JPS6345322A - Production of steel sheet for enamel - Google Patents

Abstract

PURPOSE:To produce a cold rolled steel sheet for enamel having excellent enamelability, press formability and longitudinal cracking resistance by working an ingot of a low Al killed steel contg. Ti, B, Cu, P, S, N, etc., at specific ratios to a sheet material by hot rolling and cold rolling then annealing the sheet. CONSTITUTION:The killed steel made of the compsn. which consists, by weight %, <0.005% C, 0.005-0.25% P, 0.05-0.25% Mn, 0.005-0.025% S, 0.025-0.045% Cu, 0.05-0.15% Ti, <0.090% sol.Al, 0.0040-0.0120% N, 0.0002-0.0010% B, and the balance Fe, has the content relation expressed by the formula [1] among Ti, N, S, and C, and is of Cu%/P%=1.0-4.0, P%/S%=0.5-2.5 is drawn as a continuously cast slab from a casting mold at 0.8m/min drawing speed by using powder for continuous casting having <=1.5% total C content and is worked to the sheet material by the hot rolling and cold rolling; finally the sheet material is annealed at 700-900 deg.C. The cold rolled steel sheet for enamel which decrease the loss of weight by pickling and has the excellent enamelability, etc., is obtd.

Description

[Detailed description of the invention]

<Industrial Application Fields> This invention has a small loss after pickling, and also has excellent enamel properties (enamel adhesion, pinhole resistance, nail fly resistance, etc.), press formability, and warp cracking resistance. The present invention relates to a method of manufacturing a cold-rolled steel plate for enamel. In recent years, ``enamel steel sheets,'' which are made by baking a surface glaze onto a steel sheet to form a glassy coating, have come to be used in a wide range of applications, including not only household goods but also building goods and various industrial goods. Traditionally, this enamel steel plate has been manufactured using the ``two-coat method,'' which involves applying an undercoat with good adhesion to the raw steel plate and then applying a topcoat to give it a beautiful appearance. The steel plate is thoroughly pre-treated (pickled) to improve its adhesion, and then a glaze rich in beauty and adhesion is directly baked onto it, which is a ``one-time method'' that shortens the process. Since it was developed, the trend has been to shift from "doing twice is the law" to "doing once is the law."<Prior art and its problems> By the way, "doing twice is the law" The material for manufactured enameled steel sheets has been rimmed cold-rolled steel sheets with increased P content to improve pickling performance and decarburization treatment to improve formability. Even in the case of ``one time hanging is the law'', special materials exclusively for that purpose are not used (,
The current situation is that rimmed steel cold-rolled steel sheets similar to those in the "double-rolling method" are still used. However, since rimmed steel cold-rolled steel sheets are manufactured from ingots using the "steel ingot method", productivity is extremely low. There was a major problem in that the benefits of the law could not be fully utilized. Therefore, in order to improve this problem, a lot of research has been carried out on steel plates for enameled steel that are made from continuous cast slabs of killed steel, and various proposals have been made. When cold-rolled cold-rolled steel sheets are used as materials for enamel, they can cause enamel defects such as pinholes and nail chips, and "
In addition to being prone to "vertical cracks", the press formability was also not fully satisfactory, and it was still difficult to put it into practical use.For these reasons, the inventors of the present invention aimed to solve the above-mentioned problems. first proposed a method for producing steel for enamel, the gist of which is ``continuously casting low carbon steel with a specific composition at a high speed using continuous casting powder with a low C content.'' (Japanese Patent Application No. 61-45718). However, although the steel for enamel manufactured by the above method proposed by the present inventors did have excellent pinhole resistance and enamel adhesion, there were various problems that continued after that. Through testing and study, we have also applied A! to the steel for enamel! It is desirable to take further measures to improve the problem of chipping, which is the fate of killed steel, and after rigorously evaluating the press formability and resistance to vertical cracking, we have come to the conclusion that it is still desirable to improve the current level. be. Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors have improved not only a small amount of pickling loss, but also properties such as hollow and low properties, press formability, warp cracking resistance, etc. As a result of further research to find a method of manufacturing cold-rolled steel sheets for enameled steel that fully satisfies both the ,
Ultra-low AI, containing B, Cu, P, S, N, etc., and comprehensively adjusting the component content ratio after fully understanding the interrelationships between specific components! When the raw material is a slab of killed steel that is continuously cast at a specific high drawing speed using casting powder with a low C content, A2 guild steel is created due to extremely low C and the fixation of N, S, and C by Ti. ○ Effect of improving acid loss value and enamel adhesion by adjusting the content ratio between P and S and Cu and P, improvement of warp cracking resistance due to grain boundary strengthening effect of OB Effects: ○ By lowering the C of the casting powder used and shortening the contact time with the powder (amplifying the drawing speed), the pickup of C from the powder into the steel is prevented, which is brought about by the extremely low C of the rope. Effect of suppressing the combination of C in steel and O in enamel (cause of pinholes) during enamel firing, ○ T
The effect of suppressing the fly-off of TiN caused by the N fixation of i is synergistic, and the "excessive pickling" to improve adhesion and the "open coil state after cold rolling" to improve formability are realized synergistically. Enamel that has satisfactory enamel properties (enamel adhesion, pinhole/blowhole resistance, nail fly resistance), press formability, and warp cracking resistance without requiring decarburization annealing. This led to the discovery that "it is now possible to manufacture cold-rolled steel sheets for industrial use with high production efficiency." This invention was made based on the above findings, and includes: C: 0.005% or less (hereinafter, % representing the component ratio is % by weight). Mn: 0.05-0.25%, p: 0.
oo! 5-0.025%. S: 0.005-0.025%, Cu: 0.
025-0.045%. Ti: 0.05-0.15%, sol, Al:
0.090% or less. N: 0.0040-0.0120%, B:
0.0002-0.0010%. Fe and impurities: A steel with a composition that satisfies both the formula % and the total C content is 1.5%.
Drawing speed using the following continuous casting powder: 0.
By continuously casting at 8 m/win, hot rolling and cold rolling the obtained slab, and then annealing at 700 to 900°C, it has excellent enamelability, press formability, and resistance to warp cracking. The feature is that cold-rolled steel sheets for enameled steel with excellent properties can be produced with high efficiency. It goes without saying that hot rolling and cold rolling are carried out under normal conditions (for example, in hot rolling, a slab heated to 950 to 1250°C is rolled at a finishing temperature of 00°C or higher, The objective can be fully achieved by rolling at a temperature of 50 to 300°C, and hot rolling can be performed by direct charging, hot charging, or reheating charging of cold pieces. Of course). Further, although the annealing may be continuous annealing or batch annealing, it is advantageous to employ continuous annealing. Next, in this invention, the reason why the chemical component ratio of steel and the steel plate manufacturing conditions are limited as described above will be explained. A) Chemical composition ratio of steel (a) C If the C content in steel exceeds o, oos%, an adverse effect will be observed on the press formability of the product steel sheet, and the necessary Ti addition will be required to alleviate this. Since the amount is large, the C content was limited to 0.005% or less. (b) Mn The Mn component has the effect of improving the tapping yield and preventing surface flaws due to red heat embrittlement of steel during hot rolling, but if its content is less than 0.05%, the above effect will be reduced. On the other hand, if the content exceeds 0.25%, it will cause deterioration of press formability due to solid solution hardening and enamel firing distortion due to a lowering of the transformation point. It was set at 0.05-0.25%. tc) p The P component has the effect of increasing the loss of pickling during pretreatment and improving the adhesion of the enamel, but if its content is less than 0.005%, the loss of pickling is too small. There is a risk of causing poor adhesion of the enamel, while 0.025
If the P content exceeds 20%, press formability deteriorates due to solid solution hardening, and even and finely uneven pickling cannot be obtained due to excessive pickling, resulting in poor adhesion of the enamel. It was determined to be 0.005 to 0.025. (d) SS The S component has the effect of ensuring a pickled surface with uniform fine irregularities when pickling a steel plate, but when its content is 0.0
If it is less than 0.05%, a uniform acid-reduced surface cannot be obtained;
If the S content exceeds 0.025%, a large amount of Ti will be required to ensure the effect of Ti, so the S content is determined to be o,oos~0.025. (el Cu The Cu component has the effect of creating fine irregularities through interaction with P during pickling of the steel plate and improving the adhesion of the enamel, but if the content is less than 0.025%, over-oxidation is sufficient. On the other hand, 0.04
If the Cu content exceeds 5%, it will be insufficiently oxidized and cause poor adhesion of the enamel, so the Cu content should be 0.025 to 0.
．． It was set as 0.045%. (f) Ti The Ti component not only fixes C, N, and S in the steel to improve the press formability of the steel sheet, but also forms N and TiN.
This TiN also has the effect of suppressing nail flying, but if its content is less than 0.05% or less than the amount calculated by the formula, it is due to insufficient adhesion of C, N and S. Ti content is determined to be 0.05 to 0.15% because it causes poor formability and, on the other hand, if it is contained in excess of 0.15%, the above effect is saturated and no further improvement effect can be obtained. Ta. (g) 5olJi! sot', Aj! is an effective component as a deoxidizing agent for steel, but if it is contained in excess of 0.090%, not only will no further effect be obtained, but it will also cause poor press formability of the steel plate. so/! , Al content is 0.09
It was set as 0% or less. (The N component has the effect of forming Ti and TiN to prevent the enamel from flying off, but if its content is less than 0.0040%, the desired effect cannot be obtained; on the other hand, 0.0
If the N content exceeds 120%, not only no further effect can be obtained, but also the press formability of the steel plate will be impaired, so the N content should be 0.0040 to 0.0120%.
It was determined that (i) B The B component has the effect of strengthening the grain boundaries of steel and improving the longitudinal cracking resistance of the steel plate, but when its content is 0.0002
If it is less than 0%, the desired effect cannot be obtained;
．． If the S content exceeds 0.0010%, not only will no further effect be obtained, but the press formability of the steel sheet will deteriorate, so the S content should be 0.0002 to 0.001
It was set as 0%. (JI Ratio of Cu content to P content (Cu(χ)/
If the value of P(χ)] is less than 1.0, there will be too much oxidation and sufficient adhesion of the enamel cannot be ensured. On the other hand, if the value of the ratio exceeds 4.0, there will be too little oxidation and the adhesion of the enamel will be poor. Therefore, the value of (Cu (χ)/P(χ)) is between 1.0 and 4.
It was set to 0. (k) If the ratio of P content to S content (P(χ)/S(χ)) is less than 0.5, the adhesion of Ni, which is the enamel base, will be poor, resulting in poor adhesion of the enamel. CP(χ)/S(χ)]
The value of is determined to be 0.5 to 2.5. There is no particular limit to the Si content, but since there is a concern that solid solution hardening may cause deterioration in formability, it is recommended that the Si content be suppressed to 0.03% or less. B) Steel sheet manufacturing conditions (a) C content ratio of continuous casting powder When the C content ratio of continuous casting powder exceeds 1.5%, C pick-up from the powder occurs on the surface of the slab, sometimes causing enamel burning. Since this would cause pinhole defects and blowhole defects in the enamel, the C content in the powder was set at 1.5% or less. (bl) Pulling speed in continuous casting If the drawing speed of the continuously cast slab is less than 0.8 m/1IIin, the contact time between the slab and the continuous casting powder becomes long, and C from the powder is deposited on the surface of the slab. The drawing speed of the slab was limited to 0.8 m/min or higher to avoid pickup, which would cause pinhole defects and blowhole defects. Any type of batch annealing may be used, but recrystallization will be insufficient if the annealing temperature is less than 700°C, while annealing above 900°C may cause in-furnace heat buckling or abnormal grain growth. was determined to be 700 to 900°C. Note that the above annealing can of course be continuous annealing in which recrystallization treatment at 700 to 900°C is followed by primary cooling, and further overaging treatment. The invention will be explained using examples and comparing with comparative examples. <Example> First, after adjusting the composition of steel with the composition shown in Table 1 by the RH method, it was continuously cast under the conditions shown in Table 2. , hot rolling, cold rolling, and annealing were performed to produce cold rolled steel plates for enamel.The mechanical properties (formability) and warp cracking resistance transition temperature of each steel plate thus obtained were investigated. ,
This was then enamel-finished using the 1-time method under the following conditions, and its enamel properties were also investigated.

[Enamel finishing conditions]

[Pretreatment conditions] 1) Pickling liquid: 7% H, SO, aqueous solution, 2) Ni flash: ~iS○4.7 HtO solution used, 3) Neutralization [Enamel glazing conditions] Frit composition: Titanium milky white frit # 1553B (Nippon Ferro brand name), glazed varnish spray, firing temperature: 2820°C, firing time: 2.5m1n. The results of the investigation conducted as described above are shown in Table 3. The results shown in Table 3 also show that the method of the present invention has excellent enameling properties, press formability, and It is clear that it is possible to stably produce a steel plate for enameled steel that has vertical cracking resistance.As explained above, according to the present invention, all of the various properties required of a steel plate for enameled steel can be sufficiently achieved. It is possible to manufacture satisfactory cold-rolled steel sheets extremely efficiently and stably, and it brings about extremely useful effects in industry, such as further improving the quality of enamel-finished products and expanding the field of application. .

Claims (1)

[Claims] C: 0.005% or less, Mn: 0.05 to 0.25%, in terms of weight percentage.
P: 0.005-0.025%, S: 0.005-0.
025%, Cu: 0.025-0.045%, Ti: 0
．． 05-0.15%. sol, Al: 0.090% or less, N: 0.0040 to 0.0120%, B: 0.0002 to 0.0010%. Fe and impurities: Consists of the remainder and has the formula Ti (%) ≧ (48N (%) / 14) + (48S (%)
/32)+(48C(%)/12), Cu(%)/P(
%) = 1.0 to 4.0, P (%) / S (%) = 0.5 to 2.5, and the total C content is 1.5% by weight or less. Drawing speed using continuous casting powder: 0
．． A method for manufacturing a cold-rolled steel sheet for enamel, which comprises continuously casting at 8 m/min, hot rolling and cold rolling the obtained slab, and then annealing at 700 to 900°C.