JP3491432B2 - Manufacturing method of austenitic stainless steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an austenitic stainless steel sheet having improved surface quality, and
For details, refer to No. A hot-rolled annealed pickling plate (hereinafter, cold-rolled mother plate) having less color tone unevenness when finished into a 2B or BA plate or the like.

[0002]

2. Description of the Related Art No. Since the 2B and BA plates have a beautiful surface and have excellent corrosion resistance, they are often used as an exterior material without being peeled off. In such applications, it is important that the steel sheet has a uniform color tone and no pattern. However, in an austenitic stainless steel sheet, it is difficult to obtain a uniform color tone, and in particular, a portion having a high whiteness and a portion having a low whiteness appear alternately in the width direction to form a striped pattern. The cause of this striped pattern is not always clear, but No. It is considered that the striped pattern of the 2B or BA plate having a high whiteness is a region having many fine surface defects of the cold-rolled mother plate. Until Ra ≦ 0.2 μm as disclosed in JP-A-23001, or in JP-A-57-
As disclosed in Japanese Patent No. 356887, the whiteness is 70
Surface defects are reduced to ± 2. However, in the former technique, it is disclosed that a grinder process is added in order to reduce Ra. However, seizure of the grinder or the surface significantly hardened by the grinder causes cracks during cold rolling, which causes another problem. Since patterns are often generated, sufficient effects cannot be obtained as measures against patterns. On the other hand, in the latter technique, in order to increase the whiteness, it is disclosed that the concentration of acid is increased or the pickling time is lengthened.However, when the concentration of acid is increased, the acid after rinsing is increased. The (acid) pattern is often generated due to the residual, and a sufficient effect cannot be obtained as a pattern countermeasure. Further, even if the pickling time is increased with a normal pickling solution, the unevenness of the surface is not necessarily reduced, only the plate thickness is reduced, and a sufficient effect cannot be obtained as a pattern countermeasure.

[0003]

In view of the above situation, the present invention does not require a post-process such as surface grinding or dissolution of the surface by nitric hydrofluoric acid pickling with a high hydrofluoric acid concentration, and No. 2B, B
It is an object of the present invention to provide a cold-rolled mother board having a small unevenness in color tone when finished into a board A or the like.

[0004]

[Means for Solving the Problems] First, based on the above-mentioned findings, the inventors of the present invention have found that the surface defects of the cold-rolled mother board and the No.
The relationship between the surface defects of the 2B plate was examined. As a result, the surface of the cold-rolled mother plate has a large number of recesses having a depth of about 10 μm. It was found that even the 2B plate remains, and the portion with many defects has diffused light and has high whiteness. Further, the inventors of the present invention have found that the density of surface defects of the cold-rolled mother board and the number of the surface defects of No. As a result of investigating the relationship of the color tone of the 2B plate, the density of surface defects of the cold rolled mother plate is J
Whiteness L of the cold rolled mother board measured according to ISB8729
It can be sorted out well with ^* , and if the difference in whiteness of the cold-rolled mother plate is set to 5 or less, No. It was discovered that the 2B plate did not cause uneven color tone.

Next, the present inventors have examined the cause of the occurrence of surface defects in the cold rolled mother plate. As a result, it was found that most of the surface defects of the cold-rolled base plate already existed in the state of the hot-rolled plate, and the surface defects of the hot-rolled plate were due to the biting of the scale during hot rolling. . Furthermore, the present inventors have examined the mechanism of occurrence of biting of the scale during hot rolling. As a result, in austenitic stainless steel, a wedge-shaped scale significantly develops during slab heating, so even if the descaling process in which high-pressure water is sprayed before rolling is performed, the scale partially remains, and the remaining scale remains. It was found that a striped surface defect extending in the rolling direction was generated by biting during rolling.

Therefore, the present inventors have studied a method for preventing the scale from being caught during hot rolling of austenitic stainless steel. As a result, descaling was performed on slabs of SUS304 heated at various temperatures and for various impact pressures, and the residual rate of the scale generated during heating was investigated. As shown in FIGS.
℃ or less, heating time is 4h or less, collision pressure is 25kgf
It was discovered that the descaling rate of / cm ² or more significantly reduces the residual rate of the scale. Then, as a result of producing a hot-rolled sheet under these conditions and performing pickling, it became possible to produce a cold-rolled mother sheet in which biting of the scale was hardly observed. In such a cold-rolled mother board, the difference between the maximum and minimum whiteness in the width direction of the steel strip, which is a parameter representing the density of surface defects, is 5 or less. Further, since such a cold rolled mother plate is not pickled with a grinder or a high concentration of acid, an extremely uniform color tone can be obtained.

The present invention has been completed based on the above findings. The present invention is the maximum and the minimum difference of 5 or less der Luo austenitic stainless steel to techniques whiteness of the width direction of the steel strip. In the present invention, the whiteness is the whiteness L ^* of the cold-rolled mother board measured according to JIS B8729.

Further, according to the present invention, C: 0.005 to 0.1 wt%, Si: 0.05 to 0.5 wt% Mn: 0.1 to 1.5 wt%, P: ≦ 0.06 wt%, S : 0.003 to 0.01 wt%, Sol. Al: ≤ 0.005 wt%, Cr: 12 to 30 wt%, Ni: 5 to 20 wt%, N: 0.005 to 0.1 wt%, with the balance being Fe and inevitable impurities, and associated with the maximum and minimum difference is 5 or less der Luo austenitic stainless steel of whiteness in the width direction of the steel strip
To do .

[0009] The austenitic stainless steel sheet, further the following (A), (B), Ru also because Ah <br/> containing 1 or 2 or more selected from the group consisting of (C) as components. (A) Mo: 0.1-5 wt%, W: 0.1-5 wt%
1 type or 2 types or more of (B) Ti: 0.01 to 0.5 wt% (C) Cu: 0.1 to 1.5 wt% In the present invention, the slab heating temperature: 1100 to 1200 ° C., the slab heating time: 1-4 hours, collision pressure: 25 kgf / cm ²
Austenite characterized in that the difference between the maximum and the minimum whiteness in the width direction of the steel strip produced by pickling after performing hot rolling characterized by the above-mentioned ultrahigh pressure descaling treatment is 5 or less. It is a manufacturing method of a stainless steel plate.

In the present invention, the collision pressure means the pressure of water actually colliding with the steel plate, and can be measured by inserting a pressure sensor at the actual position of the steel plate. Further, according to the present invention, C: 0.005-0.1 wt%, Si: 0.05-0.5 wt% Mn: 0.1-1.5 wt%, P: ≤ 0.06 wt%, S: 0. 0.003-0.01 wt%, Sol. Al: ≤ 0.005 wt%, Cr: 12 to 30 wt%, Ni: 5 to 20 wt%, N: 0.005 to 0.1 wt%, with the balance being Fe and inevitable impurities, Slab heating temperature: 1100 to 1200 ° C., slab heating time: 1 to 4 h, collision pressure: 25 kgf / cm ^2.
An austenitic system characterized in that the difference between the maximum and minimum whiteness in the width direction of the steel strip produced by pickling after hot rolling characterized by the above-mentioned ultra-high pressure descaling treatment is 5 or less. A method for manufacturing a stainless steel plate is provided.

Also in this case, it is preferable to further contain one or more selected from the group consisting of the following (A), (B) and (C) as a component. (A) Mo: 0.1-5 wt%, W: 0.1-5 wt%
1 or 2 or more of (B) Ti: 0.01 to 0.5 wt% (C) Cu: 0.1 to 1.5 wt% Next, the reasons for limitation of the present invention will be described.

C: C is a strong austenitizing element and is added in an amount of 0.005 wt% or more. If it exceeds 0.1 wt%, blowholes tend to occur during welding. Therefore, in the present invention, it is set to 0.005 to 0.1 wt%. Si: Si is added at 0.05 wt% or more as a deoxidizing agent during melting. In Figure 5, 0.05wt% C-1.0wt%
Mn-0.03 wt% P-0.04 wt% S-0.00
2 wt% Al-18 wt% Cr-8.3 wt% Ni-
By changing the amount of Si based on 0.03 wt% N-0.3 wt% Cu, the SUS304 slab is heated at 1150 ° C. for 4 hours in a coke gas combustion atmosphere to obtain 30 kgf / c.
The results of investigating the residual rate of the heating scale when descaling with the collision pressure of m ² are shown. The amount of Si added is 0.5
When it exceeds wt%, descaling during hot rolling becomes extremely difficult. Therefore, Si is limited to 0.05 to 0.5 wt%.

Mn: Mn is added in an amount of 0.1 wt% or more in order to stabilize austenite and fix S to improve hot workability. In Figure 6, 0.05w
t% C-0.5 wt% Si-0.03 wt% P-0.0
04wt% S-0.002wt% Al-18wt% Cr
-8.3 wt% Ni-0.03 wt% N-0.3 wt%
A SUS304 slab in which the amount of Mn was changed based on Cu was heated at 1150 ° C. for 4 hours in a coke gas combustion atmosphere, and the residual ratio of the heating scale when descaling at a collision pressure of 35 kgf / cm ² was investigated. Indicated. M
If the added amount of n exceeds 1.5 wt%, descaling during hot rolling becomes extremely difficult. Therefore, Mn is 0.1 to
It is set to 1.5 wt%.

P: P is an element that reduces corrosion resistance,
It is desirable to have few. However, it is technically difficult and economically disadvantageous to reduce the amount extremely, so that the upper limit is set to 0.06 wt% in the present invention. S: S is an element that reduces hot working and corrosion resistance, and it is desirable that S is small. In Figure 7, 0.05wt
% C-0.5 wt% Si-1.0 wt% Mn-0.03
wt% P-0.002 wt% Al-18 wt% Cr-
8.3 wt% Ni-0.03 wt% N-0.3 wt% C
A SUS304 slab in which the amount of S is changed based on u is heated at 1150 ° C. for 4 hours in a coke gas combustion atmosphere,
The results of investigating the residual rate of the heating scale when descaling with a collision pressure of 40 kgf / cm ² are shown. If S is less than 0.003 wt%, descaling during hot rolling becomes extremely difficult. Therefore, in the present invention, 0.0
It was set to 03 to 0.01 wt%.

Sol. Al: Al is added as a deoxidizing agent when necessary during melting. However, 0.05 wt% C
-0.5 wt% Si-1.0 wt% Mn-0.03 wt
% P-0.003 wt% S-18 wt% Cr-8.3w
t% Ni-0.03 wt% N-0.3 wt% A SUS304 slab with an Al amount varied based on Cu was heated at 1150 ° C. for 4 h in a coke gas combustion atmosphere, and 30 k
As shown in FIG. 8 in which the residual rate of the heating scale when descaling with a collision pressure of gf / cm ² was investigated, when the addition amount exceeds 0.005 wt%, descaling during hot rolling becomes extremely difficult. Therefore, in the present invention, the upper limit is set to 0.005 wt%.

Cr: Cr is an element that improves corrosion resistance and oxidation resistance, and is added to stainless steel at 12 wt% or more. However, if the added amount exceeds 30 wt%, the steel tends to become brittle. Therefore, in the present invention, it is set to 12 to 30 wt%. Ni: Ni is an element that stabilizes austenite and improves toughness and corrosion resistance, and is added in an amount of 5 wt% or more. However, even if the added amount exceeds 20 wt%,
These effects saturate. Therefore, in the present invention, 5-2
It was set to 0 wt%.

One or two kinds of Mo and W: Mo and W are elements for improving corrosion resistance, and each is 0.1 wt%.
The above is added. However, the amount added is 5w each
If it exceeds t%, there is a problem that the steel is apt to become brittle. Therefore, in the present invention, it is set to 0.1 to 5 wt%. Ti: Ti is added in an amount of 0.01 wt% or more in order to suppress the generation of Cr carbonitride in the heat-affected zone of welding and to improve the intergranular corrosion susceptibility of the heat-affected zone of welding. However, if the addition amount exceeds 0.5 wt%, large inclusions are generated and the toughness is significantly deteriorated. Therefore, in the present invention, 0.01
˜0.5 wt%.

Cu: Cu is an element that stabilizes austenite and improves corrosion resistance, and is 0.1 wt.
% Or more is added. However, the amount added is 1.5 wt%
If it exceeds, a low melting point phase is generated at high temperature and hot workability is deteriorated. Therefore, in the present invention, it is set to 0.1 to 0.5 wt%.

Slab heating temperature, heating time: In austenitic stainless steel, the scale grows in a wedge shape during slab heating and the descaling property is extremely poor. In order to suppress the growth of this scale and improve the descaling property during hot rolling, it is necessary to set the slab heating temperature to 1200 ° C. or less and the heating time to 4 h or less. However, if the heating temperature is lower than 1100 ° C. and the heating time is shorter than 1 h, the deformation resistance becomes large and hot rolling becomes difficult. Therefore, in the present invention, the slab heating temperature is set to 1100 to 1200.
The slab heating time was 1 to 4 hours.

Ultra-high pressure descaling: In austenitic stainless steel, the scale grows in a wedge shape during slab heating, and the descaling property is extremely poor. Therefore, even when the chemical composition, slab heating temperature, and heating time are limited as in the present invention, ultrahigh pressure descaling with a collision pressure of 25 kgf / cm ² or more is required to remove the scale generated during slab heating. Is. Therefore, in the present invention, the collision pressure is set to 25 kgf / cm ² or more.

Whiteness: The whiteness of the cold-rolled mother plate is a parameter indicating the density of surface defects, and the larger the whiteness, the smaller the number of defects. If the difference between the maximum and minimum whiteness in the width direction of the steel strip is 5 or less, cold rolling of 30% or more is performed, and No. Two
D, No. No color difference is visually observed when the 2B or BA plate is finished. Therefore, in the present invention, the difference in whiteness is limited to 5 or less.

[0022]

DETAILED DESCRIPTION OF THE INVENTION

Example-1 The present invention will be described below based on examples. Austenitic stainless steels having the chemical composition shown in Table 1
It was melted by a normal converter method and continuously cast into a slab having a thickness of 200 mm.

This slab was heated in a slab heating furnace in a coke gas combustion atmosphere at the heating temperature and heating time shown in Table 1 and then extracted. Immediately before rough rolling, the collision pressure shown in Table 1 was extracted. Descaling is performed using high-pressure water that causes heat, rough rolling and finish rolling are performed, and the winding temperature is 650 ° C.
Was finished into a hot-rolled steel sheet having a thickness of 4 mm. About this hot rolled steel sheet, in a continuous annealing furnace, in a coke gas combustion atmosphere,
After annealing at 50 ° C. for 30 seconds and preliminary descaling treatment by shot blasting, soaking in 24% sulfuric acid at 80 ° C. for 30 seconds, mixed acid of 15% nitric acid and 3% hydrofluoric acid at 60 ° C. for 30 seconds, After finishing the cold rolled mother plate, the difference between the maximum and minimum whiteness in the coil was investigated. The results are also shown in Table 1.

With respect to this cold-rolled mother board, the roll diameter is 250.
In a coke gas combustion atmosphere, after finishing the cold-rolled sheet having a thickness of 1.5 mm with a tandem rolling mill of 1.5 mm and degreasing,
Annealed at 100 ° C. for 30 sec, 20% Na ₂ SO
₄ Electrolyze at 50 ° C (coulomb) / dm ^{2 in} an aqueous solution at 80 ° C and mix with 5% nitric acid and 3% hydrofluoric acid at 50 ° C for 30
dip for sec and 40 C / dm ² at 50 ° C in 10% nitric acid
No. The 2B plate was finished and the occurrence of color unevenness was visually inspected. The results are also shown in Table 1.

Sample No. of the embodiment within the scope of the present invention. 1
In the cold-rolled mother board of No. 9 to No. Although the unevenness of color tone could not be visually confirmed when finished to the 2B plate, the sample No. of the comparative example in which the chemical composition was deviated. Sample Nos. 10 to 13 and heating temperatures deviating from each other. 14, sample N with the heating time off
o. Sample No. 15 with collision pressure removed No. 16 cold-rolled mother board is When the 2B plate was finished, uneven color tone was visually confirmed.

Example-2 Austenitic stainless steels having the chemical components shown in Table 2 were melted by a normal converter method and continuously cast into a slab having a thickness of 200 mm. This slab was heated in a slab heating furnace in a coke gas combustion atmosphere at the heating temperature and heating time shown in Table 2, extracted, and immediately before rough rolling at a normal collision pressure of 4 kgf / cm ^2. After descaling and rough rolling, and immediately before finish rolling, Table 2
Descaling was performed with the collision pressure shown in (1) and finish rolling was performed to finish a hot-rolled steel sheet having a sheet thickness of 4 mm at a winding temperature of 650 ° C.

This hot-rolled steel sheet was subjected to preliminary descaling treatment by shot blasting and then in 24% sulfuric acid at 80 ° C.
40 seconds at 60 ° C in a mixed acid of 15% nitric acid and 3% hydrofluoric acid
After immersing for 40 seconds in the cold rolled base plate, the difference between the maximum and minimum whiteness in the coil was investigated. The results are also shown in Table 2. The cold-rolled mother plate was finished by a Zenzimer rolling machine having a roll diameter of 70 mm to a cold-rolled plate having a thickness of 0.8 mm, and degreased.
The BA plate was finished by annealing at 30 ° C. for 30 seconds, and the occurrence of uneven color tone was visually inspected. The results are also shown in Table 2.

Sample No. within the scope of the present invention. 21-29
In the cold-rolled mother plate of No. 3, when the BA plate was finished, the unevenness of the color tone could not be visually observed, whereas the sample N in which the chemical components were removed
o. 30 to 33, sample No. with heating temperature deviated. Three
4, sample No. with heating time deviated 35, the sample No. with the collision pressure removed. Regarding the cold-rolled mother board of No. 36, color unevenness was visually confirmed when finished as a BA board.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

EFFECT OF THE INVENTION By using the austenitic stainless steel cold-rolled mother plate of the present invention, No. 1 having a uniform color tone can be obtained without using a grinder or a high-concentration acid. 2B, BA plate, etc. can be obtained. Further, No. 1 using the cold rolled mother plate of the present invention. 2B, B
Since the A plate has few surface defects, it has excellent polishing properties and high gloss.

[Brief description of drawings]

FIG. 1 is a diagram in which the residual rate of the scale generated during heating when descaling is performed on a SUS304 slab heated at various temperatures and times at a collision pressure of 30 kgf / cm ² is investigated.

FIG. 2 is a diagram in which the residual rate of scale produced during heating when descaling was performed on a SUS304 slab heated at various temperatures and for various times at a collision pressure of 25 kgf / cm ² .

FIG. 3 is a diagram in which the residual rate of the scale generated during heating was investigated when descaling was performed on a SUS304 slab heated at various temperatures and times at a collision pressure of 20 kgf / cm ² .

FIG. 4 is a diagram in which the residual rate of the scale generated during heating was investigated when descaling was performed on a SUS304 slab heated at various temperatures and times at a collision pressure of 5 kgf / cm ² .

FIG. 5: 0.05 wt% C-1.0 wt% Mn-0.0
3 wt% P-0.04 wt% S-0.002 wt% Al
-18wt% Cr-8.3wt% Ni-0.03wt%
S based on N-0.3wt% Cu and varying the amount of Si
US304 slab in coke gas combustion atmosphere 11
It is the graph which investigated the residual rate of the heating scale when it heated at 50 degreeC for 4 hours, and was descaled by the collision pressure of 30 kgf / cm < ² >.

FIG. 6 0.05 wt% C-0.5 wt% Si-0.0
3 wt% P-0.004 wt% S-0.002 wt% A
1-18 wt% Cr-8.3 wt% Ni-0.03 wt
% N-0.3 wt% Cu based slab of SUS304 with varying Mn content in coke gas combustion atmosphere 1
It is the graph which investigated the residual rate of the heating scale when it heated at 150 degreeC for 4 hours, and descaled by the collision pressure of 35 kgf / cm < ² >.

FIG. 7: 0.05 wt% C-0.5 wt% Si-1.0
wt% Mn-0.03 wt% P-0.002 wt% Al
-18wt% Cr-8.3wt% Ni-0.03wt%
SU with varying S content based on N-0.3 wt% Cu
115 S304 slab in coke gas combustion atmosphere
It is the graph which investigated the residual rate of the heating scale at the time of descaling with the collision pressure of 40 kgf / cm < ² > after heating at 0 degreeC for 4 hours.

FIG. 8: 0.05 wt% C-0.5 wt% Si-1.0
wt% Mn-0.03 wt% P-0.003 wt% S-
18 wt% Cr-8.3 wt% Ni-0.03 wt% N
SU with varying Al content based on -0.3 wt% Cu
115 S304 slab in coke gas combustion atmosphere
It is a graph which investigated the residual rate of the heating scale when it heated at 0 degreeC for 4 hours, and was descaled by the collision pressure of 30 kgf / cm < ² >.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI C22C 38/50 C22C 38/50 C23G 1/08 C23G 1/08 (56) Reference JP-A-6-304606 (JP, A) JP-A-4-168227 (JP, A) JP-A-57-35687 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/46 B21B 3/02 B21B 45/08 C23G 1/08 C22C 38/00 302

Claims (3)

(57) [Claims] 1. Slab heating temperature: 1100 to 1200
C, slab heating time: 1 to 4 h, collision pressure: 25 kgf /
Heat characterized by ultra-high pressure descaling of cm ² or more
A method for producing an austenitic stainless steel sheet , wherein the difference between the maximum and minimum whiteness in the width direction of the steel strip produced by performing pickling and pickling is 5 or less. 2. C: 0.005-0.1 wt%, Si: 0.05-0.5 wt% Mn: 0.1-1.5 wt%, P: ≤ 0.06 wt%, S: 0.003 ~ 0.01 wt%, Sol. Al: ≤ 0.005 wt%, Cr: 12 to 30 wt%, Ni: 5 to 20 wt%, N: 0.005 to 0.1 wt%, with the balance being Fe and inevitable impurities, Slab heating temperature: 1100 to 1200 ° C, slab
Lab heating time: 1 to 4 h, collision pressure: 25 kgf / cm ²
Hot rolling featuring the above-mentioned ultra-high pressure descaling
The method for producing an austenitic stainless steel sheet is characterized in that the difference between the maximum and minimum whiteness in the width direction of the steel strip produced by pickling and then pickling is 5 or less. 3. The following components (A),
The method for producing an austenitic stainless steel sheet according to claim 2, further comprising 1 or 2 or more selected from the group consisting of (B) and (C). (A) Mo: 0.1 to 5 wt%, W: 0.1 to 5 wt%, one or more types (B) Ti: 0.01 to 0.5 wt% (C) Cu: 0.1 to 1 0.5 wt%