JPH0688250A - Rust preventive steel plate for civil engineering and building structure and its production - Google Patents

Abstract

PURPOSE:To provide the rust preventive steel plate for civil engineering and building structures which omits coating of a primary primer and surface prepn. and enables the leveling off of the deterioration rate of coating films by parts and the prolonging of the period for recoating of the entire surface and the process for production of such steel plate. CONSTITUTION:This rust preventive steel plate for civil engineering and building structures is formed with the metal coating layers nobler than base material steel having >=250g/m<2> and <=7500g/m<2> coating amt. and >=150mum and <=70mum surface roughness Rz and is formed by interposing boron nitride of <=10mum grain size at >=5g/m<2> and <=200g/m<2> between the cladding metal and cladding metal of a sandwich type and semi-sandwich type composite slab consisting of the base material steel and the cladding metals nobler than the steel or between the cladding metal and the dummy metal and hot rolling the composite slab under >=3 and <=10 total draft, then peeling the cladding metal and the cladding metal or the cladding metal and dummy steel at the plane where the boron nitride is interposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rustproof thick steel plate for civil engineering and construction, which can omit the application of a primary primer and is excellent in coating film adhesion and corrosion resistance after coating, and a method for producing the same.

[0002]

2. Description of the Related Art Civil engineering structures such as bridges and offshore structures are exposed to atmospheric atmosphere containing pollutants and chlorides for many years and are required to have high durability. It is also necessary to harmonize the landscape with the surrounding environment. Therefore, coating is applied for the purpose of imparting corrosion resistance and color.

Conventional steel sheets used for this type of application are:
Since it is necessary to prevent the generation of rust after hot rolling until the steel structure is assembled, the mill maker removes the black skin on the surface of the rolled steel by blasting, and then the primary primer (wash primer or wash primer Zinc rich primer) is applied and delivered to the fabricator.

In a fabricator, a block is manufactured at a factory, and then a base coat is applied by adjusting the base material for the purpose of imparting rust resistance and water resistance. The blocks are transported to the site, assembled, installed, and finally used with a middle / top coat for the purpose of imparting weather resistance and color. During the service period, repainting is generally repeated according to the rusted area and the degree of blistering.

[0005]

However, when a conventional steel material is used, a great deal of labor and cost are required to adjust the base material during block manufacturing and installation and to maintain and prevent rust during service. There is. That is, in the block manufacturing stage, if welding is performed with the primary primer applied, defects such as blowholes occur in the welded portion and a weld burned portion is generated, which adversely affects the adhesion of the coating film. Therefore, it is necessary to remove the primer on the planned welding line before welding.

Further, even after the welding and assembling, in order to secure the adhesion of the undercoat paint, it is necessary to adjust the substrate for the purpose of removing the primary primer deteriorated by welding burn and the generation of red rust and providing an appropriate anchor pattern. is there. In particular, when thick film type zinc rich paint is applied to the undercoat paint, not only red rust on the primary primer surface but also white rust will deteriorate the adhesion of the coating film, so the entire surface will be blasted. ing. Therefore, these foundation adjustment work requires a great deal of labor and a high construction cost even in a bad working environment.

When the steel structural block is transported or installed on site, the coating film of the undercoat coating material may be damaged. In that case, the steel material is easily exposed and rusts.
It is necessary to adjust the base material of the damaged part and perform partial repairs such as touch-up during the finish painting on site.

During the service period, the rust-preventive life of the paint does not reach the service life of the steel structure at present, and therefore repainting must be repeated for the purpose of maintaining rust-prevention. In the case of a bridge, the lower flange lower surface that is prone to water retention and the members located in the splash zone where wet, wet and dry conditions are repeated are more likely to corrode earlier than other parts and are applied in submerged areas. Often, cathodic protection is ineffective. Therefore, the rate of corrosion of these members is limited and the interval of the entire repainting must be shortened.

As a solution to these problems, it is possible to apply a thick plate clad steel material having a laminated material thickness of 1 mm or more, which is specified by JIS, but this steel material is considerably more expensive than general steel materials. . At present, it is used naked in extremely severe corrosive environments such as chemical refining plants and pressure vessels, which cannot withstand painting. Therefore, regarding the surface properties of the laminated material, only the oxide scale and flaws generated in the manufacturing process are removed by surface polishing, and the coating film adhesion of the paint for civil engineering and construction is not considered. Therefore, it is difficult to directly apply the thick plate clad steel material having a laminated material thickness of 1 mm or more as specified in JIS directly to the members for civil engineering and building structures.

Further, for civil engineering construction, from the viewpoint of cost reduction and adhesion of coating film, the thickness of the laminated material of the thick plate clad steel is thinned, and the surface of the laminated material is adjusted with a grindstone or blast after rolling. Can be considered. However, if the conventional method for manufacturing a thick plate clad steel material is followed, a deep flaw occurs due to the oxide scale layer and the indentation of the scale and the separating agent in the manufacturing process. For this reason, it is extremely difficult to adjust the base material of a thin laminated material while controlling the thickness of the laminated material to a desired value. Therefore, it was not possible to manufacture a thick plate clad steel material suitable for the above application.

The present invention has been made in order to solve the above-mentioned problems. By thinning the thickness of the bonding material and forming an anchor pattern on the surface of the bonding material, application of the primary primer and adjustment of the base material are omitted. An object of the present invention is to provide a rustproof thick steel plate for civil engineering and building structures and a method for producing the same, which can make the deterioration rate of the coating film uniform depending on the part and prolong the entire repainting cycle.

[0012]

[Means for Solving the Problems] The first invention is that the surface of a thick steel plate is coated with a coating amount of 250 g / m ² or more by a roll-bonding method.
A rustproof thick steel plate for civil engineering and building structures, in which a metal coating layer having a surface roughness of 00 g / m ² or less and a surface roughness Rz of 15 μm or more and 70 μm or less, which is more precious than the base metal steel, is formed as rolled.

A second aspect of the present invention is a sandwich type or semi-sandwich type composite slab comprising a base material steel and a noble metal composite material in the production of a rust preventive steel sheet. Between the material and the dummy steel, boron nitride with a grain size of 10 μm or less, 5 g / m ² or more, 20
0 g / m ² or less intervening, hot rolling this composite slab at a total reduction ratio of 3 or more and 10 or less, and then separating the composite material and the composite material or the composite material and the dummy steel at the surface where the boron nitride is present. It is a method for producing a rustproof thick steel plate for civil engineering and building structures according to item 1.

[0014]

The present inventors have made various studies in order to achieve the above object, and by forming a metal coating more noble than the base steel on the surface of the thick steel plate by the rolling joining method, the primary rust preventive property is improved. It was found that even after coating, even after coating, it is difficult to get a flaw reaching the base metal steel base, and even if it penetrates the metal coating layer, it improves the corrosion resistance after coating compared to the case without a metal coating layer. It was Furthermore, it has been found that good coating adhesion can be obtained by controlling the surface roughness of the metal coating layer during the rolling process.

[0015] Namely, the present invention is the amount coated on the surface of the steel plate by a roll-bonding method is 250 g / m ² or more, at 7500 g / m ² or less, the surface roughness or Rz15myuemu, it noble than 70μm or less of the base material steel A rustproof thick steel plate for civil engineering and building structures, in which a metal coating layer is formed as it is rolled, and a method for producing the same.

In the present invention, the metals that are more noble than the base steel at the corrosion potential for coating the surface of thick steel plates include Ni such as Co, Ni, Cu 80Ni-20Cr nichrome, Hastelloy and Inconel.
Base alloys Ferritelite, austenite, martensite, duplex stainless steels and Fe-Cr-Ni-Mo steels and their alloys.

First, the layer structure of the rustproof thick steel plate of the present invention will be described. Figure 1 is a conceptual diagram of the layer structure of rust-proof thick steel plates. Figures 1 (1) and (2) show the state before coating, and (3) and (4) show the state after coating. In the figure, a is a metal coating layer that is more precious than the base steel,
Reference numeral b indicates base steel and c indicates a paint layer.

FIG. 1 (1) shows a metal coating layer a on one surface of a base material steel b.
2 is formed by a roll-bonding method using a sandwich type composite slab shown in FIG. 2 (1) and a semi-sandwich type composite slab shown in FIG. 2 (2). Figure 1
(2) has a metal coating layer a formed on both sides of a base steel b, and is manufactured by a rolling joining method using a sandwich type composite slab shown in FIG. 2 (3).

As described above, FIG. 2 is a conceptual diagram of a composite slab for producing the rustproof thick steel plate of the present invention. FIG. 2 (1) is a sandwich type and is a noble material more than two base steels. The separating material 3 is interposed between the two, the laminated material 2 is sandwiched between two base steel materials 1, and the periphery is shield-welded 4. Figure 2
(2) is a semi-sandwich type, in which a separating agent 3 is interposed between a composite material 2 and a dummy steel 5 which are more noble than the base material steel, and the composite material 2 is sandwiched between the base material steel 1 and the dummy steel 5, It is one that is shield-welded. Fig. 2 (3) shows a sandwich type in which a base material steel 1 is provided on both sides with a noble metal material 2 and a separating agent 3 is interposed between the base material steel 2 and the dummy steel 5 to form a base metal steel. 1 and dummy steel 5 are shield-welded 4 around the periphery.

Since the inside of each of the composite slabs is shielded from the outside air, by hot rolling,
The base material steel 1 and the composite material 2 are metallurgically bonded to each other, and a clean metal coating layer surface without a black skin is obtained. Further, since boron nitride is interposed as the separating agent 3, an anchor pattern having good coating adhesion can be obtained on the surface of the metal coating layer. If the bondability between the base material steel 1 and the composite material 2 is poor, an insert metal for ensuring sound bondability is appropriately inserted between the base material steel 1 and the composite material 2.

Below, the reasons for limitation of the present invention will be explained based on the results of an examination of the bare corrosion resistance, coating adhesion and corrosion resistance of a thick steel sheet having a metal coating layer.

First, Ni-coated thick steel sheets with varying coating amounts were manufactured from a composite slab using boron nitride as a separating agent as shown in FIG. 2 (1) by a rolling joining method, and these Ni-coated thick steel sheets were subjected to 24 hours. The salt spray test (JIS Z 2371) was conducted to examine the effect of the coating amount on the area ratio of red rust on the surface of the coating layer after the test. The heating temperature of the composite slab is 1150 ° C., the total reduction ratio is 10, and the thickness of the Ni-coated thick steel plate after separation is 12 mm. The survey results are shown in FIG.

As is clear from FIG. 3, the coating amount is 250 g /
It can be seen that red rust does not occur at m ² or more. When the coating amount is less than 250 g / m ² , as shown in Fig. 4, due to the variation in the coating layer thickness that occurs during the rolling joining process and the presence of pits due to the indentation of boron nitride as the separating agent, the electrolyte solution was It comes into direct contact with the base steel material and red rust occurs. Further, since the excessive increase of the coating amount is inferior to the conventional steel sheet having no coating layer in terms of fusing property and economy, the upper limit of the coating amount is set to 7500 g / m ² . Therefore, the coating amount of 250 g / m ² or more, limited to the range of 7500 g / m ² or less.

Next, the influence of the surface roughness of the coating layer on the primary (before the corrosion test) and secondary (after the corrosion test) coating adhesion was investigated. The test materials were Ni with various surface roughnesses produced by changing the particle size, amount and total reduction ratio (composite slab thickness before rolling / thickness after rolling of composite) of the separating agent.
A coated thick steel plate was used. However, the coating amount is 250 g /
m ² . The composite slab has the shape shown in Fig. 2 (1), the heating temperature of the composite slab is 1150 ° C, and the thickness of the Ni-coated thick steel plate after separation is 12 mm.

The corrosion test is a combined cycle corrosion test in which the steps of salt spray → dry → wet shown in FIG. 5 assuming a marine atmosphere are repeated, and the corrosion test conditions are accelerated conditions in which the combined cycle is repeated 120 times. The coating system used has the specifications a shown in Table 4. The survey results are shown in Table 1.

From Table 1, the surface roughness of the metal coating layer is Rz2
Good adhesion to the primary coating was obtained in all cases of 155 μm, but it was found that it is necessary to control the surface roughness of the metal coating layer to Rz15 to 70 μm to secure the adhesion to the secondary coating. . That is, when the surface roughness of the metal coating layer is less than 15 μm or more than 70 μm, the secondary coating film adhesion is poor in the cross-cut adhesion test according to JIS K 5400. Is difficult to apply. Therefore, the surface roughness of the metal coating layer is limited to the range of Rz15 to 70 μm.

The surface roughness of the as-rolled metal coating layer is Rz15.
As shown in Fig. 6, the particle size of the separating agent should be adjusted to ~ 70μm.
Boron nitride of 10 μm or less is used, and the total reduction ratio is 3 or more,
Hot rolling at 10 or less is essential. In addition, as shown in Table 2, the amount of boron nitride used as a separating agent should be 5 g / m ² or more and 200 g / m ² or less from the viewpoint of preventing press-bonding between the bonding materials or between the bonding material and the dummy material. Should be.

When the particle size of boron nitride exceeds 10 μm,
The surface roughness of the metal coating layer after rolling may not satisfy Rz15 to 70 μm, which hinders the adhesion of the secondary coating film. From Table 2, when the amount of boron nitride is less than 5 g / m ² , the laminated materials after rolling, or the laminated material and the dummy material may be pressure bonded. When the amount of boron nitride exceeds 200 g / m ² , the surface roughness of the metal coating layer after rolling does not satisfy Rz 70 μm or less, which hinders the adhesion of the secondary coating film.

[0029]

[Table 1]

[0030]

[Table 2]

Also, from FIG. 5, even if the particle size of boron nitride is 10 μm or less and the amount of boron nitride is 5 g / m ² or more and 200 g / m ² or less, if the total reduction ratio is less than 3 or more than 10, The surface roughness of the metal coating layer may be Rz less than 15 μm and more than 70 μm, respectively, and in either case, the adhesion of the secondary coating film is hindered. Therefore, the grain size of boron nitride to be interposed between the composite material and the composite material or between the composite material and the dummy steel is 10 μm or less,
The amount is limited to 5 g / m ² or more and 200 g / m ² or less, and the total reduction ratio during hot rolling is limited to the range of 3 or more and 10 or less.

Furthermore, the influence of the presence or absence of a metal coating layer on the corrosion resistance after painting was investigated. Coating amount 250g / m ² , surface roughness
Painted on the surface of Rz15 ~ 30μm Ni coated thick steel plate,
As shown in Fig. 2, a test piece with a penetration artificial flaw with a width of 0.6 mm was applied only to the coating film and a test piece with a penetration artificial flaw with a width of 0.6 mm was applied to the coating film and the coating layer. It was subjected to the combined cycle corrosion test of FIG. 5 assuming an atmosphere. The number of cycles is 120, and the coating system is a specification in Table 4.

The penetrating artificial flaw applied only to the coating film is assumed to be a case where the environmental barrier property is lost due to deterioration of the coating film or generation of defects such as flaws and pinholes in the coating layer. The penetrating artificial flaw imparted to the metal coating layer is assumed to be a case in which a flaw that partially exposes the base steel material base occurs due to scratching or impact during installation or during service. The results of the investigation are shown in FIG. 8 and the cross-sections of these corrosion holes are shown in FIG.

As shown in FIG. 8, when the conventional steel base material was directly coated, the steel part immediately below the artificial flaw penetrating the coating film had 5.1 mm in the width direction and 0.6 mm in the plate thickness direction, which developed corrosion holes. Is recognized. On the other hand, in the case where the surface of the metal coating layer is coated, when the artificial flaw penetrates the coating film and the coating layer, the corrosion length is significantly larger in both the width direction and the plate thickness direction than the conventional uncoated material. It was found to be very small and has the effect of significantly retarding the progress of corrosion. The reason for this is as follows.

When the steel base is directly coated, water and oxygen penetrating from the flaws penetrating the coating film corrode the steel part to generate rust. At that time, the coating film is easily formed by lifting due to volume expansion. It peels off and a new surface appears. When the coating film is lifted by rust, the coating film breaks, so that the oxygen supply amount to the corrosion holes increases and the corrosion reaction amount itself increases. Therefore, it is considered that the rate of progress of corrosion in the surface direction and plate thickness direction of the steel part is high.

On the other hand, since the metal coating layer is much harder than the coating layer and is less likely to be damaged, it shields the steel part from the corrosive environment to prevent corrosion. In the unlikely event that the metal coating layer is damaged, even if rust occurs on the exposed steel portion, the bonding force between the metal coating layer and the steel portion is Since it is extremely higher than the above, peeling between the metal coating layer and the steel portion is unlikely to occur. Furthermore, even if the metal coating layer is lifted by rust, the metal coating layer is less likely to break than the paint layer, so the amount of oxygen supplied to the corrosion holes is less than that when it is directly coated on the steel substrate, The amount of reaction is considered to be small.

Further, it was found from FIG. 8 that in the environment where the wet or wet condition is repeated, the influence of galvanic corrosion is extremely small even when the base metal is coated with a metal having a higher corrosion potential. It is considered that this is because the film thickness of the electrolyte solution becomes extremely thin as compared with the immersion state in which galvanic corrosion becomes apparent.

As is clear from the above, the thick steel sheet metal-coated according to the present invention is excellent in bare corrosion resistance, coating adhesion and corrosion resistance after coating, and therefore, during construction of structures, splash zones, marine atmosphere. Even if it is placed in a corrosive environment where the anticorrosion does not work like parts, it exhibits excellent corrosion resistance. Therefore, it is possible to omit the application of the primary primer and the foundation adjustment work at the time of assembly, and it is possible to reduce the rusting area, so in steel structures that are painted and used, the deterioration rate of the coating film is leveled and the entire surface is repainted. The interval can be extended.

[0039]

EXAMPLES Examples of the present invention will be described below.
First, 50 g / m ^{2 of} boron nitride with a particle size of 1 to 10 μm was used as a separating agent, and the sandwich type composite slab shown in Fig. 2 (1) was used to obtain a coating amount of 54 g / m with a surface roughness of Rz 15 to 30 μm. ²
And 250 g / m ² Ni-coated thick steel plate and 350 g / m ² coating amount of SUS
A 316L coated thick steel plate was produced. The heating temperature is 1150 ° C,
The total reduction ratio is 10, and the thickness of the coated thick steel plate after separation is 12 mm. Figure 10 shows an example of the microstructure of 250 g / m ² thick Ni-coated steel sheet.

70 mm width x from these three types of coated thick steel plates
A 150 mm long test piece was sampled, and the exposed test piece was subjected to an atmospheric exposure test, in which a 5% NaCl aqueous solution was sprayed once a week, for 270 days with the metal-coated surface not coated, and the bare corrosion resistance was investigated. In addition, as a comparative example, a steel plate in which two types of primary primers (vinyl butyral resin-based long-wash wash primer and alkyl silicate resin-based zinc rich primer) were applied to the blasted surface of the steel plate was also added to the same test. The results are shown in Table 3.

As is clear from Table 3, the No. 3 Ni-coated thick steel sheet of the comparative example having a coating amount of 54 g / m ² and the steel sheets of the comparative examples No. 4 and 5 coated with the primary primer on the blast surface were used. Occurrence of red rust was observed. On the other hand, the coating amount of the present invention
250 g / m ² Ni-coated thick steel plate and coating amount of 350 g / m ² SUS 31
No red rust occurred on the 6L coated thick steel plate. Therefore,
The rustproof thick steel plate for civil engineering and building structures of the present invention has bare corrosion resistance superior to that of conventional rustproofing methods even without a primary primer.

[0042]

[Table 3]

Next, 70 from SUS 316L coating thickness steel plate Ni coated steel plate and coverage of 350 g / m ² of the coating amount 250 g / m ²
mm width x 150 mm length test pieces were taken, and the metal-coated surface of the taken test pieces was painted without adjustment of the base material, and some of the test pieces were given the artificial flaws shown in Fig. 7 and subjected to a corrosion test. And then
The paint adhesion and the corrosion resistance after painting when artificial defects were applied were investigated.

The coating was carried out under the conditions shown in Table 4, and the corrosion test was carried out by 120 cycles of the combined cycle corrosion test shown in FIG. The coating film adhesion was examined before and after the corrosion test by a cross-cut tape test according to JIS K 5400. In addition, as a comparative example, a product directly coated on the surface prepared by blasting was also added to the test. The results are shown in Table 5.

No. 1 to 4 anti-corrosion thick steel plates for civil engineering and building structures according to the present invention had no oxide scale on the metal coated surface as they were rolled and had a surface roughness within the range of Rz 15 to 70 μm. Since it is controlled, the adhesion of the coating film before and after the corrosion test is good, and when an artificial flaw penetrates only the coating film, rust does not occur on the steel part.

When an artificial flaw having a steel plate substrate exposed through the coating film and the metal coating layer was also formed, No. 5 in the case where an artificial flaw having a steel plate substrate exposed through the coating film was similarly attached. ~ 7
Compared with the comparative example, the progress of corrosion in the steel plate surface direction and plate thickness direction of the steel part is suppressed, and the amount of rust itself is also small. Therefore, the rust-proof thick steel plate for civil engineering and building structures of the present invention has the same coating film adhesion as the conventional rust-preventing method without adjusting the base material, and further has better corrosion resistance after painting than the conventional rust-preventing method. is doing.

[0047]

[Table 4]

[0048]

[Table 5]

Next, the corrosion resistance of the welded joint portion after coating was investigated for the above Ni-coated thick steel sheet having a coating amount of 250 g / m ² . The thickness is 12 mm. Welded joints were produced by submerged arc welding on the base steel side and reverse polarity plasma arc welding on the metal coating side using a common metal welding material. A 70 mm wide × 150 mm long test piece was collected from this welded joint material,
After coating the metal coated surface of the collected test piece without adjusting the base material, the artificial heat flaw shown in Fig. 11 was added to the heat-affected zone of the welding and a corrosion test was performed to investigate the corrosion resistance after painting when the artificial flaw was added. did.

The coating was carried out according to the specifications a shown in Table 4, and the corrosion test was carried out for 120 cycles of the combined cycle corrosion test shown in FIG. In addition, as a comparative example, a weld joint was manufactured by submerged arc welding of a steel sheet with a common metal welding material, a 70 mm wide × 150 mm long test piece was sampled from this welded joint material, and the surface of the sample piece was ground. After the adjustment, paints having the specifications a shown in Table 4 were also added to the same test, in which the weld heat-affected zone was provided with artificial flaws for penetrating the coating film. The results are shown in Table 6.

In the welded joint of Comparative Example No. 2, a corrosion hole having a length of 5.6 mm in the width direction and a length of 0.7 mm in the plate thickness direction was formed just below the artificial flaw penetrating the coating film. On the other hand, No.1
In the welded joint of the present invention example, no rusting was observed in the steel portion even if only the coating film had artificial flaws penetrating it. In the case where the steel part was exposed with an artificial flaw penetrating the metal coating layer of the heat-affected zone, the progress of corrosion in the steel plate surface direction and the plate thickness direction of the steel part was suppressed compared to the No. 2 comparative example. , The amount of rust itself is significantly reduced. Therefore, the rust-proof thick steel plate for civil engineering and building structures of the present invention has higher corrosion resistance after coating than the conventional rust-proofing method not only in the general portion but also in the welded joint portion.

[0052]

[Table 6]

[0053]

According to the present invention, the surface of the steel plate by a roll-bonding method, the amount of coating 250 g / m ² or more, 7500 g / m ² or less, and surface roughness than Rz15myuemu, than 70μm or less of the base material steel A rustproof steel plate for civil engineering and building structures, in which a noble metal coating layer is formed, and a manufacturing method thereof, wherein the rustproof steel plate for civil engineering and building structures has excellent bare corrosion resistance, coating adhesion and coating. Since it has corrosion resistance afterwards, it is possible to omit the conventional primary primer application work and the foundation adjustment work during the main painting of the structure, and the maintenance itself related to anticorrosion even when used in a severe corrosive environment where cathodic protection does not work It is possible to reduce the energy consumption and to exert a great economic effect.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a layer structure of a rustproof thick steel plate of the present invention.

FIG. 2 is a conceptual diagram of a composite slab for producing the rustproof thick steel plate of the present invention.

FIG. 3 is a diagram showing the effect of the coating amount on the area ratio of red rust on the surface of the coating layer after the salt spray test.

FIG. 4 is a diagram showing an example of a microscopic metallographic structure of a Ni-coated thick steel sheet having a weight of less than 250 g / m ² .

FIG. 5 is an explanatory diagram of a combined cycle corrosion test.

FIG. 6 is a diagram showing the influence of the total reduction ratio and the particle size of the separating agent on the surface roughness of the metal coating layer.

FIG. 7 is a diagram showing types of artificial defects used in a corrosion test.

FIG. 8 is a diagram showing types of artificial defects and corrosion states after a corrosion test.

FIG. 9 is a metallographic view showing a cross section of a corrosion hole after a corrosion test.

FIG. 10 is a view showing an example of a microscopic metallographic structure of a 250 g / m ² Ni-coated thick steel plate.

FIG. 11 is a diagram showing types of artificial flaws used in a corrosion test of a welded joint.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base material steel, 2 ... Laminating material, 3 ... Separation agent, 4 ... Shield welding, 5 ... Dummy steel, a ... Metal coating layer, b ... Base material steel, c ...
Paint layer.

Claims (2)

[Claims] To 1. A surface of the steel plate by a roll-bonding method, the amount of coating 250 g / m ² or more, 7500 g / m ² or less, and surface roughness Rz
A rust-proof thick steel plate for civil engineering and building structures, characterized in that a noble metal coating layer of 15 μm or more and 70 μm or less than the base steel is formed as rolled. 2. A sandwich type or semi-sandwich type composite slab comprising a base material steel and a noble metal composite material in the production of an anticorrosive steel sheet, between the composite material and the composite material or between the composite material and the dummy. Boron nitride with a grain size of 10 μm or less is interposed between steel and 5 g / m ² or more, 200 g / m ² or less, and this composite slab is used with a total reduction ratio of 3 or more, 10 or more.
The method for producing a rustproof steel plate for civil engineering and building structures according to claim 1, wherein hot rolling is carried out below, and thereafter, the laminated material and the laminated material or the laminated material and the dummy steel are separated at a surface on which boron nitride intervenes.