Atmospheric heat treatment furnace

Abstract

To provide an atmospheric heat treatment furnace capable of suppressing a use amount of N2 gas and avoiding or reducing deterioration of controllability in furnace atmosphere control.SOLUTION: An atmospheric heat treatment furnace 10 includes furnace temperature control means 45 for adjusting a control output to heating means so that the furnace temperature approaches a target temperature, and furnace atmosphere control means 75 for adjusting a flow rate of the atmosphere adjusting gas supplied into the furnace so that an index value (PF) of the carbon potential determined from the CO concentration and the CO2 concentration in the furnace atmosphere becomes a predetermined value. The furnace atmosphere control means 75 supplies CO-containing gas, or CO-containing gas and N2 gas into the furnace as the atmosphere adjusting gas in a heating step, and supplies CO-containing gas and CO2 gas, or CO-containing gas and air into the furnace as the atmosphere adjusting gas in a soaking step and a cooling step.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an atmospheric heat treatment furnace suitable for use in heat treating steel materials and the like. [Background technology]

[0002] In atmospheric heat treatment furnaces used for heat treatment of steel materials, the atmosphere inside the furnace is controlled using gases containing CO and CO2. The index of atmosphere control in this case is the carbon potential index value (PF = (CO%)), which is determined from the CO concentration (%) and CO2 concentration (%). 2 / CO2%) is used, and the flow rate of the atmosphere adjusting gas supplied into the furnace is adjusted so that the PF value calculated from the detected values ​​of the CO concentration and CO2 concentration in the furnace atmosphere gas matches a predetermined target value.

[0003] Generally, RX gas as a CO-containing gas and N2 gas as an inert gas are used as atmosphere adjusting gases. By supplying RX gas into the furnace, the PF of the atmosphere in the furnace can be increased, and by reducing the flow rate of RX gas, the rate at which the PF increases can be suppressed. Furthermore, by supplying N2 gas into the furnace, the atmospheric gas is diluted, and the PF can be reduced. Such PF control using RX gas and N2 gas is described in, for example, Patent Document 1 listed below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-132997 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-described PF control increases the running costs due to the increased amount of N2 gas used. Furthermore, supplying N2 gas to the furnace reduces both the CO and CO2 concentrations in the furnace atmosphere, leading to poor controllability. In particular, if the CO2 concentration in the furnace atmosphere becomes too low, it becomes difficult to control the atmosphere in the low PF region.

[0006] In light of the above circumstances, the present invention aims to provide an atmospheric heat treatment furnace that can reduce the amount of N2 gas used and avoid or reduce deterioration in the controllability of the atmosphere inside the furnace. [Means for solving the problem]

[0007] The atmospheric heat treatment furnace according to the first aspect of the present invention is defined as follows: A furnace body, an in-furnace temperature control means for adjusting a control output for the heating means so that the in-furnace temperature approaches a target temperature; an atmosphere control means for controlling the flow rate of the atmosphere adjusting gas supplied into the furnace so that PF, which is an index value of the carbon potential determined from the CO concentration and CO2 concentration in the atmosphere gas in the furnace, becomes a predetermined value; and The furnace atmosphere control means is In a heating step of heating the inside of a furnace to a predetermined temperature, a CO-containing gas or a CO-containing gas and N gas are supplied into the furnace as the atmosphere adjusting gas; In a soaking step in which the inside of the furnace is maintained within a predetermined temperature range, and in a cooling step in which the inside of the furnace is cooled to a predetermined temperature, a CO-containing gas and CO2 gas, or a CO-containing gas and air, are supplied into the furnace as the atmosphere adjusting gas.

[0008] According to the atmospheric heat treatment furnace of the first aspect defined as above, CO gas or air is supplied into the furnace instead of N gas during the PF control in the soaking step and the cooling step, so that the amount of N gas used can be reduced. Furthermore, when N2 gas is supplied into the furnace, both the CO2 and CO concentrations in the furnace atmosphere fluctuate, whereas when CO2 gas or air is supplied into the furnace, only the CO2 concentration fluctuates, improving controllability. Supplying CO2 gas or air suppresses the decrease in the CO2 concentration in the furnace atmosphere, thereby avoiding or mitigating the deterioration of controllability caused by a decrease in CO2 concentration.

[0009] Here, the atmospheric heat treatment furnace may be of a batch type in which heating, soaking, and cooling are performed in the same section of the furnace body (second aspect).

[0010] In addition, in this invention, the furnace atmosphere control means can purge N2 gas so that the CO concentration in the furnace atmosphere gas is equal to or lower than a predetermined value before the material is discharged from the furnace, and can adjust the flow rate of CO2 gas supplied into the furnace so that the PF is a predetermined value (third aspect). In this way, the PF of the furnace atmosphere before the material is discharged can be controlled to a low value, and the risk of unintended carburization can be avoided.

[0011] Furthermore, in this invention, a CO2 concentration recovery function unit can be added to the furnace atmosphere control means, which adjusts the flow rate of CO2 gas or air supplied into the furnace when the CO2 concentration in the furnace atmosphere gas falls below a threshold value so that the CO2 concentration is equal to or higher than the threshold value (fourth aspect). In this way, the reduced CO2 concentration can be quickly restored to a predetermined value or higher, compared to when the furnace atmosphere is controlled only by the above-mentioned PF control.

[0012] Furthermore, this atmospheric heat treatment furnace can be configured to further include an atmosphere adjusting gas switching means for selectively switching between CO2 gas and air as the atmosphere adjusting gas and supplying the gas into the furnace (fifth aspect). In this way, the atmosphere adjusting gas (CO2 gas or air) supplied into the furnace can be selectively switched. For example, when treating steel types that do not have problems such as intergranular oxidation, supplying air into the furnace instead of CO2 gas can reduce running costs. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic overall configuration of an atmospheric heat treatment furnace according to an embodiment of the present invention. [Figure 2] 2 is a schematic diagram showing elements involved in controlling the temperature inside the atmospheric heat treatment furnace of FIG. 1. FIG. [Figure 3] 2 is a schematic diagram showing elements related to controlling the atmosphere and pressure inside the furnace in the atmospheric heat treatment furnace of FIG. 1. FIG. [Figure 4] FIG. 10 is an explanatory diagram of PF control in the soaking and cooling steps. [Figure 5] 3A and 3B are diagrams showing an example of a heat pattern and a PF setting pattern in a heat treatment using the atmospheric heat treatment furnace of the present embodiment. [Figure 6] FIG. 1 is a diagram showing changes in CO concentration and CO2 concentration during the pre-fuel purge process. [Figure 7] FIG. 10 is an explanatory diagram of a modified example in which a function for restoring CO2 concentration is further added. [Figure 8] FIG. 10 is an explanatory diagram of a modified example further including an atmosphere adjusting gas switching means. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a diagram showing a schematic overall configuration of an atmosphere heat treatment furnace according to one embodiment of the present invention. In the figure, reference numeral 10 denotes a batch-type atmosphere heat treatment furnace used for annealing a workpiece such as a wire coil or a steel bar, and a heating chamber 13 is formed inside a box-shaped furnace body 12. An entrance / exit 14 is formed at one end in the longitudinal direction of the furnace body 12, and the workpiece is loaded into the furnace (heating chamber 13) through the entrance / exit 14 by a group of rollers 15. The entrance / exit 14 can be opened and closed by a door 17 connected to a drive device 16.

[0015] In the heating chamber 13, a plurality of radiant tube burners 20 and ceiling fans 24 are provided along the conveying direction (longitudinal direction), and a gas introduction pipe 19 for introducing various gases is connected.

[0016] 2 is a schematic diagram showing elements involved in controlling the temperature inside the atmosphere heat treatment furnace 10. As shown in the figure, the atmosphere heat treatment furnace 10 is equipped with a temperature detector 26, a plurality of radiant tube burners 20 as heating means, and a temperature control unit 43. These constitute the furnace temperature control means 45 of the present invention.

[0017] The temperature detector 26 detects the temperature inside the furnace and transmits the temperature information to the temperature control unit 43. The type of the temperature detector 26 is not particularly limited, but a known thermocouple or radiation thermometer can be used in consideration of the measurable range, responsiveness, etc.

[0018] The radiant tube burner 20 comprises a pipe-shaped tube body 21 and a combustion burner 22 arranged coaxially in the hollow section at one end of the tube body 21. A fuel supply pipe 30 and an air supply pipe 36 are connected to the combustion burner 22, and a flow control valve 33 is provided on the main pipe 31 side of the fuel supply pipe 30, and a flow control valve 39 is provided on the main pipe 37 side of the air supply pipe 36. Manual valves 34, 40 are provided on each of the branch pipes 32, 38 of the fuel supply pipe 30 and the air supply pipe 36, and the opening degrees of these valves are adjusted in advance so that fuel gas and combustion air are supplied evenly to each combustion burner 22.

[0019] The temperature control unit 43 adjusts the control output for the radiant tube burner 20 so that the detected temperature received from the temperature detector 26 becomes a preset target temperature during operation (heat pattern in FIG. 5(A)). A control signal corresponding to this control output is sent to the flow control valves 33 and 39, which increase or decrease the opening of these flow control valves 33 and 39, thereby controlling the heat output of the combustion burner 22. When cooling the inside of the furnace, the supply of fuel gas is stopped and only air is circulated through the tube body 21.

[0020] Such a temperature control unit 43 can be realized by, for example, a PLC (Programmable Logic Controller) or a temperature regulator that includes a data processing unit, a storage unit, a communication I / F unit, etc. Note that the atmosphere control unit 66 and pressure control unit 72, which will be described later, can also be realized by a PLC or various regulators.

[0021] 3 is a schematic diagram showing elements related to furnace atmosphere control and furnace pressure control in the atmospheric heat treatment furnace 10. As shown in the figure, an RX gas supply pipe 47, N2 gas supply pipes 48, 49, and 50, and a CO2 gas supply pipe 51 are connected to a gas inlet pipe 19 connected to the furnace body 12. A check valve 54 is connected to a gas delivery pipe 53 connected to the furnace body 12, and some of the various gases supplied into the furnace are discharged to the outside of the furnace through the gas delivery pipe 53.

[0022] In the figure, reference numeral 73 denotes an in-furnace pressure control means, which includes a pressure detector 68, a gas introduction pipe 19, an N2 gas supply pipe 48, a flow control valve 69, and a pressure control unit 72, and controls the in-furnace pressure to be maintained at or above atmospheric pressure.

[0023] The pressure detector 68 detects the pressure inside the furnace and transmits a signal corresponding to the detected pressure value (detected value). The detected value may be absolute pressure or a differential pressure from atmospheric pressure. The pressure detector 68 may be, for example, a manometer.

[0024] The N2 gas supply pipe 48 supplies N2 gas from an N2 gas supply source 61 to the gas introduction pipe 19 during furnace pressure control, and introduces the N2 gas into the furnace via the gas introduction pipe 19, and is equipped with a flow rate control valve 69.

[0025] The pressure control unit 72 is connected to a pressure detector 68 and a flow rate control valve 69 on the N2 gas supply pipe 48, and outputs a control output corresponding to the valve opening to the flow rate control valve 69. In this embodiment, the pressure inside the furnace is maintained at or above atmospheric pressure by supplying N2 gas into the furnace.

[0026] Next, the furnace atmosphere control means 75 will be described. The furnace atmosphere control means 75 includes an analyzer 65, a gas inlet pipe 19 as an atmosphere adjustment gas introduction means, an RX gas supply pipe 47 and flow rate control valve 58, an N2 gas supply pipe 49 and flow rate control valve 64, a CO2 gas supply pipe 51 and flow rate control valve 63, and an atmosphere control unit 66. The furnace atmosphere control means 75 performs PF control, which adjusts the flow rate of the atmosphere adjustment gas supplied into the furnace so that the carbon potential index value (PF), determined by the ratio of the CO2 gas concentration (CO2%) to the square of the CO gas concentration (CO%) in the furnace atmosphere gas, shown in the following equation (1), reaches a target value. This makes it possible to create an atmosphere inside the heating chamber 13 that does not cause decarburization or carburization. PF=(CO%) 2 / CO2% … Formula (1)

[0027] The RX gas supply pipe 47 supplies the RX gas generated in the RX gas generator 56 to the gas inlet pipe 19 and introduces it into the furnace via the gas inlet pipe 19, and is fitted with a flow control valve 58. Here, the RX gas is an endothermic modified gas, and is composed mainly of CO, H2, and N2.

[0028] The N2 gas supply pipe 49 supplies N2 gas from an N2 gas supply source 61 to the gas introduction pipe 19, and introduces the N2 gas into the furnace via the gas introduction pipe 19, and is equipped with a flow rate control valve 64. The CO2 gas supply pipe 51 supplies CO2 gas from a CO2 gas supply source 62 into the furnace via a gas introduction pipe 19, and is equipped with a flow rate control valve 63.

[0029] In FIG. 3, 65 is an analyzer and 66 is an atmosphere control unit. The analyzer 65 measures the CO 2 gas concentration (CO 2 %) and CO gas concentration (CO %) in the furnace, and sends the measurement signal to the atmosphere control unit 66. The atmosphere control unit 66 is connected to the analyzer 65 as well as the flow rate control valves 58, 64, and 63 on the RX gas supply pipe 47, N2 gas supply pipe 49, and CO2 gas supply pipe 51. The atmosphere control unit 66 receives a measurement signal from the analyzer 65 and calculates the carbon potential index value (PF) shown in the above formula (1). The atmosphere control unit 66 is configured with a PID control system, and executes feedback control based on the deviation between the calculated PF and a preset target value (PF setting pattern shown in FIG. 5(B)), and outputs a control output corresponding to the opening of each flow rate control valve. Control signals corresponding to these control outputs are then input to the flow rate control valves 58, 64, and 63, respectively, and the flow rates of the RX gas, N2 gas, and CO2 gas supplied into the furnace via these flow rate control valves are adjusted.

[0030] In the furnace atmosphere control means 75 configured in this manner, the atmosphere adjustment gas used can be changed in accordance with each step of the heat treatment. For example, the heating step of heating the furnace to a predetermined temperature is a phase in which the PF value of the furnace atmosphere is increased, as shown in Fig. 5, and in the heating step, the PF is controlled by using the RX gas as the atmosphere adjustment gas. By controlling the flow rate of the RX gas supplied into the furnace based on the deviation between the calculated PF and the PF setting pattern as a target value, the PF can be increased in accordance with the PF setting pattern. In the heating process, N2 gas can be used together with RX gas to reduce the overshooting PF, etc. However, CO2 gas is not used in the heating process. This is because, in the heating process, the CO2 concentration in the furnace atmosphere is expected to be quite high, as shown in Figure 5(B), and if CO2 gas is further introduced into the furnace in this state, the upper limit of the PF control range will be limited, and it may not be possible to quickly increase the PF.

[0031] In the soaking process and cooling process following the heating process, PF is controlled using RX gas and CO2 gas as atmosphere adjustment gases. In these sections, when PF is increased to match the target value (PF setting pattern), RX gas is supplied into the furnace with its flow rate adjusted based on the deviation between the calculated PF and the PF setting pattern as the target value, as shown in Figure 4. On the other hand, when PF is decreased, CO2 gas is supplied into the furnace with its flow rate adjusted based on the deviation between the calculated PF and the target value (PF setting pattern), as shown in Figure 4. In the example of Figure 4, the region where the deviation between the calculated PF and the target value is small is designated as a non-use region where no atmosphere adjustment gas is supplied into the furnace.

[0032] 4 shows an example in which PF is controlled by selectively using RX gas and CO2 gas, but the control method is not limited to this. For example, it is also possible to control the atmosphere so as to obtain the target PF by continuously supplying RX gas into the furnace while supplying both RX gas and CO2 gas into the furnace as needed.

[0033] Next, the operation of heat treatment (for one batch) performed in the atmospheric heat treatment furnace 10 will be described. After the object to be heated is loaded into the furnace (heating chamber 13) through the entrance / exit 14, the door 17 is closed and a series of heat treatments is initiated. First, N2 gas for purging is introduced into the furnace through the N2 gas supply pipe 49, and the air inside the furnace is exhausted to the outside. Next, atmospheric heating by the burner 20 is initiated in accordance with the heat pattern shown in Figure 5(A).

[0034] In the heating step, when the furnace is heated to a predetermined temperature, the furnace atmosphere control means 75 starts PF control so that the carbon potential index value (PF) of the furnace atmosphere coincides with the PF setting pattern shown in Fig. 5(B). In this heating step, in which the PF setting pattern also rises in accordance with the heat pattern, RX gas is supplied into the furnace as an atmosphere adjusting gas, and the PF of the furnace atmosphere is controlled so as to rise in accordance with the PF setting pattern.

[0035] In the soaking process following the heating process, the temperature inside the furnace is kept substantially constant, and the value of the PF setting pattern is also constant. In this soaking process, RX gas and CO2 gas are supplied into the furnace as atmosphere adjusting gases, and the PF of the furnace atmosphere is controlled to be substantially constant within a predetermined range. In the cooling process following the soaking process, the furnace is cooled to a specified temperature, and the PF setting pattern also decreases in accordance with the heat pattern. In this cooling process, as in the soaking process, RX gas and CO2 gas are supplied into the furnace as atmosphere adjustment gases, and the PF of the furnace atmosphere is controlled to decrease in accordance with the PF setting pattern.

[0036] As shown by the dashed line in Figure 5(B), the CO2 concentration in the furnace atmosphere gas rises significantly once during the heating process due to the reaction of iron oxide and moisture in the heated object with the RX gas, and then decreases from the soaking process to the cooling process. If N2 gas were used as an atmosphere adjusting gas to hypothetically reduce the PF of the furnace atmosphere, the N2 gas would further reduce the CO2 concentration in the furnace atmosphere gas, resulting in a decrease in PF controllability. However, in this embodiment, CO2 gas is supplied into the furnace instead of N2 gas during the soaking and cooling processes, so that deterioration in controllability due to a decrease in CO2 concentration can be avoided.

[0037] In the pre-discharge purging process, which is performed after the cooling process, N2 gas for purging is introduced into the furnace through the N2 gas supply pipe 49 to safely remove the heated material from the furnace. This reduces the CO2 concentration in the furnace to a predetermined concentration or lower, allowing the furnace to be discharged without causing a fire. FIG. 6 is a diagram showing the CO2 concentration and CO2 concentration during the pre-discharge purging process. As shown in the figure, the introduction of N2 gas into the furnace during the pre-discharge purging process significantly reduces the CO2 concentration in the furnace atmosphere gas. Normally, the CO2 concentration would also decrease at this time. However, in this embodiment, the furnace atmosphere control means 75 supplies CO2 gas into the furnace so that the PF is maintained at a predetermined value. This suppresses the decrease in CO2 concentration, and the PF of the furnace atmosphere can be reduced to a low value according to the PF setting pattern.

[0038] As described above, according to the atmospheric heat treatment furnace 10 of this embodiment, CO2 gas is supplied into the furnace instead of N2 gas during PF control in the soaking step and the cooling step, so that the amount of N2 gas used can be reduced. When N2 gas is supplied into the furnace, both the CO2 and CO concentrations in the furnace atmosphere fluctuate, whereas when CO2 gas is supplied into the furnace, only the CO2 concentration fluctuates, improving PF controllability. Furthermore, supplying CO2 gas suppresses the decrease in CO2 concentration in the furnace atmosphere, thereby avoiding or mitigating the deterioration of controllability caused by a decrease in CO2 concentration.

[0039] Furthermore, in the atmospheric heat treatment furnace 10 of this embodiment, the furnace atmosphere control means 75 purges N gas so that the CO concentration in the furnace atmosphere gas becomes a predetermined value or less before the material is removed from the furnace, and adjusts the flow rate of CO gas supplied into the furnace so that the PF becomes a predetermined value. Therefore, the PF of the furnace atmosphere before the material is removed from the furnace can be controlled at a desired low value, and the risk of unintended carburization can be avoided.

[0040] Next, a modification of this embodiment will be described. In the above embodiment, CO2 gas is used instead of N2 gas in the PF control in the soaking step and the cooling step to suppress a decrease in the CO2 concentration in the furnace atmosphere gas. However, if a large amount of N2 gas is supplied for the purpose of maintaining the furnace pressure, the CO2 concentration may decrease more than expected. Figure 7 shows an example in which a CO2 concentration recovery function unit 80 is added to the furnace atmosphere control means 75 to quickly restore the CO2 concentration to above the threshold value when the CO2 concentration in the furnace atmosphere gas falls below the threshold value.

[0041] As shown in FIG. 7(B), the CO2 concentration recovery function unit 80 includes a valve opening degree calculation unit 82 and a high selector 86. The valve aperture calculation unit 82 is connected to the analyzer 65 that measures the CO2 concentration in the furnace atmosphere, a condition setting unit 84 in which a threshold value SV for starting the valve aperture calculation operation is set, and a high selector 86. When the CO2 concentration PV from the analyzer 65 falls below the threshold value SV and it has been 30 minutes or more since the start of soaking, the valve aperture calculation unit 82 starts the valve aperture calculation operation and outputs a control output MV2 corresponding to the valve aperture (the valve aperture of the CO2 gas flow rate control valve 63) for increasing the CO2 concentration based on the deviation between the CO2 concentration PV and the threshold value SV. When the control output MV2 calculated by the valve opening calculation unit 82 and the control output MV1 as the valve opening calculated by PF control are input to the high selector 86, the high selector 86 outputs the larger of these two control outputs as the control output for the flow rate adjustment valve 63.

[0042] For example, if the CO2 concentration corresponding to the threshold value SV is E1 shown in Figure 7(A), when the CO2 concentration in the furnace atmosphere gas decreases and falls below E1 shown in Figure 7(A), the supply amount of CO2 gas increases based on the control output from the high selector 86 (the larger of MV1 and MV2), thereby increasing the CO2 concentration in the furnace atmosphere gas.

[0043] 7(A) is the CO2 concentration that is the condition for terminating the valve opening calculation operation. CO2 concentration E2 is set to a value higher than CO2 concentration E1, and in this example, when the CO2 concentration PV from the analyzer 65 reaches CO2 concentration E2, the valve opening calculation operation in the valve opening calculation unit 82 terminates, and thereafter the valve opening of the flow rate adjustment valve 63 is controlled by the control output MV1 calculated by normal PF control. As described above, according to the example of FIG. 7 equipped with the CO2 concentration recovery function unit 80, the reduced CO2 concentration can be quickly restored to above the threshold value, compared to when the atmosphere inside the furnace is controlled only by PF control.

[0044] FIG. 8 is an explanatory diagram of a modified example further including an atmosphere adjusting gas switching means. In the above embodiment, CO2 gas is used as the atmosphere adjusting gas, but in some cases, air can be used as the atmosphere adjusting gas instead of CO2 gas. When air is supplied into the furnace, the CO2 gas in the furnace is oxidized by the oxygen in the air to generate CO2 gas.

[0045] In the example of FIG. 8, an air supply pipe 91 is installed in parallel with a CO gas supply pipe 51. This air supply pipe 91 supplies air from an air supply source 92 into the furnace via a gas inlet pipe 19. In the example of FIG. 8, the parallel CO gas supply pipe 51 and air supply pipe 91 are each provided with on-off valves 95 and 96 as atmosphere adjustment gas switching means. By opening one on-off valve and closing the other on-off valve, CO gas or air can be selectively switched and supplied into the furnace as the atmosphere adjustment gas. For example, by using air as the atmosphere adjustment gas for heated objects made of steel types that do not suffer from problems such as intergranular oxidation, running costs can be reduced.

[0046] Although the embodiments of the present invention have been described in detail above, these are merely examples. For example, the heat pattern and PF setting pattern executed during heat treatment are not limited to the examples of the above embodiments and can be appropriately changed as needed. Furthermore, in the above embodiments, RX gas is used as the CO-containing gas, but CO-containing gases other than RX gas can also be used. Furthermore, while the above embodiments are directed to an atmosphere heat treatment furnace having an inlet and outlet formed at one end of the furnace body in the longitudinal direction, the present invention can also be applied to a straight-through type atmosphere heat treatment furnace having an inlet at one end of the furnace body in the longitudinal direction and an outlet at the other end. For example, the present invention can be configured in various forms with modifications within the scope of its spirit. [Explanation of symbols]

[0047] 10 Atmospheric heat treatment furnace 12 Furnace body 13 Heating chamber (inside the furnace) 20 Radiant tube burner (heating means) 45 Furnace temperature control means 75 Furnace atmosphere control means 80 CO2 concentration recovery function section 95, 96 On-off valve (atmosphere adjusting gas switching means)

Claims

1. A furnace body, an in-furnace temperature control means for adjusting a control output for the heating means so that the in-furnace temperature approaches a target temperature; CO concentration in the furnace atmosphere gas and CO 2 an atmosphere control means for controlling the flow rate of an atmosphere adjusting gas supplied into the furnace so that PF, an index value of carbon potential determined from the concentration, becomes a predetermined value; and The furnace atmosphere control means is In the heating step of heating the inside of the furnace to a predetermined temperature, a CO-containing gas or a CO-containing gas and N 2 A gas is supplied into the furnace as the atmosphere adjusting gas, In a soaking step of maintaining the inside of the furnace at a predetermined temperature range and a cooling step of cooling the inside of the furnace to a predetermined temperature, a CO-containing gas and CO 2 a gas, or a CO-containing gas and air, is supplied into the furnace as the atmosphere adjusting gas.

2. 2. The atmospheric heat treatment furnace according to claim 1, which is a batch type in which heating, soaking and cooling are performed in the same section of the furnace body.

3. The furnace atmosphere control means controls the amount of N 2 so that the CO concentration in the furnace atmosphere gas is equal to or less than a predetermined value before the furnace is taken out. 2 The gas is purged and CO is supplied into the furnace so that the PF reaches a predetermined value. 2 The atmospheric heat treatment furnace according to claim 1 , wherein the flow rate of the gas is adjusted.

4. The furnace atmosphere control means is configured to control the amount of CO in the furnace atmosphere gas. 2 When the concentration falls below a threshold, 2 CO is supplied into the furnace so that its concentration is equal to or greater than the threshold value. 2 CO to regulate the flow rate of gas or air 2 The atmospheric heat treatment furnace according to claim 1 , further comprising a concentration recovery function section.

5. CO 2 2. The atmospheric heat treatment furnace according to claim 1, further comprising an atmosphere adjusting gas switching means for selectively switching between a gas and air as the atmosphere adjusting gas and supplying the gas into the furnace.

Images