JPH0441615A - Method and device for austempering - Google Patents

Abstract

PURPOSE:To enhance the cooling power of a fluidized bed and to facilitate austempering by transforming a material to be treated heated to an austenite region by the fluidized bed with gaseous He as the fluidizing gas into bainite. CONSTITUTION:A spheroidal graphite cast iron member 2 heated to 800-900 deg.C is charged into the fluidized-bed furnace 1 of an austempering device. Gaseous He from a gaseous He cylinder 8 accelerated by a turbofan 10 is introduced into the furnace 1 through a pipeline 9. The gaseous He blown up from a diffuser plate 12 forms a fluidized bed along with alumina powder 11 and cools the member 2. The gaseous He is passed through a filter 14, discharged from the upper part of the furnace 1 and cooled by a heat exchanger 15. The gaseous He is circulated in this way to quench the member 2 to the bainite transformation temp. of about 250-400 deg.C. The furnace 1 is kept at this bainite transformation temp. by energizing a heater 16, as required, and bainite transformation is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an austempering method for transforming steel or cast iron heated to the austenite region into bainite in a fluidized bed, and an apparatus used in the method.

[Prior art]

Austempering of spheroidal graphite cast iron, etc., has been attracting attention in recent years as a heat treatment process that increases the strength and toughness of spheroidal graphite cast iron.

Generally, austempering is a heat treatment in which the material to be treated, such as steel or cast iron, is heated to the austenite region, rapidly cooled to prevent pearlite transformation, and then held at a temperature of about 250 to 400 degrees Celsius for a predetermined period of time (approximately 2 hours). refers to the law. The aim is for the base structure to turn into bainite during this retention, improving strength and toughness. The heat pattern of this austempering process is shown in FIG.

In such an austenitic region, the key points in the process are (2) cooling from the austenite region, and (2) stable isothermal transformation. (2) After cooling in an oil bath, the temperature is maintained in a constant temperature bath. (3) After cooling by spraying water and air from the nozzle hole, the temperature is maintained in a constant temperature bath. (4) Alumina and N2 Methods such as cooling and constant temperature maintenance using a fluidized bed using gas have been put into practical use or have been proposed.

[Problem to be solved by the invention]

However, each of the conventional methods described above has problems.

First, in (1), salt bath materials such as nitrates are removed from the treated material by washing with water, but in order to prevent environmental pollution due to discarded treated water, it is necessary to take environmental measures such as sub-adjustment of BOD and PH of the treated water.

In (2) and (3), it takes time and effort to transfer the material to a constant temperature bath after cooling, and requires equipment costs such as the need for a constant temperature device in addition to the cooling device.

The method using a fluidized bed (4) is optimal for maintaining constant temperature because the temperature distribution is uniform, but the conventional fluidized bed that uses alumina as the fluidizing medium and N2 gas as the fluidizing gas has a small cooling capacity. However, it was difficult to obtain a bainite structure in cast parts with thick circular parts.

The present invention has been made in view of the above-mentioned problems and to improve them.It does not require any measures against environmental pollution, saves the trouble of transferring the material to be treated from the cooling device to the thermostatic chamber, and reduces equipment costs. It is an object of the present invention to provide a method that uses a fluidized bed, which is advantageous in some respects, and further improves the cooling ability of the fluidized bed to facilitate austempering even for cast parts with thick circular parts, and an apparatus used in the method.

[Means to solve the problem]

As a result of repeated studies and tests, we found that the factors that govern the cooling ability of a fluidized bed are: ■ size and material of the fluidizing medium (particles), and ■ type of fluidizing gas. was found to have a significant impact on That is, the present invention was completed by discovering that the cooling ability of a fluidized bed can be enhanced by using He gas as a fluidizing gas. That is, the present invention is an austempering method in which a material to be treated that has been heated to an austenite region is transformed into bainite in a fluidized bed, and is characterized in that He gas is used as a fluidizing gas in the fluidized bed.

The present invention also provides an apparatus suitable for carrying out such an austempering method. That is, in an austempering treatment apparatus having a fluidized bed furnace for transforming a material heated to an austenite region into bainite, this apparatus has a means for supplying He gas as a fluidized gas to the fluidized bed furnace, and a means for supplying He gas as a fluidized gas to the fluidized bed furnace, and a means for discharging He gas from the fluidized bed furnace. He was
The present invention is characterized by a configuration comprising means for circulating gas through the fluidized bed furnace, and means coupled to the circulation means or the fluidized bed furnace for storing He gas.

In the present invention, He gas having high cooling ability may be used only for cooling, and N2 gas may be used as a fluidizing gas during constant temperature maintenance. That is, the material to be treated that has been heated to the austenite region is rapidly cooled to the bainite transformation temperature in a fluidized bed using He gas as the fluidizing gas, and then the fluidizing gas in the fluidized bed is changed from He gas to N2 gas. It is also possible to adopt a configuration in which the material to be treated is held at the bainite transformation temperature for a certain period of time. Therefore, the apparatus for carrying out this method is further provided with a supply means for supplying N2 gas to the fluidized bed furnace and a circulation means for circulating and reusing this Nt gas, and is heated to the austenite region. rapidly cooling the treated material to a pearlite transformation temperature in a fluidized bed furnace supplied with the He gas,
After quenching, the He gas is stored in the storage means and the supply of He gas is stopped, while N2 gas is supplied to the fluidized bed furnace by the supply means, and further circulated by the circulation means to collect the gas in the fluidized bed furnace. An apparatus that maintains the treated material at a bainite transformation temperature for a certain period of time can be suitably used.

[For production]

Comparing N2 gas, Ar gas and He gas in terms of thermal conductivity, N2 gas has a thermal conductivity of 0.026 at 100°C.
9kca 1/+wh″C, Ar gas is 0.018
1kcal/a+h'c, whereas for He gas it is much larger at 0.143kcal/mh'c.If we calculate the cooling curve for the center of a φ20mo cutting rod made of spheroidal graphite cast iron, it will be as shown in Figure 2. It can be seen that in the case of He gas cooling, cooling is performed more rapidly than in the case of N gas cooling. Therefore, in the present invention, the cooling ability of the fluidized bed is enhanced by using He gas as the fluidizing gas.

Although the He gas used in the present invention is more expensive than N2 gas, the device of the present invention allows He gas to be circulated and used repeatedly, and can be stored when not in use. Efficient use of He gas prevents increases in running costs.

Furthermore, He gas is used only for cooling, and N is used for constant temperature maintenance.
By using two gases as the fluidizing gas, the amount of He gas used can be reduced while maintaining high cooling performance, and manufacturing costs can be reduced. In accordance with this intention, the apparatus of the present invention commonly uses a fluidized bed furnace, and also uses ordinary N
2 gas supply means and N2 gas circulation means were added. Therefore, the structure of the device of the present invention is simplified and the equipment cost can be kept low.

〔effect〕

As explained above, in the present invention, by using He gas as the fluidizing gas, the cooling capacity of the fluidized bed is greatly increased, and a cooling capacity comparable to that obtained when using a salt bath, oil bath, etc. can be obtained. Ta. In the conventional fluidized bed using N2 gas, for example, in the austenitic region of non-alloyed spheroidal graphite cast iron, a bainite structure could only be obtained with a wall thickness of φ10III [Il or less, but with the present invention, even a wall thickness of φ20 mm can be obtained. It is now possible to convert up to bainite.

In the present invention, there is no need for environmental pollution countermeasures as in the case of using molten salt. In addition, since cooling and constant temperature maintenance can be done in one fluidized bed furnace, there is no need for the effort of transferring the processed products compared to the conventional method where cooling and constant temperature maintenance are performed in separate devices, which reduces equipment costs. But it is advantageous.

〔Example〕

Next, specific embodiments of the present invention will be described with reference to the drawings.

First, in Example (3), 800 to 900 ml of the material to be treated was placed in the fluidized bed furnace 1 of the austempering apparatus shown in FIG.
A spheroidal graphite cast iron member heated to 0°C is charged as the material to be treated 2. The valve 3°4.5 is opened, and He gas accelerated by the turbo fan 10 is introduced from the He gas cylinder 8 into the fluidized bed furnace 1 through the pipe 9. Note that the valve 3 is closed after reaching an appropriate amount of He supply. Alumina powder 11 having a particle size of about 80 mesh is charged into the furnace l first. The He gas blown up from the dispersion plate 12 forms a fluidized bed together with the alumina II, and the material 2 to be treated is cooled by the heat exchange action of this fluidized bed. On the other hand, the He gas heated by the heat exchange is discharged from above the fluidized bed furnace 1 through the filter 14 and is cooled by the heat exchanger 15. Then, it passes through the pipe 9, is accelerated again by the turbo fan 10, and is introduced into the fluidized bed furnace 1.

By circulating the He gas in this way, the material to be treated 2 is
Rapid cooling to bainitic transformation temperature of ~400°C. If necessary, the inside of the fluidized bed furnace 1 is adjusted to a predetermined constant temperature to maintain this bainite transformation temperature, and the bainite transformation is carried out in the fluidized bed. After a predetermined period of time (approximately 2 hours), valves 3 and 4 are closed and valve 6 is opened (valve 7 remains closed). He gas is extracted from the fluidized bed furnace 1 by the pump 17 and transferred to the storage tank 1.
Store at 8. After storage is completed, valve 6 is closed again. The material 2 to be treated, which is a spheroidal graphite cast iron member that has undergone bainite transformation, is taken out of the furnace and allowed to cool.

When using this fluidized bed furnace apparatus again to austemper another material 2 to be treated, after charging the material 2 to be treated,
The valve 7.4.5 is opened and the compressor 19 pressurizes the He gas discharged from the storage tank 1 and sends it to the fluidized bed furnace l.

Then, repeat the above operation. At this time, if the flow rate of He gas is insufficient, the valve 3 may be opened to supply additional He gas.

Next, another embodiment (2) will be explained with reference to FIG. In this embodiment], the cooling step of the austempering treatment is exactly the same as in the above-mentioned embodiment I, and the explanation thereof will be omitted. After cooling by the He gas flow is completed, the He gas is stored in the storage tank 18 by the pump 17. Then, all valves 4, 5, 6.7 related to He gas supply and circulation are closed. Subsequently, the valves 20 to 22 are opened, and N2 gas from the N2 gas cylinder 23 is accelerated by the turbo fan 24 and introduced into the fluidized bed furnace 1. At this time, since the spheroidal graphite cast iron, which is the material to be treated 2, has already been cooled to the bainite transformation temperature, the inside of the furnace 1 is heated by the heater 16 and maintained at the transformation temperature to cause the bainite transformation to occur. The N2 gas blown up from the dispersion plate 12 forms a fluidized bed with the alumina powder 11, and then passes through the filter 14 and is discharged to the outside of the furnace. Thereafter, the fluid is circulated through the fluidized bed furnace again through the piping 9, the turbo fan 24, and the valve 21 to perform a constant temperature maintenance step. In this embodiment, a storage means for N2 gas is not used because N2 gas is cheaper than He gas, but it is of course possible to store and reuse N2 gas as well as He gas. It is also possible to install the He gas storage tank independently and draw He gas directly into the storage tank from the fluidized bed furnace. Note that the flow rate and pressure of the He gas and N2 gas used as the fluidizing gas may be such that a fluidized bed can be formed, and there are no other limitations.

[Brief explanation of drawings]

Figure 1 is a graph showing the heat pattern of general austempering treatment, Figure 2 is a graph comparing cooling curves using N2 gas and He gas, and Figures 3 and 4 are graphs showing the method and apparatus of the present invention. FIG. 2 is an explanatory diagram of the configuration of an apparatus for explanation. 8...He gas cylinder 9...Piping 10.24...Turbo fan 11...Alumina powder 12...Dispersion plate 14... ... Filter 15 ... Heat exchanger 16 ... Heater 17 ... Pump] 8 ... Storage tank 19 ... Compressor 23・・・・・・N2 gas cylinder

Claims (1)

[Claims] 1. An austempering method in which a material to be treated that has been heated to an austenite region is transformed into bainite in a fluidized bed, characterized in that He gas is used as a fluidizing gas in the fluidized bed. Processing method. 2. After rapidly cooling the treated material heated to the austenite region to the bainite transformation temperature in a fluidized bed using He gas as the fluidizing gas, the fluidizing gas in the fluidized bed is changed from He gas to N_
Claim 1, wherein the treated material is maintained at a bainite transformation temperature for a certain period of time in the fluidized bed in place of two gases.
Austempering method described in. 3. In an austempering apparatus having a fluidized bed furnace for transforming the material to be heated to the austenite region into bainite, this apparatus has a means for supplying He gas as a fluidized gas to the fluidized bed furnace, and a means for discharging He gas from the fluidized bed furnace. means for circulating the helium gas into the fluidized bed furnace;
An austempering method comprising means for storing gas. 4. The means for circulating the He gas into the fluidized bed furnace is provided with a supply means for supplying N_2 gas to the fluidized bed furnace and a circulation means for circulating and reusing this N_2 gas. The austempering apparatus according to claim 3, characterized in that: