JP3078456B2 - Manufacturing method of high-strength hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hot-dip galvanized and alloyed hot-dip galvanized steel sheets used for automobiles, home appliances and building materials.

[0002]

2. Description of the Related Art In recent years, surface-treated steel sheets having high corrosion resistance have been required in the fields of automobiles, home appliances, etc., and hot-dip galvanized steel sheets, galvannealed steel sheets, electro-galvanized steel sheets, and Zn-Ni-coated steel sheets Is being developed and put into practical use. Above all, hot-dip galvanized steel sheets such as hot-dip galvanized steel sheet (GI) and alloyed hot-dip galvanized steel sheet (GA) are inexpensive to manufacture and have good corrosion resistance compared to electrogalvanized steel sheets. For this reason, it has been put to practical use not only as an inner plate but also as an outer plate as a rustproof steel plate for automobiles.

In recent years, reduction of the amount of exhaust gas from automobiles has been taken up as an important issue due to global environmental problems, and it has become mandatory for automobile manufacturers to reduce the body weight. Against this background, gauge down of steel sheets is effective in reducing the weight of automobile bodies.Therefore, material manufacturers are strongly required to supply high-tensile steel sheets. Si, P, Mn, Ti, Nb, Al, C as elements for increasing the strength of the steel sheet without impairing the formability of
Research and development of high-strength steel sheets to which r, Ni, Cu, B, Mo, V, and the like are added have been conducted. In addition, since steel sheets have been required to be provided with rust-preventive properties, the development of high-strength steel sheets coated with zinc, especially hot-dip galvanized, which is inexpensive to manufacture, has been required. I have.

However, the strengthening elements Si,
P, Mn, Ti, Nb, Al, Cr, Ni, Cu, B,
Since Mo and V are easily oxidized and are not easily reduced, they are currently a typical continuous production line of hot-dip galvanizing. From the entrance side of the hot-dip galvanizing line, an annealing furnace, a hot-dip coating and an alloying furnace are continuously arranged. In the production line of Sendzimir type (hereinafter referred to as a continuous hot-dip galvanizing equipment), there is an essential problem that these strengthening elements are selectively oxidized and surface concentrated during annealing. . In this case, the S concentrated on the steel sheet surface during annealing
Since the wettability between the steel sheet and the molten zinc is significantly reduced by the oxides of the reinforcing elements such as i and Mn, the adhesion of the hot-dip galvanized coating is significantly reduced. , So-called non-plating occurs. Also, in the case of GA manufactured by subjecting to galvanizing and alloying, alloying is significantly delayed due to oxides of strengthening elements generated during annealing. The problem of being unable to do so also accompanies it.

[0005] When hot-dip galvanizing or alloyed hot-dip galvanizing is applied to such a difficult-to-plate material, the above-mentioned problem is solved by pre-treating the surface of the steel sheet in advance in order to prevent non-plating and achieve proper alloying. A method of trying is disclosed. For example, JP-A-55-131165 describes a method of performing Ni plating before hot-dip galvanizing, and JP-A-57-70268 and JP-A-57-79160 describe Fe plating. Each method of application is disclosed. As a method other than the electrogalvanizing, a film thickness of 40 in a non-oxidizing furnace method (NOF) is used.
Japanese Patent Application Laid-Open No. 55-122865 discloses a method of forming an oxide film having a thickness of 0 to 10000 ° and then annealing in an atmosphere containing hydrogen.

[0006]

However, in the above-described method using electroplating, a large-scale facility is required because the amount of pre-plating required for preventing non-plating needs to be at least 7 to 10 g / m ² or more. In addition, there is a problem that the production cost is high, so that it is difficult to say that it is a preferable method for applying to a hot-dip plating line. In addition, before annealing in a hydrogen-containing atmosphere, a non-oxidizing furnace method (NO
In the method of forming a film in F), in the case of in-line processing, the amount of oxide film generated tends to fluctuate depending on the line speed, atmosphere, steel sheet temperature, and the type and amount of component elements in steel. It is difficult to obtain an amount of the film, and the effect of suppressing non-plating in an actual production line becomes unstable.

An object of the present invention is to contain one or more elements such as Si, P, Mn, Ti, Nb, Al, Cr, and B, which are more oxidizable than iron, and further include Ni, C if necessary.
When hot-dip plating is performed on a steel sheet containing u, Mo, V and other elements in a continuous line, the process becomes as complicated as possible.
An object of the present invention is to provide a method for stably suppressing non-plating while minimizing a decrease in productivity.

[0008] The present invention relates to Si, P, Mn, Ti, Nb,
After a steel sheet containing at least one of Al, Cr, and B is annealed at a recrystallization temperature of 750 to 950 ° C. in a continuous annealing facility, the components in the steel on the steel sheet surface in a continuous hot-dip galvanizing facility. the concentrated layer, pickling weight loss performs pickling in 5 g / m ² or less 0.05 g / m ² or more conditions with hydrochloric acid or sulfuric acid, 650 ° C. or higher the steel sheet by the continuous galvanizing and Recrystallization annealing in the continuous annealing equipment
This is a method for producing a high-strength hot-dip galvanized steel sheet in which hot-dip galvanizing is performed by heating and reducing to a temperature or lower . Also, the present invention
Less of Si, P, Mn, Ti, Nb, Al, Cr, B
Both steel reach the steel sheet containing one or more kinds in continuous annealing equipment
After annealing at a recrystallization temperature of 750-950 ° C. ,
In the continuous hot-dip galvanizing equipment, the concentrated layer of the steel component on the steel sheet surface is removed using hydrochloric acid or sulfuric acid to which 0.5 to 10 g / l of Fe ³⁺ ion is added, and the steel sheet is again subjected to the continuous hot-dip zinc coating. 650 ° C or higher and continuous annealing installed in plating equipment
There is a method for producing a high-strength hot-dip galvanized steel sheet in which hot-dip galvanizing is performed by heating and reducing to a temperature lower than the recrystallization annealing temperature in the equipment . Further, it is characterized in that the Fe ³⁺ ion addition is 0.5 to 5 g / l. The present invention is also characterized in that the steel sheet is hot-dip galvanized by any one of the above-mentioned methods, and then the steel sheet is heat-alloyed.

The high-strength steel sheet used in the present invention is a low-carbon steel or ultra-low-carbon steel used in automobiles, which is a strengthening element Si, which can increase the strength of a steel sheet without impairing formability.
A steel sheet containing at least one or more alloying elements such as P, Mn, Ti, Nb, Al, Cr, and B, and optionally containing components such as Ni, Cu, Mo, and V as necessary. May be. In the present invention, “containing” means “Si, Ti, Ni, Cu, Mo, V, Cr,
B is 0.1 wt% or more, Mn is 0.5 wt% or more, P, A
1, Nb indicates a case containing 0.001 wt% or more.

[0010] Si has the effect of increasing the strength of steel.
The content is set to 1 wt% or more, and is set to 2.0 wt% or less in order to form an oxide film on the surface and reduce the adhesion to the plating bath. P can be given strength by adding a small amount and is relatively inexpensive. However, it is liable to cause secondary working embrittlement and also has an adverse effect on deep drawing.
% Or less. Mn has an effect of increasing strength 0.5
wt% or more, which has an adverse effect on deep drawability.
wt% or less. Cr is set to 0.1 wt% or more at which the effect of increasing the strength of the steel appears, and is set to 2.0 wt% or less from the viewpoint of saturation of the strength improving effect and economy. Ti is contained in an amount of 0.01 wt% or more and 0.1 wt% or less at which the effect of improving the strength of the steel and the formability of the steel sheet is exhibited. Nb and Al are contained in an amount of not less than 0.005 wt% and not more than 0.05 wt% in order to improve the strength of the steel and the formability of the steel sheet. B is 0.000 in which the secondary working brittleness is improved and the weldability is improved.
1 wt% or more and 0.01 wt% or less. Ni, Cu, M
o and V are 0.1 wt% or more at which the effect of improving the formability appears.
0 wt% or less.

[0011] Of these elements, Si is the element that most affects non-plating, and its content in steel is 0.1 wt%.
% Or more, the deterioration of the plating property becomes remarkable. Therefore, the production method of the present invention works extremely effectively particularly on a steel sheet containing 0.1 wt% or more of Si.

The high-strength steel sheet which is a plating material containing at least one of the above elements is adjusted in thickness by hot rolling and cold rolling, and is annealed at a recrystallization temperature by a continuous annealing facility. The atmosphere at the time of annealing requires reducing properties of the steel sheet in order to prevent generation of scale, and generally, a nitrogen gas containing several percent hydrogen gas may be used. The ultimate temperature of the steel sheet in the continuous annealing equipment varies depending on the components in the steel and the target material, but is generally about 750 to 950 ° C.
The hot-dip galvanized steel sheet is continuously subjected to pickling, annealing reduction, cooling, immersion in a hot-dip zinc bath, and weight adjustment by gas wiping, using a continuous hot-dip galvanizing equipment. It is manufactured by

In a steel sheet annealed at a recrystallization temperature by a continuous annealing facility, Si, Mn, Cr, etc. are concentrated as oxides on the surface due to components in the steel. In order to perform hot-dip galvanizing on a high-tensile steel sheet containing elements such as Si, Mn, and P described above, the wettability between the base steel sheet and the hot-dip zinc is impaired when the steel sheet enters the hot-dip galvanizing bath. What is necessary is just to reduce the surface concentration layer of Si, Mn, etc.

The focus of the present invention is that, after annealing at a recrystallization temperature in a continuous annealing facility, a concentrated layer of a steel component on the steel sheet surface is subjected to pickling reduction using hydrochloric acid or sulfuric acid in a continuous galvanizing facility. There by performing pickling in 5 g / m ² or less 0.05 g / m ² or more conditions, to suppress the generation of Si, the surface concentrated layer of Mn be heated reducing the steel plate again, better plating It is the point that they discovered that they could obtain adhesion. that time,
The heating temperature of the steel sheet in the continuous galvanizing equipment is preferably 650 ° C. or more and the recrystallization annealing temperature in the continuous annealing equipment or less. As the atmosphere, a nitrogen gas containing several% hydrogen gas may be used as in the case of annealing in the continuous annealing equipment.

Furthermore, short time to meet the conditions of pickling weight loss 5 g / m ² or less 0.05 g / m ² or more, hydrochloric acid and the Fe ³⁺ ions added 0.5 to 10 g / l as the pickling solution Alternatively, it is preferable to use sulfuric acid. More preferably, 0.5 to 5 g / l of Fe ³⁺ ions are added to hydrochloric acid or sulfuric acid. The Fe ³⁺ ions are preferably added to the above pickling solution as ferric chloride or ferric sulfate.

When removing Si, Mn-based surface oxides concentrated on the steel sheet surface after annealing in a continuous annealing facility by pickling,
Excessive etching is not preferred. This is because not only the Si and Mn-based surface oxides are removed by excessive etching, but also (1) a large amount of Fe-based oxides is generated on the steel sheet surface and remains unreduced during re-reduction, impairing wettability. (2) P-based oxides are formed on the surface and hinder wettability during re-reduction. On the other hand, if the pickling loss is less than 0.05 g / m ² , the Si, Mn-based surface oxide is not removed, and the residual Si, Mn-based surface oxide at the time of re-reduction impairs wettability during plating.

Therefore, in the present invention, as a result of various examinations of the pickling conditions, when the concentrated layer of the components in the steel on the surface of the steel sheet is removed using hydrochloric acid or sulfuric acid, the pickling loss is 5 g / m ² or less and 0.05 g / m ² or less. / M ² or more. Pickling weight loss of 5 g / m ² or less 0.05 g / m ²
The reason for setting m ² or more is to prevent adverse effects due to excessive etching as described above. On the other hand, when the Fe ³⁺ ion is less than 0.5 g / l, the pickling for a short time does not change as compared with the case where the acid washing loss is not added. Short time on the production line (about 5
The pickling weight loss of 5 g / m ² or less can be achieved by adding 0.5 to 10 g / l of Fe ³⁺ ions to the acid to be used. The object can be removed. Further, preferably, Fe
^It is preferable to add 0.5 to 5 g / l of ³⁺ ions to hydrochloric acid or sulfuric acid.

After that, the pickled steel sheet needs to be reduced again in an annealing step in a continuous hot-dip galvanizing equipment line. The annealing condition in this case is such that the Fe-based oxide film is reduced. Good. As the atmospheric gas, hydrogen alone or a mixed gas of hydrogen and nitrogen, argon, or the like can be used, but it is practical to use a nitrogen gas containing 3 to 25% hydrogen gas industrially. Although the annealing temperature varies depending on the type of steel, in the case of a cold-rolled steel sheet, it is preferably 650 ° C. or more and the recrystallization temperature of the above continuous galvanizing equipment. Annealing reduction in continuous galvanizing equipment is
For hot rolled steel sheets with little addition of Si, Mn, Cr, etc., about 600 ° C is common and sufficient plating is possible.
In a steel sheet annealed after recrystallization annealing after adding Si, Mn, Cr, etc., from the viewpoint of plating wettability and alloying speed, an improvement effect appears at a reannealing reduction temperature of 650 ° C. or higher, and enters a suitable range at 700 ° C. or higher. . However, in order to prevent re-surface enrichment and the material of the steel sheet, the temperature is preferably not higher than the recrystallization temperature in the continuous hot-dip galvanizing equipment, and more preferably (recrystallization annealing temperature in the continuous hot-dip galvanizing equipment minus 30) ° C. The annealing time is desirably 10 sec or more and 300 sec or less.

The steel sheet re-annealed and reduced in the above temperature range is cooled to about 500 ° C. in the same manner as ordinary hot-dip galvanizing, and then is heated to about 460 to 500 ° C., and the dissolved Al concentration is 0.15 wt%.
Introduced to the front and back hot dip galvanizing baths and galvanized,
The weight per unit area is adjusted by gas wiping when rising from the bath. As described above, a high-strength hot-dip galvanized steel sheet is manufactured, and if necessary, a hot-alloyed hot-dip galvanized steel sheet is immediately manufactured. The alloying temperature is 460 ° C. or higher for productivity and 560 ° C. or less for plating adhesion at the time of press molding.

According to the method disclosed in the present invention, hot-dip plating of a high-strength steel sheet material without non-plating can be obtained.
The high-strength hot-dip galvanized steel sheet treated according to the present invention is 45
Alloying can be easily performed in a temperature range of about 0 to 550 ° C., and an alloyed hot-dip galvanized steel sheet made of a high-strength steel sheet material can be obtained. The alloying time is 20-18
About 0 sec is desirable. Steel sheets containing component elements such as Si, Mn, and P that significantly slow the alloying rate are 5
It is difficult to alloy in a temperature range of 50 ° C. or less,
Although the alloying occurs at around 600 ° C., the adhesion deteriorates. However, in the method of the present invention, the concentration of elements such as Si, Mn, and P at the plating-steel plate interface can be suppressed, so that the alloying temperature is reduced. Therefore, it is possible to obtain an alloyed hot-dip galvanized steel sheet made of a high-tensile steel sheet material having good adhesion. The alloying temperature varies depending on the amount of plating applied, the line speed, and the like, but it is desirable that the alloying temperature be as low as possible in order to obtain GA with good adhesion. After hot-dip galvanizing or alloyed hot-dip galvanizing, it is also possible to perform upper layer plating as required to achieve better plating characteristics. For example, as the upper layer plating, Fe-Zn plating, Fe-P plating, or the like, which is performed to improve the sliding property during press forming, may be performed. The upper plating may be any plating depending on the application.

[0021]

The present invention will be described below in detail with reference to examples.

(Examples 1 to 24, Comparative Examples 1 to 3) A test steel sheet having the composition shown in Table 1 and previously subjected to a cleaning treatment was subjected to hot-dip galvanizing without removing a concentrated layer after annealing once. Examples (Comparative Examples 1 to 3) and Examples (Examples 1 to 24 of the present invention) in which the concentrated layer was removed using hydrochloric acid or sulfuric acid after the first annealing and then the second annealing was performed. At that time, ferric chloride or ferric sulfate was added to the pickling solution to add Fe
The concentration of ³⁺ was changed. The annealing and hot-dip galvanizing were performed by a hot-dip galvanizing simulator, and the alloying treatment was performed by an infrared heating furnace in a laboratory. Annealing, removal of the concentrated layer by pickling, hot-dip galvanizing conditions, and alloying conditions are as follows.

[0023] -: Not added

The steel sheets A to C having the compositions shown in Table 1 were subjected to annealing, concentrated pickling, and hot-dip plating under the following conditions, and evaluated as described below. These processing conditions are shown in Table 2. (1) Annealing conditions (including the first and second times) Heating rate: 10 ° C./sec Holding temperature: shown in Table 2 Holding time: 30 sec Cooling temperature: 20 ° C./sec Atmosphere in annealing furnace: 5% H ₂ -95 % N ₂ (dew point -20
° C) In the one-time annealing method, the steel sheet is put into a plating bath when the steel sheet reaches a predetermined temperature after annealing. In the double annealing method, after the steel sheet is once cooled to room temperature after the annealing, the concentrated layer is removed, the steel sheet is annealed again, and the steel sheet is put into a plating bath when the temperature is lowered to a predetermined temperature.

(2) Pickling conditions for removing the concentrated layer As a pickling solution, a 5 wt% hydrochloric acid aqueous solution (temperature: 60 ° C.) prepared by diluting commercially available 12N hydrochloric acid and 36N sulfuric acid with water,
Using a 10 wt% sulfuric acid aqueous solution (temperature: 60 ° C.), the annealed test material was immersed for 5 seconds. At this time, the Fe ³⁺ ion concentration was changed as shown in Table 2 by adding and dissolving ferric chloride in the case of an aqueous hydrochloric acid solution and adding ferric sulfate in the case of an aqueous sulfuric acid solution. The pickling loss was determined by measuring the weight of the steel sheet before and after pickling. FIGS. 1 and 2 show the test materials C shown in Table 1.
1 shows the relationship between the amount of Fe ³⁺ ions added and the amount of pickling loss when immersed in hydrochloric acid and sulfuric acid after annealing at 860 ° C. In pickling for a short time of about 5 seconds, there was almost no loss in pickling without the addition of Fe ³⁺ ions, and it was considered that the removal of the surface concentrated layer was insufficient. Further, as the Fe ³⁺ was added, the pickling loss increased.

(3) Hot-dip plating conditions Bath temperature: 470 ° C. Infiltration plate temperature: 470 ° C. Al content: 0.15 wt% Plating weight: 60 g / m ² (one side) Plating time: 1 sec (4) Alloying conditions Alloy 550 ° C Heating rate 20 ° C / s
ec Alloying time 30 sec Cooling rate 15 ° C / s
ec

<Evaluation method for hot-dip galvanizing property> The appearance after hot-dip galvanizing was observed with a video camera, image processing was performed, and the non-plating area ratio was determined and evaluated. 5: Non-plated area ratio 0% 4: Non-plated area ratio 0 to 0.1% 3: Non-plated area ratio 0.1 to 0.3% 2: Non-plated area ratio 0.3 to 0.5% 1: Non-plating area ratio 0.5% or more

<Evaluation of Plating Adhesion> Plating adhesion was evaluated by a DuPont impact test (a 1/4 inch diameter, weight of 1 kg dropped onto a steel plate from a height of 50 cm). The criteria are shown below. ○: No plating peeling △: Some plating peeling ×: Plating peeling

<Evaluation of alloying rate> Evaluation was made based on whether or not the zinc η phase remained on the surface of the alloyed material. ○: without zinc η phase ×: with zinc η phase

Table 2 shows the evaluation results of Comparative Examples 1 to 3 and Examples 1 to 24. 1 and 2, the test material C was 860
Fe when immersed in hydrochloric acid and sulfuric acid after annealing at ℃
The relationship between the ³⁺ addition amount and the pickling loss is shown. As shown in FIGS. 1 and 2, in the case of pickling for a short time of about 5 seconds, there is almost no loss in pickling unless Fe ³⁺ ions are added, and it is considered that the removal of the surface concentrated layer is insufficient. Was. Further, as the Fe ³⁺ ion was added, the loss in pickling increased. As is clear from FIGS. 1 and 2 and Table 2, the plating appearance and plating adhesion were not good unless the concentrated layer was pickled.
3). However, when the method of the present invention is used, even when a steel sheet containing an element that is more oxidizable than iron is used, it is possible to produce a high-strength hot-dip galvanized steel sheet with excellent adhesion without non-plating. (Examples 1 to 24). In addition, the alloying speed was moderately promoted, and an alloyed hot-dip galvanized steel sheet could be obtained by the same method as the conventional method.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

When hot-dip galvanizing is performed on a high-tensile steel sheet, the method of the present invention makes it possible to manufacture a galvanized steel sheet having excellent adhesion without any plating at low cost and in a stable manner. Moreover, when alloying the hot-dip galvanized steel sheet treated according to the present invention, an alloyed hot-dip galvanized steel sheet can be obtained at a relatively low temperature. Recently, the development of hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets has been desired due to the urgency of reducing the weight of automobiles, and the contribution of the present invention to the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of Fe ³⁺ added during hydrochloric acid pickling and the amount of pickling loss.

FIG. 2 is a diagram showing the relationship between the amount of Fe ³⁺ added during sulfuric acid pickling and the amount of pickling loss.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Inside the Steel Research Laboratory, Steel Development & Production Headquarters (72) Inventor Masayoshi Kuwagata Chiba Prefecture 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Corp. Inside steelworks (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (4)

(57) [Claims] 1. The method according to claim 1 , wherein the elements are Si, P, Mn, Ti, Nb, Al, and C.
After annealing a steel sheet containing at least one of r and B at a recrystallization temperature of 750 to 950 ° C. in a continuous annealing facility at a steel sheet arrival temperature, enriching steel components on the steel sheet surface in a continuous galvanizing facility. the layers pickling weight loss performs pickling in 5 g / m ² or less 0.05 g / m ² or more conditions with hydrochloric acid or sulfuric acid, the steel sheet by the continuous galvanizing line 65
0 ° C or higher and below the recrystallization annealing temperature in the continuous annealing equipment
A hot-dip galvanized steel sheet, wherein the hot-dip galvanized steel sheet is subjected to hot reduction. 2. Si, P, Mn, Ti, Nb, Al, C
After annealing a steel sheet containing at least one of r and B at a recrystallization temperature of 750 to 950 ° C. in a continuous annealing facility at a steel sheet arrival temperature, enriching steel components on the steel sheet surface in a continuous galvanizing facility. The layer is made of 0.5-10 g / Fe ³⁺ ions.
l using a hydrochloric acid or a sulfuric acid added thereto, and removing the steel sheet at 650 ° C.
A method for producing a high-strength hot-dip galvanized steel sheet, wherein the hot-dip galvanizing is performed by heating and reducing the temperature to a recrystallization annealing temperature or lower in a continuous annealing facility . 3. The method according to claim 2, wherein the Fe ³⁺ ions are added.
Of a high-strength hot-dip galvanized steel sheet having a 0.5 to 5 g / l
Production method. 4. The method according to claim 1, wherein
After hot-dip galvanizing the steel sheet,
High-strength alloyed molten alloy characterized by heat alloying
Manufacturing method of lead plated steel sheet.