Method for rapidly predicting core hardness of stepped shaft parts after carburizing and quenching heat treatment

Abstract

The application provides a kind of stepped shaft part carburizing quenching heat treatment after the quick prediction method of heart hardness, comprising: step one, obtain hardenability curve;Step two, process into step sample;Step three, carburizing quenching treatment;Step four, detect heart hardness;Step five, draw diameter-heart hardness curve;Step six, data processing;Step seven, parameter fitting: according to the relationship between the diameter of step sample and material end quenching point obtained in step six, the least square method is used for polynomial regression, to determine the relationship between the diameter D n and the end quenching point J m , as shown in formula I: J m =a+b×D n +c×D n 2 +d×D n 3 Step eight, heart hardness prediction. The prediction method of the application only needs to detect the hardenability of one kind of material, and perform a step carburizing quenching experiment, to establish the relationship between different diameters D and material end quenching point of stepped shaft type parts after carburizing quenching, through the formula, the heart hardness of shaft type parts after heat treatment can be accurately predicted, the result is accurate and reliable, greatly improves the work efficiency, shortens the product design and development cycle, and reduces the verification cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of mechanical transmission technology, and relates to carburizing and quenching, in particular to a method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment. BACKGROUND

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

[0003] For a shaft part subjected to carburizing and quenching treatment, the core hardness is directly related to the load capacity of the part, and the higher the core hardness, the higher the strength of the part, so the core hardness is one of the most critical technical indexes of such a part. The stepped shaft is a common transmission part, and in the design stage, the core hardness of the selected material of the shaft part under the actual heat treatment condition of the enterprise needs to be accurately predicted, so as to determine whether the design requirements can be met and whether the core hardness can be stably controlled within the required range. However, at present, there is still a lack of accurate and scientific prediction means in the industry, and more reliance is placed on the experience of engineering and technical personnel and a large number of heat treatment process experiments, which requires a large amount of manpower and time, and often results in the need for re-design due to the failure of heat treatment experiment verification to meet the design requirements, resulting in high design cost and long part design and development cycle. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for rapidly predicting the core hardness of a stepped shaft part after carburizing and quenching heat treatment, which solves the technical problem that the accuracy and efficiency of the prediction method in the prior art are difficult to balance.

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

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

[0007] Step 1: Obtain the hardenability curve:

[0008] Sample and sample on the bar, detect the actual hardenability of the bar, and draw the hardenability curve of the material of the bar.

[0009] The material used in the bar is the same as the material used in the stepped shaft part.

[0010] Step 2: Process into a stepped sample:

[0011] The bar of the same material as the bar in step 1 is forged and normalized, and is turned into a stepped sample.

[0012] Step 3, carburizing and quenching treatment:

[0013] The stepped sample obtained in step two was subjected to carburizing and quenching treatment, and then subjected to low-temperature tempering.

[0014] Step 4, test heart hardness:

[0015] The hardness of the specimen is tested at the core hardness testing location of the stepped specimen after step three.

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

[0017] Based on the core hardness test results obtained in step four, a diameter-core hardness curve is plotted.

[0018] Step Six, Data Processing:

[0019] Based on the diameter-core hardness curve obtained in step five, the relationship between the diameter of the stepped specimen and the quenching point at the material end is determined using a coordinate method or a graphical method.

[0020] Step 7, Parameter Fitting:

[0021] Based on the relationship between the diameter of the stepped specimen and the quenching point of the material obtained in step six, polynomial regression using the least squares method is used to determine the diameter D of the part. n With end quenching point J m The relationship is shown in Equation I:

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

[0023] In the formula:

[0024] J m Indicates the end-quench point;

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

[0026] D n This refers to the shaft diameter of the part.

[0027] Step 8, Heart Hardness Prediction:

[0028] After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters is... n Input formula I to determine the end quenching point J corresponding to the shaft diameter. m Check the material selected for this stepped shaft part at the end quenching point J. m The hardness range at that point corresponds to the diameter D of the stepped shaft part. nThe heart hardness value range of the step 4.

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

[0030] In the step one, the actual hardenability of the bar is detected according to GB / T225. The end-quench test sample should be ≥3, and the average value of the three test samples is taken.

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

[0032] In the step one, the hardenability of the material of the bar cannot be too high or too low, and the hardenability is required to be controlled in J30 / 49-9, J26 / 43-13, J25 / 41-15, J22 / 39-20, and the hardness drop between adjacent two end-quench points J1.5-J11 is more than 1HRC, and the hardness drop between adjacent two end-quench points J13-J20 is more than 2HRC. It is suggested that 20MnCr5, 20CrNi3, 22CrMoH or 20CrMnMoH can be used.

[0033] In the step two, the diameter d of the step test sample is increased by 10mm as a change amount, and each step length l is ≥3d.

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

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

[0036] In the step four, the heart hardness detection position should correspond to the required heart hardness position of the stepped shaft: if the required heart hardness detection position of the stepped shaft is 1 / 2r, then the cross section of the axial center of each step of the step test sample is taken as the detection surface, four points are taken on the circle with a distance of 1 / 2r from the center axis to the outer surface in the detection surface along the radial direction, and the included angle of the adjacent two points is 90°; if the required heart hardness detection position of the stepped shaft is 3 / 4r, then four points are taken on the circle with a distance of and 3 / 4r from the center axis to the outer surface in the detection surface along the radial direction, and the included angle of the adjacent two points is 90°.

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

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

[0039] (I) The prediction method of the present application only needs to detect the hardenability of a material, and a step carburizing and quenching experiment is performed to establish the relationship between the diameter D of the stepped shaft part and the end quenching point of the material after carburizing and quenching of the stepped shaft part, so that the core hardness of the shaft part after heat treatment can be accurately predicted. n The relationship with the end quenching point of the material, through the formula, the core hardness of the shaft part after heat treatment can be accurately predicted, the result is accurate and reliable, greatly improves the work efficiency, shortens the product design and development cycle, and reduces the verification cost.

[0040] (II) The prediction method of the present application does not need to use physical parts for heat treatment production verification, the test quantity 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 prediction method of the present application aims at how to accurately predict the core hardness of the shaft part in the design stage of the shaft part which needs to be carburized and quenched in the automobile transmission system, and whether it can meet the design requirements. The present application provides a core hardness prediction method for carburizing and quenching heat treatment of shaft parts, which establishes the relationship between the diameter of the shaft and the end quenching point of the material through a simple and effective heat treatment test of the step sample combined with the hardenability of the test material, and then the core hardness of the shaft part can be quickly and accurately predicted through the hardenability of the material. The difference between the actual value and the predicted value is within ±1.5HRC. BRIEF DESCRIPTION OF DRAWINGS

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

[0043] Figure 2 It is a schematic diagram of the hardenability curve of the material which is too high (the curve is flat, and the hardness difference between adjacent points J1.5mm-J11mm is less than 1HRC).

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

[0045] Figure 4 It is a schematic diagram of the step sample in the embodiment.

[0046] Figure 5 It is a schematic diagram of the hardness detection position in the embodiment.

[0047] Figure 6 It is a schematic diagram of the diameter-core hardness curve in the embodiment.

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

[0049] Figure 8 It is a fitting line diagram of the end quenching point J m and the diameter D n of the part shaft.

[0050] Figure 9 Fig. 1 is a schematic view of a stepped shaft part of a transmission.

[0051] Figure 10 Fig. 2 is a schematic view of a stepped sample in Example 1.

[0052] Figure 11 Fig. 3 is a graph of the fitting line of the Jominy end quench point J m and the part shaft diameter D n .

[0053] Figure 12 Fig. 4 is a schematic view of a stepped sample in Example 2.

[0054] Figure 13 Fig. 5 is a graph of the fitting line of the Jominy end quench point J m and the part shaft diameter D n .

[0055] The specific content of the present application is further explained in detail below in connection with the examples. DETAILED DESCRIPTION

[0056] It should be noted that all the equipment and raw materials in the present application, if not specifically stated, all use the equipment and raw materials known in the prior art.

[0057] The general inventive concept of the present application is that the higher the core hardness, the higher the strength of the part, and the core hardness is directly related to the load capacity of the part and is the most critical technical index of the carburized and quenched shaft part, but during the design stage of the new part, how to accurately predict whether the core hardness can meet the design requirements is still a difficult problem due to the change of the part size and the steel grade: when the diameter or the material of the new design part changes, especially the shaft part is often a stepped shaft, the shaft diameters on each step are different, and the core hardnesses of the shafts on each step are also different, at this time, how are the core hardnesses of the shafts on each step, and can they meet the design requirements? At present, there is no scientific evaluation method in engineering, and the heat treatment engineers need to rely on experience for prediction, and then a large number of heat treatment experiments are needed for verification. On the one hand, the accuracy of the prediction is poor, and the experience of the person plays a decisive role, and on the other hand, in order to ensure the reliability of the results, a plurality of experiments are often needed, and the engineering quantity required for the experimental verification is also very large, the verification cost is relatively high, and the part design and development cycle is long. Therefore, the present application provides a scientific method for predicting the core hardness of the carburized and quenched stepped shaft part, a stepped sample is designed, the core hardnesses of the stepped sample on each step after quenching under the actual heat treatment process condition and the hardenability of the corresponding material are detected, a mathematical relationship model of the core hardnesses of the stepped shaft part at different shaft diameters after carburizing and quenching and the material end quenching value under the actual heat treatment condition of the enterprise is established, and the accurate prediction of the core hardnesses of the stepped shaft at different shaft diameter positions is realized. The method does not need to use the physical part for heat treatment production verification, the test quantity is small, the prediction is scientific and accurate, the product design and development cycle is greatly improved, and the part design and development cost is reduced.

[0058] The specific embodiments of the present application are given below, and it should be noted that the present application is not limited to the following specific embodiments, and any equivalent transformation made on the basis of the technical solutions of the present application falls within the protection scope of the present application.

[0059] Embodiment:

[0060] The present embodiment gives a fast prediction method for the core hardness of the carburized and quenched stepped shaft part, and the method is performed according to the following steps:

[0061] Step one, obtain the hardenability curve:

[0062] According to GB / T225, the sample is taken and prepared on the bar, the actual hardenability of the bar is detected, and the hardenability curve of the material of the bar is drawn. As shown in Figure 1 .

[0063] The material of the bar is the same as that of the stepped shaft part.

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

[0065] Preferably, the hardenability of the bar cannot be too high or too low, such asFigure 2 and Figure 3 As shown in Fig. 1, the hardenability of the bar is controlled as follows: J30 / 49-9, J26 / 43-13, J25 / 41-15, J22 / 39-20, and the hardness drop between the two adjacent end-quench points J1.5~J11 is more than 1HRC, and the hardness drop between the two adjacent end-quench points J13~J20 is more than 2HRC. It is suggested that the material of the bar is 20MnCr5, 20CrNi3, 22CrMoH or 20CrMnMoH.

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

[0067] In this embodiment, the hardness values at 1.5mm, 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 20mm, 25mm, 30mm, 35mm from the quenching end face should be detected, and when the hardness is lower than 20HRC, the hardness of the points after the end-quench point is not detected. Taking the end-quench point J m as the X axis, and the end-quench value Y jm as the Y axis, the hardenability curve of the material is drawn.

[0068] Step two, processing into a stepped sample:

[0069] The bar of the same material as the bar in step one is forged and normalized, and is processed into a stepped sample by turning.

[0070] Preferably, as shown in Fig. 2, the diameter d of the stepped sample is increased by 10mm as a change amount in stages in turn, such as 30mm, 40mm, 50mm. The length l of each step is ≥3d; generally l=3d can be selected. Figure 4 Preferably, the minimum diameter of the stepped sample is less than or equal to the minimum diameter of the stepped shaft part, and the maximum diameter of the stepped sample is greater than or equal to the maximum diameter of the stepped shaft part.

[0071] In this embodiment, the total length L of the stepped sample does not exceed the processing capacity of the heat treatment equipment.

[0072] Step three, carburizing and quenching treatment:

[0073] The stepped sample obtained in step two is subjected to carburizing and quenching treatment, and is subjected to low-temperature tempering at a temperature of 160℃~200℃.

[0074]

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

[0076] In this embodiment, in order to ensure the effectiveness of the simulation data, the carburizing quenching test of the step sample should be consistent with the actual heat treatment conditions of the part as much as possible. Therefore, the heat treatment equipment selected for the carburizing 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 result, so the carburizing process can be freely set, 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 in the circumferential direction of the step sample, the step sample should be vertically placed during the carburizing quenching.

[0077] In this embodiment, after the carburizing quenching of the step sample, the step sample is cooled to room temperature, and low-temperature tempering should be performed in time within 2h, the tempering temperature is 160-200℃, and the step sample is taken out of the furnace after 2h of heat preservation and air-cooled to room temperature.

[0078] Step four, detecting the core hardness:

[0079] The hardness of the step sample is detected at the core hardness detection position of the step sample after the treatment in step three.

[0080] Preferably, as shown in Figure 5 , the core hardness detection position is that: taking the cross section at the axial center of each step of the step sample as a detection surface, four points are taken on the circle with a distance of 1 / 2r from the center axis to the outer surface in the radial direction on the detection surface, and the included angle of the circular arcs of the adjacent two points is 90°; four points are taken on the circle with a distance of 1 / 2r and 3 / 4r from the center axis to the outer surface in the radial direction on the detection surface, and the included angle of the circular arcs of the adjacent two points is 90°.

[0081] Step five, drawing the diameter-core hardness curve:

[0082] According to the core hardness detection results obtained in step four, taking the part diameter D n of the step sample as the X axis, the core hardness Y dn of the step sample as the Y axis, the diameter-core hardness curve is drawn, as shown in Figure 6 .

[0083] Step six, data processing:

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

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

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

[0087] Assume the diameter is D n The core hardness is Y dn Y dn =Y jm Y jm The coordinates on the material hardenability curve are (J) m Y jm Then the end quenching point J m With part diameter D n Corresponding. J m The end-quench value at that point is the diameter D. n Hardness of the core of the shaft.

[0088] The specific process of the graphical method is as follows:

[0089] The hardenability curve and diameter-core hardness curve of the material were plotted on the same graph to determine the correspondence between the core hardness and the end quenching point of the step specimens with different diameters under the process conditions. Figure 7 As shown (hardness curve at 3 / 4r core hardness). The curve passes through diameter D in the figure. 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 that point, intersecting the hardenability curve of the material at point (J). m Y jm If the diameter is D, then the diameter is D. n The core hardness of shaft-type parts is equal to the material J. m Hardness at the end-quench point. For example... Figure 7 In the middle, diameter D n For a shaft with a diameter of 50 mm, under the heat treatment process conditions, the core hardness (at 3 / 4r) corresponds to the end quench value at material J25.

[0090] Step 7, Parameter Fitting:

[0091] Based on the relationship between the diameter of the stepped specimen and the quenching point of the material obtained in step six, polynomial regression is performed using the least squares method, such as... Figure 8 As shown, determine the diameter D of the part. n With end quenching point J mThe relationship is shown in the following formula:

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

[0093] In the formula:

[0094] J m represents 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 speed during quenching;

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

[0097] Step eight, heart hardness prediction:

[0098] After the step shaft part is carburized and quenched, the shaft diameter D n at different shaft diameters is input into Formula I to determine the corresponding end quenching point J m , and by consulting the hardness range of the material selected for the step shaft part at the end quenching point J m , the heart hardness value range of the step shaft part at the shaft diameter D n is obtained.

[0099] Application Example 1:

[0100] This application example gives a kind of fast prediction method for heart hardness of step shaft part after carburizing and quenching heat treatment based on the above-mentioned embodiment. In this application example, as shown in the following formula: Figure 9 , the step shaft part is a transmission step shaft made of 18CrNiMo7-6 material. The heart hardness (heart hardness is the hardness at the radius 1 / 2) of the part after carburizing and quenching at the shaft diameters of 60mm, 63mm, 67mm, and 87.16mm is predicted.

[0101] The method is carried out according to the following steps:

[0102] Step one, obtain the hardenability curve:

[0103] The material with a diameter greater than 90 mm and slightly higher hardenability is 20CrNi3H. The 20CrNi3H bar with a diameter of 120 mm is selected. According to GB / T225, three end-quench samples are prepared on the 20CrNi3H bar with a diameter of 120 mm, normalized at 860℃±10℃, and end-quench tested at 830℃±5℃, to detect the hardenability of the material, take the average value of the three samples, and draw the hardenability curve.

[0104] Step two, processing into a stepped sample:

[0105] The bar of the same material as the bar in step one is forged and normalized, and turned into a stepped sample.

[0106] In this application example, considering that the minimum diameter of the existing shaft parts is 45 mm, and the maximum diameter in the later stage is expected to be no more than 90 mm, the test steel is forged, normalized, and processed into stepped samples with diameters of 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, and 90 mm.

[0107] The test steel is heated to 1150℃±20℃, and forged into a stepped sample blank by free forging. After isothermal normalizing, it is roughly turned to the size as shown in Figure 10

[0108] Step three, carburizing and quenching:

[0109] The stepped sample obtained in step two is subjected to carburizing and quenching in a box-type multi-purpose furnace, the quenching liquid is good fortune G oil, the stirring speed is 850 / 750 r / min, after quenching, it is cooled to room temperature, and low-temperature tempering is carried out at 185℃ for 2h.

[0110] Step four, detecting the core hardness:

[0111] The hardness of the stepped sample is detected at the core hardness detection position after step three.

[0112] In this application example, the hardness of the stepped sample at the center of each stepped length direction section 1 / 2r is detected, four points are detected, the adjacent two points are 90°, and the average value of the detection results is taken.

[0113] Step five, drawing the diameter-core hardness curve:

[0114] According to the core hardness detection results obtained in step four, the part diameter D n of the stepped sample is taken as the X-axis, and the core hardness Y dn of the stepped sample is taken as the Y-axis, and the diameter-core hardness curve is drawn.

[0115] Step six, data processing:

[0116] ​According to the diameter-core hardness curve obtained in Step 5, the relationship between the diameter of the step sample and the material end quenching point is determined by coordinate method, as shown in Table 1.

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

[0118] Diameter D / mm 40 50 60 70 80 90 Jominy end quench 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 sample and the material end quenching point obtained in Step 6, polynomial regression is performed by least square method, as shown in Table 2, to determine the relationship between the diameter D of the part and the end quenching point J, as shown in Formula II: Figure 11 n m

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

[0122] Step 8, core hardness prediction:

[0123] After carburizing and quenching heat treatment of the stepped shaft part, the shaft diameter D at different shaft diameters is input into Formula II to determine the corresponding end quenching point J, as shown in Table 2. n m

[0124] Referring to the hardness range of the material 18CrNiMo7-6 selected for the stepped shaft part at the end quenching point J, the core hardness value range at the shaft diameter D of the stepped shaft part is determined, as shown in Table 3. m n

[0125] Table 2 End quenching point corresponding to different shaft diameters of the stepped shaft in Application Example 1.

[0126] Diameter Dn / mm 60 63 67 87.16 end quench point J m / mm]] 21 22 23 29

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

[0128] Diameter Dn / 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] ​​​​​​​The application example gives a kind of ladder shaft part carburizing quenching heat treatment after the rapid prediction method of heart hardness. The purpose of the application example is to estimate whether a certain ladder shaft material can meet the design requirements after changing. In the application example, the material used in the current transmission shaft is 17NiCrMo6-4. In order to reduce the cost, 20CrMnMo material is used. The heart 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 is carried out according to the following steps:

[0132] Step one, get the hardenability curve:

[0133] The material with slightly high hardenability in the stock diameter greater than 80mm is 17NiCrMo6-4 material. Select 17NiCrMo6-4 bar with a diameter of 110mm. According to GB / T225, 3 end quenching samples are prepared on the 17NiCrMo6-4 material bar with a diameter of 110mm. Normalize at 910℃±10℃, end quenching test at 880℃±5℃, detect the hardenability of the material, take the average value of the three samples, and draw the hardenability curve.

[0134] Step two, process into step sample:

[0135] The same material bar as in step one is forged and normalized, and turned into a step sample.

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

[0137] The test steel is heated to 1150℃±20℃, and the step sample blank is forged by free forging. After isothermal normalizing, it is roughly turned to the size as shown in Figure 12 .

[0138] Step three, carburizing quenching treatment:

[0139] The step sample obtained in step two is subjected to carburizing quenching treatment in a box-type multi-purpose furnace. The quenching liquid is good fortune 355 oil, the stirring speed is 600 / 500r / min, the sample is vertically placed on the tray during preparation, and after quenching, it is cooled to room temperature. Low temperature tempering is carried out at 180℃ for 2h.

[0140] Step four, detect the heart hardness:

[0141] The hardness of the step sample is detected at the heart hardness detection position of the step sample after step three.

[0142] In this application example, the hardness of each step length direction center section 3 / 4r of the step sample is detected, four points are detected, and the average value of the detection results is taken.

[0143] Step five, draw the diameter-core hardness curve:

[0144] According to the core hardness detection results obtained in step four, the part diameter D n of the step sample is taken as the X axis, the core hardness Y dn of the step sample is taken as the Y axis, and the diameter-core hardness curve is drawn.

[0145] Step six, data processing:

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

[0147] Table 4 Relationship between diameter of step sample and material end quenching point in application example 2

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

[0149] Step seven, parameter fitting:

[0150] According to the relationship between the diameter of the step sample and the material end quenching point obtained in step six, the least square method is used for polynomial regression, as shown in Figure 13 , the relationship between the part diameter D n and the end quenching point J m is determined, as shown in formula II:

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

[0152] Step eight, core hardness prediction:

[0153] After the step shaft part is carburized and quenched, the shaft diameter D n at different shaft diameters is input into formula III, and the corresponding end quenching point J m is determined, as shown in Table 5.

[0154] Referring to the hardness range of the material 20CrMnMo selected for the step shaft part at the end quenching point J m , the core hardness value range of the step shaft part at the shaft diameter D n is obtained, as shown in Table 6.

[0155] Table 5 The end quenching point corresponding to different shaft diameters of the stepped shaft of application example 2.

[0156] Diameter D n / mm]] 63 76 End quench point J m / mm]] 20 27

[0157] Table 6 The estimated results of 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 requirement / HRC 35-45 32-42

[0159] From the above table 6, the core hardness after replacing the 20CrMnMo material has a certain probability of being lower than the lower limit requirement of the drawing, and the hardenability of the material needs to be limited and the quenching cooling condition needs to be strengthened.

Claims

1. A rapid prediction method for the core hardness of stepped shaft parts after carburizing and quenching heat treatment, characterized in that, This method is performed according to the following steps: Step 1: Obtain the hardenability curve: Samples were taken and prepared from the bar stock, the actual hardenability of the bar stock was tested, and the hardenability curve of the bar stock was plotted. The material used for the bar is the same as the material used for the stepped shaft part; Step 2: Process the specimen into a stepped sample. A bar of the same material as the bar in step one is forged and normalized, and then machined into a stepped sample. Step 3, carburizing and quenching treatment: The stepped sample obtained in step two was subjected to carburizing and quenching treatment, and then subjected to low-temperature tempering. Step 4, test heart hardness: The hardness of the specimen is tested at the core hardness testing location of the stepped specimen after step three. Step 5: Plot the diameter-core hardness curve: Based on the core hardness test results obtained in step four, plot the diameter-core hardness curve; Step Six, Data Processing: Based on the diameter-core hardness curve obtained in step five, the relationship between the diameter of the stepped specimen and the quenching point at the end of the material is determined using the coordinate method or the graphical method. Step 7, Parameter Fitting: Based on the relationship between the diameter of the stepped specimen and the quenching point of the material obtained in step six, polynomial regression using the least squares method is used to determine the diameter D of the part. n With end quenching point J m The relationship is shown in Equation I: J m =a + b × D n +c×D n 2 +d×D n 3 Formula I; In the formula: J m Indicates the end-quench point; a, b, c, and d are all regression coefficients; D n The diameter of the part's shaft; Step 8, Heart Hardness Prediction: After carburizing and quenching heat treatment, the shaft diameter D at different shaft diameters is... n Input formula I to determine the end quenching point J corresponding to the shaft diameter. m Check the material selected for this stepped shaft part at the end quenching point J. m The hardness range at that point corresponds to the diameter D of the stepped shaft part. n The range of values ​​for core hardness at that location.

2. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step one, samples are taken and prepared on the bar stock in accordance with GB / T225 to test the actual hardenability of the bar stock; at least 3 end-quenched samples should be taken, and the average value of the 3 samples should be taken.

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

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

5. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step two, the diameter d of the stepped sample increases progressively in increments of 10 mm, and the length l of each step is ≥3d.

6. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step two, the minimum diameter of the stepped sample is smaller than the minimum diameter of the stepped shaft part, and the maximum diameter of the stepped sample is larger than the maximum diameter of the stepped shaft part.

7. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step three, the carburizing and quenching conditions of the stepped specimen should be consistent with the actual carburizing and quenching conditions of the stepped shaft.

8. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step four, the core hardness testing position should correspond to the core hardness position required by the stepped shaft: if the required core hardness testing position of the stepped shaft is at 1 / 2r, then take the cross-section at the axial center of each step of the stepped sample as the testing surface, and take four points on a circle along the radial direction from the central axis to the outer surface at a distance of 1 / 2r, with the included angle of the arc between any two adjacent points being 90°; if the required core hardness testing position of the stepped shaft is at 3 / 4r, then take four points on a circle along the radial direction from the central axis to the outer surface at a distance of 3 / 4r, with the included angle of the arc between any two adjacent points being 90°.

9. The method for rapid prediction of core hardness after carburizing and quenching heat treatment of stepped shaft parts as described in claim 1, characterized in that, In step seven, formula I is obtained using polynomial regression with the least squares method, where the diameter D of the part is... n The value range is 25mm≤D n ≤110mm.

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