JP3857807B2 - Method for producing ferritic stainless steel with excellent surface properties and low anisotropy - Google Patents

Description

【００４８】
【表２】

【００４９】
【発明の効果】
上記のように、本発明は熱延板焼鈍を省略した簡略なプロセスで成分制御と熱延条件を一貫で制御することにより、フェライト系ステンレス鋼の課題である加工性の異方性を改善し、かつリジング特性を改善したフェライト系ステンレス鋼を製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy.
[0002]
[Prior art]
Since ferritic stainless steel has a lower Ni content and is lower in price than austenitic stainless steel, it is widely used for kitchen appliances and automobile exhaust system parts.
[0003]
Properties required for processing into such products include press workability and surface properties after processing, but ferritic stainless steels are more workable and surface properties than austenitic stainless steels. The actual situation is inferior.
[0004]
In the case of ferritic stainless steel, an r value is given as a characteristic value indicating press workability. The deep drawing characteristics improve as the r value increases. However, in ferritic stainless steel, the in-plane anisotropy is large. In particular, the r value in the 45 ° direction with respect to the rolling direction is the r value perpendicular to the rolling direction or the rolling direction. Usually lower.
[0005]
For this reason, increasing the overall r value has been studied from the viewpoint of improving workability. However, if the r value in the 45 ° direction is low, the workability is affected by the r value in the 45 ° direction, so that a steel sheet with rather small in-plane anisotropy is desirable from the viewpoint of workability.
[0006]
Further, as surface characteristics, it is known that surface irregularities called ridging are generated when processed. Since this ridging becomes larger in proportion to the degree of processing, the aesthetics are remarkably impaired when strongly processed. In addition, once subjected to secondary processing after forming, the processing conditions may locally change due to the unevenness, which may cause cracking, and a steel plate with good ridging resistance is desired.
[0007]
Many studies have been made on the above. That is, from the viewpoint of improving workability, Japanese Patent Application Laid-Open No. 4-99151 discloses that rolling reduction at 900 ° C. or lower is 50% or higher, rolling is performed at a finishing temperature of 800 ° C. or lower, and scraping is performed at 600 ° C. or higher. A method of performing hot-rolled sheet annealing is disclosed. Similarly, Japanese Patent Laid-Open No. 5-98352 discloses a method of annealing a hot rolled sheet with a finish rolling temperature of 800 ° C. or lower. Furthermore, Japanese Patent Application Laid-Open No. 9-235621 discloses a method for prescribing ingredients and scoring at 600 ° C. or higher.
[0008]
As a countermeasure against ridging, JP-A-9-53155 discloses an alloy having good ridging resistance. However, as shown in the examples, hot rolling is performed after hot rolling. This causes an increase in cost due to hot-rolled sheet annealing and an increase in pickling cost due to an increase in scale due to annealing.
[0009]
Therefore, adding a new process to the conventional process to reduce ridging is likely to lose the merit of inexpensive ferritic stainless steel, and hot-rolling ferritic stainless steel with good ridging resistance and workability. If it can be manufactured by a so-called ordinary steel process in which annealing is omitted, ferritic stainless steel can be provided at a lower cost.
[0010]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for producing a ferritic stainless steel that can improve the anisotropy of ferritic stainless steel and improve ridging resistance.
[0011]
[Means for Solving the Problems]
The inventors have achieved ridging resistance and workability without using hot-rolled sheet annealing, which is performed in a conventional process, or intermediate annealing between cold-rolling and so-called cold rolling. The method that can be improved was examined. As a result, it was found that ridging resistance and workability can be improved at the same time by consistently optimizing the rolling conditions during hot rolling and the milling conditions after hot rolling by defining trace components, and completed the present invention. .
[0012]
That is, the gist of the present invention is as follows.
(1) By mass % C: 0.0005 to 0.010%, Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%, S: 0.0010 to 0.040%,
P: 0.025% or less, Cr: 10.0-20.0%,
Ti: 0.4% or less, Al: 0.005 to 0.05%,
N: 0.0005 to 0.020%, O: 0.01% or less, consisting of the balance Fe and inevitable impurities, 2 ≦ S / C ≦ 4 and 1.5 (P + S) +4 (C + N + O) ≦ When hot rolling ferritic stainless steel satisfying Ti, the heating temperature is 1250 ° C. or less, the total rolling reduction of rough rolling is 80% or more, and the final three passes of rough rolling are cumulative rolling reduction of 60% or more. After finishing rough rolling at 1000 ° C. or higher, finish rolling is performed so that the total strain of the rough rolling (logarithmic strain: εr) and the total strain of the finish rolling (logarithmic strain: εf) are εr ≦ εf, and then 600 A method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy, characterized by pickling at less than 0 ° C., pickling without performing hot-rolled sheet annealing, and performing cold-rolling and annealing.
[0013]
(2) The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to item (1), further comprising B: 0.0003 to 0.0020% by mass % .
[0014]
(3) Ferritic stainless steel having excellent surface characteristics and low anisotropy as described in (1) or (2) above, further containing Mg: 0.0005 to 0.0050% by mass % Steel manufacturing method.
[0015]
(4) Furthermore, in mass %,
Mo: 0.05-2.0%, Nb: 0.05-2.0%,
Zr: 0.05 to 2.0%, W: 0.05 to 2.0%,
V: 0.05-2.0%
The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to any one of (1) to (3), wherein the ferritic stainless steel has one or more of the following.
[0016]
(5) In hot rolling, lubrication is performed so that an average friction coefficient between a roll and a rolled plate in finish rolling is 0.2 or less. Any one of (1) to (4) above Of ferritic stainless steel with excellent surface properties and low anisotropy.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The inventors melted a 50 kg ingot of ferritic stainless steel containing 11Cr-0.002-0.007C-0.004-0.015N-Ti added steel as a basic component in a laboratory, Experiments were conducted to produce hot rolled sheets of 3 to 5 mm, and pickling, cold rolling and annealing were performed. The r value was measured after a JIS No. 5 test specimen was taken from the direction of 0, 45, 90 ° C. from the product plate in the rolling direction and a 15% tensile test was performed. Further, the ridging characteristics were obtained by collecting JIS No. 5 test specimens from the rolling direction of the product plate, performing a 16% tensile test, and then measuring irregularities in a direction perpendicular to the rolling direction with a roughness meter. It became possible to improve the surface characteristics and workability by investigating the influence of the components and hot rolling conditions on both of these characteristic values and controlling the components and hot rolling consistently.
[0018]
The present invention is described in detail below.
In the component, P is 0.025% or less from the viewpoint of improving ridging resistance and workability, and ridging satisfying the relationship between S and C and P, S, C, N, O and Ti represented by the following formulas: It was found that the r value was improved.
2 ≦ S / C ≦ 4 and 1.5 (P + S) +4 (C + N + O) ≦ Ti
When this formula is satisfied, the precipitates during heating to hot rolling can be stabilized, grain growth during heating can be prevented, and recrystallization during rough rolling can be promoted. Can push the destruction of.
[0019]
In the present invention, the heating temperature is set to 1250 ° C. or less because the particle size becomes coarse at high temperature heating exceeding 1250 ° C., even if recrystallization during hot rolling is delayed or the component control of the present invention is performed. The precipitate is dissolved at the time of heating, and is re-precipitated during hot rolling, at the time of cutting, or at the time of annealing after cold rolling.
[0020]
The lower limit of the heating temperature is not particularly defined. However, if the temperature is lower than 1000 ° C., recrystallization during rolling cannot be utilized, and the rolling temperature is lowered, so that seizure due to seizure is likely to occur. It is considered the lower limit of the heating temperature.
[0021]
In rough rolling, it is important to destroy the cast structure and make it a recrystallized structure before finish rolling. For this purpose, in rough rolling, a rolling reduction of 80% or more of the initial sheet thickness is taken. In order to sufficiently promote recrystallization during the finishing rolling, a cumulative rolling reduction ratio of the final three passes of rough rolling (a rolling reduction ratio with respect to the plate thickness before the final three passes) is secured to 60% or more, and the rough rolling finish temperature is 1000 When the temperature is higher than or equal to ° C., structural anisotropy such as a mixed grain structure can be eliminated as a structure before finish rolling.
[0022]
Regarding finish rolling, finish rolling may be performed so that the above-mentioned rough rolling conditions are satisfied and the total strain of the rough rolling (logarithmic strain εr) and the total strain of the finish rolling (logarithmic strain εf) are εr ≦ εf. It is effective for reducing the anisotropy of the r value and improving ridging.
[0023]
Moreover, since there exists an effect which prevents the shear deformation of a hot-rolled sheet surface layer by application of lubrication rolling, workability improvement will be attained if it implements for finish rolling. At this time, it is important to carry out lubrication rolling in which the average friction coefficient between the roll and the rolled sheet is 0.2 or less as finish rolling. Here, the reason why the friction coefficient between the roll and the rolled sheet is set to 0.2 or less is that it is possible to reduce the influence of the shear strain due to the frictional force. The smaller the friction coefficient, the greater the effect of improving the r value. Become.
[0024]
It is desirable that the cooling after hot rolling is as rapid as possible, and the scraping is performed at a temperature lower than 600 ° C. When the cutting temperature is 600 ° C. or higher, recovery and recrystallization occur during cooling after cutting, the r value in the 45 ° direction of the product plate becomes smaller and the anisotropy becomes larger, and when the coil is cooled This is because the thermal history changes in the longitudinal direction, resulting in variations in workability, and in the present invention, the variation in characteristics in the coil can be prevented by winding at a temperature lower than 600 ° C.
[0025]
As a result of expanding the component range for the above relationship, it was found that the present invention is composed of the following component systems. That is, the ferritic stainless steel of the present invention is in mass %,
C: 0.0005 to 0.010%, Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%, S: 0.0010 to 0.040%,
P: 0.025% or less, Cr: 10.0-20.0%,
Ti: 0.4% or less, Al: 0.005 to 0.05%,
N: 0.0005 to 0.020%, O: 0.01% or less,
If necessary,
One or two of B: 0.0020% or less, Mg: 0.0005 to 0.0050%, and one or more of the following elements can be added as selective elements.
Mo: 0.05-2.0%, Nb: 0.05-2.0%,
Zr: 0.05 to 2.0%, W: 0.05 to 2.0%,
V: 0.05-2.0%
[0026]
The reasons for limiting the components in the present invention will be described below.
C: C is harmful in terms of workability and corrosion resistance, and particularly adversely affects the corrosion resistance of welds. At present, if it is less than 0.0005%, the production cost becomes high, and if added over 0.010%, workability, toughness and corrosion resistance deteriorate, so C is 0.0005 to 0.01%. did.
[0027]
S: S is an element important for improving workability and ridging characteristics in the present invention, and is regulated by the relationship with C. Therefore, the lower limit is 0.0010%, and the upper limit is 0.04%. Even if it is added in excess of this, the effect of improving the characteristics is small, the yield strength is increased and the workability is deteriorated.
[0028]
P: P is also harmful to ridging resistance and processability in the present invention, and its content is preferably as small as possible, and is 0.025% or less.
[0029]
Cr: Cr is a main element of the ferritic stainless steel of the present invention, and it is necessary to add 10% or more from the viewpoint of corrosion resistance. However, even if added over 20%, the corrosion resistance is improved, but the cost increases greatly, and the workability and toughness deteriorate, so the upper limit of Cr was made 20%.
[0030]
Ti: In the present invention, from the viewpoint of ridging resistance and processability, it is an element necessary for fixing C, N, P, S, O, and 1.5 (P + S) +4 ( C + N + O) or more. Moreover, since it will reduce toughness and workability when it contains excessively, it is 0.4% or less.
[0031]
N: N, like C, the smaller the content, the better for corrosion resistance and workability, but it is industrially difficult to make it less than 0.0005%, and if it is added over 0.02%, it is processed. N is added in the range of 0.0005 to 0.02% in order to deteriorate the properties and toughness.
[0032]
O: O deteriorates the toughness of the hot-rolled sheet, causes nozzle clogging and scratching during casting, and causes the deterioration of the toughness of the hot-rolled sheet.
[0033]
B: B is an element that easily segregates at grain boundaries, and is added to improve workability as in the present invention, and is particularly effective for secondary processing cracks, and is added at 0.0003% or more. . Further, if added over 0.0020%, recrystallization at the time of hot rolling or after cold rolling annealing is delayed to deteriorate workability and ridging resistance, so 0.0003 to 0.0020% is added.
[0034]
Mg: Mg is effective for refining the solidified structure, and is added in an amount of 0.0005% or more. Moreover, since the effect will be saturated even if it adds exceeding 0.0050%, it adds at 0.0005 to 0.0050%.
[0035]
In the present invention, any one or more of Mo, Nb, Zr, W, and V can be added as a selective element.
Mo: Mo is an effective element even in the case of requiring corrosion resistance and high-temperature strength as an exhaust material, and can be added by 0.05% or more. Moreover, even if added over 2.0%, the effect is saturated and expensive, so the content was made 0.05 to 2.0%.
[0036]
Nb: Nb is an element that fixes C and N and is preferable in terms of corrosion resistance, and is also an effective element when high-temperature strength is required as an exhaust material, and can be added at 0.05% or more. Moreover, even if added over 2.0%, the effect is saturated and expensive, so the content was made 0.05 to 2.0%.
[0037]
Zr: Zr is effective for fixing C and N, and particularly for suppressing corrosion of Cr carbonitride in the weld zone to improve corrosion resistance, and also requiring high-temperature strength as an exhaust material. It is an element and can be added at 0.05% or more. Moreover, even if added over 2.0%, the effect is saturated and expensive, so the content was made 0.05 to 2.0%.
[0038]
W: W is effective for fixing C and N, and in particular, suppressing the precipitation of Cr carbonitride in the welded portion to improve corrosion resistance, and is also effective when high temperature strength is required as an exhaust material. It is an element and can be added at 0.05% or more. Moreover, even if added over 2.0%, the effect is saturated and expensive, so the content was made 0.05 to 2.0%.
[0039]
V: V is effective for fixing C and N, and particularly for suppressing the precipitation of Cr carbonitride in the weld zone to improve corrosion resistance, and also requiring high-temperature strength as an exhaust material. It is an element and can be added at 0.05% or more. Moreover, even if added over 2.0%, the effect is saturated and expensive, so the content was made 0.05 to 2.0%.
[0040]
Also, Si in the present invention is usually used as a deoxidizing element, Mn, to use Al. In this case , the following component ranges are used as ranges that do not affect the characteristics of the present invention.
Si: 0.01-1.0%, Mn: 0.01-1.0%,
Al: 0.005 to 0.05%.
[0041]
Si: Si is not sufficiently effective as a deoxidizer if less than 0.01%, and if added over 1%, the workability of the present invention is deteriorated, so 0.01 to 1.0% is desirable.
Mn: Mn is a deoxidizing element, and if less than 0.01%, the effect is not sufficient, and even if added over 1%, the effect is saturated, so 0.01 to 1.0% is desirable. Al: Al is effective as a deoxidizing element at 0.005% or more, and even if it exceeds 0.05%, the degree of deoxidation is saturated, so 0.005% to 0.05% is desirable.
[0042]
【Example】
Next, examples of the present invention will be described. Using a ferritic stainless steel slab having a thickness of 250 mm having the components of Table 1, heating and hot rolling were performed under the conditions shown in Table 2, followed by hot rolling to produce 3-5 mm hot rolled sheets.
After this, No. in which hot-rolled sheet annealing was performed. Except for B, hot-rolled sheet annealing was omitted, pickling and cold rolling were performed, and workability and ridging characteristics were evaluated. Hot-rolled sheet annealing material No. The hot-rolled sheet annealing condition for B was 820 ° C. × 6 h, and was performed by box annealing. The cold rolling reduction was 80%, and the finish annealing was 800 ° C. to 1070 ° C. for 30 to 60 seconds.
[0043]
From the obtained product, r value, anisotropy Δr, and ridging height were measured by the following methods.
Δr, which is a measure of r value and anisotropy, is obtained by taking a JIS No. 5 test specimen from 0 ° direction, 45 ° direction and 90 ° direction with respect to the rolling direction, and performing a 15% tensile test. Asked.
r value = (rL + 2rD + rC) / 4
Δr = (rL -2rD + rC) / 2
Here, rL: r value in the rolling direction, rD: r value in the 45 ° direction with respect to the rolling direction, and rC: r value in the 90 ° direction with respect to the rolling direction.
If the r value is 1.5 or more and Δr is 0.3 or less, there is no problem of deterioration of workability due to the lack of r value in the 45 ° direction.
[0044]
For ridging characteristics, a JIS No. 5 tensile test piece was taken from the rolling direction of the product plate, a 16% tensile test was performed, and unevenness was measured using a roughness meter in a direction perpendicular to the rolling direction.
[0045]
The evaluation of ridging was A: less than 7 μm, B: 7 μm to less than 15 μm, C: 15 μm to less than 30 μm, and D: 30 μm or more. In practice, the A and B ranks are not a problem.
[0046]
As a result, the steel of the present invention has a workability and an r value of 1.5 or more, and Δr indicating anisotropy is also 0.3 or less, compared with the hot-rolled sheet annealing process material and those not satisfying the conditions of the present invention. The ridging properties were also very good.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
【The invention's effect】
As described above, the present invention improves the workability anisotropy, which is a problem of ferritic stainless steel, by consistently controlling the component control and hot rolling conditions by a simple process that omits hot rolling sheet annealing. In addition, ferritic stainless steel having improved ridging characteristics can be produced.

Claims (5)

% By mass
C: 0.0005 to 0.010%,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
S: 0.0010 to 0.040%,
P: 0.025% or less,
Cr: 10.0-20.0%,
Ti: 0.4% or less,
Al: 0.005 to 0.05%,
N: 0.0005 to 0.020%,
O 2: Hot containing ferritic stainless steel containing 0.01% or less, balance Fe and inevitable impurities, and satisfying 2 ≦ S / C ≦ 4 and 1.5 (P + S) +4 (C + N + O) ≦ Ti When rolling, the heating temperature is 1250 ° C. or less, the total rolling reduction of rough rolling is 80% or more, and the final three passes of rough rolling are cumulative rolling reduction of 60% or more and finish rough rolling at 1000 ° C. or more. After finishing rolling so that the total strain of the rough rolling (logarithmic strain: εr) and the final strain of the finish rolling (logarithmic strain: εf) are εr ≤εf, it is picked at less than 600 ° C. A method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy, characterized by pickling without performing, cold rolling, and annealing. The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to claim 1, further comprising B: 0.0003 to 0.0020% by mass %. The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to claim 1 or 2, further comprising Mg: 0.0005 to 0.0050% in mass %. Furthermore in mass%,
Mo: 0.05-2.0%,
Nb: 0.05 to 2.0%,
Zr: 0.05 to 2.0%,
W: 0.05-2.0%,
V: 0.05-2.0%
The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to any one of claims 1 to 3, wherein the ferritic stainless steel has one or more of the following.   In the hot rolling, the surface characteristics according to any one of claims 1 to 4 are excellent so that the average friction coefficient between the roll and the rolled sheet in the finish rolling is 0.2 or less. A method for producing ferritic stainless steel with low anisotropy.