Non-adjusted steel for hydraulic rods and method for manufacturing same

Abstract

The application provides a non-adjusted steel for hydraulic rods and a preparation method thereof. The chemical composition of the non-adjusted steel for hydraulic rods comprises, in mass percentage, C 0.41-0.43%, Si 0.28-0.32%, Mn 0.98-1.02%, Cr 0.16-0.20%, Al 0.010-0.020%, V 0.09-0.11%, N 0.013-0.017%, P≤0.025%, S≤0.005%, and the balance of Fe and other inevitable impurities. The non-adjusted steel of the application is designed with a narrow component of chemical composition, so that fine ferrite and pearlite structure is obtained, and the non-adjusted steel does not need to be quenched and tempered, so that the strength, toughness and plasticity of the steel material are significantly improved, and the service requirements of the hydraulic rod under different load grades, high pressure, reciprocating impact and alternating load are met; and the performance of the steel material is further improved through control casting and control rolling in the preparation process.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel technology, specifically relating to a non-adjustable steel for hydraulic rods and its preparation method. Background Technology

[0002] Hydraulic rods are core load-bearing components in engineering machinery, agricultural machinery, and heavy equipment. They are used in extreme conditions such as high pressure, reciprocating impact, and alternating loads for a long time, which puts forward more stringent requirements on the strength, plasticity, toughness, fatigue resistance, and processing performance of the steel used in them.

[0003] Traditionally, hydraulic rods are mostly made of quenched and tempered steel, such as 45 steel or 40Cr medium carbon or alloy structural steel. The process involves quenching followed by high-temperature tempering (quenching and tempering) to obtain a tempered sorbite structure, achieving the desired mechanical properties. However, this process has significant drawbacks: the heat treatment process is lengthy and energy-intensive, and long rods are prone to bending deformation or even cracking during quenching, increasing the scrap rate. Furthermore, the environmental risks associated with quenching and the reliance on expensive alloys keep production costs high, making it difficult to meet the industry's development needs.

[0004] To address this issue, existing processes have implemented "rolling instead of tempering," eliminating quenching and tempering processes through micro-alloying of the steel composition. This improves steel performance and solves the problems of high energy consumption, complex processes, and high deformation risk associated with traditional quenched and tempered steel. However, currently manufactured non-quenched steel still has significant shortcomings: it requires the addition of various alloying elements, such as Nb, Mo, and Ti, to compensate for strength loss. On the one hand, this significantly increases alloying costs; on the other hand, it presents challenges in process control, poor production stability, and difficulty in balancing various aspects of the steel's properties.

[0005] Therefore, there is a need for a non-heat-resistant steel for hydraulic rods that is heat-free, low-cost, and high-performance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a non-adjustable steel for hydraulic rods and its preparation method, which simultaneously improves the strength and toughness of non-adjustable steel and reduces its alloying cost.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a non-adjustable steel for hydraulic rods, wherein the chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, comprises: C 0.41%-0.43%, Si 0.28%-0.32%, Mn 0.98%-1.02%, Cr 0.16%-0.20%, Al 0.010%-0.020%, V 0.09%-0.11%, N 0.013%-0.017%, P≤0.025%, S≤0.005%, with the balance being Fe and other unavoidable impurities.

[0009] The non-cooled steel for hydraulic rods provided by this invention uses Al and V as microalloying elements to achieve precipitation strengthening and fine grain strengthening. Combined with the narrow composition design of other alloying elements such as Mn and Cr, the microstructure of the steel can be controlled, so that the steel can directly obtain appropriate fine-grained ferrite and pearlite structure during hot rolling or forging. Without the need for quenching and tempering, it can achieve a synergistic improvement in high strength, high toughness and high plasticity, thereby meeting the service requirements of hydraulic rods under high pressure, reciprocating impact and alternating loads under different load levels.

[0010] In this invention, the mass percentage of C in the non-adjustable steel used for the hydraulic rod is 0.41%-0.43%, for example, it can be 0.41%, 0.415%, 0.42%, 0.425% or 0.43%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] Carbon (C) is the most fundamental strengthening element in steel. It can enhance the strength of ferrite in non-quenched steel through solid solution strengthening and form cementite, thereby increasing the steel's strength and hardness. It also interacts with elements such as Mn and Cr to promote pearlite transformation. Simultaneously, it reacts with vanadium (V) in steel to form carbides. This invention controls the C content range to form an appropriate ratio of vanadium carbides and vanadium nitrides in the steel, thus achieving a good precipitation strengthening effect on non-quenched steel.

[0012] In this invention, the mass percentage of Si in the non-adjustable steel used for the hydraulic rod is 0.28%-0.32%, for example, it can be 0.28%, 0.29%, 0.30%, 0.31% or 0.32%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] In non-quenched steel, Si can form solid solution strengthening of ferrite, improve the yield strength of steel, and work with Mn to deoxidize during steelmaking.

[0014] In this invention, the mass percentage of Mn in the non-adjustable steel used for the hydraulic rod is 0.98%-1.02%, for example, it can be 0.98%, 0.99%, 1.00%, 1.01% or 1.02%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Mn is also a solid solution strengthening element that refines the pearlite structure, thereby increasing the strength of steel. It can also react with S to form MnS, which inhibits the formation of harmful FeS, suppresses the formation of hot cracks, and improves the machinability of steel.

[0016] In this invention, the mass percentage of Cr in the non-adjustable steel used for the hydraulic rod is 0.16%-0.20%, for example, it can be 0.16%, 0.17%, 0.18%, 0.19% or 0.20%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Cr can refine the pearlite structure together with Mn, improve the strength of steel, and form carbides with C, thereby improving the wear resistance of steel. By controlling the Cr content within a certain range, the formation of vanadium carbides can also be reduced, indirectly promoting the precipitation of vanadium nitrides.

[0018] In this invention, the mass percentage of Al in the non-adjustable steel used for the hydraulic rod is 0.010%-0.020%, for example, it can be 0.010%, 0.012%, 0.015%, 0.018% or 0.020%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Al is a strong deoxidizer and forms AlN pinning grain boundaries with N, controlling grain size and thus refining grains. By controlling the Al content within a certain range, AlN is formed to refine grains and improve the strength of steel. At the same time, excessive content should be avoided to prevent the precipitation of vanadium nitrides.

[0020] In this invention, the mass percentage of V in the non-adjustable steel used for the hydraulic rod is 0.09%-0.11%, for example, it can be 0.09%, 0.095%, 0.10%, 0.105% or 0.11%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] In this invention, V is added as a microalloying element. By controlling the V content within a certain range, nanoscale carbonitrides can be precipitated during controlled rolling and cooling, resulting in a strong precipitation strengthening effect. At the same time, the ferrite grains are refined, and high strength can be obtained without tempering, without the need to add other complex alloying components such as Nb, Ti, and Mo.

[0022] In this invention, the mass percentage of nitrogen in the non-adjustable steel used for the hydraulic rod is 0.013%-0.017%, for example, it can be 0.013%, 0.014%, 0.015%, 0.016% or 0.017%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Nitrogen (N) can form vanadium nitrides with v, resulting in precipitation strengthening in steel and AlN grain refinement. By controlling the N content within a certain range, the grains can be significantly refined and the steel strength can be improved while ensuring the steel's plasticity.

[0024] In this invention, the mass percentage of P in the non-adjustable steel used for the hydraulic rod is ≤0.025%, for example, it can be 0.025%, 0.022%, 0.020%, 0.015% or 0.010%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Polymer (P) can play a certain role in solid solution strengthening in steel, but it is prone to segregation at grain boundaries, which can cause brittleness during air cooling. Controlling the content of P can ensure the toughness of steel.

[0026] In this invention, the mass percentage of S in the non-adjustable steel used for the hydraulic rod is S≤0.005%, for example, it can be 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] S can combine with Mn to form MnS, which can improve the machinability of steel. However, it can also combine with Fe to form FeS inclusions, which can easily cause hot cracking. Therefore, the S content needs to be controlled within a certain low range.

[0028] In a second aspect, the present invention provides a method for preparing non-adjustable steel for hydraulic rods as described in the first aspect, the method comprising: sequentially subjecting blast furnace molten iron to converter smelting, ladle refining, vacuum refining, continuous casting and rolling to obtain the non-adjustable steel for hydraulic rods.

[0029] Before converter smelting, the molten iron in the blast furnace undergoes pretreatment for desulfurization. Commonly used desulfurizing agents in this field, such as lime and fluorite, are selected according to conventional practices in the field.

[0030] Preferably, the final C content of the converter smelting is 0.06%-0.15% by mass, for example, it can be 0.06%, 0.08%, 0.10%, 0.12% or 0.15%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the final P content of the converter smelting is ≤0.014% by mass percentage, for example, it can be 0.014%, 0.012%, 0.010%, 0.008% or 0.005%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the slag system used in the ladle refining comprises, by mass percentage: CaO 50%-60%, Al2O3 20%-35%, SiO2 8%-18%, MgO 4%-8%, FeO+MnO≤1.0%, and the basicity (CaO / SiO2) of the slag system is 3.0-6.0.

[0033] Preferably, the refining time of the ladle refining is ≥48 min, for example, it can be 48 min, 49 min, 50 min, 52 min, 55 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the white slag time in the ladle refining is ≥15 min, for example, it can be 15 min, 16 min, 18 min, 20 min or 25 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the mass percentage of Al in the molten steel is controlled to be 0.010%-0.020% during the ladle refining process. For example, it can be 0.010%, 0.012%, 0.015%, 0.018% or 0.020%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the mass percentage of V in the molten steel is controlled to be 0.09%-0.11% during the ladle refining process. For example, it can be 0.09%, 0.095%, 0.10%, 0.105%, or 0.11%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the vacuum degree in the vacuum refining is ≤67Pa, for example, it can be 67Pa, 65Pa, 62Pa, 60Pa, 55Pa or 50Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the vacuum time in the vacuum refining is ≥18 min, for example, it can be 18 min, 19 min, 20 min, 22 min, 25 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the soft blowing time in the vacuum refining is ≥15 min, for example, it can be 15 min, 16 min, 18 min, 20 min, 25 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the H content in the molten steel is controlled to be ≤2.0×10⁻⁶ during the vacuum refining process. -6 .

[0041] Preferably, the mass percentage of N in the molten steel is controlled to be 0.013%-0.017% during the vacuum refining process. For example, it can be 0.013%, 0.014%, 0.015%, 0.016% or 0.017%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, argon sealing is used in the continuous casting process.

[0043] Preferably, the specific water content in the continuous casting is 0.7-0.9 L / kg, for example, it can be 0.7 L / kg, 0.75 L / kg, 0.8 L / kg, 0.85 L / kg or 0.9 L / kg, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the casting speed in the continuous casting is 0.44-0.52 m / min, for example, it can be 0.44 m / min, 0.46 m / min, 0.48 m / min, 0.50 m / min or 0.52 m / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the superheat of the tundish in the continuous casting is controlled at 20-30°C, for example, 20°C, 22°C, 25°C, 28°C or 30°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] By coordinating and controlling the specific water content, casting speed, and superheat parameters in continuous casting, the billet can be formed uniformly, thereby avoiding cracking and segregation, and improving the yield and uniformity of the steel's microstructure and properties.

[0047] Preferably, after continuous casting, the resulting billet is heated.

[0048] Preferably, the heating temperature is 1100-1180℃, for example, it can be 1100℃, 1120℃, 1140℃, 1150℃, 1160℃ or 1180℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0049] Preferably, the heating time is 390-600 min, for example, it can be 390 min, 400 min, 450 min, 500 min, 550 min or 600 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] By controlling the heating temperature and time, elements in the steel diffuse at high temperatures, promoting homogenization of composition and structure, thereby improving the uniformity of composition and structure, strength and surface quality of the steel.

[0051] Preferably, the initial rolling temperature is 1000-1080℃, for example, it can be 1000℃, 1020℃, 1040℃, 1050℃, 1060℃ or 1080℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the final rolling temperature is 900-950℃, for example, it can be 900℃, 910℃, 920℃, 930℃, 940℃ or 950℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, the material is subjected to slow cooling in a pit after rolling.

[0054] Preferably, the cooling time for slow cooling in the pit is ≥24h, for example, it can be 24h, 25h, 26h, 28h, 30h, 35h or 40h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the temperature at which the material is slowly cooled after entering the pit is ≤150℃, for example, it can be 150℃, 140℃, 120℃, 100℃, 80℃ or 50℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0057] The non-heat-treated steel of this invention achieves a fine-grained ferrite and pearlite microstructure through a narrow composition design of its chemical composition. This eliminates the need for heat treatment, significantly improving the steel's strength, toughness, and plasticity. The yield strength is ≥509 MPa, tensile strength ≥757 MPa, impact energy ≥52 J, hardness ≥231 HBW, reduction of area ≥45%, and elongation ≥18.5%, meeting the service requirements of hydraulic rods under high pressure, reciprocating impact, and alternating loads at different load levels. Furthermore, controlled casting and rolling during the manufacturing process further enhance the steel's properties. Detailed Implementation

[0058] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0059] Example 1

[0060] This embodiment provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, includes: C 0.42%, Si 0.29%, Mn 1.00%, Cr 0.19%, Al 0.014%, V 0.10%, N 0.015%, P 0.022%, S 0.004%, with the balance being Fe and other unavoidable impurities.

[0061] The non-adjustable steel used for the hydraulic rod is prepared using the following method:

[0062] After pretreatment and desulfurization of blast furnace molten iron, it is sequentially smelted in a converter, refined in a ladle, refined in a vacuum, continuously cast and rolled to obtain the non-adjustable steel for the hydraulic rod.

[0063] The final carbon content of the converter smelting is 0.11% by mass, and the final phosphorus content of the converter smelting is 0.013% by mass.

[0064] In the ladle refining process, the slag system used comprises, by mass percentage: CaO 52%, Al2O3 27%, SiO2 10%, MgO 6%, FeO+MnO≤1.0%, and the basicity of the slag system is 5.2. The refining time is 50 min, the white slag time is 16 min, the mass percentage of Al in the molten steel is controlled at 0.014%, and the mass percentage of V in the molten steel is controlled at 0.10%.

[0065] In the vacuum refining process, the vacuum time controlled at below 67 Pa is 19 min, the soft blowing time is 15 min, and the H content in the molten steel is controlled at 2.0 × 10⁻⁶. -6 The mass percentage of nitrogen in the molten steel is controlled at 0.015%.

[0066] In the continuous casting process, argon sealing is used for full protection to prevent secondary oxidation of molten steel. The specific water content is 0.8 L / kg, the casting speed is 0.46 m / min, the superheat of the tundish is controlled at 25℃, and the billet obtained after continuous casting is heated at 1150℃ for 500 min.

[0067] During the rolling process, the initial rolling temperature is 1050℃, and the final rolling temperature is 930℃. After rolling, the steel is placed in a pit for slow cooling for 24 hours. The pit is then opened at 180℃, and the exit temperature is 150℃. This process yields the non-adjustable steel for the hydraulic rod.

[0068] Example 2

[0069] This embodiment provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, includes: C 0.43%, Si 0.31%, Mn 0.99%, Cr 0.18%, Al 0.018%, V 0.11%, N 0.016%, P 0.024%, S 0.003%, with the balance being Fe and other unavoidable impurities.

[0070] The non-adjustable steel used for the hydraulic rod is prepared using the following method:

[0071] After pretreatment and desulfurization of blast furnace molten iron, it is sequentially smelted in a converter, refined in a ladle, refined in a vacuum, continuously cast and rolled to obtain the non-adjustable steel for the hydraulic rod.

[0072] The final carbon content of the converter smelting is 0.13% by mass, and the final phosphorus content of the converter smelting is 0.014% by mass.

[0073] In the ladle refining process, the slag system used comprises, by mass percentage: CaO 55%, Al2O3 23%, SiO2 12%, MgO 7%, FeO+MnO≤1.0%, and basicity 4.6; the refining time is 48 min, the white slag time is 15 min, the mass percentage of Al in the molten steel is controlled at 0.018%, and the mass percentage of V in the molten steel is controlled at 0.11%.

[0074] In the vacuum refining process, the vacuum time is controlled to be below 67 Pa for 20 minutes, the soft blowing time is 16 minutes, and the H content in the molten steel is controlled to be below 2.0 × 10⁻⁶. -6 The mass percentage of nitrogen in the molten steel is controlled to be 0.016%.

[0075] In the continuous casting process, argon sealing is used for full protection to prevent secondary oxidation of molten steel. The specific water content is 0.8 L / kg, the casting speed is 0.46 m / min, the superheat of the tundish is controlled at 25℃, and the billet obtained after continuous casting is heated at 1120℃ for 450 min.

[0076] During the rolling process, the initial rolling temperature is 1030℃, and the final rolling temperature is 942℃. After rolling, the steel is placed in a pit for slow cooling for 24 hours, and then uncovered at 180℃. The exit temperature is 150℃, and the non-adjustable steel for the hydraulic rod is obtained after the process.

[0077] Example 3

[0078] This embodiment provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, includes: C 0.43%, Si 0.32%, Mn 0.98%, Cr 0.16%, Al 0.010%, V 0.11%, N 0.017%, P 0.025%, S 0.003%, with the balance being Fe and other unavoidable impurities.

[0079] The non-adjustable steel used for the hydraulic rod is prepared using the following method:

[0080] After pretreatment and desulfurization of blast furnace molten iron, it is sequentially smelted in a converter, refined in a ladle, refined in a vacuum, continuously cast and rolled to obtain the non-adjustable steel for the hydraulic rod.

[0081] The final carbon content of the converter smelting is 0.13% by mass, and the final phosphorus content of the converter smelting is 0.014% by mass.

[0082] In the ladle refining process, the slag system used comprises, by mass percentage: CaO 53%, Al2O3 26%, SiO2 13%, MgO 7%, FeO+MnO≤1.0%, and basicity 4.1; the refining time is 48 min, the white slag time is 15 min, the mass percentage of Al in the molten steel is controlled at 0.010%, and the mass percentage of V in the molten steel is controlled at 0.11%.

[0083] In the vacuum refining process, the vacuum time is controlled to be below 67 Pa for 18 minutes, the soft blowing time is 15 minutes, and the H content in the molten steel is controlled to be below 2.0 × 10⁻⁶. -6 The mass percentage of nitrogen in the molten steel is controlled to be 0.017%.

[0084] In the continuous casting process, argon sealing is used for full protection to prevent secondary oxidation of molten steel. The specific water content is 0.9 L / kg, the casting speed is 0.5 m / min, the superheat of the tundish is controlled at 20℃, and the billet obtained after continuous casting is heated at 1100℃ for 600 min.

[0085] During the rolling process, the initial rolling temperature is 1080℃, and the final rolling temperature is 919℃. After rolling, the steel is placed in a pit for slow cooling for 24 hours, and the cover is removed at 180℃. The exit temperature is 150℃, and the non-adjustable steel for the hydraulic rod is obtained after the process.

[0086] Example 4

[0087] This embodiment provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, includes: C 0.41%, Si 0.28%, Mn 1.02%, Cr 0.20%, Al 0.020%, V 0.09%, N 0.013%, P 0.023%, S 0.005%, with the balance being Fe and other unavoidable impurities.

[0088] The non-adjustable steel used for the hydraulic rod is prepared using the following method:

[0089] After pretreatment and desulfurization of blast furnace molten iron, it is sequentially smelted in a converter, refined in a ladle, refined in a vacuum, continuously cast and rolled to obtain the non-adjustable steel for the hydraulic rod.

[0090] The final carbon content of the converter smelting is 0.10% by mass, and the final phosphorus content of the converter smelting is 0.013% by mass.

[0091] In the ladle refining process, the slag system used comprises, by mass percentage: CaO 58%, Al2O3 22%, SiO2 10%, MgO 6%, FeO+MnO≤1.0%, and basicity 5.8; the refining time is 52 min, the white slag time is 16 min, the mass percentage of Al in the molten steel is controlled at 0.020%, and the mass percentage of V in the molten steel is controlled at 0.09%.

[0092] In the vacuum refining process, the vacuum time controlled at below 67 Pa is 19 min, the soft blowing time is 15 min, and the H content in the molten steel is controlled at 2.0 × 10⁻⁶. -6 The mass percentage of nitrogen in the molten steel is controlled at 0.013%.

[0093] In the continuous casting process, argon sealing is used for full protection to prevent secondary oxidation of molten steel. The specific water content is 0.7 L / kg, the casting speed is 0.4 m / min, the superheat of the tundish is controlled at 30℃, and the billet obtained after continuous casting is heated at 1180℃ for 400 min.

[0094] During the rolling process, the initial rolling temperature is 1000℃, and the final rolling temperature is 937℃. After rolling, the steel is placed in a pit for slow cooling for 24 hours, and then uncovered at 180℃. The exit temperature is 150℃, and the non-adjustable steel for the hydraulic rod is obtained after the process.

[0095] Example 5

[0096] This embodiment provides a non-adjustable steel for hydraulic rods, the chemical composition of which is consistent with that of Embodiment 1.

[0097] The method for preparing the non-adjustable steel for the hydraulic rod differs from that in Example 1 in that the specific water content in continuous casting is set to 0.5 L / kg.

[0098] Example 6

[0099] This embodiment provides a non-adjustable steel for hydraulic rods, the chemical composition of which is consistent with that of Embodiment 1.

[0100] The method for preparing the non-adjustable steel for the hydraulic rod differs from that in Example 1 in that the specific water content in continuous casting is set to 1.1 L / kg.

[0101] Example 7

[0102] This embodiment provides a non-adjustable steel for hydraulic rods, the chemical composition of which is consistent with that of Embodiment 1.

[0103] The method for preparing the non-adjustable steel for the hydraulic rod differs from that in Example 1 in that the heating temperature of the billet after continuous casting is set to 1000℃.

[0104] Example 8

[0105] This embodiment provides a non-adjustable steel for hydraulic rods, the chemical composition of which is consistent with that of Embodiment 1.

[0106] The method for preparing the non-adjustable steel for the hydraulic rod differs from that in Example 1 in that the heating temperature of the billet after continuous casting is set to 1250°C.

[0107] Example 9

[0108] This embodiment provides a non-adjustable steel for hydraulic rods, the chemical composition of which is consistent with that of Embodiment 1.

[0109] The method for preparing the non-adjustable steel for the hydraulic rod differs from that in Example 1 in that the heating time of the billet after continuous casting is set to 350 min.

[0110] Comparative Example 1

[0111] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.40%, Si 0.28%, Mn 1.01%, Cr 0.19%, Al 0.016%, V 0.10%, N 0.014%, P 0.024%, S 0.004%, with the balance being Fe and other unavoidable impurities.

[0112] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0113] Comparative Example 2

[0114] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.42%, Si 0.30%, Mn 0.90%, Cr 0.19%, Al 0.013%, V 0.09%, N 0.015%, P 0.024%, S 0.005%, with the balance being Fe and other unavoidable impurities.

[0115] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0116] Comparative Example 3

[0117] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, by mass percentage, includes: C 0.42%, Si 0.29%, Mn 0.99%, Cr 0.18%, Al 0.016%, V 0.06%, N 0.016%, P 0.023%, S 0.004%, with the balance being Fe and other unavoidable impurities.

[0118] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0119] Comparative Example 4

[0120] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.41%, Si 0.31%, Mn 0.99%, Cr 0.10%, Al 0.015%, V 0.10%, N 0.016%, P 0.024%, S 0.005%, with the balance being Fe and other unavoidable impurities.

[0121] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0122] Comparative Example 5

[0123] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.41%, Si 0.30%, Mn 1.01%, Cr 0.19%, Al 0.006%, V 0.10%, N 0.014%, P 0.024%, S 0.004%, with the balance being Fe and other unavoidable impurities.

[0124] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0125] Comparative Example 6

[0126] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.42%, Si 0.30%, Mn 1.15%, Cr 0.18%, Al 0.016%, V 0.11%, N 0.014%, P 0.024%, S 0.004%, with the balance being Fe and other unavoidable impurities.

[0127] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0128] Comparative Example 7

[0129] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.42%, Si 0.28%, Mn 1.01%, Cr 0.19%, Al 0.015%, V 0.10%, N 0.010%, P 0.023%, S 0.005%, with the balance being Fe and other unavoidable impurities.

[0130] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0131] Comparative Example 8

[0132] This comparative example provides a non-adjustable steel for hydraulic rods. The chemical composition of the non-adjustable steel for hydraulic rods, in mass percentage, includes: C 0.45%, Si 0.28%, Mn 1.01%, Cr 0.19%, Al 0.015%, V 0.10%, N 0.140%, P 0.023%, S 0.005%, with the balance being Fe and other unavoidable impurities.

[0133] In the preparation process of the non-adjustable steel for the hydraulic rod, the composition of the molten steel is controlled to obtain the chemical composition of the non-adjustable steel for the hydraulic rod, and the other preparation parameters are the same as in Example 1.

[0134] Performance testing

[0135] The hydraulic rods prepared in the examples and comparative examples were subjected to mechanical property tests using non-adjustable steel, and the results are shown in Table 1.

[0136] Table 1

[0137]

[0138] As can be seen from the results in Table 1, the non-adjustable steel for hydraulic rods of the present invention achieves microstructural control through the synergistic regulation of alloying elements, thereby synergistically improving the strength, toughness, and plasticity of the steel. The yield strength is ≥509 MPa, tensile strength ≥757 MPa, impact energy ≥52 J, hardness ≥231 HBW, reduction of area ≥45%, and elongation ≥18.5%. In contrast, in Comparative Examples 1-8, when the amount of alloying elements exceeded the range of this application, the steel performance showed a significant deterioration.

[0139] Furthermore, compared to other embodiments, the steel properties of Embodiments 1-4 are superior. A comparison of the results of Embodiment 1 with those of Embodiments 5-9 shows that by controlling the process parameters of continuous casting and rolling within the preferred range of this invention, the steel properties can be further improved.

[0140] In summary, the non-heat-treated steel of the present invention obtains a fine-grained ferrite and pearlite structure through a narrow composition design of chemical composition, without the need for heat treatment, which significantly improves the strength, toughness and plasticity of the steel, meeting the service requirements of hydraulic rods under high pressure, reciprocating impact and alternating loads under different load levels; furthermore, the steel performance is further improved through controlled casting and rolling during the preparation process.

[0141] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-adjustable steel for a hydraulic rod, characterized in that, The chemical composition of the non-adjustable steel used in the hydraulic rod, by mass percentage, includes: C 0.41%-0.43%, Si 0.28%-0.32%, Mn 0.98%-1.02%, Cr 0.16%-0.20%, Al 0.010%-0.020%, V 0.09%-0.11%, N 0.013%-0.017%, P≤0.025%, S≤0.005%, with the balance being Fe and other unavoidable impurities.

2. A method for preparing non-adjustable steel for hydraulic rods as described in claim 1, characterized in that, The preparation method includes: sequentially subjecting blast furnace molten iron to converter smelting, ladle refining, vacuum refining, continuous casting, and rolling to obtain the non-adjustable steel for the hydraulic rod.

3. The preparation method according to claim 2, characterized in that, The final carbon content of the converter smelting is 0.06%-0.15% by mass. Preferably, the final P content of the converter smelting is ≤0.014% by mass percentage.

4. The preparation method according to claim 2 or 3, characterized in that, The composition of the slag system used in the ladle refining, by mass percentage, includes: CaO 50%-60%, Al2O3 20%-35%, SiO2 8%-18%, MgO 4%-8%, FeO+MnO≤1.0%, and the basicity of the slag system is 3.0-6.

0. Preferably, the refining time of the ladle refining is ≥48 min; Preferably, the white slag time in the ladle refining process is ≥15 min.

5. The preparation method according to any one of claims 2-4, characterized in that, The mass percentage of Al in the molten steel is controlled to be 0.010%-0.020% during the ladle refining process. Preferably, the mass percentage of V in the molten steel is controlled to be 0.09%-0.11% during the ladle refining process.

6. The preparation method according to any one of claims 2-5, characterized in that, The vacuum degree in the vacuum refining process is ≤67Pa; Preferably, the vacuum time in the vacuum refining process is ≥18 min; Preferably, the soft blowing time in the vacuum refining process is ≥15 min.

7. The preparation method according to any one of claims 2-6, characterized in that, In the vacuum refining process, the H content in the molten steel is controlled to be ≤2.0×10⁻⁶. -6 ; Preferably, the mass percentage of N in the molten steel is controlled to be 0.013%-0.017% during the vacuum refining process.

8. The preparation method according to any one of claims 2-7, characterized in that, Argon sealing is used in the continuous casting process; Preferably, the specific water content in the continuous casting is 0.7-0.9 L / kg; Preferably, the casting speed in the continuous casting process is 0.44-0.52 m / min; Preferably, the superheat of the tundish in the continuous casting is controlled at 20-30°C.

9. The preparation method according to any one of claims 2-8, characterized in that, After continuous casting, the resulting billet is heated; Preferably, the heating temperature is 1100-1180℃; Preferably, the heating time is 390-600 min.

10. The preparation method according to any one of claims 2-9, characterized in that, The initial rolling temperature is 1000-1080℃; Preferably, the final rolling temperature is 900-950℃; Preferably, the material is subjected to slow cooling in a pit after rolling; Preferably, the cooling time for slow cooling in the pit is ≥24 hours; Preferably, the temperature of the pit after slow cooling is ≤150℃.

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