TWI385278B - Nitrogen treatment for iron-based material - Google Patents

Description

Nitriding treatment method for iron metal substrate

The present invention relates to a nitriding treatment method for an iron metal substrate, and more particularly to a nitriding treatment method for an iron metal substrate which can reduce the ratio of pores.

Because the nitrided workpiece has excellent properties such as high temperature resistance, fatigue resistance, corrosion resistance and wear resistance, it has been widely used in various fields such as drill bits, screw taps, die-casting molds, screws, connecting rods and gear cams. All are used.

The conventional nitriding treatment method is a gas nitriding method, which usually places a metal substrate to be treated in a nitriding furnace, and then directly feeds ammonia gas (NH ₃ ) into the nitriding furnace. Heating the iron metal substrate to a predetermined temperature to decompose the ammonia gas and the hydrogen (H ₂ ) in the high temperature environment and the catalysis of the iron metal substrate, and a part of the nitrogen atoms and the iron metal group The atoms of the material combine to form a compound layer 1 to improve the surface properties of the iron metal substrate; the pressure in the nitriding furnace is maintained above atmospheric pressure (positive pressure) to avoid inhalation of air from the outside to cause the iron metal substrate Oxidation or explosion hazard; thus, the ferrous metal substrate can be nitrided.

Another conventional nitriding treatment method is an ion nitriding method in which the iron metal substrate is placed in the nitriding furnace, a vacuum is introduced into the furnace, nitrogen gas is introduced, and the nitriding furnace is connected to the anode. The iron metal substrate is connected to the cathode, and a direct current voltage of several hundred volts is applied between the two poles in a low voltage environment. At this time, the nitrogen gas in the nitriding furnace will undergo glow discharge to form positive ions, and the iron metal is bombarded by the positive ions. a substrate, the temperature of the iron metal substrate is increased, and an element produced by bombardment of the surface of the iron metal substrate is combined with a nitrogen atom to form a compound, and adsorbed on the surface of the iron metal substrate to form a compound layer 1, so that The nitriding treatment of the iron metal substrate is completed.

In general, the nitriding treatment method of the above-mentioned conventional iron metal substrate has the following disadvantages. For example, in the conventional gas nitriding method, since the pressure in the nitriding furnace is large, the nitriding atom concentration in the furnace is relatively high. High, causing the compound layer 1 to be relatively thick, so that the surface of the iron metal substrate is too brittle, thereby causing the defect that the compound layer 1 is brittle; further, as shown in Fig. 1, due to nitriding in the nitriding furnace The atomic concentration is relatively high, causing a large amount of reactive nitrogen atoms to fail to bond with the atoms of the iron metal substrate to form the compound, and mutually combine to form nitrogen molecules and aggregate in the compound layer 1 to form bubbles 11, resulting in the compound layer 1 The porosity is too high, and thus has the disadvantages of reduced strength, easy peeling, and deterioration of corrosion resistance.

In addition, the equipment cost of the conventional ion nitridation method is relatively high, resulting in an increase in manufacturing cost; further, in the nitriding furnace, an appropriate spacing between the ferrous metal substrates is required to avoid adjacent iron metal bases. The glow discharges also affect each other and cause excessive heating, so the method can simultaneously treat the amount relatively low; further, the iron metal substrate is heated by the glow discharge method, if the iron When the thickness of the metal substrate is different, the heating rate of each of the iron metal substrates is different, and the iron metal substrate cannot be simultaneously reached the same processing temperature. Therefore, the iron metal substrates of different shapes cannot be simultaneously processed. Further, the inconvenience in use is caused; further, the heating uniformity of the glow discharge heating is not good, causing the temperature of the surface of the iron metal substrate to be relatively uneven, so that the uniformity of the compound layer 1 is poor, and for the shape Complex iron metal substrates and deep holes cannot be handled. For the above reasons, it is necessary to further improve the nitriding treatment method of the above-described conventional iron metal substrate.

The main object of the present invention is to provide a nitriding treatment method for an iron metal substrate, which uses a pulse mode to adjust the concentration of the working gas, so that the invention has the effects of reducing porosity and improving strength.

A secondary object of the present invention is to provide a nitriding treatment method for an iron metal substrate which is subjected to the nitriding treatment in a low pressure environment of less than one atmosphere, so that the present invention has the effect of reducing the amount of working gas consumed.

A method for nitriding a ferrous metal substrate according to the present invention, comprising the steps of: placing a ferrous metal substrate to be treated into a chamber, and pumping the chamber to form a pressure in the chamber a low pressure environment below atmospheric pressure; heating the chamber to raise the temperature of the iron metal substrate in the chamber to a working temperature; charging a working gas into the chamber by a pulse mode to the iron metal The surface of the substrate is subjected to nitriding treatment. Thereby achieving the effect of reducing porosity, working gas consumption and increasing strength.

The above and other objects, features and advantages of the present invention will become more <RTIgt; The first step S10 of the nitriding treatment method for the iron metal substrate according to the first embodiment of the present invention is: placing a metal substrate to be treated into a chamber, and pumping the chamber to make the A low pressure environment with a pressure below atmospheric pressure is formed in the chamber. More specifically, in the present embodiment, the iron metal substrate is selected to be a steel material. The chamber is a closable chamber for use as a nitriding furnace; the chamber is provided with an opening, a cover corresponding to the opening, and a heating device; the ferrous metal substrate is placed through the opening a chamber is formed by the cover body to form a closed space; the heating device is configured to adjust an operating temperature of the chamber; and the chamber is connected to an air intake device and an air extracting device by a pipeline ( For example, the pumping device is configured to charge a predetermined gas into the chamber; the pumping device is configured to extract the gas in the chamber to form the low-pressure environment, and the pressure system of the low-pressure environment is selected Between 0.01 and 0.1 mbar (mBar), in this embodiment, the pressure in the low pressure environment is 0.05 mbar (mBar).

Referring to FIG. 2 again, the second step S20 of the nitriding treatment method for the iron metal substrate of the embodiment is: heating the chamber to raise the temperature of the iron metal substrate in the chamber to an operating temperature. . More specifically, heating is performed by the heating means of the chamber to raise the temperature of the ferrous metal substrate in the chamber to the operating temperature. Preferably, the heating device is used to pass a heating gas to make the heating in the chamber more uniform. The operating temperature is selected to be between 550 and 600 ° C. In this embodiment, the operating temperature is At 570 ° C, the heating gas system is selected to be nitrogen (N ₂ ), and the pressure of the heating gas is selected to be between 700 and 1000 mbar. In the present embodiment, the pressure of the heating gas is 800. millibar.

Referring to FIG. 2 again, the third step S30 of the nitriding treatment method for the iron metal substrate of the embodiment is: charging a working gas into the chamber by a pulse mode to the iron metal base. The surface of the material is nitrided. More specifically, the working gas contains at least ammonia gas (NH ₃ ), and in order to prevent the nitriding atom concentration generated by the decomposition of the ammonia gas at the working temperature is too high, the working gas may optionally include nitrogen gas or Laughing gas (N ₂ O) to reduce the concentration of ammonia in the working gas, thereby reducing the concentration of nitriding atoms during the nitriding process; the pulse mode is controlled by an intake solenoid valve to control the air intake device The gas is charged into the chamber, the pulse frequency of the intake solenoid valve is selected to be 25 times/hour, and the gas pressure is selected to be between 250 and 300 mbar. Wherein, when the nitriding treatment is initially performed, the concentration of nitriding atoms on the surface of the ferrous metal substrate is not high, so the working gas can be first selected as pure ammonia gas and passed for 2 minutes to establish a sufficient nitriding atom concentration. Then, the working gas is replaced with a mixed gas of nitrogen, ammonia, and nitrous oxide, and the volume ratio is preferably selected to be nitrogen: ammonia gas: laughing gas is 28:70:2, and the introduction time is 3 hours. The pulse frequency of the intake solenoid valve, the composition and composition ratio of the working gas, and the working gas access time can be adjusted according to the size of the chamber, the number of iron metal substrates, the size of the nitriding surface area, and the nitriding depth. Limited to the above values.

Referring to FIG. 2 again, it is preferable to perform a depassivation process S21 before performing the third step S30. In more detail, the depassivation process S21 is performed after the operating temperature is maintained for 10 minutes in the second step S20, and the pressure in the chamber is extracted to 0.1 mbar by the air extracting device to remove the heating gas; An activating gas to form an oxide film on the surface of the iron metal substrate by the activating gas, so that the nitriding atom in the subsequent third step S30 can be more easily landed on the surface of the iron metal substrate, and the iron metal The substrates together form a compound layer 2; wherein the activation gas system is selected to be laughing gas.

Referring to FIG. 2 again, after performing the third step S30, a cooling process S31 is preferably performed to cool the ferrous metal substrate to a cooling temperature. In this embodiment, after the nitriding treatment in the third step is completed, the air intake device and the heating device are turned off, and the chamber is evacuated until the iron metal substrate is cooled to 60 ° C and then taken out.

Referring to FIGS. 1 to 3, when the nitriding treatment method of the ferrous metal substrate of the embodiment is used, first, the first step S10 is performed, and the iron metal substrate is placed in the chamber. And using the pumping device to pump the chamber, so that a low pressure environment with a pressure lower than one atmosphere is formed in the chamber to prevent the original gas (such as air) or impurities in the chamber from affecting the subsequent nitriding treatment. Efficiency; then, performing the second step S20, introducing the heating gas, and heating the chamber by the heating device to raise the temperature of the iron metal substrate to the working temperature; and performing the depassivation process S21, pumping The gas is removed from the heating gas, and then the activation gas is charged to activate the surface of the iron metal substrate and promote nucleation, thereby improving the subsequent nitriding treatment efficiency; then performing the third step S30 to charge the working gas After entering the chamber for a predetermined time, the working gas is decomposed at the working temperature to generate a nitriding atom, so that a nitriding atom of a sufficient concentration is formed on the surface of the ferrous metal substrate, and the nitriding atom and the ferrous metal substrate are Atomic total Forming the compound layer 2 in combination with the same, and then controlling the air intake device to charge the working gas into the chamber in the pulse mode by the intake electromagnetic valve to reduce the concentration of the nitriding atom, and thus, the nitriding atom Having time to migrate to the atoms of the iron metal substrate, and reducing the chance of the nitriding atoms being combined with each other to form nitrogen molecules, thereby reducing the bubble generation rate and porosity in the compound layer 2; finally, the cooling process S31 is performed. The iron metal substrate is cooled in a low pressure environment, thereby completing the nitriding treatment method of the iron metal substrate.

Referring to Figures 1 and 3, Figure 1 is a cross section of an iron metal substrate after conventional nitriding treatment; and Figure 3 is an iron metal substrate treated by a nitriding treatment method of the iron metal substrate of the present invention. The cross-sectional view of the surface; it can be clearly observed that the compound layer 1 of the iron metal substrate of Fig. 1 has many pores and has obvious cracks; in comparison, the layer of the compound layer 2 formed by the treatment of the present invention is obviously denser. And there is no crack; therefore, the nitriding treatment method of the iron metal substrate of the present invention does have the effect of reducing porosity and increasing strength.

As described above, compared with the conventional nitriding treatment method of the iron metal substrate, since the concentration of the nitriding atoms in the furnace is relatively high, the active nitrogen atoms are combined with each other to form nitrogen molecules and aggregated in the compound layer 1 to form bubbles. The porosity of the compound layer 1 is too high, and thus has the disadvantages of reduced strength, easy peeling, and deterioration of corrosion resistance; further, the conventional ion nitriding method has a relatively high equipment cost and can be simultaneously processed in a relatively low amount. At the same time, the handling of iron metal substrates of different shapes and the poor uniformity of heating are disadvantages. In contrast, the present invention utilizes the pulse mode to control the charging pressure of the working gas, and performs nitriding treatment in the low pressure environment, thereby achieving the effects of reducing porosity, working gas consumption, and strength.

While the invention has been described in connection with the preferred embodiments described above, it is not intended to limit the scope of the invention. The technical scope of the invention is protected, and therefore the scope of the invention is defined by the scope of the appended claims.

1. . . Compound layer

2. . . Compound layer

11. . . bubble

Fig. 1 is a cross-sectional view showing an iron metal substrate treated by a conventional nitriding treatment method.

Figure 2 is a flow chart showing a method of nitriding a ferrous metal substrate in accordance with a preferred embodiment of the present invention.

Fig. 3 is a cross-sectional view showing an iron metal substrate treated by the nitriding treatment method of the present invention.

Claims (17)

A method for nitriding an iron metal substrate, comprising the steps of: placing a metal substrate to be treated into a chamber, and pumping the chamber to form a pressure lower than one in the chamber a low pressure environment at atmospheric pressure; heating the chamber to raise the temperature of the iron metal substrate in the chamber to an operating temperature; and charging a working gas into the chamber by a pulse mode to the iron metal substrate The surface is subjected to a nitriding treatment; wherein the pulse mode controls the frequency at which the working gas is charged into the chamber. The nitriding treatment method of the iron metal substrate according to the first aspect of the patent application, wherein the pulse mode uses an intake electromagnetic valve to control the pressure and frequency of the working gas to be charged into the chamber. A method of nitriding a ferrous metal substrate according to claim 1 or 2, wherein the pulse mode has a frequency of 25 times per hour. A method of nitriding a ferrous metal substrate according to claim 1 or 2, wherein the pulse mode controls a gas pressure of between 250 and 300 mbar. The method for nitriding a ferrous metal substrate according to the first aspect of the invention, wherein the chamber is a closable chamber, and the ferrous metal substrate is placed in the chamber through an opening of the chamber. And heating is performed by using a heating device of the chamber, and an air suction device connected to the chamber is used for pumping, and an air intake device connected to the chamber is used for intake. The nitriding treatment method of the iron metal substrate according to claim 1, wherein the pressure in the low pressure environment is between 0.01 and 0.1 mbar. The nitriding treatment method for an iron metal substrate according to the first aspect of the patent application, wherein the iron metal substrate is a steel material. According to the nitriding treatment method of the iron metal substrate according to the first aspect of the patent application, in the step of heating the chamber, a heating gas is further charged into the chamber to make the heating in the chamber more uniform. . A method for nitriding a ferrous metal substrate according to claim 8 wherein the heating gas is nitrogen and the heating gas has a pressure of between 700 and 1000 mbar. A method for nitriding a ferrous metal substrate according to claim 1, wherein the operating temperature is between 550 and 600 °C. The method for nitriding a ferrous metal substrate according to claim 1, wherein before the step of charging the working gas into the chamber, a depassivation process is performed, and the depassivation process is performed first. The heating gas is removed; and then an activation gas is introduced to form an oxide film on the surface of the iron metal substrate. The nitriding treatment method of the iron metal substrate according to claim 11 of the patent application, wherein the activation gas is laughing gas. According to the nitriding treatment method of the iron metal substrate according to the first aspect of the patent application, after the ferrous metal substrate is subjected to nitriding treatment, a cooling process is further performed, and the cooling process is performed by the nitriding treatment. The metal substrate is cooled in a vacuum environment. The method for nitriding a ferrous metal substrate according to claim 1, wherein the working gas contains at least ammonia gas. A method for nitriding a ferrous metal substrate according to claim 14 wherein the working gas further comprises nitrogen or nitrous oxide. According to the nitriding treatment method of the iron metal substrate according to claim 15, wherein the working gas has a volume ratio of nitrogen: ammonia gas: laughing gas of 28:70:2. The nitriding treatment method of the iron metal substrate according to the first aspect of the invention, wherein the treatment time of the nitriding treatment on the surface of the iron metal substrate is 3 hours.