JPS59166693A - Alloyed zinc-coated steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the alloyed zinc-coated steel sheet suited to a precoated steel sheet, by specifying the phase structure of a coating film. CONSTITUTION:The alloyed zinc-coated steel sheet in which a coating film formed on a steel sheet comprises a single phase of GAMMA1-Fe5Zn21 or a dual phase of zeta-FeZn13. Hereon, the formed Zn coating film under a coating condition as such has the alloyed structure such that the ratio of the intensity of diffractor rays at a lattice distance of 2.60Angstrom in X-ray diffraction to that of the strongest diffractor rays existent in a lattice distance of 2.11-2.15Angstrom exists in a range satisfying Formula, wherein I(GAMMA1) is the difference between the peak intensity of diffraction at d=2.60Angstrom and a background, and Im is the difference between the strongest peak intensity in the range of d=2.11-2.15Angstrom and the background. The coating film of this kind is obtained by applying a zinc electroplating layer in an amount of about 10-60g/m<2> per one side onto a steel strip and then heat treating the coated steel strip at about 230-300 deg.C for about 3-1,000hr in a batch annealing oven for alloying treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alloyed galvanized steel sheet and a method for manufacturing the same.

Zinc-based surface-treated steel sheets are used for various purposes due to their anti-corrosion performance and economic efficiency.Among these, alloyed galvanized steel sheets are especially supplied as materials for painting due to their advantages in weldability and post-painting corrosion resistance. There is.

Conventionally, alloyed galvanized steel sheets are mainly produced by continuously heat-treating hot-dip galvanized steel sheets at approximately 600°C immediately after plating, but some are produced by hot-dip galvanized steel sheets that are subjected to hatch heat treatment. It is produced by

In either case, the plating film on the product is an intermetallic compound, and the formability of the plating film is limited due to the brittle mechanical properties unique to intermetallic compounds, but the film is mainly formed from δ1-FeZn7. has been done. However, in the case of electroplated base material, it is often hatched at 350'C or less, so ζ-FeZn, % and δ
1-FeZn, which often has a multiphase structure.

In recent years, there has been a movement to use this alloyed galvanized steel sheet as a pre-coated material. However, the following problems have occurred when used as a pre-coat layer. The problem is that when a coating film with a high modulus of elasticity is applied, the impact resistance and shear resistance become extremely poor. In reality, for example, when these are sheared to make cut plates, the cut ends are less than 11 in diameter, but the plating and the plating peel off, and the exposure of the steel base leads to a decrease in the appearance commercial value and corrosion resistance. This phenomenon is caused by an increase in the elastic modulus of the coating film, that is, an increase in the coating film hardness after baking, which causes the deformation mechanism of the steel plate during shoaling.
This is explained by the occurrence of significant stress concentration at the plating interface.

As a countermeasure to this problem, the present inventors proposed a patent application filed in 1983.
-127355 discloses an increase in plating thickness and limitations on base material components, particularly P and C1. However, the special application 1987-
In 127355, a sufficient effect can be expected when the elastic modulus of the coating film is extremely high, and an increase in plating thickness generally tends to cause powdering, which is problematic. On the other hand, materials other than intermetallic compounds such as zinc plating, Zn
- When Al2 plating or the like is used as a pre-coating material, the coating film may peel off quickly if the elastic modulus of the coating film is high.

Therefore, in conventional products, some problems arise when a precoat material is coated with a coating film having a high elastic modulus.

The inventors of the present invention have solved this problem, have diligently inspected plated steel sheets suitable for pre-coated steel sheets, and have completed the present invention. The inventors of the present invention have considered using electroplated galvanized base material (hereinafter abbreviated as EGA) in place of alloyed hot-dip galvanized steel sheets, which had insufficient shear resistance after pre-coating. As mentioned above, the shear resistance was poor as in the melt type.

However, we found that shear resistance is related to the alloying temperature regardless of melt system or EGA, and we assumed that this was related to the phase structure of the plating film.As a result of further investigation, we found that it is far from conventional wisdom. By setting separate heat treatment conditions, we developed a new phase composition method and completed the present invention.

The alloyed galvanized steel sheet of the present invention has the following configuration.

The formed film phase is ζ-FeZn, and pH-pe5 Zn21 in the range obtained by X-ray diffraction method.
It becomes more. ζ-FeZn, 1 is a long-known phase, "
1-Fe5ZrIII, P, J, Gellings
This is the phase shown by etc. However, as is well known, the X-ray diffraction peaks of Fe--Zn based intermetallic compounds are extremely complex, and academic debate is expected in identifying the diffraction lines. Furthermore, since the crystal structure of "and F" is a double ratio sum-like type, there is a problem that it cannot be distinguished by discussing only the lattice constant of X-ray diffraction.

Therefore, the present inventor further embodies the present invention as follows. The phase structure consisting of ζ-FeZn and ``1-Fes Znz'' is defined as d=2. of δ1-FeZn T.
526 people (C.

Refers to a case in which the diffraction line of the index finger (41.2° at Kα2θ) is hardly detected. Next, the presence of the ζ-phase is due to the detection of the diffraction line of d=2.44 (42.8 to 43.1° in Co Kcx 2θ). Next, the existence of r] is d=2.
60 people (C.

Diffraction line of Kα2θ 40.2-40.3° (FI(4
44) by detection of surface). However, r, (444) and “(2
22) have almost the same lattice constant (d value), so this diffraction line does not have a firm physics theory that it is l''t (444).

As a result of studies by the inventors, the d=2.
The 60 person diffraction line is clearly a mixture of 1 and this diffraction line, d = 2.09 person (Co Kcx 2θ-50,8
d = 2.44 people's diffraction line (ζ
) and form a linear regression equation with a sufficiently high contribution rate. Therefore, for the diffraction line of a person with d = 2.60, ``t(444) is the main one''. This is based on the estimation result that there is
V-Fe:+ This does not stipulate that Zn1o is not contained.

In a more excellent form of such a plated steel sheet, the intensity of the above-mentioned diffraction line of d=2.60 is relatively defined by the following equation.

0.1<, 1m/I (+”+) 'i4.5 However, r (r,) is the difference between the diffraction line intensity of a = 2.60 person and the hack ground level, and the present inventors 1 (444
), 1m is estimated as the diffraction line of d=2.11
~d = 49.3 to 5 in the range CoKα2θ of 2.15 people
This is the difference between the strongest peak intensity existing in a range of 0.2° and the hack ground. The reason for setting these two limitations is that in order to maintain shear resistance, it is required that δ1-Fe Zn 7 be small or not present at all, and that the diffraction line intensity of rl (444) be sufficiently high. If 1 m/I (F) > 4.5, the shear resistance deteriorates significantly, and if 1 m/I (Fco) < 0.1, the effect will be saturated, and the manufacturing process described below will be required. This is because the method is extremely uneconomical.Note that the diffraction line shown at 1 m is generally ζ-FeZn, , δ, -F from a crystallographic point of view.
eZn7, "1-Fe5Zn,, r-Fe+Zn1
It is a hybrid diffraction line of ζ-Fe in the scope of the present invention.
It is estimated that it will be a hybrid of Zn, 3 and F]-Fe5Zn2+.

When manufacturing the alloyed galvanized steel sheet of the present invention, an electrogalvanized steel sheet with a weight of 10 to 60 g/m per side is treated in a hatch furnace at a temperature of 230 to 300° C. for 3 to 1000 hours.

The relationship between the heating temperature and the holding time in the annealing furnace is determined by the plate thickness and the amount of plating.
The conditions in the shaded area shown in the figure are good, but preferably 250~
Treatment at a temperature of 280°C for 8 to 1.00 hours is preferred. 30
At temperatures above 0°C, precipitation of the δ phase occurs, and below 230'C, the reaction is too slow. Sufficient r is required below the minimum time at each temperature.
There is no development of l(444), and above the upper limit, alloying becomes excessive. Tight annealing is also possible as long as the highest temperature point of the coil is maintained at 300°C or less.

The present invention will be explained in more detail below based on Examples.

ZnSo4-71120 400g / 12. , Na
2 So470g/a111ac120.4g/I
Plating bath containing 2 (pH 3.3, bath temperature 50°C) 1
40% with high purity zinc as anode at a current density of 68%/dm.
0.5t electrogalvanized steel sheet with coating amount of g/m
A size of N80 x 150mm was made.

The above-mentioned plated steel plate was heat treated in a N2 atmosphere under the heat treatment conditions shown in Table 1, the core material was treated with zinc phosphate using the same method, and 25 μm of acrylic resin paint with a baked pencil hardness of 4H was applied, followed by clearance at 10°C. Shear tests were conducted with a 0.05 am shear machine. X by separate Co Kα monochromatic light
Line diffraction was performed.

From Table 1, it can be easily understood that the product performance according to the present invention is extremely excellent.

Note that FIG. 2 shows an X-ray diffraction diagram.

A is EGA 260 °C x 6 hr B is EGA 260 °C x 20 hr (invention) C is EGA
At 320°C x lhr, there is a δ1 phase diffraction line in C.

The present invention extends to heat-treated zinc-based plated steel sheets in general, and also includes the case where electric Fe-Zn plated steel sheets containing approximately 20% or less of Fe are heat-treated. Furthermore, the principle is exactly the same even for a zinc-coated vapor-deposited film that is heat-treated.

The detailed structure of Fl-Fe5Zn, which is described in this specification, is described in the following document, but the conventional AST
It does not exist on M cards.

(1st, J. Gellings, G. GIER
MAN et al., Z. Metallkde, ;Bd, 71
(1980) H, 2, P, 70 Delusion 4, Brief explanation of drawings
8. Figure 1 is a diagram showing the relationship between heating temperature and holding time in an annealing furnace, and Figure 2 is an X-ray diffraction diagram.

Figure 1 time (h'')

Claims (1)

[Claims] (1) The film formed on the steel plate is r 1-Fes Zr
An alloyed galvanized steel sheet characterized by consisting of +++ single phase or multiple phase with ζ-FeZr++3. (2) Intensity of diffraction lines and lattice spacing of X-ray diffraction of the uncoated state of the Fe-Zn coating formed on the steel plate in the production of alloyed galvanized steel sheet: 2.60 Diffraction line intensity and lattice spacing: 2.
An alloy galvanized steel sheet characterized by having an alloy layer structure in which the intensity ratio of the strongest diffraction lines existing in the range of 11 to 2.15 satisfies the following formula. 0.1≦1m/I, ('t)≦4.5 provided that I ('
+ ): d = 2.60 Difference between the diffraction peak intensity of a person and the ground: 1 m: d = 29. Difference between the strongest peak strength in the range of H ~ 2.15 people and hack ground (3) The film formed on the steel plate is r4-Fe5 Zn,
, a single phase or a multi-phase alloyed galvanized steel sheet with ζ-FeZn, etc., the steel strip is electrolytically galvanized at a rate of lO to 60 g/r/per one side, and then galvanized at a rate of 230 to 300 g/r/l in a Hutch annealing furnace. 1. A method for producing an alloyed galvanized steel sheet, which comprises performing a heat treatment for alloying at °C for 3 to 1000 hours.