Easily-processed crankshaft steel, production method and crankshaft manufactured by using easily-processed crankshaft steel

Abstract

The invention discloses steel for a crankshaft easy to machine, a production method and a crankshaft manufactured through the steel, the steel for the crankshaft easy to machine comprises, by mass, 0.37%-0.45% of C, 0.17%-0.35% of Si, 0.60%-0.80% of Mn, smaller than or equal to 0.025% of S, smaller than or equal to 0.020% of P, 1.00%-1.20% of Cr, smaller than or equal to 0.040% of Al, smaller than or equal to 0.20% of Cu, 0.15%-0.30% of Mo and the balance Fe and inevitable impurities. Electromagnetic stirring is combined with a tail end soft reduction process and a rolling process to improve segregation in a casting blank, a crankshaft is prepared by controlling a quenching process, meanwhile, the internal quality of the steel for the easily-machined crankshaft is controlled by adopting a set of process method, and by combining the use characteristics of the crankshaft, the mechanical property of round steel is ensured, and meanwhile the machining quality is improved. And the machining performance and the using performance of the crankshaft can meet the machining and using performance requirements of the crankshaft.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and more particularly, to a steel for easily machined crankshafts, a production method thereof, and a crankshaft manufactured using the same. Background Art

[0002] Competition in the automotive industry is becoming increasingly fierce, and the requirements for steel in automotive parts are getting higher and higher. Not only good product quality is required, but also low cost is demanded. Therefore, when designing and manufacturing steel, not only the performance requirements need to be considered, but also the subsequent machining performance requirements of parts should be taken into account, such as extending the life of the cutting tools used in machining and reducing the production cost of parts machining. Summary of the Invention

[0003] The purpose of the present invention is to provide a steel for easily machined crankshafts, a production method thereof, and a crankshaft manufactured using the same, so as to overcome the defects existing in the above-mentioned prior art.

[0004] The present invention solves its technical problems by adopting the following technical solutions.

[0005] The present invention provides a steel for easily machined crankshafts, comprising the following components by mass percentage: C: 0.37 - 0.45%, Si: 0.17 - 0.35%, Mn: 0.60 - 0.80%, S: ≤0.025%, P: ≤0.020%, Cr: 1.00 - 1.20%, Al: ≤0.040%, Cu ≤0.20%, Mo: 0.15 - 0.30%, and the rest is mainly Fe and inevitable impurities.

[0006] The present invention also provides a production method of the above-mentioned steel for easily machined crankshafts, which includes: improving the segregation in the continuous casting billet by adopting electromagnetic stirring combined with the final soft reduction process and the rolling process to obtain a continuous casting billet.

[0007] The present invention also provides a crankshaft prepared using the above-mentioned steel for easily machined crankshafts, which includes: heating the continuous casting billet smelted and cast according to the elemental composition and then forging to obtain a crankshaft blank, and then cooling the crankshaft blank to obtain a crankshaft.

[0008] The present invention has the following beneficial effects:

[0009] The present invention provides a steel for easily machined crankshafts, a production method thereof, and a crankshaft manufactured using the same. The present invention provides a steel for crankshafts with optimized composition, and at the same time adopts a set of process methods to control the internal quality of the steel. Considering the usage characteristics of the crankshaft, while ensuring the mechanical properties of the crankshaft, the machining performance and service performance of the crankshaft can meet the requirements of the machining and service performance of the crankshaft. Detailed Embodiments

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0011] The present invention uses a steel for crankshaft with optimized composition and process control. At the same time, a set of process methods is adopted to control the internal quality of the steel. Combining the usage characteristics of the crankshaft, while ensuring the mechanical properties of the round steel, the machining performance and service performance of the crankshaft are guaranteed to meet the requirements of the machining and service performance of the crankshaft.

[0012] The following specifically describes a steel for easy-to-machine crankshaft, a production method, and a crankshaft manufactured using the same provided by the embodiments of the present invention.

[0013] In a first aspect, an embodiment of the present invention provides a steel for easy-to-machine crankshaft, which includes the following components by mass percentage: C: 0.37 - 0.45%, Si: 0.17 - 0.35%, Mn: 0.60 - 0.80%, S: ≤0.025%, P: ≤0.020%, Cr: 1.00 - 1.20%, Al: ≤0.040%, Cu ≤0.20%, Mo: 0.15 - 0.30%, and the rest is mainly a steel for crankshaft with Fe. To ensure the strength, toughness, and hardenability requirements of the round steel, it is necessary to ensure the content ranges of each key component.

[0014] The preferred composition control is: 0.38 - 0.42% C, 0.70 - 0.78% Mn, 1.05 - 1.15% Cr, Mo: 0.17 - 0.25%, 0.015 - 0.030% Al, 40 - 80 ppm of N, and Al / N ≥ 3.0. The carbon equivalent Ceq = C + Mn / 5 + Cr / 4 + Mo / 5 + (Ni + Cu) / 15 + 1.8V, and CE is controlled at: 0.85 - 0.90; the manganese equivalent Mneq = Mn + 1.5*Cr + 1.8*Mo + 0.25*Ni + 0.18*Cu, and Mneq is controlled at: 2.65 - 2.75.

[0015] To improve the machining efficiency of rough machining of the crankshaft blank, a certain amount of sulfur needs to be added. The morphology of sulfides in the steel is used to break the continuity of the matrix, play a stress concentration role, and improve the cutting chip breaking property; at the same time, sulfides can reduce the surface roughness of the workpiece to play a lubricating role, reduce the wear of the tool, thereby improving the service life of the machining tool and reducing the processing cost. However, if the sulfur content is too high, it is easy to cause the concentrated distribution of sulfides or promote the positive segregation of the steel, increase the probability of cracking along the sulfide concentration area during the quenching process of the crankshaft, and also cause the crankshaft to form magnetic marks and be scrapped at the sulfide aggregation site. The sulfur content is controlled at 0.005 - 0.012%.

[0016] In a second aspect, an embodiment of the present invention further provides a production method of the above-mentioned steel for easily machined crankshafts, which includes: improving segregation in the continuous casting billet by using electromagnetic stirring in combination with soft reduction at the end and a rolling process to obtain a continuous casting billet. Among them:

[0017] To improve segregation in the continuous casting billet steel, electromagnetic stirring in combination with soft reduction at the end is adopted. In particular, the electromagnetic stirring intensity in the mold is reduced to prevent excessive stirring in the mold and form severe positive segregation in the region from 1 / 2R (radius of the continuous casting billet) to the center of the continuous casting billet. The electromagnetic stirring process in the mold is controlled at 100±20 A and 2.5 Hz, and the electromagnetic stirring process at the end is controlled at 600±20 A and 4.0 Hz. To reduce the segregation degree in the region near the center, a soft reduction process is implemented with a reduction amount of 11 mm, which is controlled in 4 segments. According to the solidification temperature of this type, soft reduction is implemented starting from the second segment, and only the second to fifth segments are subjected to soft reduction. The reduction amount distribution of soft reduction is 2 mm, 2 mm, 4 mm, and 3 mm.

[0018] To further improve the segregation of the steel and prevent the regions with severe segregation in the steel from being exposed on the surface of the crankshaft journal and the connecting rod journal, resulting in quenching cracks or magnetic mark rejection during quenching. In the rough rolling stage of the continuous casting billet, the reduction rate per pass and the roller table speed in the rolling stage are controlled. The number of rolling passes is reduced from the conventional 11 passes to 9 passes, and it is ensured that the reduction rate per pass ≥ 15%. The roller table speed of the rolling mill is reduced to 75% of the conventional speed, ensuring that the deformation process per pass in the rough rolling process penetrates to the center, improving the central porosity and segregation.

[0019] In a third aspect, an embodiment of the present invention further provides a crankshaft prepared by using the above-mentioned steel for easily machined crankshafts, which includes: heating the continuous casting billet smelted and cast according to the elemental composition and then forging to obtain a crankshaft blank, and then cooling the crankshaft blank to obtain a crankshaft.

[0020] There are many factors that cause the crankshaft to crack during the quenching process. It is prone to cracking in areas of stress concentration, especially at the parting surface of the crankshaft. Affected by the uneven material flow during the forging process, the severely segregated areas of the steel are exposed at the parting surface of the crankshaft or on the inner side of the connecting rod journal, increasing the probability of quenching cracking. In addition, the crankshaft quenching process, especially the selection of quenching temperature, cooling rate, and cooling medium, are all the main factors leading to crankshaft quenching cracking. Therefore, in order to reduce the probability of quenching cracking, in addition to controlling steel segregation, it is also necessary to control the quenching process well. According to production performance and material conditions, the crankshaft is heated in five sections in a continuous furnace. The first and second zones are the heating-up zones, with temperatures controlled at 750°C ± 5°C and 800°C ± 5°C respectively; the third to fifth zones are the holding zones, with the temperature controlled at 820°C ± 5°C; the total quenching heating time is controlled at (1.5 - 2.0)*D (D is the main journal diameter) min, and the heating time in the holding zone is ensured to be ≥ 1.0*D min; a special coolant is selected, and on the basis of ensuring the strength of the crankshaft, the cooling intensity of the coolant is controlled, and the cooling rate is controlled at 40 ± 5°C / s.

[0021] The following further describes the present invention in conjunction with embodiments.

[0022] The chemical compositions of the easy-to-machine crankshaft steel used in the examples and comparative examples are shown in the following table:

[0023]

[0024] The production process of the easy-to-machine crankshaft steel and the crankshaft quenching process in the examples and comparative examples are shown in the following table:

[0025]

[0026] The performance of the easy-to-machine crankshaft steel used in the examples and comparative examples is shown in the following table:

[0027] Serial number Rp0.2 / MPa Rm / MPa A / ％ <![CDATA[Ku 2 / J]]> J5mm / HRC J12mm / HRC Example 1 1116 1215 17.5 82 57 51.5 Example 2 1130 1231 15.5 78 55.5 53 Example 3 1139 1235 16 89 56.5 52 Comparative example 1 1113 1135 16 91 52 46 Comparative example 2 1225 1317 13 64 61 56

[0028] The performance and quenching quality of the crankshafts machined from the easy-to-machine crankshaft steel used in the examples and comparative examples are shown in the following table:

[0029] Serial number Tool life Quenching cracking rate / PPM Example 1 1.21*N 2 Example 2 1.15*N 0 Example 3 1.13*N 1 Comparative example 1 0.92*N 18 Comparative example 2 0.89*N 24

[0030] Remarks: The rated life of the rough machining tool is N. Quenching cracking rate: When the number of cracks in 10,000 pieces is processed, the cracking rate PPM = number of cracks / 10,000.

[0031] It can be seen from the above experimental results that the easy-to-machine crankshaft steel prepared by the solution provided in the embodiment of the present invention has good mechanical properties, and further, the crankshaft prepared by the above easy-to-machine crankshaft steel has a low quenching cracking rate and good cutting performance.

[0032] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An easy-to-process crankshaft steel, characterized in that: The invention comprises the following components in mass percentage: C: 0.37-0.45%, Si: 0.17-0.35%, Mn: 0.60-0.80%, S: ≤0.025%, P: ≤0.020%, Cr: 1.00-1.20%, Al: ≤0.040%, Cu≤0.20%, Mo: 0.15-0.30%, and the rest are mainly Fe and unavoidable impurities.

2. The easy-to-process crankshaft steel according to claim 1, characterized in that: The invention comprises the following components in mass percentage: C: 0.38-0.42%, Si: 0.17-0.35%, Mn: 0.70-0.78%, S: ≤0.025%, P: ≤0.020%, Cr: 1.05-1.15%, Al: 0.015-0.030%, Cu≤0.20%, Mo: 0.17-0.25%, N: 40-80ppm, and Al / N≥3.0, and the rest are mainly Fe and unavoidable impurities.

3. The easy-to-process crankshaft steel according to claim 1, characterized in that: The carbon equivalent Ceq in the easy-to-process crankshaft steel is between 0.85-0.90, and the manganese equivalent Mneq is between 2.65-2.75, wherein the carbon equivalent Ceq=C+Mn / 5+Cr / 4+Mo / 5+(Ni+Cu) / 15+1.8V; the manganese equivalent Mneq=Mn+1.5*Cr+1.8*Mo+0.25*Ni+0.18*Cu.

4. The easy-to-process crankshaft steel according to claim 1, characterized in that: The sulfur content in the easy-to-process crankshaft steel is between 0.005% and 0.012%.

5. The easy-to-process crankshaft steel according to any one of claims 1 to 4, characterized in that: The mechanical properties of the easy-to-process crankshaft steel meet the following requirements: Rp0.2≥980MPa, Rm≥1150MPa, A≥15, Ku2≥75J; hardenability J5mm: 53-59HRC, J12mm: 49-55HRC.

6. A method for producing an easily machined crankshaft steel according to any one of claims 1 to 5, characterized in that: It includes: Electromagnetic stirring combined with terminal soft reduction process and rolling process is used to improve segregation in the ingot and produce a continuous casting ingot.

7. The production method according to claim 6, characterized in that: The electromagnetic stirring combined with the end light reduction process is used to improve the segregation in the ingot, including: controlling the electromagnetic stirring parameters of the crystallizer to 100±20A, 2.5Hz, the end electromagnetic stirring parameters to 600±20A, 4.0Hz, controlling the reduction amount to 11mm, and controlling it in 4 stages. According to the solidification temperature of the steel grade, light reduction is implemented from the second stage, and only the second to the fifth stages are lightly reduced, and the reduction amounts of light reduction are distributed as 2mm, 2mm, 4mm, and 3mm.

8. The production method according to claim 6, characterized in that: The rolling process is used to improve the segregation in the ingot, including: in the rough rolling stage of the continuous casting ingot, the rolling passes are reduced from the conventional 11 passes to 9 passes, and the reduction rate of each pass is ensured to be ≥15%, and the roller speed of the rolling mill is reduced to 75% of the conventional speed, ensuring that the deformation process of each pass in the rough rolling process penetrates into the core, thereby improving the shrinkage and segregation of the core.

9. A crankshaft made of the easy-to-process crankshaft steel according to any one of claims 1 to 5, characterized in that: include: The continuous casting billet smelted and cast according to the element composition is heated and then forged to obtain a crankshaft blank, and then the crankshaft blank is cooled to obtain a crankshaft.

10. The crankshaft according to claim 9, characterized in that The preparation of the crankshaft comprises the following steps: The crankshaft blank is quenched in a continuous furnace, wherein the quenching furnace is divided into five zones for heating, the first zone and the second zone are heating zones, and the temperatures are controlled at 750°C±5°C and 800°C±5°C respectively; Zones 3 to 5 are insulation zones, and the temperature is controlled at 820°C±5°C; the total quenching heating time is controlled at (1.5-2.0)*Dmin, where D is the main shaft neck diameter, and the heating time in the insulation zone is ensured to be controlled ≥1.0*Dmin; during the cooling process of the crankshaft blank, a special coolant is selected, and the cooling intensity of the coolant is controlled on the basis of ensuring the strength of the crankshaft, and the cooling rate is controlled at 40±5°C / s.

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