JPH0472914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for descaling a cold-rolled titanium plate, which has a smooth surface texture after descaling and can be applied to thin plates.

(Prior Art) When manufacturing a cold-rolled titanium plate, annealing is usually performed after cold rolling, but when annealing is performed, oxide scale (hereinafter simply referred to as scale) is generated on the surface of the cold-rolled titanium plate. Since this scale must be removed in the case of cold-rolled titanium sheets, descaling has conventionally been carried out after annealing. In the case of cold-rolled titanium sheets, the scale is thick, dense, and has excellent corrosion resistance, so descaling cannot be done only by chemical treatment with an aqueous solution such as pickling. mechanical treatment to remove most of the scale,
Conventionally, the remaining scale was then removed by immersion in an aqueous mixed acid solution of nitric acid and hydrofluoric acid.

(Problems to be Solved by the Invention) However, although this method has excellent descaling properties, the surface of the cold-rolled titanium sheet becomes rough due to the mechanical treatment, and furthermore, the roughened surface remains after the treatment with the mixed acid aqueous solution. Although this method is preferable in terms of appearance, it is still unsatisfactory. Furthermore, when descaling a thin plate using this method, numerous irregularities that reach the back side are generated, so it cannot be used for thin plates.

(Means for solving the problem) Therefore, the present inventors conducted various studies to develop a descaling method that does not cause the surface to become rough after descaling and can also be used for thin plates. They developed a method that combines treatment with mixed acid aqueous solution.

In general, a chemical treatment using an aqueous solution is sufficient to descale thin plates without making the surface rough, and without any problems, but as mentioned above, the scale on cold-rolled titanium plates is thick, dense, and corrosion-resistant. Therefore, it is difficult to descale by chemical treatment using an aqueous solution. Therefore, the present inventors focused on a molten alkali salt bath, and when a cold-rolled titanium plate was subjected to severe treatment in a molten alkali salt bath, the scale reacted with the molten alkali and easily dissolved in a mixed acid aqueous solution of nitric acid and hydrofluoric acid. They discovered that the scale layer changes to scale, and the scale layer also generates grids due to heat, making it easier for the mixed acid aqueous solution to penetrate.
However, when treating materials treated in a molten alkali salt bath with a mixed acid aqueous solution of nitric acid and hydrofluoric acid, descaling cannot be achieved unless the acid concentration is adjusted appropriately, and titanium metal is easily attacked by a mixed acid aqueous solution of nitric acid and hydrofluoric acid. However, the base material was also dissolved and the surface became rough, resulting in an unsatisfactory surface texture. Therefore, the present inventors further investigated the concentration of the mixed acid aqueous solution in order to obtain a good surface texture. Thus, the present inventors made sodium hydroxide the main component and added an oxidizing agent to it at a temperature of 450 to
A process of immersing a cold-rolled titanium plate in a molten alkali salt bath at 600°C for 10 seconds or more, and a molten alkali salt bath in a mixed acid aqueous solution containing 50 to 200 g of nitric acid and 2 to 20 g of hydrofluoric acid at a temperature of 40 to 60°C. They have developed a method for descaling a titanium plate, which is characterized in that it is carried out by a method that includes the step of treating the cold-rolled titanium plate after being immersed in the water.

The molten alkali salt bath used in the present invention has sodium hydroxide as its main component, to which an oxidizing agent is added. This oxidizing agent is an inorganic compound, such as sodium nitrate, and is preferably added in an amount of 15 to 45% by weight. The cold-rolled titanium plate is treated by immersing it in this molten alkali salt bath, and the immersion is carried out at a bath temperature of 450 to 600°C for 10 seconds or more. This is because if the bath temperature is lower than 450℃, the time required for descaling with the mixed acid aqueous solution in the next step will be significantly longer, and if the bath temperature is not immersed for more than 10 seconds, descaling with the mixed acid aqueous solution will be insufficient even if the bath temperature is increased to 600℃. This is because. Furthermore, the reason for setting the bath temperature below 600°C is that maintaining the bath temperature above 600°C is difficult to keep warm, and fuel costs are high.

After the molten alkali salt bath treatment under the above treatment conditions, the cold-rolled titanium sheet is treated with an aqueous mixed acid solution of nitric acid and hydrofluoric acid;
A mixed acid aqueous solution containing 50 to 200 g of hydrofluoric acid and 2 to 20 g of hydrofluoric acid at a temperature of 40 to 60° C. is used, and the cold-rolled titanium plate is usually immersed therein. Here, if the nitric acid concentration of the mixed acid aqueous solution is less than 50g/, descaling will be insufficient even if the hydrofluoric acid concentration is increased, and if the hydrofluoric acid concentration is less than 2g/, the descaling will be insufficient even if the nitric acid concentration is increased. The scale is insufficient. On the other hand, if the nitric acid concentration is higher than 200 g/L, acid will be carried out or evaporated from the cold-rolled titanium sheet during treatment, and the surface of the cold-rolled titanium sheet will also be excessively pickled.
Also, in the case of hydrofluoric acid, if the acid content is higher than 20 g, excessive pickling will occur and the surface of the cold-rolled titanium sheet will become rough. Further, if the temperature is less than 40°C, the time required for descaling will be longer, and if the temperature is higher than 60°C, acid evaporation will increase.

The present invention will be explained below with reference to Examples.

(Example) Example 1 A cold-rolled titanium plate with a thickness of 1.0 mm that had been annealed at 650°C for 120 seconds and had scales formed on its surface was treated with a molten alkali salt having a composition of 65% by weight of sodium hydroxide and 35% by weight of sodium nitrate. Nitric acid after immersion in various conditions in the bath
When the relationship between the molten alkali salt bath treatment conditions and the time required for descaling in the mixed acid aqueous solution treatment was determined by immersing the sample in a mixed acid aqueous solution containing 100 g/fluoric acid and 5 g/fluoric acid at a temperature of 55°C, the results shown in Figure 1 were obtained. The surface of the cold-rolled titanium sheet after descaling was smooth.

Example 2 The cold-rolled titanium plate used in Example 1 was immersed in a molten alkali salt bath (500°C) with the same composition as in Example 1 for 20 seconds, and then immersed in a mixed acid aqueous solution with different concentrations of nitric acid and hydrofluoric acid for 60 seconds. When the descaling state and surface texture were investigated, the results shown in Figure 2 were obtained.If the mixed acid aqueous solution treatment conditions were outside the range of the present invention, descaling could not be achieved, the surface texture would become rough,
Furthermore, the mixed acid aqueous solution evaporated significantly and was unsuitable.

(Effects) As explained above, the present invention descales a cold-rolled titanium plate by molten alkali salt bath treatment and nitric acid-fluoric acid mixed acid aqueous solution treatment without using mechanical treatment. The surface texture of the cold-rolled titanium sheet is smooth, and there will be no unevenness even when it is applied to descaling thin sheets.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the molten alkali salt bath treatment conditions and the time required for descaling in mixed acid aqueous solution treatment when a cold rolled titanium plate after annealing was descaled in Example 1, and FIG. FIG. 7 is a diagram showing the relationship between the concentration of the nitric acid-fluoric acid mixed acid aqueous solution, the descaling state, the surface texture, etc. when the titanium cold rolled plate after annealing is descaled in Example 2.

Claims (1)

[Claims] 1. When removing oxidized scale generated on the surface of a cold-rolled titanium plate due to annealing, the main component is sodium hydroxide, and an oxidizing agent is added to it at a temperature of 450 to 600°C.
A process of immersing a cold-rolled titanium plate in a molten alkali salt bath for 10 seconds or more, and adding 50 to 200 g of nitric acid and 2 g of hydrofluoric acid.
1. A method for descaling a titanium plate, comprising the step of treating the cold-rolled titanium plate after immersing it in a molten alkali salt bath with a mixed acid aqueous solution at a temperature of 40 to 60°C containing ~20 g/ml.