JPS62211364A - Gas carburizing method - Google Patents

Abstract

PURPOSE:To maintain the amt. of the atmosphere gas during carburization at a required min. specified amt. and to considerably decrease the consumption of a base gas for forming the atmosphere gas by decreasing the amt. of the base gas in proportion to the amt. of an enriching gas to be added at the time of making a gas carburization treatment of a metal. CONSTITUTION:Steel products to be treated are put into a muffle type carburization furnace 1 and the surface thereof are subjected to gas carburization treatment. Gaseous N2, 5 and org. liquid 9 of a lower alcohol such as methanol or ethanol are supplied respectively through flow rate control mechanism 3, 7 as the base gas to be supplied to the carburization furnace. On the other hand, the supply rate of gaseous hydrocarbon such as CH4 or C2H6 as the enriching gas 13 is automatically controlled by a controller 17 and a flow rate control mechanism 11 in such a manner that the equil. carbon concn. of the atmosphere gas in the stage of the carburization process (3hr at 930 deg.C) in the carburization furnace attains 1.1% and that the equil. carbon concn. of the atmosphere gas in a diffusion process (1.5hr at 930 deg.C) attains 0.8%. The amt. of the base gas is thus efficiently and effectively used and is made considerably lower than heretofore.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a gas carburizing method for metal products such as steel.

Conventional techniques and their problems As a gas carburizing method for gold 1iiXk products such as steel, conventionally,
Hydrocarbon gas such as methane, ethane, propane, etc. and air are introduced into a shift furnace, and in the presence of a nickel-based catalyst, etc.
A method has been used in which an endothermic metamorphosed gas containing N2 and N2 as main components is generated, and an enriched gas is added thereto to form an atmospheric gas. In the method using this endothermic metamorphic gas as the base gas, it is necessary to always maintain a constant ratio of the raw material hydrocarbon gas and air, so it is difficult to rapidly change the flow rate of the atmospheric gas. Therefore, as shown in Fig. 2, even during the carburizing operation period (T2), when the carburizing furnace door is open when the carburized product is being carried in (T+) and when it is being carried out (T3), outside air etc. are prevented from entering. It is necessary to supply a large excess amount (Q2) of base gas and enriched gas (E) necessary to prevent this, into the carburizing furnace, and there is a problem that gas consumption is extremely large.

U.S. Patent No. 4145232, 1984-12
Publication No. 8576 and Metals and Materials, October 1979, pages 44 to 47 disclose that an inert gas such as nitrogen and an organic liquid should be directly introduced into a carburizing furnace. The present invention discloses a carburizing method in which a gas is formed and an enriched gas is further added thereto to form an atmospheric gas. In this method, it is easy to change the flow rate of inert gas such as nitrogen, so as shown in Figure 3, the carburizing furnace door is in the open state ((T1) and (T3)
)), the large excess ff necessary to prevent the intrusion of outside air, etc.
1 (Q2) of the base gas is supplied, but when the door is closed ((T2)) during the carburizing process, the minimum necessary base gas (Ql) and the enriched gas (E) are supplied. In this case, the atmospheric gas consumption m is reduced to about 115 to 1/2 (equity) compared to the method using the endothermic metamorphic gas as the base gas. However, even in this method, undecomposed CH4,1- produced from the enriched gas supplied at a rate of 5 to 20% of the base gas flow ff1(Q+)
The mother of 12 mag is 10 to 40 of the base gas flow rate (Q+)
%, and these are lost without being used effectively.

The present invention is a step toward solving problem 1. The present invention relates to an improvement in a carburizing gas method in which an enriched gas is added to a base gas consisting of nitrogen and a decomposed gas of an organic liquid to obtain an atmospheric gas. This relates to a gas carburizing method characterized in that the atmospheric gas during the carburizing operation is kept constant by reducing the base gas of the melon in proportion to .

When hydrocarbons are used as enrichment gas in carburizing steel, they are thermally decomposed in a carburizing furnace as shown by the following formula.

CmH, → (m-(Z) ・C+αCHt + (” 2(Z
) H3P (1) The carbon generated in equation (1) is absorbed into the steel as a carburizing component. Regarding undecomposed CH4, once the temperature of the atmospheric gas and the average residence time in the furnace are determined, the residual fraction α can be determined experimentally. Also, depending on the initial state of the atmosphere, a part of the enriched gas may be used to reduce CO2, 02, etc. in the atmosphere to produce Co, H20, etc., but if the atmosphere is in a controlled state, these fleas will , CH4, and H2, and can be ignored.

From the above considerations, if the temperature and average residence time of the atmosphere in the carburizing furnace are kept constant, the increase in atmospheric gas due to the addition of enriched gas will be (n-α)X(CmH, ), and the enriched gas The addition of is approximately proportional to . Therefore,
As shown in Fig. 1, by subtracting ff1 (E'), which is proportional to the atmosphere increase due to the addition of enrichment gas, from the base gas (B), the atmospheric gas flow ω is always reduced to the minimum value f2t (Q + ) can be held. In this case, the reduction of the base gas concentration is achieved by reducing the flow rate by easily controlling N2
This is done by reducing supply days.

Hereinafter, the method of the present invention will be explained in more detail with reference to the flowchart shown in FIG.

The carburizing furnace (1) is equipped with a nitrogen supply line (5) equipped with a flow rate control mechanism (3), an organic liquid supply line (9) equipped with a flow rate control mechanism (7), and a flow rate control mechanism (11). An enriched gas supply line (13) is connected thereto.

Examples of organic liquids include lower alcohols such as methanol and ethanol, and examples of enriched gas include CH.
Examples include hydrocarbons such as t, C2H6,03Ha, and Ct H+ o, propatool, butanol, and the like. During the carburizing operation, nitrogen from the feed line (5) and organic liquid from the feed line (9) are introduced into the carburizing furnace (1) to form a base gas consisting of nitrogen and decomposition gas of the organic liquid. When no enrich gas is added, the flow rate reference set values for nitrogen and constituent liquids are set by the flow rate control mechanisms (3) and (7) so that the minimum required ff1 (Q+) during carburization is maintained using only the base gas. Each is set.

Equilibrium carbon concentration control in the carburizing furnace (1) is carried out according to the conventional method.
The concentration of one or more of 02, CO2, co, etc. in the atmospheric gas is measured and sent to the controller (17) via the signal line (15), where it is compared with the equilibrium carbon concentration set value and its value is determined. The signal line (19) is connected to increase or decrease the enriched gas supply from the supply line (13) depending on the result.
) to adjust the flow rate control mechanism (11). On the other hand, as mentioned above, the output of the controller (17) sent from the signal line (21) (i.e., the enriched gas (flow rate setting value). The obtained value is sent via a signal line (25) to an adder (27), where it is subtracted from a predetermined nitrogen quantity reference set value. The obtained result is sent to the flow rate control mechanism (3) via the signal line (29) as the set value for the nitrogen flow rate.
) to control the nitrogen flow rate.

Note that when alcohols such as propatool and butanol are used as the enriched gas source, the nitrogen flow rate may be controlled using a proportionality constant determined from a thermal decomposition reaction equation in place of equation (1) above.

Effects of the Invention According to the present invention, no matter how the enrichment gas addition amount changes based on various factors such as the toxicity of the product to be carburized, the level of the set equilibrium carbon concentration, and the elapse of carburizing time, The atmospheric gas flow can be maintained at a constant minimum necessary amount. Therefore, compared to the conventional technology that uses a base gas consisting of an inert gas such as nitrogen and a decomposed gas of an organic liquid (see Figure 3), the amount of base gas used (2 m) can be reduced by about 10 to 40%. be able to.

EXAMPLES Examples will be shown below to further clarify the characteristics of the present invention.

Example 1 Matsufuru type carburizing furnace using city gas 13A as a heating source (effective dimensions inside the furnace: height 550 ma + x width 600 max length 1
23011m), round steel (80M415, diameter 35111x length 300mm) was prepared according to the flow shown in Figure 4.
) Approximately 300 ko carburizing treatment was performed.

As base gas sources, nitrogen with a standard flow rate of 20Q/inch (however, the amount is automatically reduced in proportion to the enriched gas described below) and methanol with a steady flow m 18 mQ/1n were used.

On the other hand, the equilibrium carbon concentration of the atmospheric gas during the carburizing process (3 hours at 930°C) was set to 1.1%, and the diffusion process (
Using the 02 sensor signal, the equilibrium carbon concentration controller (17) controls the use of the soybean gas 13A ( CHi88%, C2
The supply ports of H66%, 03Hs4%, and CL1 (+O2%) were automatically controlled.

The proportionality constant given to the ratio setter (23) is n=4.
4. α=0.36 to −α=1.84.

After the diffusion process has been completed, the treated product is cooled to 870°C, held at that temperature for 0.5 hours, and then quenched using conventional methods.

The amount of nitrogen consumed in this example was 6.5 m3, whereas the amount of nitrogen consumed by the conventional method shown in FIG. 3 was 9 rll3, and the amount of nitrogen used by the method of the present invention was 26.7%. reduced.

The properties of the carburized product are similar to those of the product processed by the method using endothermic metamorphosed gas as the base gas (see Figure 2) and the conventional method using nitrogen-based gas as the base gas (see Figure 3). , surface carbon concentration 0.81%, effective hardening depth 0.
No abnormal tissue was observed at 75 mm.

[Brief explanation of drawings]

Figure 1 shows the minimum necessary atmosphere ff1 (Q+) in the carburizing furnace in the method of the present invention, ff1 (E') which is proportional to the amount of atmosphere increase due to the addition of enriched gas, and base gas ff1.
2 and 3 are graphs showing the relationship between the base gas (Q2) or (Ql) and the enriched gas all (E) in the prior art. FIG. 4 is a flowchart showing one example of an embodiment of the present invention. (1) Carburizing furnace (3) Nitrogen flow control mechanism (5) Nitrogen supply line (7) Organic liquid flow rate control mechanism (9) Organic liquid supply line ( 11)... Enriched gas flow maximum control t11 mechanism (13
)...Enrich gas supply line (15)...Signal line (17)...Controller (19)...Signal line (21)...Signal line (23)...Ratio setter (25 )...Signal line (27)...Adder (29)...Signal line (and above)

Claims (1)

[Claims] [1] In a gas carburizing method in which an enrichment gas is added to a base gas consisting of nitrogen and decomposition gas of an organic liquid to create an atmosphere gas, the atmosphere during the carburizing operation is reduced by reducing an amount of base gas proportional to the amount of added enrichment gas. A gas carburizing method characterized by keeping the amount of gas constant.