Engine balance shaft steel and method of making

Abstract

The application provides an engine balance shaft steel and a preparation method thereof. The engine balance shaft steel comprises the following components in percentage by mass: C 0.44-0.46wt%, Si 0.25-0.35wt%, Mn 0.80-0.90wt%, P≤0.015wt%, S 0.010-0.025wt%, Al 0.015-0.025wt%, Cr 0.10-0.15wt%, and the balance is Fe and inevitable impurities. The engine balance shaft steel is prepared by using blast furnace molten iron with specific chemical components and content, through the molten iron pretreatment, converter smelting, ladle refining, vacuum degassing, continuous casting and rolling process, the engine balance shaft steel with high strength and high plasticity is obtained, wherein the tensile strength is greater than or equal to 710 MPa, the yield strength is greater than or equal to 400 MPa, the elongation after fracture is greater than or equal to 18%, and the reduction of area is greater than or equal to 47%.

Description

Technical Field

[0001] This invention belongs to the field of steel technology, specifically relating to a steel for engine balance shafts and its preparation method. Background Technology

[0002] Balance shaft technology is a core vibration reduction technology widely used in motorcycle engines. This technology is simple in structure and highly practical. It uses the eccentric movement of the balance shaft to counteract the inertial forces and vibrations generated by engine operation, effectively reducing overall motorcycle vibration and significantly improving riding comfort and handling stability. It is a key component technology for enhancing the riding experience of mid-to-high-end motorcycles and extending engine lifespan. The material properties, internal structure uniformity, and mechanical strength of the balance shaft directly determine its vibration reduction effect and service reliability. The smelting, continuous casting, and rolling processes of its raw material, the round billet, are the core aspects ensuring the overall performance of the balance shaft.

[0003] Currently, the mainstream production process for round steel billets used in motorcycle engine balance shafts is as follows: converter smelting - LF ladle refining - VD vacuum refining - round billet continuous casting - rolling. This process completes basic steelmaking and initial composition adjustment in the converter, achieves precise fine-tuning of the steel composition, heating and desulfurization treatment through LF ladle refining, and then completes purification treatment such as degassing and removal of non-metallic inclusions through VD vacuum refining. Subsequently, it is formed into round billets through the round billet continuous casting process, and finally obtains round steel profiles suitable for subsequent forging and machining of balance shafts through the rolling process.

[0004] Although this traditional process has achieved large-scale industrial application, significant technical shortcomings still exist in actual production and product application. Balance shaft billets prepared using this process are prone to problems such as insufficient control of molten steel purity, microstructure segregation, and uneven grain size. This leads to insufficient fatigue strength and stress concentration in the balance shaft under high-frequency engine vibration conditions, which not only reduces the vibration damping stability of the balance shaft and weakens the overall vehicle vibration damping effect but also shortens the service life of the balance shaft. Furthermore, the limited parameter matching between traditional continuous casting and rolling processes, coupled with poor billet density and machinability, increases the difficulty of subsequent machining of the balance shaft, affecting the dimensional accuracy and assembly effect of the finished product. This makes it difficult to meet the stringent requirements of high vibration damping and high reliability for balance shafts in high-performance motorcycle engines.

[0005] The limitations of existing balance shaft raw material preparation processes directly restrict further improvement of balance shaft vibration reduction performance. Therefore, developing optimized balance shaft billet production processes and improving the internal structure and material properties of round billets have become urgent technical problems to be solved in the field of motorcycle engine parts manufacturing. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a steel for engine balance shafts and its preparation method. This invention employs a specific chemical composition design and precise refining process, enabling the direct acquisition of engine balance shaft steel with excellent comprehensive performance under high-temperature rolling conditions, without the need for subsequent quenching and tempering treatment.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a steel for an engine balance shaft, the steel comprising, by weight percentage: C 0.44~0.46wt%, Si 0.25~0.35wt%, Mn 0.80~0.90wt%, P≤0.015wt%, S0.010~0.025wt%, Al 0.015~0.025wt%, Cr 0.10~0.15wt%, with the balance being Fe and unavoidable impurities.

[0008] The engine balance shaft steel described in this invention, through the rational combination of elements such as Mn, Al, and Cr, and by controlling the content of P and S within a specific range, enables the engine balance shaft steel to have both high strength and excellent plasticity.

[0009] For example, the C content in the steel used for the engine balance shaft is 0.44~0.46wt%, such as 0.44wt%, 0.445wt%, 0.45wt%, 0.455wt%, or 0.46wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Si content is 0.25~0.35wt%, for example, it can be 0.25wt%, 0.27wt%, 0.29wt%, 0.31wt%, 0.33wt% or 0.35wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Mn content is 0.80~0.90wt%, for example, it can be 0.80wt%, 0.82wt%, 0.84wt%, 0.86wt%, 0.88wt% or 0.90wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The P content is ≤0.015wt%, for example, it can be 0.015wt%, 0.0148wt%, 0.0146wt%, 0.0144wt%, 0.0142wt%, or 0.014wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The sulfur content is 0.010~0.025wt%, for example, it can be 0.010wt%, 0.013wt%, 0.016wt%, 0.019wt%, 0.022wt% or 0.025wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Al content is 0.015~0.025wt%, for example, it can be 0.015wt%, 0.017wt%, 0.019wt%, 0.021wt%, 0.023wt% or 0.025wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Cr content is 0.10~0.15wt%, for example, it can be 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt% or 0.15wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0010] Preferably, the steel used for the engine balance shaft comprises, by weight percentage: C 0.44~0.45wt%, Si 0.27~0.32wt%, Mn 0.83~0.88wt%, P≤0.012wt%, S 0.015~0.020wt%, Al 0.018~0.022wt%, Cr 0.12~0.15wt%, with the balance being Fe and unavoidable impurities.

[0011] As a preferred embodiment of the present invention, the tensile strength of the steel used for the engine balance shaft is ≥710MPa, for example, it can be 710MPa, 715MPa, 720MPa, 725MPa, 730MPa or 740MPa, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0012] Preferably, the yield strength of the steel used for the engine balance shaft is ≥400MPa, for example, it can be 400MPa, 402MPa, 404MPa, 406MPa, 408MPa or 410MPa, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0013] Preferably, the elongation after fracture of the steel used for the engine balance shaft is ≥18%, for example, it can be 18%, 18.2%, 18.4%, 18.6%, 18.8% or 19%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the section reduction rate of the steel used for the engine balance shaft is ≥47%, for example, it can be 47%, 47.2%, 47.4%, 47.6%, 47.8% or 48%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] In a second aspect, the present invention provides a method for preparing steel for an engine balance shaft as described in the first aspect, the method comprising: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The final P content of the converter smelting is ≤0.017wt%, and the final S content of the VD vacuum degassing is 0.010~0.025wt%.

[0016] The method for preparing engine balance shaft steel described in this invention employs blast furnace hot metal with a specific chemical composition, followed by a rationally designed smelting, refining, continuous casting, and rolling process. This allows the engine balance shaft steel to possess excellent comprehensive performance in its hot-rolled state, eliminating complex and energy-intensive subsequent quenching and tempering processes, thus reducing energy consumption and time costs in the production process. Furthermore, this invention utilizes VD vacuum degassing after LF ladle refining, effectively removing impurities such as O, N, and H from the molten steel, thereby improving the overall performance of the engine balance shaft steel.

[0017] This invention controls the phosphorus (P) content during the converter smelting process and the sulfur (S) content through vacuum degassing (VD). After subsequent continuous casting and rolling, the final steel for engine balance shafts has a P content of ≤0.015% and exhibits excellent comprehensive performance.

[0018] The final P content of the converter smelting described in this invention is ≤0.017wt%, for example, it can be 0.017wt%, 0.016wt%, 0.015wt%, 0.014wt%, or 0.013wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The endpoint S content of the VD vacuum degassing is 0.010~0.025wt%, for example, it can be 0.010wt%, 0.013wt%, 0.016wt%, 0.019wt%, 0.022wt%, or 0.025wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] As a preferred embodiment of the present invention, the blast furnace molten iron comprises, by mass percentage: C 3.8~4.4wt%, Si 0.07~0.16wt%, Mn 0.14~0.19wt%, Cr 0.23~0.28wt%, with the balance being Fe and unavoidable impurities.

[0020] For example, the C content in the blast furnace molten iron is 3.8~4.4wt%, such as 3.8wt%, 4.0wt%, 4.2wt% or 4.4wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Si content is 0.07~0.16wt%, for example, it can be 0.07wt%, 0.09wt%, 0.11wt%, 0.14wt% or 0.16wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Mn content is 0.14~0.19wt%, for example, it can be 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt% or 0.19wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The Cr content is 0.23~0.28wt%, for example, it can be 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.27wt% or 0.28wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the final C content of the converter smelting is 0.08~0.15wt%, for example, it can be 0.08wt%, 0.10wt%, 0.12wt%, 0.14wt% or 0.15wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] It is worth noting that the converter smelting described in this invention adopts a high-pulling and supplementary blowing operation mode.

[0023] Preferably, the slag system used in the LF ladle refining is a high-alumina slag system.

[0024] Preferably, the high-alumina slag system comprises, by mass percentage: Al2O3 32~36wt%, SiO2 4~9%, CaO 55~60%.

[0025] For example, the Al2O3 content in the high-alumina slag system is 32~36wt%, such as 32wt%, 33wt%, 34wt%, 35wt% or 36wt%, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable. The SiO2 content is 4~9%, for example, it can be 4wt%, 5wt%, 6wt%, 7wt%, 8wt% or 9wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The CaO content is 55-60%, for example, it can be 55wt%, 56wt%, 57wt%, 58wt%, 59wt% or 60wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the white slag refining time of the LF ladle is ≥15min, for example, it can be 15min, 16min, 17min, 18min, 19min or 20min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the final Al content of the LF ladle refining is 0.020~0.030wt%, for example, it can be 0.020wt%, 0.022wt%, 0.024wt%, 0.026wt%, 0.028wt% or 0.030wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] This invention can further refine the grains and improve the toughness of the resulting balance shaft steel by controlling the Al content in the ladle refining process.

[0029] Preferably, the vacuum degree of the VD vacuum degassing is ≤67Pa, for example, it can be 67Pa, 66Pa, 65Pa, 64Pa or 63Pa, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the VD vacuum degassing time is ≥12 min, for example, it can be 12 min, 13 min, 14 min or 15 min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the soft blowing time of the VD vacuum degassing is ≥20 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min or 25 min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] In this invention, by strictly controlling the vacuum time and soft blowing time of VD vacuum degassing, the S content in the molten steel is ensured to be 0.010~0.025wt%, thereby further improving the material's machinability.

[0033] Preferably, the specific water content in the continuous casting is 0.35~0.40L / kg, for example, it can be 0.35L / kg, 0.36L / kg, 0.37L / kg, 0.38L / kg, 0.39L / kg or 0.40L / kg, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the casting speed in the continuous casting is 0.45~0.50 m / min, for example, it can be 0.45 m / min, 0.46 m / min, 0.47 m / min, 0.48 m / min, 0.49 m / min or 0.50 m / min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the superheat of the tundish in the continuous casting is 15~25℃, for example, it can be 15℃, 17℃, 19℃, 21℃, 23℃ or 25℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the heating temperature of the billet is 1130~1220℃, for example, it can be 1130℃, 1150℃, 1170℃, 1190℃, 1210℃ or 1220℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heating time of the billet is 150~260min, for example, it can be 150min, 170min, 190min, 210min, 230min or 260min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] This invention ensures billet quality by strictly controlling the heating temperature and time of the billet and employing a high-temperature diffusion process to promote the homogenization of various elements in the billet.

[0039] Preferably, the initial rolling temperature is 1080~1130℃, for example, it can be 1080℃, 1090℃, 1100℃, 1120℃ or 1130℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] After the steel for the engine balance shaft prepared by this invention is produced, it is placed in a pit for slow cooling to avoid the formation of abnormal structures.

[0041] As a preferred embodiment of the present invention, the method for preparing the steel for the engine balance shaft according to the second aspect of the present invention includes: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The molten iron in the blast furnace comprises, by mass percentage: C 3.8~4.4wt%, Si 0.07~0.16wt%, Mn 0.14~0.19wt%, Cr 0.23~0.28wt%, with the balance being Fe and unavoidable impurities; The converter smelting adopts a high-pressure blowing operation mode, with a final C content of 0.08~0.15wt% and a final P content ≤0.017wt%. The slag system used in the LF ladle refining process is a high-alumina slag system, with a white slag time ≥15 min and an Al content of 0.020~0.030 wt% at the endpoint. The vacuum degree of the VD vacuum degassing is Pa, the time is ≥12 min; the soft blowing time is ≥20 min; and the final S content is 0.010~0.025 wt%. The specific water content in the continuous casting is 0.35~0.40L / kg, the casting speed is 0.45~0.50m / min, and the superheat of the tundish is 15~25℃; The billet is heated at a temperature of 1130~1220℃ for a time of 150~260min; The initial rolling temperature is 1080~1130℃.

[0042] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0043] Compared with the prior art, the present invention has the following beneficial effects: The preparation method for engine balance shaft steel provided by this invention has a simple operation process and low preparation cost. Through reasonable chemical composition design and reasonable smelting, refining, continuous casting and rolling process design, the engine balance shaft steel can have good comprehensive performance in the hot-rolled state, and has the prospect of large-scale promotion and application. Detailed Implementation

[0044] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0045] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0046] The following are typical but non-limiting embodiments of the present invention: Example 1 This embodiment provides a steel for engine balance shafts, which comprises, by weight percentage: C 0.45wt%, Si 0.30wt%, Mn 0.85wt%, P 0.01wt%, S 0.020wt%, Al 0.020wt%, Cr 0.12wt%, with the balance being Fe and unavoidable impurities.

[0047] This embodiment also provides a method for preparing the steel for the engine balance shaft described above, the method comprising the following steps: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The molten iron in the blast furnace comprises, by mass percentage: 4.0 wt% C, 0.12 wt% Si, 0.16 wt% Mn, 0.25 wt% Cr, with the balance being Fe and unavoidable impurities; The converter smelting adopts a high-pulling and supplemental blowing operation mode, with a final C content of 0.10 wt% and a final P content of 0.012 wt%. The slag system used in the LF ladle refining process is a high-alumina slag system, with a white slag time of 18 minutes and an Al content of 0.025 wt% at the endpoint. The vacuum degree of the VD vacuum degassing was 64 Pa, the time was 15 min; the soft blowing time was 25 min; and the final sulfur content was 0.020 wt%. The specific water content in the continuous casting is 0.38 L / kg, the casting speed is 0.48 m / min, and the tundish superheat is 20°C. The billet is heated to 1180℃ for 200 minutes. The initial rolling temperature is 1100℃.

[0048] Example 2 This embodiment provides a steel for engine balance shafts, which comprises, by weight percentage: C 0.44wt%, Si 0.25wt%, Mn 0.80wt%, P 0.015wt%, S 0.010wt%, Al 0.015wt%, Cr 0.10wt%, with the balance being Fe and unavoidable impurities.

[0049] This embodiment also provides a method for preparing the steel for the engine balance shaft described above, the method comprising the following steps: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The molten iron in the blast furnace comprises, by mass percentage: C 3.8wt%, Si 0.09wt%, Mn 0.14wt%, Cr 0.23wt%, with the balance being Fe and unavoidable impurities; The converter smelting adopts a high-pulling and supplemental blowing operation mode, with a final C content of 0.08wt% and a final P content of 0.017wt%. The slag system used in the LF ladle refining process is a high-alumina slag system, with a white slag time of 15 minutes and an Al content of 0.020 wt% at the endpoint. The vacuum degree of the VD vacuum degassing was 65 Pa, the time was 12 min; the soft blowing time was 20 min; and the final sulfur content was 0.010 wt%. The specific water content in the continuous casting is 0.35 L / kg, the casting speed is 0.45 m / min, and the tundish superheat is 15℃. The billet is heated to 1130℃ for 260 minutes. The initial rolling temperature is 1080℃.

[0050] Example 3 This embodiment provides a steel for engine balance shafts, which comprises, by weight percentage: C 0.46wt%, Si 0.35wt%, Mn 0.90wt%, P 0.018wt%, S 0.025wt%, Al 0.025wt%, Cr 0.15wt%, with the balance being Fe and unavoidable impurities.

[0051] This embodiment also provides a method for preparing the steel for the engine balance shaft described above, the method comprising the following steps: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The molten iron in the blast furnace comprises, by mass percentage: 4.4wt% C, 0.16wt% Si, 0.19wt% Mn, 0.28wt% Cr, with the balance being Fe and unavoidable impurities; The converter smelting adopts a high-pressure blowing operation mode, with a final C content of 0.15 wt% and a final P content of 0.020 wt%. The slag system used in the LF ladle refining process is a high-alumina slag system, with a white slag time of 25 minutes and an Al content of 0.030 wt% at the endpoint. The vacuum degree of the VD vacuum degassing was 66 Pa, and the time was 20 min; the soft blowing time was 30 min; the final sulfur content was 0.025 wt%. The specific water content in the continuous casting is 0.40 L / kg, the casting speed is 0.50 m / min, and the tundish superheat is 25°C. The billet is heated to 1220℃ for 150 minutes. The initial rolling temperature is 1130℃.

[0052] Example 4 This embodiment provides a steel for engine balance shafts, which comprises, by weight percentage: C 0.45wt%, Si 0.32wt%, Mn 0.88wt%, P 0.010wt%, S 0.015wt%, Al 0.018wt%, Cr 0.12wt%, with the balance being Fe and unavoidable impurities.

[0053] This embodiment also provides a method for preparing the steel for the engine balance shaft described above, the method comprising the following steps: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The molten iron in the blast furnace comprises, by mass percentage: 4.2wt% C, 0.15wt% Si, 0.16wt% Mn, 0.24wt% Cr, with the balance being Fe and unavoidable impurities; The converter smelting adopts a high-pressure blowing operation mode, with a final C content of 0.08~0.15wt% and a final P content ≤0.017wt%. The slag system used in the LF ladle refining process is a high-alumina slag system, with a white slag time of 22 minutes and an Al content of 0.028 wt% at the endpoint. The vacuum degree of the VD vacuum degassing was 67 Pa, and the time was 22 min; the soft blowing time was 23 min; the final sulfur content was 0.015 wt%. The specific water content in the continuous casting is 0.37 L / kg, the casting speed is 0.46 m / min, and the tundish superheat is 22℃. The billet is heated to 1200℃ for 220 minutes; The initial rolling temperature is 1110℃.

[0054] Example 5 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0055] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the final C content of the converter smelting is adjusted to 0.05 wt%.

[0056] Example 6 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0057] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the final C content of the converter smelting is adjusted to 0.20 wt%.

[0058] Example 7 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0059] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the heating temperature of the billet is adjusted to 1000℃.

[0060] Example 8 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0061] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the heating temperature of the billet is adjusted to 1280℃.

[0062] Example 9 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0063] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the initial rolling temperature is adjusted to 1030℃.

[0064] Example 10 This embodiment provides a steel for engine balance shafts, the composition of which is the same as that in Embodiment 1.

[0065] This embodiment also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and that of Embodiment 1 is that: In this embodiment, the initial rolling temperature is adjusted to 1180℃.

[0066] Comparative Example 1 This comparative example provides a steel for an engine balance shaft, the composition of which differs from that of Example 1 only in that: In this embodiment, the phosphorus content in the steel used for the engine balance shaft is adjusted to 0.02 wt%.

[0067] This comparative example also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and Example 1 is that the final P content of the converter smelting is not controlled.

[0068] Comparative Example 2 This comparative example provides a steel for an engine balance shaft, the composition of which differs from that of Example 1 only in that: In this comparative example, the Al content in the steel used for the engine balance shaft is adjusted to 0.01 wt%.

[0069] This comparative example also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and Example 1 is that the Al content at the end of the refining of the LF steel ladle in this comparative example is adjusted to 0.015 wt%.

[0070] Comparative Example 3 This comparative example provides a steel for an engine balance shaft, the composition of which differs from that of Example 1 only in that: In this comparative example, the Al content in the steel used for the engine balance shaft was adjusted to 0.03 wt%.

[0071] This comparative example also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and Example 1 is that the Al content at the end of the refining of the LF steel ladle in this comparative example is adjusted to 0.035 wt%.

[0072] Comparative Example 4 This comparative example provides a steel for an engine balance shaft, the composition of which differs from that of Example 1 only in that: In this comparative example, the sulfur content in the steel used for the engine balance shaft is adjusted to 0.005 wt%.

[0073] This comparative example also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and Example 1 is that the S content at the endpoint of the VD vacuum degassing in this comparative example is adjusted to 0.008 wt%.

[0074] Comparative Example 5 This comparative example provides a steel for an engine balance shaft, the composition of which differs from that of Example 1 only in that: In this comparative example, the sulfur content in the steel used for the engine balance shaft is adjusted to 0.03 wt%.

[0075] This comparative example also provides a method for preparing the steel for the engine balance shaft described above. The only difference between this method and Example 1 is that the S content at the endpoint of the VD vacuum degassing in this comparative example is adjusted to 0.032 wt%.

[0076] Performance testing: The performance of the engine balance shaft steel provided in the above embodiments and comparative examples was tested, and the results are shown in Table 1. The testing methods for tensile strength, yield strength, elongation and reduction of area include GB / T228.1 Metallic Materials Tensile Testing Method.

[0077] Table 1 According to Table 1, the following points can be observed: (1) According to the comprehensive analysis of Examples 1-4, the method for preparing engine balance shaft steel provided by the present invention uses blast furnace molten iron with specific chemical composition and content, and obtains high-strength and high-plasticity engine balance shaft steel through molten iron pretreatment, converter smelting, ladle refining, vacuum degassing, continuous casting and rolling processes, wherein the tensile strength is ≥710MPa, the yield strength is ≥400MPa, the elongation after fracture is ≥18%, and the reduction of area is ≥45%.

[0078] (2) Comprehensive analysis of Examples 1 and 5-6 shows that if the C content at the end point of the converter smelting is too low, it will lead to a decrease in tensile strength and yield strength, while if the content is too high, it will lead to a decrease in elongation and shrinkage. (3) Comprehensive analysis of Examples 1 and 7-8 shows that if the temperature of the billet heating is too high, the tensile strength and yield strength will decrease, and if the temperature is too low, the elongation and shrinkage will decrease. A comprehensive analysis of Examples 1 and 9-10 shows that if the initial rolling temperature is too high, the tensile strength and yield strength will decrease, while if the temperature is too low, the elongation and shrinkage will decrease. (4) A comprehensive analysis of the embodiments and comparative examples 1-5 shows that the content of any chemical component in the steel used for the engine balance shaft will affect the overall performance of the product; If the phosphorus content in the steel used for the engine balance shaft is too high, it will cause the material to become brittle at cold, and reduce the material's strength and toughness. If the Al content in the steel used for the engine balance shaft is too high, it will lead to more inclusions in the steel, resulting in reduced strength; if the content is too low, it will lead to coarse grains and reduced strength. If the sulfur content in the steel used for the engine balance shaft is too high, it will lead to more inclusions and reduced strength and toughness; if the content is too low, it will lead to reduced machinability.

[0079] In summary, the method for preparing engine balance shaft steel provided by the present invention uses blast furnace molten iron with specific chemical composition and content, and undergoes molten iron pretreatment, converter smelting, ladle refining, vacuum degassing, continuous casting and rolling processes to obtain high-strength and high-plasticity engine balance shaft steel, wherein the tensile strength is ≥710MPa, the yield strength is ≥400MPa, the elongation after fracture is ≥18%, and the reduction of area is ≥47%.

[0080] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A type of steel for engine balance shafts, characterized in that, The steel used for the engine balance shaft comprises, by weight percentage: C 0.44~0.46wt%, Si 0.25~0.35wt%, Mn 0.80~0.90wt%, P≤0.015wt%, S 0.010~0.025wt%, Al 0.015~0.025wt%, Cr 0.10~0.15wt%, with the balance being Fe and unavoidable impurities.

2. The steel for engine balance shafts according to claim 1, characterized in that, The steel used for the engine balance shaft comprises, by weight percentage: C 0.44~0.45wt%, Si 0.27~0.32wt%, Mn 0.83~0.88wt%, P≤0.012wt%, S0.015~0.020wt%, Al 0.018~0.022wt%, Cr 0.12~0.15wt%, with the balance being Fe and unavoidable impurities.

3. The steel for engine balance shafts according to claim 1 or 2, characterized in that, The tensile strength of the steel used for the engine balance shaft is ≥710MPa; Preferably, the yield strength of the steel used for the engine balance shaft is ≥400MPa; Preferably, the elongation after fracture of the steel used for the engine balance shaft is ≥18%; Preferably, the reduction of area of ​​the steel used for the engine balance shaft is ≥47%.

4. A method for preparing steel for an engine balance shaft as described in any one of claims 1-3, characterized in that, The preparation method includes: The steel for the engine balance shaft is obtained by sequentially processing blast furnace molten iron through converter smelting, LF ladle refining, VD vacuum degassing, continuous casting, billet heating, rolling, and slow cooling. The final P content of the converter smelting is ≤0.017wt%, and the final S content of the VD vacuum degassing is 0.010~0.025wt%.

5. The preparation method according to claim 4, characterized in that, The molten iron in the blast furnace comprises, by mass percentage: C 3.8~4.4wt%, Si 0.07~0.16wt%, Mn 0.14~0.19wt%, Cr 0.23~0.28wt%, with the balance being Fe and unavoidable impurities.

6. The preparation method according to claim 4, characterized in that, The final carbon content of the converter smelting is 0.08~0.15wt%.

7. The preparation method according to any one of claims 4-6, characterized in that, The slag system used in the LF ladle refining process is a high-alumina slag system. Preferably, the white slag refining time of the LF ladle is ≥15 min; Preferably, the final Al content of the LF ladle refining is 0.020~0.030wt%.

8. The preparation method according to any one of claims 4-7, characterized in that, The vacuum degree of the VD vacuum degassing is ≤67Pa; Preferably, the VD vacuum degassing time is ≥12 min; Preferably, the soft blowing time of the VD vacuum degassing is ≥20 min.

9. The preparation method according to any one of claims 4-8, characterized in that, The specific water content in the continuous casting is 0.35~0.40 L / kg; Preferably, the casting speed in the continuous casting process is 0.45~0.50 m / min; Preferably, the superheat of the tundish in the continuous casting is 15~25℃; Preferably, the temperature for heating the billet is 1130~1220℃; Preferably, the heating time of the billet is 150~260 min.

10. The preparation method according to any one of claims 4-9, characterized in that, The initial rolling temperature is 1080~1130℃.

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