Heat treatment equipment and heat treatment method

Abstract

To provide heat treatment equipment capable of subjecting an article to be treated to a series of heat treatments of vacuum carburization and following nitriding and capable of solving the problem of unstable control for nitriding.SOLUTION: Heat treatment equipment 1 includes a batch-type carburization chambers 12-1, 12-2 and a nitriding chamber 13. An article to be treated W is carburized in the carburization chambers 12-1, 12-2 and the carburized article to be treated W is nitrided in the nitriding chamber 13. Atmosphere control means in the nitriding chamber 13 includes an ammonia sensor 182 for sensing ammonia concentration in an atmosphere gas and a control unit 186 for controlling the ammonia concentration in an atmosphere gas. The control unit 186 introduces an ammonia-containing gas into the nitriding chamber 13 at a predetermined condition and carries out ammonia concentration raising treatment for raising the ammonia concentration in an atmosphere gas and target concentration maintaining treatment for feedbacking the ammonia concentration sensed by the sensor and adjusting a flow rate of the gas to be introduced.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to a heat treatment apparatus for performing carburizing and nitriding treatment on a workpiece, and a heat treatment method using the same. [Background technology]

[0002] In metal materials such as steel, carburizing is performed as a surface treatment to improve properties such as surface hardening, by introducing carbon atoms into the surface layer of the metal material. Traditionally, gas carburizing was used as the carburizing method, but it had problems such as long carburizing time, and in recent years, vacuum carburizing, which is more advantageous than gas carburizing in terms of energy saving and labor saving, has been widely adopted.

[0003] In addition, carbonitriding treatment is sometimes performed to introduce nitrogen atoms along with carbon atoms into the surface layer. In carbonitriding treatment, first, a carburizing treatment is performed to introduce carbon atoms into the surface layer, followed by a nitriding treatment to introduce nitrogen atoms into the surface layer. Such carbonitriding treatment is considered effective in improving properties such as wear resistance. For example, a heat treatment facility that performs nitriding following vacuum carburizing is disclosed in the following patent document.

[0004] In the nitriding treatment that follows the carburizing treatment, ammonia contained in the atmosphere decomposes on the surface of the steel material as shown in formula (1) below, and nitrogen atoms are introduced into the surface layer of the metal material. Here, [N] represents the nitrogen atoms incorporated into the metal material. NH3→[N]+3 / 2H2...Equation (1)

[0005] The nitriding is controlled by the furnace nitriding potential K shown in equation (2) below. N This is mainly done by controlling P. NH3 This refers to the partial pressure of ammonia inside the furnace, P H2 This refers to the partial pressure of hydrogen inside the reactor. K N =P NH3 / P H2 3 / 2 ...Equation (2)

[0006] However, in heat treatment equipment that performs vacuum carburizing treatment, there has been a problem that it is difficult to stabilize the control of nitriding performed subsequent to carburizing.

Prior Art Document

Patent Document

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0008] An object of the present invention, against the background of the circumstances described above, is to provide a heat treatment facility and a heat treatment method that are capable of subjecting an article to be treated to a series of heat treatments including vacuum carburizing followed by nitriding, and that can solve the problem of variation in nitriding control.

Means for Solving the Problem

[0009] The inventors of the present invention obtained the following findings while investigating the cause of variation in the control of nitriding performed subsequent to vacuum carburizing. (1) When nitriding treatment is performed subsequent to carburizing treatment in the same furnace, nitriding control becomes unstable due to the influence of residual acetylene. (2) In nitriding treatment, the nitriding potential K N When the furnace atmosphere is controlled using , when the hydrogen concentration in the denominator (see the above formula (2)) is low (particularly in the initial stage of nitriding treatment), K N control becomes unstable. (3) The concentration of N atoms introduced into the surface layer is affected by pressure, and the lower the pressure is, the lower the absorption amount of N atoms becomes. For this reason, even when carburizing treatment is performed under vacuum, it is effective to perform the subsequent nitriding treatment at a pressure higher than the pressure of vacuum carburizing (for example, 2000 Pa or lower). The present invention has been made based on these findings.

[0010] Therefore, the heat treatment equipment in the first aspect of this invention is defined as follows: (A) Batch-type carburizing chambers and nitriding chambers arranged along a transport track, (B) A transport unit comprising a heating chamber for housing the workpiece to be processed and maintaining its temperature with a heater, and a transfer chamber for transferring the workpiece between the carburizing chamber or nitriding chamber and the heating chamber, wherein the transport unit is configured separately from the carburizing chamber and the nitriding chamber. A heat treatment apparatus comprising: a carburizing chamber for the workpiece to be treated; a transport unit for transporting the carburized workpiece received from the carburizing chamber to the nitriding chamber while keeping it warm in the warming chamber; and a nitriding chamber for nitriding treatment, wherein The atmosphere control means in the nitriding chamber includes an ammonia sensor for detecting the ammonia concentration in the atmospheric gas in the nitriding chamber, and a control unit for controlling the ammonia concentration in the atmospheric gas. The control unit, An ammonia concentration increasing treatment is performed by introducing an ammonia-containing introduction gas into the nitriding chamber under predetermined conditions to increase the ammonia concentration in the atmospheric gas, A target concentration maintenance process is performed, which involves adjusting the flow rate of the introduced gas by feeding back the ammonia concentration detected by the ammonia sensor in order to maintain the target ammonia concentration.

[0011] According to the heat treatment equipment in the first phase as defined in this way, the treatment chamber for carburizing and the treatment chamber for nitriding are completely separated, so that carburizing and nitriding can be performed as a series of treatments while avoiding the effects of residual acetylene.

[0012] Furthermore, since atmosphere control in the nitriding chamber is performed independently of the hydrogen concentration, instability in atmosphere control caused by low hydrogen concentration can be avoided. In addition, avoiding the aforementioned instability would require considering the introduction of hydrogen gas, resulting in a complex equipment configuration, but this heat treatment equipment allows for a simple configuration that does not require a hydrogen supply line for atmosphere control.

[0013] Furthermore, in the heat treatment equipment of this invention, an introduction gas is introduced into the nitriding chamber under predetermined conditions at the start of the nitriding treatment, and an ammonia concentration increase treatment is performed to increase the ammonia concentration in the atmospheric gas. In this way, the ammonia concentration in the atmospheric gas can be brought closer to the target concentration at an early stage. In particular, when the atmospheric gas inside the furnace is removed from the furnace and the ammonia concentration is measured, as in the third phase below, a time lag occurs, making it difficult to rapidly introduce ammonia using feedback control, and the above ammonia concentration increase treatment, which is not based on the ammonia concentration detected by the ammonia sensor, is effective.

[0014] The second aspect of this invention is defined as follows: In the first phase, the specified heat treatment equipment is configured such that nitrogen gas and ammonia gas can be introduced into the nitriding chamber, and the ammonia concentration in the introduced gas can be changed. The gas introduced into the furnace for nitriding may be ammonia gas alone, or it may be a mixture of ammonia and nitrogen gas. If the ammonia concentration in the introduced gas mixture can be changed, for example, in an ammonia concentration increase process, the ammonia concentration in the gas mixture can be decreased over time to suppress overshoot of the target ammonia concentration.

[0015] The third aspect of this invention is defined as follows: In the heat treatment equipment specified in the first or second phase, there is a gas extraction line connected to the nitriding chamber that extracts the atmospheric gas from inside the chamber and leads it to an exhaust gas pipeline. The ammonia sensor is provided on the gas extraction line.

[0016] It is also possible to detect the ammonia concentration in the atmospheric gas by inserting the ammonia sensor directly into the nitriding chamber, but in this case, the sensor is constantly exposed to high temperatures, which shortens the service life of the sensor. In the heat treatment equipment defined in the third aspect, a gas extraction line that takes out the atmospheric gas from the nitriding chamber and guides it to an exhaust gas pipe is provided, and the ammonia sensor is provided on this gas extraction line, whereby the sensor can be prevented from being constantly exposed to high temperatures.

[0017] Furthermore, in the heat treatment equipment of the present invention, there may be provided: an exhaust line connected to the carburizing chamber and exhausting atmospheric gas in the furnace to the outside of the furnace by a vacuum pump; and a pressure adjustment line connected to the nitriding chamber and maintaining the pressure in the furnace at the nitriding treatment pressure (fourth aspect). Here, from the viewpoint of improving the N atom concentration in the surface layer portion, the nitriding treatment pressure is 0.1 atm or more, preferably in the range of 0.8 atm or more and 5 atm or less.

[0018] Furthermore, in the heat treatment equipment of the present invention, a plurality of the nitriding chambers may be provided, and the gas extraction line and the ammonia sensor may be provided for each of the nitriding chambers (fifth aspect).

[0019] Furthermore, the heat treatment method according to the sixth aspect of the present invention is defined as follows. That is, (A) a batch-type carburizing chamber and a nitriding chamber arranged along a conveyance track; (B) a conveyance unit that includes a heat-retaining chamber that accommodates an article to be treated and retains heat with a heater, and a delivery chamber that delivers the article to be treated between the carburizing chamber or the nitriding chamber and the heat-retaining chamber, and is configured separately and independently from the carburizing chamber and the nitriding chamber; a heat treatment equipment is used, which comprises, as atmosphere control means for the nitriding chamber: an ammonia sensor that detects the ammonia concentration in the atmospheric gas in the nitriding chamber; and a control unit that controls the ammonia concentration in the atmospheric gas, The process involves supplying a carburizing gas under reduced pressure in the carburizing chamber to perform vacuum carburizing on the workpiece, The process of transporting the transport unit to the nitriding chamber, keeping the carburized workpiece received from the carburizing chamber warm in the warming chamber, and then transporting it to the nitriding chamber, The process involves supplying an ammonia-containing introduction gas to the nitriding chamber under nitriding pressure to perform nitriding on the workpiece, Includes.

[0020] According to the heat treatment method specified in the sixth phase as defined in this way, the treatment chamber for carburizing and the treatment chamber for nitriding are completely separated, so that carburizing and nitriding can be performed as a series of treatments while avoiding the influence of residual acetylene. Furthermore, since atmosphere control in the nitriding chamber is performed independently of the hydrogen concentration, instability in atmosphere control caused by low hydrogen concentration can be avoided.

[0021] The seventh aspect of this invention is defined as follows: In the sixth phase of the heat treatment method, in the atmosphere control during the nitriding process, the introduced gas is introduced into the nitriding chamber under predetermined conditions, and an ammonia concentration increase process is performed to increase the ammonia concentration in the atmospheric gas. Subsequently, a target concentration maintenance process is performed to maintain the target ammonia concentration by feeding back the concentration detected by the ammonia sensor and adjusting the flow rate of the introduced gas. By doing so, the ammonia concentration in the atmospheric gas can be brought closer to the target concentration at an earlier stage. [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows the overall configuration of the heat treatment equipment according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the internal structure of the carburizing chamber and conveying unit in the same embodiment. [Figure 3] This is a plan view of the carburizing chamber and conveying unit. [Figure 4] This diagram shows the supply lines, exhaust lines, and other connections for various gases to the carburizing chamber and nitriding chamber. [Figure 5] Figure 2 is a cross-sectional view of the VV section. [Figure 6] This is a diagram illustrating the operation of the transfer mechanism in the same embodiment. [Figure 7] This figure shows each step of the heat treatment process in the embodiment, along with the heat pattern and pressure pattern applied to the workpiece. [Figure 8] This figure shows an example of atmosphere control within a nitriding chamber. [Figure 9] This figure shows a different example from Figure 8 regarding atmosphere control within a nitriding chamber. [Figure 10] This figure shows the main parts of a second embodiment of the present invention. [Figure 11] This is a diagram illustrating the operation of the nitriding process in the same embodiment. [Figure 12] Figure 11 is a diagram illustrating the operation of the nitriding process. [Figure 13] Figure 12 is a diagram illustrating the operation of the nitriding process. [Figure 14] This is a modified version of the same embodiment in which a relief valve is provided in the nitriding chamber. [Modes for carrying out the invention]

[0023] Next, embodiments of the present invention will be described in detail below. Figure 7 shows each step of the heat treatment in the first embodiment of the present invention, along with the heat pattern and pressure pattern applied to the workpiece W. As shown in the figure, the workpiece W is subjected to carburizing, followed by nitriding and quenching. Specifically, in step K1, the workpiece W is heated to the carburizing temperature of 930°C and soaked, and then vacuum carburizing is performed on the workpiece W at 930°C, more specifically, carburizing under reduced pressure and subsequent diffusion. After that, in step K2, the workpiece W is cooled to 850°C and then kept at 850°C.

[0024] In the next step K3, the pressure is increased to a predetermined nitriding pressure, and nitriding is performed at a temperature of 850°C. In this embodiment, 850°C is also the quenching temperature. After maintaining the temperature of the workpiece W at 850°C in step K4, the workpiece W is rapidly cooled from the quenching temperature and quenched in step K5.

[0025] Figure 1 shows the schematic overall configuration of the heat treatment equipment 1 of this embodiment. In the figure, 10 is a rail that serves as a transport track extending in a straight line in the left-right direction in the figure, and along this rail 10 are a plurality of batch-type processing chambers (here, carburizing chambers 12-1, 12-2, nitriding chamber 13, and quenching chamber 14) arranged in a straight line with the opening 44 (see Figure 2) facing upward in the same direction as in the figure.

[0026] In this embodiment, the carburizing chambers 12-1 and 12-2 perform carburizing on the workpiece W at a predetermined temperature (e.g., 930°C). Subsequently, the nitriding chamber 13 performs nitriding on the workpiece W at a predetermined temperature (e.g., 850°C).

[0027] A charging table 16 is provided on the far right side of Figure 1, and the workpieces W from the upstream process are first placed on this charging table 16. The workpieces W placed on the charging table 16 are carburized in carburizing chambers 12-1 and 12-2, and then nitrided in nitriding chamber 13. After that, they are hardened in quenching chamber 14, and then discharged to extraction table 18 located on the far left side of the figure and below quenching chamber 14, and subsequently extracted to the downstream process.

[0028] In this embodiment, the heat treatment equipment 1 includes, in addition to the carburizing chambers 12-1, 12-2, nitriding chamber 13, and quenching chamber 14 described above, a transport unit 20 that travels on rails 10. The transport unit 20 receives the workpiece W on the loading table 16, travels on rails 10, and loads the workpiece W into either the carburizing chamber 12-1 or 12-2. Alternatively, the workpiece W, which has been carburized in these carburizing chambers 12-1 and 12-2, is received from these carburizing chambers 12-1 and 12-2, travels along the rail 10, and is loaded into the nitriding chamber 13 where it undergoes nitriding treatment. The transport unit 20 receives the workpiece W after nitriding from the nitriding chamber 13, travels along the rail 10, and passes it to the quenching chamber 14 where it undergoes quenching.

[0029] Figure 2 shows the internal structure of the carburizing chamber 12-1 and the conveying unit 20. As shown in the figure, the carburizing chamber 12-1 has a bottomed cylindrical furnace shell 22 and an insulating material 24 placed inside it. The insulating material 24 constitutes a bottomed cylindrical insulating wall 25, and this insulating wall 25 forms a processing chamber 26 on its inside. The carburizing chamber 12-1 is equipped with suction ports 32 and 33. The first exhaust line 162, which will be described later, is connected to suction port 32, and the second exhaust line 166 is connected to suction port 33 (see Figure 4). In addition, the nitrogen introduction line 146 is also connected to suction port 33, and suction port 33 also serves as a gas supply port for introducing pressurized nitrogen gas into the chamber.

[0030] The carburizing chamber 12-1 is also provided with a supply port 34 for supplying carburizing gas into its interior. The carburizing gas supplied from the supply port 34 is first guided to a header 36, and then introduced into the carburizing chamber 12-1, specifically the processing chamber 26 inside the insulating wall 25, through a branch pipe 37 connected to the header 36 and a nozzle 38 provided on the branch pipe 37. Although one nozzle 38 is provided on the branch pipe 37 here, multiple nozzles 38 may be provided.

[0031] The insulated wall 25 is equipped with a convection heating fan 39 that agitates and circulates nitrogen gas supplied in the processing chamber 26 to promote heating during the heating phase of the workpiece W, and a motor 40 that rotates the fan. The insulated wall 25 is also equipped with a water-cooling panel 41 near the motor 40 to protect the motor 40 from heat.

[0032] The carburizing chamber 12-1 is provided with a sliding door 42 that opens and closes the opening 44. The door 42 slides along the inner surface of the flange 48 by a cylinder 46, and in the closed state, it airtightly seals the opening 44 via a rubber packing. A plate-shaped insulating material 55 is provided on the door 42 in a manner that allows it to move integrally with the door, and this insulating material 55 closes the opening 52 of the cylindrical insulating wall 25. In the carburizing chamber 12-1, a water-cooling panel 51 is also provided on the inner surface of the door 42 to protect the rubber gasket that airtightly seals the opening 44 from heat.

[0033] The structure of the carburizing chamber 12-1 has been described above, but the other carburizing chambers 12-2 and nitriding chamber 13 have basically the same structure. For this reason, in the internal structure of the carburizing chamber 12-2 and nitriding chamber 13, parts that are the same as those in the carburizing chamber 12-1 are indicated only by symbols, and detailed explanations are omitted.

[0034] However, the nitriding chamber 13 is further equipped with an outlet 170 and an outlet 176 that communicate with the inside of the furnace (inside the chamber) (see Figure 4). A pressure adjustment line 172, which will be described later, is connected to the outlet 170 of the nitriding chamber 13, and a sampling line 177 is connected to the outlet 176.

[0035] Figure 4 shows the supply lines, exhaust lines, etc., of various gases connected to the carburizing chambers 12-1, 12-2 and the nitriding chamber 13. As shown in the figure, a first supply line 149 is connected to each supply port 34 of the carburizing chambers 12-1 and 12-2 to supply acetylene gas and nitrogen gas, respectively, as carburizing gases into the chambers. The first supply line 149 includes a mass flow controller 150 for controlling the gas flow rate and on-off valves 151 and 152. The upstream side of the first supply line 149 is divided into branch pipes 149a and 149b. Branch pipe 149a is connected to piping 153a extending from the nitrogen gas supply source 153, and branch pipe 149b is connected to piping 154a extending from the acetylene gas supply source 154. With the first supply line 149 configured in this way, nitrogen gas and acetylene gas can be supplied into the carburizing chambers 12-1 and 12-2.

[0036] Meanwhile, a second supply line 156 for supplying ammonia gas as a nitriding gas is connected to the supply port 34 of the nitriding chamber 13. The second supply line 156 includes a mass flow controller 157 and an on / off valve 158 for controlling the gas flow rate, and the upstream side of the second supply line 156 is connected to a pipe 160a extending from an ammonia gas supply source 160. Nitrogen gas can also be supplied to the supply port 34 of the nitriding chamber 13 via a pipe 159. Therefore, nitrogen gas and ammonia gas can be introduced into the nitriding chamber 13.

[0037] In addition, a nitrogen introduction line 146 is connected to the carburizing chambers 12-1, 12-2 and the nitriding chamber 13, separate from the supply lines 149 and 156 mentioned above. One end of the nitrogen introduction line 146 is connected to the chamber's supply port 33, and the other end is connected to a pipe 153a extending from the nitrogen gas supply source 153, with an on / off valve 147 provided in its flow path. The nitrogen introduction line 146 is used to introduce nitrogen gas when pressurizing the inside of the chamber under reduced pressure.

[0038] The suction ports 32 of the carburizing chambers 12-1, 12-2 and the nitriding chamber 13 are each connected to a first exhaust line 162 for exhausting gas from inside the chambers. The first exhaust line 162 consists of a vacuum pump 163 and on-off valves 164 corresponding to each chamber, and the opening and closing of the on-off valves 164 connects and disconnects each processing chamber from the vacuum pump 163. In this example, by connecting the processing chamber to the vacuum pump 167, the inside of the chamber is maintained at a predetermined reduced pressure state (e.g., 1500 Pa).

[0039] Furthermore, the suction ports 33 of the carburizing chambers 12-1, 12-2 and the nitriding chamber 13 (the suction ports 33 also serve as gas supply ports when introducing nitrogen gas) are each connected to a second exhaust line 166 for exhausting the gas inside the chambers. The second exhaust line 166 consists of a vacuum pump 167 and an on-off valve 168 corresponding to each chamber, and the opening and closing of the on-off valve 168 connects and disconnects each processing chamber from the vacuum pump 167. In this example, by connecting the processing chamber to the vacuum pump 167, the pressure inside the chamber is rapidly reduced from atmospheric pressure to a predetermined reduced pressure state.

[0040] In the nitriding chamber 13, a pressure adjustment line 172 is connected to the outlet 170 to maintain the pressure inside the chamber near atmospheric pressure during the nitriding process. The pressure adjustment line 172 consists of a pressure adjustment valve 173 and an on-off valve 174, and the pressure adjustment valve 173 adjusts the pressure inside the chamber to near atmospheric pressure, or more specifically, slightly higher than atmospheric pressure (for example, 105 kPa).

[0041] Furthermore, one end of a sampling line 177 for removing the atmospheric gas from inside the chamber to the outside of the furnace is connected to the outlet 176 of the nitriding chamber 13. The sampling line 177 consists of a pump 178 and an on / off valve 179. An analyzer 180 is provided at the other end of the sampling line 177, and the atmospheric gas removed from inside the nitriding chamber 13 by the pump 178 is supplied to the analyzer 180.

[0042] The analyzer 180 analyzes the elemental concentrations in the atmospheric gas supplied through the sampling line 177. The analyzer 180 is equipped with an ammonia sensor 182 for detecting ammonia concentration and a hydrogen sensor 184 for detecting hydrogen concentration, and detects the ammonia and hydrogen concentrations in the atmospheric gas taken out through the sampling line 177. Signals corresponding to the detected concentrations are then output to the control unit 186. Here, hydrogen concentration detection is performed as part of the equipment's safety measures and is not used for atmosphere control purposes. For example, an NDIR (non-dispersive infrared) gas sensor can be used as the ammonia sensor 182. Similarly, for example, a gas thermal conduction sensor can be used as the hydrogen sensor 184. In this example, taking into account the lifespan of these sensors, the analyzer 180 is positioned at a location where the gas supplied through the sampling line 177 is at approximately room temperature (25°C).

[0043] The atmospheric gas extracted through the sampling line 177 is sent to the exhaust gas pipeline 192 via the analyzer exhaust line 190, which extends downstream of the analyzer 180. In this embodiment, the sampling line 177 and the analyzer exhaust line 190 constitute a gas extraction line. In the exhaust gas pipeline 192, the atmospheric gas extracted through this gas extraction line, as well as gases sent from the first exhaust line 162, the second exhaust line 166, and the pressure adjustment line 172, merge together and are then burned and released as exhaust gas.

[0044] The control unit 186 controls various operations in the heat treatment equipment 1. In controlling the atmosphere inside the nitriding chamber 13, it sends signals to the on-off valve 152 for nitrogen gas supply and the mass flow controller 150, and to the on-off valve 158 for ammonia gas supply and the mass flow controller 157 to control the flow rates of nitrogen gas and ammonia gas introduced into the nitriding chamber 13. The control unit 186 then introduces an ammonia-containing introduction gas into the nitriding chamber 13 under predetermined conditions, performing an ammonia concentration increase process to increase the ammonia concentration in the atmospheric gas, and a target concentration maintenance process that adjusts the flow rate (introduction amount) of the introduction gas by feeding back the ammonia concentration detected by the ammonia sensor 182 to bring the ammonia concentration in the atmospheric gas closer to the target concentration.

[0045] Figure 8 shows an example of atmosphere control within the nitriding chamber 13. In the example in Figure 8(A), after the workpiece W is placed in the nitriding chamber 13 under reduced pressure, nitrogen gas is introduced into the chamber to raise the pressure to a predetermined level (pressure boosting control), and then ammonia gas for nitriding is introduced. At the start of ammonia gas introduction, the ammonia gas is quantitatively controlled (for example, under conditions such as 1000 L / h for 15 minutes) to raise the ammonia gas concentration in the chamber to a range of 50% to 150% (for example, 0.4 volume%) relative to the target concentration (for example, 0.5 volume%). A more desirable ammonia concentration in the chamber after quantitative control is in the range of 70% to 90% relative to the target concentration. This quantitative control operation corresponds to the ammonia concentration increase process performed by the control unit 186. In this quantitative control, no feedback of the concentration detected by the ammonia sensor 182 is performed. This is to approach the predetermined ammonia concentration range (50% to 150% relative to the target concentration) as quickly as possible.

[0046] The above quantitative control can be any control that introduces ammonia gas into the chamber under predetermined conditions (flow rate, time, etc.). In addition to introducing a constant flow rate of ammonia gas into the chamber as shown in Figure 8(A), the flow rate of ammonia gas introduced may be gradually reduced towards the end of the quantitative control, as shown in Figure 8(B). This can suppress an overshoot in ammonia concentration.

[0047] After the quantitative control operation is completed, feedback control (PID control) is performed to adjust the flow rate (introduced amount) of ammonia gas by feeding back the ammonia concentration detected by the ammonia sensor 182 in order to maintain the ammonia concentration in the chamber at the target concentration (e.g., 0.5 volume%). The conditions for feedback control do not need to be constant; for example, the setting values ​​of each element of P, I, and D can be appropriately changed between the start of feedback control, when it is required to reach the target concentration as quickly as possible, and the stabilization period after the target concentration has been reached. This feedback control operation corresponds to the target concentration maintenance process executed by the control unit 186. The target ammonia concentration in the chamber, as described above, will vary depending on the type of steel and the specifications (hardness) required by the user, so it should be set accordingly. Specifically, a preliminary evaluation should be conducted to determine the ammonia concentration that satisfies the required hardness.

[0048] Figure 9 shows an atmosphere control within the nitriding chamber 13 that differs from the example in Figure 8. In the example in Figure 8, ammonia gas was introduced after pressurization control by introducing nitrogen gas, but as shown in Figure 9, it is also possible to introduce ammonia gas together with nitrogen gas during pressurization control. In this way, the atmosphere gas can be brought closer to a predetermined ammonia concentration range in a shorter time. In this example, the pressurization control operation and the quantitative control operation correspond to the ammonia concentration increase process performed by the control unit 186. Furthermore, by increasing the proportion of ammonia gas introduced during pressurization control, if the ammonia gas concentration in the chamber is raised to a range of 50% to 150% (e.g., 0.4 volume%) relative to the target concentration (e.g., 0.5 volume%) during pressurization control, quantitative control can be omitted and the system can be switched to feedback control.

[0049] As described above, in this embodiment, the sampling line 177, analyzer 180 (including ammonia sensor 182), control unit 186, on-off valves 152, 158, and mass flow controllers 150, 157 constitute the atmosphere control means in the nitriding chamber 13.

[0050] On the other hand, the quenching chamber 14 shown in Figure 1 has an oil cooling tank inside, and the workpiece W that has undergone nitriding treatment and been loaded by the transport unit 20 is immersed in the oil cooling tank to rapidly cool and perform quenching. This quenching chamber 14 has an opening 44 on the same side as the carburizing chambers 12-1, 12-2 and the nitriding chamber 13, i.e., on the upper side in Figure 1, and also has an opening 44 on the opposite side (lower side in the figure), and these openings 44 are opened and closed by sliding doors 42. 46 in Figure 1 is a cylinder that opens and closes the doors 42.

[0051] In Figure 2, the transport unit 20 has a traveling trolley 90 that runs on the rails 10, and further on the traveling trolley 90, there is a connecting trolley 92 that moves back and forth in the left-right direction in Figure 2, which is perpendicular to the rails 10, along with the transfer chamber 54, and connects and disconnects the transfer chamber 54 and the heating chamber 56 to the carburizing chambers 12-1, 12-2 and the nitriding chamber 13. 94 is a cylinder that moves the connecting trolley 92 forward and backward in a small stroke in the left-right direction in Figure 2, and the heat retention chamber 56 and the transfer chamber 54 are moved forward and backward in the left-right direction in Figure 2 by this cylinder 94, accompanied by the rolling of the roller 96. In this embodiment, these connecting trolleys 92, rollers 96, cylinders 94, etc., constitute the means for moving forward and backward.

[0052] The transport unit 20 has a transfer chamber 54 at the front on the side of the carburizing chambers 12-1, 12-2 and the nitriding chamber 13, and a heat retention chamber 56 at the rear on the opposite side for keeping the workpiece W warm during processes K2 and K4 in Figure 7.

[0053] The transfer chamber 54 has a pressure-resistant rectangular cylindrical wall 58, and a storage chamber 60 for accommodating the workpiece W to be processed is formed inside it. A transfer mechanism 62 is provided in this storage chamber 60. The transfer mechanism 62 transfers the workpiece W between the carburizing chambers 12-1 and 12-2 and the rear heat retention chamber 56. As shown in Figure 6, it has a fork section 62A and horizontal sliding members 62B and 62C, and the workpiece W is transferred at the fork section 62A by sliding them horizontally.

[0054] The transfer chamber 54 is provided with a suction port 63, which is connected to the vacuum pump 64 shown in Figure 3 via a suction pipe 66A, so that the inside of the transfer chamber 54 is vacuum-suctioned by the vacuum pump 64. An on-off valve 68A, which consists of a solenoid valve, is provided on the suction pipe 66, and the suction port 63 and the vacuum pump 64 are connected and disconnected by opening and closing the on-off valve 68A.

[0055] The transfer chamber 54 is also provided with a supply port 70, as shown in Figure 3, through which nitrogen gas is supplied into the transfer chamber 54. The transfer chamber 54 has an opening 72 at its front end, i.e., the left end in Figure 2, which does not have a door. The transfer chamber 54 is provided with a flat, frame-shaped packing 74 around this opening 72. The transfer chamber 54 is docked with the carburizing chambers 12-1, 12-2 and nitriding chamber 13 by moving forward toward the carburizing chambers 12-1, 12-2 and nitriding chamber 13, with the frame-shaped packing 74 in airtight contact with the outer surfaces of the carburizing chambers 12-1, 12-2 and nitriding chamber 13.

[0056] On the other hand, the latter heating chamber 56 has an insulating material 78 inside a bottomed cylindrical furnace shell 76, and this insulating material 78 constitutes an insulating wall 80. The insulated wall 80 forms a storage chamber 82 on its interior side, where the product to be processed W is stored. A support frame 84 is provided in the storage chamber 82. The items to be processed W in the storage chamber 82 are placed on and supported by the support frame 84.

[0057] As shown in Figure 5, the insulated chamber 56 is provided with a suction port 86 for vacuuming its interior, and this suction port 86 is connected to the vacuum pump 64 via a suction pipe 66B, as shown in Figure 3. An on-off valve 68B, which consists of an electromagnetic valve, is provided on the suction pipe 66B, and the opening and closing operation of the on-off valve 68B connects and disconnects the suction port 86 and the vacuum pump 64.

[0058] The heat-insulating chamber 56 has a heater 120 inside the insulating wall 80 for keeping the workpiece W warm. As shown in Figure 2, the heat-insulating chamber 56 is also provided with insulating doors 110 and 112 that open and close the upper opening 104 and lower opening 106 of the insulating wall 80, and these doors are opened and closed by cylinders 114 and 116.

[0059] The heating chamber 56 also has a supply port 88 in the furnace shell 76 for supplying nitrogen gas as a cooling gas to the interior, as shown in Figure 5. Furthermore, the device includes a heat exchanger 98 that lowers the temperature of supplied nitrogen gas by passing it through water-cooling pipes through heat exchange, a cooling fan 100 that agitates the cooled nitrogen gas and circulates it within the heat-insulating chamber 56, and a motor 102 that rotates the fan. These components constitute a gas cooling device for the workpiece W.

[0060] In this gas cooling system, the rotation of the cooling fan 100 causes the temperature of nitrogen gas to decrease, which then flows upward through the opening 106 at the bottom of the insulated wall 80, hitting the workpiece W. After cooling, the nitrogen gas flows out through the opening 104 at the top of the insulated wall 80, passes through the heat exchanger 98 again, and is further cooled there. The workpiece W is then cooled while this circulating flow is maintained.

[0061] In other words, in this embodiment, the heat retention chamber 56 is equipped with a cooling function in addition to a heat retention function for keeping the workpiece W warm.

[0062] As shown in Figure 2, an opening 122 is provided between the heat retention chamber 56 and the transfer chamber 54, specifically at the end of the heat retention chamber 56 on the transfer chamber 54 side. This opening 122 is opened and closed by a door 128 that slides along the inner surface of the flange 126 by a cylinder 124.

[0063] Similar to the carburizing chamber 12-1 described above, the door 128 of this heat-insulating chamber 56 is also provided with a plate-shaped insulating material 130 that moves integrally with the opening 129 of the insulating wall 80, and a water-cooling panel 132 is provided on the door 128 to protect the rubber gasket that airtightly seals the opening 122 from heat.

[0064] Next, the series of heat treatments in this embodiment will be described. The transport unit 20 receives and transports the workpiece W on the loading table 16 in Figure 1, and loads it into either the carburizing chamber 12-1 or 12-2. The carburizing chamber 12-1 or 12-2 that receives the product W to be processed performs the carburizing treatment on the product W inside the chamber. The transport unit 20 then removes the carburized workpiece W from either the carburizing chamber 12-1 or 12-2, keeps it warm in the warming chamber 56, and then loads the workpiece W into the nitriding chamber 13. Upon receiving this, the nitriding chamber 13 performs nitriding on the workpiece W.

[0065] Once the nitriding process is complete, the transport unit 20 removes the nitrided workpiece W from the nitriding chamber 13 and passes it to the quenching chamber 14. The quenching chamber 14, which receives the workpiece W after nitriding, is rapidly cooled by immersing it in an internal oil-cooling bath and then quenched. The workpiece W, after quenching, is then discharged from the quenching chamber 14 onto the extraction table 18.

[0066] The following provides a detailed explanation of the key parts of the above-mentioned heat treatment process. Note that in the following explanation, the carburizing treatment will be performed in carburizing chamber 12-1. First, the transport unit 20 receives the workpiece W on the loading table 16 via the transfer mechanism 62 in the transfer chamber 54 and places it inside the transfer chamber 54. Subsequently, the transport unit 20 moves to the location of one of the carburizing chambers, in this case for example, carburizing chamber 12-1, and transports the product W to be processed.

[0067] Subsequently, the transfer unit 20 uses the cylinder 94 to move the transfer chamber 54 forward a small distance towards the carburizing chamber 12-2 side together with the rear heat retention chamber 56, docking the transfer chamber 54 with the carburizing chamber 12-1 so that the frame-shaped packing 74 at the tip of the transfer chamber 54 is in close contact with the outer surface of the carburizing chamber 12-1.

[0068] Then, with the door 128 between the transfer chamber 54 and the heat-insulating chamber 56 closed, the inside of the transfer chamber 54 is vacuum-suctioned through the suction port 63 by the vacuum pump 64, and the pressure inside the transfer chamber 54 is reduced to a vacuum pressure similar to that of the carburizing chamber 12-1.

[0069] When the pressure inside the transfer chamber 54 becomes a vacuum pressure similar to the pressure inside the carburizing chamber 12-1, the door 42 of the carburizing chamber 12-1 is opened, and the workpiece W to be processed in the transfer chamber 54 is loaded into the processing chamber 26 inside the carburizing chamber 12-1 by the transfer mechanism 62 and set on the stand 30.

[0070] When the product to be treated W is placed inside the carburizing chamber 12-1, heating of the product to be treated W is started and the temperature is raised to the carburizing temperature of 930°C.

[0071] To accelerate the temperature rise, nitrogen gas is supplied into the carburizing chamber 12-1 from the supply port 34, and a convection heating fan 39 is rotated. The convection heating by the convection heating fan 39 and the radiant heat from the heater 28 quickly raise the temperature of the workpiece W to the carburizing temperature of 930°C.

[0072] When the workpiece W has been heated to the carburizing temperature of 930°C, the nitrogen gas inside the carburizing chamber 12-1 is evacuated through the suction port 33, and the pressure inside the carburizing chamber 12-1 is reduced to the set vacuum pressure (1500 Pa). Subsequently, the gas introduced into the carburizing chamber 12-1 through the supply port 34 is switched from nitrogen gas to carburizing gas, and carburizing is performed on the product W to be processed. At this time, the amount of carburizing gas (acetylene gas) introduced into the carburizing chamber 12-1 is determined in advance by simulation and introduced at a predetermined time. Subsequently, with the supply of carburizing gas stopped, the workpiece W is maintained at a temperature of 930°C, and the C atoms that have entered the workpiece W are diffused.

[0073] Once the carburizing treatment of the workpiece W is completed in this manner, the transport unit 20, which had temporarily moved away from the carburizing chamber 12-1, is moved forward again toward the carburizing chamber 12-1, and the transfer chamber 54 is docked with the carburizing chamber 12-1. Then, with the door 128 between the transfer chamber 54 and the heat retention chamber 56 open, the inside of the transfer chamber 54 and the inside of the heat retention chamber 56 are evacuated using the vacuum pump 64 to create a vacuum pressure.

[0074] Subsequently, the door 42 of the carburizing chamber 12-1 is opened, and the carburized workpiece W inside the carburizing chamber 12-1 is moved into the transfer chamber 54. Then, it is moved from the transfer chamber 54 to the heat retention chamber 56, where the workpiece W is placed.

[0075] Once the workpiece W is placed inside the heating chamber 56, the door 128 is closed, and then the workpiece W is heated to the desired temperature (850°C) inside the heating chamber 56 using the heater 120. Alternatively, a gas cooling device can be used to forcibly cool the workpiece W to the desired temperature (850°C).

[0076] The transport unit 20 maintains the temperature of the workpiece W even while it is moving away from the carburizing chamber 12-1. When the pressure in the transfer chamber 54 and the pressure in the nitriding chamber 13 become approximately the same vacuum pressure, the workpiece W, which has been maintained at the target temperature, is then loaded into the nitriding chamber 13 through the transfer chamber 54.

[0077] The workpiece W, which is placed in the nitriding chamber 13, is then subjected to nitriding treatment inside the nitriding chamber 13 while being maintained at the nitriding temperature of 850°C. In detail, with the door 42 (see Figure 2) of the nitriding chamber 13 closed, the workpiece W is heated by the heater 28 to maintain a nitriding temperature of 850°C. Meanwhile, nitrogen gas is introduced into the processing chamber 26 through the supply port 33, and the processing chamber 26 is pressurized (re-pressurized) as shown in Figure 8(A), for example. After re-pressurization, an introduction gas (nitriding gas) containing ammonia is introduced through the supply port 34, and thereafter the pressure is maintained at a predetermined nitriding pressure (in this case, 105 kPa, slightly higher than atmospheric pressure) by the pressure adjustment line 172.

[0078] As mentioned above, the flow rate of the gas introduced into the processing chamber 26 for the nitriding treatment is adjusted by quantitative control and feedback control, for example, as shown in Figure 8(A).

[0079] Once the nitriding process is complete, the gas inside the nitriding chamber 13 is evacuated through the suction port 33, and when the vacuum pressure inside the nitriding chamber 13 is approximately the same as the pressure inside the transfer chamber 54, the transfer chamber 54 is docked with the nitriding chamber 13. The nitrided workpiece W is then removed from the nitriding chamber 13 and placed in the heat-insulating chamber 56, where it is kept at the desired temperature (850°C).

[0080] Next, the transport unit 20 moves to the left in Figure 1, bringing the nitrided workpiece W to the front of the quenching chamber 14, and then loading it into the quenching chamber 14.

[0081] At this time, in the transport unit 20, after docking the transfer chamber 54 with the quenching chamber 14, the inside of the transfer chamber 54 is first vacuumed with the door 128 closed, and then nitrogen gas is supplied into the transfer chamber 54 through the supply port 70 to bring the inside to atmospheric pressure.

[0082] Next, the vacuum suction inside the heat-insulating chamber 56 is stopped, and nitrogen gas is supplied to it through the supply port 88 to bring the inside to atmospheric pressure. In this state, the door 128 and the door 42 on the quenching chamber 14 side are opened, and the carburized and nitrided workpiece W inside the heat-insulating chamber 56 is loaded into the quenching chamber 14 via the transfer chamber 54. In this example, the transfer of the workpiece W from the heat-insulating chamber 56 to the quenching chamber 14 is shown under atmospheric pressure. However, it is also possible to transfer the workpiece W under other predetermined pressures (for example, under vacuum).

[0083] The quenching chamber 14, upon receiving the workpiece W, immerses it in an oil-cooling tank located inside to rapidly cool it and perform quenching. The hardened workpiece W is then discharged through the opening 44 on the opposite side of the rail 10 of the hardening chamber 14 to the extraction table 18 at the bottom of Figure 1. The processed product W, which has been discharged onto the extraction table 18, is then taken down to the downstream process.

[0084] With the heat treatment equipment 1 of this embodiment configured as described above, the carburizing chambers 12-1 and 12-2 that perform carburizing and the nitriding chamber 13 that performs nitriding are completely separated, so that carburizing and nitriding can be performed as a series of processes while avoiding the influence of residual acetylene.

[0085] In the heat treatment equipment 1 of this embodiment, the atmosphere control means for the nitriding treatment includes an ammonia sensor 182 for detecting the ammonia concentration in the atmospheric gas and a control unit 186 for controlling the ammonia concentration in the atmospheric gas. Since the atmosphere control in the nitriding chamber 13 is performed independently of the hydrogen concentration, instability of the atmosphere control caused by low hydrogen concentration can be avoided.

[0086] In the heat treatment equipment 1 of this embodiment, at the start of the nitriding treatment, an introduction gas is introduced into the nitriding chamber 13 under predetermined conditions, and quantitative control is performed as an ammonia concentration increase treatment to increase the ammonia concentration in the atmospheric gas. In this way, the ammonia concentration in the atmospheric gas can be brought closer to the target concentration at an early stage.

[0087] Furthermore, the heat treatment equipment 1 of this embodiment is arranged so that nitrogen gas and ammonia gas can be introduced into the nitriding chamber 13, and the ammonia concentration in the mixed gas (introduced gas) introduced into the nitriding chamber 13 via mass flow controllers 150 and 157 can be changed. For example, in an ammonia concentration increase treatment, overshoot with respect to the target ammonia concentration can be suppressed by decreasing the ammonia concentration in the introduced gas over time.

[0088] Furthermore, the heat treatment equipment 1 of this embodiment is equipped with a gas extraction line (sampling line 177, analyzer exhaust line 190) that extracts the atmospheric gas from the nitriding chamber 13 and leads it to the exhaust gas pipeline 192. By installing an ammonia sensor 182 and a hydrogen sensor 184 on the gas extraction line, it is possible to prevent these sensors from being constantly exposed to high temperatures and to extend their lifespan.

[0089] In this embodiment, the heat treatment equipment 1 has exhaust lines 162 and 166 connected to the carburizing chambers 12-1 and 12-2 to exhaust the internal atmospheric gas to the outside of the furnace, and a pressure adjustment line 172 connected to the nitriding chamber 13 to maintain the pressure inside the furnace at near atmospheric pressure. Therefore, vacuum carburizing can be performed in the carburizing chambers 12-1 and 12-2, and nitriding at near atmospheric pressure can be performed in the nitriding chamber 13, and these vacuum carburizing and nitriding processes can be performed simultaneously in their respective processing chambers.

[0090] Next, a heat treatment apparatus according to a second embodiment of the present invention will be described. In heat treatment equipment that performs nitriding treatment following carburizing treatment, shortening the nitriding treatment time is considered one of the challenges. Since the surface reaction rate of nitriding depends on the magnitude of the treatment pressure, increasing the nitriding treatment pressure is effective in shortening the nitriding treatment time. While the heat treatment equipment 1 in the first embodiment described above performed nitriding treatment at a pressure near atmospheric pressure, the heat treatment equipment 1B in this embodiment enables stable treatment at a higher nitriding pressure (140 kPa) in addition to the nitriding pressure near atmospheric pressure (105 kPa).

[0091] The heat treatment apparatus 1B of this embodiment, like the heat treatment apparatus 1 of the above embodiment, has carburizing chambers 12-1, 12-2, a nitriding chamber 13, a quenching chamber 14, and a transport unit 20 that travels on rails 10, but the configuration of the exhaust line connected to the nitriding chamber 13, the pressure adjustment line, etc. are different. In the configuration of the heat treatment apparatus 1B of this embodiment, parts that are the same as those of the heat treatment apparatus 1 of the above embodiment are indicated only by reference numerals and detailed explanations are omitted.

[0092] Figure 10 shows the supply lines, exhaust lines, etc., of various gases connected to the nitriding chamber 13. As shown in the figure, the suction port 33 of the nitriding chamber 13 is connected to a second exhaust line 166B which includes a vacuum pump 167, a main line 169 that guides the gas from the suction port 33 to the vacuum pump 167, and an on / off valve 168 provided on the main line 169. In this example, the second exhaust line 166B is provided with a slow exhaust line 200, which serves as a bypass passage for the gas to flow while avoiding a portion of the main pipeline 169, including the on-off valve 168. This slow exhaust line 200 consists of a pipe 201 and an on-off valve 202, and its diameter and other dimensions are set smaller to reduce the gas flow rate compared to when the gas flows through the main pipe 169, which includes the on-off valve 168. In this example, when exhausting high-pressure nitriding gas from the nitriding chamber 13, temporarily passing it through the slow exhaust line 200 reduces the flow rate of high-pressure gas flowing towards the vacuum pump 167, thereby reducing the load on the vacuum pump 167 and preventing equipment problems such as the vacuum pump 167 stopping.

[0093] Furthermore, the nitriding chamber 13 in this embodiment is equipped with a first pressure adjustment line 172 and a second pressure adjustment line 172B as pressure adjustment lines for maintaining the pressure inside the chamber at a predetermined nitriding pressure during the nitriding process. The first pressure regulating line 172 includes a pressure regulating valve 173 and an on-off valve 174, and the pressure regulating valve 173 adjusts and controls the pressure inside the chamber to near atmospheric pressure, specifically slightly higher than atmospheric pressure (105 kPa). On the other hand, the second pressure regulating line 172B includes a pressure regulating valve 173B and an on-off valve 174B, and the pressure regulating valve 173B adjusts and controls the pressure inside the chamber to an even higher pressure (140 kPa). According to this example, even when switching to different nitriding pressures for nitriding, it is not necessary to adjust the pressure regulating valve itself. The desired pressure regulating line can be selected by opening and closing valves 174 and 174B, thus simplifying the switching work associated with changes in nitriding conditions.

[0094] Based on Figures 11 to 13, we will explain the nitriding process at a high pressure (140 kPa) using heat treatment equipment 1B. When the carburized workpiece W is loaded into the reduced-pressure nitriding chamber 13 via the transfer chamber 54 (see Figure 1), nitrogen gas is introduced into the furnace (processing chamber 26) through the supply port 33, as shown in Figure 11, and the processing chamber 26 is pressurized (re-pressurized).

[0095] After repressurization, a nitriding gas containing ammonia is introduced through the second supply line 156, as shown in Figure 12. In this example, of the two pressure adjustment lines, the second pressure adjustment line 172B for high pressure is selected, and thereafter the furnace is adjusted and controlled to a predetermined nitriding pressure (140 kPa in this case) by the second pressure adjustment line 172B. Here, the flow rate of the ammonia-containing nitriding gas introduced into the furnace for the nitriding process is adjusted by the aforementioned quantitative control and feedback control.

[0096] Once the nitriding process is complete and the supply of nitriding gas is stopped, the gas inside the nitriding chamber 13 is exhausted through the suction port 33 and the second exhaust line 166B. When exhausting the high-pressure gas, as shown in Figure 13(A), the slow exhaust line 200 is first selected as the exhaust flow path (in this case, the on-off valve 202 is open and the on-off valve 168 is closed), and the chamber is slowly depressurized until the inside of the furnace reaches approximately atmospheric pressure. Then, as shown in Figure 13(B), the gas flow path from the suction port 33 to the vacuum pump 167 is switched to the main line 169 (in this case, the on-off valve 202 is closed and the on-off valve 168 is open), and the inside of the chamber is rapidly depressurized from atmospheric pressure to a predetermined depressurized state. After reaching the predetermined depressurized state, the system switches to the first exhaust line 162, and that depressurized state is maintained. The nitrided workpiece W is then removed from the depressurized nitriding chamber 13 through the transfer chamber 54 (see Figure 1).

[0097] As described above, according to the heat treatment equipment 1B of this embodiment, the nitriding chamber 13 is equipped with a plurality of pressure adjustment lines 172, 172B that can be adjusted to different pressures, and by selecting any of the pressure adjustment lines, the nitriding treatment pressure can be easily changed in a single nitriding chamber, thereby allowing adjustment of the nitriding treatment time.

[0098] Furthermore, according to the heat treatment equipment 1B of this embodiment, a slow exhaust line 200 is provided in the second exhaust line 166B for exhausting gas from the chamber, which restricts the flow rate of gas flowing toward the vacuum pump 167. When exhausting nitriding gas under high pressure, temporarily passing it through the slow exhaust line 200 reduces the load on the vacuum pump 167, thus avoiding equipment problems such as the vacuum pump 167 stopping.

[0099] Furthermore, in the nitriding chamber 13 of this embodiment, as shown in Figure 14, a relief valve 205 with a check valve can be provided, taking into account the pressure resistance of the nitriding chamber 13 and its surrounding equipment. This relief valve 205 is connected to the gas outlet 206 of the nitriding chamber 13, and the relief gas from the relief valve 205 is sent to the exhaust gas pipeline 192 through the exhaust line 207 and burned out. In this way, even if a malfunction occurs in the pressure regulating valve 173B during high-pressure nitriding and the furnace pressure rises, any pressure exceeding the operating pressure of the relief valve 205 is released outside the furnace through the relief valve 205, thus preventing the nitriding chamber 13 and its surrounding equipment from being pressurized beyond their resistance limit.

[0100] Although embodiments of the present invention have been described in detail above, these are merely examples, and the present invention can be configured in various modified forms without departing from its spirit. For example, the carburizing gas may be replaced with other acetylene-based gases such as ethylene gas. The number of carburizing chambers and nitriding chambers in the heat treatment equipment of the present invention can be changed as appropriate, and it is also possible to provide multiple nitriding chambers. In this case, a gas extraction line and an ammonia sensor can be provided for each nitriding chamber. Furthermore, when performing both atmospheric pressure nitriding and high-pressure nitriding at a pressure higher than atmospheric pressure, atmospheric pressure nitriding and high-pressure nitriding can be performed in a single nitriding chamber by changing the furnace pressure as in the second embodiment above, or dedicated atmospheric pressure nitriding treatment chambers and high-pressure nitriding treatment chambers can be provided in advance. [Explanation of Symbols]

[0101] 1,1B Heat treatment equipment 10 rails 12-1, 12-2 Carburizing Chamber 13 Nitriding Chamber 14. Hardening Chamber 20 transport units 28 Heater 54 Transfer Chamber 56 Insulation Chamber 162 First exhaust line 163,167 Vacuum pumps 166, 166B Second exhaust line 172, 172B Pressure Regulating Line 177 Sampling line (gas extraction line) 182 Ammonia Sensor 184 Hydrogen Sensor 190 Analytical meter exhaust line (gas extraction line) 192 Exhaust gas pipeline W - Items to be processed

Claims

1. (A) Batch-type carburizing chambers and nitriding chambers arranged along a transport track, (B) A transport unit comprising a heating chamber for housing the workpiece to be processed and maintaining its temperature with a heater, and a transfer chamber for transferring the workpiece between the carburizing chamber or nitriding chamber and the heating chamber, wherein the transport unit is configured separately from the carburizing chamber and the nitriding chamber. A heat treatment apparatus comprising: a carburizing chamber for the workpiece to be treated; a transport unit for transporting the carburized workpiece received from the carburizing chamber to the nitriding chamber while keeping it warm in the warming chamber; and a nitriding chamber for nitriding treatment, wherein The atmosphere control means in the nitriding chamber includes an ammonia sensor for detecting the ammonia concentration in the atmospheric gas in the nitriding chamber, and a control unit for controlling the ammonia concentration in the atmospheric gas. The control unit, A process performed at the start of introducing an ammonia-containing introduction gas, wherein the ammonia concentration in the introduction gas and the flow rate of the introduction gas are set to predetermined conditions, the introduction gas is introduced into the nitriding chamber, and an ammonia concentration increase process is performed to increase the ammonia concentration in the atmospheric gas. A heat treatment facility characterized by performing a process after the ammonia concentration increasing process, which involves a target concentration maintenance process that adjusts the flow rate of the introduced gas by feeding back the ammonia concentration detected by the ammonia sensor in order to maintain a target ammonia concentration.

2. The heat treatment apparatus according to claim 1, characterized in that nitrogen gas and ammonia gas are arranged in the nitriding chamber so as to be able to be introduced, and the ammonia concentration in the introduced gas can be changed in the ammonia concentration increasing treatment.

3. It has a gas extraction line connected to the nitriding chamber, which extracts the atmospheric gas from inside the chamber and leads it to an exhaust gas pipeline. The heat treatment equipment according to either claim 1 or 2, characterized in that the ammonia sensor is provided on the gas extraction line.

4. An exhaust line connected to the carburizing chamber, which exhausts the atmospheric gas inside the furnace to the outside of the furnace using a vacuum pump, A pressure adjustment line connected to the nitriding chamber maintains the pressure inside the furnace at the nitriding pressure, A heat treatment apparatus according to either claim 1 or 2, characterized by having the following features.

5. The heat treatment apparatus according to claim 3, comprising a plurality of nitriding chambers, wherein each nitriding chamber is provided with the gas extraction line and the ammonia sensor.

6. (A) Batch-type carburizing chambers and nitriding chambers arranged along a transport track, (B) A transport unit comprising a heating chamber for housing the workpiece to be processed and maintaining its temperature with a heater, and a transfer chamber for transferring the workpiece between the carburizing chamber or nitriding chamber and the heating chamber, wherein the transport unit is configured separately from the carburizing chamber and the nitriding chamber. A heat treatment apparatus is used which has, as an atmosphere control means in the nitriding chamber, an ammonia sensor for detecting the ammonia concentration in the atmospheric gas in the nitriding chamber and a control unit for controlling the ammonia concentration in the atmospheric gas, The process involves supplying a carburizing gas under reduced pressure in the carburizing chamber to perform vacuum carburizing on the workpiece, The process of transporting the transport unit to the nitriding chamber, keeping the carburized workpiece received from the carburizing chamber warm in the warming chamber, and then transporting it to the nitriding chamber, The process involves supplying an ammonia-containing introduction gas to the nitriding chamber under nitriding pressure to perform nitriding on the workpiece, Includes, A heat treatment method characterized in that, in the nitriding process, the ammonia concentration in the introduced gas and the flow rate of the introduced gas are set to predetermined conditions, the introduced gas is introduced into the nitriding chamber, an ammonia concentration increase process is performed at the start of the introduction of the introduced gas to increase the ammonia concentration in the atmosphere gas, and thereafter, a target concentration maintenance process is performed to maintain the target ammonia concentration by feeding back the concentration detected by the ammonia sensor and adjusting the flow rate of the introduced gas.

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