WO2018117724A1 - High strength hot rolled steel sheet and cold rolled steel sheet having excellent continuous productivity, high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion, and manufacturing method therefor - Google Patents

Abstract

Disclosed are a high strength hot rolled steel sheet and the like, the hot rolled steel sheet comprising: by wt%, 0.14-0.3% of C, 1-2.0% of Si, 2.6-5% of Mn, 0.001-2% of sol.Al, (48/14)*[N]-0.1% of Ti, 0.04% or less (excluding 0%) of P, 0.015% or less (excluding 0%) of S, 0.02% or less (excluding 0%) of N, 0.08-0.2% of a sum of one or more types among Sb, Bi, Sn, and Zn, and the balance of Fe and inevitable impurities, wherein an internal oxide containing one or more types of elements among Si, Mn, Al, and Fe is present in the surface layer part of the hot rolled steel sheet, and a maximum depth of the internal oxide is 1 μm or less (including 0 μm).

Description

High strength hot rolled steel sheet and cold rolled steel sheet with excellent continuous productivity and high strength hot dip galvanized steel sheet with excellent surface quality and plating adhesion and manufacturing method thereof

The present invention relates to a high strength hot rolled steel sheet and a cold rolled steel sheet having excellent continuous productivity, and a high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion and a method of manufacturing the same.

Recently, there is a continuous demand for increasing the strength of automobile steel plates to reduce the weight of automobiles and to improve the stability of collisions due to the regulation of carbon dioxide for the preservation of the global environment.

In order to satisfy these demands, high strength steel sheets of 950 MPa or more have been recently developed and applied to automobiles.

As a method of increasing the strength of the steel sheet, it is easy to manufacture a high strength steel sheet by increasing the amount of reinforcing components of carbon and other steels, but in the case of steel sheet for automobile body, cracks should not occur during forming into the vehicle body. Therefore, the elongation of the steel sheet must also be secured at the same time.

Mn, Si, Al, Cr, Ti, etc. are added to steel in order to secure both strength and ductility of automotive steel sheets at the same time. A steel sheet having ductility can be produced.

In general, the steel sheet used in the automobile for extending the life of the vehicle needs to improve the corrosion resistance, for which hot-dip galvanized steel sheet is used.

In the case of high strength steel sheets for automobiles having a strength of 950 MPa or more, components such as Si, Mn, and Al are added to steel to secure a target strength and elongation. However, high strength steel sheets containing Mn, Si and / or Al, which are easily oxidized in steel, react with trace amounts of oxygen or water vapor in the annealing furnace to form Mn, Si, Al alone or composite oxides on the surface of the steel sheet, and melt It hinders the wettability of zinc, so that uncoated, which is not attached to zinc locally or entirely on the surface of the plated steel, occurs, which greatly reduces the surface quality of the plated steel sheet.

Conventional continuous process for manufacturing such high strength galvanized steel sheet is made of molten steel and then made slab through continuous casting and hot rolling by heating the slab to high temperature and then removing iron oxide from the surface of hot rolled steel sheet in the pickling process The steel sheet is made by rolling, and then manufactured by performing hot dip plating through annealing in a hot dip plating facility.

In the case of high-strength steel containing a large amount of Si, Mn and / or Al in the steel, Mn, Si, and Al are mainly composed of Fe, Si, Mn, Al, etc. When the internal oxide is formed and is not completely removed in the pickling process and cold rolling is carried out, the oxide present in the grain boundary of the steel sheet surface is destroyed by rolling, so that the grain is weakened and it is easy to fall off, and then in the annealing and plating process The crystal grains dropped from the surface stick to various rolls and are then transferred to the steel sheet to cause defects called dents.

In order to prevent internal oxidation in such a hot rolling process, it is possible to make winding temperature low temperature below 550 degreeC so that internal oxidation does not occur. However, in high strength steels, when the coiling temperature is low, the structure of the hot rolled steel sheet includes bainite or martensite structure, which causes an increase in the strength of the hot rolled steel sheet, which makes it difficult to cold roll. Normally, it should be higher than 600 ℃, and the higher the strength of the hot rolled steel sheet, the higher the coiling temperature can reduce the load on the roll during cold rolling, thus making it cold rolled. However, the higher the coiling temperature, the higher the internal oxidation depth, and the higher the content of oxidizing components such as Mn, Si, and Al in the steel at the same coiling temperature, the deeper the internal oxidation, especially the Si content. Greatly affects

On the other hand, if the content of Mn, Si, Al, etc., in the steel is low, the internal oxidation hardly occurs even if the coiling temperature is increased, but in order to secure the desired strength and elongation of products with tensile strength of 950Mpa or higher, Addition is essential.

In the steel plate where internal oxidation occurs, internal oxides present in the grain boundary are also dissolved by some acid in the pickling process, and the grain boundary is weakened. Afterwards, in the cold rolling process, the grain boundary in which the internal oxidation occurred is destroyed and the crystal grains are excited and then annealed. In the furnace, grains are dropped by various rolls, which are attached to the rolls, and then cause dent defects in the form of stamping on the steel sheet.

Therefore, when the steel sheet is first produced, no dent defects occur, but as the production continues, the number of dents on the steel sheet increases, making production difficult. On the other hand, the dents (Dent) generated in the steel sheet is a problem because it is a concave defect of the stamped form is clearly revealed in the coating process after processing to automotive parts.

As a result, a high strength steel sheet having a high tensile strength of 950 MPa or more, which is used for automobile body structural members, can be stably produced continuously without occurrence of dent defects, but is manufactured to produce hot-dip galvanized steel sheet having excellent surface quality and plating adhesion. The invention was proposed.

In order to improve the plating quality, various techniques have been proposed. Among them, Patent Literature 1 controls air and fuel at an air-fuel ratio of 0.80 to 0.95 during annealing to oxidize the steel sheet in a direct flame furnace of an oxidizing atmosphere, so that Si, Mn, or Al alone to a certain depth inside the steel sheet. Alternatively, the present invention provides a technique of forming iron oxide including a composite oxide, reducing annealing in a reducing atmosphere, and then reducing the iron oxide and performing hot dip galvanizing. When the reduction method after oxidation is used in the annealing process as described above, components having a high affinity for oxygen such as Si, Mn, and Al are internally oxidized at a predetermined depth from the surface of the steel sheet, and diffusion into the surface is suppressed. As the single or composite oxide is reduced, the wettability with zinc in the plating bath is improved, thereby reducing the unplating. In other words, when heated under a high oxygen partial pressure where iron can be oxidized, iron is oxidized to a certain depth of the surface layer to form an iron oxide layer. Elements that are easier to oxidize than iron can no longer diffuse to the surface because they oxidize under the iron oxide layer and are present as oxides. In the subsequent reduction process, the iron oxide is easily reduced to iron in an atmosphere containing a certain amount of hydrogen and is present as a reduced iron layer in the surface layer, so that the wettability with zinc improves and the plating property is improved. However, even if the plating property is improved by the post-oxidation reduction method of the high strength steel sheet, it is not possible to prevent liquefied brittle cracks during spot welding in the assembling process after forming the structural member using the steel sheet.

As another method for improving the high-strength steel plating property, Patent Document 2 maintains the dew point in the annealing furnace to maintain a high dew point in the annealing furnace to oxidize components such as Mn, Si, Al, etc. The present invention provides a technique for improving plating property by reducing oxides that are externally oxidized. Internal oxidation of the oxidizing component by this method reduces the external oxidation and improves the plating property, but like the internal oxide in the hot rolling process, the internal oxide formed at the grain boundary of the steel sheet during the annealing is attached to various rolls in the annealing furnace. There is a problem that a dent defect occurs.

Therefore, the present invention suppresses the generation of internal oxides in the steel plate surface layer after hot rolling and winding high-strength steel containing a large amount of Mn, Si, and / or Al in the steel, thereby suppressing the occurrence of steel sheet dent during subsequent annealing, thereby continuously producing The purpose of the present invention is to provide a high-strength hot-dip galvanized steel sheet having excellent surface quality and adhesion by suppressing the formation of Mn, Si, Al, etc. alone or composite oxide on the surface of the steel sheet during annealing.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Korean Unexamined Patent Publication No. 10-2010-0030627

(Patent Document 2) Korean Unexamined Patent Publication No. 10-2009-0006881

One of the various objects of the present invention is to provide a high strength hot rolled steel sheet and a cold rolled steel sheet having excellent continuous productivity, a high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion, and a method of manufacturing the same.

In one aspect of the present invention, in weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [ N] ~ 0.1%, P: 0.04% or less (except 0%), S: 0.015% or less (except 0%), N: 0.02% or less (except 0%), at least one of Sb, Bi, Sn, Zn : A hot rolled steel sheet containing 0.08 to 0.2% in total, balance Fe and unavoidable impurities, wherein an internal oxide containing at least one element of Si, Mn, Al, and Fe is present in the hot rolled steel sheet surface layer, and the maximum of the internal oxide is present. Provide a high strength hot rolled steel sheet with a depth of 1 μm or less (including 0 μm).

According to another aspect of the present invention, in weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [ N] ~ 0.1%, P: 0.04% or less (except 0%), S: 0.015% or less (except 0%), N: 0.02% or less (except 0%), at least one of Sb, Bi, Sn, Zn : A cold rolled steel sheet containing 0.08 to 0.2% in total, balance Fe and unavoidable impurities, and a hot dip galvanized layer formed on the surface of the cold rolled steel sheet, wherein the surface layer portion of the cold rolled steel sheet includes at least one of Si, Mn, Al, and Fe. An internal oxide containing an element is present, and the maximum depth of the internal oxide is 0.3 μm or less (excluding 0 μm) to provide a high strength hot dip galvanized steel sheet.

Another aspect of the invention is, in weight percent, C: 0.14-0.3%, Si: 1-2.0%, Mn: 2.6-5%, sol.Al: 0.001-2%, Ti: (48/14) * [N]-0.1%, P: 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), Sb, Bi, Sn, or Zn Or more: reheating the slab containing a total of 0.08 to 0.2%, balance Fe and unavoidable impurities, and then hot rolling to obtain a hot rolled steel sheet under a condition of a finish hot rolling temperature Ar3 ° C. or higher, and the hot rolled steel sheet at a temperature of 600 to 800 ° C. Winding at, provides a method for producing a high strength hot rolled steel sheet comprising the step of cooling the wound hot rolled steel sheet to a temperature of 550 ℃ or less at an average cooling rate of 2 ℃ / min or more.

Another aspect of the invention is, in weight percent, C: 0.14-0.3%, Si: 1-2.0%, Mn: 2.6-5%, sol.Al: 0.001-2%, Ti: (48/14) * [N]-0.1%, P: 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), Sb, Bi, Sn, or Zn Or more: reheating the slab containing a total of 0.08 to 0.2%, balance Fe and unavoidable impurities, and then hot rolling to obtain a hot rolled steel sheet under a condition of a finish hot rolling temperature Ar3 ° C. or higher, and the hot rolled steel sheet at a temperature of 600 to 800 ° C. Winding in the step, cooling the wound hot rolled steel sheet to an average cooling rate of 2 ° C./min or more to a temperature of 550 ° C. or less, cold rolling the cooled hot rolled steel sheet to obtain a cold rolled steel sheet, and dew point the cold rolled steel sheet. After heating to a temperature of 820 ~ 870 ℃ under a temperature of -60 ~ -30 ℃, and holding for 5 ~ 120 seconds to recrystallize annealing, the recrystallized annealing cold rolled steel sheet at a rate of 20 ℃ / sec or more 250 ~ 350 Up to a temperature of ℃ After cooling, holding for 50 to 150 seconds, and heating the cooled and held cold rolled steel sheet to a temperature of 460 ~ 500 ℃ at a rate of 30 ℃ / sec or more, and then plated by plating in a zinc plating bath within 7 seconds It provides a method of manufacturing a high strength hot dip galvanized steel sheet comprising a step.

As one of the effects of the present invention, the high strength hot rolled steel sheet according to the present invention has an advantage of excellent continuous productivity.

In addition, the high strength hot-dip galvanized steel sheet according to the present invention has an advantage of excellent surface quality and plating adhesion.

Various and advantageous advantages and effects of the present invention is not limited to the above description, it will be more readily understood in the course of describing specific embodiments of the present invention.

Figure 1 shows the results of analyzing the cold rolled steel sheet according to Inventive Example 9 by 3D-AP.

2 (a) is an SEM image of the cross section of the cold rolled steel sheet according to Comparative Example 31, Figure 2 (b) is an SEM image of the cross section of the invention example 33.

Hereinafter, a high strength hot rolled steel sheet having excellent continuous productivity, which is an aspect of the present invention, will be described in detail.

First, the alloy component and the preferred content range of the high strength hot rolled steel sheet of the present invention will be described in detail. It is noted that the content of each component described below is based on weight unless otherwise specified.

C: 0.14 ~ 0.3%

C is an essential element for securing martensite strength, and in order to obtain such an effect in the present invention, it is preferably included 0.14% or more. However, if the content is excessive, the ductility, bending workability and weldability is reduced, the press formability and roll workability is deteriorated, the upper limit is preferably limited to 0.3%.

Si: 1 ~ 2.0%

Si improves the yield strength of the steel and at the same time stabilizes ferrite and residual austenite at room temperature. Especially, in the case of TRIP (Tranformation Induced Plasticity) steel, it inhibits cementite precipitation from austenite during cooling and inhibits the growth of carbides. Thereby stabilizing residual austenite. Therefore, it is an essential element for producing a steel sheet excellent in ductility with a tensile strength of 950 MPa or more as in the present invention. In order to obtain such an effect in the present invention, it is preferably included 1% or more, more preferably 1.1% or more. However, if the content is excessive, internal oxides containing a large amount of Si are formed in the grain boundary of the hot-rolled steel sheet and in the mouth, and due to such internal oxides, the crystals of the surface layer are eliminated during cold annealing and adhered to the rolls to be taken on the steel sheet. Mold defects are caused. In addition, since the Ar3 transformation temperature is greatly increased during hot rolling and is rolled in an austenite and ferrite abnormal region, the strength of the hot rolled steel sheet is greatly increased, which may cause cracking during cold rolling. In consideration of this, the upper limit of the Si content is preferably limited to 2.0%.

Mn: 2.6 ~ 5%

Mn is well known as a hardenability increasing element that inhibits ferrite formation and stabilizes austenite. In particular, in order to ensure the strength and ductility desired in the present invention, Mn is preferably contained at 2.6% or more. However, if the content is excessive, it is difficult to secure the plating property by increasing the amount of surface oxidation of Mn during annealing, so the upper limit is preferably limited to 5%.

sol.Al: 0.001 ~ 2%

sol.Al is an element added for deoxidation in the steelmaking process. In addition, sol.Al also helps to form carbonitrides and reduces the annealing cost by expanding the ferrite region and lowering the Ac1 transformation point. In order to obtain such an effect in the present invention, it is preferable to include 0.001% or more. However, if the content is excessive, it is difficult to secure the plating property by increasing the surface oxidation amount of sol.Al during annealing, so the upper limit is preferably limited to 2%.

Ti: (48/14) * [N]-0.1%

Ti is a nitride forming element, lowers the content of solid solution N in steel, and serves to suppress AlN formation, which is a cause of hot rolling cracks. In order to obtain such an effect in the present invention, it is necessary to add chemically equivalent (48/14) * [N] or more. However, if the content is excessive, the carbon concentration and strength of martensite may be reduced by additional carbide precipitation in addition to the removal of solid solution N, so the upper limit is preferably limited to 0.1%.

P: 0.04% or less (except 0%)

P is an inevitable impurity contained in steel. When the content thereof is excessive, weldability is lowered, brittleness of steel is more likely to occur, and dent defects are more likely to occur. In order to prevent this, the upper limit of the P content is preferably limited to 0.04%.

S: 0.015% or less (excluding 0%)

S, like P, is an inevitable impurity contained in steel. When the content thereof is excessive, ductility and weldability of steel are deteriorated. In view of preventing this, the upper limit of the S content is preferably limited to 0.015%.

N: 0.02% or less (except 0%)

N is an inevitable impurity contained in steel, and if the content is excessive, the risk of cracking during playing due to AlN formation is greatly increased. In view of preventing this, the upper limit of the N content is preferably limited to 0.02%.

At least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total

There are two reasons for adding Sb, Sn, Bi, and Zn in the present invention.

First, when these components are added to steel, they are concentrated at the surface and surface layer of hot rolled steel sheet at high coiling temperature after hot rolling to prevent oxygen from diffusing into the steel, so that the internal grain boundary and the inside of Si, Mn, Al, Fe, etc. It is effective in suppressing the formation of oxides.

Second, in the process of pickling and cold rolling the hot rolled steel sheet, Sb, Sn, Bi, Zn components are first concentrated in the steel plate surface and surface layer to prevent the diffusion of oxidizing components such as Si, Mn, Al in the steel plate surface. By inhibiting the formation of oxides consisting of Si, Mn, Al on the surface of the annealed steel sheet, zinc serves to facilitate adhesion in the galvanizing bath.

One or two or more of the Sb, Sn, Bi, and Zn components suppress the formation of oxides of Si, Mn, and Al on the surface of the annealing steel sheet even when the addition amount is less than 0.08%, thereby facilitating adhesion of zinc in the galvanizing bath, thereby facilitating the plating quality. And it is possible to manufacture a high strength hot-dip galvanized steel sheet excellent in adhesion. However, since the internal oxidation of the hot rolled steel sheet is not sufficiently suppressed, this causes the surface iron crystals attached to various rolls in the annealing furnace, which causes dent defects in the steel sheet, which become more severe as steel sheet production increases. Therefore, even if the first 1 to 2 coils are manufactured with high-strength hot-dip galvanized steel sheet having excellent plating quality and adhesion, the product cannot be produced due to the occurrence of dent defects.

Therefore, at least one or more of Sb, Sn, Bi, and Zn components to be added to steel to suppress internal oxidation must be at least 0.08% or more, and the internal oxidation depth of the hot-rolled steel sheet defined in the present invention is 1 μm or less, and then pickling. In the annealing process after cold rolling, dent defects can be prevented. As a result, it is possible to continuously produce without inhibiting hot rolling internal oxidation without generating dents in the subsequent annealing process, and at the same time, the minimum addition amount to secure the plating quality by inhibiting the formation of annealing oxide on the surface of the steel sheet is limited to 0.08%. It is preferable to. In addition, when forming an alloying inhibiting layer containing 0.001 to 0.05% by weight of the total content of one or more of Sb, Bi and Sn, as described later, one or more of the elements of Sb, Sn, Bi It may include the sum of the content of more than 0.08%.

However, when the content of Sb, Sn, Bi, Zn, etc. in the steel is excessive, the internal oxidation inhibitory effect is excellent, but there is a problem that the ductility is lowered. In the present invention, a special heat treatment is carried out to prevent ductility deterioration with the addition of these components, but if the sum of the contents of these components exceeds 0.2%, even if the heat treatment proposed in the present invention is applied, the target elongation is secured. Since it is impossible to do so, the upper limit of the sum of one or more contents among Sb, Sn, Bi, and Zn is preferably limited to 0.2%.

In addition to the above composition, the rest is Fe. However, in the usual manufacturing process, unavoidable impurities that are not intended from the raw materials or the surrounding environment may be inevitably mixed, and thus, this cannot be excluded. Since these impurities are known to those of ordinary skill in the art, not all of them are specifically mentioned herein, but for example, Cu, Mg, Co, Ca, Na, V, Ga At least one of Ge, As, Se, In, Ag, W, Pb, and Cd may be used. When the content thereof is less than 0.1%, the effect of the present invention is not impaired.

On the other hand, addition of an effective component other than the composition is not excluded, for example, may further include one or more selected from the group consisting of Cr, Mo, Nb, B.

Cr: 1.0% or less

Cr is an effective hardening element to increase the strength of steel, but there is no major problem in securing physical properties even without adding Cr. On the other hand, when the Cr content is excessive, the manufacturing cost increases rapidly, which is not preferable. In consideration of this, the upper limit of the Cr content is preferably limited to 1.0%.

Mo: 0.2% or less

Mo is an effective ingredient for improving the strength of the steel without deteriorating the molten zinc wettability, but even without adding it, there is no major problem in securing the physical properties. On the other hand, when the Mo content is excessive, it is not preferable that the manufacturing cost increases rapidly. In consideration of this, the upper limit of the Mo content is preferably limited to 0.2%.

Nb: 0.1% or less

Nb segregates in the form of carbides in the austenite grain boundary, thereby suppressing grain coarsening of austenite during annealing heat treatment, thereby improving the strength of the steel, but there is no major problem in securing the physical properties even if Nb is not added. On the other hand, when the Nb content is excessive, the manufacturing cost increases rapidly, which is not preferable. In consideration of this, the upper limit of the Nb content is preferably limited to 0.1%.

B: 0.005% or less

B is an effective component for securing the strength of the steel, but there is no major problem in terms of securing physical properties even without adding B. However, when the B content is excessive, it may be concentrated on the annealing surface and greatly degrade the plating property. The upper limit of the content is preferably limited to 0.005%.

Hereinafter, the microstructure of the high strength hot rolled steel sheet according to the present invention will be described in detail.

In the surface layer portion of the hot-rolled steel sheet of the present invention there is an internal oxide containing at least one element of Si, Mn, Al, Fe, characterized in that the maximum depth of the internal oxide is 1μm or less (including 0μm).

In the case of the hot-rolled steel sheet of the present invention, since a large amount of surface thickening elements Si, Mn, Al, and the like are added, internal oxides are inevitably formed in the surface layer portion. However, as a result of the present inventors, when the maximum depth of the internal oxide exceeds a certain range, a dent defect is caused in the annealing process after cold rolling, thereby lowering the continuous productivity. In order to prevent this, it is necessary to suppress the maximum depth of the internal oxide to 1 μm or less (including 0 μm). Herein, the maximum depth of the internal oxide includes 0 μm, which means that the internal oxide does not exist at all. In one example of the present invention, the maximum depth of the internal oxide may be 0.8 μm or less (including 0 μm).

In the present invention, the microstructure of the hot rolled steel sheet is not particularly limited. For example, the microstructure of the hot rolled steel sheet may include at least one of ferrite, pearlite, and bainite at an appropriate ratio. However, when the double bainite is excessively formed, the strength of the hot rolled steel sheet is excessively increased, which may cause cracks in the steel sheet during the cold rolling process. In order to prevent this, the upper limit of the area fraction of bainite is preferably controlled to 50%, and more preferably, the upper limit may be set to 40%.

Hereinafter, a high strength cold rolled steel sheet having excellent continuous productivity, which is another aspect of the present invention, will be described in detail.

The high strength cold rolled steel sheet according to another aspect of the present invention has the aforementioned component system, and an internal oxide containing at least one element of Si, Mn, Al, and Fe is present in the surface layer portion of the cold rolled steel sheet, and the maximum depth of the internal oxide is It is characterized by being 0.3 μm or less (excluding 0 μm). If the maximum depth of the internal oxide of the cold rolled steel sheet exceeds 0.3μm, a dent defect is caused during the annealing process, and thus continuous productivity may be lowered. According to one example of the present invention, the maximum depth of the internal oxide may be 0.2 μm or less (excluding 0 μm).

Hereinafter, another aspect of the present invention will be described in detail a high-strength hot-dip galvanized steel sheet excellent in surface quality and plating adhesion.

Another aspect of the present invention is a high strength hot-dip galvanized steel sheet, comprising a cold-rolled steel sheet having the above-described component system and a hot-dip galvanized layer formed on the surface of the cold-rolled steel sheet, wherein the surface layer portion of the cold-rolled steel sheet has one of Si, Mn, Al, and Fe. Internal oxides containing more than one element are present, and the maximum depth of the internal oxides is 0.3 μm or less (excluding 0 μm). If the maximum depth of the internal oxide of the cold rolled steel sheet exceeds 0.3μm, a dent defect is caused during the annealing process, and thus continuous productivity may be lowered. According to one example of the present invention, the maximum depth of the internal oxide may be 0.2 μm or less (excluding 0 μm).

According to one embodiment, the sum of the contents of at least one of Sb, Bi, Sn, Zn in the thickness direction 0.001μm from the surface of the cold rolled steel sheet Sb, Bi, Sn in the thickness direction 0.02μm from the surface of the cold rolled steel sheet , Zn may be 3 to 15 times the sum of one or more contents of Zn.

The concentration of Sb, Bi, Sn and Zn components in the surface layer of cold rolled steel sheet has the effect of suppressing the surface diffusion of Mn, Si and / or Al during the high temperature annealing process, so the higher the concentration of these components, the higher the surface of Mn, Si, Al. The effect of suppressing diffusion is great, and in order to secure plating quality and adhesion, at least 0.001μm in the thickness direction of the base iron from the interface of the plating layer and the base iron is 0.02μm in the thickness direction of the base iron from the base iron interface. It needs to be concentrated at least three times as much. However, if it exceeds 15 times, the upper limit is limited to 15 times because the adhesion decreases by preventing the formation of the alloying inhibitory layer composed of Fe-Al-Zn in the plating bath. According to one embodiment of the present invention, the content at the 0.001 μm point and the content of the 0.02 μm point in the thickness direction of the base iron may be determined as an average of five measurements each.

In the present invention, the microstructure of the cold rolled steel sheet is not particularly limited. For example, the microstructure of the cold rolled steel sheet may include at least one of ferrite, pearlite, bainite, martensite, and retained austenite in an appropriate ratio. However, in terms of ensuring strength and ductility at the same time, the area fraction of the double retained austenite is preferably controlled to 5 to 50%.

According to one example, the high-strength hot-dip galvanized steel sheet of the present invention may further include an alloying suppression layer formed at the interface between the cold-rolled steel sheet and the hot-dip galvanized layer, in this case, the alloying inhibitory layer is one of Sb, Bi and Sn The above may include 0.001 to 0.05% by weight of the total content. In one example, these elements may comprise 0.001 to 0.03% of the total content. As such, when at least one of Sb, Bi, and Sn in the alloying suppression layer is included in a predetermined amount or more, the plating adhesion is improved. However, if the content is excessively excessive, the alloying inhibitory layer may be coarse, and plating adhesion may be reduced, thereby controlling the sum of the content to 0.05 wt% or less.

High strength hot-dip galvanized steel sheet of the present invention has the advantages of excellent strength and ductility, according to one embodiment, the high-strength hot-dip galvanized steel sheet of the present invention is a tensile strength of 950Mpa or more, the product of tensile strength and elongation is 16000Mpa ·% or more Can be.

The high strength hot rolled steel sheet, the high strength cold rolled steel sheet, and the high strength hot dip galvanized steel sheet of the present invention described above may be manufactured by various methods, and the manufacturing method thereof is not particularly limited. However, as a preferred example, it may be prepared by the following method.

Hereinafter, another aspect of the present invention will be described in detail a method for producing a high strength hot rolled steel sheet and a cold rolled steel sheet having excellent continuous productivity and a high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion.

First, the slab having the above-described component system is reheated. At this time, it is preferable that reheating temperature is 1100-1300 degreeC. If the reheating temperature is less than 1100 ° C., the hot rolling load may increase rapidly. On the other hand, if the reheating temperature is higher than 1300 ° C., the reheating cost may increase and the amount of surface scale may be excessively increased.

Next, hot rolling is carried out under the condition of the finish hot rolling temperature Ar3 ° C or higher to obtain a hot rolled steel sheet. If the finish rolling temperature is less than Ar3 ℃, two-phase or ferritic rolling of ferrite and austenite is carried out to create a hybrid structure and because of the possibility of malfunction due to fluctuation of the hot rolling load, limit to the temperature of Ar3 ℃ or more.

Next, the hot rolled steel sheet is wound at a temperature of 600 to 800 ° C. If the coiling temperature is less than 600 ℃ the strength of the hot rolled steel sheet is too high may cause the fracture of the rolling roll during cold rolling process, and also the material variation in the width direction of the steel sheet is prone to bend bending easily occurs after cold rolling. On the other hand, if the coiling temperature exceeds 800 ℃, the maximum depth of the internal oxide in the hot-rolled steel sheet exceeds 1μm, the oxidation depth inside the surface layer of the cold-rolled steel sheet exceeds 0.3μm during the subsequent annealing process, resulting in a dent The defect can be severe.

Next, the wound hot rolled steel sheet is cooled to an average cooling rate of 2 ° C / min or more to a temperature of 550 ° C or lower. Normally, after winding, natural cooling, that is, air cooling is performed in air at room temperature. In the case of air cooling, the cooling rate is slow, so that it takes a long time until the internal oxidation ends up to 550 ° C. or lower, so that the internal oxidation occurs even after winding. Further progress will be made. Therefore, it is necessary to perform forced cooling until at least the surface temperature of the wound hot rolled steel sheet reaches a temperature of 550 ° C. or lower, and in the case of the present invention, it is necessary to cool at an average cooling rate of 2 ° C./min or more. On the other hand, since the higher the cooling rate after the winding is advantageous to the prevention of internal oxidation, the present invention is not particularly limited to the upper limit, but if the cooling rate is too fast, the strength of the hot rolled steel sheet may increase to increase the cold rolling load. Therefore, since cold rolling may become difficult, when considering this, the upper limit may be limited to 10 degrees C / min.

Next, optionally, the cooled hot-rolled steel sheet may be washed after pickling, in this case, pickling may be performed for 15 to 20% by volume of hydrochloric acid aqueous solution having a temperature of 60 to 80 ℃ for 30 to 60 seconds. The pickling process removes the oxidation scale present on the hot rolled steel sheet and also dissolves a portion of the surface layer portion of the hot rolled steel sheet, thereby partially dissolving internal oxides that may be present in the surface layer portion of 1 μm or less. Therefore, the higher the acid concentration, the higher the temperature, and the longer the time, the greater the amount of dissolution of the surface layer of the iron, which may reduce the internal oxidation depth after pickling. However, if the acid concentration is too high, local corrosion may occur on the surface of the steel sheet, which may cause small hole defects. When the temperature of the hydrochloric acid aqueous solution is high, the amount of hydrochloric acid evaporates, which may corrode the surrounding equipment. On the other hand, the pickling time requires at least 30 seconds to remove the surface oxidation scale, and if it is too long, productivity is limited to 60 seconds.

Next, the cold rolled hot rolled steel sheet is cold rolled to obtain a cold rolled steel sheet. In this case, the cold reduction rate may be 30 to 60%. If the cold rolling reduction is less than 30%, hot rolling may be difficult because the thickness of the hot rolled sheet needs to be made too thin. On the other hand, if the cold rolling rate exceeds 60%, the load on the cold rolling roll may increase significantly, resulting in breakage of the rolling roll. Can be.

Next, optionally, a lead gold layer made of at least one element among Fe, Ni, Co, and Sn may be formed on the surface of the cold rolled steel sheet. In this case, the amount of the lead gold layer deposited may be 0.01-2 g / m ² per side. Can be controlled. As described above, when the lead is applied, it is very effective in controlling the dew point in the target range in the subsequent recrystallization annealing process.

Next, the cold rolled steel sheet is heated to a temperature of 820 ~ 870 ℃ under a dew point temperature of -60 ~-30 ℃, then maintained for 5 to 120 seconds and recrystallized annealing.

In the present invention, it is very important that the annealing temperature is heated to the austenite single phase in order to obtain the target material. In the present invention, one or two or more Sb, Bi, Sn, and Zn are added to improve the hot rolling internal oxidation and plating property, and these additions cause a decrease in elongation. Therefore, in the present invention, in order to increase the elongation, it is important to maximize the residual austenite after annealing and cooling, and then temper some of the austenite through reheating to secure the elongation. Therefore, it is necessary to heat it to at least 820 degreeC which is austenite single phase. However, if it exceeds 870 ℃ Sb, Bi, Sn, Zn thickening on the surface is excessively increased, the double concentration of Sb, Bi, Sn is reduced the plating quality and adhesion improvement effect. Therefore, the annealing temperature is preferably limited to 820 ~ 870 ℃.

The annealing time requires at least 5 seconds to obtain a uniform recrystallized structure, and if it is too long, productivity is reduced, so it is limited to 120 seconds.

If the dew point temperature is lower than -60 ° C, the diffusion rate of Si and Al in the steel is faster than the diffusion rate of Mn, so that Si and Al of the composite oxides containing Si, Mn, and Al formed on the surface of the steel sheet as main components Since the content is significantly increased compared to Mn, and the Si or Al content of the surface complex oxide is higher than that of Mn, the plating property is inferior, which is insufficient to ensure the wettability of zinc even in the composition and manufacturing conditions of the present invention, and the dew point is -30 ° C. In case of exceeding, during the annealing process, some of the Si, Mn and Al components are oxidized in the grain boundary and the inside of the sheet steel of the steel sheet and present as internal oxides. Even if the maximum depth of internal oxide is less than 0.3μm, internal oxidation is additionally generated during annealing process. Since more than a 0.3μm limited in the present invention can cause the furnace Dent (Dent) dew point of the atmosphere gas in the annealing it is preferably also limited to -60 ~ -30 ℃.

According to one example, the recrystallization annealing may be carried out under 3 to 70 volume% H ₂ -N ₂ gas atmosphere conditions. If the hydrogen content is less than 3% by volume, the reduction of the iron oxide present on the surface of the steel sheet may be insufficient, and as the hydrogen content is increased, it is advantageous in terms of the reduction effect, but the economical efficiency is lowered and the productivity decreases, so the upper limit is 70% by volume. It is limited to.

Next, the recrystallized annealed cold rolled steel sheet is cooled to a temperature of 250 ~ 350 ℃ at a rate of 20 ℃ / sec or more, and then maintained for 50 to 150 seconds.

In the present invention, the cooling process after recrystallization annealing is also a very important process for securing the strength and ductility of the material. In order to maximize the residual austenite after cooling by minimizing the ferrite transformation in the cooling process after making the austenite single phase of the steel sheet by annealing heating and holding of the present invention, the cooling rate is better, the average cooling rate of at least 20 ℃ / sec or more It is necessary to cool to 250 ~ 350 ℃. If the average cooling rate is less than 20 ℃ / sec, the ferrite transformation during cooling increases the target strength and ductility cannot be secured. In addition, the cooling end temperature is required at least 250 ° C to maximize the residual austenite, and when the cooling temperature is less than 250 ° C some martensite phase is formed to increase the strength, but there is a problem that the elongation is greatly reduced. If the cooling temperature exceeds 350 ℃, the amount of austenite transformation to bainite increases, which is disadvantageous to secure the target strength and ductility.

On the other hand, the cooled steel plate needs a maintenance process for 50 to 150 seconds. Maintain austenite stabilization and transformation of some austenite to bainite while maintaining at a cooling temperature for at least 50 seconds. However, if the holding time exceeds 150 seconds, the bainite transformation amount may increase, thereby reducing the ductility of the final product.

Next, the cooled and held cold rolled steel sheet is heated to a temperature of 460 to 500 ° C. at a rate of 30 ° C./sec or more, and then plated by plating in a zinc plating bath within 7 seconds.

The steel plate maintained at the cooling temperature requires an elevated temperature to be immersed in the plating bath, which is the next process. In this temperature raising process, some of the retained austenite is tempered, so that the tensile strength is slightly decreased, but the elongation that is decreased by the addition of Sb, Bi, Sn, Zn and the like can be ensured. However, if the heating rate is less than 30 ℃ per second, it takes a long time to heat, so the tempering is excessively proceeded and the tensile strength drop occurs, so it should be at least 30 ℃ / sec. Similarly, after heating to 460 ~ 500 ℃ it needs to be immersed in the plating bath within 7 seconds. In addition, if the holding time after heating is long, the tempering increases, causing a drop in strength.

According to one example, the zinc plating bath may comprise 0.12 to 0.3% by weight of Al. If the alloyed hot-dip galvanized steel sheet is manufactured, it is better to manage the Al content of 0.12 to 0.15%, and when manufacturing the hot-dip galvanized steel sheet, it is better to manage it to 0.15% to 0.3%.

According to one example, the temperature of the zinc plating bath may be 450 ~ 500 ℃. It is not preferable because the viscosity of zinc increases below 450 ° C., so that the driveability of the roll in the zinc plating bath is lowered, and when the temperature exceeds 500 ° C., evaporation of zinc increases.

Next, the alloying heat treatment may optionally be performed for 1 second or more at a temperature of 480 to 600 ° C. In this case, the alloyed hot-dip galvanized layer may contain 7 to 13% by weight of Fe.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the description of these examples is only for illustrating the practice of the present invention, and the present invention is not limited by the description of these examples. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

( Example  One)

The steel slabs having the compositions of Tables 1 and 2 below were reheated at a temperature of 1200 ° C. for 1 hour, finish-rolled at 900 ° C. higher than Ar 3 of all steel slabs, and then cooled to the winding temperatures of Table 3, followed by 550 After forced cooling to an average cooling rate of 3 ℃ / min to a temperature of ℃, Furnace cooling was carried out. The cold-rolled hot rolled steel sheet was observed by scanning electron microscopy to observe the steel sheet internal oxide. At this time, the maximum depth of the internal oxide of the hot-rolled steel sheet was measured five times at 5000 times to take the maximum depth of these.

Next, the cooled hot rolled steel sheet was pickled with 60 ° C. and 17% by volume of HCl solution for 40 seconds to dissolve iron oxide on the surface, and then cold-rolled at a rolling reduction of 45%. Then, the cross section of the steel sheet was observed by scanning electron microscopy to observe the cold rolled oxide. At this time, the maximum depth of the internal oxide of the cold rolled steel sheet was measured five times at 5000 times to take the maximum depth of these. In addition, it was observed whether the crack of the cold rolled steel sheet, the results are shown in Table 3 below.

Next, after removing the foreign matter on the surface through the pre-treatment, after performing annealing under the heating and cooling conditions of Table 4, the plating bath temperature 460 ℃, Al content 0.13wt% (for GA) or 0.22wt% (GI After plating under the conditions of ()), using an air knife was adjusted to 60g / m ² single-side reference plating deposition amount and cooled to obtain a plated steel sheet. At this time, some of the specimens were not plated to observe the surface and the base iron surface thickening after annealing. Subsequently, some of the specimens were additionally subjected to alloying heat treatment for 25 seconds at 550 ° C. In Table 4, the specimens subjected to the alloying heat treatment were shown as GA, GI for the specimens that had not been alloyed.

Subsequently, the surface of the plated steel sheet is visually checked for the presence of unplated parts and degree for surface quality evaluation, and the automotive structural adhesive is applied to the surface of the steel sheet to evaluate plating adhesion, and then dried. After bending the road was confirmed whether the plating layer is buried in the adhesive, and after evaluating the surface quality and plating adhesion on the basis of the following criteria, the results are shown in Table 5 together.

Surface quality; ○: no unplated part, △: unplated in size less than 2mm in diameter, X: unplated in excess of 2mm in diameter

Plating adhesion; ○: no plating peeling, △ partial peeling, X complete peeling

Then, the tensile test was carried out in JIS No. 5 to measure the tensile strength and elongation of the plated steel sheet, the results are shown in Table 5 together. In addition, the maximum depth of the internal oxide of the plated steel sheet was measured five times at 5000 times, and the maximum depth was selected among them.

Next, in order to measure the Sb, Bi, Sn content in the alloying inhibitory layer between the hot-dip galvanized layer and the cold-rolled steel sheet interface, only the zinc-plated layer was removed and the alloying inhibitory layer at the interface was dissolved and analyzed by ICP (Inductively Coupled Plasma). . In addition, in order to observe the thickening of the cold rolled steel plate surface portion of the plated steel sheet, the cross section is processed by FIB (Focused Ion Beam), and the composition profile of 3-D Atom Probe Topography (FAT) is 0.001μm in the depth direction from the cold rolled steel plate surface layer portion. Measure the average content of Sb, Bi, Sn, Zn at the five points in the location, and measure the average content of Sb, Bi, Sn, Zn at the location of 0.02μm in the depth direction of the steel sheet from the cold rolled steel plate surface. The ratio of the content of the 0.001 μm point to the content of the μm point was measured to determine the surface concentration.

* Surface concentration = total sum of Sb, Bi, Sn and Zn components (wt%) at 0.001μm / sum of Sb, Bi, Sn and Zn components (wt%) at 0.02μm

Steel grade	Chemical composition (% by weight)
	C	Si	Mn	P	S	Sol.Al	Cr	Ti
A	0.16	1.52	2.75	0.015	0.002	0.036	0.02	0.019
B	0.17	1.55	2.7	0.0085	0.0027	0.1	0.4	0.019
C	0.17	1.55	3.05	0.015	0.0023	0.1	0.41	0.018
D	0.17	1.65	2.72	0.014	0.0021	0.7	-	0.018
E	0.15	1.15	2.65	0.015	0.0037	0.01	-	0.012
F	0.17	1.55	2.71	0.0095	0.0025	0.01	0.4	0.010
G	0.17	1.98	4.2	0.01	0.0026	0.01	-	0.01
H	0.18	1.4	3	0.015	0.003	0.5	0.1	0.012
I	0.15	1.7	3.3	0.015	0.004	0.2	-	0.008
J	0.15	3.5	4.11	0.0095	0.003	0.1	0.2	0.008
K	0.18	1.65	10.1	0.015	0.0045	0.015	0.2	0.008

Steel grade	Chemical composition (% by weight)
	B	Mo	N	Nb	Sb	Bi	Sn	Zn
A	-	0.05	0.0036	-	-	-	-	-
B	0.001	0.05	0.0032	-	0.1	-	-	-
C	0.001	-	0.0033	-	-	0.09	-	0.005
D	0.001	0.08	0.0031	-	-	-	0.11	-
E	-	0.11	0.0033	-	0.04	-	0.04	0.005
F	0.001	0.05	0.0032	0.01	0.03	-	0.06	0.001
G	-	-	0.0021	-	0.06	0.02	0.05
H	-	-	0.0031	-	0.06	-	-	-
I	0.001	0.02	0.0027	0.01	0.03	-	0.02	-
J	-	0.02	0.0015	-	0.02	0.08	-	-
K	0.002	-	0.0025	0.005	0.05	-	0.06	0.01

Psalm Number	Steel grade	Winding temperature (℃)	Hot Rolled Internal Oxidation Depth (㎛)	Steel plate cracking after cold rolling	Cold Rolled Internal Oxidation Depth (㎛)	division
One	B	610	0	radish	0	Inventive Example
2	B	720	0.6	radish	≤0.1	Inventive Example
3	B	420	0	U	-	Comparative example
4	C	680	0.2	radish	0	Inventive Example
5	C	730	0.6	radish	≤0.1	Inventive Example
6	C	650	0.1	radish	0	Inventive Example
7	C	650	0.1	radish	0	Comparative example
8	C	650	0.1	radish	0	Comparative example
9	D	630	0.1	radish	0	Inventive Example
10	D	630	0.1	radish	0	Comparative example
11	D	850	7.5	radish	3.1	Comparative example
12	A	650	12	radish	5.8	Comparative example
13	A	450	0.2	U	0	Comparative example
14	E	620	0	radish	0	Inventive Example
15	E	730	0.3	radish	0	Inventive Example
16	E	650	0.1	radish	0	Comparative example
17	E	650	0.1	radish	0	Comparative example
18	E	650	0.1	radish	0	Comparative example
19	E	650	0.1	radish	0	Comparative example
20	F	720	0.6	radish	≤0.1	Inventive Example
21	F	650	0.2	radish	0	Comparative example
22	F	650	0.2	radish	0	Inventive Example
23	G	700	0.9	radish	0.2	Inventive Example
24	G	610	0.2	radish	0	Inventive Example
25	G	870	8	radish	2.9	Comparative example
26	G	650	0.4	radish	≤0.1	Comparative example
27	H	700	3.5	radish	1.6	Comparative example
28	I	680	7.1	radish	3	Comparative example
29	J	680	0.2	U	0	Comparative example
30	K	680	0	radish	0	Comparative example

Psalm Number	Dew point temperature (℃)	Annealing Temperature (℃)	Cooling temperature (℃)	Average cooling rate (℃ / sec)	Holding time at cooling temperature (sec)	Reheating Temperature (℃)	Reheat Rate (℃ / sec)	Holding time before reimmersion of plating bath (sec)	Plating layer type	division
One	-45	840	300	28	85	480	55	4.5	GI	Inventive Example
2	-45	840	300	28	90	480	53	4.3	GI	Inventive Example
3	-	-	-	-	-	-	-	-	-	Comparative example
4	-45	840	280	35	90	480	58	4.1	GI	Inventive Example
5	-45	850	300	25	90	480	60	5.3	GI	Inventive Example
5-1	-45	920	300	25	90	480	55	4.8	GI	Comparative example
6	-40	850	320	25	70	480	56	4.1	GI	Inventive Example
7	-10	850	320	25	80	480	55	4.5	GI	Comparative example
8	-40	910	300	30	100	480	57	4.1	GA	Comparative example
9	-45	850	300	30	115	480	54	4.2	GI	Inventive Example
10	-45	850	390	25	90	480	55	5.2	GI	Comparative example
11	-45	850	320	25	70	480	54	5.6	GI	Comparative example
12	-45	830	290	25	70	500	65	4.1	GI	Comparative example
13	-	-	-	-		-	-	-	-	Comparative example
14	-45	850	300	25	70	480	55	4	GI	Inventive Example
15	-45	860	320	22	70	480	67	4.3	GI	Inventive Example
16	-45	850	300	12	70	480	48	4.8	GA	Comparative example
17	-45	850	300	25	10	480	35	5.4	GI	Comparative example
18	-45	850	300	25	80	470	15	5.3	GI	Comparative example
19	-45	850	300	25	75	480	55	12	GI	Comparative example
20	-45	860	320	22	80	480	49	5.2	GI	Inventive Example
20-1	-50	850	320	22	80	480	10	5.2	GI	Comparative example
21	-45	790	310	23	80	480	58	4.5	GI	Comparative example
22	-50	840	330	45	80	480	59	5.8	GI	Inventive Example
23	-55	840	330	45	80	480	54	5.2	GI	Inventive Example
24	-50	850	380	25	80	480	56	5.3	GA	Inventive Example
25	-50	830	290	25	80	500	61	5.6	GI	Comparative example
26	-55	800	420	45	80	480	59	4.4	GI	Comparative example
27	-45	850	280	25	90	490	41	4.6	GI	Comparative example
28	-45	850	350	25	90	480	42	4.6	GI	Comparative example
29	-	-	-	-	-	-	-	5.2	-	Comparative example
30	-45	840	420	25	78	500	45	5.2	GI	Comparative example

Psalm Number	Internal oxidation depth after annealing (㎛)	Sb, Bi, Sn, Zn surface concentration	Sb, Bi, Sn content (wt%) (Sb + Bi + Sn) in the alloying inhibition layer	Surface quality	Plating adhesion	TS (Mpa)	TS (Mpa) xEl (%)	division
One	0	9.3	0.006	○	○	≥950	19834	Inventive Example
2	≤0.1	9.1	0.0055	○	○	≥950	19481	Inventive Example
3	-	-	-	-	-	-	-	Comparative example
4	0	7.2	0.0023	○	○	≥950	18629	Inventive Example
5	0	7.7	0.0038	○	○	≥950	18596	Inventive Example
5-1	0	16.8	0.0359			≥950	16900	Comparative example
6	0	7.4	0.0026	○	○	≥950	18359	Inventive Example
7	1.1	6.9	0.0019	○	○	≥950	18975	Comparative example
8	0	26.4	0.031	○	△	≥950	18613	Comparative example
9	0	10.1	0.009	○	○	≥950	18216	Inventive Example
10	0	9.9	0.0061	○	○	≥950	15256	Comparative example
11	3.2	10.3	0.0058	○	○	≥950	18145	Comparative example
12	5.8	-	-	X	X	≥950	19856	Comparative example
13	-	-	-	-	-	-	-	Comparative example
14	0	6.8	0.0031	○	○	≥950	18945	Inventive Example
15	0.16	6.5	0.0034	○	○	≥950	18657	Inventive Example
16	0	6.9	0.003	○	○	≥950	14780	Comparative example
17	0	7.0	0.0032	○	○	≥950	15100	Comparative example
18	0	6.7	0.0031	○	○	≤900	15200	Comparative example
19	0	6.9	0.0031	○	○	≤900	16657	Comparative example
20	≤0.1	7.3	0.0396	○	○	≥950	18178	Inventive Example
20-1	≤0.1	8.2	0.0325			≥950	15210	Comparative example
21	0	4.8	0.0012	○	○	≥950	14988	Comparative example
22	0	4.9	0.0013	○	○	≥950	18083	Inventive Example
23	0.2	12.2	0.0171	○	○	≥950	18045	Inventive Example
24	0	12.8	0.0183	○	○	≥950	18231	Inventive Example
25	2.9	11.9	0.0153	○	○	≥950	18114	Comparative example
26	≤0.1	9.2	0.0109	○	○	≥950	14500	Comparative example
27	1.6	5.1	0.0021	○	○	≥950	19672	Comparative example
28	3	3.8	0.0011	○	○	≥950	19132	Comparative example
29	-	-	-	-	-	-	-	Comparative example
30	0	10.8	0.0111	△	△	≥950	18182	Comparative example

As shown in Tables 1 to 5, Examples 1 to 2, 4 to 6, 9, 14 to 15, 20, and 22 to 24, which are examples of the present invention, are limited in the present invention using steel grades having a component range defined in the present invention. A hot rolled steel sheet, a cold rolled steel sheet, and a hot dip galvanized steel sheet were manufactured by one manufacturing method, and the maximum internal oxide depth of the hot rolled steel sheet was 1 μm or less, the internal oxide maximum depth of the cold rolled steel sheet was 0.3 μm or less, and after annealing, The maximum internal oxide depth was 0.3 μm or less. In addition, the surface concentration of Sb, Bi, Sn, and Zn is 3 to 15, and one or two or more of the Sb, Bi, Sn components in the galvanized layer and the cold-rolled steel interface Fe-Al alloy suppression layer contain 0.001 to 0.05%. Tensile strength of more than 950mpa, Tensile strength (Mpa) x Elongation (%) = 16000, excellent surface quality and plating adhesion.

Comparative Examples 3 and 13 are cases in which the steel sheet winding temperature is wound at a temperature lower than 550 ° C. defined in the present invention in the hot rolling process, and the area fraction of bainite is 74% and 69%, respectively, and the strength of the hot rolled steel sheet is too high. Cracks occurred in the steel sheet during cold rolling.

On the other hand, in the case of Comparative Example 29, the Si in the steel component is higher than the range defined in the present invention, cracks occurred in the steel sheet during cold rolling process.

In Comparative Example 5-1, the cold rolled steel sheet of Specimen No. 5 in Table 3 was used, but the annealing temperature was higher than the range defined in the present invention during the hot dip plating process. After annealing, the surface concentration of Sb, Bi, Sn, and Zn was observed. The surface quality and plating adhesion after plating were inferior in excess of 15 times the range defined in the present invention.

In the case of Comparative Example 7, although the steel component and the hot rolled coil temperature satisfy the range defined in the present invention, the hot rolling internal oxidation depth satisfies the range defined in the present invention, but the dew point temperature in the annealing furnace during the annealing process is limited in the present invention. In the case of higher than one range, the internal oxidation further progressed in the annealing furnace, and the internal oxidation depth of the steel sheet after annealing exceeded the limited range of the present invention.

In the case of Comparative Example 8, the annealing temperature was higher than the range defined in the present invention, and the surface layer thickening degree of Sb, Bi, Sn, and Zn exceeded the range defined in the present invention, and partial plating peeling occurred.

In the case of Comparative Example 10, the steel component and the hot rolling conditions satisfy the range defined in the present invention, but the cooling temperature is higher than the limited range of the present invention in the annealing process, and the amount of austenite transformed to bainite increases, thereby increasing TsxEl. This was lower than the range defined in the present invention.

In the case of Comparative Examples 11 and 25, the hot-rolled coiling temperature is higher than the range defined in the present invention, and the content of the internal oxidation inhibiting components Sb, Bi, Sn, and Zn is within the hot-rolled internal oxidation depth even if the content defined in the present invention is satisfied. Was beyond the range defined in the present invention, the cold rolled steel sheet and the annealing depth after annealing exceeded the range defined in the present invention.

On the other hand, in the case of Comparative Example 12, Sb, Bi, Sn, Zn component is not added among the steel components, even if the hot rolling temperature satisfies the range of the present invention, the internal oxidation depth is 12㎛, exceeding the range defined in the present invention The annealing internal oxidation depth was also deep to 5.8 μm. In addition, during annealing of the cold rolled steel sheet, due to the concentration of oxidizing components such as Si, Mn, and Al on the surface of the steel sheet, an unplated diameter exceeding 2mm was present.

In the case of Comparative Example 13, Sb, Bi, Sn, Zn component of the steel component is not added, but the hot rolling temperature is lower than the range of the present invention, since the coiling temperature is low, the hot rolling internal oxidation is 0.2㎛ However, due to the low coiling temperature, the hot rolled strength was greatly increased, causing cracks during cold rolling.

Comparative Example 16 is a steel component, hot rolling conditions satisfy the range defined in the present invention, but the average cooling rate in the annealing process is lower than the range defined in the present invention, respectively, austenite is transformed into ferrite during the cooling process remaining The austenite content was reduced so that TSxEL was lower than the range defined in the present invention.

Comparative Example 17 is a steel component, the hot rolling conditions satisfy the range defined in the present invention, but when the holding time at the cooling temperature is outside the limited range of the present invention, austenite stabilization does not occur, the amount of tempering increases after reheating TSxEL Was low.

In Comparative Example 18, the steel component, hot rolling condition, annealing, and cooling conditions satisfy the range defined in the present invention, but the rate of reheating up to 470 ° C. after cooling and holding is slower than the range defined in the present invention. Strength and ductility fell simultaneously.

In Comparative Example 19, the steel component, hot rolling condition, annealing, cooling, and reheating conditions satisfied the range defined in the present invention, but after a long time until the immersion in the plating bath after reheating up to 480 ° C, the tempering increased, which caused TSxEL Low.

In Comparative Example 20-1, the cold rolled steel sheet of Specimen No. 20 of Table 3 was used, but the reheating rate during the hot dip plating process was lower than the range defined in the present invention, and tempering occurred during reheating for a long time. Significantly decreased, TsxEl was less than the range defined in the present invention.

In case of Comparative Example 21, the annealing temperature was lower than the range defined in the present invention. The annealing temperature was lowered in the ferrite and austenite abnormal zone, and then the residual austenite content was reduced through cooling, maintenance, and reheating, thereby lowering TSxEL.

Comparative Example 26 is a case in which the annealing temperature is higher than the range defined in the present invention after the annealing in the anomaly zone other than the austenite single-phase zone defined in the present invention, the residual austenite content is low TSxEL is limited in the present invention Lower than the range.

In the case of Comparative Examples 27 and 28, when the Sb, Bi, Sn, Zn components of the steel components were added less than the range defined in the present invention, the hot-rolled internal oxidation depth exceeded the range limited by the present invention, and then the cold rolled steel sheet And the depth of internal oxidation in the annealed steel sheet was deeper than the range defined in the present invention. However, Sb, Bi, Sn, Zn components in the annealing process, the effect of inhibiting the formation of annealing oxides, such as Si, Mn, Al was sufficient, and the plating quality and adhesion was excellent.

Comparative Example 29 is a case where the Si content of the steel component exceeds the range defined in the present invention, the abnormal reverse rolling is carried out in the hot rolling process, whereby a large amount of work hardened ferrite and cementite in which recrystallization does not occur in the hot rolled steel sheet As a result, the strength of the hot rolled steel sheet was greatly increased, which caused plate breakage during cold rolling.

 Comparative Example 30 is a case in which the Mn content in the steel component exceeds the range defined in the present invention, even if the addition amount of the Sb, Bi, Sn, and Zn components satisfies the scope of the present invention, Si, Mn, Due to the large amount of annealing oxides, such as Al, unplated spots of less than 2 mm occurred in the steel sheet, and partial peeling occurred.

On the other hand, Figure 1 shows the results of the analysis of the cold rolled steel sheet according to Inventive Example 9 by 3D-AP.

( Example  2)

In order to check the occurrence of dent defects while continuously producing coiled products, they were produced and analyzed in actual production facilities. Following the continuous casting of the components having the composition of Tables 6 and 7, to prepare a steel slab. After using it for 1 hour at 1200 ℃, after finishing rolling at 900 ℃, which is higher than Ar3 of all steel slabs, it is cooled to the coiling temperature shown in Table 8 and wound up with coils, and then heated to 3 ℃ to 550 ℃. After forced cooling at an average cooling rate of / min, the mixture was air cooled.

In the hot rolled steel sheet cooled to room temperature, the cross section of the steel sheet was observed with a scanning electron microscope to observe the hot rolled oxide. In this case, the maximum depth of the internal oxide of the steel sheet was measured five times at 5000 times, and the maximum depth was selected.

The pickling of the hot rolled steel sheet was performed at 70 ° C. and 17 Vol% HCl solution for 30 to 50 seconds, followed by cold rolling immediately. Cold rolled steel sheet was observed by scanning electron microscopy to observe the cross-sectional internal oxidation depth. In this case, the maximum depth of the internal oxide of the steel sheet was measured five times at 5000 times, and the maximum depth was selected.

The cold rolled steel sheet is subjected to annealing under the heating and cooling conditions of the following Table 8 after removing foreign substances on the surface through pretreatment, and then plated under the conditions of the plating bath temperature of 456 ° C and the Al content of 0.22wt% in the plating bath. It was used to adjust the coating weight of coating on one side of 60g / m ² and cooled to prepare a plated steel sheet. In order to confirm the occurrence of dent defects in the annealing furnace according to the production volume, the same steel is continuously produced for 15 coils under the same conditions, and the number of dent generating start coils is measured. It is shown in Table 9 below.

Then, the surface quality and plating adhesion was evaluated for the plated steel sheet, the tensile strength and elongation were measured, and the results are shown in Table 9 together. Specific measurement and evaluation methods are the same as those in Example 1.

Steel grade	Chemical composition (% by weight)
	C	Si	Mn	P	S	Sol.Al	Cr	Ti
L	0.162	1.51	2.75	0.008	0.0024	0.022	0.2	0.02
M	0.161	1.52	2.74	0.012	0.0026	0.021	0.2	0.02
N	0.162	1.50	2.72	0.011	0.0029	0.018	0.2	0.021
O	0.163	1.49	2.76	0.009	0.0022	0.015	0.2	0.021
P	0.165	1.55	2.69	0.014	0.0021	0.025	0.2	0.018

Steel grade	Chemical composition (% by weight)
	B	Mo	N	Nb	Sb	Bi	Sn	Zn
L	0.001	0.05	0.0031	-	-	-	-	0.001
M	0.001	0.05	0.0027	0.04	-	-	-	0.001
N	0.0011	0.05	0.0037	0.09	0.04	-	0.04	0.0011
O	0.001	0.05	0.0024	-	0.03	0.07	-	0.001
P	0.001	0.06	0.0031	0.05	0.04	0.04	0.0017	0.001

Psalm Number	Steel grade	Winding temperature (℃)	Hot Rolled Internal Oxidation Depth (㎛)	Cold Rolled Internal Oxidation Depth (㎛)	Annealing Process								division
					Dew point temperature (℃)	Annealing Temperature (℃)	Cooling temperature (℃)	Average cooling rate (℃ / sec)	Holding time at cooling temperature (sec)	Reheating Temperature (℃)	Reheat rate (℃ / sec)	Holding time (sec) before plating bath immersion after reheating
31	L	650	12	5.2	-43	850	300	28	78	480	55	4.2	Comparative example
32	M	650	5.5	2.4	-43	850	300	28	78	480	55	4.3	Comparative example
33	N	650	0	0	-43	850	300	28	78	480	55	4.3	Inventive Example
34	N	650	0	0	-43	850	300	23	67	480	22	8.5	Comparative example
35	O	680	0	0	-43	850	300	28	78	480	55	4.3	Inventive Example
36	P	680	0	0	-43	850	300	28	78	480	55	4.3	Inventive Example

Psalm Number	Dent Fault start coil order	Surface quality	Plating adhesion	TS (Mpa)	TS (Mpa) xEl (%)	division
31	From the second coil	X	X	≥950	19162	Comparative example
32	From the 4th coil	○	○	≥950	19081	Comparative example
33	Not all 15 coils	○	○	≥950	18881	Inventive Example
34	Not all 15 coils	○	○	≤900	15349	Comparative example
35	Not all 15 coils	○	○	≥950	18561	Inventive Example
36	Not all 15 coils	○	○	≥950	17992	Inventive Example

As shown in Tables 6 to 9, Examples 33, 35, and 36 of the present invention satisfy all of the alloy composition and manufacturing conditions proposed by the present invention. ), Surface quality and coating adhesion with Sb, Bi, Sn and Zn added at 0.08% or more, tensile strength (Mpa) x elongation (%) = 16000 It can be seen that an excellent hot-dip galvanized steel sheet can be provided.

In the case of Comparative Example 31, there is no component that can inhibit the hot rolling internal oxidation in steel, so it is internally oxidized to the depth of 12㎛ from the base iron surface of the hot rolled steel sheet, and then to the depth of 5.2㎛ from the high iron surface of the cold rolled steel sheet even after pickling and cold rolling. After internal oxidation, the internally oxidized grains of the surface layer were dropped during the annealing process, and the Dent defects were observed from the second coil after being attached to the roll in the annealing furnace.

In the case of Comparative Example 32, Sb, which is a hot rolled internal oxidation inhibiting component in steel, is added 0.04%, and the hot rolled internal oxidation is reduced compared to P steel, and the internal oxidation depth of hot rolled steel sheet is decreased to 5.2 μm compared to Comparative Example 31. Dent was observed from the fourth production coil as 2.4 μm deeper than the internal oxidation depth defined in the present invention even in cold rolled steel sheets after pickling and cold rolling exceeding the limited 1 μm.

In the case of Comparative Example 34, the steel component is a range defined in the present invention, but Dent did not occur until all 15 coils were produced because hot rolling internal oxidation did not occur, but the reheating rate after annealing heating and cooling was limited in the present invention. The slower and longer holding time until the plating bath was immersed after reheating led to the decrease of strength and TSxEl due to tempering of the retained austenite.

On the other hand, Figure 2 (a) is an SEM image observed the cross section of the cold rolled steel sheet according to Comparative Example 31, Figure 2 (b) is an SEM image observed the cross section according to the invention example 33.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and changes can be made without departing from the technical spirit of the present invention described in the claims. It will be obvious to those of ordinary skill in the field.

Claims (32)

1. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, A hot rolled steel sheet containing residual Fe and unavoidable impurities, wherein an internal oxide containing at least one element of Si, Mn, Al, and Fe exists in the surface layer portion of the hot rolled steel sheet, and the maximum depth of the internal oxide is 1 μm or less (0 μm) High strength hot rolled steel sheet.
2. The method of claim 1,

   The hot rolled steel sheet is by weight, Cr: 1.0% or less, Mo: 0.2% or less, Nb: 0.1% or less, B: 0.005% or less selected from the group consisting of high strength hot rolled steel sheet further.
3. The method of claim 1,

   The hot rolled steel sheet further comprises one or more from the group consisting of Cu, Mg, Co, Ca, Na, V, Ga, Ge, As, Se, In, Ag, W, Pb, Cd, the content of each High strength hot rolled steel sheet less than 0.1%.
4. The method of claim 1,

   A high-strength hot rolled steel sheet containing bainite as its microstructure and having an area fraction of 50% or less.
5. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, A high strength cold rolled steel sheet containing residual Fe and unavoidable impurities, and having an internal oxide containing at least one of Si, Mn, Al, and Fe in the surface layer portion, and having a maximum depth of 0.3 μm or less (excluding 0 μm). .
6. The method of claim 5,

   The sum of the contents of at least one of Sb, Bi, Sn and Zn in the thickness direction from 0.001 μm in the thickness direction from the surface of the cold rolled steel sheet in the Sb, Bi, Sn, Zn in the thickness direction from 0.02 μm in the thickness direction from the surface of the cold rolled steel sheet. High strength cold rolled steel sheet having 3 to 15 times the sum of at least one content.
7. The method of claim 5,

   High-strength cold-rolled steel sheet containing residual austenite as a microstructure and having an area fraction of 5 to 50%.
8. The method of claim 5,

   A high strength cold rolled steel sheet further comprising at least one selected from the group consisting of Cr: 1.0% or less, Mo: 0.2% or less, Nb: 0.1% or less, B: 0.005% or less.
9. The method of claim 5,

   Cu, Mg, Co, Ca, Na, V, Ga, Ge, As, Se, In, Ag, W, Pb, Cd further comprises one or more, each of which is less than 0.1% high strength Cold rolled steel sheet.
10. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, Cold rolled steel sheet containing remainder Fe and unavoidable impurities; And a hot dip galvanized layer formed on the surface of the cold rolled steel sheet.

    A high strength hot dip galvanized steel sheet having an internal oxide containing at least one of Si, Mn, Al, and Fe in the surface layer portion of the cold rolled steel sheet, and having a maximum depth of 0.3 μm or less (excluding 0 μm).
11. The method of claim 10,

    The sum of the contents of at least one of Sb, Bi, Sn and Zn in the thickness direction from 0.001 μm in the thickness direction from the surface of the cold rolled steel sheet in the Sb, Bi, Sn, Zn in the thickness direction from 0.02 μm in the thickness direction from the surface of the cold rolled steel sheet. High strength hot-dip galvanized steel sheet having 3 to 15 times the sum of at least one content.
12. The method of claim 10,

    High strength hot dip galvanized steel sheet having a tensile strength of 950 Mpa or more and a product of tensile strength and elongation of 16000 Mpa ·% or more.
13. The method of claim 10,

    The cold-rolled steel sheet includes residual austenite as its microstructure, and the area fraction is 5 to 50% high strength hot-dip galvanized steel sheet.
14. The method of claim 10,

    A high strength hot dip galvanized steel sheet further comprising an alloying inhibitory layer formed at an interface between the cold rolled steel sheet and the hot dip galvanized layer, wherein the alloying inhibitory layer comprises 0.001 to 0.05% by weight in total of at least one of Sb, Bi, and Sn.
15. The method of claim 10,

    The cold rolled steel sheet by weight, Cr: 1.0% or less, Mo: 0.2% or less, Nb: 0.1% or less, B: 0.005% or less selected from the group consisting of high strength hot-dip galvanized steel sheet further.
16. The method of claim 10,

    The cold rolled steel sheet further comprises one or more from the group consisting of Cu, Mg, Co, Ca, Na, V, Ga, Ge, As, Se, In, Ag, W, Pb, Cd, the content of each High strength hot dip galvanized steel sheet less than 0.1%.
17. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, Reheating the slab including the balance Fe and unavoidable impurities, and then hot rolling under a condition of a finish hot rolling temperature Ar3 ° C. or higher to obtain a hot rolled steel sheet;

    Winding the hot rolled steel sheet at a temperature of 600 to 800 ° C .; And

    Cooling the wound hot rolled steel sheet to an average cooling rate of 2 ° C./min or more to a temperature of 550 ° C. or less;

    Method for producing a high strength hot rolled steel sheet comprising a.
18. The method of claim 17,

    The reheating temperature of the slab is 1100 ~ 1300 ℃ manufacturing method of high strength hot rolled steel sheet.
19. The method of claim 17,

    Cooling rate of the wound hot rolled steel sheet is a manufacturing method of high strength hot rolled steel sheet is 2 ~ 10 ℃ / sec.
20. The method of claim 17,

    The slab is a weight%, Cr: 1.0% or less, Mo: 0.2% or less, Nb: 0.1% or less, B: 0.005% or less selected from the group consisting of a high strength hot rolled steel sheet manufacturing method.
21. The method of claim 17,

    The slab further comprises one or more from the group consisting of Cu, Mg, Co, Ca, Na, V, Ga, Ge, As, Se, In, Ag, W, Pb, Cd, their content is each 0.1 Method for producing high strength hot rolled steel sheet less than%.
22. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, Reheating the slab including the balance Fe and unavoidable impurities, and then hot rolling under a condition of a finish hot rolling temperature Ar3 ° C. or higher to obtain a hot rolled steel sheet;

    Winding the hot rolled steel sheet at a temperature of 600 to 800 ° C .;

    Cooling the wound hot rolled steel sheet to an average cooling rate of 2 ° C./min or more to a temperature of 550 ° C. or less; And

    Cold rolling the cooled hot rolled steel sheet to obtain a cold rolled steel sheet manufacturing method of high strength hot-dip galvanized steel sheet.
23. By weight%, C: 0.14 to 0.3%, Si: 1 to 2.0%, Mn: 2.6 to 5%, sol.Al: 0.001 to 2%, Ti: (48/14) * [N] to 0.1%, P : 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), at least one of Sb, Bi, Sn, and Zn: 0.08 to 0.2% in total, Reheating the slab including the balance Fe and unavoidable impurities, and then hot rolling under a condition of a finish hot rolling temperature Ar3 ° C. or higher to obtain a hot rolled steel sheet;

    Winding the hot rolled steel sheet at a temperature of 600 to 800 ° C .;

    Cooling the wound hot rolled steel sheet to an average cooling rate of 2 ° C./min or more to a temperature of 550 ° C. or less;

    Cold rolling the cooled hot rolled steel sheet to obtain a cold rolled steel sheet;

    Heating the cold rolled steel sheet to a temperature of 820 to 870 ° C. under a dew point temperature of −60 to −30 ° C., followed by holding for 5 to 120 seconds to recrystallize annealing;

    Cooling the recrystallized annealed cold rolled steel sheet to a temperature of 250 ° C. to 350 ° C. at a rate of 20 ° C./sec or more, and maintaining the same for 50 to 150 seconds; And

    And heating the cooled and retained cold rolled steel sheet to a temperature of 460 to 500 ° C. at a rate of 30 ° C./sec or more, and depositing and plating a zinc plating bath within 7 seconds.
24. The method of claim 23,

    After the winding and before cold rolling, the pickled hot rolled steel sheet further comprises the step of washing with water,

    The method of manufacturing a high strength hot-dip galvanized steel sheet wherein the wound hot-rolled steel sheet is pickled for 30 to 60 seconds in an aqueous solution of 15-20% by volume of hydrochloric acid having a temperature of 60-80 ° C.
25. The method of claim 23,

    The cold rolling reduction rate is 30 to 60% of the production method of high strength hot-dip galvanized steel sheet.
26. The method of claim 23,

    The recrystallization annealing is a manufacturing method of high strength hot-dip galvanized steel sheet is carried out under 3 ~ 70 volume% H ₂ -N ₂ gas atmosphere conditions.
27. The method of claim 23,

    The galvanizing bath is a method for producing a high strength hot dip galvanized steel sheet containing 0.12 ~ 0.3% by weight of Al.
28. The method of claim 23,

    The temperature of the galvanizing bath is a manufacturing method of high strength hot-dip galvanized steel sheet of 450 ~ 500 ℃.
29. The method of claim 23,

    Before the recrystallization annealing of the cold rolled steel sheet, further comprising the step of forming a lead gold layer consisting of at least one element of Fe, Ni, Co, Sn on the surface of the cold rolled steel sheet, the adhesion amount of the lead gold layer is 0.01 ~ 2g per one side Method for producing a high strength hot dip galvanized steel sheet / m ² .
30. The method of claim 23,

    After the plating, the method of producing a high-strength hot-dip galvanized steel sheet further comprising the step of alloying heat treatment for 1 second or more at a temperature of 480 ~ 600 ℃.
31. The method of claim 23,

    The slab is a weight%, Cr: 1.0% or less, Mo: 0.2% or less, Nb: 0.1% or less, B: 0.005% or less selected from the group consisting of high strength hot-dip galvanized steel sheet manufacturing method .
32. The method of claim 23,

    The slab further comprises one or more from the group consisting of Cu, Mg, Co, Ca, Na, V, Ga, Ge, As, Se, In, Ag, W, Pb, Cd, their content is each 0.1 Method for producing a high strength hot dip galvanized steel sheet less than%.

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