JPH03232947A - Steel sheet for porcelain enameling having few defects such as bubbles and black spots - Google Patents

Abstract

PURPOSE:To make better the press formability in a steel sheet and to improve its porcelain enameling properties such as fishscale resistance and resistance to defects such as bubbles and black spots by incorporating a trace amt. of B into steel sheet stock having a specified compsn. and forming a B concentrated layer on the surface of the stock. CONSTITUTION:Steel sheet stock for porcelain enameling is incorporated with <=0.0050wt.% B. In this steel sheet, the average B concn. from at least either side surface to a depth of 1% of the sheet thickness is regulated to the one more than that of the stock by >=5ppm. Or, a B concentrated layer in which the average B concn. is regulated to the one more than that of the stock by >=1.3 times is formed. As the compsn. of the steel sheet stock, the one constituted of, by weight, <=0.050% C, <=1.0% Mn, <=0.10% P, <=0.10% S, <=0.20% Al, <=0.020% N, <=0.10% Cu, <=0.10% O and the balance Fe with inevitable impurities is preferably regulated. By this steel sheet stock, a sheet for porcelain enameling of good quality can be manufactured.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to an enameled copper plate having an enameled layer on the surface of the steel plate material, and the present invention relates to an enameled copper plate having an enameled layer on the surface of the steel plate material. It is intended to advantageously improve properties such as jumpability, adhesion during direct-roll enameling, bubble resistance and black spot defect resistance.

(Conventional technology) HAUROU is a non-combustible material made of glass baked onto the surface of a steel plate material, and has properties such as heat resistance, weather resistance, chemical resistance, and heat resistance.
In addition to having unique characteristics such as water resistance and stain resistance, it also has a beautiful surface. By the way, the surface material of such steel sheet material has to be subjected to a fairly severe press, as exemplified by its enameling properties, enamel adhesion, firing distortion, and resistance to chipping, as well as for applications such as washbasins and bathtubs. Since it is processed, good deep drawability is also required. In addition, in order to maintain the beautiful surface and properties described above, it is necessary to have bubble resistance and black spot defect resistance.

Conventionally, the steel plate materials for enameling as mentioned above are:
Decarburized capped steel was used. This decarburized capped steel is produced by going through an ingot making and blooming process, then hot rolling, then cold rolling, and then being decarburized and denitrified by an open coil annealing method. However, the current manufacturing processes in the steel industry are becoming more continuous, such as continuous casting and continuous annealing, from the viewpoint of energy and cost savings, and the manufacturing methods and processes for steels such as decarburized capped steel have already been developed. This is becoming a manufacturing process of the past, and the same is true in the field of steel sheets for crawlers.

In order to apply the continuous casting/continuous annealing method to produce a steel plate for enameling with excellent press formability, Ti-added steel is advantageous, especially when the C content is 0.005 wt% (hereinafter simply expressed as %). ) It has been known that excellent press workability can be obtained in ultra-low carbon steel with a carbon content of less than Steel was known to have excellent enameling properties in addition to press workability (Japanese Patent Publication No. 45-40655, Japanese Patent Application Laid-Open No. 53-1)
31919 and Japanese Patent Application Laid-open No. 56-9357).

The above techniques are intended to improve not only good press workability but also enameling properties, particularly chipping resistance. That is, Ti forms carbides, nitrides, and sulfides, and these precipitates have the effect of trapping hydrogen in the steel, which causes the jumpiness, and advantageously improve the jumpability.

However, even with Ti-added steel that has excellent press workability and chipping resistance, as reported in JP-A No. 60-110845, it has problems with respect to crawling adhesion, bubble resistance, and black spot defects. There were problems such as being far inferior to the decarburized capped steel used since then.

Widely used as a steel plate for crawlers (known as T
In addition to i-added steel, there is B-added steel and Al-killed steel (see Japanese Patent Publication No. 54-3446, Japanese Patent Publication No. 54-39308, and Japanese Patent Publication No. 63-540494049). The purpose is to form a product and use this to improve the chipping resistance.If you also want to improve the press formability, open coil annealing is performed in the annealing process, decarburization treatment and AIN
A method of forming a 1111 texture, which is advantageous for improving drawability by utilizing the precipitation of Ti, is applied, but solid solution B has a negative effect on the material quality of the steel sheet, making it difficult to obtain a material comparable to that of Ti-added steel. there were.

On the other hand, in the case of Al-killed steel, it is coiled at high temperature after hot rolling.
A method of forming coarse carbide and then destroying the carbide by cold rolling to form voids that become hydrogen trap sites is applied, and when press formability is also improved, it is the same as B-added steel. It was common to perform open coil annealing.

(Problem to be Solved by the Invention) However, when open coil annealing is performed, elements such as P and S, which are easily dissolved in acids, segregate on the screen plate surface and grain boundaries, resulting in sulfuric acid acid in the enameling pretreatment. During washing, grain boundaries on the surface of the steel sheet tend to be preferentially corroded. Particularly, when direct diffraction enameling is performed, there is a disadvantage that air tends to accumulate in such preferentially corroded grain boundaries, making it easy for bubbles and sunspot defects to occur.

The above-mentioned conventional problems have been solved, and the steel sheet material not only has good press formability, but also has enameling properties such as flaking resistance, bubble resistance, and black spot defect resistance, which are superior to conventional decarburized capped steel. It is an object of the present invention to propose an enameled steel plate that is equivalent to or better than an enameled steel plate that is made of a steel plate and has an enameled layer on its surface.

(Means for Solving the Problems) The present invention provides a steel plate having an enamel layer on the surface of a steel plate material containing 0.0050% or less of B: 0.0050% or less, wherein the steel plate material has a thickness of 0.0050% or less from at least one surface. The average B concentration up to a depth of 5% is lower than the average B concentration of the steel sheet material.
ppm or more, or M@1 of the average B concentration of the temporary material.
This is an enameled steel sheet with few bubbles and black spot defects, which is characterized by having a B-concentrated layer with a B concentration of 3 times or more. Here, in this invention, as the above-mentioned steel sheet material, C: 0.
050% or less, Mn: 1.0% or less, P: 0.10
% or less, S: 0.10% or less, Al: 0.20% or less, N: 0.020% or less, Cu: 0.10% or less, and 0: 0.10% or less.

In addition, in this invention, the composition of the steel plate material having the above-mentioned structure includes one or more selected from Ti, Nb, Zr, V, Se, old sb, and REM in a total of 0.001 to 1. It can also contain 0%.

(Function) This invention is based on the discovery that a small amount of B has a remarkable effect on reducing bubbles, black spot defects, etc. that occur during the manufacturing process of enamel plates. The reason why it is particularly effective to form the B-enriched layer up to a depth of 1% of the thickness will be explained.

First, C: 0.0021%, Mn: 0.26%,
P: 0.018%, S: 0.022%, Al
: 0.056%, N: 0.0018%, Cu:
0.031%, O: 0.0026%, other Ti
: When a steel sheet material with a composition containing 0.089% is subjected to the crawling force treatment, the average B concentration in the steel sheet material and the surface B concentration are changed to a specified level for the steel sheet material. Enameling was performed under the following conditions, and the occurrence of bubbles and sunspot defects was investigated (evaluated by the critical time for bubbles and sunspot defects to occur). The results are shown in FIG.

In any case, the manufacturing conditions for the floating plate are as follows: After continuous casting of molten copper having the above-mentioned composition, the plate is roughly rolled to a thickness of 3.
It was made into a 0M sheet bar, then inserted into a heating furnace at a temperature of 1200°C for 3 hours, and then made into a sheet bar with a thickness of 3.2m in 3 passes.
m, hot rolled under the conditions of finishing temperature = 880°C, cooled to room temperature at a cooling rate of about 3°C/min, pickled, cold rolled, plate thickness: 0. A cold-rolled plate with a thickness of 8 mm (cold rolling reduction ratio: about 75%) was then degreased and then continuously annealed, heating rate: about 5”C/sec, soaking temperature x time: 8
Recrystallization annealing was performed with a heat cycle of 60"CX 3 seconds and a cooling rate of approximately 10°C/second, followed by skin pass rolling with a rolling reduction of 0.5%, and then through the steps shown in Table 1. Enamel pretreatment [pickling time = 1 to 40 minutes, old immersion time: 10 minutes (Ni adhesion amount = 0.2 to 4.0 g/m2)], Direct -
It was then enameled and fired.

In Figure 1, the index ΔB of the B concentration in the B-concentrated layer is expressed as ΔB - (average B concentration in the surface layer (% of sheet thickness)) - (average B concentration in the steel plate), and ΔB is When the average B concentration of the steel plate material is 0.3 times or more, that is, the average B concentration of the steel sheet material is 1.3 times or more, the critical time for the generation of bubbles and sunspot defects is the same as that of conventional decarburized capped steel. It is about
Furthermore, it was observed that if ΔB is 5 pl)m or more, a similar tendency exists even if the average B concentration of the steel sheet is 1.3 times or less.

The reason why providing a concentrated layer of B on the surface of the steel sheet improves the enameling properties, especially the bubbles and sunspot defects that are a problem during enameling, is that B exists on the surface, especially at the grain boundaries of fine products. This is because during the sulfuric acid pickling for enameling pretreatment, preferential corrosion at grain boundaries is suppressed and the surface of the steel sheet is etched smoothly, thereby eliminating unevenness on the surface of the steel sheet that causes bubbles and black spot defects.

In addition, in the production of enamel steel plates, the average B from the surface of the steel plate material of the enamel steel plate is
In order to set the concentration to a predetermined value, the average B concentration from the surface of at least one side to a depth of approximately 5% of the plate thickness must be 5 pp
It is desirable to form in advance a B-concentrated layer that is either 1.3 times or more or more than m.

This invention is effective regardless of whether the steel sheet material is a cold-rolled steel sheet or a hot-rolled steel sheet.

Next, the reason for limiting the component composition will be explained.

C: 0.050% or less C is an interstitial solid solution element, and if its content is high, Ac3
It lowers the transformation point and causes firing distortion during firing, and CO□
It also generates gas and causes bubbles and sunspot defects. By precipitating C as TiC by adding Ti, for example, it is possible to reduce solid solution C and improve the material quality, prevent firing distortion, and prevent the generation of CO□ gas, but essentially the amount of C increases. Then, fine TiC particles tend to precipitate and deteriorate the material. Therefore, in this invention, C is set to 0.050% or less.

Mn: 1.0% or less 1'In replaces S, which causes cracking during hot rolling, with MnS.
It is a useful element that can be fixed as However, if its content exceeds 1.0%, it hardens the material and deteriorates its ductility and press formability. Therefore, Mn was set to 1.0% or less.

P: 0.10% If the P content exceeds 0.10%, the material will harden,
Not only does it significantly deteriorate press formability, but it also speeds up the pickling speed during enameling pretreatment, increases smut that causes bubbles and black spot defects, and deteriorates secondary processing brittleness. Therefore, P was set to 0.10%.

s: O, compounds with 10% or less S, such as MnS and TiS, form dense irregularities on the surface of the steel sheet during sulfuric acid pickling, not only improving the adhesion of the steel sheet but also eliminating jump defects. It is also a useful ingredient in trapping the hydrogen that causes it. however,
Mn, which fixes S when the S content exceeds 0.10%;
The Ti content is forced to increase, which not only increases the cost of molten steel but also disadvantages the material. Therefore, S is 0.1
It was set to 0% or less.

Al: 0.20% or less ^1 is used as a deoxidizing agent in the steel manufacturing stage, and controls the oxygen content, fixes N as AIN, and traps hydrogen, which causes thread defects, with AIN precipitates. It is a useful element because it has the effect of For this purpose, it is necessary to contain at least about 0.001%, but since 81 is an expensive element, adding a large amount leads to an increase in cost. Therefore, AI was set to 0.20% or less.

N: 0.020% N is an element that normally forms a solid solution in steel like C and deteriorates the material, but for example, when Ti is added, N
Since it can be fixed as a N precipitate, there is no particular problem in terms of the material. Rather, this precipitate forms a site that traps hydrogen, which causes the jump defect.
A higher N content is preferable, and at least 0.0020% N is required to prevent skipping defects. However, if it exceeds 0.020%, the amount of Ti or Δ■ added will increase, inevitably leading to an increase in cost. Therefore, N was set to 0.0203% or less.

Cu: 0.10% or less Cu is an effective element for controlling the pickling speed during pickling during enameling pretreatment, especially in steel with Ti added, compared to decarburized capped steel. Since the pickling speed is about 2 to 3 times faster, the content of Cu is important. However, if it is less than 0.01%, the effect of addition is poor, while if it exceeds 0.10%, the pickling speed becomes too slow and the enamel adhesion during short-time pickling treatment is reduced.

Therefore, the Cu content was set to 0.10% or less.

0:0.10% Oxygen forms oxides such as MnO or B2O3,
It is an effective element for enameling steel sheets because it has the effect of trapping hydrogen, which causes skipping defects. However, if it exceeds 0.10%, the properties of the slab surface will be significantly deteriorated, so in this invention, the upper limit is set at 0.10%.
It was set at 10%.

B is an element effective in reducing the creeping property, especially the occurrence of bubbles and sunspot defects. However, when 4B is present in a 1liil plate material in an amount exceeding soppm, the deterioration of workability becomes significant. Therefore, in this invention, B is set to 50 ppm or less.

In addition, when the Bfi layer satisfies the conditions specified in the present invention, the amount of B in the entire steel plate may be less than the detection limit (0,0001%). Furthermore, the upper limit of the B concentration in the B-concentrated layer is preferably about 500 ppm since there is a risk of material deterioration.

In addition, Ti, Nb, Zr, and V are carbonitride-forming elements that help improve the mechanical properties of steel sheet materials, and Se, Bi+Sb reduce the amount of smut generated during sulfuric acid pickling during enameling pretreatment. REM has the effect of reducing the occurrence of bubbles and sunspot defects, and, like Ti, REM forms sulfides and is useful for improving flaking resistance. Here, the total of one or more of the above elements is 0.00
If it is less than 1%, the effect cannot be obtained, while if it is added in excess of 1.0%, the cost will increase.

Therefore, in this invention, the content is set in the range of 0.001 to 1.0%.

When steel with the above composition system is used as a material, it can be made into a hot copper plate or a cold rolled annealed plate that has good properties, especially bubble resistance and black spot defect resistance, by performing normal hot rolling, cold rolling and annealing. Therefore, there are no particular restrictions on manufacturing conditions in this invention.

Next, as a means for concentrating B in the surface layer of the steel sheet material, it is most effective to apply the method disclosed in Japanese Patent Application No. 1-286022. In this case, a molding powder for continuous casting containing 5% or more of a boride such as 8203 is used. Another effective method for concentrating B is to apply a boride to the surface of the slab or during the hot rolling or cold rolling/annealing stage to allow B to penetrate into the surface layer of the object to be coated.

Next, the desirable conditions for enameling the above-mentioned steel sheet material are: in the case of straight-turn enameling, the steel sheet is degreased with alkaline, then washed with hot water and water, and the weight loss after pickling is 10 to 100 g/m2. After washing with water, the material is immersed in Ni7 sulfuric acid solution so that the amount of Ni attached becomes 0.1 to 20 g/1112, followed by washing with water, neutralization, and drying. In this case, the amount of pickling loss and the amount of Ni deposited are determined by the temperature, concentration, and treatment time of each treatment solution, and therefore can be known in advance. Then, add the top medicine,
After applying it to a film thickness of 100 to 150 μm,
All you have to do is fire it for a time that is appropriate for the Yuyaku.

In addition, in the case of double application, Cod,
Since adhesion-promoting oxides such as NiO are already contained, strong sulfuric acid pickling and high Ni deposition as described above are not necessary, and Ni immersion may be omitted.

(Example) After melting steel having the composition shown in Table 2, it was continuously cast and rough rolled to obtain a sheet bar having a thickness of 30 mm. Next, it was hot-rolled to a plate thickness of 3.2 mm and a finishing temperature of 880°C, and wound at 600°C to form a hot-rolled coil. After pickling, cold rolling is performed to obtain a JE0.8 m plate.
m (cold rolling reduction ratio: about 75%), then after degreasing and annealing, in the case of continuous annealing, average heating rate: about 5 ° C / sec, soaking temperature x time 2860 °
C x 3 sec, average cooling rate: approximately 10” C/sec heat cycle, while for open coil annealing, 670°C x
Recrystallization annealing was performed for 2 days, and skin pass rolling was performed at a rolling reduction of 20.5%. In addition, steel No. 4 was descaled by pickling treatment after hot rolling and was used as a test material. After that, enameling treatment was carried out in the steps shown in Table 1 [pickling time: 1 to 40 minutes, Ni immersion time: 10 minutes (Ni coating amount:
0.2-4.0 g/m2)), direct-pass and double-pass enameling and firing. The thus obtained enameled steel plate was visually judged to contain bubbles and
In addition to investigating the occurrence tendency of sunspot defects (small, medium, large) (30 minutes is the standard time limit for the occurrence of bubbles and sunspot defects),
PEI adhesion test CP, E, I (U.S. Deafness Association)
] Recommended adhesion test method (ASTM: C313-
59), the crawling adhesion was measured. In addition, the mechanical properties of the steel sheet material after temper rolling with a rolling reduction of 0.5% were also investigated.

The results are shown in Table 3.

In addition, the mechanical properties of the steel sheet material were determined by processing samples in the 0', 45°, and 90° directions relative to the rolling direction into JISS No. y, s, , T, S, , Effi, Y, E
The tensile properties and r value (Lankford value) of fi were measured, and both were averaged [χ-(Xo・+2×X45°+
Bubble/sunspot defects showed the critical time when the tendency to occur was [medium] or higher.

As is clear from Table 3, the enamel plate according to the present invention is made of conventionally known decarburized capped steel (Steel No. 5
, No. 30), it was confirmed that the critical time for bubble/sunspot defect occurrence was the same or significantly extended.

Furthermore, in all cases of twice-applied enameling, the adhesion was 90% or more, and no surface defects such as bubbles or black spots were observed.

(Effects of the Invention) Thus, according to the present invention, the characteristics of the steel sheet material include not only the press formability required for a steel sheet for enameling, but also the resistance to chipping, wax adhesion, and surface quality, all of which are suitable for decarburized caps. It is advantageous for obtaining high-quality enamel plates that are equivalent to or better than deep-drawn steel, and this invention also enables the production of high-grade deep-drawn enamel steel plates, which could only be achieved by conventional ingot-forming methods. Since it can be manufactured by continuous casting, it has great advantages in terms of cost reduction and energy saving.

Furthermore, the present invention is applicable not only to direct enameling but also to enameled steel plates that are applied twice or more and fired.

[Brief explanation of drawings]

Figure 1 shows the effect of B on bubbles and sunspot defects during enameling.
This is a graph investigating the influence of a concentrated layer. 2

Claims (3)

[Claims] 1. A steel plate having an enamel layer on the surface of a steel plate material containing B: 0.0050 wt% or less, the steel plate material having an average B concentration from at least one surface to a depth of 1% of the plate thickness, An enameled steel sheet with few bubbles and black spot defects, characterized by having a B-enriched layer that is either 5 ppm or more higher than the average B concentration of the steel sheet material or 1.3 times or more the average B concentration of the steel sheet material. 2. The steel plate material is: C: 0.050wt% or less, Mn: 1.0wt% or less, P: 0.10wt% or less, S: 0.10wt% or less, Al: 0.20wt% or less, N: 0.020wt%. The enameled steel sheet according to claim 1, which contains Cu: 0.10 wt% or less and O: 0.10 wt% or less, with the balance consisting of Fe and inevitable impurities. 3. The steel plate material contains one or more selected from Ti, Nb, Zr, V, Se, Bi, Sb and REM, with a total of 0.0
The enameled steel sheet according to claim 2, containing 01 to 1.0 wt%.