Guardrail beam

Abstract

Provided are: a guardrail beam comprising a plated steel material provided with a steel material and plating layers formed on both surfaces of the steel material and including a Zn-based plating layer, at least one end surface of the steel material being coated with the plating layers, and satisfying 0.60 tc < = tilt; tc, We > = Wc, and Wt > = Wc (tc is the average plate thickness (mm) of the steel material at a position of 10 mm or more inward from the end surface coated with the plating layer, te is the average plate thickness (mm) of the steel material at a position of 1-10 mm from the end surface coated with the plating layer, We is the average thickness ([mu] m) of one surface of the plating layer at a position of 1-10 mm from the end surface coated with the plating layer, and Wt is the average thickness ([mu] m) of the other surface of the plating layer at a position of 1-10 mm from the end surface coated with the plating layer. Wc is the average thickness ([mu] m) of one surface of the plating layer at a position 10 mm or more inward from the end surface coated with the plating layer, and Wt is the average thickness ([mu] m) of the plating layer at the end surface coated with the plating layer.

Description

Technical Field

[0001] The invention relates to a guardrail beam. Background Art

[0002] Guardrails are generally composed of guardrail beams with corrugated cross-sections and pillars, and plated steel is sometimes used for the guardrail beams. The plated steel is plated in two ways, for example, pre-plating in which the steel sheet is plated in advance, and post-plating (sometimes also called immersion plating) in which the steel sheet is plated after being processed into a product.

[0003] Regarding the pre-plating treatment, for example, Patent Document 1 teaches that when wiping the plated steel strip, the amount of the plating metal adhered increases at the edge portion of the steel strip, and as a result, over-coating of the edge occurs, which may cause poor quality such as poor flatness. Therefore, by supplying preheated auxiliary wiping gas from an auxiliary wiping nozzle corresponding to the edge portion of the plated steel strip, the amount of the plating metal adhered is adjusted to prevent the occurrence of over-coating of the edge on the plated steel strip.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 6-122953 Summary of the invention

[0006] As a guardrail beam, for example, when using a plated steel material that has been subjected to a post-plating treatment, it is necessary to process the steel plate into a product, transport the processed product, and then subject it to a post-plating treatment. Therefore, in the case of a post-plating treatment, it is troublesome and the cost is also increased. On the other hand, in the case of the pre-plating treatment described in Patent Document 1, since the plating is performed in advance, the plating after the processing is not required, which has the advantage of being able to reduce costs compared to the post-plating treatment. However, the pre-plating treatment generally has a smaller amount of coating adhesion than the post-plating treatment, so sometimes the corrosion resistance is poor. In addition, in the pre-plating treatment, the end portion after the processing is cut by a cutting machine or the like is not covered by the coating, so there is a problem of corrosion easily occurring from such an end portion compared to the case of a post-plating treatment in which the plating is performed after processing.

[0007] Even if the use of the edge of the pre-plated steel material that has not been cut and processed for guardrail beams is studied, it is necessary to be able to solve the quality problems such as poor flatness caused by excessive edge coating described in Patent Document 1, and to achieve the high corrosion resistance and the associated long life required for guardrail beams generally used in relatively harsh outdoor environments, which is very difficult.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a guardrail beam having improved corrosion resistance by a new structure.

[0009] In order to achieve the above-mentioned object, the inventors conducted research focusing on the structure of the end portion of the guardrail beam where corrosion is more likely to occur. As a result, the inventors found that by making the thickness of the end portion of the steel material suitable for the guardrail beam thinner within a predetermined range, and making the plating thickness within the predetermined range relatively thicker, and then making the plating thickness of the end face relatively thicker, the corrosion of the end portion of the guardrail beam can be significantly suppressed or prevented, thereby completing the present invention.

[0010] The present invention for achieving the above-mentioned object is as follows.

[0011] (1) A guardrail beam, characterized in that it is composed of a plated steel material having a steel material and a plated layer, wherein the plated layer is formed on both surfaces of the steel material and includes a Zn-based plated layer,

[0012] At least one end surface of the steel material is coated with the plating layer, and the following formulas 1 to 3 are satisfied.

[0013] 0.60 × tc ≤ te < tc Formula 1

[0014] We ≥ Wc Equation 2

[0015] Wt ≥ Wc Formula 3

[0016] in,

[0017] tc is the average plate thickness (mm) of the steel material at a position 10 mm or more inward from the end surface covered by the coating.

[0018] te is the average plate thickness (mm) of the steel material at a position of 1 to 10 mm from the end surface covered with the coating.

[0019] We is the average thickness (μm) of the coating on one side at a position 1 to 10 mm from the end surface covered by the coating.

[0020] Wc is the average thickness (μm) of a single surface of the plating layer at a position 10 mm or more inward from the end surface covered with the plating layer, and Wt is the average thickness (μm) of the plating layer at the end surface covered with the plating layer.

[0021] (2) The guardrail beam according to (1) above, characterized in that the plating layer is a Zn-Al-Mg based plating layer.

[0022] (3) The guardrail beam according to (1) or (2) above, characterized in that the coating has the following chemical composition, expressed in mass %, comprising:

[0023] Al: more than 15.0% and less than 30.0%,

[0024] Mg: more than 5.0% and less than 15.0%,

[0025] Sn: 0~0.70%,

[0026] Ca: 0~0.60%,

[0027] Si: 0-0.75%,

[0028] Ti: 0~0.25%,

[0029] Ni: 0-1.00%,

[0030] Co: 0-0.25%,

[0031] Fe: 0-5.0%,

[0032] B: 0 to 0.50%, and

[0033] Balance: Zn and impurities.

[0034] (4) The guardrail beam according to any one of (1) to (3) above, wherein the end portion covered with the plating layer is arranged to face upward relative to the ground.

[0035] (5) The guardrail beam according to any one of (1) to (4) above, wherein the coating coverage from the end surface coated with the coating to a position 10 mm is 90% by area or more.

[0036] (6) The guardrail beam according to any one of (1) to (5) above, characterized in that at least one end face other than the end face covered by the coating is a cut end face, and the cut end face has: an inclined face inclined from the first surface to the second surface of the steel material relative to the plate thickness direction, and a fracture face, or has: an inclined face inclined from the first surface to the second surface of the steel material relative to the plate thickness direction, a shear face, and a fracture face,

[0037] The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material.

[0038] The total coating coverage of the inclined surface and the sheared surface is 50% by area or more.

[0039] (7) The guardrail beam according to any one of (1) to (5) above, characterized in that:

[0040] At least one end face other than the end face covered by the plating layer is a cut end face, and the cut end face has:

[0041] A first inclined surface inclined with respect to the plate thickness direction from the first surface toward the center of the steel material;

[0042] A second inclined surface inclined with respect to the plate thickness direction from the second surface toward the center of the steel material; and

[0043] a fracture surface formed between the first inclined surface and the second inclined surface,

[0044] The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material.

[0045] The total plating coverage of the first inclined surface and the second inclined surface is 50 area % or more.

[0046] According to the present invention, it is possible to provide a guardrail beam having improved corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram showing the structure of an end portion of a plated steel material constituting a guardrail beam according to an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram showing a cutting state by a conventional cutting device.

[0049] Figure 3 It is a schematic diagram showing a cut end surface of a plated steel material after being cut by a conventional cutting device.

[0050] Figure 4 It is a schematic diagram showing a cut state when a cut end face according to the additional preferred embodiment 1 is obtained.

[0051] Figure 5 It is a schematic diagram showing a cut state when a cut end face according to the additional preferred embodiment 1 is obtained.

[0052] Figure 6 It is a schematic diagram showing a cut end surface of the additional preferred embodiment 1.

[0053] Figure 7 It is a schematic diagram showing a cut end surface of an additional preferred embodiment 2.

[0054] Figure 8 This is a schematic diagram showing a state of a plated steel material before cutting for obtaining a cut end surface according to an additional preferred embodiment 2.

[0055] Fig. 9 Is based on Figure 8 Schematic diagram of the state after the plated steel material is cut by the cutting device shown. DETAILED DESCRIPTION

[0056] <Guardrail beam>

[0057] The guardrail beam according to the embodiment of the present invention is composed of a plated steel material including a steel material and a plated layer, wherein the plated layer is formed on both surfaces of the steel material and includes a Zn-based plated layer.

[0058] At least one end surface of the steel material is coated with the plating layer, and the following formulas 1 to 3 are satisfied.

[0059] 0.60 × tc ≤ te < tc Formula 1

[0060] We ≥ Wc Equation 2

[0061] Wt ≥ Wc Formula 3

[0062] in,

[0063] tc is the average plate thickness (mm) of the steel material at a position 10 mm or more inward from the end surface covered by the coating.

[0064] te is the average plate thickness (mm) of the steel material at a position of 1 to 10 mm from the end surface covered with the coating.

[0065] We is the average thickness (μm) of the coating on one side at a position 1 to 10 mm from the end surface covered by the coating.

[0066] Wc is the average thickness (μm) of a single surface of the plating layer at a position 10 mm or more inward from the end surface covered with the plating layer, and Wt is the average thickness (μm) of the plating layer at the end surface covered with the plating layer.

[0067] In a guardrail beam made of a steel material with a coating, sometimes the ends of the steel material are not sufficiently covered with the coating. In this case, there is a problem that corrosion is more likely to occur and progress at the ends than at the front and back of the steel material. If red rust is generated due to corrosion of the ends and it progresses from the ends, it will not only lead to a reduction in lifespan, but also a significant reduction in appearance quality, so it is not preferred. Therefore, the inventors have conducted research focusing on the structure of the ends of the guardrail beam where corrosion is more likely to occur and progress. The following is a more detailed description with reference to the accompanying drawings.

[0068] Figure 1 Schematic diagram showing the structure of the end portion of the plated steel material constituting the guardrail beam according to the embodiment of the present invention. Figure 1 The plated steel material 1 constituting the guardrail beam of the embodiment of the present invention comprises a steel material 2 and a coating 3 including a Zn-based coating formed on both sides, i.e., the front and back sides, of the steel material 2, and an end face 4 of the steel material 2 is coated with the coating 3. First, the inventors have found that by reducing the thickness within a predetermined range of the end of the steel material 2, more specifically, by thinning the end face 4 of the steel material 2 at a position 1 to 10 mm from the end face 4 of the steel material 2 coated with the coating 3, i.e., at a position 1 to 10 mm perpendicular to the plate thickness direction and 1 to 10 mm inside the end face 4 ( Figure 1 The average plate thickness (mm) of the steel material 2 in the A region in the coating layer 3 is set as te, and the position 10 mm or more inward from the end face 4 of the steel material 2 coated with the coating layer 3 ( Figure 1 When the average plate thickness (mm) of the steel 2 in the B area) is set to tc, their average plate thickness is controlled to satisfy the following formula 1, thereby even if the coating 3 at the end disappears and a part of the steel 2 is exposed, the area of ​​the cathode reaction region can be reduced by the thin plate thickness of the exposed part, so the sacrificial corrosion protection effect of the coating 3 including the Zn-based coating can be suppressed to a minimum, thereby improving the corrosion resistance of the plated steel 1 and the guardrail beam composed of it, thereby achieving a longer service life.

[0069] 0.60 × tc ≤ te < tc Formula 1

[0070] In addition, the inventors have found that, in association with thinning the average plate thickness te (μm) of the steel 2A region, the average thickness We (μm) of the coating 3 on one side of the A region is made the same as or relatively thicker than the average thickness Wc (μm) of the coating 3 on one side of the B region, more specifically, by controlling their average thicknesses to satisfy the following formula 2, and further by making the average thickness Wt (μm) of the coating 3 on the end face 4 of the steel 2 thicker, more specifically, by controlling it to satisfy the following formula 3, the corrosion resistance and life of the plated steel 1 and the guardrail beam formed thereby can be more significantly improved.

[0071] We ≥ Wc Equation 2

[0072] Wt ≥ Wc Formula 3

[0073] Regardless of the pre-plating treatment or post-plating treatment, by controlling the end of the plated steel material to Figure 1 The structure shown in the figure, and then applying it to the guardrail beam, can significantly improve the corrosion resistance of the guardrail beam, and further significantly improve its life. This fact was not known in the past, and was first clarified by the inventors this time. In fact, in the previous pre-plating treatment, as taught in Japanese Patent Publication No. 6-122953, due to the excessive coating of the edge where the coating adhesion increases at the end of the steel material, poor quality such as poor flatness is caused, so it is generally required to prevent this from happening. In contrast, in the guardrail beam of the embodiment of the present invention, the thickness of the coating at the end of the steel material is relatively thickened by thinning the plate thickness at the end, so high corrosion resistance and long life can be achieved without causing poor quality problems such as poor flatness caused by excessive coating of the edge as in the previous pre-plating treatment.

[0074] Hereinafter, the guardrail beam according to the embodiment of the present invention will be described in more detail, but these descriptions are merely simple examples of preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments.

[0075] [Formula 1: 0.60×tc≤te <tc]

[0076] In the guardrail beam of the embodiment of the present invention, it is necessary to control the average plate thickness te (mm) of the steel at a position 1 to 10 mm from the end face of the plated steel, and the average plate thickness tc (mm) of the steel at a position more than 10 mm inward from the end of the plated steel, so that their average plate thicknesses satisfy the following formula 1.

[0077] 0.60 × tc ≤ te < tc Formula 1

[0078] Thus, even if the coating at the end of the steel material disappears due to corrosion, peeling, etc., so that a part of the steel material is exposed, the area of ​​the cathode reaction region can be reduced by the thin plate thickness of the exposed part as described above, so the sacrificial corrosion protection of the coating containing the Zn-based coating can be suppressed to a minimum. Therefore, the sacrificial corrosion protection of the coating can be maintained for a long time, so that the corrosion resistance and long life of the plated steel material and the guardrail beam composed of it can be improved. In addition, by making te thinner, the average thickness We of the coating in the same area can be made relatively thicker, so the corrosion resistance and life can be further improved. From this point of view, the smaller te is, the better, for example, it can also be less than 0.98 times (≤0.98×tc), less than 0.95 times (≤0.95×tc), less than 0.93 times (≤0.93×tc), less than 0.90 times (≤0.90×tc) or less than 0.88 times (≤0.88×tc) of tc. On the other hand, if te is too thin, the strength of the end portion decreases, and deformation may occur during the handling of the guardrail beam during transportation, installation, etc. Therefore, te is 0.60 times or more of tc (0.60×tc≤), for example, 0.65 times or more (0.65×tc≤), 0.70 times or more (0.70×tc≤), 0.75 times or more (0.75×tc≤), or 0.80 times or more (0.80×tc≤).

[0079] The specific value of tc can be any appropriate value generally used as a guardrail beam, without special limitation, for example, it can be greater than 2.0 mm, greater than 2.5 mm, greater than 3.0 mm or greater than 3.5 mm, and / or can be less than 6.0 mm, less than 5.5 mm, less than 5.0 mm or less than 4.5 mm.

[0080] In the present invention, the reference position of the end face of the steel material in the expressions such as "the position 1 to 10 mm from the end face" and "the position 10 mm or more inside from the end face" is determined based on the cross-sectional photograph of the end of the plated steel material. More specifically, when a straight line parallel to the plate thickness direction is drawn in the cross-sectional photograph of the end of the plated steel material, the outermost point of the end of the plated steel material that contacts the straight line is determined as the reference position of the end face of the steel material. Therefore, for example, in the case where it is not as Figure 1In the case where the end face is not a straight line parallel to the plate thickness direction as shown, but a concave-convex end face or an inclined end face, the outermost point in such an end that contacts the straight line parallel to the plate thickness direction on the cross-sectional photograph is determined as the reference position of the end face of the steel material. In addition, te refers to the arithmetic mean of the plate thickness obtained by measuring the plate thickness of the steel material at a position of 1 to 10 mm from the end face at intervals of 2 mm at 5 points in the cross-sectional photograph of the end face of the plated steel material. Similarly, tc refers to the arithmetic mean of the plate thickness obtained by measuring the plate thickness of the steel material at a position more than 10 mm inward from the end face at intervals of more than 50 mm at more than 3 points, and one of the measurement points is the plate thickness near the center of the steel material.

[0081] [Formula 2: We ≥ Wc]

[0082] [Formula 3: Wt ≥ Wc]

[0083] In the guardrail beam of the embodiment of the present invention, it is necessary to control the average thickness We (μm) of a single side of the coating at a position of 1 to 10 mm from the end face of the coated steel, and the average thickness Wc (mm) of a single side of the coating at a position more than 10 mm inward from the end face of the coated steel, so that their average thicknesses satisfy the following formula 2. Similarly, it is necessary to control the average thickness Wt (μm) and Wc (mm) of the coating at the end face of the coated steel, so that their average thicknesses satisfy the following formula 3.

[0084] We ≥ Wc Equation 2

[0085] Wt ≥ Wc Formula 3

[0086] By making We and Wt corresponding to the plating thickness at the end of the steel material where corrosion is more likely to occur and advance equal to or thicker than Wc corresponding to the plating thickness on the front and back sides of the steel material, the corrosion resistance and life of the plated steel material and the guardrail beam composed of it can be effectively improved. From the perspective of improving corrosion resistance, the larger We and Wt are, the better. More specifically, in relation to Formula 2 and Formula 3, We and Wt can also be, for example, independently greater than 1.00 times (>Wc) of Wc, 1.10 times or more (≥1.10×Wc), 1.20 times or more (≥1.20×Wc), 1.30 times or more (≥1.30×Wc), 1.40 times or more (≥1.40×Wc) or 1.50 times or more (≥1.50×Wc). On the other hand, even if We and Wt are too thick, the effect of improving corrosion resistance is saturated. In particular, if We is too thick, poor quality such as poor flatness of the steel material sometimes occurs. Therefore, We and Wt are not particularly limited, but are preferably each independently 2.50 times or less (≤2.50×Wc) of Wc, for example, 2.30 times or less (≤2.30×Wc), 2.00 times or less (≤2.00×Wc), or 1.80 times or less (≤1.80×Wc) of Wc.

[0087] The specific value of Wc may be any appropriate value, and is not particularly limited. For example, it may be 3 μm or more or 5 μm or more. From the viewpoint of improving corrosion resistance, Wc is preferably 10 μm or more, more preferably 15 μm or more, and most preferably 20 μm or more. The upper limit is not particularly limited, but Wc may be, for example, 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less.

[0088] Regarding formula 2, as long as the surface of at least one of the coatings formed on both sides of the steel material satisfies the relationship of We≥Wc. This is because as long as the surface of either side satisfies formula 2, the corrosion resistance of the plated steel material and the guardrail beam formed therefrom can be improved compared with the case where the surfaces of both sides do not satisfy formula 2. From the viewpoint of further improving corrosion resistance, it is preferred that formula 2 be satisfied in the coatings formed on both sides of the steel material. In addition, regarding formula 3, as long as the surface of at least one of the coatings formed on both sides of the steel material satisfies the relationship of Wt≥Wc, that is, as long as the average thickness Wt of the coating on the end face satisfies the relationship of Wt≥Wc for the Wc of at least one of the surfaces. This is because as long as the surface of either side satisfies formula 3, the corrosion resistance of the plated steel material and the guardrail beam formed therefrom can be improved compared with the case where the surfaces of both sides do not satisfy formula 3. From the viewpoint of further improving corrosion resistance, it is preferred that the coatings formed on both sides of the steel material satisfy formula 3, and it is more preferred that the coatings formed on both sides of the steel material satisfy both formulas 2 and 3.

[0089] We refers to the arithmetic mean of the values ​​obtained by measuring the single-side thickness of the coating at a position of 1 to 10 mm from the end face at 5 points at intervals of 2 mm in a cross-sectional photograph of the end of the plated steel material. Among the 5 measurement points, for example, when a measurement point is included where the steel substrate is partially exposed and the measured value of the coating thickness is 0 (zero), We refers to the arithmetic mean of the remaining measurement values ​​excluding the measurement value. Similarly, Wc refers to the arithmetic mean of the values ​​obtained by measuring the single-side thickness of the coating at a position of more than 10 mm inward from the end face at intervals of more than 50 mm at more than 3 points, and one of the measurement points is the single-side thickness of the coating measured near the center of the steel material. In addition, Wt refers to the arithmetic mean of the measurement values ​​of more than 3 points excluding the minimum measurement value among the 4 or more measurement values ​​obtained by measuring the coating thickness at any different 4 or more points on the end face. Among the 4 or more measurement values, the measurement value of one point is the measurement value of the thickest coating thickness on the end face. In addition, the measuring points where the measured value of the coating thickness is 0 (zero) are not included in the more than 4 measuring points. In connection with this, the coating on the end face is sometimes shaved off due to processing, resulting in a local thinning of the coating thickness and / or exposure of the steel substrate. However, the exposure of the steel substrate is local, and as long as the values ​​of We and Wt measured and calculated by the above method satisfy Formula 2 and Formula 3 respectively, the effect of the present invention can be obtained through the sacrificial corrosion protection effect of the surrounding coating and the coating effect of the corrosion products of the coating. Furthermore, the exposure of the portion of the steel substrate within 10 mm from the reference position of the end face defined above, preferably includes the total exposure length of the front and back sides when observing the cross section is less than 200 μm.

[0090] [Plating]

[0091] The plated steel material of the embodiment of the present invention has a coating layer including a Zn-based coating layer on both sides of the steel material. In the present invention, the Zn-based coating layer refers to a coating layer with Zn as the main component. As long as Zn is the main component, the Zn content in the coating layer is not particularly limited. For example, the Zn content in the coating layer may also be 30.0% by mass or more or 40.0% by mass or more. By constituting the coating layer with a Zn-based coating layer, high corrosion resistance can be ensured by the sacrificial corrosion protection effect of Zn. For example, the coating layer may also be a hot-dip galvanized layer or an alloyed hot-dip galvanized layer. From the viewpoint of further improving corrosion resistance, the coating layer is preferably a Zn-Al-Mg-based coating layer. Although not particularly limited, the Zn content in the coating layer is preferably 50.0% by mass or more, for example, it may also be 55.0% by mass or more, 60.0% by mass or more, 65.0% by mass or more, or 70.0% by mass or more. The upper limit is not particularly limited, and the Zn content in the plating layer may be 100 mass %, or, for example, may be 95.0 mass % or less, or 90.0 mass % or less.

[0092] [Preferred chemical composition of the coating]

[0093] As described above, the object of the present invention is to provide a guardrail beam with improved corrosion resistance, the guardrail beam is composed of a plated steel material having a coating, the coating is formed on both sides of the steel material and includes a Zn-based coating, and further, the above-mentioned object is achieved by coating at least one end face of the steel material with the coating, and making the structure of the end of the plated steel material satisfy the above-mentioned formulas 1 to 3. Therefore, the coating can be a Zn-based coating, and it is obvious that the specific chemical composition of the entire coating is not a necessary technical feature in achieving the purpose of the present invention. The following is a detailed description of the preferred chemical composition of the coating applicable to the plated steel material of the embodiment of the present invention, but these descriptions are only simple examples of the preferred chemical composition of the coating for further improving the corrosion resistance, and are not intended to limit the present invention to the case of using a coating having such a specific chemical composition. In addition, in the following description, the "%" of the content of each component refers to "mass %" unless otherwise specified.

[0094] [Al: more than 15.0% and 30.0% or less]

[0095] Al is an element effective in improving the corrosion resistance and processability of the coating. In order to fully obtain these effects, the Al content is preferably greater than 15.0%. The Al content may also be 17.0% or more. On the other hand, if Al is excessively contained, the effect is saturated or the processability is reduced. Therefore, the Al content is preferably 30.0% or less. The Al content may also be 28.0% or less, 26.0% or less, 24.0% or less, 22.0% or less, or 20.0% or less.

[0096] [Mg: more than 5.0 and 15.0% or less]

[0097] Mg is an element effective in improving the corrosion resistance of the coating. In order to fully obtain this effect, the Mg content is preferably greater than 5.0%. The Mg content may also be 5.5% or more. On the other hand, if Mg is excessively contained, the brittle MgZn2 phase is coarse and excessively generated, thereby reducing the workability. Therefore, the Mg content is preferably 15.0% or less. The Mg content may also be 13.0% or less, 10.0% or less, or 8.0% or less.

[0098] The basic chemical composition of the plating layer is as described above. In addition, the plating layer may contain one or more selected from Sn: 0-0.70%, Ca: 0-0.60%, Si: 0-0.75%, Ti: 0-0.25%, Ni: 0-1.00%, Co: 0-0.25%, Fe: 0-5.0% and B: 0-0.50% as needed. These arbitrarily selected elements are described in detail below.

[0099] [Sn: 0~0.70%]

[0100] Sn is an element effective in improving the corrosion resistance and processability of the coating. The Sn content may be 0%, but in order to obtain these effects, the Sn content is preferably 0.01% or more. The Sn content may also be 0.05% or more. On the other hand, if Sn is excessively contained, coarse and brittle Mg2Sn or the like is generated, which reduces the processability. Therefore, the Sn content is preferably 0.70% or less. The Sn content may also be 0.60% or less, 0.40% or less, or 0.25% or less.

[0101] [Ca: 0~0.60%]

[0102] Ca is an element effective in suppressing the formation of top dross formed on the plating bath during the manufacture of the coating, and also has the effect of improving the workability of the coating. The Ca content may also be 0%, but in order to obtain these effects, the Ca content is preferably 0.01% or more. The Ca content may also be 0.05% or more. On the other hand, if Ca is excessively contained, a brittle Ca-Zn phase is generated, which reduces the workability. Therefore, the Ca content is preferably 0.60% or less. The Ca content may also be 0.50% or less, 0.40% or less, or 0.30% or less.

[0103] [Si: 0-0.75%]

[0104] Si is an element effective in improving the adhesion of the coating to the steel. The Si content may be 0%, but in order to obtain such an effect, the Si content is preferably 0.01% or more. The Si content may also be 0.05% or more or 0.10% or more. On the other hand, if Si is excessively contained, a coarse Mg2Si phase is generated, which reduces the workability. Therefore, the Si content is preferably 0.75% or less. The Si content may also be 0.60% or less, 0.40% or less, or 0.20% or less.

[0105] [Ti: 0~0.25%]

[0106] Ti is an element effective in improving the corrosion resistance of the coating. The Ti content may be 0%, but in order to obtain such an effect, the Ti content is preferably 0.01% or more. On the other hand, if excessive Ti is contained, the effect is saturated, so containing more Ti than necessary in the coating may lead to an increase in manufacturing costs. Therefore, the Ti content is preferably 0.25% or less. The Ti content may also be 0.20% or less, 0.15% or less, or 0.12% or less.

[0107] [Ni: 0~1.00%]

[0108] Ni is an element effective in improving the corrosion resistance of the coating. The Ni content may be 0%, but in order to obtain such an effect, the Ni content is preferably 0.01% or more. The Ni content may also be 0.10% or more, 0.15% or more, or 0.20% or more. On the other hand, if Ni is excessively contained, the effect is saturated, so containing more Ni than necessary in the coating may lead to an increase in manufacturing costs. Therefore, the Ni content is preferably 1.00% or less. The Ni content may also be 0.80% or less, 0.60% or less, or 0.40% or less.

[0109] [Co: 0~0.25%]

[0110] Co is an element effective in improving the corrosion resistance of the coating. The Co content may be 0%, but in order to obtain such an effect, the Co content is preferably 0.01% or more. The Co content may also be 0.02% or more. On the other hand, if Co is excessively contained, the effect is saturated, so containing more Co than necessary in the coating may lead to an increase in manufacturing costs. Therefore, the Co content is preferably 0.25% or less. The Co content may also be 0.20% or less, 0.15% or less, or 0.10% or less.

[0111] [Fe: 0-5.0%]

[0112] In order to suppress the dissolution of Fe from the plating tank, Fe can be included in the plating layer by intentionally adding it to the plating bath or dissolving it from the steel material into the plating bath. The Fe content may be 0%, but when Fe is included in the plating layer, the Fe content may be 0.1% or more, 0.3% or more, or 0.5% or more. Similarly, when Fe is included in the plating layer, the Fe content is generally 5.0% or less, and may be 3.0% or 1.0% or less.

[0113] [B: 0~0.50%]

[0114] B is an element effective in improving the corrosion resistance of the coating. The B content may be 0%, but in order to obtain such an effect, the B content is preferably 0.001% or more. The B content may also be 0.01% or more or 0.02% or more. On the other hand, if B is excessively contained, the effect is saturated, so containing more B than necessary in the coating may lead to an increase in manufacturing costs. Therefore, the B content is preferably 0.50% or less. The B content may be 0.30% or less, 0.20% or less, or 0.10% or less.

[0115] [Ballast: Zn and impurities]

[0116] In the plating layer, the balance other than the above elements includes Zn and impurities. The impurities in the plating layer refer to components mixed into the raw materials and other materials due to various reasons in the manufacturing process when the plating layer is manufactured industrially.

[0117] The chemical composition of the coating is determined by dissolving the coating in an acid solution to which an inhibitor for inhibiting corrosion of steel materials has been added and measuring the resulting solution by ICP (inductively coupled plasma) emission spectrometry.

[0118] [Steel]

[0119] The steel material used in the guardrail beam of the embodiment of the present invention can be any suitable material known to those skilled in the art that is generally used in the guardrail beam. There is no particular limitation, for example, it is preferred to have a tensile strength of 400 MPa or more. The steel material may also have a tensile strength of 480 MPa or more, 590 MPa or more, or 780 MPa or more. By using such a high-strength material, the plate thickness of the steel material can be made thinner. The upper limit is not particularly limited, for example, the tensile strength of the steel material may also be 980 MPa or less. The tensile strength of the steel material is determined by making a No. 5 test piece according to JIS Z 2241:2011 and performing a tensile test. There is no particular limitation on the chemical composition and microstructure of the steel material, and it can be appropriately determined according to the expected tensile strength, etc.

[0120] [Orientation of the end surface covered by the plated layer]

[0121] According to a preferred embodiment of the present invention, the end face of the plated steel is configured to face upward relative to the ground. The so-called "facing upward relative to the ground" does not necessarily mean facing directly upward relative to the ground, but also includes a state in which the axis perpendicular to the end face is inclined at an angle of less than 80° relative to the vertical upward direction. The axis perpendicular to the end face can also be inclined at an angle of less than 70°, less than 60°, or less than 45° relative to the vertical upward direction. In addition, the so-called "facing upward relative to the ground" does not necessarily mean that the position of the end of the steel is on the upper side, but refers to whether the axis perpendicular to the end face is always facing upward relative to the ground regardless of the position of the end of the steel. Among the end faces of the guardrail beam, the end face facing upward relative to the ground generally becomes a part where corrosion is prone to occur and advance. Therefore, by applying the end structure of the guardrail beam of an embodiment of the present invention to such a part, the corrosion resistance of the guardrail beam can be more significantly improved.

[0122] The advantages of configuring the end face of the steel material covered with the coating to face upward relative to the ground are described in more detail. First, as the corrosion protection effect brought by the Zn-based coating, in addition to the high corrosion resistance of the Zn-based coating itself, the so-called sacrificial corrosion protection brought by the Zn-based coating is also considered. Moreover, the corrosion products of the Zn-based coating act as a protective film of the steel material, thereby having a corrosion protection effect of suppressing the corrosion rate. Here, in the guardrail beam to which the Zn-based coating is applied, if red rust is generated on the exposed part of the steel material on the end face facing upward relative to the ground (hereinafter also referred to as the "upper end face") among the end faces of the guardrail beam, the coating near the upper end face becomes easy to corrode due to the sacrificial corrosion protection brought by the Z-based coating near it. In connection with this, the corrosion products of the Zn-based coating are formed, but the formed corrosion products sometimes cannot fully cover the vicinity of the upper end face due to gravity. Therefore, for example, compared with the case of other end faces that are fully covered by corrosion products, the sacrificial anti-corrosion effect of the Zn-based coating continues to work for a long time, which will promote the corrosion of the Zn-based coating. Even if the upper end face is covered by the corrosion products of the Zn-based coating, the corrosion products are also easy to flow out to the lower side due to gravity, and the state of being covered by the corrosion products cannot be properly maintained. Therefore, although the lower part of the guardrail beam is covered by the corrosion products to suppress the corrosion rate, the upper part has a tendency to promote and expand the corrosion compared to the lower part due to the outflow of the corrosion products of the Zn-based coating. That is, for the exposed steel part of the upper end face of the guardrail beam, the Zn-based coating near it will corrode. If the exposed steel part is not fully covered by the protective film formed by such corrosion products, the corrosion of the exposed steel part will be further promoted. In order to prevent this, the sacrificial anti-corrosion brought by the Zn-based coating will continue to work. As a result, the Zn-based coating gradually disappears from the upper end surface of the guardrail beam, thereby expanding the exposed portion of the steel material. In order to prevent this, it is necessary to perform sacrificial corrosion protection. However, due to the disappearance of the Zn-based coating, the sacrificial corrosion protection becomes ineffective over a distance, and the red rust advances and expands.

[0123] In contrast, in the guardrail beam of the embodiment of the present invention, first, since the end surface is fully covered with a relatively thick coating, the corrosion resistance to the initial red rust is very high. Second, as mentioned above, since the plate thickness at the end of the steel is thin, even if the coating at the end of the steel disappears and a part of the steel is exposed, the area of ​​the cathode reaction region can be reduced, and the sacrificial corrosion protection effect of the coating including the Zn-based coating can be suppressed to a minimum. Therefore, in the guardrail beam of the embodiment of the present invention, by Figure 1The plated end face shown is configured to face upward relative to the ground. Compared with the case where such an end structure is not applied, it can fully suppress or prevent the generation of red rust on the upper end face of the guardrail beam and the expansion of red rust from the upper end face, thereby significantly improving the corrosion resistance and life of the guardrail beam.

[0124] [Coating rate from the end surface covered by the coating to a position 10 mm: 90% by area or more]

[0125] In the guardrail beam of the embodiment of the present invention, the coating coverage from the end face covered with the coating to a position of 10 mm, more specifically, from the end face covered with the coating to a position perpendicular to the plate thickness direction and 10 mm inward is preferably 90% by area or more. By making the coating coverage 90% by area or more, the generation of red rust at the end face of the guardrail beam and the expansion of the red rust from the end can be more effectively suppressed or prevented. The coating coverage can also be, for example, 92% by area or more, 95% by area or more, or 97% by area or more. The upper limit is not particularly limited, and the coating coverage can be, for example, 100% by area or less, or 99% by area or less.

[0126] The coating coverage from the end face covered by the coating to the position of 10 mm is determined as follows. First, the image data obtained by photographing the end of the coated steel material from the direction of the surface, back and end face is input into the computer. Then, in each photo from the surface and back direction, the area from the outermost part of the coating to the position from the end face to 10 mm determined by the cross-sectional photo of the end of the coated steel material described above is calculated by image processing based on the difference in gloss between the coating and the steel material. Then, in the photo from the end face direction, the overall area and coating coverage area are calculated in the same way. Finally, the coating coverage from the end face covered by the coating to the position of 10 mm is determined by dividing the total of the coating coverage areas of the surface, back and end face by the total of the overall area of ​​each.

[0127] [Length of ridge line of the end surface covered by the plated layer: 1.3 times or more of tc]

[0128] According to a preferred embodiment of the present invention, the ridgeline length of the end face covered by the coating is more than 1.3 times of tc. More specifically, the end face covered by the coating has a concave-convex shape in which the ridgeline length of the end face is more than 1.3 times of tc. By making the ridgeline length of the end face covered by the coating more than 1.3 times of tc, the shape of the end face can be made more concave-convex. Therefore, the adhesion between the coating at the end and the steel material can be improved by the so-called anchoring effect. In this case, the occurrence and advancement of corrosion caused by coating peeling, etc. can be significantly suppressed or prevented. From the viewpoint of improving the adhesion of the coating, the ridgeline length of the end face covered by the coating is as long as possible, for example, it can also be more than 1.4 times, more than 1.5 times, more than 1.7 times or more than 2.0 times. The upper limit is not particularly limited, but the ridgeline length of the end face covered by the coating can also be, for example, less than 2.5 times or less than 2.2 times.

[0129] The ridgeline length of the end face covered by the plated layer is obtained by analyzing the image of the end face using image analysis software in the cross-sectional photograph of the end of the plated steel material described in relation to the definition of tc. Next, based on the obtained ridgeline length of the end face and the previously obtained value of tc, the ratio of the ridgeline length of the end face to tc is determined.

[0130] [Shape of guardrail beam]

[0131] The guardrail beam of the embodiment of the present invention can be applied to any known shape according to the standards of various countries. For example, with respect to the installation standard of the protective fence in Japan, the guardrail beam of the embodiment of the present invention can be applied to any shape of the guardrail beam among SS type, SA type, SB type, SC type, A type, B type and C type.

[0132] <Manufacturing method of guardrail beam>

[0133] The guardrail beam of the embodiment of the present invention can be manufactured by any appropriate method known to those skilled in the art. Among the structures of the guardrail beam, especially the parts other than the end structures satisfying the above-mentioned formulas 1 to 3, SS materials (general structural rolled steel) such as SS400 having a tensile strength of more than 400 MPa can be used, and can be easily manufactured by conventionally known methods. Therefore, the manufacture of the end structure portion will be described in detail below for the case where a pre-plated plated steel plate is used. However, the following description is merely an illustration of the method for manufacturing the guardrail beam of the embodiment of the present invention, and it is not intended to limit the guardrail beam to a guardrail beam manufactured by the manufacturing method described below.

[0134] In the pre-plating treatment, since the end portions cut by a cutting machine or the like are not coated with a plating layer, if such cut end faces are applied to the end structure of the guardrail beam according to the embodiment of the present invention (hereinafter also simply referred to as "the end structure of the guardrail beam"), an additional plating process is required, which is not suitable. Therefore, it is preferable to apply the end portions in the width direction of the pre-plated steel sheet where no cutting process has been performed to the end structure of the guardrail beam. Such a structure has not been proposed in the prior art. In this regard, for example, the width of the plated steel sheet before being processed into a corrugated shape of the guardrail beam is generally about 400 to 500 mm. Therefore, if a plated steel sheet with a similar plate width is manufactured, the two end faces in the width direction can be applied to the end structure of the guardrail beam without performing a cutting process. In this case, two of the end faces of the steel material of the finally obtained guardrail beam are coated with a plating layer. However, manufacturing such a plated steel sheet with a relatively short plate width will reduce the manufacturing efficiency, and as a result, the manufacturing cost will increase. Therefore, it is preferable to manufacture a plated steel sheet with a plate width approximately twice the width of the target guardrail beam, and cut the plated steel sheet in half in the width direction using a cutting machine or the like. In this case, in each of the plated steel sheets cut in half, the end portions in the width direction that have not been cut are coated with a plating layer, so the end portions in the width direction of each plated steel sheet can be applied to the end structure of the guardrail beam.

[0135] The end structure of the guardrail beam satisfying Equation 1: 0.60×tc ≤ te < tc can be manufactured, for example, by rolling using rolls with an inclination applied in such a way as to thin the plate thickness of the end portions in the width direction of the steel material during the rolling process. As another end face processing method, for example, it is also possible to manufacture the end structure satisfying the above Equation 1 by performing a process of compressing or forging the end face when trimming the end portions in the width direction of the steel sheet before the plating process, or similarly grinding the end portions in the width direction of the steel sheet before the plating process to make them thinner.

[0136] The end structure of the guardrail beam that satisfies Formula 2: We≥Wc and Formula 3: Wt≥Wc can be manufactured, for example, by appropriately controlling the conditions of gas wiping in the plating process after the rolling process. In more detail, in the plating process, the amount of coating adhesion is generally controlled by gas wiping. Gas wiping is a technology that removes excess coating by blowing gases such as nitrogen and air to the front and back sides of the plated steel sheet taken out of the hot dip coating bath. The amount of coating adhesion is generally controlled by adjusting the gas pressure of the gas wiping, the nozzle spacing for blowing gas, and the blowing position. However, near the end face of the plated steel sheet, the gas is blown from both the surface and the back of the plated steel sheet by gas wiping, and these gases interfere with each other. The blowing pressure of the gas decreases due to the interference of the blowing gas. Therefore, by appropriately controlling the decrease in this blowing pressure, the amount of coating adhesion at the end of the plated steel sheet can be greater than that in the central part, that is, a thick coating can be attached in a manner that satisfies the above-mentioned Formulas 2 and 3. In the plating process, conditions other than gas wiping are not particularly limited, and an appropriate hot dip plating bath for Zn-based plating can be used, for example, a hot dip plating bath in which the composition is adjusted so that the chemical composition of the plating is within the range of the preferred chemical composition of the plating described above, and the plating treatment can be carried out by a hot dip plating process under appropriate conditions known to those skilled in the art.

[0137] As another method for manufacturing the end structure of the guardrail beam that satisfies the above-mentioned formulas 1 to 3, the following method can be cited. Specifically, first, the steel plate itself before the plating process is manufactured in a flat shape, and then, in the subsequent plating process, the gas wiping conditions (gas pressure, nozzle spacing and blowing position, etc.) are appropriately adjusted to manufacture a plated steel plate with a thicker coating thickness at the end. Next, the obtained plated steel plate is subjected to skin smooth rolling, etc. to appropriately press down the end of the plated steel plate, thereby manufacturing an end structure in which the thickness of the end of the steel plate in the width direction is thin and the coating thickness of the end in the width direction is thick, that is, an end structure that satisfies the above-mentioned formulas 1 to 3.

[0138] Next, the obtained plated steel sheet is processed into a desired shape corresponding to the use of prefectural roads, national roads, trunk roads with heavy traffic, expressways, etc. by using a conventionally known appropriate method, thereby manufacturing the guardrail beam of the embodiment of the present invention. Furthermore, from the viewpoint of landscape and for longer-term durability, the guardrail beam may also be post-coated by powder coating or the like.

[0139] The guardrail beam manufactured by the above manufacturing method satisfies the above formula 1. Therefore, even if the coating at the end of the steel material disappears due to corrosion, peeling, etc., thereby exposing a part of the steel material, the area of ​​the cathode reaction region can be reduced due to the thin plate thickness of the exposed part, and the sacrificial corrosion protection effect of the coating including the Zn-based coating can be suppressed to a minimum, and the sacrificial corrosion protection effect can be maintained for a long time. In addition, by satisfying formulas 2 and 3, the coating thickness at the end of the steel material, where corrosion is more likely to occur and advance, can be made equal to or thicker than the coating thickness on the front and back of the steel material, and compared with the case of a guardrail beam that does not include such a structure, its corrosion resistance and life can be effectively improved.

[0140] [Additional preferred embodiment]

[0141] As described above, the guardrail beam of an embodiment of the present invention is characterized in that at least one end face is covered with a coating and has an end structure that satisfies equations 1 to 3. Hereinafter, in the case where at least one end face other than the end face covered with a coating is a cut end face, additional preferred embodiments 1 and 2 (hereinafter also referred to as "embodiment 1", etc.) are described in detail in which other characteristics are given to the cut end face.

[0142] [Implementation Method 1]

[0143] The guardrail beam of embodiment 1 is characterized in that, in addition to the end structure in which at least one end face is coated with a coating and satisfies equations 1 to 3, at least one, for example, two or three end faces other than the end face coated with a coating are cut end faces, and the cut end faces have an inclined surface and a fracture surface inclined from the first surface of the steel material to the second surface relative to the plate thickness direction, or have an inclined surface, a shear surface and a fracture surface inclined from the first surface of the steel material to the second surface relative to the plate thickness direction,

[0144] The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material.

[0145] The total coating coverage of the inclined surface and the sheared surface is 50% by area or more.

[0146] In the conventional cutting device 10, Figure 2 As shown, the blade tip 11a of the first blade 11 and the blade tip 12a of the second blade 12 are in a right angle shape. Therefore, when such a cutting device is used to cut the plated steel material 1 coated with a plating layer on the upper surface (first surface) and the lower surface (second surface) of the steel material, the plated steel material 1 is clamped by the first blade 11 and the second blade 12, and a shear force is applied to the plated steel material 1 by pressing it to cut it. In this case, Figure 3 As shown in FIG. 1 , the obtained cut end face 5 has a shear surface and a fracture surface in order from the upper surface. Figure 3As shown in FIG. 1 , in the fracture surface, burrs 6 are generally formed at the corners on the second surface side. The shear surface is a smooth surface formed by the movement of the first blade 11 that penetrates into the plated steel material 1, and the fracture surface is a surface where the plated steel material 1 is fractured starting from the crack generated in the plated steel material 1. Figure 3 As shown, in the cut end face 5 of the plated steel material 1, the plating layer 3, especially when the gap between the blades is small, hardly remains on the sheared surface, and the steel material 2 is exposed on the fracture surface. Therefore, the corrosion resistance of such a cut end face 5 is low, and red rust may be generated.

[0147] In this regard, it is believed that Figure 2 In the case of cutting with the conventional right-angled blade tip shown in FIG. 1 , due to the small shear surface, the penetration (or spread) of the plating 3 from the upper surface of the plated steel material 1 to the cut end surface 5 becomes less until the plated steel material 1 is cut. Similarly, it is believed that when cutting with the conventional right-angled blade tip, stress is concentrated at the corners of the upper and lower blade tips, and cracks are generated in a manner connecting these corners, so the cutting timing is advanced and the exposed area (i.e., the fracture surface) of the steel material 2 becomes larger. Therefore, in order to improve the corrosion resistance of the cut end surface 5, it is important to delay the cutting timing, make the proportion of the exposed fracture surface of the steel material 2 smaller, and increase the coating coverage of the portion other than the fracture surface in the cut end surface 5.

[0148] During the cutting process, as a method for making the plating layer more penetrate into the cut end face 5 of the plated steel material 1, for example, a tapered inclined surface may be provided to the blade. In this case, when the blade is pressed in, the plating layer 3 on the upper surface of the plated steel material 1 follows the movement of the blade and penetrates into the cut end face 5 along the inclined surface of the blade. Therefore, the plated layer 3 on the upper surface of the plated steel material 1 is not as good as the plated layer 3 on the plated steel material 1. Figure 2 Compared with the case where the plated steel material 1 is cut with a right-angled blade tip as shown, the coating coverage of the cut end surface 5 can be improved. However, even in this case, if the corners of the upper and lower blade tips are angular, the stress concentration at the corners is not relieved, and cracks are generated in a manner connecting these corners, so the cutting timing is not delayed and the ratio of the fracture surface is kept large.

[0149] Therefore, in order to improve the corrosion resistance of the cut end surface, in association with the additional preferred embodiment 1, for example, at least one of the first blade 21 and its blade tip 21a or the second blade 22 and its blade 22a may be formed into a shape having an inclined portion P1 and a protrusion P2. More specifically, Figure 4 As shown, the first blade 21 and its blade tip 21a may be formed into a shape having an inclined portion P1 and a protruding portion P2, and the second blade 22 and its blade tip 22a may be formed into a right angle shape. Figure 5 As shown in FIG. 1 , the first blade 21 and its blade tip 21a and the second blade 22 and its blade tip 22a may both be formed into a shape having the inclined portion P1 and the protruding portion P2. Figure 4 and Figure 5 The cutting device 20 shown performs cutting processing, which can suppress the generation of burrs 6, and when the blade is pressed in, the plating material in the plating layer 3 on the upper surface or lower surface of the plated steel material 1 follows the movement of the blade and can enter the cut end surface 5 along the inclined surface of the blade. The stress concentration at the corner of the blade tip is also alleviated, so the cutting timing can be delayed. As a result, the proportion of the exposed fracture surface of the steel material 2 can be sufficiently reduced, and the coating coverage of the portion other than the fracture surface in the cut end surface 5 can be significantly increased.

[0150] Figure 6 is a schematic diagram showing a cut end face of an additional preferred embodiment 1, showing that Figure 4 and Figure 5 The cut end surface 5 of the plated steel material 1 cut by the pair of blades 21 and 22 shown. Figure 6 Indicates that Figure 4 and Figure 5 The inclined portion P1 of the first blade portion 21 and the upper surface (first surface) opposite to the inclined portion P1 are pressed into the cutting end surface 5 on one side. Figure 6 As shown, the cut end face 5 has an inclined surface, a shear surface, and a fracture surface in order from the upper surface, and the inclined surface is inclined relative to the plate thickness direction in a manner protruding from the upper surface (first surface) to the lower surface (second surface). The inclined surface is a surface formed along the inclined portion P1 of the first blade portion 21, and is inclined relative to the plate thickness direction from the upper surface (first surface) to the lower surface (second surface) of the steel material 2. The shear surface is a smooth surface formed by the movement of the first blade portion 21 that is sunk into the plated steel material 1, and sometimes only slightly or not at all. The fracture surface is a surface where the plated steel material 1 is fractured starting from the crack generated in the plated steel material 1.

[0151] exist Figure 6 In the cut end face 5 of the plated steel material 1 shown in FIG. 1 , the plating layer 3 on the first surface follows the movement of the first blade 21, enters the inclined surface and covers the inclined surface. Figure 6 It shows that by using Figure 4 and Figure 5 The cutting device 20 shown in the figure can cut the plated steel material 1, and the ratio of the "shear surface" where the plating layer is almost not left and the "fracture surface" where the steel material 2 is exposed can be made very small compared with the case of using the conventional cutting device 10. In this regard, many areas of the cut end surface 5 can be covered with the plating layer from the first surface, so that the corrosion resistance of the cut end surface 5 can be significantly improved. In addition, in Figure 4 and Figure 5 In the pair of blades shown, since the final cutting to generate the fracture surface is performed by the protrusion P2 having a substantially right-angled corner, the generation of burrs is suppressed.

[0152] like Figure 4 As shown in the figure, when the first blade 21 and its blade tip 21a are formed into a shape having an inclined portion P1 and a protruding portion P2, and the second blade 22 and its blade tip 22a are formed into a right angle shape, one of the plated steel materials 1 after being cut into two has Figure 6 However, the cut end face 5 of the other plated steel material 1 is not coated with the plating layer, and thus becomes waste. Figure 5 As shown, if both the first blade 21 and its blade tip 21a and the second blade 22 and its blade tip 22a have a shape having the inclined portion P1 and the protrusion P2, then both of the plated steel material 1 cut into two can have Figure 6 The cut end face 5 is shown.

[0153] According to the first embodiment, the length of the fracture surface in the plate thickness direction of the cut end surface 5 can be reduced to less than 40% of the plate thickness of the steel material 2, and can be further reduced to less than 30%, less than 25%, or less than 20% of the plate thickness of the steel material 2 by appropriately adjusting the shape of the inclined portion and the protrusion, the gap between the first blade 21 and the second blade 22, etc. In addition, in the case of the presence of the inclined surface, the total coating coverage rate in the shear surface can be increased to more than 50 area%, and similarly, by appropriately adjusting the shape and gap of the inclined portion and the protrusion, it can be increased to more than 60 area%, more than 80 area%, or 100 area%. Therefore, according to the first embodiment, the area where red rust is generated on the cut end surface 5 can be extremely small.

[0154] The length of the fracture surface in the plate thickness direction of the cut end face is calculated based on the cross-sectional photograph of the cut end face. When the fracture surface is inclined relative to the plate thickness direction, the length of the fracture surface along the plate thickness direction is calculated instead of the length of the inclined surface. The coating coverage of the inclined surface and the shear surface is determined as follows. First, the image data obtained by photographing the cut end face of the plated steel material is input into the computer. Then, in the area other than the fracture surface (inclined surface and shear surface when it exists), the overall area and coating coverage area are calculated by image processing based on the difference in gloss between the coating and the steel material, and the coating coverage of the inclined surface and the shear surface is determined by dividing the calculated coating coverage area by the overall area.

[0155] [Implementation Method 2]

[0156] The guardrail beam of embodiment 2 is characterized in that, in addition to the end structure in which at least one end face is covered by the plating layer and satisfies equations 1 to 3, at least one, for example, two or three end faces other than the end face covered by the plating layer are cut end faces, and the cut end has:

[0157] A first inclined surface inclined with respect to the plate thickness direction from the first surface toward the center of the steel material;

[0158] A second inclined surface inclined with respect to the plate thickness direction from the second surface toward the center of the steel material; and

[0159] The fracture surface formed between the first inclined surface and the second inclined surface,

[0160] The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material.

[0161] The total coating coverage of the first inclined surface and the second inclined surface is 50% by area or more.

[0162] Figure 7 Schematic diagram showing the cut end of the additional preferred embodiment 2. Figure 7 , the cut end face 5 of the plated steel material 1 has: a first inclined surface inclined relative to the plate thickness direction in a manner protruding from the upper surface (first surface) of the steel material 2 toward the central portion; a second inclined surface inclined relative to the plate thickness direction in a manner protruding from the lower surface (second surface) of the steel material 2 toward the central portion; and a fracture surface formed between the first inclined surface and the second inclined surface. In addition, it can be seen that in the cut end face 5 of the second embodiment, Figure 6 In the case of the first embodiment shown in FIG. 1 , the length of the exposed fracture surface of the steel material 2 in the plate thickness direction is sufficiently reduced to a level far below 40% of the plate thickness of the steel material 2, and the coating 3 on the first surface and the second surface enters the first inclined surface and the second inclined surface respectively, and the first inclined surface and the second inclined surface are widely coated with the coating in a range far exceeding 50% by area in total. Figure 7 In the cut end surface of the second embodiment shown, the corrosion resistance of the cut end surface 5 can be significantly improved similarly to the case of the first embodiment.

[0163] The cut end surface of the second embodiment can be obtained by, for example, Figure 8 and Fig. 9 The cutting device 30 shown is manufactured. Figure 8 is a schematic diagram showing a state of a plated steel material 1 before cutting for obtaining a cut end surface according to an additional preferred embodiment 2, Fig. 9 It means to use Figure 8 The schematic diagram of the state after the cutting device 30 cuts the plated steel material 1. Figure 8 As shown in FIG. 1 , the cutting device 30 is composed of a punch 33 and a die 34. The punch 33 has a wedge-shaped first blade 31 with a blade tip 31a, and the die 34 has a wedge-shaped second blade 32 with a blade tip 32a. The first blade 31 and the second blade 32 are arranged opposite to each other. By moving the punch 33 relative to the die 34, the wedge-shaped first blade 31 and the second blade 32 are pressed into the plated steel material 1, respectively, so that Fig. 9 As shown, the plated steel material 1 is cut.

[0164] When the first blade 31 and the second blade 32 are pressed into the plated steel material 1, the tensile force generated therebetween causes the plated material in the plated layer 3 on the first surface and the second surface of the plated steel material 1 to follow the movement of the first blade 31 and the second blade 32 and enter the cut end face 5. Figure 7 As shown, the cut end face 5 is covered with the coating. As a result, the first inclined surface and the second inclined surface can be formed on the cut end face 5 of the plated steel material 1 and their coating coverage can be increased, and the proportion of the exposed fracture surface of the steel material 2 formed between them can be significantly reduced. In addition, the shape of the cut end face 5 of the plated steel material 1 cut by the cutting device 30 of this embodiment depends on the shapes of the first blade 31 and the second blade 32. Here, since the first blade 31 and the second blade 32 are wedge-shaped, the cut end face 5 of the plated steel material 1 is Figure 7 The shape of the first inclined surface or the second inclined surface along the wedge-shaped inclined surface is a shape that protrudes toward the center in the plate thickness direction. In addition, by making the first blade 31 and the second blade 32 wedge-shaped, the plating material on the first surface and the second surface of the plated steel material 1 easily follows the movement of the first blade 31 and the second blade 32 along the wedge-shaped inclined surface when the plated steel material 1 is cut. As a result, the plating layer on the first surface and the second surface of the plated steel material 1 can cover a wider area of ​​the first inclined surface and the second inclined surface.

[0165] According to the second embodiment, the length of the fracture surface in the plate thickness direction of the cut end surface 5 can be reduced to less than 40% of the plate thickness of the steel material 2, and can be further reduced to less than 30%, less than 25%, or less than 20% of the plate thickness of the steel material 2 by adjusting the wedge shape of the first blade 31 and its blade tip 31a and the second blade 32 and its blade tip 32a to a more appropriate shape, and / or adjusting the gap between the first blade 31 and the second blade 32. In addition, the coating coverage of the first inclined surface and the second inclined surface can be increased to a total of more than 50 area%, and can also be increased to more than 60 area%, more than 80 area%, or 100 area% by appropriately adjusting the above-mentioned wedge shape and gap. Therefore, according to the second embodiment, the area where red rust is generated on the cut end surface 5 can be extremely small.

[0166] The length of the fracture surface of the cut end surface in the plate thickness direction and the plating coverage of the first inclined surface and the second inclined surface are calculated based on the cross-sectional photograph of the cut end surface and the photograph of the cut end surface, similarly to the first embodiment.

[0167] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples at all.

[0168] Example

[0169] [Example A]

[0170] In this example, plated steel materials having various end structures in which one end surface was coated with a plating layer were manufactured, and their corrosion resistance was investigated.

[0171] First, a general structural rolled steel material SS400 having a thickness of 4.0 mm (tc), a width of 90 mm, and a length of 150 mm was prepared. Next, for one end face of the short side of the steel material, a portion from the end face to 10 mm was pressed down or ground by a press machine, thereby setting the average plate thickness (te) of the steel material at a position of 1 to 10 mm from the end face to the plate thickness shown in Table 1. Next, the obtained steel material was plated by a hot dip coating process using a hot dip coating bath having a chemical composition shown in Table 2. At this time, by appropriately controlling the conditions such as the blowing pressure of the gas for gas wiping, especially at the end of the steel material, a steel material having a coating layer having each average thickness of Wc, We, and Wt shown in Table 1 was produced. tc, te, Wc, We, and Wt in Table 1 correspond to the arithmetic mean of the plurality of measured values ​​described above, and represent values ​​obtained by rounding off the arithmetic mean to one decimal place. Next, the long sides, i.e., both end faces of the steel material were cut by 10 mm each, thereby preparing a plated steel material a having a width of 70 mm and a length of 150 mm in which the steel material was exposed at both end faces of the long sides. Regarding Example 51, in order to simulate partial exposure of the steel substrate, a portion of the plating layer on the end face (corner when observed in cross section) of the evaluation object was polished with sandpaper (#1000 finishing) to prepare a sample in which 50 μm of the steel substrate was exposed (in terms of the exposed length when observed in cross section).

[0172] In addition, as a reference sample for evaluation, a plated steel material b having a coating composition corresponding to each of the plated steel materials a was prepared. Specifically, first, a general structural rolled steel material SS400 having a thickness of 4.0 mm, a width of 70 mm, and a length of 150 mm was prepared, and a coating treatment was performed by a hot dip coating process using a hot dip coating bath having a chemical composition shown in Table 2. At this time, the conditions such as the blowing pressure of the gas for gas wiping were appropriately controlled, especially at the ends of the steel material, thereby producing a plated steel material b having an average thickness Wc shown in Table 1 (all four end faces of the plated steel material b were coated with the coating).

[0173] [Evaluation of Corrosion Resistance]

[0174] The plated steel material a thus obtained was placed with the end face of the short side adjusted in thickness facing upward, and was subjected to a cyclic corrosion test (CCT, JIS H 8502: 1999 neutral salt spray cyclic test) in a state where the lower end face and the left and right end faces were sealed to a portion of 15 mm. During the cyclic corrosion test, the appearance of the flat surface was visually observed, and the number of cycles at which the red rust generation area reached 3% of the flat surface was investigated. In addition, the plated steel material b was subjected to a similar cyclic corrosion test in a state where the portion from the entire end face to a portion of 15 mm was sealed. The case where the red rust area rate of the flat part of the plated steel material b reaches 3% is 1.1 times or more, or the difference between the number of cycles A and the number of cycles B, that is, the number of cycles A-the number of cycles B, is 30 cycles or more, is recorded as ◎, the case where the number of cycles A relative to the number of cycles B is 1.0 times or more and less than 1.1 times, or the number of cycles A-the number of cycles B is less than 30 cycles, is recorded as ○, and the case where the number of cycles A relative to the number of cycles B is less than 1.0 times is recorded as ×, and ◎ and ○ are examples (inventive examples), and × is evaluated as comparative examples. If described in more detail, in this test, the corrosion resistance of the plated steel material a, in which the end face of the plate thickness of the short side is plated, is compared and evaluated with the plated steel material b, in which the plate thickness of the short side is not adjusted and the normal end face is plated and then sealed, thereby making it more difficult to corrode. The results are shown in Table 1. Furthermore, Example 42 is an example in which an inorganic Zr-containing chromium-free chemical conversion treatment is performed after plating, and Example 43 is an example in which an organic V-containing polyurethane resin-based chromium-free treatment is performed after plating.

[0175] Table 1

[0176]

[0177]

[0178] In Table 1, as long as either of the front and back sides satisfies Formula 2, Formula 2 is judged as OK, and in the case where neither of the front and back sides satisfies Formula 2, Formula 2 is judged as NG. Because as long as either one satisfies Formula 2, the corrosion resistance of the plated steel can be improved compared to the case where neither of the front and back sides satisfies Formula 2. The same is true for Formula 3. Referring to Table 1, in Comparative Examples 37 to 41, although Formula 1 is satisfied at the end face where the plate thickness of the short side is adjusted, the thickness of the plating layer at the end face and / or its vicinity is relatively thin, so one or both of Formulas 2 and 3 are not satisfied, and thus the corrosion resistance is reduced. In contrast, in all embodiments, by satisfying all of Formulas 1 to 3 in association with the end face where the plate thickness of the short side is adjusted, high corrosion resistance can be achieved even compared to the plated steel b that is more difficult to corrode by plating the usual end face where the plate thickness of the short side is not adjusted and then sealing the end face. In particular, in Examples 48 to 50, only one surface satisfies Formula 2, and in Example 50, only one surface satisfies Formula 3, but good corrosion resistance can be achieved in any of the examples. Similarly, in Example 51, although the end face covered by the plated layer is partially exposed, high corrosion resistance can be achieved by satisfying all of Formulas 1 to 3. In addition, in all examples other than Examples 46, 47, and 51, the coating coverage from the end face covered by the plated layer to the position of 10 mm is 100%, and the ridgeline length of the end face covered by the plated layer is the same as tc. In Example 46, the coating coverage from the end face covered by the plated layer to the position of 10 mm is 93% by area, and the ridgeline length of the end face covered by the plated layer is the same as tc. On the other hand, in Example 47, the coating coverage from the end face covered by the plated layer to the position of 10 mm is 100% by area, and the ridgeline length of the end face covered by the plated layer is 1.5 times tc. Furthermore, in Comparative Example 45, since te is too thin and does not satisfy Formula 1, the strength of the end portion is reduced, and the end surface covered by the coating is deformed during shearing of the long side, making it unsuitable for use as a guardrail beam. Therefore, the corrosion resistance of Comparative Example 45 was not evaluated.

[0179] [Example B]

[0180] In this example, within the range evaluated as an example (inventive example) in Example A, a plated steel material having a cut end surface corresponding to the additional preferred embodiment 1 was produced, and the corrosion resistance of the cut end surface was investigated.

[0181] First, a general structural rolled steel material SS400 with a thickness of 4.0 mm (tc), a width of 90 mm and a length of 150 mm is prepared. Next, for one end face of the short side of the steel material, the portion from the end face to 10 mm is pressed down or ground using a press to obtain a plate thickness (te) of the steel material at a position 1 to 10 mm from the end face as shown in Table 3. Next, the obtained steel material is plated by a hot dip plating process using a hot dip plating bath of plating type N shown in Table 2. At this time, by appropriately controlling the conditions such as the blowing pressure of the gas for gas wiping, especially at the end of the steel material, a steel material having a plating layer with average thicknesses of Wc, We and Wt shown in Table 3 is produced. Finally, using Figure 4 The cutting device shown cuts off 10 mm of each of the long sides, i.e., the two end faces of the steel material, thereby producing a steel material having a plurality of Figure 6 The plated steel material of 70 mm × 150 mm is shown in the cut end faces of the inclined surface, shear surface and fracture surface. When cutting, in each case, the coating coverage of the inclined surface and the shear surface and the fracture surface length in the plate thickness direction are changed as shown in Table 3 by appropriately adjusting the gap between the first blade and the second blade.

[0182] [Evaluation of Corrosion Resistance of Cut End Surface]

[0183] The obtained plated steel material was set with the end face of the short side adjusted to face upward, and was subjected to a cyclic corrosion test (CCT, JIS H8502: 1999 neutral salt spray cycle test) in a state where the portion from the lower end face to 15 mm was sealed. In addition, the number of cycles at which the red rust area ratio of the flat portion of the plated steel material reached 3% without sealing the left and right sides of the same plated steel material but maintaining the normal shear state and sealing only the lower side was set as cycle number B, and the above-mentioned Figure 4 The number of cycles at which the red rust area ratio of the flat portion of the plated steel material after cutting by the cutting device shown reaches 3% is set as cycle number A, and the case where the cycle number A is 1.1 times or more relative to the cycle number B or the cycle number A-cycle number B is 30 cycles or more is marked as ◎, and the case below is marked as ×, and the corrosion resistance of the cut end surface (corrosion resistance caused by the properties of the cut end surface) is evaluated. The results are shown in Table 3.

[0184]

[0185] Referring to Table 3, in the shearing which serves as the evaluation criterion for each example, the ratio of the length of the fracture surface (exposed portion of the steel material) in the direction of the plate thickness to the plate thickness of the steel material is large (in all shearings, the length of the fracture surface is more than 70% of the steel material plate thickness). In contrast, in all of Examples 101 to 104, by controlling the length of the fracture surface in the direction of the plate thickness to less than 40% of the plate thickness and controlling the coating coverage of the inclined surface and the shear surface to a total of more than 50 area%, many areas of the cut end surface can be covered with the coating, thereby achieving high corrosion resistance on the cut end surface.

[0186] [Example C]

[0187] In this example, within the range evaluated as an example (inventive example) in Example A, a plated steel material having a cut end surface corresponding to the additional preferred embodiment 2 was produced, and the corrosion resistance of the cut end surface was investigated.

[0188] First, a general structural rolled steel material SS400 having a thickness of 4.0 mm (tc), a width of 90 mm, and a length of 150 mm is prepared. Next, for one end face of the short side of the steel material, the portion from the end face to 10 mm is pressed down or ground using a press, and the average plate thickness (te) of the steel material at a position 1 to 10 mm from the end face is set to the plate thickness shown in Table 4. Next, the obtained steel material is plated by a hot dip plating process using a hot dip plating bath of plating type N shown in Table 2. At this time, by appropriately controlling the conditions such as the blowing pressure of the gas for gas wiping, especially at the end of the steel material, a steel material having a plating layer with average thicknesses of Wc, We, and Wt shown in Table 4 is produced. Finally, by using Figure 8 and Fig. 9 The cutting device shown cuts off 10 mm of each of the long sides, i.e., the two end faces, of the steel material to produce the two end faces of the long side. Figure 7 As shown, a 70 mm × 150 mm plated steel material includes a cut end surface, wherein the cut end surface has: a first inclined surface and a second inclined surface inclined relative to the plate thickness direction in a manner of protruding from the upper surface and the lower surface (the first surface and the second surface) of the steel material toward the central portion, respectively, and a fracture surface formed therebetween. During cutting, by appropriately adjusting the gap between each first blade portion and the second blade portion, the coating coverage of the first inclined surface and the second inclined surface and the fracture surface length in the plate thickness direction are changed as shown in Table 4.

[0189] [Evaluation of Corrosion Resistance of Cut End Surface]

[0190] The obtained plated steel material was set with the end face of the short side adjusted in thickness facing upward, and was subjected to a cyclic corrosion test (CCT, JIS H 8502:1999 neutral salt spray cyclic test) in a state where the portion from the lower end face to 15 mm was sealed. In addition, the number of cycles at which the red rust area ratio of the flat portion of the plated steel material reached 3% without sealing the left and right sides of the same plated steel material but only sealing the lower side while maintaining the normal shear state was set as cycle number B, and the above-mentioned Figure 8 and Fig. 9 The number of cycles at which the red rust area ratio of the flat portion of the plated steel material after cutting by the cutting device shown reaches 3% is set as cycle number A, and the case where the cycle number A is 1.1 times or more relative to the cycle number B or the cycle number A-cycle number B is 30 cycles or more is marked as ◎, and the case below is marked as ×, and the corrosion resistance of the cut end surface (corrosion resistance caused by the properties of the cut end surface) is evaluated. The results are shown in Table 4.

[0191]

[0192] Referring to Table 4, in the shearing which serves as the evaluation criterion for each example, the ratio of the length of the fracture surface (exposed portion of the steel material) in the direction of the plate thickness to the plate thickness of the steel material is large (the length of the fracture surface in all shearing is more than 70% of the steel material plate thickness). In contrast, in all of Examples 201 to 204, by controlling the length of the fracture surface in the direction of the plate thickness to less than 40% of the plate thickness and controlling the coating coverage of the first inclined surface and the second inclined surface to a total of more than 50 area%, many areas of the cut end surface can be covered with the coating, thereby achieving high corrosion resistance on the cut end surface.

[0193] Description of Reference Numerals

[0194] 1. Coated steel

[0195] 2Steel

[0196] 3. Plating

[0197] 4 End face

[0198] 5. Cut off the end face

[0199] 6. Burr

[0200] 10, 20, 30 cutting device

[0201] 11, 21, 31 1st blade

[0202] 11a, 21a, 31a The first blade tip

[0203] 12, 22, 32 2nd blade

[0204] 12a, 22a, 32a The tip of the second blade

[0205] 33 Punch

[0206] 34 Die

Claims

1. A guardrail beam, characterized in that: The invention is composed of a plated steel material including a steel material and a plated layer, wherein the plated layer is formed on both surfaces of the steel material and includes a Zn-based plated layer. At least one end surface of the steel material is coated with the plating layer and satisfies the following formulas 1 to 3: 0.60 × tc ≤ te < tc Formula 1 We ≥ Wc Equation 2 Wt ≥ Wc Formula 3 in, tc is the average plate thickness in mm of the steel material at a position 10 mm or more inward from the end surface covered by the coating. te is the average plate thickness of the steel material in mm at a position 1 to 10 mm from the end surface covered with the coating. We is the average thickness of the coating on one side in μm at a position 1 to 10 mm from the end surface covered by the coating. Wc is the average thickness in μm of a single surface of the plating layer at a position 10 mm or more inward from the end surface covered by the plating layer. Wt is the average thickness in μm of the plating layer at the end surface covered with the plating layer.

2. The guardrail beam according to claim 1, characterized in that: The coating is a Zn-Al-Mg coating.

3. The guardrail beam according to claim 2, characterized in that: The coating has the following chemical composition, In terms of mass%, it contains Al: more than 15.0% and less than 30.0%, Mg: more than 5.0% and less than 15.0%, Sn: 0~0.70%, Ca: 0~0.60%, Si: 0-0.75%, Ti: 0~0.25%, Ni: 0-1.00%, Co: 0-0.25%, Fe: 0-5.0%, B: 0 to 0.50%, and Balance: Zn and impurities.

4. The guardrail beam according to any one of claims 1 to 3, characterized in that: The end surface covered with the plating layer is arranged to face upward with respect to the ground.

5. The guardrail beam according to any one of claims 1 to 3, characterized in that: The coating coverage from the end surface coated with the coating to a position 10 mm is 90 area % or more.

6. The guardrail beam according to any one of claims 1 to 3, characterized in that: At least one end face other than the end face covered by the plating layer is a cut end face, and the cut end face has: an inclined face inclined from the first surface to the second surface of the steel material relative to the plate thickness direction, and a fracture face, or has: an inclined face inclined from the first surface to the second surface of the steel material relative to the plate thickness direction, a shear face, and a fracture face, The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material. The total coating coverage of the inclined surface and the sheared surface is 50% by area or more.

7. The guardrail beam according to any one of claims 1 to 3, characterized in that: At least one end face other than the end face covered by the plating layer is a cut end face, and the cut end has: A first inclined surface inclined with respect to the plate thickness direction from the first surface toward the center of the steel material; a second inclined surface inclined with respect to the plate thickness direction from the second surface toward the center of the steel material; and a fracture surface formed between the first inclined surface and the second inclined surface, The length of the fracture surface in the plate thickness direction is less than 40% of the plate thickness of the steel material. The total plating coverage of the first inclined surface and the second inclined surface is 50 area % or more.

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