JP2015078416A - Heat treatment method of steel product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve strength and durability of a steel product by preventing delayed fracture (hydrogen embrittlement) caused by hydrogen in a carburization heat treatment method using a gas.SOLUTION: A hydrogen-free carbon compound gas such as CO gas is used as a carbon source gas. The hydrogen-free carbon compound gas introduced in a furnace 1 by vacuuming is separated into C and O when contacting a steel product W at a high temperature and the C penetrates in a surface layer of a work piece to form a carburized layer. Because of no penetration of hydrogen, no vacancy is generated between grains of the work piece. Strength and durability of the work piece are thus improved. A catalyst 14 is preferably used to promote separation of CO. When a hydrocarbon gas is used as a carbon source, hydrogen is deactivated by a chemical action or physical action to prevent penetration of hydrogen to the work piece.

Description

  The present invention relates to a heat treatment method for steel products (steel members) made of carbon steel or alloy steel. The alloy steel includes various types mainly composed of iron (Fe) such as chromium steel, molybdenum steel, chromium-molybdenum steel, bearing steel, and stainless steel. Steel products include a wide variety of fasteners such as bolts, tappings, drive-in pins, various shafts, gears, shafts, bearings, and the like.

  Heat treatment of steel products includes quenching, tempering, and tempering. As this heat treatment method, an atmospheric gas atmosphere furnace (atmosphere furnace) or a reduced pressure (vacuum) gas atmosphere furnace (vacuum furnace) is used. A method (gas treatment method) of exposing a gas to a high-temperature gas is widely used. In the case of carburizing heat treatment using these furnaces and gas, there are carburizing quenching and carbonitriding quenching, but the amount of carbon contained in the gas used for heat treatment of steel products is contained in the raw material carbon steel and alloy steel It is controlled by the “carbon potential (equilibrium carbon concentration%)” corresponding to the amount of carbon present.

“Propane (C ₃ H ₈ )” and “acetylene (C ₂ H ₂ )” are mainly used as the carbon potential supply source (carbon source), but “hydrogen (H ₂ )” is used in the process. Occur. Since hydrogen has the smallest molecular weight among all elements, it has the property that it can easily penetrate into the grain boundaries of steel, and this causes “delayed fracture (hydrogen embrittlement)” of steel product fracture. .

  Therefore, hydrogen storage in the heat treatment stage is unavoidable, and it has been proposed or practiced to remove “hydrogen” from the steel product after the heat treatment and quenching. For example, hydrogen is removed by tempering (for example, Patent Document 1), and the steel product is kept at a temperature equal to or lower than the tempering temperature to remove hydrogen (for example, Patent Document 2).

  Since hydrogen is also contained in the atmosphere and in lubricants, if hydrogen enters the steel product from the outside after quenching, the problem of hydrogen embrittlement will still appear. Therefore, shot peening is also performed on the surface of steel products as a means for preventing hydrogen from entering after quenching (for example, Patent Document 3).

JP 05-255733 A Japanese Patent Laid-Open No. 11-029820 Japanese Patent Application Laid-Open No. 07-29212

  It is common sense that delayed fracture (hydrogen embrittlement) of steel products caused by hydrogen is caused by hydrogen itself, and no hydrogen occlusion occurs during the heat treatment process, and hydrogen occlusion occurs during surface treatment after heat treatment. (Especially during electroplating).

  Grain boundary fractures are observed on the fracture surface of steel products due to hydrogen embrittlement, but if the general sense that hydrogen embrittlement is caused by the presence of hydrogen is correct, hydrogen can be completely removed by tempering in the heat treatment process. Thus, the phenomenon of delayed fracture should not occur, and the fracture surface should exhibit a ductile fracture surface rather than a grain boundary fracture surface.

  However, the inventors of the present application pull the test pieces (bars) of carbon steel and chrome / molybdenum steel heat-treated with hyper-eutectoid, eutectoid and hypoeutectoid carbon potentials, and observe the fracture surface in detail. As a result, despite the fact that hydrogen should have been completely removed by tempering in the heat treatment step, a grain boundary fracture surface (see FIG. 12) was found on the fracture surface in any specimen ((B) It is the elements on larger scale of (A).).

  Having witnessed the results different from the common general knowledge, the inventors of the present application suspected hydrogen storage during the heat treatment process, and measured the amount of diffusible hydrogen during each process of quenching and tempering. As a result, a large amount of hydrogen occlusion was observed during quenching, but an amount of hydrogen that caused delayed fracture was not observed during tempering.

  However, since a brittle fracture surface showing traces of hydrogen storage is observed on the fracture surface of the test piece from which this hydrogen should have been released, the test piece (carbon steel (SWCH22A)) is polished and the nital solution When this was observed with an electron microscope, as shown in FIG. 13, it was found that there were innumerable pores (gap) S reaching the depth of the carburized hardened layer of the steel product. It was. Since vacancies S exist at the same locations as the grain boundary fracture surfaces showing traces of hydrogen occlusion, it came to be believed that these vacancies S were traces of hydrogen that entered and was released into the steel during heat treatment.

  In other words, even though the hydrogen that has entered the steel product from the surface layer during quenching is released by tempering, the infinite number of vacancies S formed during the release continue to exist at the grain boundary, so the bond between particles is reduced. As a result, it is assumed that the product strength is reduced. In addition, since there are an infinite number of large holes S, it is presumed that there is a high possibility of inducing a delayed fracture phenomenon that will occur after actual use.

  Thus, when hydrogen penetrates into the steel in the heat treatment step, the fracture surface of the surface layer portion of the steel product exhibits a brittle fracture surface due to hydrogen occlusion, and vacancies S indicating traces of hydrogen release remain. Therefore, it is important to prevent hydrogen from entering during heat treatment such as quenching.

  The present invention has been made on the basis of knowledge based on such research and analysis, and is intended to supply a high-strength steel product that hardly or does not cause delayed fracture due to hydrogen storage. This is the main purpose.

  Although the present invention has many configurations, typical examples are specified in claims 1 to 8. Of these, the invention of claim 1 is a heat treatment method for enhancing the mechanical properties of the steel product by exposing the steel product to a high-temperature carbon-containing gas in a furnace in a high-temperature atmosphere, and no or little hydrogen is present. It is characterized in that the treatment is performed in a state or in an inactivated state so as not to penetrate into the steel product even if it exists.

  In the invention of claim 2, a vacuum furnace is used as the furnace, and in the invention of claim 3, an atmospheric furnace is used as the furnace. In the invention of claim 4, the heat treatment is performed by any one or more of quenching and tempering or tempering. In the invention of claim 5, a carbon compound gas not containing hydrogen is used as the carbon-containing gas.

  In the invention of claim 6, the carbon compound gas of claim 5 is entirely or mostly carbon monoxide (CO) gas. A seventh aspect of the present invention provides the steel product according to any one of the first to fourth aspects, wherein a gas containing hydrogen is introduced into the furnace before or after the hydrogen is introduced into the furnace. Inactivated not to penetrate inside. The invention of claim 8 is the method according to any one of claims 1 to 7, wherein a catalyst for promoting separation of carbon from the carbon-containing gas is disposed inside the furnace.

  In the present invention, since hydrogen does not enter the steel product in the furnace during the heat treatment, voids due to hydrogen do not occur in the surface layer of the steel product. Therefore, the problem of hydrogen embrittlement (delayed fracture) in which the steel product in use suddenly breaks does not occur, and the steel product can ensure high strength and durability. In addition, since a tempering process and a heat retaining process for removing hydrogen are unnecessary, the number of steps can be reduced and high hardness can be maintained. Furthermore, since no voids are generated due to hydrogen storage, it can contribute to the improvement of corrosion resistance.

  The present invention can be applied to a vacuum furnace as in claim 2 or to an atmospheric furnace as in claim 3 because the vacuum furnace is excellent in carbon penetration efficiency into steel products. Suitable for quenching. On the other hand, the atmospheric furnace has an advantage that a large amount of steel products can be processed.

  The present invention can be applied to various heat treatments as in claim 4, but in any case, the quality can be improved by preventing hydrogen occlusion in the steel product.

  When a gas not containing hydrogen is used as in claim 5, it is not necessary to separate hydrogen, so that the structure can be simplified and the quality can be stabilized. Various carbon compound gases containing no hydrogen can be used, but the carbon monoxide (CO) gas specified in claim 6 is preferable in view of carbon separability and availability. .

A carrier gas and an enriched gas may be used as the processing gas. When the carrier gas is used in claims 5 and 6, the carrier gas should be non-intrusive (non-diffusible) to the steel product. Thus, hydrogen stored in the steel product can be eliminated or minimized. As the non-infiltrating (non-diffusing) gas for the steel product, “nitrogen (N ₂ )”, “argon (Ar)”, “helium (He)”, etc. are suitable. An appropriate amount of the same non-hydrogen-based carbon-containing gas as in the previous section is added to the “enriched gas”.

In claim 5, only the non-hydrogen-based carbon-containing gas is added to the enriched gas. Thus, if a non-hydrogen based gas containing carbon and carbon monoxide (CO) ", a chemical reaction at the interface of the steel product is a Budowa reaction of Fe + 2CO = [Fe-C ] + CO 2. Of course, there is no generation of hydrogen during processing, so there is no need to consider the storage of hydrogen in the steel product.

Then, due to the Boudwa reaction, carbon C is taken into the interface of the steel product and oxygen O is separated. The case where oxygen O is combined with carbon monoxide, the case where the surface of the treated steel product is oxidized, and the case where oxygen (O ₂ ) is assumed are also assumed. Is also preferable. It would be optimal to use carbon dioxide (CO ₂ ) as the furnace atmosphere after carbon is taken into the steel by carburization.

Even in the case where hydrogen is contained in the gas for heat treatment as in claim 7, for example, a carrier gas (carburizing gas) and an enriched gas may be used. Conventionally, propane gas (C ₃ H ₈ ) ”or“ acetylene (C ₂ H ₂ ) ”has been used as the enriched gas, but hydrogen is generated by thermal decomposition. As a means for inactivating this hydrogen, for example, a non-hydrogen-based carbon-containing gas can be added.

Thus, when the carbon-containing gas for deactivation is carbon monoxide (CO),
3C ₂ H ₂ → 6 (C) + 3H ₂
2C ₂ H ₂ + 2CO → 6 (C) + 2H ₂ O
Thus, the amount of acetylene gas is 2/3. Considering the decomposition speed of carbon monoxide (CO) and “acetylene (C ₂ H ₂ )”, the acetylene gas (C ₂ H ₂ ) is clearly faster and into the steel of “hydrogen H ₂ ” generated by thermal decomposition. Therefore, it is preferable that carbon monoxide (CO) gas is added first, and then acetylene gas (C ₂ H ₂ ) is added.

Conventionally, for heat treatment of steel products, carrier gas transformed by a transformation furnace or carrier gas produced by dropping an organic liquid has been used, and hydrogen inevitably contained in these various gases is , “Pressure swing adsorption method PSA (Pressure Swing Adsorption)” or “gas film (for example, Japanese Patent Laid-Open No. 5-317708)” can be used for separation. Further, hydrogen contained in the hydrocarbon-based gas as the enriched gas can be inactivated as “water (H ₂ O)” by adding an appropriate amount of a non-hydrogen-based carbon-containing gas.

When propane gas (C ₃ H ₈ ) is used as the enriched gas and carbon monoxide (CO) is used as the non-hydrogen carbon-containing gas, the chemical reaction formula is
C ₃ H ₈ → 3 (C) +8 (H)
C ₃ H ₈ + 4CO → 7 (C) + 4H ₂ O
Thus, the amount of propane gas is 3/7 compared to the conventional method. As the non-hydrogen-based carbon-containing gas for inactivating hydrogen of the hydrocarbon-based gas, oxygen, ozone, air, or the like can be used instead of carbon monoxide (CO).

FIG. 14 shows a graph published as FIGS. 9 and 12 in a non-patent document “Denso Technical Review VOL5 NO1 2000“ Vacuum Carburization Using Acetylene ”(DENSO Corporation). 14A shows how C ₂ H ₄ and CH _n as material gases react in a furnace without a processed product (steel product), and FIG. 14B shows the material It shows how C ₂ H ₄ and CH _n as gases react in a furnace with treated products (whether plot points are displayed in the figure of the paper, but the plot points are discarded in FIG. 14) doing.).

From comparison of (A) and (B) in FIG. 14, it can be read that when a steel product (processed product) is put into a furnace, the material gas is separated and a large amount of hydrogen gas (H ₂ ) is generated. However, this is presumed to prove that the steel product itself acts as a catalyst to promote the separation of the material gas. In heat treatment using a vacuum furnace or an atmospheric furnace, it is clear that a part of the material gas is thermally decomposed, and it was traditionally assumed that steel products act as a catalyst. It can be said that the paper of Denso Technical Review VOL5 NO1 2000 proves that the conventional guess was correct.

  Also in the present invention, by providing a catalyst in the furnace as in claim 8, it is expected that efficient and stable heat treatment can be realized by promoting gas separation. As the catalyst, various metals such as nickel, copper, titanium, gold, silver and platinum can be used, and various arrangements of the catalyst are also conceivable. The example is clarified in the embodiment.

It is a conceptual diagram of the apparatus which concerns on 1st Embodiment, (A) is a longitudinal front view, (B) is a side view of a furnace. It is a figure which shows 2nd-4th embodiment. It is a figure which shows 5th Embodiment. It is a figure which shows 6-9 embodiment. It is a figure which shows 10th Embodiment. It is a schematic diagram of 11th Embodiment. It is a conceptual diagram of 12th Embodiment. It is a schematic diagram of 13th Embodiment. It is a schematic diagram of 14th Embodiment. It is a schematic diagram of 15th Embodiment. (A) is a partial conceptual diagram of 16th Embodiment, (B) is a partial conceptual diagram of 17th Embodiment. It is a microscope picture which shows the fracture state of the conventional steel product. It is a microscope picture which shows the trace in which hydrogen existed conventionally. It is the graph which extracted a part of nonpatent literature.

(1). Outline of Apparatus Used in First Embodiment Next, an embodiment of the present invention will be described with reference to the drawings. First, the first embodiment shown in FIG. 1 will be described. This first embodiment is embodied in a heat treatment (vacuum carburization) using a vacuum furnace, and the furnace 1 includes a bottomed cylindrical main body 2 having one end opened, and the main body 2 has an opening horizontally. A rotary door 2a is attached. Note that both ends of the main body 2 may be opened and doors may be provided at both ends. The furnace 1 may be box-shaped.

  A number of heaters 3 are arranged inside the furnace 1. The heater 3 has a rod-like shape and extends in the axial direction of the furnace 1, and a large number of heaters 3 are arranged in parallel in a state of being separated in the circumferential direction. The form and arrangement of the heater 3 can be arbitrarily set, such as being arranged in a state of being wound in the circumferential direction. The heater 3 is made of a metal such as nichrome and is not a carbon heater.

  A workpiece storage trough 4 is arranged in the approximate center of the furnace 1. The work storage trough 4 has a rectangular box shape opened upward, and is made of a porous material such as a wire net or punching metal, and is supported by the frame 5 via a frame (not shown). Needless to say, the workpiece storage trough 4 can be removed from the furnace 1.

  One or a plurality of exhaust ports 6 are opened inside the furnace 1, and a discharge passage 8 sucked by a vacuum pump 7 is connected to the exhaust port 6. A filter or the like is provided in the middle of the discharge passage 8. A processing chamber 9 provided with is inserted. When combustible gas is discharged, it is burned downstream of the vacuum pump 7. In addition, although the exhaust port 6 is provided in the trunk | drum of the furnace 1, you may provide in the bottom part on the opposite side to the door 2a.

  The furnace 1 is provided with one or a plurality of gas introduction ports 10, and a carbon monoxide (hereinafter abbreviated as CO) gas cylinder 13 is connected to the gas introduction port 10 via a gas introduction passage 11. Yes. A fixed amount tank 12 for introducing a certain amount of CO gas is inserted into the gas introduction passage 11.

  Furthermore, a catalyst 14 surrounding the work storage rod 4 is disposed inside the furnace 1 used in the present invention. The catalyst 14 is made of a metal porous material such as a wire mesh or punching metal, and surrounds the entire circumference of the work storage case 4. Accordingly, the portion of the catalyst 14 located on the back door 2a side is an openable lid, and the work storage rod 4 can be taken in and out by opening the lid. Although the catalyst 14 has a cylindrical shape, the catalyst 14 may have a square shape similar to the workpiece storage rod 4.

  The catalyst 14 may be an iron-based material, but it is presumed that a material that does not penetrate carbon is preferable. Therefore, nonferrous metals are preferred. For example, simple substance or alloy, such as nickel, copper, tungsten, titanium, is mentioned. It is also possible to use a wire mesh made of different materials, or to arrange the catalysts 14 of different materials in parallel. Since copper is used as a carburizing prevention material and itself is not violated by carbon, it can be said that it is suitable as a catalyst.

  As the material of the catalyst 14, other metals such as vanadium, manganese, cobalt, zinc, zirconium, niobium, molybdenum, palladium, silver, tin, tantalum, platinum, gold, lead, bismuth and the like can be used. Of course, an alloy composed of a plurality of types of various metals can also be used. Furthermore, since only the surface functions as a catalyst, the same catalytic effect as that of the metal of the plating layer can be obtained by plating a base material such as iron.

  It is also possible to use an inorganic material such as ceramic as a base material, form a metal layer by dipping, and allow the metal layer or plating layer to function as a catalyst. From the economical point of view, it is beneficial to plate a precious metal such as gold or silver on an inexpensive metal such as copper or iron.

(2). Method of First Embodiment In this embodiment, CO gas is filled into the metering tank 12 from the cylinder 13 and then the CO gas is decompressed at a high temperature (for example, about 930 to 1050 ° C.) ( The inside of the furnace 1 evacuated) is filled at once. The steel product W is heated to the atmospheric temperature inside the furnace 1. Then, the high-temperature CO filled in the furnace 1 reacts with the surface layer portion of the heated steel product W, and carbon (C) forms a carburized layer in the steel product W.

  It is not clear at what stage the CO gas is separated into C and O, but it is presumed that the CO gas is roughly divided into when it contacts the catalyst 14 and when it contacts the steel product W (and the work storage basket 4). . Since the carbon molecules separated from the CO gas are considered to have a high property of bonding to each other to form carbon particles, it is preferable that the C is separated from the CO gas as close to the steel product W as possible. .

  Therefore, in this embodiment, as an efficiency improvement measure, a) The separation performance of C by the contact with the steel product W is enhanced by destabilizing CO into a state where it can be easily separated into C and O by the catalyst 14. B) Bring the catalyst 14 as close to the steel product W as possible, and immediately contact the C separated by the catalyst 14 with the steel product W. c) Subdivide the steel product W into a large number of workpiece storage rods 4 and store the steel product W. It is conceivable that the work storage trough 4 has a closed structure with a lid so that the work storage trough 4 has a catalyst function to promote the separation of C.

  In the case where the contact of C to the steel product W is suppressed because the workpiece storage basket 4 is made of metal, the workpiece storage basket 4 (at least the surface thereof) may be made of ceramic. If the formation of the carburized layer is insufficient in one treatment, the filling and discharging of CO gas may be repeated at very short time intervals.

  It is possible that the CO gas is not completely separated into C and O but is discharged as it is, but in this case, the CO gas is taken out of the waste gas by means of liquefaction / separation and reused. May be. Further, the amount of CO gas required for carburizing a predetermined amount of steel product W can be obtained by calculation. Therefore, a sensor for measuring the concentration of CO gas is provided in the discharge passage 6, and the amount of CO gas in the discharge passage 6 is The CO gas may be returned to the furnace 1 until the concentration becomes lower than a predetermined value (return of the exhausted gas to the furnace 1 is performed while the furnace 1 is decompressed). Thereby, a carburized layer having a desired depth can be formed on the steel product W without wasting the raw material gas.

In the present embodiment, the raw material gas may be another carbon compound gas instead of the CO gas. For example, CO ₂ can be used. Although CO ₂ has high chemical stability and it is difficult to separate C in a normal state, it can be said that C can be easily separated by selecting the material of the catalyst 14 or the like.

(3). Second to Fifth Embodiments It is assumed that the decomposition of gas proceeds more easily as the temperature increases. On the other hand, if the atmospheric temperature in the furnace is excessively increased, the particles of the steel product are combined to cause a coarsening phenomenon, which lowers the strength of the steel product. Therefore, when the atmospheric temperature in the furnace is maintained at an appropriate temperature (for example, 880 to 950 ° C.), the carbon separation gas can be improved by preheating the carbon compound gas to a temperature higher than the furnace temperature and then ejecting it into the furnace. It is guessed. In FIG. 2, the example of the preheating means of this hydrogen-free carbon compound gas is shown.

  In the second embodiment shown in FIG. 2A, a gas heating furnace 17 is inserted in the gas introduction passage 11 so that the carbon compound gas (CO gas) is heated to a temperature higher than the inside of the heating furnace 1 (for example, 950). To 1000 ° C.). Reference numeral 18 denotes a heater.

  By preheating in this way, the binding force between carbon and oxygen constituting the CO gas is weakened, the rate of thermal decomposition increases, and the resolution rate when contacting with a steel product is increased. Since there is a concern that carbons bond to each other and grow into carbon particles over time after pyrolysis, it can be said that the preheating of the carbon compound gas is preferably performed in as short a time as possible before jetting.

  In the third embodiment shown in FIG. 2B, an appropriate number of gas jets 19 projecting into the furnace 1 are provided, and the preheated CO gas is jetted as close to the steel product W as possible. According to this configuration, it can be said that the efficiency can be improved because the gas can be concentrated on the steel product.

  In the fourth embodiment shown in FIG. 2C, an annular preheat space 21 partitioned by a wall 20 is formed inside the furnace 1, and many heaters 18 are provided in the preheat space 21. The wall 20 has a heat insulating property, and a number of gas outlets 19 are provided. The gas outlet 19 is provided with a valve (not shown), and the valve is opened and closed by an actuator 22 provided on the outer surface of the main body 2.

  FIG. 3 also shows an example of preheating means. In this example, two gas heating furnaces, a first gas heating furnace 17a and a second gas heating furnace 17b, are provided in the gas introduction passage 11, and a carbon compound gas ( CO) gas is heated in two stages. In this embodiment, an air supply pump 23 is provided on the downstream side of the gas heating furnaces 17a and 17b, respectively, so that the CO gas is pressurized to a high pressure in advance and jetted into the furnace at a high speed.

(4). Sixth to Ninth Embodiments FIG. 4 shows another example of the catalyst 14. First, in the sixth embodiment shown in FIG. 4A, the work storage trough 4 is also used as the catalyst 14 and the shallow work storage troughs 4 are stacked in multiple stages, so that the surface area of the work storage trough 4 as the catalyst 14 is increased. The sum is large. The steel product W stored in the uppermost work storage basket 4 is covered with a wire mesh lid 25 as the catalyst 14.

  In the seventh embodiment shown in FIG. 4B, the steel products W and the partition net-like catalyst 14 are alternately stacked inside the work storage basket 4 that functions as the catalyst 14. Also in this case, the total area of the catalyst 14 becomes very large, so that the separation performance of the catalyst 14 can be improved.

  In the eighth embodiment shown in FIG. 4C, a large number of rod-shaped catalysts 14 are erected on the work storage trough 4 (may be mounted sideways). Also in this case, since the gas is efficiently decomposed inside the workpiece storage trough 4 due to the presence of the catalyst 14, the steel product W can be carburized evenly and efficiently.

  In the ninth embodiment shown in FIG. 4 (D), the catalyst 14 has a ball shape, and a large number of the catalyst 14 is put into the workpiece storage case 4 in a state of being mixed with the group of steel products W. The work storage rod 4 also has a perforated structure and functions as a catalyst 14. The outer periphery is finer than the outer diameter of the catalyst 14, while the bottom is the roughness of the eyes through which the catalyst 14 can pass. When a receiving mesh 26 having a mesh size smaller than the outer diameter of the catalyst 14 is arranged on the bottom of the catalyst 4 and the receiving mesh 26 is slid, the catalyst 14 falls below the work storage rod 4. The dropped catalyst 14 is received in the container 27. Therefore, only the steel product W can be performed in a process such as oil cooling.

(5). Tenth Embodiment FIG. 5 shows a tenth embodiment. In this embodiment, the carburizing method is performed in the same pattern as in the prior art, but pulse carburizing is performed in which the ejection and discharge of gas are repeated in the carburizing process. In this embodiment, as shown in (B), the gas introduction passage 11 and the discharge passage 8 are connected by a bypass passage 28, and a heater (not shown) and a carbon source 29 are connected to the bypass passage 28. Are inserted in the combined reactor 30.

  The gas introduction passage 11 and the bypass passage 28, and the discharge passage 8 and the bypass passage 28 are connected via a three-way valve 31, respectively. Further, a vacuum pump (or blower) 32 is interposed between the gas introduction passage 11 and the compound reactor 30 in the bypass passage 28.

  In this embodiment, the CO gas ejected into the furnace returns to the furnace again via the compound furnace 30, but oxygen separated from carbon in the furnace contacts the carbon source 29 in the compound furnace 30. As a result, it becomes CO and returns to the furnace 1 again. Therefore, the CO gas can be circulated through the furnace 1 many times without decreasing the carbon concentration (or suppressing the decrease amount). Therefore, it is economical. When performing pulse carburization, as shown in (C), it is possible to perform evacuation gradually.

(6). First to Fifteenth Embodiments In the eleventh embodiment shown in FIG. 6, gas inlets 10 are provided at a plurality of locations (four locations) around the furnace 1. In addition, an exhaust port 6 is opened at the center of the furnace 1, and the workpiece storage trough 4 has a donut shape so as to surround the exhaust port 6. Two layers of the catalyst 14 are arranged.

  In the twelfth embodiment shown in FIG. 7, the reticulated catalyst 14 is configured in two layers of an outer layer 14a and an inner layer 14b, and a DC power supply 15 is connected to both the layers 14a and 14b. A potential difference is provided between them. The separation of CO gas can be expected to be accelerated by the potential difference.

(7). Thirteenth to Fourteenth Embodiments A thirteenth embodiment shown in FIG. 8 embodies claim 7. In this embodiment, a hydrocarbon gas such as acetylene or propane is used as a raw material gas, and oxygen is used as a gas for inactivating hydrogen of the hydrocarbon gas. Therefore, it has a hydrocarbon gas cylinder 34 and an oxygen gas cylinder 35.

A predetermined amount of hydrocarbon gas and oxygen gas are mixed and stored in the metering tank 12, and this is introduced into the furnace 1 at a reduced pressure. Then, by the reaction of C _n H _2m + (1/2) _m O ₂ → C _n + mH ₂ O, C was separated (released) from the hydrocarbon gas and hydrogen was inactivated and separated (released). C is permeated into the surface layer portion of the steel product W by the action of heat.

In the thirteenth embodiment, hydrocarbon gas and oxygen gas are mixed in the metering tank 12, but in the fourteenth embodiment shown in FIG. 9, hydrocarbon gas and oxygen are introduced into the furnace 1 from separate gas inlets 10. Introducing gas. In both embodiments, N ₂ may be filled instead of oxygen gas. In this case, ammonia is generated instead of water.

  The fifteenth embodiment shown in FIG. 10 is a modification of the thirteenth and fourteenth embodiments, and a hydrocarbon gas and an oxygen gas are introduced into the furnace 1 (both gases are mixed as shown in FIG. 8). May be introduced.) In this embodiment, the hydrogen absorbing material 36 is disposed between the catalyst 14 and the work storage case 4 to prevent hydrogen separated into a single substance without reacting with oxygen from coming into contact with the steel product W. ing. As the hydrogen absorber 36, for example, a hydrogen storage alloy can be used.

  In the embodiment of FIG. 10, it is possible to introduce only the hydrocarbon gas into the furnace 1 without introducing the oxygen gas and allow the hydrogen absorbent 36 to absorb the hydrogen separated by the catalyst 14. . In this case, it becomes a specific example of a configuration in which hydrogen is inactivated by a physical action.

(5). Sixteenth and Seventeenth Embodiments The embodiment shown in FIG. 11 is a specific example of a method for inactivating hydrogen by physical action. Among these, in 16th Embodiment shown to FIG. 11 (A), the pre-processing chamber 37 is arrange | positioned in the part between the fixed_quantity | quantitative_assay tank 12 and the furnace 1 among the gas introduction passages 11, inside the pre-processing chamber 37, The catalyst 14 and the heater 38 are alternately arranged, and the hydrogen absorbing material 36 is arranged in the exit side portion of the pretreatment chamber 37.

In this embodiment, the main source gas is a hydrocarbon gas such as acetylene or propane (city gas can also be used), and the hydrocarbon gas is separated into C and H ₂ in the pretreatment chamber 37, and H ₂ is hydrogen. Only C collected by the absorbent 36 is introduced into the furnace 1. The H ₂ gas collected in the hydrogen absorbing material 36 is recovered and effectively used as fuel.

The separation step in the pretreatment chamber 37 can be performed in a state where the pretreatment chamber 37 and the furnace 1 are communicated with each other. However, the separation step is performed in a state where the pretreatment chamber 37 is closed, and then the gas is removed. C in a state may be introduced into the furnace 1. In this case, N ₂ gas may be introduced into the furnace 1 in order to secure the pressure inside the furnace.

When separation of C from hydrocarbon gas is performed in the pretreatment chamber 37, it is expected that carbon will be bound and carbon particle formation will progress. However, a carrier gas that reaches the steel product W with ionized carbon remains as it is. It is also beneficial to enclose it in a pretreatment chamber. As the carrier gas, N ₂ , CO, CO _{2 and the} like can be considered. On the other hand, when C particles become a workpiece and reaches the workpiece, the C particles are regarded as a raw material for solid carburization, and once ionized carbon is attached to the surface of the workpiece, decompression is released and heating is performed for a predetermined time. It is possible to carburize by continuing to do so.

  The seventeenth embodiment shown in FIG. 11 (B) is another example of the hydrocarbon gas decomposition treatment means. In the pretreatment chamber 37, heaters 38 and high-voltage charging materials 39 are alternately arranged, and the high-voltage charging material 39. In addition, a high voltage obtained by increasing the voltage of the AC power supply 40 by the transformer 41 is applied. The hydrogen absorbing material 36 is arranged as another case on the downstream side of the pretreatment chamber 37. The high-voltage charging material 39 is composed of a porous material such as a wire mesh, and gas can pass freely.

In this embodiment, the hydrocarbon gas is supplied with electrons in the process of passing through the high-voltage charging material 39, so that the hydrocarbon gas is exposed to plasma, and the hydrocarbon gas is separated into C and H _2. It is expected to be promoted. It is also possible to use the catalyst 14 in combination. Although not shown in the figure, the steel product W can be charged and then exposed to a carbon compound gas such as CO gas.

(6). Others The present invention can be embodied in various ways other than the above embodiment. For example, in the case of claim 7, it is also possible to use dry air as a gas for inactivating hydrogen and react the hydrogen separated from the hydrocarbon gas with oxygen to change it into water.

  The present invention is actually applicable to a vacuum carburizing and quenching method. Therefore, it can be used industrially.

W Steel product 1 Vacuum carburizing and quenching furnace 2 Furnace main body 3 Heater 4 Workpiece storage 6 Exhaust port 7 Vacuum pump 10 Gas inlet 12 Metering tank 13 CO gas cylinder 14 Catalyst 34 Hydrocarbon gas cylinder 35 Oxygen gas cylinder

Thus, when the carbon-containing gas for deactivation is carbon monoxide (CO),
3C ₂ H ₂ → 6 (C) +6 (H)
2C ₂ H ₂ + 2CO → 6 (C) + 2H ₂ O
Thus, the amount of acetylene gas is 2/3. Considering the decomposition speed of carbon monoxide (CO) and “acetylene (C ₂ H ₂ )”, the acetylene gas (C ₂ H ₂ ) is clearly faster and into the steel of “hydrogen H ₂ ” generated by thermal decomposition. Therefore, it is preferable that carbon monoxide (CO) gas is added first, and then acetylene gas (C ₂ H ₂ ) is added.

Claims (8)

A heat treatment method for enhancing the mechanical properties of the steel product by exposing the steel product to a high temperature carbon-containing gas in a furnace in a high temperature atmosphere,
The treatment is carried out in a state in which there is no or almost no hydrogen, or in a state of being deactivated so as not to penetrate into the steel product even if present.
Heat treatment method for steel products. A vacuum furnace is used as the furnace,
A heat treatment method for a steel product according to claim 1. An atmospheric furnace is used as the furnace,
A heat treatment method for a steel product according to claim 1. The heat treatment is any one or more of quenching and tempering or tempering,
The heat processing method of the steel products in any one of Claims 1-3. Carbon compound gas not containing hydrogen is used as the carbon-containing gas,
The heat processing method of the steel products in any one of Claims 1-4. The carbon compound gas is entirely or mostly CO gas.
A method for heat treating a steel product according to claim 5. Gas containing hydrogen is introduced into the furnace, and the hydrogen is inactivated so as not to penetrate into the steel product before or after being introduced into the furnace.
The heat processing method of the steel products in any one of Claims 1-4. Inside the furnace, a catalyst is arranged to help separate carbon from the carbon-containing gas,
The heat processing method of the steel products in any one of Claims 1-7.