JP2005200694A - Hot dip galvanized high strength steel sheet having excellent plating adhesion and hole expansibility, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip galvanized high strength steel sheet having excellent plating adhesion and hole expansibility, and to provide its production method. <P>SOLUTION: The hot dip galvanized high strength steel sheet having excellent plating adhesion and hole expansibility has a composition comprising, by mass, 0.12 to 0.35% C, 0.2 to 1.0% Si, 0.8 to 3.5% Mn, ≤0.03% P, ≤0.03% S, 0.25 to 1.8% Al, 0.05 to 0.35% Mo and ≤0.010% N, and the balance Fe with inevitable impurities, and has a metallic structure composed of ferrite, bainite, tempered martensite in 0.5 to 10% by area ratio and retained austenite in ≥7% by volume ratio. Regarding its production method, after annealing at 680 to 930°C in a continuous annealing stage, at the time when it is cooled to a martensitic transformation point or below and is subsequently subjected to hot dip galvanizing, after heating at 250 to 600°C, the hot dip galvanizing treatment is performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility and a method for producing the same.

  In recent years, there has been a further demand for improvement in fuel consumption and weight reduction of automobiles, and there is an increasing need for high-strength steel sheets having excellent tensile strength and yield strength for increasing the diameter. However, this high strength steel sheet becomes difficult to form as the strength increases, and in particular, the elongation of the steel material decreases. In contrast, recently, TRIP steel (high residual austenitic steel), which has both high strength and elongation, has been used for automobile frame members.

  However, since conventional TRIP steel contains more than 1% Si, there is a problem that the plating is difficult to adhere uniformly and the hot dip galvanizing property is poor. For this reason, Patent Document 1 and Patent Document 2 propose hot-dip galvanized high-strength steel sheets in which the amount of Si is reduced and Al is added as an alternative. However, since the former has a relatively high Si content of 0.53% or more, there is still a problem in plating adhesion, and in the latter, the Si content is reduced to less than 0.2% to prevent plating adhesion. Although improving the properties, there is a problem that the cooling rate cannot be stably controlled due to the formation of retained austenite at a relatively high cooling rate, and the material becomes unstable.

  Further, depending on the member, there are many members that are subjected to burring processing for expanding the processed hole portion to form a flange, and a steel plate having hole expandability as an important characteristic is required. The conventional TRIP steel for this demand has the problem that the hole austenite becomes martensite after induced plastic transformation and the hardness difference from ferrite is large, so that the hole expandability is inferior. Furthermore, steel sheets that have been hot dip galvanized are becoming widespread in response to requests from automobile manufacturers and home appliance manufacturers for rust prevention of steel sheets. In this way, in addition to changing the type of products from conventional cold-rolled steel sheets to surface-treated steel sheets from various manufacturers, it is possible to receive large-scale orders for surface-treated steel sheets, especially hot-dip galvanized steel sheets in an urgent and short delivery period by shortening the manufacturing process. A production system that can respond is necessary. However, in the case of the high-temperature annealed material and high-strength steel sheet for producing the above-described hot-dip galvanized steel sheet, the productivity is low because of the high-temperature annealing. In some cases, there is a problem that production cannot be concentrated on a hot dip galvanizing line that has an annealing furnace.

  On the other hand, the normal continuous annealing line that anneals cold rolled steel sheets and electrogalvanized steel sheets generally has high speed and high productivity. In some cases, there is no material to pass through, and there is a problem that the production line is temporarily stopped, which has a serious problem of surplus production capacity.

Japanese Patent No. 2962038 JP 2003-105486 A

  The object of the present invention is to solve the above-described conventional problems and to realize a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility and a manufacturing method thereof on an industrial scale.

As a result of intensive studies on the hot-dip galvanized high-strength steel sheet and its manufacturing method excellent in plating adhesion and hole expansibility, the present inventors have optimized the steel components, that is, reduced Si content, Al as an alternative element In addition, the adhesion of hot dip galvanizing is improved, and Mo is added to give material properties that are excellent in both strength and elongation. In addition, before the hot dip galvanizing process, it is cooled to below the martensitic transformation point. After that, by heating to the temperature required for the plating treatment, it was found that steel containing stable retained austenite and tempered martensite can be produced industrially, and further the hole expandability can be improved. did. That is, the steel sheet of the component system designed based on the above knowledge is subjected to recrystallization annealing in the ferrite / austenite two-phase region in the continuous annealing process, and then subjected to appropriate overaging as necessary, and the martensitic transformation point. The following is cooled, and then heated to the temperature necessary for the plating treatment to perform the hot dip galvanizing treatment, ferrite is the main phase, and tempered martensite is produced in an area ratio of 0.5% to 10%. Furthermore, it has been found that a composite metal structure containing 7% or more of retained austenite as a low-temperature generation phase and having a bainite phase can be obtained, and in addition, the hole expandability is improved. Furthermore, if recrystallization annealing is carried out in a continuous annealing line and hot dip galvanizing treatment is carried out in a continuous hot dip galvanizing line, it is possible to respond to urgent and large orders / production. The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) By mass%, C: 0.12-0.35%, Si: 0.2-1.0%, Mn: 0.8-3.5%, P: 0.03% or less, S: Hot dip galvanizing containing 0.03% or less, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, N: 0.010% or less, the balance being Fe and inevitable impurities Plating adhesion, characterized in that the metallographic structure of the steel sheet has ferrite, bainite, tempered martensite in an area ratio of 0.5% to 10%, and retained austenite in a volume ratio of 7% or more. Hot-dip galvanized high-strength steel sheet with excellent properties and hole expandability.
(2) In mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Cu: 1% or less, Ni: 1% or less, Cr: 1% or less, B: 1 type or 2 types or more of 0.0001-0.0030% are contained, The plating adhesiveness and hole expansibility as described in (1) characterized by the above-mentioned Hot-dip galvanized high-strength steel sheet.
(3) By mass%, C: 0.12-0.35%, Si: 0.2-1.0%, Mn: 0.8-3.5%, P: 0.03% or less, S: A slab containing 0.03% or less, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, N: 0.010% or less, and remaining Fe and unavoidable impurities is heated. After rolling, after coiling at a temperature of 400 to 750 ° C., cold rolling, and then annealing at a temperature of 680 to 930 ° C. in a continuous annealing process, cooling to below the martensitic transformation point, and then applying hot dip galvanizing In this case, a hot dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility, characterized by performing hot dip galvanizing after heating to 250 to 600 ° C.
(4) After the over-aging treatment step of the continuous annealing step, one type or two or more types of pre-plating among Ni, Fe, Co, Sn, and Cu is performed at 0.01 to 2.0 g / m ² per one side of the steel plate. The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility according to (3), characterized in that it is applied.
(5) The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility according to (4), wherein the steel sheet is subjected to a pickling treatment before the pre-plating.
(6) The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expandability according to (3), wherein the galvanized layer is alloyed after the hot dip galvanizing step.
(7) The galvanized layer or the alloyed galvanized layer is further subjected to any one or more post-treatments of chromate treatment, inorganic film treatment, chemical conversion treatment, and resin film treatment. (3) The manufacturing method of the hot-dip galvanized high-strength steel plate excellent in the plating adhesiveness and hole expansibility as described in any one of the items of (6).
(8) The hot-dip galvanized high-strength steel sheet is further mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3%. Cu: 1% or less, Ni: 1% or less, Cr: 1% or less, and B: 0.0001 to 0.0030%, or one or more of (3) to (7) The manufacturing method of the hot dip galvanized high-strength steel plate excellent in the plating adhesiveness and hole expansibility according to any one of the items.

  According to the present invention, it is possible to provide a hot-dip galvanized high-strength steel sheet with excellent plating adhesion and hole expandability used for automobile parts, home appliance parts, etc., and further, change of varieties, increase of production by various manufacturers, etc. It is possible to respond flexibly even when there is a production change due to, a large amount of orders / production with urgent and short delivery times.

  First, the reasons for limitation to the components and metal structure of the hot-dip galvanized high-strength steel sheet defined in the present invention will be described.

  C is an essential component from the viewpoint of ensuring strength and as a basic element for stabilizing austenite. If C is less than 0.12%, the strength cannot be secured, and no retained austenite is formed. On the other hand, if it exceeds 0.35%, the strength is excessively increased and the ductility is insufficient. Therefore, the range of C is 0.12-0.35%, preferably 0.15-0.25%.

  Si is an element effective for producing retained austenite in addition to adding it from the viewpoint of securing strength. For this reason, the range of Si is 0.2 to 1.0%. Addition of 0.2% or more is necessary from the viewpoint of securing strength, and if it exceeds 1.0%, hot dip galvanizing properties deteriorate. Preferably it is 0.5% or less.

  Mn is an element that delays the formation of carbides in addition to the addition from the viewpoint of securing strength, and is an element necessary for the formation of retained austenite. If Mn is less than 0.8%, the strength is not satisfied, and the generation of retained austenite becomes insufficient, resulting in deterioration of ductility. On the other hand, if Mn exceeds 3.5%, martensite increases in place of retained austenite, leading to an increase in strength, resulting in increased product variation and insufficient ductility, and cannot be used as an industrial material. For this reason, the range of Mn was made into 0.8 to 3.5%.

  P is added according to the strength level required as an element for increasing the strength of the steel sheet. However, if the added amount is large, it segregates at the grain boundary, so that local ductility is deteriorated and weldability is also deteriorated. The value was 0.03%. Further, S is an element that deteriorates local ductility and weldability by generating MnS, and is preferably an element that does not exist in steel, so the upper limit was made 0.03%.

  If Mo is less than 0.05%, pearlite is formed, and the retained austenite ratio is reduced. Excessive Mo addition may lower the ductility and deteriorate the chemical conversion property, so 0.35% was made the upper limit. Preferably, a high strength-ductility balance can be obtained by setting the Mo addition amount to 0.15% or less.

  Al is an element necessary for allowing austenite to remain, and has the effect of stabilizing the austenite by promoting the formation of ferrite and suppressing the formation of carbides, and also acts as a deoxidizing element. To stabilize austenite, Al addition of 0.25% or more is necessary. On the other hand, even if Al is added excessively, the above effect is saturated, and on the contrary, the steel is embrittled and at the same time the hot dip galvanizing property is lowered. Therefore, the upper limit was made 1.8%.

  N is an element that is inevitably included, but when it is contained in a large amount, it not only degrades aging, but also increases the amount of precipitated AlN and decreases the effect of Al addition, so 0.01% The following contents are desirable. Further, unnecessarily reducing N increases the cost in the steel making process, so it is usually preferable to control the N to about 0.0020% or more.

  Further, in the present invention, in addition to the above components, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Cu: 1% or less , Ni: 1% or less, Cr: 1% or less, B: 0.0001 to 0.0030%, or one or more of them can be added. Ti, Nb, and V can be added for the purpose of precipitation strengthening and strength improvement, but at 0.3% or more, workability deteriorates. Cr, Ni, and Cu can also be added as strengthening elements, but at 1% or more, ductility and chemical conversion treatment properties deteriorate. Further, B can be added as an element for improving local ductility and hole expansibility, but the effect cannot be exhibited at 0.0001% or less, and elongation and plating adhesion deteriorate at 0.0030% or more.

  In the present invention, the metal structure described in relation to the manufacturing method is a very important requirement.

  That is, the greatest feature in the metal structure of the hot-dip galvanized high-strength steel sheet according to the present invention is that the steel has tempered martensite in an area ratio of 0.5% to 10%. This tempered martensite is obtained by heating the martensite generated in the cooling step subsequent to continuous annealing at 680 to 930 ° C. to 250 to 600 ° C., preferably 460 to 530 ° C., for continuous hot-dip galvanizing treatment. Tempered to become tempered martensite. When the amount of tempered martensite is less than 0.5%, the hole expansion rate is not improved, and when it exceeds 10%, the difference in hardness between the structures becomes too large and the workability is lowered. Further, by securing a retained austenite of 7% or more by volume ratio, the tensile strength × ductility is dramatically improved. And, this tempered martensite, ferrite, bainite, and retained austenite with a volume ratio of 5% or more become the main phase, and it is considered that the workability and hole expandability are improved by being in a well-balanced state in the steel sheet. .

  Next, the manufacturing method of the hot dip galvanized high strength steel plate by this invention is demonstrated. The slab having the steel component described above is rolled up at a temperature of 400 to 750 ° C. after hot rolling under normal conditions. The reason for setting the coiling temperature within the above temperature range is that the structure after hot rolling is made of pearlite with a low sensation or a mixed structure of pearlite and bainite, making it easy to dissolve cementite in the annealing process, and suppressing the generation of scale and descaling. Low temperature winding in the temperature range of 400 to 750 ° C. is preferable in order to improve the properties, increase the hard phase, and make cold rolling difficult.

  The hot-rolled steel sheet wound up in this way is cold-rolled under normal conditions to obtain a cold-rolled steel sheet. Next, the cold-rolled steel sheet is recrystallized and annealed in a two-phase coexisting temperature range of austenite and ferrite, that is, a temperature range of 680 to 930 ° C. If the annealing temperature exceeds 930 ° C., the structure in the steel sheet becomes an austenite single phase, and C in the austenite becomes dilute, so stable austenite cannot be left by subsequent cooling, so the upper limit temperature is 930 ° C. It was. On the other hand, if the temperature is lower than 680 ° C., C concentration of austenite becomes insufficient due to insufficient solute C, and the ratio of retained austenite decreases, so the lower limit temperature was set to 680 ° C. The annealed steel sheet is cooled to a martensite transformation point or lower, and the cooling means is not specified regardless of water spray cooling, air-water cooling, water immersion cooling, or gas jet cooling. It is preferable to perform an overaging treatment at a temperature of 300 to 500 ° C. during the cooling from the annealing to the martensite transformation point or less. This overaging treatment efficiently transforms austenite into bainite to secure a bainite phase, transforms martensite generated by annealing into tempered martensite, and further concentrates C in the retained austenite. In order to stabilize, it is preferable to hold | maintain for 60 second-20 minutes in the temperature range of 300-500 degreeC.

  Furthermore, in this invention, it cools to the martensite transformation point or less after overaging, and a martensite is ensured. The martensitic transformation point Ms is Ms (° C.) = 561−471 × C (%) − 33 × Mn (%) − 17 × Ni (%) − 17 × Cr (%) − 21 × Mo (%) Desired.

  The reason why the hole expandability is improved is not clear, but after annealing and cooling to below the martensite transformation point, the balance between the hardness of the soft and hard structures is improved by heating at a low temperature to achieve hot dip galvanizing. Therefore, it is considered that the hole expandability is improved by improving the local elongation.

  Furthermore, in this invention, the steel plate cooled to below the martensitic transformation point is pickled as necessary before pre-plating. By performing this pickling before pre-plating, the steel sheet surface can be activated and the plating adhesion of pre-plating can be improved. Further, oxides such as Si and Mn generated on the surface of the steel sheet in the continuous annealing process can be removed, and the adhesion of hot dip galvanization performed thereafter can be improved. The pickling treatment is preferably performed in a pickling solution containing 2 to 20% hydrochloric acid for 1 to 20 seconds. Ni flash plating may be performed after the pickling treatment. In addition, when the cooling after recrystallization in the continuous annealing process is cooling by water spray cooling, air-water cooling, or water immersion cooling, the continuous annealing process outlet side is during continuous annealing or during cooling. Since the pickling process to remove the oxide film on the surface of the steel sheet is necessary, the pickling equipment is installed on the outlet side of the continuous annealing equipment, so the Si and Mn generated on the steel sheet surface simultaneously with the removal of the oxide film on the steel sheet surface It is possible to remove oxides such as Thus, although it is efficient to perform the pickling process with the equipment attached to the continuous annealing process, you may perform it with the pickling line provided separately.

Furthermore, in this invention, in order to improve plating adhesiveness to the steel plate cooled to below the martensite transformation point, one or more types of pre-plating among Ni, Fe, Co, Sn, and Cu are applied to one side of the steel plate. It is preferable to apply 0.01 to 2.0 g / m ² , preferably 0.1 to 1.0 g / m ² . The pre-plating method can be any of electroplating, immersion plating, and spray plating. If the coating adhesion is less than 0.01 g / m ² , the effect of improving adhesion by pre-plating cannot be obtained, and if it exceeds 2.0 g / m ² , the cost is high. ^Two .

  The steel sheet treated as described above is then subjected to hot dip galvanization, but it is preferable to perform pretreatment before entering this hot dip galvanizing process. This pretreatment is a treatment for cleaning the steel plate surface with a grinding brush or the like. The grinding brush is preferably a brush with abrasive grains, and the cleaning treatment liquid is preferably warm water, caustic soda liquid or both.

  In order to be able to cope with urgent and large orders / production, it is preferable that the existing continuous annealing process and the hot dip galvanizing process are separate lines, but this is not specified. In the case of a separate line, shape correction such as temper rolling can be performed to correct the deformation of the steel plate in the continuous annealing furnace, or the electrolytic cleaning line can be used to remove stains on the steel plate. Furthermore, since a material sample can be collected between continuous annealing and hot dip galvanizing, the material can be predicted in advance.

  The steel sheet thus treated is then galvanized in a hot dip galvanizing process. In this hot dip galvanizing process, the steel sheet surface is heated to a temperature higher than the temperature at which the steel sheet surface is activated, that is, in a temperature range of 250 to 600 ° C. In consideration of the temperature difference between the galvanizing bath and the steel sheet, a temperature range of 460 to 530 ° C. is preferable. Although a heating means is not specified, a radiant tube or induction heating is preferable. In order to be able to cope with urgent and large orders / production, the heating furnace of the existing continuous hot dip galvanizing line can be used. In addition, since the steel sheet is already subjected to the recrystallization annealing in the continuous annealing process described above, it can be passed at a higher speed than the case where the steel sheet is directly sent from the cold rolling process to the hot dip galvanizing process. This is preferable when dealing with urgent and large orders / production.

  In addition, the galvanized steel sheet that has been galvanized in the hot dip galvanizing step is 470 to 600 in order to obtain a hard and tough plated layer with a dense plated structure by further alloying the plated layer. Heat treatment can be performed in a temperature range of ° C. to obtain an alloyed hot-dip galvanized steel sheet. In particular, in the present invention, the Fe concentration in the plating layer can be controlled to, for example, 7 to 15% by mass by performing an alloying treatment.

  Furthermore, in the present invention, in order to improve the corrosion resistance and workability, the surface layer of the hot dip galvanized steel sheet or alloyed hot dip galvanized steel sheet manufactured in the above-described process is chromated, oriented coating, and chemical conversion treatment. Any one or more of the resin film treatments can be post-treated.

<Example 1>
A steel slab obtained by melting and casting a steel having the component composition shown in Table 1 in a vacuum melting furnace is reheated to 1200 ° C, and then hot rolled to finish rolling at a temperature of 880 ° C to obtain a hot-rolled steel plate, Rewinding heat treatment was performed by cooling, winding at a winding temperature of 600 ° C., and holding at that temperature for 1 hour. The obtained hot-rolled steel sheet is scaled by grinding, subjected to cold rolling at a reduction rate of 70%, and then heated to a temperature of 770 ° C. using a continuous annealing simulator, and then subjected to continuous annealing for 74 seconds. went. Subsequently, it was cooled to 450 ° C. at 10 ° C./s, and galvanized steel sheets were produced by the following two production methods, that is, the conventional method and the method of the present invention.
(1) Conventional method After cooling to 450 ° C. as described above, hot-dip galvanizing at a temperature of 500 ° C. and further galvannealing at a temperature of 500 ° C. without any pickling and pre-plating, and cooling to room temperature 1% temper rolling was performed to obtain a product. Various properties such as mechanical properties, metal structure, hole expandability, plating adhesion, etc. of this product are shown in Table 2 (Production method i)).
(2) Method of the present invention After the cooling to 450 ° C. described above, an overaging treatment is performed at a temperature of 400 ° C. for 180 seconds, followed by cooling to the martensite transformation point or lower, and then pickling with 5% hydrochloric acid. After performing Ni pre-plating of 0.5 g / m ² per side of the steel sheet, it is heated to a temperature of 500 ° C., galvanized, further galvannealed, cooled to room temperature, and adjusted to 1%. Quality rolling was performed to obtain a product. Various properties of this product, such as mechanical properties, metal structure, hole expansibility, and plating adhesion, are shown in Table 3 (Production Method ii)).

The tensile strength (TS), hole expansion ratio, metal structure, retained austenite, tempered martensite, plating adhesion, and plating appearance shown in Tables 2 and 3 are as described below.
-Tensile strength: JIS No. 5 tensile test piece was evaluated by L-direction tension.

TS was 540 MPa or more, and the product of TS × El (%) was 18,000 MPa or more.
-Hole expansion rate: Adopts Japan Iron and Steel Federation standard, JFS T1001-1996 hole expansion test method. A conical punch with an apex angle of 60 ° is pushed into a punched hole of 10 mmφ (die inner diameter: 10.3 mm, clearance: 12.5%) at a rate of 20 mm / min in the direction in which the burrs of the punched hole are outward.

Hole expansion rate: λ (%) = {D−Do} × 100
D: Hole diameter (mm) when the crack penetrates the plate thickness
Do: Initial hole diameter (mm)
The hole expansion rate was determined to be 50% or more.
Metal structure: Observation with an optical microscope and measurement of residual austenite ratio by X-ray diffraction. Ferrite was observed by nital etching, and martensite was observed by repeller etching.
・ Tempered martensite ratio: The tempered martensite is quantified by repeller etching. The sample is polished (alumina finish) and then used as a corrosive solution (mixed solution of pure water, sodium pyrosulfite, ethyl alcohol, and picric acid). After soaking for 10 seconds, polishing is performed again, and after washing with water, the sample is dried with cold air. After drying, the area of 100 μm × 100 μm area of the sample structure was measured with a Luzex device at 1000 times to determine the area% of tempered martensite. In Tables 2 and 3, this tempered martensite area ratio is expressed as tempered martensite area%.
-Residual austenite ratio: MoKα line ferrite (200), (210) area strength and austenite (200), (220), and austenite on the surface chemically polished to 1/4 thickness from the surface layer of the specimen plate (311) Residual austenite was quantified from the area strength. A residual austenite ratio of 5% or more was considered good. In Tables 2 and 3, this residual austenite volume fraction was expressed as residual γ volume%.
-Plating adhesion: Evaluated from the state of plating peeling at the bent part in a 60 ° V bending test.

A: Plating peeling small (peeling width less than 3mm)
○: Minor peeling to a practical level
(Peeling width 3mm or more and less than 7mm)
Δ: A considerable amount of peeling is observed
(Peeling width 7mm or more and less than 10mm)
X: Thick peeling (peeling width 10 mm or more)
As for plating adhesion, ◎ and ○ were acceptable.
・ Plating appearance: Visual observation
A: Uniform appearance with no plating or unevenness
○: Appearance unevenness with no plating and practically acceptable
Δ: Appearance unevenness is remarkable
×: Non-plating occurs and appearance unevenness is remarkable
As for the plating appearance, ◎ and ○ were accepted.

<Example 2>
A steel slab obtained by melting and casting E, H, and P steels within the range of the present invention listed in Table 1 in a vacuum melting furnace is reheated to 1200 ° C, and then hot-rolled and finish-rolled at a temperature of 880 ° C. After forming a hot-rolled steel sheet, it was cooled, wound at a winding temperature of 600 ° C., and a winding heat treatment was maintained for 1 hour at that temperature. The obtained hot-rolled steel sheet is scaled by grinding, subjected to cold rolling at a reduction rate of 70%, and then heated to a temperature of 770 ° C. using a continuous annealing simulator, and then subjected to continuous annealing for 74 seconds. The sample was cooled to 450 ° C. at 10 ° C./s, then subjected to overaging treatment at a temperature of 400 ° C. for 180 seconds, and then the following five types of experiments were performed on the steel sheet cooled to the martensite transformation point or lower. .

Experiment 1 (Invention Example) Pickled with 5% hydrochloric acid, and Ni pre-plating was performed at 0.5 g / m ² Experiment 2 (Invention Example) Ni pre-plating was performed at 0.5 g / m ² without pickling. Experiment 3 (Comparative Example) Pickling with 5% hydrochloric acid and performing Ni pre-plating 0.005 g / m ² Experiment 4 (Comparative Example) Pickling with 5% hydrochloric acid and without Ni pre-plating Experiment 5 (Example of the present invention) Without pickling, without Ni pre-plating Then, after performing brush grinding as equivalent to surface cleaning on the entry side of the continuous hot dip galvanizing line, it is heated to a temperature of 500 ° C. and hot dip galvanized. Alloyed hot-dip galvanizing treatment was performed, and after cooling to room temperature, 1% temper rolling was performed to obtain a product. Table 4 shows the plating adhesion and various characteristics of the plating appearance of this product.

  In Example 1, the present invention in Table 3 has improved hole expansibility due to an increase in tempered martensite compared to the comparative example having the same experiment number in Table 2. In addition, the adhesion and plating appearance are improved by pickling and pre-plating. In the comparative example of Table 3, although plating adhesion and plating appearance are improved by pickling and pre-plating, the component is outside the scope of the present invention, so any of TS, TS × El, and hole expansion rate is selected. The passing value is not met.

  In the difference in pickling and pre-plating conditions of Example 2, it is preferable that the plating adhesion and the plating appearance are greatly improved by pre-plating according to Experiment 1, Experiment 2, and Experiment 5, and that pickling is performed before pre-plating. In Experiment 3, if the amount of pre-plating is small, there is no effect, and in Experiment 4, it is worsened by pickling alone. In the case of pickling only, the plating adhesion and plating appearance deteriorate on the contrary, because the surface is heated too much in the continuous hot dip galvanizing heating process, so that the oxides such as Si and Mn of the steel sheet again. It seems to occur on the steel plate surface and deteriorate the plating property.

Claims (8)

  In mass%, C: 0.12-0.35%, Si: 0.2-1.0%, Mn: 0.8-3.5%, P: 0.03% or less, S: 0.03 %, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, N: 0.010% or less, and a hot dip galvanized steel sheet comprising the balance Fe and inevitable impurities. The metal structure of the steel sheet has ferrite and bainite, plating adhesion and holes characterized by having tempered martensite in an area ratio of 0.5% to 10% and retained austenite in a volume ratio of 7% or more. Hot-dip galvanized high-strength steel sheet with excellent spreadability.   In mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Cu: 1% or less, Ni: 1% or less Cr: 1% or less, B: One or more of 0.0001 to 0.0030% are contained, and excellent in plating adhesion and hole expansibility according to claim 1 Hot-dip galvanized high-strength steel sheet.   In mass%, C: 0.12-0.35%, Si: 0.2-1.0%, Mn: 1.2-3.5%, P: 0.03% or less, S: 0.03 %, Al: 0.25 to 1.8%, Mo: 0.05 to 0.35%, N: 0.010% or less, and after hot rolling a slab composed of the balance Fe and inevitable impurities, After winding at a temperature of 400 to 750 ° C., cold rolling, and then annealing at a temperature of 680 to 930 ° C. in a continuous annealing process, cooling to below the martensitic transformation point, and then applying hot dip galvanization, 250 A method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility, characterized by performing a hot-dip galvanizing treatment after heating to ~ 600 ° C. After cooling to below the martensitic transformation point in the continuous annealing step, one or more of pre-plating of Ni, Fe, Co, Sn, and Cu is performed at 0.01 to 2.0 g / m ² per one side of the steel sheet. The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility according to claim 3.   The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expansibility according to claim 4, wherein the steel sheet is pickled before the pre-plating.   4. The method for producing a hot-dip galvanized high-strength steel sheet excellent in plating adhesion and hole expandability according to claim 3, wherein the galvanized layer is alloyed after the hot dip galvanizing step.   The post-treatment of any one or more of chromate treatment, inorganic film treatment, chemical conversion treatment, and resin film treatment is further performed on the galvanized layer or alloyed galvanized layer. The manufacturing method of the hot-dip galvanized high-strength steel plate excellent in the plating adhesiveness and hole expansibility as described in any one of -6.   The hot-dip galvanized high-strength steel sheet is further, in mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Cu: 1% or less, Ni: 1% or less, Cr: 1% or less, B: 0.0001-0.0030% of 1 type or 2 types or more are contained, The any one of Claims 3-7 characterized by the above-mentioned The manufacturing method of the hot dip galvanized high strength steel plate excellent in the plating adhesiveness and hole expansibility as described in the above item.