JP4359474B2 - Cold-rolled steel sheet for bell and method for producing the same - Google Patents

Description

  The present invention relates to a cold-rolled steel sheet having excellent timbre and surface properties after processing as a bell material for musical instruments and toys, and a method for producing the same.

  As a bell material for musical instruments and toys, generally, a cold-rolled steel plate made of rimmed steel is used from the viewpoint of timbre and workability. However, since there is no document that specifies this, no known document can be presented in this specification.

If an attempt is made to produce a bell using rimmed steel as a raw material, the ingot-making process and the ingot-making process are added, so that the production efficiency is low and the production cost is considerably higher than when a continuous cast material is used as the raw material.
The present invention has been devised to reduce the cost by switching from rimmed steel to continuous casting material, and has been conventionally used by providing specific physical properties even if continuous casting material is used. An object of the present invention is to obtain a cold rolled steel sheet for bells having a tone color equivalent to or higher than that of rimmed steel and surface properties after processing.

In order to achieve the object, the bell cold rolled steel sheet of the present invention has an aging index (AI value) evaluated by a tensile test of 40 to 80 N / mm ² and a ferrite crystal grain size of 40 μm or less. It is characterized by its size.
Its components and composition are: C: 0.001 to 0.03 mass%, Si: less than 0.01 mass%, Mn: 0.1 to 1.5 mass%, P: 0.05 mass% or less, S: 0.01 wt% or less, acid-soluble Al: 0.01 wt% or less, N: from .034 to .010 include mass%, that having a composition the balance being Fe and unavoidable impurities.
Such a cold-rolled steel sheet for bells is a hot-rolled steel having the above-mentioned components and composition continuously cast, hot-rolled finishing temperature: Ar ₃ transformation point or higher, hot-rolled coiling temperature: 450-600 ° C. It is obtained by rolling, followed by pickling, followed by cold rolling at a cold rolling rate of 50 to 80% and then annealing in the range of 650 to 850 ° C.

The inventors of the present invention have made various studies on continuous casting materials from the viewpoints of timbre and surface properties after processing as substitutes for the rimmed material as the material for the bell. As a result, a cold-rolled steel sheet having an aging index (AI value) evaluated by a tensile test of 40 to 80 N / mm ² and a ferrite crystal grain size of 40 μm or less is a conventional rimmed material. It was confirmed that good characteristics equivalent to or better were obtained.
Generally, the quality of the timbre, which is the most important characteristic for bell materials, is determined by the reverberation time. It can be said that the longer the reverberation time, the better the material for the bell. When reverberation is interpreted as a phenomenon in which vibration remains as damped vibration, the smaller the vibration damping capability of the material itself, the longer the reverberation time, and the better the bell material. Since the vibration damping ability of the steel sheet is represented by a loss coefficient η, the smaller the loss coefficient η, the longer the reverberation time, and the more suitable as a bell material.

The present inventors have investigated studied the relationship between loss factor η and mechanical properties of the steel sheet in detail.
As a result, it was found that there is a correlation between the aging index (AI value) evaluated in the tensile test and the loss coefficient η, and the larger the AI value, the smaller the loss coefficient η. By the way, the aging index (AI value) is obtained by applying a pre-strain of a predetermined ratio to a tensile test piece, for example, a JIS No. 5 test piece, unloading and heating it at a predetermined temperature for a predetermined time, and then pulling again. This is a numerical value obtained by testing and determining the difference in yield stress before and after aging. In addition, in this specification, after giving a pre-strain of 2.0%, the numerical value when performing aging of 100 degreeC x 1 hour is used. The AI value is handled as a parameter indicating the existence state of the solid solutions C and N. The larger the value, the more the solid solutions C and N.

In cold-rolled steel sheets having the same C and N contents, the smaller the aging index AI value is, the more contained C and N are fixed as carbides and nitrides. That is, the smaller the Al value, the more fine carbides and nitrides are precipitated in the ferrite grains or grain boundaries as the parent phase. And when an external force is applied to such a steel plate and it is vibrated, it is presumed that the more fine carbides and nitrides are, the larger the so-called pinning effect is, and the vibration is rapidly attenuated and the loss factor η is increased. On the contrary, it is presumed that the larger the aging index AI value, the more the dissolved C and N, that is, the fewer precipitated carbides and nitrides.
For these reasons, it is presumed that a cold-rolled steel sheet excellent in timbre as a bell material was obtained by adjusting the aging index AI value to a predetermined range. As a result of repeating various preliminary experiments, in the low C steel such as the steel of the present invention, if the AI value measured under the above conditions is less than 40 N / mm ² , the loss coefficient η increases and the reverberation time decreases. It was unsuitable as a bell material. On the other hand, if the AI value exceeds 80 N / mm ² , not only does the strain pattern easily occur during deep drawing, but also the waist breaks easily during bending.

Next, workability as a bell material was examined.
In general, the larger the crystal grain size after annealing, the better the deep drawability. However, when trying to form into a bell shape by deep drawing, if the crystal grain size is too large, the surface becomes rough and the appearance of the product deteriorates. In order to obtain a bell-shaped product having a good appearance without generating rough skin on the surface, it was also confirmed that the grain size of the ferrite crystal grains after annealing must be 40 μm or less.

In obtaining the cold rolled steel sheet for bells of the present invention, first, the component composition of the steel is determined as follows.
C: 0.001 to 0.03 mass%
C is preferably as small as possible from the viewpoint of deep drawability, but if it is less than 0.001% by mass, it hardly remains as solid solution C, and the AI value tends to decrease and the crystal grains tend to become coarse. However, if it exceeds 0.03% by mass, deep drawability and ductility are lowered, and workability is deteriorated. Further, the solid solution C hardly remains and the AI value becomes small.
Si: Less than 0.01% by mass Si is an alloy component added as necessary. Like Al, it may be added as a deoxidizer. However, if it exceeds 0.5 mass%, the deep drawability is lowered and the surface properties are likely to deteriorate.

Mn: 0.1 to 1.5% by mass
Mn is a component that contributes to improvement in strength. The strength improvement effect by Mn is not exhibited unless it is less than 0.1% by mass. The greater the Mn content, the more effective, but if it exceeds 1.5 mass%, the deep drawability will be reduced.
P: 0.05% by mass or less P causes low temperature brittleness. The adverse effect of P on the low temperature brittleness can be suppressed by regulating the P content to 0.05% by mass or less.
S: 0.01% by mass or less S, if contained in a large amount, impairs cold or hot workability, so it is preferable to reduce S as much as possible. If the amount of sulfide of MnS becomes too large, the deep drawability deteriorates, so S is set to 0.01% by mass or less.

Acid-soluble Al: 0.01% by mass or less Al is an alloy component added as a deoxidizer, and it is preferable to add a relatively large amount of Al in order to obtain a sufficient deoxidation effect. However, when the Al content exceeds 0.01% by mass as acid-soluble Al, the solid solution N is precipitated as AlN, so the solid solution N is reduced, the AI value is reduced, and the reverberation time is remarkably shortened.
N: 0.0034 to 0.010 mass%
N is an element harmful to deep drawability, and the smaller the number, the better. However, if it is less than 0.001% by mass, the effect of solute N is hardly obtained. In order to leave the solid solution N, the amount of Al is reduced and N is added. Since excessive addition of N lowers the deep drawability, it is necessary to stop at 0.01% by mass or less. Even if N is added excessively, it is not effective for increasing the AI value.

Next, the manufacturing process will be described.
After the steel material having the above component composition is melted, it is continuously cast into a slab. The obtained slab is directly sent as it is, or once cooled to be a cooled piece, and then hot-rolled. The obtained hot-rolled sheet is pickled, subjected to cold rolling, and then annealed.
Each condition is as follows.
Hot rolling finishing temperature: the Ar ₃ transformation point or more Ar ₃ below transformation temperature, variation of the hot intensity with the transformation is large, causing to lower the accuracy of plate thickness.

Hot rolling coiling temperature: 450-600 ° C
The higher the coiling temperature, the more the ductility is improved. However, when the temperature exceeds 600 ° C., the solid solution N decreases due to coarsening of carbides and generation of AlN, and the AI value decreases. When the coiling temperature is lower than 450 ° C., the shape of the steel sheet deteriorates and becomes hard.
Cold rolling: Cold rolling reduction 50 to 80%
In cold rolling, sufficient workability cannot be obtained unless the reduction rate is 60% or more, so the rolling rate is 60% or more. If the rolling reduction exceeds 80%, not only the workability is lowered but also the cost is increased, so the upper limit of the rolling reduction is 80%.
Annealing temperature after cold rolling: 650-850 ° C
Annealing is performed at a temperature in the range of 650 to 850 ° C. For annealing, either batch annealing or continuous annealing may be adopted. If the annealing temperature is below 650 ° C., sufficient workability cannot be obtained. On the other hand, if the temperature exceeds 850 ° C., the crystal grains become coarse, and the surface becomes extremely rough after processing.

The steel slab having the composition shown in Table 1 was heated and soaked at 1200 ° C., and then subjected to rough rolling and finish rolling to produce a 3.3 mm thick hot rolled steel sheet. After pickling the obtained hot-rolled steel sheet, it was subsequently cold-rolled at a cold rolling reduction of about 70% to a thickness of 1.0 mm, and then subjected to continuous annealing at 750 ° C.
About the obtained steel plate, the tensile test was done at room temperature and the tensile characteristic was measured. For the tensile test, No. 5 test piece of JIS Z2201 was used. The AI value was measured by applying a strain of 2.0% to a JIS No. 5 test piece, followed by heat treatment at 100 ° C. for 1 hour, and obtaining the difference in yield stress before and after the heat treatment.
Moreover, the average particle diameter of the ferrite crystal grain of each cold-rolled steel sheet was measured based on JIS G0552.
Furthermore, the loss factor was measured for each cold-rolled steel sheet, and the reverberation time after impact vibration was measured for the sample subjected to cup drawing. The loss factor η was measured at a frequency of 125 Hz at room temperature in accordance with JIS G0602 using a test piece of 15 mm width × 250 mm length. The reverberation time was measured by measuring the time required for the sound pressure level to decrease by 60 dB when the cup subjected to drawing processing was subjected to impact excitation with an energy of 40 N · cm.
The results are shown in Table 2 and FIGS.

As can be seen from the above results, No. 1 as an example of the present invention. In the samples 1 to 4, the AI values are all 50 N / mm ² or more and the loss coefficient η is less than 0.01, which is suitable as a bell material.
On the other hand, No. with a large Al content. In the samples 5 and 6, since the solid solution N is small, the AI value is lower than 40 N / mm ² defined in the present invention, the loss coefficient η is large, and the reverberation time is short.
In addition, No. which is an example of the present invention. In the sample No. 1, the crystal grain size was 38 μm, and there was no problem with the surface skin after deep drawing. It was confirmed in another example that the surface properties after processing deteriorated as the crystal grain size further increased.

The figure which shows the measurement result of the relationship between the loss factor of each cold-rolled steel plate and the reverberation time after impact vibration in an Example. The figure which shows the measurement result of the relationship between AI value of each cold-rolled steel plate and a loss coefficient in an Example.

Claims (2)

C: 0.001 to 0.03 mass%, Si: less than 0.01 mass%, Mn: 0.1 to 1.5 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less , Acid-soluble Al: 0.01% by mass or less, N: 0.0034 to 0.010% by mass, with the balance being Fe and inevitable impurities, and an aging index evaluated by a tensile test ( A cold rolled steel sheet for bells having an AI value of 40 to 80 N / mm ² and a ferrite crystal grain size of 40 μm or less. C: 0.001 to 0.03 mass%, Si: less than 0.01 mass%, Mn: 0.1 to 1.5 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less , Acid-soluble Al: 0.01% by mass or less, N: 0.0034 to 0.010% by mass, continuously casting steel having a composition composed of Fe and inevitable impurities, and hot rolling finish temperature: Hot rolling at an Ar ₃ transformation point or higher, hot rolling coiling temperature: 450 to 600 ° C., subsequent pickling, cold rolling at a cold rolling ratio of 50 to 80%, and then 650 to 850 ° C. A method for producing a cold rolled steel sheet for bells, characterized by annealing in a range.

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