JP2001279410A - Manufacturing method for galvanized steel sheet and galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet excellent in external appearance of a coated layer, a coating adhesive strength, a coating property and a weldability, which is obtained in a stable process, and its manufacturing method. SOLUTION: After sticking of an ammonium salt containing S at 0.1-1,000 mg/m2 in the amount of S on the surface of a high tension steel sheet containing Mn, a heat treatment is applied and successively the galvanizing treatment is applied and further if necessary, an alloying treatment is applied. The high tension steel sheet contains by wt.% of >=0.8% Mn or if necessary, may contain >=0.1% Si and, <0.02% P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet suitable for automobiles, wherein a high-tensile steel sheet containing Mn is used as a base steel sheet and the base steel sheet is subjected to hot-dip galvanizing. The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet having excellent plating adhesion, press formability, and weldability.

[0002]

2. Description of the Related Art In the fields of automobiles and home appliances, surface-treated steel sheets having high corrosion resistance are required in view of their usage environment, and various zinc-based plated steel sheets have been developed and put to practical use. Among them, hot-dip galvanized steel sheets such as hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets are widely used due to their lower manufacturing costs and better corrosion resistance than electrogalvanized steel sheets. I have.

[0003] On the other hand, from the viewpoint of preventing global warming, improving the fuel efficiency of automobiles is one of the major issues. With the aim of achieving both reduction in the weight of automobile bodies and ensuring safety of occupants,
There is a demand for gauge down and high strength steel sheets to be used. Generally, a solid-solution strengthening element such as Si, Mn, or P is added to increase the strength of a steel sheet. However, when the steel sheet is subjected to reduction annealing in a continuous hot-dip coated steel sheet production line or the like, these solid solution strengthening elements are selectively oxidized and concentrated on the surface. The oxides of these solid solution strengthening elements concentrated on the surface of the steel sheet significantly reduce the wettability between the steel sheet and the molten zinc during the hot-dip galvanizing treatment, so that the adhesion of the hot-dip galvanized layer is significantly reduced. In an extreme case, a phenomenon such as so-called non-plating that the molten zinc does not adhere to the steel sheet occurs. In particular, Si is known as an element that significantly deteriorates the plating property.

[0004] Further, when an alloying heat treatment is performed subsequent to hot-dip galvanizing, alloying is significantly delayed due to the presence of the oxide of the solid solution strengthening element concentrated on the surface. Therefore, in order to achieve alloying, it is necessary to extremely increase the alloying heating temperature or extremely reduce the line speed. However, when the alloying heating temperature is extremely increased, the formation of a hard and brittle alloy phase is promoted and the plating layer is easily peeled off during press molding, and when the line speed is extremely reduced, the productivity is significantly reduced. The problem arises. In addition, an increase in the alloying heating temperature and an increase in the line speed make it difficult to perform the alloying process using the conventional alloying apparatus.

[0005] Frequently changing the alloying processing conditions such as the alloying heating temperature and the line speed for each difference in the composition of the base steel sheet, that is, for each type of steel, requires time to change the conditions. In addition, there are problems that many difficulties are involved in maintaining a stable alloying process, such as a decrease in yield, a reduction in yield, and a considerable skill required to stabilize the processing conditions in a short time.

Further, when P is contained in a steel sheet in a large amount, there is a problem that a difference in alloying behavior occurs due to the segregation of P at the grain boundaries, causing uneven color tone. To cope with such a problem, for example, Japanese Patent Application Laid-Open No. 2-11746 discloses that C: 0.02% or less, Si: 0.1% or less, N: 0.01% or less, Al: 0.1% or less, Ti or Ti and A cold-rolled steel sheet containing 0.2% or less of Nb in total is previously treated with an aqueous solution containing at least one kind of thiosulfuric acid or a salt thereof, and then treated with H ₂ : 15
%, Dew point: 700 to 900 in a reducing atmosphere of + 15 ° C or less
There has been proposed a method for producing a hot-dip galvanized steel sheet which is annealed at a temperature of ℃, immersed in a hot-dip galvanizing bath at a temperature of at least 350 ° C., and then subjected to an alloying treatment.

In Japanese Patent Application Laid-Open No. 2-11746, examples of thiosulfuric acid or salts thereof include thiosulfuric acid, sodium thiosulfate, potassium thiosulfate, iron thiosulfate, magnesium thiosulfate, bismuth thiosulfate, and barium thiosulfate. There is. However, when a steel sheet immersed in an aqueous solution of thiosulfuric acid or a salt thereof or a steel sheet coated with the aqueous solution disclosed in Japanese Patent Application Laid-Open No. 2-11746 is immersed in a galvanizing bath, significant dross formation is observed in the bath. Was. If the generated dross adheres to a steel plate, it causes a pressing scratch during press forming.

For this reason, there has been a problem that the thiosulfuric acid or its salt disclosed in JP-A-2-11746 cannot be used stably in the process. In order to use these in a process, an epoch-making dross removal measure in a galvanizing bath is required. However, these dross removal countermeasures have a problem that a huge capital investment is required and permanent equipment maintenance costs are required.

JP-A-5-163558 discloses a high-strength steel sheet having a Si content of 0.2%, and JP-A-5-148603 discloses a high-strength steel sheet having a P content of 0.02% or more. A method for producing a hot-dip galvanized steel sheet has been proposed in which an aqueous solution of a sulfur compound having a concentration of 0.1% or more is applied, annealed in a non-oxidizing atmosphere, then hot-dip galvanized, and then subsequently subjected to heat alloying. . JP-A-5-163558 and JP-A-5-148603 exemplify effective sulfur compounds such as thiourea, organic thiourea, alkali thiourea, and various sulfates such as sodium sulfite, sodium sulfate, and sodium thiosulfate. Have been. However,
Immediately after application, the steel compound coated with these sulfur compounds turns brown or black, deteriorating the plating properties, and the adhered S component has poor adhesion to the steel sheet. However, there is a problem that it can easily fall off due to bending, rubbing, etc., and cannot be used stably in the process. Also, JP-A-5-163558, JP-A-5-148603
In the technology described in the above publication, the effect of suppressing the surface concentration of Si and P at the time of annealing is not sufficient, and minute non-plating is generated or locally (for example, an edge portion of a steel sheet). There were also problems such as plating.

Japanese Patent Application Laid-Open No. H5-247614 discloses that after a film containing 0.01 mg / m ² or more of sulfur alone and / or a sulfur compound in advance is formed on the surface of a steel sheet containing Si, A hot-dip galvanizing method for a silicon-containing steel sheet which is heated in a non-oxidizing atmosphere and subsequently subjected to hot-dip galvanizing has been proposed. As the sulfur compound used, Japanese Patent Laid-Open No. 5-247614, an organic compound having an SCN group of methyl thiocyanate, thiophene and its derivatives, the general formula organic compound represented by R-SO ₃ -R ', mercaptans, etc. Organic compounds having an SS bond, such as an organic compound represented by the general formula RSH, an organic compound represented by the general formula RS-R ', and methyl disulfide are exemplified. R and R 'are not only alkyl groups,
Other organic substances are also acceptable.

However, in the case of a steel sheet in which a film is formed using a sulfur compound described in Japanese Patent Application Laid-Open No. H5-247614, the color of the steel sheet changes to brown or black immediately after application, and the plating property deteriorates. The adhered S component has poor adhesion to the steel sheet, has a problem that it easily falls off due to bending or rubbing by a roll during conveyance of the steel sheet in a continuous production line, and there is a problem that it cannot be used stably in a process. Was. In addition, the technology described in Japanese Patent Application Laid-Open No. H5-247614 still has problems in that minute non-plating still occurs or non-plating occurs locally (for example, at the edge of a steel plate). .

Japanese Patent Application Laid-Open No. 11-50220 discloses that one or more of Mn content of 0.2% or more, Nb content of 0.005% or more, Ti content of 0.01% or more and P content are satisfied. After attaching sulfur or a sulfur compound to the high-strength steel sheet having an amount of 0.02% or more as sulfur in an amount of 0.1 to 1000 mg / m ² , annealing at a temperature of 680 ° C. or more in a non-oxidizing atmosphere containing hydrogen,
Thereafter, a method for producing a P-containing high-strength hot-dip galvanized steel sheet in which plating is performed by immersing in a hot-dip zinc bath containing at least 0.05 to 0.30% Al has been proposed.

Japanese Patent Application Laid-Open No. 11-50221 discloses that the surface of a steel sheet satisfying one or more of Mn content of 0.2% or more, Nb content of 0.005% or more and Ti content of 0.01% or more is satisfied. , One or more selected from carbon compounds, nitrogen compounds and boron compounds as C, B and N contents
0.1 1000 mg / m ² adhered to, and sulfur or after the sulfur compound is 0.1 1000 mg / m ² deposited as S content, annealing at temperatures above 680 ° C. in a non-oxidizing atmosphere containing hydrogen, then at least 0.05 There has been proposed a method for producing a hot-dip galvanized steel sheet in which plating is performed by immersion in a hot-dip zinc bath containing 0.30% Al.

JP-A-11-50223 discloses that the Mn content is 0.2% or more, the Nb content is 0.005% or more, the Ti content is one or more of 0.01% or more, and the Si content is 0.1 to 1000 mg / m ^{2 of} sulfur or sulfur compound as S content on a high strength steel sheet having 0.2% or more, then annealed at a temperature of 680 ° C. or more in a non-oxidizing atmosphere containing hydrogen,
Then, a method for producing a Si-containing high-strength hot-dip galvanized steel sheet in which plating is performed by immersion in a hot-dip zinc bath containing at least 0.05 to 0.30% Al has been proposed.

[0015]

In Japanese Patent Application Laid-Open Nos. 11-50220, 11-50221 and 11-50223, sodium sulfate, sodium thiosulfate, sodium sulfate, Examples thereof include inorganic sulfates such as sodium sulfite, thiocyanates such as ammonium thiocyanate and potassium thiocyanate, and aliphatic organic substances such as alkyl mercaptan and thiourea.

However, Japanese Patent Application Laid-Open No. H11-50220 discloses
When the sulfur or the sulfur compound exemplified in JP-A-11-50221 and JP-A-11-50223 is used, the details are unknown, but the following problems have occurred. Illustrated, sodium sulfate, sodium-containing sodium salts such as sodium thiosulfate, sulfur alone, sodium sulfate, potassium thiocyanate, thiourea aqueous solution is applied,
Alternatively, the steel sheet immersed in these aqueous solutions immediately turned brown or black (presumably oxidized on the surface) after coating, and the plating property was deteriorated. Furthermore, the S component adhered to the surface of the steel sheet had poor adhesion to the steel sheet, and easily dropped off due to bending by a roll, rubbing, etc., during conveyance of the steel sheet in a continuous production line. Further, although not remarkable, when an aqueous solution in which the above-mentioned sulfur or sulfur compound is dissolved is applied, there is a problem that the amount of dross generated in the zinc plating bath is increased as compared with the case where the aqueous solution is not applied.

Further, in an aqueous solution in which these S-containing sodium salt, sulfur alone, sodium sulfate, potassium thiocyanate, and thiourea are dissolved, the solution is decomposed, and the amount of S component attached to the steel sheet is not stable. occured. Also,
There is also a problem that the reaction in these aqueous solutions is slow, and a long immersion is required in order to obtain a target S component adhesion amount.

Although the detailed mechanism of the above-mentioned problems is unknown, unless the above-mentioned problems are solved, JP-A-11-50220, JP-A-11-50221,
The sulfur or sulfur compound exemplified in JP-A-11-50223 cannot be used stably in the process. Furthermore, in order to use these aqueous solutions in a process, the atmosphere during or after coating must be maintained in a non-oxidizing atmosphere, and epoch-making dross removal measures in a zinc plating bath are required. In addition, these dross removal countermeasures include:
There is a problem that a huge capital investment is required and permanent equipment maintenance costs are required.

It should be noted that Japanese Patent Application Laid-Open Nos.
In the case of using ammonium thiocyanate among sulfur or sulfur compounds exemplified in JP-A-50221 and JP-A-11-50223, the plating film characteristics were good, but the characteristics of the base iron itself during annealing. , The steel sheet becomes hard and brittle, and cracks occur during press forming.

Further, in a steel sheet containing 0.02% or more of P described in Japanese Patent Application Laid-Open No. 11-50220, spot weldability is deteriorated, and a member may be broken from a welded portion. For this reason, there is also a problem that the steel sheet which has been strengthened by P cannot be applied to uses requiring welding. The present invention
Solving the problems of the prior art described above, there is no dross generation in the plating bath, stable process production is possible, and the plating appearance, plating adhesion, plating properties, weldability, and also excellent in press formability An object of the present invention is to provide a galvanized steel sheet and a method for manufacturing the same.

[0021]

Means for Solving the Problems In order to achieve the above object, the present inventors have intensively studied a chemical agent which can be attached to the surface of a high-tensile steel sheet containing Mn to improve hot-dip galvanizing properties. As a result, it was found that hot-dip galvanizability was significantly improved by applying an S component-containing ammonium salt to the surface of a high-strength steel sheet and performing heat treatment.

First, the results of experiments conducted by the present inventors will be described. Mn: 50 mg / m ^{2 of} an S component-containing ammonium salt was adhered to the surface of a high strength steel sheet containing 1.8 mass% using an aqueous solution of ammonium sulfate, and N ₂ + 5% H ₂
Annealing (heat treatment) at 800 ° C in the atmosphere
Immediately after heat treatment, bath temperature: 470 ° C, bath composition: Zn-0.14
% Hot-dip galvanizing was performed. For the steel sheet after the heat treatment and the steel sheet after the hot-dip galvanizing treatment, the glow discharge spectroscopy (GDS) was used to determine the M
The distribution of n, S, Fe, Al, Zn was analyzed. Figure 1 shows the results.
(After heat treatment) and FIG. 2 (after hot-dip galvanizing).
For comparison, FIG. 3 shows a GDS analysis result when the steel sheet was heat-treated without attaching the ammonium salt containing the S component.

As shown in FIG. 3, when the steel sheet is heat-treated without attaching the ammonium salt, Mn concentration is observed on the surface layer. On the other hand, as shown in FIG. 1, in the steel sheet to which the ammonium salt was adhered and heat-treated, the concentration of Mn in the surface layer was significantly suppressed. The S and Mn enrichment were also observed on the steel sheet surface and on the side of the steel sheet below the surface,
X-ray diffraction showed that MnS was generated. It can be seen that MnS remains in the base iron immediately below the hot-dip galvanized layer even after the hot-dip galvanizing treatment as shown in FIG. As described above, it has been found that, by attaching an ammonium salt to the surface of a steel sheet, the surface concentration of Mn can be suppressed, and the plating property can be improved.

Further, even when an S-containing ammonium salt is dissolved in water and applied to a steel sheet or immersed in an aqueous solution in which an S-containing ammonium salt is dissolved, the steel sheet surface after application is discolored when exposed to the air. It was also found that no deterioration in plating property was observed. Furthermore, it was found that there was no problem in the adhesion between the deposit and the steel sheet, and that no dross was found even in the galvanizing bath. Furthermore, the solution in which the ammonium salt containing S is dissolved is also stable, and the target adhesion amount can be obtained by adjusting the concentration of the aqueous solution even in a short time immersion, and between the immersion time in the aqueous solution and the adhesion amount. Has a good correlation.

The present invention has been further studied and completed based on the above findings. That is, the first aspect of the present invention is to deposit 0.1 to 1000 mg / m ² of S-containing ammonium salt on the surface of a high-tensile steel sheet containing Mn,
A method for producing a hot-dip galvanized steel sheet, which comprises performing a heat treatment and then performing a hot-dip galvanizing treatment. In the first invention, an alloying treatment is immediately performed after the hot-dip galvanizing treatment. preferable.

In the first aspect of the present invention, the high-tensile steel sheet containing Mn preferably contains 0.8% or more of Mn by mass%, and further contains less than 0.02% of P. Is preferable, and further preferably contains 0.1% or more of Si. Further, the second invention is a hot-dip galvanized steel sheet having a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface of the steel sheet of the steel sheet, wherein the steel sheet is a high-tensile steel sheet containing Mn. A sulfur-enriched layer on the ground iron side as a lower layer of the hot-dip galvanized layer or the alloyed hot-dip galvanized layer from the interface between the hot-dip galvanized layer or the alloyed hot-dip galvanized layer and the ground iron of the steel sheet; The sulfur-enriched layer contains a sulfur compound in an amount of 0.1 to 1000 mg / m ^{2 in} terms of S, and extends in a depth direction from an interface between the hot-dip galvanized layer or the alloyed hot-dip galvanized layer and the steel sheet. A hot-dip galvanized steel sheet characterized by having a thickness of 0.01 μm or more, and in the second invention,
Preferably, the sulfur compound is a sulfide of Mn.
In the second invention, the high-tensile steel sheet containing Mn is
Contains 0.8% or more of Mn by mass%, or
It is preferable to use a steel sheet containing less than 02% or further containing 0.1% or more of Si.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. Unless otherwise specified, the mass% in the composition is simply described as%. In the present invention, a high-tensile steel sheet containing Mn is used as a base steel sheet for plating. The Mn content in the steel sheet is preferably set to 0.8% or more. Mn content is 0.
If it is less than 8%, the surface concentration of Mn during annealing is small, the plating property is good, and the alloying is not delayed and the powdering resistance is good. In the present invention, contained in the steel sheet
Mn is preferably set to 5% or less from the viewpoint of cold rolling property. Excess Mn of more than 5% hardens the steel and makes cold rolling difficult.

In the present invention, the chemical components other than Mn do not need to be particularly limited. However, Si, which is a solid solution strengthening element like Mn, may be contained in an amount of 0.1% or more and 2.0% or less. There is no problem even if P is contained in a large amount, but when the P content is less than 0.02%, the present invention can provide a further dramatic effect. In addition, P is a strong grain boundary segregation element, and when P is large, the effect of suppressing the surface concentration of Mn or Si may be reduced.
Preferably it is less than 02%.

Further, when the content of P is large, the spot weldability deteriorates. Therefore, the P content is preferably set to less than 0.02%. The chemical components other than those described above do not need to be particularly limited as long as they do not inhibit the formation of Mn sulfide during the heat treatment, and can be appropriately contained according to desired characteristics.
For example, C: 0.0005 to 0.5%, S: 0.05% or less, Nb: 0.
001 to 0.20% or less, B: 0.005% or less, Ti: 0.1% or less, Cr: 0.05% or less are acceptable.

In the present invention, an ammonium salt containing an S component is adhered to the surface of a high-tensile steel sheet containing Mn as described above. The surface of the steel sheet is preferably made hydrophilic by alkali degreasing and / or pickling. By providing a hydrophilic surface, the ammonium salt containing the S component adheres uniformly.

Examples of the ammonium salt containing the S component include ammonium sulfate, ammonium sulfite, ammonium thiosulfate, ferrous ammonium sulfate, ferric ammonium sulfate, aluminum ammonium sulfate solution, and magnesium ammonium sulfate solution. However, ammonium sulfate, ammonium sulfite, ammonium thiosulfate, ferrous ammonium sulfate, and ferric ammonium sulfate are preferred.

The ammonium salt containing these S components is dissolved or mixed in water or an organic solvent, mixed in a pretreatment liquid (for example, a degreasing liquid or a washing liquid), or is used to prevent rust during cold rolling. It can be used by mixing in oil. Further, a surfactant may be added to enhance the adhesion, and a reaction accelerator may be added to increase the reactivity.

The concentration of the ammonium salt containing the S component in the solution is determined by the relationship with the thickness of the adhered film.
It is preferably 50% or less, and 0.1 to 30% for ease of drying. In the present invention, it is not preferable to use a chemical containing an alkaline earth metal such as Na or K. This is because, when an alkaline earth metal such as Na or K is contained, a metal oxide having a low melting point is generated on the surface of the steel sheet and may adhere to a roll in the heat treatment furnace and damage the roll surface. Therefore, the content of the alkaline earth metal is preferably set to 3 mg / m ² or less.

The method of attaching the ammonium salt containing the S component to the steel sheet is not particularly limited, and a method which is advantageous in terms of equipment or cost may be used. For example, a method in which a steel sheet is immersed in a solution in which an ammonium salt containing an S component is dissolved and adhered, a method in which a solution in which an ammonium salt containing an S component is dissolved is applied by a roll coater and adhered, a cloth-like material The method of applying and attaching by spraying, the method of attaching by spraying with a spray, and the method of attaching an ammonium salt containing an S component by an electroplating method, an electroless plating method, a vapor deposition method, or the like are preferable.

The amount of the ammonium salt containing the S component adhered to the surface of the steel sheet is 0.1 to 1000 mg / m ^{2 in} terms of S. If the amount is less than 0.1 mg / m ² , it is insufficient to suppress the surface concentration of Mn, P, Si and the like during the heat treatment, and the plating property is reduced and non-plating occurs. On the other hand, in accordance with the amount of deposition is increased, although the effect of suppressing the surface segregation is improved, whereas, when the amount of adhesion deposit 1000 mg / m ² beyond, the effect is saturated,
An effect commensurate with the adhesion amount cannot be expected, which is economically disadvantageous and may adversely affect the plating property. In addition,
Preferably from 0.1 ~200mg / m ^2. More preferably 1 to
It is 120mg / m ^2. Note that the preferable range of the adhesion amount varies depending on production conditions such as the gas flow rate in the heat treatment furnace, the hydrogen concentration, the line speed, and the like. In addition, adjustment of the adhesion amount
It is preferable to use a ringer roll, gas wiping or the like.

As described above, the steel sheet having the surface to which the ammonium salt containing the S component is adhered is then subjected to a heat treatment before being subjected to hot-dip galvanizing. Before the heat treatment, natural drying, forced drying, or heating for drying may be performed. Alternatively, heat treatment may be performed immediately after the ammonium salt containing the S component is attached.

In the heat treatment, the heating temperature is set to 600 ° C. or higher, preferably 950 ° C. or lower. If the heating temperature is below 600 ° C,
The formation of sulfur compounds such as MnS on the surface of the steel sheet is slow, requires long-time heating, and reduces the production efficiency, which is not economical. If the heating temperature exceeds 950 ° C., there is a problem that it is too high for recrystallization and is economically disadvantageous. The atmosphere during the heat treatment is preferably non-oxidizing or reducing. Note that the heat holding time in the heat treatment is preferably 0 to 120 sec from the viewpoint of recrystallization. As the heating method, any conventionally known method such as a continuous method such as an all-radiant tube method, a gas heating method, or an induction heating method, or a batch-type heating method can be applied.

After the ammonium salt containing the S component was attached to the surface of the steel sheet and then subjected to a heat treatment, the S component attached to the surface of the steel sheet was diffused into the ground iron of the steel sheet and uniformly dispersed in the steel sheet. Reacts with Mn to produce sulfur compounds such as MnS. This sulfur compound is not limited to the steel grain,
It also forms at the grain boundaries and forms a sulfur-enriched layer. As a result, the surface concentration of Mn (the formation of Mn oxide on the surface layer) is suppressed, and the sulfur-concentrated layer forms a kind of barrier layer. It blocks the diffusion path in the steel sheet, and also suppresses the surface enrichment of Si (generation of Si oxide on the surface layer). In addition, a part of the above-mentioned sulfur compounds may be contained in the plating layer.

The sulfur-enriched layer on which MnS or the like is deposited is
From the interface between the hot-dip galvanized layer or the alloyed hot-dip galvanized layer and the steel sheet, the steel sheet has a thickness of at least 0.01 μm on the steel sheet side. That is, it preferably exists in the depth direction from the interface between the plating layer and the ground iron to a range of 0.01 μm or more. Thereby, the adhesiveness of hot-dip galvanizing improves.
On the other hand, the range in which the sulfur compound exists
When only the surface layer is less than 0.01 μm, the effect of suppressing the concentration of Mn, Si, etc. on the surface becomes insufficient, and although local plating occurs, non-plating occurs or the alloy phase is The growth rate becomes non-uniform, and streaks occur.

The steel sheet subjected to the above heat treatment is immediately subjected to a hot dip galvanizing treatment. The hot-dip galvanizing treatment is preferably performed by immersing a steel sheet (base steel sheet) in a hot-dip zinc bath at a bath temperature of 450 to 550 ° C. As the molten zinc bath, it is preferable to use a conventionally used molten zinc bath having a composition containing 0.1 to 0.2% by mass of Al or further containing 0.005 to 0.05% by mass of Fe. If the Al content in the molten zinc bath is less than 0.1% by mass, the steel sheet and zinc easily react in the plating treatment, and a large amount of the Fe-Zn alloy phase is generated. For this reason, plating adhesion deteriorates. Also, the Al content is 0.
If the content exceeds 2% by mass, the steel sheet reacts with Al to form a thick Fe-Al
Produces an alloy phase. Therefore, alloying after the plating process is significantly delayed.

The bath temperature of the molten zinc bath during the plating process is 450 to
The temperature should be 550 ° C. When the bath temperature is lower than 450 ° C., the formation of an appropriate Fe—Al alloy phase during the plating process is suppressed. on the other hand,
When the bath temperature exceeds 550 ° C, the formation of the Fe-Zn alloy phase is promoted, and the plating adhesion is deteriorated, and the erosion by zinc is promoted in the melting furnace holding the zinc bath, and the wall surface of the melting furnace is deteriorated. . In the plating bath, Fe, Si, Mg, Mn, N
There is no problem even if unavoidable impurities such as i, Pb, Sb, Sn, La, In, Ce, Cd, and Co are contained.

The amount of the hot-dip galvanized coating may be adjusted by a generally known method such as gas wiping.
It is preferably about 120 g / m ² . By performing an alloying process after the plating process, an alloyed hot-dip galvanized steel sheet may be obtained. The average Fe content of the plating layer after the alloying treatment is preferably set to 7 to 13% by mass. If the average Fe content of the plating layer is less than 7% by mass, a part of η phase (Zn phase) remains, alloying is not completed, or a relatively soft ζ phase (Fe- Zn alloy phase) remains in large quantities,
Deterioration of flaking resistance during press molding. On the other hand, when the average Fe content of the plating layer exceeds 13% by mass, a hard and brittle Γ phase (high Fe content) is formed at the interface between the plating layer and the base steel sheet.
Fe-Zn alloy phase) remains and deteriorates the powdering resistance during press molding.

The heating temperature of the steel sheet in the alloying treatment is 45
The temperature is preferably from 0 to 600 ° C. If the heating temperature is lower than 450 ° C., a long-time heat treatment or a long alloying furnace is required to make the Fe content of the plating layer 7% by mass or more,
Alternatively, measures such as lowering the transport speed of the steel plate are required, and the productivity is reduced. On the other hand, when the heating temperature exceeds 600 ° C., a hard and brittle Γ phase is formed in a short time of heating, and the powdering resistance is deteriorated.

The method of heating the steel sheet during the alloying treatment is not particularly limited, and any of a gas heating method, an induction heating method, a current heating method and the like can be applied. The hot-dip galvanized steel sheet obtained by the above-described manufacturing method has a hot-dip galvanized layer, or an alloyed hot-dip galvanized layer on the ground iron surface of the steel sheet, and further has the hot-dip galvanized layer or the alloyed hot-dip galvanized layer. And a steel sheet having a sulfur-enriched layer on the base iron side as a lower layer of the hot-dip galvanized layer or the alloyed hot-dip galvanized layer from an interface between the steel sheet and the steel sheet. MnS and the like are precipitated as sulfur compounds in the sulfur-enriched layer. The thickness of the sulfur-enriched layer is 0.01 μm or more in the depth direction from the interface between the hot-dip galvanized layer or the alloyed hot-dip galvanized layer and the
The following is preferred. The thickness of the sulfur-enriched layer is 0.01μ
If it is less than m, the surface concentration of solid solution strengthening elements such as Mn, Si, and P cannot be suppressed. If the thickness of the sulfur-enriched layer exceeds 1.0 μm, there is a problem that the steel becomes hard and the mechanical properties (eg, elongation) deteriorate.

The thickness of the sulfur-enriched layer is determined by the cross section of the hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet.
It is preferable to determine by quantitative analysis with a line microanalyzer (EPMA) or by performing component analysis in the depth direction by the GDS method. In this case, in the present invention, the range where the S content (S strength) exceeds the S content in the base steel sheet is defined as the thickness of the sulfur-enriched layer. Therefore, in the present invention,
The sulfur-enriched layer includes both the case where the sulfur compound is precipitated and the case where the sulfur is simply concentrated. Note that the presence of the sulfur-enriched layer caused Si, M
It advantageously acts to suppress the surface concentration of n and P.

In the hot-dip galvanized steel sheet of the present invention,
The formed sulfur-enriched layer contains a sulfur compound in an amount of 0.1 to 1000 mg / m ^{2 in} terms of S (including sulfur that is not a sulfur compound). The amount of sulfur in the sulfur-enriched layer is 0.1m
If it is less than g / m ² , it is insufficient to suppress the surface concentration of Mn, P, Si, etc. during the heat treatment, and the plating property is reduced and non-plating occurs. On the other hand, when the sulfur content is more than 1000 mg / m ^2,
The effect is saturated and the effect corresponding to the amount of sulfur cannot be expected, which is economically disadvantageous. Preferably, it is 0.1 to 200 mg / m ² . More preferably 1~120mg / I m ^2.

The amount of sulfur in the sulfur-enriched layer is determined by first using a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet by a general wet analysis method (acid dissolution method, alkali electrolysis method, etc.). The total amount of S contained in is determined. Then, the amount of sulfur in the sulfur-enriched layer can be calculated by subtracting the S content in the base steel sheet as a background. The S content in the base steel sheet is determined by, for example, dissolving and removing the plating layer and the sulfur compound with an appropriate acid solution (hydrochloric acid or the like) and then quantifying the S content in the base steel sheet by wet analysis or mechanical polishing. After removing the hot-dip galvanized layer and the sulfur compound layer by, for example, the S content of the base steel sheet may be quantified by wet analysis.

The amount of S adhered to the ammonium salt containing S can be determined by dissolving and removing only the attached matter with water or an acid, and quantifying the amount of S by wet analysis. The amount of S of the steel sheet subjected to only the heat treatment after the attachment of the ammonium salt containing S is obtained by subtracting the S amount in the steel after removing the sulfur-enriched layer on the steel surface by grinding from the total S amount in the steel as a background. Thus, it can be quantified.

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example 1) Cold rolled steel sheet having the composition shown in Table 1 (sheet thickness: 0.7 to
1.2 mm), subjected to alkali degreasing and pickling treatments, and then uniformly applying an aqueous solution of an ammonium salt containing the S component shown in Table 2 to the surface of the cold-rolled steel sheet using a bar coater, and immediately drying with a dryer. did. Ammonium sulfate, ammonium thiosulfate, and ammonium ferrous sulfate were used as ammonium salts containing the S component. In addition,
The concentrations of ammonium salts in the aqueous solution are 3% and 10%, respectively.
% And 30%. In addition, as a comparative example, the case where no drug was attached and the case where an aqueous solution of a drug other than the ammonium salt containing the S component was applied and attached were also carried out.

The amount of the drug adhered was 80
The substance was immersed in warm water and stirred to dissolve the deposit, and the amount of S in the solution was quantified by an atomic absorption method. Next, these steel sheets were subjected to heat treatment and hot-dip galvanizing treatment using a hot-dip galvanizing simulator. The heat treatment conditions were as follows: sheet temperature: 850 ° C., holding time: 60 seconds, atmosphere: N ₂ -5 vol% H ₂ (dew point: -40 ° C.). The hot-dip galvanizing treatment conditions were as follows: bath composition: 0.14 mass% Al-Zn bath temperature: 470 ° C (≒ plate temperature) Immersion time: 2 seconds Adhesion amount: 30 g / m ^{2 on} one side (adjusted with gas wiper) .

Incidentally, all the steel sheets were further subjected to an alloying treatment after the galvanizing treatment. The alloying treatment conditions were as follows: sheet temperature: 490, 520, 550 ° C., three levels, holding time: 30 seconds. The average Fe content in the alloyed hot-dip galvanized layer was determined by wet-analyzing the plated layer.

First, the amount of sulfur in the sulfur-enriched layer and the depth of the sulfur-enriched layer were measured for the steel sheet after the galvanizing treatment. The sulfur content of the sulfur-enriched layer was determined by subtracting the S content in the base steel sheet obtained by wet analysis from the total S content in the hot-dip galvanized steel sheet obtained by wet analysis. As the base steel sheet for sulfur analysis, a hot-dip galvanized steel sheet was used by immersing it in hydrochloric acid to dissolve and remove the plating layer. Also,
As for the depth of the sulfur-enriched layer, the distribution of S in the depth direction was obtained by GDS analysis, and the range showing the S intensity exceeding the S content in the base steel sheet was defined as the depth of the sulfur-enriched layer.

Further, the steel sheet after the hot-dip galvanizing treatment was subjected to a plating property test and a ball impact test to evaluate the plating property and the plating adhesion. In addition, the test method was as follows. (1) Plating property test The galvanized surface of the hot-dip galvanized steel sheet was magnified 10 times,
The occurrence of non-plating was visually observed to evaluate the plating property. In addition, the case where the number of unplated portions was 5 or more per 1 m ² was x, the case where the number was less than 5 to 1 or more, and the case where 0 was 0. (2) Ball impact test (plating adhesion test) In the ball impact test, a 1 kg weight is dropped from a height of 1 m onto a hot-dip galvanized steel sheet placed on a 1/2 inch diameter hemispherical projection. Then, the peeling state of the plating layer is investigated. The peeling state of the plating layer was evaluated by bonding a cellophane adhesive tape and peeling it off to evaluate the plating adhesion. In addition,
The peeling state of the plating layer after peeling off the cellophane tape was evaluated as × with plating peeling, Δ with no plating peeling / plating crack, and ○ with plating peeling and no cracking.

Next, an appearance test, a powdering resistance test, a cup drawing test, and a spot welding test were performed on the galvannealed steel sheet. (3) Appearance test The appearance of each galvannealed steel sheet is visually observed,
The situation such as adhesion of foreign matter, uneven color tone, or uneven alloying was investigated. The observation results were as follows: ○: good without foreign matter adhesion, color tone unevenness and alloying unevenness, Δ: fine foreign matter adhesion or thin color tone unevenness or fine streaky alloying unevenness occurred, ×: clear foreign matter adhesion or clear Evaluation was made as color tone unevenness, clear streak-like alloying unevenness, or local burn unevenness. (4) Powdering resistance test A 90 ° bending back was performed on a bending test piece (30mm width × 40mm length) obtained from each galvannealed steel sheet, and then a cellophane adhesive tape was attached to the plating surface and pulled. After peeling off, the powdering resistance was evaluated based on the amount of plating adhered to the tape. 1000 cps Zn on 24mm wide tape
The following were evaluated as ○, 1000 or more and 2000 cps or less as Δ, and 2000 cps or more as ×. (5) Cup drawing test (slidability test) A test piece (φ73) taken from each galvannealed steel sheet
mm disc), after applying cleaning oil to both sides, punch diameter:
33mm, wrinkle pressure: 500kgf (4.90kN), drawing ratio 2.
A 0 cup was molded. 24 mm wide on the side walls of these cups
Adhere the cellophane adhesive tape and peel it off, 8mm
The amount of Zn adhering to the tape having a length of 24 mm and a width of 24 mm was measured, and the slidability was evaluated. ○, when the amount of Zn adhering to the tape is 200 cps or less,
200 or more and 300 cps or less were evaluated as △, and 300 cps or more as x. (6) Spot welding test Some galvannealed steel sheets (sheet thickness: 0.8 mm) are superimposed on each galvanized steel sheet and a frustoconical electrode made of Cu-Cr alloy (tip diameter: 5 mmφ) is used. , Pressure: 20
0kgf (1.96kN), initial pressurizing time: 30 cycles, energizing time: 10 cycles, holding time: 5 cycles, welding current: 9
Continuous welding was performed under welding conditions of kA, and the number of continuous welding until electrode replacement was used as one index of spot weldability. The number of continuous hits was 3000 or more, ○, less than 3000 to 2000 or more, Δ, and less than 2000 ×. In addition, the tensile shear strength of the spot weld was determined,
It was used as one index of spot weldability. Tensile shear strength 15
kN or more was rated as ○, and less than 15 kN was rated as x.

Table 2 shows the results.

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

[Table 3]

Each of the examples of the present invention is a hot-dip galvanized steel sheet excellent in plating quality such as plating appearance, plating properties, plating adhesion and the like, and weldability. On the other hand, in any of Comparative Examples outside the scope of the present invention, either the plating quality or the weldability was deteriorated. (Example 2) After subjecting a cold-rolled steel sheet having the composition shown in Table 1 to alkali degreasing treatment and pickling treatment, the cold-rolled steel sheet was heated to a liquid temperature of 60%.
After immersion in an aqueous solution containing 30% of ammonium thiosulfate at 1 ° C. for 1 second, 10 seconds and 30 seconds, it was immediately pulled up and dried with a dryer.

Next, these steel sheets were subjected to a heat treatment under the conditions shown in Table 3 in an atmosphere of N ₂ -5 vol% H ₂ (dew point: -40 ° C.) using a hot-dip plating simulator. Under the same conditions, hot dip galvanizing and alloying were performed. First, the amount of sulfur in the sulfur-enriched layer and the depth of the sulfur-enriched layer were measured for the steel sheet after the hot-dip galvanizing treatment in the same manner as in Example 1.

Further, a plating property test and a ball impact test were performed on the steel sheet after the hot-dip galvanizing treatment under the same test conditions as in Example 1 to evaluate the plating property and the plating adhesion. Further, an appearance test, a powdering resistance test, a cup drawing test, and a spot welding test were performed on these galvannealed steel sheets under the same test conditions as in Example 1.

Table 3 shows the results.

[0063]

[Table 4]

Each of the examples of the present invention is a hot-dip galvanized steel sheet excellent in plating quality such as plating appearance, plating properties, plating adhesion and the like, and weldability. On the other hand, in any of Comparative Examples outside the scope of the present invention, either the plating quality or the weldability was deteriorated. (Example 3) A cold-rolled steel sheet (Steel No. C) having the composition shown in Table 1 was subjected to alkaline degreasing treatment, and then an aqueous solution of ammonium sulfate having a concentration shown in Table 4 was applied to the surface of the cold-rolled steel sheet using a roll coater. Then, the sulfur compound in an amount (in terms of S) shown in Table 4 was adhered and dried with a drier. N ₂ -5 vo
1% H ₂ (dew point: −40 ° C.), heat treatment under the conditions shown in Table 3, hot-dip galvanizing under the same conditions as in Example 1, and then alloy under the conditions shown in Table 4. A hot-dip galvanized steel sheet was obtained.

First, the amount of sulfur in the sulfur-enriched layer and the depth of the sulfur-enriched layer were measured for the steel sheet after the hot-dip galvanizing treatment in the same manner as in Example 1. Further, a plating property test and a ball impact test were performed on the steel sheet after the hot-dip galvanizing treatment under the same test conditions as in Example 1 to evaluate the plating property and the plating adhesion. Further, an appearance test, a powdering resistance test, a cup drawing test, and a spot welding test were performed on these galvannealed steel sheets under the same test conditions as in Example 1.

Table 4 shows the results.

[0067]

[Table 5]

Each of the examples of the present invention is a hot-dip galvanized steel sheet excellent in plating quality such as plating appearance, plating properties, plating adhesion and the like, and weldability. On the other hand, in any of Comparative Examples outside the scope of the present invention, either the plating quality or the weldability was deteriorated. (Example 4) After subjecting a cold-rolled steel sheet (Steel No. G) having the composition shown in Table 1 to alkaline electrolytic degreasing treatment, a chemical solution having a concentration shown in Table 5 was applied to the surface of the cold-rolled steel sheet using a doctor blade. Then, a sulfur compound in an amount shown in Table 5 (in terms of S) was adhered and dried with a drier. N ₂ -7 vo
After heat treatment under the conditions shown in Table 5 in an atmosphere of l% H ₂ (dew point: -40 ° C), hot dip galvanization was performed. The hot-dip galvanizing conditions were as follows: bath composition: 0.14% Al-0.05Fe-Zn bath temperature: 470 ° C (≒ plate temperature) Immersion time: 2 seconds Adhesion amount: 55 g / m ^{2 on} one side (adjusted with gas wiper) And

Next, these steel sheets were further subjected to alloying treatment under the conditions shown in Table 5 to obtain alloyed hot-dip galvanized steel sheets. The Fe content in the plated layer after alloying was determined, and the alloying rates were compared. The Fe content in the plated layer after alloying is
It was determined by wet analysis. Table 5 shows the results.

[0070]

[Table 6]

In each of the examples of the present invention, when compared with the comparative example at the same alloying time, the Fe in the plated layer after the alloying was compared.
It can be seen that the content is increasing, and the alloying speed is high and alloying is promoted.

[0072]

As described above, according to the present invention,
Even if hot-dip galvanizing or further alloying treatment is applied to a high-strength steel sheet containing Mn as a base steel sheet, coated steel sheets with excellent plating appearance, plating adhesion, plating properties and weldability can be manufactured with high productivity. As a result, the application can be expanded for use in automobiles, which require a high level of plating quality.

[Brief description of the drawings]

FIG. 1 is a graph showing the distribution in the depth direction of each element in a cross section of a steel sheet after heat treatment to which the method of the present invention is applied.

FIG. 2 is a graph showing the distribution in the depth direction of each element in a cross section of a steel sheet after a hot dip galvanizing process to which the method of the present invention is applied.

FIG. 3 is a graph showing the distribution in the depth direction of each element in a cross section of a steel sheet after heat treatment in a comparative example.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 2/02 C23C 2/02 2/28 2/28 2/40 2/40 // C21D 9/46 C21D 9/46 J (72) Inventor Kazuaki Kyono 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term in Technical Research Institute, Kawasaki Steel Co., Ltd. 4K027 AA02 AA23 AB02 AB07 AB13 AB15 AB26 AB28 AB42 AC12 AC15 AC73 AE23 4K037 EA01 EA04 EA05 EA15 EA16 EA19 EA23 EA25 EA27 EA31 FH01 FH03 FJ02 FJ04 FJ05 FJ06 GA05 JA06

Claims (8)

[Claims] The present invention is characterized in that an S-containing ammonium salt of 0.1 to 1000 mg / m ² in S conversion is adhered to the surface of a high-tensile steel sheet containing Mn, and then heat-treated, followed by hot-dip galvanizing. Method for producing a hot-dip galvanized steel sheet. 2. The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein an alloying treatment is performed immediately after the hot-dip galvanizing treatment. 3. The high-tensile steel sheet containing Mn contains Mn in mass%.
The method for producing a hot-dip galvanized steel sheet according to claim 1 or 2, which contains 0.8% or more. 4. The steel sheet according to claim 1, wherein the high-tensile steel sheet containing Mn further contains, by mass%, P: less than 0.02% and / or Si: 0.1% or more. Production method of hot-dip galvanized steel sheet. 5. A hot-dip galvanized steel sheet having a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on a ground iron surface of a steel sheet, wherein the steel sheet is a high-tensile steel sheet containing Mn. From the interface between the galvanized layer or the alloyed galvanized layer and the ground iron of the steel sheet, as a lower layer of the galvanized layer or the alloyed galvanized layer,
It has a sulfur-enriched layer on the base iron side, and the sulfur-enriched layer
Characterized in that it has a 0.1 1000 mg / m include ² sulfur compounds, and the galvanized layer or galvannealed layer and 0.01μm or more thickness in the depth direction from the interface between the base steel of the steel sheet Hot-dip galvanized steel sheet. 6. The galvanized steel sheet according to claim 5, wherein the sulfur compound is a sulfide of Mn. 7. The high-tensile steel sheet containing Mn contains Mn in mass%.
7. The hot-dip galvanized steel sheet according to claim 5, wherein the hot-dip galvanized steel sheet contains at least 0.8%. 8. The steel sheet according to claim 5, wherein the high-tensile steel sheet containing Mn further contains, by mass%, P: less than 0.02% and / or Si: 0.1% or more. Hot dip galvanized steel sheet.