JP2021176977A - Clad steel sheet having excellent resistance to atmospheric corrosion and method for producing the same - Google Patents

Abstract

To provide a clad steel sheet having excellent resistance to atmospheric corrosion that can be used suitably in an environment with an extremely great amount of wafting salt, and a method for producing the same.SOLUTION: A clad steel sheet has a base steel sheet having a nickel steel layer as a laminated material on at least one side of the base steel sheet. The base steel sheet has, in mass%, C: 0.02-0.16%, Si: 0.02-0.50%, Mn: 0.50-2.00%, P≤0.03%, S≤0.010% and Al: 0.01-0.06%. The laminated material has a composition having, in mass%, C: 0.02-0.13%, Si: 0.04-0.5%, Mn: 0.2-1.0%, P≤0.03%, S≤0.010%, Ni: 7.0-12.0% and Al: 0.005-0.10% with the balance being Fe and inevitable impurities. A production method includes the steps of: combining the base material with the laminated material and heating them to 1050-1200°C; subjecting it to hot rolling with a reduction ratio of 1.5 or more at a steel sheet surface temperature of 850°C or higher; and forming a rolled body.SELECTED DRAWING: None

Description

The present invention has atmospheric corrosion resistance that can be suitably used in an ultra-high flying salt environment such as an offshore steel structure (offshore plant, offshore wind power generation, bridge, etc.) or a steel structure near the beach (bridge, building, etc.). It relates to an excellent clad steel sheet and a method for manufacturing the same.

Weathering steel, which has improved corrosion resistance in the atmosphere by adding alloying elements such as P, Cu, Cr, and Ni to the steel, is widely used for steel structures such as bridges. Weathering steel forms a highly protective rust layer composed of fine rust particles on the ground iron in an outdoor environment, thereby forming corrosive factors such as water, oxygen, and corrosive anions (chloride ions and sulfates). It is a steel material that has improved corrosion resistance by preventing the intrusion of particles (such as ions) into the base iron. For this reason, weathering steel does not require the coating of rust preventive paint, and is a steel material that can be used in so-called bare specifications. In general, a coated steel material is deteriorated due to corrosion caused by its coating defect portion, and finally it is necessary to repaint. At that time, a great deal of cost is required, such as the cost of repainting paint and the cost of painting, as well as the cost of assembling scaffolding locally. Furthermore, in places where scaffolding is difficult to assemble, such as at sea, a greater amount of cost and labor is required. Weathering steel that can be used without painting is a material with excellent life cycle cost because it does not require painting as described above.

Conventional weathering steel (JIS G 3114: 2016 weathering steel for welded structures) ^{cannot be used without coating in areas where the amount of flying salt is 0.05 mg / dm 2} / day or more, that is, in beach areas. (Non-Patent Document 1). In recent years, high weathering steel materials that can be used in environments with higher flying salt content have been developed. For example, Patent Document 1 proposes a beach weathering steel for structural use, which contains Ni: 0.25 to 5.0% and Mn, Cu, without adding a large amount of P. By adjusting the contents of Cr and Mo, it is said that excellent weather resistance is exhibited in the beach area and coating on the steel sheet can be omitted. Further, Patent Document 2 contains Ni: 0.1 to 6.0%, and by adjusting the content of Cu, Sb, etc., the amount of flying salt is 0.8 mg / dm ² / day. A steel material with excellent beach weather resistance that can be used in the Naru beach area has been proposed.

On the other hand, general stainless steel and Ni alloy are superior in corrosion resistance in an air corrosion environment as compared with weathering steel because the amount of alloy contained therein is high, but the price is high. Therefore, stainless steel clad steel sheets (Patent Document 3) and Ni alloy clad, which are economically superior by using expensive stainless steel and Ni alloy as a composite material and relatively inexpensive ordinary steel and low alloy steel as a base material. Steel plates (Patent Document 4) have been developed.

Further, after the base material is ordinary steel, in Patent Document 5, the laminated material is Ni: 1.0 to 4.0% weathering steel, and in Patent Document 6, the laminated material is Ni: 3.0 to 7. Coastal high weathering resistant clad steel sheets with 0% weathering steel have been developed.

Japanese Unexamined Patent Publication No. 3-158436 JP-A-2002-53929 Japanese Unexamined Patent Publication No. 2015-105399 Japanese Unexamined Patent Publication No. 2015-86422 Japanese Unexamined Patent Publication No. 4-143251 Japanese Unexamined Patent Publication No. 3-284491

"Joint Research Report on Application of Weathering Steel to Bridges (XX)", Public Works Research Institute, Ministry of Construction, Steel Club, Japan Bridge Association, 1993 A. C. Dutra, R.M. deO. Viana, Atmosphere Corrosion Testing in Brazil, p. 755 (1982)

However, the steel described in Patent Document 1 has a high Cr content, and has a problem of deterioration in toughness and weldability. Further, in a high flying salt environment, the amount of Ni added is not sufficient from the viewpoint of corrosion resistance, and Cr has a large amount of flying salt, that is, in an environment with a large amount of chloride ions, there is a problem that corrosion progresses. Further, when the amount of flying salt differs greatly depending on the beach area and the amount of flying salt exceeds 10 mg / dm ² / day as reported in Non-Patent Document 2, it is described in Patent Documents 1 and 2. It is expected that the corrosion resistance of the steel will be insufficient.

Stainless steel, which is a laminated material of Patent Document 3, contains Ni: 12.00 to 15.00% and Cr: 16.0 to 18.00%, and the Ni alloy of the laminated material of Patent Document 4 is , 60% of Ni and Cr: 20.0 to 23.0% are contained, so that the corrosion resistance is good. However, it is an excessively high-grade (expensive) material because it contains an excess alloy component for use in offshore and beach areas. In addition, since the laminated material is a high alloy compared to ordinary steel and low alloy steel, in hot rolling performed to obtain bondability as a clad material, during hot rolling in a high temperature range that has the greatest effect on bondability. Since the deformation resistance of the steel is much larger than that of ordinary steel and low alloy steel, there is a problem that it is very difficult to secure the bondability.

The clad steel sheets described in Patent Documents 5 and 6 are economically superior to stainless clad steel sheets and Ni alloy clad steel sheets, but have a problem that they are inferior in essential corrosion resistance for use in offshore or beach areas.

Therefore, in view of the above circumstances, the present invention can be suitably used in an ultra-high flying salt environment such as an offshore structure (offshore plant, offshore wind power generation, bridge, etc.) or a steel structure near the beach (bridge, building, etc.). It is an object of the present invention to provide a clad steel sheet having excellent air corrosion resistance and a method for producing the same.

The clad steel sheet having excellent air corrosion resistance according to the present invention, which has been developed to solve the above problems and realize the above object, is a clad steel sheet having a nickel steel layer as a mating material on at least one side of the base steel sheet. , C: 0.020 to 0.16%, Si: 0.02 to 0.50%, Mn: 0.50 to 2.00%, P: 0.03% in mass% of the base steel sheet. Hereinafter, it is a steel sheet containing S: 0.010% or less and Al: 0.01 to 0.06%, and the component composition of the laminated material is C: 0.020 to 0.13% in mass%. Si: 0.04 to 0.50%, Mn: 0.2 to 1.0%, P: 0.03% or less, S: 0.010% or less, Ni: 7.0 to 12.0% and Al : It contains 0.005 to 0.10% and is characterized by being composed of the balance Fe and unavoidable impurities.

Regarding the clad steel sheet having excellent atmospheric corrosion resistance according to the present invention,
a. The component composition of the laminated material is further in mass%, and is group A [at least one selected from Mo: 0.5% or less, Cr: 0.5% or less, and V: 0.1% or less] and group B [ Ti: 0.03% or less], including at least one group of elements.
b. The composition of the base steel plate is further mass%, Ni: 0.75% or less, Cr: 0.35% or less, Mo: 0.20% or less, Cu: 0.35% or less, Ti: 0. At least one selected from 007 to 0.020%, Nb: 0.03% or less, V: 0.005 to 0.050%, B: 0.0005% or less, and Ca: 0.0005 to 0.0050%. Including,
Etc. may be a more preferable solution.

Further, the method for producing a clad steel sheet having excellent air corrosion resistance according to the present invention, which has been developed to solve the above problems and realize the above object, uses a base material and a laminated material having any of the above component compositions as materials. After combining the base material to be the base material and the material to be the base material, the heat is heated to 105 to 1200 ° C. and the rolling reduction ratio is 1.5 or more when the surface temperature of the steel sheet is 850 ° C. or higher. It includes a step of performing inter-rolling to form a rolled body, wherein the reduction ratio is the plate thickness before reduction divided by the plate thickness after reduction.

As described above, according to the clad steel sheet having excellent atmospheric corrosion resistance and the manufacturing method thereof according to the present invention, ^{severe corrosion such that the flying salt content is 10 mg / dm 2} / day or more as in the offshore or beach environment. It is possible to obtain a clad steel sheet in which the corrosion resistance of the laminated material can be ensured in the environment and the base material has high strength and high toughness.

Hereinafter, embodiments of the present invention will be described. The clad steel sheet has a structure in which a laminated material is joined to one side or both sides of a base steel sheet. First, the limited range of the component composition will be described in detail. The unit in the component composition is "mass%", but hereinafter, unless otherwise specified, it is simply indicated by "%".

1. 1. About the composition of the base steel sheet C: 0.020 to 0.16%
C is an element necessary for ensuring the strength of the base metal. If C is less than 0.020%, the hardenability is lowered and the strength of the base metal is insufficient. Therefore, in order to secure the strength of the base metal, it is necessary to add a large amount of hardenable elements such as Cu, Ni, Cr and Mo, which leads to high cost and deterioration of weldability. On the other hand, if it exceeds 0.16%, the toughness of the weld deteriorates. Therefore, the C content is in the range of 0.020 to 0.16%. Preferably, it is in the range of 0.03 to 0.08%.

Si: 0.02 to 0.50%
Si is a component added as a deoxidizing agent and in order to obtain the strength of the base material. The effect is exhibited by adding 0.02% or more. However, the addition of a large amount exceeding 0.50% causes a decrease in weldability and a decrease in weld joint toughness, so the Si content needs to be in the range of 0.02 to 0.50%. It is preferably in the range of 0.02 to 0.25%.

Mn: 0.50 to 2.00%
Mn is added in an amount of 0.50% or more in order to secure the strength of the base metal and the strength of the welded joint. However, if the addition exceeds 2.00%, the weldability is lowered, the hardenability becomes excessive, and the toughness of the base metal and the toughness of the welded joint are lowered. Therefore, the range is set to 0.50 to 2.00%.

P: 0.03% or less P is an impurity element and is 0.03% or less in order to reduce the toughness of the base metal and the toughness of the weld. Although the lower limit is not set in particular, 0.001 to 0.01 is preferable because an excessive refining load and an expensive raw material having a low P content are required to reduce the P content to less than 0.001%. It is in the range of%, more preferably 0.001 to 0.005%.

S: 0.010% or less S is an impurity that is unavoidably mixed, and if it is contained in excess of 0.010%, the toughness of the base metal and the welded portion is lowered, so the content is 0.010% or less. Although the lower limit is not set, it is preferable to set the S content to less than 0.0001% because an excessive refining load and an expensive raw material having a low S content are required. It is in the range of 005%.

Al: 0.01-0.06%
Al is an element added for deoxidizing molten steel, and must be contained in an amount of 0.01% or more. On the other hand, if it is added in excess of 0.06%, the toughness of the base metal and the welded portion is lowered, and the toughness is lowered by being mixed into the metal portion of the welded portion due to dilution by welding. Therefore, the toughness is limited to 0.06% or less. It is preferably 0.02 to 0.04%. In the present invention, the Al content is defined by acid-soluble Al (also referred to as Sol.Al or the like).

Although the basic components of the base steel sheet have been described above, the following elements can be appropriately contained as needed. That is, as optional components, in mass%, Ni: 0.75% or less, Cr: 0.35% or less, Mo: 0.20% or less, Cu: 0.35% or less, Ti: 0.007 to 0. It may contain at least one selected from 020%, Nb: 0.03% or less, V: 0.005 to 0.050%, B: 0.0005% or less, and Ca: 0.0005 to 0.0050%. can.

Ni: 0.75% or less Ni is an element effective for improving the strength and toughness of steel. In order to obtain this effect, it is preferable to contain 0.01% or more. However, since Ni is an expensive element and excessive addition tends to cause slab surface defects during casting, the upper limit is preferably 0.75%.

Cr: 0.35% or less Cr is an element effective for increasing the strength of the base material. In order to obtain this effect, it is preferable to contain 0.01% or more. However, if Cr is contained in excess, the toughness is adversely affected. Therefore, when Cr is contained, 0.35% or less is preferable.

Mo: 0.20% or less Mo is an element effective for increasing the strength of the base material. In order to obtain this effect, it is preferable to contain 0.01% or more. However, if Mo is contained in an excessive amount, the toughness is adversely affected. Therefore, when Mo is contained, 0.20% or less is preferable.

Cu: 0.35% or less Cu can improve the strength of the base material. In order to obtain this effect, it is preferable to contain 0.01% or more. However, if the Cu content exceeds 0.35%, the hot ductility decreases, so the Cr content is preferably 0.35% or less.

Ti: 0.007 to 0.020%
Ti has the effect of forming TiN and suppressing grain growth during slab heating, resulting in finer microstructure and improving strength and base metal toughness. If the content is less than 0.007%, the effect is small, so that the content is preferably 0.007% or more. On the other hand, if the Ti content exceeds 0.020%, not only the above effect cannot be obtained, but also the toughness is deteriorated. Therefore, the Ti content is preferably in the range of 0.007 to 0.020%.

Nb: 0.03% or less Nb contributes to the formation of unrecrystallized regions in the low temperature region of austenite. At that time, by rolling in the temperature range, the structure of the base metal can be miniaturized and the toughness can be increased. It is also effective in improving hardenability and tempering softening resistance, and is also an effective element for improving the strength of the base metal. In order to obtain these effects, it is preferably contained in an amount of 0.005% or more, and more preferably 0.010% or more. However, if the content exceeds 0.03%, the toughness deteriorates, so the upper limit is preferably 0.03%.

V: 0.005 to 0.050%
V is an element effective for improving the strength and toughness of the base metal when the content is 0.005% or more, but when the content exceeds 0.050%, the toughness is lowered, so 0.005 when added. It is preferably in the range of ~ 0.050%.

B: 0.0005% or less B contributes to strength because it segregates into austenite grain boundaries when the steel is cooled from the austenite region, suppresses ferrite transformation, and produces a bainite structure containing a large amount of island-like martensite. However, since excessive addition leads to deterioration of toughness, the upper limit is preferably 0.0005%.

Ca: 0.0005 to 0.0050%
Ca is an element that improves toughness by fixing S. To obtain this effect, an addition of at least 0.0005% is required. However, even if it is contained in excess of 0.0050%, the effect is saturated, so it is preferable to add it in the range of 0.0005 to 0.0050%. More preferably, it is 0.0008 to 0.0040%.

As for the component composition of the base steel sheet, it is preferable that the balance other than the above is Fe and unavoidable impurities. Examples of unavoidable impurities include O and N.

2. Regarding the chemical composition of the laminated material The most required performance of the laminated material is corrosion resistance, but it is desirable to have high strength because it is one of the components of the clad member.

C: 0.020 to 0.13%
C is an element that increases the altitude of steel, and its content is required to be 0.020% or more in order to secure the desired high strength as nickel steel. On the other hand, if the content exceeds 0.13%, excessive carbides will be formed at the bonding interface between the laminated material and the base material when the clad steel sheet is used, and the bondability between the laminated material and the base material will deteriorate. Therefore, the C content is set in the range of 0.020 to 0.13%.

Si: 0.04 to 0.50%
Si is an effective component for deoxidation and an element that improves the strength of nickel steel, and a content of 0.04% or more is required to obtain such an effect. However, if it is contained in excess of 0.50%, it remains as a non-metal inclusion and the corrosion resistance is deteriorated. Therefore, the Si content is set in the range of 0.04 to 0.50%.

Mn: 0.2 to 1.0%
Mn is an element that is effective for bondability by improving hot ductility and hot workability, and also contributes to strength improvement. Requires a content of 2% or more. However, if it is contained in excess of 1.0%, it remains as a non-metal inclusion and the corrosion resistance is deteriorated. Therefore, the Mn content is in the range of 0.2 to 1.0%.

P: 0.03% or less P is an impurity element and is 0.03% or less in order to reduce the toughness of the base metal and the toughness of the weld. Although the lower limit is not set in particular, 0.001 to 0.01 is preferable because an excessive refining load and an expensive raw material having a low P content are required to reduce the P content to less than 0.001%. It is in the range of%, more preferably 0.001 to 0.005%.

S: 0.010% or less S is an impurity that is unavoidably mixed, and if it is contained in excess of 0.010%, the toughness of the base metal and the welded portion is lowered, so the content is 0.010% or less. Although the lower limit is not set, it is preferable to set the S content to less than 0.0001% because an excessive refining load and an expensive raw material having a low S content are required. It is in the range of 005%.

Ni: 7.0-12.0%
Ni is the most important element in the present invention and is a very effective element for improving corrosion resistance. Even if the addition amount is less than 7.0%, the corrosion resistance improves as the Ni content increases, but in ^{a severe corrosion environment where the flying salt content is 10 mg / dm 2} / day or more, such as offshore or beach areas, the corrosion resistance The improvement effect is not sufficient. Therefore, the Ni content is 7.0% or more, preferably 7.5% or more, and more preferably 8.0% or more. On the other hand, if it exceeds 12.0%, the effect is saturated and it causes an increase in cost, so 12.0% is set as the upper limit.

Al: 0.005-0.10%
Al is an effective deoxidizing element, and the effect is exhibited from 0.005% or more. However, if it exceeds 0.10%, the cleanliness deteriorates and the corrosion resistance is adversely affected. Therefore, the Al content is in the range of 0.005 to 0.10%.

Although the basic components of the laminated material have been described above, the following elements can be appropriately contained as needed. That is, as optional components, in mass%, group A [Mo: 0.5% or less, Cr: 0.5% or less, and V: at least one selected from 0.1% or less] and group B [Ti: 0]. It can contain at least one group of elements selected from [.03% or less].

Group A [At least one selected from Mo: 0.5% or less, Cr: 0.5% or less, and V: 0.1% or less]
Mo: 0.5% or less Mo is an element that contributes to strength improvement and also contributes to corrosion resistance. On the other hand, if it exceeds 0.5%, the effect is saturated and the cost increases, so that the upper limit is preferably 0.5% or less.

Cr: 0.5% or less Cr is also an element that contributes to strength improvement and also contributes to corrosion resistance, like Mo. On the other hand, if it exceeds 0.5%, the effect is saturated and the cost increases, so that the upper limit is preferably 0.5% or less.

V: 0.1% or less V is also an element that contributes to strength improvement and also contributes to corrosion resistance, like Mo. On the other hand, if it exceeds 0.1%, the effect is saturated and the cost increases, so that the upper limit is preferably 0.1% or less.

Group B [Ti: 0.03% or less]
Ti: 0.03% or less,
Ti is effective as an fixing element for C of carbides that adversely affect the bondability of the clad steel sheet, and C diffused to the bonding interface in the thermal history during the production of the clad steel sheet is not in the bonding interface but in the laminated material. Precipitates in and secures bondability. If it is contained in excess of 0.03%, the effect is saturated and it is economically disadvantageous. Therefore, it is preferable to specify 0.03% or less.

In the component composition of the laminated material, the balance other than the above is Fe and unavoidable impurities. Examples of unavoidable impurities include O and N.

3. 3. About the manufacturing method An embodiment of the manufacturing method of the clad steel sheet of the present invention will be described. The laminated material of the clad steel sheet is adjusted to the above-mentioned composition, and is cast by an appropriate casting technique such as a continuous casting method or an ingot forming method to be used as a material for the laminated material, and then rolled to a desired plate thickness by hot rolling. Adjusted to the body. The base metal is adjusted to the above-mentioned composition, cast by an appropriate casting technique such as a continuous casting method or an ingot forming method, and if necessary, hot-rolled to a desired plate thickness to obtain a base metal material. .. Assembling slabs for clad rolling (hereinafter referred to as "assembly slabs") are assembled using these base metal materials and rolled bodies of laminated materials.

The assembled slab can be made using a known method. Of these, the superposed form such as base material / laminated material / laminated material / base material is efficient in manufacturing. Further, considering the warp at the time of cooling, it is desirable that the base materials and the laminated materials have the same thickness. It is preferable that the assembled assembly slab for clad rolling is temporarily attached by electron beam welding in a pressure-adjusted vacuum chamber. When assembled as described above, it is preferable to apply a release agent such as _{Al 2} O _{3 or Mg O between the opposing mating materials.} Of course, it goes without saying that it is not necessary to limit the assembly method described above. The assembly slab for clad rolling is heated, and hot rolling is further carried out. In the following description, unless otherwise specified, the temperature is the average temperature in the plate thickness direction. The average temperature in the plate thickness direction can be obtained by simulation calculation or the like from the plate thickness, surface temperature, cooling conditions, and the like. For example, the average temperature in the plate thickness direction can be obtained by calculating the temperature distribution in the plate thickness direction using the difference method.

(I) Heating temperature of the assembled slab: 1050 ° C. or higher and 1200 ° C. or lower The heating temperature of the assembled slab is preferably high from the viewpoint of the bondability of the clad steel sheet, that is, the bondability between the base steel sheet and the laminated material. Bondability is improved by heating at 1050 ° C. or higher. However, when heated above 1200 ° C., the hot ductility of the laminated material deteriorates, causing cracking of the material during rolling, and coarsening of the crystal grains of the base material causes deterioration of toughness. Therefore, the heating temperature is set in the range of 1050 to 1200 ° C. from the viewpoint of the properties of the base material, the mechanical properties of the base material, and the bondability. The heating time in this temperature range is preferably 60 to 300 minutes. By heating for 60 minutes or more, the assembled slab can be brought to a uniform temperature. On the other hand, if it is held in a high temperature range for too long, the crystal grains of the base metal become coarse when the assembled slab is heated, and the metal structure of the base metal after rolling and cooling also becomes coarse, which may cause deterioration of toughness. ..

(II) Rolling ratio at a steel sheet surface temperature of 850 ° C or higher: 1.5 or higher Clad steel sheets are rolled in a high temperature range to ensure their bondability. The reason why rolling in a high temperature range is important is that the difference in deformation resistance between nickel steel, which is a laminated material, and low alloy steel, which is a base material, is small, so that an ideal bonding interface is formed by rolling, and This is because mutual diffusion of elements tends to proceed at the boundary between the laminated material and the base material in the high temperature region. In particular, nickel steel having a Ni content of 7.0 to 12.0%, which is a composite material of the present invention, is more than stainless steel or a Ni alloy having a Ni content of about 40 to 60% (for example, Alloy 825 or Alloy 625). Also has low deformation resistance. Therefore, in the clad steel of the present invention, the rolling reduction ratio (= (plate thickness before rolling) ÷ (plate thickness before rolling) ÷ ( Sheet thickness after rolling)) Bondability can be ensured by rolling 1.5 or more. Therefore, in the present invention, rolling is carried out under the condition that the rolling reduction ratio at a steel sheet surface temperature of 850 ° C. or higher is 1.5 or higher. The upper limit of the rolling ratio is not particularly limited, but is more preferably 1.5 to 20.0 in consideration of rolling efficiency.

In order to secure the strength of the base metal and the toughness of the base metal, the clad steel sheet of the present invention may be further subjected to controlled rolling or accelerated cooling after the hot rolling. Alternatively, after hot rolling and cooling to room temperature, reheating quenching and further tempering may be performed.

Next, examples of the present invention will be described. The present invention is not limited to these examples.
A clad steel sheet was produced using a base material having the component composition shown in Table 1 and a laminated material having the component composition shown in Table 2. As for the manufacturing conditions, the base material / laminated material / laminated material / base material were stacked and assembled into a set of assembly slabs. The thickness of the base material in the assembled slab was 160 mm, and the thickness of the laminated material was 15 mm. Then, the assembled slab was heated and hot-rolled under the manufacturing conditions shown in Table 3. Except for the items listed in Table 3, hot rolling and subsequent cooling were carried out according to a conventional method. As for the thickness of the clad steel sheet on one side after rolling, a clad steel sheet having a base material of 32 mm and a laminated material of 3 mm was manufactured.

As an evaluation method of the base material, in the tensile test, the JIS No. 4 test piece was collected from the plate thickness 1/2 position of the base material steel plate so that the longitudinal direction of the test piece was perpendicular to the rolling direction of the steel plate, and JIS Z2241: 2011. Yield stress YS (MPa) and tensile strength TS (MPa) were measured according to the above. In the Charpy impact test, JIS V notch test pieces were collected from the position of 1/2 of the thickness of the steel sheet so that the longitudinal direction of the test piece was perpendicular to the rolling direction of the steel sheet, and the absorbed energy vE _{− at −40 ° C. 40} (J) was measured. Those satisfying all of YS ≧ 460 MPa, TS ≧ 570 MPa and vE _-40 ≧ 200 J were evaluated as having good mechanical properties of the base material.

The bondability as a clad steel sheet was carried out in accordance with the shear strength test described in the test method for clad steel of JIS G0601: 2012. As for the evaluation criteria, those having a shear strength of 300 MPa or more were judged to have good bondability.

As the corrosion resistance test of the laminated material, a dry / wet repeated corrosion test was carried out in accordance with the ISO 16539B method. Artificial seawater was used in the salt adhesion process in order to simulate an environment with a large amount of flying salt and extremely severe corrosion. The corrosion test period was 26 weeks. After the completion of the corrosion test, the corrosion products formed on the surface were removed using a pickling solution, and the weight loss before and after the corrosion test was converted into the average plate thickness reduction for evaluation. When the average plate thickness decrease after 26 weeks was 0.5 mm or less, it was judged that the corrosion resistance was good.

Table 4 summarizes the evaluation results of the clad steel sheet manufactured under each of the above manufacturing conditions by combining the various base materials and the laminated materials. The clad steel sheet produced by combining the base material and the laminated material with the conforming steel under the manufacturing conditions of the conforming example had good mechanical properties of the base material, the bondability of the clad steel plate, and the corrosion resistance of the laminated material. On the other hand, a clad steel sheet in which the base material or the laminated material is a comparative steel or whose manufacturing conditions are out of the scope of the present invention is inferior in either the mechanical properties of the base material, the bondability of the clad steel sheet, or the corrosion resistance of the laminated material. Was there.

In the present invention, 7 to 12% nickel steel is used as the laminated material, and the component composition of the base material is specified to obtain a clad steel sheet having excellent air corrosion resistance. Applicable to offshore steel structures (offshore plants, offshore wind power generation, bridges, etc.) and steel structures near the beach (bridges, buildings, etc.) used in severe corrosive environments such as / dm ^{2 / day or more.} Suitable.

Claims (4)

A clad steel sheet having a nickel steel layer as a mating material on at least one side of the base steel sheet.
The base steel sheet is C: 0.020 to 0.16%, Si: 0.02 to 0.50%, Mn: 0.50 to 2.00%, P: 0.03% or less in mass%. , S: 0.010% or less and Al: 0.01 to 0.06%.
The component composition of the laminated material is C: 0.020 to 0.13%, Si: 0.04 to 0.50%, Mn: 0.2 to 1.0%, P: 0.03 in mass%. % Or less, S: 0.010% or less, Ni: 7.0 to 12.0% and Al: 0.005 to 0.10%, and the resistance is characterized by being composed of the balance Fe and unavoidable impurities. Clad steel plate with excellent atmospheric corrosion resistance. The component composition of the laminated material is further in mass%, and is group A [at least one selected from Mo: 0.5% or less, Cr: 0.5% or less and V: 0.1% or less] and group B [ The clad steel sheet having excellent air corrosion resistance according to claim 1, which contains at least one group of elements selected from [Ti: 0.03% or less]. The composition of the base steel plate is further mass%, Ni: 0.75% or less, Cr: 0.35% or less, Mo: 0.20% or less, Cu: 0.35% or less, Ti: 0. At least one selected from 007 to 0.020%, Nb: 0.03% or less, V: 0.005 to 0.050%, B: 0.0005% or less, and Ca: 0.0005 to 0.0050%. The clad steel plate having excellent air corrosion resistance according to claim 1 or 2, wherein the clad steel plate contains. In the method for producing a clad steel sheet using the base material and the laminated material having the component composition according to any one of claims 1 to 3, the base material material to be the base material and the laminated material material to be the laminated material are used. After the combination, the steel sheet is heated to 105 to 1200 ° C. and hot-rolled so that the reduction ratio at a steel sheet surface temperature of 850 ° C. or higher is 1.5 or higher to form a rolled body. Is a method for producing a clad steel sheet having excellent air corrosion resistance, which is obtained by dividing the plate thickness before rolling by the plate thickness after rolling.