JPS6350430B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controllably gas carburizing steel components at a predetermined C-level in a furnace atmosphere consisting of a carrier gas derived from methanol and nitrogen and a carburizing agent. The method likewise relates to a method for heating steel parts, which ensures that the carbon content of the part remains constant by means of an adjusted C-level, without increasing or decreasing it.

Various gas carburizing methods are known. According to one known method, a carrier gas is formed in a generator from natural gas, propane or other hydrocarbons, and air in an endothermic reaction, and this gas is then introduced into a carburizing or heat treatment furnace. Propane, natural gas or other hydrocarbons are introduced directly into the furnace atmosphere as a carburizing agent to adjust the desired C-level. Such a method provides the possibility of automatically controlling the supply of carburizing agent via the gas component critical to the C-level of the furnace atmosphere depending on the instantaneous demand to maintain a predetermined C-level. is obtained. Water vapor (dew point), CO ₂ or O ₂ are suitable for this purpose. A disadvantage of this method is that it requires a generator for producing the carrier gas and thermal energy for the operation of the generator outside the heat treatment or carburizing furnace.

Gas carburizing processes without a generator furnace are also known, in which methanol and nitrogen are introduced directly into the furnace in a suitable ratio, thereby forming a carrier gas in the furnace. By this method, a carrier gas with a composition similar to that obtained by the above method is obtained from natural gas and air in the generator (Heat Treatment
of Metals, 1979, pp. 53-58).

These two known methods are based on the following reaction equation: 2CH ₄ + Air → 2CO + 4H ₂ + 4N ₂ 2CH ₃ OH + 4N ₂ → 2CO + 4H ₂ + 4N ₂ Based on equilibrium conditions, small amounts of carbon dioxide, water vapor and oxygen in the carrier gas are This is ignored for the purpose of providing an overview. In the case of the generator method, 5 parts by volume of air are required for 2 parts by volume of natural gas. In the case of methanol method, 0.14m of nitrogen per 100g of methanol ³ _S
is necessary.

From German Patent No. 1 192 486 a controllable carburizing process for steel parts is known, in which two substances are used, one of which can form a carrier gas that generates an overpressure, the other It is a natural carburizing agent. After the carburizing reaction, the composition of the gaseous products in the furnace atmosphere remains the same or nearly the same. This method makes it possible to automatically control the supply of one or both substances, in particular those generating carburizing gases, using the content of one gas component of the furnace atmosphere as a control value. According to this known method, the water vapor content of the furnace atmosphere can be determined continuously or from time to time, in particular by measuring the dew point, or the CO ₂ content, and the supply of substances via these gas components can be controlled. be done. If methanol is used as the material for producing the carrier gas, ethyl acetate, acetone, isopropanol or a mixture of isopropanol and water are suitable as carburizing agents. When acetone is used as the carburizing agent, a mixture of methanol and isopropanol is suitable as the substance forming the carrier gas.

However, the disadvantage of this method is that the dew point is relatively high at low quenching temperatures and/or low C-levels.
Since this is approximately in the room temperature range, this method results in water condensation in the measuring tube, which disturbs the control values and thus leads to incorrect dosing of the carburizing agent.

The object of the invention is to provide a controllable carburizing or heating process for the surface of a steel component at a predetermined C-level, which is simple and reliable to control and can significantly reduce the carrier gas requirements.

The process of the invention starts from gas carburizing in the furnace atmosphere consisting of a carrier gas carburizing agent obtained from methanol and nitrogen, and additionally to the carburizing agent in the form of an oxygen derivative of the hydrocarbon, the gas is added after the carburizing reaction. Nitrogen is supplied in an amount such that the composition has approximately the same composition or remains approximately the same, and the carburizing agent and/or additional nitrogen is supplied in a known manner with a gas critical to the C-level of the furnace atmosphere. It is characterized in that it is controlled by continuously measuring the content of the components. In particular, ethyl acetate is used as a carburizing agent.
Acetone, ethanol or isopropanol are used. Control is preferably carried out via measurement of the oxygen potential or the water vapor content, ie the dew point, of the furnace atmosphere. The gas after carburizing reaction is CO 10~25
%, containing 20-50% _H2 and 70-20% _N2 .

According to the present invention, the additionally supplied nitrogen is adjusted according to the supply amount of the carburizing agent, so that the gas composition in the furnace atmosphere is the carrier gas (2CO + 4H ₂ + 4N ₂ ).
Accordingly, there is little or no change, thereby ensuring controllability over the critical gas component of the furnace atmosphere and significantly reducing the required amount of carrier gas and therefore of methanol compared to known processes. I can do it.

The process of the invention not only allows the carrier gas produced endothermically in the generator and consumed during carburization to be replaced by methanol and nitrogen in a suitable ratio;
This has the advantage of significantly reducing gas requirements. This is because according to the present invention, by supplying the carburizing agent with an appropriate amount of nitrogen, migration of the gas composition is avoided.

Only a small gas supply is required just to maintain overpressure or to avoid air ingress into the furnace chamber.
This means that the economics of the process of the invention lies in the firstly low carrier gas requirements.

According to the state of the art, for example by adding hydrocarbons as carburizing agent in a carrier gas generator or when introducing methanol or nitrogen, a carburizing reaction (for example CH ₄ →C+2H ₂ ) is carried out in the furnace.
Therefore, the larger the area to be carburized, the more hydrogen is generated. If the surface area is thereby large,
It can occur that the composition of the furnace atmosphere shifts very quickly. To avoid this, ensure not only a sufficient overpressure but also, in particular, a constant gas composition.
A large excess of endothermically produced carrier gas had to be supplied. According to the law of mass action, for satisfactory control of the CO ₂ content of the furnace gas or the C level via the oxygen potential, the CO content must be reduced to 1.
must be maintained at a constant level.

In the case of the known control method by dew point, the product of the partial pressures of H ₂ and CO must be constant. All these prerequisites for satisfactory control of the C-level could up to now only be maintained with a suitably large excess of carrier gas. However, this means excessive consumption of natural gas and therefore uneconomical carburization.

On the other hand, according to known techniques, it has become clear that if the amount of carrier gas is reduced, it becomes very difficult to control the carburizing reaction. When a hydrocarbon is used as a carburizing agent, only hydrogen is generated in the carburizing reaction, as is known. If the amount of carrier gas is too low, the composition of the furnace atmosphere will shift significantly, so that the C-level will be reduced by the critical gas components (CO ₂ , H ₂ O,
can no longer be reliably dominated by control via O ₂ ). The method of the invention avoids these difficulties. It (a) supplies the carrier gas with its oxygen derivatives, such as alcohols, esters, ketones or aldehydes, instead of pure hydrocarbons as carburizing agent, thereby avoiding large fluctuations in the CO content of the furnace atmosphere, and (b) carburizing. Due to the controlled intermittent or continuous supply of carburizing agent and simultaneous introduction of nitrogen into the furnace in an amount corresponding to the amount of carburizing agent, the gas mixture generated during the carburizing process corresponds to the composition of the carrier gas or is very similar to this. Because it approaches.

The rationale for the method of the invention will now be explained by way of example: (A) Methanol and nitrogen for producing carrier gas: CH ₃ OH+2N ₂ →CO+2H ₂ +2N ₂ The CO content of the 2 gas is approximately 20%. Introducing isopropanol as a carburizing agent or for C-level adjustment, thereby increasing the
A gas with a CO content of 20% is obtained: C ₃ H ₇ OH→2C+CO+4H ₂ If the C level is controlled via the CO ₂ content, no nitrogen addition is necessary even with very small amounts of carrier gas. This is because the CO content remains constant even when the isopropanol content is high.

On the other hand, the P _H2 P _CO product is significantly higher with isopropanol, so for control via dew point, especially when the required amount of carburizing agent is large and the carrier gas is small, it is necessary to supply nitrogen at the same time as isopropanol addition. There must be.

(B) Acetone as carburizing agent or for C-level control: Acetone alone as carburizing agent easily increases the CO content if 100 g methanol and 0.14 m ³ _S of nitrogen are used for carrier gas production. Therefore, if the carrier gas quantity is significantly reduced or the acetone feed rate is high, controlling the C-level via a constant CO ₂ content or a constant O ₂ potential will result in significantly higher C-levels. However, if 0.0386 m ³ _S of nitrogen is added to 100 g of acetone simultaneously with the controlled acetone feed, the CO content and C-level also remain constant with the same adjustment of the controller. On the other hand, when controlling the C-level via the dew point, in the case of the same carrier gas, 0.082 m ³ _S of nitrogen must be additionally supplied with 100 g of acetone so that the product of P _H2 · P _CO remains approximately constant. .

(C) If B is varied and ethyl acetate is used as the carburizing agent, feeding ethyl acetate alone will significantly increase the CO and H ₂ content, which, with the same control adjustment, will cause the C level to be too high. Make it. Therefore, when reducing the amount of carrier gas, add nitrogen to 100g of ethyl acetate.
It is necessary to simultaneously feed 0.102 m ³ _S and keep the CO content and the product of the partial pressures of CO and H ₂ constant. In this way C-levels can be reliably controlled via oxygen potential or dew point. Control via CO ₂ is inappropriate due to the intermediate formation of CO ₂ during decomposition.

Additional nitrogen supply A, B suitable for carburizing agent demand
The method described in and C makes it possible to avoid changes in the gas composition that would interfere with the precise control process. The invention therefore makes it possible to significantly reduce the amount of carrier gas supplied per unit time, in extreme cases down to the amount required to maintain a slight overpressure.

The method of the invention can be used for carburizing as well as for heating to quenching temperatures at controlled C-levels. The control principle is the same in either case.

Next, the method of the present invention will be explained using the implementation device shown in the drawings.

The carburizing furnace 1 is connected to a C-level control device 2 via a control gas line 1a. Carburizing furnace 1 is a pot furnace,
It can be a shaft furnace, a retort furnace or a continuous heating furnace. The C-level control device 2 is a device that operates via the CO ₂ content, dew point or oxygen potential determined by infrared spectroscopy as control values.
The carburizing furnace 1 is connected to a methanol tank 3 through a methanol supply pipe 6 having a first sight port 6a and a first pump 5 with variable capacity, and a second sight port 8.
a and a conduit 8 with a variable capacity second pump 7
It is connected to the carburizing agent storage tank 4 via. The second pump is operated by the control device 2. Carburizing furnace 1
The nitrogen supply pipe 13 to the nitrogen tank 9 is connected to the nitrogen tank 9 with a common pressure regulator 10 via a first flow meter 12 and a first control valve and a second flow meter and a second control valve. A solenoid valve 16 operated by the control device 2 is provided between the second flow meter 15 and the nitrogen supply pipe 13, and this valve supplies nitrogen only when the second pump supplies carburizing agent to the furnace. useful for. In the first control valve 11, therefore, the amount of nitrogen proportional to methanol is regulated, and in the second control valve 14, the amount of nitrogen supplied together with the carburizing agent is regulated.

The furnace is, for example, the furnace described in German Patent No. 1192486. The furnace has a lining 17 with heating elements 18. A retort 19 with a heat-insulating lid 20 is arranged inside the lining and is closed airtight at position 21. Inside the retort there is a charging frame 22 which supports the parts 23 to be processed during furnace operation. The parts to be treated are thoroughly flushed by the furnace gas circulated by the ventilator 24. The arrangement of the ventilator 24, the upper guide plate 25 and the side guide plate 26 results in a gas flow shown by the arrows. Furnace gas is discharged from 27.

Next, carburizing in the apparatus shown in this drawing will be explained by example: Example 1 A pinion made of 17 CrNiMo 6 in a pot furnace.
Carburize 20 charges to a carburizing depth of 1mm.

The pinion is placed into a furnace preheated to approximately 750°C using a conventional mount, the furnace is closed, and the furnace chamber is immediately flushed with nitrogen to expel air. The furnace temperature was adjusted to the carburizing temperature using a temperature controller. Already during heating, the amount of nitrogen was reduced to 0.63 m ³ _S / h by means of a manually actuated valve 11.
The amount of methanol was adjusted to 450 g/h by pump 5, so that when the carburizing temperature of 920 °C was reached, the desired basic composition of the furnace atmosphere was already CO 18-20%, H ₂
38-40% and about 40% _N2 resulted. So valve 1
4, the additional amount of nitrogen was adjusted to 0.574 m ³ _S /h, and the supply amount of the acetone pump was adjusted to 700 g/h. A controller controlled the supply of acetone and additional nitrogen necessary to maintain the desired C-level. Methanol pump 5 now has a low feed rate of 300g/h,
The nitrogen supply could be adjusted to 0.420 m ³ _S /h by means of a manually operated valve 11 and a flow meter 12. Dew point, CO ₂ content and oxygen potential decreased. These were held by controller 2 at a constant value of 1 or C 1%. Carburizing was completed after 6.25 hours.

Example 2 In the case of heating a charge of 6 pinions of 14 NiCr 14 steel, after carburizing and cooling, reheating to a quenching temperature of 800 °C adjusts the furnace atmosphere to ensure a C-level of 0.80%. I had to.
On the one hand, decarburization is thereby avoided, and on the other hand, the partially decarburized surface area is again carburized to the standard value of the surface carbon content.

In this case, the treatment was carried out in a double chamber furnace in exactly the same manner as in the case of carburizing. The pinion was loaded into the furnace chamber, which was preheated to about 750° C., through a charging cage through the prechamber.
After closing the intermediate door and front room door, immediately wash with nitrogen to expel air and raise the furnace temperature to 800℃.
During heating, the amount of nitrogen was adjusted to 0.630 m ³ _S / h.
Since the amount of methanol was adjusted to 450g/h, the temperature was 800℃.
The desired basic gas composition is already present when the quenching temperature is reached.
18-20% CO, 38-40% _H2 and about 40% _N2 were achieved. Additional titanium content via manual valve 14
0.155m ³ _S / h, the supply amount of acetone pump is 400
g/h. Controller 2 controlled the supply of acetone and nitrogen necessary to maintain the 0.80% C-level. Next, add methanol pump 5 to 300g/
The nitrogen supply was adjusted to 0.420 m ³ _S /h. After heating for 2 hours, the methanol pump 5 and the acetone pump 7 were stopped, and the nitrogen feed rate was adjusted to a significantly higher value in order to purge the furnace chamber and the front chamber. Next, the pinion was hardened in the front chamber.

[Brief explanation of the drawing]

The drawing is a schematic illustration of an apparatus for carrying out the method of the invention. 1... Carburizing furnace, 2... C-level control device, 3... Methanol tank, 4... Acetone tank, 5, 7...
Pump, 6a, 8a... Peephole, 9... Nitanium tank, 12, 15... Flow meter, 18... Heating element, 19
... Retort, 22... Frame, 24... Ventilator.

Claims (1)

[Claims] 1. Controllable gas-gassing of steel parts in a protective gas at a predetermined C-level in the furnace atmosphere consisting of a carrier gas obtained from methanol and nitrogen and a carburizing agent in the form of an oxygen derivative of a hydrocarbon. In the carburizing or heating method, in addition to the carburizing agent,
Supplying an amount of nitrogen such that the gas after the carburizing reaction has approximately the same or approximately the same gas composition, and supplying the carburizing agent and/or additional nitrogen to the C-level of the furnace atmosphere in a known manner. 1. A method for controllably carburizing or heating steel parts in a protective gas, characterized in that the amount of a gas component critical to the gas is controlled by continuous measurement. 2 Ethyl acetate, acetone, as a carburizing agent
2. A method according to claim 1, wherein ethanol or isopropanol is used. 3. The method as claimed in claim 1 or 2, wherein the oxygen potential, the CO ₂ content or the water vapor content of the furnace atmosphere is controlled, in particular by measuring the dew point.