KR20140048668A - Baking hardening type galvanized steel sheet having excellent formability and powdering resistance, and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a baking-hardening galvanized steel sheet with a bake hardening (BH) of 30MPa or greater and elongation of 35% or greater, thereby having excellent aging resistance at room temperature, ductility, and powdering resistance. For the same, the component composition contained in ultra-low carbon steel is controlled, while rationalizing the manufacturing condition so as to control the crystal grain and precipitate, at the same time controlling the alloy phase.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvannealed galvanized steel sheet having excellent workability and resistance to powdering, and a method of manufacturing the galvannealed galvanized steel sheet. 2. The galvanized galvanized steel sheet according to claim 1,

The present invention relates to a galvannealed galvanized steel sheet used as a material for automobiles, home appliances, and the like, and a method of manufacturing the same.

Hot dip galvanized steel sheets applied to automobiles or household appliances are required to have excellent formability and plating ability in addition to strength.

In the past, high-strength steel plates with high tensile strength were actively employed to lighten the weight of automobile bodies and ensure passenger stability. These high-strength steel plates were used in close cooperation with various legal regulations surrounding the automobile industry such as automobile safety regulation law, fuel efficiency regulation law, Has been developed with relevance. Furthermore, fuel economy regulations due to high oil prices have intensified, and weight reduction of automobiles has become a major concern in the automobile industry. As a result, research and development have been accelerated and many types of high strength steel plates have been developed.

On the other hand, P-containing Al killed steels and high tensile steels for deep drawing were developed as steel plates requiring workability. However, the Al-killed steel is manufactured by subjecting the steel sheet to an impregnation, so that the annealing time is long, the productivity is low, and there is a disadvantage that material variation is large in each part.

As a method for solving the above problems, there has been proposed a continuous annealing method in which a strong carbon and nitride forming elements are added. Research and development of IF (Interstitial Free Steel) steel, which is a high tensile steel having improved processability, . However, in order to produce such an IF steel, it is necessary to add elements such as Ti and Nb, which are strong carbon and nitride forming elements, to increase the recrystallization temperature. Therefore, annealing must be performed at a high temperature. There is a problem that it is difficult to secure the elongation.

In addition to the above-mentioned measures, extreme low carbon strength using precipitates such as MnS and CuS has been proposed without addition of Ti, Nb, etc. However, this also causes a problem of material failure due to aging phenomenon.

One aspect of the present invention is to provide a bake-curing type alloyed hot-dip galvanized steel sheet in which processability is improved through control of added elements and precipitates, and a method of manufacturing the same.

Another aspect of the present invention is to provide a bake-hardening type alloyed hot-dip galvanized steel sheet having excellent resistance to powdering.

An aspect of the present invention provides a method of manufacturing a semiconductor device, which comprises 0.002 to 0.004% carbon, 0.3 to 0.8% manganese (Mn), 0.06% or less phosphorus (P) , 0.001 to 0.007% of aluminum (Al), 0.01 to 0.04% of niobium (Nb), 0.01 to 0.03% of copper (Cu), 0.001 to 0.005% of nitrogen (N) Fe and unavoidable impurities, wherein the composition ratio of C and Nb (C / Nb) is 0.01 to 0.50,

CuS, comprising the MnS and CuMnS 1 or more kinds of precipitates, the average crystal grain size of the precipitate is 100 ~ 400nm, and the average density of the precipitates from 0.01 to 0.20 piece / μm ^2,

The microstructure of the steel sheet is composed of a ferrite single phase structure,

A bake-hardening type alloyed hot-dip galvanized steel sheet excellent in workability and resistance to powdering including a galvannealed galvanized layer on the surface of a steel sheet.

According to another aspect of the present invention, there is provided a method of manufacturing a steel slab, comprising the steps of: reheating a steel slab satisfying the above-described composition of the composition to 1150 to 1250 占 폚;

Preparing a hot rolled steel sheet by hot rolling the reheated steel slab at a finishing rolling temperature of Ar 3 to 950 캜;

Winding the hot-rolled steel sheet at 700 to 750 ° C;

Rolling the steel sheet at a reduction ratio of 60 to 80% after the rolling to produce a cold-rolled steel sheet;

Annealing the cold-rolled steel sheet at 820 to 880 ° C;

Performing hot dip galvanizing on the annealed cold rolled steel sheet to produce a hot-dip galvanized steel sheet; And

And a step of heating the hot-dip galvanized steel sheet to a temperature of 400 to 600 ° C to produce an alloyed hot-dip galvanized steel sheet, wherein the hot-dip galvannealed steel sheet has excellent processability and resistance to powdering.

(BH) by controlling the size and fraction of the crystal grains and controlling the fraction of the alloy phase and the degree of alloying by controlling Nb and Cu, which are elements forming the precipitate, to an appropriate range, A hot-cure type alloyed hot-dip galvanized steel sheet excellent in hygroscopicity at room temperature and above 30 MPa and excellent in anti-powdering property can be provided.

Hereinafter, embodiments of a galvannealed steel sheet excellent in workability and resistance to powdering and a method of manufacturing the same will be described in detail. However, the present invention is not limited to the following embodiments. Therefore, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Hereinafter, the present invention will be described in detail.

First, the reasons for limiting the composition and content of the galvannealed steel sheet according to the present invention will be described in detail. At this time, the content of the elemental elements means weight%.

C: 0.002 to 0.004%

When the content is less than 0.002%, the carbon (C) has an absolute carbon content lower than that of Nb added to improve the hygroscopicity at room temperature due to grain refinement, On the other hand, when the content of C is more than 0.004%, the amount of carbon in the steel is large, so that it is difficult to secure endurance, and the crystal grains of the annealed plate become finer and the ductility is greatly lowered. Therefore, the content of C in the present invention is preferably controlled to 0.002 to 0.004%.

Mn: 0.3 ~ 0.8%

Manganese (Mn) is an element which prevents the sulfur shortness caused by the sulfur by precipitating solid sulfur in MnS. In the present invention, it is preferable to control Mn to 0.3 to 0.8% in order to improve the yield strength and in-plane anisotropy while fundamentally securing the anti-aging property by controlling the content of Mn and S by precipitating fine MnS.

That is, in order to secure fine MnS precipitates, Mn should be added in an amount of 0.3% or more, but if the content is more than 0.8%, the content of Mn is high and coarse MnS precipitates and the endurance is poor have.

P: not more than 0.06%

Phosphorus (P) plays a role in improving the in-plane anisotropy and improving the strength as a substitutional alloying element having a large solid solution strengthening effect.

If the content of P exceeds 0.06%, the ductility and formability are lowered, and the hardening of the hardening is also reduced, and there is a problem that the strength increase due to solid solution strengthening is drastically increased. Therefore, the content of P in the present invention is preferably limited to 0.06% or less.

S: 0.008% or less

Sulfur (S) precipitates as a sulfide of MnS at a high temperature to prevent hot brittleness due to FeS.

If the content of S exceeds 0.008%, the content of S dissolved is excessively excessive, so that ductility and moldability are greatly lowered, and there is a fear of redispersible brittleness. Therefore, the content of S in the present invention is preferably limited to 0.008% or less.

Si: 0.001 to 0.007%

Silicon (Si) is a solid solution strengthening element, which is advantageous from the viewpoint of strength improvement. However, there is a problem that the Si-based oxide is eluted on the surface during annealing to deteriorate the surface characteristics, and therefore the content thereof is preferably limited to 0.001 to 0.007%.

Al: 0.01 ~ 0.04%

Aluminum (Al) is an element to be added as a deoxidizing agent and serves to deposit nitrogen in the steel to prevent aging by solid nitrogen. When the content is less than 0.01%, the effect of preventing aging is insufficient due to the large amount of nitrogen employed. On the other hand, when the content exceeds 0.04%, there is a problem that the amount of Al existing in a solid state is large and ductility is deteriorated. Therefore, the content of Al in the present invention is preferably limited to 0.01 to 0.04%.

Nb: 0.005 to 0.020%

Niobium (Nb) is an element that has the greatest influence on the grain refinement among the carbon and nitride forming elements. It forms NbC precipitates by binding with carbon and is positioned in the grain boundaries and the mouth of microstructure to suppress the growth of crystal grains, Thereby improving the workability. As described above, Nb is a very important element in terms of ensuring workability, and it is preferable that Nb is added in an amount of 0.005 to 0.020% in consideration of the workability increasing effect and the economical aspect.

If the content of Nb is less than 0.005%, it is difficult to expect the effect of NbC precipitation. On the other hand, if the content exceeds 0.020%, it is economically disadvantageous and also deteriorates plating performance during plating.

Cu: 0.01 to 0.03%

Copper (Cu) is a solid solution strengthening element. In order to obtain such an effect, it is necessary to add at least 0.01%. However, if the content exceeds 0.03%, there is a problem that a low melting point phase is formed in the hot rolling and defects are formed on the surface of the steel sheet, so the upper limit is limited to 0.03%.

N: 0.001 to 0.005%

Nitrogen (N) is an element that is inevitably added during steelmaking. It is preferable that the content is lower, but the content thereof is limited to 0.001 to 0.005% in consideration of the steelmaking process. When the nitrogen content of N exceeds 0.005%, the aging index is increased and the formability and workability are deteriorated.

The present invention further provides a method of manufacturing a copper alloy comprising one kind selected from the group consisting of 0.01 to 0.03% of Cr, 0.001 to 0.005% of molybdenum (Mo), 0.001 to 0.03% of nickel (Ni), and 0.0001 to 0.010% of vanadium (V) Or two or more of them.

0.01 to 0.03% of Cr, 0.001 to 0.005% of Mo,

Chromium (Cr) and molybdenum (Mo) are added as effective elements for securing the strength of the steel. In order to obtain the above effect, it is preferable to add Cr at 0.01% or more and Mo at 0.001% or more. However, when the content of Cr exceeds 0.03%, there is a problem that the formability and workability are lowered. When the content of Mo is more than 0.005%, the recrystallization in the austenite region is delayed, . Therefore, in the present invention, it is preferable to limit the content of Cr to 0.01 to 0.03% and the content of Mo to 0.001 to 0.005%.

Ni: 0.001 to 0.030%

Nickel (Ni) is an element to be added for the solid solution strengthening effect. To obtain the above effect, it is necessary to add Ni at not less than 0.001%, but if the content is more than 0.030%, the transformation point is greatly lowered, There is a problem that a low-temperature transformation image appears at the time of rolling. Therefore, the content of Ni in the present invention is preferably limited to 0.001 to 0.030%.

V: 0.0001 to 0.010%

Vanadium (V) is an effective component for securing the non-aging property by precipitating solid solution C, and it is necessary to add V at 0.0001% or more in order to obtain the above-mentioned effect. However, when the content exceeds 0.010%, the plasticity anisotropy index is lowered and the workability is lowered. Therefore, in the present invention, it is preferable to limit the content of Ni to 0.0001 to 0.010%.

The present invention includes Fe and unavoidable impurities as the remainder other than the above-mentioned components, and does not exclude the addition of other elements in addition to the above-mentioned composition.

In the present invention, the component ratio (C / Nb) of C and Nb is preferably 0.01 to 0.50.

In the present invention, C and Nb are important parameters for securing the tensile strength by precipitating NbC. When the component ratio (C / Nb) is less than 0.01, NbC precipitation is not sufficient. On the other hand, when C / Nb exceeds 0.50, NbC precipitation is excessive There is a problem that workability is deteriorated.

Hereinafter, the microstructure and precipitates of the galvannealed steel sheet according to the present invention will be described in detail.

The microstructure of the galvannealed steel sheet according to the present invention is preferably a ferrite single-phase structure. Since the present invention corresponds to an ultra low carbon steel having a content of C of 20 to 40 ppm, the microstructure is composed of a ferrite single phase structure.

It is preferable that the average crystal grain size of at least one precipitate of CuS, MnS and CuMnS is 100 to 400 nm and the average density of the precipitates is 0.01 to 0.20 / μm ² .

The size of the precipitate directly affects the sintering property, the secondary process brittleness, the plastic anisotropy index and the in-plane anisotropy index. In the present invention, when the average particle size of at least one precipitate among CuS, MnS and CuMnS exceeds 400 nm It is difficult to obtain the above characteristics excellently, and it is particularly difficult to secure the curing properties of the resin. Therefore, in order to obtain the above-mentioned effects, it is preferable that at least one precipitate of CuS, MnS and CuMnS having an average particle size of 100 to 400 nm is contained in the range of 0.01 to 0.20 / μm ² .

Hereinafter, an alloyed hot-dip galvanized layer of the galvannealed steel sheet according to the present invention will be described in detail.

The alloyed hot-dip galvanized layer of the galvannealed steel sheet according to the present invention preferably contains a delta (delta) phase in an area fraction of 80% or more.

If the delta phase of the structure in the plating layer is less than 80%, there is a problem that the powdering property becomes weak.

The alloying degree of the galvannealing layer is preferably 13 or less. It is necessary to control the degree of alloying of the plating layer because it is closely related to the plating characteristics such as resistance to workability and resistance to powdering.

If the degree of alloying is too high to exceed 13, there is a problem that the diffusion of Fe into the steel sheet excessively occurs and the plating adhesion of the plated layer, such as the anti-powdering property, deteriorates. Therefore, in the present invention, it is preferable to control the degree of alloying of the galvannealed galvanized layer to 13 or less, more preferably 9 to 13%, which is effective in securing excellent plating characteristics.

The most preferable method derived by the present inventors for producing an alloyed hot-dip galvanized steel sheet satisfying the above-mentioned conditions will be specifically described below.

First, the steel slab having the above-mentioned composition is reheated at 1150 to 1250 DEG C, and then the reheated steel slab is hot-rolled to produce a hot-rolled steel sheet.

At this time, the finish rolling is preferably performed in a temperature range of Ar 3 to 950 ° C. When the finish rolling is performed at a temperature less than Ar3, there is a high possibility that the hot deformation resistance is rapidly increased, and there is a high possibility that micro cracks occur due to high temperature brittleness. On the other hand, when the finish rolling is carried out at a high temperature exceeding 950 占 폚, there is a problem that defective is likely to occur due to the occurrence of a mixed grain structure due to an anomalous hot rolling.

It is preferable that the hot rolled steel sheet is rolled in a temperature range of 700 to 750 ° C.

If the temperature at the time of coiling is less than 700 캜, the crystal grains of the hot-rolled steel sheet do not sufficiently grow during the cooling process after the coiling, resulting in a deterioration in the workability of the steel. On the other hand, when the coiling temperature exceeds 750 캜, There is a problem that the workability is reduced and a large scale is generated on the surface of the steel sheet, which is a cause of poor pickling in the pickling process.

The rolled hot-rolled steel sheet is preferably cold-rolled at a reduction ratio of 60 to 80% to produce a cold-rolled steel sheet.

When the cold rolling reduction rate is less than 60% in the cold rolling, the annealing recrystallization nuclei are formed in a small amount so that the crystal grains grow too large during the annealing and the strength and the workability are lowered due to the coarsening of the annealed recrystallized grain. If the reduction rate exceeds 80%, the workability is improved, but the amount of nucleation is too large, so that the recrystallization annealing is too fine and the ductility is deteriorated.

Before the cold rolling, the produced hot-rolled steel sheet can be pickled by a conventional method.

It is preferable that the cold-rolled steel sheet is subjected to annealing in a temperature range of 820 to 880 캜.

When the annealing temperature is less than 820 DEG C, recrystallization is not completed and it is difficult to secure a desired ductility value. On the other hand, when the annealing temperature exceeds 880 DEG C, there is a problem that strength is lowered due to coarsening of recrystallized grains.

At this time, it is preferable that the annealing is performed by the continuous annealing method, and it is preferable that the annealing time is performed for about 10 seconds or more since it is necessary to keep the annealing time to complete the recrystallization. Preferably 10 seconds or more and 30 minutes or less.

The annealed cold rolled steel sheet may be subjected to hot dip galvanizing treatment to produce a hot dip galvanized steel sheet.

At this time, the hot-dip galvanizing treatment can be carried out by a conventional hot-dip galvanizing method, for example, preferably by immersing the cold-rolled steel sheet annealed in a galvanizing bath.

Thereafter, the produced hot-dip galvanized steel sheet is heated to 450 to 550 ° C and then subjected to alloying heat treatment, whereby the hot-dip galvanized steel sheet can be manufactured.

At this time, if the alloying heat treatment temperature is lower than 450 ° C, the alloying temperature is too low to ensure proper alloying degree and stable growth of the plating layer. On the other hand, when the temperature exceeds 550 ° C, have.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example )

A steel slab having the composition shown in the following Table 1 was prepared, and the steel slab was reheated at 1200 ° C and finishing rolled at Ar 3 to 950 ° C, rolled at 700 ° C, cold rolled at 70% To prepare a cold-rolled steel sheet.

Thereafter, the cold-rolled steel sheet thus prepared was subjected to hot-dip galvannealing to produce a hot-dip galvanized steel sheet, and then the hot-dip galvanized steel sheet was heated to 500 ° C to conduct alloying heat treatment to produce a galvannealed steel sheet.

The tensile strength, elongation and curing amount of the prepared cold-rolled steel sheet were measured, and the microstructure was observed. The results are shown in Table 2 below. The thus-prepared galvannealed steel sheet was measured for delta phase fraction and degree of alloying, and resistance to corrosion resistance, which was evaluated for workability and plating characteristics, was evaluated. The results are shown in Table 2 below.

The amount of hardening was determined by baking the specimen at 170 ℃ for 20 minutes and measuring the yield strength before and after.

The results are shown as ○ when the tensile strength is 300 to 370 MPa, the elongation is 35% or more, and the hardening amount is 30 MPa or more, satisfies all three items, △ when two items are satisfied, And when it is not satisfactory or not satisfactory, it is marked with X.

In addition, the cellulosic tape was removed from the test piece after bending the cellophane tape attached to the test piece, and the adhesion of the plating was judged by the amount of plating adhered on the cellophane tape. In this case, when no peeling or cracking occurred, the symbol was marked as?, When the powder was partially generated,?, When the peeling and cracking occurred many times.

division C Mn P S Si Al Nb Cu Cr Mo N Ni Inventive Steel 1 0.0022 0.35 0.059 0.0021 0.004 0.037 0.005 0.015 0.014 - 0.0021 Invention river 2 0.0033 0.34 0.057 0.0034 0.0068 0.029 0.013 0.013 0.017 - 0.0032 Invention steel 3 0.0037 0.38 0.056 0.0051 0.0039 0.039 0.011 0.026 0.021 - 0.0023 Inventive Steel 4 0.0024 0.44 0.049 0.0029 0.0038 0.027 0.009 0.017 0.029 - 0.0019 Invention steel 5 0.0027 0.5 0.031 0.0076 0.0021 0.021 0.018 0.014 0.011 - 0.0032 Invention steel 6 0.0031 0.78 0.054 0.0079 0.0062 0.032 0.015 0.021 - 0.004 0.0025 Invention steel 7 0.0039 0.49 0.045 0.0067 0.0047 0.039 0.01 0.020 - 0.002 0.0028 Inventive Steel 8 0.0024 0.51 0.034 0.0054 0.0042 0.039 0.006 0.015 - 0.001 0.0026 Invention river 9 0.0027 0.63 0.032 0.0072 0.0012 0.026 0.009 0.011 - 0.005 0.0023 Invented Steel 10 0.0029 0.76 0.039 0.0067 0.0029 0.029 0.018 0.018 - 0.003 0.0028 Invention steel 11 0.0031 0.49 0.042 0.0061 0.0053 0.031 0.012 0.029 - - 0.0018 0.012 Invention steel 12 0.0025 0.54 0.049 0.0057 0.0051 0.029 0.014 0.018 - - 0.0025 0.029 Invention steel 13 0.0022 0.61 0.059 0.0054 0.0048 0.012 0.011 0.026 - - 0.0034 0.021 Invented Steel 14 0.0023 0.76 0.047 0.0045 0.0037 0.013 0.007 0.022 - - 0.0032 0.017 Invented Steel 15 0.0021 0.45 0.032 0.0061 0.0015 0.017 0.02 0.026 - - 0.0022 0.021 Comparative River 1 0.0019 0.09 0.0088 0.0059 0.0038 0.033 0.0043 - - - 0.0022 Comparative River 2 0.0017 0.1 0.0091 0.0067 0.004 0.035 0.0068 - - - 0.0024 Comparative Steel 3 0.0015 0.05 0.0076 0.0061 0.0062 0.028 0.0044 - - - 0.0025 Comparative Steel 4 0.0018 0.14 0.0061 0.0079 0.0058 0.029 0.0067 - - - 0.0034 Comparative Steel 5 0.0014 0.13 0.0098 0.0061 0.0062 0.033 0.0093 - - - 0.0021 Comparative Steel 6 0.0019 0.15 0.0112 0.0072 0.0038 0.039 0.0090 - - - 0.0028 Comparative Steel 7 0.0019 0.14 0.0097 0.0061 0.0048 0.029 0.0049 - - - 0.0039 Comparative Steel 8 0.0055 0.05 0.0102 0.0054 0.0049 0.034 0.0138 - - - 0.0019 Comparative Steel 9 0.0054 0.09 0.0097 0.0045 0.0038 0.023 0.018 - - - 0.0023 Comparative Steel 10 0.0052 0.09 0.0087 0.0062 0.0052 0.021 0.0325 - - - 0.0026 Comparative Steel 11 0.0051 0.1 0.0051 0.0057 0.0053 0.026 0.0196 - - - 0.0032 Comparative Steel 12 0.005 0.15 0.0106 0.0076 0.0051 0.024 0.0278 - - - 0.0032 Comparative Steel 13 0.0045 0.13 0.0078 0.0076 0.0049 0.028 0.0225 - - - 0.0029 Comparative Steel 14 0.0042 0.05 0.0099 0.0077 0.0062 0.037 0.0127 - - - 0.0039 Comparative Steel 15 0.0041 0.05 0.0061 0.0079 0.0038 0.034 0.0372 - - - 0.0026

division C / Nb TS
(MPa) Hand
(%) BH
(Mpa) Precipitate
(nm) Precipitate
/ Μm ² TS, El, BH
evaluation Delta phase
(%) Alloying degree
(%) My powder ring Inventory 1 0.44 321 37 37 197 0.010 ○ 96 12.9 ○ Inventive Example 2 0.25 337 35 37 236 0.200 ○ 81 11.0 ○ Inventory 3 0.34 358 32 33 110 0.140 ○ 94 11.3 ○ Honorable 4 0.27 352 43 43 299 0.070 ○ 91 10.2 ○ Inventory 5 0.15 337 34 46 392 0.080 ○ 86 10.9 ○ Inventory 6 0.21 332 33 42 361 0.050 ○ 93 12.7 ○ Honorable 7 0.39 349 32 57 330 0.090 ○ 91 12.5 ○ Honors 8 0.40 312 42 49 144 0.080 ○ 83 12.8 ○ Proposition 9 0.30 347 43 59 268 0.130 ○ 85 11.3 ○ Inventory 10 0.16 364 44 47 237 0.030 ○ 87 12.8 ○ Exhibit 11 0.26 352 41 42 206 0.060 ○ 82 11.8 ○ Inventory 12 0.18 343 38 51 175 0.110 ○ 92 11.2 ○ Inventory 13 0.20 367 37 49 144 0.070 ○ 91 10.6 ○ Inventory 14 0.33 331 36 39 113 0.020 ○ 95 10.9 ○ Honorable Mention 15 0.11 367 33 54 330 0.090 ○ 89 12.9 ○ Comparative Example 1 0.44 271 36 37 501 0.001 △ 71 10.5 △ Comparative Example 2 0.25 276 35 36 567 0.004 △ 78 11.4 × Comparative Example 3 0.34 267 35 35 541 0.002 △ 72 11.9 × Comparative Example 4 0.27 297 36 37 601 0.001 △ 67 11.7 × Comparative Example 5 0.15 496 34 17 67 0.001 × 74 10.1 △ Comparative Example 6 0.21 401 33 9 43 0.003 × 71 12.6 △ Comparative Example 7 0.39 411 27 11 27 0.002 × 88 13.9 △ Comparative Example 8 0.40 389 28 14 62 0.002 × 87 13.7 △ Comparative Example 9 0.30 379 39 17 77 0.004 × 91 14.5 △ Comparative Example 10 0.16 381 34 10 92 0.001 × 93 14.2 △ Comparative Example 11 0.26 277 33 21 192 0.002 × 77 10.7 △ Comparative Example 12 0.18 291 32 23 202 0.001 × 84 14.2 × Comparative Example 13 0.20 284 36 17 83 0.002 × 91 14.7 × Comparative Example 14 0.33 290 35 11 222 0.002 × 87 14.1 × Comparative Example 15 0.11 265 47 14 232 0.005 △ 72 11.9 △

(In Table 2, the precipitate means at least one precipitate of CuS, MnS and CuMnS.)

As shown in Table 2, in Examples 1 to 15, which satisfied all of the suggestions of the present invention, both strength, elongation, and hardening curability were all good, and the plating properties such as resistance to powdering .

In Comparative Examples 1 to 15, the contents of C and Mn in the composition do not satisfy the requirements of the present invention.

It can be confirmed that the cold-rolled steel sheets of Comparative Examples 1 to 4 produced very coarse crystal grains and the grains were not distributed appropriately and had low strength. The cold-rolled steel sheets of Comparative Examples 5 to 10 had fine grains and excellent strength, but were too fine as compared with the aimed grains and the grain size distribution was not appropriate, so that it was confirmed that the elongation was low or the cemented amount (BH) was small. In addition, the cold-rolled steel sheets of Comparative Examples 11 to 15 did not have an appropriate distribution of crystal grains, and the amount of hardened sintering was also low.

In addition, the alloyed hot-dip coated steel sheets of Comparative Examples 1 to 6, 11 and 15 had a delta phase fraction of less than 81%, and the alloying hot-dip coated steel sheets of Comparative Examples 7 to 10 and Comparative Examples 12 to 14 had alloyability Which is too high. As a result, the powdering properties of the galvannealed steel sheets of Comparative Examples 1 to 15 were weakened.

Claims (7)

By weight%, carbon (C): 0.002 to 0.004%, manganese (Mn): 0.3 to 0.8%, phosphorus (P): 0.06% or less, sulfur (S): 0.008% or less, silicon (Si): 0.001 to 0.007 %, Aluminum (Al): 0.01 to 0.04%, niobium (Nb): 0.005 to 0.020%, copper (Cu): 0.01 to 0.03%, nitrogen (N): 0.001 to 0.005%, balance Fe and inevitable impurities , Component ratio (C / Nb) of C and Nb is 0.01 to 0.50,
CuS, comprising the MnS and CuMnS 1 or more kinds of precipitates, the average crystal grain size of the precipitate is 100 ~ 400nm, and the average density of the precipitates from 0.01 to 0.20 piece / μm ^2,
The microstructure of the steel sheet is composed of a ferrite single phase structure,
A hardening type alloyed hot-dip galvanized steel sheet having excellent workability and powder resistance including an alloyed hot-dip galvanized layer on the surface of a steel sheet.
The method of claim 1,
The galvanized hot-dip galvanized steel sheet according to claim 1, wherein the galvannealed steel sheet comprises at least one member selected from the group consisting of 0.01 to 0.03% of chromium (Cr), 0.001 to 0.005% of molybdenum (Mo), 0.001 to 0.030% of nickel (Ni) and 0.0001 to 0.010% of vanadium A hot-curing type alloyed hot-dip galvanized steel sheet excellent in workability and resistance to powdering, further comprising one or more selected ones.
The method of claim 1,
The delta-phase fraction of the alloyed hot-dip galvanized layer is 81% or more, alloying degree is 9 ~ 13% characterized in that the hardening-type hot-dip galvanized steel sheet excellent in workability and powder resistance.
4. The method according to any one of claims 1 to 3,
The galvannealed steel sheet of claim 1, wherein the galvannealed steel sheet has a tensile strength of 300 to 370 MPa, an elongation of 35% or more, and a bending hardening (BH) value of 30 MPa or more.
By weight%, carbon (C): 0.002 to 0.004%, manganese (Mn): 0.3 to 0.8%, phosphorus (P): 0.06% or less, sulfur (S): 0.008% or less, silicon (Si): 0.001 to 0.007 %, Aluminum (Al): 0.01 to 0.04%, niobium (Nb): 0.005 to 0.020%, copper (Cu): 0.01 to 0.03%, nitrogen (N): 0.001 to 0.005%, balance Fe and inevitable impurities Reheating the steel slab having a component ratio (C / Nb) of C and Nb of 0.01 to 0.50 to 1150 to 1250 ° C .;
Preparing a hot rolled steel sheet by hot rolling the reheated steel slab at a finishing rolling temperature of Ar 3 to 950 캜;
Winding the hot-rolled steel sheet at 700 to 750 ° C;
Rolling the steel sheet at a reduction ratio of 60 to 80% after the rolling to produce a cold-rolled steel sheet;
Annealing the cold-rolled steel sheet at 820 to 880 ° C;
Performing hot dip galvanizing on the annealed cold rolled steel sheet to produce a hot-dip galvanized steel sheet; And
The hot dip galvanized steel sheet is heated to 400 to 600 ° C to produce a galvannealed steel sheet
Wherein the galvannealed steel sheet has excellent workability and resistance to powdering.
6. The method of claim 5,
Wherein the steel slab is made of one selected from the group consisting of 0.01 to 0.03% of Cr, 0.001 to 0.005% of molybdenum (Mo), 0.001 to 0.030% of nickel (Ni), and 0.0001 to 0.010% of vanadium (V) Or two or more of the above-mentioned hot-dip galvannealed steel sheet and hot-dip galvanized steel sheet.
The method according to claim 5 or 6,
Wherein the annealing step is carried out by a continuous annealing method and is carried out for 10 seconds to 30 minutes, wherein the annealing step is carried out by a continuous annealing method and is excellent in workability and resistance to powdering.