JP2005336545A - Steel sheet to be galvannealed - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet to be galvannealed which attains all of superior workability, formability and high adhesiveness to a plated film. <P>SOLUTION: The steel sheet to be galvannealed comprises, by mass%, 0.0001-0.004% C, 0.001-0.10% Si, 0.01-0.50% Mn, 0.001-0.015% P, 0.015% or less S, 0.008% or less Al, 0.002-0.10% Ti, 0.0005-0.004% N, further 0.0001-0.01% one or more elements among Ce, La, Nd, Pr and Sm in total and the balance Fe with unavoidable impurities. The steel sheet is galvannealed, as needed, to form the galvannealed layer thereon which comprises 0.05-0.5 mass% Al, 7-15 mass% Fe and the balance Zn with unavoidable impurities. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steel sheet for alloying hot dip galvanizing, and more particularly to a steel sheet that has excellent formability and workability including deep drawability and at the same time excellent plating adhesion.

  Alloyed hot-dip galvanized steel sheets are widely used in automobiles, home appliances, building materials, etc. because of their excellent paint adhesion, corrosion resistance, and weldability. An alloyed hot-dip galvanized steel sheet is formed by coating hot-dip zinc on the surface of the steel sheet and immediately holding it at a temperature above the melting point of zinc to diffuse Fe from the steel sheet into the zinc, thereby forming a Zn-Fe alloy. However, since the alloying speed varies greatly depending on the composition and structure of the steel sheet, its control requires a fairly advanced technique. On the other hand, steel sheets used for automobile outer plates and difficult-to-form parts are required to have extremely high formability, and in recent years the demand for rust prevention performance of automobiles has increased. The number of cases where is applied is increasing. In this case, since the steel sheet is formed with a very high degree of work, the steel sheet is required to have both excellent workability and high plating adhesion.

  In the alloyed hot-dip galvanized steel sheet, as a result of alloying reaction between the steel sheet and the zinc layer, the plated layer changes to Zn-Fe intermetallic compounds called ζ phase, δ1 phase and Γ phase. While these alloy phases improve paintability, paint adhesion, and weldability, the hardness of the alloy layer itself is high, and the Γ phase is particularly brittle. It becomes easy to cause the so-called powdering phenomenon. In addition to impairing the soundness of plating, powdering causes the powdered plating that has peeled off to accumulate on the press mold and significantly deteriorate the appearance of the pressed product. In recent years, thickened alloyed hot-dip galvanized steel sheets are becoming popular for the purpose of enhancing the anti-corrosion performance of automobile bodies. However, the above-mentioned powdering phenomenon is more likely to occur as the coating amount increases, so that it is resistant to powdering. There is a strong demand for improvement in performance.

  On the other hand, as the car body shape becomes more complicated, the demands on the formability of steel sheets have become more severe, and steel sheets with excellent formability such as deep drawability have been transformed into galvannealed steel sheets. Is also required. In order to obtain such workability, the steel is typically steel that has Ti added to it after reducing C to an extremely low level, or steel that has Ti and Nb added in combination. However, these steels have a problem that the alloying rate of hot dip galvanizing is so high that the alloying progresses too much and the Γ phase grows thick and the powdering performance tends to deteriorate. For such steels, measures from the operational aspect such as lowering the plating bath temperature, increasing the Al concentration in the plating bath, lowering the alloying temperature and increasing the heating time have been attempted. , Since such countermeasures cause another problem that the alloying is insufficient and the slidability of the surface is liable to be lowered, it is difficult to achieve both excellent workability and high plating adhesion only by handling from the operational aspect. Have difficulty. In addition, these changes in operating conditions are accompanied by production line stoppages, reducing productivity and raising costs.

As a method for producing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance, a technique for defining soaking conditions after alloying as well as alloying heat treatment conditions and cooling conditions has been proposed (for example, Patent Document 1). 2), so long time soaking is required, so the productivity of the plating line is reduced and it is not economical. Also, as a method for producing an alloyed hot-dip galvanized steel sheet having excellent deep drawability and plating adhesion, in addition to the composition of the steel sheet, hot rolling conditions and cooling conditions, annealing conditions after cold rolling, P and Ti of the steel sheet are used. A technique for limiting the relational expression between the content and the effective Al concentration in the plating bath has been proposed (see, for example, Patent Document 3). In addition to the steel sheet composition, hot rolling conditions, and annealing conditions after cold rolling, 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 has been proposed (see, for example, Patent Document 4). However, in these methods, the productivity of the plating line is lowered and the cost is increased due to the change or adjustment of the operation condition of the plating line by controlling the Al concentration.
Japanese Patent Laid-Open No. 2-310352 Japanese Patent Laid-Open No. 2-310353 Japanese Patent Laid-Open No. 5-331612 JP-A-6-17142

  An object of the present invention is to provide a steel sheet for galvannealing that can simultaneously achieve excellent workability / formability and high plating adhesion.

As a result of various studies on means for improving the plating adhesion without degrading the workability of the steel sheet and the productivity of the hot dip galvanizing line, the present inventor has obtained Ce, La, etc. By adding one or more of Nd, Pr, and Sm, it was found that the workability of the steel sheet and the plating adhesion can be compatible, leading to the present invention.
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: 0.008% or less,
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
Alloying melt, characterized in that it contains 0.0001 to 0.01% in total of one or more of Ce, La, Nd, Pr, and Sm, and the balance is Fe and inevitable impurities. Galvanized steel sheet.

  (2) The steel sheet for galvannealing according to (1) above, wherein the steel sheet further contains Nb: 0.002 to 0.10% by mass as an additional component.

(3) 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%): Steel sheet for alloying hot dip galvanization described in 1.
[% 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) ([% X] is the content of alloy element X expressed in mass%). The steel sheet for alloying hot dip galvanizing as described in (2) above.
([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (2)
[% Ti] ≧ 0.009% (3)

  (5) The alloyed molten zinc 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. Steel plate for plating.

(6) 70% or more of non-metallic inclusions having an equivalent circle diameter of 10 μm or more observed with a microscope are within the composition range of the following formula, (1) to (5) Steel sheet for alloying hot dip galvanizing.
30% ≦ TiO ₂ / (TiO ₂ + Al ₂ O ₃ + REM oxide) ≦ 50% (4)
0 ≦ Al ₂ O ₃ ≦ 20% (5)
50% ≦ REM oxide ≦ 70% (6)
TiO ₂ : concentration of Ti oxide in non-metallic inclusions on the steel sheet. Ti oxides include Ti ₂ O ₃ ,
There is a Ti ₃ O ₅ form, but the Ti oxide concentration converted as TiO ₂ .
Al ₂ O ₃ : Concentration of Al oxide in non-metallic inclusions in the steel plate.
REM oxide: The total concentration of Ce, La, Nd, Pr, and Sm oxides in the nonmetallic inclusions in the steel sheet. Oxide amount converted as Ce ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Pr ₂ O ₃ , Sm ₂ O ₃ .

  (7) Al: 0.05 to 0.5% by mass, Fe: 7 to 15% by mass, balance of Zn and inevitable in the steel sheet for galvannealing according to any one of (1) to (6) Alloyed galvanized steel sheet with an alloyed galvanized layer composed of mechanical impurities.

  (8) d = 1.26 and d = 1.222 X-ray diffraction intensities Iζ and IΓ of the steel plate for alloying hot dip galvanizing described in the above (7) and d = 3.13 of the Si standard plate An alloyed hot-dip galvanized steel sheet characterized in that the ratios Iζ / ISi and IΓ / ISi with the X-ray diffraction intensity ISi are Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.

  The present invention makes it possible to provide a steel sheet to be plated that can produce an alloyed hot-dip galvanized steel sheet that is excellent in all of workability, formability, and plating adhesion, and contributes greatly to industrial development. It is.

  The present invention is described in detail below. First, the reason for limiting the range of each component 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 the steel, and it is effective to contain 0.0001% or more. However, if it is excessively contained, the strength is excessively increased and the workability is lowered, so the upper limit content is 0.8. 004%. In particular, when high workability is required, the C content is preferably 0.003% or less, and more preferably 0.002% or less.

  Si: Si is also an element that improves the strength of steel and contains 0.001% or more. However, if excessively contained, 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 should be 0.05% or less.

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

  P: P is an element that increases the strength of the steel while decreasing the workability, so the upper limit content is 0.015%. The smaller 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 large, 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 lowers the hot workability and corrosion resistance of steel, it is preferably as small as possible. The upper limit is 0.015%, 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, S should be reduced to the required level due to corrosion resistance.

  Al: Al is generally added as a deoxidizing element for steel. However, Al produces alumina inclusions by deoxidation, which aggregate and coalesce into coarse alumina clusters. In particular, in low carbon steel with low carbon concentration and high dissolved oxygen concentration after refining, the amount of alumina clusters is very large, and when the Al content exceeds 0.008%, the incidence of surface defects becomes extremely high. The amount of Al added should be 0.008% or less.

  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 preferable to make it 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, it 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 0.0005%.

  Ce, La, Nd, Pr, Sm: Alloying of hot-dip galvanized layer and steel sheet by adding 0.0001 to 0.01% of one or more of Ce, La, Nd, Pr, Sm in total It is possible to obtain an alloyed hot-dip galvanized steel sheet with good properties by controlling the reaction. When one or more of Ce, La, Nd, Pr, and Sm are added, the alloying rate can be reduced without substantially increasing the strength of the steel sheet, so the workability and plating adhesion of the steel sheet. Can be satisfied. Here, for the purpose of suppressing the formation of brittle intermetallic compounds typified by the Γ phase at the iron / plating interface and improving the plating adhesion, the addition amount of one or more of Ce, La, Nd, Pr, and Sm Is required to be 0.0001% or more. Further, in order to deoxidize steel with an Al addition amount of 0.008% or less, the addition amount of one or more of Ce, La, Nd, Pr, and Sm needs to be 0.0001% or more. . However, if it exceeds 0.01%, not only will the cost increase, but the oxides of these metals will become inclusions in the steel sheet, which will likely cause surface defects after press working, so the total amount added will be 0.01%. % Or less.

  The reason why the alloying speed can be reduced by adding one or more of Ce, La, Nd, Pr, and Sm is that these elements exist in the crystal grains and in the grain boundaries. This is thought to be due to the effect of delaying the diffusion of Fe.

  From the balance of plating adhesion and cost, the addition amount of one or more of Ce, La, Nd, Pr, and Sm is more preferably 0.001 to 0.01%.

  Ce, La, Nd, Pr, and Sm can be added with a single metal, but it can also be added with an alloy containing Ce, La, Nd, Pr, and Sm such as misch metal.

Further, when the addition amount of Ce, La, Nd, Pr, and Sm is small with respect to the amount of Ti oxide, the inclusion composition is mainly TiO ₂ -Al ₂ O ₃ inclusions, which are agglomerated and coarsened. Cluster. Conversely, if the amount of Ce, La, Nd, Pr, and Sm added is too large relative to the amount of Ti oxide, the inclusions are mainly oxides with a REM oxide concentration of 90% or more, which aggregate and coalesce. It becomes a coarse cluster. The presence of such clusters causes surface defects after press working. Therefore, the steel sheet is examined under a microscope, and 70% or more of non-metallic inclusions having an equivalent circle diameter of 10 μm or more are within the composition range of the following formula. More preferably.
30% ≦ TiO ₂ / (TiO ₂ + Al ₂ O ₃ + REM oxide) ≦ 50% (4)
0 ≦ Al ₂ O ₃ ≦ 20% (5)
50% ≦ REM oxide ≦ 70% (6)
TiO ₂ : concentration of Ti oxide in non-metallic inclusions on the steel sheet. Ti oxides include Ti ₂ O ₃ ,
There is a Ti ₃ O ₅ form, but the Ti oxide concentration converted as TiO ₂ .
Al ₂ O ₃ : Concentration of Al oxide in non-metallic inclusions in the steel plate.
REM oxide: The total concentration of Ce, La, Nd, Pr, and Sm oxides in the nonmetallic inclusions in the steel sheet. Oxide amount converted as Ce ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Pr ₂ O ₃ , Sm ₂ O ₃ .

  Here, “equivalent to a circle observed with a microscope” is an index indicating the size of non-metallic inclusions in a steel sheet and is defined as follows. In other words, “equivalent to a circle observed with a microscope” means that in a sample obtained by mirror polishing an arbitrary cross section of a steel plate, the inclusions in the steel plate are observed with an optical microscope at a magnification of 200 to 1000 times. The length (L) and width (D) are measured, the area of the nonmetallic inclusion is assumed to be a rectangle (LxD), and the area is obtained and defined as the diameter of a circle having the same area as the rectangular area. In addition, when the observed nonmetallic inclusions were in a form close to a circle, the diameter was taken as the equivalent circle diameter.

  In the present invention, in addition to the above, as an additional component, Nb can be added under the Ti addition to fix C and N in the steel as carbides and nitrides. In order to fully exhibit the C and N fixing effect, 0.002% or more must be added, 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 only increases 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, in order to further increase the formability and workability of the steel sheet, the Ti content is set to a range that satisfies the following formula (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, can be 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 contents of Ti and Nb are in the above ranges, C and N, which are elements that hinder 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. If the content satisfies the formula (2), C and N can be effectively fixed with Ti and Nb.

  In the present invention, the steel sheet can further contain 0.0002 to 0.003% of B as an additional component, which 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 formability is reduced. Therefore, when B is added, the range is 0.0002 to 0.003%. In particular, when high deep drawability is required, it is more preferable that the amount of B added is 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 if it is less than 0.05% by mass, Zn-Fe alloying proceeds too much during the alloying process. 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 process. This is because the desired iron content cannot be obtained because it does not progress. Desirably, it is 0.1-0.3 mass%.

  The reason why the Fe composition is limited to 7 to 15% by mass is that if it is less than 7% 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 too much at the iron interface and the plating adhesion deteriorates. Desirably, it is 9-12 mass%.

Next, the alloyed hot-dip galvanized layer is described. In the present invention, the alloyed hot-dip galvanized layer refers to a plated layer mainly composed of an Fe-Zn alloy in which Fe in steel is diffused during Zn plating by an alloying reaction. This plating layer forms alloy layers called ζ phase, δ ₁ phase, and Γ phase due to the difference in Fe content. Of these, the ζ phase has a high coefficient of friction due to its soft plating and easy adhesion to the press die, and is likely to cause plate breakage when severe pressing is performed. In addition, the Γ phase is hard and brittle, so it tends to cause plating peeling called powdering during processing. Therefore, press workability and plating adhesion can be improved by reducing the ζ phase and Γ phase as much as possible and making the plating layer δ ₁ phase. Here, it is known that a hard and brittle phase called Γ ₁ phase is also present in the plating layer. However, since the Γ phase and Γ ₁ phase cannot be distinguished from the X-ray diffraction intensity, the Γ phase And Γ ₁ phase are combined and treated as Γ phase.

  Specifically, the ratio between the X-ray diffraction intensity Iζ and IΓ of d = 1.26 and d = 1.222 indicating the ζ phase and the Γ phase and the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate. Let Iζ / ISi and IΓ / ISi be Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.

  The reason why Iζ / ISi is limited to 0.004 or less is that when Iζ / ISi is 0.004 or less, the ζ phase is very small, and the press workability is not deteriorated.

The reason why IΓ / ISi is limited to 0.004 or less is that when IΓ / ISi is 0.004 or less, the Γ phase is insignificant and no decrease in plating adhesion is observed.
As a manufacturing process of the steel sheet of the present invention, a manufacturing process of a normal hot-rolled steel sheet (hot strip) or a cold-rolled steel sheet (cold strip) may be applied.

  In the present invention, O in the steel sheet is not particularly limited. However, since O generates oxide inclusions and impairs the workability and corrosion resistance of the steel, the content is desirably 0.007% or less, and the smaller the better.

  In addition to the above components, the steel sheet of the present invention may contain other alloying 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. Examples of such alloy elements include Cu, Ni, Cr, Mo, W, Co, Ca, Y, V, Zr, Ta, Hf, Pb, Sn, Zn, Mg, Ta, As, Sb, and Bi.

  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 with excellent workability, formability and plating adhesion, and there is no particular restriction on the manufacturing process. . The process should be selected appropriately in consideration of cost and productivity.

The steel sheet of the present invention is one of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth elements during hot dip galvanizing bath or galvanizing. Alternatively, even if two or more kinds are contained or mixed in, 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 alloyed hot-dip galvanized 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 hot dipping method can be applied. The alloying treatment conditions are not particularly defined, but a treatment temperature of 460 to 550 ° C. and a treatment time of 10 to 40 seconds are appropriate for actual operation.

  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 to any sheet thickness that is normally used. Furthermore, the effect of the steel sheet of the present invention is sufficiently exerted regardless of 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. . In addition, the hot rolling conditions, cold rolling conditions, annealing conditions, etc. may be selected according to the steel sheet dimensions and required strength, depending on the hot rolling conditions, cold rolling conditions, annealing conditions, etc. The effect of the steel sheet of the present invention is not impaired.

  Naturally, 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. It does not depart from the present invention. In addition, 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. Even if a treatment for improving, a lubricity improving treatment, a weldability improving treatment, a resin coating treatment, etc. are performed, it does not depart from the scope of the invention of the present application. Can be processed.

As the strength of the steel sheet of the present invention, high-strength steel (300, 340, 400, 440 N / mm ² grade) of 300 N / mm ² or more from ordinary steel having a tensile strength of less than 300 N / mm ² or ultra deep drawing steel Is a wide range of

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

  First, the test materials shown in Table 1 were prepared, and an alloyed hot-dip galvanized steel sheet was manufactured using an in-line annealing method of continuous hot-dip galvanizing equipment. Table 1 shows the chemical component values of the test material, that is, the steel plate before plating, and the chemical component values of the nonmetallic inclusions in the steel plate. Here, the chemical component value of the nonmetallic inclusion was determined as follows. Specimen sample is embedded in resin so that the longitudinal section (cross section parallel to the rolling direction) of the steel sheet becomes the spectroscopic observation surface, and mirror polishing is performed, and non-metallic inclusions with a circle equivalent diameter of 10 μm or more are arbitrarily selected 20 were identified, and the composition was determined by EPMA. Table 1 shows the average chemical composition of 20 non-metallic inclusions.

During 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. The molten zinc bath was molten zinc containing 0.12% Al, and the basis weight of zinc was adjusted to 50 g / m ² with a gas wiper. The alloying was heated by induction heating equipment so that the Fe content in the galvannealed alloy was 10.5 to 11.5%. However, hot-rolled steel sheets were preheated to 90 ° C (90 seconds) instead of annealing and cooling. The Al content in the galvannealed steel sheet thus obtained was 0.15 to 0.25%.

Samples were taken from each steel plate and the plating adhesion was evaluated by the V-bending method. That is, a test piece with adhesive tape (cellophane tape) applied to the compression side in advance is bent in a V shape so that the bending angle is 60 °. The plating adhesion was evaluated according to the following classification.
◎: Plating layer does not peel at all ○: Peeling of plating is slight △: Plating is peeled off to some extent ×: Plating is almost peeled off

  In addition, as an index of workability, a tensile test was performed on each alloyed hot-dip galvanized steel sheet, and the elongation and the Rankford value (r values; average r values of 0 °, 45 °, 90 °, however, cold-rolled steel plates) Only), the cold-rolled sheet passed 50% or more elongation and the r value 1.5 or more passed, and the hot-rolled steel sheet passed 45% or more elongation.

Surface defects after press working were evaluated by a ball head overhang test. The test conditions are shown below.
・ Sample drawing width: 200 × 200mm
・ Mold: Ball head punch with radius 60mm, Dies with beads
・ Pressing load: 60t
-Overhang speed: 30 mm / min
・ Oiling: Antirust oil applied

The surface defects were evaluated by performing 1,000 sphere head overhang tests and evaluating them according to the following classifications, with ○ being a pass.
○: Crack occurrence rate due to non-metallic inclusions is less than 0.5% △: Crack occurrence rate due to non-metallic inclusions is 0.5% or more and less than 3% ×: Caused by non-metallic inclusions Crack occurrence rate is 3% or more

The results are shown in Table 1. In No. 22, since the addition amount of Ce, La, Nd, Pr, and Sm was outside the range of the present invention, the REM oxide became a cluster and the surface defect after press working was rejected. Nos. 23, 24, 25, and 28 have Al, Ce, La, Nd, Pr, and Sm addition amounts outside the scope of the present invention, so that alumina clusters increase and surface defects after press working are rejected. The plating adhesion was also rejected. In No. 26, since the amount of Al added was outside the range of the present invention, alumina clusters increased and surface defects after press working were rejected. In No. 27, since the addition amount of Al, Ce, La, Nd, Pr, and Sm is outside the range of the present invention, the alumina cluster increases, the surface defect after press working becomes rejected, and the workability of the steel sheet is reduced. It was insufficient.
The products of the present invention other than these were plated steel sheets with excellent plating adhesion.

  First, the test materials shown in Table 2 were prepared, and an alloyed hot-dip galvanized steel sheet was manufactured using a vertical hot-dip plating machine capable of simulating the thermal cycle and atmosphere of CGL. During 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. The molten zinc bath was made of molten zinc containing Al, and the basis weight of zinc was adjusted to 50 g / m @ 2 by gas wiping. The alloying was heated using an induction heating system so that the Fe content in the alloyed hot dip galvanizing was as shown in Table 3. Various changes were made to the Al concentration in the plating bath so that the Al content in the galvannealed alloy was the value shown in Table 3.

  Elongation and Rankford values (r values; average r values of 0 °, 45 °, 90 °, but only for cold-rolled steel sheets) are measured by performing a tensile test on each alloyed hot-dip galvanized steel sheet, and the elongation is 50% or more. The r value was confirmed to be 1.5 or more.

  The Fe content and Al content of the plating were measured by ICP after dissolving the coating with hydrochloric acid containing an inhibitor.

  X-ray diffraction is the ratio of the X-ray diffraction intensities Iζ and IΓ of d = 1.26 and d = 1.222 indicating the ζ phase and the Γ phase to the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate. Iζ / ISi and IΓ / ISi were measured.

  The obtained plated steel sheets were examined for press formability and plating adhesion.

For the press formability, a bead pull-out test was conducted to investigate the slidability of plating during press working. The test conditions are shown below.
・ Sample drawing width: 30mm
・ Die: Square bead with one side shoulder R1mmR (convex part is 4 × 4mm) convex, the other side is concave shape with shoulder R1mmR ・ Pressing load: 800,1000kg
・ Pullout speed: 200mm / min
・ Oiling: Antirust oil applied

The press formability was evaluated according to the following classification, and ◎ and ○ were accepted.
◎: Pulled out with a pressing load of 1000 kg ○: Pulled out with a pressing load of 800 kg, but broken with a load of 1000 kg ×: Broken with a pressing load of 800 kg

For plating adhesion, the test piece with adhesive tape (cellophane tape) on the compression side is bent in a V shape so that the bending angle is 60 °, and after bending back, the adhesive tape is peeled off. The degree of peeling was visually observed and evaluated according to the following classifications, and ◎ and ○ were accepted.
◎: Plating layer does not peel at all ○: Peeling of plating is slight △: Plating is peeled off to some extent ×: Plating is almost peeled off

The evaluation results are shown in Table 3. Nos. 1 and 26 failed in press formability because Fe% and Iζ / ISi in the plating were outside the scope of the present invention. Nos. 5 and 30 failed in plating adhesion because Fe% and IΓ / ISi in the plating were outside the scope of the present invention. In Nos. 6 and 31, Al% in plating and IΓ / ISi were out of the scope of the present invention, so the plating adhesion was unacceptable.
The products of the present invention other than these were plated steel sheets with excellent plating adhesion.

  As described above, the present invention makes it possible to provide a steel sheet to be plated that can produce an alloyed hot-dip galvanized steel sheet that is excellent in all of workability, formability, and plating adhesion. The place that contributes to development is extremely large.

Claims (8)

% 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: 0.008% or less,
Ti: 0.002 to 0.10%,
N: 0.0005 to 0.004%,
Alloying melt, characterized in that it contains 0.0001 to 0.01% in total of one or more of Ce, La, Nd, Pr, and Sm, and the balance is Fe and inevitable impurities. Galvanized steel sheet.   The steel sheet for alloying hot-dip galvanizing according to claim 1, wherein the steel sheet further contains, as an additional component, Nb: 0.002 to 0.10% by mass. 2. The alloy 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%): Steel plate for hot dip galvanizing.
[% 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 steel sheet for galvannealing according to claim 2.
([% Ti] +0.52 [% Nb]) ≧ 4 [% C] +3.4 [% N] +1.5 [% S] (2)
[% Ti] ≧ 0.009% ・ ・ ・ (3)   The steel sheet for alloying hot dip galvanizing 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. The alloyed hot-dip galvanized steel according to any one of claims 1 to 5, wherein 70% or more of non-metallic inclusions having an equivalent circle diameter of 10 µm or more observed with a microscope are within the composition range of the following formula: Steel plate.
30% ≦ TiO ₂ / (TiO ₂ + Al ₂ O ₃ + REM oxide) ≦ 50% (4)
0 ≦ Al ₂ O ₃ ≦ 20% (5)
50% ≦ REM oxide ≦ 70% (6)
TiO ₂ : concentration of Ti oxide in non-metallic inclusions in the steel sheet. Ti oxides include Ti ₂ O ₃ ,
Would also be present in the form of Ti ₃ O ₅ but, Ti oxide concentrations calculated as TiO _2.
Al ₂ O ₃ : Concentration of Al oxide in non-metallic inclusions in the steel sheet.
REM oxide: The total concentration of Ce, La, Nd, Pr, and Sm oxides in the nonmetallic inclusions in the steel sheet. Oxide amount converted as Ce ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Pr ₂ O ₃ , Sm ₂ O ₃ .   The alloyed hot-dip galvanized steel sheet according to any one of claims 1 to 6, wherein Al: 0.05 to 0.5% by mass, Fe: 7 to 15% by mass, the balance being Zn and inevitable impurities An alloyed hot-dip galvanized steel sheet with a hot-dip galvanized layer.   The X-ray diffraction intensities Iζ and IΓ of d = 1.26 and d = 1.222 of the steel plate for galvannealed alloy according to claim 7 and the X-ray diffraction intensities of d = 3.13 of the Si standard plate. An alloyed hot-dip galvanized steel sheet characterized in that the ratios Iζ / ISi and IΓ / ISi with ISi are Iζ / ISi ≦ 0.004 and IΓ / ISi ≦ 0.004.