KR100402009B1 - A method for manufacturing a hot rolled sheet steel for the both side enamel coating - Google Patents

Abstract

The present invention relates to a method for manufacturing a hot rolled steel sheet for enamel, by adding alloying elements such as C, B, N, Mn and S appropriately and controlling the hot rolling conditions, the fish scale resistance and plasticity required for the hot rolled steel sheet for enamel It is intended to provide a method for producing an enameled hot rolled steel sheet having excellent strength and enamel adhesion, and the purpose thereof.

The present invention for achieving the above object, in the manufacturing method of the hot rolled steel sheet for enamel,

C: 0.1% or less, Mn: 0.1 to 0.5%, S: 0.01 to 0.05%, P: 0.03% or less, B: 0.004 to 0.015%, N: 0.006 to 0.02%, Al: 0.01 to 0.1% by weight% Steel, which satisfies 0.0005% <N-1.3B, and re-heats the steel containing the remaining Fe and other unavoidable impurities at 1300 ° C. or lower, and then hot-rolls to obtain a hot finish rolling start temperature of 1150 ° C. or lower, and finish rolling The total rolling reduction is 80% or more, and the technical gist of the method for producing a double-sided enameled hot rolled steel sheet, which is wound at a temperature of 600 ° C or higher.

Description

Manufacturing method of hot rolled steel sheet for double-sided enamel {A METHOD FOR MANUFACTURING A HOT ROLLED SHEET STEEL FOR THE BOTH SIDE ENAMEL COATING}

The present invention relates to a method for manufacturing an enameled hot rolled steel sheet used in hot water tanks, liquid fertilizer tanks, silos and gas stove parts, more specifically, a relatively high strength is required and the thickness of the material thick enamel enamel should be used The present invention relates to a method for producing enameled hot rolled steel sheet.

In general, the steel sheet for enamel is produced by appropriately adjusting the components or processes so that various enamel defects do not occur after enamel processing. Enamel processing is performed using general steel sheet instead of enamel steel sheet, the most fatal one of which is fish scale defect. The fish scale defect is related to the behavior of hydrogen in the river, and to prevent this, it is necessary to provide a place for storing hydrogen in the river. The place where hydrogen can be stored may include an interface between inclusions, precipitates, and the base iron, or a minute gap generated while rolling them. Among these, the micro cracks are mainly generated during cold rolling, and are known as the largest places for storing hydrogen. When rolling at high temperatures, it is difficult to form micro cracks, and thus fish scale resistance must be secured by inclusions or precipitates. do. Therefore, in order to secure fish-scale resistance in the case of hot rolled sheet, a larger amount of precipitates or inclusions must be deposited.

As an example of a conventional hot rolled steel sheet for double-sided enamel, the components described in Japanese Patent Publication No. 58-1170 are C: 0.02 to 0.1%, Mn: 0.05 to 0.4%, and Ti: 0.05 to 0.3%, using Ti carbide. It is a technology that has secured fish scale resistance. However, in the above method, since the content of Ti added is high, the Ti oxide is attached to the tundish nozzle by the addition of a large amount of Ti having a high manufacturing cost and very oxidizing property, and it is easy to cause nozzle clogging. There is a problem with progress.

Accordingly, the present invention is to solve the above problems, and by using alloys such as C, B, N, Mn and S appropriately and controlling hot rolling conditions without using Ti, which is a problem in the prior art, To provide a method for producing a hot rolled steel sheet for double-sided enamel having excellent fish scale and enamel adhesion and strength, the object is to.

Method for producing a double-sided enameled hot rolled steel sheet of the present invention for achieving the above object,

C: 0.1% or less, Mn: 0.1 to 0.5%, S: 0.01 to 0.05%, P: 0.03% or less, B: 0.004 to 0.015%, N: 0.006 to 0.02%, Al: 0.01 to 0.1% by weight% Steel, which satisfies 0.0005% <N-1.3B, and re-heats the steel containing the remaining Fe and other unavoidable impurities at 1300 ° C. or lower, and then hot-rolls to obtain a hot finish rolling start temperature of 1150 ° C. or lower, and finish rolling The total rolling reduction is 80% or more, and relates to a method for producing a double-sided enameled hot rolled steel sheet, which is wound at a temperature of 600 ° C. or higher.

Hereinafter, the present invention will be described in detail.

First, the reason for limitation of the said component range is demonstrated.

The amount of C added is preferably 0.1% or less. The reason for this is that when the amount is more than 0.1%, the amount of cementite increases on the surface of the steel sheet, which is caused by bubbles growing abnormally due to the oxidation of carbides during enameling. This is because the probability of defects is high.

The Mn usually serves to prevent hot shortness caused by solid solution sulfur by precipitating sulfur dissolved in steel as manganese sulfide. In the present invention, Mn is added to take advantage of the improvement of hydrogen absorption ability of manganese sulfide. If the amount of Mn is less than 0.1%, the amount or size of manganese sulfide is little, and there is little effect of improving fish scale resistance. If the amount of Mn added is 0.5% or more, there is no further effect of improving fish scale resistance and manufacturing cost. Since it increased, the amount of Mn added was limited to 0.1 to 0.5%.

The S is generally known as an element that inhibits the physical properties of the steel, but in the present invention, it is added to precipitate into manganese sulfide to improve fish scale resistance. If the added amount is less than 0.01%, the amount of precipitated manganese sulfide is too small to have little effect. If the amount is more than 0.05%, the ductility is lowered. Therefore, sulfur is preferably added at 0.01 to 0.05%.

When P is added at 0.03% or more, ductility decreases, so the upper limit is limited to 0.03%.

B is added because it combines with nitrogen to form boron nitride to improve fish scale resistance. Since the fish scale defect did not generate | occur | produce when the addition amount B was 0.004% or more, the lower limit was made into 0.004%. As the amount of boron added increases, the hydrogen absorbing ability increases to improve fish scale resistance, but it is not necessary to secure fish scale resistance higher than the appropriate amount. When the amount is excessive, the upper limit is limited to 0.015% because the moldability greatly decreases. .

The N is added to bind with B because it precipitates as boron nitride to secure fish scale resistance. The theoretical amount of nitrogen needed to deposit all of the minimum amount of boron added, 0.004% (for example, precipitation as BN) is 0.0052%, but at least 0.006% of nitrogen is required to completely deposit boron remaining in solid solution, so the lower limit is 0.006%. It was. As the amount of nitrogen increases, the amount of precipitates precipitated increases so that the fish scale resistance is improved, but when too much, the ductility decreases, so the upper limit is limited to 0.02%.

Since Al is a deoxidizer, the deoxidation effect is less at 0.01% or less and the probability of surface defects is increased due to the increase of Al oxide at 0.1% or more, so the upper limit is limited to 0.1%.

The amount of B and N added to 0.0005% <N-1.3B is limited to improve the efficiency of fish scale resistance when the boron remains in the steel, and lower the ductility so that the lower limit of N-1.3B is reduced. It was set as 0.0005%.

Next, the reason for limitation of hot rolling conditions is demonstrated.

In the manufacturing method of the enameled hot rolled steel sheet to reheat the steel slab formed as described above and hot rolled and wound, the reheating temperature is 1300 ℃ or less, because the BN precipitate is completely dissolved when the reheating temperature is higher than 1300 ℃ This is because fish scale resistance decreases due to the smaller size and amount of the precipitates. In addition, the lower limit of the reheating temperature is preferably about 1200 ° C, and most preferably about 1250 ° C.

It is preferable that the finish rolling start temperature be 1150 ° C. or lower, because rolling at a temperature higher than 1150 ° C. decreases the amount of precipitates and decreases the fish scale resistance due to the small interfacial area between the precipitates serving as a hydrogen storage source and the base metal. to be. Therefore, finish rolling start temperature is limited to 1150 degrees C or less, Preferably about 1100 degreeC is good. In addition, when the total rolling reduction rate of the finish rolling is lower than 80%, since the interface area between the precipitate and the base metal decreases, the fish scale resistance is lowered, the final rolling total reduction rate is preferably controlled to 80% or more.

In general, the higher the coiling temperature is advantageous because the size and amount of the precipitate increases, the present invention limited the lower limit of the coiling temperature to 600 ℃. The reason for this is that the fish scale resistance is lowered when winding at less than 600 ° C. In addition, the winding temperature is most preferably about 650 ℃, the upper limit is about 700 ℃.

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

(Example)

Steel having a composition as shown in Table 1 below was manufactured as a slab, and maintained at 1250 ° C. for 1 hour, followed by hot rolling. At this time, the hot finish rolling start temperature was 1100 ° C., the coiling temperature was 650 ° C., and the final thickness was 3.2% with a total finishing reduction of 89%. In addition, in order to investigate the change of material and enamel characteristics according to the change of hot rolling condition, the finish rolling start temperature was 1200 ℃, the total rolling rate was 75% and the winding temperature was changed to 550 ℃. Then, the hot-rolled specimen was pickled to remove the oxide film on the surface, and the enamel treated specimens were then cut into 70 mm × 150 mm sizes to examine the enamel and mechanical properties, and the tensile specimen was ASTM standard. It was processed into a standard specimen according to ASTM E-8 standard).

Yield strength, tensile strength and elongation were measured using a tensile tester (INSTRON, Model 6025) on the tensile specimens prepared as described above, and the results are shown in Table 2 below. The enameled specimens were subjected to acid treatment for 5 minutes in 70 ° C. and 10% sulfuric acid solution, and then washed with hot water and nickel treated for 5 minutes in 7% nickel sulfate solution maintained at 80 ° C. . The nickel-treated specimens were washed with warm water and neutralized by immersion in 3.6 g / l sodium carbonate + 1.2 g / l borax solution maintained at 85 ° C for 5 minutes. Next, after the pretreatment was completed, the coating was applied to the ground glaze (Ground Coat) and dried at 200 ° C. for 10 minutes to completely remove moisture. The dried specimens were kept at 830 ° C. for 7 minutes and subjected to firing in an atmosphere of dew point temperature of 30 ° C., followed by enameling of air cooling. Then, the number of fish scale defects were visually inspected, and the adhesion was visually observed by dropping the 200 g steel ball at 1M height and visually dropping the enamel layer, and the evaluation results are shown in Table 2 below.

Psalm Number Chemical composition (% by weight) N-1.3B Hot Rolling Condition C Mn P S Al B N Rolling start temperature Coiling temperature Total reduction Inventive Steel 1 0.052 0.42 0.013 0.015 0.035 0.0066 0.011 0.0024 1100 ℃ 650 ℃ 89% Inventive Steel 2 0.058 0.44 0.011 0.021 0.038 0.0072 0.012 0.0026 Invention Steel 3 0.049 0.36 0.011 0.018 0.041 0.011 0.015 0.0007 Inventive Steel 4 0.082 0.42 0.012 0.016 0.042 0.0098 0.016 0.0033 Comparative Steel 1 0.056 0.34 0.011 0.017 0.038 0.0028 0.012 0.0084 Comparative Steel 2 0.065 0.20 0.012 0.019 0.036 0.012 0.0038 -0.0118 Comparative Steel 3 0.059 0.21 0.010 0.017 0.035 0.0066 0.011 0.0024 1200 ℃ 550 ℃ 75% Comparative Steel 4 0.120 0.25 0.011 0.019 0.042 0.0088 0.012 0.0006 1100 ℃ 650 ℃ 89%

Psalm Number Enamel Mechanical properties Fish Scale Outbreaks Enamel thickness Speculative Surface defects Yield strength (kgf / ㎡) Tensile strength (kgf / ㎡) Elongation (%) Strength after firing (kgf / mm2) Inventive Steel 1 0 142 ㎛ Good none 27 34 42 25 Inventive Steel 2 0 137㎛ 〃 〃 28 36 39 26 Invention Steel 3 0 140 μm 〃 〃 27 36 40 28 Inventive Steel 4 0 149 ㎛ 〃 〃 29 39 36 30 Comparative Steel 1 33 129㎛ 〃 〃 27 35 40 28 Comparative Steel 2 46 141 μm 〃 〃 20 42 42 23 Comparative Steel 3 25 148㎛ 〃 〃 26 34 42 24 Comparative Steel 4 0 139㎛ 〃 Occur 34 46 33 32

As shown in Tables 1 and 2, the invention steels (1) to (4) belonging to the scope of the present invention did not generate fish scale even under severe conditions, and the yield strength after firing became 25 kgf / mm 2 or more, so that the hot rolled enamel was treated. It was suitable as a plate. On the other hand, the comparative steel (1), the content of boron is lower than the range of the present invention 33 fish scale defects occurred. Comparative steel (2) is 46 fish scale because boron content is within the scope of the present invention, but the nitrogen content is 0.0038%, not only out of the scope of the present invention, but also the N-1.3B value is negative value of -0.0118. A defect occurred. Comparative steel (3) is a component within the scope of the present invention, but the hot rolling start temperature of the hot rolling conditions, the winding temperature is low, the total reduction rate is also very low as 75% occurred 25 fish scale defects. On the other hand, the comparative steel (4) is too high in the carbon content bubble defects during the enamel processing can not be used for enamel.

As described above, the enameled hot rolled steel sheet produced by the present invention has excellent fish scale resistance, so that no fish scale defects, which are fatal defects of enamel products, are generated at all, and both enamel adhesion and post-calcination strength are excellent. In particular, it can be applied to products that need to be thick and have enamel processing on both sides.

Claims (1)

In the manufacturing method of the hot rolled steel sheet for enamel, C: 0.1% or less, Mn: 0.1 to 0.5%, S: 0.01 to 0.05%, P: 0.03% or less, B: 0.004 to 0.015%, N: 0.006 to 0.02%, Al: 0.01 to 0.1% by weight% Steel, which satisfies 0.0005% <N-1.3B, and re-heats the steel containing the remaining Fe and other unavoidable impurities at 1300 ° C. or lower, and then hot-rolls to obtain a hot finish rolling start temperature of 1150 ° C. or lower, and finish rolling A total rolling reduction of 80% or more, the method of producing a hot rolled steel sheet for double-sided enamel characterized in that the winding at a temperature of 600 ℃ or more.