JPH01108355A - Method for alloying hot dip galvanized steel sheet - Google Patents

Abstract

PURPOSE:To carry out Fe-Zn alloying treatment without causing the occurrence of stripped pattern by subjecting a hot dip galvanized steel sheet to heating from the initial temp. of Zn melting up to an alloying holding temp. at a specific temp.-rising velocity by means of high frequency induction heating. CONSTITUTION:A hot dip galvanized steel sheet is passed through a high frequency induction-type heating and holding furnace to undergo heating and subjected to Fe-Zn alloying treatment, by which the corrosion resistance, weldability, painting suitability, etc., of a plated product are improved. In the above treatment, heating is applied at <=50 deg.C/sec temp.-rise rate from the initial temp. of Zn melting of about 410 deg.C up to the alloying and holding temp. of about 550 deg.C. The regulation of the above temp.-rise rate can be easily carried out by reducing high-frequency output and decreasing magnetic force. By decreasing temp.-rise rate as mentioned above, the ripple of molten Zn is prevented and the occurrence of stripped pattern is prevented and, as a result, superior products can be obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for alloying hot-dip Zn-plated steel sheets.

[Conventional technology]

For the purpose of improving corrosion resistance, spot weldability, and paintability, hot-dip Zn-plated steel sheets are heated and held, and the Zn layer is coated with Fe-Z.
There is a method of forming an alloyed layer of n.

Conventional heating and holding methods have been gas heating and electric resistance heating, but recently high-frequency induction heating methods have been adopted from the viewpoints of uniform heating, holding time, and coordination of temperature control.

[Problem that the invention seeks to solve]

As mentioned above, the development of high-frequency induction heating methods is progressing, but with this method, after the Zn in the hot-dip Zn-plated steel sheet is melted, stripes occur on the steel sheet due to the influence of the magnetic force of induction heating. There is a problem that quality deteriorates significantly.

[Purpose of the invention]

In view of the above-mentioned state of the art, the present invention seeks to provide a method for alloying hot-dip Zn-plated steel sheets that does not produce stripes even when using a high-frequency induction heating method.

[Means for solving problems]

The present invention is based on the F
e-Zn alloying heat treatment is a method for alloying a hot-dip Zn-plated steel sheet, which is characterized by heating from the melting start temperature of zinc to the alloying holding temperature at a temperature increase rate of 50 C/sec or less.

[Effect]

Zn in hot-dip Zn-plated steel sheet begins to melt (419℃)
By heating at a slow rate of 50C/sa until it reaches the alloying holding temperature, in other words, by reducing the high frequency output during this period and reducing the magnetic force, it is possible to eliminate the cause of line generation. Certain molten Zn ripples can be prevented.

〔Example〕

An alloying heat line was applied to the hot-dip Zn-plated steel plate using the test line shown in FIG. 1, and the presence or absence of a striped pattern was confirmed.

To explain the test fin in FIG. 1, a molten Zn-plated steel plate 1 passes through deflector rows 2 and 2, and then enters a high-frequency induction heating and holding furnace 4 in which a predetermined power is output from a t-source device and an oscillating device (not shown). YoF) Fe-Z! 1 alloy layer is formed. Thereafter, it passes through the deflector row/I/2 and is wound up by the tension row/I15. Note that 5 is a guide row.

To explain the high frequency induction heating holding furnace 4, which is the main equipment, the high frequency output is current: 500A.

Maximum voltage: 1soov, oscillation frequency: I KHz ~
Four furnaces with a specification of 50 KHz were installed. In addition, the shape of the coil is 2000 x 2 QO x 5 x 5000 m in internal dimensions.
” and all four have the same dimensions.

Of the above four furnaces, the 4-A furnace and the 4-B furnace were used as heating furnaces until just before the start of melting, and the output of the 4-C furnace was controlled to achieve the temperature increase rate of the present invention. Also, 4
The -D furnace was used to maintain the alloying holding temperature. Note that the line speed is 40 m depending on the heating rate in the 4-C furnace.
/ min~1301! l/min.

Next, the heat lines of Examples and Comparative Examples will be explained with reference to FIG. 2. Examples are pattern (■) in FIG. This is a pattern in which the temperature is raised to the holding temperature at a rate of 50°C/s6c or less from directly below. Comparative Example (1) is pattern 2 in FIG. 2. The difference from pattern 2 is that the rate of temperature increase from just below the melting temperature is greater than 50° C./Sec.

Furthermore, Comparative Example (1) is pattern 2 in FIG. 2, which differs from pattern 2 in that the starting temperature of heating at a heating rate of 50° C./sec is higher than the melting temperature.

〔Example〕

A hot-dip Zn-plated steel plate was heated and held using the testing apparatus shown in FIG. 1, and alloyed with Fe-Zn.

■ Dimensions of molten @zn plated steel plate are: 9001. Thickness: α3■, (L5■, 10■
It is.

■ Alloying holding temperature and time Holding temperature---550℃ Holding time---30sec ■ Until heating at a temperature increase rate of 50℃/atm or less! +Temperature rate 80℃/y! c ■ Temperature at which heating starts at a temperature increase rate of 50℃/sec or less and temperature increase rate start temperature ---410℃ Temperature increase rate - m-20 to 50℃/sec ■ Oscillation frequency Under conditions of 103G'fz or more As a result of Fe-Zn alloying, a good steel plate without stripes could be manufactured.

[Comparative Example 1] Using the test apparatus shown in FIG. 1, the conditions of Example (1) were as follows except that the temperature at which heating was started was set at 425°C to 430°C at a temperature increase rate of 50°C/sec or less. Heating and holding the same molten @zn plated steel plate in the same manner as
Alloying of n was carried out.

As a result, a striped pattern appeared on the steel plate.

[Comparative Example 2] The same molten Zn was tested using the test apparatus shown in FIG. 9. Alloying Fe-Zn by heating and holding the plated steel plate.

As a result, stripes appeared on the steel plate.

Table 1 shows the results of Examples and Comparative Examples.

〔Effect of the invention〕

Fe-Z by high-frequency induction heating of hot-dip galvanized steel sheets
In the alloying heat cycle A/, by heating Zn at a rate of 50C/sec or less from the melting start temperature to the alloying holding temperature, striped patterns do not occur on the iron plate and a good product can be obtained. can get.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an apparatus for manufacturing an alloyed hot-dip Zn-plated steel sheet, and FIG. 2 is a chart showing a thermal size of 7μ of the Dorio side of the present invention and a comparative example.

Claims (1)

[Claims] Fe-Zn by high-frequency induction heating of hot-dip Zn-plated steel sheet
A method for alloying a hot-dip Zn-plated steel sheet, characterized in that in alloying heat treatment, heating is performed from the melting start temperature of zinc to the alloying holding temperature at a temperature increase rate of 50° C./sec or less.