JPH0452265A - Parts for machine structure - Google Patents

Abstract

PURPOSE:To improve wearing resistance and pitching resistance of parts by subjecting highly-carburized parts having specified surface carbon concn. and carbide area rate to high frequency quenching or laser quenching. CONSTITUTION:Structural parts for machine are treated by plasma carburization so that the parts have >=1.4% surface carbon density, more preferably about 1.7%, and >=10% carbide area rate, preferably about 20%. The parts are then subjected to high frequency quenching or laser quenching. The obtd. parts have extremely high surface hardness and pitching resistance. The parts material to be treated is such one generally used for machine structure, such as plain carbon steel, case hardening steel, stainless steel, tool steel, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mechanical structural component having excellent wear resistance and pitting resistance.

[Conventional technology]

Conventionally, as mechanical structural parts, eutectoid carburized parts whose surface carbon concentration is adjusted to about 0.8% or less by so-called gas carburization are generally used.

In addition, as a carburizing method for steel, an anode and a cathode are placed facing each other in a vacuum container, and a direct current voltage is applied between the two electrodes to cause glow discharge. A plasma carburizing method that introduces carburizing is known.

[Problem to be solved by the invention]

With the recent increase in strength and miniaturization of mechanical structural parts,
There has been a demand for parts that have better wear resistance and pitting resistance than conventional parts.

The present invention provides a mechanical structural component that meets these needs.

[Means to solve the problem]

The present inventors completed the present invention by subjecting machine structural parts to high-concentration carburizing treatment by plasma carburizing, and further by induction hardening or laser hardening to significantly improve wear resistance and pitting resistance. did.

The present invention provides excellent wear resistance and pitting resistance by performing induction hardening or laser hardening on parts that have been subjected to high concentration carburizing treatment with a surface carbon concentration of 1.4% or more and a carbide area ratio of 10% or more by plasma carburization. It is a mechanical structural part.

Part materials to which the present invention is applied are those commonly used as mechanical structural parts, such as carbon steel, case hardened steel, stainless steel, and tool steel.

The plasma carburizing method used in the present invention is a commonly used plasma carburizing method. For example, an anode and the object part of the present invention are placed as a cathode in a vacuum container, facing each other,
When the pressure inside the container is set to 0.1 to 10 Torr, a DC voltage is applied between both electrodes, and the voltage is gradually increased.

Finally, it starts discharging. The discharge voltage varies depending on the type of gas and pressure, but it is about several 100V, and the current is several 100m.
A to number A. Under these conditions, glow discharge is caused,
Carburizing is performed using hydrocarbon gas such as methane or propane as carburizing gas.

The present invention applies the plasma carburizing treatment to the mechanical structural parts to increase the surface carbon concentration of the parts to 1.4% or more, preferably about 1.7%, and the carbide area ratio to 10% or more, preferably 2.
It should be about 0%.

The parts thus subjected to high-concentration carburizing treatment by plasma carburizing treatment are then subjected to induction hardening or laser hardening.

As the induction hardening method and laser hardening method used in the present invention, general induction hardening methods and laser hardening methods are employed.

The parts manufactured by the above method have extremely high surface hardness and pitting resistance.

Next, examples of the present invention and test examples regarding the effects thereof will be shown to specifically explain the present invention.

〔Example〕

Example 1 Steel parts with composition A shown in Table 1 are placed in a furnace, and the temperature inside the furnace is 1O.
After reducing the pressure to -2 Torr and heating to 920°C, Ar and H2 were supplied to adjust the inside of the furnace to 3 Torr. The component was used as a cathode, and a direct current voltage of 200 V was applied between it and the anode to cause glow discharge.

As a pretreatment, surface cleaning was performed using Ar and H ions for 20 minutes, and then Ar and H2 were exhausted.

Next, propane is fed into the furnace and carburized for 3 hours to obtain a carburized part with a surface carbon concentration of 1.89% and a carbide area ratio of 15%. This was moved in a high frequency electric field of 100 KHz at a speed of 7 mm/see to perform induction hardening to produce the parts of the present invention.

Example 2 Steel parts with composition B shown in Table 1 were treated with the same plasma carburizing method as in Example 1 to produce a surface carbon concentration of 2.10% and a carbide area ratio of 2.
Obtain 1% carburized parts. This was subjected to induction hardening in the same manner as in Example 1 to produce parts of the present invention.

Example 3 Steel parts with composition D shown in Table 1 were treated with the same plasma carburizing method as in Example 1, with a surface carbon concentration of 2.22% and a carbide area ratio of 1.
Obtain 8% carburized parts. This was subjected to induction hardening in the same manner as in Example 1 to produce parts of the present invention.

Example 4 Steel parts with the C composition shown in Table 1 were processed using the same plasma carburizing method as in Example 1 to produce a surface carbon concentration of 2.2% and a carbide area ratio of 1.
Obtain 7% carburized parts. This was coated with zinc phosphate and CO
Using 2 lasers, output 3! , moving speed Lm/mi
The parts of the present invention were manufactured by laser hardening under the conditions of n.

Example 5 Steel parts with composition E shown in Table 1 were processed using the same plasma carburizing method as in Example 1 to produce a surface carbon concentration of 2.48% and a carbide area ratio of 2.
Obtain 3% carburized parts. This was subjected to laser hardening in the same manner as in Example 4 to produce parts of the present invention 6 Table 1 in the margin below (chemical composition wt% of parts) Parts manufactured by the manufacturing method of the present invention in Examples 1 to 5 above 1
Tests showing excellent surface area hardness, wear resistance, and pitting resistance of 5 to 5 were carried out using the respective processing methods, surface carbon concentration, and carbide area ratio of parts A-H having the same composition as the parts used in the present invention. The following are the results of a comparison with parts obtained in a comparative example, which differs from the method of the present invention.

1. Carburizing characteristics a) Test sample Obtained by the method of the invention in Examples 1-5 parts (sample Nos. 1 to 5 of the present invention).

The alloy of steel type A in Table 1 was used as the plastic of Example 1. Parts treated by the plasma carburizing method (comparative sample Nα1).

The alloy of steel type B in Table 1 was heated in a furnace to 920°C.
Soak the sample for a minute and remove the carburizing gas (carbon potential).

About 0.9%) was supplied into the furnace and carburizing treatment was performed for 3.5 hours. Next, the supply of this enriched gas was stopped and the temperature was maintained for 2 hours to diffuse carbon (parts subjected to gas carburization treatment (comparative sample No. 2)).
. A part obtained by subjecting the alloy of steel type E in Table 1 to the same gas carburizing treatment as above, followed by induction hardening (comparative sample N03)
.

A part obtained by induction hardening the alloy of steel type B in Table 1, which was made to have a surface carbon concentration of 1.30% and a carbide area ratio of 7% by the plasma carburizing method of Example 1 (comparative sample Nα4).

A part obtained by laser hardening an alloy of steel type C in Table 1, which was made to have a surface carbon concentration of 1.02% and a carbide area ratio of 4% by the plasma carburizing method of Example 1 (comparative sample Na 5
), a part in which the alloy of steel type A in Table 1 was made to have a surface carbon concentration of 1.52% and a carbide area ratio of 14% by the plasma carburizing method of Example 1 (comparative sample Na 6 ).

b) Carburizing properties The results were as shown in Table 2 below.

Table 2 Note that the surface hardness is the hardness at a depth of 0.05 mm from the surface (
HV).

2. Wear test a) Test sample The same sample as in Test 1 above was used.

b) Test method Ogaki abrasion test method, load 6.9 kgf, distance 20
0m, wear rate 1.96m/see, partner machine SCM42
The test was carried out under the conditions of 0 and HRC60.

C) Test results It was as shown in Table 3.

Roller pitching test a) Test sample The same sample as in Test 1 above was used.

b) Test method Surface pressure 375 kg f/mm2, rotation speed 150o
The test was carried out under the conditions of rpm and slip: 40%.

C) Test results It was as shown in Table 3.

As is clear from the test results shown in Table 3, Samples 1 to 5 of the present invention have better wear resistance and pitting resistance than Comparative Samples 1 and 2, which were subjected to eutectoid carburization by ordinary gas carburization and plasma carburization. has been significantly improved.

In addition, Comparative Sample 3, which was subjected to high-concentration carburizing by gas carburizing and then induction hardening, had the same carburizing properties as the samples of the present invention in Table 2, but as shown in Table 3. , the roller pitting properties are deteriorated compared to the sample with normal carburization. This is thought to be due to the grain boundary oxidation layer formed near the surface during gas carburizing.

Comparative sample 4.5 has a lower surface carbon concentration and a lower carbide area ratio than the sample of the present invention. Comparative Sample 4 does not have enough surface hardness to contribute to wear resistance and pitting resistance. Furthermore, in Comparative Sample 5, the amount of retained austenite increased, and the surface hardness was lower than that of the normal eutectoid carburized sample.

For this reason, the amount of wear is increasing. That is, since the surface carbon concentration is as low as 1 to 1.4% during high-concentration carburizing, it is difficult to improve wear resistance and pitting resistance.

〔Effect of the invention〕

The present invention has extremely excellent wear resistance as a mechanical structural component.
This is a useful invention for manufacturing parts with pitting resistance.

Claims (1)

[Claims] 1. Machine structural parts that have been subjected to high-concentration carburizing treatment with a surface carbon concentration of 1.4% or more and a carbide area ratio of 10% or more through plasma carburization, and then induction hardened or laser hardened.