KR20070023995A - Steel sheet for galvanizing with superior formability and method for manufacturing the steel sheet - Google Patents

Abstract

A steel sheet for galvanizing which has a tensile strength of 28 to 50 kg/mm^2, superior formability, superior secondary working embrittlement resistance, superior fatigue strength of welding parts and superior surface quality, and a method for manufacturing the same are provided. A method for manufacturing a steel sheet for galvanizing with superior formability comprises: reheating a steel slab having a composition comprising, by weight percent, 0.010% or less of C, 0.1% or less of Si, 0.06 to 1.5% of Mn, 0.15% or less of P, 0.020% or less of S, 0.10 to 0.40% of soluble Al, 0.010% or less of N, 0.003 to 0.010% of Ti, 0.003 to 0.040% of Nb, 0.0002 to 0.0020% of B and 0.05% or less of Mo, 0.005 to 0.05% of Sb or/and 0.005 to 0.05% of Sn with the balance of Fe and other inevitable impurities, wherein the sum of Sb and Sn is 0.005 to 0.1% when Sn and Sb are added to the composition; hot finish rolling the reheated steel slab in an austenite single phase region to obtain a hot rolled steel sheet; coiling the hot rolled steel sheet; cold rolling the hot rolled steel sheet coil; and continuously annealing the cold rolled steel sheet coil in a temperature range of 700 deg.C or more.

Description

Galvanized steel sheet with excellent processability and its manufacturing method {Steel Sheet for Galvanizing with Superior Formability and Method for Manufacturing the Steel Sheet}

1 is a graph showing the change in the amount of steel plate surface concentrate by steel grade and annealing temperature

Figure 2 is a photograph showing the distribution of steel plate surface concentrates for air-cooled and water-cooled material after steel type and hot rolled winding

3 is a photograph showing the distribution of steel plate surface concentrate by steel grade and annealing temperature

The present invention relates to a soft and high-strength thin steel sheet and a manufacturing method for the super-core processing mainly used for automotive interior and exterior panels, more specifically 28 ~ 50kg / mm ² tensile strength, excellent formability, excellent secondary secondary processing The present invention relates to a galvanized steel sheet having excellent brittleness and excellent weld fatigue properties as well as excellent workability and a method of manufacturing the same.

Recently, steel sheets for automobiles have been required to have a higher level of formability due to the complexity and integration of automobile molded articles, and on the other hand, secondary processing brittleness and weld fatigue characteristics in terms of automotive use environment. There is a demand for a steel sheet that is excellent and has a beautiful plating surface.

However, in general, in order to increase the formability and strength of the steel sheet, high purity steel which minimizes impurities in the steel is used, and it is usually manufactured by adding Si, Mn, Ti, Nb, Al, and the like.

After cold rolling, the annealing heat treatment is performed at a temperature of 700 ° C. or higher to recrystallize the hardened structure. However, since the additive elements are mostly oxygen affinity elements compared to Fe, MnO, SiO ₂ , and Al ₂ O ₃ during cold rolling annealing are performed. Grow as surface concentrates, either alone or in combination.

As the amount of these surface concentrates increases, the wettability of the plating bath is reduced during the hot dip plating, and the alloying reaction is inhibited, so that surface defects such as unplated are likely to occur.

In addition, when the surface thickener is coarsened, it is adsorbed on the hearth roll of the continuous annealing furnace to cause micro dents on the surface of the coated steel sheet, which greatly affects the surface quality.

As a technique for improving the above problems of plating defects, a technique for improving plating by adding specific elements such as Cr and Sb (JP2002-146477, JP2001-64750, JP2002-155317), and preliminary to the hot rolled coil before cold rolling Techniques for suppressing the concentrate formed on the surface during cold rolling annealing by oxidizing (JP2001-288550) and the like have been proposed.

However, the above-mentioned techniques have not been evident in the effect of the addition of specific elements, and are not actually produced in the current commercial hot rolled-cold-rolled annealing facility.

The present invention is to provide a galvanized steel sheet having excellent workability having a tensile strength of 28 ~ 50kg / mm ² , excellent moldability, excellent secondary workability and excellent weld fatigue properties, as well as excellent surface quality, The purpose is.

In addition, the present invention is to provide a method for producing a galvanized steel sheet excellent in the workability, which is the object.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, by weight%, C: 0.010% or less, Si: 0.1% or less, Mn: 0.06% to 1.5%, P: 0.15% or less, S: 0.020% or less, Sol.Al: 0.10-0.40%, N: 0.010% or less, Ti: 0.003-0.010%, Nb: 0.003-0.040%, B: 0.0002-0.0020%, and Mo: 0.05% or less, including Sb: 0.005-0.05% and Sn 0.005-0.05% One or two kinds are added, and when the two kinds are added, the sum is 0.005 to 0.1%, and it is composed of the balance Fe and other unavoidable impurities, and a thickener having an average diameter of 1 µm or less is formed on the surface thereof. And it relates to a galvanized steel sheet having excellent workability having a tensile strength of 28 ~ 50kg / mm ² .

Preferably, the galvanized steel sheet is to suppress the growth of the average diameter of the thickener within 10% with respect to the increase in annealing temperature 10 ℃.

In addition, the present invention is a weight%, C: 0.010% or less, Si: 0.1% or less, Mn: 0.06% to 1.5%, P: 0.15% or less, S: 0.020% or less, Sol.Al: 0.10-0.40%, N: 0.010% or less, Ti: 0.003-0.010%, Nb: 0.003-0.040%, B: 0.0002-0.0020%, and Mo: 0.05% or less, including Sb: 0.005-0.05% and Sn 0.005-0.05 One or two of the% is added, and when the two are added, the sum is 0.005 to 0.1%, and the steel slab composed of the remaining Fe and other unavoidable impurities is reheated, and then hot-rolled in the austenitic single phase region. After the cold rolled hot rolled steel sheet, the present invention relates to a method for producing a galvanized steel sheet excellent in workability, characterized in that the continuous annealing at a temperature range of 700 ℃ or more.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The composition of the said steel plate is demonstrated.

The steel C acts as an invasive solid solution element and inhibits formation of {111} texture structure, which is advantageous for processability during the formation of the texture structure of the steel sheet during cold rolling and annealing, and when carbon content is high, Since the addition amount of Ti and Nb must be increased, it is economically disadvantageous, so the content is limited to 0.010% or less.

The Si not only causes surface scale defects, but also generates tempered color during annealing and unplated during plating, so its content is limited to 0.1% or less.

The Mn is added as a substituted solid solution strengthening element to secure the strength, but when the content exceeds 1.5%, the r value rapidly decreases with elongation, and when the content is less than 0.06%, brittleness due to S in steel is concerned. The content is limited to 0.06% to 1.5%.

P is a representative solid solution strengthening element added for strength increase together with Mn. In the steel grades of the Ti-Nb-based component system as in the present invention, {111} which is advantageous in r value due to not only strength increase but also grain refinement and grain boundary segregation, etc. However, if the content exceeds 0.15%, the brittleness of the steel is greatly increased with the rapid decrease in elongation, and the content thereof is preferably limited to 0.15% or less, more preferably 0.03-0.15. It is limited to%.

In general, in the case of manufacturing deep-processed steel, the S content in the steel is generally limited to less than 0.005%, but in the present invention, since the steel is Mn added, all the steel S is precipitated as MnS, so that the workability decrease by the solid solution S is avoided. Can be.

Therefore, in the present invention, it is preferable to limit the S content to 0.020% or less, which is an amount that can avoid the area where the risk of edge cracking occurs during rolling.

It is common to produce Sol.Al in steel in the case of cold rolled products in consideration of economic aspects while keeping the dissolved oxygen level in the steel sufficiently low, and manage the content of 0.02 ~ 0.07%.

However, in the steel of the present invention, Sol.Al plays a role of stably securing deep workability even at a relatively low annealing temperature.

In other words, in the steel of the present invention, when the amount of Sol.Al in the steel is 0.10% or more, the precipitates in the steel are coarsened and the effect of inhibiting the recrystallization inhibition of P is clearly shown, thereby promoting recrystallization, as well as the {111} series texture. However, if the content exceeds 0.40%, the content is limited to 0.10% to 0.40% because the cost increases and the continuous casting performance is impaired.

In addition, in the steel of the present invention, Sol.Al in the steel affects the formation behavior of Ti, Nb-based precipitates, which are carbonitrides, to make the precipitates coarse, and thus, Ti and Nb are added even less than conventional IF steels. It is to play a role to obtain a good processability.

The N in the steel not only greatly impairs the workability when present in solid solution, but when the amount is large, the amount of Ti and Nb to be fixed as a precipitate should be increased, so the content thereof is limited to 0.010% or less.

B in the steel is an element which is added to improve the fatigue characteristics of the spot weld as a grain boundary strengthening element and to prevent P grain boundary brittleness, and should be added at least 0.0002% in order to exhibit the addition effect, and the content thereof is more than 0.0020%. If the workability drops sharply and the surface characteristics of the plated steel are degraded, the content is limited to 0.0002 to 0.002%.

Mo in the steel is an element added to improve the secondary workability and plating resistance, when the content exceeds 0.05%, the improvement effect is not only greatly reduced but also economically disadvantageous, the content is less than 0.05% Limited to

In the present invention, Ti and Nb are very important elements in terms of securing the workability of the steel, the minimum for synergistic effect (especially r value). In consideration of the optimum amount, Ti is limited to 0.003-0.010% and Nb to 0.003-0.040%.

Sb in the steel is a very important element in the present invention, and has an excellent effect of suppressing the occurrence of surface thickening such as MnO, SiO ₂ , Al ₂ O ₃ , and also suppressing the coarsening of the surface thickener due to the temperature rise and the change of the hot rolling process. There is. In order to obtain the above effect, the content is required at least 0.005% or more, but when added over a certain limit, the upper limit is limited to 0.05% because a predetermined effect cannot be obtained.

Sn in the steel is a component having a similar effect to the Sb, the content is required at least 0.005% or more to obtain the addition effect, but the upper limit is 0.05% because a predetermined effect is not obtained when added over a certain limit Restrict.

In addition, when the Sb and Sn are added at the same time the sum of the content is limited to 0.005 ~ 0.1%.

Hereinafter, the manufacturing conditions of this invention are demonstrated.

After reheating the steel slab formed as described above, the hot rolled steel sheet wound by completing the finish rolling in the austenite single phase region is cold rolled steel sheet, and it is continuous at a temperature of 700 ° C. or higher to secure the workability of the material. It is preferable to anneal.

In general, as the temperature increases, the ductility and r value of the material improve.

However, as the annealing temperature increases, the amount of surface concentrates (single or complex oxides such as Si, Al, Mn, etc.) formed on the surface of the material increases, and the tendency to coarsen is obvious. Surface defects such as dents are liable to occur.

In the present invention, the growth of the surface concentrate in the annealing temperature section is suppressed to ensure an excellent steel sheet surface quality.

Preferable steel slab heating temperature in the present invention is 1100 to 1300 ° C, preferred hot-rolling rolling temperature is 830 to 920 ° C, and preferred winding temperature is 500 to 700 ° C.

In the present invention, it is applied to both air cooling or water cooling after hot rolling.

In addition, in order to obtain a high r value of 1.9 or more, it is preferable to limit the reduction ratio during cold rolling to 65% or more.

In addition, when the annealing temperature of the cold rolled steel sheet is too low, it is difficult to obtain a high r value of 1.9 or more. If the annealing temperature is too high, there is a risk of problems in the sheet flowability due to high temperature annealing, so the annealing temperature is 700 ° C. As mentioned above, Preferably it limits to 780-860 degreeC.

In the annealing temperature section, it is preferable that the growth of the average diameter of the granular thickener is within 10% with respect to the increase in the annealing temperature of 10 ° C.

In the conventional method for manufacturing a super deep steel sheet, the continuous annealing of the cold rolled steel sheet is performed at about 880 ~ 930 ℃.

As described above, since the continuous annealing temperature of the present invention is lower than the annealing temperature applied to the production of ordinary super-core steel sheets, the present invention is more economical and has excellent operability.

According to the present invention, it is possible to produce a galvanized steel sheet having a machinable powder having a mean diameter of 1 μm or less on the surface thereof and having excellent workability having a tensile strength of 28 to 50 kg / mm ² .

The concentrate is composed mainly of single or complex oxides such as Si, Al, Mn and Ti.

It is preferable that the concentration of the concentrate is suppressed to within 10% of the increase in the annealing temperature of 10 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples.

 (Example)

The steel slab, as shown in Table 1, was heated to a temperature range of 1200 ° C. to finish rolling at a hot finishing rolling temperature of 890 ° C., wound at a winding temperature of 660 ° C., followed by air cooling, and then a reduction ratio of 80%. Cold rolled to prepare a cold rolled steel sheet.

Further, for steel grades 4 and 5, the hot rolled steel sheet was wound as described above, followed by water cooling, followed by cold rolling at a reduction ratio of 80% to prepare a cold rolled steel sheet.

Steel grades 1 to 3 of the cold rolled steel sheets prepared as described above were subjected to annealing for 86 seconds at a temperature range of 780 to 830 ° C. in an N ₂ -10% H ₂ atmosphere, and then concentrated on the surface of the steel sheet. The amount was investigated and the result is shown in FIG.

In addition, after the annealing heat treatment for steel grades 4 and 5 (air-cold and water-cooling material after winding) for 86 sec. In an N ₂ -10% H ₂ atmosphere of 860 ℃ in the cold-rolled steel sheet prepared as described above, it is produced on the steel surface The shape of the concentrate to be prepared was investigated, and the results are shown in FIG. 2.

The cold rolled steel sheets 4 and 5 of the cold rolled steel sheets after winding are subjected to annealing for 86 sec. In an N ₂ -10% H ₂ atmosphere at 800 to 850 ° C., followed by The shape was investigated and the result is shown in FIG.

Steel grade Chemical composition (wt%) Remarks C Si Mn P S Mo S-Al Nb Ti B Sn Sb N One 0.0038 0.01 0.81 0.08 0.01 0.01 0.1 0.005 0.04 0.0002 - - 0.0019 Comparative steel 2 0.0037 0.01 0.82 0.08 0.01 0.01 0.1 0.005 0.04 0.0002 0.05 - 0.0022 Invention steel 3 0.0041 0.01 0.81 0.08 0.01 0.01 0.1 0.005 0.04 0.0002 - 0.05 0.0022 Invention steel 4 0.0019 0.06 0.87 0.08 0.01 0.09 0.115 0.007 0.021 0.0005 - - 0.0040 Comparative steel 5 0.0023 0.06 0.87 0.08 0.01 0.09 0.15 0.007 0.021 0.0006 - 0.01 0.005 Invention steel

As shown in FIG. 1, it can be seen that steel grades 2 and 3 conforming to the present invention have less surface concentration of Mn and Al than steel grade 1 outside the scope of the present invention.

In addition, as shown in Figure 2, steel grade 5 in accordance with the present invention can be seen that the amount of surface concentrate less than the steel grade 4 outside the present invention, the size is small.

Particularly, in case of steel grade 4, the surface concentrate is considerably larger in size than the air-cooled material when water-cooled after hot-rolled winding, whereas in the case of steel grade 5, the surface concentrate is almost the same size as the air-cooled material even when water-cooled after hot-rolled winding. It can be seen that it has.

In addition, as shown in FIG. 3, in the case of steel grade 4, the size of the surface thickener increases with an increase in annealing temperature, whereas in the case of steel grade 5, the size of the surface concentrate is hardly changed with an increase in the annealing temperature. It can be seen that.

As described above, according to the present invention, not only has a tensile strength of 28 to 50kg / mm ² , excellent moldability, excellent secondary workability, and excellent weld fatigue properties, but also excellent workability with excellent surface quality A steel sheet for gold is provided.

Claims (8)

By weight%, C: 0.010% or less, Si: 0.1% or less, Mn: 0.06% to 1.5%, P: 0.15% or less, S: 0.020% or less, Sol.Al: 0.10-0.40%, N: 0.010% or less , Ti: 0.003-0.010%, Nb: 0.003-0.040%, B: 0.0002-0.0020%, and Mo: 0.05% or less, including Sb: 0.005-0.05% and Sn 0.005-0.05%, or Two kinds are added, and the sum of the two kinds is 0.005 to 0.1%, and it is composed of the balance Fe and other unavoidable impurities, and a thickener having a size of 1 μm or less is formed on the surface thereof, and 28 to 50 kg Galvanized steel sheet with excellent workability with a tensile strength of / mm ² The galvanized steel sheet having excellent workability according to claim 1, wherein the increase in the average diameter of the granular thickener is within 10% when the annealing temperature is increased by 10 ° C. The galvanized steel sheet having excellent workability according to claim 1 or 2, wherein the concentrate has a single component or a complex oxide of Si, Al, Mn, and Ti as a main component. By weight%, C: 0.010% or less, Si: 0.1% or less, Mn: 0.06% to 1.5%, P: 0.15% or less, S: 0.020% or less, Sol.Al: 0.1-0.40%, N: 0.010% or less , Ti: 0.003-0.010%, Nb: 0.003-0.040%, B: 0.0002-0.0020%, and Mo: 0.05% or less, including Sb: 0.005-0.05% and Sn 0.005-0.05%, or After adding two kinds, the sum of two kinds is 0.005 ~ 0.1%, after reheating the steel slab composed of the balance Fe and other unavoidable impurities, and winding the hot-rolled hot rolled steel sheet in the austenitic single phase region. After the cold rolling, a method of producing a galvanized steel sheet with excellent workability, characterized in that the continuous annealing at a temperature range of 700 ℃ or more The steel slab heating temperature is 1100-1300 ° C, the hot finishing rolling temperature is 830-920 ° C, the winding temperature is 500-700 ° C, the cold rolling rate is 65% or more, and the annealing temperature is 5 ° C. Process for producing galvanized steel sheet excellent in workability, characterized in that 780 ℃ ~ 860 ℃ The method for manufacturing a galvanized steel sheet having excellent workability according to claim 4 or 5, wherein the hot rolled steel sheet is wound up and then air cooled or water cooled. The method according to claim 4 or 5, wherein the coarsening of the concentrate in the annealing temperature section is suppressed to within 10% when the annealing temperature is increased by 10 ° C. The method of claim 6, wherein the coarsening of the concentrate in the annealing temperature section is suppressed to within 10% when the annealing temperature is increased by 10 ° C.

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