JP5014940B2 - Alloyed hot-dip galvanized steel sheet excellent in deep drawability and manufacturing method of alloyed hot-dip galvanized steel sheet - Google Patents

Description

  The present invention relates to an alloyed hot-dip galvanized steel sheet and a method for producing the same, and more specifically, an alloyed hot-dip galvanized steel sheet and an alloyed hot-dip galvanized sheet that are excellent in deep drawability and at the same time have excellent plating adhesion. The present invention relates to a method of manufacturing a steel plate.

  Alloyed hot-dip galvanized steel sheets are extremely used in automobiles, home appliances, building materials and the like because they are excellent in coating adhesion, coating corrosion resistance, weldability, and the like. An alloyed hot-dip galvanized steel sheet forms a Zn-Fe alloy by coating hot-dip zinc on the surface of the steel sheet and immediately holding it at a temperature equal to or higher than the melting point of zinc and diffusing Fe from the steel sheet into the zinc. However, since the alloying speed varies greatly depending on the composition and structure of the steel sheet, the control thereof requires a considerably advanced technique. On the other hand, steel sheets for automobiles that are pressed into complex shapes are required to have very high formability, and in recent years, alloyed hot dip galvanizing has been applied due to an increase in demand for rust prevention performance of automobiles. Increasing cases.

  As the car body shape becomes more complex, the demands on formability of steel sheets have become more severe, and steel sheets with excellent formability such as deep drawability are also required for galvannealed steel sheets. Has been. In order to obtain such workability, Ti is added as a component of the steel sheet after Ti is reduced to a very low level, or Ti-added ultra-low carbon IF steel in which Ti and Nb are added together, or Ti-Nb. It is common to use added extra low carbon IF steel.

  For example, Patent Document 1 and Patent Document 2 disclose a manufacturing method in which a steel sheet having high ductility and a high r value is manufactured by subjecting the steel sheet components, hot rolling conditions and annealing conditions, and hot-plating is performed on the surface thereof. Has been.

  However, these steels, in which the amount of solid solution C and N is reduced for the purpose of improving formability, have a very high alloying speed in the alloying of hot dip galvanizing, so that alloying proceeds too much and the Γ phase becomes thick. There is a problem that it grows and the powdering performance tends to decrease.

  As a method for solving such a problem, Patent Documents 3 and 4 propose a technique for defining soaking conditions after alloying together with alloying heat treatment conditions and cooling conditions. Furthermore, in Patent Document 5, in addition to the steel sheet composition, hot rolling conditions and cooling conditions, and annealing conditions after cold rolling, the relational expression between the P and Ti contents of the steel sheet and the effective Al concentration in the plating bath is limited. Technology has been proposed.

  Furthermore, Patent Document 6 proposes an alloyed hot-dip galvanized steel sheet having excellent powdering resistance and sliding properties.

JP 59-74231 A JP 59-190332 A Japanese Patent Laid-Open No. 2-310352 Japanese Patent Laid-Open No. 2-310353 Japanese Patent Laid-Open No. 5-331612 Japanese Patent No. 2709173

  However, the above-mentioned and other alloyed hot-dip galvanized steel sheets disclosed so far do not have sufficient performance as automobile outer plates or difficult-to-form members.

  The alloyed hot-dip galvanized steel sheets described in Patent Document 1 and Patent Document 2 exhibit relatively high ductility and r value, but because the alloying speed is very fast, alloying progresses too much and powdering performance decreases. The problem of being easy to do is not solved.

  As a method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance, Patent Document 3 and Patent Document 4 propose a technique for defining soaking conditions after alloying together with alloying heat treatment conditions and cooling conditions. However, since soaking for a long time is required, the productivity of the plating line is lowered, which is not economical. Further, in Patent Document 5, a technique for limiting the relational expression between the P and Ti contents of the steel sheet and the effective Al concentration in the plating bath is proposed. However, in order to control the Al concentration, the operation condition of the plating line is Changing or adjusting reduces the productivity of the plating line and increases the cost. In addition, the manufacturing method for improving the powdering resistance has another problem that it causes insufficient alloying and tends to lower the slidability of the surface, so that both excellent workability and high plating adhesion are achieved. It is difficult to make it.

In order to improve the slidability of the surface, as described in Patent Document 6, it has been considered effective to make the plating layer a δ ₁ phase. Since IF steel or Ti-Nb-added ultra-low carbon IF steel has a very high alloying speed, it is extremely difficult to make the plating layer a δ ₁ phase. Further, even if the plating layer can be a δ ₁ phase, the improvement in formability is not sufficient by itself.

  In addition, a technique for suppressing alloying of IF steel by utilizing the phenomenon that the alloying rate decreases when P or Si is added has been proposed, but the addition of such an element leads to a decrease in ductility and r value. Therefore, even though powdering can be suppressed, it cannot be used for the production of a plated steel sheet for the purpose of improving formability.

  In view of the above-mentioned present situation, an object of the present invention is to provide an alloyed hot-dip galvanized steel sheet that can simultaneously achieve excellent deep drawability and high plating adhesion.

As a result of examining various means for improving workability without reducing productivity and plating adhesion of a hot dip galvanizing line, the present inventor has obtained a phase structure of a plated layer of a plated steel sheet with reduced C, P, N, etc. The inventors have found that by controlling and mainly using the δ _1k phase, the workability can be remarkably improved without lowering the plating adhesion, and the present invention has been achieved.

  That is, the gist of the present invention is as follows.

(1) In mass%,
C: 0.0001 to 0.004%,
Si: 0.001 to 0.10%,
Mn: 0.01 to 0.50%,
P: 0.001 to 0.015%,
S: 0.015% or less,
Al: 0.0005 to 0.05%,
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%
A steel sheet is characterized by comprising the balance Fe and unavoidable impurities on one or both sides of Al: 0.05 to 0.5 mass%, Fe: 10 to 17 mass%, the balance being Zn and unavoidable impurities Thus, an alloyed hot-dip galvanized layer characterized in that the ratio of the δ _1k phase to the surface is 50 to 100% and the Γ phase thickness at the plating / steel interface is 0.1 to 0.8 μm was formed. Alloyed hot-dip galvanized steel sheet with excellent deep drawability.

  (2) The alloyed molten zinc having excellent deep drawability as described in the above item (1), wherein the steel sheet further contains, as an additional component, Nb: 0.002 to 0.10% by mass. Plated steel sheet.

(3) The above-mentioned (1), wherein the Ti content in the steel satisfies the condition given by the following formula (1) (where [% X] is the content of alloy element X expressed in mass%): An alloyed hot-dip galvanized steel sheet excellent in deep drawability as described in the item.
[% Ti] ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (1)

(4) The content of Ti and Nb in the steel satisfies the conditions given by the following formulas (2) to (3) (where [% X] is the content of alloy element X expressed in mass%). The alloyed hot-dip galvanized steel sheet excellent in deep drawability as described in the above item (2).
([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1.5 [% S]
(2)
[% Ti] ≧ 0.009% (3)

  (5) The deep drawability according to any one of (1) to (4) above, wherein the steel sheet further contains B: 0.0002 to 0.003% by mass% as an additional component. Excellent galvannealed steel sheet.

  The present invention makes it possible to provide an alloyed hot-dip galvanized steel sheet that is excellent in both deep drawability and plating adhesion, and contributes greatly to industrial development.

  Hereinafter, the present invention will be described in detail. First, the reason why the range of each component is limited in the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

  C: C is an element that increases the strength of steel. If it is excessively contained, the strength increases excessively and the workability decreases, so the upper limit content is made 0.004%. In particular, when high workability is required, the C content is preferably 0.003% or less, and more preferably 0.002% or less. The smaller the C, the better the workability, but in order to make it less than 0.0001%, the scouring cost becomes large, so the lower limit content is made 0.0001%.

  Si: Si is also an element for improving the strength of steel, and if contained excessively, workability and hot dip galvanizing properties are impaired, so the upper limit is made 0.10%. In particular, when high workability is required, the Si content is 0.01% or less. However, in order to make it less than 0.001% or more, the scouring cost becomes great, so the lower limit content is made 0.001%.

  Mn: Since Mn is an element that increases the strength of steel while reducing workability, the upper limit content is set to 0.50%. The smaller the Mn, the better the workability, but in order to make it 0.01% or less, the scouring cost becomes large, so the lower limit content is made 0.01%.

  P: P is an element that increases the strength of the steel while decreasing the workability, so the upper limit content is set to 0.015%. The lower the P, the better the workability and the more preferable it is 0.010% or less. On the other hand, in order to reduce the P content to less than 0.001%, the scouring cost becomes great, so the lower limit content is 0.001%. From the balance of strength, workability and cost, the P content is more preferably 0.003 to 0.010%.

  S: Since S is an element that decreases the hot workability and corrosion resistance of steel, it is preferably as small as possible. The upper limit content is 0.015%, and more preferably 0.010% or less. However, since it takes cost to reduce the amount of S of the ultra-low carbon steel as in the present invention, it is not necessary to excessively reduce S from the viewpoint of workability and plating adhesion, What is necessary is just to reduce S to the required level from corrosion resistance etc.

  Al: Al needs to contain 0.0005% or more as a deoxidizing element of steel. However, if excessively contained, a coarse intermetallic compound is formed and workability is impaired, so the upper limit content is 0. .05%.

  Ti: In order to fix C and N in steel as carbides and nitrides, 0.002% or more of addition is necessary, and it is more preferable to contain 0.010% or more. On the other hand, even if added over 0.10%, the effect is no longer saturated, but the alloy addition cost only increases unnecessarily, so the upper limit content is 0.10%. Since excessive solute Ti may impair the workability and surface quality of the steel sheet, it is more preferably 0.050% or less.

  N: N increases the strength of the steel while lowering the workability, so the upper limit is made 0.004%, and when high workability is particularly required, it is more preferably 0.003% or less. More preferably, the content is 0.002% or less. N is preferably as little as possible, but reducing it to less than 0.0005% requires excessive cost, so the lower limit content is made 0.0005%.

  In the present invention, in addition to the above, as an additional component, Nb can be added under the above Ti addition in order to fix C and N in the steel as carbides and nitrides. In order to fully exhibit the C and N fixing effect, addition of 0.002% or more is necessary, and more preferably 0.005% or more. Even if Nb is added in excess of 0.10%, the effect is no longer saturated, but the cost is increased unnecessarily, so the upper limit content is 0.10%. Excessive Nb addition raises the recrystallization temperature of the steel sheet and lowers the productivity of the hot dip galvanizing line.

In the present invention, when the formability and workability of the steel sheet are further increased, the Ti content is set in a range satisfying the following expression (1).
[% Ti] ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (1)
This is because when the Ti content is in the above range, C and N, which are elements that hinder workability, are effectively fixed with Ti, and the workability of the steel sheet can be improved. Or let content of Ti and Nb be the range which satisfies the following (2) Formula and (3) Formula.
([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1.5 [% S]
(2)
[% Ti] ≧ 0.009% (3)
This is because, if the content of Ti and Nb is in the above range, C and N, which are elements inhibiting workability, can be effectively fixed by the combined effect of Ti and Nb, and the workability of the steel sheet can be improved. However, when Nb alone is added, the effect of improving the workability is not sufficient, and when Ti content is 0.009% or more, the combined effect of Ti and Nb becomes remarkable. When the content satisfies the formula (2), C and N can be effectively fixed with Ti and Nb.

  In the present invention, the steel sheet may further contain 0.0002 to 0.003% of B as an additional component, and this is intended to improve secondary workability. If the B content is less than 0.0002%, the secondary workability improvement effect is not sufficient, and even if added over 0.003%, the effect is no longer saturated, and the moldability is reduced. Therefore, when adding B, the range is made 0.0002 to 0.003%. In particular, when high deep drawability is required, the amount of B added is more preferably 0.0015% or less.

  In the present invention, the reason why the Al composition of the galvannealed layer is limited to 0.05 to 0.5% by mass is that when it is less than 0.05% by mass, Zn-Fe alloying proceeds too much during the alloying treatment. This is because a brittle alloy layer develops too much at the iron interface and the plating adhesion deteriorates. If it exceeds 0.5 mass%, the Fe—Al—Zn-based barrier layer is formed too thick and alloying occurs during the alloying treatment. This is because the desired iron content plating cannot be obtained because it does not progress.

  The reason why the Fe composition is limited to 10 to 17% by mass is that if it is less than 10% by mass, a soft Zn—Fe alloy is formed on the plating surface and press formability is deteriorated. This is because a brittle alloy layer develops excessively at the steel plate interface and the plating adhesion deteriorates.

In the present invention, for the purpose of improving the deep drawability of the galvannealed steel sheet, the proportion of the δ _1k phase in the plating layer surface is set to 50 to 100%. In the present invention, the alloyed hot dip galvanized layer is a plated layer mainly composed of an Fe—Zn alloy in which Fe in steel can diffuse during Zn plating by an alloying reaction. The plating layer, the difference in content of Fe far, zeta phase, [delta] ₁ phase, .GAMMA.1 phase, but that the alloy layer is formed called Γ phase was known, recent studies, [delta] ₁ It has become clear that the phase further includes two phases of δ _1p phase and δ _1k phase.

In the present invention, the ζ phase refers to an intermetallic compound having a monoclinic structure and lattice constants of a = 13.4７, b = 7.6Å, c = 0.06 ＝, and β = 127.3. The composition of the ζ phase is considered to be FeZn ₁₃ . In the present invention, the δ _1p phase is an intermetallic compound having a hexagonal crystal lattice constant of a = 12.8Å and c = 57.4Å, and the δ _1k phase is a lattice having a period three times that of the δ _1p phase. An intermetallic compound having a constant is shown. Any of the intermetallic compound also compositions is believed to be FeZn _7. In the present invention, the Γ1 phase refers to an intermetallic compound having a face-centered cubic crystal and a lattice constant of a = 17.96Å. The composition of the Γ1 phase is considered to be Fe ₅ Zn ₂₁ or FeZn ₄ . In the present invention, the Γ phase refers to an intermetallic compound having a body-centered cubic crystal and a lattice constant of a = 8.97. The composition of the Γ phase is considered to be Fe ₃ Zn ₁₀ .

The phase structure of the alloyed hot-dip galvanized steel sheet consists of Fe-Zn intermetallic compounds in the order of Γ phase, Γ1 phase, δ _1k phase, δ _1p phase, and ζ phase from the steel plate side. Depending on the conversion conditions, a δ _1p phase or a ζ phase may not be possible.

Of these, the δ _1k phase significantly improves the deep drawability of the alloyed hot dip galvanized steel sheet. Therefore, for the purpose of improving the deep drawability of the alloyed hot dip galvanized steel sheet, the ratio of the δ _1k phase to the plating layer surface is 50. ~ 100%. The reason why the proportion of the δ _1k phase in the plating layer surface is limited to 50 to 100% is that the effect of improving the deep drawability is remarkable at 50% or more.

The reason why the deep drawability is improved by setting the phase structure of the plating layer to the δ _1k phase is considered to be that the inflow resistance from the wrinkle suppressing portion to the vertical wall portion is reduced by increasing the hardness of the plating. It is done. To improve phase structure of [delta] deep drawability With _1k phase 10-20% of the plating layer and the plating layer of the deep drawability of good steel sheet and [delta] _1k phase, galvannealed its synergy The deep drawability of the plated steel sheet is remarkably improved. Therefore, it is preferable to produce alloyed hot-dip galvanized mainly composed of δ _1k phase on a steel sheet having a strength of less than 340 MPa, an elongation of 46% or more, and an r value of 1.6 or more.

However, such a steel sheet with good deep drawability has a very high alloying speed in the alloying of hot dip galvanizing, so that the alloying progresses too much and the Γ phase grows thick, and the powdering performance decreases. There is a problem that it is easy. In order to prevent this, the thickness of the Γ phase at the plating / steel plate interface is set to 0.8 μm or less. The thinner the Γ phase thickness is, the better the adhesion of the plating is. However, since the cost is enormous in order to reduce the Γ phase thickness to less than 0.1 μm while keeping the phase structure of the plating layer in the δ _1k phase, The lower limit thickness is 0.1 μm. Particularly for parts that are severely molded, the Γ phase thickness is preferably 0.1 to 0.5 μm.

Next, the reasons for limiting the manufacturing conditions will be described. In the present invention, Al: 0.05 to 0.5% by mass, Fe: 10 to 17% by mass, the balance is made of Zn and unavoidable impurities, and the proportion of δ _1k phase in the surface is 50 to 100%. In order to form an alloyed hot-dip galvanized layer characterized in that the Γ phase thickness at the steel plate interface is 0.1 to 0.8 μm, after plating, the plate temperature on the heating furnace exit side exceeds 530 ° C., A method of heating to 600 ° C. or lower and cooling to 400 ° C. within 10 seconds is effective.

A steel sheet with good deep drawability has a very high alloying speed in alloying of hot dip galvanizing, and thus alloying has been performed at a low temperature of 530 ° C. or lower. However, in order to set the plating layer surface to the δ _1k phase, as shown in the phase diagram of Fe—Zn shown in FIG. 1, the alloying temperature must be higher than 530 ° C., and the alloy needs to be alloyed in the two-phase region of δ _1k + L. There is. When alloyed at 530 ° C. or lower, the alloy layer has primary crystals of ζ phase or δ _1p phase. Even if the primary crystal is a ζ phase or δ _1p phase, if it is kept at a high temperature as it is, Fe diffuses from the steel and _eventually transforms into the δ _1k phase, but at the same time the Γ phase grows, so the powdering performance is It drops significantly. Therefore, when alloying at 530 ° C. or lower, it is possible to achieve both that the ratio of the δ _1k phase to the surface is 50 to 100% and that the Γ phase thickness at the plating / steel interface is 0.1 to 0.8 μm. Can not.

In addition, the two-phase region of δ _1k + L is 530 to 665 ° C., but if the alloying temperature is too high, the Γ phase grows at the plating / steel interface immediately after the formation of the δ _1k phase, and the powdering performance decreases. The upper limit of the alloying temperature is 600 ° C.

  Furthermore, if the alloy is kept at a high temperature after the alloying, Fe diffuses from the steel, the Γ phase grows, and the powdering performance is remarkably lowered. Therefore, after the alloying temperature reaches 530 to 600 ° C., 10 seconds. Within 400 ° C.

That is, after the plating, heating is performed so that the plate temperature on the heating furnace exit side is over 530 ° C. and 600 ° C. or less, and cooling to 400 ° C. within 10 seconds, the ratio of δ _1k phase in the surface is 50 to 50%. It is possible to achieve both 100% and a Γ phase thickness of 0.1 to 0.8 μm at the plating / steel plate interface. Especially for parts with severe molding, in order to set the Γ phase thickness to 0.1 to 0.5 μm, heating is performed so that the plate temperature on the exit side of the heating furnace is over 530 ° C. and 570 ° C. or less, and within 10 seconds. It is preferable to cool to 400 ° C.

  In the production of the galvannealed steel sheet of the present invention, the hot dip galvanizing bath used is preferably adjusted to have an Al concentration of 0.10 to 0.15 mass% as an effective Al concentration in the bath. Here, the effective Al concentration in the plating bath is a value obtained by subtracting the Fe concentration in the bath from the Al concentration in the bath.

When the effective Al concentration is lower than 0.10%, the formation of the Fe—Al—Zn phase that becomes an alloying barrier at the initial stage of plating becomes insufficient, and the alloying is completed before the alloying temperature reaches 530 ° C. Therefore, it is impossible to satisfy both the ratio of the δ _1k phase in the surface to 50 to 100% and the Γ phase thickness at the plating / steel sheet interface to 0.1 to 0.8 μm. On the other hand, when the effective Al concentration is higher than 0.15%, high temperature and long time alloying is required. Therefore, it is necessary to decrease the productivity of the plating line and increase the cost, such as decreasing the line speed. Occurs.

  Other manufacturing methods may be similar to known manufacturing methods depending on the purpose.

  In the present invention, O in the steel sheet is not particularly limited, but O generates oxide inclusions and impairs the workability and corrosion resistance of the steel. Therefore, the O content is desirably 0.004% or less, and the smaller the better.

  In addition to the above components, the steel sheet of the present invention may contain other alloy elements for the purpose of further improving the corrosion resistance and hot workability of the steel sheet itself, or as an inevitable impurity from secondary materials such as scrap. Even if other alloy elements are contained, it does not depart from the scope of the present invention. Such alloy elements include Cu, Ni, Cr, Mo, W, Co, Ca, rare earth elements (including Y), V, Zr, Ta, Hf, Pb, Sn, Zn, Mg, Ta, As, Sb, Bi. Is mentioned.

  Since the steel sheet of the present invention can be applied to a normal hot dip galvanized steel sheet production line to obtain an alloyed hot dip galvanized steel sheet having excellent workability, formability and plating adhesion, there is no particular restriction on the manufacturing process. . A process may be selected as appropriate in consideration of cost and productivity.

The steel sheet of the present invention is made of Pb, Sb, Si, Fe, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, rare earth elements during hot dip galvanizing bath or during galvanizing. Even if one kind or two or more kinds are contained or mixed, the effects of the present invention are not impaired, and depending on the amount, the corrosion resistance may be improved. There are no particular restrictions on the amount of galvannealed coating, but it is preferably 20 g / m ² or more from the viewpoint of corrosion resistance and 150 g / m ² or less from the viewpoint of economy.

  In the present invention, the method for producing the plated steel sheet is not particularly limited, and a normal non-oxidizing furnace type or all-radiant type hot dipping method can be applied.

  In the present invention, the thickness of the steel sheet does not impose any restrictions on the present invention, and the present invention can be applied as long as it is a commonly used sheet thickness. Furthermore, the steel sheet of the present invention is sufficiently effective whether it is a cold-rolled steel sheet or a hot-rolled steel sheet manufactured by a normal process, and the effect does not change greatly depending on the history of the steel sheet. . Moreover, the hot rolling conditions, the cold rolling conditions, the annealing conditions, etc. may be selected according to the dimensions of the steel sheet and the required strength, depending on the hot rolling conditions, the cold rolling conditions, the annealing conditions, etc. The effect of the steel sheet of the present invention is not impaired.

  Of course, it is of course possible to apply various types of upper plating, especially electroplating, on the galvannealed steel sheet obtained by using the steel sheet of the present invention in order to improve the paintability and weldability. And does not depart from the present invention. Further, it is of course possible to add various treatments to the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention. For example, chromate treatment, phosphate treatment, and phosphate treatment properties can be achieved. Even if the treatment for improving, the lubricity improving treatment, the weldability improving treatment, the resin coating treatment, etc. are performed, it does not depart from the scope of the present invention. Processing can be performed.

  Hereinafter, the present invention will be described specifically by way of examples.

A slab having the composition shown in Table 1 was heated to 1150 ° C. to form a 4 mm hot-rolled steel strip at a finishing temperature of 910 to 930 ° C. and wound at 680 to 720 ° C. After pickling and cold rolling to obtain a 0.8 mm cold rolled steel strip, an alloyed hot dip galvanized steel sheet was produced using an in-line annealing continuous hot dip galvanizing facility. In plating, the annealing atmosphere was 5% hydrogen + 95% nitrogen mixed gas, the annealing temperature was 800 to 840 ° C., and the annealing time was 90 seconds. As the molten zinc bath, a plating bath having an effective Al concentration of 0.102% in the bath was used, and the basis weight of zinc was adjusted to 50 g / m ² with a gas wiper. The alloying was heated using induction heating system heating equipment under the conditions shown in Table 2.

  Fe% and Al% during plating were obtained by dissolving the plating with hydrochloric acid containing an inhibitor and measuring by ICP.

The ratio of each alloy phase on the surface of the plating layer was measured by preparing a cross-sectional sample using the FIB μ-sampling method and analyzing the electron diffraction pattern with FE-TEM. The cross-sectional sample was sampled at five points from an arbitrary location. Two-point phase structures were measured from the plating surface layer of each sample, and the ratio of each alloy phase on the plating layer surface was determined using a total of ten measurement data. The identification analysis of the phase structure shows that the monoclinic crystal lattice constants are a = 13.4１３, b = 7.6Å, c = 0.06Å, β = 127.3 and the lattice constant is ζ phase and hexagonal crystal. In which a = 12.8ｐ and c = 57.4Å were observed as the δ _1p phase, and those in which a three-fold period of the δ _1p phase was observed were performed as the δ _1k phase.

  The thickness of the Γ phase in the plating layer was measured by etching the Γ phase of the embedded and polished cross-sectional sample with nital and using SEM. The thickness of the Γ phase was measured at five points from an arbitrary place, and the values were averaged.

  In addition, as an index of workability, tensile tests were performed on each alloyed hot-dip galvanized steel sheet, and the strength, elongation, and rankford value (r values; average r values of 0 °, 45 °, and 90 °) were measured. .

For deep drawability, a TZP test was performed under the following conditions, and a blank diameter with a T value of 0 was evaluated as a limit draw ratio (LDR).
Blank diameter (D ₀ ): φ90-φ125mm
Tool size:
Punch diameter (D ₀ ) φ50mm, shoulder r: 5mm
Die hole diameter φ51.6mm, shoulder r: 5mm
BHF:
5kN when measuring molding load (P)
100kN when measuring breaking load (P _f )
Lubricating oil: Rust-proof oil evaluation value Molding margin T value = (P _f −P) / P _f

The plating adhesion was evaluated by performing a square tube drawing test under the following conditions, and measuring the mass of the plating peeled from the mass difference before and after the test.
Square tube drawing test condition blank size: 150 × 110mm
Punch size: 80 × 40mm
Punch shoulder r: 5mm
Dice shoulder r: 5mm
Molding depth: 25mm

Adhesion was evaluated according to the following classification, and x was rejected.
：: Plating layer peeling amount of 50 mg or less ○: Plating layer peeling amount of more than 50 mg and 150 mg or less Δ: Plating layer peeling amount of more than 150 mg and 300 mg or less ×: Plating layer peeling Amount exceeding 300mg

The results are shown in Table 2 (Tables 2-1 and 2-2). Nos. 1, 2, 9, 10, 17, 18, 25, 26, 33, 34, 41, and 42 have low alloying temperatures, and therefore, steel plates for alloying hot dip galvanization in which the δ _1k phase is not formed on the plating surface layer It is an example. Nos. 3, 11, 19, 27, 35, and 43 were alloyed at low temperature for a long time for the purpose of forming a δ _1k phase on the plating surface layer. Therefore, the Γ phase thickness was out of the scope of the present invention, and the plating adhesion was It was rejected. Nos. 6, 14, 22, 30, 38, and 46 had a long time until reaching 400 ° C. after reaching the alloying temperature, so the Γ phase thickness was out of the scope of the present invention, and the plating adhesion was rejected. . In Nos. 49, 50, 51, and 52, the P content of the steel sheet was outside the scope of the present invention, so the material and formability were inferior to those of the steel sheet of the present invention. In Nos. 53, 54, 55, and 56, the Si content of the steel sheet was outside the scope of the present invention, and therefore the material and formability were inferior to those of the steel sheet of the present invention. Nos. 57, 58 and 59 were inferior in quality and formability to the steel plate of the present invention because the N content of the steel plate was outside the scope of the present invention.

The products of the present invention other than these were alloyed hot-dip galvanized steel sheets that have both excellent deep drawability and high plating adhesion and can be used as automotive outer plates. In the product of the present invention in which the ratio of the δ _1k phase occupying the surface of the plating layer is 50 to 100%, the LDR value is improved by 1 to 1.6 compared to the comparative example in which the δ _1k phase is not formed on the plating surface layer. As can be seen by comparing the results in Table 2 (Tables 2-1 and 2-2), this was an effect of improving deep drawability equivalent to increasing the r value by 0.2 to 0.4. .

It is a phase diagram of Fe-Zn.

Claims (6)

% By mass
C: 0.0001 to 0.004%,
Si: 0.001 to 0.10%,
Mn: 0.01 to 0.50%,
P: 0.001 to 0.015%,
S: 0.015% or less,
Al: 0.0005 to 0.05%,
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%
A steel sheet comprising the balance Fe and inevitable impurities on one or both sides of Al: 0.05 to 0.5% by mass, Fe: 10 to 17% by mass, the balance consisting of Zn and inevitable impurities and occupying the surface A depth characterized by forming an alloyed hot dip galvanized layer having a ratio of δ _1k phase of 50 to 100% and a Γ phase thickness of 0.1 to 0.8 μm at the interface between the plated layer and the underlying steel plate. Alloyed hot-dip galvanized steel sheet with excellent drawability.   The alloyed hot-dip galvanized steel sheet excellent in deep drawability according to claim 1, wherein the steel sheet further contains, as an additional component, Nb: 0.002 to 0.10% by mass. 2. The depth according to claim 1, wherein the Ti content in the steel satisfies a condition given by the following formula (1) (where [% X] is the content of alloy element X expressed in mass%): Alloyed hot-dip galvanized steel sheet with excellent drawability.
[% Ti] ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (1) The content of Ti and Nb in the steel satisfies the conditions given by the following formulas (2) to (3) (where [% X] is the content of alloying element X expressed in mass%): The alloyed hot-dip galvanized steel sheet excellent in deep drawability according to claim 2.
[% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1.5 [% S]
(2)
[% Ti] ≧ 0.009% (3)   The alloyed molten zinc having excellent deep drawability according to any one of claims 1 to 4, wherein the steel sheet further contains B: 0.0002 to 0.003% by mass% as an additional component. Plated steel sheet.   After plating, it heats so that the plate | board temperature by the side of a heating furnace may be over 530 degreeC and 600 degrees C or less, and it cools to 400 degreeC within 10 second, It is characterized by the above-mentioned. A method for producing a galvannealed steel sheet excellent in deep drawability.

Images