JP2001254154A - Ferritic stainless cold rolled steel sheet excellent in punchability and formability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless cold rolled steel sheet (inclusive of cold rolled steel strip) particularly excellent in both characteristics of punchability and formability in a ferritic stainless steel sheet used by being subjected to forming after punching. SOLUTION: This steel sheet has a componential composition containing <=0.03% C, 0.11 to 2.00% Si, <=1.00% Mn, <=0.03% S, 10.00 to 25.00% Cr, <=0.03% N, <=0.08% Al, 0.10 to 0.50% Ti, 0.02 to 0.40% V, 0.0002 to 0.0050% B and <=0.012% O, in which Ti, C and N also satisfy the relation of Ti/(C+N):>=8, and, further, V and B are contained so as to satisfy the relation of V/B:>=10, 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 ferritic stainless steel sheet (a cold-rolled steel strip) having excellent both punchability and formability in a ferritic stainless steel sheet which is used after being formed after a punching process. And the same applies hereinafter).

[0002]

2. Description of the Related Art Since ferritic stainless steels are slightly inferior in formability to austenitic stainless steels, many proposals for improving formability have been made. For example, as disclosed in JP-A-51-14811, JP-A-51-14812, and JP-A-52-31919, elements such as Ti and Nb are added to solidify in steel. This is a technique for fixing an impurity element such as C or N to be dissolved. Recently, Japanese Patent Application Laid-Open No. 9-3606 discloses a technique regarding a ferritic stainless steel hot-rolled steel sheet aiming at cost reduction by omitting steps after the cold rolling.

[0003]

However, even when these prior arts are applied, when a steel sheet material for forming is punched out of a ferritic stainless steel sheet, there is a problem that "sagging" often occurs on the shear surface. . When sagging occurs, the shape of the raw material changes to an unexpected range, making it impossible to manufacture a product having a precise shape, or hindering positioning in a molding machine in the next process. Therefore, it is necessary to minimize sagging during punching.

Generally, it is considered that the softer the steel plate is, the more the material of the steel plate is softened, and the more easily the portion near the shearing portion is plastically deformed and flows into the shearing surface when sheared by the punching die, and thus the more easily the sagging occurs. . On the other hand, when a product design in which the steel sheet is hardened to give priority to the suppression of sagging is performed, usually, as the material of the steel sheet is softer, good formability must be sacrificed. The occurrence of such sagging appears more remarkably in a hot-rolled steel sheet. This is because, in a hot-rolled steel sheet, unlike a cold-rolled steel sheet, there is little chance of being subjected to a heat treatment for recrystallization, and thus the crystal grain of the steel sheet is larger, softer, and sagging is more likely to occur.

In a conventional ferritic stainless steel sheet,
Even with cold-rolled steel sheets, no sagging occurred during punching, and none of them had good formability. Accordingly, an object of the present invention is to provide a ferritic stainless steel cold-rolled steel sheet having both excellent punchability and good formability.

[0006]

Means for Solving the Problems In order to realize the above-mentioned object, the present inventors aimed at a cold rolled steel sheet which is relatively advantageous in terms of punching properties, while further improving its characteristics.
In order to provide properties that also have good moldability, research was repeated. As a result, it was concluded that the above problems could be solved by optimizing the component composition, and the present invention was completed.

[0007] That is, the present invention provides, in terms of mass%, C:
0.03% or less, Si: 0.11 to 2.00%, Mn: 1.00% or less, S:
0.03% or less, Cr: 10.00 to 25.00%, N: 0.03% or less,
Al: 0.08% or less, Ti: 0.10 to 0.50%, V: 0.02 to 0.40
%, B: 0.0002 to 0.0050%, O: 0.012% or less,
Ti, C and N satisfy the relation of Ti / (C + N): 8 or more, and V and B satisfy the relation of V / B: 10 or more, and the balance is Fe and inevitable impurities. It is a ferritic stainless cold-rolled steel sheet having excellent punchability and formability, characterized by comprising:

[0008]

The reasons for limiting the chemical components of the steel according to the present invention to the above ranges will now be described. C: 0.03% or less C is an element that lowers the formability (particularly, the deep drawability: evaluated by the r value) and the corrosion resistance. Therefore, it is desirable to reduce C as much as possible. Also, in order to exert the effect of V described later, it is desirable to reduce the amount of C in the solid solution state as much as possible. For this reason, in the present invention, C in steel is precipitated by addition of Ti, combined and fixed, and the adverse effect of solid solution C on formability and ferrite stability is reduced.
The effect of is fully exhibited. However, the C content is
If it exceeds 0.03%, the amount of precipitates in the steel sheet will increase too much,
The content is limited to 0.03% or less, and preferably 0.015% or less, since this causes a reduction in moldability and a deterioration in surface properties.

Si: 0.11 to 2.00% Si is an element that is effective for deoxidizing steel and also improves oxidation resistance at high temperatures and high-temperature salt damage characteristics. Such an effect can be obtained by adding 0.11% or more. However, if the content exceeds 2.00%, the elongation property is deteriorated.
Limited to. Note that a more preferable Si content is 0.11 to 0.1.
It is in the range of 75%.

Mn: 1.00% or less Mn is an element effective for precipitating and fixing S in steel and suppressing cracks generated on the surface of the steel sheet during hot rolling, but is an element harmful to formability. . Therefore, its addition range is 1.00%
Or less, preferably 0.5% or less.

S: 0.03% or less S is a harmful element that easily causes cracks on the surface of a steel sheet during hot rolling. However, S is usually combined with Mn to form MnS.
If the content is less than 0.03%, the adverse effect is small. However, if the content exceeds 0.03%, the precipitated MnS becomes a starting point of initial rust and deteriorates corrosion resistance, and segregates at crystal grain boundaries to promote grain boundary embrittlement. Therefore, the S content is 0.03%
Or less, preferably limited to 0.005% or less.

Cr: 10.00-25.00% Cr is an essential element for improving corrosion resistance and oxidation resistance at high temperatures. If the added amount of Cr is less than 10.00%, a sufficient effect cannot be obtained. On the other hand, if the added amount exceeds 25.00%, the workability is deteriorated and the material cost is increased.
The addition amount is 10.00 to 25.00%. In addition, when it is intended to be used for applications that prioritize moldability, the content is desirably 15% or less.

N: not more than 0.03% N, like C, is an element that lowers the formability (r value) of a steel sheet, and therefore it is desirable to reduce it as much as possible. Also, in order to exert the effect of B described later, it is desirable to reduce the amount of N in the solid solution state as much as possible.
Therefore, in the present invention, N in steel is precipitated by adding Ti, combined and fixed, and rendered harmless. However, if the content exceeds 0.03%, the amount of precipitates in the steel sheet increases, leading to a decrease in formability and a deterioration in surface properties. Therefore, the N content is limited to 0.03% or less, preferably 0.01% or less.

Al: 0.08% or less Al is an element effective for deoxidation, but is combined with N to reduce formability, particularly elongation.

Ti: 0.10 to 0.50% Ti is a strong C and N stabilizing element and has an effect of improving formability. It also has the effect of suppressing the grain boundary precipitation of Cr carbonitride and improving the corrosion resistance. In order to exert these effects, it is necessary to add Ti in an amount of 0.10% or more and satisfying the relationship with C and N described later. On the other hand, if the added amount of Ti exceeds 0.50%, the formability rather deteriorates, and the workability of the welded portion also decreases. Furthermore, manufacturability also deteriorates due to a decrease in toughness. Therefore, Ti is added in the range of 0.10 to 0.50%.

V: 0.02 to 0.40%, B: 0.0002 to 0.0050
% And V / B: 10 or more V and B are extremely important elements for preventing sagging in the present invention. V and B are 0.02 to 0.40% and 0.00, respectively.
By adding 0.2 to 0.0050% and V / B of 10 or more in combination, there is an effect of refining the crystal grains of the cold-rolled steel sheet. The reason why such an effect can be obtained is not necessarily clear, but V makes a solid solution in ferrite grains to make recrystallized grains fine during annealing, and B concentrates at ferrite grain boundaries after annealing recrystallization. It is thought that delaying the movement of the grain boundary assists in suppressing grain growth. Also, V
The content ratio of B and B seems to be related to the balance between the volume of ferrite crystal grains and the area of the ferrite grain boundary.

The reason why the grain refinement is promoted in this way, dripping after forming is remarkably improved, and at the same time, the formability is maintained is considered as follows. 1) Dislocations in the crystal lattice easily accumulate at grain boundaries,
The resistance to plastic deformation increases. As a result, the plastic deformation region at the time of punching is limited to a narrow range near the shear surface, and the sag is reduced. 2) When the resistance to plastic deformation increases due to the addition of V, the elongation tends to decrease. However, as a result of the improvement of the grain boundary strength due to the concentration of B at the grain boundary, the elongation is maintained, and it becomes difficult to break in the forming process.

Here, when the precipitation and fixation of C by Ti is not sufficient, V reacts with C and precipitates as V ₂ C or VC, and the effect of suppressing grain growth is reduced. On the other hand, when the precipitation and fixation of N by Ti is not sufficient, B reacts with N and precipitates as BN, and conversely promotes grain growth. Therefore, C must be deposited and fixed by sufficient addition of Ti, a carbide-forming element stronger than V, and N by sufficient addition of Ti, a nitride-forming element stronger than V and B. In addition, B promotes the accumulation of processing strain during rolling and improves the formability of the recrystallized texture after annealing, in addition to the effect of the addition. The effect of adding V and B described above is as follows.
It is exhibited only when the V amount is 0.02% or more, the B amount is 0.0002% or more, and the ratio V / B of each addition amount is 10 or more. On the other hand, if V and B are added in excess of 0.40% and 0.0050%, respectively, the effects of grain refinement, suppression of grain growth and improvement of formability during annealing are saturated, and conversely, the material hardens and elongation increases. Deterioration deteriorates moldability. Therefore, the V content is 0.02-0.40%, the B content is 0.0002-0.0050%, and V / B> 10.

O: 0.012% or less O binds to Ti and inhibits the effect of Ti to stabilize C and N. For this reason, O indirectly impedes the crystal grain refinement effect by V. Such an effect increases rapidly when the amount of O exceeds 0.012%, so that the amount of O
Must be limited to 2% or less.

Ti / (C + N): 8 or more Ti is added to effectively exert the effects of V and B described above, that is, to precipitate and fix N as TiN and C as TiC. Therefore, a sufficient effect can be obtained by adding a Ti amount that satisfies Ti / (C + N): 8 or more more than the stoichiometric ratio.

[0021] Other than the above-mentioned components, Fe is inevitably contained. In the present invention, it is desirable that, among impurities unavoidably contained, particularly Cu, is suppressed to 0.20% or less from the viewpoint of preventing surface defects due to cracks caused by deterioration in hot rolling workability. Furthermore, P
In order to prevent the corrosion resistance from deteriorating, it is desirable to suppress the content to 0.035% or less. Further, in manufacturing the steel sheet of the present invention, a heating temperature: 1,250 to 1,050 ° C and a finishing temperature: 900 to 600 ° C.
℃, winding temperature: 800 ~ 11 after hot rolling of 700 ℃ or less
It is desirable to anneal at 00 ° C, cold-roll, and then finish anneal at 800 to 1100 ° C.

[0022]

The present invention will be described below in detail with reference to examples. Steel having the chemical composition shown in Table 1 was melted in a converter and made into a billet by continuous casting. The slab was heated to 1150 ° C., hot-rolled to a finishing temperature of 800 ° C. and made 5.0 mm. This hot-rolled steel strip is annealed at 800 ° C., pickled, cold-rolled, and subjected to finish annealing at 900 ° C. and pickling once to a thickness of 1.0 m.
m of cold-rolled steel sheet. From the obtained cold rolled steel sheet, JIS1
A No. 3 B-shaped tensile test piece was sampled from a direction at 0 ° to the rolling direction, and the yield strength, tensile strength and elongation were measured. In addition, a disk-shaped blank having a diameter of 300 mm was removed from the cold-rolled steel sheet, and the disk was placed on a surface plate, and the maximum height of the warp including the edge of the blade was measured to determine the amount of sag. Table 2 shows the results.

[0023]

[Table 1]

[0024]

[Table 2]

From Table 2, it can be seen that, in the example of the invention, the sag during the punching process is extremely small and the improvement in the punching property is remarkable. Furthermore, it can be seen that the invention example has an elongation of 34% or more and an r-value of 1.50 or more, and has excellent moldability as compared with the conventional material. Thus, it can be said that the steel sheet of the present invention has both excellent punchability and good formability.

[0026]

As described above, according to the present invention, it is possible to provide a ferritic stainless steel cold-rolled steel sheet in which the occurrence of sag during punching is effectively prevented without deteriorating formability. Become.

Claims (1)

[Claims] [Claim 1] In terms of mass%, C: 0.03% or less, Si: 0.11 to 2.00%, Mn: 1.00% or less, S: 0.03% or less, Cr: 10.00 to 25.00%, N: 0.03% or less, Al: 0.08% or less, Ti: 0.10 to 0.50%, V: 0.02 to 0.40%, B: 0.0002 to 0.0050%, O: 0.012% or less, and Ti, C and N are Ti / (C + N): 8 or more And V and B satisfy the relationship of V / B: 10 or more, and the balance is made of Fe and unavoidable impurities. Stainless cold rolled steel sheet.