KR19980052509A - Method for manufacturing a low-carbon cold-rolled steel sheet for vacuum deposition plating in which changes in material after plating are suppressed - Google Patents

Abstract

The present invention relates to a method for manufacturing a cold-rolled steel sheet for vacuum metallization plating, and its object is to provide a method of manufacturing a cold-rolled steel sheet for vacuum metallization by suppressing changes in material and exhibiting strength and elongation similar to those before plating, And a method for manufacturing a cold-rolled steel sheet.

According to an aspect of the present invention, there is provided a method of manufacturing a cold-rolled steel sheet for vacuum metallization comprising the steps of: C: 0.018-0.030%; Mn: 0.20-0.45%; S: 0.015-0.020% Or less of Si, 0.01% or less of Al, 0.05% or less of Al, 0.0030-0.0040% of B, 0.002% or less of N and the value of B / N of 1.5-2.0, The aluminum killed steel made of the impurities is homogenized at a temperature range of 1100-1250 캜, the hot rolling is finished in the temperature range of 900-950 캜, and the hot rolling is carried out at a temperature range of 720-750 캜, After cold rolling in a rolling reduction range, the carbonization is dulled at a recrystallization temperature range of 640 to 680 DEG C at which the carbide is not completely re-dissolved, and thereafter, rough rolling to a reduction ratio of 0.5% or less is suppressed The present invention relates to a method of manufacturing a low-carbon cold-rolled steel sheet for vacuum vapor deposition plating.

Description

Method for manufacturing a low-carbon cold-rolled steel sheet for vacuum deposition plating in which changes in material after plating are suppressed

More particularly, the present invention relates to a method for manufacturing a cold-rolled steel sheet for vacuum deposition, and more particularly, to a method for manufacturing a cold- To a method of manufacturing a cold-rolled steel sheet,

Plating using the conventional cold-rolled steel sheet is mostly accomplished by electroplating or hot-dip coating. In the electroplating process, there is almost no change in the material of the steel sheet because the temperature does not increase and it is carried out at room temperature. Further, in the case of hot-dip coating, the cold-rolled sheet which is not subjected to recrystallization treatment is used to pass hot-dip metal, and the base steel sheet is annealed simultaneously with the plating.

Since such an electric and hot-dip coating technology is difficult to obtain a large and uniform plating layer, it is difficult to obtain a plating layer having excellent properties such as plating layer characteristics, diversification of plating materials, simplification of equipment, and vacuum deposition plating Technology has recently been developed, and has been attracting attention as a next generation technology.

However, since the material is heated to a high temperature of 500 ° C or higher in the vacuum evaporation plating method, the material changes and deteriorates.

Accordingly, in order to apply such new technology, it is urgently required to develop a cold-rolled steel sheet capable of suppressing changes in materials due to high-temperature heating.

On the other hand, in the laboratory examination for applying the vacuum deposition plating technique, such a material change problem was not understood. This is due to the nature of the laboratory equipment, which is immediately collineated after the vacuum deposition plating and the vacuum deposited plated steel has cooled very slowly. That is, due to the very slow cooling rate, the solid carbon in the steel precipitated as carbide sufficiently, and the material did not change. However, in the actual commercialized equipment, in order to reduce the cost, the length of the line was reduced and the cooling in the vacuum atmosphere was required to prevent the oxidation of the plating layer. As shown in FIG.

In the vacuum deposition system as shown in FIG. 1, the steel sheet 1 is rapidly preheated by the electron beam in order to facilitate the vacuum deposition plating. In this case, the heating rate is 400 seconds in 0.2 seconds as shown in FIG. 2, ° C. If the temperature of the steel sheet is not high due to the preliminary heating, the temperature difference between the plating material and the base material is too large to obtain a good vacuum vapor deposition plating layer. The hot-rolled steel sheet thus heated passes through two vacuum vapor deposition platings 2 and 3 for plating the upper surface and the lower surface, respectively. The crucible 5 containing copper, zinc, and aluminum heated by the electron beam 4 is melted (2, 3).

At this time, since the vacuum deposition platens 2 and 3 are maintained in a vacuum atmosphere, the molten material for plating, such as copper, zinc and aluminum, is evaporated (6) by the vapor pressure, and the metal vapor (6) (Deposited) on the preheated cold-rolled steel sheet 1 passing over the crucible 5 inside.

This process is the core of the vacuum deposition plating technology, and when the vapor of the plating material again contacts the cold rolled steel sheet, it changes into a liquid phase and a solid phase, and latent heat is generated in this process. As shown in FIG. 2, 540 < 0 > C. The cold-rolled steel sheet plated in the vacuum evaporation plating furnace is immediately quenched and cooled at a high rate of -13.3 ° C / sec.

The material deterioration due to the temperature rise and rapid cooling in the vacuum deposition process can be roughly classified into two types: increase in strength and decrease in elongation. In general, the cold-rolled steel sheet for electroplating has a strength of about 10 kgf / mm ² , Lt; / RTI >

Such material changes are basically caused by difficulty in dissolving the carbide due to high temperature heating and precipitation of carbide due to rapid heating. In other words, if the re-dissolved carbide precipitates again as a carbide, the material does not change. In this vacuum deposition plating, since the rapid cooling is performed, the carbide material precipitation time is not ensured and therefore a large amount of solid carbon exists in the cold- do. FIG. 3 shows the results of measurement of the size and distribution of the carbonization inside the cold-rolled steel sheet before and after the plating, and shows that the carbonized material after plating has been partially reused in the vacuum deposition process. The carbon solidified as described above causes deformation aging of the cold-rolled steel sheet as well known, which is generated by the interaction between the solid carbon and the dislocation, resulting in an increase in strength and a decrease in elongation.

Generally, as shown in FIG. 4, when the strength is increased by the deformation aging after plating and the elongation is decreased, the material can not be used for processing.

The reason for this is that the increase in the strength causes wear of the machined metal mold or difficulty in machining into a desired shape. Further, if the elongation rate is lowered, the plated steel sheet can not accommodate sufficient deformation during the molding process, Because.

The above reason can be more clearly understood from the amount of elastic recovery that occurs in the bending process shown in the following formula. The larger the amount of elastic recovery shown in the following equation becomes, the more difficult it is to obtain a desired shape.

Elastic recovery amount =

Where σ _s is the strength of the steel plate, R is the bending angle, t is the thickness of the material, and E is the modulus of elasticity of the material. In this equation, R, t, and E are constant values that are fixed when the material and the product are determined. Therefore, it is σ _s, that is, the strength of the steel sheet, which determines the success or failure of the processing after plating.

Therefore, suppressing changes in strength and elongation after plating is a major demand characteristic of the cold-rolled steel sheet for vacuum evaporation copper plating, and it is necessary to develop a new cold-rolled steel sheet to meet new plating techniques.

Normally, carbon is the most important element for determining the strength in a steel sheet. Carbon steel is classified into high carbon steel, medium carbon steel, low carbon steel, and ultra low carbon steel because of its high carbon content. Low carbon steel is used for steel plate production. . Carbon in steel is present in the form of Fe ₃ C compound carbide, ie carbide form and atomic solid carbon (C), and the amount of solid carbon increases with increasing temperature. As a result, when the temperature is higher than 300 ° C in a conventional low-carbon cold-rolled steel sheet, deformation aging due to the solid carbon is severely generated. Considering the 540 ° C temperature at which the cold- rolled steel sheet is actually plated, the yield strength is about 7-10 kgf / mm ² is raised level.

This phenomenon can be seen from the aging index before and after plating shown in FIG. The aging index is a value calculated from the difference in yield strength before and after the heat treatment at 100 ° C for 60 minutes. The aging index is directly proportional to the amount of solid carbon in the steel. As shown in FIG. 5, it can be seen that a very large amount of solid carbon is present after the vacuum deposition plating.

As the temperature increases during the plating process, the redeposition of the carbides becomes easier, which causes many problems in the forming and secondary processing of the vacuum vapor-deposited coated steel sheet due to the increase of the yield strength and the lowering of the elongation.

Accordingly, the present inventor has conducted metal metallurgical research and experiments to solve the problem caused by deformation aging occurring in a conventional low carbon steel sheet in a conventional low carbon steel sheet, and has proposed the present invention based on the results. (Mn), carbon (C), boron (B), and addition ratio of aluminum killed steel as a basic component and control each process variable during hot rolling, annealing and temper rolling, The present invention aims to provide a method for manufacturing a cold-rolled steel sheet for pipes having a small change in material before and after vacuum deposition by suppressing the dissolution of carbonitride and reducing the amount of carbon dissolved again, that is, have.

1 is a schematic view of a vacuum vapor deposition

FIG. 2 is a graph showing the temperature history during vacuum deposition

3 is a graph showing the distribution of carbides before and after plating

4 is a graph showing changes in material before and after plating

5 is a graph showing changes in aging index before and after plating

6 is a graph showing changes in strength before and after the plating heat treatment of the comparative steel and the invention steel

7 shows a photograph showing the carbide distribution according to the coiling temperature

8 is a graph showing the change in strength with the reduction rate

Description of the Related Art [0002]

1: Cold rolled steel plate 2: # 1 deposition furnace

3: # 2 deposition furnace 4: electron beam

5: Crucible 6: Plating solution steam

According to an aspect of the present invention, there is provided a method of manufacturing a cold-rolled steel sheet for vacuum metallization comprising the steps of: C: 0.018-0.030%; Mn: 0.20-0.45%; S: 0.015-0.020% Or less of Si, 0.01% or less of Al, 0.05% or less of Al, 0.0030-0.0040% of B, 0.002% or less of N and the value of B / N of 1.5-2.0, The aluminum killed steel made of the impurities is homogenized at a temperature range of 1100-1250 캜, the hot rolling is finished in the temperature range of 900-950 캜, and the hot rolling is carried out at a temperature range of 720-750 캜, After cold rolling in a rolling reduction range, the carbonization is dulled at a recrystallization temperature range of 640 to 680 DEG C at which the carbide is not completely re-dissolved, and thereafter, rough rolling to a reduction ratio of 0.5% or less is suppressed To a method for manufacturing a low-carbon cold-rolled steel sheet for vacuum vapor deposition plating.

Hereinafter, the present invention will be described in detail.

In order to achieve the above object, it is preferable to select aluminum-killed steel satisfying the above-mentioned composition range in the present invention, for the following reasons.

When the amount of carbon (C) is 0.03% or more, the solid carbon in the steel tends to remain, and the carbon content in the vicinity of 0.015% is a carbon amount that changes the properties of the steel very sensitively. It is very hard to avoid this range. In particular, when the amount of carbon is 0.05% or more, the strength is excessively increased or excessive carbide is generated, which causes deterioration of the molding. Therefore, the addition range of carbon is preferably 0.018-0.03%.

The manganese (Mn) is generally added in an amount of 0.05% or more to prevent embrittlement of embrittlement due to sulfur, and sulfur compounds such as MnS are formed to fix the sulfur. In addition to these functions, such a sulfur compound has a function of facilitating the formation of carbide such as Fe ₃ C, that is, a function of providing a nucleation site where a carbide is likely to be formed. Therefore, the sulfur compound is added to the range of 0.20 to 0.45% .

Sulfur (S) is an element that is inevitably entered into the steel during its manufacture, and is an element that causes red brittleness generated in the steel making process. Sulfur was limited to a range of 0.015-0.020% to a degree suitable for the manganese of the composition range set in the present invention to appropriately form sulfur compounds and facilitate carbide formation.

A sufficient amount of manganese (Mn) was added so that the ratio of Mn / S was 10-30 as compared with that of sulfur (S), so that harmful sulfur (S) was produced as MnS.

Since phosphorus (P) and silicon (Si) are elements that cause solid solution strengthening, it is preferable that the phosphorus (P) and silicon (Si) are limited to not more than 0.20% and not more than 0.01% so as to be able to control the strength by carbon of the present invention.

In the case of aluminum (Al), it is added for deoxidation of steel. When the amount of solid solution aluminum is increased, the workability of steel is lowered.

The boron (B) generates nitrogen (N) in the steel as an interstitial element and a BN-type compound during the hot rolling process. Nitrogen in the steel is small and it is easy to cause diffusion even at a small temperature increase, which means that material degradation due to strain aging is well caused. It is required to allow nitrogen to be present in the form of a compound in the form of a solid without solidifying it in the steel because it exhibits strain aging characteristics much larger than that of normally employed carbon. Therefore, the B / N ratio is specified to be 1.5 or more so as to add equal to or more than the nitrogen content of boron (N), which is a strong nitrogen compound, and this is also effective to compensate for a slight decrease in strength, which is limited to a carbon content of 0.03% . When the amount of boron is too large, the boron hardening effect is too large. Therefore, the B / N ratio is regulated to 2.0 or less so as to have an appropriate strength strengthening effect. This B / N ratio is one of the requirements for the manufacture of low carbon cold-rolled steel sheets that require strength but require no change in material before and after plating.

In the case of nitrogen (N), as described above, since the aging effect is very large, its inhibition is required and is limited to 0.002 or less.

In the present invention, it is indispensable to prepare cold-rolled steel sheets of the present invention by hot-rolling and cold-rolling so as to satisfy the following composition conditions after forming aluminum-killed steel to satisfy the composition ranges as described above. Respectively.

It is preferable to homogenize the steel in the temperature range of 1100-1250 占 폚 in order to set the internal structure of the steel to the initial state and form the sulfur compound.

The homogenized specimen as described above is subjected to hot rolling at a temperature range of 900-950 ° C, which facilitates hot rolling, and coarse carbide is formed by hot rolling at a temperature range of 720-750 ° C. The higher the coiling temperature, the easier the movement of the solid carbon in the steel and the longer the time to precipitate as a carbide, the larger the size and amount of carbide, and the smaller the amount of solid carbon. Also, coarse carbide is effective in suppressing the material change because the redeposition is difficult compared to the fine carbide during the vacuum deposition plating process with rapid heating and rapid cooling process.

The hot rolled steel sheet thus rolled is preferably cold-rolled in a rolling reduction range of 65 to 70% in order to suppress fine dispersion of coarse carbides at a large reduction ratio. If the reduction rate is 70% or more, the coarse carbide produced at the time of high temperature winding is finely dispersed, and the redeposition is very easy when the vacuum vapor deposition is performed. Also, when the reduction rate is increased, the sticking phenomenon of the steel plate and the steel plate is easily generated. Therefore, the upper limit of reduction of 70% is determined. The currently used cold-rolled steel sheet for vacuum vapor deposition plating has a reduction ratio of 80% or more, which is a condition that does not secure suppression of material change after plating. In addition to the above-described carbide distribution according to the cold rolling rate, crystal grains after steel sheet annealing vary greatly. As the reduction rate is increased, the grain size becomes smaller and the strength is increased. Therefore, the optimum reduction rate should be determined to determine the strength of the desired steel sheet.

The cold-rolled steel sheet at the reduction ratio in the above-described range is subjected to recrystallization annealing through the hot rolling. When continuous annealing is used, the crystal grains become too fine due to rapid heating and cooling process, and sufficient amount of carbide is not precipitated so that the amount of solid carbon is increased. Therefore, recrystallization annealing in an annealing method is indispensable. In general, the cold rolled steel sheet produced by the hot rolling method is wound at a low temperature around 540 DEG C in order to ensure processability. In the present invention, however, even if the hot rolling is newly applied and the temperature is set, So as to be suitable for the purpose of the cold-rolled steel sheet as a negative sign. At this time, the recrystallization annealing is preferably performed at a low temperature at which the carbide obtained through the high-temperature winding is not completely re-dissolved, that is, within the recrystallization temperature range of 640-680 캜.

Since the temper rolling performed after the recrystallization annealing treatment as described above generates a large amount of dislocations in the steel, it becomes a step of further facilitating generation of deformation aging due to the action of dislocations and solid carbon in accordance with the temperature rise during the plating process. Therefore, it is advantageous to manufacture cold-rolled steel sheets for vacuum plating without possible temper rolling, but it is preferable to perform temper rolling with a rolling reduction of 0.5% or less in order to secure a final shape.

Hereinafter, the present invention will be described more specifically by way of examples.

[Example]

The steel slabs prepared so as to satisfy the composition shown in the following Table 1 were held in a heating furnace at 1200 DEG C for 1 or 2 hours and then subjected to hot rolling. At this time, the hot rolling finishing temperature was changed to 920 ° C and the coiling temperature was changed to 500-730 ° C.

The hot-rolled steel sheet after the hot-rolling as described above was cold-rolled at a reduction ratio in the range of 30-85%, and subjected to cold rolling at 670 ° C. Cold rolled steel sheets having been subjected to tempering were subjected to temper rolling at a rate of 0.5-1.0% to prepare cold rolled steel sheets.

The cold-rolled steel sheet thus prepared was subjected to heat treatment at a furnace temperature of 540 ° C for 20 seconds and then subjected to a tensile test to measure the generation of strain aging, to determine the yield strength increase and the elongation change, Is shown in FIG.

[Table 1]

* Hot rolling condition

Homogenization treatment: 1200 占 폚, hot rolling finishing temperature: 920 占 폚, annealing temperature 670 占 폚

As shown in Tables 1 and 6, the steel of the present invention has a yield strength of 21-22 kgf / mm ² , and no significant material change occurred after the vacuum deposition plating heat treatment process. The increase in yield strength after vacuum deposition plating heat treatment was less than ² kgf / mm ² and the decrease in elongation was less than 4%. This intensity is almost equivalent to the level of the base material and relies on the effect that the carbon present in the steel is distributed in the form of coarse carbide and the nitrogen is completely precipitated through the proper B / N ratio.

In the case of the comparative steel (1), the coiling temperature of about 640 캜 and the steel subjected to 1% temper rolling were overlapped with the potential increasing effect by temper rolling, and the yield strength was increased to about 10 kgf / mm ² after the plating heat treatment It was not possible to expect a good quality of the coated steel sheet after the vacuum deposition plating.

In Comparative robust Steel No. 2 has a low temperature when the take-up consists of the yield strength of the lecture was 32.8kgf / mm ² according to the yield strength increase of about 7.8kgf / mm ^2. Further comparison exhibited a robust Steel No. 3, the yield strength of 34.5kgf / mm ² according to the increased take-up by the low temperature and the temper rolling reduction of 1.6% of the 540 ℃ also plated after heat-treated to yield 9.9kgf / mm ² strength when lectures . In addition, in the case of the comparative strength steel number (4), there is no solid nitrogen due to the formation of B / N compound, and yield strength can be increased compared with other comparative steels. However, ² , respectively.

On the other hand, in FIG. 7, the carbide distribution of Comparative Steel 3 (FIG. 7 (b)) obtained by winding at 730 ° C. at a high temperature is shown in FIG. 7 (a) Respectively. Coarse carbide was clearly observed in the high temperature coiling temperature zone where the inventive steel was operated.

The strength change according to the reduction ratio of the steel is shown in FIG. 8. As the reduction rate increases, the strength increases, and this relationship changes almost linearly. If the reduction rate is too high, the strength increases too much. If the reduction rate is too low, it shows low strength. Therefore, to obtain adequate cold-rolled steel strength, a range of 65-70% pressure is preferable. And the desired grain size can be obtained to obtain the desired strength.

As described above, according to the present invention, an aluminum-killed low-carbon steel is used as a material and sulfur, carbon and manganese are appropriately controlled and added, and hot rolling conditions, cold rolling rate, tempering temperature and temper rolling reduction ratio are appropriately set A low carbon cold-rolled steel sheet which can suppress deformation aging by appropriately controlling the distribution and size of carbide (Fe ₃ C) and which is fixed by boron added so as to satisfy an appropriate B / N ratio, And the steel sheet provided has a useful effect that can be applied to a plating method of heat treatment at a high temperature such as a vacuum deposition plating method.

Claims (1)

A method of manufacturing a cold-rolled steel sheet for vacuum vapor deposition, comprising the steps of: C: 0.018-0.030%, Mn: 0.20-0.45%, S: 0.015-0.020%, P: 0.02% : 0.05% or less, B: 0.0030-0.0040%, N: 0.002% or less, the value of B / N satisfying the range of 1.5-2.0, and the balance of Fe and other inevitably contained impurities, 1250 캜, hot rolled in a temperature range of 900-950 캜, rolled in a temperature range of 720 - 750 캜, cold-rolled in a rolling reduction range of 65-70% Wherein the substrate is subjected to rough rolling in a recrystallization temperature range of 640 to 680 DEG C which is not fully re-dissolved, and thereafter rough-rolling to a reduction ratio of 0.5% or less. A method for manufacturing a cold rolled steel sheet.