TWI243211B - Method for manufacturing high adherence enamel-coating steel sheet with superior formability - Google Patents

Abstract

A method for manufacturing a cold rolled steel sheet to be enamel-coated and to be used as raw steel sheets for enamel-coated products such as bath tubs and components of electric appliances is disclosed. The optimum contents of the alloying elements such as S, P and N are realized, thereby satisfying the enamel layer adherence, the fishscale resistance and the formability. First, there is prepared a steel composed of, in weight %, 0.004% or less of C, 0.3% or less of Mn, 0.02-0.05% of S, 0.005-0.03% of P, 0.08-0.15% of Ti, 0.004% or less of N, 0.04% or more of an excess Ti* (being defined to be Ti*=Ti-(48/32)S-(48/14)N-(48/12)C), and a balance of Fe and other unavoidable impurities so as to form an aluminum killed steel. The aluminum killed steel is reheated, and then a hot rolling is carried out, with the finish rolling temperature being above the Ar3 transformation point. Then a coiling is carried out in the normal manner, and then, a cold rolling is carried out with a reduction rate of 50-85%. A continuous annealing is carried out above the recrystallization temperature.

Description

1243211 V. Description of the invention (1) <Scope of the invention> The present invention relates to a method for manufacturing a cold-rolled steel sheet for green coating 'as a method of coating a steel sheet material such as a bathtub and an electrical appliance part. In particular, the present invention relates to a method for manufacturing a cold-rolled steel sheet, which can guarantee properties such as enamel adhesion, fish scale resistance, and forming ability above a certain level. <Background of the invention> Generally, the enamel surface is subjected to the resistance of the finished product of the J. Falang steel, and the enamel layer is formed into fish scales, that is, when it is manufactured or cooled, it forms a kind of steel, such as hydrogen supply. , T i carbon can absorb hydrogen, or steel recommended for high carbon steels, or decarburized Lang-coated cold-rolled steel sheets, and then made. The cooling capacity of the French coating and the adhesion of the steel plate raw materials are due to the enamel enamel-covered products, which are later released. Due to fish scale-like deterioration space. This is greatly affected by the existence of species and quantity. T i, B, N compounds, B nitrides are well-known. It is decarburized in this way to ensure that it is mostly Ti-added steel.

High-temperature fire to complete the enamel quilt | The main characteristic required for rolling the steel plate is the adhesion between the fish pan and the enamel layer. Add elements and surface roughness.

Caused by defects on the surface of the coated product. ’The solid solute hydrogen in the steel is under the pressure of hydrogen and the hardened layer is broken ^’ To avoid fish scaling, it is necessary to face the deposits or non-golden shoulders in the steel plate. In order to avoid fish scale formation, it is recommended to form Ti sulfide, Ti + gas Mn oxide or other, which are all 'sinks or oxides that are precipitated to eliminate fish scale phenomenon. So far, primary steel, steel with added B, high oxygen content

1243211 V. Description of the invention (2) However, the forming ability is also important, because the cold-rolled steel sheet must be pressed into the required shape before covering the enamel layer. Japanese Patent Publication No. Sho 63-50 0 discloses a method for manufacturing an enamel-coated steel sheet. In this steel sheet, it contains C in a weight ratio of 0.05% or less; 0.03% or less Si; 0.50% or less Mn; 0.02% or less P; 0.03% or less s; 〇〇〇〇5〜01% 的 Ν; 0.15% or less Ti [Ti &gt; (48 / 12C + 48 / 14N + 48 / 3 2S)]; 0.08% or less of Cu, one or more of 0.003 ~ 0.03% selected from a group of As, Sb, and Bi

The sum of elemental additives; and the rest are other unavoidable impurities. The content of 'N in this steel is high, so if a TiN deposit is exposed on the surface of the steel sheet, a bubble bed is formed. Another Korean Patent No. 97-63270 discloses another method for manufacturing an enamel-coated steel plate. In this method, the weight ratio of the composition of the steel is 0. 〇 丨% or less C '〇3% or less Mn; 〇. ~ 〇. 1% p; 〇. 〇2 ~ 0 · 04% S; 〇〇〇4 ～ 〇 · 10% Ti; 〇〇〇〇5% or less, the atomic ratio of Ti / (c + N + j) is 10 or more, the rest is And other unavoidable impurities. In this steel, the content of P is high, so although the strength of the steel sheet is acceptable, the forming ability is deteriorated.

&amp; As described above, the enamel-coated cold-rolled steel sheet developed so far has not yet met the characteristics of the adhesion of the rural layer, the characteristics of fish scale resistance and forming ability, but there is a sacrifice of another property in order to maintain one property Question "General Summary of Invention" The present invention is intended to overcome the above-mentioned shortcomings in the conventional technology.

Page 7 1243211

V. Description of the invention (3) Therefore, one of the objects of the present invention is to maintain the most appropriate content of alloying elements such as S and p in the plate ', so as to satisfy the characteristics of enamel forming ability. Provided is an enamel-coated cold-rolled steel, N, Ti and effective Ti (Ti *) which can maintain the adhesion of the beetle layer, fish scale resistance and formation &gt; t Ϊ I to achieve the purpose of disclosure. There are: preparing a steel whose composition weight ratio is 0.00 U or less, c, 0.3% or less Mn, 0.002 ~ 005% §, ΗΜ ~ 0 · 03 ^ P ' 〇 · (] 8 ~ 〇 · 15 "Τί'〇〇〇〇〇4 ^ Μ〇ιΝ, 0.4% or more excess Ti * (definition * Ti * = Ti_ (48/32) s —

(W / 12) C), and the rest are Fe and other unavoidable impurities to form a pure static steel of aluminum; the pure static steel reheated on this aluminum; hot rolling is performed, and the completion hot rolling temperature is higher than A. Switching points; coiling in the usual way; cold rolling at a reduction ratio of 50 to 85%; and continuous annealing above the recrystallization temperature. <Detailed description of a preferred embodiment> The steps included in the method for manufacturing a pearl-coated cold-rolled steel sheet according to the present invention are: preparing a steel having a composition of 0.004% by weight or less C

0.3% or less Mn, 0.02 to 0.05% S, 0.005 to 0.03% P, 0.008 to 0.015% Ti, 0.004% or less N, 0.004% Or more excess Ti * (defined as Ti * = Ti-(48/32) S— (48/14) N— (48/12) C) 'The rest is Fe and other unavoidable impurities to form a Pure static steel of aluminum; pure static steel reheated to this aluminum; hot rolling applied to complete hot rolling temperature higher than the Ar3 transition point; coiling applied in a general manner; applied at a reduction ratio of 50 to 85% Cold rolling; and continuous annealing above recrystallization temperature.

1243211 V. Description of the invention (4) In the following, the reasons for limiting the number of ingredients of the present invention will be explained in more detail. If the content of C is more than 0.004%, the solid solute carbon becomes excessive. As a result, the development of the structure is hindered during annealing, or the amount of precipitation of fine Ti carbides becomes excessive. As a result, the particles become fine and the forming ability becomes poor. Therefore, the content of C must be limited to 0.04% or less. The addition of Mn is to precipitate the solid solute S in the form of Mn sulfide, thereby avoiding the hot brittleness caused by the Fes film. In any case, in the present invention, the addition of T i precipitates s as a Ti sulfide, thereby completely removing the residual S. Therefore, Mn does not have to be added separately. If Mn exists in the state of a solid solution, the strength of the steel is increased, but such an increase in strength is not significant, but the forming ability is deteriorated. Therefore, the content of Mn is preferably limited to 0.3% or less. S is generally considered to be an element that deteriorates mechanical properties, but in the present invention, S is added to strengthen the resistance of the fish scale. If the content of s is less than 0.22%, the amount and size of Ti sulfide become insufficient, and as a result, the fish scale resistance cannot be improved. If the content of S is 0.05% or more, the excessive T i * becomes too small to deteriorate the forming ability. Therefore, the content of S should be limited to 〇 2 〇 0. 05% is appropriate. It is better if it is limited to 0.02 ~ 0.03% to ensure higher forming ability. P is also an element that deteriorates the mechanical properties of steel, which is the same as S. Therefore, its content should be as small as possible. In the present invention, the addition of p is used to form a precipitate of Ti (Fe, P) after chemical reaction with Ti to improve fish scale resistance. If the content of P is less than 0.05%, no precipitation will occur, p)

1243211 V. Description of the invention (5) Therefore, the fish scale resistance cannot be improved. If its content is more than 0.3%, the recrystallized particles become too fine due to the formation of fine Ti (Fe, P) precipitates, resulting in poor forming ability. Therefore, the content of P should be limited to 0.005 ~ 03%. · Ding 1 removes the solid solutes c and 1 ^ by the formation of Ti carbides and Ti nitrides, thereby improving the forming ability of steel sheet raw materials. In particular, Ti can improve fish scale resistance by precipitating Ti sulfides (TiS) and Ti (Fe, P). If its content is less than 0.08%, the amount of Ti precipitates is too small to improve the fish scale resistance. If the Ti content is greater than 0.15%, Ti precipitation will increase to improve the fish scale resistance, but the adhesion to enamel will be worsened due to the higher. Therefore, the content of Ti should be limited to 0.88% to 0.15%. In addition, N reacts with Ti to precipitate with the formation of Ti nitride, thereby changing the scale to prepare scale resistance. However, when Ti nitride is exposed on the surface of the steel sheet, radon occurs and gas is generated, which causes the surface to deteriorate. Therefore, the content of N should be reduced as much as possible. From risotto to less than 0.00, Ti nitrides precipitate with a small amount, which has a low probability of causing surface degradation. Therefore, the N content should be at or less. Excessive Ti is defined as Ti * = Ti — (48/3 — (48/12) (^ Τι ^, _μ_ · ν, τ)). The excess Ti * is attributed to the residual if, Shangdan's evening, //, all the added elements will not completely react, because there are quite a lot of residual solid solutes_ 的 沉 = 于 ο 〇4Γ Yodo improves the resistance of fish scales. If Ti * is excessive, the C And N will cease to exist, because

Page 10 1243211 V. Description of the invention (6) Therefore, the forming ability with a value of 2. Or or greater can be guaranteed. With r values of 2.0 or greater, complex shapes can be formed. And with the appropriate amount of Ti (Fe, P) sinking, sufficient fish scale resistance can be obtained. Therefore, the lower limit of the excess T 丨 * should be 0.04%. Especially excessive] ^ * is less than 0.04 ° /. At this time, no 1 ^ (? 6 ,?) precipitates are formed, thus reducing fish scale resistance. Hereinafter, the manufacturing conditions of the steel plate of this invention are described. It is reheated to the above-mentioned aluminum pure still steel and hot rolled. In this case, the temperature for completion of hot rolling should be higher than the Ar3 transition point. This reason is that if the hot rolling system is implemented below the Ar3 transition point, the pellets will be rolled out and the forming ability will be reduced. After hot rolling is performed, coiling is performed in a general manner and then cold rolling is performed, and the reduction ratio is limited to 50 to 85%. The precipitate formed during hot rolling is broken or elongated during cold rolling. During this process, tiny cavities are formed, and these cavities are preserved intact as a source of hydrogen absorption even after continuous annealing. Due to this relationship, the reduction ratio of cold rolling should be controlled. That is, if the reduction ratio of the cold rolling is less than 50%, all the micro cavities become too small to reduce the absorption of hydrogen, so there is a tendency to cause fish scales. On the other hand, if the reduction ratio is more than 85%, the tiny holes collapse due to the high reduction ratio. Therefore, the 'comprehensive cavity space' is further reduced and the ability to absorb hydrogen is drastically reduced. After the cold rolling is completed, continuous annealing of the steel is performed in a general manner. That is, continuous annealing is performed above the recrystallization temperature. The invention is described below on the basis of examples. <Example>

Page 11 1243211 V. Description of the invention (7) The steel ingots as shown in Table 1 are prepared and maintained in a furnace at 125 ° C for 1 hour, and then hot rolled. The temperature at which hot rolling was completed was 900 °, and coiling was then applied at 650 °. The final thickness is 3 · 2 legs. The hot-rolled samples were impregnated to remove the surface oxide film. Cold rolling was then applied at a reduction ratio of 70%. The cold rolled samples were processed into enamel coated samples and tensile samples. The two samples were then continuously annealed. J Farang coated samples were cut into 70 mm X 1 50 mm sizes, while tension samples were formed in accordance with ASTME-8 standards. The continuous annealing was performed at 83 seconds. ,

InStron's Model 6025 tensile tester was used for the tensile test of the samples, so the flexural strength, tensile strength, elongation, and r were measured. The measurement results are shown in Table 2 below. The Lulang coated sample completely removed the fat, and was immersed in (10%, 7 (TC) for 5 minutes. Then washed with hot water, and then 3. 6g / L sodium carbide +!. 2g / L aqueous solution 5 = shell-like ^ neutralization. The pre-treatment is completed, the enamel is coated on the sample, and it is dried at 20 ° C for 10 minutes. King spear, '..., dan. Drying treatment = Bi ^ 叩 placed at 83 0 C for 7 minutes, and then treated + lice cooling, so that the enamel coating process is completed., Then 5 The dew point temperature of the atmosphere of the stove is 30 ° cm-heavy and it is easy to generate the bad situation of fish scales. ㈣ Covering this = the number of severe fish scales, the number of pots is required and ^^^ Μ under the sun inspection inspection double a / ,,,,. The results are listed in Table 2 below. As for the evaluation of the adhesion of the Zhuxiang layer, an adhesion tester is used

1243211

5. Description of the invention (8) (according to ASTMC313-78) to measure the adhesion index. As shown in Tables 1 and 2, the excellent ichthyosaur resistance was not produced even when the present invention was excellent. To / ΛΛ Adhesiveness' whose index is higher than 95%. "/, Ruiying layer, in contrast, the control material 1 5 content is as high as 00" fish scales occurred, but its C content was 0% (42%). Therefore, it is as low as 0.005% 'Therefore, the r value is exactly 17, and the forming energy is two.' In the case of Comparative Material 2, 'the amount of excess Ti * is as high as 0.057%, and the r value is 2.25, resulting in excellent forming ability. 〇m '® this' has 25 fish scale deterioration points forming steel. Can be used as an enamel coating. This steel plate is not = material 3, its S content is 〇032%' Therefore, not produced = 2 and its excess Ti The amount of * is 0.1115%, and the r value is 23 °, so as to realize the forming ability. However, the Ti content is as high as 0.182%, so the enamel layer is as low as 83%. Therefore, this material cannot be used as enamel Coated steel sheet. For the control material 4, its S content was as high as 0.03%, but its τi content was as low as 0.072%, resulting in 38 fish scale degradation points. It was also excessive 丨 * .00. 2%, so its Γ value is just 1 &gt; 72, and the result is that the forming ability is very low. As for the traditional materials 1 and 2, the τ i content is as high as 〇 · 丨 2 2% and 0.110%, and N The content is also as high as 0.0075% and 0.0082%. Therefore, Ti compounds forming coarse grains in the steel will not cause fish scale degradation. Also, the amount of Ti * is 0.061%, and the value of Γ is as high as 2.12. Excellent ability

1243211-: ® Coarse TiN compounds are present on the surface of the steel sheet, so surface degradation occurs due to the generation of large bubbles. f Conventional material 3, the content of P is as high as 0.058%. Therefore, the flexion strength is too high, and at the same time, it exhibits a low r value, resulting in low forming ability. Therefore, when this steel sheet is used to form a complicated shape, cracks may occur. According to the invention disclosed above, the adhesion of the pearl layer is excellent in fish scale resistance and forming ability. Furthermore, the steel sheet of the present invention is suitable for press forming into a complicated shape. In summary, these are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. That is, all equivalent changes and modifications according to the scope of patent application of the present invention shall be covered by the scope of patent of the present invention.

1243211 V. Description of the invention (ίο) Table 1 Chemical composition (wt%) Cold rolled steel C Μη Ρ S Ti Ν Ti Reduction ratio (%) Hair 1 0.0025 0.12 0.015 0.023 0.098 0.0021 0.046 Ming 2 0.0018 0.23 0.008 0.025 0.114 0.0018 0.063 of 3 0.0033 0.15 0.012 0.025 0.121 0.0019 0.064 Steel 4 0.0014 0.20 0.010 0.022 0.118 0.0015 0.074 Pair 1 0 · 0042Λ 0.22 0.014 0 · 042Λ 0.095 0.0030 0 · 005Λ Photo 2 0.0012 0.25 0.011 0.012Λ 0.095 0 · 0045Λ 0.057 Steel 3 0.0023 0.26 0.013 0.032Λ 0.182Λ 0.0030 0.115 70 4 0.0015 0.14 0.011 0.038Λ 0.072Λ 0.0021 0 · 002Λ Pair 1 0.0039 0.15 0.010 0 · 013Λ 0.122 0.0075Λ 0.061 Photo 2 0.0029 0.25 0.015 0.028 0.132 0 · 0082Λ 0.050 Steel 3 0Ό025 0.20 0 · 058Λ 0.025 0.110 0.0032 0.052 The Λ symbol indicates that the conditions of the present invention have been removed. Page 15 1243211 V. Description of the invention (π) Table 2 Test piece Enamel Tiber mechanical dagger quality Note The occurrence of fish scales (each) Enamel thickness (m) Attachment Property index (%) Yield strength (kgf / mm2) Tensile strength (kgf / mm2) Elongation (%) 1 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 Inventive steel 3 4 0 121 99 12.3 29.9 48.9 2.38 Inventive steel 4 \ Material 1 0 100 97 15.8 32.4 44.3 1.72 Control steel 1 2 25 135 100 12.1 30.9 49.0 2.25 Control steel 2 3 0 104 83 14.6 32.3 46.8 2.37 Control steel 3 4 38 120 99 15.9 33.1 44.0 1.72 Control steel 4 Traditional material 1 0 99 85 13.6 31.7 46.4 2.12 Conventional steel 1 (surface deterioration has occurred) 2 0 135 92 12.7 30.8 46.8 2.05 Conventional steel 2 (surface deterioration has occurred) 3 0 115 92 22.4 36.4 42.8 1.82 Conventional steel 3 page 16

Claims (1)

1243211 Case No. 88114234 Date of the month _ Amendment VI. Application for patent scope 1 · A method for manufacturing an enamel-coated cold-rolled steel sheet, comprising the steps of: preparing a steel whose weight ratio is 0 &lt; CS 0 , 〇〇4%, 〇 &lt; Mn € 0.3%, 0.02 to 0.03% of S, 0. 0 0 5 to 0.03% of p, 〇8 to 0.15% Ti ， 0 &lt; N $ 0 ♦ 0 04%, at least 0.04% excess D * (defined as Ti * = Ti— (48/32) S— (48/14) N— (48 / l2) C), and the rest are Fe and other unavoidable impurities to form an aluminum static steel; and then under normal conditions (1 50 0 ° C ~ 1 3 0 0 ° C), the aluminum is heated and cleaned. Steel; hot rolling is applied, and its completion hot rolling temperature is the Ar3 transition point [the temperature at which the steel transitions from the austenite state to the ferrite state when cooling the steel] to a temperature between 9 50 ° C Temperature; coiling in a general manner; cold rolling at a reduction ratio of 50 to 85%; and continuous annealing at a temperature between recrystallization temperature and 900 ° C. Page 17