TWI675924B - Hot-dip galvanized steel sheet - Google Patents

Abstract

A hot-dip galvanized steel sheet has a hot-dip galvanized layer on at least one side of a base material steel sheet, and the hot-dip galvanized steel sheet is characterized in that the Fe content in the hot-dip galvanized layer is greater than 0% and less than 3.0%, and Al The content is greater than 0% and less than 1.0%; an Fe-Al alloy layer is provided at the interface between the hot-dip galvanized layer and the base material steel plate; the thickness of the Fe-Al alloy layer is 0.1 μm to 2.0 μm; and the width direction of the base material steel plate The difference between the maximum 値 and the minimum 前述 of the thickness of the foregoing Fe-Al alloy layer is within 0.5 μm; the base metal steel plate has a micronized layer in direct contact with the Fe-Al alloy layer, and the average thickness of the micronized layer It is 0.1 μm to 5.0 μm, the average particle size of the iron phase of the fertilizer particles in the micronized layer is 0.1 μm to 3.0 μm, the micronized layer contains one or two or more oxides of Si and Mn, and the oxidation The maximum diameter of the object is 0.01 μm to 0.4 μm; the difference between the maximum 値 and the minimum 厚度 of the thickness of the aforementioned miniaturized layer in the width direction of the base material steel plate is within 2.0 μm.

Description

Hot-dip galvanized steel sheet

The present invention relates to a hot-dip galvanized steel sheet excellent in strength, ductility, hole expandability, plating adhesion and appearance uniformity.

BACKGROUND OF THE INVENTION High strength has been required for steel sheets mainly used for automobile frame members. In order to obtain high strength and excellent formability, these high-strength steel plates generally contain alloy elements represented by Si and Mn, which contribute to strength improvement. However, the alloying elements represented by Si and Mn also reduce the plating adhesion. In addition, since steel plates for automobiles are generally used outdoors, excellent corrosion resistance is generally required.

For automotive exterior panels and the like, press-processing is generally used to perform severe bending processing (folded bending) on the peripheral portion of the panel. Moreover, not only automotive exterior panels, but also other applications are often used after pressing to carry out severe bending or reaming. On the other hand, when the conventional hot-dip galvanized steel sheet is subjected to severe bending or hole-reaming processing, the processed part may peel off the plating layer from the base material steel sheet. If the plating layer is peeled off like this, the corrosion resistance will be lost there, and the base material steel plate will corrode and rust from an early stage. Even if it is not to the extent that the plating layer is peeled off, the adhesion between the plating layer and the base material steel plate will be lost, resulting in some voids in this part, causing outside air or moisture to penetrate through the voids, and causing the plating layer to lose its anti-corrosion function. . As a result, as mentioned above, the base steel plate is corroded and rusted from an early age. Based on these problems, high-strength steel sheets to be used after severe bending and the like are strongly desired to use a galvanized steel sheet having a hot-dip galvanized layer having excellent adhesion to the base steel sheet.

In order to improve the adhesion of the plating layer, for example, as disclosed in Patent Documents 1 to 3, a method has been proposed to generate oxides inside the steel sheet to reduce the oxides at the interface between the base iron and the plating layer that cause plating peeling. Method. However, when the oxide is generated on the surface layer of the steel sheet, the carbon on the surface layer of the steel sheet is combined with oxygen to gasify. As a result, carbon is detached from the steel sheet, so the area where the carbon is detached may be significantly reduced in strength. When the strength of the steel sheet surface layer is reduced, the fatigue resistance, which is strongly affected by the characteristics of the surface layer portion, will be deteriorated, and there is a possibility that the fatigue strength will be greatly reduced.

Or in order to improve the adhesion of the plating layer, Patent Document 4 proposes a new annealing step and a pickling step to be performed before the general annealing step to modify the surface of the base material steel plate and improve the plating adhesion. Sexual methods. However, the method described in Patent Document 4 requires a number of steps for a general method for manufacturing a high-strength plated steel sheet, and has a cost problem.

In addition, Patent Document 5 proposes a method of removing carbon from a surface layer portion of a base material steel sheet to improve plating adhesion. However, the method described in Patent Document 5 significantly reduces the strength of the carbon-removed region. Therefore, the method described in Patent Document 5 deteriorates the fatigue resistance characteristics greatly affected by the characteristics of the surface layer portion, and there is a possibility that the fatigue strength is significantly reduced.

In addition, Patent Documents 6 and 7 propose steel plates in which the amounts of Mn, Al, and Si in the plating layer are controlled within a suitable range to improve the adhesion of the plating. However, the steel sheets described in Patent Documents 6 and 7 require a high-precision control of the amount of elements in the plating layer during manufacture, which causes a large burden on the work and has a cost problem.

Regarding a method for improving the adhesion of the plating, Patent Document 8 proposes a high-strength steel sheet whose microstructure of a steel sheet is composed of only ferrous iron. However, the steel sheet described in Patent Document 8 cannot obtain a sufficiently high strength because the microstructure is only soft ferrous iron.

Nowadays, alloyed hot-dip galvanized steel sheets that are subjected to alloying treatment after hot-dip galvanizing are widely used. The alloying treatment is a treatment in which the plating layer is heated to a temperature above the melting point of Zn, a large amount of Fe atoms are diffused from the base material steel plate into the plating layer, and the plating layer is made into a layer of a Zn-Fe alloy body. For example, Patent Documents 9, 10, and 11 propose an alloyed hot-dip galvanized steel sheet having excellent plating adhesion. However, in order to sufficiently alloy the plating layer, the steel sheet must be heated to a high temperature. If the steel sheet is heated to a high temperature, the internal structure of the steel sheet will be deteriorated, and coarse iron-based carbides are particularly likely to be generated, thereby deteriorating the properties of the steel sheet, which is unfavorable.

On the other hand, for example, the hot-dip galvanized steel sheet described in Patent Document 12 has a problem of uneven appearance due to unevenness in Fe content in the width direction of the plating layer.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 2008-019465 Patent Literature 2: Japanese Patent Laid-Open No. 2005-060742 Patent Literature 3: Japanese Patent Laid-Open No. 9-176815 Patent Literature 4: Japanese Patent Laid-Open No. 2001- Patent Document No. 026853 Patent Document 5: Japanese Patent Application Publication No. 2002-088459 Patent Document 6: Japanese Patent Application Publication No. 2003-055751 Patent Document 7: Japanese Patent Application Publication No. 2003-096541 Patent Document 8: Japanese Patent Application Publication No. 2005-200750 Patent Document 9: Japanese Patent Application Laid-Open No. 11-140587 Patent Document 10: Japanese Patent Application Laid-Open No. 2001-303226 Patent Literature 11: Japanese Patent Application Laid-Open No. 2005-060743 Patent Literature 12: International Publication No. 2016/072477

Summary of the Invention Problems to be Solved by the Invention In view of the foregoing, the present invention is to provide a hot-dip galvanized steel sheet having excellent strength, ductility, hole expandability, spot-welding plating adhesion, and uniform appearance.

Means for Solving the Problems The present inventors have been actively reviewing repeatedly to obtain a hot-dip galvanized steel sheet having excellent plating adhesion and uniform appearance. As a result, it was found that even if a steel plate containing a large amount of Si and Mn is used as a plating base plate, a Fe-Al alloy layer formed directly at an interface between a plating layer formed using a plating bath containing a specific amount of Al and a base steel plate By forming a specific micronized layer composed of extremely fine particles of a fat iron phase, it is possible to suppress generation and propagation of cracks during processing, and to prevent plating peeling from occurring there. In addition, it has been found that when a steel sheet containing a large amount of Si and Mn is used as a plating original sheet, an uneven internal oxide layer is formed in the width direction of the steel sheet, resulting in uneven Fe content in the plating layer of the hot-dip galvanized steel sheet. Uneven appearance. Therefore, the inventors of the present inventors have further actively reviewed the factors that cause the formation of a non-uniform internal oxide layer, and found that the reason lies in the difference in the oxygen concentration in the width direction after the hot-rolled steel sheet is coiled. The inventors of the present inventors have further actively reviewed in order to suppress the uneven appearance caused by the plating layer. As a result, it was found that by controlling the thickness of the micronized layer and the Fe-Al alloy layer in the width direction of the steel sheet within a specific range, it is possible to obtain a hot-dip galvanized steel sheet that is excellent not only in plating adhesion but also in appearance uniformity.

This invention is made | formed in view of the said knowledge, and its aspect is as follows.

(1) A hot-dip galvanized steel sheet having a hot-dip galvanized layer on at least one side of a base metal steel sheet, and the hot-dip galvanized steel sheet is characterized in that the above-mentioned base metal steel sheet has a chemical composition shown below: C% by mass, C : 0.040% to 0.400%, Si: 0.05% to 2.50%, Mn: 0.50% to 3.50%, P: 0.0001% to 0.1000%, S: 0.0001% to 0.0100%, Al: 0.001% to 1.500%, N: 0.0001 % ~ 0.0100%, O: 0.0001% ~ 0.0100%, Ti: 0.000% ~ 0.150%, Nb: 0.000% ~ 0.100%, V: 0.000% ~ 0.300%, Cr: 0.00% ~ 2.00%, Ni: 0.00% ~ 2.00%, Cu: 0.00% ~ 2.00%, Mo: 0.00% ~ 2.00%, B: 0.0000% ~ 0.0100%, W: 0.00% ~ 2.00%, Ca, Ce, Mg, Zr, La, and REM: 0.0000% in total ~ 0.0100%, and the remainder: Fe and impurities; the Fe content in the aforementioned hot-dip galvanized layer is greater than 0% and less than 3.0%, and the Al content is greater than 0% and less than 1.0%; The interface of the steel sheet has a Fe-Al alloy layer; the thickness of the Fe-Al alloy layer is 0.1 μm to 2.0 μm; the difference between the maximum 値 and the minimum 厚度 of the thickness of the Fe-Al alloy layer in the width direction of the base material steel plate is 0.5. Within μm; the aforementioned base material steel plate There is a micronized layer in direct contact with the Fe-Al alloy layer, and the average thickness of the micronized layer is 0.1 μm to 5.0 μm, and the average particle size of the iron phase of the fertilizer particles in the micronized layer is 0.1 μm to 3.0 μm. In the foregoing micronized layer, one or two or more oxides of Si and Mn are contained, and the maximum diameter of the oxide is 0.01 μm to 0.4 μm; the maximum thickness of the micronized layer in the width direction of the base material steel plate The difference between 値 and minimum 値 is within 2.0 μm.

(2) The hot-dip galvanized steel sheet according to (1), which satisfies the following formula 1 when the Si content (mass%) in the aforementioned base material steel sheet is [Si] and the Al content (mass%) is [Al]; The total thickness of the base metal steel plate is 1% or more of the residual Vosstian iron in the range of 1/8 thickness to 3/8 thickness centered on 1/4 thickness from the surface of the base metal steel plate. [Si] +0.7 [Al] ≧ 0.30 (Equation 1).

(3) The hot-dip galvanized steel sheet according to (1) or (2), wherein the coating adhesion amount per one side of the aforementioned hot-dip galvanized layer is 10 g / m ² or more and 100 g / m ² or less.

(4) The hot-dip galvanized steel sheet according to any one of (1) to (3), wherein the aforementioned chemical composition satisfies: Ti: 0.001% to 0.150%, Nb: 0.001% to 0.100%, or V: 0.001% to 0.300%, or any combination of these.

(5) The hot-dip galvanized steel sheet according to any one of (1) to (4), wherein the aforementioned chemical composition satisfies: Cr: 0.01% to 2.00%, Ni: 0.01% to 2.00%, Cu: 0.01% to 2.00% , Mo: 0.01% ~ 2.00%, B: 0.0001% ~ 0.0100%, or W: 0.01% ~ 2.00%, or any combination thereof.

(6) The hot-dip galvanized steel sheet according to any one of (1) to (5), wherein the foregoing chemical composition satisfies: Ca, Ce, Mg, Zr, La, and REM: 0.0001% to 0.0100% in total.

Advantageous Effects of Invention According to the present invention, a hot-dip galvanized steel sheet excellent in strength, ductility, hole expandability, spot weldability, plating adhesion, and appearance uniformity can be provided.

Embodiments for Carrying Out the Invention Embodiments of the present invention will be described in detail below.

First, a hot-dip galvanized steel sheet according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a sectional view showing a hot-dip galvanized steel sheet according to an embodiment of the present invention. The hot-dip galvanized steel sheet 1 according to this embodiment is provided with a hot-dip galvanized layer 3 on the surface of the base metal steel sheet 2, and an Fe-Al alloy layer 4 is provided at the interface between the hot-dip galvanized layer 3 and the surface of the base metal steel sheet 2. A micronization layer 5 and a decarburization layer 6 are provided in contact with the Fe-Al alloy layer 4.

(Base material steel plate 2) The chemical composition of the base material steel plate 2 constituting the hot-dip galvanized steel plate 1 according to the embodiment of the present invention and the steel billet used for its production will be described. The details will be described later. The hot-dip galvanized steel sheet 1 according to the embodiment of the present invention is manufactured by casting a steel billet, hot rolling, cold rolling, annealing, and plating. Therefore, the chemical composition of the base material steel plate 2 and the steel billet used for its manufacture is not only the characteristics of the base material steel plate 2 but also such treatments. In the following description, the "%" of each element content unit contained in the base steel plate 2 or the steel blank means "mass%" as long as there is no particular limitation. The base material steel plate has the following chemical composition: C: 0.040% ~ 0.400%, Si: 0.05% ~ 2.50%, Mn: 0.50% ~ 3.50%, P: 0.0001% ~ 0.1000%, S: 0.0001% ~ 0.0100%, Al: 0.001% to 1.500%, N: 0.0001% to 0.0100%, O: 0.0001% to 0.0100%, Ti: 0.000% to 0.150%, Nb: 0.000% to 0.100%, V: 0.000% to 0.300%, Cr: 0.00% ~ 2.00%, Ni: 0.00% ~ 2.00%, Cu: 0.00% ~ 2.00%, Mo: 0.00% ~ 2.00%, B: 0.0000% ~ 0.0100%, W: 0.00% ~ 2.00%, Ca, Ce, Mg, Zr, La and REM: 0.0000% ~ 0.0100% in total, and the rest: Fe and impurities. Examples of the impurities include those contained in raw materials such as ore and waste, and those contained in the manufacturing steps.

(C: 0.040% ~ 0.400%) C can improve the strength of the base material steel plate. When the C content is more than 0.400%, the spot weldability is deteriorated. Therefore, the C content is set to 0.400% or less. From the viewpoint of point fusion properties, the C content should preferably be 0.300% or less, and more preferably 0.220% or less. In order to obtain higher strength, the C content should be set to 0.055% or more, and more preferably 0.070% or more.

(Si: 0.05% to 2.50%) Si can suppress the formation of iron-based carbides in the base material steel sheet and improve the strength and formability. On the other hand, Si embrittles the steel sheet. Therefore, when the Si content is greater than 2.50%, the cast steel embryo is liable to crack. Therefore, the Si content is set to be 2.50% or less. Si will form oxides on the surface of the base material steel plate during annealing, which significantly deteriorates the adhesion of the plating. Therefore, the Si content should be set to 2.00% or less, and more preferably 1.60% or less. When the content of Si is less than 0.05%, a large amount of coarse iron-based carbides are generated during plating of a base material steel plate, which deteriorates strength and formability. Therefore, the Si content is set to be 0.05% or more. From the viewpoint of suppressing the formation of iron-based carbides, the Si content should preferably be 0.10% or more, and more preferably 0.25% or more.

(Mn: 0.50% to 3.50%) Mn can improve the strength by improving the hardenability of the base material steel sheet. When the Mn content is greater than 3.50%, a high Mn concentration portion is generated in the central portion of the base material steel sheet thickness, which easily causes embrittlement, and the cast steel billet becomes easily cracked. Therefore, the Mn content is set to 3.50% or less. From the viewpoint of worsening of the spot weldability, the Mn content should preferably be 3.00% or less, and more preferably 2.80% or less. When the Mn content is less than 0.50%, a large amount of soft structure is formed during cooling after annealing, and it is difficult to ensure sufficiently high tensile strength. Therefore, the Mn content is set to be 0.50% or more. In order to obtain higher strength, the Mn content should be set to 0.80% or more, and more preferably 1.00% or more.

(P: 0.0001% ~ 0.1000%) P makes the steel brittle. Therefore, when the P content is more than 0.1000%, the cast steel billet will become easily cracked. Therefore, the P content is set to 0.1000% or less. In addition, P causes brittleness of the portion that is melted through the penetration point. Therefore, in order to obtain sufficient fusion bonding strength, the P content should preferably be 0.0400% or less, and more preferably 0.0200% or less. When the P content is less than 0.0001%, the manufacturing cost will increase significantly. Therefore, the P content is set to be 0.0001% or more, and is preferably set to 0.0010% or more.

(S: 0.0001% to 0.0100%) S combines with Mn to form coarse MnS, which reduces the formability such as ductility, stretch flangeability, and bendability. Therefore, the S content is set to 0.0100% or less. In addition, S deteriorates the spot weldability. Therefore, the S content should preferably be 0.0060% or less, and more preferably 0.0035% or less. When the S content is less than 0.0001%, the manufacturing cost will increase significantly. Therefore, the S content is set to be 0.0001% or more, preferably 0.0005% or more, and more preferably 0.0010% or more.

(Al: 0.001% to 1.500%) Al embrittles the steel. Therefore, when the Al content is greater than 1.500%, the cast steel billet is liable to crack. Therefore, the Al content is set to 1.500% or less. From the viewpoint that the spot weldability will deteriorate, the Al content should preferably be 1.200% or less, and more preferably 1.000% or less. The lower limit Al content is not particularly limited, and Al may be contained in the steel as an impurity. In order to make the Al content less than 0.001%, the manufacturing cost will be greatly increased. Therefore, the Al content is set to 0.001% or more. Al is a deoxidizing element of steel. In order to obtain a sufficient deoxidation effect, the Al content should preferably be set to 0.010% or more.

(N: 0.0001% to 0.0100%) N forms coarse nitrides, which deteriorates moldability such as ductility, stretch flangeability, and bendability. When the N content is more than 0.0100%, the formability is significantly deteriorated. Therefore, the N content is set to 0.0100% or less. If the N content is too high, pores will be generated during welding, so the N content should be set to 0.0070% or less, and more preferably 0.0050% or less. The lower limit 値 of the N content is not particularly limited, and N may be contained in the steel as an impurity. In order to make the N content less than 0.0001%, the manufacturing cost will be greatly increased. Therefore, the N content is set to be 0.0001% or more, preferably 0.0003% or more, and more preferably 0.0005% or more.

(O: 0.0001% to 0.0100%) O forms oxides and deteriorates moldability such as ductility, stretch flangeability, and bendability. When the O content is more than 0.0100%, the formability is significantly deteriorated. Therefore, the O content is set to 0.0100% or less, preferably 0.0050% or less, and more preferably 0.0030% or less. The lower limit of the O content is not particularly limited, and O may be contained in the steel as an impurity. In order to make the O content less than 0.0001%, the manufacturing cost will be greatly increased. Therefore, the N content is set to be 0.0001% or more, preferably 0.0003% or more, and more preferably 0.0005% or more.

([Si] +0.7 [Al]: 0.30 or more) Si and Al can suppress the formation of carbides that are accompanied by the toughening iron metamorphosis. In order to obtain residual Vosstian iron, it is preferable to contain more than a predetermined amount of Si and / or Al. The TRIP effect can be obtained by making a residual Vosstian iron. From this viewpoint, when the Si content (% by mass) in the base material steel sheet is [Si] and the Al content (% by mass) is [Al], it is preferable to satisfy the following formula 1. That is, 値 on the left side of the following formula 1 ([Si] +0.7 [Al]) is preferably 0.30 or more, more preferably 0.45 or more, and still more preferably 0.70 or more. [Si] +0.7 [Al] ≧ 0.30 (Equation 1).

Ti, Nb, V, Cr, Ni, Cu, Mo, B, W, Ca, Ce, Mg, Zr, La, and REM are not essential elements, and they can be contained in the steel sheet to a limited extent and may contain a predetermined amount of any element .

(Ti: 0.000% to 0.150%) Ti can increase the strength of steel sheets by strengthening the precipitates, suppressing the growth of ferrous iron grains to strengthen the fine grains, and inhibiting the differential strengthening by recrystallization. Therefore, Ti may be contained. When the Ti content is more than 0.150%, carbonitrides are precipitated more, resulting in poor formability. Therefore, the Ti content is set to 0.150% or less. From the viewpoint of formability, the Ti content should preferably be 0.080% or less. The lower limit of the Ti content is not particularly limited, but in order to fully obtain the effect of improving the strength, the Ti content should be set to 0.001% or more. In order to fully obtain the above effects, the Ti content is more preferably 0.010% or more.

(Nb: 0.000% to 0.100%) Nb can increase the strength of steel sheets by strengthening the precipitates, suppressing the growth of ferrous iron grains to strengthen the fine grains, and inhibiting the differential strengthening by recrystallization. Therefore, Nb may be contained. When the content of Nb is more than 0.100%, carbonitrides are precipitated more, resulting in poor formability. Therefore, the Nb content is set to 0.100% or less. From the viewpoint of moldability, the Nb content is preferably 0.060% or less. The lower limit Nb content 値 is not particularly limited, but in order to fully obtain the effect of improving the strength, the Nb content should be set to 0.001% or more. In order to fully obtain the above effects, the Nb content is more preferably set to 0.005% or more.

(V: 0.000% ~ 0.300%) V can increase the strength of steel sheets by strengthening the precipitates, suppressing the growth of ferrous iron grains to strengthen the fine grains, and inhibiting the differential strengthening by recrystallization. Therefore, V may be contained. When the V content is more than 0.300%, the carbonitrides are precipitated more, resulting in poor formability. Therefore, the V content is set to 0.300% or less, and preferably 0.200% or less. The lower limit of the V content 特别 is not particularly limited, but in order to fully obtain the effect of improving the strength, the V content should be set to 0.001% or more, and more preferably 0.010% or more.

(Cr: 0.00% ~ 2.00%) Cr can suppress the phase transformation at high temperature to further improve the strength of the steel sheet. Therefore, Cr may be substituted for part of C and / or Mn. If the Cr content is more than 2.00%, the workability may be deteriorated during hot rolling and the productivity may be reduced. Therefore, the Cr content is preferably 2.00% or less, and preferably 1.20% or less. The lower limit Cr content is not particularly limited, but in order to fully obtain the effect of further improving the strength, the Cr content should preferably be set to 0.01% or more, and more preferably 0.10% or more.

(Ni: 0.00% ~ 2.00%) Ni can suppress the phase transformation at high temperature to further improve the strength of the steel sheet. Therefore, Ni and C and / or Mn may be substituted. If the Ni content is more than 2.00%, the weldability may be impaired. Therefore, the Ni content is set to 2.00% or less, and preferably 1.20% or less. The lower limit of the Ni content 値 is not particularly limited, but in order to fully obtain the effect of increasing the strength, the Ni content should be set to 0.01% or more, and more preferably 0.10% or more.

(Cu: 0.00% to 2.00%) Cu can exist as fine particles in steel to improve strength. Therefore, Cu and / or Mn may be substituted by Cu. When the Cu content is more than 2.00%, the weldability may be impaired. Therefore, the Cu content is preferably 2.00% or less, and preferably 1.20% or less. The lower limit of the Cu content is not particularly limited, but in order to fully obtain the effect of improving the strength, the Cu content should be set to 0.01% or more, and more preferably 0.10% or more.

(Mo: 0.00% ~ 2.00%) Mo can suppress the phase transformation at high temperature to further improve the strength of the steel sheet. Therefore, Mo may be substituted for part of C and / or Mn. When the Mo content is more than 2.00%, the workability may be deteriorated during hot rolling and the productivity may be reduced. Therefore, the Mo content is preferably 2.00% or less, and preferably 1.20% or less. The lower limit of Mo content is not particularly limited, but in order to fully obtain the effect of further improving the strength, the Mo content should preferably be set to 0.01% or more, and more preferably set to 0.05% or more.

(B: 0.0000% ~ 0.0100%) B can suppress the phase transformation at high temperature to further improve the strength of the steel sheet. Therefore, B and C and / or Mn may be substituted. When the B content is more than 0.0100%, the workability may be deteriorated during hot rolling and the productivity may be reduced. Therefore, the B content is set to 0.0100% or less. From the viewpoint of productivity, the B content should preferably be 0.0050% or less. The lower limit of the B content 値 is not particularly limited, but in order to fully obtain the effect of further improving the strength, the B content should be set to 0.0001% or more, and more preferably 0.0005% or more.

(W: 0.00% ~ 2.00%) W can suppress the transformation at high temperature to improve the strength of the steel sheet. Therefore, it may contain W in place of C and / or Mn. If the W content is more than 2.00%, the workability may be deteriorated during hot rolling and the productivity may be reduced. Therefore, the W content is set to 2.00% or less, and preferably 1.20% or less. The lower limit of W content 値 is not particularly limited, but in order to fully obtain the effect of further improving the strength, the W content should be set to 0.01% or more, and more preferably 0.10% or more.

(Ca, Ce, Mg, Zr, La, and REM: 0.0000% to 0.0100% in total) Ca, Ce, Mg, Zr, La, or REM can improve formability. Therefore, Ca, Ce, Mg, Zr, La, or REM may be contained. If the total content of Ca, Ce, Mg, Zr, La, and REM is more than 0.0100%, the ductility may be impaired. Therefore, the total content of Ca, Ce, Mg, Zr, La, and REM is set to 0.0100% or less, and the total content is preferably set to 0.0070% or less. The lower limit 含量 of the contents of Ca, Ce, Mg, Zr, La, and REM is not particularly limited. In order to fully obtain the effect of improving the formability of the steel sheet, the total content of Ca, Ce, Mg, Zr, La, and REM should be 0.0001% or more , More preferably set to more than 0.0010%. In addition, REM is an abbreviation of Rare Earth Metal, and refers to an element belonging to the lanthanide series. In the embodiment of the present invention, for example, REM or Ce may be added as a rare earth metal alloy, and in addition to La or Ce, there may be a case where the compound contains a lanthanoid element. Lanthanides other than La or Ce may be contained as impurities. It may also contain metal La or metal Ce.

In addition, Ti, Nb, V, Cr, Ni, Cu, Mo, B, and W may also be contained if they are impurities and fall below the lower limit of the content of each element. Ca, Ce, Mg, Zr, La, and REM may be contained as impurities that are below the above-mentioned total lower limit.

(Hot galvanized layer 3) [Fe content in the hot-dip galvanized layer 3: more than 0% and 3.0% or less] The Fe content in the hot-dip galvanized layer 3 is more than 0% and 3.0% or less. It is difficult to produce a hot-dip galvanized layer 3 having an Fe content of 0%. Therefore, let the Fe content be greater than 0%. From the viewpoint of ensuring plating adhesion, the Fe content is preferably 0.3% or more, and more preferably 0.5% or more. When the Fe content is more than 3.0%, the plating adhesion is reduced. Therefore, the Fe content is set to 3.0% or less. From the viewpoint of ensuring plating adhesion, the Fe content should preferably be 2.5% or less, and more preferably 2.0% or less.

[Al content of the hot-dip galvanized layer 3: more than 0% and 1.0% or less] The Al content of the hot-dip galvanized layer 3 is more than 0% and 1.0% or less. If the Al content is 0%, Fe atoms will diffuse into the hot-dip galvanized layer 3 and promote the alloying of the Zn-Fe alloy, resulting in a decrease in plating adhesion. Therefore, let the Al content be greater than 0%. From the viewpoint that the progress of the alloying can be suppressed, the Al content is preferably 0.1% or more, and more preferably 0.2% or more. When the Al content is more than 1.0%, the plating adhesion is reduced. Therefore, the Al content is set to 1.0% or less. From the viewpoint of ensuring plating adhesion, the Al content is preferably 0.8% or less, and more preferably 0.5% or less.

[Plating adhesion amount per side of the hot-dip galvanized layer 3: 10 g / m ² or more and 100 g / m ² or less] When the plating adhesion amount is less than 10 g / m ² , sufficient corrosion resistance may not be obtained. Therefore, the plating adhesion amount should preferably be 10 g / m ² or more. From the viewpoint of corrosion resistance, the plating adhesion amount is more preferably 20 g / m ² or more, and more preferably 30 g / m ² or more. When the plating adhesion amount is more than 100 g / m ² , electrode loss during spot welding becomes intense, and when the continuous welding is performed, the diameter of the molten block is reduced, and the welding strength may be deteriorated. Therefore, the plating adhesion amount should be 100 g / m ² or less. From the viewpoint of the continuous weldability, coating weight of plating is more appropriate to 93g / m ² or less, again to 85g / m ² or less is preferable.

The hot-dip galvanized layer 3 may also contain Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb , Ni, Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, and REM. By containing these elements, corrosion resistance and processability can be improved.

The hot-dip galvanized layer 3 may contain columnar crystals composed of a zeta phase (FeZn ₁₃ ). From the viewpoint of plating adhesion, the ζ-phase coating ratio in the entire interface between the hot-dip galvanized layer 3 and the base metal steel plate 2 is preferably set to less than 20%.

(Fe-Al alloy layer 4) [Thickness of Fe-Al alloy layer 4: 0.1 μm to 2.0 μm] In the embodiment of the present invention, the interface system between the hot-dip galvanized layer 3 and the surface of the base material steel plate 2 is formed with an Fe-Al alloy. Layer 4. The formation of the Fe-Al alloy layer 4 can suppress the alloying of the Zn-Fe alloy, and can suppress the decrease in plating adhesion. In addition, it is possible to suppress uneven appearance due to uneven alloying. Compared with an alloyed hot-dip galvanized steel sheet that has been subjected to an alloying treatment after the hot-dip galvanizing process, a non-alloyed hot-dip galvanized steel sheet is more likely to cause uneven appearance due to uneven alloying. When the thickness of the Fe-Al alloy layer 4 is less than 0.1 μm, the plating adhesion and appearance are deteriorated. Therefore, the thickness of the Fe-Al alloy layer 4 is set to be 0.1 μm or more. When the thickness of the Fe-Al alloy layer 4 is more than 2.0 μm, the plating adhesion is reduced. Therefore, the thickness of the Fe-Al alloy layer 4 is set to 2.0 μm or less, and preferably 1.0 μm or less.

[Difference between the maximum and minimum thicknesses of the thickness of the Fe-Al alloy layer 4 in the width direction of the base material steel plate 2: within 0.5 μm] The maximum and minimum thicknesses of the Fe-Al alloy layer 4 in the width direction of the base material steel plate 2 The difference refers to the measurement of the thickness of the Fe-Al alloy layer 4 at a distance of 50 mm from both ends of the Fe-Al alloy layer 4 and the Fe-Al alloy layer 4 divided into 7 equal parts at a total of 8 thicknesses. difference. The thinner the thickness of the Fe-Al alloy layer 4, the easier it is to alloy the Zn-Fe alloy. Therefore, the larger the thickness difference of the Fe-Al alloy layer 4 in the width direction of the base steel plate 2 is, the more uneven its alloying becomes. When the difference between the maximum 値 and the minimum 厚度 of the thickness of the Fe-Al alloy layer 4 is greater than 0.5 μm, the plating adhesion and the uniformity of the plating appearance are deteriorated. Therefore, the difference between the maximum 値 and the minimum 値 of the thickness of the Fe-Al alloy layer 4 is set to be within 0.5 μm, preferably within 0.4 μm, and more preferably within 0.3 μm.

(Refinement layer 5) The base material steel plate 2 includes a refinement layer 5 and a decarburization layer 6 which are in contact with the Fe-Al alloy layer 4. As described later, the micronized layer 5 and the decarburized layer 6 are layers formed by performing a decarburization reaction under conditions of controlling a specific temperature range and a specific gas environment during annealing. Therefore, the structure constituting the micronization layer 5 screens out oxides and inclusion particles, which essentially consists of the fertile phase 7 as the main body, and the structure constituting the decarburized layer 6 screens out oxides and inclusion particles, which substantially The fertile iron phase 8 is the main component. Specifically, the volume fractions of the fertile iron phases 7, 8 are 70% or more, and the remainder is a mixture of one or more of the Vostian iron phase, the toughened iron phase, the Asada loose iron phase, and the boron iron phase. organization. The micronized layer 5 exists when the average particle diameter of the ferrous iron phase 7 in the outermost part of the base material steel plate 2 is 1/2 or less of the average particle diameter of the ferrous iron phase 8 of the decarburized layer 6. The boundary between the micronized layer 5 and the decarburized layer 6 is a boundary where the average particle diameter of the ferrous iron phase 7 which is the micronized layer 5 is larger than 1/2 of the average particle diameter of the ferrous iron phase 8 of the decarburized layer 6.

[Average thickness of the micronized layer 5: 0.1 μm to 5.0 μm] When the average thickness of the micronized layer 5 is less than 0.1 μm, cracks may occur, and stretching cannot be suppressed, which may cause poor plating adhesion. Therefore, the average thickness of the micronization layer 5 is set to be 0.1 μm or more, preferably 0.2 μm or more, and more preferably 0.3 μm or more. When the average thickness of the micronized layer 5 is more than 5.0 μm, the alloying of the Zn-Fe alloy is promoted, the Fe content in the hot-dip galvanized layer 3 is increased, and the plating adhesion is deteriorated. Therefore, the average thickness of the micronization layer 5 is 5.0 μm or less, preferably 4.0 μm or less, and more preferably 3.0 μm.

[Average particle diameter of the ferrous iron phase 7: 0.1 μm to 3.0 μm] When the average particle diameter of the ferrous iron phase 7 is less than 0.1 μm, cracks may occur and the stretching cannot be suppressed, which may cause poor plating adhesion. Therefore, the average particle diameter of the ferrous iron phase 7 is assumed to be 0.1 μm or more. When the average particle diameter of the ferrous iron phase 7 is more than 3.0 μm, the plating adhesion is deteriorated. Therefore, the average particle diameter of the ferrous iron phase 7 is set to 3.0 μm or less, and preferably set to 2.0 μm or less.

The average thickness of the micronized layer 5 and the average particle diameter of the ferrous iron phase 7 in the micronized layer 5 were measured by the following methods. A sample was taken from the hot-dip galvanized steel sheet 1 with a cross section parallel to the rolling direction of the base steel sheet 2 as an observation surface. The observation surface of the sample was processed with a CP (Cross section polisher) device, and measured at 5000 times observation with a reflected electron image in a FE-SEM (Field Emission Scanning Electron Microscopy).

[Maximum diameter of oxide: 0.01 μm to 0.4 μm] The micronized layer 5 contains one or more oxides of Si and Mn. The oxide may be, for example, one or more members selected from the group consisting of SiO ₂ , Mn ₂ SiO ₄ , MnSiO ₃ , Fe ₂ SiO ₄ , FeSiO ₃ , and MnO. As described later, this oxide is formed in the base material steel plate 2 in a specific temperature range during annealing. The oxide particles can suppress the growth of the ferrous grain iron phase crystals in the surface layer of the base material steel plate 2 and form a fine layer 5. When the maximum oxide diameter is less than 0.01 μm, the micronized layer 5 cannot be sufficiently formed, and thus the plating adhesion is deteriorated. Therefore, the maximum oxide diameter is set to 0.01 μm or more, and preferably set to 0.05 μm or more. When the maximum oxide diameter is larger than 0.4 μm, the ferrous iron phase 7 will be coarsened, and the micronized layer 5 will not be sufficiently formed, and the oxide itself will become the starting point of plating peeling, which will deteriorate the plating adhesion. Therefore, the maximum diameter of the oxide is set to 0.4 μm or less, and preferably 0.2 μm or less.

The maximum oxide diameter is measured by the method shown below. A sample was taken from the hot-dip galvanized steel sheet 1 with a cross section parallel to the rolling direction of the base steel sheet 2 as an observation surface. The specimen observation surface was processed into a film specimen by FIB (Focused Ion Beam). Then, the film sample was observed at 30,000 times with FE-TEM (Field Emission Transmission Electr on Microscopy). Observe 5 fields of view for each film sample, and use the maximum diameter in the measurement grate obtained by the full field measurement as the maximum oxide diameter.

[Difference between the maximum and minimum thicknesses of the thickness of the micronized layer 5 in the width direction of the base material steel plate 2: within 2.0 μm] The difference between the maximum and minimum thicknesses of the thickness of the micronized layer 5 in the width direction of the base material steel plate 2 is The thickness of the micronized layer 5 was measured at a distance of 50 mm from both ends of the micronized layer 5 and divided into 7 equal parts, and the thickness of the micronized layer 5 was measured. The thicker the thickness of the micronized layer 5 is, the easier it is to alloy the Zn-Fe alloy. Therefore, the larger the difference in thickness of the micronized layer 5 in the width direction of the base material steel plate 2 is, the more uneven its alloying becomes. If the difference between the maximum 値 and the minimum 厚度 of the thickness of the micronized layer 5 is larger than 2.0 μm, the plating adhesion and the uniformity of the plating appearance are deteriorated. Therefore, the difference between the maximum 値 and the minimum 厚度 of the thickness of the micronization layer 5 is set to be within 2.0 μm, preferably within 1.5 μm, and more preferably within 1.0 μm.

(Microstructure) The microstructure of the base material steel sheet 2 of the hot-dip galvanized steel sheet 1 according to the embodiment of the present invention is not particularly limited, and it is preferable to have the following microstructure. The characteristics of the steel plate vary with the microstructure. In order to quantify the microstructure, it is impossible to quantify the entire area of the steel plate in reality. Therefore, it is centered on the surface of the base steel plate 2 and the thickness is 1/8 to 3/8. The scope of the microstructure represents the microstructure of the steel plate to be quantified. The microstructure at the center of the plate thickness changes due to strong solidification segregation, so it cannot be said to represent the microstructure of a steel plate. The microstructure near the surface layer of the base material steel plate 2 changes due to local temperature changes and / or reaction with external air, so it cannot be called a microstructure that can represent the steel plate.

The microstructure of the base material steel plate 2 of the hot-dip galvanized steel sheet 1 according to the embodiment of the present invention may be granular ferrous iron, acicular ferrous iron, unrecrystallized ferrous iron, boron iron, toughened iron, and toughened fertilizer. More than one type of granulated iron, Asada loose iron, tempered Asada loose iron, residual Vosda iron, and heavy cuming carbon iron. In order to obtain the characteristics corresponding to the application of the hot-dip galvanized steel sheet 1, the base steel sheet 2 can appropriately select the details of each phase and the volume fraction of each structure, the size of the structure, and the arrangement.

[Residual Vosstian Iron: 1% or more] Residual Vosstian Iron is a structure that can greatly improve the balance between strength and ductility. When the volume fraction of the residual Vostian iron in the range of 1/8 thickness to 3/8 thickness centered on 1/4 thickness from the surface of the base steel plate 2 is less than 1%, the effect of improving the balance between strength and ductility can be improved. May become smaller. Therefore, the volume fraction of residual Vosstian iron should be set to 1% or more. In order to improve the balance between strength and ductility, the volume fraction of residual Vosstian iron should be more than 3%, and more than 5%. In order to obtain a large amount of residual Wastfield iron, the C content will be greatly increased. However, a large amount of C may significantly deteriorate the weldability. Therefore, the volume fraction of residual Vosstian iron should be set to 25% or less. The residual Vostian iron will transform into hard Asada loose iron as it deforms, and this Asada loose iron will become the starting point of damage and affect it, so the extension flangeability may be deteriorated. Therefore, it is more preferable to set the volume fraction of the residual Vosstian iron to 20% or less.

The volume fraction of each structure contained in the base material steel sheet 2 of the hot-dip galvanized steel sheet 1 according to the embodiment of the present invention is measured by, for example, the following method.

The volume fraction of the residual Vosstian iron contained in the base material steel sheet 2 of the hot-dip galvanized steel sheet 1 of this embodiment is evaluated by the X-ray diffraction method. Centering 1/4 thickness from the surface of the base steel plate 2 in the range of 1/8 thickness to 3/8 thickness, the surface parallel to the plate surface is processed into a mirror surface, and the FCC (Face) is measured by X-ray diffraction method. Centered Cubic) area fraction of iron, and this measurement was used as the volume fraction of residual Vosstian iron.

Ferritic iron, toughened ferrous iron, toughened iron, tempered Asada loose iron, fresh Asada loose iron, bolai iron, and heavy cis-carbon iron The volume fraction was measured using a field emission scanning electron microscope (FE-SEM). Samples were taken with a cross section parallel to the rolling direction of the base steel plate 2 as the observation surface. The observation surface of the sample was ground and etched with nitrate. FE-SEM was used to observe the observation surface in the range of 1/8 thickness to 3/8 thickness with the plate thickness 1/4 as the center, and the area fraction was measured, and this measurement was regarded as the volume fraction.

In the hot-dip galvanized steel sheet 1 of this embodiment, the thickness of the base material steel sheet 2 is not particularly limited. From the viewpoint of the flatness of the hot-dip galvanized steel sheet 1 and the controllability during cooling, the thickness of the base material steel sheet 2 is preferably 0.6 mm or more and less than 5.0 mm.

Next, a method for manufacturing a hot-dip galvanized steel sheet according to an embodiment of the present invention will be described. In this method, a steel blank having the above-mentioned chemical composition is subjected to casting, hot rolling, cold rolling, annealing, plating, and cooling after plating. Between annealing and plating and / or during cooling after plating, in order to obtain residual Vosstian iron, a toughening iron metamorphosis treatment is performed as needed.

(Casting) First, casting is performed on a hot-rolled billet. The steel slabs to be supplied for hot rolling can be produced by continuous casting steel slabs or using thin steel slab continuous casting machines.

(Hot Rolling) In order to suppress the anisotropy of the crystal direction caused by casting, the heating temperature of the steel billet should be set to 1080 ° C or more, and more preferably 1150 ° C or more. On the other hand, the upper limit 値 of the heating temperature of the steel billet is not particularly limited. When the heating temperature of the steel billet is higher than 1300 ° C, a large amount of energy may be input, and the manufacturing cost may increase significantly. Therefore, the heating temperature of the steel billet should preferably be 1300 ° C or lower.

Hot rolling is performed after heating the steel billet. When the end temperature of the hot rolling (rolling end temperature) is lower than 850 ° C, the reaction force of the rolling becomes high, and it is difficult to stably obtain a predetermined sheet thickness. Therefore, the hot-rolling end temperature is preferably 850 ° C or higher, and more preferably 875 ° C or higher. If the end temperature of hot rolling is higher than 980 ° C, the steel sheet may be heated after the heating of the steel billet and before the end of the hot rolling, which may increase the cost. Therefore, the end temperature of hot rolling is preferably 980 ° C or lower, and more preferably 960 ° C or lower.

Next, the hot-rolled steel sheet after hot rolling is rolled into a coil. In addition, the average cooling rate when cooling after hot rolling and before coiling is preferably set to 10 ° C./second or more. The reason is that by deforming at a lower temperature, the grain size of the hot-rolled steel sheet can be made smaller, and the effective grain size of the base material steel sheet after cold rolling and annealing is made fine.

The coiling temperature should preferably be 350 ° C or higher and 750 ° C or lower. On the other hand, boron iron and / or coarse skeletal carbon iron with a major diameter of 1 μm or more are dispersed and formed into the microstructure of the hot-rolled steel sheet, and localized strain is introduced into the hot-rolled steel sheet by cold rolling. This is to reverse the Vostian iron in various crystal directions during annealing afterwards. This makes it possible to refine the effective grain size of the annealed base material steel sheet. When the take-up temperature is lower than 350 ° C, there is a case where it is impossible to generate boron iron and / or coarse skeletal carbon iron. Therefore, the winding temperature should be set to 350 ° C or higher. In order to reduce the strength of the hot-rolled steel sheet and facilitate cold rolling, the coiling temperature is more preferably set to 450 ° C or higher. When the coiling temperature is higher than 750 ° C, long band-shaped wave iron and ferrous iron are formed in the rolling direction, and the effective grain direction of the base material steel plate generated from the ferrous iron after cold rolling and annealing is The rolling direction is extended and coarsened. Therefore, the winding temperature should be set to 750 ° C or lower. In order to reduce the effective grain size of the annealed base material steel sheet, the coiling temperature is more preferably 680 ° C or lower. After the hot-rolled steel sheet is coiled, the internal oxide layer is formed thicker at the center than the end of the steel sheet, so that the internal oxide layer is unevenly formed under the scale layer. This situation becomes more pronounced when the coiling temperature exceeds 650 ° C. When the internal oxide layer cannot be removed by acid pickling and cold rolling described later, the micronized layer and the Fe-Al alloy layer may be formed unevenly, and the plating adhesion and appearance uniformity may be deteriorated. . Therefore, the coiling temperature should be more than 650 ° C.

Next, the hot-rolled steel sheet produced as described above is pickled. Pickling can remove oxides formed on the surface of hot-rolled steel sheet and help improve the plating properties of the base material steel sheet. Pickling can be performed once or several times. From the viewpoint that the micronized layer and the Fe-Al alloy layer can be formed uniformly and the uniformity of the appearance achieved can be ensured, it is preferable to strengthen the pickling to remove as much as possible the internal oxide layer formed under the scale layer. The pickling conditions are not particularly limited as long as the internal oxide layer can be removed. For example, from the viewpoint of pickling efficiency and economy, hydrochloric acid is preferably used for pickling. Conditions for removing the internal oxide layer, for example, the concentration of hydrochloric acid should be set to 5 mass% or more, the pickling temperature should be set to 80 ° C or higher, and the pickling time should be set to 30 seconds or more. For example, when the take-up temperature is higher than 650 ° C., it is better to strengthen the pickling to remove the internal oxide layer as much as possible, and the pickling time is more preferably set to 60 seconds or more.

(Cold Rolling) Next, the hot-rolled steel sheet after pickling is cold-rolled. When the total reduction ratio is more than 85%, the steel sheet loses ductility, and the steel sheet may break during cold rolling. Therefore, the total reduction ratio should be 85% or less, more preferably 75% or less, and 70% or less. The lower limit 値 of the total reduction ratio is not particularly limited. However, when the total reduction ratio is less than 0.05%, the shape of the base material steel plate is not uniform, and the plating cannot adhere uniformly, which may damage the appearance. Therefore, the total reduction ratio should preferably be 0.05% or more, and more preferably 0.10% or more. In addition, the cold rolling should be carried out in multiple passes, and there are no restrictions on the number of cold rolling passes and the allocation of the rolling reduction ratio for each pass.

When the total reduction ratio is more than 10% and less than 20%, recrystallization cannot be sufficiently performed in subsequent annealing, and coarse grains that lose ductility due to a large amount of differential discharge remain near the surface layer of the steel sheet, causing bending. When the properties and fatigue resistance are deteriorated. Therefore, reducing the total of the rolling reduction ratio can effectively reduce the ductility of the accumulated grains while retaining the grains. Or increase the total reduction ratio, and recrystallization can be sufficiently performed during annealing, so that the processed structure can effectively be made into recrystallized grains with little internal differential accumulation. From the viewpoint of reducing the accumulation of differential emissions in the crystal grains, the total reduction ratio should preferably be 10% or less, and more preferably 5.0% or less. On the other hand, in order to sufficiently recrystallize during annealing, the total reduction ratio is preferably 20% or more, and more preferably 30% or more.

(Annealing) Next, annealing is performed on the cold-rolled steel sheet. For annealing, continuous annealing plating production line with pre-heating zone, soaking zone and plating zone should be used. It is appropriate to anneal the cold-rolled steel sheet and pass it through the preheat zone and the soaking zone, and finish the annealing when the cold-rolled steel plate reaches the plating zone, and perform plating on the plating zone.

As described above, when using a continuous annealing plating line, for example, the following method is preferably used. In particular, in order to uniformly form a predetermined micronization layer and an Fe-Al alloy layer to ensure plating adhesion and appearance uniformity, it is important to control a pre-tropical gas environment and a heating method, and control a uniform tropical gas environment.

Preheating belt, based _{Log (P (H 2 O)} / P (H 2)) Log Zhi controlled water vapor partial pressure P (H ₂ O) and the hydrogen partial pressure P (H ₂₎ in a ratio of -1.7 In a gas environment of ~ -0.2, use a preheated burner with an air ratio of 0.7 ~ 1.0 to heat to 400 ° C ~ 800 ° C, and pass the cold-rolled steel plate at the same time. Adjusting the ratio of the water vapor partial pressure P (H ₂ O) to the hydrogen partial pressure P (H ₂ ) in the pre-tropic zone will cause the Fe-Al alloy phase to uniformly precipitate in the width direction at the interface during subsequent galvanizing and The surface properties of the steel sheet before plating affect. Adjusting the air ratio in the preheat zone can prevent the formation of oxide films of strong deoxidizing elements such as Si on the surface of the steel sheet. In addition, adjusting the air ratio and adjusting the ratio of the water vapor partial pressure P (H ₂ O) to the hydrogen partial pressure P (H ₂ ) can prevent excessive decarburization on the surface of the steel sheet. Thereby, in the subsequent plating step, excessive Fe-Zn alloy reactions at the grain boundaries on the surface of the steel plate can be suppressed, and Fe-Al alloy reactions can be selectively performed. By selectively performing the Fe-Al alloy reaction, formation of a uniform Fe-Al alloy layer can be promoted, and excellent plating adhesion and uniform appearance can be obtained. When Log (P (H ₂ O) / P (H ₂ )) is greater than -0.2, it is easy to cause Fe-Zn alloying in the subsequent plating step, so that the Fe concentration in the plating becomes high. As a result, plating adhesion is reduced, and uneven appearance is liable to occur. On the other hand, when Log (P (H ₂ O) / P (H ₂ )) is less than -1.7, a high carbon concentration portion is formed on the surface of the steel sheet, and a fine layer cannot be formed on the surface, which reduces the plating adhesion. .

The "air ratio" refers to the ratio of the volume of air contained in a unit volume of a mixed gas to the volume of air theoretically required to completely burn a fuel gas contained in a unit volume of a mixed gas, and it can be expressed by the following formula. Air ratio = [Air volume (m ³ ) contained in mixed gas per unit volume] / [Air volume (m ³ ) theoretically required for complete combustion of fuel gas contained in unit gas per mixed volume] Air ratio is greater than 1.0 In this case, an Fe oxide film is excessively formed on the surface layer portion of the steel sheet, the decarburized layer after annealing is enlarged, and a micronized layer is excessively formed. Therefore, plating alloying progresses excessively, and plating adhesion, chipping, and pulverization are reduced. Therefore, the air ratio should preferably be 1.0 or less, and more preferably 0.9 or less. When the air ratio is less than 0.7, a fine layer cannot be formed, and the plating adhesion is lowered. Therefore, the air ratio is preferably 0.7 or more, and more preferably 0.8 or more.

If the temperature of the steel sheet to pass the preheating zone is lower than 400 ° C, a sufficient micronized layer cannot be formed. Therefore, the temperature of the steel sheet to pass the preheating zone should be set to 400 ° C or more, and more preferably 600 ° C or more. If the temperature of the steel sheet to be passed through the preheating zone is higher than 800 ° C, coarse oxides containing Si and / or Mn are formed on the surface of the steel sheet, and the plating adhesion is reduced. Therefore, the temperature of the steel sheet to pass the preheating zone should be 800 ° C or lower, and more preferably 750 ° C or lower.

If the heating speed of the preheating zone is slow, the inside will be oxidized, and coarse oxides will be generated inside the steel sheet. The heating rate at 600 ℃ ~ 750 ℃ is especially important. In order to suppress the excessive decarburization of the steel sheet surface layer and the formation of coarse oxides, the average heating rate at 600 ° C to 750 ° C should preferably be 1.0 ° C / sec or more. When the average heating rate is less than 1.0 ° C / second, coarse oxides are generated in the fine-grained layer, and the plating adhesion or pulverization are reduced. Therefore, the average heating rate should preferably be 1.0 ° C / second or more. From the viewpoint of suppressing excessive decarburization of the steel sheet surface layer to generate coarse oxides, the average heating rate is more preferably 1.5 ° C / second or more, and more preferably 2.0 ° C / second or more. From the viewpoint of ensuring a preheating zone treatment time, the average heating rate should preferably be 50 ° C / sec or less. If the average heating rate is 50 ° C / sec or less, a uniform fine-grained layer can be easily obtained, and a molten zinc-plated layer having excellent plating adhesion and uniform appearance can be obtained.

To control the volume fraction of the microstructure related to the formability of the steel sheet within a predetermined range, the maximum heating temperature for annealing is an important factor. If the maximum heating temperature is low, coarse iron-based carbides will melt and remain in the steel, resulting in poor formability. Therefore, in order to sufficiently solid-solve iron-based carbides to improve formability, the maximum heating temperature should preferably be 750 ° C or higher. In particular, in order to obtain residual Vosstian iron, the maximum heating temperature is more preferably set to (Ac1 + 50) ° C or higher. The upper limit 値 of the maximum heating temperature is not particularly limited, but from the viewpoint of plating adhesion, in order to reduce the oxides formed on the surface of the base material steel plate, the maximum heating temperature should be 950 ° C or lower, and more preferably 900 ° C or lower. .

The Ac1 points of the steel plates are the starting points of Vostian Iron inversion. Specifically, the Ac1 point can be obtained by cutting a small piece from a hot-rolled steel sheet that has been post-hot rolled, and heating it to 1200 ° C at 10 ° C / second, and measuring the volume expansion during this period.

The maximum heating temperature for annealing will reach the point of homogeneity. In this uniform tropical gas environment, Log (P (H ₂ O) / P (H ₂ )) is controlled to -1.7 to -0.2. When Log (P (H ₂ O) / P (H ₂ )) is less than -1.7, a fine layer cannot be formed, and the plating adhesion is reduced. Therefore, Log (P (H ₂ O) / P (H ₂ )) should be set to -1.7 or more. When Log (P (H ₂ O) / P (H ₂ )) is greater than -0.2, decarburization will proceed excessively, and not only the hard phase of the surface layer of the base material steel plate will be significantly reduced, but coarse oxides will also be formed in the refined layer. To reduce plating adhesion and pulverization. Therefore, Log (P (H ₂ O) / P (H ₂ )) should be set to -0.2 or less.

When the log (P (H ₂ O) / P (H ₂ )) of the soaking zone is -1.7 to -0.2, the Si oxide and / or Mn oxide, which will be the starting point of plating peeling, will not be formed on the outermost layer of the steel sheet. In the surface layer of the steel sheet, fine oxides of Si and / or Mn having a maximum diameter of 0.01 μm to 0.4 μm will be formed. Fine oxides of Si and / or Mn can suppress the growth of Fe recrystallization during annealing. And because the water vapor in the annealing gas environment will decarburize the surface layer of the base material steel plate, the microstructure of the surface layer of the base material steel plate after annealing will become a ferrous iron phase. As a result, the average thickness of the surface layer of the base material steel sheet after annealing is 0.1 μm to 5.0 μm, the average particle size of the ferrous iron phase is 0.1 μm to 3.0 μm, and the maximum diameter is 0.01 μm to 0.4 μm containing Si and / or Mn Refinement layer of oxide.

The cooling conditions before the plating from the maximum heating temperature to the plating bath are not particularly limited. However, in order to obtain residual Vostian iron, it is necessary to suppress the generation of bolai iron and Xueming carbon iron. Therefore, in terms of cooling conditions before plating, the average cooling rate from 750 ° C to 700 ° C should preferably be 1.0 ° C / second or more, and more preferably 5.0 ° C / second or more. The upper limit of the average cooling rate is not particularly limited. However, in order to obtain an excessively large average cooling rate, special cooling equipment or a refrigerant which does not affect the plating may be used. From this viewpoint, the average cooling rate from 750 ° C to 700 ° C should preferably be 100 ° C / sec or less, and more preferably 70 ° C / sec or less.

In order to obtain the tempered Asada loose iron after the subsequent plating, the Asada loose iron metamorphic treatment can also make the steel plate stay in the predetermined temperature range for a certain period of time after the temperature of the steel plate reaches 500 ° C and reaches the plating bath. The temperature for processing the metamorphism of loose iron in Asada should be set to less than the temperature at which the metamorphism of Masada loose iron starts (Ms point), and more preferably (Ms point -20) ° C or lower. The temperature of Asada loose iron metamorphosis treatment should be set to 50 ° C or more, and more preferably 100 ° C or more. It should be set to 1 second to 100 seconds, and more preferably set to 10 seconds to 60 seconds. In addition, the Asada loose iron, which can be obtained by the abnormal treatment of the Asada loose iron, will be transformed into tempered Asada loose iron by immersing the steel plate in a high-temperature plating bath during plating.

Let VF be the volume fraction (%) of ferrous iron, C content (mass%) be [C], Si content (mass%) be [Si], Mn content (mass%) be [Mn], and Cr content ( Mass%) is [Cr], Ni content (mass%) is [Ni], and Al content (mass%) is [Al], the Ms point can be calculated by the following formula. In addition, it is difficult to directly measure the volume fraction of ferrous iron in the production of a hot-dip galvanized steel sheet. Therefore, the cold-rolled steel sheet is cut into small pieces before passing through the continuous annealing production line, and the small pieces are annealed with the same temperature history as when passing through the continuous annealing production line, and the volume change of the ferrous iron in the small pieces is measured. The volume fraction (VF) of the fertilized iron was calculated by measuring the ferrite. Ms point [℃] = 541-474 [C] / (1-VF) -15 [Si] -35 [Mn] -17 [Cr] -17 [Ni] +19 [Al]

After cooling before plating, in order to obtain residual Vostian iron, the deformed iron deforming treatment can also make the steel plate stay in the temperature range of 250 ° C to 500 ° C for a certain time. The toughening iron metamorphosis treatment may be performed between annealing and plating, or during cooling after plating, and may be performed on both sides between annealing and plating and during cooling after plating.

When the toughened iron metamorphic treatment is performed between annealing and plating and on both sides during cooling after plating, the sum of the residence time of the toughened iron metamorphic treatment should be 15 seconds or more and 500 seconds or less. When the sum of the dwell times is less than 15 seconds, the toughening iron metamorphosis cannot proceed sufficiently, and sufficient residual Vostian iron cannot be obtained. Therefore, the sum of the dwell times should be 15 seconds or more, and more preferably 25 seconds or more. When the sum of the dwell times is more than 500 seconds, boron iron and / or coarse citronite are generated. Therefore, the sum of the residence time should be 500 seconds or less, and more preferably 300 seconds or less.

When the tempered iron metamorphic treatment is performed between annealing and plating, if the tempered iron metamorphic processing temperature is higher than 500 ° C, boron iron and / or coarse citron iron will be generated, and the residual Vostian cannot be obtained. iron. Therefore, the tempering iron transformation temperature should be set to 500 ° C or lower. In addition, in order to promote the concentration of carbon to Vostian iron with the transformation of toughened iron, the tempered iron metamorphosis treatment temperature is more preferably set to 485 ° C or lower, and more preferably 470 ° C or lower. If the tempering iron metamorphic treatment temperature is lower than 250 ° C., the tempering iron metamorphosis will not proceed sufficiently, and residual Vostian iron cannot be obtained. Therefore, the tempering iron transformation temperature should be set to 250 ° C or higher. In order to effectively perform the toughening iron metamorphosis, the toughening iron metamorphosis treatment temperature is more preferably set to 300 ° C or more, and more preferably to 340 ° C or more. In addition, after cooling before plating, both the toughened iron metamorphic treatment and the Mata loose iron metamorphic treatment are performed, and the Mata loose iron metamorphic treatment is performed before the toughened iron metamorphic treatment.

(Plating) Next, the obtained base material steel plate was immersed in a plating bath. The plating bath has zinc as a main component, and a composition obtained by subtracting the total Fe amount from the total Al amount in the plating bath, that is, the effective Al amount is 0.180 mass% to 0.250 mass%. When the effective Al amount in the plating bath is less than 0.180% by mass, the Fe-Al alloy layer may not be sufficiently formed, and Fe may enter the molten zinc plating layer, thereby impairing the plating adhesion. Therefore, the effective Al amount in the plating bath is preferably set to 0.180% by mass or more, more preferably set to 0.185% by mass or more, and more preferably set to 0.190% by mass or more. If the effective Al amount in the plating bath is greater than 0.250% by mass, the Fe-Al alloy layer at the interface between the surface of the base material steel sheet and the hot-dip galvanized layer may be excessively formed, thereby impairing the plating adhesion. Therefore, the effective Al amount in the plating bath is preferably 0.250% by mass or less, more preferably 0.240% by mass or less, and even more preferably 0.230% by mass or less.

The plating bath may also contain Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni , Pb, Rb, Sb, Si, Sn, Sr, Ta, Ti, V, W, Zr, and REM. The content of each element can improve the corrosion resistance and workability of the hot-dip galvanized layer.

When the temperature of the plating bath is lower than 440 ° C, the viscosity of the plating bath will be excessively increased, and it will be difficult to control the thickness of the hot-dip galvanized layer, which will damage the appearance of the hot-dip galvanized steel sheet. Therefore, the temperature of the plating bath is preferably 440 ° C or higher, and more preferably 445 ° C or higher. When the temperature of the plating bath is higher than 470 ° C, a large amount of smoke is generated, which is difficult to manufacture safely. Therefore, the temperature of the plating bath is preferably 470 ° C or lower, and more preferably 460 ° C or lower.

If the temperature of the steel sheet when the base steel sheet enters the plating bath is lower than 430 ° C, it is not practical to give a large amount of heat to the plating bath in order to stabilize the plating bath temperature above 440 ° C. Therefore, the temperature of the steel sheet when the base steel sheet enters the plating bath should be 430 ° C or higher. In order to form a predetermined Fe-Al alloy layer, the steel plate temperature when the base material steel plate enters the plating bath is more preferably 440 ° C or higher. If the temperature of the steel plate when the base steel plate enters the plating bath is higher than 480 ° C, in order to stabilize the temperature of the plating bath below 470 ° C, equipment that can discharge a large amount of heat from the plating bath will be introduced, which will reduce the manufacturing cost. high. Therefore, the temperature of the steel sheet when the base steel sheet enters the plating bath should be 480 ° C or lower. In order to form a predetermined Fe-Al alloy layer, the temperature of the steel sheet when the base steel sheet enters the plating bath is more preferably 470 ° C or lower.

The temperature of the plating bath is more preferably stable in a temperature range of 440 ° C to 470 ° C. If the temperature of the plating bath is unstable, the Fe content in the Fe-Al alloy layer or the hot-dip galvanized layer will be uneven, and the appearance of the plating layer will be uneven, resulting in poor plating adhesion. Therefore, in order to stabilize the temperature of the plating bath, the temperature of the steel plate when entering the plating bath should be approximately the same as the temperature of the plating bath. Specifically, the temperature controllability of the actual manufacturing equipment is limited, and the steel plate temperature when entering the plating bath should preferably be within ± 10 ° C of the plating bath temperature, and more preferably within ± 5 ° C of the plating bath temperature.

In addition, in order to obtain a predetermined amount of plating after dipping in the plating bath, it is desirable to spray a high-pressure gas mainly composed of nitrogen on the surface of the steel plate to remove excessive zinc on the surface layer. After that, it was cooled to room temperature. During cooling, Fe atoms hardly diffuse from the base material steel sheet to the molten galvanized layer. Therefore, in order to ensure the adhesion of the plating, it is preferable to set the cooling rate to 1 ° C until the temperature (350 ° C) at which the ζ phase formation almost stops. / S or more.

After cooling to 350 ° C, in order to obtain residual Vosstian iron, it is also possible to perform a toughening iron metamorphosis treatment which stays in a temperature range of 250 ° C to 350 ° C. If the tempering iron metamorphism treatment temperature is lower than 250 ° C, the tempering iron metamorphosis cannot be performed sufficiently, and residual Vostian iron cannot be obtained sufficiently. Therefore, the tempering iron transformation temperature should be set to 250 ° C or higher. In order to effectively perform the toughening iron metamorphosis, the tempering iron metamorphosis treatment temperature is more preferably set to 300 ° C or higher. If the tempering iron deforming temperature is higher than 350 ° C, Fe atoms will be excessively diffused from the base material steel plate to the hot-dip galvanizing layer, and the plating adhesion will be deteriorated. Therefore, the tempering iron transformation temperature should preferably be 350 ° C or lower, and more preferably 340 ° C or lower.

In order to stabilize the residual Vosstian iron, it may be cooled to 250 ° C or lower and then reheated. The processing temperature and processing time of the reheating process can be appropriately set according to needs. When the reheating temperature is lower than 250 ° C, a sufficient effect cannot be obtained. Therefore, the reheating temperature is preferably 250 ° C or higher, and more preferably 280 ° C or higher. When the reheating temperature is higher than 350 ° C, Fe atoms will diffuse from the base material steel plate to the hot-dip galvanized layer, and the plating adhesion will be deteriorated. Therefore, the reheating temperature is preferably 350 ° C or lower, and more preferably 330 ° C or lower. When the reheating time exceeds 1000 seconds, the above-mentioned effect will be saturated. Therefore, the reheating treatment time should preferably be 1000 seconds or less.

The hot-dip galvanized steel sheet according to the embodiment of the present invention can be manufactured as described above.

In the embodiment of the present invention, for example, the surface of the hot-dip galvanized layer of the hot-dip galvanized steel sheet obtained by the above method may be provided with a film composed of phosphorus oxide and / or a phosphorus-containing composite oxide. The film composed of phosphorus oxide and / or phosphorus-containing composite oxide can function as a lubricant when processing hot-dip galvanized steel sheet, and can protect the hot-dip galvanized layer formed on the surface of the base material steel sheet.

In the embodiment of the present invention, for example, in order to correct the shape, the hot-rolled galvanized steel sheet that has been cooled to room temperature may be subjected to cold rolling with a reduction ratio of 3.00% or less.

In addition, the method for manufacturing a hot-dip galvanized steel sheet according to the embodiment of the present invention is suitable for manufacturing a hot-dip galvanized steel sheet having a base material steel sheet thickness of 0.6 mm or more and less than 5.0 mm. When the thickness of the base material steel plate is less than 0.6 mm, it may be difficult to keep the shape of the base material steel plate flat. On the other hand, when the thickness of the base material steel plate is more than 5.0 mm, it may be difficult to control the annealing and cooling of the plating.

In addition, the above-mentioned embodiments are merely specific examples for implementing the present invention, and the technical scope of the present invention is not limited to these examples. That is, the present invention can be implemented in various forms without departing from the technical idea of the present invention or its main features.

Examples Next, examples of the present invention will be described. The condition in the examples is an example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to the one example of conditions. As long as the object of the present invention can be achieved without departing from the gist of the present invention, the present invention can adopt various conditions.

The steel billet with the chemical composition (steel type A to steel type AT) shown in Tables 1 to 4 is cast, and hot rolled is performed under the conditions (steel billet heating temperature and rolling end temperature) shown in Tables 5 and 6, and The conditions (average cooling rate and coiling temperature from the end of hot rolling to coiling) shown in Tables 5 and 6 were cooled to obtain a hot-rolled steel sheet. Thereafter, 10% hydrochloric acid at 80 ° C. was used to pickle the hot-rolled steel sheets at the pickling times shown in Tables 5 and 6, and cold rolled at the rolling reduction rates shown in Tables 5 and 6. Cold-rolled steel sheet. The bottom line in Tables 1 to 4 indicates that the number is outside the scope of the present invention. The remaining parts of steel type A to steel type AT are Fe and impurities. The bottom line in Tables 5 to 6 indicates that this number is outside the range suitable for manufacturing a hot-dip galvanized steel sheet.

Next, for the obtained cold-rolled steel sheet, the conditions shown in Tables 7 and 8 (pre-tropical air ratio, pre-heating end temperature of pre-tropical zone, Log (P (H ₂ O) / P (H ₂ )), Log (P (H ₂ O) / P (H ₂ )) in reducing zone gas environment, average heating speed in the temperature range of 600 ℃ ~ 750 ℃, maximum heating temperature (Tm)) Perform annealing. In addition, the preheating end temperature of Experimental Example 1 to Experimental Example 50 is set in a range of 623 ° C to 722 ° C. Then, under the conditions shown in Tables 7 and 8 (cooling rate 1 (average cooling rate in the temperature range of 750 ° C to 700 ° C), cooling rate 2 (average cooling rate in the temperature range of 700 ° C to 500 ° C), Toughened iron metamorphic treatment 1 conditions (processing temperature, processing time), Asada loose iron metamorphic processing (processing temperature, processing time)) cooling treatment. In addition, regarding steel plates that have not been subjected to the toughening iron metamorphism treatment 1 and the Asada loose iron metamorphosis treatment, the condition column of the treatment is shown as "-" in Tables 7 and 8. The bottom line in Tables 7 to 8 indicates that this number is outside the range suitable for manufacturing a hot-dip galvanized steel sheet.

Next, the plating conditions (effective Al amount, plating bath temperature (bath temperature), steel plate entry temperature, and immersion time) shown in Tables 9 and 10 were immersed in a zinc plating bath to perform plating. After plating, the conditions shown in Tables 9 and 10 (cooling rate (average cooling rate in the temperature range of the steel plate temperature to 350 ° C after plating), toughening iron and metamorphic treatment 2 conditions (processing temperature, processing time), and then Heat treatment conditions (treatment temperature, treatment time)) are performed for cooling treatment. In addition, regarding steel plates which have been subjected to the deformed iron deforming treatment 2 and which have not been subjected to the reheating treatment, the conditions of the treatment are shown in Tables 9 and 10 as "-". Then, cold rolling was performed at the rolling reduction rates shown in Tables 9 and 10, and hot-dip galvanized steel sheets of Experimental Examples 1 to 97 were obtained. Among them, there are interrupted experimenters in some experimental examples. The bottom line in Tables 9 to 10 indicates that this number is outside the range suitable for manufacturing a hot-dip galvanized steel sheet.

The microstructure and hot-dip galvanized layer of the base material steel plate were observed on the obtained plated steel plates (Experimental Example 1 to Experimental Example 97). Table 11 and Table 12 show the observation results of the microstructure of the base material steel sheet and the hot-dip galvanized layer. The bottom lines in Tables 11 and 12 indicate that the number is outside the scope of the present invention.

First, a sample was taken from a hot-dip galvanized steel sheet with a cross section parallel to the rolling direction of the base steel sheet as an observation surface. A field emission scanning electron microscope (FE-SEM) was used to observe the sample observation surface and EBSD method was used to analyze the high-resolution energy crystal direction. From the surface of the base steel plate, the thickness of the base steel plate was 1/8 to 3 Microstructures in the range of / 8, identifying constituent tissues. In Tables 13 and 14, F is granular ferrous iron, WF is acicular ferrous iron, NRF is non-recrystallized ferrous iron, P is boron iron, and θ is coarse cis carbon iron. BF indicates toughened ferrous iron, B indicates toughened iron, M indicates Asada loose iron, tM indicates tempered Asada loose iron, and γ indicates residual Vostian iron for observation.

A small piece of 25 mm × 25 mm was taken as a test piece from the hot-dip galvanized steel sheet. For the test piece ranging from 1/8 thickness to 3/8 thickness from the plate thickness surface, the surface parallel to the plate surface was processed into a mirror surface, and the volume fraction of residual Vostian iron was measured by X-ray diffraction method (γ Score).

The amount of plating deposit was determined by melting and melting the galvanized layer using hydrochloric acid doped with an inhibitor, and comparing the weights before and after melting. Then, Fe and Al were quantified by ICP to measure the Fe concentration and Al concentration in the hot-dip galvanized layer.

Then, a sample was taken from the hot-dip galvanized steel sheet with a cross section parallel to the rolling direction of the base steel sheet as an observation surface, and the Fe-Al alloy layer formed on the interface between the surface of the base steel sheet and the hot-dip galvanized layer was obtained by the above-mentioned measurement method. Difference between the maximum thickness and the minimum thickness of the thickness of the Fe-Al alloy layer in the width direction of the base material steel plate, the average thickness of the micronized layer in contact with the Fe-Al alloy layer, and the fineness in the width direction of the base material steel plate The difference between the maximum 値 and minimum 厚度 of the thickness of the formation layer, the average grain size of the ferrous iron phase in the refinement layer, and the diameter of one or more oxides of Si and Mn in the refinement layer. The results are shown in Tables 11 and 12.

Next, in order to investigate the characteristics of the hot-dip galvanized steel sheet, a tensile test, a hole expansion test, a bending test, an adhesion evaluation test, a spot welding test, a corrosion test, a chipping test, a crushability test, and a plating appearance were performed. Homogeneity assessment. Tables 13 and 14 show the characteristics of each experimental example.

The tensile test is made from the hot-dip galvanized steel sheet No. 5 test piece described in JIS Z 2201, and the yield drop strength (YS), maximum tensile strength (TS), and total elongation (TS) are determined according to the method described in JIS Z 2241. El). The tensile properties were evaluated as being good when the maximum tensile strength (TS) was 420 MPa or more.

The hole expansion test was performed in accordance with the method described in JIS Z 2256. In terms of moldability, although ductility (total elongation) (El) and hole expansion (λ) change depending on the maximum tensile strength (TS), the strength, ductility, and hole expansion are evaluated when the following formula (2) is satisfied. Sex is good. TS ^1.5 × El × λ ^0.5 ≧ 2.0 × 10 ⁶ ... (2)

The plating adhesion was performed by a DuPont punching test on a hot-dip galvanized steel sheet having a uniaxial tensile strain of 5%. The hot-dip galvanized steel sheet after the punching test was peeled off after being attached with an adhesive tape. The case where the plating was not peeled was evaluated as particularly good (◎), and the case where the plating was peeled by more than 5% was evaluated as bad (×). A case where the plating peeling was less than 5% was evaluated as good (○). The DuPont punch test uses a punch with a radius of curvature at the front end set to 1/2 inch, and a 3 kg hammer is dropped from a height of 1 m.

The spot weldability was evaluated by continuous dot test. Continuously perform 1000 spot welding under the welding condition that the diameter of the molten part is 5.3 to 5.7 times the square root of the plate thickness, and compare the first point d ₁ of the diameter of the molten part with the 1000 point d ₁₀₀₀ , where d ₁₀₀₀ / d ₁ is 0.90 The above conditions were evaluated as good (○), and the cases below 0.90 were evaluated as bad (×).

The corrosion resistance was evaluated by cutting a 150 mm × 70 mm test piece from a hot-dip galvanized steel sheet. The test piece was subjected to a zinc phosphate-based immersion type chemical conversion treatment, followed by cationic plating coating of 20 μm, intermediate coating of 35 μm, and surface coating of 35 μm, and then the back and ends were sealed with insulating tape. The corrosion resistance test was performed using CCT with SST 6hr, dry 4hr, wet 4hr, and freeze 4hr for 1 cycle. The evaluation of the corrosion resistance after painting was performed by cutting the coated surface with a cutter to the base metal steel plate to measure the swelling width after the CCT 60 cycle. A case where the swelling width was 3.0 mm or less was evaluated as good (○), and a case where the swelling width was more than 3.0 mm was evaluated as bad (×).

The crushability was evaluated by cutting a 70 mm × 150 mm test piece from a hot-dip galvanized steel sheet. First, a test piece was degreased for automobiles, a chemical conversion film was formed, and three-layer coating was performed. Next, 10 pieces of crushed stone (0.3 g to 0.5 g) were irradiated vertically with the air pressure of ² kgf / cm ² while the test piece was cooled and maintained at -20 ° C. The irradiation of crushed stones was performed repeatedly for each test piece five times. Thereafter, a total of 50 cracks were observed in each test piece, and the position of the peeling interface was evaluated according to the following criteria. The peeling interface was evaluated higher than the hot-dip galvanized layer (the interface between the hot-dip galvanized layer and the chemical conversion film, or the interface between the electroplating coating and the intermediate coating), and was evaluated as good (○). The peeling was evaluated as bad (×) in one place.

The pulverizability was evaluated using V-bending (JIS Z 2248) to evaluate the workability of the hot-dip galvanized layer. The hot-dip galvanized steel sheet was cut into 50 mm × 90 mm, and a molded body was formed with a 1R-90 ° V-shaped die press to form a test body. The valley portion of each test body was subjected to tape peeling. Specifically, after the cellophane tape having a width of 24 mm was pressed against the bending portion of the test body and peeled off, a portion of the cellophane tape having a length of 90 mm was visually determined. The evaluation criteria are as follows. The peeling of the hot-dip galvanized layer was evaluated as good (○) with respect to the area of the processed portion of 5% or less, and the peeling of the hot-dip galvanized layer was evaluated as bad (×) with respect to the area of the processed portion of more than 5%.

Appearance uniformity is measured by measuring the brightness (L * 値) at a total of 8 places from the position of the steel plate in the width direction at a distance of 50 mm from the end of the steel plate and dividing it into 7 equal parts. 5 was evaluated as good (○), 5 or more and less than 10 were evaluated as slightly bad (Δ), and 10 or more was evaluated as bad (×).

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[TABLE 6]

[TABLE 7]

[TABLE 8]

[TABLE 9]

[TABLE 10]

[TABLE 11]

[TABLE 12]

[TABLE 13]

[TABLE 14]

In Experimental Example 64 and Experimental Example 86 with an effective Al amount of 0.180%, the Fe-Al alloy layer was uniformly formed in the width direction, and therefore, the plating adhesion described in the aforementioned Patent Document 12 did not decrease.

In Experimental Example 3, the effective Al concentration in the plating bath was extremely low to form an Fe-Al alloy layer, and the Fe content in the hot-dip galvanized layer was too high to obtain sufficient plating adhesion and chipping. Properties, pulverization, and uniform appearance of plating.

In Experimental Example 6, the cold rolling was not performed on the hot-rolled steel sheet, so the flatness of the steel sheet was poor and annealing could not be performed. Therefore, the experiment was terminated.

Since the cooling rate after plating in Experimental Example 20 is small, the Fe content in the hot-dip galvanized layer is too high, and sufficient plating adhesion, chipping, and pulverization cannot be obtained.

The annealing rate of the experimental example 26 is small, and the oxide in the base material steel sheet is excessively grown to form a coarse oxide which will be the starting point of the surface damage of the base material steel sheet. Therefore, the plating adhesion and pulverization are deteriorated.

The cold rolling reduction of Experimental Example 28 was too large and the steel plate was broken, so the experiment was terminated.

In Experimental Example 33, the log (P (H ₂ O) / P (H ₂ )) of the uniform tropical zone is large, and the micronized layer on the surface layer of the base material steel plate is excessively thickened, and a fused zinc coating of the Zn-Fe alloy is formed. The alloying progresses excessively and the Fe content in the hot-dip galvanized layer is increased, so the plating adhesion, chipping, and pulverization are deteriorated.

The large pre-tropical air ratio of Experimental Example 36 caused excessive decarburization on the surface of the steel sheet, making the average thickness of the micronized layer thicker, and excessive alloying of the hot-dip galvanized layer that would generate a Zn-Fe alloy, causing the hot-dip As the Fe content in the zinc layer increases, the plating adhesion, chipping, and pulverizing properties deteriorate.

The effective Al concentration in the plating bath of Experimental Example 40 was low, and a Fe-Al alloy layer of sufficient thickness could not be formed. Therefore, the Fe content in the hot-dip galvanized layer was too high, and sufficient plating adhesion and chipping could not be obtained. Properties, pulverization, and uniform appearance of plating.

The effective Al concentration in the plating bath of Experimental Example 42 was high, the Al content in the hot-dip galvanized layer was too high, and an excessively thick Fe-Al alloy layer was formed, and sufficient plating adhesion and spot weldability could not be obtained.

In Experimental Example 46, the log (P (H ₂ O) / P (H ₂ )) of the average tropical zone is small, and it may not be plated, so the plating adhesion is poor. In addition, Experimental Example 46 did not form a micronized layer, and the average particle size of the ferrous phase of the ferrous phase on the surface of the base material steel plate was 3.6 μm, and the maximum diameter of the oxide inside the steel plate ranging from the surface to a depth of 0.5 μm was less than 0.01. μm.

Experimental Example 47 had a large Si content, and the steel billet cracked during cooling during casting, so the experiment was interrupted.

Experimental Example 48 had a large Mn content, and the hot-rolled delayed steel billet cracked during heating, so the experiment was terminated.

The content of P in Experimental Example 49 was large, and the hot-rolled delayed steel billet cracked during heating, so the experiment was terminated.

Experimental Example 50 had a large Al content, and the steel billet cracked during cooling during casting, so the experiment was interrupted.

The maximum heating temperature for annealing of Experimental Example 54 was low, so that residual Vosstian iron could not be generated, which caused a large amount of coarse citronite in the steel sheet, resulting in deterioration of TS ^1.5 × El × λ ^0.5 and failure to obtain sufficient characteristics.

In Experimental Example 55, the average cooling rate from 750 ° C to 700 ° C was small, a large amount of carbides were generated, and residual Vostian iron could not be obtained, so the balance between strength and formability deteriorated.

The tempered iron metamorphic treatment temperature after the plating treatment of Experimental Example 58 is high, and the Fe content in the hot-dip galvanized layer is increased, so the plating adhesion, chipping, and pulverizing properties are deteriorated.

The toughening iron metamorphic treatment time before the plating process of Experimental Example 59 is short, and the toughening iron metamorphosis cannot be sufficiently performed, and the residual Vosstian iron cannot be obtained, so the balance between strength and formability is deteriorated.

The amount of effective Al in the plating bath of Experimental Example 60 is too small to form an Fe-Al alloy layer with a sufficient thickness, so the Fe content in the hot-dip galvanized layer is too high, and sufficient plating adhesion and chipping cannot be obtained Smashability.

In Experimental Example 65, the average cooling rate from 700 ° C. to 500 ° C. was small, a large amount of carbides were generated, and residual Vostian iron could not be obtained, so the balance between strength and formability was deteriorated.

The tempered iron metamorphic treatment temperature of the experimental example 66 after the plating treatment was low, excessively inhibited the progress of the toughened iron metamorphosis, and the residual Vosted iron could not be obtained, so the balance between strength and formability deteriorated.

The effective Al concentration in the plating bath of Experimental Example 67 was high, the Al content in the hot-dip galvanized layer was too high, and an excessively thick Fe-Al alloy layer was formed, and sufficient plating adhesion and spot welding properties could not be obtained.

The end temperature of the hot rolling of Experimental Example 68 was low, which significantly deteriorated the shape of the steel sheet, so the experiment was terminated.

The coiling temperature of Experimental Example 72 was low, and the steel sheet fractured during the cold rolling delay, so the experiment was terminated.

The pre-tropical Log (P (H ₂ O) / P (H ₂ )) of Experimental Example 73 is small, and it may not be plated. Therefore, the surface layer particle size cannot be miniaturized, and the plating adhesion is deteriorated. In addition, Experimental Example 73 did not form a micronized layer, and the average particle size of the ferrous iron phase on the surface of the base material steel plate was 3.3 μm, and the maximum oxide diameter inside the steel plate ranging from the surface to a depth of 0.5 μm was less than 0.01 μm.

In Experimental Example 74, the toughening iron metamorphic treatment was not performed before and after the plating treatment, and the residual Vostian iron could not be obtained, so the balance between strength and formability was deteriorated.

In the example 75, the tempering temperature of the toughened iron before the plating treatment was high, and a large amount of carbides were generated, so that residual Vostian iron could not be obtained, so the balance between strength and formability was deteriorated.

The tempered iron metamorphic treatment temperature of the experimental example 76 before the plating treatment was low, and the progress of the toughened iron metamorphosis was excessively suppressed, so that the residual Vostian iron could not be obtained, so the balance between strength and formability was deteriorated.

The maximum heating temperature of the annealing of Experimental Example 78 is lower than Ac1 + 50 ° C, and the residual Vosstian iron cannot be generated, resulting in a large amount of coarse cis-carbon iron in the steel sheet, which causes the TS ^1.5 × El × λ ^{0.5 to} deteriorate, and cannot Get full characteristics.

The sum of the toughening iron metamorphic processing time before the plating treatment of Experimental Example 80 and the toughening iron metamorphic processing time after the plating treatment is small, and the toughened iron metamorphism cannot be fully performed, and the residual Vostian iron cannot be obtained, so the strength The balance with formability deteriorates.

The Si content and Al content of Experimental Example 84 did not satisfy the formula (1), a large amount of carbides were generated, and residual Vosstian iron could not be obtained, so the balance between strength and formability was deteriorated.

The toughened iron before the plating treatment of Experimental Example 87 had a long metamorphic treatment time, and a large amount of carbides were generated, and residual Vostian iron could not be obtained, so the balance between strength and formability was deteriorated.

Since the C content in Experimental Example 88 was large, the spot weldability and formability were deteriorated.

The content of C in Experimental Example 89 was small, and it was not possible to generate residual Vosstian iron, so that the volume fraction of the hard phase was reduced, and sufficient tensile strength could not be obtained.

Experimental Example 90 has a small Mn content, so that a large amount of boron iron and coarse skeletal iron are generated during annealing and plating, and residual Vosted iron cannot be generated, so the tensile strength and formability of the steel sheet cannot be fully obtained.

The S content in Experimental Example 91 was large, and a large amount of coarse sulfides were generated, which resulted in poor ductility and hole expandability.

The N content in Experimental Example 92 was large, and a large amount of coarse nitrides were generated, which resulted in poor ductility and hole expandability.

The content of O in Experimental Example 93 was large, and a large amount of coarse oxides were generated, resulting in poor ductility and hole expansion.

The high pre-heating end temperature of Experimental Example 94 caused excessive growth of oxides in the base material steel plate, and formed coarse oxides that would be the starting point of the surface damage of the base material steel plate, resulting in poor plating adhesion.

The log (P (H ₂ O) / P (H ₂ )) of the pre-tropic zone of Example 95 is too large, which makes the micronized layer of the surface layer of the base material steel plate excessively thick, resulting in the formation of a molten zinc-plated layer of a Zn-Fe alloy. The alloying progresses excessively and the Fe content in the hot-dip galvanized layer is increased, so the plating adhesion, chipping, and pulverization are deteriorated. In addition, since the difference between the maximum 値 and the minimum 厚度 of the thickness of the Fe-Al alloy layer in the width direction of the steel sheet is larger than 0.5 μm, the plating appearance is not uniform.

The coiling temperature of Experimental Example 10, Experimental Example 22, Experimental Example 30, Experimental Example 43, and Experimental Example 44 is above 650 ° C. The difference between the maximum and minimum thicknesses of the thickness of the Fe-Al alloy layer in the width direction of the steel plate is greater than 0.5 μm. , So the plating appearance is slightly uneven. In addition, the difference between the maximum 値 and the minimum 厚度 of the thickness of the micronized layer in the width direction of the steel sheet is greater than 2.0 μm. Although the coiling temperature of Experimental Example 11 and Experimental Example 45 is above 650 ° C, there is an increase in pickling time. Therefore, the difference between the maximum and minimum thicknesses of the micronized layer thickness in the width direction of the steel plate is within 2.0 μm, and good results are obtained. Uniform plating appearance. Although the coiling temperature of Example 97 is lower than 650 ° C, the pickling time is 15 seconds and the time is short, so the uneven internal oxide layer generated cannot be completely removed, and the thickness of the fine layer in the width direction of the steel plate The difference between the maximum 値 and the minimum 値 is greater than 2.0 μm, and the plating appearance is slightly uneven. The average heating rate of the preheat zone of Experimental Example 99 is greater than 50 ° C / sec. Therefore, the difference between the maximum and minimum thicknesses of the thickness of the Fe-Al alloy layer in the width direction of the steel plate is greater than 0.5 μm, and the thickness of the fine layer in the width direction of the steel plate is The difference between the maximum 値 and the minimum 値 is greater than 2.0 μm, and the plating appearance is slightly uneven.

INDUSTRIAL APPLICABILITY The present invention is applicable to industries related to, for example, hot-dip galvanized steel sheets suitable for automotive exterior panels.

1‧‧‧ hot-dip galvanized steel sheet

2‧‧‧ mother steel plate

3‧‧‧ Fused galvanized layer

4‧‧‧Fe-Al alloy layer

5‧‧‧ Fine layer

6‧‧‧ decarburized layer

7, 8‧‧‧ fat phase iron phase

Fig. 1 is a sectional view showing a hot-dip galvanized steel sheet according to an embodiment of the present invention.

Claims (6)

A hot-dip galvanized steel sheet has a hot-dip galvanized layer on at least one side of a base metal steel sheet, and the hot-dip galvanized steel sheet is characterized in that the aforementioned base metal steel sheet has a chemical composition shown below: C: 0.040% by mass% ~ 0.400%, Si: 0.05% ~ 2.50%, Mn: 0.50% ~ 3.50%, P: 0.0001% ~ 0.1000%, S: 0.0001% ~ 0.0100%, Al: 0.001% ~ 1.500%, N: 0.0001% ~ 0.0100 %, O: 0.0001% to 0.0100%, Ti: 0.000% to 0.150%, Nb: 0.000% to 0.100%, V: 0.000% to 0.300%, Cr: 0.00% to 2.00%, Ni: 0.00% to 2.00%, Cu: 0.00% to 2.00%, Mo: 0.00% to 2.00%, B: 0.0000% to 0.0100%, W: 0.00% to 2.00%, Ca, Ce, Mg, Zr, La, and REM: 0.0000% to 0.0100% in total And the remainder: Fe and impurities; the Fe content in the aforementioned hot-dip galvanized layer is greater than 0% and less than 3.0%, and the Al content is greater than 0% and less than 1.0%; The interface has an Fe-Al alloy layer; the thickness of the foregoing Fe-Al alloy layer is 0.1 μm to 2.0 μm; the difference between the maximum value and the minimum value of the thickness of the foregoing Fe-Al alloy layer in the width direction of the base material steel plate is within 0.5 μm; The base material steel plate has a combination with the Fe-Al The micronized layer in direct contact with the layer, and the average thickness of the micronized layer is 0.1 μm to 5.0 μm, the average particle size of the iron phase of the fertilizer particles in the micronized layer is 0.1 μm to 3.0 μm, and the micronized layer contains Si. And one or more oxides of Mn, and the maximum diameter of the oxide is 0.01 μm to 0.4 μm; the difference between the maximum value and the minimum value of the thickness of the refined layer in the width direction of the base material steel plate is 2.0 Within μm; and the difference between the maximum and minimum thicknesses of the thickness of the aforementioned Fe-Al alloy layer and micronized layer in the width direction of the base material steel plate is the difference between the maximum and minimum values of the thickness measurement values at the following 8 points The value obtained by the form: a total of 8 positions of the Fe-Al alloy layer and the aforementioned miniaturized layer at a distance of 50 mm from both ends, and each of the positions is divided into 7 equal parts. For example, the hot-dip galvanized steel sheet of claim 1 satisfies the following formula 1 when the Si content (mass%) in the aforementioned base material steel sheet is [Si] and the Al content (mass%) is [Al]; The total thickness of the steel plate is 1% or more of the residual Vostian iron in the range of 1/8 thickness to 3/8 thickness centered on the 1/4 thickness from the surface of the base material steel plate; [Si] +0.7 [Al] ≧ 0.30 (Equation 1). The hot-dip galvanized steel sheet according to claim 1 or 2, wherein the coating amount per one side of the hot-dip galvanized layer is 10 g / m ² or more and 100 g / m ² or less. For example, the hot-dip galvanized steel sheet of claim 1 or 2, wherein the aforementioned chemical composition satisfies: Ti: 0.001% to 0.150%, Nb: 0.001% to 0.100%, or V: 0.001% to 0.300%, or any combination thereof . For example, the hot-dip galvanized steel sheet of claim 1 or 2, wherein the aforementioned chemical composition satisfies: Cr: 0.01% to 2.00%, Ni: 0.01% to 2.00%, Cu: 0.01% to 2.00%, Mo: 0.01% to 2.00%, B: 0.0001% ~ 0.0100%, or W: 0.01% ~ 2.00%, or any combination of these. For example, the hot-dip galvanized steel sheet of claim 1 or 2, wherein the foregoing chemical composition satisfies: Ca, Ce, Mg, Zr, La, and REM: 0.0001% to 0.0100% in total.