JPH032317A - Method for regulating atmospheric gas in bright annealing furnace - Google Patents

Abstract

PURPOSE:To prevent the oxidation and decarburization of a material to be treated with certainty by subjecting an exothermic converted gas containing hydrocarbon by the amount corresponding to the amount of carbon contained in a material to be treated and the value of equilibrium partial pressure of oxygen in a furnace to heating up to high temp., to rapid cooling, and to dehumidification and then feeding the above gas to an annealing furnace. CONSTITUTION:A material to be treated is heat-treated and annealed in a bright annealing furnace in which an exothermic converted gas of hydrocarbon is used as heat-treatment atmosphere. In the above heat treatment method, the amount of hydrocarbon mixed into the exothermic converted gas is changed in the range of 1-20% of the amount of the exothermic converted gas according to the amount of carbon contained in the material to be treated. Simultaneously, the amount of the above hydrocarbon is further corrected according to the value of equilibrium partial pressure of oxygen in the furnace. The resulting gaseous mixture of exothermic converted gas and hydrocarbon is heated up to >=1100 deg.C, cooled rapidly, and dehumidified. By this method, the amounts of CO2 and H2O as decarburization components in the above gas are markedly reduced. By feeding the above gas after regulation as atmospheric gas into an annealing furnace, the local irregularities of atmospheric components can be prevented and the oxidation and decarburization of the material to be treated can be prevented with certainty.

Description

[Detailed Description of the Invention] Industrial Application Field This invention is directed to the adjustment of atmospheric gas in a bright annealing furnace for heat treatment by controlling the furnace atmosphere in order to prevent oxidation and decarburization of objects to be treated such as steel pipes. By heating a mixture of exothermic gas and hydrocarbon gas to a high temperature,
The present invention relates to a method for adjusting atmospheric gas in a bright annealing furnace that reliably prevents oxidation and decarburization of a workpiece.

Conventional technology In continuous furnaces, which are most commonly used as heat treatment furnaces for steel pipes, in order to prevent oxidation and decarburization on the inner and outer surfaces of the pipes, the atmosphere inside the furnace is controlled and the steel pipes are heated indirectly using radiant tubes. The adoption of annealing furnaces is noticeable. In particular, it is often applied to heat treatment of handling pipes.

In this bright annealing furnace, it is common to use an exothermic transformed gas as the atmosphere gas in the furnace, but since the exothermic transformed gas has a weak carburizing power (carbon potential value 0.015%), the carbon in the steel pipe to be treated is Contains maximum (usually 0.1-1.0%
There is a possibility of decarburization in C). Furthermore, since the dew point temperature is relatively high, scale is likely to occur due to fluctuations in furnace conditions.

On the other hand, recent product trends have led to stricter quality requirements such as decarburization and surface properties of steel pipes, and in order to meet these demands, it has become necessary to work on non-decarburization and non-oxidation heat treatment.

For this reason, for example, in Utility Model Publication No. 63-13242,
A method has been proposed in which hydrocarbons are added to hydrocarbon converted gas or nitrogen gas and the mixture is fed to a heat treatment furnace.

However, in the method of using a mixture of hydrocarbon gas, nitrogen gas, etc., in the heat treatment atmosphere of a bright annealing furnace, a decomposition reaction of hydrocarbons occurs near the inlet of the furnace, and the local atmosphere There is a problem in that the ingredients become disordered.

Therefore, simply adding hydrocarbons to hydrocarbon converted gas or nitrogen gas and supplying the gas cannot sufficiently prevent oxidation and decarburization of the material to be treated in the furnace.

Problems to be Solved by the Invention In view of the above-mentioned actual situation, this invention aims to prevent local disturbance of atmospheric components in a bright annealing furnace that uses a mixture of an exothermic modified gas and a hydrocarbon in the atmospheric gas. However, this paper attempts to propose a method for adjusting the atmospheric scum that can reliably prevent oxidation and decarburization of the treated material.

Means for Solving the Problems This invention provides a method for mixing hydrocarbons with exothermic gas and sending the mixture to a bright annealing furnace. The amount of hydrogen,
The amount of hydrocarbons is varied in the range of 1 to 20% of the exothermic gas foot, and the amount of hydrocarbons is corrected according to the equilibrium oxygen partial pressure value in the furnace, and the mixed gas of this exothermic gas and hydrocarbons is The gist is to rapidly cool and dehumidify after heating to a temperature of °C or higher.

The reason why we decided to vary the amount of hydrocarbons mixed into the exothermic modified gas in the range of 1 to 20% of the exothermic modified gas depending on the carbon content of the object to be treated is that 1% or less is sufficient. No decarburization prevention effect can be obtained.

Further, a sufficient decarburization prevention effect of 1q can be obtained when the amount of carbon contained in the object to be treated is 20% or less.

The reason why the amount of hydrocarbon gas is corrected according to the equilibrium oxygen partial pressure value in the furnace is to obtain a carbon potential corresponding to the carbon content of the object to be treated.

The reason why the mixed gas of exothermic gas and hydrocarbon is heated to a high temperature of 1100'C or higher and then rapidly cooled and dehumidified is as follows.

When a mixed gas of an exothermic gas and a hydrocarbon is heated to a high temperature, the following reaction occurs.

4H2010C4)1+o -4CO+9824CO20C4HID -) aco+ 5822CO2+H2→
C○1H20 Therefore, the above-mentioned mixed gas is rapidly cooled and further dehumidified (thereby, CO2 and H2O, which are bundle components of one gas, are reduced).

Note that the heating temperature of the mixed gas of exothermic gas and hydrocarbon was limited to 1100° C. or higher in order to promote the reduction of the CO2 component.

Embodiment FIG. 1 is a block diagram showing an example of the configuration of an apparatus for carrying out the method of this invention, and (1) shows an exothermic modified gas generator;
(2) is a dehumidifier, (3) is a gas mixer, (4) is a hydrocarbon gas supply device, (5) is a gas conversion device with heating function, (6
) is a gas quenching/dehumidifying device, (7) is a bright annealing furnace, (8)
is an oxygen partial pressure meter, (9) is a carbon potential calculation controller, and Vl is a flow rate control valve.

That is, the exothermic converted gas that exits the exothermic converted gas generator (1) is introduced into the gas mixer (3) via the dehumidifier (2), where the flow rate is adjusted by the hydrocarbon gas supplier (4). Valve V
1 and mixed with hydrocarbon gas supplied via 1.

At this time, in order to adjust the atmosphere gas to be non-oxidizing and tax-free for the workpiece in the bright annealing furnace (7), the amount of hydrocarbons to be mixed is adjusted according to the amount of carbon contained in the workpiece. The calculation controller (9) determines the amount of heat-generating transformed gas.
~20%, correct the amount to an appropriate amount according to the oxygen partial pressure value in the furnace measured with the oxygen partial pressure meter (8), and operate the flow rate control valve v1 to adjust the appropriate amount of gas. mixer (
3).

The mixed gas of exothermic converted gas and hydrocarbon mixed in the gas mixer (3) is heated to a temperature of 1100'C or higher in the heat-sensing gas converter (5), and then passed through the quenching/dehumidifying device (
6) and is supplied to the bright annealing furnace (7).

Next, using the above equipment, carbon steel pipe (
Table 1 shows the results of the heat treatment (0.15% C) in comparison with the conventional method.

In this example, hydrocarbons were mixed at a ratio of 5% to the exothermic modified gas, and this mixed gas was heated to a temperature of 1100° C., and the gas that was rapidly cooled and dehumidified was used as the atmospheric gas.

Note that the heat treatment pattern in this example is shown in FIG.

As is clear from Table 1, the method of the present invention significantly reduces CO2 and H2Ota, which are components harmful to decarburization.
No decarburization or scale formation was observed in the treated steel pipe.

As described in detail in Table 1 below, according to the method of this invention, a mixed gas of an exothermic gas and a hydrocarbon is heated to a high temperature, and then rapidly cooled.
By dehumidifying, CO2, which is harmful to decarburization, can be significantly lowered by 8,208 degrees, so it is possible to reliably prevent oxidation and decarburization of the processed material in the bright annealing furnace, which requires particularly high quality. This is highly effective in manufacturing steel pipes for machine structures, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an apparatus for carrying out the method of the present invention, and FIG. 2 is a diagram showing a heat treatment pattern. 1... Exothermic transformed gas generator 3... Gas mixer 4... Hydrocarbon gas supplier 5... Gas converter with heating function 6... Gas quenching/dehumidifying device 7... Kouki Annealing furnace 8...Oxygen partial pressure h1 9...Carbon potential calculation controller Applicant: Sumitomo Kinkuta Industries, Ltd.

Claims (1)

[Claims] A method of adjusting the atmosphere gas to be non-oxidizing and non-decarburizing for objects to be treated in the furnace in a bright annealing furnace using exothermic modified gas of hydrocarbons (hereinafter simply referred to as exothermic modified gas) in the heat treatment atmosphere. , the amount of hydrocarbons mixed into the exothermic modified gas is varied in the range of 1 to 20% of the amount of exothermic modified gas according to the amount of carbon contained in the workpiece, and the amount of hydrocarbons is adjusted to the equilibrium oxygen level in the furnace. Bright annealing characterized by correcting according to the partial pressure value and heating the mixed gas of the exothermic modified gas and hydrocarbon to a temperature of 1100°C or higher, followed by rapid cooling and dehumidification and sending the air to an annealing furnace. How to adjust the furnace atmosphere gas.