KR20140076829A - Method for manufacturing high manganese galvanized steel steet having excellent pickling property and coatability and high manganese galvanized steel steet produced by the same method - Google Patents

Abstract

The present invention relates to a method to manufacture a high manganese hot-dip galvanized steel sheet with excellent pickling and galvanizing properties, and a high manganese hot-dip galvanized steel sheet manufactured thereby. According to an embodiment of the present invention, the method to manufacture a high manganese hot-dip galvanized steel sheet comprises: a step of reheating a steel slab at 1050-1150°C, wherein the steel slab is composed of 0.3-1 wt% of C, 8-25 wt% of Mn, 0.1-3 wt% of Si, 0.1-8 wt% of Al, 0.1-2 wt% of Cr, 0.01-0.2 wt% of Ti, 0.0005-0.01 wt% of B, 0.01-0.3 wt% of P, 0.01-2.0 wt% of Ni, 0.06-0.2 wt% of Sn, and the remainder being Fe and other inevitable impurities; a step of obtaining a bar by roughly rolling the reheated steel sheet, wherein the rough rolling is ended at 1000-1040°C; a step of obtaining a steel sheet by performing a finish hot-rolling work for the bar; a step of winding the steel sheet at 100-600°C; a step of pickling the wound steel sheet; and a step of hot-dipping and galvanizing the pickled steel sheet. The present invention provides the method to manufacture a high manganese hot-dip galvanized steel sheet with excellent pickling and galvanizing properties which properly controls the hot rolling conditions and prevents the generation of residual scale during a pickling work and of galvanizing defects such as the occurrence of an ungalvanized part and a falling-off in plating adhesion; and a high manganese hot-dip galvanized steel sheet manufactured thereby.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a high manganese hot-dip galvanized steel sheet excellent in pickling and plating properties, and a hot- THE SAME METHOD}

The present invention relates to a method for producing a hot-rolled hot-dip galvanized steel sheet excellent in pickling and plating properties, and a hot-rolled hot-dip galvanized steel sheet produced thereby.

The hot-dip galvanized steel sheet is excellent in corrosion resistance, weldability, and paintability, and is widely used as a steel sheet for automobiles. In addition, from the viewpoint of improving the fuel efficiency by reducing the weight of automobiles and the stability of passengers, it is required to increase the strength of automobile bodies and structural materials, and therefore, many types of high strength steels for automobiles have been developed.

However, most of the steel plates (ash) have a decreased ductility as the steel is made to have a higher strength, and as a result, there are many limitations in machining into parts. As a result, as shown in Patent Documents 1 to 4, when the steel material contains 5 to 35% of manganese so that the steel material is twinned when plastic deformation occurs, An austenitic high-manganese steel having improved ductility with high strength has been proposed.

However, for the hot-dip galvanized steel sheet using such high-manganese steel as the plating material, annealing is performed in a nitrogen atmosphere including hydrogen for securing the material and for surface activation (reduction) While the element which is easily oxidized such as Mn, Si, Al and the like contained in the high manganese steel acts as an oxidizing atmosphere. Therefore, when recrystallization annealing of high manganese steel to which a large amount of Al, Si, etc., as well as Mn is added in such an atmosphere, alloying elements are selectively oxidized (selectively oxidized) by water or oxygen contained in a small amount in the atmosphere, ) Surface oxides such as Mn, Al and Si are formed on the surface. Therefore, when a high manganese steel containing not only Mn but also a large amount of Al, Si or the like is used as a plating material, unplated by the surface oxide formed in the annealing process as a pre-plating process, There is a problem that peeling occurs.

As a typical technique for solving such a problem, Patent Document 5 discloses that the above-described technique is Ni plating so as to have an adhesion amount of 50 to 100 mg / m < 2 > before annealing and plating, and alloying elements of Mn, Al, Of the surface of the substrate. However, the above-described technique can prevent the surface elements of Mn and Si from being surface-concentrated and oxidized when the Ni-plated layer is annealed. However, in the case of Al, the Ni-plated layer promotes surface diffusion of Al, There is a problem that an oxide layer is formed and the plating property is deteriorated.

Another technique is Patent Document 6, which relates to a method of adjusting a component by adding Si to form a thin Si oxide layer on the surface to inhibit the formation of manganese oxide. However, since Si has a higher oxidizing power than Mn, the above-mentioned technique has a disadvantage in that a stable film-like oxide is formed and the wettability with molten zinc is lowered.

Another technology is Patent Document 7. The present invention relates to a plating pretreatment method for preventing the formation of Mn oxide by plating with aluminum of 50 nm to 1000 nm by vacuum evaporation (PVD) before annealing. However, the above-described technique requires a vacuum deposition process before annealing of the plating process. Since Al, which is a plating material to be deposited, is easily oxidized, the deposited Al in the annealing process, which is the next process, There arises a problem of deteriorating the plating ability due to the formation of such a bad Al oxide.

Japanese Patent Application Laid-Open No. 4-259325 International Patent Publication No. WO 93/013233 International Patent Publication No. WO 99/001585 International Patent Publication No. WO 02/101109 Korean Patent Publication No. 2011-0087800 Korean Patent Publication No. 2007-0067950 Korean Patent Publication No. 2007-0107138

The present invention solves the problems such as residual scale remaining when Ni and Sn are added to high manganese steel, and thereby causes problems such as unplated and galvanized peeling, and thus provides a high manganese hot dip galvanized steel sheet And a hot-dip galvanized steel sheet produced by the method.

An embodiment of the present invention is a steel sheet comprising, by weight%, 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 8% of Al, 0.1 to 2% of Cr, The steel slab containing the remaining Fe and other unavoidable impurities is reheated to 1050 to 1150 占 폚. The steel slab is reheated to 1050 to 1150 占 폚. The steel slab contains 0.2% of B, 0.0005 to 0.01% of P, 0.01 to 0.3% of P, 0.01 to 2.0% of Ni, 0.06 to 0.2% of Sn, step; Subjecting the reheated steel slab to rough rolling to finish at 1000 to 1040 캜 to obtain a bar; Finishing hot rolled bar to obtain a steel sheet; Twisting the steel sheet at 100 to 600 ° C; Picking up the wound steel sheet; And hot-dipping the pickled steel sheet to obtain a hot-dip galvanized steel sheet.

In another embodiment of the present invention, there is provided a steel sheet comprising, by weight%, 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 8% of Al, The present invention provides a hot-dip galvanized steel sheet comprising 0.2 to 0.2% of B, 0.0005 to 0.01% of P, 0.01 to 0.3% of P, 0.01 to 2.0% of Ni, 0.06 to 0.2% of Sn and the balance Fe and other unavoidable impurities.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a hot-rolled hot-dip galvanized steel sheet excellent in pickling resistance and plating ability that does not cause residual scale during pickling and does not cause plating difficulty such as non- And a hot-dip galvanized steel sheet produced by the method.

Fig. 1 is a photograph showing scale and remanent scale behaviors of high manganese steel in the process, wherein (a) shows the scale in the hot-rolled steel sheet, (b) shows the residual scale in the hot- ≪ / RTI >
FIG. 2 is a graph showing the relationship between the rough rolling termination temperature and the uncoated and plated adhesion index.

The present inventors have found that, in order to prevent unplated or plating peeling due to the formation of a thick annealed oxide when plating a high manganese steel containing a large amount of aluminum and silicon as well as manganese under ordinary annealing and plating conditions, -0085845 (currently unpublished). This application relates to a technique of adding a valuable element such as Sn, Ni, Cr and the like so that the coating of the above elements prevents the surface enrichment and oxidation of Mn, Al, Si and the like during annealing. However, in the above-mentioned application, it is economically possible to secure the plating property, but in the ordinary hot rolling condition, the hot-rolled scale is changed into a composition or structure difficult to pick up by the addition of Ni and Sn, And the present invention has been proposed.

More specifically, when the hot manganese steel to which Ni, Sn or the like is added is hot rolled and pickled in a state where the hot rolling condition is not properly controlled, as shown in FIG. 1, And the scale remains on the surface of the material without being removed in cold rolling as a post-process. Such residual scale is composed of not only Ni but also oxides such as Mn, Al and Si, so that even if annealing is carried out before plating, it is not reduced and remains (remains) in oxide (scale). As a result, there arises a problem that plating deterioration occurs due to a decrease in wettability with molten zinc during hot-dip coating, or plating peeling occurs in which the plating layer falls off during processing.

Accordingly, the inventors of the present invention conducted studies to solve the problems such as remnant scale remaining due to the addition of precious elements such as Ni and Sn to high manganese steel and the problems of unplated and plating peeling, And the hot rolling conditions such as the slab reheating temperature, the rough rolling finishing temperature, and the winding temperature are appropriately controlled in the manufacturing conditions, the residual scale during pickling does not occur, and plating such as unplated plating or deterioration of the plating adhesion at the time of hot- It is possible to produce a hot-dip galvanized steel sheet excellent in pickling resistance and plating ability without occurrence of defects and the present invention has been completed.

Hereinafter, the present invention will be described. First, the selection of alloy components and composition ranges will be described. However, it should be noted that the following percentages are by weight unless otherwise specified.

C: 0.3 to 1%

The carbon (C) is a component contributing to stabilization of the austenite. It is preferable that the amount of carbon (C) increases as the addition amount thereof is increased. However, when the content of C exceeds 1%, the stability of the austenite phase greatly increases and the workability is lowered due to the deformation behavior transition due to slip, so that the content thereof is preferably in the range of 0.3 to 1%.

Mn: 8 to 25%

The manganese (Mn) is an essential element of the manganese steel which causes the twinning to be induced during the plastic deformation due to the stabilization of the austenite phase, thereby remarkably improving the ductility at the same time as increasing the strength. In order to obtain such an effect, it is advantageous to add at least 8% or more. However, when the content of Mn exceeds 25%, the high-temperature ductility is lowered, cracks are generated in the casting process, the high-temperature oxidation occurs rapidly in the reheating step for hot rolling and the surface quality of the product is lowered, The surface oxidation (selective oxidation) during the annealing in the process not only hinders the plating property but also increases the production cost due to the addition of a large amount of Mn. Therefore, the content of Mn is preferably 8 to 25%.

Si: 0.1 to 3%

When the silicon (Si) is added singly, it is preferable that the silicon (Si) is not added because it is surface-enriched in the melting and monolithic annealing step to form dense film (film) type Si oxide, Similarly, when it is added in combination with Mn, film-shaped Si oxide is interrupted by Mn to change into a particle type, and the effect of reducing the thickness of Mn oxide is also exhibited. In order to exhibit the above-mentioned effects, Si is added in an amount of not more than 1/5 times (Si / Mn? 0.2) relative to the amount of Mn added. When the amount of Si is more than 5 times, Si and Mn oxides are formed, And undesirably plating and plating peeling occur. However, since the ductility of the high manganese steel is drastically lowered at an addition amount of Si exceeding 3%, the upper limit of the Si content is limited to 3% or less. If the Si content is less than 0.1%, the effect of improving the strength is insignificant, and therefore, the Si content is preferably in the range of 0.1 to 3%.

Al: 0.01 to 8%

The aluminum (Al) is usually added as a deoxidizer but is added in order to prevent delayed fracture in the high manganese steel of the present invention. Al is a component that stabilizes the ferrite phase but increases the stacking fault energy on the slip surface of the steel to suppress the formation of ε (Epsilon) -martensite phase to improve ductility and improve delayed fracture resistance. In addition, Al suppresses the formation of the? -Martensite phase even in the case of a low Mn addition amount, thereby contributing to the minimization of the Mn addition amount. In order to exhibit such effects in the high manganese steel, it is preferable that 1% or more of Al is added. However, when the Al content exceeds 8%, the twin generation is suppressed to decrease the ductility. In addition, since Al is an element to be oxidized well, the surface is oxidized during the annealing process, And the Al content is preferably in the range of 0.01 to 8%.

Cr: 0.1 to 2%

The chromium (Cr) has an effect of inhibiting corrosion by forming a passive film in the atmosphere like Si, preventing the decarburization of carbon in the steel during high temperature hot rolling, suppressing the formation of? '- martensite phase on the surface of the steel sheet Thereby improving the formability of the steel. For this effect, it is preferable to add Cr by 0.1% or more. However, when the addition amount of Cr, which is a ferrite stabilizing element, exceeds 2%, the formation of? '- martensite phase is rather promoted and the ductility of the steel is reduced. In addition, even in terms of plating, the surface hardening of Mn, Si and Al, which are poor in plating property due to the formation of Cr oxide immediately under the surface when Cr is added, is prevented and oxidation is prevented. The composite oxide is formed to inhibit the wettability with molten zinc to cause plating or peeling of the plating. Therefore, the content of Cr is preferably in the range of 0.1 to 2%.

Ti: 0.01 to 0.2%

The titanium (Ti) increases the melting temperature of the low-melting point compound in which Al is concentrated by being solidified in the columnar phase boundary phase to prevent formation of a liquid film at 1300 ° C or lower, and has high affinity with nitrogen, It acts as nuclei of coarse aluminum nitride (AlN) precipitation and strengthens the column phase boundary. However, if it is less than 0.01%, there is no effect. If it exceeds 0.2%, excess Ti is segregated in grain boundaries to cause intergranular separation, so that the content of Ti is preferably in the range of 0.01 to 0.2%.

B: 0.0005 to 0.01%

The boron (B) is solid at the column phase boundary phase at a temperature of 1000 ° C or higher to inhibit generation and migration of vacancies, thereby strengthening the column phase boundary phase. However, when the addition amount is less than 0.0005%, it is difficult to secure the above effect. When the addition amount exceeds 0.01%, a large amount of carbide and nitride is generated to act as nuclei of aluminum nitride precipitation to promote coarse aluminum nitride precipitation, Take off. On the other hand, if the amount of boron added exceeds 0.01% in terms of plating, unburnt occurs due to the formation of boron oxide by the grain boundary thickening and oxidation in the annealing step before plating. Therefore, the boron has a range of 0.0005 to 0.01% desirable.

P: 0.01 to 0.3%

The phosphorus (P) serves as an element which induces interfacial precipitation phenomenon and precipitates on the scale and the steel sheet interface in the hot-rolled steel sheet to facilitate pickling. As the content of P increases, the surface shape becomes uniform and the pickling is easy, but when P is less than 0.01%, it is difficult to obtain the above effect. When the content of P exceeds 0.3%, the main composition is deteriorated and a problem arises in that the hot-rolling brittleness is caused in the hot rolling. Further, since P precipitated along the grain boundaries during the annealing reacts with oxygen to form oxides, alloying is delayed in the alloying treatment, so that it is preferable to control the amount of P to be less than 0.3%. Therefore, it is preferable that P is in the range of 0.01 to 0.3%.

Ni: 0.01 to 2.0%

The nickel (Ni) increases the stability of the austenite phase as a material, thereby suppressing the formation of the α '(alpha re-) martensite phase which damages the formability. Therefore, in high manganese steel having an austenite phase even at room temperature, twinning is promoted, which contributes to an increase in strength and an improvement in ductility during processing. In terms of plating, since Ni is a valuable element, it does not oxidize itself at high temperature and suppresses the surface diffusion of elements such as Al, Mn and Si precipitated on the surface, which are easily oxidized, It exhibits excellent wettability with molten zinc because it causes compositional change. In order to exhibit such an effect, the Ni addition amount should be at least 0.01%, but if the Ni addition amount exceeds 2%, the internal oxidation rapidly proceeds along the crystal grain boundaries, cracking can occur during hot rolling, and the cost increases , And the content of Ni is preferably in the range of 0.01 to 2.0%.

Sn: 0.06 to 0.2%

Since tin (Sn) is a precious element and does not form an oxide film itself at high temperature, the tin (Sn) precipitates on the surface of the substrate during melting and monolithic annealing, and the oxidizing elements such as Al, Si and Mn are diffused on the surface to form oxides And the plating ability is improved. However, when the addition amount of Sn is less than 0.06%, the effect is not clear. As the amount of Sn increases, the formation of selective oxides is inhibited. However, when the amount of Sn exceeds 0.2%, hot brittleness is generated to deteriorate hot workability. Is controlled in the range of 0.06 to 0.2%.

In the present invention, steel slabs having the above-described alloying components and composition ranges are prepared, and reheating is performed to homogenize the steel slabs. At this time, when the slab reheating temperature (SRT) exceeds 1150 ° C, a compound of an element reinforcing the columnar phase boundary will form a liquid film on the grain boundaries of the slab, thereby causing cracks in hot rolling. In order to improve the plating performance, Ni added forms a Ni-based oxide such as Ni-Mn-Fe-O between the scale and the slab surface. This Ni-based oxide (scale) It is not preferable because it is not peeled (eliminated) in descaling process by water jetting. On the other hand, when the slab reheating temperature is lower than 1050 ° C, the temperature range up to the finish rolling temperature is excessively narrow, resulting in a hot rolling load. Therefore, the slab reheating temperature is preferably in the range of 1050 to 1150 ° C.

As described above, the reheated slab is subjected to rough rolling as a preliminary work for finish hot rolling. The above-mentioned rough rolling is performed by descaling a slab having a thickness of about 250 mm while descaling by high-pressure water to produce a bar having a thickness of 25 to 35 mm. At this time, the Rough mill delivery temperature (RDT), which is the temperature of the final bar, is determined according to the degree of descaling by the slab temperature and the high-pressure water. When the rough rolling temperature is high enough to exceed 1040 ° C Since the rough rolling is performed in a state where the descaling by the high-pressure water is not properly operated, the Ni-based oxide remains without being removed. The Ni-based oxide remaining between the scale and the substrate remains after the pickling because it is difficult to remove under the usual pickling conditions as shown in Fig. 1, and the Ni-based oxide remaining after the pickling does not reduce even during annealing before plating, The lowering of the wettability with zinc results in unplated or peeling of the plating. On the other hand, when the rough rolling finish temperature is less than 1000 占 폚, hot rolling to a predetermined thickness becomes impossible due to the pressing load of the finish hot rolling as the next step. Therefore, it is preferable that the rough rolling finish temperature is in the range of 1000 to 1040 캜.

In order to obtain the hot-rolled steel sheet as described above, it is preferable to finish the hot-rolled steel sheet. The finishing mill delivery temperature (FDT) has a small effect on the residual scale of the Ni-based oxide, so that it can be carried out under normal finishing hot rolling conditions. However, if the finish hot rolling temperature is excessively low, the rolling load may increase and the rolling mill and the rolling roll may be unreliable. Also, since the steel sheet itself may be subjected to work hardening to deteriorate the internal quality, the finish hot rolling temperature is preferably 850 Lt; 0 > C to 950 < 0 > C.

Thereafter, the hot-rolled steel sheet obtained through the hot-rolling is wound. If the coiling temperature (CT) is higher than 600 ° C, the picked-up cargo such as Mn, Al and Si is added to the Ni-based residual scale, which makes the pickling more difficult. Therefore, Plating and plating peeling occurs. The coiling temperature is preferably as low as possible, but it is difficult to cool it to less than 100 占 폚 even if it is rapidly cooled, so that the coiling temperature is preferably in the range of 100 to 600 占 폚.

The step of water cooling the steel sheet may further include a step of cooling the steel sheet after the winding, so that the thickness of the scale layer becomes as thin as possible by keeping the temperature of the steel sheet as low as possible. The water-cooling process may be a method of immersing a steel sheet in a water tank at room temperature or the like.

The rolled steel sheet may be manufactured as a hot-dip galvanized steel sheet by hot-dip galvanizing after the pickling process. The pickling can be governed by the influence of acid tax concentration, temperature, and time. The pickling is preferably carried out in an aqueous hydrochloric acid solution at a concentration of 5 to 25% by volume. The higher the concentration of hydrochloric acid in the aqueous hydrochloric acid solution, the easier the pickling. However, if the concentration of hydrochloric acid is less than 5%, it is impossible to completely pick up the organic acid within the limited pickling time and the scale remains. But since the formation of the passive film thereafter, the pickling rate abruptly falls and the scale remains, and the high concentration of hydrochloric acid may lead to corrosion of the tank and the equipment. Therefore, the hydrochloric acid concentration of the hydrochloric acid aqueous solution preferably ranges from 5 to 25% by volume.

When the pickling temperature is lower than 70 ° C, the pickling reaction is not active, and it may be impossible to completely remove the scale within a limited pickling time. In addition, the pickling may be performed at 70 to 85 ° C for 40 to 60 seconds. And if it exceeds 85 ° C, due to over-oxidation, not only the scale but also the iron (Fe) of the substrate may be removed to cause a smut in which carbon remains. When the smut due to over-acidification occurs, not only the surface appearance of the plating material is lowered but also the smut remains after the annealing, which lowers the plating property, which may cause plating and peeling at the time of plating. In addition, hot acid solutions can cause equipment corrosion. Therefore, the pickling temperature is preferably in the range of 70 to 85 캜.

When the pickling time is less than 40 seconds, it is impossible to completely remove the Ni-based scale. When the pickling time exceeds 60 seconds, smut due to over-picking may occur. Therefore, the pickling time is in the range of 40 to 60 seconds desirable.

The hot-dip galvanizing is preferably performed by immersing the hot-dip galvanizing bath in a hot-dip galvanizing bath containing 0.2 to 0.25% by weight of Al at a temperature of 480 to 520 ° C. Al in the plating bath reacts preferentially with the steel sheet when the heat treated steel sheet is immersed in the plating bath to reduce the oxide film on the surface of the steel sheet and form a soft interfacial suppression layer Fe-Mn-Al-Zn film, -Fe intermetallic compound. When the Al concentration in the plating bath is more than 0.25%, floating dross, which is an oxide of Fe-Al, is likely to occur, and a flow pattern in which the plating layer flows down is generated. Range. However, when the Al concentration is less than 0.2%, it is not preferable because uneven plating or peeling off occurs due to the formation of the non-uniform interface restraining layer. Therefore, the Al concentration in the plating bath preferably ranges from 0.2 to 0.25 wt% Do. In addition, when the plating material is immersed in the plating bath, the oxide film or the residual scale on the surface of the iron must be dropped in order for the Fe of the ferrous iron and the Al of the plating bath to react preferentially. However, if the oxide film is thick or the immersion temperature of the steel sheet is low, the oxide film of the oxide film may not fall off, so that the wettability with the molten zinc may be poor and unplated. Therefore, in order to prevent this, it is preferable that the drawing temperature of the steel sheet is 480 DEG C or higher. This is because the higher the drawing temperature of the steel sheet is, the easier the removal of the oxide film is. However, when the temperature of the steel sheet is higher than 520 ° C., excess Fe is eluted from the base steel and Zn and Al of the plating bath react with the Al. Therefore, the Fe-Zn-based bottom dross and the Fe- A floating dross is generated, and a part of the dross is mixed with the plating layer to deteriorate the surface appearance, which is not preferable.

On the other hand, the temperature of the plating bath is preferably in the range of 450 to 500 ° C. If the temperature is lower than 450 ° C, the flowability of the molten zinc is drastically lowered, and surface defects such as flow patterns may occur. , The upper dross of the Zn-Al oxide is excessively formed due to the reaction of the molten zinc and aluminum of the plating bath with oxygen, and these oxides adhere to the plated steel sheet to cause surface defects, which is preferable not.

On the other hand, the hot-dip galvanized steel sheet of the present invention may be manufactured by hot-dip galvanizing the hot-rolled steel sheet as described above, but may also be manufactured by hot-dip galvanizing the cold-rolled steel sheet obtained by cold rolling the hot-rolled steel sheet. To this end, the method for producing a hot-dip galvanized steel sheet of the present invention may further comprise a step of cold-rolling the hot-rolled steel sheet after the pickling process of the hot-rolled steel sheet to obtain a cold-rolled steel sheet and annealing the cold-rolled steel sheet. The annealed cold rolled steel sheet can be preferably made of a hot-dip galvanized steel sheet by hot-dip galvanizing using the above-described plating conditions.

At this time, it is preferable that the annealing treatment is performed under the condition that the dew point temperature is -80 to -30 占 폚 and the temperature is 700 to 850 占 폚. When the dew point temperature is higher than -20 占 폚, it is practically an oxidizing atmosphere, so it is impossible to prevent the surface enrichment and oxidation of Mn, Al, Si and the like, and plating and plating peeling occur. However, the dew point temperature of -30 占 폚 or lower is a reducing atmosphere, and valuable elements such as Ni and Sn are concentrated on the surface, and the diffusion and oxidation of alloying elements such as Mn, Al and Si which are easy to oxidize can be prevented. On the other hand, in order to maintain the dew point temperature of the heating atmosphere at -80 캜 or lower, many purification devices are required to remove oxygen and water from the gas, which is not preferable. Therefore, it is preferable that the dew point temperature in the annealing has a range of -80 to -30 占 폚.

The annealing temperature is preferably as low as possible because surface concentration and oxidation of Mn, Al, Si, etc. decrease as the annealing temperature is lower. However, when the annealing temperature is lower than 700 ° C, recrystallization of the rolled structure does not occur, Which is undesirable. On the other hand, when the annealing temperature exceeds 850 deg. C, it is impossible to prevent the surface enrichment and oxidation of Mn, Al, Si and the like, as well as material softening according to high temperature and high manganese steel added with Ni and Sn. In order to prevent this, there may be a method of adding Sn or Ni in a larger amount, but in this case, the Ni-based oxide remains, which is undesirable because it causes unplated and plating peeling. Further, even if the hot-rolled condition is not suitable and the residual scale of the Ni-based oxide is formed, it is impossible to reduce such a residual scale by high-temperature annealing, and therefore, it is not preferable to anneal more than 850 ° C. Therefore, the annealing temperature is preferably in the range of 700 to 850 ° C.

According to the manufacturing method of the present invention provided as described above, it is possible to provide a hot-dip galvanized steel sheet which does not cause generation of residual scale during pickling, has no unplated defects during hot dip galvanizing and does not cause peeling after 0T bend test after hot dip galvanizing 0.1 to 3% of Si, 0.1 to 8% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.01 to 0.2% of Ti, A hot dip galvanized steel sheet containing 0.0005 to 0.01% of P, 0.01 to 0.3% of P, 0.01 to 2.0% of Ni, 0.06 to 0.2% of Sn, the balance Fe and other unavoidable impurities.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to further illustrate the present invention and do not limit the scope of the present invention.

(Example)

0.5% C-15% Mn-0.6% Si-2% Al-0.1% Cr-0.1% Ti-0.001% B-0.017% P-0.0005% S-0.3% Ni-0.06% The slabs were homogenized by reheating at 1050 to 1160 ° C as shown in Table 1 below and then descaled by high pressure water to a finish roughing temperature of 1020 to 1080 ° C, Hot rolled to a finish hot rolling temperature of 900 占 폚 to produce a hot rolled steel sheet having a thickness of 2.4 mm. The hot-rolled steel sheet was wound at 100 to 700 ° C, and then immersed in an aqueous hydrochloric acid solution to remove the oxide scale and pickled. At this time, the concentration of the hydrochloric acid aqueous solution was 13%, the pickling temperature was 80 ° C, and the pickling time was 50 seconds. The pickling resistance of the high-manganese hot-rolled steel sheets thus prepared was evaluated and reported in Table 1, and the pickling performance was evaluated according to the following criteria.

- Level 1: No residual scale

- Class 2: Residual scale less than 2% of total area

- Class 3: Residual scale occurs in excess of 2% to less than 5% of the total area

- Grade 4: Residual scale is greater than 5% of the total area

Further, the steel sheet was cold-rolled at a reduction ratio of 50% after pickling to obtain a cold-rolled steel sheet having a thickness of 1.2 mm. The cold-rolled steel sheet was heated at a temperature of 750 ° C for 40 seconds in a reducing atmosphere having 5% of hydrogen and nitrogen as the remainder, and having a dew point temperature of -40 ° C. 0.23%, and was immersed in a zinc plating bath having a temperature of 460 DEG C for 5 seconds to prepare a hot dip galvanized steel sheet by air kneading so that the coating amount on one surface was 60 g / m < 2 >. The evaluation of plating quality of the prepared high manganese hot dip galvanized steel sheet was evaluated by the degree of uncoated plating and the degree of superiority of adhesion to the plating by the following criteria.

The degree of uncoated plating was evaluated by hot dip galvanizing and then the surface appearance was subjected to image processing to measure the size of the uncoated portion and the coating was graded according to the following criteria.

-1 Grade: No plating defect

-2 grade: uncoated average diameter less than 1mm

-3 grade: Uncoated average diameter is 1mm ~ 2mm

-4 grade: Uncoated average diameter is over 2mm ~ less than 3mm

-5 grade: uncoated average diameter 3mm or more

The plating adhesion of the hot-dip galvanized steel sheet was evaluated by the following criterion for the degree of peeling of the plating layer during the taping test of the 0T-bend test and the bending outer sheet.

-1 Class: No peeling

-2 Rating: Less than 5% exfoliation

-3 Rating: Less than 5 ~ 10% exfoliation

-4 Rating: Less than 10 ~ 30% exfoliation

-5 Rating: More than 30% exfoliation

division Hot rolling condition Pickling castle Plating quality Reheat temperature
(° C) Rough rolling finish temperature
(° C) Winding temperature
(° C) Residual scale
(Good 1↔4 bad) Unplated
(Good 1↔5 bad) Plating adhesion
(Good 1↔5 bad) Comparative Example 1 1250 1030 450 3 ranks 3 ranks 5 ratings Comparative Example 2 1200 1030 450 2 ratings 2 ratings 2 ratings Comparative Example 3 1160 1030 450 2 ratings 2 ratings 3 ranks Inventory 1 1150 1030 450 1 rating 1 rating 1 rating Inventory 2 1100 1030 450 1 rating 1 rating 1 rating Inventory 3 1050 1030 450 1 rating 1 rating 1 rating Comparative Example 4 1040 1030 450 3 ranks 3 ranks 5 ratings Comparative Example 5 1050 1080 450 4 ratings 5 ratings 5 ratings Comparative Example 6 1050 1060 450 3 ranks 4 ratings 5 ratings Honorable 4 1050 1040 450 1 rating 1 rating 1 rating Inventory 5 1050 1020 450 1 rating 1 rating 1 rating Inventory 6 1050 1000 450 1 rating 1 rating 1 rating Comparative Example 7 1100 1060 450 3 ranks 4 ratings 5 ratings Honorable 7 1100 1040 450 1 rating 1 rating 1 rating Honors 8 1100 1020 450 1 rating 1 rating 1 rating Proposition 9 1100 1000 450 1 rating 1 rating 1 rating Comparative Example 8 1100 1020 700 3 ranks 4 ratings 4 ratings Comparative Example 9 1100 1020 620 2 ratings 2 ratings 3 ranks Inventory 10 1100 1020 600 1 rating 1 rating 1 rating Exhibit 11 1100 1020 450 1 rating 1 rating 1 rating Inventory 12 1100 1020 400 1 rating 1 rating 1 rating Inventory 13 1100 1020 200 1 rating 1 rating 1 rating Inventory 14 1100 1020 100 1 rating 1 rating 1 rating Comparative Example 10 1150 1020 700 4 ratings 5 ratings 5 ratings Comparative Example 11 1150 1020 620 3 ranks 2 ratings 3 ranks Honorable Mention 15 1150 1020 600 1 rating 1 rating 1 rating Inventory 16 1150 1020 450 1 rating 1 rating 1 rating Inventory 17 1150 1020 400 1 rating 1 rating 1 rating Inventory 18 1150 1020 200 1 rating 1 rating 1 rating Evidence 19 1150 1020 100 1 rating 1 rating 1 rating

As shown in FIG. 2, which is a graph showing the relationship between the finish rolling finish temperature and the uncoated and plated adhesion index in Table 1, it is preferable that the reheating temperature range, the rough rolling termination temperature range and the winding temperature range In Examples 1 to 19, no residual scale was generated, and no plating defects such as unplated or plated-off were observed.

However, in the case of Comparative Examples 1 to 4, in which the reheating temperature deviates from the range proposed by the present invention, it can be seen that the residual scale occurred at a certain portion, and the plating quality was lowered as compared with the inventive examples. In Comparative Examples 5 to 7 in which the rough rolling termination temperature was outside the range proposed by the present invention, it was found that the residual scale occurred to some extent and the plating quality was remarkably lowered to a very low level. In the case of Comparative Examples 8 to 11 in which the winding temperature is out of the range proposed by the present invention, it is also found that a residual scale exists and a plating defect such as unplated or peeling off occurs during plating.

Claims (9)

0.1 to 3% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 5% of B, Reheating the steel slab to 0.01 to 10% by mass, 0.01 to 0.3% of P, 0.01 to 2.0% of Ni, 0.06 to 0.2% of Sn, balance Fe and other unavoidable impurities;
Subjecting the reheated steel slab to rough rolling to finish at 1000 to 1040 캜 to obtain a bar;
Finishing hot rolled bar to obtain a steel sheet;
Twisting the steel sheet at 100 to 600 ° C;
Picking up the wound steel sheet;
And galvanizing the pickled steel sheet by hot-dip galvanizing. The method according to claim 1,
Wherein the finish hot rolling is performed at a temperature of 850 to 950 占 폚. The method according to claim 1,
Further comprising a step of water-cooling the steel sheet after the winding. The method according to claim 1,
Wherein said pickling is carried out in an aqueous hydrochloric acid solution having a concentration of 5 to 25%. The method according to claim 1,
Wherein the pickling is carried out at 70 to 85 캜 for 40 to 60 seconds. The method according to claim 1,
Wherein the hot-dip galvanizing is performed by immersing the hot-dip galvanizing bath in a hot-dip galvanizing bath containing 0.2 to 0.25% by weight of Al so that the hot-dip galvanizing temperature is 480 to 520 ° C. The method according to claim 1,
After the pickling, cold rolling the steel sheet to obtain a cold-rolled steel sheet; And
Further comprising the step of annealing the cold-rolled steel sheet. The method of claim 7,
Wherein the annealing is performed under a condition that a dew point temperature is -80 to -30 占 폚 and a temperature is 700 to 850 占 폚. 0.1 to 3% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 5% of B, 0.01 to 0.3%, P: 0.01 to 0.3%, Ni: 0.01 to 2.0%, Sn: 0.06 to 0.2%, the balance Fe and other unavoidable impurities.

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