JPS6057505B2 - Gas carburizing method using nitrogen, organic liquid, and hydrocarbon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas carburizing method using nitrogen, an organic liquid, and a hydrocarbon, and in particular, a method in which nitrogen and an organic liquid are directly introduced into a carburizing furnace without using a conversion furnace for generating a carrier gas. The amount of Co in the atmosphere gas in the furnace and the amount of CO are reduced by introducing a carrier gas.

This is an economical carburizing method that can significantly reduce the consumption of gas raw materials, has a stable carburizing effect, and is easy to control the atmosphere. get. Common conventional gas carburizing methods include a conversion furnace gas carburizing method and a dripping gas carburizing method. In the shift furnace type gas carburizing method, the carrier gas is a hydrocarbon gas such as propane or methane. It is produced by introducing it into contact with a nickel catalyst in a shift furnace.

In other words, when using methane (CH0) as a raw material, 2CH
, +O2+3.76N2■2C0+4H2+3.76N
2CH, +20, +7.52N. ■CO. +2H20+
7.52 When a reaction of N2 occurs and propane (C, Ho) is used as a raw material, 2C3Hf3+ 302+ 3×3
．． 76N2:6CO+8H2+11.28N2C3H
(ρ2+ 5×3.76N2 ■3C02+4H20+18.8N2 reaction occurs.

The gas produced in this way contains 24.5% Co and H
2 is 31.2%, C02 is 0.26%, H (50 is 0.
The composition is 4% and the rest is N2.

This endothermic transformed gas is introduced into the carburizing furnace as a carrier gas, but this alone does not provide the carbon potential necessary for carburizing.

Therefore, in order to increase the carbon potential in the furnace, a hydrocarbon gas such as propane is added to this carrier gas as an enrichment gas. The gas reaction inside the carburizing furnace at this time is as follows. C3HB+C00=2C0+2CH
.

CH, +C0, =2C0+ S In this way, C02 decreases and Co increases, so steel products can be carburized by the Boudouard reaction, which is the basic reaction of carburization.

As mentioned above, in the shift furnace type gas carburizing method, a shift furnace is indispensable, and this shift furnace must be able to withstand high temperatures and be large in size.Additionally, there are problems in that the operation of the shift furnace must be constantly controlled. Furthermore, carburizing has the disadvantage that it requires the use of large quantities of expensive hydrocarbons as raw materials for endothermic metamorphic gas and enrichment gas.

Furthermore, since the carrier gas must be passed through 8 to 1@ of the furnace internal volume per hour, there is also the drawback that the amount of gas consumed is large. On the other hand, the dripping gas carburizing method uses C, H, and O as raw materials.
An organic liquid containing the following components is directly injected into a carburizing furnace, CO gas is generated by thermal decomposition of this organic liquid, and carburization is similarly carried out by the Boudouard reaction.

Examples of organic liquids used in dripping gas carburizing include methyl acetate (Group C COOCH3), isopropanol (
] CH・0H), methanol (CH3OH), etc., and these decompose and react in the carburizing furnace as follows.
--1---V-! ^AZln8l- Among these, [C] in formulas (1) and (2) works for carburizing, but formula (3) has a weak carburizing ability and is used as a carrier gas.

When methanol is used as a carrier gas, the CO2 gas in the furnace is measured with an infrared analyzer, and an organic liquid with strong carburizing properties such as isopropanol or a hydrocarbon gas such as propane is added as an enrichment gas.
The carbon potential is controlled by adding an organic liquid agent that maintains a constant carbon potential during the carburization period and the diffusion period.
The dripping gas carburizing method described above does not require a conversion furnace, the atmosphere can be easily controlled, and it is suitable for intermittent operation of the furnace. The disadvantage is that the fuel consumption is high, since approximately 2 to 3 times the product must flow. In addition, both the shift furnace type gas carburizing method and the dripping type gas carburizing method have a strong risk of explosion due to the large amounts of CO and H2 in the atmospheric gas, and surface abnormalities such as grain boundary oxidation due to the large amount of CO. Layers are becoming a problem.

This conventional gas carburizing method is disadvantageous in today's resource-saving and energy-saving era, so the gas necessary for carburizing is directly supplied without using a conversion furnace.
The N2-based carburizing method, which generates carburizing in a furnace, is attracting attention.

However, currently announced N2-based carburizing methods use a mixture of methane and CO2 as nitrogen gas, or use high-purity nitrogen and high-purity methanol, but these methods do not allow It is difficult to easily generate carburizing gas and control the atmosphere. In addition, even with the carburizing method using nitrogen, organic liquid, and hydrocarbon, which can easily generate a carrier gas, if only JCO2 is measured and the atmosphere is controlled, the carbon
Since the O concentration fluctuates and the hydrocarbon gas is further enriched, the fluctuation is further exacerbated by the amount added, making it difficult to adjust the atmosphere. This invention was made to eliminate such drawbacks of the conventional gas carburizing method,
The purpose of this invention is to accurately and easily control the carbon potential during carburizing in an atmospheric gas containing nitrogen as a main component, and the purpose of this invention is to provide a carburizing method with simple implementation equipment. A further object of the present invention is to provide an economical carburizing method that meets the requirements for resource saving and energy saving, and a further object of the invention is to provide a method that provides a good carburizing effect. A further object of the invention is to provide a less dangerous gas carburizing method.

That is, in this invention, nitrogen and an organic liquid agent are introduced into a carburizing furnace as a carrier gas, and the CO concentration of the carrier gas is set to 10 to 20%, and then the carbon in the furnace atmosphere gas is
Measure the amount of O and CO2, compare the measured values with the set value of CO2 corresponding to the equilibrium carbon concentration of the atmospheric gas, and add hydrocarbon gas according to the deviation to adjust the equilibrium carbon concentration in the furnace. The present invention relates to a gas carburizing method characterized in that carburizing is carried out while adjusting.

In this invention, a carrier gas with a lower CO concentration than the conventional gas carburizing method is directly generated in the furnace using inexpensive nitrogen and a small amount of organic liquid such as methanol, without the need for a shift furnace. of. Measure the amount of CO and CO2,
This method is characterized by carburizing by enriching it with a hydrocarbon gas such as puyamaman to control the atmosphere.

That is, since the present invention controls the atmosphere by measuring both CO and CO2 components, there is no need to flow a large amount of carrier gas to keep the CO concentration constant (less than 2 times the internal volume of the furnace). h) Since the CO concentration is lower than in the conventional gas carburizing method (CO: 10-20%), the consumption of expensive organic liquid or hydrocarbon gas as enrichment gas can be significantly reduced. Furthermore, since nitrogen and organic liquid agents such as methanol are used, a carrier gas can be easily generated in the furnace and enriched with a hydrocarbon gas such as propane, so the atmosphere can be easily controlled. The gas reaction inside the carburizing furnace will now be explained as follows. That is, when methanol is added to the furnace, a reaction occurs as shown in equation (3) above, and CO<5H2 is produced at a volume ratio of 1:2.

In this case, nitrogen is also introduced into the furnace at the same time, so
If nitrogen and methanol are introduced into the furnace at a constant flow rate ratio, a carrier gas with a nearly constant composition will be generated in the furnace, although the CO concentration will fluctuate depending on the conditions inside the furnace and the condition of the product being processed. .

(However, there is a drawback in the accuracy of the technology for keeping the flow rate ratio of nitrogen and methanol constant.) Since the carbon potential necessary for carburizing cannot be obtained with the generated carrier gas alone, a hydrocarbon gas such as propane is added as an enrichment gas in order to increase the carbon potential of the atmosphere in the carburizing furnace. The gas reaction inside the furnace at this time is as follows. Controlling carbon potential through enrichment with propane, etc. is based on the Boudouard reaction used in conventional carburizing methods.
? Rib 2) Here, c: Saturation PCO, PCO2; Partial pressure of CO and CO2, respectively Now, if we transform equation (5) into equation (4), we get
Cpsat, where S=K, is a constant determined by temperature.

From equation (6), the CO concentration and CO2 concentration in the atmosphere inside the furnace are measured, and the equilibrium carbon concentration of the atmospheric gas is determined from the measured value of CO concentration, the furnace temperature, and the target carbon concentration set value on the steel surface. Calculate the corresponding CO2 concentration, use this value as the set value, compare it with the previously measured CO2 concentration value in the furnace, and calculate the amount of enrichment gas supplied to the furnace based on the deviation at this time. By controlling this, a stable potential atmosphere can be obtained regardless of any compositional fluctuations.

FIG. 1 is a block diagram showing an embodiment of the control device used in the present invention. A heat treatment furnace 1 maintained at a constant processing temperature is equipped with a motor M and a fan F facing into the furnace. This heat treatment furnace 1 has a furnace lid with a heater H installed inside the furnace.
Processed steel products are charged into the tank and carburized. Into this heat treatment furnace 1, a dropping agent for generating nitrogen and carburizing gas is supplied from a supply source (not shown) through a pipe line 2, and enrichment gas is similarly supplied from a supply source (not shown) through a control valve 4.
The carbon gas is supplied through the pipe line 3 to generate an atmospheric gas having a predetermined equilibrium carbon concentration. This atmospheric gas is supplied from a pipe 5 to a CO analyzer 6 connected to the pipe 5.
sent to. The CQ image analyzed by the CO analyzer 6 is input to the arithmetic unit 10 as a CQ analysis signal. Also,
The temperature inside the furnace is measured by the thermocouple 7 and used as a temperature signal, or a signal corresponding to the temperature inside the furnace is set in advance and inputted to the calculation device 10 in the same way. On the other hand, set the surface carbon concentration setting device 8 of the desired steel material treatment product,
Similarly, the calculation device 10 uses this as a target carbon concentration setting signal.
Enter. The arithmetic unit 10 has a built-in arithmetic circuit according to the above-mentioned formula (6), and calculates the equilibrium carbon concentration of the atmospheric gas by performing calculations based on the input CO analysis signal, temperature signal, and target carbon concentration setting signal. Target CO equivalent to
2 Calculate the amount.

This target CO2 amount is input as a set value of the CO2 controller 9. Moreover, the atmospheric gas in the furnace is connected to the pipe 5.
The amount of CO2 is analyzed by the O2 analyzer 11 and fed back to the CO2 controller 9 as a CO2 analysis signal.

C.O. The controller 9 compares the target CO2 amount signal input as a set value from the arithmetic unit 10 with the CO2 analysis signal input as a measured value from the CO2 analyzer 11, and adjusts the pipe line using the deviation signal generated thereby. control valve 4 connected to 3
The control valve 4 is operated to adjust the opening degree of the control valve 4 according to the magnitude of the deviation signal. In this way, the amount of enrichment gas supplied into the heat treatment furnace 1 is increased or decreased, and the equilibrium carbon concentration of the atmospheric gas within the furnace is maintained at a desired value. CO. in the atmospheric gas in the above examples. As a method for analyzing the CO content and CO content, for example, an infrared absorption method, a gas chromatography method, or any other appropriate method may be employed.

Further, as the CO2 controller, a servo setting type one is suitable. As the arithmetic unit, either an analog type or a digital type can be employed. Figure 2 shows two calculation steps when an analog calculation device is used in the embodiment shown in Figure 1.
FIG. The CO analysis signal PcO from the CO analyzer 6 (FIG. 1) is input to a square calculator 12, subjected to a square calculation, and sent to the next multiplier 13 as Pc♂. On the other hand, the temperature signal from the thermocouple 7 is sent by the function generator 14 to the temperature 3CPsat degree coefficient S (=K
) and sent to the multiplier 13.

The multiplier 13 multiplies the signals PcO2 and S, and inputs the signal as PcO2.S to the next divider 15.
The divider 15 divides this PcO2.S by the target carbon concentration setting signal CPeqPcO2.S from the carbon concentration setting device 8.

, E, to the Cα controller 9. In this way, the target CO2 amount corresponding to the equilibrium carbon concentration of the atmospheric gas is input to the CO2 controller 9 as a set value. From the time chart in Figure 3, first, when the product is put into the furnace, the temperature inside the furnace drops, so only nitrogen gas is flowed to sufficiently purge the inside of the furnace until the temperature rises to the carburizing temperature.

Next, as the temperature is raised, nitrogen and methanol are flowed at a constant rate.
The product is allowed to heat up until it is soaked, and once the soaking is complete, propane is added to control the atmosphere during the carburizing, temperature lowering, and quenching holding periods. The implementation specifications are as follows.

N2: 1.2577? Ih Methanol 200cc'H C3H8:2e1m Setting CP: 0.8% The average gas composition during carburizing is as follows.

CO: &9~11.3% CO2: 0.022~0.053% H2: 21.10% CH! : 0.08% N2: Remaining The results of sampling test pieces during the carburizing process are shown in the table below.

In this way, even when the amount of CO is about 10%, carburizing is performed at a carburizing speed comparable to that of the conventional carburizing method, and the carbon potential also matches well with the set value.

According to this invention, since a conversion furnace is not required, there is no need for its management.

Furthermore, since the CO concentration is lower than in conventional gas carburizing methods and the flow rate of the carrier gas is reduced, the consumption of expensive organic liquids or hydrocarbon gases as enrichment gases can be significantly reduced. Further, since a carrier gas is easily generated using nitrogen and an organic liquid agent, and since the carrier gas is added as a hydrocarbon gas, the atmosphere can be easily controlled. Furthermore, since there is little twisting component, there is little risk of explosion, and since the amount of CO is small, abnormal surface layers such as grain boundary oxidation are less likely to be formed.

[Brief explanation of drawings]

FIG. 1 is a systematic explanatory diagram of an apparatus for implementing the method of the present invention, FIG. 2 is a block diagram showing a control system, FIG. 3 is a control time chart, and numeral 1 in the figure is a carburizing furnace.

Claims (1)

[Claims] 1. Introduce nitrogen and an organic liquid agent into a carburizing furnace as a carrier gas, and set the CO concentration of the carrier gas to 10 to 20%. Then, measure the amount of CO and the amount of CO_2 in the atmosphere gas in the furnace, and It is characterized by comparing the measured value with the set value of CO_2, which corresponds to the equilibrium carbon concentration of the atmospheric gas, and performing carburizing while adjusting the equilibrium carbon concentration in the furnace by adding hydrocarbon gas according to the deviation. Gas carburizing method.