Nbx-Vy-Tiz composite microalloyed non-quenched and tempered steel for high detonation pressure crankshaft and preparation method of Nbx-Vy-Tiz composite microalloyed non-quenched and tempered steel

Abstract

The invention discloses Nbx-Vy-Tiz composite microalloyed non-quenched and tempered steel for a high detonation pressure crankshaft. The Nbx-Vy-Tiz composite microalloyed non-quenched and tempered steel comprises the following components in percentage by weight: 0.35-0.45% of C; mn: 1 to 1.45%; 0.9 to 1.6 percent of Si; p is less than or equal to 0.035%; s is 0.04 to 0.065 percent; cr: 0.1 to 0.4%; 0.01 to 0.04 percent of Al; the content of N is 0.011 to 0.02 percent; x% of Nb, y% of Ti and z% of V; and the balance of Fe and inevitable impurities. X + y + z is less than or equal to 0.40, and z is more than 0.15 and less than 0.25. The invention also discloses a preparation method. The problems that traditional ferrite and pearlite type non-quenched and tempered steel for the crankshaft is insufficient in tensile strength and fatigue strength, and bainite non-quenched and tempered steel is low in fatigue strength, poor in machining performance and high in cost are solved. Provided is a non-quenched and tempered steel having high tensile strength, high fatigue strength, and low processing cost.

Description

Technical Field

[0001] The present invention relates to the field of non-quenched and tempered steel for automobile crankshafts, and in particular to a Nb x -V y -Ti z Composite microalloyed non-quenched and tempered steel and preparation method thereof. Background Art

[0002] With the development of society, the demand for high-efficiency, high-explosive automobile engines and their engine steel has expanded accordingly. The crankshaft is the core component of the automobile engine, bearing the impact of the high explosion pressure of the engine, thereby transmitting the power generated by the engine. Therefore, the quality of the crankshaft directly determines the reliability and service life of the engine, so the crankshaft steel also needs to meet the requirements of high-efficiency, high-explosive automobile engines. The materials used for engine crankshafts are subject to torsional stress and bending stress during use, which also means that the crankshaft steel needs to have the characteristics of high tensile strength, high fatigue strength, and good plastic-toughness matching.

[0003] Non-quenched and tempered steel has the characteristics of high performance and low cost, so it is more and more widely used in automotive parts. At present, the commonly used non-quenched and tempered steel for automotive crankshafts is ferrite + pearlite non-quenched and tempered steel. The strength level of traditional ferrite + pearlite non-quenched and tempered steel is usually 700-1000MPa, and the fatigue strength, plasticity and toughness are poor. For example, 38MnVS6, Rp0.2≥550MPa, Rm≥850MPa, elongation after fracture A≥12%, and cross-sectional shrinkage ≥25%. It cannot meet the high performance requirements of high-explosion compression crankshafts in the automotive industry. In addition, although bainitic crankshaft non-quenched and tempered steel has become a research hotspot today, it has not been widely used in industry due to its complex process and high cost. The main reason is that bainitic steel is a medium-temperature transformation metastable structure after forging and cooling, with high volume free energy and a tendency to transform to an equilibrium structure. Therefore, it must be tempered to meet the performance requirements. In addition, its material hardness is about 340-370HBW, and it is difficult to process. In particular, the grinding and drilling of the crankshaft after surface quenching is more difficult and is more prone to grinding cracks.

[0004] Therefore, in order to prepare crankshafts that meet the requirements of high-efficiency, high-explosion engines, it is necessary to develop non-quenched and tempered steels with high tensile strength, high fatigue strength, good plasticity and toughness matching, low cost and easy processing, so as to improve the crankshaft's strength and service life under the operation of high-explosion pressure engines, so as to keep up with the current development trend of the automotive engine industry. Summary of the invention

[0005] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a Nb x -V y-Ti z Composite microalloyed non-quenched and tempered steel and its preparation method solve the problems of insufficient tensile strength and fatigue strength of traditional ferrite + pearlite non-quenched and tempered steel for crankshafts, low fatigue strength, poor processing performance and high cost of bainite non-quenched and tempered steel; provide non-quenched and tempered steel with high tensile strength, high fatigue strength and low processing cost suitable for high explosion pressure engine crankshafts.

[0006] Technical solution: The present invention is a kind of Nb for high-explosive compression crankshaft x -V y -Ti z Composite microalloyed non-quenched and tempered steel, characterized in that it comprises the following components in weight percentage: C: 0.35%-0.45%; Mn: 1.00%-1.45%; Si: 0.90%-1.60%; P≤0.035%; S: 0.040%-0.065%; Cr: 0.10%-0.40%; Al: 0.010%-0.040%; N: 0.011%-0.020%; Nb: x%, Ti: y%, V: z%; the rest are Fe and unavoidable impurities; wherein x+y+z≤0.40, 0.15<z<0.25.

[0007] The high explosion pressure crankshaft of the present invention is made of Nb x -V y -Ti z The preparation method of composite microalloyed non-quenched and tempered steel is characterized by: adopting the method of EAF smelting → LF refining → VD vacuum treatment → light reduction process square billet continuous casting → rolling → pit slow cooling → straightening and peeling → flaw detection → induction heating → forging → controlled cooling after forging → pile cooling.

[0008] In the EAF smelting, the electric furnace end point carbon is controlled to be ≥0.06%, the end point phosphorus is ≤0.015%, an eccentric furnace bottom is used for slag-free steel tapping, refined slag and silicon-manganese alloy are added to the ladle for pre-deoxidation during the steel tapping process, and an infrared device is used to control the slag removal.

[0009] In the LF refining, in order to ensure that the contents of Nb, Ti and V meet the composition design, ferroniobium, ferrotitanium and ferrovanadium intermediate alloys are added in small amounts multiple times, and the refining time is between 35 minutes and 45 minutes.

[0010] Among them, in the VD vacuum treatment, the treatment is carried out for 15min-20min at a vacuum degree of less than 1mbar, the Al, N, and Ti contents are fine-tuned, and the soft blowing time is ensured to be 15min-20min after breaking the vacuum.

[0011] Among them, in the light reduction process for continuous casting of square billets, the large-section continuous casting machine uses electromagnetic stirring + light reduction continuous casting at the end of solidification, the superheat is 15°C-30°C, in order to reduce the segregation of components such as Ti, C, Si, S, the continuous casting temperature is 1510°C-1520°C, the light reduction amount is 5.5mm-7.5mm, and the size of the continuously cast square billet is 300mm-450mm.

[0012] Among them, in the rolling, rolling heating: the rolling heating temperature is 950℃-1250℃, and the total heating time is ≥340min; rolling dephosphorization: high-pressure water descaling is used, and the pressure is ≥13MPa.

[0013] Among them, in the rolling, the temperature-controlled rolling process: the starting rolling temperature is 1050℃-1150℃, after large pressure reduction and multiple rolling, the final rolling temperature is 950℃-1050℃, realizing continuous temperature-controlled rolling.

[0014] Among them, in the slow cooling in the pit, the cooling process is controlled: after rolling, the steel is cooled on a step-type cooling bed, the temperature of the upper cooling bed is controlled below 750°C, the upper cooling bed is cooled evenly, and the steel is cooled in the pit at 550°C-600°C for slow cooling.

[0015] Among them, in the above-mentioned flaw detection, ultrasonic flaw detection and magnetic leakage flaw detection: the accuracy of ultrasonic flaw detection meets the A-level requirement of GB / T 4162, and the surface defect depth is ≤0.30mm.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention solves the problems of insufficient tensile strength and fatigue strength of non-quenched and tempered steel for crankshafts of traditional ferrite + pearlite type, low fatigue strength, poor processing performance and high cost of bainite non-quenched and tempered steel; by designing and optimizing the chemical composition and regulating the process parameters of each step, non-quenched and tempered steel with high tensile strength, high fatigue strength and low processing cost suitable for high explosion pressure engine crankshafts is produced. The yield strength Rp0.2 of the non-quenched and tempered steel obtained by the present invention is ≥700MPa, the tensile strength Rm is 1030-1100MPa; the elongation after fracture A is ≥12%, the section shrinkage Z is ≥40%, and the fatigue bending moment is ≥900NM. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the metallographic structure diagram of round steel of the present invention;

[0018] Figure 2 This is a diagram of the 8.5 grade austenite grain size of the round steel of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0020] The present invention increases a small amount of C, Si, and Mn while adding a trace amount of Nb, V, and Ti, removes Mo and Ni elements, and adjusts the hardness, strength, fatigue, and processability of the non-quenched and tempered steel of the present invention, which directly affect the performance of the crankshaft, to a range of excellent comprehensive values ​​through the deployment of multi-element microalloying. The addition of Nb, V, and Ti composite microalloying elements makes it easier for the precipitated second phase particles such as carbides, nitrides, and carbon-nitrogen composite compounds to disperse and precipitate and pin the grain boundaries, thereby achieving the purpose of refining the grain structure and adjusting the pearlite lamella spacing, thereby improving the strength, hardness, and fatigue performance of the ferrite + pearlite non-quenched and tempered steel. At the same time, a small amount of S is added to promote the formation of sulfides such as MnS. At the same time, the second phase particles formed by the addition of Nb, V, and Ti provide nucleation points for the later precipitated MnS, thereby making the sulfides precipitate more dispersedly, and making MnS exist in a spherical or spindle-shaped state, thereby reducing the difficulty of cold processing such as grinding and drilling.

[0021] When adding trace amounts of Nb: x%, Ti: y%, V: z%, where x+y+z≤0.40, 0.15<z<0.25, the Nb element of non-quenched and tempered steel mainly exists in the form of dispersed carbides, the vast majority of V elements (about 80%) are in solid solution, and almost all of Ti elements are in carbonitrides M(C,N). In this regard, Nb+V+Ti is used for composite microalloying. On the one hand, it ensures the appropriate amount of NbC dispersed distribution and refines all grains. On the other hand, there is an appropriate amount of undissolved Ti-rich M(C,N) to inhibit grain growth during austenitizing heating, and at the same time, there are appropriate amounts of dissolved V and Ti to play a solid solution strengthening role.

[0022] Under the action of Nb, V and Ti alloy elements, the main effects of other elements are as follows:

[0023] C, N: When the content is 0.3%-0.4%, it has an effective content for improving the strength, hardness and hardenability of non-quenched and tempered steel. In the present invention, the C content is appropriately increased to 0.35%-0.45%, which improves the strength, hardness and hardenability of non-quenched and tempered steel and ensures the hardness of the induction quenching layer on the crankshaft surface. Its main function is that due to the addition of Nb, V and Ti alloy elements, C needs to be appropriately increased to fully form corresponding NbC, VC, TiC strong carbides and part of NbC-NbN, VC-VN, TiC-TiN carbon-nitrogen composite precipitates, thereby appropriately reducing the generation of TiN, effectively avoiding the coarse TiN particles precipitated in liquid during hot working, and then refining the grains of non-quenched and tempered steel, especially refining the ferrite structure to 35μm-50μm, thereby achieving the best nucleation state, and finally improving the strength, hardness and fatigue strength of non-quenched and tempered steel.

[0024] Si: About 0.6% is added to the traditional ferrite + pearlite non-adjustable steel. The present invention adds Si to 0.90%-1.60%, part of which is a deoxidizer to remove harmful gases in the steel. Since Si has a strong solid solution strengthening effect, under the joint action of Nb, V, and Ti microalloying, more and more dispersed second phase structures are formed, pinned to the edge of the grain boundary, continuously promoting the formation and precipitation of pearlite, and reducing the pearlite lamella spacing, thereby improving the dislocation energy of the alloy material, thereby improving the strength, hardness and corrosion resistance of the alloy material.

[0025] S, Mn: Mn is an effective element for deoxidation and desulfurization in steel, and can also improve the hardenability and strength of steel. While the strength and hardness of steel are improved, its machinability will deteriorate. Therefore, adding an appropriate amount of S element promotes the formation of sulfides such as MnS. At the same time, the second phase particles formed by the addition of Nb, V, and Ti inhibit the formation of long MnS during hot working, so that MnS always exists in a spherical or spindle-shaped state, making it easy to break chips during the processing of steel and reducing the difficulty of cold working such as grinding and drilling.

[0026] Embodiment 1:

[0027] The high explosion pressure crankshaft of this embodiment is made of Nb x -V y -Ti z The composite microalloyed non-quenched and tempered steel has the following chemical compositions by weight percentage: C: 0.40%, Mn: 1.28%, Si: 1.20%, P: 0.011%, S: 0.060%, Cr: 0.30%, Al: 0.020%, N: 0.0182%, Nb: x%, Ti: y%, V: z%, and the rest are Fe and unavoidable impurities. Among them, x=0.022, y=0.014, z=0.23, and x+y+z=0.266<0.40, 0.15<z<0.25 are satisfied at the same time.

[0028] In the EAF smelting process: control the electric furnace end carbon to 0.10% and the end phosphorus to 0.011%. In the F refining process: ensure that the white slag time is 42 minutes, and at the end of the LF, except for Al, S and other easily burned elements, the rest are controlled according to the judgment limit. In the VD vacuum treatment process: treat for 18 minutes at a vacuum degree of less than 1mbar, fine-tune the Al, N, and Ti contents, and ensure the soft blowing time of 16 minutes after breaking the vacuum. Large-section continuous casting machine electromagnetic stirring + light pressure continuous casting at the end of solidification, superheat 28℃. Rolling heating: rolling heating temperature 965℃-1238℃, total heating time 410min. Rolling dephosphorization: use high-pressure water to remove scales, pressure 18MPa. Temperature-controlled rolling process: rolling start temperature 1080℃, after large pressure billet opening, multiple rolling, final rolling temperature 980℃, to achieve continuous temperature-controlled rolling. In the controlled cooling process: after rolling, the steel is cooled on a step-type cooling bed, the upper cooling bed temperature is 720℃, the upper cooling bed is cooled evenly, and the steel is slowly cooled in a pit at 570℃.

[0029] Result analysis: The round bar specification is 170mm, the number of crankshafts processed is 100, the number of microcracks produced is 0, the chips are "C-shaped", the tool is damaged 0, the crankshaft surface quenching hardness is 55HRC, the yield strength is 710MPa, the tensile strength is 1060MPa, the elongation is 15%, the surface reduction is 50%, the hardness is 300HBW, the fatigue bending moment is ≥900NM, and the grain size is level 5. The grain size of traditional crankshaft forgings is level 3, and the grain size of existing forgings is level 5.

[0030] Embodiment 2:

[0031] The high explosion pressure crankshaft of this embodiment is made of Nb x -V y -Ti z The composite microalloyed non-quenched and tempered steel has the following chemical compositions by weight percentage: C: 0.41%, Mn: 1.28%, Si: 1.25%, P: 0.035%, S: 0.055%, Cr: 0.32%, Al: 0.022%, N: 0.0170%, Nb: x%, Ti: y%, V: z%, and the rest are Fe and unavoidable impurities. Among them, x=0.023, y=0.016, z=0.23, and x+y+z=0.269<0.40, 0.15<z<0.25 are satisfied at the same time.

[0032] In the EAF smelting process: control the electric furnace end carbon to 0.08% and the end phosphorus to 0.010%. In the LF refining process: ensure that the white slag time is 40min. At the end of the LF, except for the easily burnt elements such as Al and S, the rest are controlled according to the judgment limit. In the VD vacuum treatment process: treat for 17min at a vacuum degree of less than 1mbar, fine-tune the Al, N, and Ti contents, and ensure the soft blowing time of 18min after breaking the vacuum. Large-section continuous casting machine electromagnetic stirring + light pressure continuous casting at the end of solidification, superheat 26℃. Rolling heating: rolling heating temperature 970℃-1236℃, total heating time 412min. Rolling dephosphorization: use high-pressure water to remove scale, pressure 18MPa. Temperature-controlled rolling process: rolling start temperature 1078℃, after large pressure billet opening, multi-pass rolling, final rolling temperature 986℃, to achieve continuous temperature-controlled rolling. In the controlled cooling process: after rolling, the steel is cooled on a step-type cooling bed, the upper cooling bed temperature is 710℃, the upper cooling bed is evenly cooled, and the steel is slowly cooled in a pit at 580℃.

[0033] Result analysis: The round bar specification is 150mm, the number of crankshafts processed is 100, the number of microcracks produced is 0, the processing chips are "C-shaped", the tool is damaged 0, the crankshaft surface quenching hardness is 55HRC, the yield strength is 710MPa, the tensile strength is 1060MPa, the elongation is 15%, the surface reduction is 50%, the hardness is 300HBW, the fatigue bending moment is ≥900NM, and the grain size is level 5. The grain size of traditional crankshaft forgings is level 3, and the grain size of existing forgings is level 5.

[0034] Embodiment 3:

[0035] The high explosion pressure crankshaft of this embodiment is made of Nb x -V y -Ti z The composite microalloyed non-quenched and tempered steel has the following chemical compositions by weight percentage: C: 0.43%, Mn: 1.26%, Si: 1.30%, P: 0.013%, S: 0.046%, Cr: 0.25%, Al: 0.019%, N: 0.1680%, Nb: x%, Ti: y%, V: z%, and the rest are Fe and unavoidable impurities. Among them, x=0.022, y=0.018, z=0.22, and x+y+z=0.26<0.40, 0.15<z<0.25.

[0036] In the EAF smelting process: control the electric furnace end carbon to 0.08%, and the end phosphorus to 0.013%. In the LF refining process: ensure that the white slag time is 38 minutes. At the end of the LF, except for Al, S and other easily burned elements, the rest are controlled according to the judgment limit. In the VD vacuum treatment process: treat for 18 minutes at a vacuum degree of less than 1mbar, fine-tune the Al, N, and Ti contents, and ensure the soft blowing time of 18 minutes after breaking the vacuum. Large-section continuous casting machine electromagnetic stirring + light pressure continuous casting at the end of solidification, superheat 25℃. Rolling heating: rolling heating temperature 972℃-1235℃, total heating time 418min. Rolling dephosphorization: use high-pressure water to remove scales, pressure 18MPa. Temperature-controlled rolling process: rolling start temperature 1085℃, after large pressure billet opening, multi-pass rolling, final rolling temperature 987℃, to achieve continuous temperature-controlled rolling. In the controlled cooling process: after rolling, the steel is cooled on a step-type cooling bed, the upper cooling bed temperature is 716℃, the upper cooling bed is cooled evenly, and the steel is slowly cooled in the pit at 574℃.

[0037] Result analysis: The round bar produced is 110mm, 100 crankshafts are processed, 0 grinding microcracks are generated, the machining chips are "C-shaped", 0 tools are damaged, the crankshaft surface quenching hardness is 55HRC, the yield strength is 710MPa, the tensile strength is 1060MPa, the elongation is 15%, the surface reduction is 50%, the hardness is 300HBW, the fatigue bending moment is ≥900NM, and the grain size is 5.5. The grain size of traditional crankshaft forgings is 3, and the grain size of existing forgings is 5.5.

[0038] Table 1

[0039]

[0040] Table 1 (unit: %) is the specification The embodiments and comparative examples of the specific composition of the high-strength non-quenched and tempered steel bars for high-explosion pressure engine crankshafts of embodiments 1-3 of the present invention do not use precious metals such as Mo and Ni, and the alloy cost is better controlled.

[0041] Table 2

[0042]

[0043] Table 2 shows the various properties of the crankshaft forgings of various embodiments and comparative examples. It can be seen from Table 2 that the mechanical properties of the high-strength non-quenched and tempered steel bars for high-explosion compression engine crankshafts of embodiments 1-3 of the present invention have both high strength and plasticity, and the performance far exceeds the performance level of comparative example 1. Comparative example 2 is not conducive to machining due to its excess strength and high hardness.

[0044] Table 3

[0045]

[0046] Table 3 shows the machining performance of the crankshaft forgings of various embodiments and comparative examples. The non-quenched and tempered steel forgings for high-strength crankshafts for high-explosion pressure engine crankshafts of embodiments 1-3 of the present invention have good machining performance.

[0047] In summary, the present invention solves the problems of insufficient tensile strength and fatigue strength of non-quenched and tempered steel for crankshafts of traditional ferrite + pearlite type, low fatigue strength, poor processing performance and high cost of bainite non-quenched and tempered steel; by designing and optimizing the chemical composition and regulating the process parameters of each step, non-quenched and tempered steel with high tensile strength, high fatigue strength and low processing cost suitable for high explosion pressure engine crankshafts is produced. The yield strength Rp0.2 of the non-quenched and tempered steel obtained by the present invention is ≥700MPa, the tensile strength Rm1030-1100MPa; the elongation after fracture A≥12%, the cross-sectional shrinkage Z≥40%, and the fatigue bending moment ≥900NM.

Claims

1. A Nb alloy for high explosive crankshaft x -V y -Ti z Composite microalloyed non-quenched and tempered steel, characterized by: The invention comprises the following components in weight percentage: C: 0.35%-0.45%; Mn: 1.00%-1.45%; Si: 0.90%-1.60%; P≤0.035%; S：0.040％-0.065％； Cr: 0.10%-0.40%; Al: 0.010%-0.040%; N: 0.011%-0.020%; Nb: x%, Ti: y%, V: z%; the rest are Fe and unavoidable impurities; wherein x+y+z≤0.40, 0.15<z<0.

25.

2. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: The product is prepared by the method of EAF smelting → LF refining → VD vacuum treatment → light reduction process square billet continuous casting → rolling → slow cooling in the pit → straightening and peeling → flaw detection → induction heating → forging → controlled cooling after forging → pile cooling.

3. The Nb for high explosion compression crankshaft according to claim 1. x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the EAF smelting, the electric furnace end point carbon is controlled to be ≥0.06%, the end point phosphorus is controlled to be ≤0.015%, an eccentric furnace bottom is used for slag-free steel tapping, refined slag and silicon-manganese alloy are added to the ladle for pre-deoxidation during the steel tapping process, and an infrared device is used to control the slag removal.

4. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the LF refining, ferroniobium, ferrotitanium and ferrovanadium intermediate alloys are added in several batches, and the refining time is between 35 minutes and 45 minutes.

5. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the VD vacuum treatment, the treatment is carried out for 15-20 minutes at a vacuum degree of less than 1 mbar, the contents of Al, N and Ti are fine-tuned, and the soft blowing time is ensured to be 15-20 minutes after breaking the vacuum.

6. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the light reduction process for continuous casting of billets, the large-section continuous casting machine uses electromagnetic stirring + light reduction continuous casting at the end of solidification, the overheat is 15°C-30°C, the continuous casting temperature is 1510°C-1520°C, the light reduction is 5.5mm-7.5mm, and the size of the continuously cast billets is 300mm-450mm.

7. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the rolling, the rolling heating: the rolling heating temperature is 950°C-1250°C, and the total heating time is ≥340min; the rolling dephosphorization: high-pressure water descaling is adopted, and the pressure is ≥13MPa.

8. The Nb2O3 for high explosion compression crankshaft according to claim 7 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the rolling, the temperature-controlled rolling process is as follows: the rolling start temperature is 1050°C-1150°C, after large pressure reduction, blanking, multiple rolling passes, the final rolling temperature is 950°C-1050°C, and continuous temperature-controlled rolling is achieved.

9. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: In the described slow cooling in the pit, the cooling process is controlled: after rolling, the steel is cooled on a step-type cooling bed, the temperature of the upper cooling bed is controlled below 750°C, the upper cooling bed is cooled evenly, and the steel is slowly cooled in the pit at 550°C-600°C.

10. The Nb for high explosion compression crankshaft according to claim 1 x -V y -Ti z The method for preparing composite microalloyed non-quenched and tempered steel is characterized by: Among the above-mentioned flaw detection, ultrasonic flaw detection and magnetic leakage flaw detection: the accuracy of ultrasonic flaw detection meets the A-level requirement of GB / T4162, and the depth of surface defects is ≤0.30mm.

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