JP5040182B2 - Pickling method and manufacturing method of stainless steel - Google Patents

Description

  The present invention relates to a pickling method and a manufacturing method for stainless steel materials, and in particular, when performing pickling with a sulfuric acid solution, an effective pickling method and the pickling method for reducing the time required for pickling treatment are used. The present invention relates to a method for producing a stainless steel material.

  In the manufacturing process of stainless steel, in order to remove the scale and surface dechromation layer formed during hot rolling or annealing, first, a non-oxidizing acid solution such as sulfuric acid or hydrochloric acid, that is, hydrogen accompanying the dissolution reaction of the metal. The steel sheet surface smut is removed by immersing in an acid solution that generates gas and then rinsing with water, or immersing in an oxidizing acid (nitric acid, nitric hydrofluoric acid, etc.) solution and then rinsing with water. The former pickling with a non-oxidizing acid solution is referred to as “crude pickling” or simply “pickling”, and the latter pickling with an oxidizing acid solution is referred to as “finish pickling”.

In the series of steps described above, the role of the rough pickling is to remove scales and dechromed layers generated during hot rolling or annealing after hot rolling by dissolving the base iron, or by shot blasting. It is to smooth the surface irregularities. Therefore, as the acid solution used for this rough pickling, a sulfuric acid solution having a higher dissolving power than hydrochloric acid is generally used.
However, in recent years, stainless steel having high corrosion resistance has been frequently used, and there has been a problem that the corrosion resistance is lowered unless the dechromed layer on the surface of the base iron is sufficiently removed. Moreover, development of the pickling power reinforcement | strengthening technique in rough pickling is desired also from the point of productivity improvement.

Patent Document 1 discloses a pickling method for increasing the amount of dissolution during pickling as one of the techniques for enhancing pickling power in rough pickling. Patent Document 1 describes a pickling solution for stainless steel in which an organic compound containing a mercapto group is added to a non-oxidizing acid solution.
Japanese Unexamined Patent Publication No. 8-333692

  In the technique described in Patent Document 1, the pickling power is about twice that in the case of no addition. However, it is insufficient as a pickling solution for high Cr steel such as SUS430, which requires a large amount of dissolution, and further improvement in pickling ability is required.

  From the above, the present invention has been made in view of such conventional problems, and in the pickling treatment using a sulfuric acid solution, the pickling time can be greatly shortened, and the pickling exceeding the above-mentioned known technology. It is an object of the present invention to provide a pickling method for a stainless steel material having an ability and a method for producing a stainless steel material using the pickling method.

  In order to solve the above-mentioned problems, the present inventors pay attention to a pickling accelerator to be added to the pickling solution when preparing the pickling solution in the pickling of stainless steel using a sulfuric acid solution. Study was carried out. As a result, it was found that by adding an organic compound containing a mercapto group to the sulfuric acid solution and further nickel chloride, the pickling efficiency is improved and the pickling ability is greatly improved.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A pickling method for a stainless steel material, characterized in that when pickling a stainless steel material with a pickling solution, the pickling solution comprises an organic compound containing a mercapto group and a sulfuric acid solution to which nickel chloride is added.
[2] The pickling method for stainless steel material according to [1], wherein the mercapto group-containing organic compound is added in a concentration of 0.001 mol / l or more in a sulfuric acid solution.
[3] The pickling method for stainless steel material according to [1] or [2], wherein the nickel chloride is added in a concentration of 0.01 to 0.4 mol / l in a sulfuric acid solution.
[4] A method for producing a stainless steel material, comprising subjecting a hot-rolled sheet or a hot-rolled annealed sheet made of ferritic stainless steel to pickling according to any one of [1] to [3].

  According to the present invention, the pickling ability is greatly improved. And the pickling process of a stainless steel material can be performed efficiently, and as a result, the pickling time is shortened compared with the past.

  In addition, since the amount of stainless steel dissolved during pickling can be greatly increased, it is possible to easily remove the scale and ground iron deCr-free layer in a short period of time and increase the plate speed of the pickling line. Speed and other industrial effects will be achieved. Furthermore, by using a sulfuric acid solution, it is possible to reduce the cost, for example, the equipment cost required for waste liquid treatment is reduced.

Hereinafter, the present invention will be specifically described.
In order to investigate the pickling accelerator to be added to the sulfuric acid solution, the inventors first focused on the organic compound containing a mercapto group described in Patent Document 1 described above, and investigated the effect of pickling promotion. did. Specifically, mercaptoacetic acid is added as an organic compound containing a mercapto group to a 25 wt% sulfuric acid solution at 80 ° C. to prepare a pickling solution, and using this pickling solution, a hot rolled annealed plate of SUH409L is shot. The blasted test material was pickled for 60 seconds. Next, the pickling loss was investigated. The pickling solution used was a 25 wt% sulfuric acid solution collected from a sulfuric acid pickling line in an actual factory. In addition, the pickling loss is evaluated by calculating the pickling weight loss per unit area by cutting the test material into 30 mm x 40 mm dimensions as a pickling test piece, measuring the weight change before and after pickling. It was. The obtained results are shown in FIG. FIG. 1 shows the results of examining the pickling loss when SUH409L was pickled using a pickling solution obtained by adding 0 to 0.05 mol / l of mercaptoacetic acid to a 25 wt% sulfuric acid solution at 80 ° C. Thus, when 0.001 mol / l or more of mercaptoacetic acid is added, the pickling loss is increased to about 90 g / m ² , and in particular, the addition of 0.01 mol / l is about 2 compared with the case of no addition. It can be seen that the pickling loss is increased up to twice. From the above results, it was confirmed that mercaptoacetic acid has a pickling accelerating action and enhances the dissolution of stainless steel.
Thus, the pickling-promoting effect when mercaptoacetic acid is added to the sulfuric acid solution was also observed in an organic compound containing a mercapto group (—SH group) such as mercaptoethanol or mercaptosuccinic acid. Therefore, in the present invention, an organic compound containing a mercapto group is first added to a sulfuric acid solution which is a pickling solution.
However, as described above, simply adding an organic compound containing a mercapto group in sulfuric acid is not sufficient as a pickling solution for high Cr steel such as SUS430 having a large required amount of dissolution. Accordingly, the present inventors have investigated in detail the effect of various additives on the pickling loss of stainless steel in order to further enhance the pickling promoting action of the sulfuric acid solution to which an organic compound having a mercapto group is added. As a result, the following knowledge was obtained.
1) By adding nickel chloride to a sulfuric acid solution containing an organic compound having a mercapto group, the pickling weight loss is greatly increased.
2) The addition amount of nickel chloride has a remarkable pickling promotion effect in the range of 0.01 to 0.4 mol / l, and even if it exceeds 0.4 mol / l, the pickling promotion effect is saturated. .
Hereinafter, the obtained knowledge will be described in detail.
As an organic compound having a mercapto group, 0 to 0.5 mol / l of nickel chloride is added to 25 wt% sulfuric acid solution containing 0.005 mol / l and 0.02 mol / l of mercaptoacetic acid to prepare a pickling solution. did. Further, as a comparative solution, a solution containing only 25 wt% sulfuric acid (no addition of an organic compound containing a mercapto group and nickel chloride) was also prepared. Using these pickling solutions, pickling was performed at 80 ° C. for 60 seconds on a test piece obtained by shot blasting a SUH409L hot-rolled annealed plate. The obtained results are shown in FIG. The pickling solution used was a 25 wt% sulfuric acid solution collected from a sulfuric acid pickling line in an actual factory. The pickling weight loss was evaluated by cutting the test material into 30 mm × 40 mm dimensions as a pickled test piece, measuring the weight change before and after pickling, and calculating the pickling weight loss per unit area. From FIG. 2, it can be seen that when nickel chloride is added to a sulfuric acid solution to which an organic compound having a mercapto group is added, the pickling weight loss is greatly increased (in the case of adding 0.005 mol / l of mercapto group to the comparative solution). About 4 times maximum, and when mercapto group is added at 0.02 mol / l, the pickling weight loss is about 7 times that of the comparative solution). This tendency is particularly great when a large amount of an organic compound having a mercapto group is added. Further, with the increase in the amount of nickel chloride added, the pickling loss increases, and a remarkable pickling promotion effect is obtained in the range of 0.01 to 0.4 mol / l. On the other hand, even if added over 0.4 mol / l, the pickling promoting effect tends to be saturated.
The action of pickling promotion by the addition of nickel chloride is not always clear, but S, which has an unshared electron pair contained in an organic compound having a mercapto group, increases the adhesion between the acid and the steel and helps dissolve the steel. Assuming that there is an action to suppress the generated hydrogen from covering the steel sheet surface, it is considered that the action of nickel chloride further promotes this hydrogen releasing action.
From the above, in the present invention, an organic compound containing a mercapto group is added to a sulfuric acid solution that is a pickling solution, and as shown in FIG. 1, the pickling promoting action is large at 0.001 mol / l or more. The amount added is preferably 0.001 mol / l or more. On the other hand, as shown in FIG. 1, when added over 0.02 mol / l, the pickling promoting effect of the present invention is sufficient, but the pickling promoting effect is weakened, so the upper limit is 0.02 mol. / L or less is preferable. Examples of the organic compound having a mercapto group include mercaptoethanol and mercaptosuccinic acid in addition to the aforementioned mercaptoacetic acid.
In the present invention, nickel chloride is further added to a sulfuric acid solution to which an organic compound containing a mercapto group is added. By adding nickel chloride, the pickling loss is greatly increased. As is clear from FIG. 2, the pickling promoting action by nickel chloride is obtained at 0.01 mol / l or more. However, since the effect tends to be saturated when the amount exceeds 0.4 mol / l, the amount of nickel chloride added is preferably in the range of 0.01 to 0.4 mol / l from the viewpoint of cost. Nickel chloride may be either an anhydride or a hydrate.

In addition, the pickling process of this invention has an effect irrespective of the pickling pre-processing of steel materials, steel types, and also a hot-rolled sheet and a cold-rolled sheet. However, in order to perform the pickling process more efficiently in industrial production, it is preferable to perform a mechanical preliminary descaling process before pickling that is generally performed in descaling. Examples of the mechanical preliminary descaling process include shot blasting and bending. The effects of the present invention can also be obtained in Ni-containing austenitic stainless steels and Mo-containing stainless steels that are difficult to scale steel materials. In particular, in ferritic stainless steel, the present invention is more effective. Therefore, a stainless steel material is manufactured on a hot-rolled sheet or hot-rolled annealed sheet made of ferritic stainless steel through the above pickling process of the present invention. Is preferred.
Further, as the next step of the pickling according to the present invention, finishing pickling with nitric hydrofluoric acid or the like may be performed in order to obtain good surface properties.

Hereinafter, the present invention will be described based on examples.
Hot rolling was performed on SUH409L and SUS430 produced by ordinary methods, and some of the obtained hot-rolled steel strips were further subjected to hot-rolled sheet annealing. Next, these steel strips were subjected to shot blasting, and then subjected to pickling (rough pickling) with pickling solutions having different addition conditions of the pickling accelerator as shown in Table 1. Thereafter, some of the pieces were subjected to finish pickling and water washing, and the other portions were washed without being subjected to finishing pickling. The obtained results are shown in Table 1 together with the conditions.
In conducting the experiment, the pickling solution used was a 25 wt% and 27 wt% sulfuric acid solution collected from a sulfuric acid pickling line in an actual factory. Further, the pickling loss was evaluated by cutting the test material into 30 mm × 40 mm dimensions as a pickling test piece, measuring the weight change before and after pickling, and calculating the pickling loss per unit area.

  From Table 1, in the present invention example in which both an organic compound containing a mercapto group and nickel chloride were added, a solution in which neither an organic compound containing a mercapto group nor nickel chloride was added, and only an organic compound containing a mercapto group It can be seen that the pickling weight loss is greatly increased as compared with the comparative example in which nickel chloride is not added.

Since the pickling method of the present invention can greatly increase the amount of dissolution during pickling, the scale and the Cr-free layer can be easily removed by short-time immersion. From the above, the pickling method of the present invention is a particularly useful method for high Cr steels such as SUS430 having a large required dissolution amount, Ni-containing austenitic stainless steels and Mo-containing stainless steels that are difficult to remove scale steel materials. . Moreover, not only a stainless steel material but utilization with respect to all the steel plates can be attained.

It is a figure which shows the relationship between the addition amount of mercaptoacetic acid in a sulfuric acid solution, and pickling loss. It is a figure which shows the relationship between the addition amount of nickel chloride in a sulfuric acid solution, and pickling loss.

Claims (2)

Stainless steel Upon pickling by pickling solution, the acid washings, the organic compound containing a mercapto group, Ri Do from the sulfuric acid solution was added nickel chloride, an organic compound containing the mercapto group, the sulfuric acid solution of the concentration added 0.001mol / l or more, the nickel chloride, the pickling method of the stainless steel which is characterized that you added 0.01~0.4mol / l and the concentration of the sulfuric acid solution. A method for producing a stainless steel material, wherein the hot-rolled plate or hot-rolled annealed plate made of ferritic stainless steel is pickled according to claim 1.

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