JPH0610172A - Treatment of hot finished austenitic stainless steel strip - Google Patents

Abstract

PURPOSE:To provide the method for treatment of a hot rolled austenic stainless steel strip which efficiently executes the removal of the surface scale, grain boundary oxide layers and the scale flaws of the steel strip by combining mechanical grinding and pickling and selecting the conditions thereof. CONSTITUTION:This method for treatment of the hot finished oustenitic stainless steel strip consists in subjecting the hot finished austenitic stainless steel strip to a grinding treatment of a 10 to 100mum surface range with a mechanical grinding means to remove the surface scale at least down to the grain boundary oxide layers, then subjecting the steel strip to a pickling treatment with a hydronitrofluoric acid pickling soln. which contains 30 to 210g hydrofloric acid per 1 liter hydronitrofluoric acid soln. mixture and 50 to 150g nitric acid and is kept at 50 to 80 deg.C until the amt. of scarfing attains 1 to 30mum. As a result, the grinding and pickling treatments are simplified and the efficiency thereof is enhanced. The product having excellent surface quality is obtd. and the improvement in productivity and the reduction of the production cost are resulted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a treatment method for effectively removing surface oxide scales and scale flaws in a hot-finished austenitic stainless steel strip.

[0002]

2. Description of the Related Art A surface oxide scale and an intergranular oxide layer between the surface oxide scale and the base iron are formed on a stainless steel strip after hot rolling. Due to such factors as scale adhesion, the scale may erode into the steel strip, causing scale defects that reach a considerable depth.

Conventionally, as a method for removing scale flaws of an austenitic stainless steel strip, first, a nitric hydrofluoric acid pickling treatment at a relatively low concentration is carried out, and then the steel strip is passed through a cold rolling mill to correct the shape of the steel strip surface. There is a method of belt grinding. That is, as shown in FIG. 4A, the surface scale 20 and the grain boundary oxide layer 21 are formed on the base metal on the lower surface of the steel strip surface. However, although the surface scale 20 is removed and a part of the grain boundary oxide layer 21 is removed, groove-like corrosion 22 due to acid occurs from the remaining grain boundary oxide layer (FIG. 7B). If this groove-like corrosion remains, it deteriorates the surface quality of the product, so in order to remove it, the grinding is carried out up to about 30 μm in the belt grinding. In this belt grinding, the steel strip is subjected to the shape-correcting treatment prior to this. It is necessary to flatten the surface to facilitate uniform grinding, and after the grinding, the grind marks 23 remain (FIG. C), which adversely affects the product surface gloss. As described above, in the conventional method, not only the pickling step but also the belt grinding step which is a separate step must be performed, and further, in order to improve the efficiency of belt grinding, a pretreatment step such as steel strip shape correction is performed. It is necessary and there is a problem that a grind is left after grinding.

On the other hand, there is also a proposal to remove the scale and grain boundary oxide layer on the surface of the produced steel strip by only nitric hydrofluoric acid pickling treatment. In this case, nitric acid and hydrofluoric acid are used although the process is simple. It is necessary to increase the concentration of slag and perform a long time of ablation process. However, since there is no scale flaw removal process, it is impossible to remove flaws from a material with many flaws.

Further, Japanese Patent Publication No. 3-36891 discloses a method of surface-grinding a hot rolled annealed steel sheet with a grinder and then pickling or electrolytically polishing. However, this method relates to ferritic stainless steel, and the pickling or electrolytic polishing is performed to remove the surface hardened layer formed by the grinder treatment. Therefore, it is not intended to remove scale defects of austenitic stainless steel and prevent the occurrence of groove-like corrosion due to the remaining grain boundary oxide layer. In other words, when applied to austenitic stainless steel, since grinder grinding conditions (grinding amount) are not taken into consideration, there arises a problem of occurrence of groove-like corrosion due to residual bald spots or residual grain boundary oxide layer. .

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above problems, and removes the surface scale, grain boundary oxide layer and scale flaws of a steel strip by mechanical grinding and pickling. It is an object of the present invention to provide a method for treating a hot-rolled austenitic stainless steel strip which is efficiently carried out by combining these conditions and optimizing these conditions.

[0007]

In order to achieve the above-mentioned object, the present invention provides a hot-finished austenitic stainless steel strip with a surface of 10 μm to 10 μm by mechanical grinding means.
After performing grinding treatment in the range of 0 μm to remove at least the grain boundary oxide layer, hydrofluoric acid per liter of the mixed solution of hydrofluoric acid:
An austenitic system containing 30 to 210 g and nitric acid: 50 to 160 g, and subjected to a pickling treatment with a nitrifying hydrofluoric acid pickling solution kept at 50 to 80 ° C. so that the amount of ablation is 1 to 30 μm. The gist is the method of processing stainless steel hot-finished steel strip. In the present invention, the mechanical grinding means may be any grinder grinding such as belt-shaped or roll-shaped, but an elastic grindstone roll is particularly preferable and it is recommended to use it. At the time of grinding, it is preferable to arrange a plurality of stages of stands, each pair of which is a pair of a pressing roll facing the elastic grindstone roll. As a result, the surface scale formed on the steel strip, the grain boundary oxide layer that causes groove-like corrosion during pickling, and, if scale flaws are formed, are removed by grinding according to their depth. Further, in the present invention, as pretreatment of the mechanical grinding means, trimming or grinding treatment of the edge of the strip-shaped metal body having a scale on the surface is performed, and then the surface scale is modified as necessary to cause cracks or peeling. For this purpose, heating, cooling, shape correction, shot blasting, etc. may be performed.

[0008]

The method of processing a steel strip according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic explanatory view showing an embodiment of a process line for carrying out the method of the present invention. In the figure, 1 is a pay-off reel for rewinding and supplying a hot-finished austenitic stainless steel strip (hereinafter simply referred to as steel strip), 2 is a hot-finished steel strip, and 3 is a dummy plate for a strip-shaped metal body ( Hereinafter, it is a welding machine for performing (1) welding and (2) welding between leaders, and for example, a submerged arc welding machine, a TIG welding machine, a plasma welding machine, a spot welding machine, etc. are used.
4 is a trimmer that cuts and removes edge flaws and hot cracks that occur in the steel strip, and 5 is an edge grinder that grinds and removes relatively minute of such flaws and cracks. Reference numeral 6 denotes a heating furnace installed as necessary for heating the steel strip, which is usually a heating furnace for burning heavy oil or gas, but an electric heating furnace such as induction heating or direct current heating may be used. . Reference numeral 7 is a cooling zone for cooling the steel strip after heating, such as gas cooling, spray cooling, water spray cooling and roll cooling. 8 is a leveler for bending or stretching a steel strip, 9 is a bridle roll for applying a tension necessary for grinding the steel strip, and 8 is a dry or wet shot blast for projecting a steel ball on the surface of a strip-shaped metal body. Is. Each of the above devices is a pretreatment unit in the present invention, and may be arranged as necessary.

After the above-mentioned pretreatment is appropriately performed, steel strip surface grinding and pickling treatment, which are the basics of the present invention, are performed. In the figure, 1
1 is an in-line grinding device for performing grinder grinding,
For example, the elastic grindstone roll 11a and the pressing roll 11b are arranged in a plurality of stands, each pair forming a pair, and both the front and back surfaces of the steel strip are ground. The elastic whetstone roll referred to here is a roll-shaped whetstone that has some elasticity in order to make it easier to fit into the shape of the plate, for example, a roll formed by laminating discs coated with abrasive grains. There are (laminate type), one in which flap wheels are laminated and formed into a roll shape (flap type), and one in which nylon resin with abrasive grains is integrally formed into a roll shape (integrated type), and any of these can be used. You can In an in-line grinding machine with such an elastic whetstone roll, the abrasive grain count of the final stand should be an elastic whetstone roll larger than the upstream, and at least the first stand should be arranged so that a laminated elastic whetstone roll is used. It is preferable to have a configuration in terms of grinding efficiency.

Reference numeral 12 denotes a degreasing / cleaning device installed after the grinding device, for example, a brush roll 12a and a press roll 1.
A plurality of stands each forming a pair with 2b are arranged, or brush rolls are provided so that both front and back surfaces of the steel strip face each other. This brush roll includes, for example, a roll made of a brush made of nylon fiber containing abrasive grains. Further, the hot water spray 12c is arranged after the degreasing device. Reference numeral 13 denotes a pickling device, which performs a pickling process for adjusting the amount of surface ablation after cleaning the heavy-ground steel strip. 14
Is a cleaning device, and, for example, a plurality of stands, each pair of which is composed of a brush roll 14a and a press roll 14b, are arranged, or brush rolls are provided so as to face both sides of the steel strip. Further, the hot water spray 14c is arranged after the brush cleaning device. Reference numeral 15 is a tension reel for winding the steel strip.

In the steel strip processing step having such a structure,
The strip-shaped metal body 2 is unwound from the pay-off reel 1, and first the welding machine 3 welds the leader, and then the leader of the preceding material. Next, after removing the flaws and cracks at the edge portion with the trimmer 4 or the edge grinder 5,
By heating in the heating furnace 6 as necessary, cavitation of the scale near the strip-shaped metal body progresses, and the cooling zone 7 continues.
In the rapid cooling performed in step 1, the strain generated during cooling may cause cracks or peeling in the scale, which may facilitate subsequent descaling.

A band-shaped metal body having a scale on its surface is passed through a tension leveler 8 to promote cracks or peeling on the scale of the surface, or to further promote it, and to correct the shape of a plate for facilitating uniform grinding and polishing. Bending and bending of the ears are corrected, and the impact force of the steel balls projected onto the surface in the subsequent dry or wet shot blasting 10 treatment further promotes cracking and peeling of the scale.

The steel strip in such a state is introduced into the in-line grinding apparatus 11, and the surface layer portion is ground by the elastic whetstone roll 11a to descale (remove the surface scale and the grain boundary oxide layer) and / or remove the scale flaw. At the same time. Generally, the cross-section of the surface layer of the hot-rolled austenitic stainless steel strip is shown in FIG. 2 (a) or FIG. 3 (a).
As schematically shown in FIG. 3, a surface scale 20 is formed at a maximum depth of about 5 μm, and a grain boundary oxide layer 21 is formed immediately below the surface scale 20.
If the nitric acid hydrofluoric acid pickling treatment is performed while the grain boundary oxide layer 21 remains, it causes groove corrosion. In addition, depending on the surface condition of the roll in the hot rolling process, there may be a scale flaw 24 in which the scale penetrates into the steel strip and reaches a considerable depth, and the depth reaches a maximum of approximately 200 μm. And if this remains, it will affect the product surface quality.

In the present invention, as shown in FIG. 2B, the surface scale 20 and the grain boundary oxide layer 21 are removed by the grinding device 11. On the other hand, when the scale flaw 24 is generated, as shown in FIG. 3A, grinding is performed to a portion where the scale flaw can be removed by the subsequent pickling treatment. That is, these grinding amounts are required to be at least 10 μm in order to remove at least the surface scale 20 and the grain boundary oxide layer 21 sufficiently, and depending on the depth of the scale flaw, to reduce the pickling load. In this case, grinding is performed up to 100 μm.

The steel strip subjected to the above grinding treatment is subjected to pickling treatment with a nitric hydrofluoric acid pickling solution. As described above, since at least the grain boundary oxide layer is removed by the grinder grinding treatment, the problem of groove-like corrosion is solved by the pickling treatment, so that the hydrofluoric acid solution can be used in a wide range from low concentration to high concentration. 1 to change
2 (c) and FIG.
As shown in (c), it is possible to remove the remaining scale flaws, deburring the grinding, and smoothing the grinding. In order to play such a role, hydrofluoric acid: 30 to 210 g and nitric acid:
50 to 160 g, and these mixed solutions are 50 to 8
Must be kept at 0 ° C. Hydrofluoric acid 30g or more, nitric acid 50
It is the minimum condition that is required to efficiently remove scale flaws, remove grinding burrs and smooth the grinding surface, and keep the mixed solution at 50 ° C. or higher.
More than 10g, nitric acid more than 160g, and mixture temperature 80 ℃
This is because if it exceeds the above level, the equipment cost and the solution cost increase, which is disadvantageous for industrial operation. The amount of fusing is 30 μm
The reason for the following is that if it exceeds this, the surface irregularities in the form of etch pits will become severe and the surface quality will deteriorate. As described above, in the present invention, by setting appropriate grinding conditions and pickling conditions, by adjusting the grinding amount in the grinding process and the fusing amount in the pickling process, a product with excellent surface gloss can be obtained. It can be obtained with high productivity. After pickling, wash the pickling solution and wind it on a tension reel.

[0016]

EXAMPLES Examples of the present invention will be described below. According to the continuous process shown in Fig. 1, various austenitic stainless steel strips were ground and pickled under the conditions shown in Table 1 to investigate and evaluate the surface quality after blast cutting and the quality of cold rolled annealed products. The results are also shown in Table 1. The conditions and methods for heat treatment and pretreatment before in-line grinding are also described. In this table, the amount of grinding and the amount of fusing were measured before and after the treatment, and the removed thickness was calculated from the specific gravity. The evaluation of descaling and flaw removal was as follows. ○: No scale remains and no scale flaws. Δ: No scale residue is observed, but scale defects remain. X: Scale and scale flaw remaining. The surface quality of cold rolled and annealed products depends on the degree of gloss,
Evaluation was made in 5 ranks of D, and B ranks or higher were regarded as passing.
The presence or absence of groove corrosion and etch pits after grinding and fusing was observed and evaluated by a scanning electron microscope.

The cold rolling annealing conditions were normal conditions. As is clear from this table, the evaluation results of the strip-shaped metal bodies according to the method of the present invention are all good, no scale residue or scale flaws are observed, and the product after cold rolling annealing also has good surface properties. .

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

As is apparent from the above, according to the present invention, when removing the surface scale and scale flaws of the austenitic stainless hot-finished steel strip, the grinding and the nitric hydrofluoric acid pickling treatment are continuously performed to ensure proper operation. By treating the steel strip under the conditions, it is possible to simplify the grinding and pickling treatment and increase the efficiency, which makes it possible to obtain products with excellent surface quality, improve productivity and reduce manufacturing costs. Become.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment for carrying out the present invention.

2 (a), (b) and (c) are explanatory views schematically showing a process example of the present invention.

3 (a), (b), and (c) are explanatory views schematically showing another example of the process of the present invention.

4 (a), (b) and (c) are explanatory views schematically showing a conventional process example.

[Explanation of symbols]

 1 Payoff reel 2 Band-shaped metal body 3 Welding machine 4 Trimmer 5 Edge grinder 6 Heating furnace 7 Cooling zone 8 Leveler 9 Bridle roll 10 Dry or wet shot blasting 11 In-line heavy grinding device 11a Elastic grindstone roll 11b Pressing roll 12 Degreasing cleaning device 12a Brush Roll 12b Presser roll 12c Spray 13 Light pickling device 14 Cleaning device 14a Brush roll 14b Presser roll 14c Spray 15 Tension reel 20 Surface scale layer 21 Grain boundary oxide layer 22 Groove corrosion 23 Grinding marks 24 Scale flaw

Front page continuation (72) Inventor Yoshio Uzuki 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside the Advanced Technology Research Laboratories, Nippon Steel Corporation (72) Yoshifumi Takai, 3434 Shimada, Hikari City, Yamaguchi Prefecture Made in Japan Inside the Hikari Steel Works (72) Inventor Takahiro Fujiwara 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Works Inside the Hikari Works (72) Inventor Kazuyuki Takagi 3434 Shimada, Hikari City, Yamaguchi Prefecture Made in Japan Inside the Hikari Steel Co., Ltd. (72) Inventor Takeshi Tanaga 3434 Shimada, Hikari City, Yamaguchi Prefecture Inside the Hikari Works, Nippon Steel Co., Ltd. (72) Haruo Oguro 3434 Shimada, Hikari City, Yamaguchi Prefecture New Nippon Steel Corporation Hikari Steel Works

Claims (1)

[Claims] 1. A hot-finished austenitic stainless steel strip having a surface of 10 μm to 1 by mechanical grinding means.
After removing at least the grain boundary oxide layer by performing a grinding treatment in the range of 00 μm, it contains hydrofluoric acid: 30 to 210 g and nitric acid: 50 to 160 g per liter of a mixed solution of hydrofluoric acid, and the temperature is adjusted to 50 to 80 ° C. A method for treating an austenitic stainless hot-finished steel strip, characterized in that the retained nitric hydrofluoric acid pickling solution is subjected to a pickling treatment such that the amount of scraping is 1 to 30 µm.