WO2007110905A1

WO2007110905A1 - Method of nitriding of iron group base alloy substrate

Info

Publication number: WO2007110905A1
Application number: PCT/JP2006/306034
Authority: WO
Inventors: Tadao Baba; Masahiro Akaishizawa; Masanori Kosugi
Original assignee: Honda Motor Co., Ltd.
Priority date: 2006-03-24
Filing date: 2006-03-24
Publication date: 2007-10-04
Also published as: CN101405425A

Abstract

Engine valve (10) is placed in a treatment oven. Thereafter, while vacuuming, a temperature raising is effected, and at a temperature higher than 400°C, preferably 450°C or higher, the supply of hydrogen gas is initiated to thereby initiate hydrogen gas sputtering (first step). Thus, any passive film existing on the surface of the engine valve (10) is reduced and removed. Vacuuming and temperature raising are carried on while conducting the hydrogen gas sputtering, and upon arrival at preferably 500°C, nitrogen gas together with hydrogen gas is introduced to thereby initiate the second step. By virtue of this nitrogen gas, the surface of the engine valve (10) devoid of the passive film is nitrided to result in formation of a nitride layer.

Description

Specification

Method for nitriding iron group alloy base material

Technical field

The present invention relates to a method for nitriding an iron group alloy base material having a hydrogen gas sputtering step and a plasma nitriding step.

Background art

[0002] For example, a nitriding treatment applied to an iron-based alloy base material such as stainless steel, that is, an alloy base material mainly containing a metal element belonging to Group 8 of the periodic table, This is a treatment performed to increase the hardness of the surface by forming nitride on the surface of the alloy substrate and to improve the wear resistance and the like.

[0003] Here, there is usually a passive film made of an oxide formed spontaneously on the surface of the iron group alloy substrate, and this passive film inhibits the nitriding reaction. For this reason, prior to the nitriding process, a removing process for removing the passive film is performed.

[0004] Examples of the removal treatment method include a wet method of immersing in a chemical solution such as cyan. However, in this case, a process for treating the chemical solution is necessary to avoid environmental pollution, which is complicated and has a problem that the nitriding treatment cost increases due to the treatment cost of the chemical solution.

[0005] In contrast, Non-Patent Document 1 and Patent Document 1 introduce nitrogen gas and hydrogen gas, or ammonia gas and hydrogen gas into a processing furnace containing an iron group alloy base material, and Glow discharge is generated in the treatment furnace, and the passive film on the substrate surface is generated by H + and NH + generated by this.

Four

It describes that (oxide) is reduced. In this case, since it is not necessary to process the chemical solution, the removal process and the nitriding process can be performed in the same processing furnace. Therefore, there is an advantage that the operation is simple and the apparatus configuration is simplified. . Non-Patent Document 1 describes both the reduction reaction mechanism of the passive film and the nitride diffusion mechanism.

[0006] Further, Patent Document 2 proposes that only hydrogen gas is introduced into the processing furnace from less than 350 ° C, preferably less than 150 ° C, and hydrogen gas sputtering is started at a relatively low temperature. . According to Patent Document 2, the temperature after diffusion and penetration of H + into the iron group alloy base material is increased. It is said that the passive film can be reduced from the inside by raising the temperature above the reduction temperature of the passive film and thereby moving H + to the surface side of the substrate.

[0007] Patent Document 1: Japanese Patent Publication No. 2-2945

Patent Document 2: Pamphlet of International Publication No. WO01Z34867

Non-Patent Document 1: Takao Takao “Appearance of Rival Ion Nitriding Method in Soft Nitriding Method”, “KINZOK U”, March 1996, pp. 48-54

Disclosure of the invention

[0008] According to the method described in Patent Document 1, when the content of Cr and Ni is relatively high and the steel-passive film is to be reduced and removed, the diffusion depth of H + and NH + is not sufficient. Not good for

Four

Removal of the kinetic membrane may be insufficient. When such a situation occurs, the thickness of the nitride layer formed by the nitriding process becomes nonuniform, and a defect that the nitride layer is not partially formed is caused.

On the other hand, in the method described in Patent Document 2, the reduction reaction of the passive film does not occur, and only the diffusion and penetration of hydrogen ions into the iron group alloy base material occurs. The diffusion penetration state such as the depth, penetration amount, and distribution of hydrogen ions varies greatly depending on the sputtering conditions. And, if hydrogen ions are diffused and penetrated too deeply, or if the amount of hydrogen ions penetrated is excessive, hydrogen embrittlement will occur. In particular, this tendency becomes prominent when the shape of the components of the internal combustion engine is complicated.

[0010] Therefore, for example, in order to bring the hydrogen ions into a desired diffusion and penetration state in order to avoid that the hydrogen ions remain and the iron group alloy base material exhibits so-called hydrogen embrittlement, the sputtering conditions are set. It is necessary to control with high accuracy. However, in order to perform such high-precision control, data must be collected by repeating many tests, which is complicated.

[0011] A general object of the present invention is to provide a method for nitriding an iron group alloy base material capable of making the formed nitride layer substantially uniform in thickness.

[0012] A main object of the present invention is to provide a method for nitriding an iron group alloy substrate that can avoid the brittleness of the iron group alloy substrate after nitriding.

[0013] According to one embodiment of the present invention, the first step of removing the passive film present on the surface of the iron group alloy substrate by hydrogen gas sputtering; Applying a plasma nitriding treatment to the iron group alloy substrate from which the passive film has been removed, and nitriding the iron group alloy substrate; and

Have

When the temperature of the processing furnace exceeds 400 ° C. during the temperature rise until the start of the second process, the first step is performed by circulating hydrogen gas in the processing furnace. A nitriding method is provided. Here, the iron group-based alloy refers to an alloy whose main component is a metal element belonging to Group 8 of the periodic table.

[0014] When hydrogen gas sputtering is performed at 350 ° C or lower, the reduction reaction of the passive film does not occur, and only the diffusion and penetration of hydrogen ions by sputtering into the iron group alloy substrate occurs. Also, at 350 ° C to 400 ° C, the passive membrane is reduced, but the reaction rate is slower than the release rate of hydrogen ions. For this reason, in the temperature range below 400 ° C, the diffusion penetration state such as the hydrogen depth, penetration amount, and distribution changes greatly depending on the sputtering conditions. For example, when the voltage is excessively high, problems such as excessive diffusion of hydrogen ions or excessive diffusion depth of hydrogen ions occur. Therefore, it is necessary to control the sputtering conditions with high accuracy in order to bring hydrogen ions into the desired diffusion and penetration state in a temperature range of 400 ° C or lower.

[0015] On the other hand, in the present invention, hydrogen ions stored in advance by being occluded in the iron group alloy base material are released very actively from the iron group alloy base material. The supply of hydrogen gas begins after the temperature rises above 400 ° C. In such a high temperature range, the release of hydrogen ions from the iron group alloy substrate and the reduction reaction of the passive film occur in competition. Therefore, for example, even if hydrogen ions permeate deeply into the iron group alloy substrate due to the slightly higher voltage, the hydrogen ions are released as described above, or the passive film is reduced. Or quickly consumed. For this reason, it is possible to avoid excessive diffusion of hydrogen ions and excessive diffusion depth. In other words, the reduction and removal of the passive film is controlled by starting hydrogen gas sputtering in the high temperature range as described above, that is, the temperature range in which the internal force of the iron group alloy base material is actively discharged. Easy to do.

[0016] In this case, since the implanted hydrogen ions cause a reduction reaction quickly, It is possible to avoid ions remaining on the iron group alloy base material, and thus it is possible to avoid the iron group alloy base material from exhibiting so-called hydrogen embrittlement.

[0017] Here, it is preferable to perform the first step with ^^ exceeding 40 CTC and 580 or less. In the temperature range of 580 ° C or less, the discharge rate of hydrogen ions inside the iron group alloy substrate is high. large. On the other hand, the passive J reaction is remarkably active. Therefore, it is possible to easily remove the passive film without setting the sputtering conditions with high accuracy. In the temperature range exceeding 580, since the release rate of hydrogen ions becomes small, it is not easy to avoid the remaining hydrogen ions. In addition, the structure of the iron group alloy base material starts to change, and the tendency of the physical properties to change with this changes becomes remarkable.

[0018] A suitable temperature at which the first step is performed is a force approximately 450 to 52 depending on the main component of the iron group alloy base material and its content.

[0019] Further, it is preferable to start the second step by introducing nitrogen gas during the temperature rise. As a result, it is possible to reach the holding temperature at which plasma nitriding is performed in a state where the mixing ratio of nitrogen gas and hydrogen gas is stable. Accordingly, the iron group alloy base material can be nitrided well in a short time, and as a result, a nitride layer with good quality can be efficiently formed. Moreover, since the holding time can be shortened, the time required for the nitriding process can be shortened.

[0020] When both hydrogen gas and nitrogen gas are circulated, sputtering of the iron group alloy base material with hydrogen gas and nitriding with nitrogen gas are performed simultaneously.

Brief Description of Drawings

FIG. 1 is an overall schematic side view of an engine valve that is an iron group alloy base material to which hydrogen gas sputtering treatment and plasma nitridation treatment are applied in the present embodiment.

[FIG. 2] FIG. 2 is a graph showing a temperature pattern when performing a hydrogen gas sputtering process and a plasma nitriding process.

FIG. 3 is a graph showing the relationship between temperature and the amount of hydrogen ions released from various iron group alloy substrates.

[FIG. 4] FIG. 4 is a chart showing the thickness of a nitride layer formed by plasma nitriding and the Hv before and after the plasma nitriding (NCF 600, SUH 11 M5 0 0) 20 minutes later, hold for 50 minutes at 5 2 O t: others start nitriding from 5 20 ° C, hold for 60 minutes at 5 20 ° C).

Replacement bowl (Rule 26) BEST MODE FOR CARRYING OUT THE INVENTION

[0022] Preferred embodiments of the nitriding treatment method for an iron group alloy substrate according to the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the iron group alloy base material to which the nitriding treatment is applied is the engine valve 10 shown in FIG.

[0023] The engine valve 10 has a wide head portion 12, a long rod portion 14, and an end portion 16. The rod portion 14 is also divided at a portion where the central portion force is slightly closer to the head portion 12. Has been. That is, the rod portion 14 includes a first rod 18 and a second rod 20 that is slightly longer than the first rod 18.

Of these, the head 12 and the first rod 18 are made of NCF600, and the second rod 20 and the end portion 16 are made of SU H11M. On the surface of the engine valve 10, there is a passive film formed by spontaneous oxidation of NCF600 and SUH11M.

[0025] The engine valve 10 configured as described above is first degreased with an organic solvent or the like and then accommodated in a processing furnace. Then, the engine valve 10 and the furnace wall of the processing furnace are electrically connected to the power source, and energization is started. If the current and voltage are about 25A and 220-250V, respectively!

Next, while the process furnace is sealed and the inside is evacuated, the temperature of the process furnace is started as shown in FIG. 2 as a temperature pattern. The temperature raising rate may be, for example, 3 to 5 ° CZ.

[0027] FIG. 3 shows the relationship between the temperature at which hydrogen gas sputtering is performed and the release rate of hydrogen ions stored in advance in SUH11M, which is an iron group alloy substrate, from SUH11M. From Fig. 3, it can be seen that hydrogen ions are released at a large rate when the temperature exceeds 400 ° C, in other words, the amount of released hydrogen ions increases and reaches a maximum at around 580 ° C. It is understood. Fig. 3 shows the data of three measurements. Hydrogen ions are stored in SUH11M by occlusion.

[0028] In the temperature range of more than 400 ° C to 580 ° C, a reduction reaction of the passive film also occurs. In the present embodiment, hydrogen gas sputtering is performed in a temperature range in which hydrogen ions are actively released from the iron group alloy base material and a reduction reaction of the passive film occurs.

[0029] That is, while continuing the temperature rise, the introduction of hydrogen gas was started when the temperature exceeded 400 ° C (point A in Fig. 2), and the passive film was reduced and removed by hydrogen gas sputtering (No. 1 Process) I do. Since hydrogen gas is introduced while evacuating, the pressure in the processing furnace becomes lower than atmospheric pressure. The specific pressure in the processing furnace may be set to approximately 0.7 to 1.5 Torr, for example.

Hydrogen gas generates a plasma state, and H + in the plasma collides with the surface of the engine valve 10 under the action of an electric field. This H + enters the passive film on the surface of the engine valve 10 as diffuse hydrogen ions.

[0031] Since the diffusible hydrogen ion is a temperature at which the reduction reaction of the passive film occurs, it quickly reacts with the passive film. That is, the passive film is attacked by diffusible hydrogen ions, and as a result, the passive film is reduced and removed.

Thus, in this embodiment, since hydrogen gas sputtering is started at a temperature higher than 400 ° C., diffusible hydrogen ions colliding with the engine valve 10 and entering the passive film. Undergoes a rapid reduction reaction with the passive membrane and is thereby consumed. For this reason, the passive film can be reduced and removed efficiently, and diffusible hydrogen can be prevented from remaining inside the engine nozzle 10. The force that generates H 2 O as the passive membrane is reduced This H 2 O is quickly discharged out of the system.

twenty two

Here, if hydrogen gas sputtering is started at 350 ° C. or lower, the reduction reaction of the passive film does not occur, so that only the diffusion and penetration of hydrogen ions into the engine valve 10 occurs. In addition, above 350 ° C and below 400 ° C, the diffusion permeation rate of hydrogen ions becomes larger than the reduction reaction of the passive membrane.

In such a case, the diffusion penetration state such as the depth, penetration amount, and distribution of hydrogen ions varies greatly depending on the sputtering conditions. For example, when the voltage is excessively high, the diffusion penetration amount of hydrogen ions is excessively increased, or the diffusion penetration depth of hydrogen ions is excessively increased. Therefore, it is necessary to control the sputtering conditions with high precision in order to bring hydrogen ions into the desired diffusion and penetration state in a temperature range of 400 ° C or lower.

In contrast, in the present embodiment in which hydrogen gas sputtering is performed at a temperature exceeding 400 ° C., hydrogen ions are rapidly consumed by reducing the passive film, while engine valves 10 Since hydrogen gas is released from the inside of the gas, for example, even when the voltage is somewhat high, the diffusion penetration amount of hydrogen ions is excessively increased or the diffusion penetration depth is excessive. Can be avoided. Therefore, it becomes easy to control the reduction and removal of the passive film.

[0036] Hydrogen gas sputtering is preferably performed at 450 ° C or higher. In this temperature range, hydrogen ions are released from the engine valve 10 at a high speed, while the reductive reaction of the passive membrane becomes extremely active. For this reason, the passive film can be reduced and removed without controlling the sputtering conditions with high accuracy.

[0037] When the temperature rise is continued for a predetermined time while performing hydrogen gas sputtering, most of the passive film is removed. When the temperature is further increased and the temperature exceeds 550 ° C, especially around 580 ° C, the release rate of internal force hydrogen ions decreases (see Fig. 3). That is, it is not easy to discharge hydrogen ions from the internal force of the engine valve 10, and it is not easy to avoid hydrogen ions remaining inside the engine valve 10.

Therefore, according to the present embodiment, when the temperature reaches 550 ° C. or lower, preferably 500 ° C.

At point B in Fig. 2, the introduction of nitrogen gas is started while the amount of hydrogen gas is reduced. As the nitrogen gas is introduced, the first step is completed and the second step in which the plasma nitriding treatment is performed is started. Nitrogen gas collides with the surface of the engine valve 10 from which the passive film has been reduced and removed while being ionized into nitrogen ions. As a result, the surface of the engine valve 10 is nitrided, and a nitrided layer is formed on the surface.

[0039] The vacuuming is continued and the pressure in the processing furnace is maintained at about 0.7 to 1.5 Torr.

The volume ratio of nitrogen gas and hydrogen gas may be, for example, N: H = 2: 1.

twenty two

[0040] As can be seen from this, hydrogen gas is also supplied during the plasma nitriding process. For this reason, hydrogen gas sputtering also proceeds in conjunction with the plasma nitriding treatment, which can suppress the formation of a passive film on the surface of the engine valve 10.

[0041] The temperature is further increased while plasma nitriding is performed, and reaches 520 ° C after about 20 minutes. At this point, both gases are supplied with a stable mixing ratio of nitrogen gas and hydrogen gas. Therefore, by maintaining this temperature for about 40 minutes, the engine valve 10 can be uniformly nitrided, and as a result, a nitride layer with good quality can be efficiently formed. Can do.

[0042] In a general plasma nitriding process, the supply of nitrogen gas is started when a predetermined temperature to be maintained is reached, and then maintained at a constant temperature for about 60 minutes. In this case, Retention time can be as low as 40 minutes. As can be understood from this, the plasma nitriding treatment holding time in the processing method according to the present embodiment is significantly shorter than the holding time in a general plasma nitriding method. Thus, the holding time can be shortened by starting the plasma nitriding process in the middle of the temperature rise. In other words, the processing time including the sputtering process and the nitriding process time can be shortened, and as a result, the nitride layer can be efficiently formed on the engine valve 10.

[0043] After the holding is completed, the temperature is lowered to about 200 ° C, the processing furnace is opened, and the engine valve 10 is taken out.

A nitrided layer is formed on the surface of the engine valve 10 that has been subjected to plasma nitriding. For example, the thickness of the nitride layer formed on the surface of the second rod 20 and the end 16 that also has SUH11M force is approximately 81.1 μm.

[0045] The presence of the nitride layer makes the surface of the engine valve 10 hard. Specifically, after the plasma nitriding treatment, the Vickers hardness (Hv) on the surface of the second rod 20 and the end portion 16 (SUH11M) shows a remarkably large value of 771.

[0046] The start temperature of the second step is not particularly limited, but the reduction and removal of the passive film by hydrogen gas sputtering has progressed so much that the introduction of nitrogen gas starts at that time. The thickness of the nitride layer tends to be non-uniform. That is, it becomes difficult to obtain a nitride layer with excellent quality. For this reason, it is preferable that the start temperature of the second step, that is, the temperature at which the introduction of nitrogen gas is started is close to the holding temperature. The second step may start when the holding temperature is reached.

[0047] The holding temperature is not limited to 520 ° C, but if it is excessively high, the re-forming rate of the passive film becomes larger than the reduction-removing rate, and the generated nitride is iron. Since it starts to diffuse in the group-base alloy base material (engine valve 10), it becomes difficult to form a nitride layer. In order to avoid the formation of a passive film and the diffusion of nitrides, it is preferable to set the temperature to 590 ° C or lower, and more preferable to set the temperature to 550 ° C or lower. 520 to 540 ° C It is most preferable to be within the range.

[0048] The material of the head 12 and the first rod 18 is not limited to NCF600, but may be NCF3015 or NCF440! / !. Similarly, the material of the second rod 20 and the terminal 16 is not limited to SUH11M, but may be SKH51, for example. FIG. 4 shows the thickness and Hv of the nitrided layer when NCF3015, NCF440, and SKH51 are subjected to the above hydrogen gas sputtering treatment and plasma nitriding treatment. In this case, when the temperature of the processing furnace reached 520 ° C, nitrogen gas was introduced to start the plasma nitriding treatment, and the temperature was maintained for 60 minutes.

[0049] Furthermore, the workpiece subjected to the plasma nitriding treatment is not limited to the engine valve 10, but may be a member that also has an alloy metal force mainly composed of a metal element belonging to Group 8 of the periodic table, such as Cr and Ni. Good. What is necessary is just to set suitably the holding | maintenance temperature, time, etc. of a plasma nitriding process according to the material of a workpiece | work.

Claims

The scope of the claims

[1] a first step of removing the passive film present on the surface of the iron group alloy substrate (10) by hydrogen gas sputtering;

A second step of performing a plasma nitriding treatment on the iron group alloy substrate (10) from which the passive film has been removed, and nitriding the iron group alloy substrate (10);

Have

The first step is performed by flowing hydrogen gas through the processing furnace when the temperature of the processing furnace exceeds 400 ° C. during the temperature rise until the start of the second step. A method for nitriding a group alloy base material (10).

[2] The nitriding method according to claim 1, wherein the first step is performed at 580 ° C. or lower.

[3] The nitriding method according to claim 2, wherein the first step is performed at 450 ° C. to 520 ° C.

[4] The nitriding method according to any one of claims 1 to 3, wherein the second step is started by introducing nitrogen gas during the temperature rise. Nitriding treatment method for wood (10).