KR100435463B1 - A method for manufacturing high strength ultra thin surface treatment blackplate with high corrosion resistant property - Google Patents

Abstract

The present invention relates to a method for manufacturing a highly processed ultra-thin surface treatment disc, and has a high-strength ultra-thin surface treatment disc excellent in corrosion resistance, having not only a roughness T5 to T6 and elongation of 25% or more, but also hardly occurring after drawing and fracturing cracks. The purpose is to manufacture with higher productivity.

The present invention provides a method for producing an ultrathin surface treated disc,

By weight percentage, C: 0.04 ~ 0.07%, Mn: 0.4 ~ 0.6%, N: 0.006 ~ 0.012%, hot rolled low-carbon aluminum-kilted steel composed of balance Fe and other unavoidable impurities and wound at a temperature below 600 ° C. Next, pickling and cold rolling at a reduction ratio of 84 to 87%, followed by continuous annealing at a temperature range of recrystallization temperature to 650 ° C., and temper rolling at a reduction ratio of 5 to 10% to prepare a high-strength ultra-thin surface treatment disc having excellent corrosion resistance. A method is made into the technical summary.

Description

Method for manufacturing high strength ultra-thin surface treatment disc with excellent corrosion resistance {A METHOD FOR MANUFACTURING HIGH STRENGTH ULTRA THIN SURFACE TREATMENT BLACKPLATE WITH HIGH CORROSION RESISTANT PROPERTY}

The present invention relates to a method for manufacturing a high processing type high strength ultra-thin surface treatment disc applied to light processing cans and food pipes, and more particularly, by performing an annealing process and a temper rolling process appropriately, a high-strength ultra-thin surface treatment disc excellent in corrosion resistance can be obtained. It relates to a method that can be produced with high productivity.

In general, hard surface treatment discs are those of the T4 ~ T6 quality, the Rockwell surface hardness of 30T value satisfies the material of 61 ± 3 ~ 70 ± 3, the elongation is to prevent cracking in the flange processing It should be at least 25% secured. Since the hard surface-treated disc has high strength, it is excellent in the container preservation even if it is thin, and is surface-treated with tin plated or tin-free steel plate, and then processed shallowly such as the body of the beverage can, lid and food can. Applied to a two-piece can.

In general, when the thickness of the can is thin, the number of cans that can be manufactured per tonne of steel sheet is increased, but the manufacturing cost of the can is lowered. However, in order to preserve the contents, strength should be secured as the thickness becomes thinner. For this reason, in recent years, a surface-treated steel sheet having a thickness of about 5 mm and having a roughness of T5 and T6 is required. However, such a thin steel sheet has a problem that it is difficult to manufacture a cold rolled coil directly by continuous annealing.

As a prior art for solving the above problems, Korean Patent No. 1992-26503 discloses that the first cold rolled and annealed aluminum alloy steel with a carbon content of 0.03 to 0.06% at a rolling reduction rate of 86 to 88%. Thereafter, secondary cold rolling is carried out at a high reduction ratio of 40% or less or 10 to 40%, thereby providing a method for producing a surface-treated disc having an ear generation rate of 3% or less. However, there is no mention of hardness or elongation in this technique.

Thus, the present inventors have conducted research and experiments to solve the above problems, and proposed the present invention based on the results. The present invention is annealed in a continuous annealing line and temper-rolled at an appropriate reduction ratio, so that the quality is T5. In addition to having ~ T6 and elongation of 25% or more, and to produce a high-strength ultra-thin surface treatment disk excellent in corrosion resistance with almost no post-drawing ear and fringe processing cracks, the purpose is to produce a higher productivity.

1 is a graph showing the effect of the temper reduction rate on the Δr value.

2 is a graph showing the effect of the temper reduction ratio on the elongation

Figure 3 is a photograph of the cross-sectional view of the coating film in the processed tin-plated steel sheet by electron microscope

Figure 4 is a photograph showing the salt spray test results

This invention is a manufacturing method of an ultra-thin surface treatment original plate,

By weight percentage, C: 0.04 ~ 0.07%, Mn: 0.4 ~ 0.6%, N: 0.006 ~ 0.012%, hot rolled low-carbon aluminum-kilted steel composed of balance Fe and other unavoidable impurities and wound at a temperature below 600 ° C. Next, high strength ultra-thin surface having excellent corrosion resistance including pickling, cold rolling at a reduction ratio of 84 to 87%, continuous annealing at a temperature range of recrystallization temperature to 650 ° C., and temper rolling at a reduction ratio of 5 to 10%. It relates to a method for producing a treated original.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The C is an element that greatly contributes to the strengthening of the steel together with nitrogen. When the content thereof is increased, the roughness T5 and T6 are easily manufactured, but the value of Δr is changed to a negative value. The value of Δr indicates the degree of earing during drawing, and the closer the absolute value is to 0, the less the degree of earing occurs. The main factors that change the value to negative are an increase in carbon content and an increase in cold reduction rate. There is this.

In the present invention, it is necessary to increase the cold reduction rate in order to manufacture the ultra-thin steel sheet within 0.2mm, so the carbon content should be reduced, the upper limit was set to 0.07%. On the other hand, in terms of securing strength, the lower limit is preferably set to 0.04% in order to obtain a quality of T5 or more.

The Mn also contributes to the increase in strength of the steel, but the upper limit thereof is set to 0.6% according to the standard of the surface-treated disc (ASTM MR standard). The lower limit was 0.4% for the purpose of preventing high temperature brittleness and increasing the strength by grain boundary segregation S during hot rolling. That is, it is preferable to add Mn at 0.4 to 0.6%.

N is about 5 to 10 times higher in reinforcing effect than carbon, and unlike carbon, N is actively used in the present invention because it does not significantly affect the change in the Δr value. Accordingly, the lower limit of nitrogen was 0.006% or less, which is a range in which strength can be sufficiently secured. On the other hand, although nitrogen is 0.02% or less as a residual element in the standard of surface-treated discs, in the general steelmaking method, containing nitrogen in steel at 0.013% or more causes problems of cost increase due to excessive input of iron nitride, Even if it contains nitrogen up to 0.012%, the desired quality can be obtained sufficiently, so it can be easily secured through vacuum degassing and bubbling nitrogen gas during performance, and it is easy to control the components by adding a little iron nitride. 0.012% which is the range which can be used as an upper limit was made. That is, it is preferable to add said N in 0.012-0.006%.

Other residual elements are preferably limited as specified in the specification.

On the other hand, in the present invention, Al does not need to be excessively added because solid solution nitrogen is used as one of the reinforcing mechanisms of steel, unlike ordinary surface treatment discs.

The aluminum-kilted steel formed as described above was hot rolled in a conventional manner and then wound to a temperature of 600 ° C. or lower, for the purpose of suppressing AlN precipitation.

Thereafter, the hot iron oxide layer formed on the surface during hot rolling was pickled and removed by a conventional method, followed by cold rolling. Cold reduction rate affects the ear formation formed in the cup after drawing processing of the surface treated disc. As can be seen in FIG. 1, the low carbon steel of the present invention has a negative Δr value when the cold reduction rate is high. Change to a value. That is, when the cold reduction rate is high, the hot rolled sheet can be made thick, so that the hot rolled sheet can be easily manufactured, and the temperature can be secured and the variation is reduced.

However, since the suppression of the occurrence of ear during the drawing process is most important, an appropriate cold reduction rate range considering the temper reduction rate, that is, 84 to 87% that can minimize the absolute value of the Δr value, is set as the cold reduction rate range.

The rolled steel sheet is again degreased by a conventional method and continuously annealed, preferably at a recrystallization temperature of 650 ° C. for 30 seconds or more. The reason is that when the annealing temperature exceeds 650 ° C, the strength decreases due to grain growth.

In general, the temper rolling of the annealing plate has the purpose of correcting the roughness and shape of the plate, but in addition to the present invention also serves to secure the strength by work hardening. However, if the tempered rolling elongation is too high, as shown in Fig. 1, the absolute value of the Δr value increases, and as shown in Fig. 2, a sudden decrease in elongation occurs.

Thus, the present inventors found through the study that the decrease in elongation rate is not large up to 10%, and the upper limit of the crude reduction rate to 10%. On the other hand, when the temper reduction rate is less than 5%, the working hardness is not large and the target hardness cannot be obtained, so the lower limit is 5%.

In general, in manufacturing a surface-treated disc of 0.2 mm or less in thickness, when the thickness of the continuous annealing plate becomes 0.2 mm or less, since the thin plate is plated by a driving roll at a high temperature, there is a risk of buckling and plate breaking, so the productivity is very low. . However, in the case of performing temper rolling of 5% or more as in the present invention, since the plate of about 0.21 mm is plated, the productivity is very high and the risk of fatal defects is reduced.

Compared with the DR-8 (Double Reduced, HR30T 73 ± 3) material, the surface-treated disc manufactured in this way has a low thickness and similar thickness, which is low in cost and high in productivity. It has the advantage of being excellent in workability. In addition, since the temper reduction ratio is higher than that of T5 to T6 materials produced by conventional methods, it is easy to manufacture ultra-thin steel sheets, and very fine surface irregularities are generated during pickling before tin plating due to the potential formed on the surface during temper rolling. Since the bonding property of the plated film and the steel surface is improved, as shown in Fig. 3, it has excellent corrosion resistance.

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

(Example)

The steel ingot having the chemical composition of Table 1 below was prepared by vacuum induction to a thickness of 60 mm and a width of 175 mm, and re-heated at 1200 ° C. for 1 hour, and then hot rolled to a thickness of 1.32 to 1.71 mm. At this time, the finish hot rolling temperature was set to 870 ° C or more, which is equal to or more than the Ar ₃ transformation point. Then, after winding at various temperatures, it was maintained in a preheated furnace for 1 hour, and after the furnace was cooled, pickled to remove the hot iron oxide film, cold rolled and continuously annealed, and then tempered again in 11 passes to give a final thickness of 0.2 mm. It was made.

Thereafter, the mechanical properties of each specimen were measured, and the results are shown in Table 1 below.

division Chemical composition (wt%) Manufacture conditions Mechanical property Thickness (mm) C Mn N Winding temperature (℃) Cold rolling reduction (%) Annealing Temperature (℃) Temper reduction rate (%) Hardness (HR30T) Elongation (%) Δr Annealed Plate Hot rolled sheet Comparative Steel 1 0.03 0.4 0.008 570 85 650 0.8 57.1 33 0.188 0.2 1.34 Comparative Steel 2 0.03 0.5 0.011 570 87 650 15 63.4 19.5 -0.075 0.23 1.8 Comparative Steel 3 0.04 0.4 0.003 570 84 650 5 61.4 31.7 0.13 0.21 1.32 Inventive Steel 1 0.05 0.5 0.009 570 85.5 650 7.5 65.6 28.2 0.005 0.22 1.49 Comparative Steel 4 0.05 0.5 0.009 700 85.5 650 5 61.7 31 0.01 0.21 1.45 Comparative Steel 5 0.05 0.5 0.009 570 84 650 15 69.9 17.2 -0.07 0.23 1.44 Comparative Steel 6 0.05 0.5 0.009 570 84 700 10 61.3 33.6 -0.03 0.23 1.44 Inventive Steel 2 0.05 0.4 0.006 600 84 650 5 62.9 28 0.08 0.21 1.32 Invention Steel 3 0.07 0.6 0.012 600 87 630 10 72.7 25.7 -0.14 0.22 1.71 Comparative Steel 7 0.09 0.5 0.012 570 87 640 10 73.8 20.4 -0.21 0.22 1.71 * Product final thickness: 0.20 ~ 0.195mm, * Δr (In-plane anisotropy) = (r ₀ + r ₉₀ -2r ₄₅ ) / 2 ※ The HR30T is the hardness measured under Rockwell hardness measurement HR30T conditions

As can be seen in Table 1, the comparative steel (1) has a low carbon content of 0.03% and a temper reduction pressure ratio of 0.8%, showing the hardness level and material performance corresponding to the conventional T3 material. Comparative steel (2) has a low carbon content, a high nitrogen content and a 15% crude reduction ratio, which satisfies the T5 material level. However, due to excessive crude rolling, the elongation is low and the workability is insufficient. Comparative steel (3) except the nitrogen and the other components and manufacturing conditions satisfy the present invention, but the nitrogen is very low showing the material level of T4.

On the other hand, the invention steel (1) is a composition and manufacturing conditions corresponding to the median value of the present invention, the hardness is about 66 to meet the target hardness T5 (HR30T 65 ± 3) and at the same time △ r value and elongation is the target of the present invention Enough to meet.

Comparative steel (4) has the same composition as invention steel (1), but the hot-rolled coiling temperature is increased to 700 ° C to precipitate solid nitrogen into AlN, resulting in a hardness value of T4.

Therefore, it can be seen that when using solid nitrogen as one of the reinforcing mechanisms as in the present invention, the hot-rolled coiling temperature needs to be 600 ° C or less.

Comparative steels (5) and (6) are manufactured under the same composition and hot rolling conditions as invented steel (1), but have a crude reduction ratio of 15% or an annealing temperature of 700 ° C. If the temperability reduction rate is high, as in the comparative steel (5), the hardness satisfies T6, but it can be seen that the elongation is sharply lowered to a level of 17%, which is disadvantageous to the french workability. In addition, since the annealing temperature is high, the comparative steel 6 has good workability such as elongation, but does not satisfy the strength at the hardness value of T4 level. Therefore, the annealing temperature needs to be 650 ° C or lower.

Inventive steel (2) is manufactured by applying the lowest composition, the highest hot-rolling and annealing temperature, and the lowest crude pressure reduction rate presented in the present invention, which is the strength level of the lower limit that can be produced by the present invention. However, the hardness is about 63 level, the material of T5 can be stably manufactured, and the elongation is 28%, indicating that the workability is very excellent.

In addition, the invention steel (3) satisfies T6 (HR30T 70 ± 3) as well as the material of the DR-8 (HR30T 73 ± 3) as the material of the highest strength in the present invention. In particular, the elongation is 26% and the Δr value is -0.14, which is much superior to the DR-8 product applied to ordinary ultrathin materials with drawability and flange workability.

Comparative steel (7) is nitrogen with an upper limit of the present invention and carbon content of 0.09%, which is higher than 0.07% of the present invention. In this case, although the strength is high, the elongation is low at the level of 20%, and the Δr value is -0.21, which causes severe ear drawing, resulting in inferior drawing workability and flange workability.

On the other hand, Figure 1 shows the effect of the temper reduction rate on the Δr value and Figure 2 shows the effect of the temper reduction rate on the elongation under the same conditions.

The steel used for the test had the same composition as the invention steel (1), and the hot-rolled coiling temperature and the annealing temperature were also the same. In order to maintain the final thickness at 0.2 mm, the hot-rolled sheet was ground in a plane and its thickness was adjusted in advance. .

Thereafter, a tensile test was performed while changing the cold rolling rate and the temper rolling reduction rate, and the elongation rate and Δr value were measured.

As a result, as described above, when the cold reduction rate increased, the Δr value changed to a negative value, and the crude reduction rate also showed the same effect.

Therefore, in the case where the cold reduction ratio is 84 to 87% as in the present invention, it is understood that the crude reduction ratio for setting the absolute value of the Δr value to 0.15 or less is preferably 5 to 10%.

In addition, as shown in Fig. 2, when the temper reduction rate is 15% or more, the elongation is drastically lowered because the work hardening phenomenon occurs even inside the matrix. That is, when the temper reduction rate is low, only the surface can be hardened to secure an appropriate strength increase and elongation at the same time.

However, there was little influence of the cold reduction rate on the elongation in the samples of the same thickness.

Therefore, according to the results of Figs. 1 and 2, it was found that the target material can be obtained when the cold reduction rate is 84 to 87% and the temperability reduction ratio is 5 to 10% in the Δr value and the elongation.

Figure 3 (a), (b) is a cross-sectional electron microscope observation photograph of the coating film of the tin-plated steel sheet processed for the comparative steel (1) and the invention steel (1), Figure 4 (a), (b) is a comparison The salt spray test results of steel (1) and inventive steel (1) are shown.

The tin plating was performed at 5.6 g / m ² and the can was processed by drawing, and the cross-sectional observation of the coating and the salt spray test of the can were performed without a separate lacquer coating treatment.

The film cross-sectional observation was observed by SEM microscopic backscattered images, and the salt spray test was performed for 3 hours at 35 ° C.

As shown in Fig. 3, the Fe-Sn alloy layer was present between the matrix and the tin coating film, but in 7.5% of the crude rolled invention steel 1, no peeling occurred between the hard alloy layer and the soft tin plating layer after processing. .

The reason for this is that the dislocation of the surface layer introduced by temper rolling during the lactic acid pickling before tin plating improves the adhesion by forming fine unevenness, and the surface dislocation between the Fe-Sn during reflow treatment after electro-tin plating. This is because active energy is given to diffusion. Accordingly, as shown in FIG. 4, in the invention steel 1 of FIG. 4 (b) in which the plated layer was sound after processing, almost no red rust occurred after salt spraying, but in the comparative steel 1 of FIG. A lot of red blue was observed.

Therefore, it can be seen that the corrosion resistance is greatly improved when the ultra-thin hard surface treated disc is manufactured by the present invention.

As described above, the present invention by annealing the thicker steel plate in the continuous annealing line and then subjected to temper rolling, has a roughness T5 ~ T6 and elongation of 25% or more, -0.15≤ △ r≤0.15, after drawing Highly processed high strength ultra-thin surface treatment discs with excellent corrosion resistance with little generation and fracturing cracks can be produced with higher productivity.

Claims (1)

In the manufacturing method of ultra-thin surface treatment disc, By weight percentage, C: 0.04 ~ 0.07%, Mn: 0.4 ~ 0.6%, N: 0.006 ~ 0.012%, hot rolled low-carbon aluminum-kilted steel composed of balance Fe and other unavoidable impurities and wound at a temperature below 600 ° C. Next, pickled, cold rolled at a reduction ratio of 84 to 87%, continuous annealing at a temperature range of recrystallization temperature to 650 ° C., and tempered rolling at a reduction ratio of 5 to 10%. Manufacturing Method of Treated Disc