KR101721483B1 - Galvanized steel sheet for press-forming - Google Patents

Abstract

A hot-dip galvanized steel sheet excellent in plating adhesion after press working, spot weldability, corrosion resistance after coating, and excellent appearance.
0.10% or less of Si, 0.30% or more and 0.70% or less of Mn, 0.040% or less of P, 0.010% or less of S, 0.010% or less of S, 0.005% or less of N and 0.10% or less of Al, And a balance of Fe and inevitable impurities; a hot-dip galvanized layer formed on at least a part of the surface of the steel sheet, the hot-dip galvanized layer containing Al in an amount of 0.3% or more and 0.6% or less by mass; the melt contains, 0.12gm ^-2 least 0.22gm of Al ^-2 or less which is present between the zinc coating layer, and having an intermetallic compound comprising Fe ₂ Al ₅ having an average particle size of less than 1㎛, yield stress (YS) is Galvanized steel sheet of 260 MPa or more and 350 MPa or less.

Description

[0001] GALVANIZED STEEL SHEET FOR PRESS-FORMING [0002]

The present invention relates to a hot-dip galvanized steel sheet which can be suitably used for outer and inner plates of automobiles.

Recently, in the fields of automobiles, household appliances, and construction materials, surface treated steel plates having rust-inhibiting properties are used, and hot-dip galvanized steel plates having excellent rust prevention properties are used. In particular, automakers in Europe and America are thinking about improving the rust prevention performance by applying hot-dip galvanized steel sheet which can simply increase the plating thickness. In addition, in the East Asian region, where economic growth is prominent, demand for automotive steel sheets is expected to surge.

Further, in the case of a steel sheet for automobiles in which good processability is strictly demanded, the durability of the product can not be maintained unless the plating adhesion after the press working and the corrosion resistance after the press working are satisfactory.

In addition, the so-called high-strength steel sheet used particularly as a strength member is required to have strict press workability and rust prevention property of the machined portion after press working, so that the plating adhesion of the machined portion becomes very important.

Patent Document 1 discloses a method of manufacturing a hot-dip galvanized steel sheet which is excellent in slidability at the time of press working, which specifies the amount of Al in the plated layer and the amount of Al at the plating / steel plate interface. However, in Patent Document 1, the durability of the product such as the plating adhesion of the processed portion after the press working and the corrosion resistance after the press working is not sufficiently considered. Therefore, it can not be said that there is no such problem at all.

As described above, there is no durability steel sheet in the past due to good plating adhesion after press working and good corrosion resistance after coating.

Further, the hot-dip galvanized steel sheet is also required to have excellent appearance and spot weldability after coating because it is used in fields such as automobiles, home appliances and building materials.

Japanese Laid-Open Patent Publication No. 2004-315965

The present invention has been made in view of such circumstances, and an object thereof is to provide a hot-dip galvanized steel sheet having excellent plating adhesion after press working, excellent spot weldability, excellent post-coating corrosion resistance after press working, and excellent appearance after painting.

The present inventors have conducted diligent studies to solve the above problems. The hot dip galvanizing treatment is performed in which the structure of the hot dip galvanized layer is controlled so that the intermetallic compound is formed between the steel sheet and the hot-dip galvanized layer in a predetermined form, instead of merely performing the hot dip galvanizing treatment as in the prior art. Preferably, the hot-dip galvanizing treatment is carried out to control the solidification structure and the texture of the surface of the hot-dip galvanized layer and to control the internal oxidation state at the steel sheet surface portion of the steel sheet surface. It has been found that such a hot-dip galvanizing treatment results in a hot-dip galvanized steel sheet having excellent plating adhesion after press working, excellent spot weldability, excellent post-coating corrosion resistance after press working, and excellent appearance after painting, . More specifically, the present invention provides the following.

The hot-dip galvanized steel sheet according to the present invention contains, by mass%, C: 0.05 to 0.10%, Si: 0.10%, Mn: 0.30 to 0.70%, P: 0.040% : 0.005% or less, Al: 0.10% or less, and the balance of Fe and inevitable impurities; and Al, which is formed on at least a part of the surface of the steel sheet in an amount of 0.3% to 0.6% And an intermetallic compound containing 0.12 g / m 2 or more and 0.22 g / m 2 or less of Al, which is present between the steel sheet and the hot dip galvanized layer and contains Fe ₂ Al ₅ having an average particle diameter of 1 μm or less And a yield stress (YS) of 260 MPa or more and 350 MPa or less.

In the hot-dip galvanized steel sheet of the present invention, it is preferable that the surface of the hot-dip galvanized layer has a surface roughness Ra of 0.8 μm or more and 1.6 μm or less, a glossiness (G value) of the surface of the hot- (Zn (002) / (004)), which is the ratio of the crystal orientation of the (002) plane of the Zn crystal to the crystal orientation of the (004) plane of the Zn crystal on the surface of the hot dip galvanized layer, ) Is not less than 0.60 and not more than 0.90, and the inner oxidation amount of the steel surface layer portion contacting the hot dip galvanized layer on the surface of the steel sheet is not more than 0.05 g / m 2.

The hot-dip galvanized steel sheet of the present invention has excellent plating adhesion after press working, excellent spot weldability, excellent corrosion resistance after press working, and excellent appearance after coating.

(Mode for carrying out the invention)

Hereinafter, the present invention will be described in detail. The present invention is not limited to the following embodiments.

The hot-dip galvanized steel sheet of the present invention has a steel sheet, a hot-dip galvanized layer formed on at least a part of the surface of the steel sheet, and a metal compound present between the steel sheet and the hot-dip galvanized layer.

<Steel plate>

The steel sheet used in the present invention preferably contains 0.05 to 0.10% of C, 0.10% or less of Si, 0.30 to 0.70% of Mn, 0.040% or less of P, 0.010% or less of S, Or less, Al: 0.10% or less, and the balance of Fe and inevitable impurities. Hereinafter, the composition of the above components will be described. In the present specification, &quot;% &quot; in component composition means &quot; mass% &quot; unless otherwise specified.

C: not less than 0.05% and not more than 0.10%

An increase in the content of C can contribute to the strengthening of the steel sheet. For this high strength, the content of C must be 0.05% or more. On the other hand, a large amount of C causes an increase in solid solution C, greatly increasing the yield strength and elongation, and also greatly reducing the weldability. Therefore, the content of C must be 0.10% or less.

Si: not more than 0.10%

When a large amount of Si is added, the adhesion of the steel sheet after press working is deteriorated due to the generation of Si oxide during annealing. Therefore, the Si content needs to be 0.10% or less. The preferable content of Si is 0.03% or less.

Mn: 0.30 to 0.70%

Mn contributes to enhancement of strength by solid solution strengthening. Further, Mn suppresses the diffusion of C and reduces the solid solution C by making the cementite finer, thereby decreasing the yield strength and elongation. Mn also has an action of making S in harmful steel as MnS, thereby detoxifying it. In order to obtain such an effect, the content of Mn should be 0.30% or more. On the other hand, the incorporation of a large amount of Mn not only leads to a decrease in ductility due to hardening but also causes generation of Mn oxides at the time of annealing, thereby deteriorating the plating adhesion of the steel sheet after press working. Therefore, the content of Mn should be 0.70% or less.

P: not more than 0.040%

P contributes to the enhancement of strength as an employment strengthening element. However, P deteriorates ductility and toughness. Therefore, the content of P must be 0.040% or less. The preferable content of P is 0.015% or less.

S: not more than 0.010%

If the content of S is large, the toughness of the welded portion is deteriorated. Therefore, the upper limit of the content of S is 0.010%. The preferable content of S is 0.007% or less.

N: 0.005% or less, Al: 0.10% or less

Al (sol.Al) and N do not impair the effect of the present invention as long as they are contained in a usual steel sheet. Further, N may be combined with Ti to form TiN, or may be combined with Al to form AlN. Therefore, the content of Al is limited to 0.10% or less and the content of N is limited to 0.005% or less. When the content of Al exceeds 0.10%, the formation of an intermetallic compound to be described later is inhibited. When the content of Al exceeds 0.10%, nucleation is inhibited and the crystals of each steel sheet are coarsened to deteriorate the plating adhesion after press working. In addition, nitrides having an N content exceeding 0.005% are dispersed in the ferrite grains, and the work hardening rate is lowered. The content of Al is preferably 0.04% or less, and the content of N is preferably 0.002% or less.

<Hot-dip galvanized layer>

The hot-dip galvanized layer is a hot-dip galvanized layer formed by a conventional hot-dip galvanizing treatment. The hot dip galvanized layer contains Al in an amount of 0.3% or more and 0.6% or less by mass%. In the present invention, components other than Zn and Al may be contained in the hot-dip galvanized layer within a range that does not impair the effect of the present invention. Examples of the components other than Al include Fe, Mg, and Cr.

When the content of Al is less than 0.3%, it is necessary to lower the Al concentration in the plating bath. If the Al concentration is lowered, there is elution of Fe, so that a dross is precipitated to deteriorate the external appearance, or the hard dross is dispersed in the hot-dip galvanized layer. When the drawstock is dispersed in the hot-dip galvanized layer, it is brought into contact with the metal at the time of press working, whereby the press-formability of the hot-dip galvanized steel sheet is deteriorated. When the content of Al exceeds 0.6%, a large amount of Al oxide film is formed on the surface of the hot-dip galvanized layer, and the spot weldability of the hot-dip galvanized steel sheet is deteriorated.

In the hot-dip galvanized layer, the surface roughness Ra of the surface of the hot-dip galvanized layer is preferably 0.8 μm or more and 1.6 μm or less. If the surface roughness Ra is less than 0.8, the oil may not be retained (held) on the surface of the hot-dip galvanized layer during the pressing of the hot-dip galvanized steel sheet, and the press workability may be deteriorated. If the surface roughness Ra is more than 1.6 占 퐉, there is a case where the after-painting sharpness or the plating adhesion after press working is deteriorated and excellent appearance can not be given to the hot-dip galvanized steel sheet after painting. The surface roughness Ra means the surface roughness Ra measured by the method described in the embodiment.

It is preferable that the gloss (G value) of the surface of the hot-dip galvanized layer is 550 or more and 750 or less. When the glossiness (G value) is less than 550, the post-coating sharpness deteriorates, and a good appearance can not be given to the hot-dip galvanized steel sheet after painting. When the glossiness (G value) is more than 750, the steel sheet is excessively smooth, and oil is not stored and held on the surface of the hot-dip galvanized layer during pressing of the hot-dip galvanized steel sheet, resulting in poor moldability. The glossiness (G value) means the glossiness (G value) measured using a glossmeter as described in the examples.

(Zn (002) / (004)), which is a ratio of the crystal orientation of the (002) plane of the Zn crystal to the crystal orientation of the (004) plane of the Zn crystal on the surface of the hot dip galvanized layer is 0.60 or more Is preferably 0.90 or less. If the orientation ratio of the zinc base plane is less than 0.60, the orientation of the zinc crystals is relatively random and the crystal size when the zinc coagulates immediately after the plating becomes finer. Therefore, the surface of the hot-dip galvanized layer becomes excessively smooth, And the press workability may be deteriorated in some cases. If the orientation ratio of the zinc base is more than 0.90, the orientation of the base of the Zn crystal is too high, and the crystal grains are liable to grow, resulting in the development of a dendrite arm, resulting in deterioration in sharpness after coating, There is a possibility that the appearance of the display device may deteriorate. Also, if the orientation ratio of the zinc base is more than 0.90, the corrosion resistance may also deteriorate. Here, the orientation ratio of the zinc base plane can be defined by the following formula.

The zinc base plane orientation ratio (Zn (002) / (004)) represents the Zn crystal orientation property of the (002) plane} / {the Zn crystal orientation property of the (004) plane}. I ( _xyz ) represents the Zn intensity measured by the X-ray on the (xyz) plane of the sample and I _std ( _xyz ) represents the intensity of the Zn measured by the X-ray on the (xyz) plane of the standard sample Zn intensity, and? Is the sum of the Zn intensities in all directions.

If the orientation ratio of the zinc base is defined as described above, Zn is easily oriented to the basal plane by taking the hcp structure, and it can be known to what extent crystals are randomly oriented. The degree of orientation of the solidification structure affects luster, crystal size, and surface roughness (surface roughness). Therefore, precisely controlling the zinc base orientation ratio is important in controlling the press formability as well as the surface properties of the hot-dip galvanized steel sheet.

The hot dip galvanized layer may be formed on at least a part of the surface of the steel sheet. Since the hot-dip galvanized layer is formed on the surface of the steel sheet by dipping the steel sheet in a plating bath, a hot-dip galvanized layer is usually formed on the entire surface of the steel sheet.

The thickness of the hot-dip galvanized layer is not particularly limited, but the thickness of the hot-dip galvanized layer can be adjusted by controlling the amount of the deposited layer during the hot-dip galvanizing treatment.

<Intermetallic compound>

The intermetallic compound is composed of an intermetallic compound containing Fe ₂ Al ₅ having an average particle diameter of 1 μm or less and exists between a steel sheet and a hot-dip galvanized layer. Further, the intermetallic compound contains Al of not less than 0.12 g / m 2 and not more than 0.22 g / m 2. The presence of the intermetallic compound containing Fe ₂ Al ₅ suppresses the formation of the FeZn alloy phase (alloy phase) and secures good plating adhesion. This effect is not obtained in the case of an intermetallic compound other than an intermetallic compound containing Fe ₂ Al ₅ because it is hard and is often soft. In addition, an intermetallic compound other than an intermetallic compound containing Fe ₂ Al ₅ sometimes produces a hard and loose FeZn intermetallic compound, and when this is produced, the adhesion of the plating is deteriorated. The content of Fe ₂ Al ₅ may be suitably adjusted so as to obtain the effect of the present invention. The presence of the intermetallic compound can be confirmed by a method of analyzing and analyzing the vicinity of the interface between the hot dip galvanized layer and the steel sheet in the cross section of the hot dip galvanized layer by electron beam diffraction in a transmission electron microscope.

If the average particle diameter of Fe ₂ Al ₅ exceeds 1 탆, the hard intermetallic compound is excessively grown and the impact resistance characteristic of the hot-dip galvanized steel sheet is deteriorated. For this reason, the upper limit of the average particle diameter is 1 mu m.

If the content of Al in the intermetallic compound is less than 0.12 g / m 2, it is necessary to set the Al concentration to be low in the molten zinc bath for plating. If the Al concentration is set to a low value, dross is precipitated and the appearance of the hot-dip galvanized steel sheet, The processability, the plating adhesion after the press working, and the corrosion resistance of the hot-dip galvanized steel sheet are deteriorated. If the content of Al in the intermetallic compound is more than 0.22 g / m &lt; 2 &gt;, it is necessary to set the Al concentration in the plating bath to be high. When the Al concentration is set to be high, a large amount of Al oxide film is formed on the surface of the hot dip galvanized layer, do.

<Physical properties of hot-dip galvanized steel sheet>

The hot-dip galvanized steel sheet of the present invention is excellent in plating adhesion after press working and excellent in corrosion resistance after coating of the processed portion after press working. The hot-dip galvanized steel sheet of the present invention has an appearance after excellent coating. For this reason, the hot-dip galvanized steel sheet of the present invention is also applicable to products having extremely strict processing regions such as back doors and hoods.

Further, the hot-dip galvanized steel sheet of the present invention has a yield stress (YS) of 260 MPa or more and 350 MPa or less. When the yield stress is within the above range, the hot-dip galvanized steel sheet can be suitably used for applications such as inner plates and the like, which must secure rigidity and shape-conformity. The preferred yield stress is 270 MPa or more and 310 MPa or less.

In order to further secure good plating adhesion, it is preferable that the inner oxidation amount at the base steel surface layer portion after the removal of the plating layer is 0.05 g / m 2 or less per one surface. Internal oxidation is caused by oxidation of an easily oxidizing element such as Si, Mn, Al, P added in steel into an annealing process in a hot rolling process or an annealing process in CGL. In order to suppress the internal oxidation amount, it is necessary not to increase the winding temperature at the time of hot rolling excessively, or to increase the dew point in the annealing atmosphere in CGL excessively. If the amount of internal oxidation is large, grain boundaries may become brittle in the processed portion after the pressing, deteriorating the plating adhesion after press working, and also deteriorate the spot weldability. Further, the steel surface layer portion refers to a range from the interface between the hot-dip galvanized layer and the steel sheet to 50 mu m in the thickness direction of the steel sheet.

The method of removing the plating layer for measuring the internal oxidation amount is not particularly limited, and it can be any of acid and alkali removal. Take care not to remove the substrate and to prevent the surface after the removal from being oxidized by the use of an inhibitor (base iron dissolution inhibitor). As an example, it is possible to use a 20% by mass NaOH-10% by mass aqueous solution of triethanolamine in 195 cc and a 35% by mass aqueous H ₂ O ₂ solution in 7 cc. It is also possible to use a dilute HCl solution containing an inhibitor.

The internal oxidation amount is obtained by measuring the amount of oxygen in the surface layer of the steel sheet after the removal of the plating layer. The amount of internal oxide in the surface layer of the base steel is measured, for example, by "impulse melting-infrared ray method". However, in order to accurately predict the internal oxidation amount immediately below the plating layer, it is necessary to subtract the oxygen amount contained in the base material itself. For this reason, the oxygen amount in the steel for a specimen in which the surface layer portion of the front and back surfaces of the sample, from which the plating layer has been removed in the same way, is mechanically polished more than 100 占 퐉 is separately measured and the oxygen amount of the sample is determined from the oxidized amount in the steel surface layer portion after the plating layer is removed , The oxidation increase amount of only the surface layer portion is calculated and converted into the amount per unit area to obtain the value.

&Lt; Production method of hot-dip galvanized steel sheet &gt;

Next, a method of producing a hot-dip galvanized steel sheet will be described. For example, a hot-dip galvanized steel sheet can be produced by the following method. First, a steel having the above-mentioned composition is made into a slab by continuous casting, and the slab is heated to perform descaling and rough rolling. Subsequently, the steel sheet is cooled, followed by finish rolling, cooling, winding, pickling, and cold rolling. Next, annealing and hot-dip galvanizing of the steel sheet are performed in the continuous hot-dip galvanizing facility.

The heating time, the heating temperature, the rough rolling condition, the cooling condition, the finish rolling condition, the winding condition, and the like when the slab is heated can be appropriately set. However, in the present invention, in order to adjust the internal oxidation amount in the steel surface layer portion to the above-mentioned range, it is preferable to adjust the conditions of finish rolling (hot rolling) and the winding speed.

The annealing condition of the steel sheet affects the yield stress of the hot-dip galvanized steel sheet. In the present invention, it is preferable to set the heating temperature (annealing temperature, which means the maximum temperature of the steel sheet) at the time of annealing to 760 DEG C or more and 840 DEG C or less in order to set the yield stress in the above range.

Also, the annealing atmosphere may be adjusted appropriately. In the present invention, it is preferable to adjust the dew point to -55 DEG C or more and 0 DEG C or less. If the dew point is higher than 0 ° C, it is not preferable because the surface of the furnace body tends to become brittle. If the dew point is lower than -55 ° C, securing the airtightness is not preferable because of technically difficultness.

The hydrogen concentration in the annealing atmosphere is preferably 1 vol% or more and 50 vol% or less. When the hydrogen concentration is 1 vol% or more, it is preferable because the surface of the steel sheet is activated. When the hydrogen concentration is 50 vol% or more, it is not preferable because it is economically disadvantageous.

In the present invention, it is necessary to adjust the conditions of the hot-dip galvanizing treatment in order to control the Al content of the hot-dip galvanized layer and to allow the intermetallic compound to exist between the steel sheet and the hot-dip galvanized layer. It is also necessary to adjust the conditions of the hot-dip galvanizing treatment in order to set the surface state (surface roughness Ra, gloss (G value), and zinc base orientation ratio) of the hot-dip galvanized layer to a desired state. Hereinafter, the conditions of the hot-dip galvanizing treatment will be described.

There is no particular limitation on the penetration plate temperature (penetration plate temperature), which is the temperature of the steel sheet when the steel sheet after annealing enters the plating bath. In the present invention, the invading plate temperature is preferably the temperature of the plating bath (bath temperature) -20 占 폚 or higher and the bath + 20 占 폚 or lower. If the invading plate temperature is within the above range, the change in the bath temperature is small, and the desired hot-dip galvanizing treatment can be performed continuously. The Al content in the hot dip galvanized layer and the Al content in the intermetallic compound tend to decrease by raising the bath temperature. Further, the gloss of the surface of the hot-dip galvanized layer tends to rise when the bath temperature is raised.

The composition of the plating bath in which the steel sheet after annealing enters may be any as long as it contains Al besides Zn, and may contain other components as required. The concentration of Al in the plating bath is not particularly limited. The concentration of Al in the plating bath is preferably 0.16 mass% or more and 0.25 mass% or less. When the concentration of Al is in the above range, an FeAl alloy phase is formed and formation of an FeZn alloy phase is suppressed, which is preferable. The glossiness can be adjusted according to the Al concentration in the plating bath. When the Al concentration in the plating bath is lowered, not FeAl but FeZn crystals are slightly formed at the interface, and as a result, a large number of zinc crystals are generated by becoming a Zn solidification nucleus generating site, and the orientation of zinc crystals is randomized, . As a result, the lower the Al concentration is, the more the dendritic Zn crystal growth is suppressed, the unevenness of the surface is reduced and smoothed, and the glossiness is increased. More preferably, the concentration of Al is 0.19 mass% or more and 0.22 mass% or less. Further, since the Al concentration also affects the Al content in the hot dip galvanized layer and the Al content in the intermetallic compound, it is preferable to determine the Al concentration in consideration of these contents.

The temperature (bath temperature) of the plating bath is not particularly limited. In the present invention, the bath temperature is preferably 430 캜 or more and 470 캜 or less. When the bath temperature is 430 占 폚 or higher, the zinc bath is preferably used because it is not solidified but stably dissolved. When the bath temperature is 470 占 폚 or lower, the Fe elution is small and the dross defect is reduced. More preferably, the range of the bath temperature is 450 ° C or higher and 465 ° C or lower.

The immersion time when the steel sheet is immersed in the plating bath is not particularly limited. In the present invention, the immersion time is preferably 0.1 seconds or more and 5 seconds or less. With the immersion time in the above range, it is easy to form a desired hot-dip galvanized layer on the surface of the steel sheet.

Immediately after lifting the steel sheet from the plating bath, adjust the amount of plating adhered by gas jet wiping or the like. The plating adhesion amount in the present invention is not particularly limited. In the present invention, the plating adhesion amount is preferably in the range of 20 g / m 2 to 120 g / m 2. If the plating adhesion amount is less than 20 g / m &lt; 2 &gt;, it may become difficult to secure corrosion resistance. On the other hand, if the plating adhesion amount exceeds 120 g / m &lt; 2 &gt;, the plating peeling resistance may deteriorate.

After the plating adhesion amount is adjusted as described above, tempering (SK treatment) is performed. The kind of the roll used for the SK treatment is not particularly limited, and it is possible to use an electro-discharge texture roll (EDT roll), an electron beam texture roll (EBT roll), a short dull roll, a topochrome roll It is possible.

The reduction rate (SK reduction rate (%)) at the time of SK treatment is also not particularly limited. In the present invention, the SK reduction rate is preferably 0.7 to 0.9%. When the SK reduction rate is in the above range, it is easy to adjust the surface roughness to the above preferable range. If the SK reduction rate is out of the above range, dull grooves for storing and retaining the rolling oil are not formed, the formability is lowered, and the yield strength is lowered in some cases.

The cooling rate after pulling the steel sheet from the plating bath is preferably -5 ° C / sec to -30 ° C / sec.

As described above, the hot-dip galvanized steel sheet of the present invention has been described. Hereinafter, the use of the hot-dip galvanized sheet of the present invention will be described.

The hot-dip galvanized steel sheet of the present invention is preferably used for the purpose of forming a coating film on the surface of the hot-dip galvanized layer because of excellent corrosion resistance after coating after press working. Further, the hot-dip galvanized steel sheet of the present invention is excellent in plating adhesion even when it is applied to applications requiring strict workability, and the corrosion resistance and mechanical properties are not significantly deteriorated. Examples of applications in which strict workability is required and in which a coating film is formed include automotive steel sheets such as outer plates and inner plates of automobiles. The method of forming the coating film is not particularly limited. In the present invention, it is preferable to perform a chemical treatment (chemical conversion treatment) on the surface of the hot-dip galvanized layer to form a chemical conversion coating, and then to form a coating film on the chemical conversion coating.

As the chemical conversion solution, both a coating type and a reaction type can be used. The components contained in the chemical conversion solution are not particularly limited, and a chromate treatment solution may be used, or a chrome-free treatment solution may be used. The chemical conversion coating film may be a single layer or a multilayer.

The coating method for forming the coating film is not particularly limited. Examples of the coating method include an electrodeposition coating, a roll coater coating, a curtain flow coating, and a spray coating. In order to dry the paint, means such as hot air drying, infrared heating, induction heating and the like may be used.

Example

Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited to the following examples.

The steel sheet had a steel composition (composition) as shown in Table 1, and had a finish rolling temperature as shown in Table 2 (Table 2-1 and Table 2-2 shown in Table 2), a coiling temperature of 650 占 폚 or less The black scale of the hot-rolled steel sheet produced by winding was removed by pickling and cold-rolled at a reduction ratio of 65%, and the sheet thickness was 0.8 mm and 1.8 mm. Thereafter, the surface was subjected to degreasing treatment at the inlet (inlet side) of CGL (continuous hot dip galvanizing line), and subjected to annealing and hot dip galvanizing under the conditions shown in Table 2 to produce a hot-dip galvanized steel sheet. The Al concentration in the bath or bath was appropriately changed. The rolls were appropriately changed in the reduction rate using an EDT processing roll. The deposition amount was 55 g / m 2 per one side. Further, the steel plate was lifted from the plating bath, and the amount of plating adhered by the gas jet wiping was adjusted, and SK treatment was performed under the conditions shown in Table 2 before cooling.

[Table 1]

The following measurements were carried out on the hot-dip galvanized steel sheet obtained as described above.

The composition of the intermetallic compound was classified by the X-ray diffraction method on the surface of the zinc plated layer removed by fuming nitric acid. With respect to the amount, the surface of the intermetallic compound on the surface of the sample prepared in the same manner was dissolved in dilute hydrochloric acid and quantified (quantified) by ICP. The amount of Al in the plating layer was also dissolved in the same amount of diluted hydrochloric acid and quantified by ICP.

The particle diameter of the intermetallic compound was measured by the following method. A test piece was taken from the steel sheet and the metal structure of the cross section parallel to the rolling direction was observed at a magnification of 5000 times using a scanning electron microscope (SEM) to measure the average particle diameter of the intermetallic compound. The results are shown in Table 2.

The internal oxidation amount was measured by first removing the hot dip galvanized layer with 195 cc of a 20 mass% NaOH-10 mass% aqueous triethanolamine solution and 7 cc of a 35 cc mass% H ₂ O ₂ aqueous solution of 7 mass%, and measuring the amount of oxygen in the steel- Was measured by a water supply method. However, in order to accurately predict the internal oxidation amount immediately below the plating layer, it is necessary to subtract the oxygen amount contained in the base material itself. For this reason, by separately measuring the oxygen content in the steel with respect to a specimen in which the front and rear surface layer portions of the sample from which the plating layer has been removed are mechanically polished by 100 μm or more, and by subtracting the oxygen amount of the sample from the oxidized amount in the steel surface layer portion after the removal of the plating layer, The oxidation increase amount of only the surface layer portion was calculated and converted into the amount per unit area. The results are shown in Table 2.

The surface roughness Ra of the hot-dip galvanized layer was measured by the following method. In accordance with JIS B 0601, an arithmetic mean roughness Ra was measured using a contact type surface roughness meter. The measurement results are shown in Table 2.

The glossiness (G value) was measured using a gloss meter. The measurement results are shown in Table 2.

(002) / (004) crystal orientation orientation of the Zn crystal on the surface of the hot dip galvanized layer and the crystal orientation of the (004) plane of the Zn crystal were measured using an X-ray diffraction apparatus to determine the zinc base surface orientation ratio )). Table 2 shows the orientation ratios of the zinc base.

The plating adhesion of the processed portion after the press working was measured at 1843 g on the basis of the warp diameter of 5 / An impact resistance test was performed in which an 8-inch punch was dropped from a height of 1 m, and a cellophane tape peeling was evaluated. The peeling was evaluated as poor adhesion (X), and the absence of peeling was evaluated as good adhesion (O). The evaluation results are shown in Table 2.

A tensile test specimen of JIS No. 5 was taken from the hot-dip galvanized steel sheet in the direction of 90 占 with respect to the rolling direction and subjected to a tensile test under conditions of a crosshead speed of 10 mm / min (constant) in accordance with JIS Z 2241. The yield stress (YS (MPa)) was measured to give a YS of 260 to 350 MPa.

The spot weldability was evaluated by spot welding continuous rubbing. Specifically, after degreasing the steel sheet, a pressing force of 250 kgf, an initial pressing time of 35 cy / 60 Hz, an energizing time of 18 cy / 60 Hz, a holding time of 1 cy / 60 Hz, a dwell time of 16 cy / (Continuous material) was spot welded at a welding current of 10 60 and a nugget diameter of 4 4 t. Continuous score ≥2000 points were good, and less than 2,000 points were poor. The results are shown in Table 2.

Next, the hot-dip galvanized steel sheet obtained by the above method was subjected to a total coating of chemical conversion treatment, electrodeposition coating, intermediate coat, and overcoat, and the appearance of the hot-dip galvanized steel sheet was evaluated visually. When there was no bad appearance such as uneven plating, it was evaluated as good, and when there was bad, it was evaluated as bad. The evaluation results are shown in Table 2.

Conical extrusion Molded parts were subjected to a total coating of chemical conversion treatment, electrodeposition coating, intermediate coat, and overcoat, and corrosion resistance after coating was evaluated by the following method. A salt spray test based on JIS Z 2371 (2000) was conducted for 10 days, and the presence or absence of swelling in the processed portion after the press working was evaluated. (X) with expansion, and good (O) with no expansion. The evaluation results are shown in Table 2.

[Table 2-1]

[Table 2-2]

As apparent from Table 2, the hot-dip galvanized steel sheet of the present invention has good appearance, spot weldability and yield stress. In addition, the hot-dip galvanized steel sheet of the present invention has excellent plating adhesion and good corrosion resistance after coating, despite the fact that the steel sheet is subjected to press working.

Claims (2)

C: not less than 0.05% to not more than 0.10%, Si: not more than 0.10%, Mn: not less than 0.30%, not more than 0.70%, P: more than 0% to not more than 0.040% : Not less than 0% and not more than 0.005%, Al: not less than 0% and not more than 0.10%, and the balance of Fe and inevitable impurities,
A hot-dip galvanized layer formed on at least a part of the surface of the steel sheet, the hot-dip galvanized layer containing Al in an amount of 0.3% to 0.6%
An intermetallic compound present between the steel sheet and the hot dip galvanized layer and containing 0.12 g / m 2 or more and 0.22 g / m 2 or less of Al and Fe ₂ Al ₅ having an average particle diameter of 1 μm or less,
A hot-dip galvanized steel sheet for press working having a yield stress (YS) of 260 MPa or more and 350 MPa or less. The method according to claim 1,
Wherein the surface of the hot-dip galvanized layer has a surface roughness Ra of 0.8 탆 or more and 1.6 탆 or less,
(G value) of the surface of the hot-dip galvanized layer is not less than 550 and not more than 750,
(Zn (002) / (004), which is the ratio of the crystal orientation of the (002) plane of the Zn crystal to the crystal orientation of the (004) plane of the Zn crystal on the surface of the hot dip galvanized layer. ) Is not less than 0.60 and not more than 0.90,
Wherein the inner oxidation amount of the steel sheet surface layer portion in contact with the hot dip galvanized layer on the surface of the steel sheet is 0 g / m &lt; 2 &gt; or more and 0.05 g / m &lt;