JPH07126757A - Manufacture of ferritic stainless steel sheet excellent in ridging resistance - Google Patents

Abstract

PURPOSE:To manufacture a ferritic stainless steel sheet improved in ridging resistance and capable severer drawing. CONSTITUTION:In the case of hot-rolling a ferritic stainless steel slab, the total value of the drafts of the final pass and preceding pass in rough rolling is defined as >=70%, the rolling speed on the outlet side of the final pass in the rough rolling is defined as >=200m/min and the finishing temp. in the rough rolling is defined as 1100-800 deg.C at the time of rolling in the rough rolling stage. Further, in this manufacturing method, the final pass and the preceding pass are executed by lubricated rolling whose friction coefficient is <=0.25.

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 having excellent workability, particularly ridging resistance.

[0002]

2. Description of the Related Art Ferritic stainless steel sheets are excellent in corrosion resistance in various corrosive environments and are inexpensive because they do not contain Ni, so they are used as a building material, kitchen material, electrical component material, etc. Has been done. With the recent progress in steelmaking technology, it has become relatively easy to reduce impurities in the ferritic stainless steel sheet (for example, Japanese Patent Publication Nos. 59-11659 and 56-56).
Therefore, improvement of workability as well as corrosion resistance has been investigated.

By the way, generally, ferritic stainless steel sheets are called ridging when they are drawn.
Wrinkle defects of uneven striped patterns along the rolling direction are likely to occur, and this striped pattern causes a loss of aesthetics of the product. For this reason, conventionally, suppressing ridging has been a major issue in producing ferritic stainless steel sheets, and many studies have been conducted. As a conventional technique for suppressing this ridging, for example, Japanese Examined Patent Publication No. 3-48250 discloses the starting temperature of rough rolling in hot rolling, the rolling temperature and reduction rate of finish rolling, and each condition of hot-rolled sheet annealing. The regulated method is also disclosed in Japanese Unexamined Patent Publication No. 4-341521 in rolling temperature of rough rolling in hot rolling, reduction rate per pass and pass time, rolling temperature in finish rolling, reduction rate per pass. In addition to the above regulations, heat retention at a specific temperature is performed between rough rolling and finish rolling.

[0004]

However, the conventional technique for suppressing ridging does not reach the point where ridging is sufficiently suppressed. In other words, by making full use of methods such as reduction of impurities in steel, if the press working characteristics such as deep drawability and ductility are improved, the ridging resistance characteristics will be improved even if the conventional ridging suppression technology is applied. Since this is insufficient, it becomes a bottleneck in processing, and the obtained press processing characteristics cannot be fully exhibited. From this, it is necessary to further improve the ridging resistance as compared with the conventional one in order to withstand severe processing.

Therefore, an object of the present invention is to overcome the above-mentioned problems of the present ferritic stainless steel sheets. Particularly, the ridging resistance is further improved as compared with the conventional one, and even more severe drawing work is performed. We are proposing a method for manufacturing a ferritic stainless steel sheet that makes it possible.

[0006]

[Means for Solving the Problems] Now, as a result of earnest research on each condition of hot rolling which affects the ridging resistance of a ferritic stainless steel sheet in order to realize the above-mentioned object, the inventors found that It was found that the original purpose can be achieved by appropriately combining the rolling reduction of the pass, the rolling speed and the rolling finishing temperature. It was also found that the above object can be more advantageously realized by optimizing the friction coefficient of a specific pass in rough rolling and the chemical composition of stainless steel.

The present invention has been made based on the above findings. That is, the gist of the present invention is as follows. (1) In hot rolling of a ferritic stainless steel billet, during rolling at the rough rolling stage, the total value of the rolling reduction of the final pass of the rough rolling and the rolling reduction of the preceding pass is 70% or more, Rolling speed on the exit side of the final pass of rough rolling is 200m / mi
The method for producing a ferritic stainless steel sheet having excellent ridging resistance, characterized in that the finishing temperature of the rough rolling is 1100 to 800 ° C. (2) The above manufacturing method is characterized in that the final pass of the rough rolling and the pass before the rough rolling are performed by lubrication rolling having a friction coefficient of 0.25 or less. (3) In each of the above inventions, the chemical composition of ferritic stainless steel is basically C ≦ 0.07 wt%, Si ≦ 1.
5 wt%, Mn ≦ 1.5 wt%, Cr: 5-60 wt%, Al ≦ 0.15 wt
%, P ≦ 0.15 wt%, S ≦ 0.007 wt%, O ≦ 0.004 wt% and the balance Fe and unavoidable impurities, and the ferritic stainless steel is used. The chemical composition of the ferritic stainless steel is In addition to the above ingredients, if necessary
Ti: 0.002-0.4 wt%, Nb: 0.002-0.4 wt%, Zr: 0.
002-0.4 wt%, V: 0.002-0.4 wt%, B: 0.0002-
0.02 wt% and Ca: 0.0002 to 0.02 wt%, one or more selected from the total amount of 0.5 wt% or less and / or Mo: 0.02 to 5.0 wt%, Cu: 0.02 to 5.0 wt%, N
A ferritic stainless steel containing one or more selected from i: 0.02 to 5.0 wt% and Co: 0.02 to 5.0 wt% in a total amount of 6 wt% or less, with the balance being Fe and inevitable impurities. It is characterized by using.

[0008]

In the following, according to the present invention, the above-mentioned gist structure is adopted.
The reason for limiting to is explained.・ The total value of the rolling reductions of the two passes on the rear side of the rough rolling: 70% or more;
Of the rough rolling, the last rolling condition is particularly important.
Between the rolling reduction of the final pass of rough rolling and the rolling reduction of the previous pass
R is the total value, that is, the rolling reduction of the final pass of rough rolling. _f, Rough pressure
R is the rolling reduction of the last pass before the final pass_f-1And
Come, R_f+ R_f-1Is less than 70%, the rough rolling speed and the
Suppression of ridging even if the rolling finishing temperature is within the range of the present invention
Is insufficient. Therefore, rough rolling in hot rolling
The total value of the rolling reduction of the two passes on the tail side is 70% or more, preferably
Must be 75% or higher.

Rolling speed on the delivery side of the final pass of rough rolling: 200
m / min or more; rolling speed on the exit side of the final pass of rough rolling is 200
If it is less than m / min, ridging is not sufficiently suppressed even if the rough rolling reduction and the rough rolling finishing temperature are within the range of the present invention. Therefore, the rolling speed on the exit side of the rough rolling in hot rolling should be 200 m / min or more, preferably 230 to 3
It should be 50 m / min.

· Finishing temperature of rough rolling: 1100 to 800 ° C; If the finishing temperature of rough rolling is less than (RDT) 800 ° C, rolling is difficult due to a rapid increase in rolling load, while 1100 ° C
If it exceeds, the structure required to obtain ridging resistance cannot be obtained, so the finishing temperature of rough rolling must be 1100 to 800 ° C, preferably 1080 to 900 ° C.

In FIG. 1, the chemical composition is 0.02C-0.004S-0.003.
Hot rolling of O-17.1Cr stainless steel (rough rolling finish temperature
Degree: 1040 ℃, final finishing temperature: 870 ℃), then 850 ℃
Annealed hot-rolled sheet, then cold rolled to 0.8 mm thickness, cold rolled at 870 ℃
Sum of rolling reductions of two passes after rough rolling when sheet annealing is performed
Value (R_f+ R_f-1) For 78% and 62%
The effect of the rolling speed on the exit side on ridging resistance is shown.
You From Figure 1, R_f+ R _f-1Is within the scope of the present invention at 78%
Is 62% of which both the ridging index and the r value are out of the range of the present invention.
It turns out that it is remarkably superior to the time. like this
The reason why the ridging resistance is improved by the method of the present invention is
Recrystallization is promoted until the start of finish rolling thereafter.
It is easy to break the {100} -oriented grains generated during casting.
Is a set that is favorable for ridging resistance of products.
This is probably because the tissue was formed.

Two-pass rolling on the trailing side of rough rolling: Lubrication rolling with a friction coefficient of 0.25 or less; Lubricating rolling is used as the two-pass rolling after the rough rolling, which is more effective in terms of ridging resistance. However, if the coefficient of friction exceeds 0.25, a good effect on ridging resistance cannot be obtained, so the coefficient of friction in lubrication rolling is
It should be 0.25 or less. Examples of the lubricant for setting the friction coefficient to 0.25 or less include mineral oil containing an extreme pressure agent.

The manufacturing conditions after the rough rolling described above need not be specified, but the finishing hot rolling conditions include a finishing temperature (FDT) of 1000 ° C. or less and a winding temperature (C
T) is preferably 800 ° C or lower. After the above hot rolling, if necessary, it is annealed by a continuous annealing method or a box annealing method, and the obtained hot rolled steel strip is pickled to obtain a final product or a material for cold rolling. In cold rolling, it is preferable that the reduction rate is 50% or more and the annealing temperature is 800 to 1100 ° C. And after annealing, pickling, 0.3 ~
5.0% skin pass rolling may be appropriately performed. In the cold rolling process, cold rolling / annealing may be performed twice or more.

Next, the chemical composition of the ferritic stainless steel preferably applied to the present invention will be described. C ≦ 0.07 wt% C is an element that adversely affects the workability. When it exceeds 0.07 wt%, the effect becomes remarkable, so the content is limited to 0.07 wt% or less. A more preferable range is 0.05 wt% or less.

Si: 1.5 wt% or less Si is an element effective in adjusting strength, but if it exceeds 1.5 wt%, ductility deteriorates, so it is set to 1.5 wt% or less.

Mn: 1.5 wt% or less Mn is an element effective in adjusting strength, but if it exceeds 1.5 wt%, the r value deteriorates, so Mn is made 1.5 wt% or less.

Cr: 5 to 60 wt%: Cr is an element that improves the corrosion resistance, and a content of less than 5 wt% does not contribute to the improvement of the corrosion resistance. On the other hand, if it exceeds 60 wt%, the manufacturability of steel, especially the rolling property, deteriorates, so it is limited to the range of 5 to 60 wt%. From the viewpoint of corrosion resistance and manufacturability, 7-58wt
% Is more preferable.

Al: 0.15 wt% or less Al is an element effective for deoxidation, but if it exceeds 0.15 wt%, the surface quality deteriorates, so 0.15 wt% or less.

P: 0.15 wt% or less P is an element effective in improving workability, but if it exceeds 0.15 wt%, the brittleness resistance deteriorates, so P is set to 0.15 wt% or less.

S≤0.007 wt%: S is an element that adversely affects the corrosion resistance. If it exceeds 0.007 wt%, the effect becomes remarkable, so S is limited to 0.007 wt% or less. A more preferable range is 0.005 wt% or less.

O ≦ 0.004 wt%: O is an element which adversely affects the corrosion resistance, and when it exceeds 0.004 wt%, the effect becomes remarkable, so it is limited to 0.004 wt% or less. A more preferable range is 0.003 wt% or less.

Ti: 0.002-0.4 wt%, Nb: 0.002-0.4
wt%, Zr: 0.002-0.4 wt%, V: 0.002-0.4 wt%,
B: 0.0002 to 0.02 wt% and Ca: 0.0002 to 0.02 wt% One or more selected from 0.5 wt% in total
Below: Each element of Ti, Nb, Zr, V, B and Ca has a common effect of improving deep drawability without impairing ridging resistance. The effect of these additions is T
i: 0.002 wt%, Nb: 0.002 wt%, Zr: 0.002 wt%,
V: 0.002 wt%, B: 0.0002 wt% and Ca: 0.0002 wt%
It appears above. However, each Ti: 0.4 wt
%, Nb: 0.4 wt%, Zr: 0.4 wt%, V: 0.4 wt%, B0.
02wt%, Ca: 0.02wt% in the total amount of these elements
If the amount exceeds 0.5 wt%, not only the effect is saturated, but also manufacturability and economical efficiency are impaired, so these values are made the upper limits. The preferred total content of the above elements is 0.01-
It is 0.35 wt%.

Mo: 0.02-5.0 wt%, Ni: 0.02-5.0 wt%
%, Cu: 0.02 to 5.0 wt% and Co: 0.02 to 5.0 wt%, and 6 wt% or less in total of one or more selected from: Mo, Ni, Cu and Co. It has a common effect of improving corrosion resistance without impairing ridging resistance. The effects of these additions are Mo: 0.02 wt%,
Ni: 0.02 wt%, Cu: 0.020 wt% and Co: 0.02 wt% or more. However, Mo: 5 wt%, N respectively
If i: 5 wt%, Cu: 5 wt%, Co: 5 wt% or the total amount of these elements exceeds 6 wt%, not only the effect is saturated but also the manufacturability and economic efficiency are impaired. Is the upper limit.

[0024]

Example A ferritic stainless steel having the chemical composition shown in Table 1 was continuously cast into a slab having a thickness of 200 mm. This slab was heated to 1130 to 1180 ° C. and soaked, and then roughly rolled to 25 mm in 5 passes using a rough rolling machine consisting of 3 rows. 4 during rough rolling
Sum of rolling reductions in the 5th and 5th passes (R _f + R _f-1 ), 5
Rolling speed (Vf) on rough side of pass, rough rolling finishing temperature (R
DT) Further, the friction coefficient (μ) of the fourth and fifth passes was changed as shown in Table 1.

[0025]

[Table 1]

Subsequent to the above rough rolling, a finish rolling mill consisting of 7 stages was used to make C steel 1.2 mm thick,
A hot rolled steel strip with a thickness of 3.2 to 4.0 mm was used. At this time, the finishing temperature was 870 ° C and the winding temperature was 650 ° C. afterwards,
Steel strips other than A4 steel were annealed at 900 to 1040 ° C and pickled.
Annealing was omitted for A4 steel. Of the hot-rolled steel strips obtained, A
3 steels were used as test materials as they were, and other than A3 steel were further made into 1.0 mm cold-rolled steel strip by a cold rolling mill, and then heated / annealed (820-940 ° C) -pickling-skin pass ( It was used as a test material through the process of rolling reduction of 0.5 to 1.2%. The Rankford value (r value) was measured and the ridging resistance was evaluated for each of the above test materials. Here, the ridging resistance was evaluated by the grade of wrinkle generation when a tensile strain of 20% was applied to a JIS No. 5 test piece (n = 5). Ridging index is 2.0 or less (surface roughness 10
If the thickness is 1.5 μm or less), the ridging resistance is excellent, and if it is 1.5 or less, the problem of ridging is reduced even in severe drawing.

The test results are also shown in Table 1. Table 1
As is clear from the above, according to the present invention, the r value is
It has an ultra-deep drawability of 1.5 or more and excellent ridging resistance with a ridging index of 1.5 or less (maximum height of 10 μm or less measured by a roughness meter), indicating that severe press working is possible. .

[0028]

As described above, according to the present invention, the r-value and the ridging resistance of the ferritic stainless steel sheet are remarkably improved. It is possible without wrinkling. In addition, to the ferritic stainless steel sheet manufactured according to the present invention, any surface finishing method or surface treatment method that has been conventionally applied can be applied without any problem.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between rough rolling conditions, r value, and ridging index.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/54

Claims (6)

[Claims] 1. When hot rolling a ferritic stainless steel billet, the rolling reduction of the final pass of the rough rolling and the total reduction of the reduction of the preceding pass are performed during rolling in the rough rolling stage.
70% or more, the rolling speed on the exit side of the rough rolling is 200
m / min or more, finishing temperature of the rough rolling is 1100-80
A method for producing a ferritic stainless steel sheet having excellent ridging resistance, which is characterized in that the temperature is 0 ° C. 2. The method according to claim 1, wherein the final pass of rough rolling and the pass before it are carried out by lubrication rolling having a friction coefficient of 0.25 or less, to produce a ferritic stainless steel sheet having excellent ridging resistance. Method. 3. C ≦ 0.07 wt%, Si ≦ 1.5 wt%, Mn ≦ 1.5 wt
%, Cr: 5-60 wt%, Al ≦ 0.15 wt%, P ≦ 0.15 wt%, S
The manufacturing method according to claim 1 or 2, wherein a ferritic stainless steel containing ≤ 0.007 wt% and O ≤ 0.004 wt% and the balance Fe and unavoidable impurities is used. 4. C ≦ 0.07 wt%, Si ≦ 1.5 wt%, Mn ≦ 1.5 wt
%, Cr: 5-60 wt%, Al ≦ 0.15 wt%, P ≦ 0.15 wt%, S
≦ 0.007 wt%, O ≦ 0.004 wt%, and Ti: 0.002
~ 0.4 wt%, Nb: 0.002-0.4 wt%, Zr: 0.002-0.4
wt%, V: 0.002-0.4 wt%, B: 0.0002-0.02 wt%, and Ca: 0.0002-0.02 wt%, one or more selected from the total amount of 0.5 wt% or less, and the balance The manufacturing method according to claim 1 or 2, wherein a ferritic stainless steel containing Fe and inevitable impurities is used. 5. C ≦ 0.07 wt%, Si ≦ 1.5 wt%, Mn ≦ 1.5 wt
%, Cr: 5-60 wt%, Al ≦ 0.15 wt%, P ≦ 0.15 wt%, S
≤ 0.007 wt%, O ≤ 0.004 wt%, and Mo: 0.02 ~
5.0 wt%, Cu: 0.02 to 5.0 wt%, Ni: 0.02 to 5.0 wt% and Co: 0.02 to 5.0 wt% One or more selected from the total amount of 6 wt% or less, and the balance The manufacturing method according to claim 1 or 2, wherein a ferritic stainless steel containing Fe and inevitable impurities is used. 6. C ≦ 0.07 wt%, Si ≦ 1.5 wt%, Mn ≦ 1.5 wt
%, Cr: 5-60 wt%, Al ≦ 0.15 wt%, P ≦ 0.15 wt%, S
≦ 0.007 wt%, O ≦ 0.004 wt%, and Ti: 0.002
~ 0.4 wt%, Nb: 0.002-0.4 wt%, Zr: 0.002-0.4
wt%, V: 0.002-0.4 wt%, B: 0.0002-0.02 wt%, and Ca: 0.0002-0.02 wt%, and one or more selected from the total amount of 0.5 wt% or less and Mo. :
0.02-5.0 wt%, Cu: 0.02-5.0 wt%, Ni: 0.02-5.0
wt% and Co: 0.02 to 5.0 wt%, one or more selected from the total amount of 6 wt% or less, and the balance Fe
A ferritic stainless steel containing unavoidable impurities is used, and the method according to claim 1 or 2, characterized in that.