KR20140064392A - High strength alloyed galvanized steel sheet with excellent coating adhesion and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high strength alloyed galvanized steel sheet having an excellent coating adhesion, a cold-rolled steel sheet and a method for manufacturing the same. More specifically, the present invention is provided with a high strength alloyed galvanized steel sheet by controlling: a component system of the steel sheet; a refined structure of the steel sheet; a grain size of martensite among the steel sheet; and a fraction of an alloy among the alloyed galvanized steel sheet formed on one side of the steel sheet. Thereby, the high strength alloyed galvanized steel sheet having an excellent coating adhesion and a method for manufacturing the same can be provided.

Description

TECHNICAL FIELD The present invention relates to a high strength alloyed hot-dip galvanized steel sheet excellent in adhesion to a substrate and a method for manufacturing the same,

The present invention relates to a high strength alloyed hot-dip galvanized steel sheet which can be used as an automobile part material and has excellent plating adhesion and workability, and a method for producing the same.

Generally, the steel sheet used as a plate material and an outer plate material in an automobile is required to have good workability in addition to corrosion resistance to corrosion for processing. A typical example of such steel sheets is a galvanized steel sheet (GI). Such a hot-dip galvanized steel sheet is a steel sheet in which zinc is plated on the surface of a cold rolled steel sheet to improve corrosion resistance. The corrosion resistance of the hot-dip galvanized steel sheet depends on the adhesion amount of the zinc plating, and the greater the adhesion amount, the more excellent the corrosion resistance. On the other hand, however, there is a problem that the weldability of the steel sheet becomes lower as the amount of the zinc plating adhered increases. The product developed for the improvement of these problems is galvannealed steel sheet (GA).

The galvannealed galvanized steel sheet is obtained by annealing a cold rolled steel sheet that has not undergone annealing in a continuous galvanizing line, plating it in a galvanizing bath, passing it through a furnace, and alloying the Fe component of the steel substrate and the Zn component of the zinc- . Such galvanized hot-dip galvanized steel sheets are excellent in corrosion resistance due to a plated layer of a base steel sheet, and many automobile companies at home and abroad are actively expanding their use. However, such a galvannealed hot-dip galvanized steel sheet has disadvantages in that the galvanized steel sheet can be separated from the steel sheet in accordance with the degree of adhesion between the galvanized steel sheet and the plated layer at the time of elongation flange working of the steel sheet,

Therefore, in order to commercialize the coated steel sheet, research for realizing high plating adhesion of the base steel sheet has been continuously performed. Among them, there are a number of notable researches that there is an effect that an alloy component of a ground steel sheet put in the process of manufacturing a steel sheet lowers adhesion of plating. Particularly, in the case of dual phase steel (DP steel) and transformed induced plasticity (TRIP steel), which are transforming strengthened steel, manganese (Mn), silicon (Si), niobium (Nb), and aluminum (Al). These components are concentrated to the surface of the steel sheet during the cold rolling process in the production of the steel sheet, and the adhesion of the coating is deteriorated. Therefore, there is a problem in that the above steels are made of a galvannealed steel sheet and used.

In order to solve the above problems, Patent Documents 1 to 4 disclose techniques for improving the plating adhesion of a steel sheet by adding a certain amount of specific components such as chromium (Cr), antimony (Sb), and tin (Sn) However, the above-mentioned patent documents do not clarify the effect of addition of a specific element and the metallurgical behavior, and therefore, there is an aspect that is insufficient in specifying the production method thereof. Further, according to the techniques disclosed in these patent documents, there still remains a problem that the workability of the steel sheet is inferior due to low plating adhesion when it is made of galvannealed galvanized steel sheet.

Therefore, in the commercialization of the galvannealed galvanized steel sheet, there remains a need for a technique capable of realizing excellent workability and plating adhesion while maintaining high strength without adding a special alloy component whose metallurgical behavior is unclear.

1. Japanese Laid-Open Patent Publication No. 2002-146477 2. Japanese Laid-Open Patent Publication No. 2001-064750 3. Japanese Patent Application Laid-Open No. 2002-294397 4. Japanese Laid-Open Patent Publication No. 2002-155317

An object of the present invention is to provide a high strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability and a method for producing the same.

In order to achieve the above object, the steel sheet of the present invention comprises 0.07 to 0.08% by weight of C, 0.3 to 0.4% by weight of Si, 1.7 to 2.0% by weight of Mn, 0.01 to 0.02% by weight of P, 0.001 to 0.004% 0.01 to 0.04% by weight of Cr, 0.01 to 0.04% by weight of Mo, 0.02 to 0.04% by weight of Sol Al, 0.002 to 0.005% by weight of N and 0.01 to 0.04% by weight of Sb and balance Fe and other inevitable Wherein the microstructure of the steel sheet comprises 75 to 85% of ferrite and 15 to 25% of martensite in an area fraction, and the steel sheet forms an alloyed hot dip galvanized layer on at least one surface , And the alloyed molten zinc plated layer has an alloy degree of 9 to 13%, and the alloy phase contains a delta (delta) phase in an area fraction of 85 to 95%, and exhibits excellent plating adhesion and workability .

The present invention also provides a method of manufacturing a steel sheet, comprising: 0.07 to 0.08 weight% of C; 0.3 to 0.4 weight% of Si; 1.7 to 2.0 weight% of Mn; 0.01 to 0.02 weight% of P; 0.001 to 0.004 weight% %, Mo: 0.01 to 0.04 wt%, Sol Al: 0.02 to 0.04 wt%, N: 0.002 to 0.005 wt%, Sb: 0.01 to 0.04 wt%, and the remainder Fe and other unavoidable impurities step; Subjecting the reheated slab to hot rolling at 875 to 905 ° C to produce a hot-rolled steel sheet; Winding the hot-rolled steel sheet at 560 to 580 캜; Cold rolling the rolled steel sheet at a reduction ratio of 50 to 90% to produce a cold rolled steel sheet; Subjecting the cold-rolled steel sheet to recrystallization annealing at 780 to 810 ° C; Quenching the cold-rolled steel sheet after the recrystallization annealing and then hot-dipping the steel sheet; And cooling the hot-dip galvanized steel sheet at a temperature ranging from 470 to 550 ° C after the heat treatment for alloying, thereby providing a method of manufacturing a high-strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability.

The present invention provides an alloyed hot-dip galvanized steel sheet which is excellent in plating adhesion and workability and maintains high strength by controlling the component system of the steel sheet, the area fraction of the microstructure, the degree of alloying of the plated layer, and the area fraction of the alloy.

Hereinafter, the configuration of the present invention will be described in detail.

The present inventors have conducted extensive studies to control the composition of the steel sheet to suitably control the microstructure of the steel sheet using ferrite and martensite to control the size of martensite grains in the steel sheet, The present invention has been accomplished by controlling the alloying of the plated layer, the kind of the alloy phase, and the area fraction.

Accordingly, the steel sheet of the present invention is characterized in that the steel sheet comprises 0.07 to 0.08 wt% of C, 0.3 to 0.4 wt% of Si, 1.7 to 2.0 wt% of Mn, 0.01 to 0.02 wt% of P, 0.001 to 0.004 wt% of S, 0.01 0.01 to 0.04% by weight of Mo, 0.02 to 0.04% by weight of Sol Al, 0.002 to 0.005% by weight of N, 0.01 to 0.04% by weight of Sb and Fe and other unavoidable impurities, Wherein the microstructure of the steel sheet comprises 75 to 85% of ferrite and 15 to 25% of martensite in an area fraction, the steel sheet forming an alloyed hot dip galvanized layer on at least one surface thereof, The galvannealed layer has a degree of alloying of 9 to 13%, and the alloy phase has a delta (delta) phase of 85 to 95% in an area fraction, and provides a high strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability.

The present invention also relates to a ferritic stainless steel comprising 0.07 to 0.08 wt% of C, 0.3 to 0.4 wt% of Si, 1.7 to 2.0 wt% of Mn, 0.01 to 0.02 wt% of P, 0.001 to 0.004 wt% of S, And the remainder of the Fe and other unavoidable impurities is added to the reheating furnace at a ratio of 0.01 to 0.04 weight% of Mo, 0.02 to 0.04 weight% of Sol, 0.02 to 0.04 weight% of N, 0.002 to 0.005 weight% of S and 0.01 to 0.04 weight% of Sb, ; Subjecting the reheated slab to hot rolling at 875 to 905 ° C to produce a hot-rolled steel sheet; Winding the hot-rolled steel sheet at 560 to 580 캜; Cold rolling the rolled steel sheet at a reduction ratio of 50 to 90% to produce a cold rolled steel sheet; Subjecting the cold-rolled steel sheet to recrystallization annealing at 780 to 810 ° C; Quenching the cold-rolled steel sheet after the recrystallization annealing and then performing hot-dip galvanizing; And cooling the hot-dip galvanized steel sheet at a temperature ranging from 470 to 550 ° C after alloying heat treatment, and a method of manufacturing a high-strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability.

Hereinafter, the component system of the steel sheet forming one side of the galvannealed steel sheet of the present invention will be described in detail.

The carbon (C) is preferably contained in an amount of 0.07 to 0.08% by weight. Carbon (C) is an austenite stabilizing element that minimizes pearlite structure and carbide inside ferrite structure in hot rolled steel sheet, fine grain. The re-use of the composite precipitates is partially reused in the annealing process of the cold-rolled steel sheet to provide fine crystal grains having a size of about 10 to 30 mu m and to restrict the martensite appearing in grain boundaries to a volume ratio of 20% And plays a role in developing good texture 111. When the content of carbon (C) is less than 0.07% by weight, stable austenite can not be secured in the critical temperature region, and martensite is not produced in an appropriate fraction after cooling. On the other hand, when the content of carbon (C) exceeds 0.08% by weight, ductility can not be ensured and weldability is deteriorated.

The silicon (Si) is preferably contained in an amount of 0.30 to 0.40% by weight. Wherein the silicon (Si) increases the strength by solid solution strengthening as a ferrite stabilizing element while suppressing precipitation of cementite during holding at a temperature of 350 to 600 캜 after the annealing heat treatment, and the carbon (C) And accelerates the condensation to austenite, thereby contributing to formation of martensite and improvement of ductility upon cooling. However, when the content of silicon (Si) is less than 0.30 wt%, the austenite stabilizing effect described above is lowered. On the other hand, when the content of silicon (Si) exceeds 0.40 wt%, the surface properties are deteriorated and the silicon (Si) oxide is concentrated, so that both the weldability and the plating ability can be deteriorated.

The content of manganese (Mn) is preferably 1.7 to 2.0% by weight. Since manganese (Mn) is an element for stabilizing austenite, it delays decomposition of austenite into pearlite during cooling to 300 to 580 캜 after annealing. Therefore, during cooling to room temperature, manganese (Mn) Thereby allowing the tissue to be stably produced. In addition, it has an effect of enhancing the strength by strengthening of the solid solution, and is very effective in preventing hot cracking of the slab by forming MnS inclusions in combination with sulfur (S) in the steel. When the content of manganese (Mn) is less than 1.7% by weight, it is difficult to delay the decomposition of austenite into pearlite. On the other hand, when the content of manganese (Mn) exceeds 2.0% by weight, not only the slab cost is significantly increased but also the weldability and the moldability are deteriorated.

The phosphorus (P) is preferably contained in an amount of 0.01 to 0.02% by weight. The phosphorus (P) increases strength by solid solution strengthening, and when added together with silicon (Si) inhibits cementite precipitation while maintaining at 300 to 580 DEG C and promotes carbon thickening with austenite, do. If the concentration of phosphorus (P) is more than 0.02% by weight, it is disadvantageous to secondary processing brittleness and it may lower the adhesion of the zinc plating and lower the alloying property.

Sulfur (S) is preferably contained in an amount of 0.001 to 0.004% by weight. The sulfur (S) is an impurity inevitably contained, and forms FeS by binding with Fe, thereby causing hot brittleness. Therefore, it is desirable to suppress the content of Fe (S) as much as possible. In theory, it is advantageous to limit the content of sulfur (S) to 0 wt%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur (S) content is preferably limited to 0.004% by weight.

Cr (Cr) is preferably contained in an amount of 0.01 to 0.03% by weight. The chromium (Cr) improves the hardenability and is a very effective element for stably forming a low temperature transformation phase, which leads to refinement of the carbide, delaying the rate of spheroidization, reducing grain refinement, inhibiting growth of crystal grains, to be. It is also effective in suppressing the softening of the heat affected zone (HAZ) at the time of welding. However, when Cr (Cr) is added in an amount less than 0.01% by weight, the bond with carbon (C) becomes too small to be reused. On the other hand, if it exceeds 0.03% by weight, the increase in hardness of the HAZ may become excessively large.

The molybdenum (Mo) is preferably contained in an amount of 0.01 to 0.04% by weight. Since the molybdenum (Mo) is compounded in the cooling process after the hot rolling but the re-dissolution temperature is low, the molybdenum (Mo) is redissolved in the annealing process to add the molybdenum (Mo) do. However, if it exceeds 0.04% by weight, the stock capacity is decreased, so that it is difficult to form a low temperature transformation image and a remarkable increase in cost may be caused.

Aluminum (Al) is preferably contained in an amount of 0.02 to 0.04% by weight. The aluminum (Al) is used as a deoxidizing agent, and is an element which, like silicon (Si), inhibits cementite precipitation and stabilizes austenite by delaying the progress of transformation. (Al) is added in an amount of 0.02% by weight or more, which is a minimum austenite stabilization limit of the austenite stabilizing effect, so that unnecessary dissolved nitrogen (N) can be precipitated as AlN in the steel have. However, when the content of aluminum (Al) exceeds 0.04% by weight, nozzle clogging occurs during continuous casting, and hot brittleness and ductility are remarkably lowered due to Al oxide or the like during casting, and surface defects are likely to occur. Therefore, it is preferable to use the above-mentioned content range in order to remove quality defects caused by aluminum (Al) segregated in grain boundaries in a high temperature region.

The antimony (Sb) is preferably contained in an amount of 0.01 to 0.04% by weight. The antimony (Sb) is added because it suppresses the surface enrichment of MnO, SiO ₂ , Al ₂ O ₃ and the like and has an excellent effect in suppressing the coarsening of the surface agglomerates due to the temperature rise and the hot rolling process change. However, when the content of antimony (Sb) is less than 0.01% by weight, it is difficult to obtain the above effect. On the other hand, when the content of antimony (Sb) exceeds 0.04% by weight, Can be lowered.

The steel sheet contains, in addition to the above constituent elements, residual Fe and other unavoidable impurities.

The alloyed hot-dip galvanized steel sheet having the above-described component system of the present invention is a further condition for obtaining excellent mechanical properties in terms of processability, plating adhesion and strength, Size, the degree of alloying of the galvannealed hot-dip galvanized layer, and the area fraction of the alloy is suitably limited.

For example, the microstructure of the steel sheet is composed of 75 to 85% of ferrite and 15 to 25% of martensite in an area fraction, and the average grain size of martensite is controlled to be 3 탆 or less.

Further, a galvannealing layer is formed on at least one side of the steel sheet, and the degree of alloying of the plating layer is preferably 9 to 13%, more specifically 9.7 to 12.9%. If the thickness is out of the above range, the plating adhesion of the plating layer may be deteriorated, such as the inner powdering property of the plating layer.

The alloy phase of the alloyed hot-dip galvanized layer preferably contains a delta (delta) phase in an area fraction of 85 to 95%, more specifically 85.1 to 94.9%. Outside of the above range, the plating adhesion, workability, and strength of the galvannealed steel sheet may deteriorate.

Therefore, the galvannealed galvanized steel sheet preferably has a tensile strength of 600 MPa or more, more specifically 602 to 677 MPa, an elongation El of 25% or more, more specifically 25 to 29% The elongation balance (TS x El) is 15,000 MPa or more, more specifically 16050 to 17545 MPa%, and the workability and strength are excellent and the plating adhesion is excellent.

In the following, a most preferred example derived by the inventors of the present invention among the manufacturing methods for producing a high strength alloyed hot dip galvanized steel sheet having excellent plating adhesion and workability will be described in detail. However, the spirit of the present invention is not limited to the following examples.

A method of manufacturing a high-strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability according to one aspect of the present invention is characterized in that a steel slab having the above-described composition is subjected to reheating, hot rolling, coiling, cold rolling, continuous annealing, hot dip galvanizing, Through the continuous casting process, the galvannealed steel sheet having the desired mechanical properties is manufactured.

In the following, specific conditions according to each step will be described.

<Reheating process>

A slab having a composition according to the present invention is cast by a conventional method, and the cast slab is reheated for hot rolling. At this time, the slab reheating treatment is preferably performed at a temperature of 1150 to 1250 ° C.

&Lt; Hot rolling step &

Hot rolling the reheated slab is carried out at a temperature of 875 to 905 DEG C, and then the cooling is controlled to make the hot-rolled structure finer. At this time, if the hot rolling temperature is low, drawability is deteriorated due to occurrence of coarse grain in the crystal structure by strain annealing, so that hot rolling is performed at an appropriate rolling temperature to obtain a fine hot rolled structure. After hot rolling, it is advisable to use a high-pressure descaling device or to remove the scale of the surface by strong pickling.

&Lt; Winding step &

The hot-rolled steel sheet is rolled at a temperature of 560 to 580 DEG C to form carbide smoothly in a wound state to minimize the amount of dissolved carbon and minimize the formation of nitrogen dissolved in the steel. Such a coiling temperature is a temperature for obtaining a structure for obtaining optimum mechanical properties after cold rolling and recrystallization heat treatment. When the coiling temperature is less than 560 DEG C, cold rolling is difficult due to bainite or martensite structure. When the coiling temperature exceeds 580 DEG C It is difficult to produce a steel sheet having sufficient strength because the final microstructure is coarsened.

<Cold Rolling Step>

The wound hot rolled steel sheet is pickled and then cold rolled. The cold rolling reduction rate is preferably 50 to 90%. In cold rolling, hot-rolled steel is deformed and its strain energy is energy for recrystallization. If the cold rolling reduction is less than 50%, such a deformation effect is small, and cold rolling with a reduction ratio exceeding 90% In the steel sheet, the composite precipitates are decomposed in the rolling process, so that (100) texture is developed during the initial stage of recrystallization, thereby deteriorating the drawability and increasing the probability of plate cracking at the edge of the steel sheet. It is good.

<Annealing Annealing Process>

The cold-rolled steel sheet is subjected to recrystallization annealing. The annealing at this time is preferably continuous annealing. The recrystallization annealing improves the drawability by developing (111) texture through recrystallization and grain growth, and dissolves the dissolved carbon by redissolving the fine complex precipitates.

In the present invention, recrystallization annealing is performed at 780 to 810 占 폚 for 10 to 200 seconds.

The recrystallization annealing heat treatment must be carried out between the Ac1 transformation point and the Ac3 transformation point in order to make a two-phase structure of ferrite and austenite. At temperatures lower than 780 DEG C, too much time is required for re-use of cementite, , The austenite volume fraction becomes too large, resulting in a decrease in the carbon concentration of the austenite.

&Lt; Quenching and hot-dip galvanizing process >

After the recrystallization annealing heat treated steel sheet is quenched, hot-dip galvanizing is performed. At this time, the quenching is preferably performed at a cooling rate of 5 to 50 ° C / sec to 400 to 470 ° C. If the quenching termination temperature is lower than 400 캜, the whole structure of the steel sheet is transformed into martensite, so that the workability can be reduced with a rapid increase in strength. If the quenching termination temperature exceeds 470 DEG C, ductility of the steel sheet may be reduced because the steel structure is transformed into a bainite phase.

<Alloying Heat Treatment and Cooling Process>

After the hot dip galvanizing is completed, alloying heat treatment is performed in a temperature range of 470 to 550 ° C by a conventional method for stable growth of the plating layer. Thereafter, the alloyed heat treated steel sheet is cooled. At this time, the cooling is preferably performed at a cooling rate of 5 to 50 DEG C / sec or more to a temperature range of 250 to 350 DEG C.

Hereinafter, the present invention will be described in more detail by way of examples. It should be noted, however, that the following examples are illustrative of the invention and are not intended to limit the scope of the invention.

<Examples>

(FDT), cold rolling (CT), annealing of recrystallization annealing (SS), quenching and hot dip galvanizing after the quenching process was performed under the process conditions shown in Table 2 And cooling after alloying heat treatment to produce a galvannealed galvanized steel sheet.

The tensile strength (TS) and elongation (EL) of the galvannealed steel sheets produced according to the process conditions of Table 2 were measured. When all of the values are satisfied on the basis of a tensile strength (Mpa) of not less than 600 MPa, an elongation percentage of not less than 25% and an elongation balance (TS X El) of not less than 15,000 MPa% ○, when the two are satisfied, Δ, and the following is marked with × (Table 2).

The microstructure and the grain size of the martensite structure of the galvannealed galvanized steel sheet were observed and the results are shown in Table 3 below.

The alloying degree (%) and the area fraction (%) of the delta phase were observed for the produced galvannealed galvanized steel sheet, and the results are shown in Table 3 below.

As a result of evaluating the adhesion of the plating through the ordinary powdering test, it was found that when alloying to be controlled in one aspect of the present invention is 9 to 13% and the delta phase area fraction is 85 to 95% simultaneously, It was confirmed that excellent plating adhesion was observed. Therefore, when the both the degree of alloying and the percentage of delta phase are satisfied, &amp; cir &amp; is shown. When only one of them is satisfied, DELTA, and when both of them are unsatisfactory, the degree of plating adhesion is shown in Table 3.

division C Mn P S Si Mo Al Cr N Sb ferrite
(%) Martensite
(%) Inventive Steel 1 0.075 2.0 0.011 0.003 0.33 0.039 0.021 0.016 0.005 0.01 76 24 Invention river 2 0.074 1.7 0.020 0.004 0.31 0.040 0.025 0.027 0.003 0.01 78 22 Invention steel 3 0.072 1.6 0.017 0.004 0.37 0.036 0.029 0.024 0.004 0.01 76 24 Inventive Steel 4 0.061 1.8 0.014 0.001 0.37 0.037 0.023 0.029 0.005 0.01 75 25 Invention steel 5 0.079 1.9 0.015 0.001 0.37 0.033 0.036 0.022 0.003 0.02 75 25 Invention steel 6 0.071 1.9 0.013 0.003 0.36 0.025 0.031 0.019 0.004 0.02 75 25 Invention steel 7 0.070 1.7 0.012 0.003 0.37 0.026 0.027 0.027 0.002 0.02 78 22 Inventive Steel 8 0.079 1.6 0.014 0.004 0.34 0.024 0.023 0.011 0.004 0.02 78 22 Invention river 9 0.073 1.6 0.019 0.004 0.34 0.025 0.026 0.026 0.005 0.03 77 23 Invented Steel 10 0.071 1.9 0.017 0.002 0.32 0.034 0.026 0.011 0.003 0.03 77 23 Invention steel 11 0.074 1.8 0.019 0.004 0.18 0.011 0.021 0.029 0.004 0.03 85 15 Invention steel 12 0.079 1.8 0.015 0.003 0.38 0.016 0.022 0.030 0.003 0.03 83 17 Invention steel 13 0.078 1.7 0.018 0.004 0.37 0.014 0.029 0.025 0.004 0.04 76 24 Invented Steel 14 0.075 1.8 0.015 0.003 0.40 0.026 0.039 0.016 0.005 0.04 84 16 Invented Steel 15 0.077 1.7 0.014 0.004 0.30 0.013 0.040 0.015 0.002 0.04 85 15 Comparative Example 1 0.045 1.4 0.009 0.006 0.14 0.071 0.009 0.11 0.005 66 34 Comparative Example 2 0.054 1.9 0.012 0.005 0.12 0.052 0.016 0.07 0.005 69 31 Comparative Example 3 0.051 1.7 0.012 0.003 0.18 0.073 0.012 0.07 0.002 62 38 Comparative Example 4 0.063 1.9 0.005 0.005 0.17 0.063 0.016 0.08 0.005 63 37 Comparative Example 5 0.077 1.4 0.015 0.006 0.17 0.052 0.009 0.07 0.004 67 33 Comparative Example 6 0.052 1.7 0.009 0.004 0.27 0.061 0.027 0.09 0.005 62 38 Comparative Example 7 0.063 1.5 0.015 0.003 0.30 0.057 0.012 0.14 0.002 65 35 Comparative Example 8 0.084 1.7 0.012 0.004 0.14 0.068 0.016 0.12 0.004 69 31 Comparative Example 9 0.079 1.9 0.009 0.005 0.12 0.059 0.009 0.06 0.005 69 31 Comparative Example 10 0.078 1.4 0.005 0.004 0.18 0.079 0.027 0.07 0.002 62 38 Comparative Example 11 0.051 2.1 0.012 0.006 0.12 0.042 0.027 0.12 0.005 63 37 Comparative Example 12 0.064 1.9 0.007 0.003 0.18 0.042 0.012 0.06 0.005 67 33 Compare to 13 0.059 2.1 0.015 0.005 0.11 0.044 0.027 0.06 0.004 63 37 Comparative Example 14 0.076 1.5 0.009 0.004 0.23 0.055 0.009 0.12 0.002 64 36 Comparative Example 15 0.081 2.1 0.012 0.003 0.17 0.075 0.012 0.07 0.004 63 37

division FDT
(° C) CT
(° C) SS
(° C) Alloying (℃) TS
(Mpa) Hand
(%) TS × El
(Mpa%) Average size of martensite grain (mu m) TS, El and
TS × El evaluation Inventive Steel 1 881 574 781 470 605 26 15730 2.9 ○ Invention river 2 883 575 782 480 639 26 16614 1.3 ○ Invention steel 3 901 560 787 490 639 25 15975 1.1 ○ Inventive Steel 4 901 567 787 500 602 25 15050 1.8 ○ Invention steel 5 897 574 784 510 603 29 17487 0.6 ○ Invention steel 6 899 573 804 520 610 26 15860 1.2 ○ Invention steel 7 905 561 787 530 617 27 16659 2.5 ○ Inventive Steel 8 875 562 781 540 647 26 16822 1.9 ○ Invention river 9 888 562 807 550 613 27 16551 1.8 ○ Invented Steel 10 899 564 794 470 649 25 16225 2.1 △ Invention steel 11 877 580 787 480 667 26 17342 0.8 ○ Invention steel 12 899 564 784 490 621 26 16146 2.3 ○ Invention steel 13 905 575 794 500 605 29 17545 0.9 ○ Invented Steel 14 883 560 810 510 677 25 16925 2.7 ○ Invented Steel 15 905 567 787 520 663 26 17238 0.5 ○ Comparative Example 1 901 549 777 530 802 19 15238 0.9 × Comparative Example 2 897 545 774 540 754 21 15834 2.1 × Comparative Example 3 899 547 794 550 720 20 14400 0.9 × Comparative Example 4 905 539 777 470 750 20 15000 0.3 △ Comparative Example 5 874 533 774 480 738 21 15498 2.1 △ Comparative Example 6 888 593 794 490 721 21 15141 0.9 × Comparative Example 7 897 597 767 500 745 20 14900 0.9 × Comparative Example 8 899 603 771 510 745 20 14900 1.8 △ Comparative Example 9 901 591 799 520 839 18 15102 0.5 × Comparative Example 10 874 549 794 530 746 21 15666 1.7 × Compare to 11 888 545 777 540 747 20 14940 1.3 × Comparative Example 12 897 547 774 550 800 19 15200 0.5 × Compare to 13 901 539 794 490 799 19 15181 2.1 × Compare to 14 897 533 767 500 743 19 14117 1.8 × Comparative Example 15 897 612 794 510 736 20 14720 0.5 ×

division Delta phase (%) Alloying degree (%) Plating adhesion Inventive Steel 1 85.9 9.9 ○ Invention river 2 87.7 10.3 ○ Invention steel 3 85.1 10.7 ○ Inventive Steel 4 92.1 11.2 ○ Invention steel 5 93.3 12.8 ○ Invention steel 6 94.9 9.7 ○ Invention steel 7 85.2 10.2 ○ Inventive Steel 8 90.5 9.9 ○ Invention river 9 87.3 12.2 ○ Invented Steel 10 88.2 11.9 ○ Invention steel 11 89.2 10.4 ○ Invention steel 12 91.5 9.9 ○ Invention steel 13 92.2 9.7 ○ Invented Steel 14 91.5 11.7 ○ Invented Steel 15 86.2 12.9 ○ Comparative Example 1 81.9 9.1 △ Comparative Example 2 83.7 7.9 × Comparative Example 3 81.1 9.2 △ Comparative Example 4 89.3 8.9 △ Comparative Example 5 79.3 5.4 × Comparative Example 6 82.4 10.2 △ Comparative Example 7 81.2 6.2 × Comparative Example 8 84.2 7.8 × Comparative Example 9 83.3 8.9 × Comparative Example 10 84.2 8.7 × Compare to 11 85.2 8.2 △ Comparative Example 12 77.5 11.2 △ Compare to 13 78.2 8.2 × Compare to 14 77.9 7.4 × Comparative Example 15 82.2 6.5 ×

As a result of analyzing the mechanical properties of the galvannealed galvanized steel sheets produced sequentially by the respective processes including the respective process conditions shown in the above Table 2, the inventive examples 1 to 15 of the galvannealed galvanized steel sheet had tensile strengths , Elongation (El) of 25% or more, and TS × El of 15,000 MPa or more.

Further, the microstructure of Examples 1 to 15 of the alloyed hot-dip galvanized steel sheet produced through the above-mentioned process had formed an area fraction of 75 to 85% of ferrite and 15 to 25% of martensite, It was confirmed that the average crystal grain size formed 3 mu m or less in diameter.

In the case of Inventive Examples 1 to 15, the degree of alloying is 9 to 13%, and the delta (delta) phase of the plated layer is formed in the range of 85 to 95% in the area fraction, And it was confirmed that they were satisfied.

On the other hand, the comparative examples (1 to 15) were obtained from steel slabs which did not satisfy the constituent system provided by one aspect of the present invention, from the alloy melting melts which were prepared so as not to satisfy the conditions of each step provided in another aspect of the present invention A zinc-plated steel sheet which is characterized in that the steel sheet has at least one of a mechanical property (tensile strength, elongation, tensile strength x elongation), area fraction of each microstructure, grain size of martensitic structure, degree of alloying, It can be confirmed that the numerical range controlled by the present invention is not satisfied.

Particularly, the composition of the steel slab provided in the above comparative example is excessively high or low in carbon content and too low in chromium content, thereby deviating from the control range of the present invention. Further, in the case of Comparative Examples 1 and 7, the manganese component content is lower than the control range of the present invention, and in the case of Comparative Examples 11, 13 and 15, the manganese component content is higher than the control range of the present invention. In addition, in the case of Comparative Examples 4 and 10, the phosphorus content was included in an excessively lower amount than the control range of the present invention. In addition, the temperature at each stage of the manufacturing process for producing the slabs of each comparative example from the cold-rolled steel sheet was set to be lower or higher than the level controlled by the present invention.

In Comparative Examples (1 to 15) in which at least one of the content of each component or the temperature range of each process was outside the control range of the present invention, the content of each component element and the temperature control range of each manufacturing process It was not provided with the excellent workability and the plating adhesion as described above as the effect in the case of leaving. That is, at least one of the area fraction of each structure, the size of the martensite crystal grains, the degree of alloying of the plated layer and the delta phase area fraction of the alloy layer can not be secured within the control range of the present invention, It has not been possible to realize an alloyed hot-dip galvanized steel sheet satisfying both the high strength and excellent stretch flangeability of the present invention simultaneously.

In particular, in the comparative examples (1 to 15), the martensite structure was excessively generated, so that the tensile strength as a whole was realized to be higher than the control range (600 MPa or more) of the present invention. However, 25% or more). Therefore, all the comparative examples did not enter the control range of the present invention, in which the TS El value calculated as an index satisfying both sides at the same time satisfies 15,000 MPa% or more.

Further, since at least one of the degree of alloying and the area fraction of the delta phase in Comparative Examples (1 to 15) can not be secured within the range of control in one aspect of the present invention, the plating adhesion It can be confirmed that no galvannealed galvanized steel sheet having a low melting point is provided.

Claims (6)

The steel sheet is characterized by comprising 0.07 to 0.08 wt% of C, 0.3 to 0.4 wt% of Si, 1.7 to 2.0 wt% of Mn, 0.01 to 0.02 wt% of P, 0.001 to 0.004 wt% of S, 0.01 to 0.03 wt% 0.01 to 0.04% by weight of Mo, 0.02 to 0.04% by weight of Sol Al, 0.002 to 0.005% by weight of N, 0.01 to 0.04% by weight of Sb and Fe and other inevitable impurities of the remainder,
The microstructure of the steel sheet contains 75 to 85% of ferrite and 15 to 25% of martensite in an area fraction,
The steel sheet has an alloyed hot-dip galvanized layer formed on at least one surface thereof. The alloyed hot-dip galvanized layer has an alloying degree of 9 to 13%. The alloy sheet has a plating adhesion with an area fraction of 85 to 95% High strength alloyed hot - dip galvanized steel with excellent processability.
The method according to claim 1,
A high strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability having an average grain size of martensite of 3 탆 or less.
The method according to claim 1,
The galvannealed galvanized steel sheet has a tensile strength of 600 MPa or more, an elongation (El) of 25% or more, a high strength alloyed steel having excellent tensile strength and elongation balance (TS x El) of 15,000 MPa% Hot - dip galvanized steel sheet.
0.001 to 0.004% by weight of Cr, 0.01 to 0.03% by weight of Cr, 0.01 to 0.03% by weight of Cr, 0.03 to 0.08% by weight of C, 0.3 to 0.4% by weight of Si, 1.7 to 2.0% Reheating the slab containing 0.01 to 0.04% by weight of Sol, 0.02 to 0.04% by weight of Sol Al, 0.002 to 0.005% by weight of N, 0.01 to 0.04% by weight of Sb and the balance of Fe and other unavoidable impurities;
Subjecting the reheated slab to hot rolling at 875 to 905 ° C to produce a hot-rolled steel sheet;
Winding the hot-rolled steel sheet at 560 to 580 캜;
Cold rolling the rolled steel sheet at a reduction ratio of 50 to 90% to produce a cold rolled steel sheet;
Subjecting the cold-rolled steel sheet to recrystallization annealing at 780 to 810 ° C;
Quenching the cold-rolled steel sheet after the recrystallization annealing and then hot-dipping the steel sheet; And
And cooling the hot-dip galvanized steel sheet at a temperature of 470 to 550 ° C after the heat treatment for alloying, thereby obtaining a high-strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability.
5. The method of claim 4,
Wherein the annealing heat treatment step is performed for 10 to 200 seconds and has excellent plating adhesion and workability.
5. The method of claim 4,
A method for manufacturing a high strength alloyed hot-dip galvanized steel sheet excellent in plating adhesion and workability in which a cold-rolled steel sheet subjected to annealing is cooled to 400 to 470 占 폚 at a cooling rate of 5 to 50 占 폚 / sec.