JP2517500B2 - Method for producing cold-rolled steel sheet for direct enamel with excellent bubble resistance and black spot resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled steel sheet for direct single-use enamel which has excellent bubble resistance and black spot resistance.

[0002]

2. Description of the Related Art Enameled steel plates have been manufactured using capped steel in the past. However, capped steel is inferior to continuous cast steel in terms of cost and material uniformity, and inclusions are formed immediately below the rim layer. Since segregation easily occurs and causes blistering after enameling , continuous casting steel has been used in recent years, and most of the double-strand enamel has been switched to continuous casting steel and has been used without problems. . And even with enameled directly once, continuous cast steel is beginning to be used.

The continuous cast steel for enamel is roughly classified into: Ti-added steel that uses Ti carbonitride as a hydrogen storage site, B-added steel that uses B nitride, and ingot-capped in order to prevent nail jumping. Like steel, it will be three types of high oxygen steel that utilizes MnO-based inclusions.

In the case of enamel directly applied once, it is necessary that bubbles and black spot defects do not occur during firing of enamel, but it is difficult to prevent bubbles and black spots in killed Ti-added steel and B-added steel. High oxygen steel is often used as a continuous cast steel having a composition relatively close to that of conventional capped steel.

As a high oxygen steel in consideration of prevention of bubbles and black spots, JP-A-62-203646 and JP-A-62-2 are known.
The methods disclosed in Japanese Patent No. 70727 and Japanese Patent Laid-Open No. 63-27742 are known. Japanese Patent Laid-Open No. 62-2036
The method of Japanese Patent Publication No. 46 aims to secure the bubble resistance and the black spot resistance by controlling the steel components, especially the amounts of P, S and Cu and their ratios, the carbon amount in the powder during continuous casting and the drawing speed.

Further, Japanese Patent Laid-Open No. 62-270727 discloses a method for producing a high oxygen steel in which C in steel and sliver flaws in a steel sheet are cited as causes of bubble defects, and the C content in steel is regulated to 0.0035 to 0.0060%. It is shown.

Further, in Japanese Patent Application Laid-Open No. 63-27742, occurrence of bubbles and black spot defects is caused by the steel composition of {P + (1/3)
S} / {(1/2) Ni + Cu} is arranged, and by regulating this parameter in the range of 0.2 to 0.9, it is supposed that bubbles and black spot defects are prevented. An example of application to high oxygen steel is also given.

[0008]

However, when these high-oxygen steels are actually used directly for enameling once in an enameled maker, when the pretreatment conditions change or the type of glaze changes, foam, Black spots may occur, and the foam resistance and black spot resistance are inferior to those of the ingot-making capped steel.

[0009] In particular, during the pretreatment of enamels, there are many problems that bubbles and black spots are generated in a portion that comes into contact with a stainless steel basket in which the products are put and a stainless steel jig for arranging the products.

However, the above shows that the conventionally proposed parameters for controlling the range of the steel components and the quantitative relationship between the components are not effective for preventing bubbles and black spots in the jig contact portion. In any case, it is possible to obtain a steel sheet for direct singling enamel by continuous casting, which has bubble resistance and black spot resistance and is also excellent in enamel adhesion, nail jump resistance and workability. Not not.

[0011]

The present invention was devised through repeated studies to solve the above-mentioned problems in the prior art, and is as follows.

C ≦ 0.0030 wt%, 0.20 ≦ Mn ≦ 0.40
wt%, 0.003 ≦ P ≦ 0.015 wt%, 0.005 ≦ S ≦ 0.
020wt%, 0.005 ≦ Cu ≦ 0.045wt%, 0.5 ≦ (P +
S) /Cu≦1.0, 0.010 ≦ Ni ≦ 0.040 wt%, N ≦ 0.0
030 wt%, 0.050 ≦ O ≦ 0.065 wt%,
Steel consisting of the balance iron and unavoidable impurities is made into a slab by continuous casting, the slab is hot-rolled, further cold-rolled, and then subjected to recrystallization annealing by batch annealing or continuous annealing. A method for producing a cold-rolled steel sheet for direct enameling, which has excellent black spot resistance.

[0013]

The present inventors observed the formation process of enamel bubbles and black spots as described above, and examined the relationship between these defects, pretreatment conditions, and steel composition. As a result, the process from applying the glaze to firing If spot rust occurs on the steel sheet in the meantime, bubbles or black spots are formed at that position, especially spot rust easily occurs at the part that was in contact with the stainless steel jig during pretreatment, and spot rust occurs It has been found that ease of use has a close relationship with the amounts of P, S, Cu, and Ni in the steel sheet. 100 x 100 mm in Figure 1
The test piece of No. 2 is pickled for 20 minutes and pre-treated with Ni flash for 10 minutes, and T3724 is applied as a glaze at 100 μm, and the temperature is 840 ° C.
The following shows an example in which point rust just before firing, which was fired for 5 minutes at a dew point of 30 ° C., caused bubbles and black spot defects after firing, but it is possible to fully understand the relationship as described above.

Based on such knowledge, the present invention is intended to suppress the generation of spot rust after pretreatment by strict regulation of steel components and to prevent the formation of bubbles and black spots during firing. The reason why the wt% (hereinafter simply referred to as "%") limitation is as follows.

C ≦ 0.0030% C is an element that causes foaming during enamel firing,
If it exceeds 0.0030%, bubble defects are likely to occur, so the upper limit was made 0.0030%.

Mn: 0.20 to 0.40% If Mn is less than 0.20%, the inclusions in the steel are not MnO but Fe.
O becomes the main component and the nail resistance is insufficient, and if it exceeds 0.40%, the elongation and r-value of the steel sheet will decrease and the workability will deteriorate, so it is necessary to set it in the range of 0.20 to 0.40%. .

P: 0.003 to 0.015%, S: 0.005
~ 0.020%, Cu: 0.005-0.045%, (P + S)
/Cu:0.5-1.0, Ni: 0.010-0.040% P, S, Cu, and Ni are the most important elements in the present invention, and are easy to generate bubbles and black spots. Dominate. Further, it is not enough to limit the range of these elements alone, and they must be regulated in relation to each other.

P has the function of increasing the pickling rate and the Ni deposition rate in (sulfuric acid pickling + Ni flash) which is directly carried out as a pretreatment for enamel. In order to suppress the generation of spot rust after pretreatment and to obtain good adhesion of enamel, it is necessary that the adhered Ni be evenly distributed in the form of fine particles, but P acts to make the distribution of the adhered Ni uneven. There is. If P exceeds 0.015%, uneven Ni distribution reduces the Ni coverage on the surface of the steel sheet and promotes rust generation, which makes it difficult to prevent bubbles and black spots during firing.
%. On the other hand, if it is less than 0.003%, the pickling rate is significantly reduced, and good enamel adhesion cannot be obtained in the usual pretreatment time, so the lower limit was made 0.003%.

S has the effect of increasing pickling speed and increasing smut generation, and 0.005% or more is necessary to secure enamel adhesion, but if S is too high, excessive smut is generated. Is generated, and bubbles and black spots are easily generated, but unlike P, since it does not affect the Ni distribution,
The restrictions are looser than P, and the upper limit is allowed up to 0.020%.

Cu has the effect of making the Ni distribution uniform, and improves enamel adhesion, bubble resistance, and black spot resistance.
If the added amount is less than 5%, this effect is insufficient. Also,
Cu also has the effect of decreasing the pickling rate, and if it exceeds 0.045%, good enameling adhesion cannot be obtained with the pickling time usually performed, so 0.015 ≤ Cu ≤ 0.045% was set.

The individual ranges of P, S and Cu have been described above, but the bubble resistance and black spot resistance can be arranged by the parameter (P + S) / Cu. If this value exceeds 1.0, stainless steel is used. Black spots occur on the jig contact area. On the other hand, (P +
If S) / Cu is less than 0.5, there will be a problem with enamel adhesion, so it is necessary to set 0.5 ≦ (P + S) /Cu≦1.0.

Ni is an essential element for effectively controlling the above P, S and Cu regulations, and plays an important role in bubble resistance and black spot resistance.

When Ni is added to steel in an amount of 0.010% or more, the pickling rate is increased, but at the same time, it has the effect of making Ni precipitation uniform during Ni flashing, and improves bubble resistance and black spot resistance. In particular, it has a great effect on the portion where the stainless jig contacts during pretreatment. Therefore, it is possible to prevent bubbles and black spots in the jig contact portion by using the addition of Ni together with the restrictions of P, S and Cu. Ni is
If it is less than 0.010%, bubbles and black spots are generated in the jig contact portion even if P, S and Cu are regulated. This effect is saturated when it exceeds 0.040%, so 0.010 ≤ Ni ≤ 0.040% was set. Fig. 2 shows the relationship between (P + S) / Cu and Ni content and the adhesion of black spots and enamel. By setting it in the range of 0.5 to 1.0, the black spot score is good and the adhesion of enamel is high. Can be maintained.

The enameling conditions in the case of FIG. 2 are as follows.

[0025]

[Equation 1]

N: 0.0030% or less N exceeds 0.0030%, and since ductility and aging resistance of the product are significantly impaired, N ≦ 0.0030% is set, but preferably ≦ 0.0025%.

O: 0.050 to 0.065% O is a component that controls nail resistance with Mn. It forms inclusions mainly of MnO in steel and is formed around it by cold rolling. The micro voids have the effect of suppressing skipping of nails. If it is less than 0.050%, this effect is not sufficient, and under severe conditions such as a high dew point during firing, it is difficult to prevent the nail popping, and if it exceeds 0.065%, the workability is significantly deteriorated. It was set to 0.050 ≦ O ≦ 0.065%.

The manufacturing conditions for the steel having the above-described composition are as follows.

The steel prepared in the above composition range is made into a slab by continuous casting. In hot rolling, the finish temperature is preferably set to an Ar ₃ transformation point or higher in order to secure workability, and therefore the slab heating temperature is appropriately set to 1100 ° C. or higher. Taking the pickling property into consideration, the winding temperature is 550.
Approximately 700 ° C.

The cold rolling is preferably 60% or more in order to secure nail flip resistance and deep drawability.

The recrystallization annealing may be either batch annealing or continuous annealing, or decarburization annealing or denitrification annealing with an open coil may be performed in pursuit of workability.

[0032]

EXAMPLES Specific examples of the present invention are described below. Steels within the scope of the present invention and comparative steels having the chemical compositions shown in Tables 1 and 2 below were melted in a converter and made into slabs by continuous casting or ingot making. It was hot-rolled and then cold-rolled to a plate pressure of 0.7 mm, and then batch-annealed or continuous-annealed to obtain a test material.

[0033]

[Table 1]

[0034]

[Table 2]

SU was attached to each test piece obtained as described above.
S 316L Round bar was contacted with sulfuric acid pickled, Ni flushed, and baked with a glaze for pickling weight loss, enamel appearance (foam, black spots), enamel adhesion, presence of nail skip test evaluation The results are shown in Table 3 below, in which ∘ indicates no defects, Δ indicates light bubbles and black spots, and x indicates severe bubbles and black spots.

[0036]

[Table 3]

That is, steels 1 to 3, 5 and 5 within the scope of the present invention
No. 8 did not cause bubbles or black spots under any conditions, and the adhesiveness is good. However, P, S, (P + S) / Cu
For steels having a higher temperature than the range of the present invention and for steels having a Ni lower than the range of the present invention, bubbles and black spots were generated due to the pretreatment conditions and the glaze, and this tendency was particularly remarkable at the portion contacting the SUS jig during the pretreatment. On the contrary, when P, S, (P + S) / Cu is lower than the range of the present invention, the adhesion is poor. Further, in steels 4, 15 and 16 in which O was lower than the lower limit of the present invention, claw skipping occurred. In addition,
With continuous cast steel , blistering does not occur, but with ingot steel ,
Blistering occurred.

[0038]

As described above, according to the present invention, there is a good enameled appearance without bubbles and black spot defects irrespective of presence / absence of jig contact in pretreatment, fluctuation of pretreatment conditions, type of glaze, etc. The product is obtained, and the good adhesion and nail resistance are secured, and the operability is good.
This is an invention having a great effect industrially because it has effects such as obtaining a stable enamel product accurately.

[Brief description of drawings]

FIG. 1 is a drawing depicting the correspondence between point rust before firing, bubbles after firing, and black spots.

FIG. 2 is a chart showing the relationship between (P + S) / Cu and Ni content, and black spots and adhesion.

Claims (1)

(57) [Claims] 1. C ≦ 0.0030 wt%, 0.20 ≦ Mn ≦ 0.4
0 wt%, 0.003 ≤ P ≤ 0.015 wt%, 0.005 ≤ S ≤
0.020 wt%, 0.005 ≦ Cu ≦ 0.045 wt%, 0.5 ≦ (P
+ S) /Cu≦1.0, 0.010 ≦ Ni ≦ 0.040 wt%, N ≦ 0.
Steel containing 0030 wt%, 0.050 ≤ O ≤ 0.065 wt% and consisting of balance iron and unavoidable impurities was continuously cast into a slab, which was hot-rolled and further cold-rolled, A method for producing a cold rolled steel sheet for direct single-use enamel having excellent bubble resistance and black spot resistance, which comprises performing recrystallization annealing by batch annealing or continuous annealing.