JPH1088377A - Descaling method for fe-ni alloy hot rolled steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a descaling method for an Fe-Ni alloy hot rolled steel strip by which surface defects such as scales, scabs or the like can perfectly be removed, rust is hard to be generated after descaling, the surface after descaling is smooth, good surface quality can be obtd. after cold rolling and etching, and furthermore, sharing with stainless pickling treatment is made possible. SOLUTION: At the time of subjecting an Fe-Ni alloy hot rolled steel strip to descaling, an Fe-Ni alloy hot rolled steel strip is subjected to descaling, is immersed in an aq. soln. of nitric acid with 10 to 20wt.% nitric acid concn. heated at 45 to 80 deg.C sol. temp. or electrolyzed, is subsequently immersed in an aq. soln. of nitric acid-hydrofluoric acid contg. 2.0 to 5.9wt.% hydrofluoric acid and >=7.0wt.%. nitric acid, in which, in the case (x) denotes the concn. (wt.%) of hydrofluoric acid and (y) denotes the concn. (wt.%) of nitric acid, the concns. of hydrofluoric acid and nitric acid satisfy the inequality of y <=1/2×(x-1.8)<2> +12 and heated at 40 to 65 deg.C soln. temp. for >=65sec and is pickled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for descaling a hot-rolled steel strip of an Fe-Ni alloy, more specifically, it is difficult to rust after descaling and has good after rolling and etching. The present invention relates to a descaling method capable of obtaining a surface quality, and at a low cost, capable of being shared with a pickling line of a stainless steel strip.

[0002]

2. Description of the Related Art An Fe-Ni alloy is hot-rolled or further cold-rolled and then used for applications such as LNG containers, lead frames, shadow masks and permalloys. Further, the Fe-Ni-based alloy needs to have a good surface appearance after cold rolling, and since some of the above-mentioned applications are subjected to etching, there is no possibility that poor etching occurs during the etching. is necessary.

[0003] In cold rolling, it is necessary to completely descaling of a hot rolled steel strip of an Fe-Ni alloy. But,
In Fe-Ni alloys, an internal oxide layer with good adhesion to the substrate is formed during slab heating, and it is difficult to remove even the descaling during hot rolling. For this reason, descaling is not easy in the Fe-Ni alloy hot-rolled steel strip because an internal oxide layer having a depth of several tens of μm remains under a uniform oxide layer (hereinafter, secondary scale) on the surface. .

[0004] For this reason, 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 referred to as 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 large, high-speed grinding is difficult, and the grinding material is expensive and has a short life, resulting in low productivity and high descaling cost. There's a problem.

[0005] Although descaling by mechanical grinding is also performed on stainless steel strips, it does not pose a problem with hard stainless steel. However, since Fe-Ni-based alloys are soft, abrasives contained in abrasives are not included. The grains are embedded in the hot-rolled steel strip of the Fe-Ni-based alloy, causing problems such as surface defects at the time of the next step of cold rolling and poor etching when processed into a shadow mask or the like.

Further, in order to increase the grinding amount in one pass by mechanical grinding to increase the grinding speed, abrasive grains having a coarse count of about # 100 must be used, and the surface after descaling becomes rough. Therefore, there is also a problem that the surface quality after cold rolling is deteriorated.

Therefore, a descaling method that does not rely only on mechanical grinding has been proposed. For example, JP-A-1-273607
In Japanese Patent Application Publication (hereinafter referred to as Conventional Technology B), cracks and peeling are generated on the scale by mechanical treatment, and then the abrasive grain is # 4.
With the first grinding roll in the range of 6 to 100, grinding is performed to the metal base just below the scale of the hot-rolled alloy steel strip, and then the abrasive grain number is in the range of # 80 to 400, and from the abrasive grain number of the first grinding roll. After leveling the ground surface using a second grinding roll of fine or equal abrasive grain count, the operation of acid solution treatment is performed continuously, causing cracks and peeling on the scale and grinding. By removing most of the scale by grinding to reduce the load on pickling and prolong the life of the acid solution, and by optimizing the abrasive grain number of the abrasive and pickling to improve the surface roughness A method of descaling a hot-rolled alloy steel strip which obtains good surface quality by reducing the surface smoothness is described.

Japanese Patent Application Laid-Open No. 62-139888 (hereinafter referred to as prior art C) discloses that nitric 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 is carried out. A descaling method of a hot-rolled steel strip of an Fe-Ni-based alloy which has improved descaling properties and has excellent surface properties while suppressing surface roughness after pickling is described.

Furthermore, Japanese Patent Application Laid-Open No. 2-70100 (hereinafter referred to as prior art D) discloses that a steel alloy strip containing at least Ni and / or Cr contains 50 to 200 g / l of NaCl as a main component. In this, HNO ₃ or FeCl ₃ is added at 0.4 mol / mol of NaCl.
In ~1.0mol / l added with a solution, the liquid temperature 20 to 80 ° C., after anodic electrolysis pickling under the conditions of a current density of 5 ~30A / dm ^2, one of sulfuric hydrofluoric acid and nitric hydrofluoric acid or Descaling by both pickling treatments is performed to improve the descaling property of the alloy steel strip, and most of the scale is removed by electrolytic pickling, so that the descaling load is reduced during the next pickling, It is described that the accumulation of scale in the pickling solution is reduced and 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, which increases the maintenance cost and running cost of the equipment. In addition, since almost all scales are removed by mechanical grinding, the problems described in the prior art A described above have not been essentially improved, and after cold rolling or etching after embedding of grinding abrasive grains. There are problems such as the occurrence of defects.

The method described in the prior art C has a problem that the surface of the steel sheet after descaling tends to rust brown. Since this rust tends to become severe with the passage of time, once rusted, it must be removed again by pickling and polishing. Further, there is a problem that the surface quality is degraded after cold rolling, and that etching defects occur when etching is performed.

[0012] Further, precipitation and complex ions of iron fluoride are easily formed ("Tomoo Takahari et al .: Iron and Steel, vol. 70, No. 11, p. 16").
05 "), causing an increase in consumption of hydrofluoric acid and blockage of piping, resulting in a decrease in productivity and an increase in cost.

In the method described in the prior art C, since descaling is performed using only nitric hydrofluoric acid, the amount of expensive hydrofluoric acid used is larger than that of nitric acid, and the scale is gradually dissolved in an aqueous nitric hydrofluoric acid solution. Therefore, nitric hydrofluoric acid is wasted by dissolving the scale once dropped and deposited in the pickling tank. For this reason,
There is a problem that the use amount of nitric acid or expensive hydrofluoric acid increases.

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

[0015] The hot-rolled steel strip of the Fe-Ni-based alloy may be descaled with the same equipment as the stainless steel strip, which is difficult to descaling. Therefore, it is advantageous that the stainless steel strip can be descaled by the equipment and treatment liquid used for descaling the hot-rolled steel strip of the Fe—Ni alloy. However, according to the method described in the prior art D, chlorinated ions are contained in the anodic electrolytic treatment solution. Therefore, when the stainless steel strip is descaled, the pitting corrosion due to the chlorine ions remaining on the stainless steel strip surface after descaling is performed. Since there is a problem that rust and rust easily occur, the descaling treatment cannot be shared with the stainless steel strip.

The present invention has been made in consideration of the above circumstances, and has a high descaling processing speed and at the same time,
Uniform wall thinning, excellent yield, chemical solution is inexpensive, chemical solution degradation, chemical solution can be descaled with little consumption, and surface defects such as secondary scale and scale consisting of internal oxide layer and scab Can be completely removed, it is hard to rust after descaling, the surface after descaling is smooth, good surface quality is obtained after cold rolling or etching, and it can be shared with stainless pickling treatment Fe
An object of the present invention is to provide a method for descaling a hot rolled steel strip of a -Ni-based alloy.

[0017]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems. As a result, weight
%, Ni: 25% or more and 85% or less, and Fe: 15% or more and 75% or less, the following was found regarding the descaling of a hot-rolled steel strip of an Fe-Ni alloy.

The brown rust on the steel strip surface after pickling is related to the concentration of hydrofluoric acid, and the brown rust can be prevented unless a high concentration of hydrofluoric acid is used. Poor surface quality, but steel strip surface roughness after pickling
Not due to the state of fine irregularities having a wavelength of about 1 mm or less measured by Ra, but due to larger irregularities on the steel strip surface after pickling, that is, unevenness of the steel strip surface after pickling In addition, this non-uniformity is caused by non-uniformity of wall thinning at the time of pickling.If the pickling is performed with nitric acid and hydrofluoric acid in an aqueous solution of nitric acid while limiting the concentration and temperature, excessive pickling must be performed. The descaling can proceed quickly and efficiently without any rust after descaling, and the surface smoothness after descaling is controlled to obtain excellent surface quality after cold rolling. Further, by performing a mechanical descaling treatment and a nitric acid pickling before the nitric acid pickling, as described below,
Before the descaling by pickling, a more effective descaling becomes possible.
The secondary scale can be easily peeled off, and the uniformity and speed of corrosion can be improved. After mechanical descaling, pickling with a nitric acid aqueous solution with a limited concentration and temperature can remove most of the secondary scale. Therefore, the amount of scale brought into the nitric acid hydrofluoric acid pickling tank is reduced, and deterioration of nitric acid hydrofluoric acid can be suppressed. In addition, mechanical descaling treatment includes shot blasting, scale breaker, rolling at a low rolling rate Or selected from the processing by brush grinding with abrasive grains
It is desirable to treat one or a combination of two or more of them.If an electric current is applied during the nitric acid immersion, the descalability of the secondary scale is further improved.The present invention has been made based on such findings. The gist is as follows.

(1) When descaling the hot-rolled steel strip of the Fe-Ni alloy, the hot-rolled steel strip of the Fe-Ni alloy is subjected to a mechanical descaling treatment and then subjected to a 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 more and 80 ° C or less, the relationship between the concentration of hydrofluoric acid and nitric acid satisfies the following formula (3) with hydrofluoric acid 2.0 wt% or more and 5.9 wt% or less and nitric acid 7.0 wt% or more, A method of descaling a hot-rolled steel strip of an Fe-Ni alloy which is immersed in an aqueous solution of nitric hydrofluoric acid at a liquid temperature of 40 ° C or higher and 65 ° C or lower for 65 seconds or longer and pickled.

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

(2) When descaling the Fe-Ni alloy hot-rolled steel strip, the Fe-Ni alloy hot-rolled steel strip is subjected to a mechanical descaling treatment and then subjected to a nitric acid concentration of 10 wt% or more and 20 wt% or less. In a nitric acid aqueous solution at a temperature between 45 ° C and 80 ° C, the current density
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 a hot-rolled steel strip of an Fe-Ni-based alloy in which the relationship satisfies the following equation (4) and is immersed in an aqueous solution of nitric hydrofluoric acid at a liquid temperature of 40 ° C to 65 ° C for 65 seconds or more and pickled.

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 shot blasting, scale breaker, rolling at a low rolling ratio, or brushing with grinding abrasives. A descaling method for Fe-Ni-based alloy hot-rolled steel strip, which is a combination of two or more types of treatments.

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

<Reason for Action and Limitation> [Alloy components] The hot rolled steel strip of the Fe—Ni alloy used in the present invention has a basic component of Ni: 25% or more and 85% or less by weight, Fe: Fe-Ni alloy containing 15% or more and 75% or less.

If Ni and Fe are out of the above range, the Fe-Ni alloy hot rolled steel strip cannot satisfy the required physical, magnetic and mechanical properties as electronic and electromagnetic materials. Limited.

The hot rolled steel strip of the Fe-Ni alloy according to the present invention includes an invar alloy (36 wt% Ni) and a super invar alloy (32 wt%) used for electronic and electromagnetic materials and LNG containers.
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).

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

[Mechanical descaling treatment] The nitric acid pickling of the hot-rolled Fe-Ni alloy steel strip does not dissolve oxides,
The descaling proceeds due to the dissolution of the substrate. At this time, if there is a crack in the secondary scale, the nitric acid reaches the base through the crack in the secondary scale, and dissolves the base immediately below the secondary scale to peel off the secondary scale.

However, since the secondary scale of the hot-rolled steel strip of the Fe—Ni alloy is dense and has few cracks, the descaling proceeds only in a non-uniform manner even if the nitric acid washing is performed in the hot-rolled state. By performing a mechanical treatment before pickling, a crack is given to the secondary scale, and the secondary scale is easily peeled off at the time of the next pickling.

As a mechanical descaling treatment, one or a combination of two or more selected from among shot blasting, scale breaker, rolling or brush grinding with abrasive grains is performed, so that nitric acid washing is performed. The peeling of the scale can be more efficiently promoted before. Shot blasting is almost unaffected by the thickness and composition of the secondary scale, with a projection density of 30 kgf / m ²
The above has a sufficient descaling effect.

[Nitric acid pickling conditions] The peeling rate of the secondary scale by nitric acid increases as the nitric acid concentration and the temperature increase. In order to obtain the industrially necessary minimum secondary scale peeling rate, the nitric acid concentration must be 10 wt% or more. However, the effect is saturated when the nitric acid concentration exceeds 20 wt%, so the nitric acid needs to be 20 wt% or less. Further, in order to obtain the industrially necessary minimum peeling rate of the secondary scale, the liquid temperature must be 45 ° C. or higher. However, if the liquid temperature exceeds 80 ° C., the evaporation of water becomes severe, and the concentration control becomes complicated.

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

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

When 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 during anodic electrolysis and the effective current used for dissolving the substrate is saturated, and the scale peeling effect due to the bubbles during cathodic electrolysis is also saturated. Therefore, the current density is 0.06 A / cm
^It is necessary to be ² or more and 0.18 A / cm ² or less.

Since the secondary scale is almost peeled off by performing the above-mentioned nitric acid pickling, Fe ions and Ni accompanying the dissolution of the secondary scale in the aqueous nitric hydrofluoric acid solution during the next step of pickling nitric hydrofluoric acid are used. The increase of ions is suppressed, and the deterioration of the nitric hydrofluoric acid aqueous solution is suppressed.

[Nitric acid hydrofluoric acid pickling conditions]
The descaling properties of a hot rolled -Ni alloy strip were investigated. In addition, stainless steel strip was also investigated in consideration that nitric hydrofluoric acid pickling was used for descaling of stainless steel strip.

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

Therefore, the descaling property in the nitric acid hydrofluoric acid pickling has been evaluated by the average thickness reduction of the entire steel strip. However, in the descaling of the hot rolled steel strip of the Fe—Ni alloy, It was found that it was important to perform descaling in consideration of the heterogeneity of dissolution.

Hereinafter, these points will be described. First, with respect to the stainless steel strip, the results of an investigation of the dissolution behavior when a hot rolled SUS304 strip is immersed in a 50 ° C. nitric hydrofluoric acid aqueous solution 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 rate of wall thinning. The average thickness reduction rate is the average of the thickness reduction rate in the steel strip plane, and the weight change of the steel strip before and after descaling, that is, the melting amount, is converted into a steel strip thickness change, and the thickness change per unit time is obtained. It is shown. The average thinning rate is an index indicating the descalability that is usually performed.

FIG. 7 shows the effect of hydrofluoric and nitric acid concentrations on the minimum reduced meat rate. The minimum thickness reduction rate is the thickness reduction rate of the portion where the thickness reduction is the smallest in the steel strip surface obtained by measuring the thickness change of the steel strip before and after descaling with a micrometer,
It is expressed as a change in sheet thickness per unit time. Since the step of removing the internal oxide layer is determined by the minimum meat speed, the minimum meat speed is an important index indicating the descalability. When the minimum reduction rate is low, the scale is not completely descaled and scale may remain on the steel strip surface.

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

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

The uniform thinning rate is little affected by the concentrations of nitric acid and hydrofluoric acid, and only a slight increasing tendency is observed with an increase in the concentrations of hydrofluoric acid and nitric acid. Therefore, unlike the case of the Fe-Ni-based alloy hot-rolled steel strip described below, the descalability of the stainless steel strip can be controlled only by the average thinning rate as usual.

Next, the hot-rolled steel strip of Fe-Ni alloy
explain. As an example, the hot pressure of commercial Fe-36wt% Ni alloy
Shot blast projection using a steel strip (projection density 100k
gf / m ^Two), Electrolysis by anodic electrolysis and cathodic electrolysis in nitric acid aqueous solution
Pickling (HNO_Three: 15wt%, temperature: 65 ℃, current density: 0.12A / cm^Two)
And then immersed in a 53 ° C aqueous nitric hydrofluoric acid solution for 120 seconds to remove
Figure 2 shows the investigation results of the dissolution behavior when scaled.
This will be described with reference to FIG.

FIG. 2 shows the effect of hydrofluoric acid and nitric acid concentrations on the average rate of wall thinning. The average thinning rate monotonically increases with an increase in the concentration of hydrofluoric acid and nitric acid, unlike the case of the stainless steel strip.

FIG. 3 shows the effect of hydrofluoric and nitric acid concentrations on the minimum reduced meat rate. The minimum reduction rate is significantly different from the behavior of the average thickness reduction rate shown in FIG. The minimum reduction meat speed is
It increases as the concentration of hydrofluoric acid increases. On the other hand, regarding the effect of nitric acid concentration, the lowest reduced meat speed increases with increasing nitric acid concentration on the lower concentration side, but decreases on the higher concentration side when the nitric acid concentration increases. An optimal nitric acid concentration exists. The nitric acid concentration showing this optimum value moves to the higher concentration side as the hydrofluoric acid concentration increases.

It is considered that the reason why the minimum reduced meat speed shows a peak value is that when the nitric acid concentration becomes higher than the nitric acid concentration showing the peak value, the smoothness of the surface of the steel strip after pickling decreases. Can be

According to FIGS. 2 and 3, as the concentration of nitric acid in the nitric acid / hydrofluoric acid aqueous solution increases, the dissolution rate increases, but the dissolution inhomogeneity also increases. . Therefore, the smoothness of the surface at the time when the descaling is completed is reduced. In addition, since the amount of pickling until the complete descaling becomes large, it is necessary to take an excessive amount of pickling allowance, which not only reduces the yield, but also reduces the consumption of the processing solution and the amount of the waste solution. And the associated costs.

Therefore, it is necessary not only that the minimum meat speed is high but also that the dissolution be as uniform as possible.
Therefore, the effects of nitric acid and hydrofluoric acid concentrations on the uniformity of dissolution, that is, the uniform thinning rate defined by the above equation (5) were investigated. Figure 4 shows the survey results.

From FIG. 4, it can be seen that the uniform thinning rate is slightly changed on the low nitric acid concentration side due to an increase in the nitric acid concentration, but is significantly reduced when the nitric acid concentration exceeds a certain concentration. The nitric acid concentration at which the decrease starts moves to the higher 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 can be achieved.

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

By the way, the present inventors have found that the uniform thinning rate is closely related to the surface quality of the steel strip after cold rolling and the poor etching 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 gloss unevenness after cold rolling decreases and surface quality improves, so that a uniform thickness reduction rate is high. In order to suppress downgrading due to uneven gloss, the uniform thinning rate must be 60% or more.
In addition, the uniform thinning rate was related to the state of occurrence of poor etching during the etching process. When the uniform thinning rate was 60% or more, the poor etching decreased. Therefore, in order to improve the surface quality of the steel strip after cold rolling and the poor etching at the time of etching, it is necessary to set the uniform thinning rate to 60% or more.

In the step of removing the internal oxide layer, the rate is determined by the minimum wall speed. In the case of the Fe-36 wt% Ni alloy, the minimum wall speed is 15 μm / min as the industrially required minimum wall speed.
It must be at least min.

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

Y ≦ 1/2 × (x−1.8) ² +12 (6) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%), and hydrofluoric acid concentration is less than 2.0 wt% Alternatively, when the nitric acid concentration is less than 7.0 wt%, the minimum reduced meat speed is less than 15 μm / min, and when the hydrofluoric acid concentration and the nitric acid concentration do not satisfy the above formula (6), the uniform thinning rate is less than 60%, In addition, the minimum reduced meat speed is 15 μm / min
Because it may be less than

However, even if the above conditions are satisfied, if the concentration of hydrofluoric acid is too high, precipitates and complex ions of iron fluoride are generated, which causes an increase in consumption of hydrofluoric acid and blockage of piping, and There is a problem that the corrosiveness increases and equipment damage becomes remarkable, or the surface after descaling rusts brown, and this rust tends to become severe over time. Therefore, the hydrofluoric acid concentration needs to be 5.9 wt% or less.

The temperature of the nitric hydrofluoric acid aqueous solution affects the wall thinning rate and the uniformity of the wall thinning. Temperature of nitric hydrofluoric acid is 40 ℃
If it is less than this, a sufficient thickness reduction rate cannot be secured. The higher the temperature, the faster the rate of wall thinning, but the less uniform the wall thinning. If the temperature of the nitric hydrofluoric acid aqueous solution exceeds 65 ° C, it is not possible to ensure a uniform thinning rate of 60% or more, and the consumption by evaporation of hydrofluoric acid also rapidly increases. . Therefore, the temperature of nitric hydrofluoric acid aqueous solution is 40 ° C or more.
It must be below 65 ° C.

Further, in order to complete descaling under the pickling conditions within the range of the present invention and to obtain a uniform thinning rate of 60% or more, it is necessary to prepare a hot rolled Fe—Ni alloy in a nitric acid hydrofluoric acid aqueous solution. The immersion time of the band must be at least 65 seconds. If the immersion time is less than 65 seconds, the removal of the scale remaining unevenly on the steel strip surface is incomplete, or even if the removal of the scale is complete, the scale missing part is a concave part, This is because the surface is not smooth and the uniform thinning rate is less than 60%.

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

Since the smoothness of the steel strip after descaling is good, it is possible to reduce unevenness in gloss after cold rolling and poor etching during etching. In addition, since it is not based on mechanical grinding, there is no occurrence of defects observed after cold rolling or etching, which are caused by abrasive grains observed in mechanical grinding.

Since descaling is performed by uniform dissolution, descaling can be completed with a minimum amount of wall thinning. Therefore, since an excessive pickling allowance is not required, a high yield can be obtained at the time of descaling. In addition, the deterioration of the processing liquid is reduced, and the consumption amount of the processing liquid and the waste liquid processing amount can be reduced, so that the descaling cost can be reduced.

Since the descaling process is performed in consideration of the minimum meat speed that controls the descaling operation, the descaling process can be performed efficiently. In addition, scale residue after descaling hardly occurs.

Since the use of expensive hydrofluoric acid can be reduced,
The chemical used is inexpensive. In addition, since the scale deposited in the pickling tank is not dissolved, deterioration and consumption of the chemical can be reduced.

Since a treatment solution containing no chloride ions is used, no pitting or rust is generated on the stainless steel strip, and the stainless steel strip can be shared with the descaling treatment.

[0067]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the descaling method of a Fe-Ni-based alloy hot-rolled steel strip according to the present invention, mechanical descaling treatment and mechanical descaling treatment include shot blasting, scale breaker, and rolling at a low rolling ratio. Alternatively, in the case of processing by brush grinding with abrasive grains, these processings can be performed by an ordinary method. Further, the predetermined projection density of the shot blast can also be obtained by an ordinary method.

After the mechanical descaling treatment, nitric acid pickling and nitric acid pickling 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.

After shot blasting (projection density 100 kgf / m ² ) onto a commercial Fe-36wt% Ni alloy hot rolled steel strip, nitric acid aqueous solution was used, and for No. 1 to No. 190, anodic electrolysis and cathodic electrolysis were used. electrolytic pickling (HNO _3: 15 wt%, temperature: 65 ° C., a current density: 0.12A / cm ²⁾ performs, also immersion pickling for No.191~No.224 (HNO _3: 15wt%, temperature: (65 ° C, no electrolysis), and then immersed in a nitric acid / hydrofluoric acid aqueous solution for a predetermined time to perform pickling.
The residual degree of scale, the rust state, and the surface roughness Ra after descaling were investigated for reference.

The minimum reduction rate was determined by measuring the thickness reduction of the test piece before and after descaling with a micrometer and calculating from the reduction rate of the portion where the change was the smallest. It was assumed that there was no problem if the minimum reduced meat speed required for descaling was 0.15 μm / min or more.

Since the value obtained by converting the change in weight into the change in sheet thickness from the density of the Fe—Ni-based alloy almost coincided with the average value of the actually measured thickness loss, the average change in thickness was calculated by converting the change in weight into the change in sheet thickness. I asked.

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 wall thinning rate (%) = minimum wall thinning rate ÷ average wall thinning rate × 100 (7) If the uniform wall thinning rate is 60% or more, the dissolution is uniform and the surface is smooth. Yes, the yield was high, and no problem was found.

The degree of residual scale was determined by visually observing the steel strip after pickling, and if the scale was visually observed, "X"; if observed with a magnifying glass of 30 times, "△";
A sample whose scale was not recognized by a magnifying glass of 30 times was designated as “○”, and a case of “○” was judged as having no problem.

The rusting condition was determined by leaving the hot-rolled Fe-Ni alloy steel strip after pickling for 10 days and then visually observing the rusting condition on the surface. 」”, Those that have slightly discolored brown but do not require re-pickling are marked with “△”, those that have strong rust and require re-pickling are marked with “x”. No problem.

Further, a total judgment of the minimum reduced meat speed, the uniform thinning rate, the rusting state and the degree of scale residue is performed, and the minimum reduced meat speed is 0.15 μm / min or more, the uniform thinning rate is 60% or more, A sample having no problem with the situation and the degree of scale retention was judged as “○”, and a sample that did not reach at least one of the evaluation items was judged as “×”.

In the case of performing nitric acid hydrofluoric acid pickling after performing electrolytic pickling in a nitric acid aqueous solution, the minimum reduced meat rate, average thinning rate, uniform thinning rate, and rusting condition for each nitric hydrofluoric acid pickling condition. Tables 1 to 7 show the results of the investigation of the surface roughness Ra and the degree of residual scale, and the results of the comprehensive judgment.

Table 8 also shows the results of the same investigation in the case of performing immersion pickling with a nitric acid aqueous solution and then performing nitric hydrofluoric acid pickling.

In Tables 1 to 8, the A value described in the column of nitric hydrofluoric acid conditions is a value calculated by the following equation (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, the invention examples satisfying the range of the present invention have the minimum reduction rate of 0.15 μm / min or more and the uniform reduction rate of 6
At 0% or more, rust and residual scale are at a level that does not cause any problem, and it can be seen that the overall judgment is “O”.

Incidentally, as seen in No. 188, the surface roughness
Even if Ra is about 17 μm, the effects of the present invention can be obtained.

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

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

Further, even when the concentration of hydrofluoric acid, the concentration of nitric acid, and the liquid temperature at which a sufficient minimum meat reduction rate can be obtained, the value A indicating the relationship between the concentrations of hydrofluoric acid and nitric acid obtained from the above equation (7) is 0. If the relationship between hydrofluoric acid and nitric acid concentration does not satisfy the following equation (8), or if the liquid temperature exceeds 65 ° C, the uniform thinning rate
Less than 60%.

Y ≦ 1/2 × (x−1.8) ² +12 (8) x: concentration of hydrofluoric acid, y: concentration of nitric acid If hydrofluoric acid exceeds 5.9 wt%, the steel after pickling and descaling is used. Severe rust occurred on the band.

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

In this embodiment, since the conditions of the nitric acid washing after the shot blasting are within the range of the nitric acid washing conditions of the present invention, the secondary scale residual area ratio after the nitric acid washing is 10%. Since the amount of secondary scale peeling was increased below, the amount of secondary scale brought into the aqueous nitric hydrofluoric acid solution was small, and the deterioration of the aqueous nitric hydrofluoric acid solution was small.

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

[0099]

As described above, according to the descaling method of the Fe-Ni-based alloy hot-rolled steel strip of the present invention, there are provided many industrially useful effects as described below.

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

Since the steel strip after descaling has good smoothness, unevenness in gloss after cold rolling and poor etching during etching can be reduced. In addition, since it is not based on mechanical grinding, there is no occurrence of defects observed after cold rolling or etching, which are caused by abrasive grains observed in mechanical grinding.

Since descaling is performed by uniform dissolution, descaling can be completed with a minimum amount of thinning. Therefore, since an excessive pickling allowance is not required, a high yield can be obtained at the time of descaling. In addition, the deterioration of the processing liquid is reduced, and the consumption amount of the processing liquid and the waste liquid processing amount can be reduced, so that the descaling cost can be reduced.

Since the descaling process is performed in consideration of the minimum speed of meat which controls the descaling operation, the descaling process can be performed efficiently. In addition, scale residue after descaling hardly occurs.

Since the use of expensive hydrofluoric acid can be reduced,
The chemical used is inexpensive. In addition, since the scale deposited in the pickling tank is not dissolved, deterioration and consumption of the chemical can be reduced.

Since a treatment solution containing no chlor ions is used, no pitting or rust is generated on the stainless steel strip, so that it can be shared with the descaling treatment of the stainless steel strip.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of the concentrations of hydrofluoric acid and nitric acid in an aqueous solution of nitric hydrofluoric acid on the minimum thickness reduction rate and the uniform thickness reduction rate in an Fe—Ni alloy hot-rolled steel strip.

FIG. 2 is a graph showing the influence of the concentrations of hydrofluoric acid and nitric acid in an aqueous solution of nitric hydrofluoric acid on the average rate of wall thinning in a hot-rolled steel strip of an Fe—Ni alloy.

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

FIG. 4 is a view showing the effect of the concentrations of hydrofluoric acid and nitric acid in an aqueous solution of nitric hydrofluoric acid on the uniform thinning rate in a hot-rolled steel strip of an Fe-Ni-based alloy.

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

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

FIG. 7 is a graph showing the effect of the concentrations of hydrofluoric acid and nitric acid in an aqueous nitric hydrofluoric acid solution on the minimum reduced wall speed in a hot-rolled stainless steel strip.

FIG. 8 is a graph showing the influence of the concentrations of hydrofluoric acid and nitric acid in an aqueous nitric hydrofluoric acid solution on the uniform thinning rate in a hot-rolled stainless steel strip.

Continuing on the front page (72) Inventor Toru Inazumi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Hiroshi Wada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock Inside the company (72) Inventor Tetsuo Sakiyama 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Pipe Co., Ltd. (72) Inventor Toshio Takano 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Pipe Co., Ltd.

Claims (4)

[Claims] When descaling a hot-rolled steel strip of an Fe-Ni-based alloy, the hot-rolled steel strip of the Fe-Ni-based alloy is subjected to a mechanical descaling treatment and then subjected to a nitric acid concentration of 10 wt% to 20 wt% and a liquid temperature of After immersion in an aqueous solution of nitric acid at 45 ° C or more and 80 ° C or less, the relationship between the concentration of hydrofluoric acid and nitric acid satisfies the following formula (1) when the concentration of hydrofluoric acid is 2.0% by weight or more and 5.9% by weight or less, and A method for descaling a hot-rolled steel strip of an Fe-Ni-based alloy, which is immersed in an aqueous solution of nitric hydrofluoric acid at a temperature of 40 ° C to 65 ° C for 65 seconds or more and pickled. y ≦ 1/2 × (x−1.8) ² +12 ・ ・ ・ (1) where x: hydrofluoric acid concentration (wt%), y: nitric acid concentration (wt%) 2. The descaling of the Fe-Ni alloy hot-rolled steel strip is performed after the mechanical descaling of the Fe-Ni alloy hot-rolled steel strip, and the nitric acid concentration is 10 wt% or more and 20 wt% or less. Current density in aqueous nitric acid solution between 45 ° C and 80 ° C
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 The relationship satisfies the following formula (2) and is characterized by immersing in a nitric hydrofluoric acid aqueous solution at a liquid temperature of 40 ° C or more and 65 ° C or less for 65 seconds or more and pickling.
A method for descaling 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 a treatment in which one or more kinds selected from shot blasting, scale breaker, rolling at a low rolling ratio or brush grinding with abrasive grains are combined. 3. The descaling method for a Fe-Ni-based alloy hot-rolled steel strip according to claim 1, wherein 4. The Fe-Ni material according to claim 1, wherein the mechanical descaling is performed by shot blasting with a projection density of 30 kgf / m ² or more.
For descaling hot rolled steel strips based on aluminum alloys.