JPH0649622A - Surface hardening method for metal - Google Patents

Abstract

PURPOSE:To form a hardened layer having high hardness on a metallic surface by subjecting the surface of the metal to nickel plating, then successively executing a chromium diffusion penetration treatment and a plasma carburization treatment. CONSTITUTION:The surface of the metal is subjected to nickel plating by an electroless nickel plating treatment, etc., and thereafter, a chromium diffusion penetrated layer is formed thereon by a chromizing treatment. The surface is further subjected to the plasma carburization treatment. As a result, multiple carbites consisting of Fe, Cr and C are formed over the entire area of the chromium diffused layer and Ni concentrates at the boundary of the chromium diffussed layer and a base metal to prohibit carburization. Then, the structure where residual austenite does not exist under the surface hardened layer is obtd. even if the base metal is a martensite stainless steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal surface hardening method, and is particularly suitable for application to the manufacture of sliding parts and mechanical structures which require wear resistance.

[0002]

2. Description of the Related Art Conventionally, for example, a method of increasing the surface hardness to about 800 to 1500 Hv by performing a plasma carburizing treatment after a Cr (chromium) diffusion and infiltration treatment is performed to improve the wear resistance of a metal and slide it. It is applied to boiler tubes that are subject to wear due to materials and coal ash.

[0003]

However, the method of increasing the surface hardness by performing the plasma carburization treatment after the Cr diffusion treatment has the following problems when the base material is martensitic stainless steel such as SUS420. . 80
At a position of about 100 μm on the base material side of the interface between the surface hardened layer of 0 to 1500 Hv and the base material, C (carbon) is enriched under the influence of the plasma carburizing treatment. The structure at this position is martensite if C is not enriched, but since C is enriched, residual austenite is present. And when such retained austenite is present,
When it is used as a material for a sliding part and its sliding surface receives a force, the retained austenite immediately below the surface hardened layer is transformed by processing and cracks occur.

In view of such circumstances, it is an object of the present invention to provide a metal surface hardening method capable of obtaining a high hardness surface hardened layer without the above-mentioned problems.

[0005]

A method for hardening a surface of a metal according to the present invention which achieves the above object is characterized in that after the surface of the metal is plated with nickel, chromium diffusion infiltration treatment and plasma carburization treatment are carried out. To do.

[0006]

When the surface of the metal is plated with Ni (nickel), the Cr diffusion and penetration treatment and the plasma carburization treatment are performed,
Composite carbides composed of Fe, Cr and C are formed in the entire Cr diffusion layer. At this time, since Ni is concentrated at the interface between the Cr diffusion layer and the base material, carburization is prevented at this interface. Therefore, even if the base material is martensitic stainless steel, a structure having no retained austenite under the surface hardened layer can be obtained.

The Ni plating in the present invention may be performed, for example, by electroless Ni plating. In addition, the Cr diffusion process is usually called a chromizing process,
Generally, a steel plate semi-closed container is used, and metal Cr powder 65 to
80 wt%, Al ₂ O ₃ powder 19 to 34 wt%, NH ₄ Cl
The material to be treated is embedded in a mixed powder of 0.5 to 1.0 wt% and heated at 950 to 1150 ° C. for 5 to 15 hours while flowing H ₂ gas. The surface of the object to be treated by the chromizing treatment has a layer thickness of 15 to 250 μm and a surface Cr concentration of 70 to 80 wt% C.
Although the r diffusion and permeation layer is obtained, the layer thickness and the surface Cr concentration can be arbitrarily changed according to the material of the material to be treated, the purpose of use, the degree of wear, and the combination of treatment conditions. On the other hand, the plasma carburizing treatment is carried out by using, for example, hydrogen gas or argon gas as a process gas of Co, N ₂ ,
Using a mixed gas of CH ₄ and C ₃ H ₈ mixed gas, glow discharge was generated in a low pressure atmosphere of several Torr to obtain 900 to 110
It is carried out by treating at a high temperature of 0 ° C. for 0.5 to 3 hours. This treatment is performed by a carburizing mechanism in which cleaning of the surface of the object to be treated, C ion capture, attachment, implantation and diffusion are linked.

[0008]

EXAMPLES The present invention will be described below based on examples.

SUS420 with a thickness of 50 mm × 80 mm and a thickness of 3 mm
The J2 test piece was immersed in an electroless nickel-boron alloy plating solution and treated at 65 ° C. for 2 hours to perform Ni plating. As a result, the plating film thickness formed on the test piece was 10 μm.

Next, using a steel plate semi-closed container, a test piece having a Ni plating film was placed in a metal Cr powder 7
5 wt%, Al ₂ O ₃ 24.5 wt% and NH ₄ Cl powder 0.5 wt% together with a mixed powder, filled and buried, and subjected to Cr diffusion and infiltration treatment at 1050 ° C. for 10 hours while flowing hydrogen gas to form a layer thickness 130 μm, surface Cr concentration 55.5
A processed material having a wt% and a hardness of 200 to 250 Hv coating layer was obtained. Note that Ni was present at the interface between this coating layer and the base material.

FIG. 1 shows the result of elemental analysis of the cross section of the material to be treated by an X-ray microanalyzer, and FIG. 2 shows the hardness distribution of the cross section.
Shown in. From these, it can be seen that the above-mentioned coating layer, that is, the Cr diffusion layer is formed on the surface, but the Ni plating layer is present at the interface between this coating layer and the base material.

After the Cr diffusion and permeation treatment, the test piece was subjected to a plasma carburizing treatment at 1050 ° C. for 2 hours, and a treated material having a hardened layer uniformly carburized with a hardness of 800 to 1500 Hv was obtained. . Further, Ni was present between the hardened layer and the base material, which prevented carburization of the base material.

FIG. 3 shows the results of elemental analysis by an X-ray microanalyzer of the cross section of the material to be treated, and FIG. 4 shows the hardness distribution of the cross section. From these figures, the material to be treated in this example is
It can be seen that the Ni plating layer prevents carburization of the base material, there is no possibility of residual austenite existing in the base material, and the surface hardened layer has a high hardness.

[0014]

As described above, according to the surface hardening method of the present invention, even if the base material is martensitic stainless steel, there is no possibility that residual austenite exists immediately below the hardened layer, A hardened layer of hardness can be formed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a result of elemental analysis by an X-ray microanalyzer of a cross section after Ni plating and Cr diffusion / permeation treatment in one example.

FIG. 2 is a sectional hardness distribution diagram after the same treatment as in FIG.

FIG. 3 is an explanatory diagram showing an elemental analysis result by an X-ray microanalyzer of a cross section after the surface hardening treatment in one example.

FIG. 4 is a sectional hardness distribution diagram after the same treatment as in FIG.

Claims (1)

[Claims] 1. A method for hardening a surface of a metal, which comprises subjecting the surface of the metal to nickel plating, and then performing a chromium diffusion infiltration treatment and a plasma carburizing treatment.