: 0.01% or less
S is an impurity, and its content is preferably low. If the S content exceeds 0.01%, precipitation of MnS becomes prominent and the ductility of the steel sheet is deteriorated, so the S content is set to 0.01% or less. A preferable content is 0.005% or less.

sol.Al: 0.01-0.5%
Al is added as a deoxidizer, but if its content is less than 0.01% as sol.Al, deoxidation is insufficient, inclusions increase, and ductility decreases. On the other hand, if the content exceeds 0.5%, the cost increases. For this reason, content of sol.Al shall be 0.01% or more and 0.5% or less.

Ti: 0.01-0.5%, Nb: 0.01-0.5%, Mo: 0-1.0%
These elements are arbitrarily added elements, and by adding them, carbide precipitates are formed in the steel, and precipitation strengthening can be achieved by the precipitates. Therefore, they can be added for the purpose of improving the strength by precipitation strengthening.

  If the Ti content is less than 0.01% and the Nb content is less than 0.01%, the amount of precipitates is small and the effect of improving the strength is small. Therefore, the lower limit for inclusion is 0.01%. On the other hand, when the Ti content exceeds 0.5% or the Nb content exceeds 0.5%, the amount of precipitates becomes excessive and the ductility of the steel sheet is significantly reduced. To do. The preferred lower limit for each of Ti and Nb is 0.02% and the upper limit is 0.10%.

  Mo is an optional additive element. When Mo is added, the strength can be further increased. If the Mo content exceeds 1.0%, the ductility deteriorates extremely. Therefore, the upper limit of the content when added is 1.0%.

  In addition, a small amount of other components such as Cr, Cu, Ni, Cu, and V may be included.

(2) Chemical composition of the plating layer used as a film
Fe: 11 ~15%
If the Fe content in the galvanized layer to be the coating is less than 11% , a soft part is likely to be formed on the surface layer portion of the plated layer after the alloying treatment, and the slidability is reduced and the coating layer of the coating is reduced. Flaking-like peeling due to peeling from the interface with the base steel sheet increases. Therefore, the lower limit of the Fe content is 11%. On the other hand, if the Fe content exceeds 15%, when the steel sheet is subjected to bending, the amount of powdering peeling due to compressive deformation of the alloyed hot-dip galvanized layer inside the bent portion increases. For this reason, the upper limit of the Fe content is 15%. A preferred upper limit is 14%.

Al: 0.20 to 0.45%
When the Al content in the galvanized layer to be the coating is less than 0.20%, the effect of suppressing the development of the alloy layer in the plating bath becomes insufficient, and the control of the coating amount becomes difficult. Therefore, the lower limit of the Al content is 0.20%. A preferred lower limit is 0.25%. On the other hand, if the Al content exceeds 0.45%, the alloying speed will decrease, so at normal line speeds the alloying temperature may have to be higher than 530 ° C in order to achieve the above Fe content. As will be described later, it becomes difficult to set the interfacial adhesion strength between the steel sheet and the galvannealed layer to 20 MPa or more. Therefore, the upper limit of the Al content is 0.45%. A preferred upper limit is 0.40%.

(3) Adhesive strength at the interface between the base material and the plating layer Adhesive strength at the interface: 20 MPa or more If the adhesive strength at the interface between the base steel sheet and the plating layer is less than 20 MPa, the plating film peels off from the interface during processing. It becomes easy and the powdering resistance decreases. More preferably, it is 25 MPa or more.

(4) Surface properties of high-tensile galvannealed steel sheets Surface roughness Ra: 0.9 μm or less, surface waviness Wca: 0.6 μm or less Surface properties of high-tensile galvannealed steel sheets, ie, coating layer The surface properties are preferably a surface roughness Ra: 0.9 μm or less and a surface waviness Wca: 0.6 μm or less. By reducing the surface roughness Ra to 0.9μm or less and the surface waviness Wca to 0.6μm or less, the sliding resistance with the mold during molding is reduced, and the peeling mode close to plating peeling is suppressed to prevent powdering. Can be improved. Since the surface waviness Wca has a greater effect of reducing the sliding resistance than the surface roughness Ra, Ra is preferably 0.7 μm or less and Wca is 0.6 μm or less. More preferable ranges are Ra of 0.9 μm or less and Wca of 0.4 μm or less, and the most preferable ranges are Ra of 0.7 μm or less and Wca of 0.4 μm or less.

Al concentration in the plating bath: 0.08 to 0.13%
When the Al concentration in the plating bath is less than 0.08%, an excessive Fe—Zn interfacial alloy layer is already formed in the plating bath before the alloying treatment, making it difficult to control the amount of adhesion. Therefore, the lower limit of the Al concentration in the plating bath is 0.08%. A preferred lower limit is 0.09%.

On the other hand, if the Al concentration in the plating bath exceeds 0.13%, the concentration of Al in the plating film proceeds excessively, resulting in a decrease in the alloying speed, and the above-mentioned Fe content is realized at a normal line speed. In some cases, the alloying treatment temperature must be higher than 530 ° C., and as described later, it becomes difficult to make the interfacial adhesion strength between the steel sheet and the galvannealed layer 20 MPa or more. Therefore, the upper limit of the Al concentration in the plating bath is 0.13%.

About immersion time, if it is less than 3 second, a performance and operativity will not be inhibited especially. Other plating conditions may be in a generally adopted range, and there is no particular problem if the plating bath temperature is 450 to 470 ° C. and the penetration plate temperature is in the range of 450 to 480 ° C. Even if 0.1% or less of each of inevitable elements Fe and Pb, Cd, Cr, Ni, W, Ti, Mg, and Si is contained as components other than Al in the plating bath, this performance is not affected. The adhesion amount may be in the range of 25 to 70 g / m ² which is generally used as a product.

(6) Alloying treatment Alloying treatment temperature: 470-530 ° C
If the alloying temperature is less than 470 ° C, coarse crystals of ζ phase are likely to be formed on the surface layer of the alloyed hot-dip galvanized layer, and the surface roughness Ra is controlled to 0.9 µm or less even after the prescribed temper rolling. Difficult to do. Therefore, the lower limit of the alloying temperature is set to 470 ° C. A preferred lower limit is 480 ° C.

On the other hand, when the alloying temperature exceeds 530 ° C., the effect of promoting the diffusion of Zn in the plating film due to the addition of Si into the steel plate described above to the grain boundary of the steel plate that is the plating base material is weakened. Since the diffusion into the grains becomes dominant, the interfacial adhesion strength between the steel sheet and the galvannealed layer is lowered. Therefore, the upper limit of the alloying temperature is set to 530 ° C. A preferred upper limit is 520 ° C. As a heating means in the alloying treatment, any means such as radiant heating, high frequency induction heating, energization heating and the like may be used.

(7) Temper rolling Roll surface roughness Ra of temper rolling roll: 3 μm or less, surface waviness Wca: 0.5 μm or less, temper rolling line load: 1.47 to 2.94 MN / m
By setting the surface roughness Ra of the temper rolling roll to 3 μm or less, it becomes easy to control the surface roughness Ra of the high-tensile galvannealed steel sheet after temper rolling to 0.9 μm or less. Therefore, the surface roughness of the temper roll is preferably 3 μm or less. More preferably, it is 2 μm or less.

  The surface waviness Wca of the temper rolling roll is 0.5 μm or less and the temper rolling line load is 1.47 MN / m or more, so that the Wca of the surface of the high-tensile alloyed hot-dip galvanized steel sheet after temper rolling is 0.6 μm or less. It becomes easy to control. Therefore, it is preferable that the surface waviness Wca of the temper rolling roll is 0.5 μm or less and the temper rolling line load is 1.47 MN / m or more. The temper rolling line load is more preferably 1.96 MN / m or more.

  Further, by setting the temper rolling line load to 2.94 MN / m or less, it is possible to suppress formability deterioration due to work hardening of the steel sheet. Therefore, the temper rolling line load is preferably 2.94 MN / m or less, more preferably 2.45 MN / m or less.

(8) Post-treatment The product surface after plating may be untreated, but may be subjected to post-treatment such as known chromic acid treatment, phosphate treatment, and resin film coating. In addition, rust preventive oil may be applied, and the rust preventive oil used for the application may be a commercially available general one, but it is highly lubricious and contains an extreme pressure additive such as S or Ca. Rust oil may be applied.

  Table 1 shows the test materials used in this example. These components were melted and cast in a laboratory to produce a slab having a thickness of 30 mm. The slab was held at 1150 ° C. for 1 hour in the atmosphere and subjected to rough rolling and finish rolling. Finish rolling was performed at 950 ° C and wound up at 600 ° C in the air. The hot rolled finish thickness is 4.5 mm. The hot-rolled sheet was pickled and then cold-rolled to a thickness of 2.3 mm.

  This specimen was plated under the following conditions using a vertical hot-dip Zn plating apparatus.

First, a steel plate having a thickness of 2.3 mm was degreased and washed with a NaOH solution at 75 ° C. and annealed in an atmosphere of N ₂ + 20% H _{2 and} dew point −40 ° C. at 820 ° C. × 60 s. After annealing, the steel plate is cooled to near the bath temperature, immersed in a hot dip galvanizing bath with an Al concentration of 0.07 to 0.15 mass% and a bath temperature of 460 ° C in the bath, immersed for 2 seconds, and then the amount of coating on one side of the plating is 50 g by the wiping method. Adjusted to / m ² . Then, the alloying process by various heat patterns was performed to the plated steel plate using the infrared heating apparatus. The cooling rate was adjusted by changing the air volume and the amount of mist sprayed. Further, as temper rolling conditions after alloying treatment, the surface roughness Ra of the roll was changed to 1.5 to 5.0 μm, the surface waviness was changed to 0.4 to 0.7 μm, and the rolling line load was changed in the range of 0.98 to 3.43 MN / m. . The results are shown in Table 2.

1) Collection of sample pieces Sample pieces of 25mmφ were collected from the alloyed sample, and the plating layer was dissolved with 10% HCl aqueous solution containing 0.5vol% inhibitor (trade name: "Ibit 710N" manufactured by Asahi Chemical). This was subjected to composition analysis of the plating layer by the ICP method.

2) Measurement of interfacial adhesion strength between steel plate and alloyed hot-dip galvanized layer The alloyed sample was cut into 20 mm x 100 mm so that the longitudinal direction was the rolling direction, and one liquid manufactured by Sunstar Co., Ltd. Type epoxy-based structural adhesive (trade name: E-6773) as an adhesive, overlap: 12.5 mm, adhesive film thickness: 200 μm, baking conditions: 180 × 20 minutes, tensile speed: 5 mm / min, room temperature A tensile test was carried out in the longitudinal direction under the following conditions. The interfacial adhesion strength in this test is affected by the substrate strength due to the deformation of the base material, but it is almost negligible for the base material with a YP of 350 MPa or more as in this case.

3) Measurement conditions for surface roughness Ra and surface waviness Wca of high-tensile hot-dip galvanized steel sheet Surface roughness Ra is measured by centerline average roughness. A value defined by JISB 0610, using a cut-off value of 0.8 mm, and measured using a surfcom (trade name) manufactured by Tokyo Seimitsu was used.
Surface waviness Wca is measured by filtered centerline waviness. As defined in JIS B0610, a high-frequency cut-off of 0.8 mm and a low-frequency cut-off of 8 mm were adopted, and values measured with the same measuring device were used.

4) Powdering test Brushed with Japanese Parkerizing anti-corrosion oil 550S on the sample cut into 30mm x 100mm (rolling direction), free of blank holder pressure (Secure a space more than the plate thickness between the die and punch) ) Was performed at room temperature. After stripping the tape on the vertical wall, the mass before and after the hat molding was measured, and the amount of powdering of the coating film per test material was measured. Other conditions are: punch parallel part: 27.6 mm, die parallel part: 30 mm, punch shoulder R: 3 mm, die shoulder R: 5 mm, molding speed: 60 mm / min.

  As described in the examples, the high-tensile alloyed hot-dip galvanized steel sheet of the present invention has excellent powdering resistance and flaking resistance during pressing, and is used as a structural member in the fields of home appliances, building materials, automobiles, and the like. Is suitable.

And the manufacturing method of this invention makes it possible to manufacture stably the high-tensile-alloyed hot-dip galvanized steel plate which has such a powdering resistance and a flaking resistance.

Claims (5)

An alloyed hot-dip galvanized steel sheet provided with an alloyed hot-dip galvanized layer on the steel sheet surface, wherein the steel sheet is in% by mass, C: 0.05 to 0.25%, Si: 0.02 to 0.20%, Mn: 0.5 to 3.0%, S : 0.01% or less, P: 0.035% or less and sol.Al:0.01-0.5%, the balance has a chemical composition consisting of Fe and impurities, and the alloyed hot-dip galvanized layer is in mass%, Fe : 11-15%, Al: containing from 0.20 to 0.45 percent, and has a chemical composition balance being Zn and impurities, that the interface adhesion strength between the galvannealed layer and the steel sheet is equal to or greater than 20MPa High-tensile alloyed hot-dip galvanized steel sheet.   The steel sheet has a chemical composition containing, in mass%, one or two of Ti: 0.01 to 0.5% and Nb: 0.01 to 0.5%, and Mo: 0 to 1.0% in place of part of Fe. The high-tensile alloyed hot-dip galvanized steel sheet according to claim 1.   The high-tensile galvannealed steel sheet according to claim 1 or 2, wherein the surface roughness Ra is 0.9 µm or less and the surface waviness Wca is 0.6 µm or less. After the steel sheet having the chemical composition according to claim 1 or 2 is immersed in a hot dip galvanizing bath having an Al concentration in the bath of 0.08 to 0.13 mass% to adhere the plating layer, the Fe content in the plating layer is A method for producing a high-tensile galvannealed steel sheet, characterized by performing an alloying treatment at a temperature of 470 to 530 ° C so as to be 11 to 15 mass%.   Rolling line load of 1.47 to 2.94 MN / m using a tempered rolling roll with surface roughness Ra of 3 μm or less and surface waviness Wca of 0.5 μm or less on the high-tensile alloyed hot-dip plated steel sheet after alloying treatment The method for producing a high-tensile galvannealed steel sheet according to claim 4, wherein temper rolling is performed.