JPH06240430A - Production of surface treated steel sheet excellent in plating suitability - Google Patents

Abstract

PURPOSE:To stably prevent the occurrence of uncoating at a low cost without adding large scale equipment at the time of applying hot dip galvanizing and galvannealing to a steel sheet containing strongly oxidizable elements, such as Si, Mn, and P, by means of a continuous line and also at the time of applying electroplating after annealing. CONSTITUTION:The surface treated steel sheet excellent in plating suitability can be produced by bringing an aqueous solution containing the salt of Bi and/or Sb into contact with at least one side of a steel sheet and drying the surface to allow the metal or compound of Bi and/or Sb to adhere to the surface of the steel sheet by (0.1 to 100)mg/m<2> expressed in terms of metal and subjecting the steel sheet to annealing treatment and then to galvanizing or to zinc alloy plating. The steel sheet contains, as component element in the steel, at least one kind among 0.1-2.0%, by weight, Si, 0.5-4.0% Mn, and 0.05-0.2% P.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a zinc-plated steel sheet or a zinc-based alloy-plated steel sheet used for automobiles, home appliances and building materials, particularly a high-strength steel sheet as a raw material, or a zinc-based alloy plating sheet. The present invention relates to a method for manufacturing a steel plate.

[0002]

2. Description of the Related Art In recent years, surface-treated steel sheets having high corrosion resistance have been required in fields such as automobiles and home appliances, and various zinc-based plated steel sheets have been developed and put into practical use. Among them, hot-dip galvanized steel sheets (hereinafter abbreviated as GI), alloyed hot-dip galvanized steel sheets (hereinafter abbreviated as GA), and the like have a lower manufacturing cost than that of galvanized galvanized steel sheets and have good manufacturing costs. Since it has corrosion resistance, it is currently used as an anti-rust steel plate for automobiles not only as an inner plate but also as an outer plate. In addition, in the field of electroplating, in addition to pure zinc, Zn-
It has become possible to provide a steel sheet having a high corrosion resistance even with a relatively thin weight by alloy plating in which an alloy such as Ni or Zn-Fe is electrodeposited.

Recently, reduction of the amount of exhaust gas from automobiles has been taken up as an important issue due to global environmental problems, and automobile manufacturers have been obliged to reduce the weight of automobile bodies.
Against this background, gauge reduction of steel sheets is effective for reducing the weight of automobile bodies, so there is a strong demand for material manufacturers to supply high-tensile steel sheets. , Mn, P, Ti, Nb, A as elements that enhance the strength of the steel sheet without impairing the formability of
Research and development of high-tensile steel plates to which 1, Ni, Cu, Mo, V, Cr, B, etc. have been added are being conducted. In addition, since steel sheets have been conventionally required to have rust-preventive properties, development of high-strength steel sheets plated with zinc-based plating, especially hot-dip zinc-based plating with low manufacturing cost, is strongly desired by automobile manufacturers. ing.

However, since the strengthening elements in the above steel are easily oxidized and difficult to be reduced, in the Sendzimir type production line which is a typical continuous production line of hot dip plating, these strengthening elements are selectively oxidized during annealing. There is an essential problem such as surface thickening. In this case, the wettability between the steel sheet and the molten zinc is significantly reduced by the oxides of the reinforcing elements such as Si, Mn, and P that are concentrated on the surface of the steel sheet during annealing, so that the adhesiveness of the hot-dip coating is significantly reduced, and In some cases molten zinc does not adhere to the steel sheet at all,
A phenomenon such as so-called non-plating occurs. Further, in the case of a GA manufactured by applying alloying treatment to hot dip plating,
The alloying is significantly delayed by the oxide of the strengthening element generated during annealing, and the problem that the alloying process cannot be performed unless the alloying temperature is raised extremely occurs.

Also, in the case of electrogalvanizing plating, the oxide film is not mechanically or chemically removed after annealing because the elements in the steel are surface-concentrated and a strong film is formed during the annealing treatment which is a pre-plating step. As far as possible, zinc-based plating cannot be electrodeposited on steel sheets.

When hot-dip galvanizing or electrogalvanizing plating is applied to such a hard-to-plate material, in order to prevent non-plating, for example, JP-A-57-70268 and JP-A-57-79160 are used. JP-A-58-104163
The publication discloses a method of applying Fe plating to a steel sheet before hot dip galvanizing.

[0007]

However, the above-mentioned method using electric Fe plating has a problem that the equipment is large in scale as pretreatment equipment for hot dipping and the manufacturing cost is high. Further, in the case of Fe plating, it is necessary to control the Fe ³⁺ concentration in the bath during plating, so it is hard to say that this method is advantageous in terms of operation.

The object of the present invention is to make Si, M which is highly oxidizable.
When hot dip galvanizing and alloying hot dip galvanizing are performed on a steel sheet containing elements such as n and P in a continuous line, and when electroplating is performed after annealing, the cost can be reduced without adding large-scale equipment. A method for stably suppressing non-plating is provided.

[0009]

Means for Solving the Problems In the case of zinc-based plating on a high-strength steel sheet containing an element that is highly oxidizable, the present inventors treat the steel sheet with an aqueous solution containing Bi and / or Sb before annealing. By carrying out, it was found that it is possible to produce a zinc-based plated steel sheet of a high-strength steel sheet material that suppresses the concentration of constituent elements in the steel during annealing and secures excellent plating properties.
The present invention has been completed.

That is, according to the present invention, an aqueous solution containing a salt of Bi and / or Sb is brought into contact with at least one surface of the steel sheet and then dried, whereby Bi and / or
Alternatively, the metal or compound of Sb is 0.1 to 1 in terms of metal.
The present invention provides a method for producing a surface-treated steel sheet having excellent plating properties, which comprises depositing 00 mg / m ² and then performing an annealing treatment and then performing a zinc or zinc alloy plating.

Here, the steel sheet subjected to the above treatment contains at least one of Si, Mn and P in the following concentration ranges as a steel component. 0.1 wt% ≤ Si ≤ 2.0 wt% 0.5 wt% ≤ Mn ≤ 4.0 wt% 0.05 wt% ≤ P ≤ 0.2 wt%

The present invention also provides a method for producing a surface-treated steel sheet having excellent plating properties, which comprises heating the steel sheet after plating by the above method to alloy iron in the plating layer.

[0013]

The present invention will be described in more detail below. The steel sheet described in the present invention is at least one of the strengthening elements Si, Mn, and P that can increase the strength of the steel sheet without impairing the formability of low carbon steel or ultra low carbon steel used in automobiles.
It is a steel sheet containing at least one kind. Here, in order to satisfy the strength required for a steel sheet for weight reduction of an automobile body and to secure sufficient formability and deep drawability, 0.1 wt% ≤ Si ≤ 2.0 wt% 0. It is necessary to contain at least one or more of Si, Mn, and P in a concentration range of 5 wt% ≤ Mn ≤ 4.0 wt% 0.05 wt% ≤ P ≤ 0.2 wt%.

The lower limit of the concentration range of each component element is the strength required for the steel sheet when the component concentration is lower than this value,
It is decided because the deep drawability cannot be secured.

The reason for setting the upper limit is as follows. That is, in the case of Si, if it exceeds 2%, the hot-rolled base plate is significantly hardened and the cold rolling property deteriorates, and in the case of Mn, if it exceeds 4%, not only the increase in steel plate strength saturates, but also r −. This is because the value is lowered. The upper limit of P concentration is P
Is more than 0.2%, the segregation at the time of solidification becomes extremely strong, not only the increase in strength is saturated, but also the workability deteriorates. In the present invention, the elements in each of the above steels may be used alone or in combination of two or more in any case, and selected according to the strength and deep drawability (r value) required for the steel sheet. You can

In the present invention, other than the above elements, Ti, Nb, Al, Ni, Cu,
It is also applied when it contains at least one selected from the group of elements Mo, V, Cr and B. The inclusion here means that Ti, Ni, Cu, Mo, Cr and V are 0.1 wt% or more, Al and Nb are 0.05 wt% or more,
B refers to the case of containing 0.001 wt% or more.

When zinc-based plating is applied to a steel sheet containing the above elements, non-plating occurs due to the oxides of the elements that are surface-concentrated during annealing of the steel sheet. In the present invention, as a result of various studies on a plating pretreatment method for suppressing the surface concentration of each of these highly oxidizable elements, the method of depositing a Bi or / and Sb metal or compound on the steel sheet surface before annealing is the most preferable. I found it to be effective. The reason why the concentration of elements in steel is suppressed by the presence of these elements is not clear, but the following mechanism is presumed. That is, B
Since i and Sb are elements that are easily oxidized, Bi and Sb are first oxidized near the surface of the steel sheet during annealing, and the oxygen potential on the surface of the steel sheet is reduced. Therefore, elements such as Si and Mn in the steel do not concentrate on the surface of the steel sheet having a low apparent oxygen potential.

In the present invention, the material is attached to the steel sheet before annealing.
The amount of Bi or Sb metal or compound adhered in terms of metal
0.1-100mg / m² The reason is as follows.
It First, if the adhesion amount is lower than this value, it is disclosed in the present invention.
Effect of suppressing element concentration in steel during annealing
The good effect will be inadequate. On the other hand, the adhesion amount is 100 mg
/ m ² If it exceeds, the above effect will be saturated and the cost
Will be disadvantageous. Therefore, B which is attached to the steel sheet before annealing
The adhesion amount of i and / or Sb is 0.
1-100mg / m² Is the optimum range.

In the present invention, the salt of Bi or Sb means B
i, Sb sulfate, nitrate, chloride, oxide, carbonate, etc. The lower the pH of the aqueous solution, the better the adhesion of Bi and Sb. Therefore, if necessary, sulfuric acid, nitric acid,
It is desirable to adjust the pH to 2 or less with hydrochloric acid or the like. The liquid temperature of the plating solution is preferably from room temperature to 80 ° C, and industrially preferably 40 to 60 ° C.

Further, although the present invention discloses a method of adhering a metal or compound of Bi and / or Sb to a steel sheet before annealing, when it is brought into contact with an aqueous solution, it is brought into contact with an aqueous solution containing both of these elements. A method of simultaneously adhering both Bi and Sb is also effective. Furthermore, if the aqueous solution contains Bi and / or Sb, other elements such as B, C, and the like which are not harmful in the subsequent hot dipping, alloying treatment, and electroplating are performed.
A small amount of S or the like may be contained.

An aqueous solution of these compounds is brought into contact with the steel sheet and then dried. Examples of the method of bringing the aqueous solution into contact with the steel sheet include dipping treatment, spraying treatment and coating with a roll coater. Further, after the aqueous solution is brought into contact with the steel sheet, it may be washed with water as needed. After contacting with an aqueous solution or washing with water, it is dried, but when performing hot-dip plating of the Sendzimir type,
A method of passing the steel sheet through the annealing furnace without drying and drying it during the annealing of the steel sheet is also possible, but it is desirable to dry it in front of the annealing furnace from the standpoint of controlling the atmosphere of the annealing furnace, especially the dew point.

The Bi and / or Sb metal or compound deposited on the steel sheet in this way needs to be reduced at the end of the annealing step in the continuous hot dip galvanizing line or the annealing step performed prior to electroplating. The annealing condition in this case may be a condition that the oxide film is sufficiently reduced. As the atmosphere gas, hydrogen alone or a mixed gas of hydrogen and nitrogen, argon or the like can be used, but 3 to 25% hydrogen gas-residual nitrogen gas is industrially practical. The annealing temperature varies depending on the steel type, but in the case of cold rolled steel sheet, it is 700 ° C or higher, and the annealing time is 10 se.
c or more is desirable.

According to the method disclosed in the present invention, when high-strength steel sheets are hot-dipped, it is possible to obtain non-plated steel sheets.
It becomes possible to easily perform alloying treatment in a temperature range of about 50 to 550 ° C., and it is possible to obtain an alloyed hot-dip galvanized steel sheet of a high-strength steel sheet material. Steel sheets containing constituent elements such as Si, P, and Mn that significantly delay the alloying rate are difficult to alloy in the temperature range of 550 ° C. or lower, and the alloying occurs near 600 ° C. However, in this method, it is considered that Bi and Sb suppress the generation of C residues, oxides, etc. on the surface of the steel sheet, thereby improving the cleanliness of the surface of the steel sheet, so that the alloying temperature can be reduced. This makes it possible to obtain an alloyed hot-dip galvanized steel sheet of a high-strength steel sheet material having good adhesion. The alloying temperature varies depending on the coating amount, line speed, etc., but it is desirable that the alloying temperature be as low as possible in order to obtain a GA having good adhesion.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples. (Examples) Steels containing the constituent elements with the concentrations shown in Table 1 were melted and subjected to hot rolling and cold rolling according to a conventional method to produce a steel sheet having a thickness of 0.7 mm. After degreasing and pickling the cold-rolled steel sheet, it was contacted with an aqueous solution containing Bi and / or Sb under the conditions shown in Tables 2 and 3, and then dried or washed with water and dried. Bi, Sb attached to these steel sheets
Table 4 shows the adhesion amount of The amount of adhesion was determined by dissolving the Bi, Sb film in sulfuric acid, and dissolving this solution with an I.D. C. P. It was determined by analysis by an emission analysis method (Inductively Coupled Plazma).

The following annealing conditions (A) were applied to the above steel sheet.
Of the present invention, which was treated with hot melt plating conditions (B) and alloying conditions (C) according to the present invention examples 1 to 3 and hot dip plating conditions (B).
The GI treated in step 1 was designated as Inventive Example 4. Further, a Zn-Ni plated steel sheet obtained by treating the steel sheet treated under the annealing condition (A) under the electroplating condition (D) was designated as Inventive Example 5.

The above-mentioned annealing and hot dip galvanizing were performed in a laboratory by a hot dip experimental apparatus, and the alloying treatment was performed in an infrared heating furnace in a laboratory. The electroplating was performed in a laboratory by fluidized bath plating.

As comparative examples, steel sheets containing the constituent elements with the concentrations shown in Table 1 were not subjected to the Bi and Sb treatments (Comparative Example 1) and the metal Bi or metal Sb deposition amount deviated from the scope of the present invention. Treated (Comparative Example 2)
3) Further, a steel plate (comparative example 4) having a composition in the steel whose composition is less than or equal to the lower limit of the range referred to in the present invention was subjected to annealing treatment, and the steel sheet subjected to GA plating in the same manner as the present invention example is shown in Table 4. Indicated.

The following evaluations were carried out on these inventive examples and comparative examples. (A) Annealing conditions Temperature rising rate: 10 ° C / SEC holding temperature: 850 ° C Holding time: 30SEC Temperature lowering rate: 20 ° C / SEC Atmosphere in annealing furnace: 5% H ₂ -N ₂ (dew point -20 ° C)

(B) Hot-dip plating conditions Bath temperature: 470 ° C. Penetration plate temperature: 470 ° C. Al content: 0.15 wt% Adhesion: 60 g / m ² (one side) Plating time: 1 SEC

(C) Conditions for alloying treatment Temperature rising rate: 20 ° C./SEC Temperature decreasing rate: 15 ° C./SEC Alloying temperature: 490 ° C. Alloying time: 30 SEC

(D) Electroplating conditions Plating bath ZnSo ₄ 200 g / l NiSO ₄ 80 g / l Na ₂ SO ₄ 50 g / l Dk 100 A / dm ² pH 1.8 Bath temperature 60 ° C. Adhesion amount 30 g / m ² Ni content Rate 12 wt%

(Evaluation method of plating property) The plating property was evaluated according to the following criteria by visually observing the appearance after hot dip galvanizing. ○ No non-plating × Non-plating occurred

(Evaluation of Plating Adhesion) Evaluation was carried out by a DuPont impact test (1/4 inch, 1 kg, 50 cm). The judgment criteria are as follows. ○ No plating peeling × Plating peeling

(Evaluation of alloying rate) The alloying rate was evaluated based on whether the zinc η phase remained on the surface of the alloyed material treated under the above conditions. ○ Without zinc η phase × With zinc η phase

Table 4 shows the evaluation results of Examples 1 to 5 of the present invention and Comparative Examples 1 to 4. From the present investigation, the method disclosed in the present invention makes it possible to manufacture a galvanized steel sheet having excellent adhesion without unplating, even in a steel sheet containing elements such as Si, Mn, and P that are highly oxidizable. It was also shown that in the case of the galvannealed steel sheet, the alloying rate was moderately accelerated, and it could be produced by a method similar to the conventional method only by performing pretreatment.

[0036]

[Table 1]

[0037]

[0038]

[0039]

[0040]

[Effects of the Invention] When performing zinc-based plating on high-strength steel,
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to inexpensively and stably manufacture a zinc-based plating that is free from non-plating and has excellent adhesion. Moreover, when performing an alloying process, a galvannealed steel sheet can be obtained at a relatively low temperature. Due to the urgent need to reduce the weight of automobiles, the development of hot-dip galvanized steel sheets, hot-dip galvanized steel sheets, and galvanized galvanized steel sheets, which are materials for high-strength steel sheets, is desired. .

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C23C 18/08 28/02 C25D 5/26 C

Claims (3)

[Claims] 1. An aqueous solution containing a salt of Bi and / or Sb is brought into contact with at least one surface of a steel sheet and then dried to obtain a metal or compound of Bi and / or Sb on the surface of the steel sheet of 0.1 in terms of metal. A method for producing a surface-treated steel sheet having excellent plating properties, which comprises depositing ˜100 mg / m ² and then performing an annealing treatment and then zinc or zinc alloy plating. 2. The steel sheet to be treated is at least one of Si, Mn, and P in the following concentration ranges as constituent elements in the steel.
The method for producing a surface-treated steel sheet having excellent plating properties according to claim 1, which contains a seed. 0.1 wt% ≤ Si ≤ 2.0 wt% 0.5 wt% ≤ Mn ≤ 4.0 wt% 0.05 wt% ≤ P ≤ 0.2 wt% 3. A method for producing a surface-treated steel sheet having excellent plating properties, which comprises heating the steel sheet after plating by the method according to claim 1 or 2 and alloying iron in the plating layer.