JP6052270B2 - High-strength hot-dip galvanized steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high-strength hot-dip galvanized steel sheet using a high-strength steel sheet containing Si as a base material and a method for producing the same.

  2. Description of the Related Art In recent years, surface-treated steel sheets imparted with rust resistance to raw steel sheets, particularly galvanized steel sheets and galvannealed steel sheets excellent in rust resistance have been used in fields such as automobiles, home appliances and building materials. In addition, from the viewpoint of improving automobile fuel efficiency and improving automobile crash safety, high strength steel sheets are applied to automobiles in order to reduce the thickness of the body by increasing the strength of the body material and to reduce the weight and strength of the body itself. Has been promoted.

  In general, hot dip galvanized steel sheets use thin steel sheets obtained by hot-rolling or cold-rolling slabs as the base material, and the base steel sheets are recrystallized and annealed in a CGL annealing furnace, and then hot-dip galvanized. Manufactured. Further, the alloyed hot-dip galvanized steel sheet is manufactured by further alloying after hot-dip galvanizing.

In order to increase the strength of the steel sheet, addition of Si or Mn is effective. However, during continuous annealing, Si and Mn are oxidized in a reducing N ₂ + H ₂ gas atmosphere in which Fe does not oxidize (reducing Fe oxide), and Si or Mn oxide is formed on the outermost surface of the steel sheet. Form. Since the oxides of Si and Mn reduce the wettability between the molten zinc and the underlying steel sheet during the plating process, non-plating frequently occurs in steel sheets to which Si or Mn is added. In addition, even when non-plating is not achieved, there is a problem that plating adhesion is poor.

  As a method for manufacturing a hot-dip galvanized steel sheet using a high-strength steel sheet containing a large amount of Si or Mn as a base material, Patent Document 1 discloses a method of performing reduction annealing after forming a steel sheet surface oxide film. However, in Patent Document 1, good plating adhesion cannot be obtained stably.

  On the other hand, in Patent Documents 2 to 8, the oxidation rate and reduction amount are regulated, the oxide film thickness is measured in the oxidation zone, and the effect is stabilized by controlling the oxidation condition and the reduction condition from the measurement result. Such a technique is disclosed.

In Patent Document 9 to 11, oxide - defines a gas composition such as _{O 2, H 2, H 2} O in the atmosphere in the reducing step.

JP 55-122865 A JP-A-4-202630 Japanese Patent Laid-Open No. 4-202631 JP-A-4-202632 JP-A-4-202633 Japanese Patent Laid-Open No. 4-254531 JP-A-4-254532 JP-A-7-34210 Japanese Patent Laid-Open No. 2004-2111157 JP 2005-60742 A JP 2007-291498 A

  When the manufacturing method of the hot dip galvanized steel sheet shown in Patent Documents 1 to 8 is applied, sufficient plating adhesion is not necessarily obtained by forming an oxide of Si or Mn on the steel sheet surface in continuous annealing. I understood that.

  In addition, when the manufacturing methods described in Patent Documents 9 to 10 are applied, the plating adhesion is improved, but due to excessive oxidation in the oxidation zone, the oxide scale adheres to the in-furnace roll, and the steel sheet is pressed. There is a problem that a so-called pickup phenomenon occurs.

  It has been found that the manufacturing method described in Patent Document 11 is effective in suppressing the pickup phenomenon, but does not necessarily provide good workability and fatigue resistance. It was also found that good plating adhesion could not be obtained.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the high strength hot-dip galvanized steel plate excellent in plating adhesiveness, workability, and fatigue resistance, and its manufacturing method.

  As described above, the addition of solid solution strengthening elements such as Si and Mn is effective for increasing the strength of steel. And about the high strength steel plate used for a motor vehicle use, since press molding is needed, the improvement of the balance of intensity | strength and ductility is requested | required. For these, Si and Mn have the advantage of being able to increase the strength without impairing the ductility of the steel, so the Si-containing steel is very useful as a high-strength steel plate. However, when manufacturing a high-strength hot-dip galvanized steel sheet using Si-containing steel and Si / Mn-containing steel as a base material, there are the following problems.

  Si and Mn form an oxide of Si and / or Mn on the outermost surface of the steel sheet in an annealing atmosphere, and deteriorate the wettability between the steel sheet and molten zinc. As a result, surface defects such as non-plating occur. Moreover, even when non-plating is not achieved, the plating adhesion is remarkably inferior. This is thought to be due to the fact that the oxides of Si and / or Mn formed on the surface of the steel sheet remain at the interface between the plating layer and the steel sheet, thereby deteriorating the plating adhesion.

  Moreover, in the Si-containing steel, the reaction between Fe and Zn is suppressed in the alloying process after the hot dipping process. Therefore, an alloying process at a relatively high temperature is required to allow the alloying to proceed normally. However, when the alloying treatment is performed at a high temperature, sufficient workability cannot be obtained.

  For the problem that sufficient workability cannot be obtained when alloying at high temperature, the remaining austenite phase in steel necessary to ensure ductility is decomposed into pearlite phase, so sufficient workability It was found that could not be obtained. In addition, when the hot dip plating and alloying treatment are performed after cooling and reheating to the Ms point or less before hot dip plating, the martensite phase is tempered to ensure strength, and sufficient strength is obtained. It was found that could not be obtained. Thus, the Si-containing steel has a problem that a desired mechanical property value cannot be obtained because the alloying temperature becomes high.

  Furthermore, in order to prevent oxidation at the outermost surface of the steel sheet of Si, a method of performing reduction annealing after the oxidation treatment is effective, but at that time, the oxide of Si moves along the grain boundary inside the steel sheet surface layer. Form. Then, it turned out that a fatigue resistance property is inferior. This is considered to occur because fatigue cracks progress from the oxide formed at the grain boundary.

As a result of repeated examination based on the above, the following knowledge was obtained. When a high-strength steel sheet containing Si or Mn is used as a base material, it is reduced after oxidation treatment to suppress oxidation of the steel sheet and molten zinc at the outermost surface of the steel sheet, which causes a reduction in wettability between the steel sheet and molten zinc. Although it is effective to perform annealing, the amount of iron oxide necessary to suppress oxidation of Si and Mn on the steel sheet surface is sufficient by changing the O ₂ concentration of the atmosphere in which the oxidation treatment is performed in the former stage and the latter stage. Picking up with iron oxide can be prevented while ensuring. Furthermore, for high temperature alloying treatment with Si-containing steel, the H ₂ O concentration in the reduction annealing is appropriately controlled, and the alloying temperature is related to the H ₂ O concentration in the reduction annealing. By prescribing, the alloying temperature can be lowered, and the workability and fatigue resistance can be improved. Moreover, plating adhesion can be improved. That is, by performing oxidation treatment with controlled O ₂ concentration and alloying treatment at a temperature according to the H ₂ O concentration in reduction annealing, high plating adhesion, workability, and fatigue resistance are excellent. It was found that a high-strength galvannealed steel sheet was obtained.

    Furthermore, by suppressing the oxides of Si and / or Mn formed at the interface between the plating layer and the steel sheet, the reactivity between the plating and the steel sheet can be increased over a wide area on the surface of the steel sheet. It was found that good plating adhesion was obtained.

The present invention is based on the above findings, and features are as follows.
[1] A steel plate containing, by mass%, C: 0.3% or less, Si: 0.1-2.5%, Mn: 0.5-3.0%, the balance being Fe and inevitable impurities On the other hand, when performing the hot dipping process after performing the oxidation treatment and then performing the reduction annealing, in the oxidation treatment, in the preceding stage, in an atmosphere having an O ₂ concentration of 1000 volume ppm or more and an H ₂ O concentration of 1000 volume ppm or more And heated at a temperature of 600 to 850 ° C. in an atmosphere having an O ₂ concentration of less than 1000 volume ppm and an H ₂ O concentration of 1000 volume ppm or more in the latter stage, , H ₂ concentration 5 to 30% by volume, H ₂ O concentration 500 to 5000 ppm by volume, and the balance is heated at a temperature of 650 to 900 ° C. in an atmosphere composed of N ₂ and inevitable impurities. Molten zinc A manufacturing method for steel sheets.
[2] A steel plate containing, by mass%, C: 0.3% or less, Si: 0.1-2.5%, Mn: 0.5-3.0%, the balance being Fe and inevitable impurities On the other hand, after performing oxidation treatment and then performing reduction annealing, when performing hot-dip plating treatment and alloying treatment, in the oxidation treatment, in the previous stage, O ₂ concentration 1000 volume ppm or more, H ₂ O concentration 1000 volume ppm In the above atmosphere, it is heated at a temperature of 400 to 750 ° C., and in the latter stage, it is heated at a temperature of 600 to 850 ° C. in an atmosphere having an O ₂ concentration of less than 1000 ppm by volume and an H ₂ O concentration of 1000 ppm by volume or more, In the reduction annealing, the alloy is heated at a temperature of 650 to 900 ° C. in an atmosphere of H ₂ concentration 5 to 30% by volume, H ₂ O concentration 500 to 5000 ppm by volume, and the balance is N ₂ and inevitable impurities. In the conversion process, A method for producing a high-strength hot-dip galvanized steel sheet, wherein the treatment is performed at a temperature T (° C.) satisfying the following formula for 10 to 60 seconds.
−50 log ([H ₂ O]) + 650 ≦ T ≦ −40 log ([H ₂ O]) + 680
However, [H ₂ O] represents the H ₂ O concentration (volume ppm) during reduction annealing.
[3] The oxidation treatment is performed by a direct-fired burner furnace (DFF) or a non-oxidizing furnace (NOF) at an air ratio of 1.0 or more and less than 1.3 in the preceding stage, and an air ratio of 0.7 or more and 0.00 in the latter stage. The method for producing a high-strength hot-dip galvanized steel sheet according to the above [1] or [2], wherein the method is performed at less than 9.
[4] The high-strength melting according to any one of the above [1] to [3], wherein the difference in H ₂ O concentration between the upper part and the lower part in the furnace is 2000 ppm by volume or less in the reduction annealing. Manufacturing method of galvanized steel sheet.
[5] The hot dip galvanizing treatment is performed in a hot dip galvanizing bath having a component composition comprising Zn and inevitable impurities, with an effective Al concentration in the bath of 0.095 to 0.175% by mass. The manufacturing method of the high intensity | strength hot-dip galvanized steel plate in any one of said [1]-[4].
[6] The hot dip galvanizing treatment is performed in a hot dip galvanizing bath having a component composition consisting of Zn and inevitable impurities, with an effective Al concentration in the bath of 0.095 to 0.115% by mass. The manufacturing method of the high intensity | strength hot-dip galvanized steel plate in any one of said [1]-[4].
[7] As a component composition, Al: 0.01 to 0.1%, Mo: 0.05 to 1.0%, Nb: 0.005 to 0.05%, Ti: 0.0. 005 to 0.05%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cr: 0.01 to 0.8%, B: 0.0005 to 0.005% 1 type or 2 types or more of these are contained, The manufacturing method of the high intensity | strength hot-dip galvanized steel plate in any one of said [1]-[6] characterized by the above-mentioned.
[8] A high-strength hot-dip galvanized steel sheet produced by the production method according to any one of [1] to [7] above, wherein an Fe—Zn alloy phase, Fe— A high-strength hot-dip galvanized steel sheet characterized in that a reaction phase composed of at least one of an Al alloy phase and an Fe—Zn—Al alloy phase has an area ratio of 70% or more.

  The high strength in the present invention means that the tensile strength TS is 440 MPa or more. Further, the high-strength hot-dip galvanized steel sheet of the present invention includes both a case where a cold-rolled steel sheet is used as a base material and a case where a hot-rolled steel sheet is used as a base material. In addition to the above, those subjected to further alloying treatment are included.

  According to the present invention, a high-strength hot-dip galvanized steel sheet excellent in plating adhesion, workability, and fatigue resistance can be obtained.

It is a diagram showing the relationship between _{H 2} O concentration of the reducing annealing furnace (ppm) and the tensile strength TS and elongation EL of the product (MPa ·%). It is a figure which shows the SEM image which observed the cross section of the steel plate surface layer part. It is a diagram showing the relationship between H _{2 O} concentration changes alloyed temperature of the reduction furnace. It is a figure which shows the SEM image which observed the reaction phase formed in the interface of a steel plate and a plating phase.

Hereinafter, the present invention will be specifically described.
In the following description, the unit of the content of each element of the steel component composition and the unit of the content of each element of the plating layer component composition are “mass%”, and are simply represented by “%” unless otherwise specified. The units of O ₂ concentration, H ₂ O concentration, and H ₂ concentration are all “volume%” and “volume ppm”, and are simply indicated by “%” and “ppm” unless otherwise specified.

The steel component composition will be described.
C: 0.3% or less Since the weldability deteriorates when C exceeds 0.3%, the C content is 0.3% or less. On the other hand, workability is easily improved by forming a retained austenite phase (hereinafter also referred to as a residual γ phase) or a martensite phase as a steel structure. Therefore, the C content is preferably 0.025% or more.

Si: 0.1-2.5%
Si is an element effective for strengthening steel and obtaining a good material. If Si is less than 0.1%, an expensive alloy element is required to obtain high strength, which is not economically preferable. On the other hand, in Si-containing steel, it is known that the oxidation reaction during the oxidation treatment is suppressed. Therefore, when it exceeds 2.5%, the formation of an oxide film by the oxidation treatment is suppressed. Further, since the alloying temperature is also increased, it is difficult to obtain desired mechanical properties. Therefore, the Si amount is set to 0.1% to 2.5%.

Mn: 0.5 to 3.0%
Mn is an element effective for increasing the strength of steel. To ensure mechanical properties and strength, 0.5% or more is contained. On the other hand, if it exceeds 3.0%, it may be difficult to secure a balance between weldability, plating adhesion, strength and ductility. Therefore, the amount of Mn is 0.5% or more and 3.0% or less.

  The balance is Fe and inevitable impurities.

  In order to control the balance between strength and ductility, Al: 0.01 to 0.1%, Mo: 0.05 to 1.0%, Nb: 0.005 to 0.05%, Ti: 0.005 -0.05%, Cu: 0.05-1.0%, Ni: 0.05-1.0%, Cr: 0.01-0.8%, B: 0.0005-0.005% One or more elements selected from among them may be added as necessary.

The reason for limiting the appropriate addition amount in the case of adding these elements is as follows.
Since Al is most easily oxidized thermodynamically, it is oxidized prior to Si and Mn, thereby suppressing the oxidation of Si and Mn on the surface of the steel sheet and promoting the oxidation inside the steel sheet. This effect is obtained at 0.01% or more. On the other hand, if it exceeds 0.1%, the cost increases. Therefore, when added, the Al content is preferably 0.01% or more and 0.1% or less.

  If Mo is less than 0.05%, it is difficult to obtain the effect of adjusting the strength and the effect of improving the plating adhesion at the time of composite addition with Nb, Ni and Cu. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when added, the Mo amount is preferably 0.05% or more and 1.0% or less.

  If Nb is less than 0.005%, it is difficult to obtain the effect of adjusting the strength and the effect of improving the plating adhesion at the time of composite addition with Mo. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when Nb is added, the Nb content is preferably 0.005% or more and 0.05% or less.

  If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain, and if it exceeds 0.05%, the plating adhesion deteriorates. Therefore, when Ti is added, the Ti content is preferably 0.005% or more and 0.05% or less.

  If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase and the effect of improving the plating adhesion when combined with Ni or Mo. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when added, Cu is preferably 0.05% or more and 1.0% or less.

  When Ni is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase and the effect of improving the plating adhesion upon the combined addition of Cu and Mo. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when Ni is added, the Ni content is preferably 0.05% or more and 1.0% or less.

  If Cr is less than 0.01%, hardenability is difficult to obtain, and the balance between strength and ductility may deteriorate. On the other hand, if it exceeds 0.8%, cost increases. Therefore, when added, the Cr content is preferably 0.01% or more and 0.8% or less.

  B is an element effective for improving the hardenability of steel. If it is less than 0.0005%, it is difficult to obtain the quenching effect, and if it exceeds 0.005%, the effect of promoting the oxidation of the outermost surface of the Si steel sheet is brought about. Therefore, when added, the B content is preferably 0.0005% or more and 0.005% or less.

Next, the manufacturing method of the high intensity | strength hot-dip galvanized steel plate of this invention is demonstrated. In the present invention, the steel sheet having the above component composition is subjected to an oxidation treatment, and then subjected to a reduction annealing, followed by a hot dipping treatment. Or, further, an alloying treatment is performed. In the oxidation treatment, heating is performed at a temperature of 400 to 750 ° C. in an atmosphere having an O ₂ concentration of 1000 ppm or more and an H ₂ O concentration of 1000 ppm or more in the former stage, and an O ₂ concentration of less than 1000 ppm and an H ₂ O concentration of 1000 ppm or more in the latter stage. In an atmosphere, heating is performed at a temperature of 600 to 850 ° C. In the reduction annealing, an H ₂ concentration of 5 to 30%, an H ₂ O concentration of 500 to 5000 ppm, and the balance of N ₂ and unavoidable impurities are 650 to 650 Heat at a temperature of 900 ° C. In the alloying treatment, the treatment is performed at a temperature T satisfying the following formula for 10 to 60 seconds. −50 log ([H ₂ O]) + 650 ≦ T ≦ −40 log ([H ₂ O]) + 680
However, [H ₂ O] represents the H ₂ O concentration (ppm) during reduction annealing.

  First, the oxidation treatment will be described. In order to increase the strength of the steel sheet, it is effective to add Si, Mn, etc. to the steel as described above. However, steel sheets with these elements added have Si and Mn oxides formed on the steel sheet surface during the annealing process (oxidation treatment + reduction annealing) performed before hot dip galvanizing treatment, ensuring plating properties. It becomes difficult to do.

  As a result of examination, by changing the annealing conditions (oxidation treatment + reduction annealing) before performing hot dip galvanizing treatment, Si and Mn are oxidized inside the steel plate, and the plating property is improved by preventing oxidation on the steel plate surface. Furthermore, it was found that the reactivity between the plating and the steel sheet can be increased, and the plating adhesion is improved.

  And, in order to oxidize Si and Mn inside the steel plate and prevent oxidation on the steel plate surface, it is effective to perform oxidation treatment, and then perform reduction annealing, hot dipping, and alloying treatment as necessary, Furthermore, it has been found that it is necessary to obtain a certain amount or more of iron oxide by oxidation treatment.

However, if reduction annealing is performed with a certain amount or more of iron oxide formed by the oxidation treatment, there is a problem that a pickup phenomenon occurs. Therefore, it is important to divide the oxidation treatment into the former stage and the latter stage and control the O ₂ concentration of the atmosphere in each. In particular, it is important to perform the subsequent oxidation treatment at a low O ₂ concentration. Hereinafter, the front-stage oxidation treatment and the rear-stage oxidation treatment will be described.

[Pre-processing]
In order to suppress Si and Mn oxidation and generate iron oxide on the surface of the steel sheet, an oxidation treatment is positively performed. Therefore, in order to obtain a sufficient amount of iron oxide, the O ₂ concentration needs to be 1000 ppm or more. Although there is no particular upper limit, it is preferably 20% or less of the atmospheric O ₂ concentration for economic reasons of oxygen introduction cost. H ₂ O, like oxygen, has an effect of promoting the oxidation of iron, so it is set to 1000 ppm or more. Although there is no particular upper limit, it is preferably 30% or less for economical reasons of humidification costs. Further, the heating temperature is required to be 400 ° C. or higher in order to promote the oxidation of iron. On the other hand, if it exceeds 750 ° C., iron is excessively oxidized and causes pickup in the next step.

[Post-processing]
This is an important requirement in the present invention in order to prevent pick-up and to obtain a beautiful surface appearance free from push-ups. In order to prevent pickup, it is important to reduce a part (surface layer) of the surface of the steel plate once oxidized. In order to perform such a reduction treatment, it is necessary to control the O ₂ concentration to less than 1000 ppm. By reducing the O ₂ concentration, part of the surface layer of the iron oxide is reduced, and during the subsequent reduction annealing, direct contact between the roll of the furnace and the iron oxide can be avoided and pickup can be prevented. Since this reduction reaction hardly occurs when the O ₂ concentration is 1000 ppm or more, the O ₂ concentration is less than 1000 ppm. The H ₂ O concentration is set to 1000 ppm or more in order to promote internal oxidation of Si and Mn described later. Although there is no particular upper limit, it is preferably 30% or less for economic reasons of humidification costs, as in the previous oxidation treatment. When the heating temperature is less than 600 ° C., the reduction reaction hardly occurs. When the heating temperature exceeds 850 ° C., the effect is saturated and the heating cost is increased.

  As described above, the oxidation furnace needs to be composed of at least two zones in order to satisfy the above conditions. When the oxidation furnace is composed of two zones, each zone may be controlled as described above, and when it is composed of three or more zones, the atmosphere is controlled similarly in any continuous zone. It can be regarded as one zone. It is also possible to perform the former stage and the latter stage in separate oxidation furnaces. However, in consideration of industrial productivity and improvement of the current production line, it is preferable to divide the same furnace into two or more zones and control the atmosphere in each zone.

Moreover, it is preferable to use a direct-fired burner furnace (DFF) or a non-oxidizing furnace (NOF) for the pre-stage oxidation treatment and the post-stage oxidation treatment. DFF and NOF are often used in hot dip galvanizing lines, and the O ₂ concentration can be easily controlled by controlling the air ratio. Moreover, since the heating rate of the steel sheet is fast, there is an advantage that the furnace length of the heating furnace can be shortened or the line speed can be increased, so that the use of DFF or NOF is preferable from the viewpoint of production efficiency. A direct-fired burner furnace (DFF) or a non-oxidizing furnace (NOF) heats a steel sheet by mixing and burning fuel such as coke oven gas (COG), which is a by-product gas of an ironworks, and air. Therefore, when the ratio of air to fuel is increased, unburned oxygen remains in the flame, and it becomes possible to promote oxidation of the steel sheet with the oxygen. Therefore, the oxygen concentration in the atmosphere can be controlled by adjusting the air ratio. In the pre-stage oxidation treatment, when the air ratio is less than 1.0, the above atmospheric conditions may be deviated, and when the air ratio is 1.3 or more, excessive iron oxidation may occur. 0.0 or more and less than 1.3 is preferable. Further, in the latter-stage oxidation treatment, when the air ratio is 0.9 or more, it may deviate from the above atmospheric conditions. The air ratio is preferably 0.7 or more and less than 0.9.

Next, reduction annealing performed after the oxidation treatment will be described.
In reduction annealing, iron oxide formed on the surface of a steel sheet by oxidation treatment is reduced, and an alloy element of Si or Mn is formed as an internal oxide inside the steel sheet by oxygen supplied from the iron oxide. As a result, a reduced iron layer reduced from iron oxide is formed on the outermost surface of the steel sheet, and since Si and Mn remain inside the steel sheet as internal oxides, oxidation of Si and Mn on the steel sheet surface is suppressed, and the steel sheet In addition, the wettability of hot-dip plating can be prevented from being lowered and a good plating appearance can be obtained without unplating.

  However, although a good plating appearance can be obtained, the formation of oxides of Si and / or Mn on the surface of the steel sheet is not sufficiently suppressed, and the hot dip galvanized steel sheet without alloying treatment has a desired plating adhesion. I can't get it. Also, when producing an alloyed hot-dip galvanized steel sheet, the alloying temperature becomes high, so the decomposition of the retained austenite phase to the pearlite phase and the temper softening of the martensite phase occur, and the desired mechanical properties are obtained. I can't get it. Therefore, studies were conducted to obtain good plating adhesion and to reduce the alloying temperature. As a result, by forming the internal oxidation of Si and Mn more positively, the formation of oxides of Si and Mn on the steel plate surface is further suppressed, and in the hot dip galvanized steel plate that does not perform alloying treatment A technique has been devised that improves the plating adhesion, further reduces the amount of solute Si in the surface layer of the steel sheet, and promotes the alloying reaction when alloying is performed.

In order to more actively form an internal oxide of Si or Mn, it is effective to control the H ₂ O concentration in the atmosphere in the reduction annealing furnace to 500 ppm or more, which is an important requirement in the present invention. It is. When the H ₂ O concentration in the reduction annealing furnace is controlled to 500 ppm or more, oxygen is supplied from the iron oxide, and even after the internal oxides of Si and Mn are formed, the oxygen supplied from the H ₂ O in the atmosphere Since internal oxidation of Si and Mn occurs continuously, more internal oxides of Si and Mn are formed. Then, it becomes difficult for Si and Mn to diffuse to the steel plate surface, and oxide formation on the steel plate surface is suppressed. As a result, the reactivity between the steel sheet and the plating layer is increased, and the plating adhesion is improved. In addition, in the region of the steel sheet surface layer where internal oxidation is formed, the amount of solute Si decreases. When the amount of solute Si decreases, the surface layer of the steel sheet behaves as if it is a low Si steel, the subsequent alloying reaction is promoted, and the alloying reaction proceeds at a low temperature. By lowering the alloying temperature, the retained austenite phase can be maintained at a high fraction and ductility is improved. The desired strength can be obtained without the temper softening of the martensite phase proceeding.

Using a steel sheet containing 0.13% C, 1.5% Si, and 2.6% Mn, in an atmosphere having an O ₂ concentration of 1000 ppm or more and an H ₂ O concentration of 1000 ppm or more, at a temperature of 650 ° C. Oxidation treatment and subsequent oxidation treatment at 700 ° C. in an atmosphere having an O ₂ concentration of less than 1000 ppm and an H ₂ O concentration of 1000 ppm or more, then reduced to a temperature of H ₂ concentration of 15% and 830 ° C. Reduction annealing was performed by changing the H ₂ O concentration in the furnace. Subsequently, the alloying process was performed at 480-560 degreeC and 25 seconds so that it might become a hot dipping process and a suitable alloying degree. For the galvannealed steel sheet obtained as described above, the tensile strength TS and the elongation EL (MPa ·%) were measured, and the H ₂ O concentration (ppm) in the reduction annealing furnace, the tensile strength TS, and the elongation EL. The relationship of product (MPa ·%) was examined. The relationship between the H ₂ O concentration (ppm) in the reduction annealing furnace, the product of the tensile strength TS and the elongation EL (MPa ·%) is shown in FIG. From FIG. 1, it can be seen that when the H ₂ O concentration in the reduction annealing furnace is 500 ppm or more, the mechanical property value indicated by TS × EL is remarkably improved.

It was also found that the fatigue resistance is improved by setting the H ₂ O concentration in the reduction annealing furnace to 500 ppm or more. FIG. 2 shows an alloying using the galvannealed steel sheet which was performed under the same conditions as the galvannealed steel sheet used in FIG. 1 except that the H ₂ O concentration in the reduction annealing furnace was changed to 300 ppm and 1500 ppm. After processing, the SEM image which observed the cross section of the steel plate surface layer part by dissolving a plating layer with hydrochloric acid is shown. FIG. 2 shows that when the H ₂ O concentration is 300 ppm, the internal oxide is formed by oxygen supplied from the iron oxide, and in this case, there is a tendency to form at the grain boundary inside the steel sheet surface layer. On the other hand, when the H ₂ O concentration is 1500 ppm, the internal oxide is formed by oxygen supplied from H ₂ O in the atmosphere, and in this case, there is a tendency to form uniformly in the grains inside the steel sheet surface layer. Recognize. This is because the internal oxidation reaction due to oxygen supplied from iron oxide occurs in a relatively low temperature range, and diffusion at the grain boundaries tends to proceed faster than in the grains, whereas the atmosphere tends to progress. Since the internal oxidation reaction by oxygen supplied from H ₂ O occurs in a relatively high temperature region, the difference in diffusion rate between the grain boundary and the grain is small, and the internal oxidation is uniformly formed in the grain. It seems to be. The internal oxide formed along the grain boundary reduces the strength of the grain boundary, becomes the starting point of cracks generated by fatigue, and further promotes the progress of cracks. The internal oxide formed in this way is less likely to cause stress concentration even if cracks occur, and the progress of cracks is suppressed, and the fatigue resistance is excellent.

For the above reasons, the H ₂ O concentration in the reduction annealing furnace is set to 500 ppm or more. Moreover, it is preferable to set it as 1000 ppm or more for the purpose of further promoting the internal oxidation within a grain. On the other hand, if the H ₂ O concentration exceeds 5000 ppm, the iron oxide formed in the oxidation furnace becomes difficult to reduce, and not only there is a risk of pick-up in the reduction annealing furnace, but also the iron oxide is in the hot-dip plating. On the other hand, the wettability between the steel sheet and the molten zinc may be reduced, leading to poor adhesion. Moreover, it leads also to the cost increase for humidification. Therefore, the upper limit of the H ₂ O concentration is set to 5000 ppm. In order to reduce iron oxide completely, 4000 ppm or less is preferable.

Although the H ₂ O concentration distribution in the reduction annealing furnace depends on the structure of the furnace, generally, the concentration tends to be high at the top of the furnace and low at the bottom. In the case of a vertical furnace which is the mainstream of the hot dip galvanizing line, if the difference in H ₂ O concentration between the upper and lower parts is large, the steel sheet will alternately pass through the high concentration and low concentration regions, and the crystal grains are uniformly distributed. It becomes difficult to form internal oxidation inside. In order to create a uniform H ₂ O concentration distribution as much as possible, it is preferable that the difference between the upper and lower H ₂ O concentrations in the furnace is 2000 ppm or less. If the difference between the upper and lower H ₂ O concentrations exceeds 2000 ppm, it may be difficult to form uniform internal oxidation. In order to control the H ₂ O concentration in the lower region where the H ₂ O concentration is low to an H ₂ O concentration within the range of the present invention, it is necessary to introduce excessive H ₂ O, resulting in an increase in cost.

Although the method for controlling the H ₂ O concentration in the reduction annealing furnace is not particularly limited, N ₂ and / or H ₂ gas humidified by bubbling or the like is introduced into the furnace. There is a way to introduce. Further, a membrane exchange type humidification method using a hollow fiber membrane is preferable because the controllability of the dew point is further increased.

The H ₂ concentration in the reduction annealing is 5% or more and 30% or less. If it is less than 5%, the reduction of iron oxide is suppressed and the risk of pick-up increases. If it exceeds 30%, it will lead to cost increase. The balance other than the H ₂ concentration of 5 to 30% and the H ₂ O concentration of 500 to 5000 ppm is N ₂ and inevitable impurities.

  The heating temperature is 650 ° C. or higher and 900 ° C. or lower. If it is less than 650 degreeC, not only the reduction | restoration of an iron oxide will be suppressed, but the desired mechanical characteristic will not be acquired. Even if it exceeds 900 ° C., desired mechanical properties cannot be obtained. From the viewpoint of improving the mechanical properties, it is preferable to hold for 10 to 600 seconds in the range of 650 to 900 ° C.

Next, the hot dipping process and the alloying process will be described.
As described above, it was found that the alloying reaction is promoted when the internal oxide of Si is positively formed by controlling the conditions during the oxidation treatment and the conditions during the reduction annealing. Therefore, using the alloyed hot-dip galvanized steel sheet used in FIG. 1, the relationship between the change in H ₂ O concentration during reduction annealing and the alloying temperature was examined. FIG. 3 shows the results obtained. In FIG. 3, ♦ indicates the temperature at which the η phase formed before alloying is completely changed to an Fe—Zn alloy and the alloying reaction is completed. Moreover, the ■ mark indicates the upper limit of the temperature at which rank 3 is obtained when the plating adhesion is evaluated by the method described in the examples described later. Moreover, the line in a figure has shown the upper limit of the alloying temperature shown by the following Formula, and the minimum temperature.

The following knowledge was obtained from FIG. When the alloying temperature is less than (−50 log ([H ₂ O]) + 650) ° C., alloying does not proceed completely and the η phase remains. If the η phase remains, the color tone of the surface becomes uneven and not only the surface appearance is impaired, but also the friction coefficient on the surface of the plating layer becomes high, resulting in poor press formability. On the other hand, when the alloying temperature exceeds (−40 log ([H ₂ O]) + 680) ° C., good plating adhesion cannot be obtained. Further, as is apparent from FIG. 3, it can be seen that as the H ₂ O concentration increases, the necessary alloying temperature decreases and the alloying reaction of Fe—Zn is promoted. Then, the effect of improving the mechanical characteristic values with increasing H _{2 O} concentration in the reducing furnace as described above is due to reduction of the alloying temperature. It can be seen that the alloying temperature after hot dipping needs to be precisely controlled in order to obtain the desired mechanical properties.

As described above, in the alloying process, the process is performed at the temperature T satisfying the following expression.
−50 log ([H ₂ O]) + 650 ≦ T ≦ −40 log ([H ₂ O]) + 680
However, [H ₂ O] represents the H ₂ O concentration (ppm) during reduction annealing.
Further, for the same reason as the alloying temperature, the alloying time is 10 to 60 seconds.

  The degree of alloying after the alloying treatment is not particularly limited, but an alloying degree of 7 to 15% by mass is preferable. If it is less than 7% by mass, the η phase remains and the press formability is inferior, and if it exceeds 15% by mass, the plating adhesion is inferior.

  The hot dip galvanizing treatment has an effective Al concentration in the bath of 0.095 to 0.175 mass% (more preferably 0.095 to 0.115 mass% when alloying treatment), and the balance is Zn and inevitable impurities. It is preferably carried out in a hot dip galvanizing bath having a component composition consisting of Here, the effective Al concentration in the bath is a value obtained by subtracting the Fe concentration in the bath from the Al concentration in the bath. Patent Document 10 describes a technique for promoting the alloying reaction by keeping the effective Al concentration in the bath as low as 0.07 to 0.092%, but the present invention does not reduce the effective Al concentration in the bath. It promotes the alloying reaction. When the effective Al concentration in the bath is less than 0.095%, a Γ phase, which is a hard and brittle Fe—Zn alloy, is formed at the interface between the steel sheet and the plating layer after the alloying treatment, and thus the plating adhesion may be inferior. On the other hand, if it exceeds 0.175%, the alloying temperature becomes high even if the present invention is applied, and not only the desired opportunity characteristics are not obtained, but also the amount of dross generated in the plating bath increases, Surface defects caused by adhesion to the steel plate become a problem. Moreover, it leads also to the cost increase which adds Al. If it exceeds 0.115%, even if the present invention is applied, the alloying temperature increases, and the desired opportunity characteristics may not be obtained. Therefore, the effective Al concentration in the bath is preferably 0.095% by mass or more and 0.175% by mass or less. More preferably, the alloying treatment is 0.115% by mass or less.

  Other conditions at the time of hot dip galvanizing are not limited, but, for example, the hot dip galvanizing bath temperature is in the normal range of 440 to 500 ° C., and the steel plate is infiltrated into the plating bath at a plate temperature of 440 to 550 ° C. The amount of adhesion can be adjusted by gas wiping.

  Next, the high-strength hot-dip galvanized steel sheet excellent in plating adhesion and fatigue resistance produced by the above production method will be described.

As described above, the plating adhesion, workability, and fatigue resistance are improved by positively forming internal oxidation of Si and Mn. This is because the reactivity of the steel sheet and the plating layer is enhanced by suppressing the formation of oxides of Si and Mn on the steel sheet surface. That is, in the hot dip galvanized steel sheet exhibiting good plating adhesion, the reaction between the steel sheet and the plating layer is promoted, and a reaction phase thereof is formed at the interface between the two. As a reaction phase of the steel plate and the plating layer, an Fe—Zn alloy phase such as FeZn ₁₃ (ζ phase) and FeZn ₇ (δ1 phase), an Fe—Al alloy phase such as FeAl ₃ and Fe ₂ Al ₅ , or Fe ₂ There are Fe—Zn—Al alloy phases such as (AlZn) ₅ and Fe ₂ Al ₄ Zn ₄ . The formation of these alloy phases indicates a high reactivity between the steel sheet and the plating layer. On the other hand, when the oxide of Si and / or Mn formed in the annealing process is formed on the steel sheet surface, the reactivity of the steel sheet and the plating layer is low, and these alloy phases are not formed. Furthermore, since the oxides of Si and / or Mn remain at the interface between the steel sheet and the plating layer, the plating adhesion deteriorates. That is, in order to ensure good plating adhesion in a high-strength hot-dip galvanized steel sheet, oxidation of Si and / or Mn on the steel sheet surface is suppressed, and the reaction phase of the steel sheet and the plating layer is formed in a wide area. This is very important.

  As a result of studying the area ratio of the alloy phase formed at the interface between the steel plate and the plating layer, the present inventors have conducted studies, and as a result, the Fe—Zn alloy phase, the Fe—Al alloy phase, and the Fe—Zn—Al alloy phase are obtained. It has been found that good plating adhesion can be obtained when formed with a high area ratio.

In FIG. 4, the SEM image which observed the alloy phase which melt | dissolved the plating layer electrochemically and formed in the interface of a steel plate and a plating layer is shown. (A) with good plating adhesion is manufactured under the manufacturing conditions for obtaining the above-mentioned good plating adhesion, and (b) with poor plating adhesion is H ₂ during reduction annealing. What was manufactured under the condition that the O concentration was lower than the lower limit, and (c) was manufactured under the condition that the O ₂ concentration in the preceding stage in the oxidation treatment was lower than the lower limit in addition to the H ₂ O concentration during the reduction annealing. It has been done. In addition, the dissolution of the plating layer was carried out by performing constant current anode electrolysis at a current value of 20 mA / cm ² in a methanol solution containing an electrolyte, and having a potential of −750 mV vs. We went to SCE. (A) is confirmed to have been totally columnar compounds formed by other analytical techniques EDS etc., it was found that these compounds are predominantly FeZn 13 _(zeta phase). On the other hand, in (b) and (c), FeZn ₁₃ (ζ phase) was partially formed, but there was a region where formation of a compound was not observed. When this part was analyzed by EDS, it was found that Si and Mn oxides were formed. That is, in (a), since the oxidation reaction of Si and Mn on the surface of the steel sheet was suppressed during annealing, the reactivity between the steel sheet and the plating layer was increased and the plating adhesion was good, but (b) and (c ), The oxide formed during annealing suppresses the reaction between the steel sheet and the plating layer, and the plating adhesion is considered to have deteriorated. Furthermore, by binarizing these observation images by image processing, the respective area ratios can be obtained and can be quantitatively evaluated. As a result of further investigation, the reaction phase formed at the interface between the steel sheet and the plating layer, which is composed of the Fe—Zn alloy phase, the Fe—Al alloy phase, and the Fe—Zn—Al alloy phase, is 70% or more in area ratio. And found that good plating adhesion can be obtained. The reaction phase of the steel plate and the plating layer observed in FIG. 4 was the Fe—Zn alloy phase of FeZn ₁₃ , but this reaction phase changes depending on the reactivity of the steel plate and the plating layer and the Al concentration in the plating bath. And an Fe—Zn alloy phase such as FeZn ₇ (δ1 phase), which is generally known as a reaction phase between the steel plate and the plating layer, an Fe—Al alloy phase such as FeAl ₃ and Fe ₂ Al ₅ , or Fe ₂ ( Even when Fe—Zn—Al alloy phases such as AlZn) ₅ and Fe ₂ Al ₄ Zn ₄ are formed, they show high reactivity between the steel sheet and the plating layer, and the plating adhesion is improved. It shows that it is. As described above, at the interface between the plating layer and the steel sheet, the reaction phase composed of at least one of the Fe—Zn alloy phase, the Fe—Al alloy phase, and the Fe—Zn—Al alloy phase has an area ratio of 70% or more. And

  A slab obtained by melting steel having chemical components shown in Table 1 was formed into a cold-rolled steel sheet having a thickness of 1.2 mm by hot rolling, pickling, and cold rolling.

Subsequently, after performing the oxidation treatment of the front | former stage and the back | latter stage by the CGL which has a DFF type oxidation furnace or a NOF type | mold oxidation furnace on the oxidation conditions shown in Table 2, reduction annealing was performed on the conditions shown in Table 2. Subsequently, after applying hot dip galvanizing treatment using a 460 ° C. bath containing effective Al concentration in the bath shown in Table 2, the basis weight was adjusted to about 50 g / m ² by gas wiping, and then shown in Table 2. Alloying treatment was performed in the temperature and time range.

  Appearance and plating adhesion were evaluated for the galvannealed steel sheets obtained as described above. Furthermore, the tensile properties and fatigue resistance properties were investigated. The measurement method and the evaluation method are shown below.

Visually observe the appearance after the appearance alloying treatment, ○ that there is no appearance defect such as uneven alloying, non-plating, or push-pull by pick-up, △ that there is a slight appearance defect but is generally good, Those having unevenness in alloying, non-plating, or pressing folds were marked with x.

A cellophane tape (registered trademark) is applied to the plated adhesive plated steel sheet, the tape surface is bent 90 degrees, bent back, and a cellophane tape with a width of 24 mm is parallel to the bent portion on the inside (compressed side) of the processed portion. Measure the amount of zinc attached to the 40 mm long part of the cellophane tape as a Zn count by fluorescent X-ray, and convert the Zn count per unit length (1 m) using the following criteria: In light of the above, ones with ranks 1 and 2 were evaluated as good (◯), three were good (Δ), and four or more were evaluated as bad (x).
X-ray fluorescence count: Rank 0 to less than 500: 1 (good)
Less than 500-1000: 2
Less than 1000-2000: 3
Less than 2000-3000: 4
3000 or more: 5 (poor)
Tensile properties The rolling direction was set to the tensile direction, and a JIS No. 5 test piece was used according to JIS Z2241.

Fatigue resistance Stress ratio R: 0.05, fatigue limit (FL) is determined at 10 ⁷ repetitions, durability ratio (FL / TS) is determined, and a value of 0.60 or more is judged as good fatigue resistance did. The stress ratio R is a value defined by (minimum repeated stress) / (maximum repeated stress).

  The results obtained as described above are shown in Table 2 together with the production conditions.

From Table 2, the present invention example is a high-strength steel containing Si and Mn, but has excellent plating adhesion, good plating appearance, excellent ductility, and good fatigue resistance. . On the other hand, the comparative example manufactured outside the scope of the present invention is inferior in any one or more of plating adhesion, plating appearance, and fatigue resistance.

  A slab obtained by melting steel having chemical components shown in Table 3 was formed into a cold-rolled steel sheet having a thickness of 1.2 mm by hot rolling, pickling, and cold rolling.

  Subsequently, after performing the oxidation treatment of the front | former stage and back | latter stage by the CGL which has a DFF type oxidation furnace on the oxidation conditions shown in Table 4, reduction annealing was performed on the conditions shown in Table 4. Other conditions are the same as in the first embodiment.

  Appearance and plating adhesion were evaluated for the galvannealed steel sheets obtained as described above. Furthermore, the tensile properties and fatigue resistance properties were investigated. The measurement method, evaluation method, and investigation method are the same as in Example 1.

  The results obtained above are shown in Table 4 together with the production conditions.

  From Table 4, although the present invention is a high-strength steel containing Si and Mn, it has excellent plating adhesion, good plating appearance, excellent ductility, and good fatigue resistance. .

  A slab obtained by melting steel having chemical components shown in Table 1 was formed into a cold-rolled steel sheet having a thickness of 1.0 mm by hot rolling, pickling, and cold rolling.

Subsequently, after performing the oxidation treatment of the front | former stage and back | latter stage on the oxidation conditions shown in Table 5 with CGL which has a DFF type oxidation furnace or a NOF type oxidation furnace, reduction annealing was performed on the conditions shown in Table 5. Subsequently, a hot dip galvanizing treatment was performed using a 460 ° C. bath containing an effective Al concentration in the bath shown in Table 5, and then the basis weight was adjusted to about 80 g / m ² by gas wiping.

  The hot dip galvanized steel sheet obtained as described above was evaluated for appearance and plating adhesion. Furthermore, the tensile properties and fatigue resistance properties were investigated. Furthermore, the reaction phase area ratio at the interface between the steel sheet and the plating phase was measured and evaluated. The measurement method and the evaluation method are shown below.

Appearance After visually observing the appearance after hot dipping treatment, ○ indicates that there is no appearance failure such as non-plating or picking up by a pick-up, △ indicates that there is a slight appearance failure but is generally good, unplating, or The thing with a push rod was set as x.

The plating layer is peeled off when the plated adhesive steel plate is bent using a 90 ° mold with a tip of 2.0R and then the cellophane tape (registered trademark) is applied to the outside of the bend and pulled away. “○” indicates that the film is not recognized, and there is no plating peeling of 1 mm or less, or no adhesion of the plating layer to the tape, but “△” indicates that the plating layer is floating from the steel plate, and the plating layer is 1 mm. What exceeded the tape and peeled off was evaluated as "x".

Tensile properties The rolling direction was set to the tensile direction, and a JIS No. 5 test piece was used according to JIS Z2241. A TS × EL value exceeding 18000 was judged to be excellent in ductility.

Fatigue resistance Stress ratio R: 0.05, fatigue limit (FL) is determined at 10 ⁷ repetitions, durability ratio (FL / TS) is determined, and a value of 0.60 or more is judged as good fatigue resistance did. The stress ratio R is a value defined by (minimum repeated stress) / (maximum repeated stress).

The reaction phase area ratio plated steel sheet was subjected to a potential of −750 mV vs. in a methanol solution containing an electrolyte. Constant current anodic electrolysis was performed at a current value of 20 mA / cm 2 up to SCE to dissolve the plating layer. Thereafter, the area ratio of each of the Fe—Zn alloy phase, the Fe—Al alloy phase, and the Fe—Zn—Al alloy phase formed at the interface between the steel sheet and the plating layer was obtained using SEM and EDS, and the total was the reaction phase area ratio. It was. The area ratio was 500 times, and five fields of view were observed, and the average value of the area ratios obtained by image processing of each was used.

  The results obtained as described above are shown in Table 5 together with the production conditions.

From Table 5, although the present invention example is a high-strength steel containing Si and Mn, it has excellent plating adhesion, good plating appearance, excellent ductility, and good fatigue resistance. . On the other hand, the comparative example manufactured outside the scope of the present invention is inferior in any one or more of plating adhesion, plating appearance, and fatigue resistance.

  A slab obtained by melting steel having chemical components shown in Table 3 was formed into a cold-rolled steel sheet having a thickness of 1.0 mm by hot rolling, pickling, and cold rolling.

  Subsequently, after performing the oxidation treatment of the front | former stage and the back | latter stage by the CGL which has a DFF type oxidation furnace on the oxidation conditions shown in Table 6, reduction annealing was performed on the conditions shown in Table 6. Other conditions are the same as in Example 3.

  Appearance and plating adhesion were evaluated for the hot dip galvanized steel sheet obtained as described above. Furthermore, the tensile properties and fatigue resistance properties were investigated. Furthermore, the reaction phase area ratio at the interface between the steel sheet and the plating phase was measured and evaluated. The measurement method, evaluation method, and investigation method are the same as in Example 3.

  The results obtained above are shown in Table 6 together with the production conditions.

  From Table 6, although the present invention example is a high-strength steel containing Si and Mn, the plating adhesion is excellent, the plating appearance is good, the ductility is excellent, and the fatigue resistance is also good. .

  The high-strength hot-dip galvanized steel sheet of the present invention is excellent in plating adhesion, workability, and fatigue resistance, and can be used as a surface-treated steel sheet for reducing the weight and strength of an automobile body.

Claims (7)

In mass%, C: 0.3% or less, Si: 0.1-2.5%, Mn: 0.5-3.0%, with the balance being a steel plate made of Fe and inevitable impurities In performing the hot dipping process after performing the oxidation treatment and then performing the reduction annealing,
In the oxidation treatment, heating is performed at a temperature of 400 to 750 ° C. in an atmosphere having an O ₂ concentration of 1000 volume ppm or more and an H ₂ O concentration of 1000 volume ppm or more in the former stage, and an O ₂ concentration of less than 1000 volume ppm in the latter stage. In an atmosphere having a H ₂ O concentration of 1000 ppm by volume or more, it is heated at a temperature of 600 to 850 ° C.,
In the reduction annealing, the difference between the upper and lower H ₂ O concentrations in the furnace is 2000 ppm by volume or less, the H ₂ concentration is 5 to 30% by volume, the H ₂ O concentration is 500 to 5000 ppm by volume, and the balance is N ₂ and A method for producing a high-strength hot-dip galvanized steel sheet, comprising heating at a temperature of 650 to 900 ° C in an atmosphere composed of inevitable impurities. In mass%, C: 0.3% or less, Si: 0.1-2.5%, Mn: 0.5-3.0%, with the balance being a steel plate made of Fe and inevitable impurities , After performing oxidation treatment and then performing reduction annealing, when performing hot dipping treatment and alloying treatment,
In the oxidation treatment, heating is performed at a temperature of 400 to 750 ° C. in an atmosphere having an O ₂ concentration of 1000 volume ppm or more and an H ₂ O concentration of 1000 volume ppm or more in the former stage, and an O ₂ concentration of less than 1000 volume ppm in the latter stage. In an atmosphere having a H ₂ O concentration of 1000 ppm by volume or more, it is heated at a temperature of 600 to 850 ° C.,
In the reduction annealing, the difference between the upper and lower H ₂ O concentrations in the furnace is 2000 ppm by volume or less, the H ₂ concentration is 5 to 30% by volume, the H ₂ O concentration is 500 to 5000 ppm by volume, and the balance is N ₂ and In an atmosphere of inevitable impurities, heated at a temperature of 650-900 ° C,
In the alloying treatment, the high strength hot-dip galvanized steel sheet is produced by performing the treatment at a temperature T (° C.) satisfying the following formula for 10 to 60 seconds.
−50 log ([H ₂ O]) + 650 ≦ T ≦ −40 log ([H ₂ O]) + 680
However, [H ₂ O] represents the H ₂ O concentration (volume ppm) during reduction annealing.   The oxidation treatment is performed using a direct-fired burner furnace (DFF) or a non-oxidizing furnace (NOF) at an air ratio of 1.0 or more and less than 1.3 in the former stage and an air ratio of 0.7 or more and less than 0.9 in the latter stage. The method for producing a high-strength hot-dip galvanized steel sheet according to claim 1 or 2, wherein the method is performed. 2. The hot dip galvanizing treatment is carried out in a hot dip galvanizing bath having a component composition comprising Zn and inevitable impurities, with an effective Al concentration in the bath of 0.095 to 0.175% by mass. The manufacturing method of the high intensity | strength hot-dip galvanized steel plate as described in any one of -3 . 2. The hot dip galvanizing treatment is performed in a hot dip galvanizing bath having a component composition comprising Zn and inevitable impurities, with an effective Al concentration in the bath of 0.095 to 0.115% by mass. The manufacturing method of the high intensity | strength hot-dip galvanized steel plate as described in any one of -3 . As a component composition, further, in mass%, Al: 0.01 to 0.1%, Mo: 0.05 to 1.0%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0 0.05%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cr: 0.01 to 0.8%, B: 0.0005 to 0.005% Or 2 or more types are contained, The manufacturing method of the high intensity | strength hot-dip galvanized steel plate as described in any one of Claims 1-5 characterized by the above-mentioned. It manufactures by the manufacturing method as described in any one of Claims 1-6 , and any of a Fe-Zn alloy phase, a Fe-Al alloy phase, and a Fe-Zn-Al alloy phase is in the interface of a plating layer and a steel plate. A method for producing a high-strength hot-dip galvanized steel sheet , wherein the reaction phase comprising at least one kind has an area ratio of 70% or more.