JP2002241843A - Method for producing ferritic stainless steel sheet having excellent surface gloss and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a ferritic stainless steel sheet which has an excellent surface gloss by stably and uniformly forming roll coating thereon without causing the increase of its cost. SOLUTION: A ferritic stainless hot rolled steel sheet is annealed, and is hereafter pickled to control loss on pickling including descaling to >=14 g/m2. Next, the steel sheet is subjected to cold rolling so that the draft per pass is >=10%, and the total draft is >=50%. The ferritic stainless hot rolled steel sheet has a composition containing, by mass, <=0.100% C, <=1.5% Mn, <=1.5% Si, <=0.030% S, <=0.04% P, <=0.050% N and 14.0 to 25.0% Cr, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferritic stainless steel sheet, and more particularly to a method for producing a ferritic stainless steel sheet having excellent surface gloss at low cost and stably. .

[0002]

2. Description of the Related Art Ferritic stainless steel is superior to austenitic stainless steel in stress corrosion cracking resistance and design, and is inexpensive. Widely used mainly in the fields that are used.

For this reason, ferrite stainless steel has been devised in various ways in order to obtain a high gloss. For example, in order to remove surface irregularities generated during pickling of hot-rolled steel sheets and flaws before hot rolling, a coil grinder (CG)
Is performed to smooth the surface and obtain uniformity of gloss after cold rolling, but the cost increases by the coil grinder process, so that the process can be omitted. There is a demand for the establishment of manufacturing technology.

[0004] In Japanese Patent No. 2960646, after performing a hot rough rolling process in which a friction coefficient in a final pass is set to 0.30 or less and a rolling reduction is 40% or more, hot finishing rolling is performed, and then annealing, After pickling, surface roughness (Ra) is 0.4 μm
A method of producing a ferritic stainless steel having excellent surface properties by performing skin pass rolling with a rolling reduction of 10 to 15% using the following rolls has been proposed.

[0005] However, the above-mentioned existing method is effective for general SUS430 steel, but has a high workability, high-temperature oxidation resistance, and excellent corrosion resistance to which a stabilizing element such as Ti or Nb is added. In stainless steel, streak-like unevenness often occurs, and it is not always possible to stably obtain a product having excellent surface gloss.

Further, as a conventional knowledge regarding the production of ferritic stainless steel having excellent gloss, Japanese Patent Publication No. 7-122149 discloses pickling. After the pickling step of a hot-rolled steel sheet is completed, it is further subjected to atmospheric annealing. , At least 0.4 μ on the surface
A method has been introduced in which an oxide scale having a thickness of m is formed and a step of removing the scale by pickling is added, but the production cost is increased by performing the pickling step twice. Furthermore, regarding cold rolling,
Japanese Patent Application Laid-Open No. 11-244911 proposes a method in which the center line roughness of a work roll at the time of cold rolling is set to 0.8 μm or less, and the work roll roughness at the time of skin pass is set to less than that. If the roughness of the work roll is finer than necessary, in the initial stage of cold rolling, rolling oil will be encapsulated in the irregularities generated on the surface by pickling of the hot-rolled steel sheet,
Since it becomes uneven and remains until the end, it is not necessarily effective.

[0007] Recent studies have revealed that the formation of roll coating by rolling is an essential condition in order to obtain ferritic stainless steel having a high gloss surface. Here, "roll coating" is presumed to be generated because the rolling wear powder generated from the rolled material during cold rolling adheres to the surface of the rolling roll. The rolled abrasion powder is mainly composed of Cr oxide, and the thickness of the roll coating is about several tens Onm. When the roll wear powder mainly composed of Cr oxide uniformly adheres to the roll surface, the roll surface during cold rolling becomes smoother than as polished roll, so the smoothness of the rolled material is also improved, and the surface gloss is excellent. It is believed that a product can be obtained.

As described above, it is clear that roll coating is a necessary condition for obtaining high gloss, and various reports have been made on this point. Japanese Patent Application Laid-Open No. 8-117805 proposes a method in which a roll coating is previously formed on a work roll used for cold rolling by pre-rolling, and then rolling is performed. Requires extra cost. In addition, this method proposes a method of generating a roll coating and using a rolling roll, and does not disclose manufacturing conditions for stably and uniformly generating a roll coating.

Further, in Japanese Patent Application Laid-Open No. 8-225794,
A method has been proposed in which roll coating is generated at an early stage and a stainless steel sheet with excellent luster is produced.In this method, a special rolling oil is used.
Since pH adjustment is an essential condition, a special rolling oil circulation and supply system is required, which increases costs.

[0010]

As described above, in the prior art, a method capable of stably and uniformly producing a roll coating without increasing the cost, particularly stabilizing elements such as Ti and Nb. No method has been established for producing a high-purity ferritic steel having excellent surface gloss in high-purity ferritic steel containing excellent workability.

Here, an object of the present invention is to provide a method capable of stably and uniformly producing a roll coating without increasing the cost, thereby producing a ferritic stainless steel excellent in surface gloss. It is to be.

[0012]

Means for Solving the Problems The present inventors have made intensive studies on the production of roll coatings in order to develop a method for more stable production.

First, as in the prior art, an attempt was made to improve the gloss by changing the work roll roughness and the work roll diameter in cold rolling. However, even under the same cold rolling conditions, high gloss by roll coating was attempted. In some cases, high-purity ferritic stainless steel containing stabilizing elements such as Ti and Nb often causes gloss unevenness. It was concluded that high gloss was not stably obtained.

[0014] Therefore, the present invention was examined in relation to the pickling conditions in the pickling process of a hot-rolled steel sheet, which is a pre-process of cold rolling, and the following findings (a) to (c) were obtained. And found that a ferritic stainless steel having excellent surface gloss was obtained, and completed the present invention.

(A) In the annealing and pickling of a hot-rolled steel sheet, the hot-rolled steel sheet is formed during hot rolling and in the annealing process of the hot-rolled steel sheet without using a grinding brush between pickling tanks used as an auxiliary means for descaling. In order to completely remove the scale thus produced, a certain amount of dissolution by the pickling treatment is required.

(B) There is an appropriate range for producing the roll coating in the cold rolling conditions. (c) By performing pickling and cold rolling under these conditions, it is possible to stably generate uniform roll coating even on high-purity steel ferritic stainless steel containing stabilizing elements such as Ti and Nb. Is possible. In particular, even when the CG process is omitted, it is possible to stably generate a uniform roll coating.

Here, the present invention is as follows. (1) After annealing a hot-rolled ferritic stainless steel sheet, it is pickled, and the pickling loss including descaling is reduced to 14 g / m ^2.
And then the rolling reduction per pass is 10% or more,
A method for producing a ferritic stainless steel sheet having excellent surface gloss, characterized in that roll rolling is stably generated by performing cold rolling at a total draft of 50% or more.

(2) The steel composition of the hot rolled ferritic stainless steel sheet is, by mass%, C: 0.100% or less, Mn: 1.5% or less, Si: 1.5% or less, S: 0.030% or less, P: 0.04%. Less than,
N: 0.050% or less, Cr: 14.0 to 25.0%, balance being Fe and unavoidable impurities, the process for producing a ferritic stainless steel sheet having excellent surface gloss as described in the above item (1).

(3) The steel composition further comprises: Mo: 0.5 to 2.5
%, Cu: 1.5% or less, Ni: 1.00% or less, Nb: 0.1 to 1.0
%, Ti: 0.03-0.15%, V: 1.0% or less, Zr: 0.3% or less,
(2) The method for producing a ferritic stainless steel sheet having excellent surface gloss as described in (2) above, which contains one or more of W: 1.0% or less, Al: 0.2% or less, and O: 0.01% or less.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the reasons for limiting the respective processing conditions and steel compositions as described above in the present invention will be explained. In this specification, “%” indicating the steel composition is “% by mass” unless otherwise specified.

According to the present invention, a ferritic stainless steel having a predetermined steel composition is formed into a hot-rolled steel sheet through melting, casting, and rolling. Cold rolled steel sheet is manufactured.

Pickling conditions for hot-rolled steel sheet The hot-rolled steel sheet is pickled before cold rolling. However, in order to obtain a desired roll coating, the dissolution amount is ≧ 14 g / m ² . Roll coating may not be stably generated under the pickling conditions that do not satisfy this. Preferably, the amount dissolved by pickling is 15 g / m ² or more. The upper limit is not particularly limited, but is preferably as small as possible in consideration of the yield. Therefore, in a preferred embodiment, it is 25 g / m ² or less.

The type of acid used in the pickling treatment is basically an acid obtained by using sulfuric acid, hydrofluoric acid, nitric acid, or hydrochloric acid alone or in combination. However, if the dissolved amount satisfies ≧ 14 g / m ² , another acid is used. There is no problem using. It is also possible to add an appropriate agent such as sulfide to the pickling solution.

Usually, the pickling amount of a hot-rolled steel sheet is related to the sheet passing speed and is at most about 10 g / m ^2, so that a considerable amount of pickling loss is observed in the present invention. In order to obtain such pickling weight loss by continuous treatment, it is necessary to take measures such as acid concentration management.

Cold Rolling Conditions Cold rolling is performed following the pickling treatment. To obtain a desired roll coating, the rolling reduction of each pass is 10%.
And the total draft is 50% or more. Roll coating may not be stably generated under cold rolling conditions that do not satisfy this.

Other Conditions In order to obtain a desired roll coating, the above-mentioned grinding brush between the pickling tanks used as an auxiliary means for descaling at the time of pickling of the hot-rolled sheet can be used without using the above-mentioned grinding brush. As described above, it is preferable to secure a predetermined cutting amount only by the pickling treatment and omit the CG process. This is because roll coating may not be generated stably if a brush between tanks or a CG process is performed as in the related art. Therefore, in a preferred embodiment of the present invention, roll coating can be stably generated by omitting mechanical coil surface grinding with a brush or the like in the CG step or the pickling step.

FIG. 1 is a graph showing the production state of roll coating when the present invention is carried out in Example 1 to be described later by changing the dissolution loss and the rolling reduction per pass, respectively. A circle indicates that the desired roll coating was generated, and a cross indicates that it was not generated.

From the results shown in the figure, it is also possible to obtain a desired roll-roll coating by subjecting a hot-rolled steel sheet having a pickling reduction of 14 g / m ² or more to cold rolling at 10% per pass and a total reduction of 50% or more. It can be seen that it can be generated stably.
In addition, whether or not the roll coating was stably generated was confirmed by visually checking the state of the coating formed on the roll surface when the work roll was replaced after the completion of the rolling.

Composition of Steel Sheet In the present invention, if a ferritic stainless steel is used,
The specific steel composition is not particularly limited, but preferably has the following steel composition.

C: C is an element that hardens the steel, lowers the workability, and deteriorates the corrosion resistance. In order to ensure excellent workability in the present invention, C is set to 0.100% or less. Preferably, 0.08%
It is as follows.

Mn: Mn has a deoxidizing effect on steel and suppresses scale exfoliation at high temperatures, so Mn is contained in a range of 1.5% or less. If it exceeds 1.5%, not only will rusting and pitting occur as starting points, the corrosion resistance will decrease, but also the cost of steel will increase and the economy will be disadvantageous. Typically, 1.2%
The following is sufficient.

Si: Si is a component effective as a deoxidizing agent for steel, and improves the oxidation resistance of steel. However, when the content exceeds 1.5%, the content increases and the workability deteriorates as the addition amount increases. Therefore, the Si content is set to 1.5% or less. Typically, 1.2%
The following is sufficient.

S: Since S becomes a starting point of rusting and pitting and deteriorates corrosion resistance, it is preferable that S is as low as possible. 0.030%
If the content exceeds the limit, the corrosion resistance deteriorates, so the upper limit is 0.030
%. It is preferably at most 0.010%.

P: As much as possible, it is desirable to lower the corrosion resistance and toughness of the steel. If the content exceeds 0.04%, the workability deteriorates, so the P content is set to 0.04% or less.
Cr: Cr is a main component for maintaining corrosion resistance and oxidation resistance. Corrosion resistance and oxidation resistance improve as the Cr content increases. 16% to ensure the desired corrosion and oxidation resistance of steel
The above content is required. If the content exceeds 25%, the manufacturability deteriorates and the cost increases, so the upper limit is set to 25%.

N: Like N, N should be as small as possible in order to increase the strength of steel. From the viewpoint of suppressing the deterioration of workability and corrosion resistance, the upper limit was made O.050%.
Mo: Mo is added to increase the high temperature strength. To exert its effect stably, it is necessary to add 0.5% or more. If added in excess of 2.5%, the strength of the steel increases and the workability deteriorates. Mo is an expensive alloy element, and its upper limit is set to 2.5% from the viewpoint of suppressing cost increase.

Cu: Cu is an essential element for ensuring the workability and high-temperature characteristics of steel, and it is necessary to add Cu and Nb appropriately in accordance with the amounts of Mo and Nb to obtain the effect stably. The optimum addition range will be described later in detail. When Cu is not added, the excellent effect cannot be obtained. On the other hand, if it exceeds 1.5%, not only the effect is saturated, but also the hot workability is deteriorated, which is not preferable. Therefore, the upper limit of Cu
1.5%. The preferred amount of Cu to obtain more stable processing characteristics and high-temperature characteristics is 0.1% or more and 1.3% or less.

Ni: Ni is added as necessary to improve the toughness of the steel. However, if added in excess of 1.00%, the cost of steel will increase, so the upper limit was made 1.00%.

Nb: Nb has the effect of suppressing the precipitation of carbides and nitrides at the crystal grain boundaries and improving the oxidation resistance. Also,
Nb has a great effect of improving high-temperature strength in a solid solution state. These effects are apparent from O.1%, but 1.0%
If the content exceeds 10%, the steel becomes hard, so the upper limit is 1.0%
And

Ti: Ti, like Nb, has the effect of suppressing the precipitation of carbides and nitrides at the crystal grain boundaries and improving the oxidation resistance. This effect becomes apparent from 0.03%. However, if the content exceeds 0.15%, the effect of improving the formability decreases, so the upper limit was made 0.15%.

V: V is effective as a fixing element of C and N like Nb and Ti. However, adding more than 1.0% saturates the effect and only increases the cost.
The content should be 1.0% or less.

W: W, like Nb, is effective as an element for improving high-temperature strength. However, if the content exceeds 1.0%, the effect is saturated and only the cost is increased. Therefore, the content is set to 1.0% or less.

Zr: Effective as a fixing element of C and N, like Nb and Ti. However, if added in a large amount, the material becomes brittle, so the content is set to 0.3% or less. Al: Al has an effect of reducing solid solution N and lowering the yield point to improve workability, and an effect of improving steel toughness. However, if added in excess of 0.2%, the solute Al lowers the toughness and adversely affects the manufacturability.
0.2%.

O: O is included in steel as an unavoidable impurity like C and N. If the O content exceeds 0.01%, workability is significantly impaired, so the O content is set to 0.01% or less.

Next, the operation and effect of the present invention will be described more specifically with reference to examples.

[0045]

EXAMPLES Example 1 A ferritic stainless steel having the composition shown in Table 1 was cast and hot-rolled.
Under the annealing and pickling conditions and cold rolling conditions shown in
Pickling and cold rolling were performed to produce a cold-rolled steel sheet.

The coating conditions of the work rolls at that time were compared. The state of coating of the work roll was confirmed by replacing the stainless steel plate with a new roll every time the rolling of the stainless steel plate was completed, and visually observing the used roll surface. Further, the same material was subjected to finish annealing pickling, and a gloss evaluation was visually performed on a product which had been subjected to skin pass rolling so that the elongation was 0.7% or more.

The results are summarized in Table 3. When the production conditions were within the range of the production conditions according to the present invention, roll coating was formed in all cases, and the obtained ferritic stainless steel sheet had good gloss.

Example 2 A ferritic stainless steel having the composition shown in Table 4 was cast and hot-rolled, and then annealed under annealing pickling conditions and cold rolling conditions shown in Table 5.
Pickling and cold rolling were performed to produce a cold-rolled steel sheet.

The coating conditions of the work rolls at that time were compared. Further, the same material was subjected to finish annealing and pickling, and the product subjected to skin pass rolling so as to have an elongation of 0.7% or more was visually evaluated for gloss.

Table 6 summarizes the results. When the production method according to the present invention was used, roll coating was formed on all the coils, and the gloss was good.

That is, within the production range according to the present invention,
It can be seen that according to the present invention, a roll coating can be stably and uniformly generated in both a component system equivalent to JIS SUS43O and a component system containing a stabilizing element.

Example 3 This example is for evaluating the anisotropy of the elongation of the plate surface and the average elongation of the plate surface. First, 30kg
In a vacuum melting furnace, steel of each component composition shown in Table 7 was melted and cut into a flat steel ingot, a block having a thickness of 45 mm, a width of 140 mm, and a length of 85 mm. Thus, a hot-rolled steel sheet with a thickness of 6.0 mm was obtained. 1000 ° C
After performing descale treatment by shot blasting using alumina spheres, cold rolling was performed from 6.0 mm thickness to 2.0 mm thickness, and recrystallization annealing was performed at 1025 ° C.

Here, in the ferritic stainless steel of the present invention, in order to obtain excellent working characteristics, the anisotropy parameter 伸 び EL (= (EL ₀ + EL ₉₀ ) /
2-EL ₄₅ ) must be 9% or less. When ΔEL exceeds 9%, ductility in processing characteristics is significantly deteriorated. The preferred range of ΔEL is 7% or less.

In order to ensure excellent processing characteristics, the average elongation of the plate surface is preferably as high as possible. In the present invention,
The average plate surface elongation ELs (%) is _{ELs = (EL 0 + EL 90} + 2EL 45)
/ 4 and needs to be at least 27%. ELs 27%
If less than, the ductility is significantly reduced. Preferably ELs
≧ 29%.

Therefore, in this example, the ferrite stainless steel sheet obtained as described above was used to determine the JlS 13B specified in JlS Z 2201 from the rolling direction, the 45 ° rolling direction, and the rolling perpendicular direction of the steel sheet. Collect the test specimen,
Perform a normal temperature tensile test by the method specified in JlS Z 2241,
EL ₀ , EL ₄₅ , and EL ₉₀ are measured, and the in-plane anisotropy parameter of elongation ΔEL (= (ELo + EL ₉₀ ) / 2−EL ₄₅ ) and the average elongation ELs of the plate surface (= (EL ₀ + EL ₉₀ + 2EL ₄₅ )) / 4).

Further, in order to clarify the correlation between ΔEL, ELs and the processing characteristics of the steel sheet, a cylindrical blank having a diameter of 90 mm was prepared from the above ferritic stainless steel sheet, and the wrinkle holding force was 1 OkN using a deep drawing test apparatus. A cylinder forming test was performed using a punch diameter of 50 mm and Nippon Machine Oil No. 660 to check for fracture and necking near the punch shoulder.

As other general characteristics, evaluations on corrosion resistance were also performed. The corrosion resistance was evaluated by performing a salt spray test specified in JIS Z 2371 for 10 consecutive days, observing the surface of the test specimen 10 days later with a 50-fold visual field of an optical microscope, and evaluating the presence or absence of rust.

In addition, the appearance of the steel sheet was observed in each manufacturing process, and the presence or absence of breakage of the steel sheet and cracks in the width portion (hereinafter referred to as edge cracks) was observed and used as an evaluation index of productivity. Table 8 shows the results.

As is apparent from the above, the ferritic stainless steel of the present invention has a ΔEL of 9 or less and shows good working characteristics. In addition, the evaluation of the oxidation resistance is good, with no abnormal oxidation occurring, no rust after the corrosion resistance test, and no defects during the production.

On the other hand, Nos. 14 to 31 whose components are outside the applicable range of the present invention simultaneously satisfy all of the workability, high temperature strength, oxidation resistance, corrosion resistance and manufacturability required for the ferritic stainless steel. I can't.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Table 3]

[0064]

[Table 4]

[0065]

[Table 5]

[0066]

[Table 6]

[0067]

[Table 7]

[0068]

[Table 8]

[0069]

According to the present invention, it is possible to stably produce a roll coating which greatly affects the gloss of ferritic stainless steel without increasing the cost. It has become possible to suppress the resulting gloss unevenness and gloss deterioration.

Further, if the manufacturing method according to the present invention is used,
It has become possible to stably generate roll coating even on high-purity ferritic steel that contains stabilizing elements such as Ti and Nb, for which high gloss was difficult to achieve.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the dissolution loss and the rolling reduction per pass.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasu Chihara 3rd Ojimitsu, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries, Ltd. Kashima Works (72) Inventor Masahiro Takahashi 3rd Ojimitsu, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries, Ltd. Inside Kashima Works (72) Inventor Tohru Matsuhashi 4-53, Kitahama, Chuo-ku, Osaka-shi, Osaka F-term in Sumitomo Metal Industries, Ltd. 4K037 EA01 EA04 EA05 EA12 EA13 EA15 EA17 EA18 EA19 EA20 EA22 EA23 EA25 EA27 EA28 EA31 EA32 EA33 EA35 EB06 EB07 EB08 EB09 FG03 FG10

Claims (3)

[Claims] 1. After annealing a hot-rolled ferritic stainless steel sheet, it is pickled to reduce the pickling loss including descaling to 14 g / m ² or more, and then to a rolling reduction of 10% per pass.
A method for producing a ferritic stainless steel sheet having excellent surface gloss, characterized in that roll coating is stably generated by performing cold rolling at a total reduction ratio of 50% or more. 2. The steel composition of the hot-rolled ferritic stainless steel sheet is, in mass%, C: 0.100% or less, Mn: 1.5% or less, Si: 1.5% or less, S: 0.030% or less, P: 0.04% or less. ,
2. The method for producing a ferritic stainless steel sheet having excellent surface gloss according to claim 1, wherein N: 0.050% or less, Cr: 14.0 to 25.0%, and the balance consists of Fe and unavoidable impurities. 3. The steel composition further comprises: Mo: 0.5 to 2.5.
%, Cu: 1.5% or less, Ni: 1.00% or less, Nb: 0.1 to 1.0
%, Ti: 0.03-0.15%, V: 1.0% or less, Zr: 0.3% or less,
3. The method for producing a ferritic stainless steel sheet having excellent surface gloss according to claim 2, comprising one or more of W: 1.0% or less, Al: 0.2% or less, and O: 0.01% or less.