JPH03274285A - Galvannealed steel sheet excellent in press formability - Google Patents

Abstract

PURPOSE:To produce the plated steel sheet excellent in press formability by forming a plating layer in which zinc alloy containing fine nonmetal grains is dispersed under specific conditions on a galvannealed layer in which Fe content, the thickness of gamma-phase in the interface between ferrite and plating, the main peak in X-ray diffraction, and coating weight are specified, respectively. CONSTITUTION:A galvannealed layer which has a composition consisting of, by weight, 6-13% Fe and the balance Zn and in which the thickness of gamma-phase in the interface between ferrite and plating, the main peak in the X-ray diffraction of the plating layer, and coating weight are regulated to <=1.0mu, zeta-phase, and 20-100g/m<2>, respectively, is formed on a steel sheet. Further, a plating layer consisting of a dispersion coating composed of zinc or zinc alloy containing, independently or in combination, 0.1-10wt.% fine grains of nonmetals (SiO2, Tic, AlN, etc.) of <=2mu average grain size is formed by 0.2-5.0g/m<2> coating weight on one side or both sides of the above layer. By this method, the galvannealed steel sheet having satisfactory powdering resistance and flaking resistance can be obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an alloyed hot-dip galvanized steel sheet with excellent press formability, and particularly powdering resistance and Both flaking resistance is satisfactory.

Alloyed hot-dip galvanized steel sheet is produced by heating the hot-dip galvanized steel sheet after plating to diffuse the iron in the base steel sheet into the coating layer.
Although it is an iron-zinc alloy, it has superior corrosion resistance compared to galvanized steel sheets, so it is used in automobiles, building materials, and houses.
Widely used as a material for products, etc.

(Prior Art) In recent years, due to the demand for improved corrosion resistance, there has been a strong demand for thicker alloyed hot-dip galvanized steel sheets. However, since alloyed hot-dip galvanized steel sheets are manufactured by thermal diffusion treatment, as the coating weight increases, the iron concentration gradient in the plating layer increases, and a brittle "phase with high Fe concentration" forms at the interface with the base steel. On the other hand, near the surface of the plating layer, a ζ phase with a low Fe concentration or, in extreme cases, an unalloyed η phase may remain.

If the r-phase is thick, powdering, which causes the plating layer to peel off during press processing, is likely to occur, resulting in scratches caused by plating peeling powder on the product, resulting in negative effects such as a decrease in yield and efficiency due to increased frequency of mold cleaning. Get out.

On the other hand, if the ζ phase is thick or the η phase remains on the surface of the plating layer, the sliding resistance of these phases is large, so mold galling is likely to occur during press processing, resulting in so-called flaking and damage to the mold bead. This also causes a decrease in yield and efficiency in the pressing process.

Such an alloyed hot-dip galvanized steel sheet with a thick coating amount (coating amount of 4537 m2 or more) is required to satisfy both powdering resistance and flaking resistance in the pressing process.

In addition, at low coating weights, alloyed hot-dip galvanized steel sheets with excellent press formability are manufactured and put into practical use by forming a plating layer mainly composed of δ phase. It continues to be desired.

(Problems to be Solved by the Invention) In the conventional method for manufacturing alloyed hot-dip galvanized steel sheets, the effective amount of Al (42%-Fe%) is set to 0.0, for example, in a hot-dip zinc bath.
Plating is carried out by passing mV through a Raku medium whose addition is adjusted to 9 to 0.15%, and after adjusting the basis weight by gas wiping etc., the plate is passed through an alloying furnace until the metallic luster on the plated surface disappears, that is, alloying is carried out to the surface. Manufactured by heat-treating until completion and immediately cooling to control the degree of alloying (Japanese Patent Application Laid-Open No. 1983-
223174). The composition of this plating layer is Fe
: 8 to 13%, AN: 0.25 to 0.35%, and the balance is Zn.

However, when a hot-dip galvanized steel sheet with a basis weight of 4537 m'' or more is alloyed in such a process, the thickness of the r-phase formed at the interface between the steel base is, for example, about 1 to 3 μm, and the bowling resistance is not sufficient.

Therefore, the effective amount of Al in the bath was reduced to about 0.10% or less, and the Fe-A1 alloy layer formed in the bath was made thinner.
By making the formation of the 2n alloy phase relatively easy, an alloyed hot-dip galvanized steel sheet can be produced by heat treatment at a lower temperature. The composition of this plating layer is Fe: 6-1
1%, A: 0.05 to 0.25%, and the remainder Zn. However, when the basis weight is 45 g/+'' or more, although there is a condition that the thickness of the r phase is 1 μm or less, the η phase and ζ phase tend to remain on the surface of the plating layer, and the flaking resistance is not sufficient. do not have.

In order to solve these drawbacks, for example, I
The generation of r-phase generated at I (boundary with the subway) is suppressed as much as possible,
It has been disclosed that the upper layer is a plating layer consisting of η phase, δ phase, and ζ phase, and that iron plating is applied on the molten alloy layer (Japanese Patent Application Laid-open No. 60-228662), but the results are still unsatisfactory. At present, no results have been obtained.

(Means for Solving the Problems) Therefore, as a result of intensive study, the present inventors found that powdering,
We have found an alloyed hot-dip galvanized steel sheet that satisfies both flaking and flaking properties.

In order to solve the above problems, the present invention has a composition consisting of 6 to 13% by weight of Fe and the balance of 2n, and the r phase at the base metal-plating interface is 1.0 μm. The peak is ζ phase, and the date amount is 20 to 100 g/m'
On the alloyed hot-dip galvanized layer of 0.2 to 5.0%, dispersion plating made of zinc or zinc alloy containing 0.1 to 10% by weight of nonmetal fine particles with an average particle size of 2 μm or less, singly or in combination, is applied. 08/- coated plating layer on one side,
Alternatively, it is an alloyed hot-dip galvanized steel sheet with excellent press formability that satisfies both powdering resistance and flaking resistance on both sides, and the non-metal fine particles for dispersion plating include 5L02. TfJ, AR20s, ZrO2
, SIC, TiC, SIN.

Features (effects) characterized by containing one or more of TiN, ANN, and graphite: Although the ζ phase has high sliding resistance and is inferior in flaking properties, it is extensible and powdering does not easily occur. In addition, in the case of only bending, it is effective to prevent the propagation of cracks that occur in the lower layer. A feature of the present invention is that it satisfies both powdering resistance and flaking resistance by taking advantage of the advantages of this ζ phase and overcoming the disadvantage of sliding resistance with the lubricity of the hard dispersion plating on the upper layer. be. Also,
Another major feature is that by making the plating layer mainly composed of ζ phase with low Fe%, the formation of r phase, which is a major cause of powdering, is suppressed, and corrosion resistance is improved due to the presence of dispersed plating that has excellent bare corrosion resistance. It is. The present invention is intended to improve the press formability of alloyed hot-dip galvanized steel sheets not only in thick coatings but also in a wide coating weight range of 20 to 100 g/n2.

The base plated steel sheet of the present invention has, for example, Affi: 0.00
3. When plating is applied in a 0.13% hot dip galvanizing bath and then heat-treated, the plate temperature is 52o~470'e and heated within 15 seconds, and the lower the AM content in the bath, the lower the temperature. By applying the 9S process, it is possible to reliably manufacture the product mainly in the ζ phase. Confirmation that the ζ phase is the main component can be carried out by electrolytic peeling or cross-sectional etching, but these methods are not preferred because the results obtained vary depending on the conditions. The ζ phase subject in the present invention is
The main peak of X-ray diffraction is used because it is relatively easy to understand the structure of the plating layer.

Next, the limited range of each component will be explained.

Fe%: If Fe is less than 6% by weight, the η phase tends to remain on the surface of the plating layer. If Eel exceeds 3% by weight, the amount of r phase tends to exceed 1μ, which is not preferable.

The r phase is preferably 1 μm or less in order to improve powdering resistance. Especially when it exceeds 1 μm, the basis weight is 4.
If it exceeds 5 g/m2, powdering resistance deteriorates and press formability is adversely affected.

Dispersion plating: The presence of dispersion plating can suppress adhesion of plated metal to the mold and improve flaking resistance. The coating weight of dispersion plating is preferably 0.2 to 5.0 g/m".0,2
If it is less than g/m2, it is difficult to completely cover the lower plating layer, and mold adhesion may occur from the exposed portion of the lower layer, which is not preferable. If it exceeds 5.0 g/m", the dispersion plating will be hard and press formability will deteriorate due to this dispersion plating, which is not preferable. Zinc alone or zinc-iron, Use zinc alloy plating such as zinc-nickel, zinc-cobalt, zinc-chromium, zinc-tin, zinc-cadmium, zinc-titanium, zinc-nickel-cobalt, zinc-nickel-titanium, zinc-nickel-iron-chromium, etc. In terms of aiming for high corrosion resistance, an alloy plating system with a low corrosion rate is effective, but in order to maintain the sacrificial corrosion protection effect of the plating layer, the total amount of alloy components is preferably 20% by weight or less.

In addition, non-metal fine particles are fine particles other than fine particles of simple metals or metal alloys, and specifically include metal, non-metal, or metalloid oxides, carbides, nitrides, graphite, organic substances, etc. . Among these, non-metal fine particles that are particularly effective in terms of hardness and corrosion resistance include oxides such as 5i02. TiO
2, Ajh (hZ "02, carbides include SiC, TiC,
For nitrides, 5iNTiN, Aj! N, and graphite. These are effective when used alone or in combination. The nonmetallic fine particles may be in the form of powder or colloid such as colloidal silica, and are not particularly limited.The size of the fine particles must be 2 μm or less on average. , especially at 0.1 am
The following ultrafine powders are effective in both press moldability and corrosion resistance. If the thickness exceeds 2 μm, film formation will not be sufficient and both press formability and corrosion resistance will deteriorate. Note that the average particle size means a particle size at which the internal distribution of all particles is large.

The content of the nonmetallic fine particles in the plating layer is 0.1 to 10% by weight. If it is less than 0.1% by weight, there is no effect of improving hardness, and if it exceeds 10% by weight, press formability deteriorates.

The plating method for dispersion plating is not particularly limited, but for example, 10 to 150 g of nonmetal fine particles or a colloidal solution of nonmetal particles in a known sulfate-based or chloride-based zinc or zinc alloy plating solution, 9 obtained from a dispersion liquid. At this time, by using an alloy plating bath containing iron group ions such as nickel, iron, and cobalt, which have the property of specifically adsorbing to nonmetallic particles and imparting a charge, the nonmetallic particles can be eutectoid into the plating layer efficiently. This method is commonly used and produces a dispersed plating layer containing more non-metallic particles than a plating bath that does not contain them.

Plating coverage: The thickness of the alloyed hot-dip galvanized layer of the present invention is within a range of 20 to 100 g/m' as a basis weight. 20
If it is less than 7m", there is a problem with corrosion resistance.100g/m
If it exceeds 2, it is practically difficult to plate the r phase with a thickness of 1 μm or less.

Although only Fe was specified as the composition of the alloyed hot-dip galvanized layer, other components such as 8! , Pb, Cd.

Sn, In, Li, Sb, As, Bi, M
g, La, Ce, Ti.

Zr, Ni, Co, Cr, Mn, P, S,
Even if a small amount of O or the like is added or unavoidably mixed, the effects of the present invention essentially remain the same. Especially ^
In the current process, about 0.1% by weight of C is added to the plating layer to control plating and alloying, and it is inevitably mixed into the plating layer. As long as the plating layer is mainly composed of ζ phase, such
There is no effect of quantity. Further, even in the case of a thermal diffusion alloyed material of an electrogalvanized material in which no sulfur is present, the effects of the present invention can be exhibited in terms of wood quality if the alloy phase is mainly composed of the ζ phase.

The plating layer of the present invention is preferably applicable to both sides when the coating weight is 20 to 100 g/m' on one side and the other side has a small coating weight. In the case of a thickened steel plate, it can also be applied only to the thickened surface. In the case of a single-sided plated steel plate, it is of course applicable only to the plated side.

(Example) Next, examples of the present invention will be described together with comparative examples. The material for plating is CC-81-km (0.8t x 100
Immediately after plating in a continuous hot-dip galvanizing line of a non-oxidizing furnace type, heat alloying treatment was carried out using an alloying treatment furnace.

The effective concentration in the plating bath was 0.10% by weight, and the Fe concentration in the plating layer was manufactured by appropriately selecting the heating conditions of the alloying furnace.

Plating was carried out under the conditions that the plate passing speed was 40 to 70 m/min and the immersion time was 2 to 5 seconds. Separately, dispersion plating was applied from 0.1 g/m' to 78/m.

Next, the method for testing the workability of the plating layer will be described.

■ Powdering resistance test Before processing, apply vinyl tape to the bent part, perform bending with the tape side on the inside (2T bending), remove the tape again, and check that the plating layer adheres to the tape and turns black. Judgment was made based on the extent of the damage.

(Good) ◎-〇-△-× (Poor) (◎, ○ indicates no practical problem) ■ Flaking resistance test Evaluation was performed by tension molding with square beats. Between the Bonchi dice 2. Okgf/cm2 (plug size 0.7 x
75 x 280+a+n) and then pull the test piece to pass through the bead.

200 sheets were repeatedly molded, and the degree of deposition of the plating layer metal on the steel plate or bead portion was relatively evaluated.

(Good) ◎−〇−△−× (Poor) (◎ and ○ indicate no practical problems) ■ Actual press test A part of the fender of an ordinary passenger car was formed using an actual press. 300 sheets were repeatedly molded, and the degree of adhesion and accumulation of the plated metal on the steel plate or press mold was evaluated relative to each other. The evaluation was based on the degree of blackening of the metal powder transferred to the tape after attaching tape to each area and removing it.

(Good) ◎-〇-△-× (Poor) (◎ and ○ indicate no practical problem) The test results for each of the above are shown in Table 1 along with comparative examples.

(Effects of the Invention) As explained above, the galvanized steel sheet of the present invention satisfies both Ct, powdering property, and flaking property, expands the uses of alloyed hot-dip galvanized steel sheet, and has great industrial effects. .

4 others

Claims (1)

[Claims] 1. A composition consisting of 6 to 13% by weight of Fe and the balance being Zn, the Γ phase at the base metal-plating interface is 1.0 μm or less, and the main peak of the X-ray diffraction of the plating layer is the ζ phase. Yes, basis weight 20
On top of ~100g/m^2 alloyed hot-dip galvanized layer,
One side is coated with a plating layer coated with 0.2 to 5.0 g/m^2 of dispersion plating made of zinc or zinc alloy containing 0.1 to 10% by weight of nonmetal fine particles with an average particle size of 2 μm or less, singly or in combination. , or an alloyed hot-dip galvanized steel sheet with excellent press formability, characterized by having , or on both sides. 2 Non-metal fine particles include SiO_2, TiO_2,
Al_2O_3, ZrO_2, SiC, TiC, SiN
The alloyed hot-dip galvanized steel sheet with excellent press formability according to claim 1, characterized in that it contains one or more of the following: , TiN, AlN, and graphite.