KR100470056B1 - A cold rolled steel sheet for direct-on enamel applications with excellent adherence - Google Patents

Abstract

The present invention relates to a steel sheet of a direct enamel processing product to be applied to home appliance parts such as a gas stove, a microwave oven, and by controlling the steel components appropriately, even when the direct enamel processing material is manufactured by a continuous casting method, It is an object of the present invention to provide a direct enameled cold rolled steel sheet that can secure enamel adhesion under pretreatment conditions.

The present invention for achieving the above object,

By weight% C: 0.005% or less, Mn: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al: 0.01 to 0.1%, B: 0.002 to 0.01%, N: 0.004 to 0.015%, above B and N are 0.0005% <N-1.3B <0.01%, Ni: 0.02 to 0.08%, Co: 0.02 to 0.08%, Nb: 0.005 to 0.05%, and the atomic ratio of Nb / C is 0.5 to 2.5, The technical gist of the direct enameled cold rolled steel sheet having excellent enamel adhesion, which is composed of the balance Fe and other unavoidable impurities, is considered.

Description

Cold rolled steel sheet for direct enamel with excellent enamel adhesion {A COLD ROLLED STEEL SHEET FOR DIRECT-ON ENAMEL APPLICATIONS WITH EXCELLENT ADHERENCE}

The present invention relates to a steel sheet of a direct enamel processing product that is applied to home appliance parts such as a gas stove, a microwave oven, and more specifically, has an excellent enamel adhesion and a fishscale defect, which is a fatal defect of an enamel product. The present invention relates to a direct cold rolled steel sheet for enamel having no moldability and excellent moldability.

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.

Conventionally, in order to prevent fishscale defects known as the most fatal defects in such enamel products and to improve formability, they have been subjected to a decarbonization annealing process, resulting in a high production cost. In addition, in the nickel treatment step of the pretreatment that must be essential to manufacture by enamel directly, there is a problem that it is difficult to secure the adhesion because the pH value to be adjusted in a narrow range.

For example, in the case of the steel component disclosed in Japanese Patent Laid-Open No. Hei 10-212546, since enamel adhesion is ensured only in a narrow section of pH 2.5 to 3.0, there is a problem that the Ni treatment solution must be strictly managed. Since the Ni treatment solution is severely changed in pH value, it is difficult to secure stable quality.

Therefore, there is a need for a cold rolled steel sheet for direct weighing which can secure adhesion even at a wide range of pH.

In order to solve the above problems, the present inventors have repeatedly studied and experimented and proposed the present invention based on the results. The present invention continuously casts the material for enamel treatment directly by appropriately controlling the steel component. Even if manufactured by the method is to provide a direct enameled cold rolled steel sheet that can secure the enamel adhesion in a relatively wide pre-treatment conditions.

The present invention for achieving the above object,

By weight% C: 0.005% or less, Mn: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al: 0.01 to 0.1%, B: 0.002 to 0.01%, N: 0.004 to 0.015%, above B and N are 0.0005% <N-1.3B <0.01%, Ni: 0.02-0.08%, Co: 0.02-0.08%, Nb: 0.005-0.05%, and the atomic ratio of Nb / C is 0.5-2.5, The present invention relates to an enameled cold rolled steel sheet having excellent enamel adhesion, which is composed of residual Fe and other unavoidable impurities.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the steel component of the present invention, it is preferable to limit the content of C to 0.005% or less. The reason is that when the content of C is more than 0.005%, the amount of carbon dissolved in the steel increases, which hinders the development of the aggregate structure during annealing, or crystal grains. This is because it is fine and greatly inhibits moldability.

Mn is an element that prevents hot shortness caused by solid solution S by precipitating solid solution S in MnS. Manganese sulfide is elongated during cold rolling, and has superior hydrogen storage ability than other oxides or precipitates except boron nitride. The Mn content is preferably 0.05% or more, which is an amount sufficient to precipitate S remaining in the steel. However, when Mn is contained in an excessively large amount, the Mn content may increase strength when present in solid solution, but may not increase the reinforcing effect. It is preferable to set the upper limit to 0.3% because it impairs.

S and P are generally elements that inhibit the properties of the steel, it is preferable to limit the content to 0.02% or less, respectively.

Al is usually added as a deoxidizer, but in the present invention, Al is added to precipitate the solid solution nitrogen remaining in the steel to improve moldability. In order to precipitate 0.0005% of N remaining in solid solution in the steel, about 0.001% of Al is required. However, sufficient amount of aluminum needs to be added to completely precipitate the solid solution nitrogen. Therefore, the Al content is set to 0.01% or more. It is preferable. However, when excessively added, not only the moldability is lowered, but also the deposition effect of boron nitride can be reduced, so the upper limit is preferably limited to 0.1%.

B is an element that combines with N to form BN to improve fish scale resistance. When the content is more than 0.002%, no fish scale defect occurs, so the lower limit is set to 0.002%. However, the larger the amount added, the better the fish scale resistance, but it is not necessary to secure the fish-resistance scale more than appropriate, and the addition of excessive N greatly reduces the moldability, so the upper limit is limited to 0.01%. desirable.

N is an element added to bond with B to precipitate as BN to secure fish scale resistance, and the content thereof is preferably set in consideration of the content of B. The amount of N required to precipitate the lower limit of 0.002% of B is 0.0026%, but at least 0.004% is required to completely deposit B remaining in the solid state, and thus the lower limit is set to 0.004%. However, as the amount of N added increases, the amount of precipitates precipitated, so that the fish scale resistance is improved. However, when the amount of N is increased too much, the moldability and aging resistance are deteriorated, so the upper limit is preferably limited to 0.015%.

On the other hand, from the B and N, to set the content range of N-1.3B, it is preferable that the range of 0.0005% <N-1.3B <0.01%. The reason is that when N-1.3B is less than 0.0005%, solid solution B remains in the steel to improve the fish scale resistance, and the efficiency is low as well as the formability decreases rapidly. When N-1.3B is more than 0.01%, This is because the amount of nitrogen remaining after bonding with B is too large, and the amount of N remaining in the excessive precipitation of AlN or the solid solution state increases, resulting in poor moldability.

Ni is an element added to improve the enamel adhesion by increasing the amount of nickel deposited on the surface of the steel sheet in the nickel treatment process, the content of the Ni should be more than 0.02%. However, since the amount of nickel adhering to the surface of the steel sheet is not large relative to the addition amount when added at 0.08% or more, the upper limit is preferably limited to 0.08%.

Co is an element that effectively increases the roughness of the steel plate surface in the acid treatment process to improve the enamel adhesion. The content of Co should be 0.02% or more. However, when the addition of 0.08% or more, the surface roughness is rather reduced, it is preferable to limit the upper limit to 0.08%.

Nb is an element added to improve the material of the steel sheet, the content must be more than 0.005% to obtain this effect. However, since moldability falls when the addition amount is 0.05% or more, it is preferable to set an upper limit to 0.05%.

On the other hand, in the said Nb and C, it is preferable to limit Nb / C atomic ratio to 0.5-2.5. The reason for this is that when the Nb / C atomic ratio is less than 0.5, the amount of C remaining in solid solution without precipitation as NbC precipitate in the steel is high, so that moldability is lowered, and when the Nb / C ratio exceeds 2.5, Nb remains in solid solution. This is because the amount of r is small and the size of the recrystallized grains decreases, resulting in deterioration of moldability.

The steel thus formed may be manufactured into a cold rolled steel sheet for legal capacity under ordinary manufacturing conditions. In particular, hot rolling is preferably performed at a finish rolling temperature of more than Ar ₃ transformation point, and cold rolling may be performed at a temperature of 50 to 85%. It is preferable to carry out by a reduction ratio.

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

(Example)

The steel ingots formed as shown in Table 1 were held in a 1250 ° C. heating furnace for 1 hour, and then hot rolled. At this time, the hot finishing rolling temperature was 900 ℃, the winding temperature was 700 ℃, the final thickness was 3.2mm. The hot rolled specimens were pickled to remove the oxide film on the surface and cold rolled. The cold reduction rate was 70%.

Cold rolled specimens were processed into enameled specimens for enameling and tensile specimens for mechanical properties, respectively, followed by continuous annealing. The enameled specimens were cut to a size of 70mm x 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, a 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 specimen was degreased and then acid-treated for 5 minutes at 70 ° C and 10% sulfuric acid solution, washed with hot water, and then nickel-treated for 5 minutes at 7% nickel sulfate solution maintained at 80 ° C. Was done. At this time, the pH value of the nickel treatment solution was changed from 2 to 4. The nickel-treated specimens were washed with warm water and neutralized by soaking in 3.6 g / l sodium carbonate + 1.2 g / l borax solution maintained at 85 ° C for 5 minutes. After coating the coated glaze (Cover Coat) on the pre-treated specimen was dried for 10 minutes at 200 ℃ completely removed the moisture. The dried specimens were kept at 800 ° C. for 7 minutes and subjected to calcination, followed by enameling of air cooling. At this time, the atmospheric conditions of the kiln was a harsh condition where the fish scale defects are most likely to occur at a dew point temperature of 30 ℃. After the enameled specimens were kept in a 200 ° C. holding furnace for 20 hours, the number of fish scale defects generated after the fish scale acceleration treatment was visually investigated, 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), and the evaluation results are shown in Table 2 below.

Steel grade C Mn P S Al N B Nb Ni Co Nb / C atomic cost (N-1.3B) value Inventive Steel 1 0.0015 0.2 0.01 0.011 0.03 0.0094 0.0055 0.024 0.05 0.03 2.06 0.00225 Inventive Steel 2 0.0021 0.2 0.01 0.009 0.04 0.0120 0.0061 0.023 0.03 0.05 1.41 0.00407 Invention Steel 3 0.0025 0.2 0.01 0.009 0.03 0.0098 0.0063 0.031 0.04 0.03 1.6 0.00161 Inventive Steel 4 0.0016 0.2 0.01 0.008 0.05 0.0106 0.0072 0.029 0.05 0.03 2.34 0.00124 Comparative Steel 1 0.0019 0.2 0.01 0.009 0.04 0.0092 0.0071 0.023 0 0 1.56 -0.00030 Comparative Steel 2 0.0031 0.2 0.01 0.009 0.03 0.0041 0.0062 0.005 0.01 0.05 0.21 -0.00406

River Mechanical property Enamel Treatment Condition and Enamel Characteristics Nickel treated pH 2.5 Nickel-treated pH 4.0 Yield strength (kg / ㎡) Tensile Strength (kg / ㎡) Elongation (%) r value Cohesion Index (%) Fish Scale Cohesion Index (%) Fish Scale Inventive Steel 1 18.2 30.8 48 1.93 98 No occurrence 98 No occurrence Inventive Steel 2 18.9 31.2 46 1.94 96 97 Invention Steel 3 19.5 31.9 46 1.96 97 96 Inventive Steel 4 17.8 30.2 48 1.96 99 95 Comparative Steel 1 18.6 30.3 47 1.96 95 Occur 25 Occur Comparative Steel 2 20.5 32.9 41 1.52 97 53

As shown in Table 2, in the case of the present invention steel (1) to (4), even if the nickel treatment pH is not a fish scale generation even in a wide range of 2.0 ~ 4.0, the adhesion index also shows a high value of 95% or more It can be seen. In addition, the mechanical properties are also equal to or greater than those of the comparative steels (1, 2). In particular, the r value, which is a formability index, is 1.9 or more, indicating high formability, and thus deep recessing is possible.

On the other hand, Comparative steel (1) is a steel grade without Ni and Co added, excellent in the adhesion index of 95 or more at pH 2.5 of nickel treatment, but it can be seen that the adhesion is very poor at the adhesion index 25 when the pH is 4.0. . In addition, the comparative steel (2) is outside the scope of the present invention with an Nb / C atomic ratio of 0.21, and significantly out of the scope of the present invention with an N-1.3B value of -0.00406%, the r value is very low and a fish scale occurs. In addition, the low content of Ni was poor adhesion to 53% at pH 4.0 conditions.

As described above, according to the present invention, by adjusting the steel component, there is an effect that can provide excellent enamel adhesion even at a wide range of pH in the nickel treatment step during direct enamel processing.

Claims (1)

By weight% C: 0.005% or less, Mn: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less, Al: 0.01 to 0.1%, B: 0.002 to 0.01%, N: 0.004 to 0.015%, above B and N are 0.0005% <N-1.3B <0.01%, Ni: 0.02 to 0.08%, Co: 0.02 to 0.08%, Nb: 0.005 to 0.05%, and the atomic ratio of Nb / C is 0.5 to 2.5, Cold rolled steel sheet for direct enamel with good enamel adhesion composed of balance Fe and other unavoidable impurities.