KR20010017493A - A method for manufacturing the cold rolled sheet steel for the direct-on enamel coating - Google Patents

Abstract

PURPOSE: A method for manufacturing cold rolled steel plate for direct porcelain enamel is provided to improve quality of porcelain enamel and greatly reduce cost for treating porcelain enamel by controlling a content of steel and a reduction ratio. CONSTITUTION: A method for manufacturing cold rolled steel plate for direct porcelain enamel comprises the processes of cold rolling the wound steel with a reduction ratio of 50 to 85 and continuously annealing the cold rolled steel after winding the steel at a normal temperature after hot rolling aluminum killed steel with a final temperature of hot rolling being Ar3 transformation point or more, wherein the aluminum killed steel comprises 0.005 wt.% or less of C, 0.05 to 0.3 wt.% of Mn, 0.005 to 0.02 wt.% of S, 0.02 wt.% or less of P, 0.01 to 0.1 wt.% of Al, 0.002 to 0.01 wt.% of B, 0.004 to 0.015 wt.% of N, and a balance of Fe and inevitable impurities, wherein 0.0005<N-1.3B<0.01.

Description

Method of manufacturing cold rolled steel sheet for direct enamel {A METHOD FOR MANUFACTURING THE COLD ROLLED SHEET STEEL FOR THE DIRECT-ON ENAMEL COATING}

The present invention relates to a method for manufacturing a steel sheet of enamel processing products applied to gas stoves, microwave ovens, and parts of home appliances, and more particularly, fish scale, which is excellent in enamel adhesion and a fatal defect of enamel products. The present invention relates to a method for producing an enameled cold rolled steel sheet which does not generate any defects.

Normally, hydrogen produced during enamel processing during enamel processing is accumulated at the interface between the steel sheet and the enamel layer during enameling and cooling to form high pressure. If the enamel layer does not withstand the high pressure of hydrogen, it is destroyed and hydrogen is released. At this time, the shape of the enamel layer is destroyed, so it is called fish scale. This defect is one of the most fatal defects in enamel products because not only the appearance is unsightly, but also the corrosion is in direct contact with the atmosphere.

In order to prevent fish scale defects, which are known to be the most fatal defects in enamel products, conventional steel is added to precipitates or oxide generating elements in the steel to secure fish scale resistance. The conventional steel produced by the continuous casting method is mainly subjected to two enamel firings twice, so that the thickness of the enamel layer is thick and easily broken even by a small impact. In the case of the decarbonized annealing steel of the conventional steel, it is possible to directly enamel treatment, but the production cost is high because the decarbonization process must be produced and decarbonized annealing.

Thus, the present invention by controlling the steel components and appropriately control the reduction ratio, when applied as an enamel product, not only enamel quality is improved and enamel processing cost is greatly reduced, but also cold rolled steel sheet which can be directly enameled while applying continuous casting method To provide a way to obtain, the purpose is.

The present invention for achieving the above object, C: 0.005 or less by weight, Mn: 0.05 to 0.3, S: 0.005 to 0.02, P: 0.02 or less, Al: 0.01 to 0.1, B: 0.002 to 0.01, N: 0.004 to The aluminum finished steel containing 0.015 and satisfying the conditions of 0.0005 <N-1.3B <0.01 and containing residual Fe and unavoidable impurities at the time of hot rolling at the hot finish rolling temperature above Ar3 transformation point and wound at a normal temperature Then, the present invention relates to a method for manufacturing a cold rolled steel sheet for direct enamel, characterized by continuous rolling after cold rolling at a reduction ratio of 50 to 85.

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

The carbon is added below 0.005. If the content exceeds 0.005, the amount of solid solution carbon in the steel is too large to hinder the development of the aggregate structure during annealing or the crystal grains are fine so that the formability is greatly lowered. The limit is 0.005.

The manganese is added to prevent the hot shortness of the solid solution of sulfur dissolved in the river as a manganese sulfide, sulfur dissolved in the solution, the manganese sulfide is stretched during cold rolling to hydrogen than other oxides or precipitates except boron nitride Since the absorbing ability is excellent, the minimum amount is added to 0.05 in order to sufficiently precipitate the sulfur remaining in the steel. When the manganese is in a solid solution state, it has an effect of increasing the strength, but the reinforcing effect is not so large that the moldability is impaired, so the upper limit is limited to 0.3.

Sulfur is generally known as an element that inhibits the properties of steel, but in the steel of the present invention, manganese sulfide is precipitated and added to improve fish scale resistance. If the sulfur content is less than 0.005, the amount of precipitation of manganese sulfide is too small to have little effect. If the amount of sulfur exceeds 0.02, the amount of precipitation of manganese sulfide is too high, so that moldability is lowered.

Phosphorus is known as an element that effectively increases the strength without significantly reducing the formability in cold rolled steel sheets. However, when the added amount exceeds 0.02, the upper limit is set to 0.02 because the formability decreases with the increase in strength.

The aluminum is added as a deoxidizer, but in the present invention, it is added in order to precipitate the solid solution nitrogen remaining in the steel to improve moldability. Although about 0.001 aluminum is required to precipitate 0.0005 nitrogen remaining in the solid solution state in the components shown in the present invention, the lower limit is set to 0.01 because a sufficient amount of aluminum needs to be added to completely precipitate the solid solution nitrogen. When the aluminum is added in excess, the upper limit is limited to 0.1 because not only the moldability is lowered but also the deposition effect of boron nitride can be reduced.

The boron combines with the nitrogen to form boron nitride to improve fish scale resistance. Since the fish scale defect does not occur when the amount of boron added exceeds 0.002, the lower limit is limited to 0.002. The more the amount of boron added, the more the fish scale is improved, but it is not necessary to secure the fish scale more than appropriate. If the amount of boron is added, the moldability is greatly reduced, so the upper limit is limited to 0.01.

The nitrogen is added because it binds to boron and precipitates as boron nitride to improve fish scale resistance. The amount of nitrogen required to precipitate 0.002, the minimum value of boron addition amount, is about 0.0026. However, at least 0.004 or more nitrogen is required to completely deposit boron remaining in solid solution, so the lower limit is 0.004. In addition, as the amount of added nitrogen increases, the amount of precipitates to be precipitated increases, and the fish scale resistance is improved. However, when the amount of nitrogen is increased, the upper limit is limited to 0.015 because the moldability decreases.

The lower limit of N-1.3B was set to 0.0005 by controlling the addition amount of boron or nitrogen to 0.0005 <N-1.3B <0.01, in order to reduce the efficiency of improving the fish scale resistance when solid boron remained in steel. The reason is that the upper limit of N-1.3B is 0.01, and the reason why the upper limit of N-1.3B is 0.01 is that if the amount of nitrogen remaining in combination with boron in the steel is too high, the amount of nitrogen that is excessively precipitated or remains in solid solution It is because a lot of moldability falls.

The aluminum-kilted steel of the steel component as described above can be continuously cast to obtain a cast steel, and a cold rolled steel sheet is obtained by the following method using the obtained cast steel.

In the present invention, hot rolling can be performed by a conventional method, and the finish rolling temperature at the time of hot rolling is performed at an Ar 3 transformation point or more. This is because, when hot rolling at a temperature below the transformation temperature, workability is reduced due to the formation of rolled grains.

Moreover, in this invention, it winds up at normal temperature and cold rolling is performed.

The cold rolling reduction rate is controlled to 50 to 85 because of the following reasons. In the process of forming or growing the precipitates during hot rolling during the cold rolling, the fine gaps are generated and remain as they are after the continuous annealing, which acts as an important hydrogen storage source. If the cold reduction rate is less than 50, the formation area of the fine gaps is Since the hydrogen storage ability decreases and the fish scale generation probability increases, the lower limit of the cold reduction rate is 50. In addition, if the cold reduction rate exceeds 85, the minute gap is too squeezed to increase the probability of occurrence of fish scale.

Moreover, in this invention, although continuous annealing is carried out, a conventional method can be applied.

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

(Example)

Next, steel having the components shown in Table 1 was produced into cast steel by continuous casting, and then hot rolling was performed after holding for 1 hour in a 1250 ° C. heating furnace. At this time, the hot finish rolling temperature was 900 ℃, the coiling temperature was 650 ℃, the final thickness was 3.2mm. The hot rolled specimen was pickled to remove the oxide film on the surface, and then cold rolled at a reduction ratio 70 as shown in Table 1 below.

Sample Number Chemical composition (weight) N-1.3B Cold Rolling Rate () C Mn P S sol.Al B N Inventive Steel 1 0.0015 0.22 0.013 0.011 0.035 0.0053 0.0077 0.0008 70 Inventive Steel 2 0.0018 0.25 0.011 0.009 0.038 0.0063 0.0116 0.0034 〃 Invention Steel 3 0.0023 0.21 0.011 0.012 0.041 0.0049 0.0083 0.0020 〃 Inventive Steel 4 0.0024 0.18 0.012 0.009 0.042 0.0044 0.0073 0.0016 〃 Comparative Steel 5 0.0022 0.19 0.010 0.012 0.039 0.0013 0.0109 0.0092 〃 Comparative Steel 6 0.0025 0.25 0.011 0.008 0.038 0.0130 0.0120 -0.0049 〃 Comparative Steel 7 0.0029 0.21 0.010 0.010 0.035 0.0066 0.0023 -0.0063 〃 Comparative Steel 8 0.0022 0.20 0.012 0.011 0.036 0.0056 0.0054 -0.0019 〃 Comparative Steel 9 0.024 0.25 0.011 0.009 0.042 0.0060 0.0092 -0.0014 〃

Cold rolled specimens were processed into enameled specimens for enameling and tensile specimens for mechanical properties, followed by continuous annealing. The enameled specimens were cut to 70mm × 150mm, and the tensile specimens were processed into standard specimens according to ASTM E-8 standard. Continuous annealing was performed at an annealing temperature of 830 ° C. After the annealing was completed, the tensile tester (INSTRON, Model 6025) was used to measure yield strength, tensile strength, elongation, and r, and the results are shown in Table 2 below. The enameled specimens were completely degreased and then subjected to acid treatment, which was then deposited for 5 minutes in a 10-sulfuric acid solution at 70 ° C., washed with hot water, and then nickel-treated for 5 minutes in a nickel sulfate solution maintained at 80 ° C. The nickel-treated specimens were washed with warm water and neutralized by immersion in 3.6 g / | soda carbonate + 1.2 g | / borax solution maintained at 85 ° C. for 5 minutes. After coating the coated glaze (Cover Coat) was completed for 10 minutes at 200 ℃ to completely remove the moisture. The dried specimens were kept at 800 ° C. for 7 minutes, and then subjected to calcination, followed by enameling of air cooling. At this time, the atmospheric conditions of the kiln were the harsh conditions where fish scale defects were most likely to occur at a dew point temperature of 30 ° C. The enameled specimens were kept at 200 ° C. for 20 hours to visually examine the number of fish scale defects that occurred after the fish scale acceleration treatment, and the results are shown in Table 2 below. In the enamel adhesion evaluation, the adhesion index was measured using an adhesion test device (test device according to ASTM C313-78 standard).

Table 2 is a table showing the results of the enamel and mechanical properties of the present invention steel and comparative steel. Inventive steels (1 to 4) belonging to the scope of the present invention did not generate fish scale even under severe conditions, thereby securing fish scale resistance, and exhibited high adhesion to the enamel adhesion index of 95 or more. On the other hand, since r value which is a moldability index is 1.75 or more, and shows high moldability, deep recessing was possible. On the other hand, the comparative steel (5) has a boron content of 0.0013 lower than the scope of the present invention, a fish scale defect occurred. Comparative steel (6) was not only higher than the amount of boron added in the range of the present invention, but also significantly lower than the value of N-1.3B in the range of the present invention at -0.0049. Comparative steel (7) was not only lower than the nitrogen content of the present invention range, but also very low N-1.3B value of -0.0063, fish scale defects occurred, r value was also very low as 1.38. Comparative steel (8) had no fish scale defect but N-1.3B was -0.0018, so the r value was very low, 1.43. Comparative steel (9) had no fish-scale defects, but the carbon content is out of the scope of the present invention and surface defects occurred, the r value was 1.21 was very low.

According to the present invention as described above, by controlling the steel components and control the rolling reduction rate, it is possible to obtain a high-quality enamel product that does not generate fish scale, which is a fatal defect of the enamel product, and also greatly reduce the enamel processing cost. have.

Claims (1)

C: 0.005 or less by weight, Mn: 0.05 to 0.3, S: 0.005 to 0.02, P: 0.02 or less, Al: 0.01 to 0.1, B: 0.002 to 0.01, N: 0.004 to 0.015, and 0.0005 <N-1.3 When hot-rolled aluminum-kilted steel containing a balance of Fe and unavoidable impurities, satisfying the condition of B <0.01, the hot rolling rolling temperature was set at an Ar3 transformation point and wound up at a normal temperature, and then the reduction ratio was 50 to 85. Method of producing a cold rolled steel sheet for direct enamel, characterized in that by continuous rolling after cold rolling.