JP7436811B2 - Protective plates and protective structures - Google Patents

Description

TECHNICAL FIELD The present invention relates to a protection plate and a protection structure.

A road surface consisting of an upper layer of asphalt and a lower layer of concrete is removed by cutting the repaired surface using a cutter or the like during repair. Underground objects such as power lines or optical cables may be buried beneath the road surface, and there is a risk that the underground objects may be damaged by cutters or the like when cutting and removing the road surface for repair. Therefore, in order to prevent the underground object from being damaged when the repaired surface is cut and removed, a protection plate is sometimes buried to cover the underground object. Regarding protective plates, measures must be taken to prevent workers from accidentally cutting underground objects.

In relation to the above measures, for example, Non-Patent Document 1 discloses a protective steel plate made of SS400 in which the Brinell hardness, elongation, and plate thickness of the steel plate are controlled to a predetermined relationship. Non-Patent Document 1 describes that if the thickness of the protection plate (SS400) is 16 mm, it will give a sense of discomfort to the operator during cutting with a concrete cutter.

Japanese Patent Application Publication No. 2000-54078 (published on February 22, 2000)

Ministry of Land, Infrastructure, Transport and Tourism Kanto Regional Development Bureau “Protection method for shallow buried sections (draft)”

However, the protective plate disclosed in Non-Patent Document 1 has a thickness of 16 mm or more. Therefore, the weight of the protection plate becomes large, and workability during construction deteriorates.

Further, Patent Document 1 describes a steel plate having a thickness of 6 to 50 mm with specified Brinell hardness and elongation in a tensile test. When the steel plate of Patent Document 1 is cut with a diamond cutter, the stickiness of the steel plate reduces the cutting speed of the cutter to make the worker aware that the cut is being made. However, the judgment of the reduction in cutting speed depends on the experience of the operator, and if it is noticed too late, there is a risk that the underground object to be protected may be cut.

According to one aspect of the present invention, when a protective plate buried underground is cut, it can be easily noticed, and even if it is delayed, damage to underground objects due to cutting can be prevented. The purpose of the present invention is to realize a protective plate that can also prevent damage to underground objects due to impact.

The protective plate according to the present invention uses a diamond cutter with a diameter of 5 inches and a tip thickness of 1.9 mm, the circumferential speed of the diamond cutter is 2000 m/min, the cutting depth is 4 mm, and the moving speed of the diamond cutter with respect to the protective plate. When cutting is performed at a cutting speed of 10 mm/min and a cooling water flow rate of 100 to 150 ml/min, the average sound pressure level for 10 seconds of the sound in the range of 2000 to 4000 Hz is 90 dB or more at a position 1 m away from the cutting position, The specific cutting resistance is 4000 MPa or more, and the Charpy impact value is 300 J/cm ² or more.

According to one aspect of the present invention, when a protection plate buried underground is cut, it can be easily noticed, and damage to underground objects due to cutting can be prevented even if the notice is delayed. It is also possible to prevent damage to underground objects due to impact.

FIG. 1 is a cross-sectional view showing a protective structure according to an embodiment of the present invention. It is a schematic diagram of the apparatus used in the cutting test shown in an example. It is a photograph which shows the state of sound pressure measurement in a cutting test and a cutting test. It is a photograph of the cut surface of the test piece according to the example after the cutting test. 5 is an enlarged view of the surface of the steel plate in the photograph shown in FIG. 4. FIG. It is a photograph of the cut surface of a test piece according to a comparative example after a cutting test. 7 is an enlarged view of the surface of the steel plate in the photograph shown in FIG. 6. FIG. It is a graph showing the relationship between the distance from the bottom of the blade and the distribution of hardness. 3 is a graph showing the ratio of specific cutting resistance and the average sound pressure level at 2000 to 4000 Hz for Examples and Comparative Examples.

Hereinafter, one embodiment of the present invention will be described in detail. The following description is provided to provide a better understanding of the gist of the invention, and is not intended to limit the invention unless otherwise specified. Furthermore, in this application, "A to B" indicates that the number is greater than or equal to A and less than or equal to B.

<Component composition of the protective plate>
The protective plate according to one embodiment of the present invention has a component composition in mass %: C: 0.7 to 1.6%, Si: 0.8% or less, Mn: 8 to 16%, P: 0. This is a high Mn austenitic steel sheet containing 0.025% or less, S: 0.025% or less, Ni: 0.25% or less, and Cr: 0.20% or less, with the remainder being Fe and inevitable impurities. Hereinafter, the significance of the content of each element contained in the protective plate in this embodiment will be explained.

(C)
C (carbon) is an element effective in stabilizing austenite and improving its strength. It preferably contains 0.7% by mass to 1.6% by mass of C, and more preferably 0.8% by mass to 1.2% by mass. When the content is 0.7% by mass or more, austenite is stabilized, and when the content is 1.6% by mass or less, grain boundary carbides are less likely to occur even when the steel plate is solutionized at high temperature and then rapidly cooled during production of the steel sheet.

(Si)
Si (silicon) is an element necessary for melting and refining as a deoxidizing element. It is preferable that Si is contained in an amount of 0.8% by mass or less, and it is more preferable that Si is contained in an amount of 0.5% by mass or less. At 0.8% by mass or less, promotion of precipitation of carbides at grain boundaries can be suppressed.

(Mn)
Mn (manganese) is an element effective in forming austenite and stabilizing austenite. It is preferable that Mn be contained in an amount of 8% by mass to 16% by mass, more preferably 11% by mass to 14% by mass. When the content is 8% by mass or more, austenite becomes stable and grain boundary carbides are difficult to form. When the content is 16% by mass or less, hot workability is good and manufacturing of the steel plate becomes easy.

(P)
Since P (phosphorus) causes slab cracking, the lower the P content, the better. A preferable range of the content of P in the protective plate is 0.025% by mass or less.

(S)
S (sulfur) forms MnS, which tends to become a starting point for pitting corrosion, so the lower the S content, the better. A preferable range of the content of S in the protective plate is 0.025% by mass or less.

(Ni)
Ni (nickel) is an element effective in stabilizing austenite and improving toughness.
At 0.25% by mass or less, austenite is stabilized and toughness is improved. Furthermore, increases in material costs can be suppressed.

(Cr)
Cr (chromium) is an element effective in stabilizing austenite and improving its strength. When the content is 0.20% by mass or less, deterioration in ductility can be suppressed. Furthermore, austenite is stabilized and strength is improved.

<Characteristics of the protective plate>
The protective plate according to the present embodiment is a steel plate with an austenitic structure, and is a steel plate in which the austenitic structure to which the impact is applied transforms into a martensitic structure when an impact is applied during cutting with a cutter. Therefore, the protection plate according to the present embodiment forms a multi-phase structure of an austenite structure and a martensitic structure at the location where the impact is applied.

Therefore, when the protection plate according to this embodiment is cut with a cutter, the resonance (vibration, harsh sound) between the protection plate and the cutter blade increases. Specifically, a diamond cutter with a diameter of 5 inches and a tip thickness of 1.9 mm was used, the circumferential speed of the diamond cutter was 2000 m/min, the cutting depth was 4 mm, and the speed of movement of the diamond cutter with respect to the protective plate was 10 mm/min. The average sound pressure level for 10 seconds of the sound in the range of 2000 to 4000 Hz generated when cutting with a cooling water amount of 100 to 150 ml/min is 90 dB or more at a position 1 m away from the cutting position. As a result, it becomes easier for the operator to notice that the protection plate according to the present embodiment is being cut due to the sound generated when cutting with the cutter. Thereby, by stopping the cutter before cutting the protection plate, cutting of the buried object to be protected can be prevented.

The above sound pressure level was measured by installing a microphone 1 m away from the cutting position and measuring the sound pressure level at the time of cutting using an acoustic vibration measuring instrument SA-A1 (manufactured by Rion Co., Ltd.). Evaluation was made using analysis software AS-70 (manufactured by Rion Co., Ltd.) using the average value of sound pressure levels at 2000 Hz, 2500 Hz, 3150 Hz, and 4000 Hz. It is known that sounds in the range of 2000 to 4000 Hz are in the audible range that humans find unpleasant.

Further, since the protection plate according to the present embodiment has a multi-phase structure of austenite and martensite at the location where the impact is applied, the specific cutting resistance increases. Specifically, the specific cutting resistance is 4000 MPa or more. Thereby, the protection plate according to this embodiment can prevent damage to underground objects due to cutting. The cutting resistance (N) is the value obtained by dividing the cutting torque (Nm) by the cutter diameter (m), and the specific cutting resistance (MPa) is the value obtained by dividing the cutting resistance (N) by the cutting area (mm ² ). This is the divided value.

Moreover, by having the above-described configuration, the protection plate according to the present embodiment has a Charpy impact value of 300 J/cm ² or more. Therefore, when a shock is applied to the protection plate, holes or the like are less likely to be formed in the protection plate.

FIG. 1 is a sectional view showing the configuration of a protective structure 1 in this embodiment. The protective structure 1 shown in FIG. 1 consists of the above-mentioned protective plate. The protective structure 1 is to be buried in a road surface formed of asphalt or concrete, and by storing underground objects 2 inside, it is possible to prevent the underground objects 2 from being removed during road surface repairs. Used to prevent being struck and cut. Note that the protective structure in the present invention is not limited to the structure shown in FIG. 1, and can be appropriately designed depending on the shape, size, etc. of the underground object.

The protective plate in this embodiment is preferably made of austenitic steel and has a thickness of 6 mm or less. This improves workability, so the protection plate can be formed into any shape, and can be inexpensively processed into a shape suitable for the object to be protected.

<Manufacturing method of protective plate>
The method for manufacturing a protective plate according to this embodiment includes a casting process, a hot rolling process, and a water toughness process.

The continuous casting process, for example, is mass%: C: 0.7 to 1.6%, Si: 0.8% or less, Mn: 8 to 16%, P: 0.025% or less, S: 0.025. % or less, Ni: 0.25% or less, Cr: 0.2% or less, and the balance is Fe and unavoidable impurities.

In the hot rolling process, the slab cast in the casting process is heated to a temperature of 1100 to 1300°C, hot rolled at a finishing temperature of 780 to 900°C to produce a hot rolled sheet, and then heated to a temperature of 350 to 500°C. Winding at a winding temperature of °C.

In the water toughness process, the hot rolled sheet obtained by hot rolling is heated and held at 900°C to 1100°C, and then cooled to a temperature of 500°C or less at a cooling rate of 10°C/sec or more. Thereby, steel having an austenitic structure can be produced.

A steel plate of Example 1 of the present invention and a steel plate of Comparative Example 1 of the present invention were manufactured using the following manufacturing method.

(Example 1)
The raw materials were melted in a vacuum melting furnace to have the components shown in Example 1 in Table 1, and hot-rolled at a hot-rolling finishing temperature of 830°C and a hot-rolling winding temperature of 430°C. A hot rolled sheet of .0 mm was obtained. The steel plate of Example 1 was obtained by holding the obtained hot-rolled plate at 1000° C. for 20 minutes and immediately cooling it with water to room temperature for water toughness treatment. Note that components other than those shown in Example 1 in Table 1 are Fe and inevitable impurities.

(Comparative example 1)
The raw material was melted in a vacuum melting furnace to have the components shown in Comparative Example 1 in Table 1, and hot rolled at a finishing temperature of 880°C and a coiling temperature of 580°C, resulting in a plate thickness of 8.0 mm. A steel plate of Example 1 was obtained. Note that the components other than those shown in Comparative Example 1 in Table 1 are Fe and inevitable impurities.

(Evaluation method)
<Impact test>
An impact test was conducted in accordance with JIS Z2242 using a Charpy impact tester with a capacity of 300 J. More specifically, a test piece with a thickness of 6 mm in which a V-shaped notch was formed was prepared, and the Charpy impact value was determined by applying an impact to the test piece.

<Cutting test>
A cutting test was conducted on the steel plates of Example 1 and Comparative Example 1. FIG. 2 is a schematic diagram showing the apparatus used in the cutting test. FIG. 3 is a photograph showing a cutting test and sound pressure measurement in the cutting test. A cutting test using a cutter blade was conducted on the test pieces under the conditions shown in Table 2. More specifically, using a diamond cutter with a diameter of 5 inches and a tip thickness of 1.9 mm, the circumferential speed of the diamond cutter was 2000 m/min, the cutting depth was 4 mm, and the moving speed of the diamond cutter with respect to the protective plate was 10 mm/min. The specific cutting resistance was evaluated by measuring the cutting torque Mz at a feed rate F of 10 mm/min and a cooling water amount of 100 to 150 ml/min. In the cutting test, when the specific cutting resistance was 4000 MPa or more, it was evaluated as good.

In addition, in the cutting test, we evaluated the relationship between the specific cutting resistance and the average sound pressure level at 2000 to 4000 Hz during cutting, and the relationship between the hardness of the cut surface of the test piece after the cutting test and the distance from the bottom of the blade. did.

(result)
The results of the impact test and cutting test in Example 1 and Comparative Example 1 are shown in Table 3 and FIGS. 4 to 7. FIG. 4 is a photograph of the cut surface of the test piece according to Example 1 after the cutting test. FIG. 5 is an enlarged view of the surface of the steel plate in the photograph shown in FIG. 4. FIG. 6 is a photograph of the cut surface of the test piece according to Comparative Example 1 after the cutting test. FIG. 7 is an enlarged view of the surface of the steel plate in the photograph shown in FIG. 6. FIG. 8 is a graph showing the relationship between the distance from the bottom of the blade (in other words, the distance from the cut surface) and hardness after the cutting test. FIG. 9 is a graph showing the ratio of specific cutting resistance and the average sound pressure level at 2000 to 4000 Hz for Example 1 and Comparative Example 1.

As shown in Table 3, as a result of the impact test, the Charpy impact value (380 J/cm ² ) of the test piece of Example 1 was higher than the Charpy impact value (89 J/cm ² ) of Comparative Example 1. The impact properties of the test pieces were good.

After the cutting test, the hardness of the test piece of Example 1 at the bottom of the blade was 640 HV or more, and the hardness of the test piece of Example 1 at the cross section other than the bottom of the blade was 200 HV. As shown in FIGS. 4 and 5, at the bottom of the blade of the test piece of Example 1, part of the austenite was transformed into deformation-induced martensite due to the strain caused by cutting, and a composite of austenite and martensite was formed. It is thought that a phase structure was formed. As a result, the bottom of the test piece cut with the concrete cutter hardened, increasing the specific cutting resistance and making it difficult to cut. In addition, due to the increase in specific cutting resistance, resonance (vibration) between the test specimen and the cutter blade generates a harsh sound (the average sound pressure level increases), giving the operator a sense of discomfort during cutting. It is thought that this was possible.

In addition, according to the "Protection Method for Shallow Buried Sections (Draft)" published by the Kanto Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism, if the thickness of the protective steel plate (SS400) is 16 mm, workers will feel uncomfortable while cutting with a concrete cutter. It is said to give. On the other hand, the steel plate of Example 1 gave the operator a sense of discomfort even though the thickness was 6 mm. Therefore, the cost for manufacturing the protection plate can be reduced. Specifically, by reducing the plate thickness from 16 mm to less than half, to 6 mm, the weight of the protective plate can be reduced and work efficiency during construction will be improved.

On the other hand, in the test piece of Comparative Example 1, as shown in Figures 6 and 7, there was no transformation from austenite to deformation-induced martensite due to the strain caused by cutting, and there was no change in hardness even at the bottom of the blade. There wasn't. Therefore, it is considered that the operator did not feel any discomfort during cutting.

As shown in Table 3, the test piece of Example 1 exhibited a specific cutting resistance of 4000 MPa or more. Further, as shown in FIG. 9, the average sound pressure level (dB) at 2000 to 4000 Hz when cutting the test piece of Example 1 was 97 dB. On the other hand, the test piece of Comparative Example 1 exhibited a specific cutting resistance of 2100 MPa, and the average sound pressure level (dB) at 2000 to 4000 Hz was 87 dB. That is, the average sound pressure level at 2000 to 4000 Hz that occurs when cutting the test piece of Example 1 is 10 dB higher than the average sound pressure level at 2000 to 4000 Hz that occurs when cutting the test piece of Comparative Example 1. In this way, the test piece of Example 1 not only gives the operator a sense of discomfort due to the increase in specific cutting resistance, but also changes the sound during the cutting test, making it even more difficult for the operator to cut the steel plate. I was able to make them realize that.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

1 Protective structure 2 Underground objects

Claims (4)

Using a diamond cutter with a diameter of 5 inches and a tip thickness of 1.9 mm, the circumferential speed of the diamond cutter was 2000 m/min, the cutting depth was 4 mm, the moving speed of the diamond cutter with respect to the protective plate was 10 mm/min, and the amount of cooling water was When cutting at 100-150ml/min,
The average sound pressure level for 10 seconds of the generated sound in the range of 2000 to 4000 Hz is 90 dB or more at a position 1 m away from the cutting position,
Specific cutting resistance is 4000 MPa or more,
Charpy impact value is 300 J/cm2 or more,
In mass %, C: 0.7 to 1.6%, Si: 0.8% or less, Mn: 8 to 16%, P: 0.025% or less, S: 0.025% or less, Ni: 0. A protective plate having a chemical composition of 25% or less, Cr: 0.20% or less, and the balance consisting of Fe and inevitable impurities . The protection plate according to claim 1, wherein the average sound pressure level is an average value of sound pressure levels of 2000 Hz, 2500 Hz, 3150 Hz, and 4000 Hz. The protective plate according to claim 1 or 2, having a plate thickness of 6 mm or less. A protective structure for protecting an underground object manufactured using the protective plate according to any one of claims 1 to 3 .

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