WO2014068889A1 - Hot-dip galvanized steel sheet - Google Patents

Abstract

Provided is a hot-dip galvanized steel sheet which not only exhibits excellent adhesion of a deposit even after press working but also ensures excellent post-coating corrosion resistance even after press working and which has excellent surface appearance. According to the present invention, the structure of a zinc deposit is controlled, said zinc deposit being formed by hot-dip galvanizing, while an intermetallic compound with prescribed characteristics is formed at a deposit/steel sheet interface. Further, the solidification structure of the deposit and the surface texture thereof are controlled. Specifically, the amount of Al in the deposit is adjusted to 0.3 to 0.6% by mass. Further, the amount of Al in the intermetallic compound is adjusted to 0.12 to 0.22gm^-2, and the mean particle diameter of the intermetallic compound is adjusted to 1μm or less, while the composition of the intermetallic compound is Fe₂Al₅ and/or FeAl₃.

Description

Hot-dip galvanized steel sheet

The present invention relates to a hot dip galvanized steel sheet that can be suitably used for an outer plate and an inner plate of an automobile.

Recently, in the fields of automobiles, home appliances, building materials, etc., surface-treated steel sheets imparted with rust resistance to raw steel sheets, especially hot-dip galvanized steel sheets with excellent rust resistance have been used. In particular, European and American automakers are considering improving rust prevention performance by applying hot-dip galvanized steel sheets that can easily increase the plating thickness. In addition, there is a great demand for automotive steel sheets in the East Asian region where economic growth is remarkable.

In addition, in the case of automotive steel sheets that are required to have good workability, the durability of the product cannot be maintained unless the plating adhesion after press working and the corrosion resistance after painting after press working are good.

Patent Document 1 discloses a method for producing a hot-dip galvanized steel sheet having excellent slidability at the time of press work, which regulates the amount of Al in the plating layer and the amount of Al at the plating / steel sheet interface. However, Patent Document 1 does not sufficiently consider the durability of the product such as plating adhesion of a processed portion after press working and corrosion resistance after press working. Therefore, it cannot be said that these problems are completely absent.

As described above, conventionally, there is no steel sheet having good plating adhesion after press working and post-coating corrosion resistance after press working.

Moreover, since the hot dip galvanized steel sheet is used in the fields of automobiles, home appliances, building materials, etc., it is also required to have an excellent appearance after painting.

JP 2004-315965 A

The present invention has been made in view of such circumstances, and provides a hot-dip galvanized steel sheet having excellent plating adhesion after press working, excellent post-paint corrosion resistance after press working, and excellent post-paint appearance. For the purpose.

The present inventors have intensively studied to solve the above problems. As a result, the hot dip galvanizing process that controls the structure of the hot dip galvanized layer and forms intermetallic compounds between the steel sheet and the hot dip galvanized layer with predetermined properties, rather than simply performing the hot dip galvanized process as in the prior art. I do. Preferably, a hot dip galvanizing process for controlling the solidified structure and surface texture of the hot dip galvanized layer is performed. By such hot dip galvanizing treatment, we found that excellent plating adhesion after press working, excellent post-coating corrosion resistance of the processed part after press working, and a hot dip galvanized steel sheet having an excellent post-painting appearance, The present invention has been completed. More specifically, the present invention provides the following.

The hot-dip galvanized steel sheet of the present invention is, in mass%, C: 0.001% to 0.005%, Si: 0.10% or less, Mn: 0.70% to 1.50%, P: 0 0.05% or more and 0.100% or less, S: 0.01% or less, N: 0.005% or less, Al: 0.10% or less, B: 0.0015% or less, and Ti: 0 .01% or more and 0.05% or less and Nb: 0.01% or more and 0.05% or less, at least one selected from the group consisting of Fe and inevitable impurities, and substantially ferrite A steel plate composed of a single phase, a hot-dip galvanized layer containing Al in an amount of 0.3% or more and 0.6% or less by mass%, formed on at least part of the surface of the steel plate, the steel plate and the hot-dip zinc present in the plating layers, 0.12gm ^-2 least 0.22Gm ^- Include the following Al, and having at least one consisting of an intermetallic compound having an average particle diameter of 1μm or less of _Fe 2 Al ₅ or FeAl _3, the yield stress (YS) is equal to or less than 320MPa or more 220 MPa.

In the hot dip galvanized steel sheet of the present invention, the surface roughness Ra of the surface of the hot dip galvanized layer is 0.8 μm or more and 1.6 μm or less, and the glossiness (G value) of the surface of the hot dip galvanized layer is 550. Zinc basal plane orientation ratio (Zn), which is the ratio of the crystal orientation of the (002) plane of Zn crystal to the crystal orientation of the (004) plane of Zn crystal on the surface of the hot dip galvanized layer. (002) / (004)) is preferably 60 or more and 90 or less.

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

Hereinafter, the present invention will be specifically described. In addition, this invention is not limited to the following embodiment.

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 existing between the steel sheet and the hot dip galvanized layer.

<Steel plate>
The steel plate used in the present invention is in mass%, C: 0.001% to 0.005%, Si: 0.10% or less, Mn: 0.70% to 1.50%, P: 0.050. %: 0.100% or less, S: 0.010% or less, N: 0.005% or less, Al: 0.10% or less, B: 0.0015% or less, and Ti: 0.01 % Or more and 0.05% or less and Nb: 0.01% or more and 0.05% or less, and the balance consists of Fe and inevitable impurities. Hereinafter, the component composition will be described. In this specification, “%” in the component composition means “% by mass” unless otherwise specified.

C: 0.001% or more and 0.005% or less When the content of C increases, deep drawability and ductility deteriorate, and the formability required for steel sheets for automobile outer sheets and inner sheets may be imparted to the steel sheets. It becomes difficult. For this reason, the upper limit of the C content is specified to be 0.005%. On the other hand, when the content of C is less than 0.001%, the crystal grains become coarse, and the surface of the steel sheet is likely to be rough when formed. For this reason, the lower limit of the C content is specified to be 0.001%. When the C content in the component composition of the steel sheet used in the present invention is in the above range, the steel sheet structure is substantially a ferrite single phase excellent in workability. Moreover, preferable content of C is 0.001% or more and 0.004% or less.

Si: 0.10% or less When the Si content exceeds 0.10%, surface defects due to scale are likely to occur. Moreover, when content of Si becomes excess, formation of the intermetallic compound mentioned later may be inhibited. Further, when the Si content is excessive, the generation of Si nuclei is suppressed, and each crystal in the steel sheet structure becomes coarse, resulting in a problem that the plating adhesion after press working deteriorates. A preferable Si content is 0.02% or less.

Mn: 0.70% or more and 1.50% or less If the Mn content is less than 0.70%, a steel sheet having sufficient strength cannot be obtained. By containing a large amount of Mn in the steel sheet, the steel sheet can be strengthened, but when Mn is contained excessively, the deep drawability is lowered. Moreover, when Mn is contained excessively, formation of the intermetallic compound mentioned later is inhibited. Moreover, when Mn is contained excessively, the nucleation of Si is suppressed, and each crystal in the steel sheet structure becomes coarse, and the plating adhesion after press working deteriorates. For this reason, the upper limit of the Mn content is 1.50%. A preferable Mn content is 0.75% or more and 1.2% or less.

P: 0.050% or more and 0.100% or less If the P content is less than 0.050%, the workability of the steel sheet is not good, and the mechanical properties such as yield stress (YS) are at a desired level. I do not meet. If the P content exceeds 0.100%, the toughness of the welded portion deteriorates or the ductility deteriorates. P content is preferably 0.050% or more and 0.085% or less.

S: 0.010% or less When the content of S is large, the toughness of the welded portion deteriorates as in the case where the content of P is large. For this reason, the upper limit of the S content is 0.010%. A preferable S content is 0.007% or less.

N: 0.005% or less, Al: 0.10% or less Al (sol. Al) and N do not impair the effects of the present invention as long as they are contained in a normal steel sheet. N combines with Ti to form TiN, or N combines with Al to form AlN. Therefore, the Al content is specified to be 0.10% or less, and the N content is specified to be 0.005% or less. If the Al content exceeds 0.10%, formation of an intermetallic compound described later is inhibited. On the other hand, if the Al content exceeds 0.10%, the generation of Si nuclei is suppressed, and each crystal in the steel sheet structure is coarsened, and the plating adhesion during processing deteriorates. On the other hand, when the N content exceeds 0.005%, the nitride is dispersed in the ferrite grains, and the work hardening rate is lowered. The preferable Al content is 0.04% or less, and the preferable N content is 0.002 or less.

B: 0.0015% or less B is an element that contributes to strengthening of grain boundaries cleaned by forming carbides. From the viewpoint of obtaining this effect, the lower limit of the B content is preferably 0.0003%. However, if the B content exceeds 0.0015%, the work hardening rate decreases due to solid solution strengthening. Further, B promotes selective oxidation of the surface during recrystallization annealing. Therefore, the upper limit of the B content is 0.0015%. Moreover, preferable content of B is 0.0003% or more and 0.0010% or less.

At least one selected from Ti: 0.01% to 0.05% and Nb: 0.01% to 0.05% Ti and Nb form carbides (TiC, NbC) in the ferrite grains. By doing, the work hardening rate of a steel plate is improved. However, when the content of Ti or Nb is less than 0.01%, the amount of carbide of Ti or the amount of carbide of Nb is small, the dislocation motion cannot be controlled, and a sufficient work hardening rate cannot be expected. On the other hand, when the Nb or Ti content exceeds 0.05%, coarse carbides are precipitated and the work hardening rate is lowered. On the other hand, if the Nb or Ti content exceeds 0.05%, the grain boundaries in the steel sheet structure are cleaned, and the intermetallic compound grows excessively during the hot dip galvanizing process, resulting in poor plating adhesion. For this reason, regardless of the combined use or single use of Ti and Nb, at least one of the Ti content and the Nb content is 0.01% or more and 0.05% or less. A preferable Ti content is 0.015% or more and 0.04% or less, and a preferable Nb content is 0.01% or more and 0.03% or less. In addition, when both Ti and Nb are included, if one content is outside the above range, it is outside the scope of the present invention.

Fe and unavoidable impurities The balance other than the above components is Fe and unavoidable impurities. Here, the unavoidable impurity is, for example, O (oxygen). O is a typical inevitable impurity inevitably mixed. The content of inevitable impurities is not particularly limited, and the allowable content of inevitable impurities depends on the type of inevitable impurities. In the case of O, there is no problem if the content is 0.005% or less.

Steel sheet structure The steel sheet structure is substantially a ferrite single phase. Since the steel sheet structure is substantially composed of a ferrite single phase, the hot dip galvanized steel sheet is excellent in workability. Here, the ferrite single phase substantially includes not only the case where the entire steel sheet structure is the ferrite phase but also the case where 95% or more of the steel sheet structure is the ferrite phase. However, it is normally considered that no phase other than ferrite is generated. Note that the fact that it is substantially a ferrite single phase is confirmed by observing a cross section of the etched sample with an optical microscope.

<Hot galvanized layer>
The hot dip galvanized layer is a hot dip galvanized layer formed by a normal hot dip galvanizing process. The hot-dip galvanized layer contains Al in an amount of 0.3% to 0.6% by mass. In the present invention, the hot dip galvanized layer may contain components other than Zn and Al as long as the effects of the present invention are not impaired. Examples of components other than Zn and Al include Fe, Al, Mg, and Cr.

When the Al content is less than 0.3%, it is necessary to reduce the Al concentration in the plating bath. When the Al concentration is lowered, Fe is eluted, so that dross is deposited and appearance is deteriorated, or hard dross is dispersed in the hot dip galvanized layer. When dross is dispersed in the hot dip galvanized layer, the workability of the hot dip galvanized steel sheet deteriorates. If the Al content exceeds 0.6%, a large amount of an oxide film of Al is formed on the surface of the hot dip galvanized layer, and the spot weldability of the hot dip galvanized steel sheet deteriorates.

The hot-dip galvanized layer preferably has a surface roughness Ra of 0.8 to 1.6 μm. If the surface roughness Ra is less than 0.8, the oil may not be retained on the surface of the hot dip galvanized layer during pressing of the hot dip galvanized steel sheet, and workability may be poor. If the surface roughness Ra exceeds 1.6 μm, the sharpness after coating may be inferior and an excellent appearance may not be imparted to the hot-dip galvanized steel sheet after coating. In addition, the said surface roughness Ra means surface roughness Ra measured by the method as described in an Example.

The glossiness (G value) of the surface of the hot dip galvanized layer is preferably 550 or more and 750 or less. If the glossiness (G value) is less than 550, the sharpness after coating may be inferior, and an excellent appearance may not be imparted to the hot-dip galvanized steel sheet after coating. If the glossiness (G value) is 750 or more, it may be too smooth, and oil may not be retained on the surface of the hot dip galvanized layer when the hot dip galvanized steel sheet is pressed, resulting in poor formability. In addition, the said glossiness (G value) means the glossiness (G value) measured by the method as described in an Example.

Zinc basal plane orientation ratio (Zn (002) / (004)), which is the ratio of the crystal orientation of the (002) plane of Zn crystal to the crystal orientation of the (004) plane of Zn crystal on the surface of the hot dip galvanized layer. ) Is preferably 60 or more and 90 or less. If the orientation ratio of the bottom surface of the zinc base is less than 60, the orientation of the zinc crystals is relatively random, and the crystal size when the zinc solidifies immediately after plating becomes fine. May be inferior in moldability without being held on the surface. If the orientation ratio of the basal plane of the zinc base is more than 90, the orientation of the basal plane of the Zn crystal is too high and the crystal grains are likely to grow. As a result, the dendritic arm develops. The appearance of the steel sheet may deteriorate. Moreover, if the zinc base bottom surface orientation ratio exceeds 90, the corrosion resistance may be deteriorated. Here, the zinc base bottom surface orientation ratio can be defined by the following formula.

The zinc base bottom orientation ratio (Zn (002) / (004)) represents {(002) plane Zn crystal orientation} / {(004) plane Zn crystal orientation}. Further, (I _(xyz) is the Zn intensity measured by X-ray on the (xyz) plane of the sample, and I _{std (xyz)} is the Zn intensity measured by X-ray on the (xyz) plane of the standard sample (pure Zn powder). means)
If the zinc basal plane orientation ratio is defined as described above, Zn has an hcp structure and is usually easily oriented to the basal plane, and it can be understood how much crystals are randomly oriented. The degree of orientation of the solidified structure affects the gloss, crystal size, and surface roughness (surface roughness). For this reason, it is important to control the press workability in addition to controlling the surface orientation of the hot-dip galvanized steel sheet in order to accurately control the zinc base orientation ratio. In addition, if the zinc base bottom surface orientation ratio is in the above range, the gloss and the surface roughness Ra satisfy the above preferable range.

Further, the hot dip galvanized layer may be formed on at least a part of the steel plate surface. Since the hot dip galvanized layer is formed on the surface of the steel plate by a method of immersing the steel plate in a plating bath, the hot dip galvanized layer is usually formed on the entire surface of the steel plate.

Further, the thickness of the hot dip galvanized layer is not particularly limited. The thickness of the hot dip galvanized layer can be adjusted by controlling the amount of plating applied during the hot dip galvanizing process.

<Intermetallic compound>
Intermetallic compound is composed of an intermetallic compound consisting of at least one of an average particle diameter of 1μm or less of Fe ₂ Al ₅ or FeAl _3, present in the steel sheet and hot-dip galvanizing layer. Further, the intermetallic compound contains 0.12 gm ⁻² or more and 0.22 gm ⁻² or less of Al. The presence of the intermetallic compound can suppress the formation of the FeZn alloy phase and ensure good plating adhesion. This effect cannot be obtained in cases other than an intermetallic compound composed of at least one of Fe ₂ Al ₅ or FeAl ₃ . Other than these, a hard and brittle FeZn intermetallic compound may be formed, and in this case, the plating adhesion deteriorates. The presence of the intermetallic compound can be confirmed by a method of analyzing and detecting the vicinity of the interface with the steel plate 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 or FeAl ₃ exceeds 1 μm, the hard intermetallic compound is excessively grown, and the impact resistance characteristics of the hot dip galvanized steel sheet deteriorate. For this reason, the upper limit of the average particle diameter is 1 μm.

If the Al content in the intermetallic compound is less than 0.12 gm ^−2, it is necessary to set the Al concentration in the molten zinc bath of the plating low. If the Al concentration is set low, dross precipitates and the molten zinc The appearance and workability of the plated steel sheet deteriorate. If the Al content in the intermetallic compound exceeds 0.22 gm ^-2 , the Al concentration in the plating bath needs to be set high. If the Al concentration is set high, an Al oxide film is formed on the surface of the hot dip galvanized layer. A large amount is formed and spot weldability deteriorates.

<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 painting of a processed part after press working. And the hot-dip galvanized steel sheet of the present invention has an excellent appearance after coating. For this reason, the hot dip galvanized steel sheet of the present invention can be applied to products having very severe processing parts such as a back door and a hood.

Moreover, the hot dip galvanized steel sheet of the present invention has a yield stress (YS) of 220 MPa or more and 320 MPa or less. If the yield stress is in the above range, the hot-dip galvanized steel sheet can be preferably applied to applications that require severe processing such as outer plates and that must ensure shape freezeability.

<Method for producing hot-dip galvanized steel sheet>
Then, the manufacturing method of a hot dip galvanized steel plate is demonstrated. For example, a hot-dip galvanized steel sheet can be manufactured by the following method. First, steel having the above component composition is made into a slab by continuous casting, the slab is heated, and scale removal and rough rolling are performed. Next, after cooling, finish rolling, cooling, winding, pickling, and cold rolling are performed. Next, the steel sheet is annealed and hot-dip galvanized in a continuous hot-dip galvanizing facility. Next, an alloying treatment is performed as necessary.

The heating time, heating temperature, rough rolling conditions, cooling conditions, finish rolling conditions, winding conditions, etc. when heating the slab can be appropriately set based on common technical knowledge.

Also, the annealing conditions of the steel sheet affect the yield stress of the hot dip galvanized steel sheet. In the present invention, in order to set the yield stress in the above range, it is preferable to set the heating temperature during annealing to 780 ° C. or more and 820 ° C. or less.

In the present invention, in order to control the Al content of the hot dip galvanized layer and allow an intermetallic compound to exist between the steel plate and the hot dip galvanized layer, the hot dip galvanizing treatment condition needs to be a specific condition. is there. Moreover, in order to make the surface state (surface roughness Ra, glossiness (G value), zinc base bottom orientation ratio) of a hot dip galvanized layer into a desired state, it is necessary to adjust the conditions of the hot dip galvanizing treatment. . Hereinafter, conditions for the hot dip galvanizing process will be described.

The intrusion plate temperature, which is the temperature of the steel plate when the annealed steel plate enters the plating bath, is not particularly limited. In the present invention, the temperature of the immersion plate is preferably a temperature of the plating bath (bath temperature) of −20 ° C. or higher and a bath temperature of + 20 ° C. or lower. If the infiltration plate temperature is in the above range, the change in bath temperature is small, and it is easy to perform desired hot dip galvanization continuously.

The composition of the plating bath into which the annealed steel sheet enters is not limited as long as it contains Al in addition to Zn, and may contain other components as necessary. The concentration of Al in the plating bath is not particularly limited. In the present invention, the Al concentration is preferably 0.16% by mass or more and 0.25% by mass or less. If the concentration of Al is 0.16% by mass or more and 0.25% by mass or less, an FeAl alloy phase is formed and formation of an FeZn alloy phase is suppressed, which is preferable. The glossiness can be adjusted by the Al concentration in the plating bath. When the Al concentration in the plating bath becomes low, FeZn crystals rather than FeAl are formed slightly at the interface between the steel sheet and the hot dip galvanized layer. When this FeZn crystal becomes a Zn solidification nucleus generation site, a large number of zinc crystals are generated, and the orientation rate tends to decrease due to randomization of the zinc crystal orientation. As a result, as the Al concentration is lower, dendritic Zn crystal growth is suppressed, and surface unevenness is reduced and smoothed, so that the glossiness increases. A more preferable Al concentration is 0.19% by mass or more and 0.22% by mass or less.

Further, the temperature of the plating bath (bath temperature) is not particularly limited. In the present invention, the bath temperature is preferably 440 ° C. or higher and 480 ° C. or lower. A bath temperature of 440 ° C. or higher and 480 ° C. or lower is preferable because an appropriate bath temperature can be stably secured and Zn does not solidify even if the bath temperature distribution is deteriorated. Moreover, since the solubility of the FeAl alloy phase decreases as the bath temperature decreases, the amount of FeAl alloy phase generated tends to increase. A more preferable range of the bath temperature is 450 ° C. or higher and 460 ° 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 0.5 seconds or more and 3 seconds or less. When the immersion time is in the above range, a desired hot dip galvanized layer is easily formed on the surface of the steel plate.

Immediately after lifting the steel plate from the plating bath, the amount of plating adhesion is adjusted by gas jet wiping or the like. In the present invention, the plating adhesion amount is not particularly limited. In the present invention, the plating adhesion amount is preferably in the range of 20 g / m ² or more and 120 g / m ² or less. If the plating adhesion amount is less than 20 g / m ² , it may be difficult to ensure corrosion resistance. On the other hand, when the plating adhesion amount exceeds 120 g / m ² , the plating peel resistance may deteriorate.

After adjusting the plating adhesion amount as described above, temper rolling (SK treatment) is performed. The type of roll used for the SK treatment is not particularly limited, and an Electro-Discharge Texture roll (EDT roll), an Electron Beam Texture roll (EBT roll), a shotdal roll, a topochrome roll, or the like can be used.

The rolling reduction rate during SK treatment (SK rolling reduction rate (%)) is not particularly limited. In the present invention, the SK pressure ratio is preferably 0.7 to 0.9%. If the SK rolling reduction is in the above range, the surface roughness can be easily adjusted to the above preferable range. Further, if the SK rolling reduction is outside the above range, the dullness that holds the rolling oil may not be obtained, and the formability may be reduced, and the yield strength may be reduced.

The cooling rate ({(cooling end temperature) − (cooling start temperature)} / cooling time) after the steel sheet is pulled up from the plating bath is preferably −5 ° C./second or more and −30 ° C./second or less. If the cooling rate is −5 ° C./second or less, spangles may become coarse, which is not preferable. If the cooling rate is −30 ° C./second or more, rapid cooling is required to secure the cooling rate, resulting in a deterioration in economy. It is not preferable. On the other hand, if the cooling rate is slow, the FeAl alloy phase is decomposed and the amount of FeAl alloy phase produced is reduced. A more preferable range of the cooling rate is −7 ° C./second or more and −22 ° C./second or less. Here, the cooling rate refers to an average cooling rate when the temperature is lowered from 420 ° C. to 400 ° C.

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

The hot dip galvanized steel sheet of the present invention is preferably used for applications in which a coating film is formed on the surface of the hot dip galvanized layer because it has excellent post-coating corrosion resistance after press working. Moreover, the hot-dip galvanized steel sheet of the present invention is excellent in plating adhesion even when applied to applications requiring strict workability, and does not significantly reduce corrosion resistance and mechanical properties. Examples of applications in which strict processability is required and a coating film is formed include automotive steel plates such as automobile outer plates and inner plates. The method for forming the coating film is not particularly limited. In the present invention, it is preferable that a chemical conversion treatment is performed on the surface of the hot dip galvanized layer to form a chemical conversion film, and then a coating film is formed on the chemical conversion film.

Either a coating type or a reaction type can be used as the chemical conversion treatment liquid. Moreover, the component contained in a chemical conversion liquid is not specifically limited, either a chromate processing liquid may be used and a chromium free chemical conversion liquid may be used. Moreover, the chemical conversion 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 electrodeposition coating, roll coater coating, curtain flow coating, and spray coating. Moreover, in order to dry a coating material, means, such as hot air drying, infrared heating, induction superheating, can be used.

Hereinafter, the present invention will be described with reference to examples. The present invention is not limited to the following examples.

The black scale of the hot-rolled steel sheet having the steel composition shown in Table 1 is removed by pickling and cold-rolled at a reduction rate of 75%, and then the surface is on the entry side of the CGL (continuous hot dip galvanizing line). After degreasing pretreatment, annealing was performed at an annealing temperature shown in Table 2 in an annealing furnace, and hot dip galvanizing treatment was performed under the conditions shown in Table 2. The average cooling rate from 420 to 400 ° C. after plating and wiping was also measured. The cooling rate is also shown in Table 2. In addition, after pulling up the steel plate from the plating bath and adjusting the plating adhesion amount by gas jet wiping, SK treatment was performed under the conditions shown in Table 2 before cooling.

It was confirmed by the following method that the structure of the steel sheet was composed of a ferrite single phase. A test piece was collected from the steel plate, the cross section in the rolling direction (L cross section) was polished, etched with a nital solution, and the structure was observed and imaged using an optical microscope (magnification: 50 to 400 times). And the kind of tissue and the fraction (area%) were measured using the image analysis apparatus. All the steel plates were steel plates substantially composed of a ferrite single phase.

The intermetallic compound composition was identified by the X-ray diffraction method after removing the zinc plating layer with fuming nitric acid. Regarding the amount, the surface of the intermetallic compound on the sample surface prepared in the same manner was dissolved in dilute hydrochloric acid and quantified by ICP. Similarly, the amount of Al in the plating layer was dissolved in dilute hydrochloric acid and determined by ICP.

The particle size of the intermetallic compound was measured by the following method. A test piece was collected from the steel plate, and the metal structure of a cross section parallel to the rolling direction was observed with a scanning electron microscope (SEM) at a magnification of 5000 to measure the average particle size of the intermetallic compound. The measurement 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 the provisions of JIS B 0601, the arithmetic average roughness Ra was measured using a stylus type surface roughness meter. The measurement results are shown in Table 2.

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

Using an X-ray diffractometer, the crystal orientation of the (002) plane 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 are measured, and the zinc base bottom orientation ratio (Zn (002 ) / (004)). The zinc base bottom surface orientation ratio is shown in Table 2.

The resulting hot-dip galvanized steel sheet is subjected to chemical conversion treatment, electrodeposition coating, intermediate coating, and top coating to produce a hot-dip galvanized steel sheet on which a coating film has been formed and visually evaluated after coating. did. When there was no appearance defect due to plating unevenness or the like, it was evaluated as good, and when it was present, it was evaluated as defective. The evaluation results are shown in Table 1.

As for the plating adhesion of the processed part after press working, the punch with a frustum diameter of 5/8 inch is heightened at 1843 g for the part subjected to frustoconical overmolding (molding equivalent to press molding) under the condition of a plate thickness reduction rate of 10%. An impact resistance test of dropping from 1 m was performed, and evaluation was performed by a method of peeling cellophane tape. Those with peeling were considered poor adhesion (x), and those without peeling were good adhesion (◯). The evaluation results are shown in Table 2.

¡Cone overhang molding part was subjected to chemical treatment, electrodeposition coating, intermediate coating, and top coating, and the 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 of the processed part after press working was evaluated. Those with blisters were judged as bad (x), and those without blisters were judged as good (◯). The evaluation results are shown in Table 2.

A JIS No. 5 tensile test piece is taken from the hot dip galvanized steel sheet in the direction of 90 ° with respect to the rolling direction, and a tensile test is performed under the condition that the crosshead speed is 10 mm / min (constant) in accordance with the provisions of JIS Z 2241. It was. A YS of 220 to 320 MPa was considered good. The evaluation results are shown in Table 2.

As is apparent from Table 2, the hot-dip galvanized steel sheet of the present invention has extremely good characteristics and does not undergo plating peeling despite being pressed. Corrosion resistance is also good.

Claims (2)

In mass%, C: 0.001% to 0.005%, Si: 0.10% or less, Mn: 0.70% to 1.50%, P: 0.050% to 0.100% , S: 0.010% or less, N: 0.005% or less, Al: 0.10% or less, B: 0.0015% or less, and Ti: 0.01% or more and 0.05% or less And Nb: containing at least one selected from 0.01% to 0.05%, the balance being a composition of Fe and inevitable impurities, and a steel plate substantially composed of a ferrite single phase;
Formed on at least a part of the surface of the steel sheet, a hot-dip galvanized layer containing Al by 0.3% to 0.6% by mass,
Between the steel sheet and the hot-dip galvanized layer, between 0.12 gm ⁻² and 0.22 gm ⁻² of Al and having an average particle size of 1 μm or less and consisting of at least one of Fe ₂ Al ₅ or FeAl ₃ And having a compound,
A hot-dip galvanized steel sheet having a yield stress (YS) of 220 MPa or more and 320 MPa or less. The surface roughness Ra of the surface of the hot dip galvanized layer is 0.8 μm or more and 1.6 μm or less,
The glossiness (G value) of the surface of the hot dip galvanized layer is 550 or more and 750 or less,
Zinc basal plane orientation ratio (Zn (002) / (004), which is the ratio of the crystal orientation of the (002) plane of Zn crystal to the crystal orientation of the (004) plane of Zn crystal on the surface of the hot dip galvanized layer. The hot dip galvanized steel sheet according to claim 1, wherein)) is 60 or more and 90 or less.