JP2000212711A - Production of p-containing high strength galvanized steel sheet and high strength galvannealed steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet excellent in uniformity and stickiness of a coated film, and a producing method, with which a galvannealed steel sheet without generating uneven alloying and excellent in powdering resistance can stably be produced. SOLUTION: In this producing process of a high strength galvanized steel sheet, with which the high strength steel sheet containing by wt.% >=0.02% P and/or >=0.2% Mn, is heated and annealed under non-oxidizing atmosphere and thereafter, dipped into a galvanizing bath containing Al to execute the galvanizing, or the producing process of the high strength galvannealed steel sheet further executing the alloying heat treatment of the galvanized coating, a coating composed essentially of sulfur and further, one or more kinds of metallic compounds selected among Ni, Co and Cu in the range of 1-200 mg/m2 as an amount converted into the metallic quantity, is stuck on the surface of the steel sheet prior to annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hot-dip galvanized steel sheet and a galvannealed steel sheet using a high-strength steel sheet as a base steel sheet, and relates to a hot-dip galvanized steel sheet having excellent uniformity and adhesion of a coating film. The present invention also relates to a method for producing an alloyed hot-dip galvanized steel sheet having excellent uniformity of plating film and powdering resistance.

[0002]

2. Description of the Related Art From the viewpoint of extending the life of a car body, alloyed hot-dip galvanized steel sheets have been used for a long time as a body material. The alloyed hot-dip galvanized steel sheet is manufactured by the hot-dip galvanizing method, which is easier to thicken than the electroplating method, so it has excellent corrosion resistance and low manufacturing cost, and the plating layer is an iron-zinc alloy. Therefore, it has material advantages such as excellent paint adhesion and spot weldability.

[0003] In recent years, improvement in fuel efficiency of automobiles has been called for from the viewpoint of prevention of global warming, and high strength and thin materials have been strongly demanded from the viewpoint of weight reduction of vehicles and ensuring safety. Generally, a solid solution strengthening element such as Si, Mn, or P is added to increase the strength of a steel sheet.

[0004] When a steel sheet containing P as a solid solution strengthening element is used as a plating base sheet, there is a problem that the alloying speed is remarkably reduced by P. This is because P concentrates on the steel sheet surface during annealing, and when the steel sheet is immersed in the plating bath, it reacts with Al added in the plating bath to suppress the Fe-Zn alloying reaction. This is for the purpose of forming a thick layer to strongly suppress the Fe-Zn reaction. Since such P enrichment tends to occur mainly at the grain boundaries of steel,
The alloying speed of the grain boundary is remarkably slowed, causing streak-like alloying unevenness, which adversely affects not only the surface appearance but also the chemical conversion property and the paintability. In addition, since the Fe-Al alloy reaction is sensitive to the bath composition, if a local Al concentration difference occurs in the plating bath, in the case of P-containing steel, partial alloying unevenness occurs and linear marks are formed. May occur.

Conventionally, as a method of promoting alloying,
Japanese Unexamined Patent Publication No. 60-110859 discloses 0.05 to 20 g / m ^TwoNi and Ni
The method of applying a coating layer of a base alloy prior to hot-dip galvanizing,
In addition, JP-A-5-148603 discloses a 0.1% or more sulfur compound solution.
Is disclosed in Japanese Patent Application Laid-open No.
0.001-5 g / m of inorganic compounds with a specific range of lugi^Twoof
In the range, a method to apply before hot-dip galvanizing has been proposed.
Have been.

[0006] However, the method of performing pre-plating as disclosed in Japanese Patent Application Laid-Open No. 60-110859 requires a large-scale pretreatment facility for hot-dip galvanizing, and also requires that the steel sheet be immersed in a plating bath. Since a phenomenon occurs in which the metal coated on the surface diffuses into the steel sheet during the heat annealing process, it is necessary to increase the amount of adhesion in order to obtain a sufficient effect, and there is a problem that the production cost increases.

On the other hand, the method of applying a sulfur compound disclosed in Japanese Patent Application Laid-Open No. 5-148603 has an effect of improving the alloying speed of a P-containing steel sheet, but the effect of applying only sulfur is insufficient. In order to obtain the effect, it is necessary to increase the S adhesion amount. In addition, when the amount of adhesion is increased, there arises a problem of a roll pickup and a problem that a sulfur compound easily reacts with a furnace material in an annealing furnace and extremely shortens the life of the furnace.
It is industrially difficult to simply apply a sulfur compound.

Further, as described in JP-A-8-188861, an inorganic compound applied to the surface of a steel sheet does not decompose and evaporate during annealing, is reduced by Zn or Al in a molten zinc bath, and In the technique of diffusing in a bath, according to the study of the present inventors, although the surface concentration of P during annealing is suppressed, the metal compound remaining on the steel sheet surface may cause the inhibition of wettability with molten zinc. There is. Even if non-plating does not occur, there is a problem that the molten zinc bath is contaminated by the diffusion of the inorganic compound.

In addition, for the purpose of smooth alloying, a pre-plated layer of Ni, Co, Fe, Cu
A method has been proposed in which an Fe oxide layer is formed on the surface of a steel sheet by oxidation treatment after the application in the range of up to 70 mg / m ² , and hot-dip galvanizing is performed using an ordinary CGL line. However, this method has a complicated line structure of pre-plating → oxidation treatment → reduction of steel sheet → hot-dip galvanizing, and in the hot-dip galvanizing line with a non-oxidizing furnace, the formed Fe-based oxide is not uniform And the above method cannot be applied.

Japanese Patent Application Laid-Open No. 1-139747 discloses Fe, N
After immersing the steel sheet in an organic or inorganic acid containing one or more of the i and Co compounds and an Sb compound, hot-dip galvanizing is performed in a normal CGL line, and Fe- By promoting the uniform formation of Al phase, Ti, T
A technique has been proposed to suppress very fast alloying such as i-Nb-added steel and to suppress the heterogeneous reaction of alloying. Although this method does not require new equipment such as pre-plating, it can suppress the increase in cost, but the thick Fe-Al which causes the alloying reaction delay in P-added steel
This is counterproductive for further promoting the formation of the phase and for promoting the alloying reaction.

The present inventors have studied various means for solving the above-mentioned problems, and as a result, by applying a metal compound solution containing a specific metal and sulfur to the surface of a steel sheet and performing galvanizing on a normal CGL line. And found that it is effective in preventing non-plating and accelerating the alloying speed.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in view of the above circumstances. An object of the present invention is to provide a manufacturing method capable of stably manufacturing an alloyed hot-dip galvanized steel sheet having excellent powdering resistance.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, a first invention is to provide a method for controlling the amount of Pn not less than 0.02% or more by weight.
High-strength steel sheet containing 0.2% or more is heat-annealed in a non-oxidizing atmosphere, and then immersed in a hot-dip zinc bath containing Al to perform plating. , Contains sulfur as an essential component, and further contains N
High-strength hot-dip galvanizing characterized in that one or more metal compounds containing any of i, Co, Sn and Cu are attached in the range of 1 to 200 mg / m ² in terms of metal amount. Provided is a method for manufacturing a steel sheet.

According to a second aspect of the present invention, in the first aspect, the steel sheet to which the metal compound is adhered is annealed by heating, and the metal compound is exposed to the molten zinc bath containing Al while the ground iron is exposed without covering the entire surface of the steel sheet. Provided is a method for producing a high-strength hot-dip galvanized steel sheet, characterized by performing plating by immersion.

According to a third invention, in the first invention or the second invention, the heat annealing in the non-oxidizing atmosphere is a treatment in which a soaking process is performed in a hydrogen atmosphere after heating by a direct flame reduction heating method. A method for producing a high-strength hot-dip galvanized steel sheet is provided.

According to a fourth invention, there is provided a method for producing a high-strength galvannealed steel sheet, which comprises subjecting a galvanized steel sheet to hot-dip galvanizing by the production method of the first to third inventions, and further performing an alloying heat treatment on the galvanized layer. provide.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

First, in the present invention, one or more metal compounds containing sulfur as an essential component and any one of Ni, Co, Sn and Cu on the surface of the steel sheet are converted into a metal amount. After being deposited in the range of 1 to 200 mg / m ² and then annealed in a non-oxidizing atmosphere, the metal compound is decomposed and / or reacted with the steel sheet in the heating annealing process, so that the solid solution of the metal on the steel sheet surface is reduced. At the same time, metal sulfide is mainly formed at the grain boundaries on the steel sheet surface. Since this metal sulfide brings about a pinning effect of the grain boundary in the process of recrystallization of the steel sheet crystal grains, the growth of the crystal grains is suppressed, and fine ferrite grains are formed only on the steel sheet surface. Then 0.05-0.
When plating by immersion in a molten zinc bath containing 30% Al, F
e-Zn crystals (ζ phase) are finely and uniformly generated, and a hot-dip galvanized steel sheet with excellent film uniformity and adhesion can be obtained. The metal sulfides described above are present in the form of dots on the surface of the steel sheet and are mostly ferrite crystals, so that good plating properties can be obtained without impairing wettability with molten zinc.

Although the cause of such an effect is not yet clear, the solid solution of metal on the steel sheet surface causes a decrease in the Fe surface concentration as compared with the steel sheet surface without any treatment. It is considered that the effect of suppressing the formation of the Fe-Al phase, which is the layer for suppressing the formation of the Fe-Zn crystal (ζ phase), is brought about. In addition, it is considered that fine ferrite grains are formed only in the surface layer of the steel sheet and the surface area of the steel sheet apparently increases, thereby suppressing the surface segregation of P, which is conventionally considered to promote the formation of the Fe-Al phase. Thus, by performing the treatment as in the present invention, the F content in the P-containing high-strength steel sheet is reduced.
Since it has the effect of suppressing the formation of the e-Al phase, Fe-Zn crystals (ζ phase) are finely and uniformly generated, and a hot-dip galvanized steel sheet having excellent coating uniformity and adhesion can be obtained.

The metal compound to be attached to the surface of the steel sheet must be a metal species compound that is not easily oxidized during the heat annealing of the steel sheet. For this reason, the metal species of the metal compound needs to be Ni, Co, Sn, or Cu, which has a lower oxidizing ability than Fe. Further, since the coating compound is stable up to a relatively high temperature, it is more preferable to use a sulfate capable of suppressing scattering of a sulfur component during heat annealing and capable of efficiently generating a metal sulfide.

Thereafter, an alloying treatment is performed if necessary. The present invention is also effective in producing an alloyed hot-dip galvanized steel sheet. In P-containing high-strength steel sheets, in addition to promoting the formation of the Fe-Al phase as described above, P segregation occurs at the grain boundaries of the steel sheet, so that the molten zinc and Reaction, so-called “outburst reaction”
Is suppressed. However, by applying the method of the present invention, the generation of the Fe-Al phase is suppressed, and fine ferrite grains are formed only on the steel sheet surface, so that the grain boundary segregation of P is suppressed, and the outburst reaction is suppressed. The origin of the crystal grain boundary increases. Therefore, an outburst reaction occurs at the entire interface between the galvanized steel sheet and the steel sheet, and a uniform plated film can be formed. As a result, an alloyed hot-dip galvanized steel sheet having excellent powdering resistance can be produced. Also, since the alloying speed is about the same as that of IF steel, etc., which is known for relatively fast alloying progress, it is not necessary to adjust the alloying treatment conditions depending on the steel type, and from the viewpoint of improving productivity, Is also effective.

As described above, at the time of heat annealing after the metal compound containing sulfur is attached to the surface of the steel sheet, the steel sheet is heated by a direct flame reduction heating method and then soaked in an atmosphere containing hydrogen. It is effective. That is, since the steel sheet can be rapidly heated by the direct fire reduction heating method, the decomposition and reaction of the metal compound attached to the steel sheet surface progress rapidly, and the coated material is removed by contact with the roll in the subsequent steps. This is because separation and scattering can be prevented.

[0023] In the present invention, the metal compound adhered on the surface of the steel sheet, was a 1 to 200 mg / m ² in terms of metal amount is insufficient effect is less than ^{1mg / m 2, 200mg / m} 2 If the temperature exceeds the limit, the reaction with the steel sheet is difficult to complete during the heat annealing, and the adhered compound remains on the steel sheet surface, thereby not only impairing the wettability with the molten zinc, but also transferring the remaining material to the roll and transferring the steel sheet. This is because it causes surface scratches. In addition, it is more preferable that it is in the range of 10 to 100 mg / m ² from the viewpoint of easy control of a uniform plating film and productivity.

In the present invention, the P content is specified as 0.02% or further the Mn content is specified as 0.2% or more because it is the minimum amount required to obtain the high-strength steel sheet targeted in the present invention. is there. The steel sheet targeted in the present invention only needs to satisfy the above-mentioned P content or further Mn content, and other components are not particularly limited. In addition to Fe and unavoidable impurities, C, S , Mg, Cr, Ni, Cu, Ta, Al etc.
It may contain one or more species. In addition, Nb and Ti may be added in order to manufacture an IF steel-based steel sheet. At this time, a few ppm of B may be added in order to prevent embrittlement due to secondary workability.

In order to attach the metal compound containing sulfur to the surface of the steel sheet, a method of dissolving the metal compound in water or an organic solvent, and applying, spraying, spraying or dipping the steel sheet surface can be applied. Further, a surfactant may be added for the purpose of increasing the adhesion of the compound to the steel sheet. Further, for the purpose of increasing the adhesion of the compound to the steel sheet, an organic resin may be dissolved in a solution and used as a binder. In addition to this, an electroplating method, a vapor deposition method, or the like may be used, but the present invention is not intended to form a metal film on the steel sheet surface, and the metal forms a solid solution on the steel sheet surface in a heating process,
It is also important to generate sulfides. Considering this point, the method using the above-described solution is most preferable in terms of processing efficiency and processing cost.

In the hot-dip galvanized or alloyed hot-dip galvanized layer of the coated steel sheet of the present invention, in addition to Zn, Fe, Al which are main elements, As, Bi,
Cd, Ce, Co, Cr, In, La, Li, Mg, Mn, Ni, O, P, Pb,
One or more of S, Sb, Sn, Ti, Zr and the like may be contained, and even if these are contained, the effect of the present invention is not impaired.

In the course of the alloying treatment, a method such as a gas heating method, an induction heating method, a direct current heating method or the like can be adopted, and the effect of the present invention is not changed by the difference in the alloying heating method. However, it is possible to rapidly heat the steel sheet by preferentially heating the steel sheet surface, and to use an induction heating method that can forcibly cause a reaction between iron and molten zinc on the surface layer of the steel sheet. It is most effective from the viewpoint of manufacturing stability.

The base steel sheet used in the present invention may be any of a hot-rolled steel sheet and a cold-rolled steel sheet, and can be applied to all uses using a galvanized steel sheet, such as automobiles, building materials, electric appliances and home appliances.

[0029]

EXAMPLES Six types of cold-rolled steel sheets shown in Table 1 were used as test materials.
Nickel sulfate (NiSO ₄ ), nickel sulfamate (Ni
_{(H 2 NO 3) 2)} , thiocyanate nickel (Ni (SCN) _2), stannous (SnSO ₄ sulfate), cobalt sulfate (CoSO _4), each aqueous solution of copper sulfate (CuSO _4), predetermined metal The concentration was adjusted so as to obtain an adhered amount. After coating with a bar coater, the coating was dried at 100 to 150 ° C. in a hot air drying furnace. For comparison, zinc sulfate (ZnSO ₄ ), magnesium sulfate (MgSO ₄ ),
For an aqueous solution of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ),
A steel sheet coated under the same conditions was produced.

[0030]

[Table 1]

These steel sheets were annealed and plated using a hot-dip galvanizing simulator. When plating,
The annealing atmosphere is 10% H ₂ -N ₂ (dew point -40 ° C) and the annealing temperature is 8
Plating was performed at 50 ° C., an annealing time of 60 seconds, and a galvanizing bath of 460 ° C. containing 0.12% of Al at an intruding plate temperature of 460 ° C. and an immersion time of 3 seconds. After plating, the amount of zinc deposited was adjusted to 60 g / m ² per one side with a N ₂ gas wiper. In addition, a sample that was subjected to only annealing without performing partial plating was also manufactured.

For the sample after coating and drying, the adhesion of the coating compound was evaluated by a 0T bending test, and for the sample after annealing, a tape peeling test was performed to measure the change in the amount of the compound attached before and after the test. The presence or absence of unreacted materials was evaluated.

The sample after plating was evaluated for the occurrence of non-plating, observation of the initial alloy phase morphology, and evaluation of plating adhesion by a 0T bending test.
The alloying rates were compared at 0, 525, 550, 575, and 600 ° C. for 20 seconds, and the alloying speed was determined by the temperature at which alloying was possible up to the surface layer. In addition, the alloying temperature was adjusted so that the iron content in the film was 10% ± 0.5%, and using a sample that had been subjected to the alloying treatment for 20 seconds, while observing the occurrence of alloying unevenness, A 90 degree bending test was performed to evaluate the powdering resistance.

The solution-coated steel sheet manufactured as described above,
Tables 2 to 4 show the results of evaluating various qualities of the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet together with the production conditions. The evaluation items and evaluation criteria for various qualities shown in these tables are as follows.

* 1. Adhesion of metal compound (steel after coating and drying) ○: good ×: film peeling * 2. Presence or absence of unreacted substances (steel sheet after heat annealing) ○: All reacted (no change in adhesion amount) ×: Unreacted compound remains (reduction in adhesion amount) * 3. Non-plating ○: good (no non-plating is observed) ×: non-plating is observed * 4. Initial alloy phase (SEM observation) ○: Fine ζ phase is uniformly formed ×: ζ phase is sparsely formed B: Outburst structure * 5. Plating adhesion ○: good (no cracks in the plating film, no peeling) △: cracks in the plating film ×: peeling of the plating * 6. Alloying speed ●: Too fast (alloyed at 450 ° C ± 25 ° C for 20 seconds) ○: Good (alloyed at 500 ° C ± 25 ° C for 20 seconds) △: Slightly slow (550 ° C ± 25 ° C for 20 seconds) Alloying) ×: Very slow (alloyed at 600 ° C ± 25 ° C for 20 seconds) * 7. Alloying unevenness (visual judgment) ○: good ×: streaks are observed * 8. Powdering resistance (90 degree bending) ○: Good (no plating peeling) ×: Plating peeling of processed part

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

As shown in Tables 2 to 4, in the examples of the present invention, good results were obtained for all evaluation items.
In the case where the metal compound containing sulfur was not adhered, any of the above-mentioned quality evaluation items was inferior in the comparative examples in which the type of metal and the amount of adhered metal were out of the range of the present invention.

[0040]

As described above, according to the present invention,
Hot-dip galvanized steel sheet with excellent powdering resistance that eliminates alloying unevenness and linear marks peculiar to hot-dip galvanized steel sheets with excellent uniformity and adhesion of plating films and high-strength steel sheets containing P A steel plate can be manufactured stably.

Continuing on the front page (72) Inventor: Ritaka Sakurai, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor: Masaru Sagiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Inside (72) Inventor Hisato Noro 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Etsuo Hamada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F term (reference) 4K027 AA02 AA23 AB07 AB26 AB28 AB44 AC12 AC15 AC73 AD25 AE33 4K044 AA02 AB02 BA10 BA19 BB03 BC05 CA02 CA04 CA11 CA53 CA62

Claims (4)

[Claims] 1% by weight or more of P0.02% or more Mn0.2
% Of the high-strength steel sheet containing at least 10% by heat in a non-oxidizing atmosphere, and then immersed in a molten zinc bath containing Al to perform plating. Contains sulfur as an essential component, and further contains N
High-strength hot-dip galvanizing characterized in that one or more metal compounds containing any of i, Co, Sn and Cu are attached in the range of 1 to 200 mg / m ² in terms of metal amount. Steel plate manufacturing method. 2. The steel sheet to which the metal compound is adhered is heated and annealed, and the steel sheet is immersed in a molten zinc bath containing Al in a state where the metal compound is exposed without covering the entire surface of the steel sheet. A method for producing a high-strength hot-dip galvanized steel sheet, comprising plating. 3. The method according to claim 1, wherein the heat annealing in the non-oxidizing atmosphere is a treatment of performing a soaking treatment in a hydrogen atmosphere after heating by a direct flame reduction heating method. Of manufacturing high-strength hot-dip galvanized steel sheet. 4. A method for producing a high-strength galvannealed steel sheet, further comprising the step of alloying heat treatment of a galvanized layer after galvanizing according to the method of claim 1.