JPH0368748A - Alloyed hot-dipped steel sheet and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a surface-treated steel sheet with excellent corrosion resistance and coating surface smoothness. The present invention relates to a method for producing a hot-dip galvanized steel sheet and a galvannealed steel sheet suitable for use as a galvannealed steel sheet.

(Prior Art) Various surface-treated steel sheets are used in fields such as automobile bodies, building materials, and home appliances. Among these, hot-dip galvanized steel sheets are often used because they are relatively inexpensive and have good corrosion resistance. In addition, galvanized steel sheets, which are hot-dip galvanized steel sheets subjected to heat diffusion treatment to alloy the plating film, so-called alloyed galvanized steel sheets, are also relatively inexpensive and have excellent corrosion resistance, paintability, weldability, etc. Widely used in similar fields.

However, in these fields of use, the requirements for surface-treated steel sheets, such as rust prevention ability and surface quality, are increasing year by year, and it is difficult for conventional hot-dip galvanized steel sheets and alloyed galvanized steel sheets to meet these requirements. It is becoming. Therefore, various new surface-treated steel sheets have been developed.6 For example, Zn-Al, Zn-Mg, Zn-
It is hot-dipped with a zinc-based alloy such as Mn. However, steel sheets hot-dipped with these zinc-based alloys have the following problems in terms of quality and manufacturing.
Uses are limited.

That is, Zn-Affi alloy plated steel sheets have already been put into practical use, and their corrosion resistance is superior to that of galvanized steel sheets, but
There is a problem that the film surface is rough and has poor surface quality, and alloying treatment cannot be performed. When this plated steel sheet is alloyed, the alloying reaction becomes non-uniform and the surface quality deteriorates further.

As a Zn-Mn alloy plated steel sheet, Mn is 0.05~
Japanese Patent Laid-Open No. 11836/1983 discloses an alloyed steel sheet made of hot-dip Zn--Mn alloy plated steel plate with a 15-layered structure. In the case of Zn-Mn alloy plating, Mn is Zn
Melt plating is possible because it has a relatively high solubility in the liquid phase. However, when Al is present in the plating bath, dross consisting of a ternary compound of Zn-Al-Mn is generated, which reduces the fluidity of the plating solution and causes the dross to adhere to the surface of the film, reducing surface quality. There is a problem.

Generally, in hot-dip galvanizing, a galvanizing bath containing 0.1 to 0.2% by weight of Al is used. This is because in hot-dip galvanizing, a hard and fragile Fe-Zn alloy layer is formed at the interface between the base steel sheet and the plating layer, but if this alloy layer is formed thickly, the plating layer has poor workability. In order to improve the properties, the addition of Al suppresses the formation of an alloy layer as much as possible, making it thinner. However, when A1 is added to the Zn--Mn alloy plating bath for the same purpose, dross consisting of ternary compounds is generated.

Furthermore, when the amount of Mn added exceeds the dark value determined by the Al concentration, alloying is promoted during plating, which is favorable for manufacturing alloyed steel sheets, but Fe is leached from the base material during hot-dip plating. becomes intense, a large amount of Fe-based dross is generated, and the operability is greatly reduced. Furthermore, the diffusion rate of pe-Zn becomes excessive during the alloying process, and the film becomes susceptible to powdering during press working.

Here, the threshold value (Mn'') is a value expressed by the following formula (1) or (2).

When Al1 degree is 0.3% or less: (Mn”) (%)z3.5 [Affi (%)] -
・s, ・, ■When Affi1 degree is more than 0.3% and less than 5%: (Mn'') (%) zo, 6%...■However, all (%) are % by weight.

In the above-mentioned Zn--Mn alloy plating, generation of dross consisting of the former ternary compound is a particularly serious problem. The amount of this dross generated increases as the A1 concentration and Mnlll degree in the bath become higher. On the other hand, this problem tends to be alleviated by increasing the bath temperature, but increasing the bath temperature increases the generation of Fe-based dross.Also, in Zn-Mn alloy plating, the amount of Mn added is below the above-mentioned dark value. If it exceeds this value, the alloy layer formed during plating will grow very thick, resulting in extremely poor workability of the film even on non-alloyed materials.

Many Zn-Mg alloy plated steel sheets have been reported, for example, in Japanese Patent Laid-Open Nos. 54-120241 and 64-41359. Even if zinc is plated with Zn, oxidation will occur, reducing operability.
-Mg alloy plating is difficult to put into practical use.

(Problem to be solved by the invention) The present invention! The first topic was a method for manufacturing a surface-treated steel sheet with excellent corrosion resistance, coating surface smoothness, and workability, specifically a method for producing a non-alloyed hot-dip galvanized steel sheet with excellent corrosion resistance, and an alloying process after hot-dip plating. The object of the present invention is to provide a galvannealed steel sheet and a method for manufacturing the galvanized steel sheet efficiently and with good quality.

(Means for solving the problem) In the case of the above-mentioned Zn-Mn alloy plated steel sheet, if Affi coexists in the plating bath, Zn-Mn-Aj will be present in the liquid phase.
Dross consisting of ternary compounds of 2 is generated, and F of the base material is
There is a problem in that the reaction between e and the plating bath is excessively accelerated and Fe-based dross is generated. However, this Zn--Mn-based material has a lower oxidation consumption rate of the plating bath than the Zn--Mg-based material, and is relatively easier to alloy than the Zn--A1-based material. Therefore, the present inventors developed Zn-Mn
We tried to overcome the above problems by focusing on the system.

That is, the present inventors have developed Zn-Mn-An!, even if Al coexists in the Zn-Mn plating bath, or in which Al is actively added for the purpose of increasing corrosion resistance. Even if it is a type of bath,
It was discovered that the above-mentioned problems could be prevented by adding Si, leading to the present invention.

The gist of the present invention lies in the following (1), (ii) and (m).

(i) Steel plate, Al: 0.05 to 5% by weight, Si:
0.005 to 0.8% by weight, Mn: 0.1 to 3% by weight, and the remainder is Zn and unavoidable impurities. Production method.

(ii) Steel plate, A10.05-5% by weight, Si:
Hot-dip plating is performed by passing through a plating bath containing 0.005 to 0.8% by weight, Mn: 0.1 to 3% by weight, and the remainder consisting of Zn and unavoidable impurities, and then alloying treatment. A method for producing a featured hot-dipped alloyed steel sheet.

(iii) A plated steel sheet that has been alloyed by thermal diffusion treatment after hot-dip plating, and the coating composition of the plated steel sheet is Af: 0.1 to 5% by weight, Si: 0.005 to 0.
．． 8% by weight, Mn: 0.1-3% by weight, Pe: 7-
An alloyed hot-dip plated plate characterized by comprising 15% by weight, balance: Zn and inevitable impurities.

(effect) The present invention will be explained in detail below.

First, the first invention of the present application will be described.

The first invention is a method for manufacturing a plated steel sheet that only undergoes hot-dip plating without performing alloying treatment. The characteristics of this method are
All on pre-treated steel plate! :Q, 35-5% by weight,
Si: 0.005-0.8% by weight, Mn: 0.
Hot-dip plating is carried out using a plating bath having a composition of 1 to 3% by weight, Zn, and the balance being unavoidable impurities.

The plating method is not particularly limited, and the Sendzima one-way method, flux method, etc. are applicable. Further, the steel sheet before plating is naturally subjected to pretreatment.For example, in the case of the Sendzima one-way method, the steel sheet is subjected to pretreatment such as oxidation and reduction treatment, and then passed through a plating bath.

In this method, the reasons for limiting the plating bath & II precepts as described above are as follows.

Al is effective in improving the processability and corrosion resistance of the film.

However, if the content is less than 0.05% by weight, it will not only reduce the workability of the coating but also promote the generation of dross, leading to a decrease in operability.On the other hand, if the content exceeds 5% by weight, there will be no effect of improving corrosion resistance. In addition, operability also decreases.

Si is effective in suppressing abnormal growth of Fe-Znji in a Mn-added system and improving workability. Particularly in the present invention where old metal coexists, Si is essential because Mn promotes the formation of the Fe-Zn layer. If Si is less than 0.005% by weight, the above effect will not be obtained, and if it exceeds 0.8% by weight, unplated spots will likely occur.

Mn is effective in improving corrosion resistance even in non-alloyed materials. However, if it is less than 0.1% by weight, the improvement in corrosion resistance will be small, and if it exceeds 3% by weight, the formation of an Fe-Zn alloy layer will be severe, thereby reducing the workability of the film.

Note that the remainder of the plating bath composition is Zn and unavoidable impurities.

Next, the second invention of the present application will be described.

The second invention is a method for producing a plated steel sheet, which is hot-dipped and then subjected to alloying treatment. After hot-dipping in a plating bath with the same composition, alloying treatment is performed.

The reason for limiting the plating bath composition is the same as above.

Note that Al has the property of being enriched in the film, and even if the Al content in the plating bath is 0.05% by weight, Affi
can be precipitated in an amount of 0.1% or more, making it possible to manufacture alloyed hot-dip galvanized steel sheets, which will be described later.

The alloying treatment after hot-dip plating is desirably carried out so that the Fe1fi degree in the coating is 7 to 15% by weight.

In addition, alloying can be done by heat-treating the steel plate after plating in a galvaneal furnace installed directly above the plating bath, or by heat-treating it in an off-line batch furnace, or in an in-line galvaneal furnace. If the steel plate temperature is 4.
The heat treatment is preferably performed at a temperature of 70 to 600°C, preferably 470 to 510°C. When carried out using a batch furnace, the alloying treatment can be performed at a temperature of 300 to 400°C.

A third invention is an alloyed hot-dip plated steel sheet manufactured by the method of the second invention. The characteristics of this alloyed hot-dip plated steel sheet are that the film composition is ^2: 0.1 to 5% by weight, Si:
0.005-0.8% by weight, Mn:O, 1-3% by weight,
Fe: 1 to 15% by weight, Zn and unavoidable impurities: balance.

The reason why the film composition after alloying is limited as described above is as follows.

Affi is effective in improving the corrosion resistance of the plating film.

However, if the amount is less than 0.1% by weight, a hard and thick Fe-Zn alloy layer will grow at the interface between the base steel sheet and the plating layer during plating, and an r-phase with a high Fe concentration will be formed, especially during the alloying process. and reduce the processability of the film, such as powdering resistance. On the other hand, if it exceeds 5% by weight, the alloying process will take a long time.

Affi has the function of suppressing the alloying reaction, and as mentioned above, Mn suppresses alloying up to a certain concentration determined by the concentration, but beyond this dark value it has the effect of promoting alloying. . Even if the Mn content is in a range that promotes alloying, if the Affi content exceeds 5% by weight, Mn
Since the alloying suppressing effect of Al is stronger than the alloying promoting effect of n, alloying is delayed.

Like i, Mn has the effect of increasing corrosion resistance.

However, if it is less than 0.1% by weight, the improvement in corrosion resistance will be small and since it is below a threshold value, alloying will be delayed. on the other hand,
When the amount exceeds 3% by weight, Al-Mn-Z
The ternary compound of n tends to precipitate into the liquid phase, resulting in deterioration of the fluidity of the plating bath and the surface quality of the plated steel sheet.

Si is an important element in the present invention, and Mn, which controls the influence of Mn on the alloying rate, suppresses alloying up to a certain concentration as described above, and conversely inhibits alloying when this dark value is exceeded. However, excessive promotion of alloying reduces the workability of the plating layer and increases the elution of Fe from the steel sheet into the plating bath during plating, causing Fe
Generates dross. Si has the effect of suppressing excessive alloying caused by Mn to an appropriate level and suppressing elution of Fe.

However, if the content is less than 0.005% by weight, there is no effect, and even if the content exceeds 0.8% by weight, the effect is saturated, and the Si metal phase separates in the liquid phase, resulting in poor wetting. Spots, that is, dark unplated spots are likely to be formed. When such bare spots exist, the steel base is exposed, resulting in a decrease in corrosion resistance.

In addition, in Zn-^ poor alloy plating, if Affi is contained in excess of 5% by weight, a small amount of Si may be added to the plating bath in order to suppress the formation of Fe-Al alloy phase. It was thought that addition was not necessary in systems containing Af of 5% by weight or less. Suppose that Si is A
Even if Si is added to a Zn-A1 alloy plating bath containing 5% by weight or less, the solubility of Si is low and it becomes dispersed, which only increases the formation of bare spots and does not provide any effect of Si. , when Mn and Si coexist, the adverse effects that occur when Si is added alone are offset,
High quality plated steel sheet.

If the Fa content is less than 7%, unalloyed zinc will remain on the surface of the film after alloying treatment, resulting in poor blister resistance and weldability after painting, and if the Fa content exceeds 15%, In this case, the workability of the film is significantly reduced, and the sacrificial anticorrosion ability of the film is also reduced, making red rust more likely to occur.

The remainder of the plating layer is zinc and unavoidable impurities.

The present invention will be further explained below with reference to Examples.

(Example 1) C: 0.03%, Si: 0.01%, Mn:
0.23%, P: 0°008%, S: 0.008
%, So7! , A1': 0.28%, plate thickness 0.
Width 100+ from 76-open aluminum killed steel plate (unannealed material)
am
40°C temperature for 60 seconds, 26% H! Ten N! After heating and annealing in a mixed gas atmosphere, the plate was immersed for 3 seconds in a plating bath with a bath temperature of 465°C consisting of the bath M shown in Table 1 for plating, and then wiped with N2 gas to reduce the adhesion amount to 60°C.
g/m" to obtain a hot-dip plated test piece.

Thereafter, a film analysis was performed on the hot-dip plated test piece to analyze Fail in the plating layer and to examine the presence or absence of non-plating points by observing the cross section of the plating layer.

The results are also shown in Table 1.

(Hereinafter, blank spaces) In Table 1, the fact that Fe in the plating layer exceeds 1 g/l indicates that the Fe-Zn alloy layer is too thick in the as-plated state. M like Nα5 and Nα6
When only n is added, the alloy layer is very thick and the workability of non-alloyed products is poor. In addition, roughness was observed on the surface of the plating layer of these Hiroshi 5 and Na6 when visually inspected. In cases where only Si was added, such as in No. 7 and N.alpha.8, unplated spots were observed in the as-plated state. k15~Nα
Even if it contains both Mn and Si like No. 17, if it is outside the range specified by the present invention, the alloy layer will be very thick;
In addition, the appearance is poor or there are imperfections.

On the other hand, in the present invention examples of Nα9 to Na14, Hiro l to l! As in the case of No. 14 in which only Al was added, the plating condition was good.

(Example 2) A test material cut from the same steel plate as in Example 1 was coated in Example 1 using a plating bath consisting of the bath shown in Table 2.
Hot-dip plating was carried out in the same manner as above, and the coating weight was 90g/m
A hot-dip plated test piece was obtained.

Using this test piece, a salt water spray test according to JIS Z2867 was conducted for 48 hours, and the corrosion loss during this period was measured.

The results are also shown in Table 2.

Table 2 (Note) The remainder of the bath composition is Zn and unavoidable impurities.

As is clear from Table 2, the inventive examples shown in Nα6 to Na19 all have less corrosion loss than the comparative examples shown in Kink 1 to Hiroshi 5, indicating that they have excellent corrosion resistance. . In particular, A
Even when l is low, good corrosion resistance is shown due to the effect of Mn.

(Example 3) Test materials cut from the same steel plate as in Example 1 are shown in Table 3! Hot-dip plating was carried out in the same manner using the 11 Precepts plating bath, and the coating weight was adjusted to 60g/*'', then 500'
Alloying treatment was performed by heating to a temperature of C.

For the alloyed hot-dipped test piece thus obtained, JIS
A salt spray test according to Z2867 was conducted, and the elapsed time until red rust appeared was measured. The results are shown in Table 3, plating bath composition, film after alloying &llTl1. and the required alloying time.

(Hereinafter, blank space) As is clear from Table 3, examples of the present invention (N11 to floor 13)
) requires less time for alloying, and the plated steel sheet after alloying has excellent corrosion resistance.

On the other hand, Zn- to which Mn and Si are not added
Comparative Examples k14 to tm17, which correspond to Al plating, have inferior corrosion resistance or require a longer alloying time than the examples of the present invention, and like Comparative Examples K18 to Na24, one or both of Mn and Si is used. Even if it contains Mn,
If the amounts of Si and i are outside the range specified in the present invention,
Alloying cannot be performed because the time required for alloying is long or the appearance after hot-dip plating is poor.

(Effect of the invention) As explained above, according to the present invention, Zn-
It is possible to obtain a hot-dip galvanized steel sheet or an alloyed galvanized steel sheet with less generation of Al-Mn ternary compounds and Fe-based dross, good operability, excellent corrosion resistance, and excellent coating surface smoothness.

Claims (3)

[Claims] (1) A steel plate was prepared with Al: 0.05 to 5% by weight and Si: 0.
005 to 0.8% by weight, Mn: 0.1 to 3% by weight, and the remainder is Zn and unavoidable impurities. . (2) A steel plate with Al: 0.05 to 5% by weight and Si: 0.
005 to 0.8% by weight, Mn: 0.1 to 3% by weight, and the remainder is Zn and unavoidable impurities. A method for producing alloyed hot-dip plated steel sheets. (3) A plated steel sheet that has been alloyed by thermal diffusion treatment after hot-dip plating, wherein the coating composition of the plated steel sheet is A.
l: 0.1 to 5% by weight, Si: 0.005 to 0.8% by weight, Mn: 0.1 to 3% by weight, Fe: 7 to 15% by weight,
The remainder: An alloyed hot-dip plated steel sheet characterized by comprising Zn and inevitable impurities.