Rapid prediction method for core hardness of stepped shaft part after carburizing and quenching heat treatment

Abstract

The invention provides a rapid prediction method for core hardness of a stepped shaft part after carburizing and quenching heat treatment. The rapid prediction method comprises the following steps: step 1, obtaining a hardenability curve; step 2, processing into a step sample; 3, carburizing and quenching treatment; 4, core hardness detection; 5, drawing a diameter-core hardness curve; step 6, data processing; and 7, parameter fitting: according to the relationship between the diameter of the step sample and the end quenching point of the material obtained in the step 6, performing polynomial regression by using a least square method, and determining the relationship between the diameter Dn of the part and the end quenching point Jm, as shown in a formula I: Jm = a + b * Dn + c * Dn2 + d * Dn3. And 8, predicting the core hardness. According to the prediction method, the relationship between different diameters D and material end quenching points after carburizing and quenching of the stepped shaft part can be established only by detecting the hardenability of one material and performing a step carburizing and quenching experiment once, the core hardness of the shaft part after heat treatment can be accurately predicted through the formula, the result is accurate and reliable, the working efficiency is greatly improved, and the method is suitable for popularization and application. The product design and development period is shortened, and the verification cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical transmission, relates to carburizing and quenching, and specifically relates to a method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment. Background Art

[0002] In the field of mechanical transmission, carburizing and quenching are performed on parts to obtain high surface hardness and good core hardness, thereby forming a hard surface and tough inner part, which can effectively improve the wear resistance and load-bearing capacity of the parts. It is a commonly used heat treatment method.

[0003] For shaft parts that have been carburized and quenched, the core hardness is directly related to the bearing capacity of the parts. The higher the core hardness, the higher the strength of the parts. Therefore, the core hardness is one of the most critical technical indicators for such parts. Step shafts are a common transmission part. During the design phase, it is necessary to accurately predict the core hardness of the material selected for shaft parts under the actual heat treatment conditions of the enterprise, so as to determine whether it can meet the design requirements and whether it can be stably controlled within the required range. However, the industry currently lacks accurate and scientific prediction methods, and relies more on the experience of engineering and technical personnel and a large number of heat treatment process experiments, which requires a lot of manpower and time. In addition, it is often verified that the heat treatment experiment fails to meet the design requirements and needs to be redesigned. The design cost is high and the part design and development cycle is long. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment, so as to solve the technical problem that it is difficult to strike a balance between accuracy and efficiency in the prediction methods in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] A method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment, the method is carried out according to the following steps:

[0007] Step 1: Get the hardenability curve:

[0008] Sampling and sample preparation are performed on the rod, the actual hardenability of the rod is detected, and a hardenability curve of the material of the rod is drawn.

[0009] The material used for the rod is the same as that used for the stepped shaft part.

[0010] Step 2: Processing into step specimens:

[0011] A bar of the same material as the bar in step 1 is forged and normalized, and then turned into a step specimen.

[0012] Step 3: Carburizing and quenching treatment:

[0013] The step sample obtained in step 2 is carburized and quenched, and then low-temperature tempered.

[0014] Step 4: Check the hardness of the core:

[0015] The hardness of the sample is tested at the hardness testing position at the center of the step sample after being processed in step three.

[0016] Step 5: Draw the diameter-core hardness curve:

[0017] According to the core hardness test results obtained in step 4, a diameter-core hardness curve is drawn.

[0018] Step 6: Data processing:

[0019] According to the diameter-core hardness curve obtained in step five, the relationship between the diameter of the step specimen and the end quenching point of the material is determined by using the coordinate method or the drawing method.

[0020] Step 7: Parameter fitting:

[0021] According to the relationship between the diameter of the step specimen and the quenching point of the material end obtained in step 6, the least squares method is used for polynomial regression to determine the part diameter D n and end quenching point J m The relationship is shown in Formula I:

[0022] J m =a+b×D n +c×D n 2 +d×D n 3 Formula Ⅰ.

[0023] Where:

[0024] J m Indicates the end quenching point;

[0025] a, b, c and d are regression coefficients;

[0026] D n is the shaft diameter of the part.

[0027] Step 8: Prediction of core hardness:

[0028] After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters n Input formula Ⅰ to determine the end quenching point J corresponding to the shaft diameter m , check the material selected for the stepped shaft part at the end quenching point J m The hardness range at is the shaft diameter of the stepped shaft part D nThe core hardness value range is .

[0029] The present invention also has the following technical features:

[0030] In step 1, samples are taken and prepared from the bar according to GB / T225 to test the actual hardenability of the bar. The number of end-quenching samples should be ≥ 3, and the average value of the 3 samples is taken.

[0031] In step 1, the diameter of the rod is greater than or equal to 20% of the maximum diameter of the stepped shaft part.

[0032] In step 1, the hardenability of the material of the bar cannot be too high or too low, and the hardenability is required to be controlled at: J30 / 49-9, J26 / 43-13, J25 / 41-15, J22 / 39-20, and the hardness drop between two adjacent end quenching points of J1.5 to J11 exceeds 1HRC, and the hardness drop between two adjacent end quenching points of J13 to J20 exceeds 2HRC. It is recommended to use 20MnCr5, 20CrNi3, 22CrMoH or 20CrMnMoH.

[0033] In step 2, the diameter d of the step sample increases step by step in increments of 10 mm, and the length of each step l≥3d.

[0034] In step 2, the minimum diameter of the step sample is less than or equal to the minimum diameter of the step shaft part, and the maximum diameter of the step sample is greater than or equal to the maximum diameter of the step shaft part.

[0035] In step three, the carburizing and quenching conditions of the step specimen should be consistent with the actual carburizing and quenching conditions of the step shaft.

[0036] In step 4, the core hardness test position should correspond to the core hardness position required for the step shaft: if the core hardness test position required for the step shaft is 1 / 2r, then the cross-section at the axial center of each step of the step specimen is taken as the test surface, and four points are taken on the circle with a radial distance of 1 / 2r from the axis of the center shaft to the outer surface in the test surface, and the arc angles of two adjacent points are both 90°; if the core hardness test position required for the step shaft is 3 / 4r, then four points are taken on the circle with a radial distance of 3 / 4r from the axis of the center shaft to the outer surface in the test surface, and the arc angles of two adjacent points are both 90°.

[0037] In step 7, formula I is obtained by polynomial regression using the least squares method, and the part diameter D n The value range is 25mm≤D n ≤110mm.

[0038] Compared with the prior art, the present invention has the following technical effects:

[0039] (I) The prediction method of the present invention only needs to detect the hardenability of one material and conduct a step carburizing and quenching experiment to establish the prediction of different diameters D of stepped shaft parts after carburizing and quenching. n The relationship between the hardness of the core of the shaft parts after heat treatment can be accurately predicted through this formula, which greatly improves work efficiency, shortens the product design and development cycle, and reduces verification costs.

[0040] (II) The prediction method of the present invention does not require the use of physical parts for heat treatment production verification, the number of tests is small, the prediction is scientific and accurate, and the product design and development cycle is greatly improved, and the part design and development cost is reduced.

[0041] (III) The estimation method of the present invention aims at the problem of how to accurately estimate the core hardness of shaft parts that need carburizing and quenching treatment in the design stage of automobile transmission systems, and whether it can meet the design requirements. The present invention provides a method for predicting the core hardness of shaft parts that require carburizing and quenching heat treatment. Through a simple and effective step specimen heat treatment test, combined with the hardenability of the test material, the relationship between the shaft diameter and the material end quenching point is established, and then the core hardness of the shaft parts can be quickly and accurately estimated through the hardenability of the material. The difference between the actual value and the estimated value is within ±1.5HRC. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the hardenability curve of the material in the embodiment.

[0043] Figure 2 This is a schematic diagram of the curve for material hardenability being too high (the curve is straight, and the hardness drop between adjacent points J1.5mm-J11mm is less than 1HRC).

[0044] Figure 3 This is a schematic diagram of the curve for material hardenability being too low (hardness at J20 is lower than 22HRC).

[0045] Figure 4 Schematic diagram of the step sample in the embodiment.

[0046] Figure 5 Schematic diagram of the hardness detection position in the embodiment.

[0047] Figure 6 Schematic diagram of the diameter-core hardness curve in the embodiment.

[0048] Figure 7 It is a schematic diagram of the corresponding relationship between the end quenching point and the step sample diameter in the embodiment.

[0049] Figure 8 is the end quenching point J in the embodiment m With the shaft diameter D n Fitted line plot of .

[0050] Fig. 9 It is a structural schematic diagram of the transmission stepped shaft parts.

[0051] Fig.10 Schematic diagram of the step sample in Application Example 1.

[0052] Fig.11 is the end quenching point J in Application Example 1 m With the shaft diameter D n Fitted line plot of .

[0053] Fig.12 Schematic diagram of the step sample in Application Example 2.

[0054] Fig.13 is the end quenching point J in Application Example 2 m With the shaft diameter D n Fitted line plot of .

[0055] The specific contents of the present invention are further explained in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0056] It should be noted that, unless otherwise specified, all equipment and raw materials in the present invention are equipment and raw materials known in the prior art.

[0057] The general inventive concept of the present invention is: the higher the core hardness, the higher the part strength. The core hardness is directly related to the bearing capacity of the part and is the most critical technical indicator of carburized and quenched shaft parts. However, in the new part design stage, due to the changes in part size and steel type, how to accurately predict whether the core hardness can meet the design requirements is still a difficult problem: when the diameter or material of the newly designed parts changes, especially the shaft parts are often stepped shafts, the shaft diameters on each step are different, and the core hardness is also different. At this time, how is the core hardness of the shaft on each step, whether it can meet the design requirements, there is currently no scientific evaluation method in engineering, and heat treatment engineers need to rely on experience to make estimates, and then conduct a large number of heat treatment experiments to verify. On the one hand, the accuracy of the estimation of this method is poor, and human experience plays a decisive role. In addition, for the reliability of the results, multiple experiments are often required, and the amount of engineering required for experimental verification is also very large, the verification cost is high, and the part design and development cycle is long. Therefore, the present invention provides a scientific method for predicting the core hardness of stepped shaft parts after carburizing and quenching, designs a step sample, and detects the core hardness of each step of the step sample after quenching under actual heat treatment process conditions and the hardenability of the corresponding material. A mathematical relationship model between the core hardness of different shaft diameters and the material end quenching value of the stepped shaft parts after carburizing and quenching under actual heat treatment conditions of the enterprise is established, and the accurate prediction of the core hardness of different shaft diameters of the stepped shaft is achieved. This method does not require physical parts for heat treatment production verification, the number of tests is small, the prediction is scientific and accurate, and the product design and development cycle is greatly improved, and the part design and development cost is reduced.

[0058] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0059] Example:

[0060] This embodiment provides a method for quickly predicting the hardness of the core of a stepped shaft part after carburizing and quenching heat treatment. The method is performed according to the following steps:

[0061] Step 1: Get the hardenability curve:

[0062] According to GB / T225, samples are taken and prepared from the bars, the actual hardenability of the bars is tested, and the hardenability curve of the bars is drawn. Figure 1 shown.

[0063] The material used for the bars is the same as that used for the stepped shaft parts.

[0064] Preferably, the diameter of the rod is greater than or equal to 20% of the maximum diameter of the stepped shaft part.

[0065] Preferably, the hardenability of the bar should not be too high or too low. Figure 2 and Figure 3 As shown, the hardenability of the bar is controlled at: J30 / 49-9, J26 / 43-13, J25 / 41-15, J22 / 39-20, and the hardness drop between two adjacent end quenching points of J1.5 to J11 exceeds 1HRC, and the hardness drop between two adjacent end quenching points of J13 to J20 exceeds 2HRC. The recommended material of the bar is 20MnCr5, 20CrNi3, 22CrMoH or 20CrMnMoH.

[0066] In this embodiment, the normalizing temperature and quenching temperature of the end quenching test are performed according to the temperature required by the material in the standard. To ensure the accuracy of the results, ≥3 end quenching samples should be taken, generally 3-4 samples can be taken, and the final result is the average of the hardness test results of the corresponding end quenching points of all samples.

[0067] In this embodiment, the end quenching point should detect the hardness values ​​of 1.5mm, 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, and 35mm from the quenching end face. When the hardness is lower than 20HRC, the hardness of the points after the end quenching point will not be detected. m The X axis is the end quenching value Y jm The Y-axis is used to draw the hardenability curve of the material.

[0068] Step 2: Processing into step specimens:

[0069] A bar of the same material as the bar in step 1 is forged and normalized, and then turned into a step specimen.

[0070] Preferably, Figure 4 As shown, the diameter d of the step specimen increases in steps of 10 mm, such as 30 mm, 40 mm, and 50 mm. The length of each step is l ≥ 3d; generally, l = 3d is sufficient.

[0071] Preferably, the minimum diameter of the step sample is less than or equal to the minimum diameter of the step shaft part, and the maximum diameter of the step sample is greater than or equal to the maximum diameter of the step shaft part.

[0072] In this embodiment, the total length L of the step sample does not exceed the processing capacity of the heat treatment equipment.

[0073] Step 3: Carburizing and quenching treatment:

[0074] The step sample obtained in step 2 is subjected to carburizing and quenching treatment, and low-temperature tempering is performed at a temperature of 160°C to 200°C.

[0075] In this embodiment, during the carburizing and quenching treatment, the step sample is placed vertically, and the quenching temperature, the type of quenching oil, and the stirring speed of the quenching tank agitator should be the same as or close to the actual quenching conditions of such parts.

[0076] In this embodiment, in order to ensure the validity of the simulation data, the carburizing and quenching test of the step sample should be kept consistent with the actual heat treatment conditions of the part as much as possible. Therefore, the heat treatment equipment selected for the carburizing and quenching test of the step sample should be the same as the equipment used for the actual heat treatment of the part. The carburizing process has little effect on the results, so the carburizing process can be set freely, but the quenching medium and the stirring speed of the oil tank should be consistent with the actual quenching conditions of the part. In order to ensure the consistency of the hardness of the step sample in the circumferential direction, the step sample should be placed vertically during carburizing and quenching.

[0077] In this embodiment, the step sample is cooled to room temperature after carburizing and quenching, and should be promptly subjected to low-temperature tempering within 2 hours, with the tempering temperature being 160-200°C. After being kept at this temperature for 2 hours, it should be taken out of the furnace and air-cooled to room temperature.

[0078] Step 4: Check the hardness of the core:

[0079] The hardness of the sample is tested at the hardness testing position at the center of the step sample after being processed in step three.

[0080] Preferably, Figure 5 As shown, the core hardness test position is: take the cross section at the axial center of each step of the step specimen as the test surface, take four points on the circle at a distance of 1 / 2r from the center axis to the outer surface along the radial direction within the test surface, and the arc angles of two adjacent points are both 90°; take four points on the circle at a distance of 3 / 4r from the center axis to the outer surface along the radial direction within the test surface, and the arc angles of two adjacent points are both 90°.

[0081] Step 5: Draw the diameter-core hardness curve:

[0082] According to the core hardness test results obtained in step 4, the part diameter D of the step specimen is n is the X-axis, and the hardness Y of the core of the step specimen dn As the Y axis, draw the diameter-core hardness curve, such as Figure 6 shown.

[0083] Step 6: Data processing:

[0084] According to the diameter-core hardness curve obtained in step 5, the relationship between the diameter of the step specimen and the end quenching point of the material is determined by using the coordinate method or the drawing method;

[0085] The specific process of the coordinate method is:

[0086] On the diameter-core hardness curve ( Figure 6), the diameter of the part and its core hardness are recorded as D n , Y dn , the coordinates are marked as (D n , Y dn ), on the material hardenability curve ( Figure 1 ), the end quenching point and its corresponding end quenching value are respectively recorded as J m , Y jm , the coordinates are marked as (J m , Y jm ).

[0087] Assume the diameter is D n The hardness of the axis is Y dn , let Y dn =Y jm , Y jm The coordinate on the material hardenability curve is (J m , Y jm ), then the end quenching point J m With the part diameter D n Corresponding. m The end quenching value at the diameter is D n The core hardness of the shaft.

[0088] The specific process of the mapping method is:

[0089] The material hardenability curve and the diameter-core hardness curve are plotted in one graph to determine the corresponding relationship between the core hardness of step specimens with different diameters and the end quenching point of the material hardenability under the process conditions, such as Figure 7 As shown (the hardness curve at the core hardness of 3 / 4r). n Draw a perpendicular line to the X-axis, intersecting the diameter-core hardness curve at point (D n , Y dn ), draw a line parallel to the X axis through this point, and intersect the hardenability curve of the material at point (J m , Y jm ), then the diameter is D n The hardness of the core of the shaft parts is equal to the material J m The hardness at the end quenching point. Figure 7 Middle, diameter D n =50mm shaft, under the heat treatment process conditions, the core hardness (3 / 4r) corresponds to the end quenching value of material J25.

[0090] Step 7: Parameter fitting:

[0091] According to the relationship between the diameter of the step specimen and the quenching point of the material end obtained in step 6, the least squares method is used for polynomial regression, such as Figure 8 As shown, determine the part diameter D n and end quenching point J mThe relationship is as shown in the formula:

[0092] J m =a+b×D n +c×D n 2 +d×D n 3 Formula Ⅰ.

[0093] Where:

[0094] J m Indicates the end quenching point;

[0095] a, b, c, d are all regression coefficients; the values ​​of a, b, c, d are related to the cooling rate during quenching;

[0096] D n D is the shaft diameter of the part n The value range is 25mm≤D n ≤110mm.

[0097] Step 8: Prediction of core hardness:

[0098] After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters n Input formula Ⅰ to determine the end quenching point J corresponding to the shaft diameter m , check the material selected for the stepped shaft part at the end quenching point J m The hardness range at is the shaft diameter of the stepped shaft part D n The core hardness value range is .

[0099] Application Example 1:

[0100] This application example provides a method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment based on the above embodiment. Fig. 9 As shown, the stepped shaft part is a transmission stepped shaft made of 18CrNiMo7-6 material. The core hardness of the part at shaft diameters of 60mm, 63mm, 67mm, and 87.16mm after carburizing and quenching is predicted (the core hardness is the hardness at 1 / 2 of the radius).

[0101] The method proceeds as follows:

[0102] Step 1: Get the hardenability curve:

[0103] The material with slightly higher hardenability in stock with a diameter greater than 90mm is 20CrNi3H material. Select 20CrNi3H bar with a diameter of 120mm. According to the requirements of GB / T225, three end-quenching specimens are made from 20CrNi3 material bar with a diameter of 120mm, normalized at 860℃±10℃, and end-quenched at 830℃±5℃. The hardenability of the material is tested, and the average value of the three specimens is taken to draw the hardenability curve.

[0104] Step 2: Processing into step specimens:

[0105] A bar of the same material as the bar in step 1 is forged and normalized, and then turned into a step specimen.

[0106] In this application example, considering that the minimum diameter of existing shaft parts is 45mm and the maximum diameter in the future is expected to not exceed 90mm, the test steel is forged, normalized, and processed into step specimens with diameters of 40mm, 50mm, 60mm, 70mm, 80mm, and 90mm.

[0107] The test steel is heated to 1150℃±20℃, forged into a step specimen blank by free forging, isothermally normalized, and rough turned to Fig.10 Dimensions shown:

[0108] Step 3: Carburizing and quenching treatment:

[0109] The step sample obtained in step 2 is carburized and quenched in a box-type multi-purpose furnace. The quenching liquid is Houghton G oil. The stirring speed is 850 / 750r / min. After quenching, it is cooled to room temperature and low-temperature tempered at 185°C for 2h.

[0110] Step 4: Check the hardness of the core:

[0111] The hardness of the sample is tested at the hardness testing position at the center of the step sample after being processed in step three.

[0112] In this application example, the hardness of the step specimen at the cross section 1 / 2r at the center of each step length direction is tested. Four points are tested, with two adjacent points at 90°, and the average of the test results is taken.

[0113] Step 5: Draw the diameter-core hardness curve:

[0114] According to the core hardness test results obtained in step 4, the part diameter D of the step specimen is n is the X-axis, and the hardness Y of the core of the step specimen dn The diameter-core hardness curve is drawn on the Y-axis.

[0115] Step 6: Data processing:

[0116] According to the diameter-core hardness curve obtained in step five, the coordinate method is used to determine the relationship between the diameter of the step specimen and the quenching point of the material end, as shown in Figure 1.

[0117] Table 1 Relationship between the diameter of the step specimen and the end quenching point of the material in Application Example 1

[0118] Diameter D / mm 40 50 60 70 80 90 End quenching point J / mm 13 19 22 24 25 30

[0119] Step 7: Parameter fitting:

[0120] According to the relationship between the diameter of the step specimen and the quenching point of the material end obtained in step 6, the least squares method is used for polynomial regression, such as Fig.11 As shown, determine the part diameter D n and end quenching point J m The relationship is shown in Formula II:

[0121] J m =-84.83+4.546D n -0.06552D n 2 +0.000324D n 3 Formula II.

[0122] Step 8: Prediction of core hardness:

[0123] After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters n Input formula II to determine the end quenching point J corresponding to the shaft diameter. m , as shown in Table 2.

[0124] Check the material 18CrNiMo7-6 selected for the stepped shaft part at the end quenching point J m The hardness range at is the shaft diameter of the stepped shaft part D n The range of core hardness values ​​at is shown in Table 3.

[0125] Table 2 shows the corresponding end quenching points at different shaft diameters of the stepped shaft in Application Example 1.

[0126] DiameterDn / mm 60 63 67 87.16 <![CDATA[End-quenching point J m / mm]]> 21 22 23 29

[0127] Table 3 Estimated results of the core hardness at different shaft diameters in Application Example 1

[0128] DiameterDn / mm 60 63 67 87.16 Core hardness / HRC 36-44 35.5-43.5 35.5-43.5 35-42

[0129] Application Example 2:

[0130] This application example provides a method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment based on the above-mentioned embodiment. The purpose of this application example is to estimate whether a stepped shaft can meet the design requirements after changing the material. In this application example, the material currently used for the transmission shaft is 17NiCrMo6-4. In order to reduce costs, 20CrMnMo material is planned to be used. The core hardness (radius 3 / 4r) at the shaft diameter of 76mm and 63mm is required to meet 32-42HRC and 35-45HRC respectively. Please determine whether it can meet the design requirements.

[0131] The method proceeds as follows:

[0132] Step 1: Get the hardenability curve:

[0133] The material with slightly higher hardenability than 80mm in stock is 17NiCrMo6-4. Select 17NiCrMo6-4 bar with a diameter of 110mm. According to the requirements of GB / T225, three end-quenching specimens are made from 17NiCrMo6-4 bar with a diameter of 110mm. Normalizing treatment is carried out at 910℃±10℃, and end-quenching test is carried out at 880℃±5℃. The hardenability of the material is tested, and the average value of the three specimens is taken to draw the hardenability curve.

[0134] Step 2: Processing into step specimens:

[0135] A bar of the same material as the bar in step 1 is forged and normalized, and then turned into a step specimen.

[0136] In this application example, considering that the minimum diameter of existing shaft parts is 30mm and the maximum diameter does not exceed 90mm, the test steel is forged, normalized, and processed into step specimens with diameters of 30, 40mm, 50mm, 60mm, 70mm, 80mm, and 90mm.

[0137] The test steel is heated to 1150℃±20℃, forged into a step specimen blank by free forging, isothermally normalized, and rough turned to Fig.12 Dimensions shown.

[0138] Step 3: Carburizing and quenching treatment:

[0139] The step sample obtained in step 2 is carburized and quenched in a box-type multi-purpose furnace. The quenching liquid is Houghton 355 oil. The stirring speed is 600 / 500r / min. The sample is placed vertically on the material tray during material preparation. After quenching, it is cooled to room temperature and low-temperature tempering is performed at 180°C for 2h.

[0140] Step 4: Check the hardness of the core:

[0141] The hardness of the sample is tested at the hardness testing position at the center of the step sample after being processed in step three.

[0142] In this application example, the hardness of the step specimen at the 3 / 4r section at the center of the length direction of each step is tested. Four points are tested, with two adjacent points at 90°, and the average of the test results is taken.

[0143] Step 5: Draw the diameter-core hardness curve:

[0144] According to the core hardness test results obtained in step 4, the part diameter D of the step specimen is n is the X-axis, and the hardness Y of the core of the step specimen dn The diameter-core hardness curve is drawn on the Y-axis.

[0145] Step 6: Data processing:

[0146] According to the diameter-core hardness curve obtained in step 5, the coordinate method is used to determine the relationship between the diameter of the step specimen and the quenching point of the material end: as shown in Table 4.

[0147] Table 4 Relationship between the diameter of the step specimen and the end quenching point of the material in Application Example 2

[0148] <![CDATA[Diameter D n / mm]]> 30 40 50 60 70 80 90 <![CDATA[End quenching point J m / mm]]> 8 11 17 18 21 33 40

[0149] Step 7: Parameter fitting:

[0150] According to the relationship between the diameter of the step specimen and the quenching point of the material end obtained in step 6, the least squares method is used for polynomial regression, such as Fig.13 As shown, determine the part diameter D n and end quenching point J m The relationship is shown in Formula II:

[0151] J m =-18.14+1.426D n -0.02357D n 2 +0.000167D n 3 Formula III.

[0152] Step 8: Prediction of core hardness:

[0153] After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters n Input formula III to determine the end quenching point J corresponding to the shaft diameter m , as shown in Table 5.

[0154] Check the material 20CrMnMo selected for the stepped shaft part at the end quenching point J m The hardness range at is the shaft diameter of the stepped shaft part D n The range of core hardness values ​​at is shown in Table 6.

[0155] Table 5 shows the corresponding end quenching points at different shaft diameters of the stepped shaft in Application Example 2.

[0156] <![CDATA[Diameter D n / mm]]> 63 76 <![CDATA[End-quenching point J m / mm]]> 20 27

[0157] Table 6 Estimated results of the core hardness at different shaft diameters in Application Example 2

[0158] Diameter D / mm 63 76 Core hardness / HRC 32-40 30-38.5 Design requirements / HRC 35-45 32-42

[0159] It can be seen from Table 6 above that after changing to 20CrMnMo material, there is a certain probability that the core hardness will be lower than the lower limit requirement of the drawing. It is necessary to limit the hardenability of the material and strengthen the quenching cooling conditions.

Claims

1. A method for quickly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment, characterized in that: The method proceeds as follows: Step 1: Get the hardenability curve: Sampling and preparing samples on the rod, detecting the actual hardenability of the rod, and drawing a hardenability curve of the material of the rod; The material used for the rod is the same as the material used for the stepped shaft part; Step 2: Processing into step specimens: Forging and normalizing a bar of the same material as the bar in step 1, and turning it into a step specimen; Step 3: Carburizing and quenching treatment: Carburizing and quenching the step sample obtained in step 2, and then performing low temperature tempering; Step 4: Check the hardness of the core: Testing the hardness of the sample at the hardness testing position of the core of the step sample after being processed in step 3; Step 5: Draw the diameter-core hardness curve: According to the core hardness test result obtained in step 4, a diameter-core hardness curve is drawn; Step 6: Data processing: According to the diameter-core hardness curve obtained in step 5, the relationship between the diameter of the step specimen and the end quenching point of the material is determined by using the coordinate method or the drawing method; Step 7: Parameter fitting: According to the relationship between the diameter of the step specimen and the quenching point of the material end obtained in step 6, the least squares method is used for polynomial regression to determine the part diameter D n and end quenching point J m The relationship is shown in Formula I: J m =a+b×D n +c×D n 2 +d×D n 3 Formula I; Where: J m Indicates the end quenching point; a, b, c and d are regression coefficients; D n is the shaft diameter of the part; Step 8: Prediction of core hardness: After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters n Input formula Ⅰ to determine the end quenching point J corresponding to the shaft diameter m , check the material selected for the stepped shaft part at the end quenching point J m The hardness range at is the shaft diameter of the stepped shaft part D n The core hardness value range is .

2. The rapid prediction method for the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1 is characterized in that: In step 1, samples are taken and prepared from the bar according to GB / T225 to test the actual hardenability of the bar; the number of end quenching samples should be ≥ 3, and the average value of the 3 samples is taken.

3. The rapid prediction method for the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1 is characterized in that: In step 1, the hardenability of the material of the rod is controlled at: J30 / 49-9, J26 / 43-13, J25 / 41-15, J22 / 39-20, and the hardness drop between two adjacent end quenching points of J1.5 to J11 exceeds 1HRC, and the hardness drop between two adjacent end quenching points of J13 to J20 exceeds 2HRC.

4. The rapid prediction method for the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1 is characterized in that: In step 1, the diameter of the rod is greater than or equal to 20% of the maximum diameter of the stepped shaft part.

5. The rapid prediction method for the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1 is characterized in that: In step 2, the diameter d of the step sample increases step by step in increments of 10 mm, and the length of each step l≥3d.

6. The method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1, characterized in that: In step 2, the minimum diameter of the step sample is smaller than the minimum diameter of the step shaft part, and the maximum diameter of the step sample is larger than the maximum diameter of the step shaft part.

7. The method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1, characterized in that: In step three, the carburizing and quenching conditions of the step specimen should be consistent with the actual carburizing and quenching conditions of the step shaft.

8. The method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1, characterized in that: In step 4, the core hardness test position should correspond to the core hardness position required for the step shaft: if the core hardness test position required for the step shaft is 1 / 2r, then the cross-section at the axial center of each step of the step specimen is taken as the test surface, and four points are taken on the circle with a radial distance of 1 / 2r from the axis of the center shaft to the outer surface in the test surface, and the arc angles of two adjacent points are both 90°; if the core hardness test position required for the step shaft is 3 / 4r, then four points are taken on the circle with a radial distance of 3 / 4r from the axis of the center shaft to the outer surface in the test surface, and the arc angles of two adjacent points are both 90°.

9. The method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment according to claim 1, characterized in that: In step 7, formula I is obtained by polynomial regression using the least squares method, and the part diameter D n The value range is 25mm≤D n ≤110mm.

Images