JPH11293438A - High tensile strength galvannealed steel sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high tensile strength galvannealed steel sheet excellent in adhesion and appearance without causing any noncoating part in the galvannealing of an Si series high tensile strength steel sheet. SOLUTION: This high tensile strength galvannealed steel sheet having a galvannealed layer obtd. by galvanizing the surface of a steel sheet contg. 0.1 to 2.5 wt.% Si with zinc or an alloy essentially consisting of zinc, and then annealing the galvanized sheet at 550 to 600 deg.C, Cu is incorporated into the plating layer by 0.01 to 3.0 g/m<2> . In this method for producing the high tensile galvannealed steel sheet, the surface of the high tensile strength steel sheet contg. Si is cleaned, thereafter, the surface is stuck with Cu or a Cu compd. by 0.1 to 3.0 g/m<2> as the Cu content, annealing is executed in a reducing or nonoxidizing atmosphere, subsequently, the plate is passed through hot dip zinc without being exposed to the air and is annealed at >550 to 600 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-tensile alloyed hot-dip galvanized steel sheet and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheet has corrosion resistance,
It has excellent paint adhesion and is widely used especially as a steel sheet for automobiles. Recently, the demand for safety, durability, and weight reduction of automobiles has increased, and as a material that meets these requirements,
Addition of silicon (Si) to increase the tensile strength of the steel sheet to improve safety and durability, and because of the high tensile strength, alloying using a high-tensile steel sheet that enables the steel sheet to be thinner and lighter Expectations for hot-dip galvanized steel sheets are high.

[0003] In such hot-dip galvanizing of a high-strength steel sheet, a non-reducible oxide mainly composed of Si is formed on the surface of the steel sheet during pre-heating (annealing) of the steel sheet. These oxides deteriorate wettability with molten zinc and cause non-plating.

[0004] To solve the above problem, for example, Japanese Patent Laid-Open No.
In JP-A-34147 and JP-A-8-170159, non-plating is prevented by forming an Fe-based oxide film in a preheating furnace. However, for example, in a line having an all-reduction type annealing furnace, it is necessary to introduce equipment for forming an oxide film, and equipment restrictions are large. In Japanese Patent Application Laid-Open No. Hei 5-239606, non-plating is prevented by forming an oxide film of iron using an oxidizing agent. However, it is very difficult to control the reaction of the oxidizing agent in a line where the production speed changes, which may cause a variation in the amount of the oxide film and adversely affect the quality.

As another example, see Japanese Patent Application Laid-Open No. 7-7072.
As disclosed in Japanese Patent Application Laid-Open No. 4 (1999) -1995, there is a method in which an oxide film concentrated by annealing is pickled or polished. However, considering the structure of the current hot-dip plating equipment that allows a steel sheet to enter a hot-dip coating bath immediately after annealing, it is not practical and requires significant equipment investment. Further, in a line where the production speed changes, the pickling amount and the polishing amount change, and there is a possibility that the quality may vary.

As an example using a pre-plating method, Japanese Patent Application Laid-Open No. 6-128758 is known.
Although e and Co are effective with a very small pre-plating adhesion amount of 5 to 70 mg / m ^2, it is necessary to form iron oxide in an oxidizing atmosphere after pre-plating, and equipment restrictions are also large here. In a line where the production speed changes, even if the pre-plating can be controlled by electroplating, the amount of the oxide film changes again in the formation of iron oxide after the pre-plating, which adversely affects the quality. As described above, there is a problem left in the conventional methods in terms of equipment restrictions and variations in quality.

As an effect of the non-reducible oxide mainly composed of Si, there is a delay in alloying in addition to non-plating. Alloying is slow with any of the above prior art techniques. As a countermeasure for optimizing the alloying speed, it is easy to raise the alloying temperature to a high degree of operation, but the method of high-temperature alloying is avoided because of the deterioration in adhesion and appearance. I have.

[0008]

In order to solve the problem, it is desired to use a method that does not significantly break existing production conditions. Of course, it is not permissible for the produced plated steel sheet to have inferior quality such as adhesion and appearance, and a steel sheet and manufacturing method that satisfy both “quality” and “compatibility with current production conditions” is necessary. In view of the above problems, the present invention provides a high-strength galvannealed steel sheet which prevents non-plating and has excellent adhesion and appearance in alloyed hot-dip galvanizing of a Si-added high-strength steel sheet. It is intended to provide a method for producing the.

[0009]

Means for Solving the Problems The present inventors have focused on high-temperature alloying as a method for promoting alloying of high-strength steel sheets to which Si has been added, and have excellent appearance and adhesion during high-temperature alloying. The method was examined. As a result, it has been found that the inclusion of Cu in the plating layer is effective for improving the appearance, particularly the uneven plating. As a result of further study, Cu
At the same time, it has been found that the adhesion is improved by compounding Ni or Co.

The present inventors have subsequently studied a technique for preventing non-plating, and as a result, have found that non-plating is completely suppressed by attaching Cu or a Cu compound before hot-dip plating. Furthermore, the adhesion of plating can be improved by combining and attaching Ni or a Ni compound or Co or a Co compound. As a result of repeated studies, by optimizing the cooling pattern after the heat alloying treatment, It has been found that the appearance and adhesion can be further improved.

The present invention has been made based on these findings, and the gist of the present invention is as follows: (1) The surface of a steel sheet containing 0.1 to 2.5% by weight of Si as a component in steel. Hot-dip galvanized with zinc or an alloy mainly composed of zinc, and then heat-alloyed at a temperature exceeding 550 ° C. to 600 ° C., in a hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer, High tensile alloyed hot-dip galvanized steel sheet characterized by containing 0.01 to 3.0 g / m ² , (2) one or two types of Ni or Co are further added to the plating layer in a total amount of 0.005 to 5 2.0 g / m ^2, wherein the high-tensile alloyed hot-dip galvanized steel sheet according to the above (1), (3) Si as a component in the steel
After cleaning the surface of a high-tensile steel sheet containing 0.1 to 2.5% by weight, the surface of the steel sheet is treated with Cu or a Cu compound as a Cu content.
After adhering 0.1 to 3.0 g / m ² and annealing in a reducing or non-oxidizing atmosphere, the steel sheet is passed through molten zinc without contacting with the atmosphere, and furthermore, over 550 ° C to 60 ° C.
A method for producing a high-tensile alloyed hot-dip galvanized steel sheet characterized by being subjected to heat alloying treatment at 0 ° C., (4) a surface of a high-tensile steel sheet containing 0.1 to 2.5% by weight of Si as a component in the steel After cleaning, Cu or Cu compound
0.1 to 3.0 g / m ² as a quantity, and one or more of Ni or a Ni compound, or Co or a Co compound is 0.005 to 0.005 in total of Ni and Co.
5.0 g / m ^{2 are} combined and adhered, and after annealing in a reducing or non-oxidizing atmosphere, the steel sheet is passed through molten zinc without contacting with the atmosphere. A method for producing a high-tensile alloyed hot-dip galvanized steel sheet characterized by performing heat alloying treatment. (5) By the heat alloying treatment, the Fe content in the hot-dip galvanized layer reaches 7 to 15% by weight%. After that, air cooling, mist cooling,
The high-tensile alloying as described in the above (3) or (4), wherein cooling is performed at a cooling rate of 10 ° C./s or more by any one or two or more cooling devices of steam-water cooling. Manufacturing method of hot-dip galvanized steel sheet.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, in the present invention, Si contained in the high-tensile steel sheet
If the content is less than 0.1% by weight, non-plating does not occur in the first place, and at the same time, the alloying delay is small and no problem occurs. If the content is more than 2.5%, the content exceeding the content becomes too hard, so that the content is set to less than this.

The Cu content in the plating layer is 0.01 g / m
^If it is less than ² , the effect of improving the appearance at the time of high-temperature alloying is hardly observed. If it exceeds 3.0 g / m ² , the effect of improving the appearance is saturated, but the adhesion tends to deteriorate.
0 g / m ² or less.

If the content of Ni or Co mixed with Cu is less than 0.005 g / m ² , the effect of improving the adhesion is hardly observed. If it exceeds 5.0 g / m ² , the effect of improving the adhesion will be saturated. Even if it is contained more than this, it does not harm the adhesiveness, but it is less than this in consideration of cost. Ni or Co to be contained may be either one, or both may be contained. The content here is the content as the sum of Ni and Co.

In the present invention, in addition to Ni and Co, which are added to Cu and Cu in the alloyed hot-dip galvanized layer, Al, Pb, Sb, Si, Fe, Sn, Mg, M
There is no problem in the manifestation of the effects of the present invention even if the plating actively contains one or more of n, Cr, Ca, Li, Ti and rare earth elements or is unavoidably mixed.

Further, in addition to the main constituent elements Fe and Si, the high-strength steel sheet of the present invention has C, Mn, P, S, Cu, Ni, Cr and M as alloying elements with Fe.
o, Co, Al, Nb, V, Ti, Zr, Ta, Hf,
Pb, Bi, Sb, B, N, O, rare earth element, Ca, M
One or more kinds of g are appropriately contained according to the required performance of the steel sheet, and contain unavoidable impurities. Also,
In the present invention, the thickness of the steel sheet does not impose any restrictions on the manifestation of the effect, and the present invention can be applied to a normally used sheet thickness (for example, 0.3 mm to 4 mm).

Further, in the present invention, after cleaning the surface of the Si-containing high-tensile steel sheet, Cu or Cu
The amount of the compound to be deposited is 0.1 to 3.0 g / m ^{2 in} terms of Cu amount, which is effective for non-plating. If Cu is less than 0.1 g / m ² , the effect of suppressing non-plating is not sufficient. If it exceeds 3.0 g / m ² , there is a possibility that the adhesion may be deteriorated.

The type of Cu to be deposited is metal C
u, a Cu compound having a monovalent or divalent oxidation form (eg, Cu ₂ O, CuO, CuSO _4, etc.) may be used as long as Cu is contained, and two or more of the above forms are mixed. It does not matter. However, when Cu is a Cu compound having an oxidized form, it is necessary to reduce Cu to a metal state. The adhesion method is not particularly limited, and an electrolytic method, an electroless method, a coating method, a spray method, a dipping method, a vapor deposition method, or the like can be used.

Ni or C to be attached in combination with Cu
The type of o is metal Ni or metal Co, divalent or trivalent.
Ni compounds and Co compounds (eg, N
iO, CoO, Co ₂ O ₃ , NiSO ₄ , CoSO ₄ ,
Ni (NO ₃ ) ₂ , Co (NO ₃ ) ₂ , NiCl ₂ , CoC
l _2, etc.), it may be in any form if it contains Ni or Co, may be mixed above embodiment two or more. Also, both Ni and Co may be attached. However, when Ni or Co is a compound having an oxidized form, it is necessary to reduce Ni or Co to a metal state. The total amount of Ni or Co is 0.005g
If it is less than / m ² , the effect of improving the adhesion is small. Also,
Since the effect is saturated at 5.0 g / m ² , the cost is preferably less than this.

The adhesion method is not particularly limited, and an electrolytic method, an electroless method, a coating method, a spray method, a dipping method, a vapor deposition method, or the like can be used. Also, as a procedure for attaching, a method of attaching Ni or Co after attaching Cu,
Either a method of previously depositing Ni or Co before Cu deposition or a method of depositing Ni or Co simultaneously with Cu does not hinder the effect of the present invention.

If the heating alloying treatment temperature is 550 ° C. or less, alloying is difficult to proceed, and if it exceeds 600 ° C., the control of alloying becomes difficult, and the Δ phase which deteriorates the adhesion is remarkably grown. The temperature is higher than 600 ° C. and lower than 600 ° C.

Further, in the present invention, the content of Fe in the hot-dip galvanized layer is 7% by weight by the heat alloying treatment.
After reaching １５15%, cooling is performed at a cooling rate of 10 ° C./s or more by one or more of air cooling, mist cooling, and air-water cooling. As a position to start, when the Fe content in the hot-dip galvanized layer is less than 7% by weight by the heat alloying treatment,
The progress of alloying is insufficient, and a predetermined alloy composition (Fe7 to 15)
%) Cannot be obtained. Also, if cooling is started at the time of exceeding 15%, not only the alloying may proceed excessively and a predetermined alloy composition may not be obtained, but also the adhesion may be deteriorated due to the growth of the Γ phase, Not preferred.

The cooling device may be any of air cooling, mist cooling, and air / water cooling, or may be a combination of two or more of them for cooling. If the cooling rate is less than 10 ° C./s, the effect of improving the appearance and adhesion is not sufficient, so the cooling rate is set to 10 ° C./s or more. Although the upper limit of the cooling rate is not particularly defined, the cooling here is a process including not only the improvement of the appearance and the adhesion but also the adjustment of the Fe content in the hot-dip galvanized layer, and the control of the progress of alloying is performed. From the point of view,
Alloying is easily controlled at a cooling rate of 10 ° C / s to 70 ° C / s, which is more preferable. As the air cooling gas,
Any non-oxidizing gas such as hydrogen, nitrogen, and argon gas can be used, and these may be used as a mixture.

For cleaning the steel sheet, a conventionally used method can be applied, and for example, any of alkali degreasing, electrolytic degreasing, and pickling, or a combination thereof can be applied.

The heat treatment temperature for annealing the steel sheet in the pretreatment furnace of the continuous galvanizing equipment is not particularly limited, and a normal temperature (for example, 650 to 950 ° C.) can be applied. The atmosphere may be performed according to a commonly used atmosphere method. For example, a non-oxidizing furnace-reducing furnace (3 to 25% of hydrogen, the remaining nitrogen) type, a total reducing furnace (hydrogen 3
-25%, with the balance being nitrogen). However, in the case of annealing in an oxidizing atmosphere (for example, air purge), an atmosphere for reducing generated oxides (Cu oxide, Ni oxide, Co oxide, Fe oxide, etc.) is necessary in the final stage of annealing. is there.

The hot-dip galvanizing bath may be a conventionally used condition, for example, a plating bath containing 0.01% to 5% by weight of Al and a bath temperature of 440 ° C. to 480 ° C. Further, if the molten metal is mainly composed of zinc, Pb, Cd, Ni, Co,
Fe, Ti, Mg, Nb, Mn, B, Si, Cu, C
r, P, and the like, and may further contain Al, Mg, Ti, Mn, Fe, Ni,
Predetermined amounts of Co and Cu may be added. By applying the hot-dip galvanizing in this manner by 20 to 200 g / m ² ,
It can be applied to various uses.

In the heating alloying treatment, the heating method for alloying is not particularly limited, and a heating method according to the conventional hot-dip plating equipment, such as direct heating by a combustion gas, induction heating, or direct current heating, is used. Can be used.

For the purpose of improving the paintability, weldability, lubricity, corrosion resistance, etc., on the surface of the high-tensile alloyed hot-dip galvanized steel sheet thus obtained, various electroplating, chromate treatment, Lubricity improving treatment, phosphate treatment, resin coating treatment, weldability improving treatment and the like can be performed.

[0029]

Next, examples of the present invention will be described together with comparative examples. The test material was a steel sheet having the components shown in Table 1, and the thickness was 0.8 mm for a cold-rolled steel sheet and 4.0 mm for a hot-rolled steel sheet. Further, after Cu, Ni, and Co were applied by the coating types, treatment methods, and procedures shown in Table 2, the pretreatment furnace (continuous hot-dip galvanizing equipment (atmosphere H ₂ gas 5%, N _{2 Two}
Annealed in a pretreatment furnace consisting of a preheating furnace, a heating furnace, a soaking furnace, and a cooling furnace).

The bath composition of the hot dip galvanizing bath is 0.10% A
1, the remaining zinc. The bath temperature was 460 ° C.

In the hot-dip plating, the passing time in the bath was set to 3 seconds in both the examples and the comparative examples, and the amount of zinc applied was adjusted to 60 g / m ² using a N ₂ gas wiper. For the alloying, an induction heating type heating equipment was used. The heating alloying temperature and the cooling after the heating alloying were performed under the conditions shown in Table 3.

Evaluation was made on the appearance, adhesion, and alloying speed. The appearance of the evaluation was evaluated as follows: ◎: uniform appearance with no plating or unevenness, etc., ○: slight appearance unevenness without non-plating and practically acceptable, Δ: severely uneven appearance When plating occurred and unevenness in appearance was remarkable, it was evaluated as x. The adhesiveness of the evaluation was evaluated by bending a high-tensile alloyed hot-dip galvanized steel sheet at 60 ° V and peeling off the plating at the bent portion. No peeling of the plating was evaluated as ◎, slight peeling of practically acceptable degree was evaluated as ○, a peeling with a considerable amount was evaluated as Δ, and a peeling was marked as x. The alloying speed was determined by calculating the time required for the Fe content in the plated layer after alloying to reach 10%.
A mark longer than 0 seconds was marked as x.

Examples 1 to 18 are the present invention, all of which have no plating and good appearance and adhesion.
The alloying speed was also high.

On the other hand, in Comparative Example 1, Cu
In Comparative Example 2, the amount of deposited Cu was too small due to the absence of, and non-plating occurred in each case. In Comparative Example 3, the alloying temperature was low, and significant time was required for alloying. In Comparative Example 4, the alloying temperature was too high and the plating adhesion was deteriorated.
In Comparative Example 5, the Cu content and the adhesion amount were too large, and the adhesion was slightly deteriorated.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

As described above, the present invention provides a Si-added high-tensile alloyed hot-dip galvanized steel sheet and a method for producing the same while suppressing remarkable investment in existing production equipment while minimizing equipment restrictions. It is capable of producing a steel sheet excellent in productivity by suppressing non-plating and excellent in appearance and adhesion, and greatly contributes to industrial development.

Claims (5)

[Claims] 1. A steel containing 0.1 to 2.5 Si as a component in steel.
A hot-dip galvanized steel sheet having an alloyed hot-dip galvanized layer after hot-dip galvanizing zinc or an alloy mainly composed of zinc on the surface of a steel sheet containing 5 wt%, 0.01% Cu in plating layer
A high-strength alloyed hot-dip galvanized steel sheet containing -3.0 g / m ² . 2. The high-tensile alloying melt according to claim 1, wherein the plating layer further contains one or two kinds of Ni or Co in a total amount of 0.005 to 5.0 g / m ^2. Galvanized steel sheet. 3. A steel containing 0.1 to 2.5 Si as a component in steel.
After cleaning the surface of the high-tensile steel sheet containing 0.1% by weight, the surface of the steel sheet is coated with Cu or a Cu compound in an amount of 0.1 to 3.
After depositing 0 g / m ² and annealing in a reducing or non-oxidizing atmosphere, the steel sheet is passed through molten zinc without contacting with the atmosphere, and further subjected to heat alloying at a temperature exceeding 550 ° C. to 600 ° C. A method for producing a high-tensile alloyed hot-dip galvanized steel sheet, comprising: 4. A steel containing 0.1 to 2.5 Si as a component in steel.
After cleaning the surface of the high-tensile steel sheet containing 0.1% by weight, the surface of the steel sheet is coated with Cu or a Cu compound in an amount of 0.1 to 3.
0 g / m ² , Ni or a Ni compound, or one or two or more of Co or a Co compound in a total amount of 0.005 to 5.0 g / m ^{2 as} a total of Ni and Co, and a reducing property or After annealing in a non-oxidizing atmosphere, the steel sheet is passed through molten zinc without being brought into contact with the atmosphere, and is further subjected to a heat alloying treatment at a temperature exceeding 550 ° C to 600 ° C. Manufacturing method of galvanized steel sheet. 5. After the Fe content in the hot-dip galvanized layer reaches 7 to 15% by weight by the heat alloying treatment,
5. The cooling device according to claim 3, wherein the cooling is performed at a cooling rate of 10 ° C./s or more by one or more of air cooling, mist cooling, and air-water cooling. 6. A method for producing a high-strength galvannealed steel sheet.