JPS62253714A - Heat treating device for improving descaling property of steel - Google Patents

Abstract

PURPOSE:To easily remove primary and secondary scales in one step by specifying the atmosphere in a reoxidation chamber, and connecting a quenching chamber to the reoxidation chamber in a heat treating furnace connected with inlet and outlet purging chambers and the reoxidation chamber. CONSTITUTION:The steel A is successively treated in the prescribed manner in a feed table 1, the inlet purging chamber 2, the heat treating furnace 3 provided with heating, soaking, and annealing regions, and the outlet purging chamber 4, and gas replacement and heat treatment are carried out. T steel A is oxidized in the reoxidation chamber 5. The reoxidation chamber 5 contains a fan 51 at the top part and a roller 52 at the lower part. The steel A is placed on a frame 53 conveyed over the roller 52, and oxidized by the steam in the combustion waste gas in the atmosphere isolated from the external air while utilizing the heat remaining after heat treatment. The steel A is quenched in the quenching chamber 6. The atmosphere of the quenching chamber 6 is also controlled by circulating the atmospheric gas cooled by a cooler 65 with a fan 61 in the direction as shown by the arrow to prevent the penetration of the external air into the reoxidation chamber 5.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a heat treatment apparatus, and particularly to a heat treatment apparatus for improving the descaling properties of steel materials.

When a steel material is subjected to high-level processing to produce a product, the hot-rolled steel material is first subjected to heat treatment such as annealing. The heat treatment in this case is usually carried out in a heat treatment furnace whose atmosphere is controlled to prevent decarburization and carburization.

By the way, primary scale adheres to hot-rolled steel materials, and secondary scale adheres to heat-treated steel materials. These scales have a negative effect on the quality of products that will be subjected to subsequent high-order processing, so it is necessary to remove them in advance. In terms of work, it is desirable to heat-treat the hot-rolled steel material as it is without removing the -order scale, and to remove the primary and secondary scales in one step after the heat treatment, but conventional heat treatment methods do not allow for this. Descaling in one step is actually difficult, and if this is done forcibly, excessive pickling or the like will be forced, which will have a negative impact on quality. Conventionally, therefore, two-stage descaling has been carried out, in which a steel material from which primary scale during hot rolling has been previously removed is heat treated, and secondary scale from the heat treatment is again removed.

The present invention relates to an improvement in a heat treatment apparatus that can remove primary scale and secondary scale together in one step after heat treatment.

<Prior art and its problems> Hitherto, a heat treatment device has been proposed that removes negative scale and secondary scale in one step (Japanese Patent Application Laid-Open No. 52-60209, Japanese Patent Publication No. 57-28725). . These conventional devices are heat treatment furnaces equipped with heating, soaking, and slow cooling zones, and the atmosphere is controlled to prevent decarburization and carburization. In addition, outlet purge chambers are connected to each other on the discharge side, and a reoxidation chamber is connected to the outlet purge chamber,
The steel material discharged from the heat treatment furnace via the outlet purge chamber is
The residual heat is used to perform oxidation treatment in an air or oxygen atmosphere in a reoxidation chamber, and then to slowly cool or allow to cool.

However, the conventional apparatus has a problem in that it is not always easy to sufficiently remove primary scale and secondary scale from the steel material after the oxidation treatment by pickling or the like.

<Problems to be Solved by the Invention and Means for Solving the Problems> The present invention provides an improved heat treatment apparatus that solves the conventional problems as described above.

However, the present inventor investigated the conventional problems and found that the cause was the oxidation treatment in a reoxidation chamber placed in an air or oxygen atmosphere and the subsequent slow cooling. Alternatively, if the steel is oxidized in an oxygen atmosphere and cooled slowly, a relatively thin film of oxide scale consisting mainly of Fe3O4 and Fe2es will strongly adhere to the steel, and as a result, it will be difficult to remove the scale sufficiently by pickling, etc. I found that it became difficult to do what I wanted to do. After further careful consideration, we found that when a heat-treated steel material is strongly oxidized in a steam atmosphere and then rapidly cooled, a relatively thick film of oxide scale containing complex cracks, mainly composed of FeO, adheres to the steel material.
It was discovered that the oxidized scale can be sufficiently and easily removed by pickling or the like.

Therefore, in the present invention, an inlet purge chamber and an outlet purge chamber are connected to a heat treatment furnace equipped with an atmosphere-controlled heating, soaking, and slow cooling zone,
The outlet purge chamber is connected to a reoxidation chamber in which outside air is shut off and oxidation is carried out with steam in an atmosphere, and a quenching chamber whose atmosphere can be controlled is connected to the reoxidation chamber.

Hereinafter, the configuration of the present invention will be explained in more detail based on the drawings.

<Example> Figure 1 is an overall view showing an example of the present invention, and Figures 2 and 3 are
The figure is a partially enlarged longitudinal sectional view. A charging table 1, an inlet purge chamber 2, a heat treatment furnace 3, an outlet purge chamber 4, a reoxidation chamber 5, a quenching chamber 6, and a charge table 7 are connected at this point, and the inlet purge chamber 2, the heat treatment furnace 3, outlet purge chamber 4,
The reoxidation chamber 5 and the quenching chamber 6 are each equipped with various opening/closing doors on the charging side and the unloading side, and these are each partitioned into sections.

The heat treatment furnace 3 has a heating, soaking, and slow cooling area, and is configured to be able to control the atmosphere so as to prevent decarburization and carburization. Further, the reoxidation chamber 5 is configured to carry out oxidation using water vapor in an atmosphere where outside air is blocked. Specifically, in the case of the drawing, there is a fan 51 at the top and a roller 52 at the bottom.
In the reoxidation chamber 5, in which the steel material A is placed on a pedestal 53 that is conveyed on rollers 52, combustion exhaust gas with an air-fuel ratio of 1.0 or less is fed into the chamber according to the arrows in FIG. It is configured to do this. The quenching chamber 6 is also configured to perform atmosphere control, in this case atmosphere replacement, so that outside air does not enter the reoxidation chamber 5. Specifically, in the case of the drawing, there is a fan 61 at the top and a roller 6 at the bottom.
2, and in a quenching chamber 6 which is equipped with a ventilation passage 64 divided by a partition wall 63 on both sides and a cooler 65 interposed in the ventilation passage 6.4, a steel material is placed on a pedestal 66 conveyed on rollers 62. A is placed therein, and atmospheric gas cooled by a cooler 65 is circulated indoors according to the arrows in FIG.

Function> Next, the present invention will be explained in detail based on the illustrated embodiments. The steel material A, which has been passed through the charging table 1→inlet purge chamber 2→heat treatment furnace 3→outlet purge chamber 4 in the order of predetermined gas exchange and heat treatment, is oxidized in the reoxidation chamber 5. This oxidation treatment utilizes the residual heat after the heat treatment, preferably 665±1
At a temperature of 5°C and in an atmosphere where outside air is blocked, the air-fuel ratio is 1.
This is carried out using the exhaust gas from a burner or radiant tube that has been burned at a temperature below 0, and the water vapor in the exhaust gas. Then, the oxidized steel material A is quenched in a quenching chamber 6. Outside air may exist in the quenching chamber 6 during quenching. The rapidly cooled steel material A is taken out of the system by the loading table 7. This process is repeated below, but when transferring the steel material A from the reoxidation chamber 5 to the quenching chamber 6, the inside of the quenching chamber 6 must be cleaned in advance to prevent outside air from entering from the quenching chamber 6 into the reoxidation chamber 5. Replace the gas.

Steel material A that has been subjected to a series of treatments has a relatively thick film of oxide scale mainly composed of FeO with complex cracks attached to it, and the oxide scale can be sufficiently and easily removed by subsequent pickling, etc. It can be removed.

<Effects of the Invention> As explained above, the present invention, which can sufficiently and easily remove primary scale during hot rolling and secondary scale during heat treatment in one step, includes a series of steel processing treatments. This has the effect of significantly improving workability and, by extension, improving the quality of the final product.

[Brief explanation of drawings]

Figure 1 is an overall view showing one embodiment of the present invention, Figures 2 and 3 are
The figure is a partially enlarged longitudinal sectional view.

Claims (1)

[Claims] 1. An inlet purge chamber and an outlet purge chamber are connected to a heat treatment furnace equipped with an atmosphere-controlled heating, soaking, and slow cooling zone, and the outlet purge chamber has a reoxidation chamber in which oxidation is performed with steam in an atmosphere where outside air is shut off. A heat treatment apparatus comprising connected chambers, and a quenching chamber whose atmosphere can be controlled is connected to the reoxidation chamber.