JP6848939B2 - Hot-dip galvanized steel sheet manufacturing method and hot-dip galvanized hot-dip steel sheet, and hot-dip galvanized steel sheet manufacturing method and hot-dip galvanized steel sheet - Google Patents

Description

The present invention relates to a method for producing a hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet, and a method for producing a hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet for hot-dip galvanizing. More specifically, in the present invention, a high-strength hot-dip steel sheet containing Si and Mn is used for the hot-dip galvanized steel sheet as a base material, and the hot-dip galvanized steel sheet for hot-dip galvanizing is hot-dip galvanized. When this is done, the present invention relates to obtaining a hot-dip galvanized steel sheet having excellent surface appearance, plating adhesion and corrosion resistance.

Conventionally, mainly in the field of steel sheets for automobiles, surface-treated steel sheets in which high-strength steel sheets are provided with rustproof properties, particularly hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets having excellent rustproof properties have been used. As these high-strength steel sheets, hot-dip steel sheets with low manufacturing cost may be used, and hot-dip galvanizing may be performed for the purpose of improving corrosion resistance and the like.

Generally, as a hot-dip galvanized steel sheet, a thin steel sheet that is hot-rolled or cold-rolled on a slab is used as a base material, and the base material steel sheet is recrystallized and annealed in a continuous hot-dip galvanizing line (hereinafter referred to as CGL). After that, it is manufactured by hot-dip galvanizing. Further, the alloyed hot-dip galvanized steel sheet is manufactured by further alloying after hot-dip galvanizing.

The hot-dip galvanized steel sheet used for the above-mentioned applications has good surface appearance and plating adhesion, and corrosion resistance of a processed portion such as a plating treatment is extremely important. However, in the process of manufacturing a hot-dip galvanized steel sheet containing Si, there are many cases where there is a local scale residue on the surface of the steel sheet after pickling or a local smut formation due to per-pickling, and the scale residue and smut formation are not possible. Prone to cause defects such as plating or alloying failure. For example, non-plating is a phenomenon in which the surface of a steel sheet is partially exposed because the plating does not adhere to a part of the surface of the steel sheet during the hot-dip galvanizing process. Since the size of the non-plated portion is usually on the order of mm, its presence can be visually confirmed.

Several suggestions have been made to solve the above problems. For example, Patent Document 1 proposes a method for improving the adhesion of a plating film, which is subjected to a skin pass treatment having an elongation rate of 0.3% to 2.0%, a pickling / hot-dip galvanizing treatment, and then an alloying treatment. Further, Patent Document 2 describes a hot-rolled steel sheet as a base material as a measure for preventing plating defects such as alloying defects when manufacturing an alloyed hot-dip galvanized steel sheet containing Si, Mn, P, etc. in the base material. A method of performing shot blasting or brush grinding prior to pickling and descaling has been proposed.

Patent Document 3 proposes a method for improving plating adhesion by forming an internal oxide layer on a steel surface layer in a hot rolling process and descaling a rolled steel sheet by high-pressure water injection. ing.

In Patent Document 4, a hot steel sheet or an annealed cold-rolled steel sheet is subjected to a light reduction with a reduction ratio of 1.0% to 20%, and is subjected to a low-temperature heat treatment of holding the temperature at 520 ° C to 650 ° C for 5 seconds or longer. A method for producing an alloyed hot-dip galvanized steel sheet, which is immersed in a hot-dip galvanized bath containing Al: 0.01% to 0.18% in mass% and then alloyed, has been proposed.

Japanese Unexamined Patent Publication No. 2000-109964 Japanese Unexamined Patent Publication No. 6-158254 Japanese Unexamined Patent Publication No. 2013-108107 Japanese Unexamined Patent Publication No. 2002-317257

The methods proposed in Patent Documents 1 and 2 are effective in improving descalability. However, in these methods, the surface physical properties of the hot-rolled plate after descaling have not been investigated. As a result, the above method cannot solve the problem that a steel sheet having a sufficiently high level of plating adhesion cannot be obtained because the control of the surface state of the hot-rolled plate after descaling is insufficient.

Further, although the technique described in Patent Document 3 is effective for improving the plating adhesion, fine cracks originating from the internal oxide layer occur in the surface layer portion and the plating layer of the steel sheet during processing, and the processed portion. The problem of deterioration of corrosion resistance cannot be solved.

Further, the method proposed in Patent Document 4 has not obtained a steel sheet having a high strength currently required for a high-strength steel sheet and a sufficiently high level of plating adhesion that can cope with workability. However, the steel sheet has not reached a level that can necessarily contribute to the improvement of the corrosion resistance of the processed portion.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for producing a hot-dip galvanized steel sheet having excellent surface appearance, plating adhesion and post-processing corrosion resistance. Another object of the present invention is to provide a method for producing a hot-dip galvanized steel sheet for hot-dip galvanizing, for producing a hot-dip galvanized steel sheet having excellent surface appearance, plating adhesion and corrosion resistance after processing.

The present inventors have diligently studied to solve the above problems. As a result, it was found that a hot-dip galvanized steel sheet having excellent surface appearance, plating adhesion and post-processing corrosion resistance can be obtained by controlling the surface shape of the steel sheet and the residual stress amount of the surface layer of the steel sheet.

Further, it has been found that it is effective to perform the blasting treatment at a specific timing, that is, under a predetermined condition after the pickling step, in order to control the surface shape of the steel sheet and the residual stress amount of the surface layer of the steel sheet.

The term "excellent in surface appearance" means having a plated appearance in which no non-plating or uneven alloying is observed.

The present invention is based on the above findings, and the features of the present invention are as follows.

[1] In terms of mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0. A steel material containing 08% or less, S: 0.02% or less, Al: 0.001% or more and 0.20% or less, and the balance having a component composition of Fe and unavoidable impurities is hot-rolled and heated. The hot rolling process for making rolled plates and
A pickling step of performing a pickling treatment on the hot-rolled plate and
A blasting step of spraying grains having an average particle size of 50 μm or more and less than 300 μm onto the hot-rolled plate after the pickling step under a pressure condition of 0.3 MPa or more and 1.0 MPa or less, and a blasting step.
A hot-dip galvanizing step of hot-dip galvanizing a steel sheet after the blasting step,
A method for manufacturing a hot-dip galvanized steel sheet.

[2] The method for producing a hot-dip galvanized steel sheet according to [1], wherein the specific surface area ratio r of the hot-dip sheet after the blasting step is 2.5 or less.

[3] The method for producing a hot-dip galvanized steel sheet according to [1] or [2], wherein the arithmetic average roughness Ra of the hot-dip sheet after the blasting step is 1.5 μm or more and 6.0 μm or less.

[4] The melting according to any one of [1] to [3], wherein the average residual stress σ of the α-Fe (211) surface of the hot-dip galvanized sheet after the blasting step is −500 MPa or more and 30 MPa or less. Manufacturing method of hot-dip galvanized steel sheet.

[5] In the hot rolling step, after rough rolling the steel material, rolling is completed at a finish rolling temperature of 820 ° C. or higher, and the steel material is wound at 450 ° C. or higher and 650 ° C. or lower to prepare a hot-rolled sheet. The method for producing a hot-rolled hot-rolled steel sheet according to any one of [1] to [4].

[6] The method for producing a hot-dip galvanized steel sheet according to any one of [1] to [5], wherein the hot-dip sheet after the blasting step is subjected to a heat treatment step.

[7] In the heat treatment step, before the hot dip galvanizing step, the atmosphere is set to a hydrogen concentration of 2% by volume or more and 20% by volume or less and a dew point of -60 ° C. or more and -10 ° C. The method for producing a hot-dip galvanized steel sheet according to [6], wherein the hot-dip galvanized steel sheet is held for 10 seconds or more and 500 seconds or less in a temperature range of ° C. or lower and T-50 ° C. or higher and T ° C. or lower.

[8] The method for producing a hot-dip galvanized steel sheet according to any one of [1] to [7], which comprises an alloying step of further performing an alloying treatment after the hot-dip galvanizing step.

[9] The steel material has Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more and 0.500% or less, Mo: 0. Any one of [1] to [8] further containing one or more selected from the group consisting of 0.01% or more and 0.50% or less and W: 0.001% or more and 0.200% or less. The method for producing a hot-dip galvanized steel sheet according to item 1.

[10] A method for manufacturing a hot-dip steel sheet for hot-dip galvanizing used in hot-dip galvanizing.
By mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0.08% or less , S: 0.02% or less and Al: 0.001% or more and 0.20% or less, and the balance is Fe and the component composition of unavoidable impurities. The hot rolling process to make and
A pickling step of performing a pickling treatment on the hot-rolled plate and
A blasting step of spraying grains having an average particle size of 50 μm or more and less than 300 μm onto the hot-rolled plate after the pickling step under a pressure condition of 0.3 MPa or more and 1.0 MPa or less, and a blasting step.
A method for manufacturing a hot-dip galvanized steel sheet for hot-dip galvanizing.

[11] A hot-dip steel sheet for hot-dip galvanizing used in hot-dip galvanizing.
By mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0.08% or less , S: 0.02% or less and Al: 0.001% or more and 0.20% or less, and the balance has a component composition of Fe and unavoidable impurities.
The surface of the base steel sheet for hot dip galvanizing has a specific surface area ratio r of 1.1 or more and 2.0 or less, an arithmetic average roughness Ra of 6.0 μm or less, and an average of α-Fe (211) surfaces. A hot-dip galvanized steel sheet having a residual stress σ of −250 MPa or more and 100 MPa or less.

[12] As the component composition, Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more and 0.500% or less in mass%. , Mo: 0.01% or more and 0.50% or less and W: 0.001% or more and 0.200% or less, further containing one or more selected from the group, according to [11]. Hot-dip steel sheet for hot-dip galvanizing.

[13] The hot-dip galvanized hot-dip steel sheet provided with a plating layer on the hot-dip galvanized steel sheet for hot-dip galvanizing according to [11] or [12].

According to the present invention, a hot-dip galvanized hot-dip steel sheet having excellent surface appearance, plating adhesion, and corrosion resistance after processing can be obtained.

Since the hot-dip galvanized steel sheet for hot-dip galvanizing obtained by the present invention is a base steel sheet of the hot-dip galvanized steel sheet, it imparts excellent surface appearance, plating adhesion and post-processing corrosion resistance to the hot-dip galvanized steel sheet. can do.

Hereinafter, the reasons for limiting the steel composition of the hot-dip galvanized steel sheet of the present invention will be described, and then each step of the manufacturing method and the hot-dip galvanized steel sheet obtained by the manufacturing method will be specifically described. In the following description, the unit of the content of each element in the steel component composition and the unit of the content of each element in the plating component composition are both "mass%", and are simply "%" unless otherwise specified. Shown. The unit of hydrogen concentration is "volume%".

"Steel composition"
C: 0.02% or more and 0.30% or less The smaller the amount of C, the better the moldability of the base metal. However, by containing C, the strength of the steel sheet can be increased at low cost. Therefore, the C content is 0.02% or more, preferably 0.04% or more. On the other hand, if C is excessively contained, the toughness or weldability of the steel sheet is lowered, so the C content is 0.30% or less, preferably 0.20% or less. As for the preferable range of C content, these upper limit values and lower limit values can be appropriately combined.

Si: 0.01% or more and 1.0% or less Si is effective as a solid solution strengthening element, and 0.01% or more is required to increase the strength of the steel sheet, preferably 0.1% or more. is there. However, if Si is excessively contained, the wettability at the time of hot-dip galvanizing is impaired and the alloying reactivity is impaired, so that the alloying is difficult to adjust and the plating appearance or the plating adhesion is deteriorated. From the above, the Si content is 1.0% or less, preferably 0.5% or less. Further, in the preferable range of the Si content, these upper limit values and lower limit values can be appropriately combined. For example, the Si content is 0.01% or more and 0.5% or less.

Mn: 0.2% or more and 3.0% or less Mn is an element useful for increasing the strength of steel. In order to obtain this effect, it is necessary to contain Mn in an amount of 0.2% or more, preferably 1.0% or more. However, if Mn is excessively contained, the wettability at the time of hot-dip galvanizing is impaired and the alloying reactivity is impaired, so that it becomes difficult to adjust the alloying and the plating appearance or the plating adhesion is deteriorated. From the above, the Mn content is 3.0% or less, preferably 2.6% or less. Further, in the preferable range of the Mn content, these upper limit values and lower limit values can be appropriately combined. For example, the Mn content is 0.2% or more and 3.0% or less, preferably 1.0% or more and 2.6% or less.

P: 0.08% or less If P is contained in excess of 0.08%, the weldability deteriorates and the surface quality deteriorates. Further, during the alloying treatment, the desired degree of alloying cannot be obtained unless the alloying treatment temperature is raised. On the other hand, when the alloying treatment temperature is raised, the ductility of the base steel sheet deteriorates, and at the same time, the adhesion of the alloyed hot-dip galvanized layer deteriorates. Therefore, the P content is 0.08% or less, preferably 0.02% or less. The lower limit of the P content is not particularly specified, but if the P content is less than 0.001%, the production efficiency is lowered and the dephosphorization cost is increased in the manufacturing process. Therefore, the P content is preferably 0.001% or more, more preferably 0.003% or more. Further, in the preferable range of the P content, these upper limit values and lower limit values can be appropriately combined.

S: 0.02% or less When S segregates at the grain boundaries or a large amount of MnS is generated, the toughness decreases, so the S content needs to be 0.02% or less, preferably 0.005%. It is as follows. The lower limit of the S content is not particularly limited and may be about impurities. For example, if the S content is less than 0.0001%, the production efficiency is lowered and the cost is increased in the manufacturing process. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0005% or more. Further, in the preferable range of the S content, these upper limit values and lower limit values can be appropriately combined.

Al: 0.001% or more and 0.20% or less Al is added for the purpose of deoxidizing molten steel, but if the content is less than 0.001%, the purpose is not achieved. Therefore, the Al content is 0.001% or more, preferably 0.00.55% or more. On the other hand, when the Al content exceeds 0.20%, a large amount of inclusions are generated, which causes a defect in the steel sheet. Therefore, the Al content is 0.20% or less, preferably 0.08% or less. Further, in the preferable range of the Al content, these upper limit values and lower limit values can be appropriately combined.

The rest other than the above is Fe and unavoidable impurities. The above are the basic components of the base steel sheet according to the present invention. In addition to the above basic components, the component composition of the base steel sheet may further contain the following components, if necessary.

In the present invention, Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more and 0. Steel composition of one or more selected from the group consisting of 500% or less, Mo: 0.01% or more and 0.50% or less, and W: 0.001% or more and 0.200% or less. Can be further contained as.

Ti, Nb, V, Mo and W are elements necessary for precipitating precipitates (particularly carbides) in the base steel sheet, and one or more selected from the group consisting of these elements. It is preferable to add it. Usually, these elements are often contained in the base steel sheet in the form of precipitates containing these elements.

Among these elements, Ti has a particularly high precipitation strengthening ability and is an effective element from the viewpoint of cost. However, if the Ti content is less than 0.01%, the amount of precipitates in the base steel sheet required to contain precipitates (particularly carbides) in the alloyed hot-dip galvanized layer may be insufficient. On the other hand, when the Ti content exceeds 0.40%, the effect is saturated and the cost is increased. Therefore, when Ti is contained, the Ti content is 0.01% or more and 0.40% or less.

The reason for containing any one or more of Nb, V, Mo and W as a steel composition component is the same as the reason for the upper and lower limits of the Ti content range, as well as the Nb content. Is 0.001% or more and 0.200% or less, V content is 0.001% or more and 0.500% or less, Mo content is 0.01% or more and 0.50% or less, and W content is 0.001%. It is preferably 0.200% or more and 0.200% or less.

The reason for limiting the steel composition of the hot-dip galvanized steel sheet according to the present invention is the same as that of the hot-dip galvanized steel sheet. Therefore, the content of the steel composition can be applied to the method for producing a hot-dip galvanized steel sheet for hot-dip galvanizing.

Next, a method for manufacturing a hot-dip galvanized steel sheet according to the present invention will be described.

In the method for producing a hot-dip galvanized steel sheet according to the present invention, a hot-rolled sheet is produced by a hot-rolling step on a steel slab having the above-mentioned composition, and then the hot-rolled sheet is pickled to obtain a scale. After the pickling step of removing, a blasting step of blasting with grains having an average particle size of 50 μm or more and less than 300 μm (for example, a propellant) under a pressure condition of 0.3 MPa or more and 1.0 MPa or less is performed, and then a hot-dip galvanizing process is performed. Has a hot-dip galvanizing process.

By the above manufacturing method, a steel sheet surface having a surface shape showing a predetermined specific surface area ratio or a predetermined arithmetic mean roughness, or a steel sheet surface layer having a residual stress amount within a predetermined range is formed, so that the surface appearance is improved. A hot-dip galvanized hot-rolled steel sheet having excellent plating adhesion and post-processing corrosion resistance can be obtained. Hereinafter, each step will be described.

"Hot rolling process"
In the hot rolling step according to the present invention, a steel material having the above-mentioned composition (for example, steel slab) is heated in a temperature range of 1100 ° C. or higher and 1300 ° C. or lower, and then hot-rolled by hot rolling. It is preferably a step of producing a plate.

Further, in the hot rolling step according to the present invention, after rough rolling the heated steel material, rolling is completed at a finish rolling temperature of 820 ° C. or higher, and the rolled steel material is wound at 450 ° C. or higher and 650 ° C. or lower and hot-rolled. It is preferable to obtain a plate.

(Steel material heating temperature)
In order to disperse fine precipitation of Ti or Nb or the like, it is necessary to temporarily dissolve Ti or Nb or the like in the steel sheet before hot rolling. Therefore, the heating temperature (slab heating temperature) before hot rolling is preferably 1100 ° C. or higher. On the other hand, if the heating temperature before hot rolling exceeds 1300 ° C., internal oxidation on the surface layer of the steel sheet is promoted, and the surface texture may be deteriorated. Therefore, the slab heating temperature before hot rolling is preferably 1100 ° C. or higher and 1300 ° C. or lower.

(Finish rolling temperature)
The finish rolling temperature is preferably 820 ° C. or higher in order to reduce the deformation resistance during hot rolling and facilitate the operation. On the other hand, if the finish rolling is performed at a temperature exceeding 1000 ° C., scale defects are likely to occur, and the surface texture of the steel sheet obtained in the subsequent process may be deteriorated. Therefore, the finish rolling temperature is preferably 820 ° C. or higher, more preferably 820 ° C. or higher and 1000 ° C. or lower.

(Taking temperature)
The steel sheet according to the present invention contains easily oxidizing elements such as Si, Mn or Ti. Therefore, in order to suppress excessive oxidation of the steel sheet and ensure good surface texture, the winding temperature is preferably 650 ° C. or lower. On the other hand, when the winding temperature is less than 450 ° C., poor coil properties due to uneven cooling are likely to occur, which may impair productivity. Therefore, the hot winding winding temperature is preferably 450 ° C. or higher and 650 ° C. or lower.

"Pickling process"
The pickling step according to the present invention is a step of performing a pickling treatment on the hot-rolled plate obtained by the hot rolling step.

The hot-rolled plate obtained by the hot rolling step is descaled by pickling and then blasted. The pickling treatment is not particularly limited, and a conventional method may be used. For example, the acid that can be used in the pickling treatment in this step may be an easy-to-handle acid that is generally used in pickling for the purpose of descaling a hot-rolled plate. For example, an acid such as hydrochloric acid, sulfuric acid or nitric acid may be used as the pickling solution, and if necessary, an inhibitor for suppressing per-pickling may be added to the pickling solution.

Further, if necessary, light rolling of 5% or less may be performed before the pickling step. Since the descalability is improved by this light rolling, the light rolling leads to the improvement of the surface texture of the steel sheet obtained after the blasting step. On the other hand, in the production method according to the present invention, it is preferable not to perform rolling at a reduction rate of 1% or more and 10% or less after the pickling step. If the hot-rolled plate is rolled with a reduction ratio in the above range after the pickling step, a new problem arises in which the arithmetic mean roughness becomes too small.

"Blasting process"
The blasting step according to the present invention is a step of blasting the pickled hot-rolled plate with grains having an average particle size of 50 μm or more and less than 300 μm under a pressure condition of 0.3 MPa or more and 1.0 MPa or less. By this step, the surface shape of the steel sheet or the residual stress amount of the surface layer of the steel sheet can be controlled. More specifically, the blasting step according to the present invention is not aimed at descaling, but is aimed at controlling the surface shape of the steel sheet and the amount of residual stress on the surface layer of the steel sheet. Therefore, it is essential that the blasting step according to the present invention be performed after the pickling step. That is, in the present invention, it is important to apply a desired surface shape and a desired residual stress amount to the surface layer of the hot-rolled plate before plating. Therefore, when pickling is performed after the blasting process, the surface shape is adjusted. Disappears by pickling. As a result, a hot-dip galvanized hot-dip steel sheet having excellent surface appearance, plating adhesion, and corrosion resistance after processing cannot be obtained.
Further, the blasting step according to the present invention is performed after the pickling step and before the hot-dip galvanizing step described later. When the heat treatment step described later is performed, it is more preferable that the blasting step is performed after the pickling step and before the heat treatment step described later.

As the injection method in the blasting according to the present invention, among the generally mentioned pneumatic (including wet and dry) or mechanical injection methods, the pneumatic method is adopted from the viewpoint of omitting the drying process during continuous operation. It is preferable to do so. In the pneumatic blasting process of the present invention, the surface of the hot-rolled sheet is physically changed by spraying particles (so-called injection material) onto the surface of the pickled hot-rolled sheet by compressed air. It is possible to control the average roughness, control the specific surface area of the steel sheet surface, or apply residual stress to the steel sheet.

Examples of the blasting process according to the present invention include sand blasting process, shot blasting process, and grit blasting process, and shot blasting process is preferable.

(Grains with an average particle size of 50 μm or more and less than 300 μm)
The particles in this blasting process generally refer to particles called a jetting material, a projecting material, an abrasive, or the like, which are sprayed onto a work piece. The grain is not particularly limited as long as it can give either a residual stress value in a predetermined range, an arithmetic average roughness in a predetermined range, or a specific surface area ratio in a predetermined range to the pickled hot-rolled plate. .. For example, cut wire, cast steel particles (steel shot, steel grid), metallic fine particles (iron, copper, lead, aluminum, nickel) or non-metallic fine particles (glass sand, alumina, silicon carbide, etc.) are used as the particles. Be done. In particular, for the grains according to the present invention, it is preferable to use a jetting material that can easily control the specific surface area of the pickled hot-rolled plate surface. A preferable example of the particles according to the present invention is a steel sheet from the viewpoint of the influence of the residual particles adhering on the pickled hot-rolled plate on the subsequent process or the relationship between the hardness of the particles and the hardness of the injection target for blasting. It is preferable to use the same metal material as above, for example, iron is preferable.

The hardness of the grains according to the present invention is preferably 150 or more in Vickers hardness Hv. If the hardness of the grains is less than 150 in Vickers hardness, the hardness of the grains is insufficient with respect to the hardness of the pickled hot-rolled plate, and as a result, the residual stress may be insufficiently applied. The Vickers hardness of the grains is determined by the Micro Vickers hardness test.

The blasting step according to the present invention is carried out after the hot rolling step and the pickling step in order to improve the plating property of the steel sheet surface. At this time, by using grains having an average particle size of 50 μm or more and less than 300 μm, the surface texture of the hot-rolled plate can be efficiently corrected. When the average particle size of the grains is less than 50 μm, a large number of fine irregularities are introduced on the surface and the specific surface area is increased, so that the effect of inhibiting plating by Si and Mn oxide becomes remarkable, and the plating property is deteriorated. On the other hand, as the average particle size of the grains increases, the residual stress introduced into the hot-rolled plate also increases, and the specific surface area decreases as the minute irregularities on the surface of the hot-rolled plate decrease. However, when the average particle size of the grains is 300 μm or more, the arithmetic average roughness Ra, which is a macro unevenness on the surface, becomes too large, and excessive residual stress is introduced into the hot-rolled plate. As a result, uneven plating adhesion or uneven alloying is induced, which causes poor plating appearance or deterioration of powdering resistance and corrosion resistance after processing, and the surface layer structure tends to be roughened during annealing, leading to a decrease in strength. .. Therefore, the upper limit of the average particle size of the grains according to the present invention is preferably less than 300 μm and preferably 200 μm. The lower limit of the average particle size of the grains is 50 μm, preferably 100 μm. These upper limit values and lower limit values can be combined as appropriate.

The average particle size of the particles in the present invention refers to the volume average particle size of the primary particles of the particles. A known method can be adopted for the measurement of the volume average particle diameter, and for example, it can be measured by using an electron microscope (SEM, TEM), a dynamic light scattering method, a laser diffraction method, an image imaging method, a Coulter method, or the like. it can. In the present invention, the volume average particle size of the primary particles of the particles is measured by the circular (sphere) approximation of the particles by the image imaging method.

(Blasting pressure)
The pressure condition at the time of blasting according to the present invention is 0.3 MPa or more and 1.0 MPa or less. The pressure referred to here corresponds to the compressed air pressure injected together with the particles (for example, the injection material), and is measured by a pressure gauge installed near the nozzle. At this time, the blasting method is not limited and may be dry or wet. As the pressure (air pressure) increases, the residual stress introduced by the grains increases, and if the average particle size of the grains is within the above-mentioned preferable range, the fine irregularities on the surface of the pickled hot-rolled plate decrease, and the specific surface area decreases. Decreases. At this time, if the air pressure is 0.3 MPa or more, the effect of introducing residual stress and reducing the specific surface area is sufficient, and the plating property of the finally obtained base steel sheet surface is improved. When the air pressure is 1.0 MPa or less, the surface texture of the pickled hot-rolled plate or the residual stress amount on the surface layer of the steel plate is controlled within a predetermined range.

On the other hand, if the injection pressure is less than 0.3 MPa, the residual stress may be insufficiently applied. If the injection pressure exceeds 1.0 MPa, excessive residual stress will be introduced into the pickled hot-rolled plate. As a result, uneven plating adhesion or uneven alloying is induced, which causes poor plating appearance or deterioration of powdering resistance and post-processing corrosion resistance. Furthermore, the surface layer structure tends to become coarse during annealing, which leads to a decrease in strength. Therefore, the upper limit of the pressure when spraying the particles according to the present invention is 1.0 MPa, preferably 0.8 MPa. The lower limit of the pressure is 0.3 MPa, preferably 0.5 MPa.

(Blasting conditions)
Known conditions can be adopted as the injection conditions other than the air pressure according to the present invention. For example, Q: particle injection flow rate (kg / min), t: particle injection time (sec), W: nozzle diameter (m). Yes, it is preferable to carry out the injection within a range satisfying the following formula (1) in combination with the grain size D (m) and ρ: grain density (kg / m ^{3) of the grains.}
[Number 1]
5.0 × 10 ⁴ ≦ E = Q × P × t / (D × π × W × ρ × 60) ≦ 1.0 × 10 ⁶ equation (1)
(In the above equation (1), P represents the injection pressure (for example, the above-mentioned air pressure) (Pa), E represents the kinetic energy (J / m ² ) received by the steel sheet, and π represents the pi (= 3.14). ).)
Each parameter "Q: grain injection flow rate (kg / min), t: grain injection time (sec), W: nozzle diameter" in the above formula (1) so that the kinetic energy E received by the steel plate is within the above range. (M), grain size D (m), ρ: grain density (kg / m ³ ) and P: injection pressure (Pa) ”can be appropriately set. For example, as an example in which the kinetic energy E received by the steel sheet is within the above range, there is a condition that each of the above parameters is within the following range.
The P (injection pressure (Pa)) is preferably 0.3 MPa or more and 1.0 MPa or less. The Q (injection flow rate of grains (kg / min)) is preferably 0.05 kg / min or more and 1 kg / min or less. The t (grain injection time (sec)) is preferably 0.5 sec or more and 12 sec or less. The W (nozzle diameter (m)) is preferably 0.005 m or more and 0.1 m or less. The D (grain size (m)) is ^{preferably 50 × 10-6} m or more and ^{less than 300 × 10-6} m. The [rho (particle density (kg ^{/ m} 3)) is, 4200kg / ^{m 3} or more 8700kg / ^{m 3} or less.

By the blasting step of the present invention, the specific surface area ratio r of the hot-rolled plate after the blasting step is preferably 2.5 or less.

If the specific surface area ratio of the surface of the hot-rolled plate after the blasting step is high, the amount of Si and Mn oxides formed after annealing in the post-step step increases, so that the plating repellent becomes remarkable and the plating wettability is greatly impaired. Therefore, if the specific surface area ratio of the surface exceeds 2.5, the powdering resistance and the corrosion resistance after processing are significantly deteriorated. The upper limit of the specific surface area ratio r is preferably 2.2, more preferably 2.0. The lower the specific surface area ratio of the surface of the hot-rolled plate after the blasting step, the more preferable. For example, the lower limit of the specific surface area ratio r is preferably 1.4, more preferably 1.2.

Here, the specific surface area ratio is a value corresponding to the ratio (actual surface area / area) of the actual surface area considering the minute irregularities on the surface of the steel sheet and the area of the two-dimensional plane not considering the irregularities on the surface of the steel sheet. The method for measuring the specific surface area ratio is not particularly limited, and can be obtained using, for example, a laser microscope. In addition, evaluation by three-dimensional SEM observation or cross-section TEM observation can be considered, but a laser microscope is considered to be the most suitable because it can evaluate fine irregularities on the order of nm in a wide range. Further, in the present specification, using a VK-X250 of a laser microscope (manufactured by Keyence Corporation), five arbitrary fields of view are selected for each steel plate, and the average value thereof is defined as the specific surface area ratio.

According to the blasting step of the present invention, the arithmetic average roughness Ra of the hot-rolled plate after the blasting step is preferably 1.5 μm or more and 6.0 μm or less.

If the arithmetic average roughness Ra becomes too large, the unevenness of the plating adhesion amount becomes large, and the appearance of the plated steel sheet deteriorates. Therefore, the Ra is preferably 6.0 μm or less, more preferably 4.5 μm or less, and further preferably 3.0 μm or less. On the other hand, if Ra becomes too small, the anchoring effect is lost due to the smoothing of the plating / base iron interface. As a result, crack growth during steel sheet processing is not suppressed, and powdering property deteriorates. Therefore, the arithmetic mean roughness Ra is preferably 1.5 μm or more, and more preferably 2.0 μm or more.

The arithmetic mean roughness Ra can be measured by the method specified in JISB0601 (2013), the stylus method, or a known optical method. In the present invention, the stylus method is adopted.

The average residual stress σ of the α-Fe (211) plane of the hot-rolled plate after the blasting step of the present invention is preferably −500 MPa or more and -30 MPa or less.

In the present invention, the Fe—Al reactivity and the Fe—Zn alloying reactivity are improved by introducing the compressive residual stress on the surface of the hot-rolled plate as the base material. Further, when a compressive residual stress is introduced on the surface, the reduction of the oxide film formed after pickling is promoted. In order to obtain such an effect of improving the plating characteristics, it is preferable that the residual stress is in the range of −500 MPa or more and −30 MPa or less. The residual stress can be introduced in this blasting process. If the residual stress exceeds −30 MPa, the introduction of the compressive residual stress becomes insufficient, and the effect of improving the plating characteristics is difficult to be exhibited. On the other hand, if the residual stress is less than −500 MPa, the effect of improving Fe—Zn reactivity becomes excessive, it becomes difficult to suppress a uniform alloying reaction, and plating defects such as uneven alloying are caused. Further, when the residual stress is less than −500 MPa, a large amount of dislocations are introduced into the surface layer of the steel sheet, so that the surface layer structure tends to be roughened during the heat treatment before the plating treatment, which leads to a decrease in strength. Therefore, the average residual stress σ of the α-Fe (211) surface on the surface of the hot-rolled plate after the blasting step is preferably −500 MPa or more and −30 MPa or less, and more preferably −250 MPa or more and −30 MPa or less.

In addition, the parallel tilt method was used to measure the average residual stress σ, and the residual stress (σ) of the steel sheet was derived from the average of 5 analysis results from any location and direction using an X-ray diffractometer. .. From the relationship between the displacement value (ΔS) of the α-Fe (211) plane peak intensity (S) and the inclination angle ψ, the gradient (R) is calculated according to the equation (2) and combined with the Young's modulus (E) of the steel material. The residual stress (σ) can be obtained by the equation (3) of.

[Number 2]
R = ΔS / (sin ² ψ) (2)
σ = R × E (3)
The measurement of the average residual stress σ of the α-Fe (211) plane of the present invention is not particularly limited and can be measured by a known method. The method described in the X-ray material strength section committee of the Society is adopted.

From the above, in the present invention, since the shape of the steel sheet surface and the amount of residual stress are controlled by the blasting step after the pickling step, in addition to suppressing the reaction unevenness during the hot-dip galvanizing process, the processed portion It is characterized by preventing local deterioration of corrosion resistance.

"Heat treatment process"
The heat treatment step according to the present invention is a step of heat-treating the blasted hot-rolled plate under temperature conditions equal to or higher than the temperature required for the hot-dip plating step of the subsequent step (for example, the plating bath temperature). When the heat treatment step is performed for the purpose of reducing the natural oxide film formed on the surface of the hot-rolled plate, it is preferable to perform the heat treatment on the blasted hot-rolled plate under a temperature condition of at least 600 ° C. Further, the heat treatment step according to the present invention is preferably performed after the blasting step and before the hot-dip galvanizing step described later.

In the heat treatment step according to the present invention, the atmosphere in the furnace is set to a hydrogen concentration of 2% by volume or more and 20% by volume or less, a dew point of -60 ° C or more and -10 ° C or less, and a steel sheet reaching temperature (T) of 600 ° C or more and 750 ° C or less. It is preferable to apply a heat treatment for holding the blasted hot-rolled sheet for 10 seconds or more and 500 seconds or less in a temperature range of T-50 ° C. or higher and T ° C. or lower.

As for the temperature condition of the heat treatment before the hot dip galvanizing step, it is preferable that the temperature reached by the steel sheet is 600 ° C. or higher and 750 ° C. or lower. If the temperature at which the steel sheet is reached is less than 600 ° C., the oxide film after pickling is not completely reduced, and the desired plating characteristics cannot be obtained. Further, when the temperature reached by the steel sheet exceeds 750 ° C., Si, Mn and the like may be surface-dense and the plating property may be deteriorated.

The atmosphere in the furnace according to the present invention preferably has a hydrogen concentration of 2% by volume or more and 30% by volume or less and a dew point of −60 ° C. or more and −10 ° C. or less. The atmosphere in the furnace may be reducible, and is preferably an atmosphere in which the dew point is -60 ° C. or higher and -10 ° C. or lower, the hydrogen concentration is 2% by volume or more and 30% by volume or less, and the balance is an inert gas. When the dew point exceeds −10 ° C., the morphology of Si and Mn oxides formed on the surface of the steel sheet tends to be film-like. Then, the film-like Si and Mn oxides cause plating repelling, and as a result, the plating wettability is greatly impaired. On the other hand, a dew point of less than -60 ° C is industrially difficult to realize.

When the hydrogen concentration is less than 2% by volume, the reducing property is weak. On the other hand, if the hydrogen concentration exceeds 30% by volume, the reducing ability is saturated and a large amount of hydrogen is introduced into the steel, which may lead to deterioration of delayed fracture resistance and drilling workability. Therefore, the upper limit of the hydrogen concentration is 30% by volume.

The method for producing a hot-dip galvanized steel sheet according to the present invention is the same as the method for producing a hot-dip galvanized steel sheet except that the hot-dip galvanizing step is not performed. Therefore, the contents of the above steps other than the hot-dip galvanizing step can be applied to the method for manufacturing a hot-dip galvanized steel sheet for hot-dip galvanizing treatment.

"Hot-dip galvanizing process"
The hot-dip galvanizing step according to the present invention is a step of hot-dip galvanizing a steel sheet after the blasting step. The hot-dip galvanizing step is preferably a step of plating the heat-treated hot-dip steel sheet using a hot-dip galvanizing bath having a bath temperature of 440 ° C. or higher and 480 ° C. or lower and containing Al.

The hot-dip galvanizing treatment according to the present invention is carried out using the hot-dip galvanizing bath after heat-treating (for example, reduction annealing) the steel sheet on a continuous hot-dip galvanizing line.

The composition of the hot-dip plating bath according to the present invention is not particularly limited, and a known plating bath such as a zinc plating bath, an aluminum plating bath or a tin plating bath can be used depending on the purpose or application. For example, when the composition of the hot-dip galvanizing bath is used for the hot-dip galvanizing treatment, the composition of the hot-dip galvanizing bath is in the range of 0.01% or more and 1.0% or less in Al concentration, and the balance is Zn and unavoidable. It is preferable to use a target impurity. When the Al concentration is less than 0.01%, a Zn—Fe alloying reaction occurs during the plating process, and a brittle alloy layer develops at the interface between the plating and the steel sheet (base material). Then, the developed alloy layer causes deterioration of plating adhesion. When the Al concentration exceeds 1.0%, the growth of the Fe—Al alloy layer becomes remarkable, and the alloy layer impairs the plating adhesion. The temperature of the hot-dip galvanizing bath is not particularly limited, and may be 440 ° C. or higher and 480 ° C. or lower, which is the normal operating range.

In particular, when the effect of suppressing the Zn—Fe alloying reaction is emphasized, the hot-dip galvanizing bath indispensably contains Al and Zn, and may further contain Mg if necessary. That is, the component composition of the hot-dip galvanizing bath contains, in mass%, Al: 0.01% or more and 1.0% or less, and if necessary, Mg: 0.5% or more and 10.0% or less. However, it is preferable that the balance shows the component composition of Zn and unavoidable impurities. Further, from the viewpoint of exerting the effect of suppressing the Zn—Fe alloying reaction, the hot-dip galvanizing bath further contains Cr, Pb, Sb, Sr, Si, Sn, Mn, Ni, Co, Zr and It is preferable that one or more selected from the group consisting of Bi is contained in a total of 0.01 to 0.5%.

Further, the amount of plating adhered in the hot-dip galvanizing step according to the present invention is preferably 20 g / m ² or more and 120 g / m ² or less per side. If the amount of adhesion is ^{less than 20 g / m 2} , the desired corrosion resistance cannot be ensured. On the other hand, if the adhesion amount ^{exceeds 120 g / m 2} , it is difficult to suppress the adhesion amount unevenness, and as a result, the appearance of the plated steel sheet may be deteriorated. For example, in the case of the plating treatment using the plating bath, the heat-treated or annealed steel sheet is immersed in the plating bath to perform a hot-dip plating treatment, and then the plated steel plate is pulled up from the plating bath and then gas-wiping treatment. The amount of plating adhesion can be adjusted within the above range.

"Alloying process"
In the alloying step according to the present invention, it is preferable to carry out a conventional heat alloying treatment. The conditions for the heat alloying treatment are not particularly limited, but for example, the alloying treatment temperature is preferably 550 ° C. or lower, and the alloying treatment time is preferably 10 seconds or more and 60 seconds or less.

When the alloying treatment temperature exceeds 550 ° C., the formation of a hard and brittle Γ phase at the interface between the steel sheet (base material) and the plating film during the alloying treatment increases remarkably, resulting in increased powdering resistance. to degrade. Therefore, the alloying treatment temperature is preferably 550 ° C. or lower, and more preferably 530 ° C. or lower. The lower limit of the alloying treatment temperature is preferably 480 ° C. The alloying treatment time is preferably 10 seconds or more and 60 seconds or less, and more preferably 40 seconds or less, from the viewpoint of cost or control problems.

The heating method in the alloying treatment is not particularly limited, and any known method such as radiant heating, energization heating, and high frequency induction heating may be used. After the alloying treatment, the steel sheet after the alloying treatment is cooled to room temperature. The post-treatment after the hot-dip galvanizing process is not particularly limited, and even if the material is adjusted by temper rolling, the flat shape is adjusted by leveling, or if necessary, post-treatment such as chromate treatment is performed. Good

One of the preferred forms of the method for producing a hot-dip galvanized steel sheet according to the present invention is to prepare a hot-rolled sheet from a steel slab having the above-mentioned composition by hot-rolling, and then pickle the hot-rolled sheet. Then, using a propellant having an average particle size of 50 μm or more and less than 300 μm, a hot-rolled sheet pickled at an air pressure of 0.3 MPa or more and 1.0 MPa or less is blasted, and further, a furnace before hot-dip galvanizing treatment is performed. A hot-dip galvanizing treatment is performed after performing a heat treatment in which the internal atmosphere has a hydrogen concentration of 2% by volume or more and 30% by volume or less, a dew point of -60 ° C. or more and -10 ° C. or less, and a steel sheet reaching temperature of 600 ° C. or more and 750 ° C. or less. Further, if necessary, after the hot-dip galvanizing treatment, the obtained steel sheet may be further alloyed. The method for producing a hot-dip galvanized steel sheet according to the present invention is preferably performed in the order of a hot rolling step, a pickling step, a blasting step, a heat treatment step, and a hot-dip galvanizing step.

The hot-dip galvanized steel sheet according to the present invention can be obtained through the steps described above or the preferred production method described above. That is, the hot-dip galvanized steel sheet of the present invention has C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more 3 in mass%. A mother containing 0.0% or less, P: 0.08% or less, S: 0.02% or less, Al: 0.001% or more and 0.20% or less, and the balance having a component composition of Fe and unavoidable impurities. A steel plate and a zinc-based plating layer having a plating adhesion amount of 20 g / m ² or more and 120 g / m ² or less per surface on the surface of the base steel plate are provided, and the specific surface area ratio r of the surface of the base steel plate is 2. It is less than or equal to 0.0.
The component composition of the hot-dip galvanized steel sheet is Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more in mass%. One or more of 0.500% or less, Mo: 0.01% or more and 0.50% or less, and W: 0.001% or more and 0.200% or less may be further contained.

Another object of the present invention is to provide a hot-dip galvanized hot-dip steel sheet having excellent surface appearance, plating adhesion, and corrosion resistance after processing. The hot-dip galvanized steel sheet according to the present invention has high corrosion resistance even after processing because the shape of the surface of the base steel sheet or the amount of residual stress is controlled within a specific range. The high corrosion resistance after processing is effective for manufacturing a member having a complicated molding, and the industrial effect obtained by the present invention is great.

Subsequently, the shapes of the zinc-based plating layer in the hot-dip galvanized steel sheet according to the present invention and the base steel sheet as the base of the hot-dip galvanized steel sheet will be described.

The upper limit of the specific surface area ratio r on the surface of the base steel sheet is preferably 2.0, more preferably 1.6. On the other hand, the lower limit of the specific surface area ratio r is preferably 1.1, preferably 1.2, and more preferably 1.6. By controlling the specific surface area ratio of the surface of the base steel sheet within the above range, the amounts of Si and Mn oxides are suppressed, so that the plating wettability, powdering resistance, and post-processing corrosion resistance are improved.

The zinc-based plating layer is preferably an Al-containing zinc-based plating layer, and the amount of plating adhesion per side is 20 g / m ² or more and 120 g / m ² or less. If the amount of plating adhered is ^{less than 20 g / m 2} , it becomes difficult to secure corrosion resistance. On the other hand, if the amount of plating adhered exceeds 120 g / m ² , the plating peeling resistance deteriorates.

The average residual stress σ of the α-Fe (211) surface of the surface of the base steel sheet according to the present invention is preferably −250 MPa or more and 100 MPa or less, and more preferably −200 MPa or more and 0 MPa or less. When the compressive residual stress within the above range is introduced into the surface layer of the base metal steel plate which is the base material, the Fe-Al reactivity and Fe-Zn reactivity are improved, so that the Fe-Al alloy layer and Fe-Zn are improved. The alloy layer can be maintained in an appropriate amount, and the plating adhesion, powdering resistance and post-processing corrosion resistance are improved.

The arithmetic mean roughness Ra of the surface of the base steel sheet is preferably 1.5 μm or more and 6.0 μm or less, and more preferably 2.0 μm or more and 4.5 μm or less. By controlling the arithmetic mean roughness Ra of the surface of the base steel sheet within the above range, the Fe—Al alloy layer and the Fe—Zn alloy layer can be appropriately maintained, so that the plating adhesion and powdering resistance are improved. ..

The method for producing a hot-dip galvanized steel sheet for hot-dip galvanizing according to the present invention is the same as the method for producing a hot-dip galvanized steel sheet except that the hot-dip galvanizing step is not performed. Therefore, it is preferable that the method for producing the hot-rolled steel sheet for hot-dip galvanizing is also performed in the order of the hot rolling step, the pickling step, the blasting step, and the heat treatment step applied if necessary.

The hot-dip galvanized steel sheet according to the present invention has a structure in which a plating layer is provided on the hot-dip galvanized steel sheet for hot-dip galvanizing treatment. The surface texture (Ra, specific surface area ratio) and residual stress of the hot-dip galvanized steel sheet for hot-dip galvanizing obtained by the method for manufacturing the hot-dip galvanized steel sheet, and the surface texture of the base steel sheet of the hot-dip galvanized steel sheet. Comparing with the residual stress, it was found that the surface texture and the residual stress before and after the hot-dip galvanizing treatment did not change substantially. On the other hand, when the surface texture and residual stress of the steel sheet were compared before and after the heat treatment step (annealing), it was confirmed that the specific surface area ratio and the residual stress changed. Therefore, the description of the base steel sheet of the hot-dip galvanized steel sheet can be used as the specific surface area ratio and the residual stress of the hot-dip galvanized steel sheet immediately before the plating step. For example, the specific surface area ratio and the residual stress of the hot-dip galvanized steel sheet are considered to be 1.1 or more and 2.0 or less and −250 MPa or more and 100 MPa or less, respectively. Further, the arithmetic mean roughness of the base steel sheet after the hot-dip galvanizing treatment is considered to be approximately the same as the arithmetic mean roughness immediately after the blasting process. Therefore, the arithmetic mean roughness Ra of the hot-dip galvanized steel sheet immediately before the plating step can be the content of the arithmetic mean roughness Ra of the hot-dip galvanized steel sheet, and may be 6.0 μm or less. preferable.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the present examples.

No. in Table 2 In the comparative example of 19, the order of the manufacturing processes is different from that of the other examples, and the normal casting process, the hot rolling process under the conditions shown in Table 2, and the blasting under the conditions shown in Table 2 are used by using the invention steel type E. A hot-dip zinc-plated steel sheet was produced by performing the steps, the pickling step, and the hot-dip zinc plating step in this order. On the other hand, for other examples and comparative examples, steel slabs having the components shown in Table 1 were used, and after normal casting, the hot rolling step, pickling step, and the conditions shown in Table 2 under the conditions shown in Table 2 were used. A hot-dip galvanized steel sheet was produced by performing a blasting step and a hot-dip galvanizing step under the following conditions in this order, and further performing an alloying treatment for a part of the step.

When the pickling step and the blasting step are performed, the pickling step is performed on the hot-rolled plate under the conditions of a bath temperature of 60 ° C. and a hydrochloric acid concentration of 5%, and then the particles (jetting material) of JIS G5903 have a particle size of S40. Was blasted using. In this embodiment, other blasting conditions are set as the conditions in the table.

When performing the hot-dip galvanizing treatment, wiping is performed using an Al-containing galvanizing bath in which the galvanizing bath temperature is 460 ° C., the Al concentration is 0.14%, and the balance is Zn and unavoidable impurities. The amount of galvanized adhesion was adjusted to ^{50 g / m 2.} The alloying treatment was carried out at an alloying temperature of 520 ° C.

The hot-dip galvanized steel sheet obtained as described above was subjected to the tests shown below to evaluate the plating surface appearance and plating adhesion. The measurement method and evaluation criteria are shown below.

"Measurement of surface texture and residual stress of hot-rolled plate after blasting"
<Arithmetic mean roughness measurement>
The arithmetic mean roughness Ra of the steel plate surface immediately after the blasting process was measured under the conditions of cutoff: 0.8 mm and measurement length: 2.5 mm for the rolling direction and the direction orthogonal to the rolling direction. The measurement was performed three times in each direction, and the average value of the obtained results was used.

<Measurement of specific surface area ratio>
The specific surface area of the steel sheet immediately after the blasting step was calculated by scanning the surface shape using a laser microscope (manufactured by Keyence: VK-X250). Observation and analysis were performed under the conditions that the observation magnification was 3000 times, the resolution of the z-axis was 0.5 nm, and the resolution of the x-axis and the y-axis was 0.1 μm. In deriving the area ratio, five arbitrary visual fields were selected for each steel plate, and the average value was taken as the specific surface area ratio r.

<Residual stress test>
The residual stress (σ) on the surface of the steel sheet immediately after the blasting step was derived by averaging 5 points of analysis results from any place and direction using an X-ray diffractometer.

"Measurement of steel sheet characteristics after plating"
<Appearance test>
The appearance after the hot-dip galvanizing process and after the alloying treatment was confirmed by visual observation, and those without non-plating and alloy unevenness were marked with ◯, and those without non-plating or alloy unevenness were marked with x.

<Peelability test>

(Plating adhesion)
The plating adhesion of the hot-dip galvanized steel sheet was evaluated by a ball impact test. That is, a ball impact test was performed under the conditions of a ball weight of 2.8 kg and a drop height of 1 m, the processed portion was peeled off from the tape, and the presence or absence of peeling of the plating layer was visually determined.
○ No peeling of plating layer × Plating layer peeling

(Powdering resistance)
The plating adhesion of the alloyed hot-dip galvanized steel sheet was evaluated by testing the powdering resistance. That is, a cellophane tape was attached to an alloyed hot-dip galvanized steel sheet, the tape surface was bent 90 degrees, then bent back and the tape was peeled off. Then, the amount of peeled plating per 10 mm × 40 mm of the bent-back portion was measured as the Zn count number by fluorescent X-rays from a part of the steel plate attached to the peeled tape, and evaluated against the following criteria.
Number of fluorescent X-ray counts Rank less than 3000: ◎ (good)
3000 or more and less than 6000: ○
6000 or more: × (inferior)
<Corrosion resistance test>

(Corrosion resistance after processing)
Perform the same processing as the above plating adhesion test, prepare a test piece that does not peel off the tape, and prepare a degreasing agent: FC-E2011, surface conditioner: PL-X, and chemical conversion treatment agent: Palbond PB-L3065 manufactured by Nihon Parkerizing Co., Ltd. Was used to perform chemical conversion treatment under the following standard conditions so that the amount of the chemical conversion-treated plating film adhered was 1.7 g / m ² or more and 3.0 g / m ^{2 or less.}

[Standard conditions]
-Degreasing step; treatment temperature 40 ° C., treatment time 120 seconds-Spray degreasing, surface adjustment step; pH 9.5, treatment temperature room temperature, treatment time 20 seconds-Chemical conversion treatment step; temperature of chemical conversion treatment liquid 35 ° C., treatment time 120 seconds The surface of the test piece subjected to the above chemical conversion treatment was electrodeposited using V-50, an electrodeposition paint manufactured by Nippon Paint Co., Ltd., so that the film thickness was 25 μm. It was subjected to the following corrosion test.

[Salt spray test (SST)]
In the GA (alloyed hot-dip galvanized steel sheet) of the above test piece that has undergone chemical conversion treatment and electrodeposition coating, the surface of the bent part and the ball impact part of the GI (hot-dip galvanized steel sheet) have cut flaws that reach plating with a cutter. After the application, the test piece was subjected to a salt spray test for 240 hours in accordance with the neutral salt spray test specified in JIS Z2371: 2000 using a 5 mass% NaCl aqueous solution. Then, a tape peeling test was performed on the cross-cut flawed portion, and the maximum total peeling width including the left and right sides of the cut flawed portion was measured. When the maximum peeling width is 2.0 mm or less, it can be evaluated that the corrosion resistance in the salt spray test is good.
◯: Maximum bulge from cut flaws Overall width 2.0 mm or less ×: Maximum bulge from cut flaws Overall width over 2.0 mm

表２より、本発明例は、表面外観性、めっき密着性（耐パウダリング性）、加工後耐食性のいずれも良好であることが確認された。一方、比較例では、表面外観性、めっき密着性（耐パウダリング性）、加工後耐食性のいずれか一つ以上が劣ることが確認された。

From Table 2, it was confirmed that the examples of the present invention had good surface appearance, plating adhesion (powdering resistance), and corrosion resistance after processing. On the other hand, in the comparative example, it was confirmed that one or more of the surface appearance, the plating adhesion (powdering resistance), and the post-processing corrosion resistance were inferior.

In addition, No. Regarding the surface characteristics (specific surface area ratio, residual stress, arithmetic average roughness) of the base steel sheet of the hot-dip galvanized steel sheet obtained under the manufacturing conditions of 3 and 11, the Zn-plated layer on the plated steel sheet had a NaOH concentration of 15%. After dissolving in the solution to expose the base metal, the measurement was performed on each base material steel plate by using the above-mentioned measuring method. As a result, Invention Example No. The surface physical properties of No. 3 had a specific surface area ratio of 1.65, an average residual stress of −32 MPa, and an arithmetic mean roughness of 2.1 μm. On the other hand, Comparative Example No. in Table 2. The surface characteristics of No. 11 were a specific surface area ratio of 2.1, an average residual stress of 10 MPa, and an arithmetic mean roughness of 2.3 μm.
From the above, it was confirmed that the hot-dip galvanized steel sheet of the present invention has good surface appearance, plating adhesion (powdering resistance), and corrosion resistance after processing.

The high-strength hot-dip galvanized steel sheet of the present invention is suitably used as an automobile part whose strength and wall thickness are rapidly increasing in recent years.

Claims (13)

By mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0.08% or less , S: 0.02% or less and Al: 0.001% or more and 0.20% or less, and the balance is Fe and the component composition of unavoidable impurities. The hot rolling process to make and
A pickling step of performing a pickling treatment on the hot-rolled plate and
A blasting step of spraying grains having an average particle size of 50 μm or more and less than 300 μm onto the hot-rolled plate after the pickling step under a pressure condition of 0.3 MPa or more and 1.0 MPa or less, and a blasting step.
A hot-dip galvanizing step of hot-dip galvanizing a steel sheet after the blasting step,
A method for manufacturing a hot-dip galvanized steel sheet. The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein the specific surface area ratio r of the hot-dip sheet after the blasting step is 2.5 or less. The method for producing a hot-dip galvanized steel sheet according to claim 1 or 2, wherein the arithmetic average roughness Ra of the hot-dip sheet after the blasting step is 6.0 μm or less. The hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the average residual stress σ of the α-Fe (211) surface of the hot-dip plate after the blasting step is −500 MPa or more and -30 MPa or less. Manufacturing method. In the hot rolling step, after rough rolling is performed on the steel material, rolling is completed at a finish rolling temperature of 820 ° C. or higher, and the steel material is wound at 450 ° C. or higher and 650 ° C. or lower to prepare a hot-rolled sheet. Item 8. The method for producing a hot-rolled hot-rolled steel sheet of hot-dip plating according to any one of Items 1 to 4. The method for producing a hot-dip galvanized steel sheet according to any one of claims 1 to 5, wherein a heat treatment step is applied to the hot-rolled steel sheet after the blasting step. In the heat treatment step, before the hot dip galvanizing step, the atmosphere is set to a hydrogen concentration of 2% by volume or more and 20% by volume or less and a dew point of -60 ° C. or more and -10 ° C. The method for producing a hot-dip galvanized steel sheet according to claim 6, wherein the hot-dip galvanized steel sheet is held in a temperature range of T-50 ° C. or higher and T ° C. or lower for 10 seconds or more and 500 seconds or less. The method for producing a hot-dip galvanized steel sheet according to any one of claims 1 to 7, further comprising an alloying step of performing an alloying treatment after the hot-dip galvanizing step. The steel material is Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more and 0.500% or less, Mo: 0.01%. The invention according to any one of claims 1 to 8, further comprising one or more selected from the group consisting of 0.50% or more and W: 0.001% or more and 0.200% or less. Hot-dip galvanized steel sheet manufacturing method. A method for manufacturing a hot-dip steel sheet for hot-dip galvanizing used in hot-dip galvanizing.
By mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0.08% or less , S: 0.02% or less and Al: 0.001% or more and 0.20% or less, and the balance is Fe and the component composition of unavoidable impurities. The hot rolling process to make and
A pickling step of performing a pickling treatment on the hot-rolled plate and
A blasting step of spraying grains having an average particle size of 50 μm or more and less than 300 μm onto the hot-rolled plate after the pickling step under a pressure condition of 0.3 MPa or more and 1.0 MPa or less, and a blasting step.
A method for manufacturing a hot-dip galvanized steel sheet for hot-dip galvanizing. A hot-dip steel sheet for hot-dip galvanizing used in hot-dip galvanizing.
By mass%, C: 0.02% or more and 0.30% or less, Si: 0.01% or more and 1.0% or less, Mn: 0.2% or more and 3.0% or less, P: 0.08% or less , S: 0.02% or less and Al: 0.001% or more and 0.20% or less, and the balance has a component composition of Fe and unavoidable impurities.
The surface of the base steel sheet for hot dip galvanizing has a specific surface area ratio r of 1.1 or more and 2.0 or less, an arithmetic average roughness Ra of 6.0 μm or less, and an average of α-Fe (211) surfaces. A hot-dip galvanized steel sheet having a residual stress σ of −250 MPa or more and 100 MPa or less. As the component composition, Ti: 0.01% or more and 0.40% or less, Nb: 0.001% or more and 0.200% or less, V: 0.001% or more and 0.500% or less, Mo: The hot-dip galvanizing treatment according to claim 11, further containing one or more selected from the group consisting of 0.01% or more and 0.50% or less and W: 0.001% or more and 0.200% or less. Hot-dip steel sheet for use. The hot-dip galvanized steel sheet provided with a plating layer on the hot-dip galvanized steel sheet for hot-dip galvanizing according to claim 11 or 12.