JPH0726189B2 - Method for producing surface-coated metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a surface-coated metal, and more specifically, coating the surface of a metal with a layer having characteristics such as corrosion resistance, oxidation resistance, and abrasion resistance. It is about how to do it.

(Prior Art) Due to industrial progress and technological development, materials have come to be used in increasingly severe environments in recent years. For example, in energy resource development, petroleum and natural gas (so-called sour oil and sour gas) containing a large amount of hydrogen sulfide and carbon dioxide in the production fluid have been developed, but materials for oil well pipes and line pipes used for the development As for low alloy steel, nickel alloys such as Hastelloy C-276 and Inconel 625 (both are trade names) have already been used because they cause corrosion and cracking. However, the major drawback of these alloys is that they are very expensive. Therefore, it has been considered to use a so-called clad steel in which these alloys are used as a composite material only on the surface of the structural material and the strength is secured by the underlying metal (for example, low alloy steel).

Various manufacturing methods have been established or proposed for the clad steel as a seamless pipe or a welded pipe when the shape thereof is a tube, and as a rolled plate when the shape is a plate. However, in addition to the drawback that the manufacturing process is complicated and the yield is poor, clad steel pipes made of nickel alloy such as Hastelloy C-276 and Inconel 625 are extremely difficult to manufacture and have not yet been put to practical use. . This is because the deformation resistance of these alloys during hot working is significantly higher than that of low alloy steel and carbon steel, which are base materials, so in normal pipe forming processes, the mating material and base material should be uniformly processed and joined. Is due to the difficulty.

On the other hand, thermal spraying has been conventionally known as a type of coating. There are various processes for thermal spraying such as plasma spraying and gas flame spraying, and they have the advantages that the final product can be coated and the coating thickness can be easily controlled. However, in all of these spraying methods, the powder is melted in the atmosphere or in an inert gas at atmospheric pressure and sprayed on the base material, so that air or an inert gas is introduced into the sprayed layer to generate pores. It has the drawback. These pores not only markedly reduce the ductility of the sprayed layer, but also serve as the starting point for corrosion and cracking. Furthermore, since the pores include through pores, that is, pores penetrating through the sprayed layer, corrosion solution and oxidation Since the volatile atmosphere reaches the base material through the through pores, the base material is damaged, and there is a serious defect that the sprayed layer completely loses its function as a protective layer.

As described above, since the through-pores exist in the sprayed layer sprayed under atmospheric pressure, when ordinary hot working is performed, the inside of the through-pores and the base metal are oxidized during heating before hot working. Therefore, there is a problem that the sprayed layer is cracked and the surface is roughened during hot working, and the through-pores are not crimped and remain as defects even by hot rolling. For this reason, conventionally, for example, a method of preventing cracks and defects caused by through pores by heating and rolling a plurality of sprayed rolling materials so that the sprayed layers are in contact with each other and heating and rolling has been performed.

For example, Japanese Patent Laid-Open No. 59-1003 discloses a method of imparting characteristics such as corrosion resistance to a surface-coated steel sheet by combining thermal spraying technology and rolling technology. However, this method has a big drawback that the shape of the product is limited to the plate. in addition,
Since a plurality of rolling materials are combined and rolled, the steps of assembling the materials and peeling after rolling are complicated.

On the other hand, Japanese Unexamined Patent Publication No. 59-120276 discloses a method of coating the inner surface of a steel pipe with a thin metal or ceramics having few pores by performing plasma spraying while reducing the pressure inside the steel pipe only. However, although this method can reduce the number of pores in the thermal spray layer as compared with thermal spraying under atmospheric pressure, the number of pores is not zero and the thermal spray layer is inferior in ductility and wear resistance.

(Problems to be solved by the invention) In view of the present situation, the present invention is a metal having improved target properties such as corrosion resistance, high temperature corrosion resistance, oxidation resistance, and wear resistance, and excellent ductility. The method for coating a metal as a base material is provided at a low cost while ensuring excellent characteristics.

(Means for Solving the Problems) The inventors of the present invention have conducted various experiments and studies in order to achieve the above-mentioned object, and as a result, have found that there are no through-pores in the thermal sprayed layer sprayed on the metal surface under reduced pressure and the atmospheric pressure. It was found that the hot workability was remarkably superior to that of the sprayed layer produced below, and that the pores in the sprayed layer could be reduced to zero by hot working. Furthermore, in such hot working, it is important to apply a compressive force at least in the thickness direction of the sprayed layer in order to eliminate pores in the sprayed layer, and such hot working reduces the thickness of the sprayed layer to 5%. It has been found that the amount of hot working required to reduce the above is necessary. In addition, they have found that it is possible to process as-sprayed material, and it is not necessary to assemble and process multiple materials.

The present invention was made based on the above findings, and the gist thereof is that the surface of a metal material has a vacuum degree of 1 Torr or more and after forming a sprayed layer of metal in a reduced pressure of 300 Torr or less, at least the sprayed layer. A method for producing a surface-coated metal is characterized in that hot working is performed to reduce the wall thickness of the sprayed layer by 5% or more while applying a compressive force in the wall thickness direction.

The present invention will be described in detail below.

(Operation) First, in the present invention, thermal spraying is carried out under reduced pressure in order to prevent the formation of through pores in the thermal sprayed layer.
In this case, the degree of vacuum is preferably 1 Torr or more and 300 Torr or less. This is because if the degree of vacuum is less than 1 Torr, the efficiency of thermal spraying is poor, and if it exceeds 300 Torr, the formation of through pores in the thermal sprayed layer cannot be prevented. The atmosphere here is an inert gas such as Ar gas, N ₂ gas, Ar + H ₂ , Ar + He.
It may be selected depending on other spraying conditions such as mixed gas, sprayed metal, base metal and required properties of sprayed layer, but in any case, it is important to set the degree of vacuum within the above range. is there.

The metal material of the present invention, that is, the metal to be sprayed can be any metal that can be hot-worked, and examples thereof include carbon steel, low alloy steel, stainless steel, nickel and nickel alloys, aluminum and aluminum alloys. , Titanium and titanium alloys. On the other hand, the sprayed metal may be selected according to the required function among corrosion resistance, high temperature corrosion resistance, oxidation resistance, wear resistance, etc., such as Hastelloy, Stellite (both are trade names), Ni-Cr alloy. , Stainless steel, titanium and titanium alloys, nickel and nickel alloys, aluminum and aluminum alloys.

Next, in the present invention, hot working is performed after forming the sprayed layer. At this time, it is important to apply a compressive force to at least the thickness direction of the sprayed layer in order to eliminate pores. Hot rolling, hot forging, hot extrusion and the like can be used. The amount of hot working was limited to reduce the wall thickness of the thermal spray layer by 5% or more because the pores in the thermal spray layer do not completely disappear when the thickness reduction of the thermal spray layer is less than 5%. In the present invention, hot working refers to working in a temperature range in which the metal material of the base material and the metal of the sprayed layer are normally processed for the purpose of forming, etc. Appropriate temperatures must be selected for both layers.

Further, in the present invention, the upper limit of the hot working amount is not particularly set,
The reason is that, for the purpose of the present invention, the hot working amount may be selected so long as the thickness of the sprayed layer is reduced by 5% or more, and can be freely selected as long as it is within the limit of the hot working ability of the sprayed layer or the material metal. Because you can. Furthermore, since the same effect can be obtained whether hot working is performed generally or in multiple stages, either one can be selected as required.

In the present invention, when the shape of the metal material is a plate or a pipe, the metal sprayed layer may be one surface, for example, the upper surface of the plate, the inner surface of the pipe, or the outer surface of the pipe. It is also possible to have both inside and outside. Depending on the situation in which the product is used, one side or both sides may be selected appropriately.

In addition, after hot working, for example, quenching and tempering for the purpose of refining the strength and toughness of the base material, heat treatment such as normalizing, solution treatment and baking for the purpose of further improving the corrosion resistance of the sprayed layer. If necessary, further processing such as heat treatment such as annealing and cold working performed for the purpose of adjusting the shape of the product can be added. Any of them can be selected according to the required strength, toughness, corrosion resistance and the like.

INDUSTRIAL APPLICABILITY The present invention can be applied to manufacture products that require resistance to corrosive substances, products that require resistance to high temperature oxidation, and products that require wear resistance, such as pipes, containers, and plates. It can be applied to various shapes such as a rod and a rod. Alternatively, it can be used as a raw material for manufacturing a product by further performing molding, welding and the like.

Examples of the present invention will be described below.

(Example) A material to be subjected to hot working was manufactured under the materials and manufacturing conditions shown in Table 1. Inventive Examples Nos. 1 to 4 are examples in which a sprayed layer is formed on the upper surface of the slab, Inventive Examples Nos. 5 to 6 are examples in which a thermal sprayed layer is formed on both sides of the slab, and Inventive Example No. 7 is an external surface of the hollow billet. It is an example of forming a layer. In all cases, the thermal spraying was performed by the plasma spraying method under reduced pressure. The respective shapes are shown in FIGS. 1, 2, and 3, respectively. FIG. 1 is an example in which a sprayed layer 2 is formed on the upper surface of a slab 1. FIG. 2 shows an example in which the sprayed layer 2 is formed on the upper surface and the lower surface of the slab 1. FIG. 3 shows an example in which the sprayed layer 2 is formed on the outer surface of the hollow billet 3.

On the other hand, Nos. 8 to 10 of the comparative examples are examples of forming a sprayed layer on the upper surface of the slab by the plasma spraying method under reduced pressure.
Nos. 11 to 12 are examples in which a sprayed layer is formed on the upper surface of the slab under atmospheric pressure.

Next, these materials were hot worked under the conditions shown in Table 2 to produce a surface-coated metal, and various tests were conducted. The test results are also shown in Table 2. Adhesion strength in Table 2 is JIS H 86
In accordance with JIS Z 2248, the bending test was carried out according to JIS Z 2248 using a JIS Z 2204 No. 1 test piece.
It was a mark. Corrosion test is 0.2 ^t × 15 ^w × 30 ^l (mm) from sprayed layer
The specimens with the corrosion loss of 0.05 mm / y or less after immersion in a 20% NaCl aqueous solution saturated with 100 atm of H ₂ S and 100 atm of CO ₂ at 250 ° C for 1 month were marked with a circle. , Those having a corrosion weight loss of more than 0.05 mm / y were marked with x.

In Comparative Examples Nos. 8 and 10 in Table 2, the thermal sprayed layer was formed under reduced pressure, but no hot working was performed. Therefore, Comparative Example No. 9 was hot worked but the hot working amount was 5%. However, the pores in the sprayed layer did not completely disappear and the corrosion resistance was poor. Further, in Comparative Examples Nos. 11 to 12, since the thermal sprayed layer was formed under atmospheric pressure, cracking occurred on the surface of the thermal sprayed layer by ordinary rolling, and the surface-coated metal could not be manufactured.

On the other hand, the samples of Examples Nos. 1 to 7 produced according to the present invention are excellent in all properties of adhesion strength, bending test and corrosion test. From the results of microscopic observation of the cross section, it was confirmed that the sprayed layer had no pores at all and a uniform and good bonding interface was obtained. Further, it was confirmed that the invention sample No. 6 was also excellent in wear resistance.

(Effects of the Invention) As described above, according to the present invention, it is possible to produce a surface-coated metal having excellent properties, which is extremely large in contributing to the development of industry.

[Brief description of drawings]

1, FIG. 2 and FIG. 3 are all sectional views showing the procedure for laminating the processed material according to the method of the present invention. 1 ... slab, 2 ... sprayed layer, 3 ... hollow billet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michitoshi Ito 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Nippon Steel Co., Ltd. 1st Technical Research Institute (72) Kazunori Hayashi Nakahara-ku, Kawasaki-shi, Kanagawa 1618 Ida, Nippon Steel Research Laboratories, Nippon Steel Corporation (56) References JP-A-51-41644 (JP, A) JP-A-59-41461 (JP, A)

Claims (4)

[Claims] 1. The degree of vacuum on the surface of the metal material is 1 Torr or more 300
After forming a thermal sprayed layer of metal under a reduced pressure of Torr or less, hot working is performed to reduce the wall thickness of the thermal sprayed layer by 5% or more while applying a compressive force in at least the thickness direction of the thermal sprayed layer. A method for producing a surface-coated metal. 2. The method according to claim 1, wherein the means for hot working is hot rolling. 3. The method according to claim 1, wherein the means for hot working is hot extrusion. 4. The method according to claim 1, 2, or 3, wherein the formation of the metal sprayed layer covers both sides of a metal material.