JP3117704B2 - Cooling method using fluidized bed - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cooling treatment method performed by burying a treated product in a fluidized bed of a fluidized bed furnace, and relates to cooling and quenching of steel or cast iron, particularly, austempering. The present invention relates to a method for performing processing efficiently.

(Conventional technology) Generally, in austempering, a treated product such as steel or cast iron is heated to an austenite region and rapidly cooled so as to prevent pearlite transformation, and then heated to a temperature of about 250 to 400 ° C for a predetermined time (about 2 hours). ) Hold heat treatment method. During this holding, it aims at improving the strength and toughness by turning the base structure into bainite.

It is known to apply a fluidized-bed furnace to the cooling step and the high-temperature holding step of the austempering described above. In the conventional fluidized-bed furnace and the fluidized bed is formed over the full term of the cooling process, the alumina powder to the fluidized medium, N ₂ to the fluidized gas
It was common to use gas.

The austempering treatment by cooling using a fluidized bed has a cooling characteristic that each part of the treated product is uniformly performed because a uniform temperature distribution is easily obtained throughout the treated product in the fluidized bed furnace. However, in a fluidized bed using a conventional N ₂ gas as a fluidized gas, the cooling capacity is small, so that when performing austempering of a cast part having a thick wall, for example, it was difficult to obtain a bainite structure up to the inside. .

The present inventor has cooled by He gas earlier noted to have a much greater thermal conductivity compared to N ₂ gas, a He gas instead of the conventional N ₂ gas as a fluidizing gas An austempering method and apparatus using a fluidized bed with enhanced performance was proposed.

(Problems to be solved by the invention) However, in such a fluidized bed by He gas flow,
Although the cooling capacity was high, a phenomenon in which the contact portion with the fluidized bed was excessively cooled was observed, and it was found that a large temperature difference occurred between the surface and the inside of the processed product during cooling. FIGS. 1 (a) and 1 (b) show the measurement results of the temperature distribution between the fluidized bed and the processed product. In the case of (a) He gas flow, (b) N ₂ gas flow It can be seen that the temperature difference between the surface of the processed product and the inside is more remarkable than in the case of Looking at the cooling curve in the case of He gas flow, as shown in Fig. 2, the temperature of the treated product surface rapidly decreases due to the high cooling power of He gas, but the internal temperature decreases with a delay. In order to proceed, the two curves are far apart as cooling proceeds. The point where the two curves are farthest from each other is where the temperature difference between the surface and the inside is maximum. Such a large temperature difference causes distortion due to thermal stress, and particularly causes deformation when the thickness of each part varies depending on the shape of the processed product.

Accordingly, an object of the present invention is to prevent the occurrence of distortion due to a temperature difference between the surface of a processed product and the inside in a highly efficient heat treatment method using He gas as a flowing gas.

(Means for Solving the Problems) In order to achieve the above object, a cooling method using a fluidized bed according to the first invention is a method for cooling a fluidized bed performed by burying a processed product in a fluidized bed of a fluidized bed furnace. In the cooling treatment method used, He gas was used as the fluidized gas in the fluidized bed, and this fluidized gas was intermittently flowed into the fluidized bed a plurality of times to alternately form the fluidized bed and the fixed bed in the fluidized bed. It is characterized in that the processed product is processed while processing.

Further, in the processing method using the fluidized bed according to the second invention, after the processed product is heated to a temperature range of an austenite region,
In a cooling treatment method using a fluidized bed performed by embedding in a fluidized bed of a fluidized bed furnace, He gas is used as the fluidized gas in the fluidized bed, and this fluidized gas is intermittently flown into the fluidized bed several times. By cooling the treated product while alternately forming a fluidized bed and a fixed bed in the fluidized bed, cooling to the bainite formation temperature range while suppressing the production of ferrite and pearlite, then stopping the flow of He gas By holding for a predetermined time in the fixed layer,
It is characterized in that the base structure of the processed product is bainite-structured.

Further, the cooling treatment method using a fluidized bed according to the third invention is a cooling treatment method using a fluidized bed performed by heating a treated product to a temperature range of an austenite region and then burying the treated product in a fluidized bed of a fluidized bed furnace. He gas is used as the fluidized gas in the fluidized bed, and the fluidized gas is intermittently flowed into the fluidized bed several times, and the processed product is cooled while alternately forming the fluidized bed and the fixed bed in the fluidized bed. by, cooled to the bainite formation temperature range while suppressing the formation of ferrite and pearlite, then Na ₂
It is characterized in that the base structure of the processed product is made bainite by switching to gas flow.

(Operation) When performing cooling treatment of a processed product in a high temperature state, the surface temperature of the processed product rapidly decreases in a fluidized bed due to He gas flow. That is, since the thermal conductivity of the He gas is large, heat is rapidly removed from the surface of the processed product. In such a state of He gas flow, the rate of heat release from the surface of the processed product to the outside is greater than the rate of heat conduction from the inside of the processed product to the surface, and there is a remarkable temperature difference between the inside of the processed product and the surface. Occurs. When He gas is stopped and the state changes from a fluidized bed to a fixed bed, the heat release rate decreases at a stretch, and conversely, the heat transfer inside the treated product becomes relatively large, so the surface temperature becomes Rise temporarily. As a result, the temperature difference between the inside of the processed product and the surface is substantially eliminated, and the temperature of the entire processed product is substantially uniform. When the cooling process is performed while repeating the intermittent flow of the He gas so that the fluidized bed and the fixed bed are alternately formed, the temperature of the surface of the processed product decreases step by step, and furthermore, Is kept small.

Therefore, in the austempering treatment to which the heat treatment method according to the present invention is applied, a cooling curve as shown in FIG. 3 is obtained. (Effect of the Invention) He gas is intermittently flowed to alternately form a fluidized bed and a fixed bed. Thus, both a high cooling effect by the fluidized bed in which the He gas flows and a slow and uniform cooling effect by the fixed bed can be obtained. When the method according to the present invention is applied to the cooling process of the austempering process, the high cooling effect exhibited by the He gas is intermittently added, so that it is difficult to use a thick part of about φ20 mm, which is difficult by the N ₂ gas flow. Parts made of alloy FCD material have also been bainitized to the inside, making it possible to perform austempering. In addition, the uniform cooling effect can reduce the distortion of the processed product.

The processing method according to the present invention is not limited to the above-described cooling process in the austempering process or quenching, but also when applied to a heat treatment method such as various post-heating processes, the uniformity is similarly high under a high processing efficiency. Enables heat treatment.

(Example) Next, a specific example of the present invention will be described in detail with reference to the drawings.

FIG. 4 shows an example of an apparatus for performing the method according to the present invention. In FIG. 4, a spheroidal graphite cast iron member heated to 800 to 900 ° C. is charged as a processed product 2 into a fluidized bed furnace 1. Also, alumina powder 11 having a particle size of about 80 mesh is charged. Next, the valves 3, 4 and 5 were opened, and the gas was accelerated from the He gas cylinder 8 by the turbo fan 10.
He gas is introduced into the fluidized bed furnace 1 through a pipe 9. Note that the valve 3 is closed after reaching an appropriate He supply amount. The valve 4 is opened and closed every few seconds to several tens of seconds, and while the valve 4 is open, He gas flows into the fluidized bed furnace. He
When the gas is introduced, in the fluidized bed furnace, He
The gas is blown up and the alumina powder 11 flows to form a fluidized bed. The processed product 2 is cooled by the heat exchange action of the fluidized bed. He warmed up by heat exchange
The gas is discharged from above the fluidized-bed furnace 1 through the filter 14 and cooled by the heat exchanger 15. Then, the fluidized bed furnace 1 is accelerated again by the turbofan 10 through the pipe 9.
Will be introduced. During the formation of the fluidized bed, the He gas is circulated to cool the treated product 2 to a bainite transformation temperature of about 250 to 400 ° C. while minimizing the temperature difference between the surface and the inside of the treated product 2. On the other hand, when the flow of the He gas is stopped by closing the valve 4, the alumina powder 11 sinks to the lower part of the fluidized bed furnace 1, and a fixed bed is formed intermittently. If necessary, the bainite transformation temperature is maintained by adjusting the inside of the fluidized bed furnace 1 to a predetermined constant temperature by the heater 16, and bainite transformation can be performed in the fluidized bed furnace. After the cooling process due to the intermittent formation of the fluidized bed or the fixed bed, the valves 3 and 4 are closed and the valve 6 is opened (the valve 7
Remains closed. 2) He gas is extracted from the fluidized bed furnace 1 by the pump 17 and stored in the storage tank 18. After the storage is completed, the valve 6 is closed again. The treated product 2 as a spheroidal graphite cast iron member after the bainite transformation is taken out of the furnace and allowed to cool.

When the fluidized bed furnace 1 is used again for austempering another treated product 2, after the treated product 2 is charged,
The valves 7, 4 and 5 are opened, and the He gas discharged from the storage tank 18 by the compressor 19 is pressurized and sent to the fluidized bed furnace 1. Then, the above operation is repeated. At this time, He
If the gas flow is insufficient, the valve 3 may be opened to supply additional He gas.

Next, a specific example in which an austempering process is actually performed using the above-described apparatus will be described.

FIG. 5 is a diagram showing the shape of a part used in the austempering process. This part is made of spheroidal graphite cast iron and has an outer diameter of 90 mm and an inner diameter of 30 mm. This part was changed to a He gas intermittent air supply condition of 5 seconds fluidized bed → 5 seconds fixed bed → 5 seconds fluidized bed → 5 seconds.
The cooling treatment was performed in such a manner that the second fixed bed → 10 second fluidized bed → 10 second fixed bed → 10 second fluidized bed → 10 second fixed bed. The cooling state in this processing was measured for the surface portion and the center of the thickness of the processed product 2 shown in FIG.
Shown in the figure. In the drawing, FP is an abbreviation for ferrite / pearlite. As a result of such intermittent He gas flow, the temperature difference between the surface of the treated product and the center of the wall thickness is 150
Below ℃, the processed product has almost no distortion due to thermal deviation,
A bainite phase was obtained up to the center.

For comparison, the same component was subjected to a conventional cooling process using a non-intermittent fluidized bed with N ₂ gas flow and a cooling process using a non-intermittent fluidized bed with continuous He gas flow. FIG. 7 shows the surface of the treated product and the cooling curve at the center of the wall thickness obtained in each treatment.

As can be seen from FIG. 7, in the conventional cooling treatment using N ₂ gas flow, although the temperature difference between the surface of the treated product and the center of the wall thickness is small, the cooling curve at the center touches the ferrite / pearlite nose. No complete bainite structure was obtained.

In the case of cooling treatment by continuous He gas flow, a uniform bainite phase was obtained up to the center of the wall thickness.
Where the temperature difference between the surface of the treated product and the center of the wall thickness was the largest, the temperature was 200 ° C. or more, and the occurrence of distortion was expected.

In the above-described embodiment, only He gas was used as the flowing gas.However, the first half of the cooling process, that is, He gas only at the stage where rapid cooling is required, such as the beginning of the cooling process or the bainite phase formation temperature range, time past the ferrite-pearlite area of the second half, i.e. changed to the N ₂ gas flow under M _S point near, or by the fixed layer to stop the flowing gas, more reliable prevention of distortion at slow cooling rate It can also be.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) show the temperature distribution of the processed product, and FIG.
FIG. 3 and FIG. 3 show a comparison between the conventional example and the present invention. FIG. 2 is a graph showing a cooling curve of the conventional austempering, and FIG. 3 is a graph showing a cooling curve of the austempering by the method according to the present invention. FIG. 4 is a block diagram showing an example of a specific apparatus for performing the method according to the present invention;
FIG. 5 is a perspective view of a processed product used in the embodiment of the present invention, and FIG.
FIG. 7 is a graph showing a cooling curve of the austempering process of the embodiment, and FIG. 7 is a graph showing a cooling curve of the austempering process of the comparative example. 1 Fluidized bed furnace 2 Processed product (spheroidal graphite cast iron) 3 to 7 Valve 8 He gas cylinder 9 Pipe 10 24 Turbo fan 11 Alumina powder 12 Dispersion plate 14 ... Filter, 15 ... Heat exchanger 16 ... Heater, 17 ... Pump 18 ... Storage tank, 19 ... Compressor

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Claims (3)

(57) [Claims] In a cooling method using a fluidized bed performed by embedding a treated product in a fluidized bed of a fluidized bed furnace, a He gas is used as a fluidized gas in the fluidized bed, and the fluidized gas is intermittently used. A cooling process using a fluidized bed, wherein the treated product is processed while flowing into the fluidized bed a plurality of times and the fluidized bed and the fixed bed are alternately formed in the fluidized bed. 2. A cooling method using a fluidized bed, which comprises heating a treated product to a temperature range of an austenite region and then burying the treated product in a fluidized bed of a fluidized bed furnace. The fluidized gas is intermittently flowed into the fluidized bed several times, and the processed product is cooled while forming the fluidized bed and the fixed bed alternately in the fluidized bed, thereby producing ferrite and pearlite. The fluidized bed is characterized by cooling to the bainite generation temperature range while suppressing the flow of He gas, and then stopping the inflow of He gas and maintaining the fixed structure in the fixed bed for a predetermined time to form the matrix structure of the treated product into bainite. Cooling treatment method. 3. A cooling treatment method using a fluidized bed performed by heating a treated product to a temperature range of an austenite region and then burying the treated product in a fluidized bed of a fluidized bed furnace. The fluidized gas is intermittently flowed into the fluidized bed several times, and the processed product is cooled while forming the fluidized bed and the fixed bed alternately in the fluidized bed, thereby producing ferrite and pearlite. A cooling method using a fluidized bed, characterized in that the base structure of the processed product is bainite-structured by cooling to a bainite generation temperature region while suppressing the temperature and then switching to a N ₂ gas flow.