Build-up layer

Abstract

To provide a build-up layer with excellent corrosion resistance and wear resistance.SOLUTION: A build-up layer material is composed of iron-based alloy. The iron-based alloy contains B: 4.0 mass% to 8.0 mass%, C: 0.10 mass% to 1.0 mass%, and Cr: 5.0 mass% to 10.0 mass%. The metal microstructure of the build-up layer contains boride. The area ratio of the boride is 20% to 50%. A method for producing the build-up layer includes (1) preparing powder composed of the iron-based alloy, (2) obtaining molten metal by heating the powder, and (3) solidifying the molten metal on a base.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification discloses a build-up layer. This build-up layer can be obtained by manufacturing methods such as laser cladding and plasma powder build-up welding.

Background Art

[0002] Steel with a hard chromium plating on its surface is used for rubbing members such as the shaft of a hydraulic cylinder. The hard chromium plating contributes to the corrosion resistance of the steel. The hard chromium plating is also excellent in wear resistance. In the formation process of the hard chromium plating, an electrolytic solution containing hexavalent chromium is used. Hexavalent chromium is a harmful substance.

[0003] Japanese Patent Application Publication No. 2020-530876 discloses a build-up layer obtained by laser cladding. This build-up layer is excellent in corrosion resistance. Therefore, this build-up layer can replace the hard chromium plating.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The wear resistance of the build-up layer disclosed in Japanese Patent Application Publication No. 2020-530876 is not sufficient. This build-up layer is not suitable for rubbing members such as hydraulic cylinders.

[0006] What the applicant intends is to provide a build-up layer excellent in corrosion resistance and wear resistance.

Means for Solving the Problems

[0007] The material of the build-up layer disclosed in this specification is an iron-based alloy. This iron-based alloy B: 4.0 mass% or more and 8.0 mass% or less, C: 0.10 mass% or more and 1.0 mass% or less, and Cr: 5.0 mass% or more and 10.0 mass% or less and contains. The metal structure of this build-up layer contains borides. The area ratio of these borides is 20% or more and 50% or less.

[0008] This specification also discloses a method for manufacturing a build-up layer. This manufacturing method is (1) A step of preparing a powder composed of a large number of particles, the material of these particles being an iron-based alloy, and this iron-based alloy being B: 4.0 mass% or more and 8.0 mass% or less, C: 0.10 mass% or more and 1.0 mass% or less, and Cr: 5.0 mass% or more and 10.0 mass% or less and containing; (2) A step of heating the above powder to obtain a molten metal, and (3) A step of solidifying the above molten metal on a base and containing.

Effects of the Invention

[0009] A build-up layer excellent in corrosion resistance and wear resistance can be obtained from this powder.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments will be described in detail with appropriate reference to the drawings.

[0012] [Metal Product] Figure 1 shows a metal product 2. This metal product 2 has a base 4 and a build-up layer 6. The build-up layer 6 covers the surface of the base 4. The build-up layer 6 can be obtained by a build-up method. A typical build-up method is laser cladding. Another build-up method includes plasma powder build-up welding. In these build-up methods, powder is used. The powder is an aggregation of a large number of particles. This powder is overheated to obtain molten metal. By solidifying this molten metal on the base 4, the build-up layer 6 is formed. A typical metal product 2 is a hydraulic cylinder.

[0013] [Iron-based alloy] The material of this build-up layer 6 is an iron-based alloy. This iron-based alloy B: 4.0 mass% or more and 8.0 mass% or less, C: 0.10 mass% or more and 1.0 mass% or less, and Cr: 5.0 mass% or more and 10.0 mass% or less is included. Preferably, the balance of this iron-based alloy is Fe and inevitable impurities. The composition of the powder is also the same as the composition of the iron-based alloy of this build-up layer 6. Hereinafter, the roles of each element will be described in detail.

[0014] [Iron (Fe)] The base element of this alloy is Fe. Fe contributes to the strength and wear resistance of the build-up layer 6. From these viewpoints, the content of Fe is preferably 60 mass% or more, more preferably 70 mass% or more, and particularly preferably 80 mass% or more. From the viewpoint that the alloy can sufficiently contain other elements, the content of Fe is preferably 95 mass% or less, more preferably 92 mass% or less, and particularly preferably 90 mass% or less.

[0015] [Boron (B)] In the build-up layer 6, B is dissolved in Fe. B further exists as a boride. A typical boride is Fe2B. Fe2B is hard. In this iron-based alloy, a eutectic structure of a solid solution phase in which Fe is the matrix and the Fe2B phase is achieved. The build-up layer 6 having this metal structure has high hardness. This build-up layer 6 is excellent in wear resistance. From the viewpoint of obtaining sufficient Fe2B, the content of B is preferably 4.0 mass% or more, more preferably 4.5 mass% or more, and particularly preferably 5.0 mass% or more. In an alloy with excessive B, due to the heat history during build-up, B may precipitate from the solid solution. This precipitation inhibits the hardness of the build-up layer 6. From the viewpoint of hardness, the content of B is preferably 8.0 mass% or less.

[0016] [Carbon (C)] In the build-up layer 6, C is dissolved in Fe. C further exists as a carbide in the build-up layer 6. C can contribute to the hardness, strength and wear resistance of the build-up layer 6.

[0017] In the production of powder, pores can occur inside the particles. In the build-up layer 6 obtained from the powder in which pores exist, the gas of these pores remains. It is difficult to obtain a dense build-up layer 6 from this powder. According to the findings obtained by the present inventors, C can unexpectedly suppress these pores. Furthermore, according to the findings obtained by the present inventors, C can unexpectedly contribute to the material yield during powder production.

[0018] From the viewpoints of the hardness, strength, wear resistance and density of the build-up layer 6, and the yield of the powder, the content of C is preferably 0.10 mass% or more, more preferably 0.15 mass% or more, and particularly preferably 0.20 mass% or more. Excessive C inhibits the toughness of the build-up layer 6. From the viewpoint of toughness, the content of C is preferably 1.0 mass% or less, more preferably 0.9 mass% or less, and particularly preferably 0.8 mass% or less.

[0019] [Chromium (Cr)] In the build-up layer 6, Cr is dissolved in Fe. Cr contributes to the corrosion resistance of the build-up layer 6. From this perspective, the Cr content is preferably 5.0% by mass or more, more preferably 5.5% by mass or more, and particularly preferably 6.0% by mass or more. From the perspective of low cost of the build-up layer 6, the Cr content is preferably 10.0% by mass or less.

[0020] [Boride] As described above, the build-up layer 6 contains boride. The area ratio of the boride is preferably 20% or more and 50% or less. The build-up layer 6 with this area ratio of 20% or more is excellent in wear resistance. From this perspective, this area ratio is more preferably 22% or more, and particularly preferably 23% or more. The build-up layer 6 with this area ratio of 50% or less is less likely to crack. From this perspective, this area ratio is more preferably 46% or less, and particularly preferably 43% or less. By subjecting a powder containing an appropriate amount of B to the build-up method, a build-up layer 6 with the area ratio of the boride within the above range can be obtained.

[0021] The area ratio is measured in a cross-section along the thickness direction of the build-up layer 6. This cross-section is observed by SEM, and a backscattered electron image is taken. The area ratio of the boride is calculated by image analysis of this image. The identification of the boride can be made by EDS analysis.

[0022] [Manufacturing method of powder] As described above, the build-up layer 6 can be obtained by subjecting a powder to the build-up method. This powder can be manufactured by an atomization method, a pulverization method, etc. Examples of the atomization method include a gas atomization method, a water atomization method, and a disk atomization method. From the perspective that impurities are less likely to be mixed into the powder, the gas atomization method and the disk atomization method are preferred. From the perspective that impurities are less likely to be mixed into the powder, atomization in an inert gas atmosphere is preferred. From the perspective of mass productivity, gas atomization is preferred.

Examples

[0023] Hereinafter, the effects of the build-up layer according to the examples will be clarified, but the scope disclosed in this specification should not be construed in a limited manner based on the description of this example.

[0024] [Example 1] Raw materials with the composition shown in Table 1 below were prepared. These raw materials were put into a crucible with refractory properties and melted by the induction method in an argon gas atmosphere to obtain a molten metal. The molten metal was made to flow out from a nozzle at the bottom of the crucible and was subjected to gas atomization with nitrogen gas to obtain raw material powder. This raw material powder was classified by a sieve to obtain build-up welding powder with a particle size of 250 μm or less. This powder was subjected to laser cladding to form a build-up layer on a steel plate to obtain a laminate. The conditions for laser cladding were as follows. Laser output: 2000 W Powder supply rate: 0.2 g / s Feed rate of the apparatus: 30 cm / min Size of the steel plate: 30 mm × 20 mm

[0025] [Examples 2 - 15 and Comparative Examples 1 - 6] Build-up layers of Examples 2 - 15 and Comparative Examples 1 - 6 were obtained in the same manner as in Example 1, except that raw materials with the composition shown in Table 1 below were prepared.

[0026] [Wear resistance] Test pieces were cut out from the laminate and subjected to the Otsuka wear test to measure the specific wear rate. The test conditions were as follows. Testing machine: "OAT-U" of Tokyo Testing Machine Co., Ltd. Ring: SCM420 (hardness: 88 HRB) Friction speed: 3.86 m / S Wear distance: 200 m Final load: 61.8 N These results are shown in Table 1 below.

[0027] [Corrosion resistance test] Salt water was sprayed onto the build-up layer in accordance with the provisions of "JIS Z 2371". After one month, this build-up layer was visually observed and classified according to the following criteria. A: No rusting at all. B: Rusting in some parts. C: Rusting all over. This result is shown in Table 1 below.

[0028]

Table 1

[0029] The balance of the composition of each alloy described in Table 1 is Fe and unavoidable impurities.

[0030] As shown in Table 1, the build-up layer of each example is excellent in various properties. From this evaluation result, the superiority of this build-up layer is clear.

Industrial Applicability

[0031] The build-up layer described above is suitable for various metal products.

Explanation of Signs

[0032] 2 ··· Metal product 4 ··· Base 6 ··· Build-up layer

Claims

1. A build-up layer whose material is an iron-based alloy, and this iron-based alloy contains B: 4.0% by mass or more and 8.0% by mass or less, C: 0.10% by mass or more and 1.0% by mass or less, and Cr: 5.0% by mass or more and 10.0% by mass or less, and its metal structure contains borides, and the area ratio of these borides is 20% or more and 50% or less. A build-up layer.

2. (1) A step of preparing a powder composed of a large number of particles, the material of these particles being an iron-based alloy, and this iron-based alloy contains B: 4.0% by mass or more and 8.0% by mass or less, C: 0.10% by mass or more and 1.0% by mass or less, and Cr: 5.0% by mass or more and 10.0% by mass or less, (2) A step of heating the above powder to obtain a molten metal, and (3) A step of solidifying the above molten metal on a base A method for manufacturing a build-up layer. ​

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