JP3484892B2 - Method for descaling hot rolled steel strip of Fe-Ni alloy - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a descaling method for hot-rolled Fe—Ni alloy steel strips, more specifically, it is difficult to rust after descaling and is suitable for use after cold rolling or etching. The present invention relates to a descaling method that can obtain surface quality, can be shared at low cost with a stainless steel strip pickling line.

[0002]

2. Description of the Related Art Fe-Ni alloys are used for applications such as LNG containers, lead frames, shadow masks and permalloys after hot rolling or cold rolling. Further, Fe-Ni alloys need to have a good surface appearance after cold rolling, and since some of them are subjected to etching processing in the above-mentioned applications, etching defects may not occur during etching processing. is necessary.

In cold rolling, it is necessary to completely descale the hot-rolled Fe-Ni alloy steel strip. But,
In Fe-Ni alloys, an internal oxide layer with good adhesion to the base material is formed when the slab is heated, and it is difficult to remove even by descaling during hot rolling. Therefore, in the Fe-Ni alloy hot-rolled steel strip, an internal oxide layer with a depth of several tens of μm remains under the uniform oxide layer on the surface (hereinafter, secondary scale), so descaling is not easy. .

Therefore, the descaling of the Fe-Ni alloy hot rolled steel strip is described in "R & D Kobe Steel Engineering Reports, vol.32, No.3,"
p.38 "(hereinafter, Prior Art A), often by mechanical grinding. However, since the grinding amount is as large as several tens of μm, the load on the grinding machine is heavy, high-speed grinding is difficult, and the abrasive material is expensive and has a short life, resulting in low productivity and high descaling cost. There's a problem.

Descaling by mechanical grinding has also been carried out on stainless steel strips, but it does not pose a problem for hard stainless steels, but since Fe-Ni alloys are soft, they are contained in abrasives. Grains are embedded in the hot-rolled steel strip of the Fe-Ni alloy, which causes problems such as surface defects during cold rolling in the next step and etching failure when processed into a shadow mask.

Furthermore, in order to increase the grinding amount in one pass in mechanical grinding and increase the grinding speed, it is necessary to use coarse-grained abrasive grains of around # 100, and the surface after descaling is rough. Therefore, there is also a problem that the surface quality after cold rolling deteriorates.

Therefore, a descaling method that does not rely on mechanical grinding alone has been proposed. For example, Japanese Patent Laid-Open No. 1-273607
No. 4 (hereinafter, Prior Art B), a mechanical treatment causes cracks and peeling of the scale, and then the abrasive grain count is # 4.
The first grinding roll in the range of 6 to 100 grinds to the metal base immediately below the scale of the hot-rolled alloy steel strip, and then the abrasive grain count is in the range of # 80 to 400 and the abrasive grain count of the first grinding roll After smoothing the ground surface using the second grinding roll with a fine or equal abrasive grain count, the acid solution treatment is continuously performed to cause cracks and peeling in the scale, which results in grinding. The descaling property of the steel is improved, and most of the scale is removed by grinding to reduce the load of pickling and prolong the life of the pickling solution, and also optimize the abrasive grain count of the abrasive and pickling A method for descaling hot-rolled alloy steel strips is described, which obtains good surface quality by reducing the thickness and smoothing the surface.

Further, in Japanese Patent Laid-Open No. 62-139888 (hereinafter, Prior Art C), nitric hydrofluoric acid pickling at a temperature of 40 to 70 ° C. containing 5 to 11 wt% of nitric acid and 6 to 11 wt% of hydrofluoric acid was performed. A method for descaling a hot-rolled Fe—Ni alloy alloy strip that improves descaling properties and suppresses surface roughness after pickling and has excellent surface properties is described.

Further, in Japanese Patent Laid-Open No. 2-70100 (hereinafter, referred to as Prior Art D), an alloy steel strip containing at least Ni and / or Cr contains 50 to 200 g / l of NaCl as a main component, 0.4 mol of HNO ₃ or FeCl ₃ per 1 mol / l of NaCl
~ 1.0 mol / l solution, after anodic electrolytic pickling under conditions of liquid temperature 20 ~ 80 ℃ and current density 5 ~ 30 A / dm ² , either sulfur hydrofluoric acid or nitric hydrofluoric acid or Performs descaling by both pickling treatments, while improving the descaling property of the alloy steel strip, removes most of the scale by electrolytic pickling, thus reducing the load of descaling during the next pickling, It is described that the accumulation of scale in the pickling solution is reduced and the deterioration of the pickling solution can be suppressed.

[0010]

However, the method described in the prior art B is a combination of mechanical grinding and descaling by pickling, resulting in high equipment maintenance costs and running costs. Further, since almost all scales are removed by mechanical grinding, the problems described in the above-mentioned prior art A are not essentially improved, and after cold rolling or etching processing due to embedding of abrasive grains. There are problems such as defects.

The method described in the prior art C has a problem that the surface of the steel sheet after descaling tends to be brown in color. Since this rust tends to become severe over time, once rusting is done, pickling and polishing must be performed again to remove the rust. Further, there are problems that the surface quality is deteriorated after cold rolling and etching failure occurs when etching is performed.

Furthermore, iron fluoride precipitates easily and complex ions are easily generated (“Takao Takahari et al .: Iron and Steel, vol.70, No.11, p.16.
05 ”), which causes an increase in the consumption of hydrofluoric acid and a blockage of the pipe, resulting in a decrease in productivity and an increase in cost.

In the method described in the prior art C, since descaling is performed only with nitric hydrofluoric acid, the amount of expensive hydrofluoric acid used is larger than that of nitric acid, and the scale gradually dissolves in the aqueous nitric hydrofluoric acid solution. Therefore, the nitric hydrofluoric acid is wasted due to the dissolution of the scale once removed and accumulated in the pickling tank. For this reason,
There is a problem that the amount of nitric acid or expensive hydrofluoric acid used increases.

The method described in the prior art D has not been studied in consideration of the surface quality after cold rolling, and there is a problem in the surface quality after cold rolling.

The Fe-Ni alloy hot-rolled steel strip may be descaled by the same equipment as the stainless steel strip which is difficult to descale. Therefore, it is advantageous that the stainless steel strip can also be descaled by the equipment and the treatment liquid used for descaling the Fe-Ni alloy hot-rolled steel strip. However, since the method described in Related Art D contains chlorion in the anodically electrolyzed solution, when descaling the stainless steel strip, pitting corrosion due to the chlorine ions remaining on the surface of the stainless steel strip after descaling is performed. The descaling process cannot be used in common with stainless steel strips due to the problem of easy formation of rust and rust.

The present invention has been made in consideration of the above circumstances, and has a high descaling processing speed and at the same time,
Not only can thinning proceed uniformly and excellent yield, the cost of chemicals is low, chemicals can be deteriorated, descaling can be done with less consumption of chemicals, and surface defects such as scales and barbs that consist of secondary scale and internal oxide layer. Can be completely removed, it is difficult to rust after descaling, the surface after descaling is smooth, good surface quality is obtained after cold rolling and etching, and it can be shared with stainless steel pickling treatment. Fe
-Providing a descaling method for Ni-based alloy hot rolled steel strip.

[0017]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to solve the above problems. As a result, the weight
%, Ni: 25% or more and 85% or less, Fe: 15% or more and 75% or less containing Fe-Ni system alloy hot-rolled steel strip descaled, the following was found.

The brown rusting on the surface of the steel strip after pickling is related to the concentration of hydrofluoric acid, and if high concentration of hydrofluoric acid is not used, brown rusting can be prevented, and after cold rolling, Poor surface quality is caused by pickling steel strip surface roughness
It is not due to the state of fine unevenness having a wavelength of about 1 mm or less measured by Ra, but due to the larger unevenness of the steel strip surface after pickling, that is, the unevenness of the smoothness of the steel strip surface after pickling. In addition, this non-uniformity occurs due to non-uniformity of thickness reduction during pickling.Excessive pickling should be performed if pickling is performed with an aqueous nitric-hydrofluoric acid solution while limiting the concentration balance of nitric acid and hydrofluoric acid and the temperature. Descaling is the fastest and most efficient, and there is no rust after descaling, and the surface smoothness after descaling is controlled to obtain excellent surface quality after cold rolling. Furthermore, by performing mechanical descaling treatment and nitric acid pickling before nitric hydrofluoric acid pickling, as described below,
More effective descaling is possible.Before descaling by pickling, mechanical descaling treatment is performed to make a crack in the secondary scale.
Secondary scale can be easily peeled off, and the uniformity and speed of corrosion can be increased. After mechanical descaling, most of the secondary scale can be removed by pickling with nitric acid aqueous solution with limited concentration and temperature. Therefore, the amount of scale brought into the nitric acid hydrofluoric acid pickling tank can be reduced, and deterioration of nitric hydrofluoric acid can be suppressed.Mechanical descaling treatment includes shot blasting, scale breaker, and rolling at a low rolling rate. Or selected from among the processes by brush grinding with abrasive grains
It is desirable to perform a treatment in which one kind or two or more kinds are combined, and to improve the descaling property of the secondary scale by applying an electric current during the nitric acid immersion, and the present invention was made based on such findings. The summary is as follows.

(1) At the time of descaling the Fe-Ni alloy hot-rolled steel strip, the Fe-Ni alloy hot-rolled steel strip was subjected to mechanical descaling treatment and then nitric acid concentration of 10 wt% or more and 20 wt% or less. After immersion in a nitric acid aqueous solution at a temperature of 45 ° C or higher and 80 ° C or lower, hydrofluoric acid 2.0 wt% or more and 5.9 wt% or less, nitric acid 7.0 wt% or more, the relationship between the concentration of hydrofluoric acid and nitric acid satisfies the following formula (3), and A descaling method for hot-rolled Fe-Ni alloy strips that is pickled by dipping it in an aqueous solution of hydrofluoric acid at a temperature of 40 ° C or higher and 65 ° C or lower for 65 seconds or longer.

Y ≦ 1/2 × (x−1.8) ² +12 (3) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%)

(2) When the Fe-Ni alloy hot-rolled steel strip is descaled, the Fe-Ni alloy hot-rolled steel strip is subjected to mechanical descaling treatment and then nitric acid concentration of 10 wt% or more and 20 wt% or less. Current density in nitric acid solution with temperature of 45 ℃ to 80 ℃
After repeated electrolysis by anodic electrolysis and cathode electrolysis at 0.06 A / cm ² or more 0.18 / cm ² or less, hydrofluoric acid 2.0 wt% or more 5.9 wt% or less, with nitric acid 7.0 wt% or more, the concentration of hydrofluoric acid and nitric acid A method for descaling Fe-Ni alloy hot-rolled steel strip which satisfies the following formula (4) and is pickled by immersion in an aqueous solution of nitric hydrofluoric acid at a liquid temperature of 40 ° C to 65 ° C for 65 seconds or more.

Y ≦ 1/2 (x−1.8) ² +12 (4) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%)

(3) In the above (1) or (2), the mechanical descaling treatment is selected from among shot blasting, scale breaker, rolling at a low rolling rate, and brush grinding with abrasive grains. Descaling method for Fe-Ni alloy hot-rolled steel strips, which is a combination of two or more treatments.

(4) A method for descaling a hot-rolled Fe-Ni alloy strip according to the above (1) or (2), wherein the mechanical descaling is shot blasting with a projection density of 30 kgf / m ² or more.

<Reaction / Reason for Limitation> [Alloy composition] The Fe-Ni alloy hot-rolled steel strip targeted by the present invention has, as a basic component, by weight%, Ni: 25% or more and 85% or less, Fe: Fe-Ni alloy containing 15% or more and 75% or less.

If Ni or Fe is out of the above range, the Fe-Ni alloy hot rolled steel strip cannot satisfy the required physical, magnetic and mechanical properties as a material for electronic and electromagnetic purposes. So limited.

The Fe-Ni alloy hot-rolled steel strip of the present invention includes Invar alloy (36 wt% Ni) and Super Invar alloy (32 wt%) used for electronic and electromagnetic materials and LNG container applications.
Ni-5wt% Co), 42wt% Ni alloy, Kovar (30wt% Ni-17wt% C
o), PB grade permalloy (45wt% Ni), PC grade permalloy (78wt)
% Ni-4wt% Mo-2wt% Cu) and the like.

These Fe-Ni alloy hot-rolled steel strips include
If necessary, the addition of elements such as Si, Mn, Cr, Cu, Co, Mo and Al does not impair the effects of the present invention, and C
, Inevitable impurities such as P, S, N, and O may be mixed.

[Mechanical Descaling Treatment] Oxides were not dissolved in nitric acid pickling of Fe-Ni alloy hot-rolled steel strip,
Descaling proceeds due to dissolution of the substrate. At this time, if the secondary scale has cracks, nitric acid reaches the substrate through the cracks in the secondary scale, and the secondary scale is peeled off by melting the substrate directly under the secondary scale.

However, since the secondary scale of the Fe-Ni alloy hot-rolled steel strip is dense and has few cracks, the descaling progresses only nonuniformly when hot-rolled and subjected to nitric acid pickling. By performing mechanical treatment before pickling, cracks are formed in the secondary scale, and the secondary scale is easily peeled off during the next pickling.

As the mechanical descaling treatment, one treatment or a combination of two or more treatments selected from treatments such as shot blasting, scale breaker, rolling or brush grinding with abrasive grains is applied to remove nitric acid. The exfoliation of the scale can be promoted more efficiently before. Shot blast is almost unaffected by the thickness and composition of the secondary scale and has a projection density of 30 kgf / m ²
Above is a sufficient descaling effect.

[Nitric Acid Pickling Condition] The rate of peeling of the secondary scale with nitric acid increases as the nitric acid concentration and temperature increase. The nitric acid concentration must be 10 wt% or more in order to obtain the minimum secondary scale peeling rate required industrially. However, when the nitric acid concentration exceeds 20 wt%, the effect is saturated, so nitric acid must be below 20 wt%. Further, in order to obtain the minimum industrially required peeling rate of the secondary scale, the liquid temperature must be 45 ° C. or higher. However, if the liquid temperature exceeds 80 ° C, water will evaporate violently and the concentration control will become complicated, so it is necessary to keep it below 80 ° C.

When descaling is performed by electrolytic pickling in the above-mentioned aqueous nitric acid solution, the peeling rate of the secondary scale can be further improved for the following reasons.

When an electric current is applied to the hot rolled steel strip of Fe-Ni alloy during nitric acid dipping to subject the steel strip to anodic electrolysis, the dissolution of the base material is promoted and the scale is easily peeled off. When the cathodic electrolysis is performed, bubbles are generated and scale peeling is promoted. Therefore, although there is an effect even if the electrolysis is not performed alternately, the scale peeling is further promoted by performing the anodic electrolysis and the cathodic electrolysis alternately.

If the current density is less than 0.06 A / cm ² , the scale peeling effect is insufficient. On the other hand, if it exceeds 0.18 A / cm ² , bubbles are generated even during anodic electrolysis, and the effective current used for melting the substrate is saturated, and the scale peeling effect due to bubbles during cathodic electrolysis is also saturated. Therefore, the current density is 0.06A / cm
^It must be ² or more and 0.18 A / cm ² or less.

Since most of the secondary scale is exfoliated by performing the above-mentioned nitric acid pickling, at the time of nitric hydrofluoric acid pickling in the next step, Fe ions and Ni accompanying the dissolution of the secondary scale in the nitric hydrofluoric acid aqueous solution are obtained. The increase of ions is suppressed, and the deterioration of the nitric hydrofluoric acid aqueous solution is suppressed.

[Conditions for Nitrofluoric Acid Pickling] Fe by nitric hydrofluoric acid pickling
The descalability of hot-rolled Ni-Ni alloy strip was investigated. Further, considering that nitric hydrofluoric acid pickling is also used for descaling of stainless steel strips, the stainless steel strips were also investigated.

According to the results of this investigation, in the hydrofluoric acid pickling of the hot-rolled Fe—Ni alloy steel strip and the stainless steel strip, descaling proceeds mainly by the dissolution of the base material. However, in nitric hydrofluoric acid pickling, the Fe-Ni alloy hot-rolled steel strip, unlike the stainless steel strip, has a marked tendency for non-uniform dissolution, and the degree of non-uniformity depends on the nitric acid concentration. It was found that the concentration of hydrofluoric acid greatly affected the concentration.

Therefore, the descaling property in nitric hydrofluoric acid pickling has been evaluated up to now by the average amount of thinning of the entire steel strip. However, in the descaling of the Fe-Ni alloy hot-rolled steel strip, Found that it was important to perform descaling in consideration of this nonuniformity of dissolution.

These points will be described below. First, with respect to the stainless steel strip, the results of investigation of the dissolution behavior when a hot rolled SUS304 steel strip is immersed in a nitric hydrofluoric acid aqueous solution at 50 ° C. for 90 seconds will be described with reference to FIGS. 6 to 8.

FIG. 6 shows the effect of hydrofluoric acid and nitric acid concentrations on the average metal loss rate. The average metal thinning speed is the average of the metal thinning speeds within the surface of the steel strip. It is represented. The average metal thinning rate is an index showing the commonly used descaling property.

FIG. 7 shows the effect of hydrofluoric acid and nitric acid concentrations on minimum meat velocity. The minimum reduction speed is the thickness reduction rate of the portion where the amount of thickness reduction is the smallest in the steel strip surface obtained by measuring the change in steel strip thickness before and after descaling with a micrometer,
It is represented by the change in plate thickness per unit time. Since the removal process of the internal oxide layer is rate-limited by the minimum reduced meat rate, the minimum reduced meat rate is an important indicator of descaling property. When the minimum reduction meat speed is low, the scale may not be completely descaled and the scale may remain on the surface of the steel strip.

FIG. 8 shows the effect of nitric acid and hydrofluoric acid concentrations on the uniform thickness reduction rate. The uniform thickness reduction rate is defined by the following equation (5) and represents the uniformity of melting in the steel strip surface. Further, the uniform thinning rate represents the smoothness of the surface of the steel strip after descaling, and when the uniform thinning rate is large, it indicates that the smoothness of the steel strip is good.

Uniform thinning rate (%) = minimum reduced meat speed ÷ average metal thinning speed × 100 (5) In the case of a stainless steel strip, there is an optimum nitric acid concentration at which the average metal thinning rate shows a peak value. Values increase with increasing hydrofluoric acid concentration. The minimum reduction rate also shows the same tendency as the average reduction rate, and the average reduction rate is the nitric acid concentration at which the peak value, and the average reduction rate also shows the peak value.

The uniform thinning rate is little affected by the concentrations of nitric acid and hydrofluoric acid, and a slight increase tendency is recognized as the concentrations of hydrofluoric acid and nitric acid increase. Therefore, for the stainless steel strip, unlike the case of the Fe-Ni alloy hot-rolled steel strip described later, the descaling property can be controlled only by the average thickness reduction rate as is usually done.

Next, regarding the Fe-Ni alloy hot rolled steel strip
explain. As an example, the hot pressure of commercial Fe-36wt% Ni alloy
Shot blast projection (projection density 100k
gf / m ²), Electrolysis by anodic electrolysis and cathodic electrolysis in nitric acid aqueous solution
Pickling (HNO₃: 15wt%, temperature: 65 ℃, current density: 0.12A / cm²)
After that, immerse in nitric hydrofluoric acid aqueous solution at 53 ℃ for 120 seconds and remove.
Fig. 2 shows the results of investigation of dissolution behavior when scaled.
~ Explain with reference to Figure 4.

FIG. 2 shows the effect of hydrofluoric acid and nitric acid concentrations on the average metal loss rate. Unlike the case of stainless steel strip, the average metal thinning rate increases monotonically with the increase of hydrofluoric acid and nitric acid concentrations.

FIG. 3 shows the effect of hydrofluoric acid and nitric acid concentration on the minimum meat velocity. The minimum reduction rate is significantly different from the behavior of the average reduction rate in Fig. 2 above. The minimum reduced meat speed is
It increases with increasing hydrofluoric acid concentration. On the other hand, regarding the effect of nitric acid concentration, the minimum reduced meat speed increases with increasing nitric acid concentration on the low concentration side, but decreases with increasing nitric acid concentration on the high concentration side. There is an optimum nitric acid concentration. The nitric acid concentration showing this optimum value moves to the high concentration side as the hydrofluoric acid concentration increases.

It is considered that the reason that the minimum reduced meat velocity shows the peak value is that the smoothness of the steel strip surface after pickling deteriorates when the nitric acid concentration becomes higher than the nitric acid concentration showing the peak value. To be

According to FIGS. 2 and 3, the dissolution rate increases as the concentration of nitric acid in the aqueous nitric-hydrofluoric acid solution increases, but the non-uniformity of dissolution also increases, and therefore the progress of descaling varies depending on the location. . Therefore, the smoothness of the surface at the time when the descaling is completed is reduced. Further, since the amount of pickling until complete descaling becomes large, it is necessary to take an excessive amount of pickling, which not only causes a reduction in yield, but also the consumption of the processing liquid and the amount of waste liquid processed. And the associated costs increase.

Therefore, it is necessary that not only the minimum reduction meat velocity is high, but also that the meat can be dissolved as uniformly as possible.
Therefore, the influence of nitric acid and hydrofluoric acid concentration on the uniformity of dissolution, that is, the uniform thinning rate defined by the above formula (5) was investigated. Figure 4 shows the survey results.

From FIG. 4, the uniform thinning rate is slightly changed on the low nitric acid concentration side due to the increase of the nitric acid concentration, but it is remarkably lowered when the nitric acid concentration exceeds a certain concentration. The nitric acid concentration at which this decrease begins moves to the high concentration side as the hydrofluoric acid concentration increases. That is, as the concentration of hydrofluoric acid increases, uneven dissolution is suppressed, and more uniform dissolution becomes possible.

From the results shown in FIGS. 3 and 4, it was found that, for a given hydrofluoric acid concentration, there is a possibility that there exists an optimum nitric acid concentration range in which both a favorable rate of metal thinning and uniformity of dissolution are compatible.

By the way, the inventors of the present invention have found that the uniform thickness reduction rate is closely related to the surface quality of the steel strip after cold rolling and the etching failure that occurs during etching. Figure 5 shows the hot-rolled steel strip of Fe-36wt% Ni alloy.
It is a figure which shows the relationship between the uniform thickness reduction rate and the surface quality of the steel strip after cold rolling, and the higher the uniform thickness reduction rate, the less the uneven gloss after cold rolling and the better the surface quality. To prevent deterioration due to uneven gloss, it is necessary to set the uniform thickness reduction rate to 60% or more.
The uniform thickness reduction rate is also related to the occurrence of etching defects during the etching process, and the etching defects decreased when the uniform thickness reduction rate was 60% or more. Therefore, in order to improve the surface quality of the steel strip after cold rolling and the etching failure during etching, it is necessary to set the uniform thickness reduction rate to 60% or more.

The removal process of the internal oxide layer is limited by the minimum reduction wall speed. In the case of Fe-36 wt% Ni alloy, the minimum reduction wall speed is 15 μm /
It must be min or more.

Then, the commercial Fe-36wt% Ni alloy hot-rolled steel strip was further examined for nitric hydrofluoric acid pickling conditions satisfying these conditions. As shown in FIG. wt% or more, nitric acid 7.0 wt% or more, and the following formula
It turns out that it is necessary to satisfy (6).

Y ≦ 1/2 × (x−1.8) ² +12 (6) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%) hydrofluoric acid concentration is less than 2.0 wt% Alternatively, if the nitric acid concentration is less than 7.0 wt%, the minimum reduction meat velocity is below 15 μm / min, and if the hydrofluoric acid concentration and nitric acid concentration do not satisfy the above formula (6), the uniform thickness reduction rate is below 60%. In addition, the minimum reduction meat speed is 15 μm / min
This is because it may fall below

However, even if the above-mentioned conditions are satisfied, if the concentration of hydrofluoric acid is too high, iron fluoride precipitates / complex ions are generated, which causes an increase in the amount of hydrofluoric acid consumed and clogging of the pipe, and There is a problem that the corrosiveness becomes high and the equipment damage becomes remarkable, or the surface after descaling rusts brown, and this rust easily becomes severe over time. Therefore, the concentration of hydrofluoric acid must be 5.9 wt% or less.

Further, the temperature of the nitric-hydrofluoric acid aqueous solution affects the metal thinning rate and the uniformity of metal thinning. Temperature of nitric hydrofluoric acid is 40 ℃
If it is less than this, it becomes impossible to secure a sufficient metal thinning speed. Higher temperatures increase the rate of metal loss, but the loss is more uneven. If the temperature of the aqueous nitric-hydrofluoric acid solution exceeds 65 ° C, it is not possible to secure a uniform thinning rate of 60% or more, and the consumption amount due to evaporation of hydrofluoric acid increases rapidly, so it is necessary to keep it at 65 ° C or less. . Therefore, the temperature of the aqueous nitric-hydrofluoric acid solution is 40 ° C or higher.
Must be below 65 ° C.

Further, in order to complete the descaling under the pickling conditions within the scope of the present invention and to obtain a uniform thinning rate of 60% or more, a hot-rolled Fe-Ni alloy alloy in an aqueous solution of nitric hydrofluoric acid is used. The soaking time of the strip must be 65 seconds or longer. If the immersion time is less than 65 seconds, the scale remaining unevenly on the surface of the steel strip is not completely removed, or even if the scale is completely removed, the scale-missing portion is a recess, This is because the surface is not smooth and the uniform metal loss rate is less than 60%.

The present invention configured as described above has the following effects. Since the steel strip after descaling is hard to rust, rework due to rusting can be reduced.

Since the smoothness of the steel strip after descaling is good, it is possible to reduce uneven gloss after cold rolling and etching defects during etching. Further, since it is not based on mechanical grinding, there are no defects observed after cold rolling or after etching due to the abrasive grains found in mechanical grinding.

Since the descaling process is carried out by uniform dissolution, the descaling can be completed with a minimum amount of wall thinning. Therefore, an excessive pickling allowance is not required, and a high yield can be obtained in descaling. Further, since the deterioration of the treatment liquid is reduced and the consumption amount of the treatment liquid and the waste liquid treatment amount can be reduced, the descaling cost can be reduced.

Since the descaling process is performed in consideration of the minimum reduction meat speed that controls the descaling work, the descaling process with good efficiency can be performed. In addition, the scale residue after descaling is less likely to occur.

Since the use of expensive hydrofluoric acid can be reduced,
The chemicals used are inexpensive. Moreover, since the scale accumulated in the pickling tank is not dissolved, deterioration and consumption of the chemical liquid can be reduced.

Since the treatment liquid containing no chlorine ion is used, pitting corrosion or rusting does not occur in the stainless steel strip, and it can be shared with the descaling treatment of the stainless steel strip.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for descaling an Fe-Ni alloy hot-rolled steel strip according to the present invention, mechanical descaling treatment, and as mechanical descaling treatment, shot blasting, scale breaker, rolling at a low rolling rate Alternatively, in the case of treatment by brush grinding containing abrasive grains, these treatments can be carried out by conventional methods. Also, the predetermined projection density of shot blast can be obtained by a conventional method.

The nitric acid pickling and the nitric acid hydrofluoric acid pickling after the mechanical descaling treatment can also be carried out using commonly used equipment.

[0069]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Commercially available Fe-36wt% Ni alloy hot-rolled steel strip was shot blasted (projection density 100 kgf / m ² ) and then treated with an aqueous nitric acid solution. For No. 1 to No. 190, anodic electrolysis and cathodic electrolysis were used. Electrolytic pickling (HNO ₃ : 15 wt%, temperature: 65 ° C, current density: 0.12 A / cm ² ) is performed, and immersion pickling (HNO ₃ : 15 wt%, temperature: No. 191-No. 224). (65 ° C, no electrolysis), and then dip in a nitric hydrofluoric acid aqueous solution for a predetermined time to perform pickling.
The surface roughness Ra after descaling was investigated for scale reference, rusting status, and for reference.

The minimum thickness reduction rate was calculated from the thickness reduction rate of the portion with the smallest change, by measuring the amount of thickness reduction of the test piece before and after descaling with a micrometer. The minimum reduced meat velocity required for descaling was 0.15 μm / min or more, and there was no problem.

The value obtained by converting the weight change from the density of the Fe-Ni-based alloy into the plate thickness change and the average value of the actually measured metal thinning amounts were almost the same. Therefore, the average metal thinning rate was obtained by converting the weight change into the plate thickness change. I asked.

Further, the uniformity of dissolution and the smoothness of the surface after descaling were evaluated by the uniform thinning rate represented by the following formula (7).

Uniform thinning rate (%) = minimum reduced meat rate / average thinning rate × 100 (7) If the uniform thinning rate is 60% or more, the dissolution is uniform and the surface is smooth. Yes, and the yield was high, so there was no problem.

The degree of residual scale is visually observed on the steel strip after pickling, and "X" indicates that the scale can be visually observed, and "△" indicates that the scale can be observed by a 30 × magnifying glass.
If the scale was not recognized with a 30-fold magnifying glass, it was designated as "○", and if "○", there was no problem.

Regarding the rusting condition, after the Fe-Ni alloy hot-rolled steel strip after pickling was left for 10 days, the rusting condition on the surface was visually observed. ○ ”, those that have changed to a little brown color but do not require re-pickling are“ △ ”, those that have strong rust and require re-pickling are“ × ”, and if“ ○ ”and“ △ ” I assumed there was no problem.

Further, a comprehensive judgment of the minimum reduced meat speed, uniform thinning rate, rusting condition and scale residual degree was made, and the minimum reduced meat speed was 0.15 μm / min or more, the uniform thinning rate was 60% or more, Those with no problem in the situation and scale residual degree were judged as "○", and those with at least one of the above evaluation items not yet evaluated were judged as "X".

When electrolytic nitric acid hydrofluoric acid pickling was performed in an aqueous nitric acid solution, the minimum meat reduction rate, average metal thinning rate, uniform metal thinning rate, and rusting condition for each nitric acid hydrofluoric acid pickling condition Table 1 to Table 7 show the results of the investigation of surface roughness Ra and the degree of scale residue, and the results of comprehensive evaluation.

Table 8 shows the results of the same investigation in the case of nitric hydrofluoric acid pickling after immersion pickling with an aqueous nitric acid solution.

In Tables 1 to 8, the A value described in the column of nitric hydrofluoric acid conditions is a value calculated by the following formula (7) based on the hydrofluoric acid concentration and the nitric acid concentration.

A value = 1/2 × (x−1.8) ² + 12−y (7) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%)

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

[Table 3]

[0085]

[Table 4]

[0086]

[Table 5]

[0087]

[Table 6]

[0088]

[Table 7]

[0089]

[Table 8]

From Tables 1 to 8, in the invention examples satisfying the scope of the present invention, the minimum reduction rate is 0.15 μm / min or more, and the uniform reduction rate is 6
From 0% or more, it can be seen that the rust and residual scale are at a level without problems, and the comprehensive judgment is “◯”.

As can be seen from No.188, surface roughness
Even if Ra is about 17 μm, the effect of the present invention can be obtained.

Comparative examples not satisfying the scope of the present invention are:
As described below, at least one of the effects of the present invention is not satisfied, and the comprehensive judgment is “x”.

That is, less than 2.0 wt% of hydrofluoric acid, 7.0 wt% of nitric acid
For nitric hydrofluoric acid having a temperature of less than 40 ° C or a liquid temperature of less than 40 ° C, the minimum reduced meat velocity was less than 0.15 μm / min, and residual scale was observed after descaling.

Even when the concentration of hydrofluoric acid, the concentration of nitric acid and the liquid temperature at which a sufficient minimum meat velocity is obtained can be obtained, the A value showing the relationship between the concentrations of hydrofluoric acid and nitric acid obtained from the above formula (7) is 0. If the relationship between hydrofluoric acid and nitric acid concentration is less than formula (8) below, or if the liquid temperature exceeds 65 ° C, the uniform thinning rate is
It was less than 60%.

Y ≦ 1/2 × (x−1.8) ² +12 (8) x: hydrofluoric acid concentration, y: nitric acid concentration When the hydrofluoric acid content exceeds 5.9 wt%, steel after pickling and descaling A severe rusting occurred on the belt.

Even if the hydrofluoric acid concentration, nitric acid concentration and liquid temperature were within the ranges of the present invention, when the nitric acid hydrofluoric acid immersion time was less than 65 sec, the uniform thinning rate was less than 60%, and descaling was insufficient. Therefore, the scale remained.

Further, in this example, the nitric acid pickling condition after shot blasting was within the range of the nitric acid pickling condition of the present invention, so that the secondary scale residual area ratio after nitric acid pickling was 10%. Since the amount of secondary scale peeling was large below, the amount of secondary scale carried into the aqueous nitric hydrofluoric acid solution was small, and the deterioration of the aqueous nitric hydrofluoric acid solution was small.

Also, Fe-N descaled according to the present invention
The i-based alloy hot-rolled steel strip has a uniform thinning rate of 60% or more.
Since the surface smoothness is good, the surface quality can be improved when cold-rolled or etched.

[0099]

As described above, the descaling method for Fe—Ni alloy hot-rolled steel strip according to the present invention has many industrially useful effects as described below.

Since the steel strip after descaling is less likely to rust, rework due to rusting can be reduced.

Since the steel strip after descaling has good smoothness, it is possible to reduce uneven gloss after cold rolling and etching defects during etching. Further, since it is not based on mechanical grinding, there are no defects observed after cold rolling or after etching due to the abrasive grains found in mechanical grinding.

Since the descaling process is carried out by uniform dissolution, the descaling can be completed with a minimum amount of wall thinning. Therefore, an excessive pickling allowance is not required, and a high yield can be obtained in descaling. Further, since the deterioration of the treatment liquid is reduced and the consumption amount of the treatment liquid and the waste liquid treatment amount can be reduced, the descaling cost can be reduced.

Since the descaling process is performed in consideration of the minimum reduction meat speed that controls the descaling work, the efficient descaling process can be performed. In addition, the scale residue after descaling is less likely to occur.

Since the use of expensive hydrofluoric acid can be reduced,
The chemicals used are inexpensive. Moreover, since the scale accumulated in the pickling tank is not dissolved, deterioration and consumption of the chemical liquid can be reduced.

Since the treatment liquid containing no chlorine ion is used, pitting corrosion or rusting does not occur in the stainless steel strip, and the stainless steel strip can be shared with the descaling treatment.

[Brief description of drawings]

FIG. 1 is a diagram showing the effects of hydrofluoric acid and nitric acid concentrations in an aqueous nitric hydrofluoric acid solution on the minimum reduction wall speed and the uniform thickness reduction rate in a hot-rolled Fe-Ni alloy alloy strip.

FIG. 2 is a diagram showing the effect of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the average thickness reduction rate in a hot-rolled Fe-Ni alloy steel strip.

FIG. 3 is a graph showing the influence of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the minimum reduction wall speed in a hot-rolled Fe—Ni alloy steel strip.

FIG. 4 is a diagram showing the effect of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the uniform thickness reduction rate in a hot-rolled Fe—Ni alloy steel strip.

FIG. 5 is a diagram showing the relationship between the uniform thickness reduction rate and the surface quality after cold rolling.

FIG. 6 is a diagram showing the effect of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the average thickness reduction rate in a stainless steel hot-rolled steel strip.

FIG. 7 is a diagram showing the influence of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the minimum meat reduction rate in a hot rolled stainless steel strip.

FIG. 8 is a diagram showing the effect of hydrofluoric acid and nitric acid concentrations in a nitric hydrofluoric acid aqueous solution on the uniform thickness reduction rate in a stainless steel hot-rolled steel strip.

Continued Front Page (72) Inventor Toru Inazumi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Pipe Co., Ltd. (72) Inventor Yutaka Wada 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Pipe Co., Ltd. (72) Inventor Tetsuo Sakiyama 1-2-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Steel Pipe Co., Ltd. (72) Inventor Toshio Takano 1-2-1 Marunouchi, Chiyoda-ku, Tokyo, Japan Steel Pipe Co., Ltd. (56) Reference References JP-A-1-247583 (JP, A) JP-A-62-139888 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23G 1/08 B24C 1/08 C23G 3 / 02 C25F 1/06

Claims (4)

(57) [Claims] 1. When the Fe-Ni alloy hot-rolled steel strip is descaled, the Fe-Ni alloy hot-rolled steel strip is subjected to mechanical descaling treatment and then nitric acid concentration of 10 wt% or more and 20 wt% or less and liquid temperature. After immersion in a nitric acid aqueous solution at 45 ° C or higher and 80 ° C or lower, hydrofluoric acid 2.0 wt% or more and 5.9 wt% or less, nitric acid 7.0 wt% or more, the relationship between the concentration of hydrofluoric acid and nitric acid satisfies the following formula (1), and A descaling method for hot-rolled steel strips of Fe-Ni alloys, characterized by immersing in a hydrofluoric acid aqueous solution at a temperature of 40 ° C or higher and 65 ° C or lower for 65 seconds or longer for pickling. y ≤ 1/2 × (x-1.8) ² +12 (1) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%) 2. When the Fe-Ni alloy hot-rolled steel strip is descaled, the Fe-Ni alloy hot-rolled steel strip is subjected to mechanical descaling treatment and then nitric acid concentration of 10 wt% or more and 20 wt% or less and liquid temperature. Current density in nitric acid aqueous solution of 45 ℃ to 80 ℃
After repeated electrolysis by anodic electrolysis and cathode electrolysis at 0.06 A / cm ² or more 0.18 / cm ² or less, hydrofluoric acid 2.0 wt% or more 5.9 wt% or less, with nitric acid 7.0 wt% or more, the concentration of hydrofluoric acid and nitric acid It is characterized in that the relationship satisfies the following formula (2) and is immersed in a nitric hydrofluoric acid aqueous solution having a liquid temperature of 40 ° C or higher and 65 ° C or lower for 65 seconds or longer for pickling.
Descaling method for Fe-Ni alloy hot rolled steel strip. y ≦ 1/2 × (x−1.8) ² +12 (2) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%) 3. The mechanical descaling treatment is one or a combination of two or more selected from shot blasting, scale breaker, rolling at a low rolling rate, and brush grinding with abrasive grains. The method for descaling an Fe-Ni alloy hot-rolled steel strip according to claim 1 or 2, wherein 4. The Fe-Ni according to claim 1 or ² , wherein the mechanical descaling process is a process by shot blasting with a projection density of 30 kgf / m ² or more.
Method for hot-rolled steel strips of base alloys.