KR20000015390A - Method for producing steel plate of good formability for enamelling - Google Patents

Abstract

PURPOSE: A method for producing cold rolled steel plates is provided, which satisfies the requirements of close adhesion of enameling, resistance to fish scale generation and formability of shape. CONSTITUTION: The method is as follows:reheating an aluminum killed steel comprising in weight C below 0.004%, Mn below 0.3%, S 0.02-0.03%, P 0.005-0.03 %, Ti 0.08-0.15%, N below 0.004%, excess Ti above 0.04% and the balance of Fe and unavoidable impurities; hot rolling at the final roll temperature above Ar3 Transformation temperature; and cold rolling at the compressibility of 50-85%; annealing continuously at above the temperature of recrystallization.

Description

Manufacturing method of high adhesion enameled steel sheet with excellent formability

The present invention belongs to a method for producing an enameled cold rolled steel sheet used as a base steel sheet of an enamel processing product such as a part of a home appliance or a bathtub. More specifically, the present invention relates to a manufacturing method that can ensure both the enamel adhesion and fish scale formability of the enameled cold rolled steel sheet to a certain level.

In general, the cold rolled steel sheet for enamel is formed into a variety of forms to suit the purpose, and then enameled on the surface and calcined at a high temperature to produce an enamel product. The main characteristics required for such an enameled cold rolled steel sheet include adhesion between the steel sheet and the enamel layer, fish scale resistance, and moldability.

Enamel adhesion is the adhesion between the steel sheet and the enamel layer, which is known to be affected by the additive elements and the surface roughness added to the steel sheet.

Fishcale refers to a defect in which the enamel layer, which has already been hardened on the surface of the steel sheet, breaks into fish scales by the hydrogen pressure generated by the release of hydrogen that has been dissolved in the steel before firing or at high temperature firing in the enamel manufacturing process. . In order to prevent fish scale defects, it is necessary to make a position to adsorb hydrogen in the steel, which is known to be greatly affected by the amount of non-metallic inclusions or precipitates present in the steel sheet.

To date, steel grades proposed to prevent fish scale may be precipitated or oxides known as hydrogen storage sources such as titanium sulfide, titanium nitride, titanium carbide, boron nitride or manganese oxide by adding titanium, boron, nitrogen and oxygen. Most of these are titanium-added steel, boron-added steel, high-oxygen steel and decarbonized steel which have decarbonized steel and high carbon steel to secure fish scale resistance.

In addition, since the moldability is processed into a desired shape before the enamel product is enameled, the moldability of the enamel material is very important.

Until now, the developed cold rolled steel sheet for enamel does not satisfy all the characteristics of enamel adhesion, fish scale resistance and formability of steel sheet, and has inevitably sacrificed some of these characteristics instead of securing any one characteristic.

Accordingly, the present invention is to provide an enameled cold rolled steel sheet that satisfies all of the properties of enamel adhesion, fish scale resistance and moldability, an object thereof.

The manufacturing method of the present invention for achieving the above object, in weight%, C: 0.004% or less, Mn: 0.3% or less, S: 0.02% -0.03%, P: 0.005% -0.03%, Ti: 0.08-0.15 %, N: 0.004% or less, and excess titanium (Ti ^* ) defined as Ti ^* = Ti-(48/32) S-(48/14) N- (48/12) C is not less than 0.04% Satisfactory, reheating the aluminum-kilted steel made of the remaining Fe and other inevitable impurities, hot-rolled under the condition that the finish rolling temperature is above the Ar ₃ transformation point, and then wound in the usual manner, followed by 50-85% Cold rolling is carried out at a reduction ratio, and then continuous annealing at a temperature higher than the recrystallization temperature.

Hereinafter, the present invention will be described in detail.

When C is added in an amount of 0.004% or more, the amount of solid solution in steel is high so that it hinders the development of the aggregate structure during annealing or the amount of fine titanium carbide is precipitated so that the crystal grains become fine and the moldability is greatly lowered.

The Mn is added to prevent hot shortness due to solid solution of precipitated sulfur in steel as manganese sulfide, but in the case of the present invention steel, sulfur is retained in solid state by adding titanium to precipitate titanium sulfide. Removes manganese separately because it is completely removed. In addition, manganese has the effect of increasing the strength when present in solid solution in the steel, but the reinforcing effect is limited to 0.3% or less because it does not damage the formability.

S is generally known as an element that inhibits the physical properties of steel, but in the case of the present invention steel, titanium sulfide is added to secure fish scale resistance. The amount and size of titanium sulfide are less than 0.02% of sulfur to secure fish scale resistance, and when added to 0.03% or more, it is preferable to add 0.02-0.03% because the amount of excess Ti decreases due to low formability. .

P is known as an element in the cold rolled steel sheet that effectively increases the strength without significantly reducing the formability. In the present invention, Ti (Fe, P) precipitates are produced by reacting with titanium and added for the purpose of improving fish scale resistance. If the addition amount of P is less than 0.005%, Ti (Fe, P) precipitates are not produced, so it is difficult to expect the improvement of fish scale resistance, and at 0.03% or more, recrystallized grains are formed by producing very fine (Ti, Fe) P precipitates. P is added at 0.005-0.03% because moldability is lowered.

The Ti improves the formability of the steel sheet by precipitating and removing solid carbon and nitrogen in the steel with titanium carbon and nitride, and precipitates titanium sulfide (TiS) and Ti (Fe, P) precipitates to improve fish scale resistance. As an element, when the added amount is 0.08% or less, the amount of titanium precipitates precipitated is small so that the fish scale resistance cannot be secured. When 0.15% or more is added, the amount of titanium precipitates is large, the fish scale resistance can be secured, but enamel adhesion It is preferable to add it at 0.08-0.15% because it lowers.

The N is combined with titanium to precipitate titanium nitride to improve fish scale resistance, but in the case of titanium nitride, surface defects are generated by oxidizing nitrogen gas when exposed to a steel sheet, so that the nitrogen content is as low as possible. It is good, and the nitrogen content is less than 0.004%, so the amount of titanium nitride is small and the probability of surface defects is very low, so the amount of nitrogen is limited to 0.004% or less.

Excess titanium (Ti ^* ), defined as Ti ^* = Ti-(48/32) S-(48/14) N- (48/12) C, is a reaction of TiN, TiS and TiC The amount of titanium remaining in the solid solution state calculated on the assumption that all of the elements added by combining with precipitates. In reality, all of these elements do not react. It not only precipitates completely but also precipitates (Ti, Fe) P precipitates, thereby improving fish scale resistance. If the excess titanium content is more than 0.04%, there is almost no carbon or nitrogen remaining in the solid solution state, so that moldability of 2.0 or more can be obtained. Since the scalability can be ensured, the lower limit is made 0.04% or less.

Re-heating and hot rolling the aluminum-kilted steel formed as described above, the hot rolling at this time is preferably a finish rolling temperature of more than Ar ₃ transformation temperature. The reason for this is that hot rolling at an Ar ₃ transformation temperature lowers workability due to the formation of rolled grains.

As described above, the hot rolling is carried out and wound in a usual manner, followed by cold rolling. The cold rolling reduction is preferably limited to 50-85%. It is produced during hot rolling, and the fine cracks are generated in the process of breaking or stretching in the cold rolling process, and these gaps remain mostly after continuous annealing and serve as an important hydrogen storage source. Is needed. In other words, if the cold reduction rate is less than 50%, the formation area of fine gaps is small, and the hydrogen absorption ability is low, and thus the probability of fish scale generation is high. This is because the area of the gap is rather reduced and the hydrogen storage capacity is drastically reduced.

Cold rolling as above and then continuous annealing in the usual manner. That is, it is good to continuously anneal above reheating temperature.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

The steel ingot prepared to be dissolved so as to satisfy the composition shown in Table 1 was maintained for 1 hour in a 1250 ℃ heating furnace and then hot rolled. At this time, the hot finishing rolling temperature was 900 ℃, winding temperature was 650 ℃, the final thickness was 3.2mm. The hot rolled specimens were pickled to remove the oxide film on the surface and then cold rolled at a 70% reduction rate.

Cold rolled specimens were processed into enameled specimens for enameling and tensile specimens for mechanical properties, followed by continuous annealing.

At this time, the enameled specimen was cut to a size of 70mm × 150mm, and the tensile specimen was processed into a standard specimen according to ASTM (ASTM E-8 standard). Continuous annealing was performed at a temperature of 830 ° C.

As described above, the tensile specimens of the specimens in which continuous annealing was completed were measured using a tensile tester (INSTRON, Model 6025) 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 acid-treated for 5 minutes at 70 ° C. and 10% sulfuric acid solution, washed with warm water, and then maintained at 85 ° C., 3.6 g / l sodium carbonate + 1.2 g / l. It was neutralized by dipping in borax aqueous solution for 5 minutes. After the pretreatment was completed, the glaze (Haewang ceramics, glaze firing temperature of 830 ° C for the first enamel) was applied 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 calcination, followed by enameling of air cooling. At this time, the atmosphere of the kiln was a harsh condition where fish scale defects were most likely to occur at a dew point temperature of 30 ° C. The enameled specimens were kept in a 200 ° C. holding furnace for 20 hours to visually examine the number of fish scale defects generated after the fish scale acceleration treatment, and the results are shown in Table 2 below.

At this time, the enamel adhesion evaluation was measured by using the adhesion test equipment (test equipment according to ASTM C313-78 standard).

Steel grade Chemical composition (% by weight) Cold rolling reduction (%) C Mn P S Ti N Ti ^* Invention steel One 0.0025 0.12 0.015 0.023 0.098 0.0021 0.046 70 2 0.0018 0.23 0.008 0.025 0.114 0.0018 0.063 3 0.0033 0.15 0.012 0.025 0.121 0.0019 0.064 4 0.0014 0.20 0.010 0.022 0.118 0.0015 0.074 Comparative steel One 0.0042 ^ 0.22 0.014 0.042 ^ 0.095 0.0030 0.005 ^ 2 0.0012 0.25 0.011 0.012 ^ 0.095 0.0045 ^ 0.057 3 0.0023 0.26 0.013 0.032 ^ 0.182 ^ 0.0030 0.115 4 0.0015 0.14 0.011 0.038 ^ 0.072 ^ 0.0021 0.002 ^ Conventional Steel One 0.0039 0.15 0.010 0.013 ^ 0.122 0.0075 ^ 0.061 ^ Is outside the terms of the present invention

Psalter Enamel Mechanical properties Remarks Fish Scale Outbreaks () Enamel thickness (μm) Cohesion Index (%) Yield strength (kgf / mm ² ) Tensile strength (kgf / mm ² ) Elongation (%) r value Invention One 0 131 100 12.2 31.3 48.6 2.15 Inventive Steel 1 2 0 103 97 13.3 31.8 47.6 2.25 Inventive Steel 2 3 0 110 96 13.8 30.9 47.3 2.28 Invention Steel 3 4 0 121 99 12.3 29.9 48.9 2.38 Inventive Steel 4 Comparative material One 0 100 97 15.8 32.4 44.3 1.72 Comparative Steel 1 2 25 135 100 12.1 30.9 49.0 2.25 Comparative Steel 2 3 0 104 83 14.6 32.3 46.8 2.37 Comparative Steel 3 4 38 120 99 15.9 33.1 44.0 1.72 Comparative Steel 4 Conventional One 0 99 85 13.6 31.7 46.4 2.12 Conventional Steel (Surface Defect)

As shown in Tables 1 and 2, the invention material (1-4) was secured high formability to the r value of 2.0 or more of the steel sheet, and fish scale does not occur even under severe conditions, and also excellent fish scale resistance. In addition, in the case of enamel adhesion index, the adhesion was high as 95% or more.

On the contrary, the comparative material (1) had a sulfur content of 0.042%, so that there was no fish scale defect, but the amount of excess titanium was 0.005%, and the r value was 1.7.

Comparative material (2) is 0.057% excess titanium, the r value is 2.25 is excellent moldability, but the sulfur content is 0.012% low 25 fish scales can not be used as an enamel steel sheet.

The comparative material (3) had a sulfur content of 0.32% and no fish scale defects. The excess titanium was 0.115%, the r value was 2.37, and the moldability was excellent.However, the titanium content was 0.182%. It is difficult to use as an enamel steel sheet.

The comparative material (4) had a high sulfur content of 0.038% but a low titanium content of 0.072%, resulting in 38 fish scales, and an excess titanium content of 0.002%.

The comparative material (5) is a conventional steel with a high titanium content of 0.122% and a nitrogen content of 0.0075%. Thus, the formation of coarse titanium nitride in the steel did not cause fish-scale defects and the excess titanium content was 0.061%. Although the formability was excellent with this 2.12, the coarse precipitate coarse titanium nitride existed in the surface, and the surface defect by the bubble generate | occur | produced.

As described above, according to the present invention, there is provided an enamel steel sheet excellent in both enamel adhesion, fishscale and moldability, and this enamel steel sheet has a useful effect that can be applied to a product that is molded into a particularly complex shape. There is.

Claims (1)

In the manufacturing method of the cold rolled steel sheet for enamel, By weight, C: 0.004% or less, Mn: 0.3% or less, S: 0.02% -0.03%, P: 0.005% -0.03%, Ti: 0.08-0.15%, N: 0.004% or less, Ti ^* = Excess titanium (Ti ^* ), defined as Ti-(48/32) S-(48/14) N- (48/12) C, satisfies 0.04% or more, and the remaining Fe and other inevitable impurities The aluminum-kilted steel is reheated, hot rolled under the condition that the finish rolling temperature is equal to or higher than the Ar ₃ transformation point, and then wound in a conventional manner, followed by cold rolling at a 50-85% reduction rate, and then at a temperature above the recrystallization temperature. Method for producing a high adhesion enamel steel sheet excellent in formability, characterized in that the continuous annealing.