JP2003073800A - Surface treatment method for steel material, and steel material having impact resistance, abrasion resistance, and corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method for a steel material, which causes little anxiety of film peeling, can form an adequate depth of a hardened layer in a range of several tens to several hundreds μm on the surface, and can form the hardened layer superior in impact resistance, abrasion resistance, and corrosion resistance, and provide a steel material having impact resistance, abrasion resistance, and corrosion resistance, manufactured with the method. SOLUTION: This method includes plasma nitriding the surface of the steel material, and then implanting nitrogen ions in the surface, to make the nitrogen concentration of the surface to be 30 atom% or higher, for diffusion treatment causing little film- peeling. The method thus provides the surface treatment layer, which has the depth of the hardened layer of several tens to several hundreds μm, and has high impact resistance, high abrasion resistance, and high corrosion resistance. The method can prolong the life of an automobile engine or the like, when applied to, for example, the automobile engine member which receives strong shock, and requires abrasion resistance and corrosion resistance, because the surface treatment layer does not peel off, even if receives shocks, is little abraded, and has little weight loss by corrosion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for steel materials and impact-, wear-, and corrosion-resistant steel materials. In particular, such as automobile engine parts, it is also required to have shock- and wear- and corrosion-resistant properties. The present invention relates to a surface treatment method for a steel material.

[0002]

2. Description of the Related Art In order to improve wear resistance, it is effective to increase hardness, and diffusion treatment such as carburizing or nitriding, PVD or CVD for forming a highly hard film, ion implantation or ion irradiation is used. Japanese Unexamined Patent Publication No. 9-53170 discloses a method of irradiating nitrogen ions to modify the surface to increase hardness and reduce the coefficient of friction.
A technique for improving wear resistance is shown.

In order to improve the corrosion resistance, PVD or CVD for forming a film having an excellent environmental barrier property, and ion implantation or ion irradiation for modifying the surface without changing the essence of the material are applied. Japanese Unexamined Patent Publication No. 6-41716 discloses a technique in which the compressive residual stress generated by heat treatment such as quenching and tempering is relaxed by nitrogen ion implantation, which is excellent in wear resistance and corrosion resistance and improves brittleness.

In particular, when an impact load is applied, the Hertzian stress acts, and a high stress is applied from the surface to the inside.
It requires a hardened layer of a few hundred μm.

Japanese Unexamined Patent Publication No. 2-15160 discloses formation of a titanium nitride coating layer and ion implantation. The purpose is to harden the titanium nitride substrate to make it difficult to peel.

[0006] However, in this method for producing a cutting tool, there is no suggestion or suggestion regarding corrosion resistance from the use environment in which it is expected that the produced cutting tool will be surrounded by a large amount of oil to cut a work, and particularly nitrogen is used. Because there is no regulation of quantity,
The critical significance of the effects of the invention is unclear.

Japanese Unexamined Patent Publication (Kokai) No. 7-1972232 is directed to an austenitic steel material, and even if gas nitriding and ion implantation are combined in some cases, the intended purpose may not be achieved. A method for forming a nitrided hardened layer of a microshaft is proposed.

This method cannot be applied as it is to the technical field to which the present invention, which mainly targets martensitic steel materials, belongs. Further, gas nitriding alone requires a long time for processing, and the manufacturing efficiency cannot be improved.

[0009]

In steel materials subjected to impact loads such as automobile engine parts, wear resistance,
In addition to corrosion resistance, there is a demand for a surface treatment method capable of forming a hardened layer having a thickness of several tens to several hundreds of μm.

When forming a highly hard film, PVD or CVD
Forms a film on the surface that does not bind to the components contained in the base material of the steel material, and thus may be essentially peeled off.

Ion implantation or ion irradiation modifies the steel material itself, but since the depth of modification is as shallow as a few μm, the hardening depth required for parts subjected to impact load cannot be obtained.

In the nitriding treatment which is a diffusion treatment, particularly the plasma nitriding treatment, nitrogen is diffused to combine with a component contained in the base material to form a nitride. Since this nitride has a higher hardness than the base material, the nitrogen diffusion region has a higher hardness and wear resistance is increased. For example, when plasma nitriding stainless steel, C which is a nitride of the elements Cr and Fe in the stainless steel is used.
rN, Cr ₂ N, Fe ₄ N, Fe ₃ N, Fe ₂ N are produced.

On the other hand, the corrosion resistance of stainless steel is exhibited by the extremely thin chromium oxide formed on the surface.

However, in plasma nitriding, chromium in the base material is generated as chromium nitride by the nitriding treatment, so the amount of chromium in the base material that contributes to corrosion resistance is reduced. As a result, the corrosion resistance of plasma-nitrided stainless steel decreases.

Further, the alloy tool steel (SKD material), the chromium-molybdenum steel (SCM material), and the high speed tool steel (SKH material) essentially have a small amount of Cr and therefore have poor corrosion resistance.

An object of the present invention is a steel material capable of forming a hardened layer having a sufficient hardening depth of several tens to several hundreds of μm without exfoliation, and having excellent impact resistance, abrasion resistance and corrosion resistance. The object of the present invention is to provide a surface treatment method, and an impact-resistant, wear-resistant and corrosion-resistant steel material produced by this method.

[0017]

In order to achieve the above object, the present invention provides a steel material in which a steel material is plasma-nitrided and then nitrogen ions are implanted so that the nitrogen concentration on the surface of the steel material is 30 atomic% or more. We propose a surface treatment method for materials.

In the surface treatment method, the steel material is
It is either stainless steel, alloy tool steel (SKD material), chrome molybdenum steel (SCM material), or high speed tool steel (SKH material).

The present invention also proposes a shock-resistant, wear-resistant and corrosion-resistant steel material in which plasma nitriding is carried out and then nitrogen ions are implanted so that the surface nitrogen concentration is 30 atomic% or more.

Among the above-mentioned impact-resistant, wear-resistant and corrosion-resistant steel materials, the steel materials are stainless steel, alloy tool steel (SKD).
Material), chrome / molybdenum steel (SCM material), high speed tool steel
(SKH material).

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention carry out a plasma nitriding treatment as a diffusion treatment with which a sufficient hardening depth can be obtained and there is no fear of peeling, and then a predetermined amount or more of nitrogen ions are implanted, It was found that a high corrosion resistant layer can be formed on the surface.

According to this method, plasma nitriding achieves a sufficient hardening depth, impact resistance and wear resistance are obtained, and nitrogen ion implantation provides high corrosion resistance.

Next, with reference to FIG. 1 to FIG. 5, an embodiment of the surface treatment method for a steel material and impact resistance, wear resistance, and corrosion resistance steel material according to the present invention will be described. First, stainless steel S
The basic matters of this embodiment will be described by taking US440C as an example.

FIG. 1 is a diagram showing the nitrogen distribution in the depth direction of a plasma nitrided product of stainless steel SUS440C analyzed by GDS (Glow Discharge Optical Emission Analysis). The nitrogen concentration on the surface varied depending on the nitriding temperature and was 26 atom% for the 410 ° C nitrided product and 9 atom% for the 570 ° C nitrided product.

FIG. 2 is a diagram showing the nitrogen distribution in the depth direction of stainless steel SUS440C implanted with nitrogen ions after plasma nitriding at 410 ° C. The implantation of nitrogen ions increases the surface nitrogen concentration to 42 atomic%.

The corrosion resistance was measured by JIS G 0577 stainless pitting potential measuring method, pH 3.0, liquid temperature 70 ° C.
Conducted a polarization test at 100 μA / cm
^It was evaluated by the potential (Vc'100) when it reached ² .

FIG. 3 is a diagram showing the corrosion resistance in the depth direction of stainless steel SUS440C implanted with nitrogen ions after plasma nitriding at 410 ° C. The potential in FIG. 3 is Ag / Ag
The potential is based on the Cl reference electrode (Ref). It can be seen that the corrosion resistance of the surface with a high nitrogen concentration is high.

FIG. 4 is based on the results of FIGS. 2 and 3.
It is a figure which shows the relationship between the surface nitrogen concentration of stainless steel SUS440C which injected nitrogen ion after plasma nitriding at 410 degreeC, and corrosion resistance. Corrosion resistance becomes more noble than that of the hardened layer of plasma nitriding at a nitrogen concentration of 30 atomic% or more, and Vc'100 becomes 0.78 V vs Ref or more.

This value exceeds 0.52 V vs Ref of the quenched and tempered product of SUS440C.

As described above, even in stainless steel whose plasma nitriding has reduced corrosion resistance, the corrosion resistance is improved by implanting nitrogen ions and increasing the nitrogen ions to 30 atomic% or more.

It should be noted that only by plasma nitriding, the nitrogen concentration is in the range of 9 to 26 atomic%, and Vc'100 is -0.4.
6 to -0.48V vs Ref, and the corrosion resistance is poor.

The results are the same for other steel grades.

Although it is possible to increase the nitrogen concentration to 30 atomic% or more by nitrogen ion implantation alone, since the nitrogen concentration of general steel materials is less than 1 atomic%, it takes a long time to increase it to 30 atomic%. Requires.

When the present invention is applied to a part which receives an impact load, the hardening depth obtained by nitrogen ion implantation is several μm, which is not sufficient.

Therefore, according to the present invention, when nitrogen concentration is increased by plasma nitriding and then nitrogen ions are implanted,
The time required for ion implantation to increase the nitrogen concentration to 30 atomic% can be shortened.

FIG. 5 is a table showing the results of the wear test as specific wear amounts. A ring-shaped movable piece was placed on a fixed piece of a rectangular parallelepiped in the same liquid of pH 3.0 as in the polarization test of FIG. 2, and a load was applied vertically from the side of the movable piece.

The movable piece was a plasma-nitrided product, and the fixed piece was a plasma-nitrided product in which the nitriding temperature was changed.

As is clear from FIG. 5, the wear amount of the sample in which nitrogen ions were implanted after plasma nitriding was about 1/100 as compared with the sample of plasma nitriding only.

As described above, after the surface is hardened to the required depth by plasma nitriding and the nitrogen concentration on the surface is increased by implanting nitrogen ions, a surface treatment layer having high impact resistance, high wear resistance and high corrosion resistance can be obtained.

In plasma nitriding, an arbitrary hardness and hardening depth can be obtained by changing the nitriding temperature and the nitriding time.

After that, nitrogen ions may be implanted until the concentration of nitrogen on the surface becomes 30 atomic% or more, which increases the corrosion resistance.

In the actual manufacturing process, it is desirable that the total processing time of plasma nitriding and nitrogen ion implantation is short. Therefore, depending on the capability of the surface processing apparatus, the nitriding temperature should be set in consideration of the processing time required for each processing. Decide

Further, the penetration depth of ions in the ion implantation differs depending on the ion species and the acceleration voltage, and the implanted ions diffuse according to the substrate temperature.

With nitrogen ions, the acceleration voltage is 50 eV and
It is about 05 μm. Therefore, in order to obtain a depth of about 1 μm, it is necessary to control the base material temperature for diffusion.

In the case of this embodiment, the base material temperature is set to the nitriding temperature or lower and 300 ° C. or higher.

As described above, when nitrogen ions are implanted after the plasma nitriding treatment and the surface nitrogen concentration is 30 atomic% or more, a surface treatment layer having a high wear resistance and a high corrosion resistance with a hardening depth of several tens to several hundreds of μm. Is obtained.

[0047]

[Example 1] 1 cm x 1 c in which stainless steel SUS440C was quenched and tempered to adjust the surface hardness to Hv680.
A sample of m × 0.5 cm was plasma-nitrided for 10 hours in an atmosphere of nitrogen / hydrogen ratio = 1/3, pressure of 430 Pa and temperature of 410 ° C. At that time, the surface hardness was Hv1370 and the curing depth was 20 μm.

After that, nitrogen ions were applied at an acceleration voltage of 50 kV,
Implanted at current density of 30 μA / cm ² for 5600 seconds, about 1 ×
The surface nitrogen concentration was set to 30 atomic% with 10 ¹⁸ ions / cm ² . As a result, the corrosion resistance shown in FIG. 3 and the wear resistance shown in FIG. 5 were obtained.

[0049]

Example 2 A sample of which die steel SKD11 was quenched and tempered to adjust the surface hardness to Hv800 was plasma-nitrided for 10 hours in an atmosphere of nitrogen / hydrogen ratio = 1/3 and pressure 430 Pa. At that time, the surface hardness was Hv1200 and the curing depth was 40 μm.

Then, as in Example 1, nitrogen ions were implanted to bring the surface nitrogen concentration to 35 atom%. as a result,
Vc′100 shows good corrosion resistance of 0.6 V vs Ref, and the specific wear amount is 2.9 × 10 ⁻¹¹ g / N · mm, which is a very small wear amount as compared with the case of only plasma nitriding treatment. Became.

[0051]

According to the present invention, since the steel material is plasma-nitrided and then nitrogen ions are implanted to make the nitrogen concentration on the surface of the steel material 30 atomic% or more, the hardening depth of several tens to several hundreds μm. As a result, a surface treatment layer having high impact resistance, high wear resistance, and high corrosion resistance can be obtained, and the life of an automobile engine using this type of steel material can be extended.

[Brief description of drawings]

FIG. 1 is a diagram showing a nitrogen distribution in a depth direction of a plasma nitrided product of stainless steel SUS440C analyzed by GDS (Glow Discharge Optical Emission Analysis).

FIG. 2 is a diagram showing nitrogen distribution in the depth direction of stainless steel SUS440C implanted with nitrogen ions after plasma nitriding at 410 ° C.

FIG. 3 is a diagram showing corrosion resistance in the depth direction of stainless steel SUS440C implanted with nitrogen ions after plasma nitriding at 410 ° C.

FIG. 4 is a stainless steel SU implanted with nitrogen ions after plasma nitriding at 410 ° C. based on the results of FIGS. 2 and 3.
It is a figure which shows the relationship between the surface nitrogen concentration of S440C, and corrosion resistance.

FIG. 5 is a chart showing the results of a wear test as specific wear amounts.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shizuka Yamaguchi             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F-term (reference) 4K028 BA02 BA12                 4K029 AA02 BC01 BC02 BD03 CA10                       FA05

Claims (4)

[Claims] 1. A steel material is plasma-nitrided, and then nitrogen ions are implanted to increase the nitrogen concentration on the surface of the steel material to 30.
A surface treatment method for steel materials, which is at least atomic%. 2. The surface treatment method for a steel material according to claim 1, wherein the steel material is stainless steel, alloy tool steel (SKD).
Material), chrome / molybdenum steel (SCM material), high speed tool steel
(SKH material), a surface treatment method for a steel material. 3. A shock-resistant, wear-resistant and corrosion-resistant steel material, which has been subjected to plasma nitriding and then nitrogen ion implantation to make the surface nitrogen concentration 30 atomic% or more. 4. The impact resistant, wear resistant and corrosion resistant steel material according to claim 3, wherein the steel material is stainless steel, alloy tool steel (SKD).
Material), chrome / molybdenum steel (SCM material), high speed tool steel
Impact resistance, characterized by being any of (SKH material),
Wear and corrosion resistant steel material.