JPH02170960A - Production of alloyed galvanized steel sheet - Google Patents

Abstract

PURPOSE:To form an alloy layer on the surface of the subject steel sheet with a delta1 phase simple substance and to improve its weldability and workability, at the time of heating a galvanized steel sheet and alloying it, by accelerating the heating speed under specific conditions. CONSTITUTION:At the time of heating a galvanized steel sheet, the heating speed from 420 deg.C in the process of the heating is regulated to >=10 deg.C/sec and the steel sheet is heated to the alloying temp. of >=530 deg.C. As the result, a delta1 phase is formed on the surface of the alloy layer. A surface film effective for spot welding is easy to form by forming the surface of the alloy layer with a delta1 phase simple substance and the frictional resistance on the surface is furthermore reduced to improve the workability by the formation of the film on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an alloyed galvanized steel sheet.

(Prior Art and Problems to be Solved by the Invention) One method for improving the powdering resistance of galvanized steel sheets is, for example, as disclosed in Japanese Patent Application Laid-open No. 61-223174, by passing a steel sheet through a hot-dip galvanizing bath. rear.

Heat treatment is performed at 550 to 700°C, and from a state where a liquid layer remains on the surface of the plating layer, it is rapidly cooled to 530°C or less, and then
It is disclosed that this can be achieved by maintaining the temperature in the range of 50 to 530°C.

Further, as a method for improving the weldability of galvanized steel sheets, for example, AQ20. By making use of the high melting point and high electrical resistance of these oxides, it improves weldability and prevents contact between the electrode tip and the plated metal, preventing melting of the tip and extending its life. It is disclosed that the goal is to achieve this goal.

Furthermore, as in JP-A-59-104463, the ZnO/Zn ratio is increased from 0.1 to 0.1 by heat treatment on the surface of the plated steel sheet.
It has been disclosed that the weldability can be similarly improved by forming an oxide film with a 0.70 0.70 oxide film.

However, even with this method, it is difficult to obtain satisfactory results on a small industrial scale, and there is a strong demand for improved powdering resistance and weldability of plated steel sheets. The present invention has been made to advantageously satisfy these requirements.

(Means for Solving the Problems) The present invention is characterized in that when a galvanized steel sheet is heated and alloyed, the heating rate from 420°C during heating is set to 10°C/see or higher, and the heating rate is set to 530°C or higher. This is a method for manufacturing an alloyed galvanized steel sheet, which is characterized by heating the steel sheet to an alloying temperature of 100 to produce a 61 phase on the surface of the alloy layer.

(Function) The galvanized steel sheet that is the object of the present invention can be produced by hot-dipping,
It is manufactured using various manufacturing methods such as electroplating, vapor deposition plating, and thermal spraying, and the plating composition includes pure Zn,
Mainly containing Zn such as Zn and Fe, Zn and Ni, Zn and AQ, Zn and Mn, and containing one or more alloying elements and impurity elements to improve various functions such as corrosion resistance, and SjO,.

lt, 0. There are ceramic fine particles such as, oxides such as Tio2, and organic polymers dispersed in the plating layer, which has a single composition in the thickness direction of the plating layer.

There are steel sheets whose composition changes continuously or in layers, and there are also multi-layer plated steel sheets whose top layer is mainly composed of Fe and Ni but also contains various alloying elements such as Zn and P.
This is an alloyed galvanized steel sheet that has an alloy layer such as n-Fe formed on its surface. For example, iron-zinc alloy hot-dip galvanized steel sheets, aluminum containing mainly zinc, hot-dip galvanized steel sheets made of alloys such as iron.

A plated steel sheet consisting of an iron-zinc alloyed hot-dip galvanized layer on one side and a hot-dip galvanized layer on the other side.1 A plated steel sheet consisting of an iron-zinc alloyed hot-dip galvanized layer on one side and iron on the other side. .

There are alloy electroplated steel sheets containing chromium and the like, single alloy layer or multilayer alloy electroplated steel sheets, and steel sheets coated with zinc and zinc-containing metals by vapor deposition. Others, SiO
□, Al1,0. Ceramic fine particles such as Tio3
There is a dispersion-plated steel sheet in which Wilt compound fine particles, organic polymers, etc. are dispersed in zinc alloy plating.

In order to generate the δ□ phase on the surface of the alloy layer, the present inventors
It has been found that after zinc plating is applied, the heating rate from 420'C during heating is increased to 10°C/see or higher to reach an alloying temperature of 530°C or higher.

The heating rate at that time may be any heating rate up to 420'C, but the heating rate is low enough to complete alloying below 420°C. Even if the heating rate is higher than ℃/see, the one-surface alloy 7M is difficult to form the δ1 phase, so it is preferable to set the heating rate faster than the slow heating rate at which alloying is completed below 420°C.

In addition, the heating rate from 420°C during heating was increased to 10°C.
The reason for increasing the heating rate to more than 10°C is to make the heating rate slow to less than 10°C/86°C. In order to follow the process of transformation from ζ phase to δ phase, a mixed phase of ζ phase, ζ + 61 phase, and δ □ phase is formed. This is because it is difficult to make the δ□ phase simple.

By making the surface of the alloy layer a single δ1 phase, it becomes easier to generate a surface film that is effective for spot welding, and the formation of this surface film reduces surface frictional resistance, improves workability, and increases the heating rate. Because it is fast, the time required to turn the surface of the alloy layer into a single phase is shortened, and it is possible to suppress the generation of the F phase at the base metal interface, which is considered to be bad for powdering properties.

In addition, the crystal grains on the surface of the alloy layer are small in the primary δ1 phase produced by increasing the heating rate, which is effective in improving workability by reducing surface frictional resistance. Zn is supplied through grain boundaries to form a surface film, which is effective in forming a surface film and leads to improved spot meltability.

Here, the ζ phase on the surface is an alloy containing 5.5 to 6.2% of Zn and Fe, and the δ1 phase on the surface is an alloy containing Zn and 7.0 to 1% Fe.
It is an alloy containing 1.4%. As for the entire plating layer,
Since the phase at the interface with the base iron has a high Fe concentration, F of one alloy layer
e concentration increases. Since it is difficult to measure the Fe concentration only on the surface, instead of measuring the Fe degree on the surface, X-ray diffraction is performed to obtain the following 61 indices, and the ζ phase, ζ+δ1 phase, δ phase on the surface can be identified.

The δ1 index is 41.8 with a diffraction angle of 20 using X-ray diffraction with Cu as a target, at a voltage of 45 kV and a current of 150 n+A.
The intensities of the X-rays appearing at 42.3' and 43.2'' are measured as ζX, δS, and ηX, respectively, and are determined by 61 index = δx/(ζχ 1 δχ + ηX).The surface is a single ζ phase. 61 index is less than 0.5, ζ+δ, phase is 0.5 or more to less than 0.6, and δ, phase is 0.6 or more.

Note that Zn and Ni, Zn and Al1. Zn and Mn etc.
In the case of plating whose main components are Zn and Fe, an alloy layer of Zn and Fe is generated while incorporating Ni, AQ, Mn, etc. into the alloy layer, and it is no different from alloying with Zn-only plating. After that, by generating an oxide film,
A steel plate with good workability and weldability can be obtained.

By the above method, the surface of one alloy layer can be made into 61 phases,
An alloyed galvanized steel sheet with excellent powdering resistance and spot weldability can be obtained.

Figure 1 shows the heating rate of hot-dip galvanized steel sheet under the following conditions:
δ represents the surface composition when changing from °C/see to 40 °C/sec and alloying treatment at 540 °C for 1 sec.
□It is a diagram showing the relationship with indicators.

Conditions Double-sided AS: Molten iron-zinc alloyed steel plate basis weight: 45
/45 (g/po) Alloying temperature: 540°C Alloying time: 1 sec Cooling rate 230°C 8 ec Dew point during cooling: 100'C Alloy on the surface when the heating rate is 10°C/see or higher The composition of the layer is not the δ1 phase changed from the ζ phase, but the primary δ□ phase formed on the surface from the beginning. then,
Many oxide films mainly composed of ZnO are formed.

In this manner, by increasing the heating rate to 10° C./sec or more, the alloy layer on the surface becomes a single phase of δ, resulting in an alloyed galvanized steel sheet with excellent weldability and workability.

(Examples) Next, Examples of the present invention are listed in Table 1 along with comparative examples.

Note 1: Types of galvanized steel sheets Double-sided AS: Molten iron-zinc alloyed steel sheet Electrical AS: Iron-zinc alloyed steel sheet that has been alloyed after electrogalvanizing Single-sided AS: One side has a molten iron-zinc alloyed plating layer The other side is iron. AS/Gi: One side has a hot-dip iron-zinc alloy plating layer, and the other side has a hot-dip galvanized layer.The steel sheet thickness is 0.8+nn+ normal steel.

Note 2: Dioxide film formation conditions Alloying conditions: double-sided AS1 single-sided AS, AS/G
In the case of i, there is an alloying furnace in the continuous hot-dip galvanizing line, and the alloying furnace is used to process the material; in the case of electric AS, the material is processed in another alloying furnace after electrogalvanizing.

The cooling rate ranges from the alloying temperature to 300°C.

A dew point of 100°C during cooling can be obtained by directly injecting water onto the steel plate.

Note 3: Welding conditions The welding conditions are as follows.

1) Pressure crab 250kgf.

2) Initial pressurization time: 40Hz, 3) Energization time: 1211z.

4) Holding time: 5Hz, 5) Welding current: 1kA, 6) Tip tip diameter: 5.0ψ (cone-shaped), 7) Electrode life end point determination: Nugget 1 to diameter 3.0 at 85% of welding current. Number of runs that can secure 6am.

8) Electrode material: Cu-Cr (commonly used).

For welding, two plated steel plates were placed one on top of the other with one side up and the other side down, and the number of consecutive welds was counted.

Note 4: Powdering resistance was determined by bending a steel plate 90', applying cellophane tape, and determining the amount of the plating layer that adhered when peeled off.

(Effects of the Invention) By doing so, the number of consecutive welding points can be increased in spot welding, welding can be performed for a long time without replacing the tip, and the durability of the tip can be improved. In addition, the welding productivity can be improved, and the suitable welding current range is the same as that of conventional materials, and excellent effects such as good weldability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the heating rate for alloying a hot-dip galvanized steel sheet and the δ1 index representing the surface composition of the alloy layer. Figure 1 Pressure ripening rate ('C/sec)

Claims (1)

[Claims] (1) When heating and alloying a galvanized steel sheet, the heating rate from 420°C during heating is set to 10°C/sec or higher, and the δ_1 phase is heated to an alloying temperature of 530°C or higher, forming a δ_1 phase on the surface of the alloy layer. A method for producing an alloyed galvanized steel sheet, the method comprising producing the following: