JPH0331466A - Production of metal coated steel having superior weldability and high corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the weldability and corrosion resistance of steel by thermally spraying an electrochemically baser metal than the steel on the surface of the steel in an atmosphere of an inert gas used to atomize a molten metal and by heat-treating the steel under prescribed conditions. CONSTITUTION:The space between a torch and a body to be thermally sprayed is filled with an atmosphere of an inert gas used to atomize a molten metal, e.g. Ar or N2. A coat of an electrochemically baser metal than steel is formed on the surface of the steel by thermal spraying with arc in 0.2-8mm thickness. No metal oxide is contained in the coat and the adhesive strength of the thermally sprayed metal to the steel is increased. The coated steel is protected from oxidation, heated to 850 deg.C to the m.p. of the thermally sprayed metal and hot worked to form a metal coating layer of >=20mum thickness on the surface.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides excellent corrosion resistance in the outdoor atmosphere, especially in humid environments such as the shaded areas of structural members, and even in corrosive environments such as freshwater and seawater. The present invention relates to a method for manufacturing metal-coated steel shown in the figure.

[Prior art and problems to be solved by the invention] In order to impart corrosion resistance to steel that is easily corroded, Zn, ^l, Sn
A plating method in which metals such as , Cr, Ni, and Pb or alloys thereof are deposited is commonly used. The plating method has a good appearance because it adheres uniformly with a thin film, and it also provides corrosion resistance, so it is often used for food cans, home appliances, etc.; There was a problem of blistering and peeling of the plating. For this reason, Ni-based steel materials used in general machinery, construction, shipbuilding, vehicles, chemical equipment, etc. that require strong corrosion resistance and wear resistance, as described in Japanese Patent Publication No. 60-31899, are Furthermore, in addition to thermal spraying methods for coating titania and alumina, metal thermal spraying methods for Ni, Cr, Ni alloys, etc., as well as Tokko Kokko 61. -25779, “B, C, St, P and Cr on the surface of the metal material,
Fe, Ni, optionally mixed with Mo, W, Ti, etc.
, Surface coating methods in which a metal group consisting of one or more types of Co is attached, rapidly melted by scanning a heating source, and then rapidly cooled are widely used, and among them, metal spraying is widely used due to the usefulness of metals. It is being utilized. However, the thermal spraying method is more expensive than the plating method because the sprayed metal is deposited more and thickly on the steel surface, and since the sprayed metal layer is porous, the corrosion resistance may be inferior. Furthermore, because the yield efficiency of thermal spraying itself is poor, its use is limited to repairing large steel structures or parts thereof. In addition, the sprayed metal obtained by ordinary arc spraying and gas spraying contains a considerable amount of these metal oxides, and if the metal is coated with steel produced through a heating and rolling process, it will not be possible to weld it. During this process, it reacts with trace amounts of hydrogen in the atmosphere to generate water vapor, which can cause blowholes and poor bonding. 4 In view of the above-mentioned problems, the present invention aims to make the sprayed metal layer a clean layer containing no or very small amounts of the metal oxide before heating, and to prevent the oxidation of the sprayed metal layer during heating. By suppressing
The purpose of this invention is to provide a method for producing highly corrosion-resistant metal-coated steel of various shapes such as shaped steel and steel pipes.

[Means for Solving the Problems] The gist of the present invention is to atomize molten metal by using ^r,,N,
Arc spraying uses an inert gas such as molten metal and shields the area around the molten metal, or gas spraying uses an inert gas to atomize the molten metal and shield the molten metal while keeping the gas flame reducing. Either a thermal sprayed layer M114 of a metal electrochemically more base than the steel is applied to the steel surface with a thickness of 0.2 mm to 81III, or a thermal sprayed layer M114 is applied to the steel surface with a thickness of 02 mm to 4 mm.
A base sprayed metal layer of 0.1 mm to 7 mm, and a sprayed layer of a metal less electrified than the base sprayed metal on top of the base sprayed metal layer.
．． 8mm thick and the total thickness of both sprayed metal layers is 8mm
The following laminated thermal spray coated steel is heated to a temperature of 850°C to below the melting point of the thermal sprayed metal with anti-oxidation measures such as thin plate covering and anti-oxidation paint, and hot worked to form a layer of 20 μm or more thick on the steel surface. This is a method for producing highly corrosion-resistant metal-coated steel having a metal coating layer and having good weldability.

[For production] The present invention will be explained in detail below.

Slabs, billets, or further rolling, forging, extrusion, etc. manufactured by continuous casting method or ingot-blowing method from molten steel produced through melting furnaces such as converter furnaces and electric furnaces, or vacuum degassing treatment, etc. After mechanically or chemically cleaning (plasting) steel in intermediate (rough) shape that has undergone hot working, the surface of the steel is coated with metals that are less electrochemically base than the steel, such as old Cu, Cu, etc. , arc spraying, which uses an inert gas to atomize the molten metal and seals around the molten metal with the same inert gas, or atomizes the sprayed metal while keeping the gas flame reducing. or by gas spraying using an inert gas for the shield. The sprayed metal layer obtained by the above thermal spraying method contains no or only a very small amount of oxide of the metal compared to conventional arc spraying, gas spraying, or sprayed metal, and also has high adhesion between the steel and the sprayed metal interface. In arc spraying, using only an inert gas for either the atomization or shielding gas will not be sufficient to prevent oxidation of the molten metal.Also, in gas spraying, if the gas flame is acidic to neutral and the atomized gas becomes air, it will be ineffective. Even if active gas shielding is applied, oxidation prevention is still insufficient.

Weldability with a clean metal coating layer is achieved by covering the thermal sprayed metal-coated steel with such a clean thermal spray coating in a thin plate, taking high-temperature oxidation prevention measures such as applying anti-oxidation paint, and performing hot working by heating. Good highly corrosion resistant metal coated steel can be obtained. If the measures to prevent oxidation during heating are insufficient, no matter how clean the sprayed metal layer is, the metal coating layer of the final product will contain oxides and weldability will be impaired.

The metal coating layer produced in this way, which is electrically baser than the steel, imparts high corrosion resistance to the metal-coated steel by inhibiting corrosion of the steel by self-melting, but the thickness of the sprayed layer is less than 0.2 mm. If the metal coating layer is thin, the thickness of the metal coating layer after hot working may be less than 20 Pm, and pinholes are likely to occur, resulting in a loss of high corrosion resistance. Furthermore, although the adhesion between the steel and the sprayed layer interface has improved compared to conventional arc spraying or gas spraying, the physical bond with the steel base is broken when the sprayed layer is thicker than 8 mm, and the physical bond with the steel substrate is broken during handling. Problems arise with interlayer or partial peeling. Therefore, in the present invention, the thickness of the sprayed layer of a metal that is less electrified than steel is limited to 0.2 m+a to 8+ am from the viewpoint of corrosion resistance and adhesion.

Furthermore, the present invention provides a base layer for the metal spray coating layer, that is, the surface of the slab, billet, or intermediate-shaped steel.
A base sprayed metal layer such as , cupronickel, or monel is applied by the above-specified thermal spraying method. This serves as a cathode for the upper sprayed metal and has the effect of suppressing corrosion of the steel. In other words, the effect is that with a thin base metal coating of less than 0.2 mm, the thickness of the base metal coating after hot working may be less than 20P, resulting in insufficient insulation between the steel and the upper metal coating. Corrosion resistance is impaired in some places, and if the sprayed layer thickness exceeds 4 cm, the thickness of the upper sprayed metal necessary to guarantee long life cannot be ensured due to the relationship between the total thickness of the base layer and the upper layer. Therefore, in order to obtain the effect of improving corrosion resistance, the base thermal sprayed metal layer in the present invention is
■The thickness is Il ~ 41-, and on top of that, a sprayed layer of a metal that is less electrified than the base sprayed metal, such as Cu or bronze, is applied to a thickness of 01+u* ~ 7.8■. By laminating thermally sprayed metals with different potentials, the laminated metal coating layer after hot processing is formed such that the base metal coating layer is the cathode,
Since the upper metal coating layer serves as an anode, corrosion of the base metal coating layer is suppressed and corrosion of the steel is prevented. However, such a corrosion-preventing effect is achieved only when the thickness of the upper metal spray layer is 0.1
If the layer is thinner than s+e, the upper layer of the laminated metal coating after hot working will be worn out early due to corrosion, and the sacrificial effect as an anode will not last for a long period of time, making it insufficient. In addition, the total thickness of the laminated thermal sprayed metal layers was set to be 8a+a+ or less in order to prevent peeling due to dropping, impact, etc. during handling.

Therefore, the thermal spray coated steel that has been thermally sprayed as described above is coated with a thin plate and coated with anti-oxidation paint to prevent oxidation.
It is heated to a temperature of 50° C. to below the melting point of the sprayed metal and subjected to hot working such as rolling, forging, and extrusion to form various shapes. At this time, if the oxidation prevention measures are insufficient, the clean metal spray coating layer will oxidize, and the weldability will deteriorate because oxides will be present in the metal coating layer of the product. Also, the heating temperature is 850℃
If the temperature is below or below, hot working of the steel becomes difficult, and if the temperature exceeds the melting point of the sprayed metal, the sprayed metal coating becomes semi-molten, making it impossible to form a homogeneous and uniform metal coating layer by hot working. It has been stipulated in consideration of the

The metal-coated steel manufactured by the method of the present invention as described above has good weldability because the coating layer contains no or extremely small amount of oxides, whether it is a single-layer coating or a laminated coating.
In addition, in the case of a single-layer coating, the corrosion-preventing effect between the steel (cathode) and the coating (anode), and in the case of a laminated coating, the corrosion-preventing effect between the base coating (cathode) and the upper coating (anode). , a product with excellent corrosion resistance can be obtained.

[Examples and effects of the invention] Next, examples of the present invention will be described.

The symbol ANE in Table 1-1 is a comparative steel with a single layer metal coating produced by arc spraying. In other words, symbol A is the one in which ^1r (compressed air) is used as the atomizing gas for arc spraying, a thermal spray coating is formed without shielding around the molten metal, and then oxidation prevention measures are taken and the metal is heated and rolled. In this case, the base steel is 5O541, which has a lower potential than the coating Cu.
0, so in the salt water spray test with a notch in the base metal, the base metal steel acts as an anode and corrodes, but red rust occurs frequently even in welded joints without a notch. This is because there are many welding defects such as blowholes and poor bonding caused by oxides in the coating layer. Symbol B uses N2 for atomization but is not shielded and is heated and rolled with anti-oxidation measures, while symbol C uses air for atomization and only Ar is used for shielding.
This is the case when . In both cases, rusting on the flat part of the weld joint is improved compared to symbol A, but it is not sufficient. In addition, symbol A is atomized using the same Ar shield and heated without taking any oxidation prevention measures. - In the case of rolling, the corrosion resistance of the flat part of the weld joint is insufficient in this case as well. Symbol E is the one that was heated and rolled using Ar for atomization and shielding, and taking measures to prevent oxidation. In this case, the corrosion resistance of the flat part of the weld joint becomes sufficient for the first time.However, since the base metal steel has a lower potential than the coating metal Cu, the corrosion resistance of the base metal steel is observed in all cases in the notched salt spray test. It has disadvantages that occur.

On the other hand, the symbol F~! is added to the atomizing gas and shielding gas of the present invention, that is, arc spraying.
Single-layer metal-coated steel is produced by heating and rolling using 2 and taking anti-oxidation measures, but none of them cause welding defects because the metal coating layer contains no or only a very small amount of oxide. , the corrosion resistance of the seam flat part is excellent. In addition, 5IJS3, which has a higher potential in the base steel than the coating metal,
Since 04 and 505316 are used, corrosion of the base material does not occur even in a salt water spray test with a notch.

Symbol J is a comparative steel with a laminated metal coating produced by atomization and arc spraying using A as the shielding gas, but even when heated and rolled with anti-oxidation measures,
Because the metal coating layer is thin, if it reaches the base steel in some areas, pinholes occur and red rust occurs in some areas, resulting in insufficient corrosion resistance. On the other hand, the symbol ~P means that the base metal coating of the product is 20μm or more thick by forming a thick thermal spray coating layer using the same method.In this case, the corrosion of the base steel is prevented because pinholes are prevented from forming. Even if the metal coating has a notch, the lower layer is protected by the cathode corrosion protection effect of the upper and lower layers of the metal coating, resulting in a long life. Furthermore, since the metal coating layer is clean, the corrosion resistance of the seam part is also excellent.

Next, symbols a to e in Table 1-2 are comparison steels of single-layer coated steels in the case of gas spraying. In other words, symbol a is a metal that uses air for atomization with a normal neutral flame, forms a Cu coating without sealing around the molten metal, takes anti-oxidation measures, and heats and rolls the metal. Due to the large amount of oxides, welding defects occur and the corrosion resistance of the joint flat area is poor.

Symbol "S" means that the gas flame is reduced and is sprayed without shielding using air for atomization. Symbol "C" is for spraying with a neutral gas flame and using air for atomization and shielding, to prevent oxidation. In both cases, the corrosion resistance of the flat part of the weld joint is improved by reducing the oxides in the metal coating layer, but it is not sufficient. In addition, symbol d indicates that the gas flame is used to reduce the gas flame to reduce atomization. This is a case where the molten metal is thermally sprayed with a shield around the molten metal and heated and rolled without taking any oxidation prevention measures, but in this case as well, the weldability decreases due to oxidation of the sprayed coating layer due to heating. The corrosion resistance of the joint is not sufficient, and symbol e means that a gas flame is used for reducing atomization, and the area surrounding the molten metal is thermally sprayed, shielded with gas, and heated while taking measures to prevent oxidation. - In the case of rolling. In this case, the oxides in the metal coating layer of the product are zero or extremely small, so there are no welding defects and the joint has sufficient corrosion resistance. However, the base steels with symbols a to e are Since the potential is lower than that of Cu in the coating layer, the notched salt water spray test has the drawback of causing corrosion of the base material.

On the other hand, the symbol f x i is a single-layer metal-coated steel manufactured by the method of the present invention, which has excellent corrosion resistance in both the base metal and the welded part. In other words, corrosion of the base metal steel is prevented by making the base metal 1 steel have a nobler potential than the coating metal, and while keeping the gas flame reducing, Ar and N2 are used for atomization, and the surroundings of the molten metal are The metal coating layer becomes extremely clean by shielding it with A or N2 and applying oxidation prevention measures and heating and rolling.
The weldability was improved and the corrosion resistance of the seam flat part was also sufficient.

The symbol j in Table 1-2 is a reducing gas flame and is atomized.
This is a comparison steel of laminated metal coated steel, which is made by shielding the periphery of molten metal to form a laminated metal sprayed coating layer, taking anti-oxidation measures, and heating and rolling it. Holes are formed and pitting corrosion occurs in part of the base steel.

For the same reason, pitting corrosion occurs partially on the flat part of the weld joint, but in the steel obtained by the invention with the symbol ~n, the thickness of the coating layer is 20 μm or more, so the upper layer coating and the lower layer Corrosion of the lower layer coating is suppressed by the cathodic corrosion protection effect during the coating, and as a result, corrosion of the base steel is prevented, resulting in a longer service life. Furthermore, since there are no defects in the welded part, the corrosion resistance of the seam flat part is also excellent.

Procedural amendment amendment 1, case indication Heisei/year patent application No. 7g Hiro (No. 2, name of invention) Applicant 11'("'V" Ote J21, Chiyo-ku, Tokyo) 6
No. 3 rt a (t) (665) Nippon Steel Corporation stock number 4, agent address 2-6-2 Marunouchi, Chiyoda-ku, Tokyo Shigesu Building 330 The following matters have been amended in the specification of the application. I will.

Record 1. The scope of claims is amended as shown in the attached sheet.

2. Page 15, 6th and 5th lines from the bottom Each word that says "air" Correct it with "^r".

3. Page 16, line 1 It says "air" Correct it as "A".

In the "Atomizing gas" section of the "Comparative method B" column on page 18. Add "N2".

5. On page 18, in the column ``Metal of base layer'' in Table 1-1r Example Method ■, correct cylindrical (Cu22n) J to read ``Red copper (Cu-Zn) J.

8. N-positive connotation As shown in the appendix 6. On page 18, Table 1-1, "Example method M", in the "upper layer metal" section, "Circle mesh (Cu-Zu) J" was replaced with "Red copper (red copper)". Cu-Zn) Correct as J.

7. Correct Table 1-2 on page 19 as follows.

1. By using an inert gas to atomize the molten metal and using the same inert gas to isolate the molten metal from the atmosphere from the torch to the object to be sprayed, the surface of the steel is more electrified than the steel itself. No base metal sprayed coating layer
．． After forming the spray coated steel to a thickness of 2m1Il to Elnm, the sprayed coated steel is subjected to oxidation prevention measures, heated at a temperature of 850T to below the melting point of the sprayed metal, and hot worked to form a steel surface with a thickness of 20Pm or more. A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, characterized by forming a metal coating layer.

2. Use an inert gas to atomize the molten metal, and use the same inert gas from the torch to the object to be sprayed.
Using arc spraying to isolate the molten metal from the atmosphere, a 0.2mm to 4mm thick sprayed layer of steel is formed, and then an electrified layer is added on top of the base gold sprayed layer. After forming a clean laminated thermal sprayed layer of 0.1 to 7.8% less base metal using the same thermal spraying method, the laminated thermal spray coated steel is subjected to oxidation prevention measures to reduce the temperature from 850℃ to below the melting point of the sprayed metal. A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, which comprises heating at a high temperature and hot working to form a laminated metal coating layer with a thickness of 20 μm or more on the steel surface.

3 Gas spraying uses inert gas to atomize the molten metal while keeping the gas flame reducing, and also shields the molten metal with inert gas while it reaches the object to be sprayed. 02m of thermally sprayed coating layer of a metal that is less electrified than the steel on the surface of the steel.
After forming the sprayed coated steel to a thickness of 20 μm or more, the sprayed coated steel is heated at 850°C to a temperature below the melting point of the sprayed metal and hot worked to provide a coating with a thickness of 20 μm or more on the steel surface. A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, the method comprising forming a metal coating layer.

In addition to using an inert gas to atomize the metal, gas spraying also shields the molten metal with inert gas while it reaches the object to be sprayed.
After forming the base metal sprayed layer to a thickness of 0.1 to 4mm, a metal that is less electrolytically base than the base metal sprayed layer is coated on top of the base metal sprayed layer to a thickness of 0.1 to 7.8mm using the same spraying method. After forming a clean laminated thermal sprayed layer with a total thickness of 8 mm or less, the laminated thermal spray coated steel is heated at a temperature of 850°C to below the melting point of the sprayed metal with oxidation prevention measures and hot worked to form the steel. A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, characterized by forming a laminated metal coating layer with a thickness of 20 μm or more on the surface.

Claims (1)

[Claims] 1. A method of atomizing molten metal using an inert gas and using the same inert gas to insulate the molten metal from the atmosphere from the torch to the object to be sprayed. After forming a sprayed coating layer of a metal that is electrochemically more base than that to a thickness of 0.2 mm to 8 mm, the sprayed coated steel is heated at a temperature of 850°C to below the melting point of the sprayed metal with anti-oxidation measures taken. , hot worked to a thickness of 20μ on the steel surface.
A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, characterized by forming a metal-coated layer with a thickness of m or more. 2. By using an inert gas to atomize the molten metal and using the same inert gas to isolate the molten metal from the atmosphere from the torch to the object to be sprayed, the surface of the steel is electrochemically less noble than the steel itself. After forming a base thermal sprayed layer of a metal with a thickness of 0.2 mm to 4 mm, a metal that is less electrified than the base metal spray layer is further applied on top of it by the same thermal spraying method to a thickness of 0.1 to 7.8 mm. After forming a clean laminated thermal sprayed layer with a thickness of 8 mm or less and a total thickness of both thermal sprayed layers of 8 mm or less, the laminated thermal spray coated steel is subjected to oxidation prevention measures and heated to 850℃~
A highly corrosion-resistant metal-coated steel with excellent weldability, which is heated at a temperature below the melting point of the sprayed metal and subjected to hot working to form a laminated metal coating layer with a thickness of 20 μm or more on the steel surface. Production method. 3 Gas spraying uses inert gas to atomize the molten metal while keeping the gas flame reducing, and also shields the molten metal with inert gas while it reaches the object to be sprayed. Electrochemically spray a coating layer of a metal that is electrochemically more base than the steel on the surface of the steel to a thickness of 0.2 mm to 8 mm.
After forming a metal coating layer with a thickness of 20 μm or more on the steel surface, the sprayed coated steel is heated at a temperature of 850°C to below the melting point of the sprayed metal to form a metal coating layer with a thickness of 20 μm or more. A method for producing highly corrosion-resistant metal-coated steel with excellent weldability, characterized by forming a metal-coated steel with excellent weldability. 4. Gas spraying uses inert gas to atomize the molten metal while keeping the gas flame reducing, and also shields the molten metal with inert gas while it reaches the object to be sprayed. After forming a base sprayed layer of a metal electrochemically more base than the steel to a thickness of 0.2 mm to 4 mm,
Furthermore, on top of that, a clean laminated sprayed layer of a metal that is electrochemically more base than the base metal sprayed layer is applied using the same spraying method to a thickness of 0.1 to 7.8mm, and the total thickness of both sprayed layers is 8mm or less. After forming, the laminated thermal spray coated steel is subjected to oxidation prevention measures, heated at a temperature of 850°C to below the melting point of the sprayed metal, and hot worked to form a laminated metal coating layer with a thickness of 20 pm or more on the steel surface. A method for manufacturing highly corrosion-resistant metal-coated steel with excellent weldability, characterized by forming a metal-coated steel.