JPH0469002B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention provides a hot-rolled steel sheet for enameling, which can omit the step of removing scale after hot rolling, has excellent adhesion of enamel after enameling firing, and can omit pretreatment for the enameling glazing step. and its manufacturing method. <Prior art and its problems> Normally, the manufacturing process for enamel products includes pretreatments such as degreasing, pickling, Ni dip, and neutralization after processing, followed by glazing and firing after drying. However, this method involves a large number of steps, resulting in high costs, and although it takes a lot of effort, it does not reduce enamel defects. Furthermore, the use of acids causes pollution problems such as pressure on the environment and treatment of waste acids, and these problems require a large amount of equipment and expense. In general, pre-treatments such as pickling and Ni dip treatment mentioned above were considered essential to improve the adhesion of enamel, but there is no method to omit the pickling and Ni dip treatment necessary for enamel adhesion. Steel plate for fired enamel (Special Publication No. 1972-29289)
was once proposed. However, with this method, the steel sheet manufacturer goes through a hot rolling stage, then glazes, dries, and then performs cold rolling, which requires specialized equipment and materials, and is especially unnecessary for the enamel coating after firing. Another drawback is that the resin is mixed with the glaze, which increases costs, and the decomposition of the resin generates graphite during the firing stage, causing air pollution. In addition, a steel plate for enameling, which is Ni-plated after recrystallization annealing and eliminates the need for pre-treatment after press working, was published in Japanese Patent Publication No. 47-4476.
Japanese Patent Laid-Open No. 59-53682 discloses a steel plate for enameling which is plated with Ni, Co and composite plating, and then recrystallized annealed to omit pre-treatment after press working. However, the former requires a protective film to be applied after Ni plating to prevent the plating from peeling off when pressed after Ni plating and reducing the adhesion of that area.
The cost increase for this is unavoidable, and in case
If Ni peels off, it will leave defects such as rust. The latter does not peel off the plating during processing, but the Ni
This requires additional equipment, which inevitably increases costs. On the other hand, as a pretreatment for enamel, a method known as "oil firing" that omit the degreasing and pickling steps before glazing the enamel has been used for a long time. This method removes fats and oils adhering to the surface of the steel plate by baking it at high temperature, making the glaze smoother, and it is said that the extremely thin oxide film produced during baking improves the adhesion of the enamel slightly after firing. ing. However, even with this method, cost increases due to the increased number of firings due to dry firing, and increased costs due to the need for various equipment and materials dedicated to dry firing cannot be avoided. On the other hand, hot edge steel plates for enameling are covered with thick scale, so the scale is removed by pickling and shot blasting, and then degreasing, pickling, and Ni dip are applied to ensure enamel adhesion. There is. However, in removing scale by pickling, pickling uses a large amount of acid, which causes pollution problems such as deterioration of the environment and waste acid treatment, and descaling by shot blasting requires a lot of labor. Both require high running costs in addition to capital investment. There is also the issue of equipment maintenance and management. Furthermore, in order to prevent a decrease in yield due to descaling, it is desired to minimize the amount of scale generated during hot rolling. <Object of the Invention> The present inventors varied the amount of scale on the surface of a hot rolled sheet and investigated the effect on enamel adhesion without enameling pretreatment. As a result, it was found that good enamel adhesion can be obtained if the scale thickness on the steel plate surface is 1.5 μm or less. By controlling the scale thickness generated on the surface of the steel sheet during hot rolling finishing to 1.5 μm or less, the present invention can omit the descaling process of the hot rolled sheet and achieves good enamel adhesion without any pretreatment before enamel application. The purpose is to obtain sex. <Structure of the Invention> That is, the present invention provides a hot-rolled steel plate for enameling, which is characterized in that the scale thickness of the surface of the steel plate for enameling after hot finish rolling is controlled to 1.5 μm or less. The present invention also provides that when hot finish rolling a steel plate for enameling, the temperature at the entrance to the finishing mill is 800°C or less and the temperature at the exit side is 400°C or less to reduce the scale thickness on the steel plate to 1.5 μm or less. The present invention provides a method for producing a hot-rolled steel plate for enameling. The present invention further provides that when hot finishing rolling a steel plate for enameling, the temperature at the entrance to the finishing rolling mill is set to 800°C.
The thickness of the scale on the steel plate is reduced by cooling at a cooling rate of 200°C/sec or more from the point closest to the exit side of the finishing mill.
The present invention provides a method for manufacturing a hot-rolled steel plate for enameling, characterized in that the thickness is 1.5 μm or less. Normally, scales with a thickness of 5 to 15 μm are formed on the surface of the steel sheet after hot rolling. If the enamel is fired without descaling and enameling pretreatment, the enamel will hardly adhere and will peel off at the scale interface. As shown in Figure 1, the enamel adhesion without descaling or enamel pretreatment is as follows when the scale thickness on the steel plate surface is 1.5 μm.
An adhesion rate of 80% or more can be obtained at m or less. Above that, the greater the scale thickness, the lower the adhesion.
When the thickness is 5 μm or more, there is almost no adhesion. Generally, it is said that the adhesion between a steel plate and enamel occurs because the surface of the steel plate is oxidized during enamel firing, and the iron oxide on the surface of the steel plate diffuses into the glaze and fuses together. Therefore, up to a certain amount of iron oxide on the steel plate surface contributes to improving the adhesion of the enamel, but if it is too large, a weak iron oxide layer is formed at the boundary between the enamel and the iron, and the enamel becomes weaker. Adhesion will be reduced. That is, in order to obtain good adhesion, the scale thickness on the surface of the hot rolled steel sheet needs to be 1.5 μm or less, preferably 1.0 μm or less. The present inventors investigated the amount of scale generated during hot finish rolling and the subsequent runout table under various hot rolling conditions, and found that the amount of scale was determined by the entrance temperature of hot finish rolling (hereinafter referred to as FET) and the amount of scale generated during hot finish rolling and the subsequent runout table. We found that it depends on the outlet temperature (hereinafter referred to as FDT). Figure 2 shows FET in hot rolling of ultra-low carbon steel.
This figure shows the relationship between the amount of scale and the amount of scale on the surface of the steel sheet after hot rolling. The lower the FET, the thinner the scale becomes, and when the FET is below 800°C (below the Ar ₃ transformation point), the scale thickness is 1.5 μm or less. On the other hand, the relationship between FDT and scale amount is shown in Figure 3, and the lower the FET, the smaller the scale amount.
When the FDT is below 400℃, the scale thickness is below 1.5μm. Furthermore, the present inventors have found that the scale on the surface of the steel sheet can be thinned by rapidly cooling the steel sheet immediately near the exit side of the hot finishing mill. FIG. 4 shows the results of measuring the cooling rate during quenching and the scale thickness on the surface of the hot rolled steel sheet near the exit side of the hot finishing mill. The faster the cooling rate, the thinner the scale becomes, and at 200°C/sec or more, the scale thickness becomes 1.5 μm or less. In other words, the FET should be below 800℃ and the FDT should be 400℃.
The scale thickness after hot rolling is reduced to 1.5 μm by a method of rapid cooling at a cooling rate of 200°C/sec or more from the exit side of the finishing mill, although FDT is not regulated.
By doing the following, we have completed a hot-rolled steel sheet for enameling, which can omit the descaling process after hot rolling and can obtain good enamel adhesion even if the enameling pretreatment process is omitted. <Example> Examples of the present invention are listed below. Example 1 200 mm thick ultra-low carbon steel slab (composition C: 0.003,
Si: 0.02, Mn: 0.10, P: 0.01, S: 0.005)
After heating at 1100℃ and rough rolling into a 17mm thick sheet bar, the temperature is changed to 550 to 1030℃ using water cooling equipment installed between the rough rolling mill and finishing mill, and further FDT is 200℃.
It was hot rolled to 1.4 mm while being cooled between stands to a temperature in the range of ~830°C. After hot rolling, the product was wound into a coil, immediately cooled with water, and its scale thickness was measured. Next, in the hot-rolled state, L manufactured by Nippon Fellow Co., Ltd.
After applying the type glaze and undercoat firing at 820℃ for 4.25 minutes, the
1553B was applied and final firing was performed at 790℃ for 4.25 minutes. After firing the enamel, PEI ( P orcelain E
ASTM C313-78 (Standard test method for the adhesion of enamel layers and ceramic coatings to thin metal sheets) recommended by the American Enamel Institute .
Adhesion was evaluated by. In addition, ASTM C313
-78 uses a steel ball with a diameter of 1 inch to press an enameled test piece with a constant pressure of 2000 pounds to deform the test piece and remove the peeled part of the enamel.
Measure electrically with 169 probes of the Adherence Meter, read the number n of needles shorted to the substrate, and calculate (1-n/
169) x 100 to display the adhesion rate (%).
That is, 100% means that the enamel layer has not peeled off at all, and 0% means that the enamel layer has completely peeled off. The results are shown in Table 1. The scale thickness is within the range of the FET method of the present invention.
The FDT was 1.5 μm or less at 800°C or lower and 400°C or lower, and the adhesion after two enameling firings also showed good adhesion of 80% or higher. However, when FET is 830℃ and FDT is 450℃ or higher,
It is clear that when the scale thickness is 2.2 μm or more, the adhesion after enamel firing is also significantly reduced. Example 2 A 200mm thick ultra-low carbon steel slab was heated to 1200℃.
After rough rolling into a 17mm thick sheet bar, the finishing temperature is
Hot rolling was carried out to 1.4 mm at 850°C. The steel sheet was rapidly cooled at a cooling temperature of 15 to 360° C./sec immediately after exiting the finishing mill, and immediately after being wound into a coil, it was cooled with water and the scale thickness on the surface of the steel sheet was measured. Next, enamel was fired under the same conditions as in Example 1, and the enamel adhesion rate was measured. The results are shown in Table 2. The scale thickness is 1.5μ when the cooling rate immediately before the finishing rolling mill exit side is 200℃/sec or more, which is within the range of the present invention method.
m or less, and the enamel adhesion rate also showed good adhesion of over 80%. It is clear that when the cooling rate is 200° C./sec or less, the scale thickness becomes 2.0 μm or more, and the enamel adhesion after enamel firing is significantly reduced.

【table】

[Table] <Effects of the Invention> Conventionally, scales of 5 to 15 μm were baked on the surface of a steel sheet after hot rolling, and removing the scales by pickling or shot blasting required a great deal of cost.
The present invention is expected to improve yield and work efficiency by omitting the descaling step. In addition, the hot-rolled steel sheets manufactured by the present invention do not have scale peeling off during light processing, and by leaving extremely thin scales, the adhesion of enamel is improved and the pre-treatment process for enamel can be omitted. There are merits.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the scale thickness of a hot-rolled sheet and the enamel adhesion rate after enamel firing.
FIG. 2 is a graph showing the relationship between the finishing entrance temperature (FET) and scale thickness. FIG. 3 is a graph showing the relationship between finish extension temperature (FDT) and scale thickness. FIG. 4 is a graph showing the relationship between the cooling rate and scale thickness immediately before the exit side of the finishing mill.

Claims (1)

[Claims] 1. A hot-rolled steel plate for enameling, characterized in that the scale thickness on the surface of the steel plate for enameling after hot finish rolling is controlled to 1.5 μm or less. 2 When hot finish rolling a steel plate for enameling,
The scale thickness on the steel plate is reduced by rolling at an input temperature of 800℃ or less and an exit temperature of 400℃ or less.
A method for producing a hot rolled steel plate for enameling, characterized in that the thickness is 1.5 μm or less. 3 When hot finish rolling a steel plate for enameling,
For enameling, the temperature at the entrance to the finishing rolling mill is 800°C or less, and the scale thickness on the steel plate is reduced to 1.5 μm or less by cooling at a cooling rate of 200°C/sec or more from the side closest to the finishing rolling mill. A method for producing hot rolled steel sheets.