JP2008266697A - Pickling method and manufacturing method for stainless steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pickling method for a stainless steel material, which needs neither of annealing treatment for a hot-rolled plate and pre-treatment for pickling, and to provide a manufacturing method therewith. <P>SOLUTION: A pickling liquid to be used when pickling the stainless steel material is a mixture solution comprising a hydrochloric acid solution of 70 to 200 g/L by concentration and a cupric chloride solution of 40 to 150 g/L by concentration. The pickling treatment in such a mixture solution inhibits intergranular erosion due to sensitization in the vicinity of a grain boundary caused by the precipitation of chromium carbonitrides occurring in a hot rolling step, and can completely remove a black skin scale. As a result, it becomes possible to directly pickle the hot-rolled stainless steel plate after having been hot-rolled without subjecting it to the annealing treatment for the hot-rolled plate and the pre-treatment for pickling. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pickling method and a manufacturing method for a stainless steel material, and more particularly, to a pickling method and a manufacturing method for a stainless steel material in which a stainless steel hot-rolled sheet is pickled without subjecting the hot-rolled sheet to annealing and pickling pretreatment. Is.

Stainless steel contains Cr and has excellent corrosion resistance, so its use tends to expand more and more. However, since it contains a large amount of expensive elements such as Cr, the cost of raw materials is increased, and the manufacturing process includes slab → hot rolling → hot-rolled sheet annealing → pre- pickling treatment such as shot blasting → pickling Since it is manufactured through a complicated process such as cold rolling, cold-rolled sheet annealing, and cold-rolled sheet pickling, it has a problem of high manufacturing cost. Therefore, a manufacturing method in which some of these manufacturing steps are omitted has attracted attention from the viewpoint of reducing the manufacturing cost and the manufacturing period.
Conventionally, stainless steel has been manufactured by performing hot-rolled sheet annealing after hot rolling.
However, in recent years, in order to improve the material properties such as r value in order to obtain high workability, the study on the omission of hot-rolled sheet annealing has been made, and the technical production of stainless steel that omits hot-rolled sheet annealing is also made. Is becoming possible.
For example, in Patent Document 1, when hot rolling a stainless steel slab in order to improve the formability of fuel tanks and pipes for automobiles and motorcycles, the slab heating temperature is set to 1100 to 1200 ° C, and the total rolling reduction ratio of rough rolling Continuous rolling with a final rolling reduction ratio of 0.8 to 1.0 is performed at a finish rolling finishing temperature of 700 to 900 ° C., wound at 650 to 850 ° C., and then hot-rolled sheet annealing is omitted. A method for producing a ferritic stainless steel sheet that is cold-rolled and annealed and has excellent workability is disclosed.
However, since the method described in Patent Document 1 is a manufacturing process in which hot-rolled sheet annealing is not performed, the Cr concentration in the vicinity of the grain boundary is reduced (sensitized) due to precipitation of Cr carbonitride during hot rolling. As a pickling solution for stainless hot-rolled steel sheets, intergranular erosion is inevitable with a mixed acid solution using a combination of nitric acid and hydrofluoric acid, which is generally used because of its high processing capability. Further, even when hydrochloric acid or sulfuric acid is used as the other pickling liquid, pickling pretreatment such as shot blasting is required.

  Moreover, as a method of avoiding grain boundary erosion during pickling due to sensitization when hot-rolled sheet annealing is not performed, in Patent Document 2, mechanical descaling is performed, and then the surface of the hot-rolled sheet is preheated and nitric acid and A method of pickling with a mixed solution of hydrofluoric acid or a mixed solution of nitric acid and hydrochloric acid is disclosed.

By the way, unlike ordinary steel, Cr-containing stainless steel forms a black skin scale containing Cr ₂ O ₃ which is difficult to scale when hot rolled or annealed. For this reason, since pickling using only acid dipping requires a long time for descaling, mechanical scale destruction such as shot blasting or strain imparted by a mechanical scale breaker (MSB) is indispensable as a pretreatment for pickling. . As this pickling pretreatment method, for example, in Patent Document 3, when the steel shot is struck against the surface of a running steel material by a projection means that rotates at high speed, and the adhesion scale on the surface is removed, the rotation speed of the projection means is set as follows. A method for descaling a steel material by shot blasting, characterized by adjusting the traveling speed of the steel material, is disclosed. Moreover, in patent document 4, in the stainless steel descaling method which gives distortion to the stainless steel which has a scale in a surface layer, and removes a scale by acid pickling after that, in the chemical component of stainless steel, it is in content of Mo and Ti. Accordingly, a method for descaling stainless steel is disclosed in which the manner of imparting the strain is changed.
However, a manufacturing process that can eliminate both hot-rolled sheet annealing and pickling pre-treatment while preventing the occurrence of surface defects in cold-rolled sheets due to grain boundary erosion and scale residue has been realized so far. Not.
JP 2006-89814 A Japanese Patent Publication No.2-50810 JP-A-9155535 JP 2006-95587 A

As described above, when omitting hot-rolled sheet annealing, sensitization in the vicinity of grain boundaries due to precipitation of Cr carbonitride during hot rolling becomes a problem, and descaling treatment to suppress grain boundary erosion is performed. Had to be done.
On the other hand, the black scale of stainless steel formed during hot rolling contains Cr ₂ O ₃ which is difficult to scale, so if the scale is not mechanically cracked, acid penetration will be insufficient and perfect descaling will not be possible. It does n’t come. Therefore, pickling pretreatment is essential.
In view of the circumstances as described above, the present inventors have paid attention to the possibility of omitting the pickling pretreatment by shot blasting, MSB or the like as a further process omission in addition to omission of hot-rolled sheet annealing of stainless steel.
And this invention provides the pickling method and manufacturing method of a stainless steel material which do not need both hot-rolled sheet annealing and pickling pretreatment which were not able to be achieved in the manufacture of stainless steel materials. Objective.

  In order to solve the above-mentioned problems, the inventors of the present invention do not perform a hot-rolled sheet annealing after hot rolling, and further, only a pickling process without performing a scale break on the black skin scale by a pre-pickling treatment. In order to scale, attention was paid to the pickling solution during pickling. And it turned out that it is effective with respect to the said subject to select a hydrochloric acid solution as a pickling solution, and to add an oxidizing agent to the hydrochloric acid solution. Furthermore, as a result of detailed investigations, the inventors have obtained knowledge that the intended purpose can be achieved by adding an appropriate amount of cupric chloride having a function as an oxidizing agent to the hydrochloric acid solution, thereby completing the present invention. It came to.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] In the pickling treatment of stainless steel material, the hot-rolled stainless steel sheet after hot rolling is treated with a hydrochloric acid solution having a concentration of 70 to 200 g / L and a concentration without subjecting the hot-rolled sheet to annealing and pickling. A pickling method for a stainless steel material, characterized in that pickling treatment is performed with a mixed solution comprising a cupric chloride solution of 40 to 150 g / L.
[2] When pickling a stainless steel material, the stainless steel hot-rolled sheet after the winding process at a temperature of 700 ° C. or lower is subjected to a hot-rolled sheet annealing and a pre-pickling treatment at a concentration of 70 to 200 g / A pickling method for a stainless steel material, characterized by subjecting pickling to a mixed solution comprising a hydrochloric acid solution of L and a cupric chloride solution having a concentration of 40 to 150 g / L.
[3] Manufacture of a stainless steel material characterized by subjecting a ferritic stainless steel hot-rolled sheet containing 10.0 to 20.0 mass% of Cr to a pickling treatment by the pickling method described in [1] or [2]. Method.

  By using the pickling method of the present invention, a stainless steel material having excellent surface properties free from scale residue and grain boundary erosion can be produced without performing hot-rolled sheet annealing and pickling pretreatment.

  Further, by omitting the steps of hot-rolled sheet annealing and pickling pretreatment, it is possible to reduce the manufacturing cost and the manufacturing period, and to obtain a highly productive stainless steel material.

Hereinafter, the present invention will be specifically described.
The present invention is a stainless steel material excellent in surface properties that is subjected to pickling treatment without hot-rolled sheet annealing and pickling pretreatment after hot rolling, and without scale residue and grain boundary erosion. It is the first feature to obtain. And as a processing solution at the time of pickling treatment, by using a mixed solution consisting of a hydrochloric acid solution having a concentration of 70 to 200 g / L and a cupric chloride solution having a concentration of 40 to 150 g / L, Cr at the time of hot rolling is used. The second feature is that the grain boundary erosion caused by sensitization in the vicinity of the grain boundary due to precipitation of carbonitride is suppressed, and the black skin scale is completely removed.

First, the pickling solution which is the main requirement of the present invention will be described.
The present inventors paid attention to a hydrochloric acid solution as a pickling solution in order to descal a black-rolled hot-rolled plate that has not been subjected to hot-rolled sheet annealing without performing a pickling pretreatment such as shot blasting. Generally, nitric hydrofluoric acid solution is used for pickling stainless steel hot-rolled sheets. However, when hot-rolled sheet annealing is not performed, Cr carbonitride precipitates at the grain boundaries during hot rolling, and the vicinity of the grain boundaries. So-called sensitization occurs in which the Cr concentration of the steel decreases. And, as the nitric hydrofluoric acid solution has a higher Cr content in the base material, the dissolving power sharply decreases. Therefore, when a sensitized hot-rolled sheet is pickled with a nitric hydrofluoric acid solution, grain boundary erosion occurs, Causes surface defects after rolling. Therefore, a hydrochloric acid solution having little dependency on the amount of Cr in the dissolution of ground iron was first selected as the pickling solution. Furthermore, when the concentration of the hydrochloric acid solution is less than 70 g / L, the dissolving power is insufficient. On the other hand, when the concentration of the hydrochloric acid solution exceeds 200 g / L, rough skin due to peracid washing occurs. Therefore, the concentration of hydrochloric acid was set to 70 g / L or more and 200 g / L or less.

Next, the addition of an oxidant into the hydrochloric acid solution was examined in order to promote the peeling of the black skin scale, which hinders the acid penetration into the base iron during pickling.
First, cupric chloride having a redox potential on the + side was selected as an additive having a function as an oxidizing agent. Next, in order to investigate the most effective concentration in using cupric chloride as an oxidizing agent, the following experiment was conducted.
After hot rolling, the winding process was performed at 700 ° C. to obtain a hot-rolled sheet of 11% Cr steel as it was. Next, using the test piece collected from the obtained hot-rolled black sheet, pickling treatment was performed under conditions of a liquid temperature of 80 ° C. for 60 seconds without performing pickling pretreatment such as shot blasting. . The test piece was prepared by cutting out a hot-rolled sheet of 11% Cr steel as a black skin into a size of 30 mm × 40 mm. In addition, as a pickling solution, a commercially available hydrochloric acid reagent is used, and a mixed solution is prepared by adding cupric chloride as an oxidizing agent to 0 to 200 g / L to a hydrochloric acid solution having a concentration of 100 g / L. Used.
After the pickling treatment, the descaling was determined. For determination of descaling, the surface of the test piece after pickling was analyzed by X-ray diffraction to confirm the presence or absence of scale residue. Moreover, the weight change before and after pickling was measured, and the pickling loss per unit area was calculated. The obtained results are shown in Table 1 and FIG.

It can be seen from Table 1 and FIG. 1 that the pickling loss increases when cupric chloride is added as an oxidizing agent to the hydrochloric acid solution. As for descaling property, the addition of cupric chloride at a concentration of 40 g / L or more completely removes the black skin scale, and a good surface with no residual black skin scale is obtained.
From the above results, it is effective for removal of black skin scale and the like to add cupric chloride having a concentration of 40 g / L or more as an oxidizing agent to a hydrochloric acid solution having a concentration of 70 to 200 g / L. I understand that.
Here, addition of cupric chloride at a concentration exceeding 150 g / L is effective for removal of the black skin scale, but is excessively added, resulting in an increase in manufacturing cost.
Therefore, in the present invention, a cupric chloride solution having a concentration of 40 to 150 g / L is added as an oxidizing agent to a hydrochloric acid solution having a concentration of 70 to 200 g / L. By using such a mixed solution of hydrochloric acid and cupric chloride, it is possible to descal the black skin scale without performing pickling pretreatment such as shot blasting.

As pickling conditions other than the pickling treatment liquid, the liquid temperature is preferably 65 to 90 ° C. Below 65 ° C, the dissolving power is insufficient. On the other hand, when the temperature exceeds 90 ° C., the concentration of hydrochloric acid fluctuates and uniform pickling becomes difficult.
The treatment time is preferably 30 to 180 seconds. If it is less than 30 seconds, the dissolution amount is insufficient. On the other hand, if it exceeds 180 seconds, the pickling time becomes longer and the productivity is lowered.

Next, the component composition of the stainless steel material of the present invention will be described.
The component composition of the stainless steel material of the present invention is not particularly limited. However, the component composition shown below is preferable for the following reasons and is preferably used.
Cr content: 10.0-20.0 mass% or less
Cr is an indispensable element for imparting corrosion resistance, and is contained according to the intended corrosion resistance level. If the Cr content is less than 10.0 mass%, the corrosion resistance improvement due to Cr is not significant, so the lower limit of the content is 10.0 mass%. On the other hand, if the Cr content exceeds 20.0 mass%, even if pickling is performed using the pickling method of the present invention, scale may remain after pickling, so the upper limit is set to 20.0 mass%.
Furthermore, the present invention is suitably used for ferritic stainless steels that are difficult to scale and have a low Ni content.

Next, the manufacturing method of the stainless steel material of this invention is demonstrated.
The stainless steel material of the present invention is manufactured by a commonly used manufacturing method. However, in the present invention, as described above, the pickling pretreatment such as hot-rolled sheet annealing and shot blasting is omitted, and after hot rolling, pickling is performed, and then cold rolling, cold-rolled sheet annealing, It is possible to obtain a stainless steel material by pickling the steel sheet.
Among these, it is preferable to perform a winding process at a winding temperature of 700 ° C. or less after hot rolling. By setting the coiling temperature to 700 ° C. or lower, it is possible to suppress the reduction of Fe oxide generated during the slow cooling of the coil and the generation of Cr-based scale due to the oxidation of Cr accompanying therewith. If the coiling temperature exceeds 700 ° C., the formation of a scale layer with a high Cr concentration in the scale inner layer is promoted during coil cooling, so the pickling property may be reduced. Therefore, the coiling temperature after hot rolling is preferably 700 ° C. or lower.
In order to obtain better surface properties after pickling, it is preferable to brush the steel plate surface for the purpose of removing smut.
Further, as the next step of the pickling of the present invention, finishing pickling with nitric acid or the like may be performed in order to obtain good surface properties.

Hereinafter, the present invention will be described based on examples.
Manufactured by a normal method, slabs containing 11 mass%, 16 mass%, and 25 mass% of Cr were hot-rolled and wound under the conditions shown in Table 2 to obtain hot-rolled sheets. Next, the obtained hot-rolled sheet was not subjected to pickling pretreatments such as hot-rolled sheet annealing and shot blasting, as shown in Table 2, with acidic treatment liquids having different hydrochloric acid concentrations and cupric chloride concentrations. The pickling treatment was performed under the conditions of a liquid temperature of 80 ° C. and a treatment time of 60 seconds. In performing the pickling treatment, a test piece cut out from a hot-rolled sheet to a size of 30 mm × 40 mm was used. The pickling solution was prepared using a commercially available hydrochloric acid reagent and cupric chloride reagent.

After the pickling treatment, the descaling was determined. For determination of descaling, the surface of the test piece after pickling was analyzed by X-ray diffraction to confirm the presence or absence of scale residue. Moreover, the pickling loss per unit area was calculated by measuring the weight change before and after pickling.
The obtained results are shown in Table 2 together with the conditions.

As shown in Table 2, the examples of the present invention had a large weight loss due to pickling, and the black skin scale was completely removed. As a result, a stainless steel material having no surface residue and good surface properties was obtained after pickling.
On the other hand, the comparative example in which the hydrochloric acid concentration or the cupric chloride concentration was outside the scope of the present invention had less pickling loss than the present invention example, and the black skin scale remained on a part of or the entire surface.

  By using the pickling method of the present invention, it becomes possible to eliminate both hot-rolled sheet annealing and pre-pickling treatment that could not be achieved by the prior art. As a result, we will provide a highly productive method for producing stainless steel, focusing on high Cr steels such as SUS430 that require a large amount of dissolution, Ni-containing austenitic stainless steels and Mo-containing stainless steels that are difficult to remove scale steel materials. It is suitably used for the stainless steel material. 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 cupric chloride addition amount, pickling loss, and descaling property.

Claims (3)

  In the pickling treatment of stainless steel material, the hot rolled stainless steel sheet after hot rolling is treated with a hydrochloric acid solution having a concentration of 70 to 200 g / L and a concentration of 40 to 40 without subjecting the hot rolled plate to annealing and pickling. A pickling method for a stainless steel material, characterized in that pickling treatment is performed with a mixed solution of 150 g / L cupric chloride solution.   When pickling stainless steel, hydrochloric acid with a concentration of 70 to 200 g / L without hot-rolling annealing and pickling pre-treatment of stainless steel hot-rolled sheet after coiling at a temperature of 700 ° C or less A pickling method for a stainless steel material, characterized by subjecting the pickling treatment to a mixed solution comprising a solution and a cupric chloride solution having a concentration of 40 to 150 g / L.   A method for producing a stainless steel material, comprising subjecting a ferritic stainless steel hot-rolled sheet containing 10.0 to 20.0 mass% of Cr to a pickling treatment by the pickling method according to claim 1 or 2.

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