CN100348743C - Process controlling quenching cooling speed by regulating pulse itt duty ratio - Google Patents

Abstract

The present invention relates to a method for regulating the pulse spraying duty ratio and controlling the quenching cooling speed. The present invention is characterized in that the present invention has the steps specifically as follows: (1) a water sprayer is arranged around quenching parts of a water spraying pipeline of a spraying device, and uses a pulse spraying method to spraying water to the quenching parts, and the pulse period is selected within the range of 1 to 20 seconds every time; (2) the duty ratio K is regulated within one pulse period, K=t< 1 >/(t< 1 >+t< 2 >), and the condition that the cooling rate can be regulated within the range of the maximal cooling speed to the minimum cooling speed is realized; (3) by regulating the cooling speed obtained by the duty ratio of different times in the quenching process in different cooling stages, the cooling curve of ensuring the quenching quality of parts is realized. The present invention obtains the perfect cooling speed through a pulse spraying method, the quenching quality of the parts is ensured, the quenching control automatization of the parts is realized, and the environment pollution is eliminated.

Description

The Method of Controlling the Quenching Cooling Rate by Adjusting the Duty Cycle of Pulse Jet

technical field

The invention relates to a method for controlling quenching in the technical field of heat treatment, in particular to a method for controlling the quenching cooling rate by adjusting the duty ratio of pulse injection.

Background technique

For a long time, heat treatment workers have used a variety of quenching cooling media with different cooling rates in order to obtain an ideal cooling curve to ensure the quality of the quenched parts when quenching the parts (for example, the cooling rate of water is 1, The cooling rates of several other cooling media are as follows: air 0.05~0.08, oil 0.35, rapid cooling oil 0.5, strong stirring water 2, brine 2) and cooling methods, but there are deficiencies. If water is used as the cooling medium, it has better cooling ability at high temperature. In the range of 300~100°C of martensitic transformation, the cooling speed of water is faster, so it is easy to cause deformation and cracking of quenched parts; mineral oil is used as quenching Cooling medium, the cooling speed is slow, the deformation and cracking tendency of the parts are small, but for the parts made of low hardenability steel or the parts with large cross-section thickness, the supercooled austenite is prone to pearlite transformation during quenching. Oil is used as a quenching cooling medium, causing serious environmental pollution. There have been many researches and practical explorations, such as adding a certain proportion of NaCl or Na(OH) to water, or adding certain additives to oil, or preparing polymer aqueous solution as a quenching cooling medium, or using dual-medium cooling, water spraying Quenching methods such as intermittent immersion cooling can improve cooling performance, but the cooling rate of a single cooling medium cannot be adjusted. Even if dual-medium or multi-media cooling is used, the adjustment range of the cooling rate is limited. Some cooling methods are very difficult to obtain the ideal cooling curve.

The ideal quenching cooling curve is shown in Figure 1. The temperature above the "nose" of the TTT curve is cooled slowly to reduce the deformation of the part due to the thermal stress caused by rapid cooling; in order to avoid the pearlite transformation of the supercooled austenite, the temperature must be fast enough near the "nose" of the TTT curve Speed cooling; during martensitic transformation (temperature near the Ms point), the cooling speed should be smaller to reduce the transformation stress of the structure. A large number of studies and experiments have already confirmed that the TTT curves of different steels are different, and the cooling speed of specific parts changes with the change of size, so various parts need to be fast enough to avoid pearlite transformation during quenching and cooling. The cooling rate is different.

After searching the existing technical documents, it is found that in the section "1. Water-air gap cooling" in "Large forging materials and heat treatment" (Edited by Kang Datao and Ye Guobin, published by Longmen Bookstore. 1998) P195, it is proposed that the larger section (diameter greater than 300mm), the forgings with high alloy content adopt the alternate quenching method of air cooling and water cooling (water immersion). This method has a long duration of water immersion and air cooling, and the surface temperature of the parts fluctuates greatly, and the cooling speed can be adjusted. The performance is poor, the operation is also difficult, and it is difficult to obtain an ideal cooling curve. Moreover, this quenching and cooling method is only suitable for large-section forgings with high alloy content, and its application range is narrow.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a method for controlling the quenching cooling rate by adjusting the duty ratio of the pulse injection. Through the method of pulse spraying, the ideal cooling rate can be obtained, the quenching quality of the parts can be guaranteed, the quenching control automation of the parts can be realized, and the environmental pollution can be eliminated.

The present invention is achieved through the following technical solutions, and the method steps of the present invention are specifically as follows:

1. Install a water sprayer around the quenching parts of the water spraying pipeline of the spraying device. The water sprayer uses the pulse jet method to spray water on the quenching parts, and the pulse period of each pulse is selected within the range of 1-20 seconds;

The pulse spraying method refers to pulse spraying the quenched parts with water at a pressure of 2-6 atmospheres according to the preset water spraying and non-spraying time, so as to obtain the required cooling rate.

The pulse period refers to the sum of the water spray cooling time t ₁ and the consecutive non-water spray time t ₂ .

2. Adjust the duty ratio K within a pulse period, K=t ₁ /(t ₁ +t ₂ ), to realize the adjustable cooling speed between the maximum cooling speed and the minimum cooling speed;

The above-mentioned duty ratio refers to the proportion of water spray cooling time in a pulse injection period in the pulse period.

The maximum cooling rate mentioned refers to 3 times of the water quenching cooling rate.

The minimum cooling rate mentioned refers to a quarter of the oil quenching cooling rate.

3. By adjusting the cooling rate obtained in different cooling stages by adjusting the duty cycle at different times during the quenching process, an ideal cooling curve that ensures the quenching quality of the parts is achieved, creating the necessary conditions for automatic operation.

Assuming that water spray cooling is used for all within a pulse period, K is equal to 1 in this pulse period; if the water spray time is 0, K is equal to 0. The duty cycle can be adjusted in the range of 0~1, that is to say, adjust t ₁ and t ₂ in a tiny pulse gap cycle, so that the average heat transfer coefficient of the part surface in this cycle is between the heat transfer coefficient of sprayed water and As the heat transfer coefficient of the air changes, the cooling rate also changes accordingly.

When the quenched parts mentioned above are graded quenched parts or isothermally quenched parts, when the surface is cooled to the graded or isothermal temperature, the duty ratio is adjusted immediately so that the surface temperature fluctuates up and down within the temperature range of ±15°C, and when the internal temperature continues to Decrease until the duty cycle is 0, and when the surface temperature continues to drop, transfer it to an air-heated isothermal furnace or a fluidized bed.

As for the quenched part, when the quenched part is less than or equal to 20 mm, since the surface of the part is cooled to the isothermal or graded temperature, the core temperature is close to the surface temperature, so it is directly transferred to an air-heated isothermal furnace or a fluidized bed for isothermal treatment .

For the pulse spraying of the quenched parts, a high-pressure air valve is installed between the water spray line shut-off valve and the water spray outlet of the spray device. When the water spray command stops, the high-pressure air valve opens instantly to blow off the remaining water. , the water spray stops immediately to ensure accurate control of the duty cycle.

Install the entire spray cooling device in a sealed container, and pass nitrogen or a mixture of nitrogen and ammonia decomposition gas into the container as a protective gas to reduce surface oxidation or decarburization of parts during the quenching process and improve quenching quality.

According to the requirements of the ideal cooling curve, the "trial and error" or computer simulation method is used to determine the duty cycle of the processed parts in different cooling stages, so as to obtain the best quenching quality.

The present invention has substantial technical progress. Compared with the existing quenching and cooling technology, the present invention adjusts the duty cycle in the pulse cycle by adopting the method of pulse spraying, so that the average heat transfer coefficient of the surface of the part in this cycle is within the range of water spraying. The heat transfer coefficient varies between that of air cooling to obtain the desired cooling rate. The duty cycle can be changed between 1 and 0, that is, it can be adjusted between the strongest cooling capacity and the weakest cooling capacity, so that the corresponding duty cycle can be selected according to the cooling rate required by the ideal cooling curve of the part , to overcome the lack of commonly used quenching medium, to ensure the quenching quality of parts. Using the pulse jet quenching method, the duty cycle can be determined by using computer simulation methods, and the quenching control automation of parts can be realized. The use of pulse jet quenching can also eliminate environmental pollution.

Description of drawings

Figure 1 Schematic diagram of several different quenching cooling curves and TTT curves

Fig. 2 is a schematic diagram of the cooling rate curve of the surface of the part under different duty ratios in the present invention

The schematic diagram of the curve shape obtained after the parts of the present invention are cooled

Fig. 4 embodiment installs the sprinkler schematic diagram of high-pressure air valve

Detailed ways

The present invention adopts the cooling rate curve obtained on the part surface under the situation of different duty ratios by the pulse jet cooling method as shown in Figure 2. When the K value in the figure is small, the curve declines gently, and when the K value is large, the slope of the curve becomes steep. It can be seen that as long as we adjust the duty cycle K value between 0 and 1, we can get the required cooling rate, which overcomes the problem that the cooling rate can only be adjusted within a limited range by using one or several cooling media. limitations. Figure 2 shows that the cooling curve of the workpiece surface is jagged during pulse jet quenching, but as the pulse period (t ₁ +t ₂ ) shortens, the jaggedness is improved and the curve tends to be smooth. During the cooling process of the surface layer, the heat of the inner layer is continuously transferred to the surface layer, and the temperature of the inner layer also changes accordingly, but the temperature changes slowly as it goes inward, and the shape of the cooling curve of the inner layer should be more continuous and smooth than that of the surface layer, as shown in Figure 3 shows.

Embodiment one

Part Name: Shaft

Material: 40Gr, size: Φ20×200mm;

Heat treatment technical requirements: Hardness: HRC 56~58;

Quenching process

Heating temperature: 840℃±5;

Cooling method: pulse jet quenching method;

Spray water pressure: 5-6 atmospheres, pulse period: 1 second, duty cycle: 0.15;

Quality checks meet technical requirements.

Embodiment two

Part Name: Ring

Material: Gr15, size: outer diameter 280mm, inner diameter 250mm, height 100mm;

Heat treatment technical requirements: hardness: HRC 58~62, deformation: ellipticity ≤ ± 0.5mm;

Quenching process

Heating temperature: 860℃±5;

Cooling method: pulse jet quenching method (N2 or N2+5%NH3 decomposition gas is used as the protective gas to prevent oxidation of parts in the sealing device);

Water spray pressure: 3 to 4 atmospheres, pulse period: 2 seconds;

800℃～700℃ K 0.1, 700℃～400℃ K 0.6, 400℃～300℃ K 0.25, 300℃ transfer to fluidized bed or air furnace;

Quality checks meet technical requirements.

Embodiment Three

Part Name: Roller

Material: 9Gr2Mo, size: diameter 360mm, length: 700mm;

Heat treatment technical requirements: Hardness: HRC 60~64, no cracks after quenching:

Quenching process

Heating temperature: 860℃±5;

Cooling method: pulse jet quenching method

Spray water pressure: 2 to 3 atmospheres;

860℃～730℃ pulse period: 20 seconds K 0.1, 730℃～680℃ pulse period: 5 seconds K 0.8;

680℃～400℃ pulse period: 5 seconds K 0.95, pulse period below 400℃: 5 seconds K 0.5;

Quality checks meet technical requirements.

In the actual operation of the above embodiment, when the water spray command stops in each pulse cycle, due to the inertia of the remaining water in the nozzle, part of the water is still sprayed out, which affects the precise control of the duty cycle. In order to avoid this phenomenon, a high-pressure water inertia effect can be installed between the water spray pipeline shut-off valve and the water spray outlet, and part of the water will still be sprayed out, which will affect the precise control of the duty cycle. In order to avoid this phenomenon, a high-pressure air valve can be installed between the shut-off valve of the water spray pipeline and the water spray outlet. When the water spray instruction stops, the high-pressure air valve will open instantly to blow off the remaining water, and the water spray will stop immediately. , to ensure accurate control of the duty cycle and improve cooling quality, as shown in Figure 4.

Claims (6)

1. a method for regulating the duty ratio of the pulse jet to control the quenching cooling rate is characterized in that the steps are as follows: ①. Install a water sprayer around the quenching parts of the water spraying pipeline of the spraying device. The water sprayer uses the pulse spraying method to spray water on the quenching parts, and the pulse period of each pulse is selected within the range of 1-20 seconds; ②. Adjust the duty ratio K within a pulse period, K=t ₁ /(t ₁ +t ₂ ), to realize the adjustable cooling rate within the range of the maximum cooling rate and the minimum cooling rate. The pulse period mentioned refers to The sum of the water spray cooling time _t1 and the time _t2 without water spraying in succession, the duty cycle refers to the proportion of the water spray cooling time in the pulse cycle in a pulse injection cycle; ③. By adjusting the cooling rate obtained in different cooling stages by adjusting the duty cycle at different times during the quenching process, the cooling curve that ensures the quenching quality of the parts is realized; The pulse spraying method in ① refers to pulse spraying the quenched parts with water at 2-6 atmospheric pressure according to the preset water spraying and non-water spraying time, so as to obtain the required cooling rate. 2. the method for adjusting the duty ratio of pulse jet according to claim 1 to control quenching cooling rate is characterized in that, described maximum cooling rate refers to 3 times of water quenching cooling rate; described minimum cooling rate , refers to a quarter of the oil quenching rate. 3. The method for controlling the quenching cooling rate by adjusting the duty ratio of the pulse jet according to claim 1, characterized in that, when the quenched parts are graded quenched parts or austempered parts, when the surface is cooled to graded or isothermal Immediately adjust the duty cycle when the temperature rises to keep the surface temperature fluctuating up and down within the temperature range of +15°C. When the internal temperature continues to drop until the duty cycle is 0 and the surface temperature continues to drop, turn it into air heating Isothermal furnace or fluidized bed. 4. The method for adjusting the duty ratio of pulse jetting according to claim 1 to control the quenching cooling rate is characterized in that, when the quenched part is less than or equal to 20 mm, the surface of the part is cooled to an isothermal or graded temperature. The core temperature is close to the surface temperature, and it is directly transferred to an air-heated isothermal furnace or a fluidized bed for isothermal treatment. 5. The method for adjusting the duty ratio of pulse jetting according to claim 1 to control the quenching cooling rate is characterized in that, the quenching part is pulse jetted, and the water jet line cut-off valve of the jetting device is connected with the water jet. A high-pressure air valve is installed between the outlets. When the water spray command stops, the high-pressure air valve opens instantly to blow off the remaining water, and the water spray stops immediately to ensure accurate control of the duty cycle. 6. The method according to any one of claims 1-5, wherein the duty ratio of the pulse jet is adjusted to control the quenching cooling rate, wherein the whole jet cooling device is installed in a sealed container, and is passed into the container Nitrogen or a mixture of nitrogen and ammonia decomposition gas is used as a protective gas to reduce surface oxidation or decarburization of parts during quenching and improve quenching quality.

Images