Oil quenching process for large-size service pin

Abstract

The application discloses a large-size working pin oil quenching heat treatment process, which comprises the following steps: S1: quenching heating and holding the first stage; S2: quenching heating and holding the second stage; S3: quenching heating and holding the third stage; S4: quenching cooling, quenching cooling of the workpiece in a quenching oil tank; S5: high-temperature tempering; and S6: furnace discharge air cooling. After the process, the tensile strength of the workpiece is 980-1020 MPa, the yield strength is 830-850 MPa, the elongation is 12-14%, the reduction of area is 53-56%, the room temperature impact energy is 55-65 J, and the technical requirements of the crane telescopic arm working pin are met, i.e. the tensile strength is greater than or equal to 980 MPa, the yield strength is greater than or equal to 830 MPa, the elongation is greater than or equal to 12%, the reduction of area is greater than or equal to 52%, and the impact energy is greater than or equal to 55 J.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, and in particular relates to a large-size working pin oil quenching heat treatment process. Background Technology

[0002] In the prior art, the crane telescopic boom Working pins are generally used The hot-rolled 40CrNiMoA bar undergoes hot forging, heat treatment normalizing, rough turning, heat treatment quenching and tempering, finish turning, and nitriding. When using... The hot-rolled 40CrNiMoA bars, after hot forging, heat treatment normalizing, and rough turning, cannot meet the technical requirements of the working pins of crane telescopic booms in terms of tensile strength, yield strength, elongation, reduction of area, and impact energy when subjected to the existing heat treatment and tempering process.

[0003] The technical requirements for the working pin of the crane telescopic boom are: tensile strength ≥980MPa, yield strength ≥830MPa, elongation ≥12%, reduction of area ≥52%, and impact energy ≥55J.

[0004] When a crane telescopic boom working pin is put into use without meeting the yield strength standard, there will be no warning before the working pin breaks. When the tensile strength of the working pin of the crane telescopic boom is not up to standard, the range of tonnage that can be lifted is reduced, and in severe cases, the working pin will break, leading to more serious consequences. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a large-size working pin oil quenching process to improve its mechanical properties.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A process for oil quenching treatment of large-size working pins includes the following steps:

[0008] S1: The first stage of quenching heating and heat preservation involves heating the workpiece to a temperature Tc1 of not less than 850 degrees Celsius and then holding it for a heat preservation time of not less than 30 minutes. At the same time, the carbon potential in the furnace is not less than 0.3% and not more than 0.5%.

[0009] S2: The second stage of quenching heating and holding, after heating the workpiece to a temperature Tc2 of not less than 880 degrees, it is held for a holding time of not less than 280 minutes, while the carbon potential in the furnace is not less than 0.5% and not more than 0.6%.

[0010] S3: quenching heating and holding the third stage, the workpiece is heated to a temperature Tc3 not less than 930 degrees, and then held, the holding time tc3 is not less than 70 minutes, and meanwhile the carbon potential in the furnace is not less than 0.5% and not more than 0.6%;

[0011] S4: quenching cooling, the workpiece is quenched in a quenching oil tank, the quenching cooling time t 淬冷 is not less than 90 minutes, and the quenching oil control temperature T 油 is not less than 55 degrees;

[0012] S5: high-temperature tempering, the workpiece is heated to a temperature Th1 not less than 515 degrees and not more than 525 degrees in a tempering furnace, and then held, the holding time th1 is not less than 480 minutes;

[0013] S6: furnace-out air cooling; wherein Tc1 < Tc2 < Tc3.

[0014] As a further improvement, S1-S3 are carried out in a quenching heating chamber of a quenching furnace, and S4 is transferred to a quenching chamber to be carried out, and the workpiece transfer time from the quenching heating chamber to the quenching chamber is not more than 40 seconds.

[0015] As a further improvement, the rotating speed of the stirring motor in the quenching oil tank in S4 is not less than 1300 r / min.

[0016] As a further improvement, the hot-rolled rod is first subjected to hot forging, normalizing heat treatment and rough turning, and then the workpiece is subjected to S1 treatment.

[0017] As a further improvement, the large-specification working pin

[0018] As a further improvement, the large-specification working pin is a crane telescopic arm working pin.

[0019] As a further improvement, the material of the large-specification working pin comprises the following elements and mass percentages: C: 0.4-0.45%, Si: 0.25-0.3%, Mn: 0.7-0.75%, P: 0.01-0.015%, S: 0.004-0.008%, Cr: 0.7-0.8%, Mo: 0.15-0.2%, Ni: 1.2-1.5%, and other elements are Fe.

[0020] As a further improvement, the material of the large-specification working pin is 40CrNiMoA.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] After the workpiece is treated by the process of the present application, the tensile strength of the workpiece is 980-1020 MPa, the yield strength is 830-850 MPa, the elongation is 12-14%, the reduction of area is 53-56%, and the room temperature impact energy is 55-65 J, which meets the technical requirements of the crane telescopic arm working pin: tensile strength ≥ 980 MPa, yield strength ≥ 830 MPa, elongation ≥ 12%, reduction of area ≥ 52%, and impact energy ≥ 55 J. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of the present application, the present application will be described in more detail below in combination with preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all the professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing the specific embodiments and are not intended to limit the protection scope of the present application.

[0025] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0026] The large-size working pin of the present application has a diameter For example, the crane telescopic arm working pin (for example ) has a large size and a specific shape, and therefore has relatively high requirements for the heat treatment process.

[0027] The elements and mass percentages of the large-size working pin alloy material of the present application are as follows: C: 0.4-0.45%, Si: 0.25-0.3%, Mn: 0.7-0.75%, P: 0.01-0.015%, S: 0.004-0.008%, Cr: 0.7-0.8%, Mo: 0.15-0.2%, Ni: 1.2-1.5%, and other elements are Fe.

[0028] For example, the process of the present application is particularly suitable for 40CrNiMoA, and the elements and mass percentages thereof are as follows: C: 0.41%, Si: 0.26%, Mn: 0.74%, P: 0.011%, S: 0.005%, Cr: 0.78%, Mo: 0.19%, Ni: 1.48%, and other elements are Fe.

[0029] The hot-rolled bar with the above alloy composition is first subjected to hot forging, normalizing heat treatment, rough turning, and then quenching and tempering heat treatment (i.e. the oil quenching heat treatment process of the present application).

[0030] The oil quenching and heat treatment process of the present application can be carried out by using existing equipment. For example, the equipment includes a quenching furnace (having a quenching heating chamber, a quenching chamber, and a temperature-controlled quenching oil tank with stirring function) and a tempering furnace.

[0031] In some embodiments, the large-size work pin oil quenching and heat treatment process of the present application comprises the following steps:

[0032] S1: quenching heating and holding the first stage, the workpiece is heated to a temperature Tc1 not lower than 850 degrees (<870 degrees) and held, the holding time tc1 is not less than 30 minutes, and the carbon potential in the furnace is not less than 0.3% and not more than 0.5%.

[0033] S2: quenching heating and holding the second stage, the workpiece is heated to a temperature Tc2 not lower than 880 degrees (<910 degrees) and held, the holding time tc2 is not less than 280 minutes, and the carbon potential in the furnace is not less than 0.5% and not more than 0.6%.

[0034] S3: quenching heating and holding the third stage, the workpiece is heated to a temperature Tc3 not lower than 930 degrees (<960 degrees) and held, the holding time tc3 is not less than 70 minutes, and the carbon potential in the furnace is not less than 0.5% and not more than 0.6%.

[0035] If S3 is omitted, the final workpiece has a tensile strength of 700-750 MPa, a yield strength of 850-900 MPa, an elongation of 14-16%, a reduction of area of 52-56%, and an impact energy of 60-65 J, which cannot meet the technical requirements of the crane telescopic arm work pin.

[0036] S4: quenching cooling, the workpiece is quenched and cooled in the quenching oil tank, the quenching cooling time t 淬冷 is not less than 90 minutes, and the quenching oil control temperature T 油 is not less than 55 degrees (<70 degrees).

[0037] S1-S3 are carried out in the quenching heating chamber, S4 is transferred to the quenching chamber, and preferably, the workpiece transfer time from the quenching heating chamber to the quenching chamber is not more than 40 seconds.

[0038] Preferably, the stirring motor speed in the quenching oil tank is not less than 1300 r / min.

[0039] S5: high-temperature tempering, the workpiece is heated to a temperature Th1 not less than 515 degrees and not more than 525 degrees in the tempering furnace and held, and the holding time th1 is not less than 480 minutes.

[0040] S6: air cooling after taking out, the workpiece is taken out from the tempering furnace and placed in the air to cool to room temperature.

[0041] Wherein, Tc1 < Tc2 < Tc3.

[0042] Because the alloy elements and content are different, the performance difference is large, and the alloy performance is sensitive to the heat treatment process parameters, the process of the application is suitable for the alloy with the above-mentioned specific component content, and the specific process conditions (the temperature of the three holding stages is increased in turn, each stage is matched with a specific holding time and carbon potential, and then the temperature and time of quenching and tempering are controlled) are matched with the alloy composition, and both of them achieve the performance requirements of the application. Meanwhile, the process of the application is particularly suitable for large-size working pins.

[0043] Examples 1-3 and Comparative Examples 1-10

[0044] The hot-rolled bar of 40CrNiMoA is subjected to hot forging, normalizing heat treatment, rough turning, and then quenching and tempering heat treatment (i.e. the oil quenching heat treatment process described below).

[0045] The hot forging is to adopt an induction heating to a certain temperature (the final forging temperature is 1100 degrees) to the part to be forged, and then adopt a punch with a die to perform forging.

[0046] The normalizing heat treatment is to adopt a normalizing furnace to normalize the workpiece after hot forging, and then take out the furnace after 880 degrees of holding for 300 minutes and air cooling.

[0047] The oil quenching heat treatment process of the large-size working pin of the example and the comparative example includes the following steps:

[0048] S0: loading the workpiece into the furnace;

[0049] S1: quenching heating and holding 1, sending the workpiece into the quenching heating chamber, heating the workpiece to a temperature Tc1 not lower than 850 degrees and holding, the holding time tc1 is not less than 30 minutes, and the carbon potential in the furnace is not less than 0.3% and not more than 0.5%;

[0050] S2: quenching heating and holding 2, after S1 is completed, the workpiece is heated to a temperature Tc2 not lower than 880 degrees and held, the holding time tc2 is not less than 280 minutes, and the carbon potential in the furnace is not less than 0.5% and not more than 0.6%;

[0051] S3: quenching heating and holding 3, after S1 and S2 are completed, the workpiece is heated to a temperature Tc3 not lower than 930 degrees and held, the holding time tc3 is not less than 70 minutes, and the carbon potential in the furnace is not less than 0.5% and not more than 0.6%;

[0052] S4: quenching cooling, after S1, S2 and S3 are completed, the workpiece is transferred from the quenching heating chamber to the quenching chamber and then put into a temperature-controlled quenching oil tank equipped with a rapid quenching oil and a stirring motor with a certain rotating speed to perform quenching cooling, the quenching cooling time t​淬冷 The rapid quenching oil temperature T in the quenching oil tank should be controlled for no less than 90 minutes. 油 The temperature shall not be lower than 55 degrees Celsius, the transfer time from the quenching heating chamber to the quenching chamber shall not be higher than 40 seconds, and the stirring motor speed in the quenching oil tank shall not be lower than 1300 r / min.

[0053] S5: High-temperature tempering. After S1, S2, S3 and S4 are completed, the workpiece is sent into the tempering furnace and heated to a temperature Th1 of not less than 515 degrees and not more than 525 degrees. The workpiece is then held at this temperature for a time th1 of not less than 480 minutes.

[0054] S6: Air cooling after removal from the furnace: After completing S1, S2, S3, S4, and S5, remove the workpiece from the tempering furnace and allow it to cool to room temperature in the air.

[0055] Samples are taken from the workpiece and then performance tests are performed according to the standards in the table below.

[0056] Table 1

[0057]

[0058] The specific process parameters and performance test results of Examples 1-3 and Comparative Examples 1-10 are detailed in the table below.

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] Table 4

[0064]

[0065]

[0066] As can be seen from the table above, when using When the hot-rolled 40CrNiMoA bar undergoes hot forging, heat treatment normalizing, rough turning, and subsequent heat treatment and tempering (i.e., the oil quenching heat treatment process in this example), the tensile strength is 980-1020MPa, the yield strength is 830-850MPa, the elongation is 12-14%, the reduction of area is 53-56%, and the room temperature impact energy is 55-65J. This meets the technical requirements for working pins of crane telescopic booms: tensile strength ≥980MPa, yield strength ≥830MPa, elongation ≥12%, reduction of area ≥52%, and impact energy ≥55J.

[0067] The quenching cooling stirring motor rotation speed of Comparative Example 1 is lower than the requirement of the present application, resulting in poor tensile strength and yield strength. The quenching cooling time t 淬冷 of Comparative Example 2 is shorter than the requirement of the present application, resulting in poor tensile strength and yield strength. The quenching oil temperature T 油 of Comparative Example 3 is lower than the requirement of the present application, resulting in poor tensile strength and yield strength. The quenching heating and holding temperature Tc3 of Comparative Example 4 is lower than the requirement of the present application, resulting in poor tensile strength and yield strength. The quenching heating and holding time tc2 of Comparative Example 5 is shorter than the requirement of the present application, resulting in poor tensile strength and yield strength. The tempering heating and holding time thl of Comparative Example 6 is shorter than the requirement of the present application, resulting in poor reduction of area and room temperature impact energy. The tempering heating and holding temperature Thl of Comparative Example 7 is higher than the requirement of the present application, and the tempering heating and holding time thl is shorter than the requirement of the present application, resulting in slightly poor tensile strength and yield strength. The tempering heating and holding temperature Thl of Comparative Example 8 is lower than the requirement of the present application, resulting in poor elongation, reduction of area and room temperature impact energy. The tempering heating and holding time thl of Comparative Examples 9 and 10 is shorter than the requirement of the present application, resulting in poor room temperature impact energy.

[0068] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Therefore, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application, which does not deviate from the technical solution of the present application, shall fall within the protection scope of the technical solution of the present application.

Claims

1. A large size workpiece oil quenching heat treatment process characterized by, The steps include the following: S1: quenching heating and holding the first stage, heating the workpiece to a temperature Tc1 not less than 850 degrees and holding, holding time tc1 not less than 30 min, while the carbon potential in the furnace is not less than 0.3% and not more than 0.5%; S2: quenching heating and holding the second stage, heating the workpiece to a temperature Tc2 not less than 880 degrees and holding, holding time tc2 not less than 280 min, while the carbon potential in the furnace is not less than 0.5% and not more than 0.6%; S3: quenching heating and holding the third stage, heating the workpiece to a temperature Tc3 not less than 930 degrees and holding, holding time tc3 not less than 70 min, while the carbon potential in the furnace is not less than 0.5% and not more than 0.6%; S4: quenching, quenching the workpiece in a quenching oil tank, quenching time t 淬冷 not less than 90 min, quenching oil control temperature T 油 not less than 55 degrees; S5: high temperature tempering, heating the workpiece in the tempering furnace to a temperature Th1 not less than 515 degrees and not more than 525 degrees and holding, holding time th1 not less than 480 min; S6: furnace discharge air cooling; wherein Tc1 < Tc2 < Tc3; The large specification work pin material is 40CrNiMoA, and the diameter is greater than or equal to 280 mm.

2. The large size service pin oil quenching and heat treatment process according to claim 1, characterized in that, S1-S3 are carried out in the quenching heating chamber of the quenching furnace, S4 is transferred to the quenching chamber, and the workpiece transfer time from the quenching heating chamber to the quenching chamber is not more than 40 s.

3. Large size service pin oil quenching heat treatment process according to claim 1 or 2, characterized in that, The stirring motor speed in the quenching oil tank in S4 is not less than 1300 r / min.

4. Large size service pin oil quenching heat treatment process according to claim 1 or 2, characterized in that, The hot rolled bar is first subjected to S1 treatment after hot forging, normalizing, and rough turning.

5. The large size service pin oil quenching and heat treatment process according to claim 1 or 2, characterized in that, The large specification work pin is a crane telescopic arm work pin.

6. The large size service pin oil quenching and heat treatment process according to claim 1 or 2, characterized in that, The elements and mass percentage in the material of the large specification work pin are as follows: C: 0.4-0.45%, Si: 0.25-0.3%, Mn: 0.7-0.75%, P: 0.01-0.015%, S: 0.004-0.008%, Cr: 0.7-0.8%, Mo: 0.15-0.2%, Ni: 1.2-1.5%, and other elements are Fe.

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