A method of determining the relationship between cooling rate and furnace gas pressure

Abstract

The application discloses a method for determining the relationship between cooling speed and gas pressure in a furnace, and comprises the following steps: S1, selecting a test sample and pre-treating; S2, quenching the test sample; S3, recording initial hardness and initial residual stress, and determining gas pressure test points; S4, tempering under different gas pressures; S5, respectively drawing the relationship curves between cooling speed and hardness and residual stress; and S6, inversely deducing the relationship between gas pressure and cooling speed. The application has the advantages that the research gap of the relationship between gas pressure and cooling speed is filled, and according to the relationship between gas pressure and cooling speed, different gas pressures are introduced into a vacuum furnace to control the cooling speed in the furnace, so that the workpiece cooling speed is controlled, and ideal performance is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of heat treatment process, in particular, relates to a method for determining the relationship between cooling rate and gas pressure in a vacuum heat treatment furnace. BACKGROUND

[0002] In the heat treatment process, including annealing, normalizing, quenching and tempering four basic processes, the heating temperature, holding time and cooling rate and other factors in the heat treatment process affect the performance of the workpiece.

[0003] The prior art mainly measures the furnace wall temperature by installing a thermocouple on the vacuum furnace wall, and obtains the cooling rate near the vacuum furnace wall by the relationship between time and temperature, but it is difficult to obtain the cooling rate at the center of the furnace, which deviates from the actual cooling rate of the workpiece. The interior of the vacuum heat treatment furnace is a sealed space, and during its heating and cooling process, it is in a vacuum state, and its heat transfer mode is mainly thermal radiation; after the medium gas is introduced, the heat transfer mode in the furnace changes, mainly thermal radiation and heat conduction. With the increase of the amount of gas introduced, the gas pressure in the furnace also increases, and the cooling speed in the furnace also increases. Different gas pressures correspond to different cooling rates. Some researchers have found that there is a critical cooling rate that can significantly reduce the temper brittleness phenomenon, but there is currently no research on the relationship between gas pressure and cooling rate, and the prior art is not convenient for controlling the cooling rate to reduce the temper brittleness phenomenon. Therefore, we propose a method for determining the relationship between cooling rate and gas pressure in a vacuum heat treatment process. SUMMARY

[0004] In view of the above prior art, the purpose of the present application is to overcome the shortcomings of the prior art and meet the needs of the present application, so as to provide a method for determining the relationship between cooling rate and gas pressure in a vacuum heat treatment process, so as to solve the problem that there is currently no research on the relationship between gas pressure and cooling rate, and the prior art is not convenient for controlling the cooling rate to reduce the temper brittleness phenomenon.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a method for determining the relationship between cooling rate and gas pressure, comprising the following steps:

[0006] S1, selecting a plurality of test samples, pretreating the test samples to obtain test samples;

[0007] S2, placing the test samples obtained from step S1 in a vacuum furnace for quenching treatment;

[0008] S3, recording the initial hardness and initial residual stress of the quenched test samples, and selecting gas pressure test points;

[0009] S4, pump in the medium gas, and temper the sample to be tested at different gas pressures respectively;

[0010] S5, record the maximum cooling rate of the medium gas, the hardness and the residual stress of the sample to be tested after the tempering treatment, and draw the cooling rate-hardness curve and the cooling rate-residual stress curve;

[0011] S6, according to the cooling rate-hardness curve and the cooling rate-residual stress curve, deduce the relationship between the gas pressure and the cooling rate.

[0012] Further, in S1, the specific steps of selecting and pretreating the test sample are as follows:

[0013] S11, take 30CrMnSiA material, and divide the 30CrMnSiA material into a plurality of rod-shaped test samples;

[0014] S12, calculate the J value of each rod-shaped test sample, and select the rod-shaped test sample meeting the national standard J value as the sample to be tested;

[0015] S13, place the sample to be tested in an ultrasonic cleaner for cleaning and standby.

[0016] Further, in S12, the J value calculation method is as follows: respectively test the weight percentage contents w Si %, w Mn %, w P % and w S % of Si, Mn, P and S of each rod-shaped test sample, and calculate the J value of each rod-shaped test sample, wherein J=(w Si +w Mn )×(w P +w S )×10 4 .

[0017] Further, in S13, the ultrasonic cleaning frequency is as follows: the order of cleaning twice with ethanol, twice with acetone and once with distilled water, and the frequency of each cleaning is 3-8 minutes.

[0018] Further, in S2, the quenching temperature is 900±10℃, and the holding time is 46min.

[0019] Further, in S3, the gas pressure test points include first test points, second test points, third test points, fourth test points, fifth test points and sixth test points, wherein the first test points, the second test points, the third test points and the fourth test points are evenly distributed on the side wall of the sample to be tested, and the fifth test points and the sixth test points are respectively located on the top surface and the bottom surface of the sample to be tested.

[0020] Further, in the S4, the tempering treatment specifically comprises the following steps:

[0021] S41, placing the to-be-tested samples in the same vacuum tempering furnace for heat preservation treatment;

[0022] S42, heating the to-be-tested samples in the tempering furnace to 150-250 DEG C under different maximum gas pressure values of medium gas;

[0023] S43, after the heat preservation treatment, taking out the to-be-tested samples to cool in air to room temperature.

[0024] Further, in the S41, the tempering temperature is 560 DEG C, and the heat preservation time is 65 min;

[0025] Further, in the S42, the medium gas is nitrogen or argon;

[0026] Further, in the S43, the heat preservation treatment is 2-4 h.

[0027] The present application has the following advantages:

[0028] For the problem that there is no research on the relationship between gas pressure and cooling rate at present, and the prior art is inconvenient to control the cooling rate to reduce the tempering brittleness phenomenon, the present application records the initial hardness and initial residual stress of the to-be-tested sample before tempering, performs the tempering treatment under different maximum gas pressure values of medium gas, records the maximum cooling rate of the medium gas, the hardness and residual stress of the to-be-tested sample, and draws the cooling rate-hardness relationship curve and the cooling rate-residual stress relationship curve, and then reversely deduces the relationship between gas pressure and cooling rate, fills the blank of the research on the relationship between gas pressure and cooling rate, and according to the relationship between gas pressure and cooling rate, the gas with different gas pressures is introduced into the vacuum furnace to control the cooling rate in the furnace, which is convenient to control the cooling rate of the workpiece and obtain the ideal performance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 It is a flowchart of the method of the present application;

[0030] Fig. 2 It is a cooling rate-hardness relationship curve diagram of the present application;

[0031] Fig. 3 It is a cooling rate-residual stress relationship curve diagram of the present application. EMBODIMENT

[0032] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used for illustrating and explaining the present application, and are not used for limiting the present application.

[0033] In this application, it is to be understood that the terms "include", "includes" or "comprise", "comprises" or "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product, device, process or method that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such product, device, process or method. Without further limitation, an element defined by the statement "comprise", "include" or "comprising" does not exclude the presence of additional identical elements in the product, device, process or method that includes the stated element. Embodiments

[0034] As shown in Figs. 1 to 3 , the present application provides a method for determining the relationship between cooling rate and gas pressure in the furnace, comprising the following steps:

[0035] S1, selecting a plurality of test samples, pretreating the test samples, and obtaining test samples, the specific steps of selecting and pretreating the test samples are:

[0036] S11, taking 30CrMnSiA material, and dividing the 30CrMnSiA material into a plurality of rod-shaped test samples;

[0037] S12, calculating the J value of each rod-shaped test sample, and selecting a rod-shaped test sample meeting the national standard J value as a test sample, wherein the J value calculation method is specifically: testing the weight percentage content w Si % of Si, Mn, P and S of each rod-shaped test sample respectively Mn % of Si, Mn, P and S of each rod-shaped test sample respectively P % of Si, Mn, P and S of each rod-shaped test sample respectively S % of Si, Mn, P and S of each rod-shaped test sample respectively, and calculating the J value of each rod-shaped test sample, wherein J=(w Si +w Mn )×(w P +w S )×10 4 ;

[0038] S13, placing the test sample in an ultrasonic cleaner, cleaning it according to the order of ethanol cleaning twice, acetone cleaning twice and distilled water cleaning once, and cleaning it for 3-8 minutes each time for standby use;

[0039] S2, placing the test sample obtained from the above step in a vacuum furnace for quenching treatment at a quenching temperature of 900±10℃ for 46min;

[0040] S3, record the initial hardness and initial residual stress of the quenched sample to be tested, and select a gas pressure test point, wherein the gas pressure test point includes a first test point, a second test point, a third test point, a fourth test point, a fifth test point and a sixth test point, wherein the first test point, the second test point, the third test point and the fourth test point are uniformly distributed on the cylindrical side wall of the sample to be tested, and the fifth test point and the sixth test point are respectively located on the top surface and the bottom surface of the sample to be tested;

[0041] S4, pump in the medium gas, and temper the sample to be tested at different gas pressures, and the tempering process comprises the following steps:

[0042] S41, place the sample to be tested in the same vacuum tempering furnace for heat preservation treatment; the tempering temperature is 560 DEG C, and the heat preservation time is 65 min;

[0043] S42, heat the sample to be tested in the tempering furnace to 150 DEG C-250 DEG C under the medium gas with different maximum gas pressure values, and the medium gas is nitrogen or argon;

[0044] S43, after 2-4 h of heat preservation, take out the sample to be tested and cool it to room temperature in air;

[0045] S5, record the maximum cooling rate of the medium gas, the hardness and the residual stress of the sample to be tested after tempering, and draw the cooling rate-hardness curve and the cooling rate-residual stress curve, as shown in the accompanying drawings Fig. 2 and Fig. 3 ;

[0046] S6, according to the cooling rate-hardness curve and the cooling rate-residual stress curve, the gas pressure and the cooling rate are inversely deduced. Embodiment

[0047] As Figs. 1 to 3 shown, the present application provides a method for determining the relationship between cooling rate and furnace gas pressure, comprising the following steps:

[0048] S1, select a plurality of test samples, pretreat the test samples, and obtain the sample to be tested, and the specific steps of selecting and pretreating the test samples are as follows:

[0049] S11, take 30CrMnSiA material, and divide the 30CrMnSiA material into a plurality of rod-shaped test samples;

[0050] S12, calculate the J value of each rod-shaped test sample, and select the rod-shaped test sample with a J value meeting the national standard as the sample to be tested, wherein the J value calculation method is as follows: respectively test the weight percentage content w Si %、w Mn %、wP % and w S %, and calculate the J value of each rod-shaped test sample, wherein J = (w Si +w Mn ) x (w P +w S ) x 10 4 ;

[0051] S13, place the test sample in an ultrasonic cleaner, clean it twice with ethanol, twice with acetone and once with distilled water, each time for 3-8 minutes, and then set it aside;

[0052] S2, place the test sample obtained from the above step in a vacuum furnace and quench it at a quenching temperature of 900±10℃ for 46min;

[0053] S3, record the initial hardness and initial residual stress of the quenched test sample, and select the gas pressure test points, wherein the gas pressure test points include the first test point, the second test point, the third test point, the fourth test point, the fifth test point and the sixth test point, wherein the first test point, the second test point, the third test point and the fourth test point are evenly distributed on the cylindrical side wall of the test sample, and the fifth test point and the sixth test point are respectively located on the top surface and the bottom surface of the test sample;

[0054] S4, pump in the medium gas, and temper the test sample at the same gas pressure, the tempering process specifically includes the following steps:

[0055] S41, place the test sample in the same vacuum tempering furnace for heat preservation; the tempering temperature is 560℃, and the heat preservation time is 65min;

[0056] S42, heat the test sample in the tempering furnace to 150℃, 200℃ and 250℃ respectively under the same gas pressure value of the medium gas;

[0057] S43, after heat preservation at 150℃, 200℃ and 250℃ for 2h, 3h and 4h respectively, take out the test sample and cool it to room temperature in air;

[0058] S5, record the maximum cooling rate of the medium gas, the hardness and the residual stress of the test sample after tempering, and draw the cooling rate-hardness curve and the cooling rate-residual stress curve, as shown in FIG. 1 and FIG. 2; Fig. 2 and Fig. 3As shown, after the sample heated to 150℃ temperature is kept for 2h, 3h and 4h, the hardness values are 309.5HV, 312.2HV, 318.9HV respectively; after the sample heated to 200℃ temperature is kept for 2h, 3h and 4h, the hardness values are 305.3HV, 309.8HV, 315.3HV respectively; after the sample heated to 250℃ temperature is kept for 2h, 3h and 4h, the hardness values are 300.9HV, 307.1HV and 312.6HV respectively;

[0059] S6, according to the cooling rate and hardness relationship curve and the cooling rate and residual stress relationship curve, the gas pressure and cooling rate relationship is deduced, according to the hardness value result, it is shown that in the range of 150℃-250℃, the holding time is 2h-4h, the sample hardness value difference is very small, the difference is not big.

[0060] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0061] In addition, those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means to be within the scope of the present application and forms different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the background section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method of determining the relationship between cooling rate and in-furnace gas pressure, characterized by: It comprises the following steps: S1, selecting a plurality of test samples, pretreating the test samples to obtain test samples to be tested; S2, placing the test samples to be tested obtained from step S1 in a vacuum furnace for quenching treatment; S3, recording the initial hardness and initial residual stress of the test samples to be tested after quenching, and selecting gas pressure test points; S4, pumping medium gas, and performing tempering treatment on the test samples to be tested under different gas pressures; the tempering treatment comprises the following steps: S41, placing the test samples to be tested in the same vacuum tempering furnace for heat preservation treatment; the tempering temperature is 560℃, and the heat preservation time is 65min; S42, heating the test samples to be tested in the tempering furnace to 150℃-250℃ under medium gas with different maximum gas pressure values; S43, after heat preservation treatment for 2-4h, taking out the test samples to be tested and cooling them to room temperature in air; S5, recording the maximum cooling rate of the medium gas, the hardness and the residual stress of the test samples to be tested after tempering treatment, and drawing the cooling rate-hardness relationship curve and the cooling rate-residual stress relationship curve; S6, according to the cooling rate-hardness relationship curve and the cooling rate-residual stress relationship curve, deducing the relationship between the gas pressure and the cooling rate.

2. The method of determining the relationship between cold speed and gas pressure in the furnace according to claim 1, characterized in that: In S1, the specific steps of selecting and pretreating the test samples are as follows: S11, taking 30CrMnSiA material, and dividing the 30CrMnSiA material into a plurality of rod-shaped test samples; S12, calculating the J value of each rod-shaped test sample, and selecting the rod-shaped test sample with a J value meeting the national standard as the test sample to be tested; S13, placing the test sample to be tested in an ultrasonic cleaner for cleaning.

3. The method of determining the relationship between cold speed and gas pressure in the furnace according to claim 2, characterized in that: In S12, the value of J is calculated as follows: the weight percentage of Si, Mn, P and S of each rod-shaped test sample is tested respectively Si %, w Mn %, w P % and w S % are calculated, and the value of J of each rod-shaped test sample is calculated, wherein J = (w Si +w Mn ) × (w P +w S ) × 10 4 .

4. The method of determining the relationship between cold speed and gas pressure in the furnace according to claim 2, characterized in that: In S13, the ultrasonic cleaning frequency is: cleaning twice with ethanol, cleaning twice with acetone, and cleaning once with distilled water, in the order of 3-8 minutes each time.

5. The method of determining the relationship between cold speed and in-furnace gas pressure according to claim 1, characterized by: In S2, the quenching temperature is 900±10℃, and the heat preservation time is 46min.

6. The method of determining the relationship between cold speed and in-furnace gas pressure according to claim 1, characterized by: In S3, the gas pressure test points include a first test point, a second test point, a third test point, a fourth test point, a fifth test point and a sixth test point, wherein the first test point, the second test point, the third test point and the fourth test point are evenly distributed on the side wall of the test sample to be tested, and the fifth test point and the sixth test point are located on the top surface and the bottom surface of the test sample to be tested, respectively.

7. The method of determining the relationship between cold speed and in-furnace gas pressure according to claim 1, characterized by: In S42, the medium gas is nitrogen or argon.

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