JP3247964B2 - Surface treatment method for metal parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the use of metal parts constituting automobiles, other transportation equipment, industrial equipment, office equipment, etc., such as seizure resistance, galling, initial conformability, abrasion resistance, and fatigue resistance. It relates to a surface treatment method for the purpose of improvement.

[0002]

2. Description of the Related Art A so-called low-temperature sulfurizing treatment method has been proposed as a surface treatment method for forming a formation layer (hereinafter referred to as a "sulfurized layer") composed of iron sulfide and a sulfur compound on the surface of a metal component (for example, see, for example, Japanese Patent Application Laid-Open Publication No. H11-163873). See Japanese Patent Publication No. 44-1809).
In this method, the material to be treated is immersed in a molten salt bath, the material to be treated is used as an anode, the salt bath is used as a cathode, and DC electrolysis is continuously performed under a constant current density. It forms a sulfurized layer of about 10 μm.

In the low-temperature sulfurizing treatment, the thickness of the sulfurized layer (hereinafter referred to as the film thickness) is governed by the load electric quantity, which is the product of the current density and the electrolysis time. Although the film thickness tends to increase with an increase in the amount of electricity, the accuracy changes such as the surface roughness of the material to be processed and the amount of change in size also increase almost in proportion to the amount of load electricity.

[0004] The mechanism of formation of the sulfurized layer is such that iron sulfide and sulfur compounds (hereinafter referred to as sulfides), which cannot be called a pit-like layer of about several μm, are formed on the surface of the material to be treated in the early stage of electrolysis. Then, when the electrolysis is further continued continuously, the sulfide is expanded in the surface and depth direction of the material to be processed starting from the pit-like nucleus, and at the time of the end of the electrolysis, the sulfide layer, that is, the sulfurized layer is formed. It is produced and is also effective for carburized, quenched, and nitrided metal parts.

[0005]

However, the thickness of the sulfurized layer formed by the above-described reaction mode is very uneven, and the material to be treated before the treatment is smooth and has been subjected to grinding or the like. In the case of the surface, the roughness of the surface of the sulfurized layer and the boundary between the sulfurized layer and the material to be treated tended to be rough. Also,
Depending on the shape of the material to be processed, the surface roughness, the thickness of the sulfurized layer, and the amount of change in the size of the vulcanized layer often vary.

[0006] Therefore, in the case of a conventionally required material to be processed with accuracy, the material is corrected by superfinishing after processing, or in the case of a material which is difficult to correct, processing is performed by lowering the amount of load electricity to change the accuracy. And other methods have been adopted.

[0007] However, if the treatment is performed with a reduced amount of load electricity in order to minimize the change in precision of the material to be treated, the thickness of the sulfurized layer is not uniform, so that the substrate is not locally formed without the formation of the sulfurized layer. Remain, and problems such as lack of wear resistance remain.

Accordingly, the present invention provides a method for forming a uniform film thickness,
The object of the present invention is to provide a processing method that can be applied to metal parts that have a small surface roughness, a small variation in the amount of size change, do not require correction after processing, and are conventionally difficult to be applied due to accuracy. And

[0009]

That is, according to the present invention, a metal part of a material to be treated is immersed in a molten salt bath maintained at 160 to 240 degrees Celsius, and iron sulfide is applied to the surface of the material by molten salt electrolysis. And a surface treatment method for obtaining a generation layer composed of a sulfur compound, wherein the DC current supplied during the electrolysis is an intermittent waveform of a rectangular wave, or the intermittent waveform of the rectangular It is a combination.

[0010]

In the salt bath electrolysis, pretreatment such as degreasing, acid washing, etc., and carburizing are carried out in a molten salt bath mainly containing rhodan sodium (NaSCN) and rhodan potassium (KSCN) maintained at 160 to 240 degrees Celsius. The material to be treated, which has been subjected to treatment, quenching, nitriding, etc., is immersed, and the material to be treated is used as an anode, and the salt bath is used as a cathode to perform DC electrolysis.

As a result, iron ions are generated at the anode as shown in the following equation (1), and sulfur ions are generated at the cathode as shown in the following equation (2). By the reaction, a sulfurized layer is generated on the surface of the material to be treated.

[0012] ^{Fe → Fe 2+ + 2e (1} ) SCN - + 2e → S 2+ CN - (2) Fe 2+ + S 2- → FeS (3)硫層immersion by the same chemical reaction in the present invention Generated. However, in the present invention, unlike the conventional method (see FIG. 4), a large number of pit-like sulfide reaction nuclei smaller than the conventional method are formed densely and uniformly on the surface of the material to be treated unlike the conventional method (see FIG. 4) in the initial stage of electrolysis. (See FIG. 3) Therefore, the sulfuration reaction proceeds from these starting points, and as a result, a uniform film thickness can be obtained, and further, effects such as a small surface roughness and a small variation in the size change can be obtained. This eliminates the need for correction after processing and makes it possible to apply the method to metal parts that have been conventionally difficult to apply due to accuracy.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail.
JIS SCM4 having predetermined components as a material to be treated
Carburizing and diffusing 15 materials at 930 degrees Celsius for 6 hours,
The temperature was lowered to 840 degrees Celsius and oil quenching was performed.
After tempering for 2 hours at a temperature, 1.6 g by grinding.
Those adjusted to s were used.

[0014] As a molten salt bath, rodan potassium (KSC
N) 75% and rhodane sodium (NaSCN) 25% were used, which was maintained at 190 degrees Celsius. The material to be treated was immersed in the salt bath, and DC electrolysis was performed using the material to be treated as an anode and the salt bath as a cathode.

In the present invention, the energization pattern during electrolysis is shown in FIG.
Is controlled as shown in FIG. That is, the predetermined current density (ip) is a rectangular wave intermittent waveform in which a predetermined current application time (t-on) and a predetermined current pause time (t-off) are repeated n cycles. The current density (ip), the current application time (t-on), the current pause time (t-off), and the number of cycles (n) are within a certain predetermined range, and the material, shape, and required accuracy of the material to be processed are specified. It is selected according to the above.

As shown in FIG. 2, in the conventional energization pattern during electrolysis, a predetermined current density (id) is kept constant and a current is continuously supplied for a predetermined time (Td). Was something.

Embodiment 1 FIG. The material to be treated is supplied to the molten salt bath using the current-carrying pattern of the present invention, specifically, current density (ip) = 32.0 (A / dm ² ), current application time (t-on) = 0. 01 (s) Current pause time (t-off) = 0.03 (s) Cycle (n) = 6000 Total load electric quantity is 1920 A / d
a m ^2.

Embodiment 2 FIG. The material to be treated was treated with the molten salt bath in combination with the conventional energizing pattern and the energizing pattern of the present invention. That is, the first step is a continuous DC electrolysis similar to the conventional one, specifically, current density (ip) = 3.2 (A / dm ² ), current application time (Td) = 150 (s) cycle (n) = 1, as a second step, the current-carrying pattern of the present invention, specifically, current density (ip) = 64.0 (A / dm ² ), current application time (t-on) = 0 .1 (s) Current pause time (t-off) = 0.9 (s) Cycle (n) = 225 Note that the total load electric quantity is the same as in the first embodiment.
It is 1920 A / dm ² similarly to.

Embodiment 3 FIG. The material to be treated is treated by the molten salt bath in the conventional energizing pattern, that is, continuous DC electrolysis similar to the conventional one, specifically, current density (ip) = 3.2 (A / dm ² ). Current application time (Td) = 600 (s) Cycle (n) = 1 Note that the total load electric quantity is the same as in the first embodiment.
And 2, as in 1920 A / dm ² .

FIGS. 3 and 4 schematically show micrographs of the surface of the material to be treated in the initial stage of the electrolysis in Examples 1 and 3, and show the conventional method shown in FIG. 4 (Example 3). 3), pit-like sulfide reaction nuclei having relatively large sizes and different sizes are generated at a relatively large distance from each other, whereas the method of the present invention shown in FIG. In 1) and 2), many small pit-like sulfide reaction nuclei are densely and uniformly generated.

FIG. 5 schematically shows a measurement result of the surface roughness after the treatment of the above-mentioned Examples 1 to 3 and a micrograph of the cross-sectional structure. When observing them, the thickness of the sulfurized layer generated under the same load electricity is the same, but the method of the present invention has a much higher uniformity of the film thickness than the conventional method, and furthermore, It is confirmed that the surface roughness is small.

Furthermore, it has been confirmed that the variation in the amount of change in the size of each part of the material to be processed can be suppressed to a small value, and it can be applied to parts requiring high precision without requiring the number of corrections after processing. .

FIG. 6 shows the seizure resistance test results of the processed product of the present invention of Example 1 and the processed product of the conventional method of Example 3, showing the transition of the coefficient of friction for each applied load and the end of the test. , The curve a shows the test result of the processed material by the method of the present invention, and the curve b shows the test result of the processed material by the conventional method. Note that a curve c is a test result of an untreated material, that is, the material to be treated that has been carburized and ground.

The test conditions are as follows.

Test machine: FAVILLE test machine (see FIG. 7) Fixed piece: V block SCM415 carburized / ground material Test environment: Non-lubricated (in air) Load: Continuous increase from initial load 150 kgf Load increase rate: 20 to 25 (Kgf / s) Sliding speed; 0.1 (m / s) Observing FIG. 6, the untreated product indicated by the curve c changes the friction coefficient around 0.2 to 0.3, and the applied load is 600 kg.
The test was completed at about f due to seizure. In contrast,
Each of the test pieces subjected to the method of the present invention and the conventional method has a coefficient of friction of about 0.1 to 0.05, and the load decreases from plastic deformation due to frictional heat at a load of about 1200 kgf, and the test ends. The difference between the untreated product and the untreated product was confirmed.

[0026]

According to the present invention, a uniform film thickness can be obtained, the surface roughness is small, and the variation in the amount of change is small. An effect that can be applied to a metal component that has been considered difficult to obtain is obtained.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing an energization pattern for implementing a method of the present invention.

FIG. 2 is a waveform diagram showing an energization pattern according to a conventional method.

FIG. 3 is a diagram schematically showing the surface of a material to be treated in the initial stage of electrolysis according to the present invention.

FIG. 4 is a diagram schematically showing the surface of a material to be treated at the initial stage of electrolysis in a conventional method.

FIG. 5 is a diagram schematically showing a measurement result of surface roughness and a cross-sectional structure of a processed product in each example.

FIG. 6 is a diagram showing a seizure resistance test result of a treated product in each example.

FIG. 7 is an explanatory diagram showing a configuration of a tester.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaru Sakurai 17 Kinuokaoka, Moka-shi, Tochigi Dowa Mining Co., Ltd. Moka Plant (72) Inventor Pierre-Mas France 42100 Saint-Etienne-en-Leu-Lasagne 8 ( 56) References JP-A-51-54041 (JP, A) JP-A-59-89793 (JP, A) JP-A-64-65295 (JP, A) JP-A-1-133794 (JP, A) Hei 2-228483 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/00-11/34 C23C 8/40

Claims (2)

(57) [Claims] 1. A metal part as a material to be treated is heated to 160 to 24 degrees Celsius.
In a surface treatment method of immersing in a molten salt bath maintained at 0 ° and obtaining a product layer composed of iron sulfide and a sulfur compound on the surface of the material to be treated by molten salt electrolysis, the DC current supplied during the electrolysis is rectangular. A surface treatment method for a metal part, characterized in that the wave has an intermittent waveform. 2. The surface treatment method for a metal part according to claim 1, wherein continuous DC electrolysis is combined with DC electrolysis using a rectangular intermittent waveform.