JPH04371558A - Production of galvannealed steel sheet having excellent powdering resistance - Google Patents

Abstract

PURPOSE:To produce the galvannealed steel sheet having excellent powdering resistance by plating a steel sheet to be plated in a galvanizing bath contg. Al and B respectively at specific ratios, then subjecting the steel sheet to an alloying treatment. CONSTITUTION:The steel sheet to be plated is plated in the galvanizing bath contg. 0.05 to 0.2wt.% Al and 0.0002 to 0.02wt.% B, contg. >=1 kinds of about 0.01 to 1.0wt.% Cr and 0.005 to 0.5wt.% Mg at need and consisting of the balance Zn and unavoidable impurities. This plated steel sheet is then transferred to an alloying furnace and is alloyed by heating and diffusing the plating layer and the base iron. The galvannealed steel sheet having the excellent powdering resistance, corrosion resistance, coatability, etc., is obtd. in this way.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed hot-dip galvanized steel sheet having excellent powdering resistance.

0002

[Prior art] Alloyed hot-dip galvanized steel sheets were manufactured by
This is introduced in many patent publications such as Publication No. 1-30017 and Japanese Patent Publication No. 56-503, but in general, plated original sheets (hot-rolled steel sheets, cold-rolled steel sheets) are treated in an oxidation furnace or non-oxidation furnace to remove surface stains and remove rolling oil. etc. are removed by oxidative combustion, heated in a reducing atmosphere to reduce the surface oxide film and annealed, cooled to a temperature suitable for plating, passed through a plating bath, and then heated in an alloying heating furnace. It is manufactured by a method of interdiffusing the base iron and the plating layer to generate an alloy layer with a high Fe concentration, and then rolling it up at a low temperature.

[0003] The alloyed hot-dip galvanized steel sheet produced in this way has poor paintability and
Due to its excellent weldability, it is often used as a material for home appliances and automobiles.

0004

[Problems to be Solved by the Invention] However, since alloyed hot-dip galvanized steel sheets produce a plating layer of a hard and brittle Fe-Zn metal compound, when subjected to severe processing such as deep drawing, the plating layer becomes powdery. There was a phenomenon called powdering, in which the plating layer peeled off.

[0005] Furthermore, this phenomenon has been a problem that frequently occurs in alloyed hot-dip galvanized steel sheets with thick plating layers, which have been required in recent years to strengthen the rust prevention ability of automobile bodies.

[0006] Therefore, to date, alloyed hot-dip galvanized steel sheets have generally been unplated due to the problem that powdering occurs when the Fe concentration in the plating layer is high, and conversely, when the Fe concentration is low, the plating often peels off. These problems are balanced by keeping the Fe concentration in the layer within a certain range.

The present invention eliminates these problems and provides a method for producing an alloyed hot-dip galvanized steel sheet with excellent powdering resistance by adding a small amount of an effective element, namely B, to an aluminum-containing galvanizing bath. The purpose is to provide.

[0008]

[Means for Solving the Problems] That is, the gist of the present invention is to coat a steel plate to be plated with 0.05 to 0.2% by weight of Al.
This is an alloyed hot-dip galvanized steel sheet which is subjected to alloying treatment after being plated in a hot-dip galvanizing bath containing 0.0002 to 0.02% by weight of B and the balance being Zn and unavoidable impurities.

In addition to the above components, the present invention can also be used as a plating bath containing one or both of Cr and Mg in order to improve corrosion resistance.

[0010] Originally, Zn and B do not alloy, so even if B is added alone to a galvanizing bath, B will not dissolve in the plating bath. However, by making an Al-B master alloy and adding this to the galvanizing bath. By doing so, alloying is possible.

The present invention will be further explained in detail.

[0012] The steel plate to be plated manufactured through the normal steel plate manufacturing process is subjected to oxidation combustion to remove surface contamination in an oxidation furnace or a non-oxidation furnace, and then led to a reduction furnace where the surface is activated and annealed to make it suitable for plating. After cooling to temperature Al 0.05~
It was immersed in a hot-dip galvanizing bath containing 0.2% by weight and 0.0002 to 0.02% by weight of B, with the remainder being Zn and unavoidable impurities, and pulled upward through a pot roll to adjust the amount of plating deposited. The plated layer and base steel are alloyed by heating and diffusion.

By containing Al in the plating bath, the growth of the alloy layer in the plating bath is suppressed, the thickness of the alloy layer is reduced, and the change in the thickness of the alloy layer due to the immersion time is reduced, making it easy to adjust the amount of plating deposited. It is necessary to improve the powdering resistance and to add it to the galvanizing bath as a mother alloy with B, and its content must be 0.05% or more to exhibit these effects. .

However, when the amount of Al in the plating bath exceeds 0.2%, a thick Fe--Zn--Al three-layer alloy layer is formed which suppresses the alloying reaction, and the Fe--Zn diffusion reaction is inhibited at high temperature and for a long time in the alloying process. This has disadvantages in that it decreases productivity by shifting to the time side, and also tends to cause incomplete alloying, which significantly reduces commercialization as alloyed hot-dip galvanized steel sheets.

[0015] Therefore, the appropriate Al content is 0.05 to 0.2% by weight.

However, the powdering resistance of the alloyed hot-dip galvanized steel sheet may not be sufficient in deep drawing or the like when used as a rust-preventing steel sheet for automobiles, simply by adding Al in the plating bath.

[0017] As a result of various searches for ways to further improve the powdering resistance of alloyed hot-dip galvanized steel sheets, the present inventors have discovered that the addition of B to the plating bath is extremely effective. be. .

That is, the effect of improving powdering resistance due to the addition of B can be obtained by adding 0.0002% by weight or more;
．． 0.02% by weight or more, the effect reaches saturation and the excess B
Additions tend to adhere in the form of dross, which tends to deteriorate the appearance of the plating. Therefore, the B content in the galvanizing bath is 0.00
02 to 0.02% by weight is suitable.

Furthermore, Cr is used as an element for improving the corrosion resistance of the plating layer.
, Mg, or two thereof may be contained at the same time.

[0020] The amount of Cr added is 0.01 to 1.0% by weight, M
In the case of 0.005 to 0.5% by weight, it is appropriate to add 0.005 to 0.5% by weight.

Furthermore, even if a small amount of Pb, Cd, Fe, Sb, etc. mixed as unavoidable impurities in galvanizing is contained, it does not have a particularly large effect on the present invention.

[0022] In the present invention, a hot-dip galvanized steel sheet immersed in a hot-dip galvanizing bath having the above-mentioned composition is subjected to alloying heat treatment.

[0023] Alloying heat treatment improves various properties necessary for use, such as paintability and weldability.

[0024] The heat treatment conditions such as heating temperature and heating time in this case are not particularly limited and may be normal conditions, but in order to prevent the powdering resistance deteriorated due to the formation of the Γ phase, Low temperature-short time treatment is preferred.

The hot-dip galvanized steel sheet produced as described above has excellent corrosion resistance, powdering resistance, and paintability.

Examples of the present invention will be described below.

[0027]

[Example 1] Plated original plate with steel components shown in Table 1 (plate thickness 0.
8mm) was passed through a hot-dip galvanizing line using a non-oxidizing furnace method, hot-dip galvanized in a plating bath containing Al and B, and the basis weight was adjusted to 60 g/m2 per side, and then led to an alloying furnace. It was heated to 510° C. for alloying treatment, cooled, and then rolled up.

[0028]

[Table 1]

[0029]

[Table 2]

As shown in Table 2, the powdering resistance was evaluated, and as shown in Table 2, the addition of B to the plating bath had a remarkable effect on improving the powdering resistance of the alloyed hot-dip galvanized steel sheet.

[0031]

[Example 2] Plated original plate with steel components shown in Table 1 (thickness 0.
8mm) was passed through a hot-dip galvanizing line using a non-oxidizing furnace method, and hot-dip galvanizing was carried out by adding Al, B, Cr, and Mg to the plating bath, and the basis weight was 60 g/m2 per side.
After adjusting so that

[0032]

[Table 3]

The powdering resistance of the obtained alloyed hot-dip galvanized steel sheet is improved not only by the addition of B but also by the addition of Cr and Mg.

[0034]

[Effects of the Invention] As described above, the present invention improves the powdering resistance of alloyed hot-dip galvanized steel sheets.

Claims (1)

[Claims] Claim 1: A steel plate to be plated is coated with Al: 0.05 to 0.
2% by weight, B: 0.0002 to 0.02% by weight, and the remainder consists of Zn and unavoidable impurities. A method for manufacturing alloyed hot-dip galvanized steel sheets with excellent powdering properties.