JPH0356302B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a cold-rolled steel sheet for enameling which is excellent in press formability, enameling properties and clogging resistance. <Prior art and its problems> Steel plates for enameling need to be ultra-low carbon steel and have a clean surface in order to suppress the occurrence of bubble defects and firing distortion. Furthermore, in order to suppress clogging defects caused by hydrogen occluded in the steel sheet during enamel firing, it is necessary to contain a large amount of second phase such as oxides, carbides, and nitrides in the steel.
Decarburized and denitrified annealed capped steel sheets meet these requirements and have excellent press workability.
Until now, it has been widely used as a steel plate for enameling. However, since decarburization and denitrification annealing is required, high costs are unavoidable. In order to solve this problem,
Many attempts have been made to use the Ti-added ultra-low carbon steel disclosed in No. 12348, which has excellent press formability, to produce steel plates for enameling by continuous annealing or box annealing instead of decarburization and denitrification annealing. For example, JP-A-51-
As disclosed in Japanese Patent Application Laid-open No. 98619 and Japanese Patent Application Laid-Open No. 125117/1984, various methods for producing steel plates for enameling with excellent press formability and resistance to clogging have been proposed. In the case of Ti-added steel, Ti is TiC, TiN or Ti
Sulfides and Ti phosphides are formed in the steel to improve flaking resistance, and at the same time, since C, N, and S are no longer in solid solution, press formability is also improved. Therefore, in order to suppress tripping, sufficient
It has been considered necessary for steel to contain elements such as C, N, S, and P along with Ti.
However, steel sheets for enameling manufactured using conventional methods have drawbacks such as inferior enamel adhesion compared to decarburized and denitrified steel sheets, and are susceptible to enamel bubble defects, which has become a problem. Ta. Due to these drawbacks, Ti-added ultra-low carbon steel
In particular, overlay enamel, which has a weak adhesion, is rarely used for direct single-glaze enamel, where the steel plate is directly glazed and fired, and the surface texture and enamel adhesion are improved without compromising press formability and flaking resistance. A method to do so was strongly desired. <Object of the invention> Therefore, the object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and provide a cold rolled steel sheet for enameling that has excellent press formability, enameling adhesion, and chipping resistance. be. <Structure of the invention> When enameled, Ti-added steel has many problems such as bubble defects and unstable adhesion, which has been an obstacle to switching to continuous cast steel sheets for enameling. . The present inventors found that Al in Ti-added steel casting is considerably concentrated on the steel plate surface compared to Al in conventional decarburized, de-chambered capped steel, which has good enameling properties, and that Al in Ti-added steel It has been found that the higher the amount and the higher the concentration of Al on the surface of the steel sheet, the more likely poor adhesion will occur. There, in the steel
By lowering the Al content as much as possible, both surface quality and adhesion were improved. That is, the present invention, when producing a cold-rolled steel sheet with excellent press formability, enameling adhesion, and chipping resistance, is characterized in that C≦0.005% and 0.008%≦N≦ in weight percent.
0.012%, Al≦0.01%, Ti is 0.12% or less and Ti
＞(48/12 C+48/14 N+48/32 S)%, the balance being iron and unavoidable impurities. The reasons for limiting the components in the present invention will be explained. C: When C exists in a solid solution state in steel, the ductility and T value of the steel sheet deteriorate. In steel with a sufficient amount of Ti added, C exists as TiC, which increases ductility and
Although the degree of deterioration of the T value becomes small, if it exceeds 0.005%, the characteristics deteriorate. Furthermore, the amount of Ti required to fix C as TiC increases, which not only reduces the adhesion of the enamel but also causes an increase in costs. Therefore, the upper limit of the amount of C is set to 0.005%. Ti: By adding Ti to steel, C, N,
S is fixed as TiC, TiN, and TiS, respectively, and has the effect of not only reducing the adverse effects of these elements on the material of the steel sheet, but also preventing the occurrence of chipping. In order to fully exhibit this effect, a Ti amount sufficient to fix C, N, and S, ie, (48/12 C+48/14 N+48/32 S)% or more is required. However, an excessive amount of Ti not only causes an increase in cost, but also causes continuous casting nozzles to become clogged, causes sludge-like defects, and furthermore causes deterioration of enamel adhesion and weldability. In order to avoid such problems, the amount of Ti needs to be 0.12% or less. N: N is an element necessary to improve the chipping resistance among the enameling properties in the steel sheet of the present invention. In steel with Ti added, N exists as TiN, and as its amount increases, the chipping resistance of the steel sheet improves. That is, due to the presence of TiN, voids are formed in the steel during cold rolling, and hydrogen, which causes skipping, is occluded in the steel, thereby suppressing the occurrence of skipping. To completely suppress blockage
N of 0.008% or more is required. However, if the amount of N increases and a sufficient amount of Ti is added to fix this as TiN, bald defects may occur on the surface of the steel sheet. When the amount of N is 0.012% or less, it is extremely rare for such bald defects to occur. The range of N needs to be 0.008% or more and 0.012% or less. Al: Al is an element that affects the adhesion of enamel among the enamel properties, and is particularly important in the steel of the present invention. In the case of Ti-added steel, Al is usually added to the molten steel to deoxidize it in order to clean the steel plate surface and ensure the yield of Ti. For this reason, Al
is unavoidably contained in steel. However, as the amount of Al increases, the enamel adhesion deteriorates, so the upper limit of Al is set at 0.01%. The reason why Al is involved in the enamel adhesion of steel plates is
This is thought to be because Al concentrated on the steel plate surface increases the solubility of the glaze that is in contact with the steel plate surface during enamel firing, resulting in poor wettability. <Example> The present invention will be explained based on an example. Steels shown in Table 1 No. 1 to 14 are used in converter and RH.
It was melted through a degassing process and made into a slab through continuous casting. Next, after hot rolling, the plate thickness was made 0.8 mm by cold rolling.
800%, continuous annealing with soaking time of 30 seconds,
It was subjected to 0.8% temper rolling. In addition, steels No. 15 to 16 were melted in a converter, then ingot-formed, bloomed, hot-rolled, and cold-rolled to a plate thickness of 0.8 mm. Then, it was decarburized and annealed to obtain a test steel. Figure 1 shows the relationship between the amount of C in steel and ductility. The tensile test piece was a JIS No. 5 tensile test piece. As the amount of C increases, ductility deteriorates. In order to ensure ductility of 50% or more, the amount of C needs to be 0.005% or less. Figure 2 shows the occurrence rate of skipping for each 20 of these steel plates. The glazing test was carried out by pickling for 20 seconds, applying a commercially available glaze (L-type bottom glaze manufactured by Nippon Ferro Co., Ltd.), enameling at 850°C in a kiln with a dew point of 40°C, and then heating to 160°C for 16 hours. The animals were kept warm and examined for the occurrence of bulge. No. 3, 5, 11, 13 with low N amount
Except for the Ti-added steel, there was no occurrence of skipping in both the decarburized and dechambered annealed sheets, and in the Ti-added steel,
It can be seen that the amount of N is required to be 0.008% or more. Next, FIG. 3 shows how the amount of Al added affects the enamel adhesion, which is particularly important in the steel of the present invention. The test steels used were 10 types of Ti-added steel shown in Table 1 that did not cause skipping, and capped steel. The enamel adhesion test was carried out using sulfuric acid pickling as a pretreatment (10% H ₂ SO ₄ at 75°C for 5 to 25 hours).
), Ni bath immersion (2% NiSO ₄ , 65℃, time 10 minutes)
Commercially available top glaze (manufactured by Nippon Fellow,
1553B (Ti white glaze)) and fired at 820℃, P.
Adhesion was measured using the adhesion test method (ASTMC313-59) recommended by EI (American Enamel Institute). In this test method, an enameled steel plate is deformed and the area ratio of the part where the enamel has not peeled off is measured in the deformed part, and the adhesion index is 100%.
Those with a score of 0% are poor. As is clear from Figure 3, the conventional decarburized, dechambered, and annealed capped steel as well as the Ti-added steels No. 7, 8, and 12, which contain less than 0.01% Al, maintain good adhesion after being pickled to some extent. , whereas
When the amount of Al added exceeds 0.01, the pickling time for obtaining good adhesion is narrow, and as the pickling time increases from 20 minutes to 25 minutes, the adhesion drops rapidly. Also Al
Boards Nos. 2, 4, and 10, in which the added amount exceeds 0.05%, have low adhesion as a whole, and No. 10 has a maximum adhesion index of less than 60%. Furthermore, when the amount of Al added exceeds 0.01%, not only does the adhesion index decrease, but also problems with surface properties such as pinholes and bubble defects occur on the overpickling side. As described above, the amount of Al added corresponds well to the results of the enamel adhesion test, and the amount of Al added should be 0.01% or less, preferably as low as possible.

【table】

[Table] <Effects of the Invention> As mentioned above, it is clear that the present invention can produce a steel plate that satisfies all of the properties necessary for a steel plate for enameling, such as press formability, chipping resistance, enamel adhesion, and surface texture. Inside the steel, as if it had been done,
In particular, this becomes possible by strictly adjusting the amount of Al. According to the present invention, high-grade enameling steel sheets, which were conventionally manufactured by the ingot method, can be manufactured by the continuous casting method, which brings about great advantages in terms of cost and energy saving.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of C in steel and ductility. FIG. 2 is a graph showing the relationship between the amount of N in steel and the number of sheets in which skipping occurs. Figure 3 shows the steel
It is a graph showing the relationship between the amount of Al and the enamel adhesion index.

Claims (1)

[Claims] 1. When manufacturing cold-rolled steel sheets with excellent press formability, enameling adhesion, and chipping resistance, C≦0.005%, 0.008%≦N≦0.012%, and Al≦0.01 in weight percent.
%, Ti is 0.12% or less and Ti>(48/12 C+
A cold-rolled steel plate for enameling consisting of 48/14 N+48/32 S)%, the balance being iron and unavoidable impurities.