A non-quenched and tempered steel crankshaft for a high-horsepower engine and a method of manufacturing the same

Abstract

The application belongs to the technical field of automobile manufacturing, and particularly relates to a non-quenched and tempered steel crankshaft for a high-horsepower engine and a preparation method thereof. The preparation method comprises the following steps: S1, obtaining a non-quenched and tempered steel crankshaft blank, and forging the non-quenched and tempered steel crankshaft blank to obtain a first crankshaft; S2, mechanically processing the first crankshaft to obtain a second crankshaft, and the cylindrical surface of the main shaft neck and the connecting rod neck of the second crankshaft is in the shape of a double-coin with high ends and a low middle part; S3, first quenching and second quenching the second crankshaft to obtain a third crankshaft, and coarsely grinding and finely grinding the third crankshaft to obtain the non-quenched and tempered steel crankshaft for the high-horsepower engine. The application adopts an original deformation advance reservation method and a two-step induction quenching method, so that the run-out of the main shaft neck in the third crankshaft is less than or equal to 0.25 mm, and the run-out of the connecting rod neck in the third crankshaft is less than or equal to 0.20 mm.

Description

Technical Field

[0001] This application belongs to the field of automobile manufacturing technology, specifically relating to a non-quenched and tempered steel crankshaft for a high-horsepower engine and its preparation method. Background Technology

[0002] The crankshaft is the most critical component of an engine. It converts the reciprocating linear motion from the piston and connecting rod assembly into its own rotational motion, generating continuous rotational torque. This torque is then transmitted to the transmission system, including the gearbox, drive shaft, and drive axle, via the flywheel, thus providing power to the entire vehicle. The timing gear or pulley at the front of the crankshaft drives the valve train, oil pump, water pump, air conditioning compressor, and other accessories. Furthermore, to balance the inertial forces generated by the crankshaft's rotation and reciprocating motion, counterweights are installed on it to reduce engine vibration. Therefore, the crankshaft is like the "backbone" of the engine, the most crucial component ensuring its continuous and efficient operation.

[0003] Currently, environmentally friendly non-quenched and tempered steel has become the preferred choice for key automotive components such as crankshafts and connecting rods. Its performance is essentially the same as quenched and tempered steel, but its processing efficiency is significantly improved. It also effectively avoids the risks of quenching cracks associated with steel tempering, resulting in substantial economic and social benefits. In recent years, with the rapid development of the commercial vehicle industry, high-horsepower engines are rapidly evolving towards "high horsepower, high explosion pressure, low noise, and long lifespan." High reliability has become a critical bottleneck technology that urgently needs to be overcome in the production process of non-quenched and tempered steel crankshafts, and it has also become the biggest weakness restricting China's heavy-duty trucks from reaching world-class standards.

[0004] After extensive exploration and statistical analysis, the dimensional accuracy of the crankshaft has been identified as the most significant factor affecting its reliability. Achieving high precision in non-quenched and tempered steel crankshafts at low cost is a crucial technology that urgently needs to be addressed. However, for high-horsepower engine crankshafts, the number and size of the main journals and connecting rod journals are numerous, resulting in severe deformation during heat treatment, with runout being the most prominent issue. Reducing crankshaft runout and minimizing grinding of the main journals and connecting rod journals has been a major challenge for the automotive industry, and is also one of the most effective measures for reducing production costs and enhancing the competitiveness of domestically produced non-quenched and tempered steel crankshafts. Therefore, a method is urgently needed to reduce crankshaft runout and minimize grinding of the main journals and connecting rod journals in the manufacture of non-quenched and tempered steel crankshafts for high-horsepower engines. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this application provides a method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, comprising the following steps: S1, obtaining a non-quenched and tempered steel crankshaft blank, and forging the non-quenched and tempered steel crankshaft blank to obtain a first crankshaft; S2, machining the first crankshaft to obtain a second crankshaft, wherein the cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle; S3, performing a first quenching and a second quenching on the second crankshaft to obtain a third crankshaft, and performing rough grinding and fine grinding on the third crankshaft to obtain a non-quenched and tempered steel crankshaft for a high-horsepower engine.

[0006] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S1, the composition of the non-quenched and tempered steel crankshaft blank, by mass percentage, is as follows: C: 0.37%-0.40%, Si: 0.60%-0.70%, Mn: 1.40%-1.50%, P≤0.015%, S: 0.030%-0.045%, Cr: 0.15%-0.25%, Al: 0.035%-0.050%, Mg: 0.0020%-0.0045%, O: 0.0003-0.0016%, N: 0.016%-0.022%, H≤0.0002%, with the balance being Fe and unavoidable impurities, and 30≤Mn / S≤50, 1.9≤Al / N≤3.5.

[0007] As a preferred embodiment of the preparation method of a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S1, the austenite grain size of the non-quenched and tempered steel crankshaft blank is grade 7-9, and the banded structure is grade ≤2.0. Under the conditions of normalizing temperature and quenching temperature, the end hardenability of the non-quenched and tempered steel crankshaft blank is: J1.5=53-58HRC, J3.0=52-57HRC, J5.0=49-55HRC. The normalizing temperature is 880±5℃, and the quenching temperature is 870±5℃.

[0008] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S1, the heating temperature of the forging is 1230-1280℃, the holding time of the forging is 65-75s, and the forging further includes: hot trimming and hot correction after forging, and the straightness after hot correction is ≤1.2mm.

[0009] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, the machining method in step S2 is specifically as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined into an ingot shape, higher at both ends and lower in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft, and D1 is 100-110mm. The difference between the two ends and the middle of main journal 1... The values ​​are 0.10±0.01mm, the difference between the two ends and the middle of the second main journal is 0.12±0.01mm, the difference between the two ends and the middle of the third main journal is 0.15±0.01mm, the difference between the two ends and the middle of the fourth main journal is 0.20±0.01mm, the difference between the two ends and the middle of the fifth main journal is 0.15±0.01mm, the difference between the two ends and the middle of the sixth main journal is 0.12±0.01mm, and the difference between the two ends and the middle of the seventh main journal is 0.10±0.01mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod journals 1, 2, 3, 4, 5, and 6 are the same, D2-(0.15±0.005)mm, where D2 is the target diameter of the connecting rod journals required for the finished crankshaft, and D2 is 90-100mm. Specifically, connecting rod journal 1... The difference between the two ends and the middle is 0.05±0.01mm; the difference between the two ends and the middle of the second connecting rod neck is 0.07±0.01mm; the difference between the two ends and the middle of the third connecting rod neck is 0.10±0.01mm; the difference between the two ends and the middle of the fourth connecting rod neck is 0.10±0.01mm; the difference between the two ends and the middle of the fifth connecting rod neck is 0.07±0.01mm; and the difference between the two ends and the middle of the sixth connecting rod neck is 0.05±0.01mm.

[0010] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S3, the first quenching method specifically involves simultaneously performing medium-frequency induction quenching and cooling on the main journal 1, connecting rod journal 1, main journal 3, connecting rod journal 4, main journal 5, connecting rod journal 6, and main journal 7 of the second crankshaft, with a rotation speed of 50-60 rpm. Specifically, the medium-frequency voltage of main journal 1, main journal 3, main journal 5, and main journal 7 is 79%-81% of a set value, the heating time is 17-19 s, and the cooling time is 12-14 s; the medium-frequency voltage of connecting rod journal 1, connecting rod journal 3, connecting rod journal 4, and connecting rod journal 6 is 74%-76% of a set value, the heating time is 15-17 s, and the cooling time is 11-13 s.

[0011] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S3, the second quenching method specifically involves simultaneously performing medium-frequency induction quenching and cooling on the second crankshaft's main journal 2, connecting rod journal 2, main journal 4, connecting rod journal 5, and main journal 6, at a rotation speed of 40-50 rpm. Specifically, the medium-frequency voltage of main journal 2, main journal 4, and main journal 6 is 77%-79% of a set value, the heating time is 16-18 s, and the cooling time is 12-14 s; the medium-frequency voltage of connecting rod journal 2 and connecting rod journal 5 is 72%-74% of a set value, the heating time is 14-16 s, and the cooling time is 11-13 s.

[0012] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S3, the cooling in the first quenching and the second quenching is PAG quenching liquid with a concentration of 10-13% and a temperature of 23-29℃.

[0013] As a preferred embodiment of the method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine as described in this application, in step S3, the runout of the main journal in the third crankshaft is ≤0.25mm, and the runout of the connecting rod journal in the third crankshaft is ≤0.20mm.

[0014] This application also provides a non-quenched and tempered steel crankshaft for a high-horsepower engine, which is prepared using the above-described method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine.

[0015] The beneficial effects of this application are as follows: This application provides a non-quenched and tempered steel crankshaft for high-horsepower engines and its preparation method. Through innovative chemical composition design, this application uses common elements such as C, Si, Mn, and Cr, and strictly controls the Mn / S and Al / N ratios to control the morphology of sulfides and refine the metallographic structure of the non-quenched and tempered steel crankshaft blank. Simultaneously, it controls grain size, banded structure, and end hardenability, ensuring high consistency in the performance of the non-quenched and tempered steel crankshaft blank. Furthermore, the high forging temperature and short holding time result in high straightness of the non-quenched and tempered steel crankshaft blank. Then, during machining, an original deformation pre-reservation method was used to machine the cylindrical surfaces of the main journal and connecting rod journal in the second crankshaft into an ingot shape with high ends and low middle. The degree of concavity in the middle of different main journals and connecting rod journals was different. Then, a highly efficient two-step induction hardening method was used to successfully reduce the runout of the main journal in the third crankshaft to ≤0.25mm and the runout of the connecting rod journal in the third crankshaft to ≤0.20mm, which is only half of the industry average of 0.40-0.50mm. This greatly reduced the subsequent grinding amount of the main journal and connecting rod journal in the third crankshaft and reduced the incidence of grinding cracks to ≤0.20%, reaching the top level in the industry.

[0016] This application pre-machines the journals into a "high at both ends and low in the middle" ingot shape, reserving "deformation space" and "material allowance" for subsequent quenching deformation. During quenching, the sharp corners at both ends have a strong effect, and the rapid heating causes thermal stress and microstructure transformation, driving the material to expand and deform outward. The pre-designed recess provides "accommodation space" for this deformation, allowing stress to be released directionally within a controlled range, rather than randomly twisting the journal. This application's step-by-step quenching avoids the simultaneous and intense heating and cooling of all journals. The first step processes a portion of the journals, allowing them to complete the main deformation within the pre-designed ingot-shaped area. After they have stabilized relatively, the second step processes adjacent journals. This avoids the stress superposition and mutual pulling caused by the simultaneous deformation of multiple journals, allowing the pre-deformed recess to accurately "absorb" the deformation amount of each step, ultimately approaching the ideal cylindrical surface.

[0017] This application uses common elements such as C, Si, Mn, and Cr in the non-quenched and tempered steel crankshaft blanks, strictly controlling the Mn / S and Al / N ratios, while also controlling grain size, banded structure, and end-hardenability. This results in stable crankshaft raw material performance and low cost. This application employs a unique deformation pre-reservation method and a two-step induction hardening process, achieving a runout of ≤0.25mm for the main journal and ≤0.20mm for the connecting rod journal in the third crankshaft, only half the industry average of 0.40-0.50mm. This significantly reduces the grinding amount of the main journal and connecting rod journal in the third crankshaft, lowering the grinding crack incidence to ≤0.20%, reaching industry-leading levels. Therefore, processing efficiency is greatly improved, and production costs are significantly reduced. The process operation of this application is simple, requiring no additional equipment, and the quenching medium is a water-based solution, making it safe and environmentally friendly. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the non-quenched and tempered steel crankshaft for the high-horsepower engine in this application.

[0020] Reference numerals: 11. Main journal 1; 12. Main journal 2; 13. Main journal 3; 14. Main journal 4; 15. Main journal 5; 16. Main journal 6; 17. Main journal 7; 21. Connecting rod journal 1; 22. Connecting rod journal 2; 23. Connecting rod journal 3; 24. Connecting rod journal 4; 25. Connecting rod journal 5; 26. Connecting rod journal 6.

[0021] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0023] This application provides a method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, comprising the following steps: S1. Obtain a non-quenched and tempered steel crankshaft blank sample, and forge the non-quenched and tempered steel crankshaft blank sample to obtain a first crankshaft; The composition of the non-quenched and tempered steel crankshaft billet, by mass percentage, is as follows: C: 0.37%-0.40%, Si: 0.60%-0.70%, Mn: 1.40%-1.50%, P≤0.015%, S: 0.030%-0.045%, Cr: 0.15%-0.25%, Al: 0.035%-0.050%, Mg: 0.0020%-0.0045%, O: 0.0003-0.0016%, N: 0.016%-0.022%, H≤0.0002%, with the balance being Fe and unavoidable impurities, and 30≤Mn / S≤50, 1.9≤ Al / N ≤ 3.5; the austenite grain size of the non-quenched and tempered steel crankshaft billet is grade 7-9, and the banded structure is grade ≤ 2.0. Under the conditions of normalizing and quenching temperature, the end hardenability of the non-quenched and tempered steel crankshaft billet is: J1.5=53-58HRC, J3.0=52-57HRC, J5.0=49-55HRC. The normalizing temperature is 880±5℃, and the quenching temperature is 870±5℃. The heating temperature for forging is 1230-1280℃, and the holding time for forging is 65-75s. The forging also includes: hot trimming and hot straightening after forging. After hot straightening, the straightness is ≤ 1.2mm. S2. The first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle. The machining method is specifically as follows: The cylindrical surfaces of main journals 11, 12, 13, 14, 15, 16, and 17 are machined into a shape resembling an ingot, high at both ends and low in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft, and D1 is 100-110mm. Specifically, main journal 1... The difference between the two ends and the middle is 0.10±0.01mm; the difference between the two ends and the middle of the second main journal is 0.12±0.01mm; the difference between the two ends and the middle of the third main journal is 0.15±0.01mm; the difference between the two ends and the middle of the fourth main journal is 0.20±0.01mm; the difference between the two ends and the middle of the fifth main journal is 0.15±0.01mm; the difference between the two ends and the middle of the sixth main journal is 0.12±0.01mm; and the difference between the two ends and the middle of the seventh main journal is 0.10±0.01mm. The cylindrical surfaces of connecting rod necks 21, 22, 23, 24, 25, and 26 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod necks 1, 2, 3, 4, 5, and 6 are the same, D2-(0.15±0.005)mm, where D2 is the target diameter of the connecting rod necks required for the finished crankshaft, and D2 is 90-100mm. In the middle, the difference between the two ends and the middle of the first connecting rod neck is 0.05±0.01mm, the difference between the two ends and the middle of the second connecting rod neck is 0.07±0.01mm, the difference between the two ends and the middle of the third connecting rod neck is 0.10±0.01mm, the difference between the two ends and the middle of the fourth connecting rod neck is 0.10±0.01mm, the difference between the two ends and the middle of the fifth connecting rod neck is 0.07±0.01mm, and the difference between the two ends and the middle of the sixth connecting rod neck is 0.05±0.01mm. S3. The second crankshaft is subjected to first quenching and second quenching to obtain a third crankshaft. The third crankshaft is subjected to rough grinding and fine grinding to obtain a non-quenched and tempered steel crankshaft for high-horsepower engines. The first quenching method specifically involves simultaneously performing medium-frequency induction hardening and cooling on the main journals 1, 3, 4, 5, 6, and 7 of the second crankshaft at a rotational speed of 50-60 rpm. Specifically, the medium-frequency voltage for main journals 1, 3, 5, and 7 is 79%-81% of the set value, with a heating time of 17-19 seconds and a cooling time of 12-14 seconds; the medium-frequency voltage for connecting rods 1, 3, 4, and 6 is 74%-76% of the set value, with a heating time of 15-17 seconds and a cooling time of 11-13 seconds. The second quenching method specifically involves simultaneously performing medium-frequency induction hardening and cooling on the main journals 2, 3, 4, 5, 6, and 7 of the second crankshaft at a rotational speed of 50-60 rpm. 2. Main journals four, five, and six are simultaneously subjected to medium-frequency induction hardening and cooling at a rotation speed of 40-50 rpm. Specifically, the medium-frequency voltage of main journals two, four, and six is ​​77%-79% of the set value, with a heating time of 16-18 seconds and a cooling time of 12-14 seconds; the medium-frequency voltage of connecting rods two and five is 72%-74% of the set value, with a heating time of 14-16 seconds and a cooling time of 11-13 seconds. PAG quenching fluid with a concentration of 10-13% and a temperature of 23-29℃ is used for cooling in both the first and second quenching processes. The runout of the main journals in the third crankshaft is ≤0.25 mm, and the runout of the connecting rod journals in the third crankshaft is ≤0.20 mm.

[0024] This application also provides a non-quenched and tempered steel crankshaft for a high-horsepower engine.

[0025] The technical solution of this application will be further described below with reference to specific embodiments.

[0026] Example 1

[0027] A method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, the specific steps of which are as follows: S1. Obtain a non-quenched and tempered steel crankshaft blank sample, and forge the non-quenched and tempered steel crankshaft blank sample to obtain the first crankshaft; The composition of the non-quenched and tempered steel crankshaft billet, by mass percentage, is: C: 0.37%, Si: 0.70%, Mn: 1.50%, P: 0.015%, S: 0.033%, Cr: 0.15%, Al: 0.035%, Mg: 0.0020%, O: 0.0016%, N: 0.016%, H: 0.0002%, with the balance being Fe and unavoidable impurities. The Mn / S ratio is 45.45, and the Al / N ratio is 2.19. The austenitic... The bulk grain size is grade 7, and the banded structure is grade 2.0. Under normalizing and quenching conditions, the end hardenability of the non-quenched and tempered steel crankshaft billet is: J1.5=56HRC, J3.0=54HRC, J5.0=52HRC. The normalizing temperature is 880℃ and the quenching temperature is 870℃. The forging heating temperature is 1242-1257℃, and the forging holding time is 68-73s. Forging also includes hot trimming and hot straightening after forging. After hot straightening, the straightness is 0.69-1.03mm. S2. The first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle. The specific machining methods are as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined into an ingot shape, higher at both ends and lower in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, all being D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft. 0.05mm, the diameter of both ends of main journal one is 104.805mm, the diameter of both ends of main journal two is 104.803mm, the diameter of both ends of main journal three is 104.795mm, the diameter of both ends of main journal four is 104.799mm, the diameter of both ends of main journal five is 104.801mm, the diameter of both ends of main journal six is ​​104.801mm, and the diameter of both ends of main journal seven is 104.802mm; main spindle The central diameter of journal 1 is 104.695 mm, the central diameter of journal 2 is 104.687 mm, the central diameter of journal 3 is 104.637 mm, the central diameter of journal 4 is 104.597 mm, the central diameter of journal 5 is 104.652 mm, the central diameter of journal 6 is 104.678 mm, and the central diameter of journal 7 is 104.709 mm. The difference between the two ends and the center of journal 1 is 0.110 mm, the difference between the two ends and the center of journal 2 is 0.116 mm, the difference between the two ends and the center of journal 3 is 0.158 mm, the difference between the two ends and the center of journal 4 is 0.202 mm, the difference between the two ends and the center of journal 5 is 0.149 mm, the difference between the two ends and the center of journal 6 is 0.123 mm, and the difference between the two ends and the center of journal 7 is 0.093 mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod journals 1, 2, 3, 4, 5, and 6 are the same, D2 - (0.15 ± 0.005) mm, where D2 is the target diameter of the connecting rod journals required for the finished crankshaft, and D2 is 95 mm. The diameters at both ends of connecting rod journal 1 are 94.845 mm, 2, 3, 4, 5, and 6 are 94.848 mm. mm; the middle diameter of connecting rod neck 1 is 94.803mm, the middle diameter of connecting rod neck 2 is 94.782mm, the middle diameter of connecting rod neck 3 is 94.753mm, the middle diameter of connecting rod neck 4 is 94.746mm, the middle diameter of connecting rod neck 5 is 94.779mm, and the middle diameter of connecting rod neck 6 is 94.797mm; among which, the difference between the two ends and the middle of connecting rod neck 1 is 0.042mm, the difference between the two ends and the middle of connecting rod neck 2 is 0.069mm, the difference between the two ends and the middle of connecting rod neck 3 is 0.098mm, the difference between the two ends and the middle of connecting rod neck 4 is 0.109mm, the difference between the two ends and the middle of connecting rod neck 5 is 0.069mm, and the difference between the two ends and the middle of connecting rod neck 6 is 0.051mm; S3. The second crankshaft is subjected to first quenching and second quenching to obtain the third crankshaft. The third crankshaft is then subjected to rough grinding and fine grinding to obtain a non-quenched and tempered steel crankshaft for high-horsepower engines. The first quenching method is as follows: The main journals 1, 3, 4, 5, 6, and 7 of the second crankshaft are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 60 rpm. Specifically, the medium-frequency voltage of main journal 1 is 79% of the set value, with a heating time of 18 seconds and a cooling time of 13 seconds; the medium-frequency voltage of main journal 3 is 81% of the set value, with a heating time of 19 seconds and a cooling time of 14 seconds; the medium-frequency voltage of main journal 5 is 81% of the set value, with a heating time of 19 seconds and a cooling time of 14 seconds; and the medium-frequency voltage of main journal 5 is 81% of the set value, with a heating time of 19 seconds and a cooling time of 13 seconds. The heating time for the first connecting rod is 14 seconds; the intermediate frequency voltage of the main spindle neck seven is 79% of the set value, the heating time is 17 seconds, and the cooling time is 12 seconds; the intermediate frequency voltage of the connecting rod neck one is 74% of the set value, the heating time is 15 seconds, and the cooling time is 11 seconds; the intermediate frequency voltage of the connecting rod neck three is 74% of the set value, the heating time is 15 seconds, and the cooling time is 11 seconds; the intermediate frequency voltage of the connecting rod neck four is 76% of the set value, the heating time is 17 seconds, and the cooling time is 13 seconds; the intermediate frequency voltage of the connecting rod neck six is ​​75% of the set value, the heating time is 16 seconds, and the cooling time is 12 seconds. The second quenching method is as follows: The second crankshaft's main journal 2, connecting rod journal 2, main journal 4, connecting rod journal 5, and main journal 6 are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 50 rpm. Specifically, the medium-frequency voltage of main journal 2 is 77% of the set value, with a heating time of 16 seconds and a cooling time of 12 seconds; the medium-frequency voltage of main journal 4 is 79% of the set value, with a heating time of 18 seconds and a cooling time of 14 seconds; the medium-frequency voltage of main journal 6 is 78% of the set value, with a heating time of 17 seconds and a cooling time of 13 seconds; the medium-frequency voltage of connecting rod journal 2 is 72% of the set value, with a heating time of 14 seconds and a cooling time of 11 seconds; and the medium-frequency voltage of connecting rod journal 5 is 74% of the set value, with a heating time of 16 seconds and a cooling time of 13 seconds. The first and second quenching processes use PAG quenching fluid with a concentration of 10.1% and a temperature of 29℃ for cooling.

[0028] The third crankshaft was inspected, and the results showed that the runout of main journal 1 was 0.13 mm, main journal 2 was 0.17 mm, main journal 3 was 0.22 mm, main journal 4 was 0.24 mm, main journal 5 was 0.21 mm, main journal 6 was 0.16 mm, and main journal 7 was 0.14 mm. Similarly, the runout of connecting rod journal 1 was 0.07 mm, connecting rod journal 2 was 0.11 mm, connecting rod journal 3 was 0.14 mm, connecting rod journal 4 was 0.20 mm, connecting rod journal 5 was 0.08 mm, and connecting rod journal 6 was 0.09 mm.

[0029] Example 2

[0030] A method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, the specific steps of which are as follows: S1. Obtain a non-quenched and tempered steel crankshaft blank sample, and forge the non-quenched and tempered steel crankshaft blank sample to obtain the first crankshaft; The composition of the non-quenched and tempered steel crankshaft billet, by mass percentage, is: C: 0.40%, Si: 0.60%, Mn: 1.40%, P: 0.012%, S: 0.040%, Cr: 0.25%, Al: 0.050%, Mg: 0.0045%, O: 0.0003%, N: 0.022%, H: 0.00012%, with the balance being Fe and unavoidable impurities. The Mn / S ratio is 35, and the Al / N ratio is 2.27. The austenite content of the non-quenched and tempered steel crankshaft billet... The grain size is grade 9, the banded structure is grade 1.5, and the end hardenability of the non-quenched and tempered steel crankshaft billet under normalizing and quenching conditions is: J1.5=55HRC, J3.0=53HRC, J5.0=52HRC. The normalizing temperature is 881℃ and the quenching temperature is 872℃. The forging heating temperature is 1259-1271℃, the forging holding time is 65-74s, and the forging also includes hot trimming and hot straightening after forging. The straightness after hot straightening is 0.51-0.83mm. S2. The first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle. The specific machining methods are as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined into an ingot shape, higher at both ends and lower in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, all being D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft. 0.02mm, the diameter of both ends of main journal one is 101.802mm, the diameter of both ends of main journal two is 101.805mm, the diameter of both ends of main journal three is 101.795mm, the diameter of both ends of main journal four is 101.801mm, the diameter of both ends of main journal five is 101.805mm, the diameter of both ends of main journal six is ​​101.799mm, and the diameter of both ends of main journal seven is 101.803mm; main spindle The central diameter of journal 1 is 101.692 mm, the central diameter of journal 2 is 101.675 mm, the central diameter of journal 3 is 101.637 mm, the central diameter of journal 4 is 101.600 mm, the central diameter of journal 5 is 101.645 mm, the central diameter of journal 6 is 101.677 mm, and the central diameter of journal 7 is 101.712 mm. The difference between the two ends and the center of journal 1 is 0.110 mm, the difference between the two ends and the center of journal 2 is 0.130 mm, the difference between the two ends and the center of journal 3 is 0.158 mm, the difference between the two ends and the center of journal 4 is 0.201 mm, the difference between the two ends and the center of journal 5 is 0.160 mm, the difference between the two ends and the center of journal 6 is 0.122 mm, and the difference between the two ends and the center of journal 7 is 0.091 mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod journals 1, 2, 3, 4, 5, and 6 are the same, D2 - (0.15 ± 0.005) mm, where D2 is the target diameter of the connecting rod journals required for the finished crankshaft, and D2 is 90 mm. The diameters at both ends of connecting rod journal 1 are 89.855 mm, connecting rod journal 2 is 89.847 mm, connecting rod journal 3 is 89.852 mm, connecting rod journal 4 is 89.850 mm, connecting rod journal 5 is 89.845 mm, and connecting rod journal 6 is 89.849 mm. mm; the middle diameter of connecting rod neck 1 is 89.814 mm, the middle diameter of connecting rod neck 2 is 89.780 mm, the middle diameter of connecting rod neck 3 is 89.753 mm, the middle diameter of connecting rod neck 4 is 89.740 mm, the middle diameter of connecting rod neck 5 is 89.780 mm, and the middle diameter of connecting rod neck 6 is 89.797 mm; among which, the difference between the two ends and the middle of connecting rod neck 1 is 0.041 mm, the difference between the two ends and the middle of connecting rod neck 2 is 0.067 mm, the difference between the two ends and the middle of connecting rod neck 3 is 0.099 mm, the difference between the two ends and the middle of connecting rod neck 4 is 0.110 mm, the difference between the two ends and the middle of connecting rod neck 5 is 0.065 mm, and the difference between the two ends and the middle of connecting rod neck 6 is 0.052 mm; S3. The second crankshaft is subjected to first quenching and second quenching to obtain the third crankshaft. The third crankshaft is then subjected to rough grinding and fine grinding to obtain a non-quenched and tempered steel crankshaft for high-horsepower engines. The first quenching method is as follows: The main journals 1, 3, 4, 5, 6, and 7 of the second crankshaft are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 60 rpm. Specifically, the medium-frequency voltage of main journal 1 is 79% of the set value, with a heating time of 18 seconds and a cooling time of 13 seconds; the medium-frequency voltage of main journal 3 is 80% of the set value, with a heating time of 18 seconds and a cooling time of 13 seconds; the medium-frequency voltage of main journal 5 is 80% of the set value, with a heating time of 18 seconds and a cooling time of 13 seconds. The heating time for the first connecting rod is 13 seconds; the intermediate frequency voltage of the main spindle neck seven is 79% of the set value, the heating time is 17 seconds, and the cooling time is 12 seconds; the intermediate frequency voltage of the connecting rod neck one is 74% of the set value, the heating time is 15 seconds, and the cooling time is 11 seconds; the intermediate frequency voltage of the connecting rod neck three is 74% of the set value, the heating time is 15 seconds, and the cooling time is 11 seconds; the intermediate frequency voltage of the connecting rod neck four is 75% of the set value, the heating time is 16 seconds, and the cooling time is 12 seconds; the intermediate frequency voltage of the connecting rod neck six is ​​75% of the set value, the heating time is 16 seconds, and the cooling time is 12 seconds. The second quenching method is as follows: The second crankshaft's main journal 2, connecting rod journal 2, main journal 4, connecting rod journal 5, and main journal 6 are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 50 rpm. Specifically, the medium-frequency voltage of main journal 2 is 77% of the set value, with a heating time of 16 seconds and a cooling time of 12 seconds; the medium-frequency voltage of main journal 4 is 78% of the set value, with a heating time of 17 seconds and a cooling time of 13 seconds; the medium-frequency voltage of main journal 6 is 78% of the set value, with a heating time of 17 seconds and a cooling time of 13 seconds; the medium-frequency voltage of connecting rod journal 2 is 72% of the set value, with a heating time of 14 seconds and a cooling time of 11 seconds; and the medium-frequency voltage of connecting rod journal 5 is 73% of the set value, with a heating time of 15 seconds and a cooling time of 12 seconds. The first and second quenching processes use PAG quenching fluid with a concentration of 10.1% and a temperature of 29℃ for cooling.

[0031] The third crankshaft was inspected, and the results showed that the runout of main journal 1 was 0.11 mm, main journal 2 was 0.14 mm, main journal 3 was 0.16 mm, main journal 4 was 0.19 mm, main journal 5 was 0.20 mm, main journal 6 was 0.17 mm, and main journal 7 was 0.13 mm. Similarly, the runout of connecting rod journal 1 was 0.05 mm, connecting rod journal 2 was 0.07 mm, connecting rod journal 3 was 0.12 mm, connecting rod journal 4 was 0.15 mm, connecting rod journal 5 was 0.09 mm, and connecting rod journal 6 was 0.07 mm.

[0032] Example 3

[0033] A method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, the specific steps of which are as follows: S1. Obtain a non-quenched and tempered steel crankshaft blank sample, and forge the non-quenched and tempered steel crankshaft blank sample to obtain the first crankshaft; The composition of the non-quenched and tempered steel crankshaft billet, by mass percentage, is: C: 0.38%, Si: 0.65%, Mn: 1.46%, P: 0.010%, S: 0.037%, Cr: 0.19%, Al: 0.043%, Mg: 0.0032%, O: 0.0010%, N: 0.019%, H: 0.0001%, with the balance being Fe and unavoidable impurities. The Mn / S ratio is 39.46, and the Al / N ratio is 2.26. The austenitic... The bulk grain size is grade 8, and the banded structure is grade 2.0. Under normalizing and quenching conditions, the end hardenability of the non-quenched and tempered steel crankshaft billet is: J1.5=55HRC, J3.0=54HRC, J5.0=53HRC. The normalizing temperature is 882℃ and the quenching temperature is 873℃. The forging heating temperature is 1239-1273℃, and the forging holding time is 65-75s. Forging also includes hot trimming and hot straightening after forging. After hot straightening, the straightness is 0.67-0.98mm. S2. The first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle. The specific machining methods are as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined into an ingot shape, higher at both ends and lower in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, all being D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft. 0.7mm, the diameters of the two ends of main journal one are 106.802mm, the diameters of the two ends of main journal two are 106.805mm, the diameters of the two ends of main journal three are 106.796mm, the diameters of the two ends of main journal four are 106.795mm, the diameters of the two ends of main journal five are 106.801mm, the diameters of the two ends of main journal six are 106.797mm, and the diameters of the two ends of main journal seven are 106.795mm; main spindle The central diameter of journal 1 is 106.697 mm, the central diameter of journal 2 is 106.695 mm, the central diameter of journal 3 is 106.644 mm, the central diameter of journal 4 is 106.603 mm, the central diameter of journal 5 is 106.652 mm, the central diameter of journal 6 is 106.684 mm, and the central diameter of journal 7 is 106.705 mm. The difference between the two ends and the center of journal 1 is 0.105 mm, the difference between the two ends and the center of journal 2 is 0.110 mm, the difference between the two ends and the center of journal 3 is 0.152 mm, the difference between the two ends and the center of journal 4 is 0.192 mm, the difference between the two ends and the center of journal 5 is 0.149 mm, the difference between the two ends and the center of journal 6 is 0.113 mm, and the difference between the two ends and the center of journal 7 is 0.090 mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod journals 1, 2, 3, 4, 5, and 6 are the same, D2 - (0.15 ± 0.005) mm, where D2 is the target diameter of the connecting rod journals required for the finished crankshaft, and D2 is 100 mm. The diameters at both ends of connecting rod journal 1 are 99.845 mm, connecting rod journal 2 are 99.851 mm, connecting rod journal 3 are 99.852 mm, connecting rod journal 4 are 99.849 mm, connecting rod journal 5 are 99.855 mm, and connecting rod journal 6 are 99.847 mm. mm; the middle diameter of connecting rod neck 1 is 99.800 mm, the middle diameter of connecting rod neck 2 is 99.781 mm, the middle diameter of connecting rod neck 3 is 99.762 mm, the middle diameter of connecting rod neck 4 is 99.748 mm, the middle diameter of connecting rod neck 5 is 99.793 mm, and the middle diameter of connecting rod neck 6 is 99.798 mm; among them, the difference between the two ends and the middle of connecting rod neck 1 is 0.045 mm, the difference between the two ends and the middle of connecting rod neck 2 is 0.070 mm, the difference between the two ends and the middle of connecting rod neck 3 is 0.090 mm, the difference between the two ends and the middle of connecting rod neck 4 is 0.101 mm, the difference between the two ends and the middle of connecting rod neck 5 is 0.062 mm, and the difference between the two ends and the middle of connecting rod neck 6 is 0.049 mm; S3. The second crankshaft is subjected to first quenching and second quenching to obtain the third crankshaft. The third crankshaft is then subjected to rough grinding and fine grinding to obtain a non-quenched and tempered steel crankshaft for high-horsepower engines. The first quenching method is as follows: The main journals 1, 3, 4, 5, 6, and 7 of the second crankshaft are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 55 rpm. Specifically, the medium-frequency voltage of main journal 1 is 80% of the set value, the heating time is 18 seconds, and the cooling time is 13 seconds; the medium-frequency voltage of main journal 3 is 81% of the set value, the heating time is 19 seconds, and the cooling time is 14 seconds; the medium-frequency voltage of main journal 5 is 80% of the set value, the heating time is 18 seconds, and the cooling time is... The heating time for the first connecting rod is 12 seconds; the intermediate frequency voltage of the main spindle neck seven is 79% of the set value, the heating time is 19 seconds, and the cooling time is 13 seconds; the intermediate frequency voltage of the connecting rod neck one is 75% of the set value, the heating time is 16 seconds, and the cooling time is 11 seconds; the intermediate frequency voltage of the connecting rod neck three is 76% of the set value, the heating time is 16 seconds, and the cooling time is 12 seconds; the intermediate frequency voltage of the connecting rod neck four is 75% of the set value, the heating time is 16 seconds, and the cooling time is 13 seconds; the intermediate frequency voltage of the connecting rod neck six is ​​75% of the set value, the heating time is 16 seconds, and the cooling time is 13 seconds. The second quenching method is as follows: The second crankshaft's main journal 2, connecting rod journal 2, main journal 4, connecting rod journal 5, and main journal 6 are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 45 rpm. Specifically, the medium-frequency voltage of main journal 2 is 78% of the set value, with a heating time of 18 seconds and a cooling time of 14 seconds; the medium-frequency voltage of main journal 4 is 79% of the set value, with a heating time of 18 seconds and a cooling time of 13 seconds; the medium-frequency voltage of main journal 6 is 79% of the set value, with a heating time of 17 seconds and a cooling time of 12 seconds; the medium-frequency voltage of connecting rod journal 2 is 73% of the set value, with a heating time of 15 seconds and a cooling time of 12 seconds; and the medium-frequency voltage of connecting rod journal 5 is 74% of the set value, with a heating time of 16 seconds and a cooling time of 13 seconds. The first and second quenching processes use PAG quenching fluid with a concentration of 11.4% and a temperature of 26℃ for cooling.

[0034] The third crankshaft was inspected, and the results showed that the runout of main journal 1 was 0.08 mm, main journal 2 was 0.11 mm, main journal 3 was 0.17 mm, main journal 4 was 0.23 mm, main journal 5 was 0.19 mm, main journal 6 was 0.16 mm, and main journal 7 was 0.13 mm. Similarly, the runout of connecting rod journal 1 was 0.06 mm, connecting rod journal 2 was 0.09 mm, connecting rod journal 3 was 0.13 mm, connecting rod journal 4 was 0.18 mm, connecting rod journal 5 was 0.12 mm, and connecting rod journal 6 was 0.07 mm.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S2, the first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are not ingot-shaped with high ends and low middle. The specific machining method is as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined to have the same diameter at both ends and in the middle. The diameters at both ends and in the middle of main journals 1, 2, 3, 4, 5, 6, and 7 are all the same, D1-(0.20±0.005)mm, where D1 is the target diameter value for the main journals required for the finished crankshaft, and D1 is 105mm. The diameters at both ends of main journal 1 are 104.802mm, main journal 2 is 104.801mm, and main journal 3 is 104.800mm. The diameters at both ends of journal four are 104.802 mm, the diameters at both ends of journal five are 104.801 mm, the diameters at both ends of journal six are 104.801 mm, and the diameters at both ends of journal seven are 104.800 mm; the middle diameters of journal one, journal two, journal three, journal four, journal five, journal six, and journal seven are 104.800 mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined to have the same diameter at both ends and in the middle. The diameters at both ends and in the middle of connecting rod journals 1, 2, 3, 4, 5, and 6 are all the same, D2 - (0.15 ± 0.005) mm, where D2 is the target diameter value for the connecting rod journals required for the finished crankshaft, and D2 is 95 mm. The diameters at both ends of connecting rod journal 1 are 94.850 mm, the diameters at both ends of connecting rod journal 2 are 94.851 mm, and the diameters at both ends of connecting rod journal 3 are... The diameters of the four connecting rod necks are 94.853 mm, the diameters of the five connecting rod necks are 94.851 mm, and the diameters of the six connecting rod necks are 94.850 mm. The middle diameters of the first connecting rod neck, the second connecting rod neck, the third connecting rod neck, the fourth connecting rod neck, the fifth connecting rod neck, and the sixth connecting rod neck are all 94.851 mm. The remaining steps are the same as in Example 1.

[0036] The third crankshaft was inspected, and the results showed that the runout of main journal 1 was 0.22 mm, main journal 2 was 0.27 mm, main journal 3 was 0.38 mm, main journal 4 was 0.40 mm, main journal 5 was 0.36 mm, main journal 6 was 0.25 mm, and main journal 7 was 0.19 mm. Similarly, the runout of connecting rod journal 1 was 0.17 mm, connecting rod journal 2 was 0.21 mm, connecting rod journal 3 was 0.35 mm, connecting rod journal 4 was 0.32 mm, connecting rod journal 5 was 0.24 mm, and connecting rod journal 6 was 0.20 mm.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S3, the second crankshaft is subjected to a single quenching to obtain the third crankshaft. Specifically, the single quenching method involves simultaneously performing medium-frequency induction hardening and cooling on the main journals 1, 2, 3, 4, 5, 6, and 7 of the second crankshaft, as well as connecting rod journals 1, 2, 3, 4, 5, and 6. The medium-frequency voltage of main journal 1 is 80% of a set value. The heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of spindle journal two is 80% of the set value. The heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of spindle journal three is 80% of the set value. The heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of spindle journal four is 80% of the set value. The heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of spindle journal five is 80% of the set value. The heating time is 18s, and the cooling time is 14s. The heating time is 14s, the intermediate frequency voltage of main shaft journal six is ​​80% of the set value, the heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of main shaft journal seven is 80% of the set value, the heating time is 18s, and the cooling time is 14s. The intermediate frequency voltage of connecting rod journal one is 75% of the set value, the heating time is 16s, and the cooling time is 13s. The intermediate frequency voltage of connecting rod journal two is 75% of the set value, the heating time is 16s, and the cooling time is 13s. The intermediate frequency voltage of connecting rod journal three is 75% of the set value, the heating time is 16s, and the cooling time is 13s. The intermediate frequency voltage of connecting rod journal four is 75% of the set value, the heating time is 16s, and the cooling time is 13s. The intermediate frequency voltage of connecting rod journal five is 75% of the set value, the heating time is 16s, and the cooling time is 13s. The intermediate frequency voltage of connecting rod journal six is ​​75% of the set value, the heating time is 16s, and the cooling time is 13s. The remaining steps are the same as in Example 1.

[0038] The third crankshaft was inspected, and the results showed that the runout of main journal 1 was 0.17 mm, main journal 2 was 0.22 mm, main journal 3 was 0.27 mm, main journal 4 was 0.35 mm, main journal 5 was 0.28 mm, main journal 6 was 0.19 mm, and main journal 7 was 0.15 mm. Similarly, the runout of connecting rod journal 1 was 0.11 mm, connecting rod journal 2 was 0.19 mm, connecting rod journal 3 was 0.32 mm, connecting rod journal 4 was 0.29 mm, connecting rod journal 5 was 0.16 mm, and connecting rod journal 6 was 0.12 mm.

[0039] As can be seen from the above embodiments and comparative examples: Embodiment 1, combined with Comparative Example 1, shows that machining the cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft into an ingot shape with high ends and low middle reduces the runout of the main journal and connecting rod journal in the third crankshaft; Embodiment 1, combined with Comparative Example 2, shows that performing a two-step quenching method on the second crankshaft to obtain the third crankshaft reduces the runout of the main journal and connecting rod journal in the third crankshaft; Combining Embodiments 1-3 and Comparative Examples 1-2, it can be seen that by using the original deformation pre-reservation method and two-step induction quenching, the runout of the main journal in the third crankshaft is ≤0.25mm, and the runout of the connecting rod journal in the third crankshaft is ≤0.20mm, which is only half of the industry average of 0.40-0.50mm. Thus, the grinding amount of the main journal and connecting rod journal in the third crankshaft is greatly reduced, and the incidence of grinding cracks is reduced to ≤0.20%, reaching the top level in the industry.

[0040] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine, characterized in that, Includes the following steps: S1. Obtain a non-quenched and tempered steel crankshaft blank sample, and forge the non-quenched and tempered steel crankshaft blank sample to obtain a first crankshaft; S2. The first crankshaft is machined to obtain the second crankshaft. The cylindrical surfaces of the main journal and connecting rod journal of the second crankshaft are ingot-shaped with high ends and low middle. S3. The second crankshaft is subjected to first quenching and second quenching to obtain a third crankshaft. The third crankshaft is subjected to rough grinding and fine grinding to obtain a non-quenched and tempered steel crankshaft for high-horsepower engines. In step S3, the first quenching method specifically involves simultaneously performing medium-frequency induction quenching and cooling on the main journals 1, 3, 4, 5, 6, and 7 of the second crankshaft at a rotation speed of 50-60 rpm. Specifically, the medium-frequency voltage of main journals 1, 3, 5, and 7 is 79%-81% of a set value, the heating time is 17-19 seconds, and the cooling time is 12-14 seconds. The medium-frequency voltage of connecting rods 1, 3, 4, and 6 is 74%-76% of a set value, and the heating time is... The second quenching method is as follows: the second crankshaft's main journal 2, connecting rod journal 2, main journal 4, connecting rod journal 5, and main journal 6 are simultaneously subjected to medium-frequency induction quenching and cooling at a rotation speed of 40-50 rpm. The medium-frequency voltage of main journal 2, main journal 4, and main journal 6 is 77%-79% of the set value, the heating time is 16-18s, and the cooling time is 12-14s; the medium-frequency voltage of connecting rod journal 2 and connecting rod journal 5 is 72%-74% of the set value, the heating time is 14-16s, and the cooling time is 11-13s.

2. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S1, the composition of the non-quenched and tempered steel crankshaft billet, by mass percentage, is as follows: C: 0.37%-0.40%, Si: 0.60%-0.70%, Mn: 1.40%-1.50%, P≤0.015%, S: 0.030%-0.045%, Cr: 0.15%-0.25%, Al: 0.035%-0.050%, Mg: 0.0020%-0.0045%, O: 0.0003-0.0016%, N: 0.016%-0.022%, H≤0.0002%, with the balance being Fe and unavoidable impurities, and 30≤Mn / S≤50, 1.9≤Al / N≤3.

5.

3. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S1, the austenite grain size of the non-quenched and tempered steel crankshaft billet is grade 7-9, and the banded structure is grade ≤2.

0. Under the conditions of normalizing temperature and quenching temperature, the end hardenability of the non-quenched and tempered steel crankshaft billet is: J1.5=53-58HRC, J3.0=52-57HRC, J5.0=49-55HRC. The normalizing temperature is 880±5℃, and the quenching temperature is 870±5℃.

4. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S1, the heating temperature of the forging is 1230-1280℃, the holding time of the forging is 65-75s, and the forging also includes: hot trimming and hot correction after forging, and the straightness after hot correction is ≤1.2mm.

5. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S2, the machining method is specifically as follows: The cylindrical surfaces of main journals 1, 2, 3, 4, 5, 6, and 7 are machined into an ingot shape, higher at both ends and lower in the middle. The diameters at both ends of main journals 1, 2, 3, 4, 5, 6, and 7 are the same, D1-(0.20±0.005)mm, where D1 is the target diameter of the main journals required for the finished crankshaft, and D1 is 100-110mm. The difference between the two ends and the middle of main journal 1... The values ​​are 0.10±0.01mm, the difference between the two ends and the middle of the second main journal is 0.12±0.01mm, the difference between the two ends and the middle of the third main journal is 0.15±0.01mm, the difference between the two ends and the middle of the fourth main journal is 0.20±0.01mm, the difference between the two ends and the middle of the fifth main journal is 0.15±0.01mm, the difference between the two ends and the middle of the sixth main journal is 0.12±0.01mm, and the difference between the two ends and the middle of the seventh main journal is 0.10±0.01mm. The cylindrical surfaces of connecting rod journals 1, 2, 3, 4, 5, and 6 are machined into a yuanbao shape, higher at both ends and lower in the middle. The diameters at both ends of connecting rod journals 1, 2, 3, 4, 5, and 6 are the same, D2-(0.15±0.005)mm, where D2 is the target diameter of the connecting rod journals required for the finished crankshaft, and D2 is 90-100mm. Specifically, connecting rod journal 1... The difference between the two ends and the middle is 0.05±0.01mm; the difference between the two ends and the middle of the second connecting rod neck is 0.07±0.01mm; the difference between the two ends and the middle of the third connecting rod neck is 0.10±0.01mm; the difference between the two ends and the middle of the fourth connecting rod neck is 0.10±0.01mm; the difference between the two ends and the middle of the fifth connecting rod neck is 0.07±0.01mm; and the difference between the two ends and the middle of the sixth connecting rod neck is 0.05±0.01mm.

6. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S3, the first quenching and the second quenching are cooled using PAG quenching liquid with a concentration of 10-13% and a temperature of 23-29℃.

7. The method for preparing a non-quenched and tempered steel crankshaft for a high-horsepower engine according to claim 1, characterized in that, In step S3, the runout of the main journal in the third crankshaft is ≤0.25mm, and the runout of the connecting rod journal in the third crankshaft is ≤0.20mm.

8. A non-quenched and tempered steel crankshaft for a high-horsepower engine, characterized in that, The crankshaft is prepared using the method described in any one of claims 1-7 for a high-horsepower engine made of non-quenched and tempered steel.

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