JP3508685B2 - Ferritic stainless steel cold rolled steel sheet with excellent punchability and formability - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel sheet which is used after being stamped, and is particularly excellent in both punchability and formability. Stainless steel cold-rolled steel sheet (including cold-rolled steel strip, the same applies hereinafter). 2. Description of the Related Art Ferritic stainless steel is slightly inferior in formability to austenitic stainless steel, and so far, many proposals have been made for improving formability. For example, as disclosed in JP-A-51-14811, JP-A-51-14812, JP-A-52-31919, etc., elements such as Ti and Nb are added to solidify the steel. This is a technique for fixing impurity elements such as C and N to be dissolved. Further, recently, a technique regarding a ferritic stainless hot rolled steel sheet aimed at cost reduction by omitting steps after cold rolling is disclosed in Japanese Patent Laid-Open No. 9-3606. However, even when these conventional techniques are applied, when a steel plate material for forming is punched from a ferritic stainless steel plate, the “sag” often occurs on the shear surface. was there. When the sagging occurs, the shape of the material changes to an unexpected range, making it impossible to manufacture a precisely shaped product, or hindering positioning with a molding machine in the next process. Therefore, it is necessary to prevent dripping as much as possible during the punching process. In general, it is considered that this sagging is more likely to occur as the material of the steel plate becomes softer, because the portion near the shearing portion is plastically deformed and flows into the shearing surface when sheared by a punching die. . On the other hand, when a product design that prioritizes the suppression of sagging by hardening a steel plate is generally required, the softer the material of the steel plate, the better the formability. Such sagging occurs more significantly in hot-rolled steel sheets. This is because, in a hot-rolled steel sheet, unlike a cold-rolled steel sheet, there is little opportunity to undergo heat treatment for recrystallization, so the crystal grains of the steel sheet are larger and softer, and sag is likely to occur. In conventional ferritic stainless steel sheets,
Even cold-rolled steel sheets were free from sagging during punching and had no good formability. Therefore, an object of the present invention is to provide a ferritic stainless steel cold-rolled steel sheet having both excellent punchability and good formability. Means for Solving the Problems Now, in order to achieve the above-mentioned object, the inventors have further improved the properties of cold-rolled steel sheets that are relatively advantageous in terms of punchability. As well as
In order to give the characteristic which also had good moldability, research was repeated. As a result, it came to the conclusion that the said subject can be solved by optimizing a component composition, and came to complete this invention. That is, in the present invention, C:
0.03% or less, Si: 0.11 to 2.00%, Mn: 1.00% or less, P:
0.019 to 0.035 %, 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.
0,12% or less, and Ti, C and N are Ti / (C
+ N): satisfies a relationship of 8 or more, and V and B are V
/ B: Ferritic stainless cold-rolled steel sheet excellent in punchability and formability, characterized in that it satisfies the relationship of 10 or more and the balance is composed of Fe and inevitable impurities. The reason why each chemical component of the steel in the present invention is limited to the above range will be described below. C: 0.03% or less C is an element that lowers moldability (particularly deep drawability: evaluated by r value) and corrosion resistance, and is therefore desirably reduced as much as possible. Moreover, in order to exhibit the effect of V described later, it is desirable to reduce the C amount in a solid solution state as much as possible. For this reason, in the present invention, by adding Ti, C in the steel is precipitated, compounded and fixed, and the adverse effect of solid solution C on formability and ferrite stability is reduced.
The effect of is fully demonstrated. However, the C content is
If it exceeds 0.03%, the amount of precipitates in the steel sheet will increase too much,
Since the moldability is deteriorated and the surface properties are deteriorated, the content range is set to 0.03% or less, preferably 0.015% or less. Si: 0.11 to 2.00% Si is an element that is effective for deoxidation of steel and improves oxidation resistance at high temperatures and salt damage characteristics at high temperatures. Such effects can be obtained by addition of 0.11% or more, but if it exceeds 2.00%, the elongation characteristics deteriorate, so 0.11 to 2.00%
Limited to. Furthermore, more preferable Si content is 0.11-0.
The range is 75%. Mn: 1.00% or less Mn is an element effective for precipitating and fixing S in steel and suppressing cracks formed on the surface of the steel sheet during hot rolling, but is harmful to formability. . Therefore, the addition range is 1.00%
Below, preferably 0.5% or less. S: 0.03% or less S is a harmful element that tends to cause cracks on the surface of a steel sheet during hot rolling, but usually combines with Mn to form MnS.
If the content is 0.03% or less, the adverse effect is small. However, if it exceeds 0.03%, the precipitated MnS becomes the starting point of the initial rust and deteriorates the corrosion resistance, and segregates at the crystal grain boundary to promote grain boundary embrittlement. Therefore, the S content is 0.03%
Below, preferably limited to 0.005% or less. Cr: 10.00 to 25.00% Cr is an indispensable element for improving corrosion resistance and oxidation resistance at high temperatures. If the amount of Cr added is less than 10.00%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 25.00%, the workability deteriorates and the material cost increases.
Addition amount shall be 10.00-25.00%. In addition, when it is intended to be used for applications in which formability is prioritized, it is desirable to make it 15% or less. N: 0.03% or less N, like C, is an element that lowers the formability (r value) of the steel sheet, so it is desirable to reduce it as much as possible. Moreover, in order to exhibit the effect of B described later, it is desirable to reduce the N amount in the solid solution state as much as possible.
Therefore, in the present invention, N in steel is precipitated by adding Ti, combined, fixed, and rendered harmless. However, if its 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. However, Al is combined with N to reduce moldability, particularly elongation, so 0.08% or less. Ti: 0.10 to 0.50% Ti is a strong C and N stabilizing element and has the effect of improving the 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 Ti addition amount exceeds 0.50%, the formability 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 elements that are extremely important for preventing sagging in the present invention. V and B are 0.02 to 0.40% and 0.00 respectively.
By adding 02 to 0.0050% and V / B satisfying 10 or more, it has the effect of refining the crystal grains of the cold-rolled steel sheet. The reason why such an effect is obtained is not necessarily clear, but V makes the recrystallized grains fine during annealing by dissolving in the ferrite grains, and B concentrates at the ferrite grain boundaries after annealing recrystallization. It is considered that grain growth suppression is aided by delaying grain boundary movement. 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 interfacial area of ferrite grains. The reason why the crystal grain refinement is promoted as described above to significantly improve the sagging after the molding process and at the same time maintain the moldability is considered as follows. 1) Dislocations in the crystal lattice tend to accumulate at the grain boundaries,
Resistance to plastic deformation increases. As a result, the plastic deformation region at the time of punching is limited to a narrow range in the vicinity of the shear plane, and sagging is reduced. 2) When resistance to plastic deformation increases due to the addition of V, the elongation tends to decrease. However, as a result of the improvement in grain boundary strength by the grain boundary concentration of B, the elongation is maintained and it is difficult to break in the molding 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 lowered. On the other hand, when the precipitation 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 precipitated and fixed by sufficient addition of Ti, which is a carbide forming element stronger than V, and N must be precipitated and fixed by sufficient addition of Ti, a nitride forming element stronger than V and B. In addition to the above addition effect, B promotes the accumulation of processing strain during rolling and improves the formability of the recrystallized texture after annealing. The addition effect of V and B described above is
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, addition of V and B exceeding 0.40% and 0.0050%, respectively, not only saturates the effect of grain refinement and grain growth suppression during annealing, but also improves formability, and conversely the material hardens and stretches. Deteriorates and moldability decreases. Therefore, the V amount is 0.02 to 0.40%, the B amount is 0.0002 to 0.0050%, and V / B> 10. O: 0.012% or less O combines with Ti and inhibits the stabilizing effect of C and N by Ti. For this reason, O indirectly inhibits the effect of crystal grain refinement by V. Such influence increases rapidly when the O content exceeds 0.012%, so the O content is 0.01%.
Must be limited to 2% or less. Ti / (C + N): 8 or more Ti is added to effectively act the above-described effects of V and B, 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 satisfying Ti / (C + N): 8 or more more than the stoichiometric ratio. In addition to the above-described components, Fe is inevitably contained. In the present invention, among impurities inevitably contained, Cu, in particular, is desirably suppressed to 0.20% or less from the viewpoint of preventing surface defects due to cracking accompanying a decrease in hot rolling processability. In addition, P
Is controlled to 0.035% or less from the viewpoint of preventing corrosion resistance deterioration .
The In the production of the steel sheet of the present invention, the heating temperature:
1255-1050 ° C, Finishing temperature: 900-600 ° C, Winding temperature: 70
After hot rolling at 0 ° C. or lower, it is desirable to anneal at 800 to 1100 ° C., and after cold rolling, to finish anneal at 800 to 1100 ° C. EXAMPLES The present invention will be specifically described below with reference to examples. Steel having the chemical composition shown in Table 1 was melted in a converter and formed into a steel piece by continuous casting. The steel slab was heated to 1150 ° C., the finish temperature was 800 ° C., and hot rolled to 5.0 mm. This hot-rolled steel strip was annealed at 800 ° C, pickled, then cold-rolled, and finally annealed at 900 ° C and pickled once.
m cold-rolled steel sheet. From the obtained cold rolled steel sheet, JIS1
A No. 3 B-shaped tensile specimen was taken from a direction of 0 ° with respect to the rolling direction, and the yield strength, tensile strength, and elongation were measured. Further, a disc-shaped blank having a diameter of 300 mm was taken from the cold-rolled steel plate, and the disc was placed on a surface plate, and the maximum height of the warp including the burr of the blade was measured to obtain a sagging amount. The results are shown in Table 2. [Table 1] [Table 2] From Table 2, it can be seen that the invention example has very little sagging during punching, and the improvement in punchability is remarkable. In addition, it can be seen that the inventive examples have an elongation of 34% or more, an r value of 1.50 or more, and a moldability superior to that of the conventional material. Thus, it can be said that the steel sheet of the present invention has both excellent punchability and good formability. As described above, according to the present invention, there is provided a ferritic stainless steel cold-rolled steel sheet that effectively prevents the occurrence of sag during punching without degrading formability. Is possible.

Claims (1)

(57) [Claims] [Claim 1] By mass%, C: 0.03% or less, Si: 0.11
~2.00%, Mn: 1.00% or less, P: 0.019 ~ 0.035%, S:
0.03% or less, Cr: 10.00-25.00%, N: 0.03% or less, A
l: 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 satisfy the relationship of Ti / (C + N): 8 or more, and V and B satisfy the relationship of V / B: 10 or more, and the balance is Fe and inevitable impurities. A ferritic stainless steel cold-rolled steel sheet having excellent punchability and formability.