JPH0440433B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for preventing the generation of gold dust on a Cr stainless steel strip, and more specifically, the present invention relates to a method for preventing the generation of gold dust in a Cr stainless steel strip, and more specifically, it involves omitting annealing or performing short-time high-temperature heat treatment. The present invention relates to a method for preventing the generation of gold dust by pickling and smutting a hot-rolled steel strip of Cr-based stainless steel that has been sensitized.

[Prior Art] As a method for pickling Cr-based stainless steel that has been hot rolled without annealing or annealed after hot rolling, it is generally carried out in a continuous annealing pickling line (commonly referred to as an AP line). A method is conventionally known in which the steel strip is subjected to mechanical preliminary descaling such as Yotsutoblasting, and then pickled in sulfuric acid and nitric/hydrofluoric acid solutions.

However, when using nitric acid or hydrofluoric acid, there are problems with NO _x ,
There is a problem in that it causes intergranular corrosion in the steel strip.
As a means to solve this problem, for example, Japanese Patent Application Laid-open No. 59-83783 discloses a first method in which oxidized scale on the surface is removed by immersing the steel strip in an aqueous sulfuric acid solution.
A pickling method is disclosed, which comprises a second step of immersing the steel strip in an aqueous nitric acid solution to remove surface dirt (smut removal) and passivation treatment.

The inventors investigated pickling methods for Cr-based stainless steel hot-rolled steel sheets that omitted annealing and those that were annealed for a short time in a temperature range of 800 to 1100°C. In particular, Cr-based stainless steel is required to have good gloss as a thin plate product surface property, and BA products (bright annealing products) are required to have no surface defects called gold dust.

In addition, the inventors investigated the effect of smutting conditions on gold dust in BA products by using nitric acid as a smutting treatment after pickling with a sulfuric acid solution or a hydrochloric acid solution. As a result, it has become clear that the higher the nitric acid concentration and the longer the treatment time, the more effective the smut removal, as disclosed in Japanese Patent Application Laid-open No. 83783/1983.

However, even in the smut treatment in nitric acid, intergranular corrosion occurs in steel strips, and intergranular corrosion occurs particularly in steel strips that do not undergo annealing after hot rolling or in steel strips that are annealed at high temperatures and for short periods of time. It has become clear that the generation of gold dust is unavoidable due to this intergranular corrosion.

[Problem to be solved by the invention] Hot-rolled sheets of Cr-based stainless steel can be sensitized by omitting annealing or by cooling process after high-temperature short-time heat treatment in the temperature range of 800 to 1100°C for less than 10 minutes. If such a steel strip is descaled in a sulfuric acid solution or hydrochloric acid solution and then smutted in a nitric acid solution as in the prior art, grain boundaries will form at the grain boundaries in the extreme surface layer of the steel strip. Corrosion occurs, and the outermost surface becomes intergranular cracked in the subsequent cold rolling process, resulting in rough skin in the product sheet, loss of gloss, and the cause of gold dust on bright annealed sheets.

On the other hand, this gold dust can be produced by sufficient annealing after hot rolling, as in the conventional manufacturing process of Cr-based stainless steel strips: steelmaking, casting, hot rolling, annealing, pickling, cold rolling, and annealing. Since the steel strip is not sensitized, there is no risk of this occurring even if nitric/hydrofluoric acid or nitric acid solution is used for pickling or smutting.
Therefore, if Cr-based stainless steel strip can be produced using a production process that is the same as that for ordinary steel, with annealing omitted or simplified, and the steel strip does not generate gold dust, it would be of great industrial significance. will be very large.

The present invention was made in view of the above points, and is intended for sensitized Cr-based stainless steel hot-rolled steel strips, and is capable of effectively preventing the generation of gold dust caused by the intergranular corrosion described above. , an efficient manufacturing process for ordinary steel that simplifies annealing.
The purpose is to provide a method by which a Cr-based stainless steel strip can be obtained.

[Means for Solving the Problems] The method for preventing gold dust of the present invention to achieve this object is a method for preventing gold dust of the present invention by hot rolling Cr-based stainless steel and then applying a high-temperature heat treatment for a short time without annealing. The hot-rolled steel strip is subjected to mechanical descaling, then pickled with a sulfuric acid solution and/or a hydrochloric acid solution, and then immediately sprayed with water or hot water and mechanically scaled the surface of the steel strip. It is characterized by grinding to remove smut, spraying with water or hot water, then cold rolling and annealing.

The reason why the material targeted in the present invention is limited to the sensitized hot-rolled steel strip that has not been annealed or has been subjected to a short high-temperature heat treatment as described above is because of the industrial advantage of ordinary steel. Cr in the manufacturing process
This is because stainless steel strips can be produced.

The present invention will be explained in detail below.

First, a sensitized Cr stainless steel hot-rolled steel strip is subjected to mechanical descaling and then pickled with a sulfuric acid solution and/or a hydrochloric acid solution, but at this point no intergranular corrosion appears in the steel strip. Not yet. However, if a smut treatment is subsequently performed with a nitric-hydrofluoric acid or nitric acid solution to remove the smut adhering to the surface of the steel strip, intergranular corrosion occurs and gold dust is generated. In other words, it can be seen that the generation of such gold dust is caused by intergranular corrosion of the steel strip after pickling.

Next, the inventors investigated in detail the properties of smuts attached to Cr-based stainless steel specimens that had been descaled with a sulfuric acid solution or a hydrochloric acid solution, and as a result, the following points were clarified.

(1) Smuts precipitate and adhere to the surface of steel strips that have been pickled (descaled) with sulfuric acid or hydrochloric acid solutions.

(2) Once the steel strip is dried after pickling with sulfuric acid or hydrochloric acid solution, it becomes extremely difficult to remove the smuts.

(3) If the smut is strongly pressed against the steel strip, it will be difficult to remove the smut in that area.

(4) Smuts can be easily removed by brushing under wet conditions such as water.

Therefore, the smut deposited on the surface of the steel strip after pickling can be removed very effectively by brushing with an acid-resistant brush or the like under a wet condition such as water. found.

Next, one embodiment of the present invention will be described in detail based on the drawings.

In FIG. 1, a hot rolled steel strip 1 to be pickled is pickled in a pickling tank filled with a solution 2 of sulfuric acid or hydrochloric acid, and is conveyed under tension by support rolls 6. In FIG. 1, a cleaning device 5 is provided between the outlet side of the pickling tank and the support roll 6. In the embodiment shown in FIGS. 1 and 2, a spray 4 that sprays water or hot water onto the surface of the steel strip is connected to a cleaning device 5.
are placed before and after. The spray 4-1 at the front stage of the polishing device 5 is provided for diluting and wetting the acid solution on the surface of the steel strip, and the spray 4-2 at the rear stage is provided for wetting the surface of the steel strip and cleaning the polished smut. Provided for discharge to the outside.

The cleaning device 5 is configured by providing acid-resistant brush rolls vertically in parallel. Instead of a brush roll,
It can also be used as a fixed brush board. In addition, the cleaning device 5
may be arranged in a water tank and configured to polish the surface of the steel strip underwater.

In FIG. 1, reference numeral 3 denotes a rubber roll that rotates while lightly touching the surface of the steel strip in order to shield the surface of the steel strip from the pickling liquid.

In the embodiment of the present invention shown in FIG. 1, since the polishing device is provided in front of the support roll 6, the support roll 6 does not force the smut against the surface of the steel strip, and the smut is removed most effectively. I can do it.

When the embodiment shown in FIG. 2 is adopted, that is, when the polishing device 5 is disposed after the support roll 6-1, compared to the case where the embodiment shown in FIG. 1 is adopted,
It is necessary to install multiple brush rolls.

[Example] Hot-rolled SUS430 stainless steel sheets without annealing and steel strips that were continuously annealed at 100°C for 1 minute were subjected to mechanical deformation in which iron sand particles were mixed and sprayed in high-pressure water. After scaling, a sulfuric acid solution with a concentration of 200 to 300 g/was acid-washed for 30 to 120 seconds in a hydrochloric acid solution with a concentration of 100 g/at a temperature of 60° C. to 90° C. After that,
Using the smut removal device shown in FIG. 1, water spray was applied to the front and back surfaces of the steel strip at the front and back stages of the polishing device 5, and smut treatment was performed using two pairs of acid-resistant brush rolls on the front and back sides.

As a comparative example, after pickling, the steel strip was immersed in a 150 g/nitric acid solution at 50 DEG C. and subjected to a smut treatment for 30 to 120 seconds, as in the prior art.

The two types of SUS430 stainless steel strips thus obtained were subjected to tandem cold rolling using rolling mill rows with large-diameter rolls (work rolls with a diameter of 200 to 600 mm) and with small-diameter work rolls (work rolls with a diameter of 1000 mm or less). A cold rolling process by a combination of cold rolling by a Sendzimer mill with
After cold rolling by a cold rolling process using only a Sendzimer mill, bright annealing was performed.

As a result of testing the product sheets thus obtained for gold dust, it was found that the products obtained by the smut treatment according to the present invention without using nitric acid did not generate any gold dust and had good surface gloss.

On the other hand, in the products obtained in the comparative example, regardless of whether hot-rolled sheets were annealed or not, gold dust started to be generated by immersion for 30 seconds or more in the gold dust test, and the immersion time became longer. As the temperature increased, the degree of generation increased, and after 60 seconds or more, gold dust was generated all over the surface and the gloss was poor.

When these steel strips after pickling and smutting were investigated, intergranular corrosion was clearly observed in the steel strips smutted with nitric acid, but no intergranular corrosion was observed in the steel strips according to the present invention. .

[Effect of the invention] The present invention provides a sensitized Cr stainless steel hot-rolled sheet or a high-temperature short-time heat-treated sheet as described above.
Because we have established a process that does not use nitric acid, hydrofluoric acid, or nitric acid for the smut treatment after pickling Cr-based stainless steel hot-rolled sheets, we are able to prevent intergranular corrosion that causes gold dust in the product. Since Cr-based stainless steel strip can be obtained through the steel manufacturing process, its industrial effects are enormous.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus for implementing the present invention, and FIG. 2 is a diagram showing another example of an apparatus for implementing the present invention. 1... Cr-based stainless hot rolled steel strip, 2... Pickling solution, 3... Rubber roll, 4... Spray, 5
...Grinding device, 6...Support roll.

Claims (1)

[Claims] 1 After hot rolling Cr stainless steel, mechanical descaling is applied to a sensitized hot rolled steel strip without annealing or only short-term high temperature heat treatment, and then sulfuric acid solution and/or hydrochloric acid solution Immediately after pickling with water or hot water, the surface of the steel strip is polished by mechanical means to remove smuts, and then water or hot water is sprayed on the steel strip, followed by cold rolling and annealing. A method for preventing gold dust generation in Cr-based stainless steel strip.