JPH07166322A - Preparation of steel part for substituting for plating treatment - Google Patents

Abstract

PURPOSE: To provide parts for plating treatment substitution without pollution with low energy by subjecting steel parts to a simultaneous oxidizing-nitriding treatment in an atmosphere contg. a nitriding gas and oxidizing gas and forming an oxide layer and an oxygen-contg. nitride layer.

CONSTITUTION: Air or the air and gaseous propane together with gaseous ammonia which is the nitriding gas are directly supplied into a furnace where the steel parts are subjected to the simultaneous oxidizing-nitriding treatment. As a result, the extreme surface oxide layer of Fe₃O₄ of a thickness 0.2 to 5 μm and the ε-niride layer or ε-precipitated niride layer of a thickness 10 to 30 μm in which the oxygen is incorporated are formed on the surfaces of the steel parts. The steel parts are thereafter cooled by furnace cooling, air cooling, water soluble org. black deposition liquid, heat treating oil, water suluble oil or the like. The steel parts after cooling are then polished and are subjected to surface finishing to surface roughness of ≤0.4 μm RA. When the steel parts are subjected to a magnetite film treatment or odixized film treatment, the steel parts are preferably finished to the surface roughness of ≤0.2 μm RA. As a result, the steel parts having the excellent corrosion resistance, wear resistance and fatigue strength are obtd.

COPYRIGHT: (C)1995,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a steel part for plating treatment substitution, and more specifically, it is a pollution-free plating or surface treatment substitute for pollution-free, low energy corrosion resistance and wear resistance. And a method of manufacturing a steel part having excellent fatigue strength.

[0002]

2. Description of the Related Art A salt bath method and a gas method have been developed up to the present as a method for manufacturing such steel parts for plating treatment. First, the salt bath method is to manufacture steel parts by two continuous molten salt bath treatments. It is known as a technique for manufacturing a steel part having corrosion resistance by heat treatment. In this case, the first molten salt bath was a nitriding bath, and the steel parts were put in a bath in which the harmful cyanide cyanide and the potassium cyanide salt medium were melted at 580 ° C., and the steel parts were subjected to a nitriding treatment for 2 hours, followed by caustic soda and caustic potash. After oxidization in a bath of 400 ° C. in which sodium hydroxide and sodium nitrate were dissolved for about 10 minutes, the parts were cooled in water and washed to obtain a desired surface roughness of the processed parts.
This is a method of manufacturing a completed corrosion-resistant steel part by reoxidizing a polished or polished product in an oxidation treatment bath (second salt bath) heated to 400 ° C. for 20 minutes and then water cooling. However, this salt bath method is accompanied by the problem of environmental pollution due to the use of toxic chemical substances, and the irrationality of the oxidation treatment caused by mixing the primary salt bath with the secondary salt bath, and the waste water by washing with water after the oxidation treatment. The biggest drawback is that it causes processing problems and that the heating for the secondary oxidation treatment reduces the fatigue strength of the parts, especially in carbon steel.

In the gas method, the components are nitrided or carbonitrided for 4 hours or more in an ammonia-endothermic gas or ammonia-exothermic gas atmosphere at 550 ° C. to 720 ° C., and then in an oxidizing atmosphere for 2 to 120 seconds. After the surface oxidation heat treatment (primary oxidation treatment) to be exposed to water, cooling with a water-oil emulsion refrigerant and then degreasing, a method of wax coating treatment for improving corrosion resistance, and after the primary oxidation treatment, This is a method in which the cooled component is polished to have a surface roughness of 0.2 μm _RA or less, reoxidized by heating (secondary oxidation treatment), and then cooled. In such a gas method, after the gas nitriding treatment is completed, the original gas remaining in the furnace for artificial primary oxidation treatment is replaced with nitrogen gas, and then, again,
Depending on the thickness of the parts, an oxidizing gas may be charged separately into the furnace.
The oxide film of 1 μm or less cannot be obtained unless the subsequent oxidation treatment time is strictly controlled, which adds complexity and difficulty to the treatment process. Especially, the amount and surface area of the components loaded in the furnace make the components It is difficult to obtain a uniform oxide layer as a whole, and after polishing, secondary oxidation treatment is performed at 350 to 550 ° C., so energy consumption by reheating, complexity of work process and surface side during nitriding treatment with carbon steel. In the nitrogen solid solution layer formed on the surface, the fatigue strength of the component is remarkably reduced due to precipitation of nitrides, ie, Fe ₄ N, by reheating during the secondary oxidation treatment, which remains a serious problem. Since the parts manufactured in 1) easily rust in 100 to 200 hours in a 5% salt spray test, they also have a drawback that corrosion resistance is not excellent.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to oxidize gas in the same gas atmosphere in the same furnace in order to minimize or completely eliminate the problems of the conventional salt bath method and gas method. -To simultaneously provide nitriding or gas oxidation-nitriding carbonization treatment to provide a steel part having low pollution, low energy, corrosion resistance, wear resistance and fatigue strength.

[0005]

According to the present invention to achieve the above object, a steel part is heat-treated in an oxidizing-nitriding gas atmosphere in which an oxidizing gas is added to a nitriding gas to form an oxide on the surface. There is provided a method for producing a high corrosion resistant steel part as an alternative to a plating treatment, which comprises forming a layer, an oxygen-containing ε-nitride layer, or an ε-carbonitride layer.

[0006]

On the other hand, the reason why the oxidation and the nitriding occur simultaneously in the oxidizing-nitriding treatment atmosphere is that the oxidizing gas is added to the nitriding gas so that the water vapor generated by the gas reaction in the furnace and the unreacted oxygen are reacted. Alternatively, an ε-nitride layer or a ε-carbonitride containing a surface oxide layer and oxygen by an oxidizing gas such as carbon dioxide and carbon monoxide formed by a direct reaction of a hydrocarbon gas and air in a furnace. This is because a layer is formed. At this time, the penetration depth of oxygen into the ε-nitride or ε-carbonitride is about 5 to 10 μm.

The gas atmosphere heat treatment for simultaneously forming the outermost surface oxide layer and the oxygen-containing ε-nitride layer or ε-carbonitride layer is carried out in the temperature range from 420 to 720 ° C. for up to 50 hours with ammonia. And 10 to 50% of air and nitrogen and ammonia and 5 to 50% of (C ₃ H ₈ + air)
And a gas atmosphere composed of nitrogen, and the heat treatment furnace used at this time was a lower gas injection type pit furnace with stirring fans attached to the upper and lower parts, a shield quench furnace, a fluidized bed furnace or three or more. This is a mesh belt type continuous furnace, etc., which is composed of chambers with stirring fans attached to the top and bottom of each chamber, where the gas that causes the oxidation-nitriding process is that ammonia supplies atomic nitrogen to the surface of the steel parts. Thus, carbon dioxide and carbon monoxide supply carbon, and water vapor, carbon dioxide and carbon monoxide formed by combustion reaction of oxygen in the air and propane gas of the air supply oxygen in the furnace. The oxide layer on the outermost surface of the component and the ε-nitride layer containing oxygen each have a thickness of 0.5 to
It is formed to 5 μm and 15 to 30 μm, which can be changed by removing the processing time, the temperature and the composition of the gas atmosphere depending on the physical characteristics of the component.

Particularly, after the simultaneous oxidation-nitridation composite treatment, the surface oxide layer is formed to a thickness of 0.5 to 5 μm for a part requiring a surface roughness of 0.2 μm _RA or less in the state where the surface is polished. And the oxygen-containing ε-nitride layer is formed to a thickness of 15 to 30 μm, wherein 1/3 to ½ of the thickness of the oxygen-containing ε-nitride layer is pores. It is composed of layers, and oxides are formed in the pores to improve the surface corrosion resistance. A typical thickness of the oxygen-containing ε-nitride layer is about 20 μm, and this thickness can be obtained by heat treatment at 570 ° C. for 2 hours or at 600 ° C. for 1 hour and 20 minutes. Formed. However, ε − containing oxygen that is thinner or thicker than this
The nitride layer is changed depending on the processing time and temperature and the composition of the gas atmosphere used. The thickness of the surface oxide layer can be changed by the composition of the oxidation-nitridation heat treatment gas,
Moreover, the heat treatment temperature and time are also variables. For _{example, 50% NH 3 -20% (} C 3 H 8 + 4air) -3
During the oxidation-nitridation heat treatment at 570 ° C. for 2 hours in a 0% N ₂ gas atmosphere, the surface oxide layer has a thickness of about 4 μm, and the oxygen-containing ε-nitride layer appears to have a thickness of 22 μm. The thickness of the ε-carbonitride layer containing oxygen is about 10 μm.

The oxide layer thickness of less than 1 μm is very suitable for improving the corrosion resistance of the same low carbon steel and low carbon alloy steel as the brake master bag, the screw, especially the thin steel plate (3 mm or less). If the surface oxide layer has a thickness of 2 μm or more, peeling will occur. Therefore, in order to prevent this, the gas atmosphere must be adjusted so that the thickness of the surface oxide layer is 1.5 μm or less. I have to.

The parts treated by the above-mentioned treatment are water-soluble organic black depositing liquid (construction chemistry, BBF-1
200) after cooling to 00)
Salt spray test over time (ASTM standa
rd B117-64). When the cooling temperature of the low carbon steel becomes lower than the oxidation-nitridation heat treatment temperature by such a treatment method, the Fe in the nitrogen solid solution layer of the low carbon steel part is cooled during cooling.
Since _{4 N} dramatically lower the yield and tensile strength of the steel by is deposited, it must be carried out with minimum 560 ° C. or higher cooling. Then, in order to adjust the cooling rate according to the shape and thickness of the component to be nitrided / oxidized,
An undeformed part can be obtained by adjusting the concentration of the water-soluble organic blackening solution, and the concentration is adjusted by adjusting the mixing amount of water.

On the other hand, after the oxidative-nitriding heat treatment, the parts which do not require cooling of the water-soluble organic black liquor are mainly cooled directly with the heat-treated oil or the water-soluble coolant.

Particularly, low carbon alloy steel, medium carbon steel, medium carbon alloy steel, etc. are subjected to oxidative-nitriding heat treatment in a lower gas injection type pit furnace having stirring fans attached to the top and bottom, and then cooled to a coolant. The fatigue strength of heat-treated parts cannot be guaranteed unless the cooling rate is adjusted so that the time does not exceed 3 minutes at the maximum, and the thickness of the surface oxide layer must not exceed 2 μm or more. The surface thus cooled exhibits an aesthetically pleasing bluish-black color or black and withstands salt spray tests for up to 70 hours.

In the case where a part requires a certain surface roughness, after the oxidation-nitriding treatment, it is cooled directly to a heat-treated oil or a water-soluble cooling agent as described above, without cooling to a water-soluble organic black coating liquid. For example, rods for shock absorbers for automobiles, various oils. In the case of parts such as pneumatic piston rod, damper rod, etc., which are hard chrome plated or subjected to high frequency heat treatment after hard chrome plating, after heat treatment in a gas oxidation-nitriding atmosphere, they were directly cooled to heat treated oil or water-soluble coolant. After that, surface polishing is performed in order to obtain the surface roughness required for the component. At this time, the surface is polished to a surface roughness of 0.15μ.
It is better to implement the following mR _A, when polishing, oxidation -
The outermost oxide layer of the nitrided component is removed.
The above-polished parts have high fatigue strength and can withstand rusting for 300 hours or more in the salt spray test without additional oxidation treatment thereafter.

Rhodes for automobile shock absorbers and various oils produced by this method. Pneumatic piston rods, damper rods, etc. are evaluated as having a specular gloss on the surface as if they were treated with chrome plating, and are superior to the mechanical properties of parts that perform high frequency heat treatment and chrome plating in parallel. Especially in the case of hard chrome plating, the plating layer is 3
Compared with the fact that rusting occurs in 72 to 96 hours in a salt spray test when treated with 0 μm, corrosion resistance of 3 times or more is guaranteed and the nitrogen solid solution layer of the surface layer of parts is maintained without reheating. Therefore, when compared with those manufactured by the conventional salt bath method and gas method for the same parts, the treatment process is greatly simplified without requiring additional reheating operation or thermal oxidation operation, This is a method that can secure high corrosion resistance and fatigue strength.

On the other hand, in the case of producing a part requiring a higher corrosion resistance and a lower surface friction coefficient, that is, a part having an excellent surface lubricity, a water-soluble alkali magnetite coating treatment is carried out. In this treatment method, after the oxidization-nitriding treatment, the cooled component is surface-polished, and then the oxidization-nitriding treatment is applied to the water-soluble alkaline solution heated to 120 to 140 ° C. The product is preheated at a temperature of 100 to 120 ° C. in advance, deposited for 3 to 5 minutes, washed with water heated to 50 ° C., and then dried to obtain a finished product. At this time, the water-soluble alkaline coating treatment agent used was 1 liter of seawater.
It is a solution in which 2 mol of caustic soda and 100 g of sodium nitrate are dissolved, and the coating layer has a thickness of 0.5 to 1 μm and is mainly composed of Fe ₃ O ₄ .

[0016]

【Example】

(Example 1) The length of the shock absorber rod is 34c.
m, diameter 18 mm, initial surface roughness 0.2-0.4 μmR
_A and processing. Polished S45C and non-coarse steels corresponding to 45C were treated at 580 ° C. for about 2 hours with 50% NH ₃ -30
% (C ₃ H ₈ + 4air) -20% N _{2 In a} gas atmosphere, oxidization-nitridation treatment was performed, followed by cooling with a water-soluble coolant. At this time, the oxide formed on the surface was approximately 2.2 μm for both materials, and the thickness of the ε-carbonitride layer was 25 μm.
The thickness of the pore layer appeared to be about 12 μm. As a result of a salt spray test in a state in which these rods were polished to 0.11 μm _RA , both of them existed for more than 300 hours without rusting, and in order to impart higher corrosion resistance, surface lubricity and aesthetic effect, both of them were 0.1. 11 μm _RA and 10 in the final polished state
1 liter of seawater that is preheated to 0 ℃ and then heated and stirred to 125 ℃
After soaking in a solution of 12 mol caustic soda and 100 g of sodium nitrate in iter for 5 minutes, washing in flowing water, and then drying and salt spray test, both materials can withstand 400 hours or more without rusting, After the rod (S45C) thus processed was assembled with hydraulic and gas shock absorbers, the reciprocating compression test showed that no problems were found even after 6 million cycles. It was more than 3 times as durable as the hard chrome plating treatment of the same type. (Example 2) Surface roughness of nitrided steel (SACM type 1) of 0.3
Screw of plastic injection molding machine processed with μm _RA at 500 ° C for about 60 hours at 30% N by volume%
After oxidizing and nitriding treatment in an atmosphere of H ₃ -60% N ₂ -10% air, cooling to 500 ° C. and cooling to a water-soluble refrigerant, and after performing surface roughness 0.2 μm _RA and polishing, As a result of salt spray test, the screw did not rust for more than 200 hours, and the abrasion resistance was improved three times or more in comparison with the hard chrome plating after nitriding.
As a result, the service life was increased three times or more. (Example 3) Quenching. Tempering
Hing-tempering nitrided steel (SACM
Spindle parts for weaving and machinery that were machined with 1st type) were polished to about 0.4 μm _RA, and then 50% NH ₃ -30 for about 30 hours at 580 ° C. in a lower gas injection type pit furnace.
% (C ₃ H ₈ + 4air) -20% N ₂ After carbonitriding and carbonizing in a gas atmosphere, cooling to a water-soluble cooling agent and then 0.2 μm
mR _A roughness results of salt spray test with the polishing state to have a, to not rust over 200 hours, was the actual fatigue strength three times or more improved.

[0017]

The present invention eliminates the pollution problem associated with the salt bath method because a gas is used, and an artificial oxidation heat treatment is additionally performed after the nitriding treatment in comparison with the existing gas method. It is not necessary but has advantages in energy saving by reheating, simplification of working process and production of parts with high fatigue strength.

Strictly speaking, the oxidization-nitridation heat treatment in the present invention means that oxidation and nitriding occur simultaneously in the same furnace, and nitriding is the same as nitriding carbonization treatment in a broad sense. Therefore, nitriding is used as a thermochemical treatment method in which nitrogen is introduced into steel and nitriding carbonization is simultaneously diffused and permeated into steel. Therefore, in the present invention, the oxidization-nitriding treatment is performed by nitriding treatment by adding 10% or more of air and nitrogen to ammonia gas, and the oxidization-nitriding carbonization treatment is only a mixture of air and propane in the composition of the gas used. When gas and nitrogen gas are added, a denitrifying carbonization process is performed.

According to the present invention, the corrosion resistance of a steel part is improved by forming oxides in the pores of the surface oxide layer and the oxygen-containing ε-nitride layer deposited on the surface of the steel part by the simultaneous oxynitriding treatment. The surface ε-nitride itself has high corrosion resistance. These oxide layers are mainly composed of Fe ₃ O ₄ and Fe ₂ O ₃ , and the surface ε-nitride layer is mainly Fe ₃ (CN).
Composed of.

Claims (15)

[Claims] 1. A method in which air or air and propane gas are directly charged into ammonia gas, which is a nitriding gas, into a furnace to simultaneously oxidize and nitridize steel parts, and an ε layer containing an oxide layer and oxygen on the surface is produced. -Nitride layer or ε containing oxygen-
A method for manufacturing a steel component for electroplating treatment, which comprises forming a nitriding carbide layer and finishing it. 2. The method according to claim 1, wherein the main components of the surface oxide layer are Fe ₃ O ₄ and a small amount of Fe ₂ O ₃ . 3. The method according to claim 1 or 2, wherein the surface oxide layer has a thickness of 0.2 to 5 μm. 4. The ε-containing oxygen according to claim 1.
A method of forming a nitride or ε-carbonitride layer to a thickness of 10 to 30 μm. 5. The method according to claim 4, wherein the oxygen-containing ε-nitride or ε-carbonitride layer includes a pore layer having a thickness of 3 to 15 μm. 6. The method according to claim 5, wherein an oxide is formed in the pore layer by an oxidation-nitridation reaction. 7. The nitriding or nitriding carbonization according to claim 1,
A method of cooling steel parts in a furnace or in air after oxidation treatment. 8. The nitriding or nitriding carbonization according to claim 1,
A method of cooling steel parts to a water-soluble organic blackening solution after oxidation heat treatment. 9. The nitriding or nitriding carbonization according to claim 1,
A method in which steel parts are directly cooled by heat treatment oil or water-soluble cooling oil after oxidation heat treatment. 10. The method according to claim 1, wherein after the cooling, 0.4
_A method which further comprises the step of polishing to obtain a surface roughness of less than μm _RA . 11. The method according to claim 10, wherein after corrosion, no additional oxidation treatment or organic coating treatment is carried out to produce corrosion-resistant steel having white luster. 12. The surface roughness according to claim 10, wherein the surface roughness is 0.2 μm.
_A method in which a magnetite film is treated with a water-soluble alkaline solution after being polished to a mRA or less. 13. The surface roughness according to claim 10, wherein the surface roughness is 0.2 μm.
_{A method of} performing an oxide film treatment in an oxidizing gas atmosphere maintained at 350 to 600 ° C. after polishing to mRA or less. 14. The nitriding or nitriding carbonization according to claim 1,
Lower gas injection type pit furnace with agitation fan attached to the top and bottom of oxidation treatment, fluidized bed furnace or shield quench (s
A method of carrying out in an oven. 15. The method according to claim 1, wherein the nitriding or nitriding carbonization-oxidation treatment is performed with three or more chambers.
The method is carried out in a continuous furnace composed of.