JPH04268062A - Atomsphere carburization method for steel - Google Patents

Abstract

PURPOSE:To easily control the content ratios of CO and CO2 and to produce a gas for the atmosphere high-speed carburization method for steel by adding the CO2 to a gaseous raw material of hydrocarbon or the hydrocarbon and air and reforming the gas. CONSTITUTION:The hydrocarbon, such as C3H8 or C4H10, and the air are reformed as the gaseous raw material to obtain the reformed gas for carburization essentially consisting of CO, H2, N2, etc. The above-mentioned gaseous raw material is reformed by adding the CO2 into this gas at this time. The content of the CO in the compsn. of the reformed gas is adjusted to 30 to 60vol.%. The adequate carbon potential is set with high accuracy and the atmosphere high-speed carburization of the steel at a high temp. is executed by using the gas compounded to allow the easy control of the content ratios of the CO and the CO2 in such a manner.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature gas carburizing method for steel.

0002

2. Description of the Related Art Endothermic gas is one of the carburizing atmosphere gases that have been widely used in the past. This endothermic gas is converted by mixing a hydrocarbon gas such as propane or butane with air and passing the mixture through a nickel catalyst heated to about 1050°C. There are also substances produced by thermally decomposing methanol. The former is CO, H2, N2
It is mainly composed of gas and contains trace amounts of CO2, CH4, and H2O, and the latter generally does not contain N2.

[0003] The composition of the shift gas is adjusted by the mixing ratio of the raw material hydrocarbon and air, but the carbon potential is usually about 0.1 to 0.3% in order to reduce the generation of soot during shift. For this purpose, an appropriate amount of hydrocarbon is added to the endothermic gas to further increase the carbon potential.

[0004] Adjustment of the carbon concentration of methanol decomposition gas is as follows:
Similar to endothermic gases, hydrocarbons or suitable alcohols are added.

Generally, natural gas (mainly CH4) is used as the raw material hydrocarbon in the United States, and LPG (butane C4H10, propane C3H8, or a mixed gas thereof) is used in Japan.

[0006] Transformation reaction equation for producing endothermic gas using propane and air as raw materials (KP is an equilibrium constant in the equation)
is as follows.

[0007] C3H8 + air 7.14 (1.5O2 + 5
．． 64N2)=3CO+4H2+5.64N2 However, the following reaction occurs between the gases produced by the above reaction formula, resulting in an equilibrium composition determined by the temperature during the reaction.

For example, the carbon potential is 0.8% at 1050°C.
The metamorphic composition to achieve this is shown in Table 1.

[0009]

[Table 1]

1050 of a converted gas using propane as a raw material
The CO content in the equilibrium composition at °C is 23.47%.

[0011] The carbon potential of the above metamorphosed gas is:
It depends on the reaction of the following equation. [However, CP: equilibrium carbon concentration % (carbon potential) AS: saturated carbon content of austenite
]

Therefore, the carbon potential of the carburizing atmosphere gas is generally adjusted by adjusting the ratio of the amount of CO gas to CO2. Maximum CO of metamorphic gas
The amount is determined by the type of raw material gas, with a maximum of 23.7% for propane and 24.2% for butane.

By the way, if the relationship between the carbon potential and the amount of CO2 at each temperature associated with CO2 is plotted as a graph, as shown in FIG. 1, when the amount of CO2 is constant at 20%. As shown by curve B in Figure 1, for example, at a carburizing temperature of 950°C, if the amount of CO2 is 0.07%, CP will be 1.2%, and if CO2 is 0.08%, CP will be approximately 1.0%. Therefore, the carbon potential suitable for carburizing can be set relatively easily.

[0014]

[Problems to be Solved by the Invention] Generally, the relationship between carburization depth and time is expressed by the following Harris equation.

For example, 3.5 hours are required to obtain a carburization depth of 1 mm at 900°C. If this is carburized at 1100°C, it will take only 0.4 hours. Rapid carburization at such high temperatures is industrially advantageous.

However, when the carburizing temperature is increased, the amount of CO2 relative to the amount of CO (as mentioned above, the maximum is 23.7% for propane and 24.2% for butane),
It becomes really difficult to obtain a suitable carbon potential for carburizing. For example, as can be seen from the C curve in Figure 1, when the carburizing temperature is 1100°C, in order to make the carbon potential 1% required for carburizing, the CO2 concentration must be reduced to 0 when the CO concentration is 20%. It must be controlled to about .02%. The absolute value of the amount of CO2 to be controlled is too small, and as can be seen from curve C, the carbon potential fluctuates greatly due to a slight change in CO2, so it is not possible to set the carbon potential with high accuracy.

[0017]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention mixes carbon dioxide gas with raw carbon hydrogen gas, adds air if necessary, and passes it through a high-temperature nickel catalyst for transformation. , C in the metamorphic gas
The aim is to increase the amount of O to 30% to 60%. By increasing the absolute value of the amount of CO in the metamorphic gas in this way, the absolute value of the amount of CO2, which is the ratio to it, can also be increased, making it easier to control the amount of CO2, resulting in high accuracy. This allows carbon potential to be managed.

For example, if the amount of CO is 50% and the carburizing temperature is 11%,
When the temperature is 00°C, in order to make the carbon potential 1%, as shown in the above equation (1), CO2
The concentration may be as high as 0.12%.

Therefore, in order to obtain a carbon potential of 1% under high-temperature carburizing at 1100°C, conventional metamorphic gas (C
(O content is only about 20%), the amount of CO2 is reduced to 0.02%.
must be held in the order of CO
When the amount of CO2 is 50%, the amount of CO2 needs to be managed on the order of 0.12%, and compared to the former case, the amount of CO2 is 6 times more, making it easier to adjust the amount of CO2, making it easier to control CP with high precision. can be controlled. The reaction formula for adding carbon dioxide gas according to the present invention is shown in Table 2.

[0020]

[Table 2]

As described above, the present invention provides an excellent technique that allows carburizing to be carried out at high temperatures with high precision.

[0022]

[Example] Using pure propane as the raw material gas, C3H
8. Mixing ratio of CO2 and air is 20.2:46.6:33
．． 2, and when transformed in a nickel catalyst transformation furnace adjusted to 1100°C, the amount of CO is 50% and the concentration of CO2 is 0.3
7%, and CP was 0.32%. Propane is added to this gas to reduce CO2 and reduce the amount of CO2.
was adjusted to 0.1%. The CP of this gas at this time is Figure 1
As shown in curve D in the middle, it was 1.15%. In this carburizing gas, 20φ x 100mm of SCM420H material
As a result of carburizing the round bar sample at 1100° C. for 1 hour, a surface carbon concentration of 1.15% and a total carburizing depth of about 1.6 mm were obtained.

[0023]

[Effects of the Invention] It has been difficult to control the carbon potential with high precision at high temperatures using conventional carburizing gases that are metamorphosed from hydrocarbons and air, but in the present invention, by adding carbon dioxide gas. By increasing the amount of CO in the metamorphic gas, the amount of CO2 can be easily controlled, and the carbon potential, which is correlated with the ratio of the amount of CO to the amount of CO2, can be easily controlled even at high temperatures. It has the outstanding effect of allowing time carburizing.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between carbon potential and CO2 amount.

Claims (1)

[Claims] Claim 1: Carbon dioxide is added to a raw material gas of hydrocarbons or hydrocarbons and air to transform the gas, and C in the gas composition is modified.
A high-speed atmospheric carburizing method for steel at high temperatures, characterized by using a gas with an O content of 30 to 60% by volume and an easy control of the CO and CO2 content ratio.