JPH0673457A - Production of cold rolled steel sheet excellent in punching property and formability - Google Patents

Abstract

PURPOSE:To obtain a steel sheet combining punching properties and good formability by a continuous annealing method, by using dead soft steel as a base, constituting deposition essentially of Ti series deposition small in the deterioration in material, adding suitable amounts of Nb, B or the like thereto and reducing its anisotropy. CONSTITUTION:A dead soft steel slab contg., by weight, <=0.005% C, <=0.5% Si, <=1.0% Mn, <=0.1% P, 0.02 to 0.10% S, 0.01 to 0.08% A1, <=0.005% N and 0.003 to 0.030% Nb together with Ti satisfying the formula of (48/12XC%+48/14XN%)+0.03 (%)<=Ti<=0.10 (%), and the balance Fe is prepd. This slab is subjected to hot rolling under the conditions of <=1300 deg.C heating temp., 850 to 950 deg.C finishing temp. and 500 to 750 deg.C coiling temp., is then subjected to cold rolling at >=50% draft and is thereafter subjected to continuous annealing in the temp. range of the recrystallization temp. to 900 deg.C. Moreover, the same steel may be incorporated with 0.0003 to 0.0030% B.

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 cold-rolled steel sheet which is excellent in punching workability and formability, and is particularly intended to obtain a cold-rolled steel sheet having both good punching property and formability at low cost. It is a thing.

[0002]

2. Description of the Related Art Conventionally, as a steel plate which is used for fine precision punching in a honeycomb shape after performing bowl-shaped overhang forming such as speaker net of audio equipment, SPCD or SPCE grade low carbon Box annealed material has been applied.

Generally, a material used for punching is required to have less burrs at the time of punching and less die wear at the time of continuous punching, but a low carbon box annealed material has an annealing process of several tens of hours. In C, C is coarsely precipitated as brittle cementite in the grain boundaries and in the grains, and this cementite divides the continuous shearing of the iron-ferrite grain during punching and also breaks brittlely, so the amount of burrs is small and It is known that wear is small and shear load is also small. Further, the formability can be easily improved by maintaining the punching property by increasing the annealing temperature.

However, for the purpose of improving the productivity and quality in the annealing process, the transition from the conventional box annealing method to the continuous annealing method of high temperature short time annealing is rapidly progressing at present.
There is an urgent need to develop a steel sheet having both punching workability and good formability even when using a continuous annealing method in which it is difficult to produce coarse cementite because it is a short time annealing.

As a method of improving the punching property of the continuously annealed material,
There are known a method of producing a large amount of MnS precipitates by adding Mn and S (JP-A-1-230748) and a method of adding a solid solution strengthening element such as P to harden a steel sheet. . However, in the former MnS-precipitated steel, although the punchability is improved, good formability cannot be obtained because this MnS is harmful to formability, while the latter hardened steel also has Although the punchability is improved, on the contrary, the moldability is significantly deteriorated, so that it is difficult to combine the punchability and the good moldability.

In view of this point, a method of hardening only the surface layer structure of a steel sheet having good formability as having both properties (Japanese Patent Laid-Open Nos. 3-56644, 3-226526, 3-277739 and 4).
-32538, 3-202442 and 3-199343)
However, this method has a disadvantage in that it requires a complicated manufacturing process and inevitably raises the cost.

[0007]

As described above, the punching property is improved by the method of containing a large amount of MnS precipitates as a substitute for the cementite in the conventionally known box-annealed material and the method of hardening the steel sheet. However, there was a problem that mechanical properties were significantly deteriorated. In addition, the inventors made a disc-shaped punching sample using several types of cold-rolled steel sheets, including conventional low-carbon box annealed materials, and investigated the form of burr formation in the circumferential direction. It was also clarified that the burr height has anisotropy and that the anisotropy of the burr height and the anisotropy of mechanical properties have a correlation. Here, it is desired that the material used for the punching process has as small anisotropy as possible in terms of mechanical properties as well as burr height.

The present invention advantageously solves the above-mentioned problems, and basically adopts a method of forming a large amount of precipitates as a method for improving the punchability of a continuously annealed material, but it is based on an ultra low carbon steel. A cold-rolled steel sheet excellent in punching workability and formability can be easily and easily formed by mainly forming Ti-based precipitates with little material deterioration and adding an appropriate amount of Nb, B, etc. to reduce anisotropy. It is an object to propose a manufacturing method that can be obtained at low cost.

[0009]

[Means for Solving the Problems] From the above viewpoints,
In the present invention, the steel type is an ultra-low carbon IF steel, and in order to impart good punchability and formability, a specific component system and a heat treatment method are effectively combined.

That is, according to the present invention, C: 0.005 wt% (hereinafter simply referred to as%), Si: 0.5% or less, Mn: 1.0% or less, P: 0.1% or less, S: 0.02 to 0.10%, Al: 0.01 ~ 0.08%, N: 0.005% or less and Nb: 0.003 to 0.030%, satisfying the range of the following formula: Ti (48/12 x C% + 48/14 x N%) + 0.03 (%) ≤ Ti ≤ 0.10
(%), With the balance being Fe and unavoidable impurities, which is an ultra-low carbon steel slab, under the conditions of slab heating temperature: 1300 ° C or less, finishing temperature: 850 to 950 ° C, winding temperature: 500 to 750 ° C. A cold-rolled steel sheet excellent in punching workability and formability, which consists of hot rolling, cold rolling at a reduction rate of 50% or more, and continuous annealing in the temperature range of recrystallization temperature to 900 ° C. It is a manufacturing method (first invention).

The present invention is also a method (second invention) for manufacturing a cold-rolled steel sheet excellent in punching workability and formability, which further contains B: 0.0003 to 0.0030% as an auxiliary component in the above-mentioned first invention. is there.

[0012]

First, the reason why the component composition of the raw material in the present invention is limited to the above range will be described. C: 0.005% or less If C is contained in excess of 0.005%, not only ductility and r-value decrease, formability deteriorates, but also the amount of Ti required for fixing C increases, which is economically disadvantageous. Therefore, the upper limit
It was set to 0.005%.

Si: 0.5% or less If Si is contained in an amount of more than 0.5%, the formability is deteriorated and the scale during hot rolling becomes difficult to peel off, so the upper limit was made 0.5%.

Mn: 1.0% or less Mn content exceeding 1.0% deteriorates formability, so the upper limit was made 1.0%.

P: 0.1% or less If P is contained in excess of 0.1%, the elongation of the steel sheet deteriorates, so the upper limit was made 0.1%.

In the present invention, it is necessary to improve the punching property and suppress the deterioration of the material due to the improvement as much as possible.
Here, TiS was used as the precipitate contained in the steel sheet to improve the punchability. The advantages of using TiS are:
It is as follows. i) Ti has a strong bonding force with C, N and S, so by controlling the addition amount of Ti to be approximately equivalent to the content of C, N and S, Ti remains in a solid solution state and adversely affects the material. It is possible to suppress the excessive addition amount. It should be noted that in the past record of Ti-based ultra-low carbon IF steel, Ti is 0.05% with respect to the content of C, N, S.
%, No significant material deterioration occurs even if added excessively. ii) As Ti-based precipitates, TiC, TiN, and TiS are known to have strong bonding strength, but when the sizes of these precipitates are compared, TiS is the largest. Therefore, the amount of Ti required to obtain the same punchability improving effect is the minimum in the case of TiS, which is particularly advantageous in terms of economy and material.

S: 0.02 to 0.10% From the above viewpoint, S must be 0.02% or more in order to improve the punching property, so 0.02% is the lower limit, and if it is added in excess of 0.10%, the formability is improved. Due to deterioration, the upper limit was made 0.10%.

(48/12 × C% + 48/14 × N%) + 0.03
(%) ≤ Ti ≤ 0.10 (%) Also, Ti can fix C, N and the lower limit of 0.02% S (48/12 x C% + 48/14 N%) + 0.03% as the lower limit. On the other hand, if added in excess of 0.10%, the moldability deteriorates, so the upper limit was made 0.10%.

Al: 0.01 to 0.08% Al is 0.01 to 0.08% as an amount necessary to obtain an Al kill.
The range is%.

N: 0.005% or less N, like C, is preferably low for obtaining good moldability, so the upper limit was made 0.005%.

Nb: 0.003 to 0.030% Nb is an element effective in reducing the anisotropy by making the structure of the hot rolled sheet finer. To reduce the anisotropy here, at least
0.003% Nb is required, while if added in excess of 0.030%, the structure becomes too fine and the formability deteriorates.
The range was 0.003 to 0.030%.

B: 0.0003 to 0.0030% B slightly reduces the elongation in the rolling direction and the r value by adding a small amount, and contributes effectively to the reduction of anisotropy. Therefore, in the present invention, the formability is deteriorated. If necessary, the effective amount for improving the anisotropy is 0.0003 to 0.0030%.

Next, the manufacturing process according to the present invention will be described. First, for the steel making process, a conventional method for producing an ultra low carbon material may be used. In the hot rolling process, when the slab heating temperature exceeds 1300 ° C, TiS, which has coarsely precipitated in the slab stage, is completely re-dissolved, and the coarse slab becomes coarse in the subsequent process.
Since it becomes difficult to obtain TiS precipitates, the upper limit was 1300 ° C.

The finishing temperature is set to 850 ° C. or higher in order to avoid material deterioration due to low temperature finishing, and conversely, at a high temperature exceeding 950 ° C., the ferrite grains of the hot rolled steel sheet become coarse and the drawability after cold rolling annealing deteriorates, so the upper limit is set. Was 950 ° C.

If the winding temperature is too high, the pickling property of the scale will be deteriorated, so that it is 750 ° C. or lower. On the other hand, if it is less than 500 ° C., good moldability cannot be obtained, so the lower limit was made 500 ° C.

In cold rolling, sufficient workability cannot be obtained without a reduction of at least 50%. Therefore, in the present invention, the reduction in cold rolling is set to 50% or more.

The annealing temperature in continuous annealing after cold rolling may be a recrystallization temperature or higher as usual, but a particularly desirable range is a temperature range of (primary recrystallization temperature + 30 ° C.) or higher. On the other hand, if the annealing temperature exceeds 900 ° C, there is a high risk of coarse grains, so the upper limit was set to 900 ° C. The temper rolling after annealing can be performed at a normal elongation rate (about plate thickness (mm)%) for the purpose of straightening the plate shape or adjusting the plate surface roughness.

[0028]

EXAMPLES Various slabs having the composition shown in Table 1 were prepared.
Each treatment of hot rolling, pickling, cold rolling, continuous annealing, and temper rolling was performed under the conditions shown in Table 2. Table 3 shows the results of an examination of the mechanical properties and burr height of the steel sheet thus obtained. Here, the burr height was obtained by punching a steel plate into a 100φ disc at the same time using the same punching tester, and measuring the burr height of the punched sample with a non-contact roughness meter. The burr height was measured in the rolling direction, 45 ° to the rolling direction, and three directions perpendicular to the rolling direction to evaluate the anisotropy of the burr height.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

As is clear from Table 3, the steel sheet obtained according to the method of the present invention has a smaller burr height and its anisotropy than those obtained by the conventional box annealing method as well as the comparative method.
Moreover, it has excellent mechanical properties.

[0033]

As described above, according to the present invention, it is possible to easily and inexpensively obtain a cold-rolled steel sheet excellent in both punching workability and formability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hagiwara, et al. 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (no address) Inside the Mizushima Works, Kawasaki Steel Co., Ltd. (72) Tokuhiro Nagamura, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama 1 chome (without street number) Kawasaki Steel Co., Ltd. Mizushima Steel Works

Claims (2)

[Claims] 1. C: 0.005 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.02-0.10 wt%, Al: 0.01-0.08 wt%, N : 0.005 wt% or less and Nb: 0.003 to 0.030 wt% satisfying the range of the following formula: Ti (48/12 × C% + 48/14 × N%) + 0.03 (%) ≤ Ti ≤ 0.10
(%), With the balance being Fe and unavoidable impurities, which is an ultra-low carbon steel slab, under the conditions of slab heating temperature: 1300 ° C or less, finishing temperature: 850 to 950 ° C, winding temperature: 500 to 750 ° C. Cold rolling with excellent punching workability and formability, which is characterized by performing hot rolling, then cold rolling at a reduction rate of 50% or more, and then performing continuous annealing in the temperature range of the recrystallization temperature or more and 900 ° C or less. Steel plate manufacturing method. 2. C: 0.005 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.1 wt% or less, S: 0.02-0.10 wt%, Al: 0.01-0.08 wt%, N : 0.005 wt% or less and Nb: 0.003 to 0.030 wt% satisfying the range of the following formula: Ti (48/12 × C% + 48/14 × N%) + 0.03 (%) ≤ Ti ≤ 0.10
(%) And B: 0.0003 to 0.0030 wt% with the balance Fe and unavoidable impurities in the very low carbon steel slab. Slab heating temperature: 1300 ° C or less, finishing temperature: 850 to 950 ° C, Winding temperature: It is characterized by hot rolling under the condition of 500 to 750 ℃, then cold rolling at a rolling reduction of 50% or more, and then performing continuous annealing in the temperature range of recrystallization temperature or more and 900 ℃ or less. A method for manufacturing a cold-rolled steel sheet having excellent punching workability and formability.