JPH08158037A - Nitrided product with excellent rolling fatigue resistance and its manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] A nitriding product of an iron-based metal product that is excellent in rolling fatigue resistance as well as wear resistance and fatigue resistance by controlling the thickness of the porous layer after nitriding treatment. And a method of manufacturing the same. [Configuration] A porous layer having a thickness of 10 μm or less, which is derived from the nitriding treatment, is provided on the outermost surface layer of the iron-based metal product capable of undergoing the nitriding treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based metal product used as a machine structural part having excellent rolling fatigue resistance, wear resistance and fatigue resistance in civil engineering machines, industrial machines and the like, and a method for producing the same. .

[0002]

2. Description of the Related Art Conventionally, surface hardening treatments such as carburizing and nitriding treatments have been performed on mechanical structural parts which are required to have wear resistance and fatigue resistance. In the carburizing process, since C penetrates and diffuses in the high temperature γ region, a deep hardening depth can be obtained, but the heat treatment distortion is large during the quenching and tempering subsequent to carburizing, and strict dimensional accuracy is required. This is a problem for mechanical structural parts such as gears.

On the other hand, the nitriding treatment includes a method of invading and diffusing only N and a method of nitriding by simultaneously invading and diffusing N and C (soft nitriding) in a temperature range below the A ₁ transformation point. In both cases, there is no problem of heat treatment strain due to phase transformation during quenching, and the soft nitriding treatment can increase the depth of the hardened layer in a short time. In the present specification, the nitriding treatment and the soft nitriding treatment are collectively referred to as a nitriding treatment for convenience hereinafter.

As shown schematically in FIG. 1, the surface of the nitridable iron-based metal product has a compound layer 10 and a diffusion layer 12 formed on the treated surface by the nitriding treatment, and the surface of the compound layer is the maximum. On the surface, there is a hollow porous layer 14 formed by a hydroxide which is inevitably present in the nitriding atmosphere. The porous layer 14 causes deterioration of surface hardness, wear resistance, and fatigue resistance, and peeling of the compound layer originating from the porous layer, pitching, spalling, and the like occur in the sliding portion, and the performance of the nitrided component is improved. Lower.

In order to solve such a problem, for example, in Japanese Patent Laid-Open No. 63-93821, the porous layer of a soft nitriding product was removed by shot peening to improve fatigue resistance. However, the rolling fatigue resistance is not sufficient, and it has been desired to develop a nitriding product having excellent rolling fatigue resistance.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to control the thickness of the porous layer after nitriding treatment to provide excellent rolling fatigue resistance and wear resistance. An object of the present invention is to provide a nitriding product of an iron-based metal product having excellent fatigue resistance and a manufacturing method thereof. Specifically, it is to provide a nitriding product of an iron-based metal product that requires surface hardness, rolling fatigue strength, wear amount, and fatigue limit, and a method for producing the product.

[0007]

[Means for Solving the Problems] The present inventors have made various studies in order to achieve such an object, and have obtained the following findings from the results of these studies.

Measures for Improving Rolling Fatigue Resistance / Abrasion Resistance The presence of a porous layer is generally a factor that hinders the above characteristics, but by adjusting the thickness of the porous layer to an optimum thickness of 10 μm or less, Unexpectedly, it was effective in improving the above characteristics.

Improvement of fatigue resistance and further improvement measures Although the fatigue resistance is affected by the notch shape of the porous layer, the notch shape of the surface porous layer can be controlled by controlling the porous layer by shot peening. Be calm and
Rather, the fatigue resistance is improved by applying compressive residual stress to the surface. This also has the effect of further improving rolling fatigue resistance and wear resistance.

The gist of the present invention completed based on these findings is that the nitriding-treatable iron-based metal article is provided with a porous layer having a thickness of 10 μm or less derived from the nitriding treatment on the outermost layer. It is a nitriding product with excellent rolling fatigue resistance.

From another aspect, according to the present invention, an iron-based metal product that can be subjected to nitriding treatment is subjected to nitriding treatment to form a porous layer on the outermost layer, and then shot peening is performed on the porous layer. The thickness of the porous layer to 10 μm
The method for producing a nitriding product having excellent rolling contact fatigue resistance is characterized by the following.

[0012]

Next, the reason for the above-mentioned definition in the present invention will be described in detail together with its operation.

Porous layer thickness: 10 μm or less Control of the porous layer thickness is an essential factor for improving rolling fatigue resistance, wear resistance, and fatigue resistance. In particular, if the thickness exceeds 10 μm, the tip of the porous layer becomes sharp and has many cavities and becomes fragile, resulting in reduced wear resistance.If a component having such a porous layer is used in the rocking part, the porous layer The stress load on the tip of the long microcracks existing inside increases, and the propagation of cracks progresses rapidly inside,
Rolling fatigue resistance decreases. Therefore, in the present invention, the thickness of the porous layer is set to 10 μm or less.

Further, considering the deterioration of the lubrication state due to the increase of frictional resistance between the contact bodies, particularly when abrasion resistance and rolling fatigue resistance are required, 1 to 5 μm is desirable. By the way, in the conventional nitriding treatment, a porous layer having a thickness of more than 10 μm is formed, which is used as it is or completely removed.

[0015] The shot peening shot peening can be mildly improved simultaneously notch shape when partially removing the porous layer, it is possible to improve the fatigue resistance. Also, by applying a compressive residual stress to the compound layer and the diffusion layer by the peening effect, the shot peening process is performed because the characteristics are improved with respect to fatigue resistance, rolling fatigue resistance, and wear resistance. Stipulated to do.

Iron-based metal product The present invention is intended for general nitridable metal-based parts. However, since it is more practically an iron-based metal, it is a nitridable iron-based metal product. Specifically, carbon steel and alloy steel are exemplified.

More specifically, those having the following composition in terms of weight% are preferable. C: 0.05 to 0.50%, Si: 0 to 1.50
%, Mn: 0.50 to 2.00%, Cr: 0 to 2.00%, Mo: 0 to 1.00
%, V: 0 to 0.50%.

Nitriding Treatment As described above, the nitriding treatment in this specification includes not only so-called nitriding treatment but also soft nitriding treatment. Specifically, gas nitriding, tuftride treatment, gas soft nitriding,
Ion nitriding etc. are illustrated. Next, the function and effect of the present invention will be described in more detail with reference to Examples.

[0019]

【Example】

(Example 1) Steels each having the chemical composition shown in Table 1 were melted into 160 mm square pieces, each of which was heated to 1100 ° C and hot-forged at a finishing temperature of 950 ° C to give a diameter of 30 mm. After forming a round bar, it was left to cool.

After cooling, the rolling fatigue test piece, the wear test piece and the JIS No. 2 rotating bending fatigue test piece were sampled and subjected to nitriding treatment under the respective nitriding conditions shown in Table 2. The thickness of the porous layer was adjusted by rough cutting with # 1500 emery paper and finishing with buffing.

Using the test piece thus prepared,
A rolling fatigue test, a wear test and a fatigue test were performed. The rolling fatigue test was performed at a rotation speed of 1000 rpm, a slip rate of 40%, and an oil temperature of 80.
The rolling contact fatigue strength was defined as the contact pressure strength when 10 ⁷ cycles were achieved under the condition of ° C. In the wear test, a pin with a diameter of 10 mm has a surface pressure of 0.
A load of 10 kgf / mm ² was applied, and the amount of wear during running at 1000 mDry was measured. The measurement results after the test are shown in Tables 3 and 4.

The target characteristics are as follows. Surface hardness: Hv 750 Core hardness: Hv 200-300 Rolling fatigue strength: 2000 N / mm ² or more Wear amount: 50 mg or less Fatigue limit: 500 N / mm ² or more.

As is clear from Tables 3 and 4, the nitriding products according to the present invention have remarkably improved rolling fatigue strength and wear characteristics, and in particular, the outermost porous layer has a thickness of 1-5.
When it becomes μm, it can be further improved. On the other hand, when the thickness of the porous layer is out of the standard, not only the upper and lower limits, but rolling fatigue strength and wear characteristics are significantly deteriorated.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

(Example 2) 160 of the test steel No. 1 shown in Table 1
A mm square steel slab is heated to 1100 ° C., and after hot forging at a finishing temperature of 950 ° C., test piece processing and soft nitriding are performed in the same manner as in Example 1, and the thickness of the porous layer is set under the shot peening conditions of Table 5. After adjusting the height, the characteristics were investigated. Table 6 shows the measurement results.

When the nitriding product according to the present invention is manufactured by shot peening, rolling fatigue strength and wear characteristics can be further improved, and fatigue strength is also improved.
However, also in this example, when the thickness of the porous layer is out of the specified range of the present invention, deterioration of the characteristics cannot be avoided regardless of either the upper or lower limit.

[0030]

[Table 5]

[0031]

[Table 6]

[0032]

EFFECTS OF THE INVENTION The steel of the present invention has excellent rolling fatigue resistance, which is not available in conventional methods, by controlling the porous layer generated after soft nitriding when it is processed as a machine structural part.
It has wear resistance or fatigue resistance and improves the performance of gears and the like.

[Brief description of drawings]

FIG. 1 is a schematic view of an outermost surface of a metal product according to the present invention on which a porous layer is formed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Nishida 1 Kunomi-cho, Kokurakita-ku, Kitakyushu City Sumitomo Metal Industries, Ltd. Kokura Works

Claims (2)

[Claims] 1. An outermost layer of an iron-based metal product capable of being nitrided,
A nitriding product with excellent rolling fatigue resistance, which is provided with a porous layer having a thickness of 10 μm or less derived from the nitriding process. 2. An iron-based metal product that can be subjected to nitriding treatment is subjected to nitriding treatment to form a porous layer on the outermost surface layer, and then shot peening is performed on the porous layer to reduce the thickness of the porous layer to 10 μm. A method for producing a nitriding product excellent in rolling contact fatigue resistance, characterized by the following.