WO2020111739A2 - Cold-rolled steel plate for enameling and method for manufacturing same - Google Patents
Cold-rolled steel plate for enameling and method for manufacturing same Download PDFInfo
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- WO2020111739A2 WO2020111739A2 PCT/KR2019/016383 KR2019016383W WO2020111739A2 WO 2020111739 A2 WO2020111739 A2 WO 2020111739A2 KR 2019016383 W KR2019016383 W KR 2019016383W WO 2020111739 A2 WO2020111739 A2 WO 2020111739A2
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
Definitions
- the present invention relates to a cold rolled steel sheet for enamel and a method for manufacturing the same. More specifically, the present invention relates to a cold-rolled steel sheet for enameling and a manufacturing method that can prevent the occurrence of bubble defects after enamel treatment and has excellent enamel adhesion and fish-scale resistance.
- Enamel steel sheet is a kind of surface treatment product that improves corrosion resistance, weather resistance and heat resistance by applying glass glaze on a steel sheet such as hot rolled steel sheet or cold rolled steel sheet, and then firing at high temperature. These enameled steel sheets are used for building exterior, home appliances, tableware and various industrial materials.
- the enamel layer known as the most fatal defect in enamel products is eliminated in the form of meat scales to prevent fishscale defects that degrade enamel, or to improve the formability.
- manufacturing costs were high and quality variations were frequent.
- a continuous annealing process is used for a steel plate for enamel recently developed, wherein titanium (Ti) or boron (B) is mainly used as a hydrogen storage source.
- Ti titanium
- B boron
- TiN titanium nitride
- inclusions occur in the continuous casting step of the steelmaking process. Nozzle clogging occurs frequently, which is a direct factor in lowering workability and production load.
- TiN mixed in the molten steel is present on the upper portion of the steel sheet, not only causes a blister defect, which is a representative bubble defect, but also a large amount of added titanium is a factor that inhibits the adhesion between the steel sheet and the glaze layer.
- the present invention is to provide a cold rolled steel sheet for enamel and a method for manufacturing the same. More specifically, it is to provide a cold-rolled steel sheet for enamel and a manufacturing method that can prevent the occurrence of bubble defects after enamel treatment and has excellent enamel adhesion and fish-scale resistance.
- Cold rolled steel sheet for enamel according to an embodiment of the present invention, by weight, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), including residual Fe and unavoidable impurities, the micropore area fraction is 0.3 to 0.8%, and expressed by the following [Relational Formula 1]
- the enamel defect relationship index (D) to be satisfied satisfies 0.45 to 4.50.
- [Mn], [Cu], [S] and [C] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D void is the area fraction (%) of micropores in a cold rolled steel sheet ).
- the steel sheet may further include at least one of P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%), and Ti: 0.001% or less (excluding 0%).
- the pickling loss of the cold rolled steel sheet may be 10 to 40 gr/m 2 .
- the hydrogen permeation ratio of the cold rolled steel sheet may be 950 seconds/mm 2 or more.
- the method of manufacturing a cold-rolled steel sheet for enamel by weight, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08% , S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), preparing a slab containing residual Fe and unavoidable impurities; Heating the slab; Hot-rolling the heated slab to produce a hot-rolled steel sheet having a carbide volume fraction of 2.5 to 7.0%; Winding the hot rolled steel sheet; Cold-rolling the wound hot-rolled steel sheet at a reduction ratio of 60 to 90% to produce a cold-rolled steel sheet; And annealing heat treatment of the cold-rolled steel sheet; and the adhesion relationship index (A) represented by the following [Relational Formula 2] satisfies 0.007 to 0.185.
- A adhesion relationship index represented by the following [Relational Formula 2] satisfies 0.007 to 0.185.
- [Mn], [Cu], and [Si] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.
- the workability relationship index (F) expressed by [Relational Formula 3] may satisfy 3500 to 7000.
- [Al], [N] and [C] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.
- the slab may further include at least one of P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%).
- a hot-rolled steel sheet may be to hot roll the heated slab at a rolling temperature of 850°C to 900°C.
- the step of winding the hot rolled steel sheet In the step of winding the hot rolled steel sheet; In the, it may be to roll the hot rolled steel sheet at 640 °C to 750 °C.
- the cold-rolled steel sheet may be heat-annealed at 700°C to 850°C.
- the cold-rolled steel sheet may be maintained for at least 30 seconds.
- the cold-rolled steel sheet for enamel according to an embodiment of the present invention is excellent in fish scale resistance and enamel adhesion, and thus can be used in household appliances, chemical equipment, kitchen equipment, sanitary equipment, and interior and exterior materials of buildings.
- the cold-rolled steel sheet for enameling suppresses the chemical composition of the steel material within an appropriate range and controls the enamel defect, adhesion, and processability relational index, thereby providing high enamel adhesion and hydrogen permeation ratio of the produced cold-rolled steel sheet. Can be secured. Therefore, the fatal defects of fish scale and bubble defects of the enameled steel sheet can be suppressed, and the enamel properties are significantly improved.
- the cold-rolled steel sheet for enameling utilizes cementite, which is a low-temperature precipitate.
- cementite is uniformly dispersed during hot rolling, and micro-voids formed by crushing during cold rolling act as a storage source of hydrogen to prevent fish scale defects caused by hydrogen.
- stable carbide at low temperature is used as a hydrogen storage source, which deteriorates the workability of operations such as melting of refractory material or clogging of the playing nozzle, which has been a problem in conventional enamel steel. And surface defects such as blacklines.
- the cold-rolled steel sheet for enameling according to an embodiment of the present invention can also improve the adhesion between the steel sheet and the glaze as elements such as titanium (Ti) having a high oxidizing property compared to Fe are not added.
- the cold-rolled steel sheet for enamel according to an embodiment of the present invention can be made of continuous casting, and as it can be produced by continuous annealing heat treatment, it can lower the steel sheeting cost and process cost by significantly lowering the mailing and manufacturing costs, Productivity is high.
- first, second, and third are used to describe various parts, components, regions, layers, and/or sections, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.
- the term "combination of these" included in the expression of the marki form means one or more mixtures or combinations selected from the group consisting of the elements described in the expression of the marki form, the components It means to include one or more selected from the group consisting of.
- a part when it is said that a part is “on” or “on” another part, it may be directly on or on another part, or another part may be involved therebetween. In contrast, if one part is referred to as being “just above” another part, no other part is interposed therebetween.
- % means% by weight, and 1 ppm is 0.0001% by weight.
- the meaning of further including an additional element means that the remaining amount of iron (Fe) is replaced by an additional amount of the additional element.
- Cold rolled steel sheet according to an embodiment of the present invention in weight percent, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), residual Fe and unavoidable impurities, and a micropore area fraction of 0.3 to 0.8%.
- the slab prepared in the method for manufacturing a cold rolled steel sheet according to an embodiment of the present invention is weight%, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), residual Fe and unavoidable impurities.
- P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%) may further include one or more.
- a step of heating the slab is performed, and the hot-rolled slab is hot-rolled to produce a hot-rolled steel sheet having a carbide volume fraction of 2.5 to 7.0%. The process after that will be described later.
- Mn is a representative solid solution strengthening element, and it is added to prevent hot shortness by precipitating solid solution sulfur as manganese sulfide (MnS), and it is necessary to add at least 0.1% or more to secure such an effect.
- MnS manganese sulfide
- the content of manganese is too large, there may be a problem that the moldability is deteriorated.
- Si is an element that promotes the formation of a carbide that acts as a hydrogen storage source, and in order to obtain such an effect, it is necessary to add 0.001% or more. On the other hand, if it is added too much, there may be a problem of forming an oxide film on the surface of the steel sheet to degrade the enamel adhesion. More specifically, it may be 0.005 to 0.025%.
- Al is used as a strong deoxidizer to remove oxygen from molten steel, and it is an element that improves aging by fixing solid nitrogen, and for this effect, addition of 0.01% or more is required. On the other hand, if too much is added, aluminum oxide may remain in the steel or on the surface of the steel, thereby causing a bubble defect in the enameling process. More specifically, it may be 0.02 to 0.044%.
- P is a typical material strengthening element, and at least 0.002% of addition is required to obtain this effect.
- P is increased, a segregation layer is formed inside the steel sheet to deteriorate the formability as well as to deteriorate the pickling property of the steel, which may adversely affect enamel adhesion. More specifically, it may be 0.005 to 0.02%.
- S is an element that causes red-brittle brittleness in combination with manganese, and in the case where too much is added, ductility deteriorates significantly, which can deteriorate processability and adversely affect fish-scale properties due to excessive precipitation of manganese sulfide. More specifically, it may be 0.003 to 0.015%.
- Cu is an element that concentrates on the surface of the steel sheet and improves the bonding strength between the enamel layer and the steel sheet, and for this, it is necessary to add 0.01% or more. However, if too much is added, the reaction between the enamel layer and the steel sheet is suppressed, thereby causing bubble defects and deteriorating processability. More specifically, it may be 0.03 to 0.13%.
- N is a typical hardening element, but if the amount added is increased, aging defects are frequently formed, poor moldability is generated, and there may be a problem of generating bubble defects in the enameling process. More specifically, it may be 0.004% or less.
- O is an essential element in forming an oxide, and such an oxide not only causes melting of the refractory material in the steelmaking step, but can also act as a factor that causes surface defects due to oxides on the surface of the steel sheet.
- Ti is known as an element added to improve processability and suppress the reaction of hydrogen, which is the cause of fish scale.
- the steel grade in one embodiment of the present invention when a large amount of Ti is added, there is a problem that causes a bubble defect such as a blister.
- the nozzle clogging phenomenon due to titanium nitride (TiN) and inclusions frequently occurs in the continuous casting step of the steelmaking process, which is a direct factor of lowering workability and production load. Therefore, when Ti is included, it can be limited to 0.001% or less.
- the present invention includes Fe and unavoidable impurities.
- the addition of effective ingredients other than the above ingredients is not excluded.
- the carbide used in the present invention steel, the carbide itself is crushed during cold rolling due to a ductility difference with the base material, and the micropores formed thereby are used as a hydrogen storage source for fixing hydrogen in the river. This plays a large role in suppressing fishscale defects, so it is very important to manage the carbide fraction within a certain range. On the other hand, such a carbide fraction affects enamel property not only alone but also by the interaction with the added elements.
- the steel sheet for enamel proposed in the present invention mainly controls carbide components such as Fe 3 C (cementite) as a storage position for hydrogen by controlling the steel component, and also affects enamel adhesion, surface defects, and formability among steel components. It is intended to provide a steel sheet excellent in enamel adhesion and fish scale resistance without surface defects by controlling the components and processes affecting it.
- cementite which is a low-temperature precipitate
- micro-voids formed by uniformly dispersing during hot rolling and crushing during cold rolling act as a storage source of hydrogen, thereby preventing fishscale defects caused by hydrogen.
- stable carbide at low temperature is used as a hydrogen storage source, which deteriorates the workability of operations such as melting of refractory material or clogging of a performance nozzle, which has been a problem in conventional enamel steel. And surface defects such as blacklines.
- the fraction of carbide not only has a close relationship with the total amount of carbon in the steel, but is also greatly influenced by operating conditions.
- the adhesion between the steel sheet and the glaze could be improved as the addition of elements such as titanium (Ti) having a high oxidation property compared to Fe is very small.
- the present invention example suppresses the generation of sulfate hydrate (H 2 SO 4 -H 2 O) generated on the surface of the steel sheet in the enamel pre-treatment step by controlling the amount of copper (Cu) and the area fraction of the micropores, resulting in fishscale resistance and It can be seen that the occurrence of bubble defects is significantly improved.
- the carbide volume fraction means the volume fraction of carbide in a hot rolled steel sheet.
- the carbide may be cementite (Fe 3 C).
- the carbon present in the metal alloy bonds with a metal atom to form a carbide. Iron is combined with carbon to form a carbide, which is called cementite.
- cementite Normally, in carbon steel, cementite is formed near 250 to 700°C, and at higher temperatures, it becomes coarse to spherical particles.
- steel materials such as white cast iron, carbon is almost in the form of cementite, and because it has excellent abrasion resistance, it is used in areas of high wear, such as a ball mill.
- the fraction of carbides generated in the hot rolling step When the volume fraction of carbides generated in the hot rolling step is too small, the fraction of carbides that can be provided as a source for storing hydrogen by crushing in the cold rolling process decreases, thereby reducing the micropore area fraction of the steel sheet via cold rolling. There may be a problem in that it is difficult to suppress fish scale and the like because there is a limit to fixing hydrogen.
- the carbide fraction when the carbide fraction is too high, it is advantageous in terms of forming micro-pore as a hydrogen storage source, and is effective in improving fish-scale resistance. However, there may be a problem that processability and corrosion resistance are deteriorated by too many pores.
- the micropore area fraction means the micropore area fraction in a cold rolled steel sheet.
- micropores act as a storage source of hydrogen in the enameled steel sheet, thereby suppressing the occurrence of fish scale defects in which the enamel layer, which is an enamel defect caused by hydrogen, falls out into the shape of meat scales.
- the micropores in the cold-rolled steel sheet were measured using a scanning electron microscope, and after taking 10 pictures at a magnification of 1000, the area fraction of micropores in these areas was measured using an image analyzer. 1 shows an example of a microscopic public observation photograph of Inventive Example 4 photographed as described above.
- the area fraction of the micropore is too low, there may be a problem that the fish scale defect rate of the enamel product increases due to the small number of sites that act as a hydrogen storage source that can fix hydrogen in the river.
- it is advantageous in terms of fish scale there may be a problem in that workability and surface defects are frequently caused by an increase in microporosity. More specifically, it may be 0.30 to 0.75%.
- Enamel defect relationship index (D), D ([Mn]x[Cu]/[S])x(D void , indicating resistance to fish scale and bubble defects in which the enamel layer falls out of the shape of meat scales /[C]) It was necessary for the value to satisfy the above range.
- [Mn], [Cu], [S], and [C] are values obtained by dividing the weight percent of each element by atomic weight
- D void is the area fraction of micropores in the cold rolled steel sheet. If the D value is too low, there may be a problem that the occurrence of fish scale defects in enamel products increases because a site capable of sufficiently storing hydrogen that causes fish scale defects may not be obtained, whereas the D value is too high. In this case, although it was advantageous in terms of securing a hydrogen storage source, there may be a problem that the workability and surface characteristics of the product are deteriorated. More specifically, it may be 0.5 to 4.2.
- Adhesion index, A ([Mn]x[Cu]xD cementite ⁇ )/[Si]: 0.007 to 0.185
- [Mn], [Cu], and [Si] are values obtained by dividing% by weight of each element by atomic weight
- D cementite represents the volume fraction of carbide in the hot-rolled steel sheet. If the value of A is too small, as the concentration of the interfacial layer concentrated on the surface decreases, the amount of formation of aluminum oxide or the like increases, and there may be a problem of deteriorating the adhesion between the enamel glaze layer and the iron.
- the amount of gas (Gas) generated on the surface of the steel sheet during the calcination heat treatment increases, which may cause a bubble defect, and thus, the adhesion may be significantly reduced. More specifically, it may be 0.008 to 0.180.
- the cold rolled steel sheet according to an embodiment of the present invention may have a pickling loss of 10 to 40 gr/m 2 . By satisfying these properties, it can be applied as an enamel material. If the pickling loss is too low, the roughness of the surface of the steel sheet is not so great that the adhesion between the glaze and the steel sheet deteriorates as the adsorption capacity of the glaze decreases, and problems such as dropping of the enamel layer may occur. On the other hand, when it is too high, a flattening operation is performed on the surface layer of the steel sheet, thereby deteriorating adhesiveness and increasing the occurrence of bubble defects. More specifically, the pickling loss may be 12 to 35gr/m 2 .
- the cold rolled steel sheet according to an embodiment of the present invention may have a hydrogen permeation ratio of 950 seconds/mm 2 or more.
- the hydrogen permeation ratio is an index for evaluating the fish-scale resistance, which indicates the resistance of fish-scale defects, which are fatal defects of enamel steel produced using cold-rolled steel sheets according to an embodiment of the present invention, and is a method registered in European Standard EN 10209. Experiment to evaluate the ability to fix hydrogen in the steel sheet. It is a value expressed by dividing by the square of the material thickness (t, unit: mm) by measuring the time (t s , unit: second) at which hydrogen is generated in one direction of the steel sheet and hydrogen permeates to the other side of the steel sheet.
- the hydrogen permeation ratio may be 950 seconds/mm 2 or more. If the hydrogen permeation ratio is too small, the fish scale defect rate is more than 50% when accelerated heat treatment at 200°C for 24 hours after enamel treatment, and there is a problem in using it as a stable enamel product. For this, it is necessary to manage the hydrogen permeation ratio to 950 seconds/mm 2 or more. In addition, more specifically, the hydrogen permeation ratio may be 1000 seconds/mm 2 or more.
- a slab satisfying the above-described composition is prepared.
- the molten steel whose components are adjusted to the above-described composition in the steelmaking step may be manufactured as slabs through continuous casting.
- heating may mean reheating.
- the slab heating temperature may be 1150 to 1250°C. If the slab heating temperature is too low, the rolling load increases rapidly during subsequent hot rolling, which can deteriorate workability. On the other hand, if the slab heating temperature is too high, it not only increases energy cost, but also increases the amount of surface scale, which can lead to material loss.
- the heated slab is hot rolled to produce a hot rolled steel sheet.
- the volume fraction of carbide of the hot rolled steel sheet may be 2.5 to 7.0%.
- the description of the carbide volume fraction is mentioned and is omitted.
- the finish rolling temperature of hot rolling may be 850 to 900°C. If the finish hot rolling temperature is too low, as the rolling is finished in the low temperature region, the crystal grains rapidly progress and tend to cause a decrease in rollability and workability. On the other hand, if the finish hot rolling temperature is too high, the peelability of the surface scale falls and uniform hot rolling may not be performed over the entire thickness, and thus impact toughness due to grain growth may appear. More specifically, the finish hot rolling temperature may be 860 to 890°C.
- the hot-rolled steel sheet produced after the hot rolling undergoes a winding process. More specifically, it may be a hot rolling process.
- the coiling temperature may be 640 to 750°C.
- the hot rolled steel sheet can be cooled in a run-out-table (ROT) before winding. If the temperature of the hot-rolled coil is too low, temperature fluctuations in the width direction occur in the cooling and maintaining process, and as the formation of low-temperature precipitates varies, it not only causes material deviation, but also adversely affects enamel properties. On the other hand, if the coiling temperature is too high, corrosion resistance is lowered as the bulking of the nitride proceeds, and a problem of deteriorating processability is caused by coarsening of the tissue in the final product. More specifically, the coiling temperature may be 650 to 710°C.
- the wound hot-rolled steel sheet may further include a step of pickling a steel sheet before cold rolling.
- the wound hot-rolled steel sheet is manufactured into a cold-rolled steel sheet through cold rolling.
- the cold reduction rate may be 60 to 90%.
- the cold reduction rate is too small, strength is increased by locally remaining unrecrystallized grains due to low recrystallization driving force in a subsequent heat treatment process, but there is a problem in that workability is remarkably deteriorated.
- the crushing capacity of the carbide formed in the hot rolling step decreases, the site capable of storing hydrogen decreases, so it is difficult to secure the fish scale resistance of the enamel product, and considering the thickness of the final product, the thickness of the hot rolled steel sheet must be lowered. There is also a problem that the rolling workability is deteriorated.
- the cold rolling reduction ratio is too high, the material is hardened to deteriorate workability, and the load of the rolling mill is increased, thereby deteriorating the cold rolling workability. More specifically, the cold rolling reduction rate may be 65 to 88%.
- the cold-rolled steel sheet can be subjected to annealing heat treatment. More specifically, it can be heat-annealed.
- the cold rolled material has a high strength due to the deformation applied in cold rolling, but the workability is extremely inferior, so that the target strength and workability are secured by performing heat treatment in a subsequent process.
- the heat treatment temperature may be 700 to 850 °C. If the continuous annealing temperature is too low, there is a problem in that workability is significantly deteriorated as deformation formed by cold rolling is not sufficiently removed. On the other hand, if the heat treatment temperature is too high, softening due to a decrease in high temperature strength causes plate fracture, which significantly reduces the mailing performance of the operation. More specifically, the annealing temperature may be 750 to 840°C.
- the heat treatment holding time during heat treatment may be 30 seconds or more. Even if the cracking time at the heat treatment holding temperature during the heat treatment is too short, unrecrystallized grains remain and act as a factor that greatly deteriorates formability, so a holding time of 30 seconds or more may be required.
- the cold rolled steel sheet may further include a step of temper rolling the heat-treated steel sheet.
- a step of temper rolling the heat-treated steel sheet.
- the shape of the material can be controlled and the desired surface roughness can be obtained through temper rolling, if the temper rolling reduction is too high, the material hardens and the workability deteriorates due to work hardening, so temper rolling can be applied at a rolling reduction of 3% or less. have.
- the rolling reduction of temper rolling may be 0.3 to 2.5%.
- Table 1 shows the chemical composition of the steels.
- the balance contains Fe and unavoidable impurities.
- the slab via the converter-secondary refining-casting process was maintained in a heating furnace at 1200°C for 1 hour, and then hot rolled. At this time, the final thickness of the hot rolled steel sheet was 4.0 mm.
- the hot-rolled specimen was cold-rolled after removing the oxide film on the surface through pickling. After the cold rolling was completed, the specimen was processed into an enameled specimen to investigate the enamel property and a tensile specimen for mechanical property analysis, followed by continuous annealing heat treatment.
- Table 2 shows the manufacturing conditions for each process of hot rolling, coiling, cold rolling, and continuous annealing applied to the steels.
- Table 3 shows enamel properties by manufacturing conditions of the material secured through the above process.
- Carbide fractions of the present invention steel and comparative steel were obtained by obtaining an image of 20 fields of view at 500 times magnification with an optical microscope, and then obtaining this as the fraction of carbide for the entire field of view using an image analyzer.
- the enameled specimen was cut to an appropriate size to meet the test purpose, and after the heat treatment was completed, the enameled specimen was completely degreased and then applied with a check frit relatively vulnerable to fish scale defects and maintained at 300°C for 10 minutes. To remove moisture.
- the dried specimen was subjected to a firing treatment at 830°C for 20 minutes, and then cooled to room temperature. At this time, the atmosphere condition of the firing furnace was a dew point temperature of 30°C, and harsh conditions that caused fish scale defects to occur were selected.
- the enamel-finished specimens were subjected to fish scale acceleration experiments maintained in an oven at 200° C. for 24 hours.
- the enamel adhesion index which evaluated the adhesion between the steel sheet and the glaze, was determined by applying a certain load to the enamel layer with a steel ball as defined in the American Society for Testing and Materials, ASTM C313-78, and then evaluating the degree of energization of the enamel layer. The degree of dropout was indicated by indexing. In the case of the adhesiveness index in the present invention, the goal was to secure at least 90% in terms of securing stability during use of the enamel layer.
- Bubble defects were determined by three stages of "O” excellent, “ ⁇ ” normal, and “X” defective, respectively, by visually observing the surface of the enamel layer for a specimen kept in an oven at 200°C for 24 hours after the enamel treatment.
- the hydrogen permeation ratio is an index for evaluating the resistance to fish scale, a fatal defect of enamel steel, and generates hydrogen in one direction of the steel sheet according to the method registered in the European standard, EN 10209 (2013).
- the time (t s , unit seconds) that is transmitted, is measured and divided by the square of the material thickness (t, unit mm), expressed as t s /t 2 (unit seconds/mm 2 ). In this case, as described above, it was necessary to secure at least 950 seconds/mm 2 to obtain stable properties of the enamel steel.
- the pickling loss (unit gr/m 2 ) is the test method shown in European standard, EN 10209 (2013), and after cutting and degreasing the steel sheet for enamel, it is immersed in a sulfuric acid solution maintained at 70g/l, 70°C for about 7 minutes. It was obtained from the weight loss. Even in this case, it was necessary to satisfy the range of 10 to 40 gr/m 2 .
- [Mn] is the value obtained by dividing the weight percent of Mn by the atomic weight of Mn (55),
- [Cu] is the value obtained by dividing the weight percent of Cu by the atomic weight of Cu (64),
- [S] is the weight% of S divided by the atomic weight of S (32),
- [C] is the weight% of C divided by the atomic weight of C (12),
- Si is the weight% of Si divided by the atomic weight of Si (28),
- [Al] is the value obtained by dividing the weight percent of Al by the atomic weight of Al (27),
- [N] is the value obtained by dividing the weight percent of N by the atomic weight of N (14).
- D void is an area fraction (%) of micropores in a cold rolled steel sheet
- D cementite is the carbide volume fraction (%) of the hot rolled steel sheet.
- Comparative Examples 1 to 4 which did not satisfy the range of manufacturing conditions, could not secure the target characteristics. That is, as shown in Table 3, there was a problem in that mailability was poor (Comparative Examples 1, 3 and 4), and the hydrogen permeation ratio was lower than the target (Comparative Examples 1 to 4), or the enamel adhesion index was less than 90% (Comparative). In Examples 1 to 4), it was confirmed that a bubble defect or a fish scale defect occurred after the enamel treatment, so that the targeted properties could not be secured overall.
- Comparative Examples 5 to 8 are the cases in which the manufacturing conditions suggested in the present invention were satisfied but the alloy composition was not satisfied. In Comparative Examples 5 to 8, most of the target carbides and micropore fractions of the present invention, hydrogen permeability ratio, enamel adhesion index, pickling loss, etc. were not satisfied, and fish scale and bubble defects also occurred in visual observation after enamel treatment.
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Abstract
The present invention relates to a cold-rolled steel plate for enameling and a method for manufacturing same. The cold-rolled steel plate for enameling according to an embodiment of the present invention comprises, based on wt%, 0.05 to 0.09% of C, 0.1 to 0.3% of Mn, 0.001 to 0.03% of Si, 0.01 to 0.08% of Al, 0.001 to 0.02% of S, 0.01 to 0.15% of Cu, 0.005% or less of N (excluding 0%), the balance of Fe, and inevitable impurities, wherein the area fraction of micro-voids is 0.3 to 0.8%, the relationship index of enameling defects (D) represented by [Relation Formula 1] below satisfies 0.45 to 4.50, the relationship index of adhesion (A) represented by [Relation Formulae 2 and 3] satisfies 0.007 to 0.185, and the relationship index of formability (F) satisfies 3500 to 7000. [Relation Formula 1] D = ([Mn] x [Cu] / [S]) x (Dvoid / [C]) [Relation Formula 2] A = ([Mn] x [Cu] x Dcementite}) / [Si] [Relation Formula 3] F = ([Al]/[N]) x (Dcementite/[C])
Description
본 발명은 법랑용 냉연 강판 및 그 제조방법에 관한 것이다. 보다 구체적으로 법랑 처리 후에 기포 결함 발생을 방지할 수 있고 법랑 밀착성 및 내피쉬스케일성이 우수한 법랑용 냉연 강판 및 제조방법에 관한 것이다.The present invention relates to a cold rolled steel sheet for enamel and a method for manufacturing the same. More specifically, the present invention relates to a cold-rolled steel sheet for enameling and a manufacturing method that can prevent the occurrence of bubble defects after enamel treatment and has excellent enamel adhesion and fish-scale resistance.
법랑 강판은 열연강판 또는 냉연강판과 같은 소지 강판 위에 유리질 유약을 도포한 후, 고온에서 소성시켜 내식성, 내후성 및 내열성 등을 향상시킨 일종의 표면처리 제품이다. 이러한 법랑 강판은 건축 외장용, 가전용, 식기용 및 다양한 산업용 소재로써 사용되고 있다.Enamel steel sheet is a kind of surface treatment product that improves corrosion resistance, weather resistance and heat resistance by applying glass glaze on a steel sheet such as hot rolled steel sheet or cold rolled steel sheet, and then firing at high temperature. These enameled steel sheets are used for building exterior, home appliances, tableware and various industrial materials.
종래의 법랑용 강판은 법랑 제품에서 가장 치명적인 결함으로 알려진 법랑층이 고기 비늘 모양으로 탈락되어 법랑성을 저하시키는 피쉬스케일 (Fishscale) 결함을 방지하거나 성형성을 향상하기 위해 탈탄소둔법 또는 상소둔 방식으로 제조함에 따라 제조 원가가 높아지고 품질 편차가 다발하는 문제점이 있었다. 이와 같은 장시간 소둔에 따른 생산성 열위 및 제조 원가 상승 문제를 극복하기 위하여 최근에 개발된 법랑용 강판은 연속 소둔 공정이 이용되고 있으며, 이때 수소 흡장원으로써 주로 티타늄(Ti) 또는 보론(B) 등을 첨가하여 이들 석출물을 활용하고 있다. 그러나, 이 경우에도 많은 양의 탄질화물 형성 원소들을 첨가하여야 함에 따라 표면 결함의 발생율이 높고, 재결정 온도가 상승하여 고온 열처리를 행해야 하므로 생산성 저하 및 원가 상승의 요인이 되고 있다.In the conventional steel sheet for enamel, the enamel layer known as the most fatal defect in enamel products is eliminated in the form of meat scales to prevent fishscale defects that degrade enamel, or to improve the formability. As it was manufactured, there was a problem in that manufacturing costs were high and quality variations were frequent. In order to overcome the problems of productivity inferiority and manufacturing cost increase due to such annealing for a long time, a continuous annealing process is used for a steel plate for enamel recently developed, wherein titanium (Ti) or boron (B) is mainly used as a hydrogen storage source. In addition, these precipitates are utilized. However, even in this case, as a large amount of carbonitride-forming elements have to be added, the incidence of surface defects is high, and the recrystallization temperature rises, so high-temperature heat treatment is required, leading to a decrease in productivity and an increase in cost.
특히, 티타늄(Ti)계 법랑용 강판의 경우, 피쉬스케일의 원인이 되는 수소의 반응을 억제하기 위해 많은 양의 티타늄이 첨가됨에 따라 제강 공정의 연속 주조 단계에서 티타늄 질화물(TiN)과 개재물에 의한 노즐 막힘 현상이 빈번히 발생하여 작업성 저하 및 생산 부하의 직접적인 요인이 되고 있다. 또한, 용강 내 혼입된 TiN이 강판의 상부에 존재하는 경우, 대표적인 기포 결함인 블리스터 (blister) 결함을 유발할 뿐만 아니라 다량 첨가된 티타늄은 강판과 유약층의 밀착성을 저해하는 요인이 되기도 한다.In particular, in the case of a titanium (Ti)-based enamel steel sheet, as a large amount of titanium is added to suppress the reaction of hydrogen, which is a cause of fish scale, titanium nitride (TiN) and inclusions occur in the continuous casting step of the steelmaking process. Nozzle clogging occurs frequently, which is a direct factor in lowering workability and production load. In addition, when TiN mixed in the molten steel is present on the upper portion of the steel sheet, not only causes a blister defect, which is a representative bubble defect, but also a large amount of added titanium is a factor that inhibits the adhesion between the steel sheet and the glaze layer.
한편, 강판 내부에 용존 산소 함량을 높여 강 중 산화물 등의 개재물을 활용하여 수소를 흡장하여 내피쉬스케일성을 확보하는 고산소계 법랑용 강판의 경우에도 근본적으로 산소의 함량이 높아 내화물 용손이 극심하여 제강 공정에서의 연주 생산성을 크게 저하시킬 뿐만 아니라 표면 결함이 다발하는 문제점이 있다.On the other hand, even in the case of a high-oxygen enamel steel sheet that secures fish-scale resistance by absorbing hydrogen by using inclusions such as oxides in steel by increasing the dissolved oxygen content inside the steel sheet, the content of oxygen is high and the refractory melting is extremely severe. In addition to significantly lowering the performance of performance in the steelmaking process, there is a problem in that surface defects frequently occur.
본 발명은 법랑용 냉연 강판 및 그 제조방법을 제공하고자 한다. 보다 구체적으로 법랑 처리 후에 기포 결함 발생을 방지할 수 있고 법랑 밀착성 및 내피쉬스케일성이 우수한 법랑용 냉연 강판 및 제조방법을 제공하고자 한다.The present invention is to provide a cold rolled steel sheet for enamel and a method for manufacturing the same. More specifically, it is to provide a cold-rolled steel sheet for enamel and a manufacturing method that can prevent the occurrence of bubble defects after enamel treatment and has excellent enamel adhesion and fish-scale resistance.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함하고, 미세 공공 면적 분율이 0.3 내지 0.8%이고, 하기 [관계식 1]로 표현되는 법랑결함 관계지수(D)가 0.45 내지 4.50을 만족한다.Cold rolled steel sheet for enamel according to an embodiment of the present invention, by weight, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), including residual Fe and unavoidable impurities, the micropore area fraction is 0.3 to 0.8%, and expressed by the following [Relational Formula 1] The enamel defect relationship index (D) to be satisfied satisfies 0.45 to 4.50.
[관계식 1][Relationship 1]
상기 관계식 1에서, [Mn], [Cu], [S] 및 [C]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dvoid는 냉연 강판에서의 미세 공공의 면적 분율(%)을 나타낸다.In the above relational expression 1, [Mn], [Cu], [S] and [C] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D void is the area fraction (%) of micropores in a cold rolled steel sheet ).
강판은, P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함) 중 1종 이상을 더 포함할 수 있다.The steel sheet may further include at least one of P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%), and Ti: 0.001% or less (excluding 0%).
냉연 강판의 산세 감량이 10 내지 40 gr/m2일 수 있다.The pickling loss of the cold rolled steel sheet may be 10 to 40 gr/m 2 .
냉연 강판의 수소투과비가 950 초/mm2 이상일 수 있다.The hydrogen permeation ratio of the cold rolled steel sheet may be 950 seconds/mm 2 or more.
한편, 본 발명의 일 실시예에 의한 법랑용 냉연 강판의 제조방법은, 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함하는 슬라브를 준비하는 단계; 슬라브를 가열하는 단계; 가열된 슬라브를 열간압연하여 탄화물 체적 분율이 2.5 내지 7.0%인 열연강판을 제조하는 단계; 열연 강판을 권취하는 단계; 권취된 열연 강판을 압하율 60 내지 90%로 냉간압연하여 냉연강판을 제조하는 단계; 및 냉연 강판을 소둔 열처리하는 단계;를 포함하고, 하기 [관계식 2]로 표현되는 밀착성 관계지수(A)가 0.007 내지 0.185을 만족한다.On the other hand, the method of manufacturing a cold-rolled steel sheet for enamel according to an embodiment of the present invention, by weight, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08% , S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), preparing a slab containing residual Fe and unavoidable impurities; Heating the slab; Hot-rolling the heated slab to produce a hot-rolled steel sheet having a carbide volume fraction of 2.5 to 7.0%; Winding the hot rolled steel sheet; Cold-rolling the wound hot-rolled steel sheet at a reduction ratio of 60 to 90% to produce a cold-rolled steel sheet; And annealing heat treatment of the cold-rolled steel sheet; and the adhesion relationship index (A) represented by the following [Relational Formula 2] satisfies 0.007 to 0.185.
[관계식 2][Relationship 2]
상기 관계식 2에서, [Mn], [Cu] 및 [Si]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dcementite는 열연 강판의 탄화물 체적 분율(%)을 나타낸다.In the relational expression 2, [Mn], [Cu], and [Si] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.
냉연 강판의 제조 방법은, [관계식 3]으로 표현되는 가공성 관계지수(F)가 3500 내지 7000을 만족할 수 있다.In the method for manufacturing a cold rolled steel sheet, the workability relationship index (F) expressed by [Relational Formula 3] may satisfy 3500 to 7000.
[관계식 3][Relationship 3]
상기 관계식 3에서, [Al], [N] 및 [C]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dcementite는 열연 강판의 탄화물 체적 분율(%)을 나타낸다.In the relational expression 3, [Al], [N] and [C] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.
슬라브는 P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함) 중 1종 이상을 더 포함할 수 있다.The slab may further include at least one of P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%).
열연 강판을 제조하는 단계;에서, 가열된 슬라브를 압연온도 850℃ 내지 900℃에서 열간 압연하는 것일 수 있다.In the step of manufacturing a hot-rolled steel sheet; may be to hot roll the heated slab at a rolling temperature of 850°C to 900°C.
열연 강판을 권취하는 단계;에서, 열연 강판을 640℃ 내지 750℃에서 권취하는 것일 수 있다.In the step of winding the hot rolled steel sheet; In the, it may be to roll the hot rolled steel sheet at 640 ℃ to 750 ℃.
냉연 강판을 소둔 열처리하는 단계;에서, 냉연 강판을 700℃ 내지 850℃에서 소둔 열처리하는 것일 수 있다.In the step of heat-treating the annealing of the cold-rolled steel sheet, the cold-rolled steel sheet may be heat-annealed at 700°C to 850°C.
냉연 강판을 소둔 열처리하는 단계;에서, 냉연 강판을 30초 이상 유지하는 것일 수 있다.In the step of heat-treating the annealing of the cold-rolled steel sheet, the cold-rolled steel sheet may be maintained for at least 30 seconds.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, 내피쉬스케일성 및 법랑밀착성이 우수하여, 가전기기, 화학기기, 주방기기, 위생기기 및 건물 내외장재 등에 사용될 수 있다.The cold-rolled steel sheet for enamel according to an embodiment of the present invention is excellent in fish scale resistance and enamel adhesion, and thus can be used in household appliances, chemical equipment, kitchen equipment, sanitary equipment, and interior and exterior materials of buildings.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, 강재의 화학 조성을 적절한 범위 내로 억제하는 동시에 법랑결함, 밀착성 및 가공성 관계지수를 제어하기 때문에, 제조되는 냉연 강판의 높은 법랑 밀착성과 수소 투과비를 확보할 수 있다. 따라서, 법랑 강판의 치명적인 결함인 피쉬스케일 및 기포 결함을 억제할 수 있어, 법랑 특성이 현저히 향상된다.The cold-rolled steel sheet for enameling according to an embodiment of the present invention suppresses the chemical composition of the steel material within an appropriate range and controls the enamel defect, adhesion, and processability relational index, thereby providing high enamel adhesion and hydrogen permeation ratio of the produced cold-rolled steel sheet. Can be secured. Therefore, the fatal defects of fish scale and bubble defects of the enameled steel sheet can be suppressed, and the enamel properties are significantly improved.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, 저온 석출물인 세멘타이트를 활용한다. 세멘타이트는 열간 압연중에 균일하게 분산되어 냉간 압연시 파쇄됨으로써 형성된 미세 공공 (Micro-void)들이 수소의 흡장원으로 작용하여 수소에 의해 발생하는 피쉬스케일 결함을 방지할 수 있다. 또한, 고온에서 응고단계에서 석출되는 석출물 계와 비교할 때 저온에서 안정한 탄화물을 수소 흡장원으로 활용하기 때문에 기존의 법랑강에서 문제가 되었던 내화물의 용손이나 연주 노즐의 막힘 현상과 같은 조업의 작업성 악화 및 블랙라인 (Blackline)과 같은 표면 결함 발생을 방지할 수 있다.The cold-rolled steel sheet for enameling according to an embodiment of the present invention utilizes cementite, which is a low-temperature precipitate. Cementite is uniformly dispersed during hot rolling, and micro-voids formed by crushing during cold rolling act as a storage source of hydrogen to prevent fish scale defects caused by hydrogen. In addition, compared to the precipitate system precipitated in the solidification step at high temperature, stable carbide at low temperature is used as a hydrogen storage source, which deteriorates the workability of operations such as melting of refractory material or clogging of the playing nozzle, which has been a problem in conventional enamel steel. And surface defects such as blacklines.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, Fe에 비하여 산화성이 높은 티타늄(Ti) 등의 원소가 첨가되지 않음에 따라 강판과 유약간의 밀착성도 개선할 수 있다.The cold-rolled steel sheet for enameling according to an embodiment of the present invention can also improve the adhesion between the steel sheet and the glaze as elements such as titanium (Ti) having a high oxidizing property compared to Fe are not added.
본 발명의 일 실시예에 의한 법랑용 냉연 강판은, 연속주조로 만들 수 있으며, 연속소둔 열처리에 의해 생산이 가능함에 따라 제강 원가 및 공정 원가를 현저히 낮춤으로써 통판성 및 제조 원가를 낮출 수 있으며, 생산성이 높다.The cold-rolled steel sheet for enamel according to an embodiment of the present invention can be made of continuous casting, and as it can be produced by continuous annealing heat treatment, it can lower the steel sheeting cost and process cost by significantly lowering the mailing and manufacturing costs, Productivity is high.
도 1은 본 발명의 일 실시예인 발명예 4의 SEM 사진이다.1 is an SEM photograph of Inventive Example 4, which is an embodiment of the present invention.
본 명세서에서, 제1, 제2 및 제3 등의 용어들은 다양한 부분, 성분, 영역, 층 및/또는 섹션들을 설명하기 위해 사용되나 이들에 한정되지 않는다. 이들 용어들은 어느 부분, 성분, 영역, 층 또는 섹션을 다른 부분, 성분, 영역, 층 또는 섹션과 구별하기 위해서만 사용된다. 따라서, 이하에서 서술하는 제1 부분, 성분, 영역, 층 또는 섹션은 본 발명의 범위를 벗어나지 않는 범위 내에서 제2 부분, 성분, 영역, 층 또는 섹션으로 언급될 수 있다.In this specification, terms such as first, second, and third are used to describe various parts, components, regions, layers, and/or sections, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.
본 명세서에서, 어떤 부분이 어떤 구성요소를 "포함"한다고 할 때, 이는 특별히 반대되는 기재가 없는 한 다른 구성요소를 제외하는 것이 아니라 다른 구성요소를 더 포함할 수 있는 것을 의미한다.In the present specification, when a part is to “include” a certain component, it means that the component may further include other components, not to exclude other components, unless otherwise stated.
본 명세서에서, 사용되는 전문 용어는 단지 특정 실시예를 언급하기 위한 것이며, 본 발명을 한정하는 것을 의도하지 않는다. 여기서 사용되는 단수 형태들은 문구들이 이와 명백히 반대의 의미를 나타내지 않는 한 복수 형태들도 포함한다. 명세서에서 사용되는 "포함하는"의 의미는 특정 특성, 영역, 정수, 단계, 동작, 요소 및/또는 성분을 구체화하며, 다른 특성, 영역, 정수, 단계, 동작, 요소 및/또는 성분의 존재나 부가를 제외시키는 것은 아니다.In this specification, the terminology used is only for referring to a specific embodiment, and is not intended to limit the present invention. The singular forms used herein include plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of “comprising” embodies a particular property, region, integer, step, action, element, and/or component, and the presence or presence of other properties, regions, integers, steps, action, element, and/or component. It does not exclude addition.
본 명세서에서, 마쿠시 형식의 표현에 포함된 "이들의 조합"의 용어는 마쿠시 형식의 표현에 기재된 구성 요소들로 이루어진 군에서 선택되는 하나 이상의 혼합 또는 조합을 의미하는 것으로서, 상기 구성 요소들로 이루어진 군에서 선택되는 하나 이상을 포함하는 것을 의미한다.In the present specification, the term "combination of these" included in the expression of the marki form means one or more mixtures or combinations selected from the group consisting of the elements described in the expression of the marki form, the components It means to include one or more selected from the group consisting of.
본 명세서에서, 어느 부분이 다른 부분의 "위에" 또는 "상에" 있다고 언급하는 경우, 이는 바로 다른 부분의 위에 또는 상에 있을 수 있거나 그 사이에 다른 부분이 수반될 수 있다. 대조적으로 어느 부분이 다른 부분의 "바로 위에" 있다고 언급하는 경우, 그 사이에 다른 부분이 개재되지 않는다.In the present specification, when it is said that a part is "on" or "on" another part, it may be directly on or on another part, or another part may be involved therebetween. In contrast, if one part is referred to as being “just above” another part, no other part is interposed therebetween.
다르게 정의하지는 않았지만, 여기에 사용되는 기술용어 및 과학용어를 포함하는 모든 용어들은 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자가 일반적으로 이해하는 의미와 동일한 의미를 가진다. 보통 사용되는 사전에 정의된 용어들은 관련기술문헌과 현재 개시된 내용에 부합하는 의미를 가지는 것으로 추가 해석되고, 정의되지 않는 한 이상적이거나 매우 공식적인 의미로 해석되지 않는다.Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are further interpreted as having meanings consistent with related technical documents and currently disclosed contents, and are not interpreted as ideal or very formal meanings unless defined.
또한, 특별히 언급하지 않는 한 %는 중량%를 의미하며, 1ppm 은 0.0001 중량%이다.In addition, unless otherwise specified,% means% by weight, and 1 ppm is 0.0001% by weight.
본 발명의 일 실시예에서 추가 원소를 더 포함하는 것의 의미는 추가 원소의 추가량 만큼 잔부인 철(Fe)을 대체하여 포함하는 것을 의미한다.In one embodiment of the present invention, the meaning of further including an additional element means that the remaining amount of iron (Fe) is replaced by an additional amount of the additional element.
이하, 본 발명의 실시예에 대하여 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자가 용이하게 실시할 수 있도록 상세히 설명한다. 그러나 본 발명은 여러 가지 상이한 형태로 구현될 수 있으며 여기에서 설명하는 실시예에 한정되지 않는다.Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.
본 발명의 일 실시예에 의한 냉연 강판은 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함하고, 미세 공공 면적 분율이 0.3 내지 0.8%이다. 또한, 강판은, P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함) 중 1종 이상을 더 포함할 수 있다.Cold rolled steel sheet according to an embodiment of the present invention in weight percent, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), residual Fe and unavoidable impurities, and a micropore area fraction of 0.3 to 0.8%. In addition, the steel sheet, P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%) It may further include one or more of.
또한, 본 발명의 일 실시예에 의한 냉연 강판의 제조방법에서의 준비하는 슬라브는 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함한다. 또한, P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함) 중 1종 이상을 더 포함할 수 있다. 그 후, 슬라브를 가열하는 단계를 거치며, 가열된 슬라브를 열간 압연하여 탄화물 체적 분율이 2.5 내지 7.0%인 열연 강판을 제조하는 단계를 거친다. 그 후 과정에 대해서는 후술한다.In addition, the slab prepared in the method for manufacturing a cold rolled steel sheet according to an embodiment of the present invention is weight%, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% or less (excluding 0%), residual Fe and unavoidable impurities. In addition, P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%) may further include one or more. Thereafter, a step of heating the slab is performed, and the hot-rolled slab is hot-rolled to produce a hot-rolled steel sheet having a carbide volume fraction of 2.5 to 7.0%. The process after that will be described later.
먼저, 냉연 강판의 성분을 한정한 이유를 설명한다.First, the reason for limiting the components of the cold rolled steel sheet will be described.
탄소 (C): 0.05 내지 0.09%Carbon (C): 0.05 to 0.09%
C를 너무 많이 첨가할 경우, 강 중 고용 탄소의 양이 증가하여 강도는 높아지고 소둔시 집합 조직의 발달을 방해하여 성형성을 나쁘게 하며 법랑층의 버블링에 의한 기포 결함을 유발하는 문제점이 있으며, C를 너무 적게 첨가할 경우, 강 내의 수소를 흡장하는 사이트로 작용하는 탄화물의 분율이 낮아 피쉬스케일 결함에 취약한 문제점이 있을 수 있다.If too much C is added, the amount of solid carbon in steel increases, the strength increases, and annealing hinders the development of aggregates, thereby deteriorating formability and causing bubble defects due to bubbling of the enamel layer. When too little C is added, there may be a problem that fish fraction defects are vulnerable due to a low fraction of carbide serving as a site for storing hydrogen in the steel.
망간 (Mn): 0.1 내지 0.3%Manganese (Mn): 0.1 to 0.3%
Mn은 대표적인 고용강화 원소이며 강 중 고용 황을 망간황화물(MnS)로 석출하여 적열 취성(Hot shortness)을 방지하기 위해 첨가하며 이와 같은 효과를 확보하기 위해서 최소한 0.1% 이상 첨가가 필요하다. 반면에 망간의 함량이 너무 많으면 성형성을 나쁘게 하는 문제점이 있을 수 있다.Mn is a representative solid solution strengthening element, and it is added to prevent hot shortness by precipitating solid solution sulfur as manganese sulfide (MnS), and it is necessary to add at least 0.1% or more to secure such an effect. On the other hand, if the content of manganese is too large, there may be a problem that the moldability is deteriorated.
실리콘 (Si): 0.001 내지 0.03%Silicon (Si): 0.001 to 0.03%
Si는 수소흡장원으로 작용하는 탄화물의 형성을 촉진하는 원소로써 이와 같은 효과를 얻기 위해서는 0.001% 이상의 첨가가 필요하다. 반면에 너무 많이 첨가되면 강판 표면에 산화물 피막을 형성하여 법랑 밀착성을 저하시키는 문제점이 있을 수 있다. 보다 구체적으로 0.005 내지 0.025%일 수 있다.Si is an element that promotes the formation of a carbide that acts as a hydrogen storage source, and in order to obtain such an effect, it is necessary to add 0.001% or more. On the other hand, if it is added too much, there may be a problem of forming an oxide film on the surface of the steel sheet to degrade the enamel adhesion. More specifically, it may be 0.005 to 0.025%.
알루미늄(Al): 0.01 내지 0.08%Aluminum (Al): 0.01 to 0.08%
Al은 용강 중 산소를 제거하는 강력한 탈산제로 사용되며, 고용 질소를 고착하여 시효성을 개선하는 원소로써 이와 같은 효과를 위해서는 0.01% 이상의 첨가가 필요하다. 반면에 너무 많이 첨가되면 알루미늄 산화물이 강 중 또는 강 표면에 잔존하여 법랑처리 공정에서 기포 결함을 발생 시키는 문제점이 있을 수 있다. 보다 구체적으로 0.02 내지 0.044%일 수 있다.Al is used as a strong deoxidizer to remove oxygen from molten steel, and it is an element that improves aging by fixing solid nitrogen, and for this effect, addition of 0.01% or more is required. On the other hand, if too much is added, aluminum oxide may remain in the steel or on the surface of the steel, thereby causing a bubble defect in the enameling process. More specifically, it may be 0.02 to 0.044%.
인(P): 0.002 내지 0.02%Phosphorus (P): 0.002 to 0.02%
P는 대표적인 재질 강화 원소로써 이와 같은 효과를 얻기 위해서는 최소한 0.002% 이상의 첨가가 필요하다. 반면에 P가 증가하면 강판 내부에 편석층을 만들어 성형성을 저하시킬 뿐만 아니라 강의 산세성을 나쁘게 하여 법랑 밀착성에도 나쁜 영향을 미칠 수 있다. 보다 구체적으로 0.005 내지 0.02%일 수 있다.P is a typical material strengthening element, and at least 0.002% of addition is required to obtain this effect. On the other hand, if P is increased, a segregation layer is formed inside the steel sheet to deteriorate the formability as well as to deteriorate the pickling property of the steel, which may adversely affect enamel adhesion. More specifically, it may be 0.005 to 0.02%.
황(S): 0.001 내지 0.02%Sulfur (S): 0.001 to 0.02%
S는 망간과 결합하여 적열 취성을 일으키는 원소이며 너무 많이 첨가된 경우에서 연성이 크게 저하하여 가공성을 나쁘게 할 뿐만 아니라 망간황화물의 과다 석출에 의한 피쉬스케일성에도 좋지 않은 영향을 미칠 수 있다. 보다 구체적으로 0.003 내지 0.015%일 수 있다.S is an element that causes red-brittle brittleness in combination with manganese, and in the case where too much is added, ductility deteriorates significantly, which can deteriorate processability and adversely affect fish-scale properties due to excessive precipitation of manganese sulfide. More specifically, it may be 0.003 to 0.015%.
구리(Cu): 0.01 내지 0.15%Copper (Cu): 0.01 to 0.15%
Cu는 강판 표면에 농화되어 법랑층과 강판의 결합력을 향상시키는 원소로써 이를 위해서는 0.01% 이상 첨가가 필요하다. 하지만 너무 많이 첨가하면 오히려 법랑층과 강판의 반응을 억제하여 기포결함을 유발할 뿐만 아니라 가공성을 나쁘게 하는 문제점이 있을 수 있다. 보다 구체적으로 0.03 내지 0.13%일 수 있다.Cu is an element that concentrates on the surface of the steel sheet and improves the bonding strength between the enamel layer and the steel sheet, and for this, it is necessary to add 0.01% or more. However, if too much is added, the reaction between the enamel layer and the steel sheet is suppressed, thereby causing bubble defects and deteriorating processability. More specifically, it may be 0.03 to 0.13%.
질소(N): 0.005% 이하(0%를 제외함)Nitrogen (N): 0.005% or less (excluding 0%)
N은 대표적인 경화 원소이지만 첨가량이 증가하면 시효 결함이 다발하고 성형성이 나빠지며 법랑 처리 공정에서 기포 결함을 발생시키는 문제점이 있을 수 있다. 보다 구체적으로 0.004% 이하일 수 있다.N is a typical hardening element, but if the amount added is increased, aging defects are frequently formed, poor moldability is generated, and there may be a problem of generating bubble defects in the enameling process. More specifically, it may be 0.004% or less.
산소(O): 0.002% 이하(0%를 제외함)Oxygen (O): 0.002% or less (excluding 0%)
O는 산화물을 형성하는데 있어 필수적인 원소로써 이와 같은 산화물은 제강 단계에서 내화물의 용손을 야기할 뿐만 아니라, 강판 표면에 산화물에 기인하는 표면결함을 유발하는 요인으로 작용할 수 있다.O is an essential element in forming an oxide, and such an oxide not only causes melting of the refractory material in the steelmaking step, but can also act as a factor that causes surface defects due to oxides on the surface of the steel sheet.
티타늄(Ti): 0.001% 이하(0%를 제외함)Titanium (Ti): 0.001% or less (excluding 0%)
Ti는 가공성 향상 및 피쉬스케일의 원인이 되는 수소의 반응을 억제하기 위해 첨가되는 원소로 알려져 있다. 그러나, 본 발명의 일 실시예에서의 강종에서는 Ti가 다량 첨가될 시, 블리스터(Blister)와 같은 기포 결함을 일으키는 문제가 있었다. 또한, 전술하였듯이, 제강 공정의 연속 주조 단계에서 티타늄 질화물(TiN)과 개재물에 의한 노즐 막힘 현상이 빈번히 발생하여 작업성 저하 및 생산 부하의 직접적인 요인이 된다. 따라서, Ti를 포함하는 경우, 0.001% 이하로 제한할 수 있다.Ti is known as an element added to improve processability and suppress the reaction of hydrogen, which is the cause of fish scale. However, in the steel grade in one embodiment of the present invention, when a large amount of Ti is added, there is a problem that causes a bubble defect such as a blister. In addition, as described above, the nozzle clogging phenomenon due to titanium nitride (TiN) and inclusions frequently occurs in the continuous casting step of the steelmaking process, which is a direct factor of lowering workability and production load. Therefore, when Ti is included, it can be limited to 0.001% or less.
상기 성분 이외에 본 발명은 Fe 및 불가피한 불순물을 포함한다. 상기 성분 이외에 유효한 성분의 첨가를 배제하는 것은 아니다.In addition to the above components, the present invention includes Fe and unavoidable impurities. The addition of effective ingredients other than the above ingredients is not excluded.
다음으로, 본 발명의 냉연 강판의 미세 공공의 면적 분율 및 준비하는 슬라브의 열연 단계에서의 탄화물의 체적 분율에 대하여 설명한다.Next, the area fraction of the micropores of the cold rolled steel sheet of the present invention and the volume fraction of carbides in the hot rolling step of the prepared slab will be described.
본 발명강에서 이용하는 탄화물의 경우, 모재와의 연성차에 의하여 냉간 압연 시 탄화물 자체가 파쇄되며 이에 의해 형성된 미세 공공들이 강내 수소를 고착하는 수소흡장원으로 활용된다. 이는 피쉬스케일 결함을 억제하는데 큰 역할을 하므로 탄화물 분율을 일정 범위 내로 관리하는 것은 매우 중요하다. 한편, 이와 같은 탄화물 분율은 단독뿐만 아니라 첨가 원소와의 상호 관계에 의해서도 법랑성에 영향을 미친다.In the case of the carbide used in the present invention steel, the carbide itself is crushed during cold rolling due to a ductility difference with the base material, and the micropores formed thereby are used as a hydrogen storage source for fixing hydrogen in the river. This plays a large role in suppressing fishscale defects, so it is very important to manage the carbide fraction within a certain range. On the other hand, such a carbide fraction affects enamel property not only alone but also by the interaction with the added elements.
법랑 강판의 가장 치명적인 결함 중의 한가지인 피쉬스케일(Fishscale) 결함은, 법랑 제품의 제조 공정 중 강내에 고용되어 있던 수소가 소성 후 냉각되는 과정에서 강중에 과포화 되어 존재하다가 강의 표면으로 방출되면서 법랑층을 고기 비늘 모양으로 탈락 시킴으로써 발생하는 법랑 결함이다. 이와 같은 피쉬스케일 결함이 발생하면 결함 부위에 집중적으로 녹(Rust)이 발생하는 등 법랑제품의 가치를 크게 떨어뜨리므로 발생을 억제하는 것이 필요하다. 피쉬스케일 결함을 방지하기 위해서는 강중에 고용된 수소를 잡아줄 수 있는 위치(site)를 강 내부에 다량 형성시킬 필요가 있다. 이에 석출물, 개재물 등을 활용한 법랑용 냉연강판이 제시한다. 지금까지 널리 알려진 대표적인 수소 흡장원으로는 MnO, CrO 등과 같은 비금속 개재물, BN, TiN, TiS 등과 같은 석출물, 그리고 압연 등에 의해 생성되는 미세 공공 (Micro-void) 등이 있다.Fishscale defects, one of the most fatal defects of enamel steel plates, are supersaturated in the steel during the cooling process after hydrogen is fired in the steel during the manufacturing process of the enamel product, and then released into the surface of the steel to release the enamel layer. It is an enamel defect caused by dropping out of the meat scales. When such a fish-scale defect occurs, it is necessary to suppress the occurrence of the enamel product, as it significantly reduces the value of the enamel product, such as intensive rust on the defect site. In order to prevent fishscale defects, it is necessary to form a large amount of sites inside the steel that can trap hydrogen dissolved in the steel. Therefore, the cold rolled steel sheet for enamel using precipitates and inclusions is proposed. Representative hydrogen storage sources widely known so far include non-metallic inclusions such as MnO and CrO, precipitates such as BN, TiN, and TiS, and micro-voids generated by rolling.
본 발명에서 제안된 법랑용 강판은 강 성분을 조절하여 수소의 흡장 위치로서 주로 Fe3C (세멘타이트)와 같은 탄화물 등을 활용함과 동시에, 강 성분 중 법랑 밀착성, 표면 결함 및 성형성에 영향을 미치는 성분 및 공정을 제어함으로써 표면결함이 없으면서 법랑밀착성 및 내피쉬스케일성이 우수한 강판을 제공하고자 한다. 저온 석출물인 세멘타이트의 경우 열간압연 중에 균일하게 분산되어 냉간압연 시 파쇄됨으로써 형성된 미세 공공 (Micro-void)들이 수소의 흡장원으로 작용하여 수소에 의해 발생하는 피쉬스케일 결함을 방지할 수 있다. 또한, 고온에서 응고 단계에서 석출되는 석출물계와 비교할 때 저온에서 안정한 탄화물을 수소 흡장원으로 활용하기 때문에 기존의 법랑강에서 문제가 되었던 내화물의 용손이나 연주 노즐의 막힘 현상과 같은 조업의 작업성 악화 및 블랙라인 (Blackline)과 같은 표면 결함 발생을 방지할 수 있다.The steel sheet for enamel proposed in the present invention mainly controls carbide components such as Fe 3 C (cementite) as a storage position for hydrogen by controlling the steel component, and also affects enamel adhesion, surface defects, and formability among steel components. It is intended to provide a steel sheet excellent in enamel adhesion and fish scale resistance without surface defects by controlling the components and processes affecting it. In the case of cementite, which is a low-temperature precipitate, micro-voids formed by uniformly dispersing during hot rolling and crushing during cold rolling act as a storage source of hydrogen, thereby preventing fishscale defects caused by hydrogen. In addition, compared to the precipitate system precipitated at a high temperature at a solidification stage, stable carbide at low temperature is used as a hydrogen storage source, which deteriorates the workability of operations such as melting of refractory material or clogging of a performance nozzle, which has been a problem in conventional enamel steel. And surface defects such as blacklines.
탄화물의 분율은 강중의 총 탄소량과 밀접한 관계를 가질 뿐만 아니라 조업 조건에도 크게 영향을 받는다. 한편, 본 발명강의 경우 Fe에 비하여 산화성이 높은 티타늄(Ti) 등의 원소의 첨가가 매우 적음에 따라 강판과 유약간의 밀착성도 개선할 수 있었다. 또한, 본 발명예는 구리(Cu)량과 미세 공공의 면적 분율을 제어함으로써 법랑 전처리 단계에서 강판 표면에 생성되는 황산수화물 (H2SO4-H2O) 발생을 억제하여 내피쉬스케일성 및 기포 결함의 발생이 현저히 개선됨을 확인할 수 있다.The fraction of carbide not only has a close relationship with the total amount of carbon in the steel, but is also greatly influenced by operating conditions. On the other hand, in the case of the steel of the present invention, the adhesion between the steel sheet and the glaze could be improved as the addition of elements such as titanium (Ti) having a high oxidation property compared to Fe is very small. In addition, the present invention example suppresses the generation of sulfate hydrate (H 2 SO 4 -H 2 O) generated on the surface of the steel sheet in the enamel pre-treatment step by controlling the amount of copper (Cu) and the area fraction of the micropores, resulting in fishscale resistance and It can be seen that the occurrence of bubble defects is significantly improved.
하기는 냉연 강판 제조 중간의 열연 강판에서의 탄화물의 체적 분율, 최종물인 냉연 강판에서의 미세 공공의 면적 분율, 법랑결함 관계지수(D), 밀착성 관계지수(A), 가공성 관계 지수(F)에 대하여 설명한다.Below is the volume fraction of carbide in the hot rolled steel sheet in the middle of manufacturing cold rolled steel sheet, the area fraction of micropores in the final cold rolled steel sheet, the enamel defect relationship index (D), the adhesion relationship index (A), and the workability relationship index (F). Will be explained.
탄화물의 체적 분율 (Dcementite): 2.5 내지 7.0%Volume fraction of carbide (D cementite ): 2.5 to 7.0%
탄화물 체적 분율은 열연 강판에서의 탄화물 체적 분율을 의미한다.The carbide volume fraction means the volume fraction of carbide in a hot rolled steel sheet.
탄화물은 세멘타이트(Fe3C)일 수 있다. 금속 합금 내에 존재하는 탄소는 금속 원자와 결합하여 탄화물을 형성하는데, 철이 탄소와 결합하여 탄화물을 형성하는 것을 세멘타이트라고 한다. 보통 탄소강에서는 250 내지 700℃ 근처에서 세멘타이트가 형성되며, 이보다 고온에서는 구형의 입자상으로 조대화된다. 철강 재료 중 백주철과 같은 재료는 탄소가 거의 세멘타이트의 형태로 존재하며, 내마모성이 뛰어나서 볼밀(ball mill)과 같은 마모가 심한 부분에 사용된다.The carbide may be cementite (Fe 3 C). The carbon present in the metal alloy bonds with a metal atom to form a carbide. Iron is combined with carbon to form a carbide, which is called cementite. Normally, in carbon steel, cementite is formed near 250 to 700°C, and at higher temperatures, it becomes coarse to spherical particles. Among steel materials, such as white cast iron, carbon is almost in the form of cementite, and because it has excellent abrasion resistance, it is used in areas of high wear, such as a ball mill.
열연 단계에서 생성된 탄화물의 체적 분율이 너무 적을 때에는 냉간 압연 공정에서 파쇄되어 수소를 흡장하는 소스로 제공될 수 있는 탄화물의 분율이 낮아짐에 따라 냉간압연을 경유한 강판의 미세 공공 면적 분율이 감소하여 수소를 고착하는데 한계가 있어 피쉬스케일 등의 억제가 어려운 문제점이 있을 수 있다. 반면에, 탄화물 분율이 너무 높을 때에는 수소흡장원으로서의 미세 공공 형성 측면에서는 유리하여 내피쉬스케일성을 개선하는 데는 효과적이었지만 너무 많은 공공들에 의해 오히려 가공성 및 내식성이 저하되는 문제점이 있을 수 있다.When the volume fraction of carbides generated in the hot rolling step is too small, the fraction of carbides that can be provided as a source for storing hydrogen by crushing in the cold rolling process decreases, thereby reducing the micropore area fraction of the steel sheet via cold rolling. There may be a problem in that it is difficult to suppress fish scale and the like because there is a limit to fixing hydrogen. On the other hand, when the carbide fraction is too high, it is advantageous in terms of forming micro-pore as a hydrogen storage source, and is effective in improving fish-scale resistance. However, there may be a problem that processability and corrosion resistance are deteriorated by too many pores.
미세 공공의 면적 분율 (Dvoid): 0.30 내지 0.80%Area fraction of micropores (D void ): 0.30 to 0.80%
미세 공공의 면적 분율은 냉연 강판에서의 미세 공공 면적 분율을 의미한다.The micropore area fraction means the micropore area fraction in a cold rolled steel sheet.
저온 석출물인 세멘타이트의 경우 열간 압연중에 균일하게 분산되어 냉간 압연 시 파쇄됨으로써 석출물 주위에 미세 공공이 형성된다. 형성된 미세 공공들은 법랑 강판에서 수소의 흡장원으로 작용하여 수소에 의해 발생하는 법랑 결함인 법랑층이 고기 비늘 모양으로 탈락하는 피쉬스케일 결함의 발생을 억제하게 된다. 냉연 강판에서의 미세 공공은 주사전자현미경을 활용하여 배율 1000배로 10매의 사진을 촬영 후 이들 면적에서 차지하는 미세 공공의 면적 분율을 화상분석기를 활용하여 측정하였다. 도 1에는 이와 같이 촬영한 발명예 4의 미세 공공 관찰 사진의 예를 나타내었다. 미세 공공의 면적 분율이 너무 낮을 경우에서는 강내 수소를 고착할 수 있는 수소흡장원으로 작용하는 사이트가 적음에 따라 법랑 제품의 피쉬스케일 결함율이 높아지는 문제점이 있을 수 있으며, 반면에 너무 높을 경우에서는 내피쉬스케일 측면에서는 유리하였지만 미세공공의 증가에 의해 가공성 및 표면 결함이 다발하는 문제점이 있을 수 있다. 보다 구체적으로 0.30 내지 0.75%일 수 있다.In the case of cementite, which is a low-temperature precipitate, it is uniformly dispersed during hot rolling and crushed during cold rolling, thereby forming fine pores around the precipitate. The formed micropores act as a storage source of hydrogen in the enameled steel sheet, thereby suppressing the occurrence of fish scale defects in which the enamel layer, which is an enamel defect caused by hydrogen, falls out into the shape of meat scales. The micropores in the cold-rolled steel sheet were measured using a scanning electron microscope, and after taking 10 pictures at a magnification of 1000, the area fraction of micropores in these areas was measured using an image analyzer. 1 shows an example of a microscopic public observation photograph of Inventive Example 4 photographed as described above. If the area fraction of the micropore is too low, there may be a problem that the fish scale defect rate of the enamel product increases due to the small number of sites that act as a hydrogen storage source that can fix hydrogen in the river. Although it is advantageous in terms of fish scale, there may be a problem in that workability and surface defects are frequently caused by an increase in microporosity. More specifically, it may be 0.30 to 0.75%.
법랑결함 관계지수, D=([Mn]x[Cu]/[S])x(Dvoid /[C]): 0.45 내지 4.50Enamel defect relationship index, D=([Mn]x[Cu]/[S])x(D void /[C]): 0.45 to 4.50
법랑층이 고기 비늘 모양으로 탈락하는 피쉬스케일에 대한 저항성 및 기포 결함에 대한 저항성 등을 나타내는 법랑결함 관계지수(D), D=([Mn]x[Cu]/[S])x(Dvoid/[C]) 값이 상기의 범위를 만족하는 것이 필요하였다. 여기에서 [Mn], [Cu], [S], [C]는 각각의 원소 중량%를 원자량으로 나누어 준 값이며, Dvoid는 냉연 강판에서의 미세 공공의 면적 분율이다. D값이 너무 낮은 경우에는 피쉬스케일 결함을 유발하는 수소를 충분히 흡장할 수 있는 사이트를 확보할 수 없기 때문에 법랑제품의 피쉬스케일 결함 발생이 증가하는 문제점이 있을 수 있으며, 반면에 D값이 너무 높은 경우에는 수소 흡장원 확보 측면에서는 유리하였지만 제품의 가공성 및 표면 특성을 나쁘게 하는 문제점이 있을 수 있다. 보다 구체적으로 0.5 내지 4.2일 수 있다.Enamel defect relationship index (D), D=([Mn]x[Cu]/[S])x(D void , indicating resistance to fish scale and bubble defects in which the enamel layer falls out of the shape of meat scales /[C]) It was necessary for the value to satisfy the above range. Here, [Mn], [Cu], [S], and [C] are values obtained by dividing the weight percent of each element by atomic weight, and D void is the area fraction of micropores in the cold rolled steel sheet. If the D value is too low, there may be a problem that the occurrence of fish scale defects in enamel products increases because a site capable of sufficiently storing hydrogen that causes fish scale defects may not be obtained, whereas the D value is too high. In this case, although it was advantageous in terms of securing a hydrogen storage source, there may be a problem that the workability and surface characteristics of the product are deteriorated. More specifically, it may be 0.5 to 4.2.
밀착성 관계지수, A=([Mn]x[Cu]xDcementite})/[Si]: 0.007 내지 0.185Adhesion index, A=([Mn]x[Cu]xD cementite} )/[Si]: 0.007 to 0.185
법랑밀착성과 연계된 밀착성 관계지수 (A), A=([Mn]x[Cu]xDcementite})/[Si] 값이 상기의 범위를 만족하는 것이 필요하였다. 여기에서 [Mn], [Cu], [Si]은 각각의 원소 중량 %를 원자량으로 나누어 준 값이며, Dcementite는 열연강판에서의 탄화물 체적 분율을 나타낸다. A값이 너무 작을 경우에는 표면에 농화되는 계면층의 농도가 감소함에 따라 알루미늄 산화물 등의 형성량이 증가하여 법랑 유약층과 소지철 사이의 밀착성을 저하시키는 문제점이 있을 수 있으며, 반면에 A값이 너무 클 경우에는 소성 열처리시 강판 표면에 발생하는 가스(Gas)의 발생량이 증가하여 기포 결함을 유발함에 따라 밀착성이 현저히 감소하는 문제점이 있을 수 있다. 보다 구체적으로 0.008 내지 0.180일 수 있다.It was necessary for the values of the adhesiveness index (A), A=([Mn]x[Cu]xD cementite} )/[Si] associated with enamel adhesion to satisfy the above range. Here, [Mn], [Cu], and [Si] are values obtained by dividing% by weight of each element by atomic weight, and D cementite represents the volume fraction of carbide in the hot-rolled steel sheet. If the value of A is too small, as the concentration of the interfacial layer concentrated on the surface decreases, the amount of formation of aluminum oxide or the like increases, and there may be a problem of deteriorating the adhesion between the enamel glaze layer and the iron. If it is too large, the amount of gas (Gas) generated on the surface of the steel sheet during the calcination heat treatment increases, which may cause a bubble defect, and thus, the adhesion may be significantly reduced. More specifically, it may be 0.008 to 0.180.
가공성 관계지수, F=([Al]/[N])x(Dcementite/[C]): 3500 내지 7000Machinability relation index, F=([Al]/[N])x(D cementite /[C]): 3500 to 7000
법랑강의 가공성도 탄화물 분율 및 강내 고용 원소와 밀접한 관계를 가지므로 가공성 관계 지수, F를 상기의 범위로 관리하는 것이 필요할 수 있다. 여기에서 [Al], [N], [C]는 각각의 원소 중량%를 원자량으로 나누어 준 값이며, Dcementite는 열연 강판에서의 탄화물의 체적 분율이다. 가공성 관계지수, F가 너무 작을 경우에는 강내 고용 원소량이 증가함에 따라 법랑 가공 단계에서 꺾임 또는 표면결함과 같은 시효 결함이 발생하여 성형품의 불량률을 높이는 문제점이 있었으며, 반면에 F값이 너무 높아지면 미세 석출물의 분율이 증가함에 따라 가공성이 열화되는 문제점이 있을 수 있다.Since the workability of enamel steel also has a close relationship with the carbide fraction and solid solution elements in the steel, it may be necessary to manage the workability relationship index, F, within the above range. Here, [Al], [N], and [C] are values obtained by dividing each element weight% by atomic weight, and D cementite is a volume fraction of carbide in a hot rolled steel sheet. When the workability relationship index, F is too small, as the amount of solid solution in the steel increases, aging defects such as bending or surface defects occur in the enamel processing step, thereby increasing the defect rate of the molded product. On the other hand, if the F value is too high, As the fraction of fine precipitates increases, there may be a problem that workability deteriorates.
다음으로, 본 발명의 냉연 강판의 산세 감량 및 수소투과비에 대하여 설명한다.Next, the pickling loss and hydrogen permeation ratio of the cold rolled steel sheet of the present invention will be described.
본 발명의 일 실시예에 따른 냉연 강판은 산세 감량은 10 내지 40 gr/m2일 수 있다. 이러한 물성을 만족함으로써 법랑용 소재로써 적용될 수 있다. 산세 감량이 너무 낮을 경우에는 강판 표면의 거칠음이 너무 없어 유약의 흡착 능력이 떨어짐에 따라 유약과 강판간의 밀착성을 나쁘게 하여 법랑층 탈락과 같은 문제가 발생할 수 있다. 반면에 너무 높을 경우에서 강판 표면층의 평탄화 작업이 이루어져 밀착성을 악화시킬 뿐만 아니라 기포 결함의 발생도 증가하는 문제점이 있다. 더욱 구체적으로 산세 감량은 12 내지 35gr/m2일 수 있다.The cold rolled steel sheet according to an embodiment of the present invention may have a pickling loss of 10 to 40 gr/m 2 . By satisfying these properties, it can be applied as an enamel material. If the pickling loss is too low, the roughness of the surface of the steel sheet is not so great that the adhesion between the glaze and the steel sheet deteriorates as the adsorption capacity of the glaze decreases, and problems such as dropping of the enamel layer may occur. On the other hand, when it is too high, a flattening operation is performed on the surface layer of the steel sheet, thereby deteriorating adhesiveness and increasing the occurrence of bubble defects. More specifically, the pickling loss may be 12 to 35gr/m 2 .
본 발명의 일 실시예에 따른 냉연 강판은 수소투과비가 950초/mm2 이상일 수 있다. 수소투과비는 본 발명의 일 실시예에 따른 냉연강판을 이용하여 제조된 법랑강의 치명적인 결함인 피쉬스케일 결함의 저항성을 나타내는 내피쉬스케일성을 평가하는 지수로써, 유럽규격 EN 10209에 등록된 방법으로 실험하여 강판내에 수소를 고착할 수 있는 능력을 평가한다. 강판의 한 방향에서 수소를 발생시키고 강판의 반대편으로 수소가 투과해 나오는 시간 (ts, 단위: 초)을 측정하여, 이를 소재 두께 (t, 단위: mm)의 제곱으로 나누어 표시한 값으로, ts/t2 (단위: 초/mm2)로 나타낸다. 구체적으로 수소 투과비가 950초/mm2 이상일 수 있다. 수소투과비가 너무 작을 경우에는 법랑처리후 200℃에서 24시간 가속 열처리한 경우에 피쉬스케일 결함율이 50% 이상으로 발생하여 안정적인 법랑제품으로 사용하는데 문제점이 있었기에 내피쉬스케일성이 우수한 강판을 확보하기 위해서는 수소 투과비가 950 초/mm2 이상으로 관리할 필요가 있다. 또한 더욱 구체적으로는 수소투과비가 1000 초/mm2 이상일 수 있다.The cold rolled steel sheet according to an embodiment of the present invention may have a hydrogen permeation ratio of 950 seconds/mm 2 or more. The hydrogen permeation ratio is an index for evaluating the fish-scale resistance, which indicates the resistance of fish-scale defects, which are fatal defects of enamel steel produced using cold-rolled steel sheets according to an embodiment of the present invention, and is a method registered in European Standard EN 10209. Experiment to evaluate the ability to fix hydrogen in the steel sheet. It is a value expressed by dividing by the square of the material thickness (t, unit: mm) by measuring the time (t s , unit: second) at which hydrogen is generated in one direction of the steel sheet and hydrogen permeates to the other side of the steel sheet. It is represented by t s /t 2 (unit: second/mm 2 ). Specifically, the hydrogen permeation ratio may be 950 seconds/mm 2 or more. If the hydrogen permeation ratio is too small, the fish scale defect rate is more than 50% when accelerated heat treatment at 200℃ for 24 hours after enamel treatment, and there is a problem in using it as a stable enamel product. For this, it is necessary to manage the hydrogen permeation ratio to 950 seconds/mm 2 or more. In addition, more specifically, the hydrogen permeation ratio may be 1000 seconds/mm 2 or more.
이하, 본 발명의 냉연 강판의 제조방법에 대하여 상세히 설명한다.Hereinafter, a method of manufacturing the cold rolled steel sheet of the present invention will be described in detail.
먼저, 전술한 조성을 만족하는 슬라브를 준비한다. 제강 단계에서 전술한 조성으로 성분이 조정된 용강은 연속 주조를 통하여 슬라브로 제조될 수 있다.First, a slab satisfying the above-described composition is prepared. The molten steel whose components are adjusted to the above-described composition in the steelmaking step may be manufactured as slabs through continuous casting.
그 후, 제조된 슬라브를 가열한다. 가열함으로써 후속되는 열간 압연 공정을 원활히 수행하고, 슬라브를 균질화 처리할 수 있다. 보다 구체적으로, 가열은 재가열을 의미할 수 있다.Thereafter, the prepared slab is heated. By heating, the subsequent hot rolling process can be performed smoothly and the slab can be homogenized. More specifically, heating may mean reheating.
이 때, 슬라브 가열 온도는 1150 내지 1250℃일 수 있다. 슬라브 가열 온도가 너무 낮으면 후속하는 열간 압연 시 압연 하중이 급격히 증가하여 작업성을 나쁘게 할 수 있다. 반면에 슬라브 가열 온도가 너무 높으면 에너지 비용이 증가할 뿐만 아니라, 표면 스케일 양이 증가하여 재료 손실로 이어질 수 있다.At this time, the slab heating temperature may be 1150 to 1250°C. If the slab heating temperature is too low, the rolling load increases rapidly during subsequent hot rolling, which can deteriorate workability. On the other hand, if the slab heating temperature is too high, it not only increases energy cost, but also increases the amount of surface scale, which can lead to material loss.
그 후, 가열된 슬라브를 열간 압연하여 열연 강판을 제조한다.Thereafter, the heated slab is hot rolled to produce a hot rolled steel sheet.
이 때, 열연 강판의 탄화물 체적 분율은 2.5 내지 7.0%일 수 있다. 탄화물 체적 분율에 대한 설명은 언급하였으므로 생략한다.At this time, the volume fraction of carbide of the hot rolled steel sheet may be 2.5 to 7.0%. The description of the carbide volume fraction is mentioned and is omitted.
또한, 열간 압연의 마무리 압연 온도는 850 내지 900℃일 수 있다. 마무리 열간 압연 온도가 너무 낮으면 저온 영역에서 압연이 마무리됨에 따라 결정립의 혼립화가 급격히 진행되어 압연성 및 가공성의 저하를 초래하는 경향이 있다. 반면에, 마무리 열간 압연 온도가 너무 높으면 표면 스케일의 박리성이 떨어지고 두께 전반에 걸쳐 균일한 열간 압연이 이루어지지 않음에 따라 결정립 성장에 의한 충격 인성의 저하가 나타날 수 있다. 더욱 구체적으로, 마무리 열간 압연 온도는 860 내지 890℃가 될 수 있다.In addition, the finish rolling temperature of hot rolling may be 850 to 900°C. If the finish hot rolling temperature is too low, as the rolling is finished in the low temperature region, the crystal grains rapidly progress and tend to cause a decrease in rollability and workability. On the other hand, if the finish hot rolling temperature is too high, the peelability of the surface scale falls and uniform hot rolling may not be performed over the entire thickness, and thus impact toughness due to grain growth may appear. More specifically, the finish hot rolling temperature may be 860 to 890°C.
그 후, 열간 압연이 끝나 제조된 열연 강판은 권취 공정을 거친다. 보다 구체적으로, 열연 권취 공정일 수 있다.Thereafter, the hot-rolled steel sheet produced after the hot rolling is finished undergoes a winding process. More specifically, it may be a hot rolling process.
이때, 권취 온도는 640 내지 750℃가 될 수 있다. 열간 압연한 강판은 권취 전 런-아웃-테이블 (ROT, Run-out-table)에서 냉각을 행할 수 있다. 열연 권취 온도가 너무 낮으면 냉각 및 유지하는 공정에서 폭방향 온도 불균일이 발생하여 저온 석출물 생성이 달라짐에 따라 재질 편차를 유발할 뿐만 아니라 법랑성에도 악영향을 나타내었다. 반면에, 권취온도 너무 높으면 틴화물의 괴상화가 진행됨에 따라 내식성이 저하될 뿐만 아니라 최종 제품에서의 조직 조대화에 의해 가공성을 나쁘게 하는 문제점이 발생하였다. 더욱 구체적으로 권취 온도는 650 내지 710℃가 될 수 있다.At this time, the coiling temperature may be 640 to 750°C. The hot rolled steel sheet can be cooled in a run-out-table (ROT) before winding. If the temperature of the hot-rolled coil is too low, temperature fluctuations in the width direction occur in the cooling and maintaining process, and as the formation of low-temperature precipitates varies, it not only causes material deviation, but also adversely affects enamel properties. On the other hand, if the coiling temperature is too high, corrosion resistance is lowered as the bulking of the nitride proceeds, and a problem of deteriorating processability is caused by coarsening of the tissue in the final product. More specifically, the coiling temperature may be 650 to 710°C.
권취된 열연강판은 냉간 압연하기 전에 강판을 산세하는 단계를 추가로 포함할 수 있다.The wound hot-rolled steel sheet may further include a step of pickling a steel sheet before cold rolling.
그 후, 권취된 열연 강판은 냉간 압연을 통해 냉연 강판으로 제조한다.Thereafter, the wound hot-rolled steel sheet is manufactured into a cold-rolled steel sheet through cold rolling.
이때, 냉간압하율은 60 내지 90%가 될 수 있다. 냉간압하율이 너무 작을 경우에는 후속 열처리 공정에서의 재결정 구동력이 낮음에 따라 국부적으로 미재결정립이 잔존함으로써 강도는 증가하지만 가공성이 현저히 떨어지는 문제점이 있다. 또한, 열연 단계에서 형성된 탄화물의 파쇄 능력이 저하함에 따라 수소를 흡장할 수 있는 사이트가 감소하여 법랑 제품의 내피쉬스케일성 확보가 어려울 뿐만 아니라 최종 생산 제품 두께를 고려하면 열연강판의 두께를 낮추어야 하므로 압연 작업성을 나쁘게 하는 문제점도 있다. 반면에 냉간압하율이 너무 높아지면 재질이 경화되어 가공성이 악화될 뿐만 아니라 압연기의 부하가 증가하여 냉간압연 작업성을 저하시키는 문제점이 있다. 보다 구체적으로, 냉간 압하율은 65 내지 88% 일 수 있다.At this time, the cold reduction rate may be 60 to 90%. When the cold reduction rate is too small, strength is increased by locally remaining unrecrystallized grains due to low recrystallization driving force in a subsequent heat treatment process, but there is a problem in that workability is remarkably deteriorated. In addition, as the crushing capacity of the carbide formed in the hot rolling step decreases, the site capable of storing hydrogen decreases, so it is difficult to secure the fish scale resistance of the enamel product, and considering the thickness of the final product, the thickness of the hot rolled steel sheet must be lowered. There is also a problem that the rolling workability is deteriorated. On the other hand, if the cold rolling reduction ratio is too high, the material is hardened to deteriorate workability, and the load of the rolling mill is increased, thereby deteriorating the cold rolling workability. More specifically, the cold rolling reduction rate may be 65 to 88%.
그 후, 냉연 강판을 소둔 열처리할 수 있다. 보다 구체적으로, 열연 소둔 열처리할 수 있다. 냉연재는 냉간 압연에서 가해진 변형으로 인해 강도는 높지만 가공성이 극히 열위하므로, 후속 공정에서 열처리를 실시함으로써 목표로 하는 강도 및 가공성을 확보한다.Thereafter, the cold-rolled steel sheet can be subjected to annealing heat treatment. More specifically, it can be heat-annealed. The cold rolled material has a high strength due to the deformation applied in cold rolling, but the workability is extremely inferior, so that the target strength and workability are secured by performing heat treatment in a subsequent process.
이때, 열처리 온도는 700 내지 850℃일 수 있다. 연속소둔 온도가 너무 낮으면 냉간 압연에 의해 형성된 변형이 충분히 제거되지 않음에 따라 가공성이 현저히 떨어지는 문제점이 있다. 반면에 열처리 온도가 너무 높으면 고온강도 저하에 의한 연화로 판 파단이 발생하여 조업의 통판성을 크게 떨어뜨리는 문제가 발생하였다. 더욱 구체적으로 소둔 온도는 750 내지 840℃일 수 있다.At this time, the heat treatment temperature may be 700 to 850 ℃. If the continuous annealing temperature is too low, there is a problem in that workability is significantly deteriorated as deformation formed by cold rolling is not sufficiently removed. On the other hand, if the heat treatment temperature is too high, softening due to a decrease in high temperature strength causes plate fracture, which significantly reduces the mailing performance of the operation. More specifically, the annealing temperature may be 750 to 840°C.
또한, 열처리 시 열처리 유지 시간은 30초 이상일 수 있다. 열처리 시 열처리 유지 온도에서의 균열 시간이 너무 짧을 경우에도 미재결정립이 잔존하여 성형성을 크게 나쁘게 하는 요인으로 작용하므로 30초 이상의 유지 시간이 필요할 수 있다.In addition, the heat treatment holding time during heat treatment may be 30 seconds or more. Even if the cracking time at the heat treatment holding temperature during the heat treatment is too short, unrecrystallized grains remain and act as a factor that greatly deteriorates formability, so a holding time of 30 seconds or more may be required.
또한, 냉연 강판을 소둔하는 단계 이후에 열처리된 강판을 조질 압연하는 단계를 더 포함할 수 있다. 조질 압연을 통하여 소재의 형상을 제어하고 원하는 표면조도를 얻을 수 있지만 조질 압하율이 너무 높으면 가공경화에 의해 재질은 경화되고 가공성이 나빠지는 문제점이 있으므로 조질 압연은 압하율 3% 이하로 적용할 수 있다. 구체적으로 조질 압연의 압하율은 0.3 내지 2.5%일 수 있다.In addition, after the step of annealing the cold rolled steel sheet may further include a step of temper rolling the heat-treated steel sheet. Although the shape of the material can be controlled and the desired surface roughness can be obtained through temper rolling, if the temper rolling reduction is too high, the material hardens and the workability deteriorates due to work hardening, so temper rolling can be applied at a rolling reduction of 3% or less. have. Specifically, the rolling reduction of temper rolling may be 0.3 to 2.5%.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명하고자 한다. 다만, 하기의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 한정하기 위한 것이 아니라는 점에 유의할 필요가 있다. 본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의해 결정되는 것이기 때문이다.Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and reasonably inferred therefrom.
[실시예] [Example]
실험 및 평가Experiment and evaluation
표 1은 본 강들의 화학 성분을 나타낸 것이다. 잔부는 Fe 및 불가피한 불순물을 포함한다. 전로~2차정련~연주 공정을 경유한 슬래브를 1200℃의 가열로에서 1시간 동안 유지한 후 열간 압연을 실시하였다. 이때 열연 강판 최종 두께는 4.0mm로 작업하였다. 열간 압연된 시편은 산세 처리를 통해 표면의 산화 피막을 제거한 후 냉간 압연을 실시하였다. 냉간 압연이 완료된 시편은 법랑 특성을 조사하기 위한 법랑처리 시편 및 기계적 특성 분석용 인장시편으로 가공한 후 연속소둔 열처리를 실시하였다.Table 1 shows the chemical composition of the steels. The balance contains Fe and unavoidable impurities. The slab via the converter-secondary refining-casting process was maintained in a heating furnace at 1200°C for 1 hour, and then hot rolled. At this time, the final thickness of the hot rolled steel sheet was 4.0 mm. The hot-rolled specimen was cold-rolled after removing the oxide film on the surface through pickling. After the cold rolling was completed, the specimen was processed into an enameled specimen to investigate the enamel property and a tensile specimen for mechanical property analysis, followed by continuous annealing heat treatment.
표 2에 각 강들에 적용된 열간압연, 권취, 냉간압연, 연속소둔 공정의 공정별 제조 조건을 나타내었다.Table 2 shows the manufacturing conditions for each process of hot rolling, coiling, cold rolling, and continuous annealing applied to the steels.
상기와 같은 과정을 거쳐 확보된 소재의 제조 조건별 법랑 특성 등을 표 3에 표시하였다.Table 3 shows enamel properties by manufacturing conditions of the material secured through the above process.
통판성의 경우 연주~열연~냉연 공정에서 통상 소재의 생산성에 비하여 90% 이상의 조업성을 나타내면 "O", 생산성이 90% 이하이거나 결함 발생율이 10% 이상인 경우를 "X"로 표시하였다.In the case of mail order, "O" when the performance is 90% or higher compared to the productivity of a normal material in a performance-hot rolling-cold rolling process, and "X" indicates a case where the productivity is 90% or less or the defect generation rate is 10% or more.
본 발명강 및 비교강의 탄화물 분율은 광학현미경으로 500배 배율로 20 시야의 영상을 확보한 후 이를 화상분석기(Image analyzer)를 이용하여 전체 시야 면적에 대한 탄화물의 분율로 구하였다.Carbide fractions of the present invention steel and comparative steel were obtained by obtaining an image of 20 fields of view at 500 times magnification with an optical microscope, and then obtaining this as the fraction of carbide for the entire field of view using an image analyzer.
법랑 처리 시편은 시험 목적에 부응할 수 있도록 적당한 크기로 절단하였으며, 열처리가 완료된 법랑 처리용 시편은 완전히 탈지한 후 피쉬스케일 결함에 비교적 취약한 표준 유약(Check frit)을 도포하고 300℃에서 10분간 유지하여 수분을 제거하였다. 건조가 끝난 시편은 830℃에서 20분간 소성 처리를 실시한 후 상온까지 냉각하였으며, 이때 소성로의 분위기 조건은 노점온도 30℃로 피쉬 스케일 결함이 발생하기 쉬운 가혹한 조건을 택하였다. 법랑 처리가 끝난 시편은 200℃의 오븐에서 24시간 동안 유지하는 피쉬스케일 가속 실험을 실시하였다.The enameled specimen was cut to an appropriate size to meet the test purpose, and after the heat treatment was completed, the enameled specimen was completely degreased and then applied with a check frit relatively vulnerable to fish scale defects and maintained at 300°C for 10 minutes. To remove moisture. The dried specimen was subjected to a firing treatment at 830°C for 20 minutes, and then cooled to room temperature. At this time, the atmosphere condition of the firing furnace was a dew point temperature of 30°C, and harsh conditions that caused fish scale defects to occur were selected. The enamel-finished specimens were subjected to fish scale acceleration experiments maintained in an oven at 200° C. for 24 hours.
피쉬스케일 가속 처리후 피쉬스케일 결함 발생 유무를 육안으로 관찰하여, 피쉬스케일 결함이 발생하지 않은 경우에는 "O", 발생한 경우는 "X"로 표시하였다.The presence or absence of occurrence of fishscale defects after the fishscale acceleration treatment was visually observed, and was indicated as "O" when no fishscale defects occurred and "X" when it occurred.
강판과 유약간의 밀착성을 평가한 법랑밀착성 지수는 미국 재료시험협회규격, ASTM C313-78에 정의된 바와 같이 강구로 법랑층에 일정 하중을 가한 후 이 부위의 통전 정도를 평가함으로써 법랑 유약층의 탈락 정도를 지수화하여 나타내었다. 본 발명에서 밀착성 지수의 경우 법랑층의 사용중 안정성 확보 측면에서 90% 이상 확보를 목표로 설정하였다.The enamel adhesion index, which evaluated the adhesion between the steel sheet and the glaze, was determined by applying a certain load to the enamel layer with a steel ball as defined in the American Society for Testing and Materials, ASTM C313-78, and then evaluating the degree of energization of the enamel layer. The degree of dropout was indicated by indexing. In the case of the adhesiveness index in the present invention, the goal was to secure at least 90% in terms of securing stability during use of the enamel layer.
기포 결함은 법랑 처리후 200℃의 오븐에서 24시간 동안 유지한 시편에 대하여 법랑층 표면을 육안으로 관찰하여, 각각 "O" 우수, "△" 보통, "X" 불량의 3단계로 판정하였다.Bubble defects were determined by three stages of "O" excellent, "Δ" normal, and "X" defective, respectively, by visually observing the surface of the enamel layer for a specimen kept in an oven at 200°C for 24 hours after the enamel treatment.
수소투과비는 법랑강의 치명적인 결함인 피쉬스케일에 대한 저항성을 평가하는 지수로써, 유럽 규격, EN 10209 (2013)에 등록된 방법에 따라 강판의 한 방향에서 수소를 발생시키면서 강판의 반대 편으로 수소가 투과해 나오는 시간 (ts, 단위 초)을 측정하여, 이를 소재 두께 (t, 단위 mm) 제곱으로 나누어 표시한 값으로, ts/t2 (단위 초/mm2)로 나타낸다. 이 값의 경우에는 앞서 설명한 바와 같이 법랑강의 안정적인 특성을 얻기 위해서 950 초/mm2 이상 확보가 필요하였다.The hydrogen permeation ratio is an index for evaluating the resistance to fish scale, a fatal defect of enamel steel, and generates hydrogen in one direction of the steel sheet according to the method registered in the European standard, EN 10209 (2013). The time (t s , unit seconds) that is transmitted, is measured and divided by the square of the material thickness (t, unit mm), expressed as t s /t 2 (unit seconds/mm 2 ). In this case, as described above, it was necessary to secure at least 950 seconds/mm 2 to obtain stable properties of the enamel steel.
산세감량 (단위 gr/m2)은 유럽 규격, EN 10209 (2013)에 나타난 실험 방법으로 법랑용 강판을 절단 및 탈지한 후 70g/l, 70℃로 유지된 황산 용액에 7분 정도 침적하여 시편의 무게 감량으로부터 구하였다. 이 값의 경우에도 10 내지 40 gr/m2의 범위를 만족하는 것이 필요하였다.The pickling loss (unit gr/m 2 ) is the test method shown in European standard, EN 10209 (2013), and after cutting and degreasing the steel sheet for enamel, it is immersed in a sulfuric acid solution maintained at 70g/l, 70℃ for about 7 minutes. It was obtained from the weight loss. Even in this case, it was necessary to satisfy the range of 10 to 40 gr/m 2 .
여기에서,From here,
D = ([Mn] x [Cu] / [S]) x (Dvoid / [C])D = ([Mn] x [Cu] / [S]) x (D void / [C])
A = ([Mn] x [Cu] x Dcementite}) / [Si]A = ([Mn] x [Cu] x D cementite} ) / [Si]
F = ([Al]/[N]) x (Dcementite/[C]) 으로 정의 되며,It is defined as F = ([Al]/[N]) x (D cementite /[C]),
[Mn]은 Mn의 중량%를 Mn의 원자량(55)으로 나눈 값이고,[Mn] is the value obtained by dividing the weight percent of Mn by the atomic weight of Mn (55),
[Cu]는 Cu의 중량%를 Cu의 원자량(64)으로 나눈 값이고,[Cu] is the value obtained by dividing the weight percent of Cu by the atomic weight of Cu (64),
[S]는 S의 중량%를 S의 원자량(32)으로 나눈 값이고,[S] is the weight% of S divided by the atomic weight of S (32),
[C]는 C의 중량%를 C의 원자량(12)으로 나눈 값이고,[C] is the weight% of C divided by the atomic weight of C (12),
[Si]는 Si의 중량%를 Si의 원자량(28)으로 나눈 값이고,[Si] is the weight% of Si divided by the atomic weight of Si (28),
[Al]은 Al의 중량%를 Al의 원자량(27)으로 나눈 값이고,[Al] is the value obtained by dividing the weight percent of Al by the atomic weight of Al (27),
[N]은 N의 중량%를 N의 원자량(14)으로 나눈 값이다.[N] is the value obtained by dividing the weight percent of N by the atomic weight of N (14).
또한, Dvoid는 냉연 강판에서의 미세 공공의 면적 분율(%)이며,In addition, D void is an area fraction (%) of micropores in a cold rolled steel sheet,
Dcementite는 열연 강판의 탄화물 체적 분율(%)이다.D cementite is the carbide volume fraction (%) of the hot rolled steel sheet.
실험 결과 Experiment result
상기 표 1 내지 표 3을 통해 알 수 있듯이, 합금조성, 미세 조직 특성 및 제조 조건을 모두 만족하는 발명예 1 내지 9는 통판성이 양호할 뿐만 아니라, 탄화물 및 미세공공 분율과 연관 지수들이 본 발명의 한정 범위를 만족하였으며, 가혹한 처리 조건에서도 피쉬스케일 및 기포 결함이 발생하지 않았을 뿐만 아니라 법랑밀착성 지수 90% 이상, 수소투과비 950초/mm2 이상, 산세 감량 10 내지 40gr/m2 범위를 만족하여 본 발명이 목표로 하는 특성을 확보할 수 있었다.As can be seen from Tables 1 to 3, Inventive Examples 1 to 9 satisfying both alloy composition, microstructure properties, and manufacturing conditions have good mailing properties, and carbides and micropore fractions and associated indices are used in the present invention. Satisfies the limited range of, and not only did fish scale and bubble defects occur under severe processing conditions, but also satisfied the enamel adhesion index of 90% or more, hydrogen permeation ratio of 950 seconds/mm 2 or more, and pickling loss of 10 to 40gr/m 2 Thus, it was possible to secure the properties targeted by the present invention.
반면에 본 발명에서 제시하는 화학 조성은 만족하였으나, 제조조건 범위를 만족하지 못한 경우인 비교예 1 내지 4는 목표 특성을 확보할 수 없음을 알 수 있다. 즉 표 3에서 보는 바와 같이 통판성이 나빠지는 (비교예 1, 3 및 4) 문제점이 있었으며, 수소투과비가 목표 대비 낮거나 (비교예 1 내지 4), 법랑밀착성 지수가 90% 미만이거나 (비교예 1 내지 4), 법랑 처리후 기포 결함 또는 피쉬스케일 결함이 발생하는 것을 확인할 수 있어 전체적으로 목표로 하는 특성을 확보할 수 없었다.On the other hand, although the chemical composition suggested in the present invention was satisfactory, it was found that Comparative Examples 1 to 4, which did not satisfy the range of manufacturing conditions, could not secure the target characteristics. That is, as shown in Table 3, there was a problem in that mailability was poor (Comparative Examples 1, 3 and 4), and the hydrogen permeation ratio was lower than the target (Comparative Examples 1 to 4), or the enamel adhesion index was less than 90% (Comparative). In Examples 1 to 4), it was confirmed that a bubble defect or a fish scale defect occurred after the enamel treatment, so that the targeted properties could not be secured overall.
비교예 5 내지 8은 본 발명에서 제시한 제조 조건은 만족하였으나 합금 조성을 만족하지 못한 경우이다. 비교예 5 내지 8은 대부분 본 발명의 목표 탄화물 및 미세 공공 분율, 수소투과비, 법랑밀착성 지수, 산세감량 등을 만족하지 못하였을 뿐만 아니라 법랑 처리후 육안 관찰에서도 피쉬스케일 및 기포 결함이 발생하였다.Comparative Examples 5 to 8 are the cases in which the manufacturing conditions suggested in the present invention were satisfied but the alloy composition was not satisfied. In Comparative Examples 5 to 8, most of the target carbides and micropore fractions of the present invention, hydrogen permeability ratio, enamel adhesion index, pickling loss, etc. were not satisfied, and fish scale and bubble defects also occurred in visual observation after enamel treatment.
본 발명은 상기 실시예들에 한정되는 것이 아니라 서로 다른 다양한 형태로 제조될 수 있으며, 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자는 본 발명의 기술적 사상이나 필수적인 특징을 변경하지 않고서 다른 구체적인 형태로 실시될 수 있다는 것을 이해할 수 있을 것이다. 그러므로 이상에서 기술한 실시예들은 모든 면에서 예시적인 것이며 한정적이 아닌 것으로 이해해야만 한다.The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and those skilled in the art to which the present invention pertains have other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that can be carried out. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.
Claims (11)
- 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함하고,In weight percent, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% Below (excluding 0%), the balance includes Fe and unavoidable impurities,미세 공공 면적 분율이 0.3 내지 0.8%이고,The micropore area fraction is 0.3-0.8%,하기 [관계식 1]로 표현되는 법랑결함 관계지수(D)가 0.45 내지 4.50을 만족하는 법랑용 냉연 강판.Cold-rolled steel sheet for enamel that satisfies the enamel defect relationship index (D) represented by the following [Relational Formula 1], which satisfies 0.45 to 4.50.[관계식 1][Relationship 1](상기 관계식 1에서, [Mn], [Cu], [S], [C]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dvoid는 냉연 강판에서의 미세 공공의 면적 분율(%)을 나타낸다.)(In the above equation 1, [Mn], [Cu], [S], [C] is the value by dividing the weight percent of each element by the atomic weight of each element, D void is the area fraction of micro-pore in the cold rolled steel sheet ( %).)
- 제1항에 있어서,According to claim 1,P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함), 중 1종 이상을 더 포함하는 법랑용 냉연 강판.P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%), cold rolled steel sheet for enamels further comprising one or more of.
- 제1항에 있어서,According to claim 1,상기 냉연 강판의 산세 감량이 10 내지 40 gr/m2인 법랑용 냉연 강판.The cold rolled steel sheet for enameling, wherein the pickling loss of the cold rolled steel sheet is 10 to 40 gr/m 2 .
- 제1항에 있어서,According to claim 1,상기 냉연 강판의 수소투과비가 950 초/mm2 이상인 법랑용 냉연 강판.The cold rolled steel sheet for enameling, wherein the cold rolled steel sheet has a hydrogen permeability ratio of 950 seconds/mm 2 or more.
- 중량%로, C: 0.05 내지 0.09%, Mn: 0.1 내지 0.3%, Si: 0.001 내지 0.03%, Al: 0.01 내지 0.08%, S: 0.001 내지 0.02%, Cu: 0.01 내지 0.15%, N: 0.005% 이하(0%를 제외함), 잔부 Fe 및 불가피한 불순물을 포함하는 슬라브를 준비하는 단계;In weight percent, C: 0.05 to 0.09%, Mn: 0.1 to 0.3%, Si: 0.001 to 0.03%, Al: 0.01 to 0.08%, S: 0.001 to 0.02%, Cu: 0.01 to 0.15%, N: 0.005% Hereinafter (excluding 0%), preparing a slab containing the residual Fe and unavoidable impurities;상기 슬라브를 가열하는 단계;Heating the slab;상기 가열된 슬라브를 열간압연하여 탄화물 체적 분율이 2.5 내지 7.0%인 열연강판을 제조하는 단계;Hot-rolling the heated slab to produce a hot-rolled steel sheet having a carbide volume fraction of 2.5 to 7.0%;상기 열연 강판을 권취하는 단계;Winding the hot rolled steel sheet;상기 권취된 열연 강판을 압하율 60 내지 90%로 냉간압연하여 냉연강판을 제조하는 단계; 및Cold-rolling the wound hot-rolled steel sheet at a reduction ratio of 60 to 90% to produce a cold-rolled steel sheet; And상기 냉연 강판을 소둔 열처리하는 단계;Annealing the cold-rolled steel sheet;를 포함하고,Including,하기 [관계식 2]로 표현되는 밀착성 관계지수(A)가 0.007 내지 0.185을 만족하는 법랑용 냉연 강판의 제조 방법.A method of manufacturing a cold-rolled steel sheet for enamel that satisfies 0.007 to 0.185 of the adhesion relationship index (A) represented by the following [Relational Formula 2].[관계식 2][Relationship 2](상기 관계식 2에서, [Mn], [Cu] 및 [Si]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dcementite는 열연 강판의 탄화물 체적 분율(%)을 나타낸다.)(In the relational expression 2, [Mn], [Cu], and [Si] are values obtained by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.)
- 제5항에 있어서,The method of claim 5,하기 [관계식 3]으로 표현되는 가공성 관계지수(F)가 3500 내지 7000을 만족하는 법랑용 냉연 강판의 제조 방법.Method of manufacturing a cold-rolled steel sheet for enamel satisfying a workability relationship index (F) expressed by the following [Relational Formula 3] meets 3500 to 7000.[관계식 3][Relationship 3](상기 관계식 3에서, [Al], [N] 및 [C]는 각 원소들의 중량%를 각 원소들의 원자량으로 나눈 값이며, Dcementite는 열연 강판의 탄화물 체적 분율(%)을 나타낸다.)(In the relational expression 3, [Al], [N], and [C] are the values by dividing the weight percent of each element by the atomic weight of each element, and D cementite represents the carbide volume fraction (%) of the hot rolled steel sheet.)
- 제5항에 있어서,The method of claim 5,상기 슬라브는 P: 0.002 내지 0.02%, O: 0.002% 이하(0%를 제외함) 및 Ti: 0.001% 이하(0%를 제외함) 중 1종 이상을 더 포함하는 것인 법랑용 냉연 강판의 제조 방법.The slab of P: 0.002 to 0.02%, O: 0.002% or less (excluding 0%) and Ti: 0.001% or less (excluding 0%) further comprising one or more of the cold rolled steel sheet for enamel Manufacturing method.
- 제5항에 있어서,The method of claim 5,상기 열연 강판을 제조하는 단계;에서,In the step of manufacturing the hot-rolled steel sheet; In,상기 가열된 슬라브를 압연온도 850℃ 내지 900℃에서 열간 압연하는 법랑용 냉연 강판의 제조 방법.Method of manufacturing a cold-rolled steel sheet for enamel hot rolling the heated slab at a rolling temperature of 850 ℃ to 900 ℃.
- 제5항에 있어서,The method of claim 5,상기 열연 강판을 권취하는 단계;에서,In the step of winding the hot-rolled steel sheet; In,상기 열연 강판을 640℃ 내지 750℃에서 권취하는 법랑용 냉연 강판의 제조 방법.Method of manufacturing a cold-rolled steel sheet for enamel winding the hot-rolled steel sheet at 640 ℃ to 750 ℃.
- 제5항에 있어서,The method of claim 5,상기 냉연 강판을 소둔 열처리하는 단계;에서,In the annealing heat treatment of the cold-rolled steel sheet; In,상기 냉연 강판을 700℃ 내지 850℃에서 소둔 열처리하는 법랑용 냉연 강판의 제조 방법.A method of manufacturing a cold-rolled steel sheet for enameling, wherein the cold-rolled steel sheet is annealed at 700°C to 850°C.
- 제5항에 있어서,The method of claim 5,상기 냉연 강판을 소둔 열처리하는 단계;에서,In the annealing heat treatment of the cold rolled steel sheet; In,상기 냉연 강판을 30초 이상 유지하는 법랑용 냉연 강판의 제조 방법.Method of manufacturing a cold-rolled steel sheet for enamel to hold the cold-rolled steel sheet for 30 seconds or more.
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