JP5944797B2 - Iron-based alloy material and method for producing the same - Google Patents

Description

  The present invention relates to an iron-based alloy material that is subjected to a surface hardening treatment and a method for producing the same.

  Various surface treatment methods have been proposed as measures for improving the wear resistance and fatigue strength of an iron-based alloy material having iron as a main component typified by steel. The most widely used processing method is carburizing and quenching performed on steel. Carburizing and quenching is a process in which carbon is infiltrated and diffused from the surface while the material to be treated is heated, and the carbon concentration in the vicinity of the surface layer is increased to perform quenching treatment from the austenite state to generate martensite in the surface layer part. It is. The martensitic surface layer contributes to improvement in wear resistance and fatigue strength.

  On the other hand, carburizing and quenching generally requires high-temperature heat treatment exceeding 727 ° C. in an atmosphere containing carbon monoxide, and the amount of energy required for this heat treatment is relatively large. Therefore, it can be said that the carburizing and quenching treatment is a treatment method in which it is difficult to suppress the carbon dioxide emission that has been attracting attention in recent years. In addition, carburizing and quenching iron-base alloy materials are not only distorted due to the phase transformation from austenite to martensite (martensitic transformation), but also due to the thermal strain associated with the rapid cooling from the high temperatures described above. Usually, a post-process for adjusting the shape is required.

  As a surface hardening process often performed along with the carburizing and quenching process, there is a nitriding process. The nitriding treatment is generally a treatment for hardening the surface layer portion by forming nitrogen by intruding and diffusing nitrogen from the surface of the iron-based alloy material under conditions lower than the carburizing and quenching treatment. Treatment methods are roughly classified into gas nitriding, gas soft nitriding, salt bath soft nitriding, and plasma nitriding. All the treatments are not hardened by the change of the structure, but are hardened by forming a nitride having high hardness. Usually, quenching is not performed after the nitriding treatment.

  As described above, the nitriding treatment is usually performed at a relatively low temperature and does not involve a phase transformation. Therefore, the amount of strain generated in the obtained iron-based alloy material can be reduced. Therefore, the nitriding treatment may be preferred to the above-described carburizing and quenching treatment as a treatment capable of suppressing strain and streamlining the process. However, many of the conventional general nitriding processes mentioned above require that a long time is required for the nitrogen intrusion / diffusion process.

  As a relatively new surface hardening treatment method, there is a nitrogen quenching treatment method described in Patent Document 1. This nitriding quenching method is performed by performing nitriding treatment using ammonia at a high temperature condition compared with the conventional general nitriding treatment of 600 ° C. to 800 ° C., and diffusing nitrogen from the surface of the material to be treated. , Quenching and quenching.

  According to the nitriding quenching method of Patent Document 1, not the hardening effect by nitride in the conventional nitriding treatment but the hardening effect by martensitic transformation in the region where nitrogen diffuses can be obtained. Further, this method is superior in that the time for the nitriding treatment can be greatly shortened as compared with the conventional general nitriding treatment. Moreover, since the heating temperature before quenching can be lowered as compared with the carburizing quenching process described above, generation of strain can be suppressed accordingly.

JP 2007-46088 A

  As described above, it can be said that the nitrogen quenching treatment method of Patent Document 1 is an excellent surface hardening treatment method, but the problem is that ammonia must be used as a treatment gas. Ammonia does not only accelerate deterioration of equipment such as a heating furnace at a high temperature, but also has a number of problems such as being required to be decomposed before exhaust. In addition, when a relatively large amount of nitrogen is infiltrated by the above nitriding and quenching method, many voids may be generated near the surface layer as a result of cross-sectional observation of the article to be treated.

  As a method not using ammonia, it is conceivable to adopt a conventional general nitriding treatment as a nitriding treatment. However, as described above, many of the conventional general nitriding processes have a problem that a long time is required for the nitrogen intrusion / diffusion process. Here, among the conventional nitriding treatments, plasma nitriding is a treatment with a relatively short nitrogen infiltration / diffusion treatment time.

Specifically, in the plasma nitriding, after the inside of the processing furnace is evacuated with a vacuum pump, a mixed gas of nitrogen (N ₂ ) and hydrogen (H ₂ ) is introduced into the furnace, and in a temperature condition of less than 590 ° C., And a material to be treated, a direct current voltage is applied to generate a glow discharge between them, and nitrogen is ionized and penetrated from the surface of the material to be treated along with the glow discharge. Although it is conceivable to employ such plasma nitriding in the nitriding treatment step in the above nitriding and quenching treatment method, an alloy component such as Al or Cl is not added simply by adopting conventional plasma nitriding. Hard to harden steel.

  The present invention has been made in view of such a background, and it is possible to infiltrate nitrogen into the surface of an iron-based alloy material without using ammonia, and surface hardening treatment in which voids are suppressed even after quenching treatment. It is intended to provide an iron-based alloy material subjected to the above and a method for producing the same.

One aspect of the present invention is a plasma nitriding process in which a workpiece made of an iron-based alloy material containing iron as a main component is heated to a temperature of 590 ° C. or higher while supplying nitrogen gas without supplying hydrogen. Processing is performed to form a nitrogen diffusion layer in which 0.1 to 1.2% by mass of nitrogen enters the vicinity of the surface layer,
Thereafter, the work is rapidly cooled from a temperature of 590 ° C. or higher to produce martensite in the nitrogen diffusion layer .

Another aspect of the present invention is an iron-based alloy material mainly composed of iron,
In the vicinity of the surface layer, it has a nitrogen diffusion layer in which 0.1 to 1.2% by mass of nitrogen has entered, and the nitrogen diffusion layer is characterized in that martensite is present and voids are not present. It is in iron-base alloy material .

  As described above, the method for producing the iron-based alloy material includes subjecting the workpiece to plasma nitriding while supplying nitrogen gas without using hydrogen gas in a state where the workpiece is heated to a relatively high temperature of 590 ° C. or more. A nitrogen diffusion layer is formed. That is, in the method for producing the iron-based alloy material, introduction of hydrogen gas can be omitted, and nitrogen can be introduced from the surface of the workpiece using nitrogen gas. Therefore, it is not necessary to use conventional ammonia as a nitrogen source. Therefore, the trouble at the time of handling ammonia can be eliminated completely.

  Moreover, the workpiece | work which completed the said plasma nitriding process is quenched by quenching from a temperature of 590 ° C. or higher. As a result, the obtained iron-based alloy material can produce martensite in the nitrogen diffusion layer in which nitrogen is infiltrated to obtain a hardening effect, and reliably suppress the generation of voids in the nitrogen diffusion layer. it can. The reason why the generation of voids can be suppressed is considered to be that a small amount of hydrogen can be prevented from entering from the surface layer of the workpiece together with nitrogen by not using hydrogen gas during the plasma nitriding treatment. The reason why the hardening effect by martensite generation is obtained in the nitrogen diffusion layer is that the nitrogen nitriding treatment is performed at a higher temperature than the conventional plasma nitriding as described above, so that nitrogen can be rapidly penetrated and diffused in the nitrogen austenite layer. This is considered to be because the effect of being able to be obtained is obtained.

  An iron-base alloy material that has a nitrogen diffusion layer containing martensite in the vicinity of the surface layer and no voids in the nitrogen diffusion layer is a defect that voids become the starting point of cracks and reduce fatigue strength. Can be reliably suppressed.

  Thus, according to the above aspect, an iron-based alloy that has been subjected to a surface hardening treatment that allows nitrogen to enter the surface of the iron-based alloy material without using ammonia and that does not cause voids even after the quenching treatment. A material and a method for manufacturing the same can be provided.

It is the figure which showed typically the outline of the plasma nitriding apparatus for performing a plasma nitriding process. It is the figure which showed the profile of the plasma nitriding process and the quenching process. It is the figure which showed the nitrogen concentration profile of sample 1 to sample 3. 3 is an optical micrograph of a cross section of Sample 2. 3 is an optical micrograph of a cross section of Sample 5. It is the figure which showed the hardness profile of sample 2, and a nitrogen concentration profile. It is the figure which showed the hardness profile and nitrogen concentration profile of the sample 6. It is the figure which showed the hardness profile of sample 7, and a nitrogen concentration profile. It is the figure which showed the nitrogen concentration profile of the sample 2, the sample 6, and the sample 7. FIG. It is the figure which showed the hardness profile of the sample 2, the sample 6, and the sample 7. FIG. It is the figure which showed the hardness profile of the sample 4 and the sample 9. It is the figure which showed the hardness profile of the sample 8, the sample 9, and the sample 10. FIG.

  Examples of the iron-based alloy material include various steel materials such as carbon steel and alloy steel, stainless steel, spring steel, bearing steel, tool steel, heat resistant steel and the like. In particular, general carbon steel can be expanded in its application by surface modification, and the use of the above production method is very effective.

  Further, it is preferable that substantially no other components are mixed in the nitrogen gas supplied during the plasma nitriding treatment, but a gas other than hydrogen gas that does not adversely affect the plasma nitriding treatment is used. Mixing for some reason is acceptable. The nitrogen gas to be supplied preferably has a nitrogen partial pressure of about 100 Pa or more, more preferably about 150 Pa or more, from the viewpoint of promoting nitrogen intrusion / diffusion. Further, the nitrogen partial pressure is preferably about 1000 Pa or less, and preferably about 500 Pa or less from the viewpoint of abnormal discharge or the like.

The nitrogen diffusion layer is a layer in which 0.1 to 1.2% by mass of nitrogen has entered . By setting the nitrogen concentration of the nitrogen diffusion layer in the above range, it is possible to promote the generation of austenite (the subsequent generation of martensite) using the lowering of the quenchable temperature by the ingress of nitrogen. From the viewpoint of sufficiently obtaining the effect of lowering the quenchable temperature, the nitrogen diffusion layer is preferably a layer in which nitrogen of 0.15% by mass or more, more preferably 0.2% by mass or more has entered. be able to. On the other hand, from the viewpoints of manufacturability, suppression of voids, and the like, the nitrogen diffusion layer can be a layer in which nitrogen of 1.15% by mass or less, more preferably 1.1% by mass or less, has entered.

In addition, the quenching treatment after the plasma nitriding treatment may employ a process of directly and rapidly quenching from the heating state during the plasma nitriding treatment, but the plasma nitriding treatment and the quenching treatment may be separated. Is possible. In the case of separating the plasma nitriding treatment and the quenching treatment, after the plasma nitriding treatment, the workpiece is cooled to at least less than 590 ° C., and then the workpiece is reheated by high frequency induction heating and then the rapid cooling is performed. Can be adopted . In this case, by adopting the high frequency induction heat treatment as a heating means before the quenching treatment, the specific portion or the whole can be heat treated with high accuracy in a short time, and the production can be rationalized.

  The temperature for cooling the workpiece is preferably about 100 ° C. or less, more preferably about 35 ° C. or less, from the viewpoint of manufacturability and the like. In addition, the temperature which cools the said workpiece | work can also be about 100 degreeC or more from viewpoints, such as cost.

In the plasma nitriding treatment, the inside of the furnace charged with the work is depressurized to a vacuum degree of 1000 Pa or less, then nitrogen is introduced from a nitrogen introducing portion provided in the furnace, and then the work is moved to 590 ° C. or higher. After the temperature has been raised, an electrode or furnace wall provided in the furnace is used as an anode, and the workpiece is used as a cathode, and a direct current voltage is applied between the two to cause glow discharge .

  As described above, before introducing nitrogen into the furnace, the inside of the furnace is depressurized to a predetermined range so that the atmospheric gas existing in the furnace before the treatment is discharged and the plasma is immersed in a very clean state. Nitrogen treatment can proceed. The lower the degree of vacuum at the time of depressurization, the better. However, at least the specific degree of vacuum may be ensured from the viewpoint of equipment problems and processing time.

  The glow discharge is preferably generated between an electrode or furnace wall provided in the furnace and a workpiece. Thereby, ionization of nitrogen can be performed efficiently, and infiltration and diffusion of nitrogen can be promoted. It is also possible to use a nitrogen inlet provided in the furnace as the electrode.

  Further, the heating temperature of the workpiece during the plasma nitriding treatment is 590 ° C. or higher as described above, but the upper limit is set to 1100 ° C. because the crystal grains are likely to be coarsened in the workpiece. preferable. Moreover, in order to perform the said plasma nitriding process more efficiently, it is preferable to set it as 600-800 degreeC especially.

  Examples and comparative examples relating to the iron-based alloy material and the manufacturing method thereof will be described. In this example, a plurality of types of iron-based alloy materials (samples 1 to 10) were manufactured, and various characteristics were evaluated. First, any of materials a to c shown in Table 1 was used as a material for samples 1 to 10.

  As each sample, a bar made of the above material and having a diameter of 10 mm × length of 35 mm was prepared. Each sample (work) was subjected to a plasma nitriding treatment under the conditions described later, and then a part of the samples was subjected to a quenching treatment under the conditions described later.

  As shown in FIG. 1, a plasma nitriding apparatus 5 for performing a plasma nitriding process includes a furnace core tube 50 that is hermetically sealed and a heating device 51 disposed on the outer periphery thereof. The furnace tube 50 has a nitrogen inlet 53 connected to a nitrogen supply pipe 52 extending from an external nitrogen supply source (not shown). A work 1 (sample) installation place is provided at a position away from the nitrogen introduction unit 53 by a predetermined distance. In addition, a vacuum pump 54 for reducing the pressure inside is connected to the core tube 50. A quenching tank 60 is connected to the core tube 50 through a valve 59 so that the workpiece 1 can be put into the quenching tank without being exposed to the atmosphere. Further, a thermocouple 55 for temperature measurement is inserted and disposed in the core tube 50. A DC power source 56 for applying a DC voltage between the two with the nitrogen introducing portion 53 as an anode and the work 1 as a cathode is installed outside the core tube 50. The DC power source 56 is electrically connected to the nitrogen introducing portion 53 by an electric wire 57 and is electrically connected to the workpiece 1 by an electric wire 58. That is, in this example, the nitrogen introduction part is used as the anode.

  In the plasma nitriding treatment, the voltage and current applied by the DC power source 56 are controlled in addition to the control of the degree of vacuum, temperature, and supply amount of nitrogen gas in the core tube 50 using the plasma nitriding apparatus 5 having such a configuration. Do by controlling.

The quenching process was performed on some samples using a high-frequency induction heating device and a predetermined cooling device (not shown).
Hereinafter, specific processing conditions for each sample will be described.

<Preparation of sample>
-Sample 1-
Sample 1 employs material b (Table 1). This sample 1 was subjected to plasma nitriding treatment according to the profile shown in FIG. Specifically, first, the workpiece 1 (sample 1) was set in the furnace core tube 50 of the plasma nitriding apparatus 5, and the pressure in the furnace was reduced to 20 Pa ((A) in FIG. 2). Thereafter, only nitrogen gas was introduced from the nitrogen introduction part 53 ((B) of FIG. 2). And when the nitrogen partial pressure in the furnace reached 150 Pa, the temperature inside the furnace was started to rise ((C) in FIG. 2). Thereafter, the overheating state was controlled so that the temperature of the workpiece 1 was constant at 750 ° C., and the nitrogen partial pressure was controlled to be 150 Pa ((D) in FIG. 2, soaking). In this atmosphere state, a glow discharge was generated by applying a DC voltage between the nitrogen introducing portion 53 as an anode and the workpiece 1 as a cathode. The conditions of the DC voltage were as follows: voltage: 700 V, energization time: 2 hours ((E) in FIG. 2). Thereafter, the heating of the core tube 50 was stopped, and the sample 1 was put into the quenching tank 60, which was decompressed in the same manner as in the furnace, without being exposed to the atmosphere and rapidly cooled ((F) in FIG. 2). Sample 1 was quenched with quenching oil at 80 ° C.

-Sample 2, Sample 3-
Sample 2 and Sample 3 are made of material b as in Sample 1, and were subjected to the same plasma nitriding and quenching as Sample 1, but only the nitrogen partial pressure conditions during plasma nitriding were changed. It is a thing. In the case of sample 2, the nitrogen partial pressure was set to 200 Pa. In the case of sample 3, the nitrogen partial pressure was set to 250 Pa.

-Sample 4-
Sample 4 is the same as sample 2 but is made of material b. The sample 4 is subjected to the plasma nitriding treatment similar to that of sample 2 and is not subjected to the quenching treatment. That is, the sample 2 differs from the sample 2 only in that the quenching process was not performed.

-Sample 5-
Sample 5 employs material b in the same manner as sample 1, but is an example in which nitriding treatment using conventional ammonia as a nitrogen source was performed. The nitriding conditions for Sample 5 are the conditions for the above nitriding treatment with ammonia. Specifically, the introduced nitrogen flow rate: 5 [L / min], the introduced ammonia flow rate: 1 [L / min], the treatment temperature: 750 ° C. The treatment time was 1.5 hours. Quenching was performed by putting in quenching oil at 80 ° C. in an air atmosphere. Other conditions were the same as those of Sample 1.

-Sample 6
Sample 6 is obtained by changing the material from Sample 2, adopting material a (Table 1), and performing the same nitriding treatment and quenching treatment as Sample 2.

-Sample 7-
Sample 7 is obtained by changing the material from Sample 2, adopting material c (Table 1), and performing the same nitriding treatment and quenching treatment as Sample 2.

-Sample 8-
Sample 8 was the same as Sample 1 in that material b was used, and the same plasma nitriding treatment as Sample 1 was performed except that the treatment time was changed to 1 hour. Thereafter, heating of the core tube 50 was stopped, and the workpiece 1 was left in the furnace and allowed to cool to 35 ° C. or lower. Next, the workpiece 1 was heated to 830 ° C. by high frequency induction heating, and then water was injected and quenched.

-Sample 9, Sample 10-
Sample 9 and Sample 10 are made of material b as in Sample 8, and were subjected to plasma nitriding and quenching similar to Sample 8, but only the nitrogen partial pressure conditions during plasma nitriding were changed. It is a thing. In the case of sample 9, the nitrogen partial pressure was set to 200 Pa. In the case of sample 10, the nitrogen partial pressure was set to 250 Pa.

<Evaluation / Discussion>

  FIG. 3 shows nitrogen concentration profiles of Sample 1 to Sample 3. Samples 1 to 3 have different nitrogen partial pressures during sample preparation. An electron probe microanalyzer (EPMA) was used for measuring the nitrogen concentration.

  As shown in FIG. 3, it can be seen that introduction of hydrogen gas can be omitted, and nitrogen can be introduced from the surface of the workpiece made of the iron-based alloy material using nitrogen gas. For this reason, it is not necessary to use ammonia as a nitrogen source as in the prior art, and it can be said that problems in handling ammonia can be completely eliminated. It can also be seen that the higher the nitrogen partial pressure in the furnace during the plasma nitriding treatment, the more nitrogen can enter from the surface of the workpiece. This is considered to be because the amount of active nitrogen ions increases as the nitrogen partial pressure in the furnace increases.

  In FIG. 4, the optical micrograph of the cross section in the sample 2 is shown. FIG. 5 shows an optical micrograph of a cross section of Sample 5. The surface nitrogen concentration of sample 2 was 1.15 mass%, and the surface nitrogen concentration of sample 5 was 1.02 mass%.

  As can be seen from these results, the sample 2 subjected to the predetermined plasma nitriding treatment and quenching treatment has a higher surface nitrogen concentration than the sample 5 subjected to the conventional nitriding treatment and quenching treatment with ammonia. Nevertheless, the sample 2 has no void V formed in the nitrogen diffusion layer. Therefore, it can be said that the method of performing the predetermined plasma nitriding treatment and quenching treatment has a high effect of suppressing void generation.

  6 to 8 show the hardness profiles and nitrogen concentration profiles of Sample 2, Sample 6, and Sample 7, respectively. These figures show the hardness profile when the material is changed to pure iron (material a), S15C (material b), S35C (material c), and subjected to predetermined plasma nitriding treatment and quenching treatment under the same conditions. It shows a nitrogen concentration profile.

  As can be seen from these results, it can be seen that the hardness of the nitrogen diffusion layer increases as the nitrogen concentration increases, regardless of which material is used. Further, when these results and the results shown in FIG. 3 are combined, the nitrogen partial pressure in the furnace during the plasma nitriding process is controlled, and the nitrogen concentration of the nitrogen diffusion layer is controlled, so that the hardness of the nitrogen diffusion layer is desired. It can be said that the value can be controlled.

  FIG. 9 shows nitrogen concentration profiles of Sample 2, Sample 6, and Sample 7. FIG. 10 shows the hardness profiles of Sample 2, Sample 6, and Sample 7. These figures show a nitrogen concentration profile for each material and a hardness profile for each material.

  As can be seen from these results, there is no great difference in the surface nitrogen concentration in any sample, but it can be seen that the sample with higher carbon concentration diffuses deeper into nitrogen. The reason for this is presumed that because nitrogen is an intrusion-type atom, the steel type with more carbon may distort the iron lattice, increase the gap, and help nitrogen diffuse.

  FIG. 11 shows hardness profiles of Sample 4 and Sample 9. Sample 4 and sample 9 have the same plasma nitriding conditions, but sample 4 is air-cooled in a furnace without quenching. On the other hand, the sample 9 is obtained by induction hardening after air cooling.

  As can be seen from this result, the work is not significantly hardened only by the plasma nitriding treatment, but it is found that the work is hardened significantly by combining a quenching treatment that is rapidly cooled from a temperature of 590 ° C. or higher.

FIG. 12 shows the hardness profiles of Sample 8, Sample 9, and Sample 10. FIG. 12 shows the hardness profiles after induction hardening at each nitrogen partial pressure.
As can be seen from this result, the higher the nitrogen partial pressure, the deeper the steel is hardened. Accordingly, the nitrogen concentration in the furnace is controlled by controlling the nitrogen partial pressure in the furnace during plasma nitriding, and the hardness of the nitrogen diffusion layer is controlled to a desired value by using induction hardening together. On the other hand, it can be said that the specific part or the whole of the workpiece can be accurately heated in a short time, and the production can be rationalized.

  According to the above, an iron-based alloy material that has been subjected to a surface hardening treatment that allows nitrogen to enter the surface of the iron-based alloy material without using ammonia and that does not cause voids even after the quenching treatment, and a method for producing the same It was confirmed that we can provide.

  As mentioned above, although the Example of this invention was described in detail, this invention is not limited to the said Example, A various change is possible within the range which does not impair the meaning of this invention.

DESCRIPTION OF SYMBOLS 1 Work 5 Plasma nitriding apparatus 50 Core tube 51 Heating apparatus 52 Nitrogen supply pipe 53 Nitrogen introduction part 54 Vacuum pump 60 Quenching tank

Claims (4)

In a state where a workpiece made of an iron-based alloy material containing iron as a main component is heated to a temperature of 590 ° C. or higher, plasma nitriding treatment is performed on the workpiece while supplying nitrogen gas without supplying hydrogen, and the vicinity of the surface layer A nitrogen diffusion layer in which 0.1 to 1.2% by mass of nitrogen has entered,
Then, the said workpiece | work is rapidly cooled from the temperature of 590 degreeC or more, The martensite is produced | generated in the said nitrogen diffusion layer, The manufacturing method of the iron-based alloy material characterized by the above-mentioned. 2. The method for producing an iron-based alloy material according to claim 1, wherein after the plasma nitriding treatment, the workpiece is cooled to at least less than 590 ° C., and then the workpiece is reheated by high-frequency induction heating and then the rapid cooling is performed. A method for producing an iron-base alloy material characterized by the above. 3. The method of manufacturing an iron-based alloy material according to claim 1, wherein the plasma nitriding treatment is performed by introducing the nitrogen provided in the furnace after reducing the vacuum inside the furnace charged with the workpiece to a vacuum degree of 1000 Pa or less. After introducing nitrogen from the part, the temperature of the work was raised to 590 ° C. or higher, and then the electrode or furnace wall provided in the furnace was used as an anode and the work was used as a cathode, and a direct current voltage was applied between them to grow A method for producing an iron-based alloy material, characterized by performing discharge. An iron-based alloy material mainly composed of iron,
  In the vicinity of the surface layer, it has a nitrogen diffusion layer in which 0.1 to 1.2% by mass of nitrogen has entered, and the nitrogen diffusion layer is characterized in that martensite is present and voids are not present. Iron-based alloy material.