JPS6365736B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to heat treatment for cooling high-temperature carbon steel materials at a predetermined cooling rate, and in particular, to a heat treatment that cools a high-temperature carbon steel material at a predetermined cooling rate. The present invention relates to a heat treatment method for carbon steel materials and an apparatus for the same.

[Prior art and its problems] It is well known that when a high-temperature metal is immersed in hot water, a film of steam is generated on the metal surface, which prevents direct contact between the metal and the hot water and slows down the cooling rate of the metal. It is being This phenomenon is called film boiling cooling, and a method of utilizing this cooling method for patenting high carbon steel wire is described in Japanese Patent Publication No. 8563/1983 and is well known. Therefore, in the following, the present invention will be explained using the patenting heat treatment of high carbon steel wire rod as an example, but it goes without saying that this method can also be used for heat treatment of other carbon steel materials.

By the way, when hot water is conventionally used for patenting high carbon steel wire, the temperature of the hot water is limited to a temperature approximately close to the boiling point. The main reasons for this are (a) temperature control of hot water (hot water) is extremely easy;
(b) If the high carbon steel wire is thin and processed even at hot water temperatures close to the boiling point, a satisfactory cooling rate can be obtained, although it is inferior to, for example, lead patented wire.
This is because the required tensile strength can be obtained. However, at this hot water temperature, if the material quality, surface condition, etc. of the material are constant, the amount of heat removed per surface area is constant, and the cooling rate cannot be changed or controlled. Therefore, this method has the drawback that as the diameter of the wire increases, the cooling rate decreases, and only a heat-treated wire with insufficient strength can be obtained.

On the other hand, there is a strong desire to increase the cooling rate, that is, in the case of patenting, to obtain the same strength as lead patenting. For this reason, attempts have been made to perform heat treatment in a state where the temperature of hot water (refrigerant) is significantly lower than the boiling point, that is, in a subcooled state, but lowering the water temperature (increasing the degree of subcooling) causes the vapor film to become unstable. The temperature at which the boiling transitions from boiling to nucleate boiling becomes higher than the transformation point. As a result, the cooling rate from the transition temperature becomes extremely (excessively) fast, leading to a phenomenon of quenching, that is, a phenomenon in which martensite is generated entirely or locally near the nuclei of nucleate boiling, so it ends in failure. There is.

In order to increase the cooling rate, attempts have also been made to stir the refrigerant to provide a relative flow rate with the object to be treated; for example, as in JP-A No. 57-9826, air is blown into hot water at approximately the boiling point and stirred to achieve a certain degree of cooling rate. Although this method has been effective, the strength of the patented wire is several kg/mm lower than that of lead patented wire.
This results in poor results.

In response to this current situation, the present applicant and others have discovered that by blowing air into hot water, film boiling can be stabilized even when the hot water is in a subcooled state, that is, the temperature is significantly lower than the boiling point.
As a heat treatment method in the so-called subcooled state,
No. 58-91923 was filed.

However, since this method simply blows air into hot water, the bubbles generated include bubbles with diameters of 5 mm or more, and the uniformity of bubble dispersion varies depending on time and location, resulting in insufficient results. However, the stabilization of the vapor film was only unsatisfactory. The present invention is an improvement on the method and can be used for general heat treatments of carbon steel other than patenting.

[Structure of the Invention] The present invention involves immersing carbon steel in a hot refrigerant by cutting the bubbles generated by the above-mentioned air blowing into the liquid to form bubbles with a diameter of about 1 mm or less. It is characterized by heat treatment.

The present inventors have discovered that if the bubbles generated by air blowing are cut into bubbles of approximately 1 mm or smaller in size in the refrigerant, the bubbles will be uniformly dispersed in the refrigerant and the vapor film will be more stable. The present invention was completed based on the finding that when the refrigerant is stirred, the cooling rate increases while the vapor film becomes more stable (the cooling rate does not become excessive due to the vapor film).

A multiphase mixture of bubbles generated by blowing gas into a refrigerant such as hot water is called a gas (foam) water mixed phase fluid (generally air (foam) liquid fluid). This state is exactly the opposite structure to the mist state in which droplets are mixed in gas.

By the way, for example, when air at room temperature is blown into the bottom of a hot water tank to generate bubbles, the bubbles naturally expand thermally, but the water in the bubbles evaporates until it reaches the equilibrium vapor pressure at the hot water temperature, so the bubbles The intestines rapidly distend and rise to the surface, dissipating from the surface of the water. To quantitatively display the state of this gas-water multiphase fluid, first, we can measure the volume of gas (bubbles) that floats and dissipates per unit time per unit surface area, and this is called the superficial velocity. The actual superficial velocity is determined by measuring the amount of air blown per unit time per unit surface area, and from this value, an approximate value can be calculated from the thermal expansion coefficient and the expansion coefficient assuming that the bubbles contain steam up to the equilibrium vapor pressure. It can be determined by calculation. The expansion rate of bubbles when room temperature air is blown into hot water as a gas is approximately as shown in Figure 1.

Further, the state of the gas-water mixed phase fluid can be quantitatively expressed by the volume ratio that the gas phase fills in the whole, that is, the gas mixed phase ratio (also referred to as gas hold up). For example, when air is blown into hot water, the gas mixture ratio can be determined from the degree of rise in the hot water level before and after air blowing, that is, the increase in the overall volume. Otherwise, the surface of the hot water will be disturbed, so it is essential that it is evenly distributed. An example of the relationship between the superficial velocity and the gas mixed phase ratio when air at room temperature is blown into hot water is shown in Figure 2.

In the above explanation, the state of the gas to be blown is assumed to be at room temperature, and the gas contains almost no refrigerant vapor (air or pressurized air that is saturated with hot water at room temperature is in this state), and the vapor pressure in the gas is taken into consideration. This is a case where it is so low that it is not necessary. In this case, the refrigerant evaporates in the bubbles and takes away the heat of evaporation from the refrigerant, so blowing the gas generally lowers the refrigerant temperature. Therefore, in order to keep the temperature of the gas-liquid multiphase fluid that is the refrigerant constant, an auxiliary device that heats or cools the refrigerant from the outside is required, taking into account the amount of heat input from the high-temperature metal material being processed to the refrigerant. Become. The inventors of the present invention have applied for a patent application filed in 1983-
If the blown gas is preheated as described in No. 91923 and the vapor pressure is increased by mixing refrigerant vapor into the gas in advance, the amount of vapor evaporating into the bubbles will be reduced, and the ability to cool the refrigerant will be correspondingly weaker. It was pointed out that the temperature of the refrigerant can be controlled by such preliminary humidity conditioning treatment of the gas. This method can also be effectively used in the present invention. Furthermore, in the present invention, the bubbles are finely divided, and the specific surface area of the bubbles is extremely large, so the time for vapor to evaporate and reach an equilibrium state within the bubbles is short, and the refrigerant remains unsaturated within the bubbles. Since it is difficult to dissipate from the surface and the amount of heat absorbed is constant, there is an advantage that temperature control of the refrigerant becomes easier.

In cases where high-temperature high-carbon steel materials are continuously processed, such as direct patenting treatment of wire rods, external cooling is generally required because the amount of heat removed by the latent heat of vaporization is insufficient. However, in ordinary heat treatment, preliminary humidity conditioning treatment of gas, that is, preheating and vapor pressure increasing treatment, is extremely effective for controlling the temperature of the refrigerant.

Since the method of the present invention is applied to a device that performs a desired heat treatment using film boiling cooling, the refrigerant conditions must be such that film boiling is easily generated during cooling. In the case of water normally used for heat treatment by this method, film boiling hardly occurs when the water is at room temperature. Therefore, in the case of water, even if it is in a subcooled state, it needs to be hot at about 45°C or higher, preferably 70°C or higher, and at low temperatures it is desirable to use an additive that helps film boiling.

In the method of the present invention, the diameter of the bubbles is subdivided into approximately 1 mm, which makes the dispersion of the bubbles in the liquid very uniform, and the vapor film formed on the surface of the carbon steel material to be treated is Air bubbles reach evenly. This has the effect of expanding the surface film on the surface, and depending on the type of gas, it may change the gas composition in the vapor film and bring about some chemical change on the surface of the metal material to be treated. It is presumed that the gas repairs the vapor-free film portion that is causing this, and as a result, the vapor film is stabilized, the induction of nucleate boiling is suppressed, and film boiling is stably continued as a whole.

Since it is necessary for the bubbles to reach the evaporation film uniformly in this way, in the present invention there is a limit to the amount of bubbles, that is, the superficial velocity or the gas mixed phase ratio, but the limit value is determined by the amount of gas and liquid used. Varies depending on type. This limit value can be understood from the following examples.

Furthermore, although the present invention has been described above with respect to a liquid whose main component is water, it is understood that it can also be used with other liquids, such as suspensions, oils, synthetic oils, etc., within the spirit and scope of the present invention. Of course.

An apparatus for carrying out the method of the present invention will be explained below based on the drawings.

FIG. 7 shows an example of the heat treatment apparatus of the present invention.

A foam cutting plate 1 is provided with a gas blowing pipe 2 at the bottom of a processing tank 1 containing a refrigerant, and is driven by a foam cutting machine motor 4 through the central axis of the gas outlet.
2 is installed. A stirrer 6 is provided in the treatment tank 1, and the carbon steel material 8 to be treated is suspended into the refrigerant in the treatment tank. Further, a piping 11 is provided so that the refrigerant 7 is extracted from the upper side of the processing tank 1, passed through a heat exchanger 9, and then sent again from the bottom of the processing tank 1 by a circulation pump 10. In addition, a supply tank for supplying refrigerant to the processing tank may be attached and connected to the processing tank via a pipe.

When refrigerant is put into the processing tank 1 and gas is blown into it from the gas blowing pipe 2 at the bottom, large diameter bubbles 3 are created.
The bubbles are cut by the rotation of the bubble cutting plate 12 provided in the rising passage, and become finely divided into bubbles 5 with a diameter of about 1 mm, uniformly dispersed, and floated in the refrigerant to form a gas-liquid multiphase fluid 7. . At this time, the fluid is strongly stirred by the stirrer 6, and the circulation pump 10 is operated to keep the temperature of the gas-liquid mixed phase fluid constant. When the carbon steel material 8 heated to a high temperature is immersed in the gas-liquid multiphase fluid thus formed, heat treatment can be performed at an appropriate cooling rate by stable film boiling as described above.

The foam cutting plate 12 may be, for example, a circular plate having a large number of small circular holes of about 10 mm, or it may be made by rotating something like an impeller. It is also possible to omit the stirrer by providing the foam cutting machine with stirring ability.

Furthermore, the temperature of the refrigerant can be controlled by providing a preliminary humidity control device for heating and humidifying the gas blowing device.

Although the example shown in FIG. 7 shows an embodiment in which the carbon steel material to be treated is intermittently immersed, the present invention can be modified so that continuous immersion treatment can be applied to long products, etc., without departing from the spirit of the present invention.

D Examples Example 1 Materials of SWRH82B, namely C0.8%, Si0.2%,
A round bar with a diameter of 13 mmφ made of high carbon steel with 0.68% Mn is heated to 950℃.
and heat-treated by immersing it in hot water using the apparatus shown in FIG. This corresponds to the patenting treatment of high carbon steel materials. In this case, a rotating perforated disk was installed as a bubble cutter in the ascending path of the air-water multiphase fluid in which room temperature air was blown into the hot water in the tank and the blown air bubbles without a bubble cutter to cut the bubbles. Experiments and comparisons were made using two types of refrigerants: air-water multiphase fluids.
According to the observation, without the bubble cutting machine, the diameter of the bubbles was about 5 mm, and sometimes there were bubbles with a diameter of 10 mm or more mixed in, but when the bubble cutting machine was rotated, the bubble diameter was about 5 mm. It was 1mm thick. The amount of gas blown is a superficial velocity of 3 cm/sec, and a gas mixed phase ratio.
I blew it with the goal of 0.1. The results obtained were as shown in Figure 3.

In other words, in the case of simple air bubbles, the results are in the range shown by the solid line in the figure, and when the water temperature is below 75°C, nucleate boiling begins and martensite is often generated, and the tensile strength obtained is This is lower than when the bubbles are cut to about 1 mm as in the invention. On the other hand, in the case of bubble cutting, no martensite is generated even when the water temperature reaches 65°C, and the strength is within the range of the dotted line in the drawing, indicating that there is a good hardening effect due to moderate rapid cooling. Obviously, the smaller the bubbles, the more stable the film boiling and the better the cooling effect.

This fact indicates that, as in the method of the present invention, fine-grained air bubbles are more uniformly dispersed throughout the tank, and are more easily caught evenly in the vapor film forming on the surface of the material to be treated, thereby expanding the vapor film. It is thought that this will stabilize the material and cause an oxidation reaction on the surface of the material to be treated, thereby preventing the destruction of the vapor film and, therefore, better preventing nucleate boiling. In addition, the rotation of the perforated disc for cutting strongly agitates the refrigerant, allowing air bubbles to reach the vapor film more evenly, promoting the capture of air bubbles, which not only stabilizes the vapor film, but also improves the relationship between the refrigerant and the material to be treated. It is thought that this is because the relative flow velocity between the two is increased, which increases the cooling rate, resulting in an improvement in the tensile strength.

This experiment shows that dividing the bubbles into smaller particles to make them uniform in particle size is effective in stabilizing film boiling, but this is especially effective when long products are continuously heat-treated in a large tank. .

Although it depends on the size of the material to be treated, the particle size of the bubbles is approximately 1 mm, which is sufficient for practical purposes.

Example 2 Using a sample having the same components as in Example 1 and having a diameter of 10 mm, the cooling curve of the center of the material was measured when it was immersed in the same two types of air-water multiphase fluid as described above at a refrigerant temperature of 80°C. In addition, in order to examine the effect of relative flow velocity, similar measurements were carried out while moving the sample through the fluid at a speed of 0.6 m/sec in a direction perpendicular to the axis of the sample when the bubble diameter was 1 mm.

The results were as shown in Figure 4.

From this result, the cooling rate given the relative flow velocity is initially a little faster, but if we pay attention to the cooling curve after pearlite transformation of this material, we find that the cooling rate is in the order of large diameter bubbles - small diameter bubbles - relative flow velocity or small diameter bubbles. The temperature at which it converts to nucleate boiling is decreasing. That is, it can be seen that the vapor film is more stable.

Example 3 A short bar of SWRH82B material with a diameter of 11 mmφ was heated to 950°C in a non-oxidizing atmosphere, and then air was blown into hot water to cut air bubbles to a diameter of about 1 mm and uniformly dispersed. Heat treatment (patenting treatment) was performed by immersing it in a refrigerant at ℃. The strength of the material obtained by varying the amount of air blown was measured. The results obtained were as shown in FIG. The horizontal axis of the drawing shows the amount of blown air as well as the superficial velocity obtained from calculation.

This result shows that martensite is generated when the superficial velocity is less than 0.5 cm/sec, and the induction of nucleate boiling cannot be completely prevented. That is, for safety reasons, nucleate boiling does not occur at a speed of 1 cm/sec or more. It is also seen that when the superficial velocity is increased, the agitation of the refrigerant becomes stronger, and therefore the cooling rate increases and the strength obtained gradually increases, but it tends to gradually become saturated. Observations have shown that when the superficial velocity is set to 20 cm/sec or more, the amount of air increases, which is not good because the air does not form into bubbles and a so-called blow-by phenomenon occurs. It is found that a superficial velocity of 1 to 20 cm/sec is appropriate. The desirable range of the superficial velocity varies slightly depending on the type of gas and liquid constituting the refrigerant, the surface condition of the carbon steel material to be treated, and the like.
These superficial velocities are expressed as gas mixed phase ratio.
Corresponds to 0.05-0.35. (See Figure 2) Example 4 The same metal material as in Example 3 was heated under the same conditions, the bubble diameter was approximately 1 mm, and the temperature of the refrigerant was changed at a superficial velocity of 5 cm/sec. Comparative measurements were made of the strength obtained when an activator was added. PVA was added at 0.03% as a surfactant.

The results obtained were as shown in FIG.

This result shows that although the strength obtained at the same refrigerant temperature at which a surfactant is added is slightly lower, martensite does not occur even in low-temperature refrigerants, and film boiling is stable up to low temperatures. It is observed that when a surfactant is added, the gas mixed phase ratio increases even at the same void ratio, and this is considered to be the cause of a slight decrease in the cooling rate.

A solution or suspension containing a substance that changes the heat transfer coefficient can be employed depending on the purpose in combination with conditions such as the amount of stirring.

[Effects of the Invention] As explained above in detail, the heat treatment method and apparatus of the present invention have the following effects.

1 Since the bubble size is subdivided into around 1mm or smaller, the bubbles are uniformly dispersed and evenly reach every corner of a complex-shaped or long carbon steel article, resulting in film boiling. , the desired film boiling cooling can be performed even in a large subcooled state.

2. The refrigerant is strongly stirred by the bubble cutter and stirrer, which increases the cooling rate and further stabilizes film boiling.

3. Since the bubble diameter is small, the vapor pressure within the bubble quickly reaches an equilibrium state, and the variation in the amount of heat taken from the refrigerant due to evaporation is small, making it easier to manage the temperature of the refrigerant into which gas is blown.

That is, by blowing gas into the heated refrigerant, giving an appropriate cooling rate to the material to be treated in a subcooled state, and preventing nucleate boiling and controlling excessive cooling, it is possible to obtain a good heat-treated material. This is an effective method and device.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the expansion rate of bubbles generated when air at room temperature is blown into hot water and hot water temperature, and Figure 2 is a graph showing the relationship between superficial velocity and gas mixed phase ratio. Figure 3 is a graph showing the comparative relationship between refrigerant temperature and tensile strength obtained when steel materials are patented by the conventional method and the method of the present invention, and Figure 4 is a graph showing the temperature at the center of the steel material when the same treatment is applied. A graph showing the reduction curve, Figure 5 is a graph showing the relationship between the amount of air blown by the method of the present invention and the tensile strength of the material obtained, and Figure 6 is a graph showing the relationship between the refrigerant temperature and the tensile strength when a surfactant is added. This is a graph showing. FIG. 7 is a front sectional view showing an example of the device of the present invention. 1... Processing tank, 2... Gas blowing pipe, 3...
Large-diameter bubbles, 4... Motor for foam cutting machine, 5... Bubbles with a diameter of approximately 1 mm, 6... Stirrer, 7... Gas-liquid mixed tank fluid, 8... Carbon steel parts, 9... Heat exchanger , 10...
...Circulation pump, 11...Piping, 12...Perforated disk.

Claims (1)

[Claims] 1. Carbon steel material is heated to a high temperature, and the carbon steel material is heated to a constant temperature between 45°C and the boiling point, in which a large number of bubbles with a diameter of 1 mm or less are uniformly dispersed in a liquid. A method for heat treatment of carbon steel material, characterized in that the metal structure is transformed into pearlite by immersing the material in a coolant consisting of a liquid multiphase fluid and performing cooling heat treatment. 2 The superficial velocity of gas in a gas-liquid multiphase fluid is 1~
2. The method of heat treating carbon steel material according to claim 1, wherein the heat treatment rate is 20 cm/sec. 3. The method for heat treatment of carbon steel materials according to claim 1 or 2, wherein the gas-liquid multiphase fluid has a gas mixed phase ratio of 0.05 to 0.35. 4. The method for heat treatment of carbon steel materials according to any one of claims 1 to 3, wherein the liquid is water or an aqueous solution or suspended water containing a substance that changes the heat transfer coefficient. 5. Claims 1 to 4 characterized in that the gas-liquid multiphase fluid is treated in a strongly agitated state.
A method for heat treatment of carbon steel material according to any one of the above. 6. A device for cooling and heat-treating high-temperature carbon steel materials by immersing them in a fluid refrigerant, which includes a device for blowing gas into the liquid refrigerant in a heat treatment tank, a bubble cutting device for dividing the generated bubbles, and a constant temperature of the refrigerant. 1. A heat treatment apparatus for carbon steel materials, comprising a heat exchanger for circulating the refrigerant and a means for circulating the refrigerant. 7. The heat treatment apparatus for carbon steel materials according to claim 6, characterized in that a device for powerfully stirring the refrigerant is provided in the heat treatment tank. 8. The heat treatment apparatus for carbon steel materials according to claim 6 or 7, further comprising a temperature control device for maintaining the refrigerant at a predetermined temperature.