Continuous casting round billet and preparation method and application thereof

Abstract

The invention provides a continuous casting round billet as well as a preparation method and application thereof. The continuous casting round billet comprises the following components: 0.30 to 0.38 weight percent of C, 0.50 to 0.80 weight percent of Mn, 1.30 to 1.70 weight percent of Cr, 0.15 to 0.30 weight percent of Mo, 1.30 to 1.70 weight percent of Ni, 0.05 to 0.10 weight percent of Nb, 0.05 to 0.08 weight percent of V, less than or equal to 0.40 weight percent of Si, less than or equal to 0.030 weight percent of P, less than or equal to 0.030 weight percent of S and the balance of Fe. By optimizing the contents of C, Mn, Cr, Mo and Ni elements and cooperatively doping Nb and V elements with specific contents, the tensile strength, the yield strength and the impact energy at-40 DEG C (KV2) of the obtained continuous casting round billet are improved; and meanwhile, the composition segregation of the cross section is improved, and the requirements of the steel for the offshore steamship generator crankshaft are met.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy materials, and relates to a continuous casting round billet and a preparation method and application thereof, and in particular to a continuous casting round billet for a marine ship engine crankshaft and a preparation method thereof. Background Art

[0002] Large marine low-speed diesel engines need huge power to propel large ships to sail in the ocean, so their crankshafts are generally very large, tens of meters long and hundreds of tons heavy, which makes crankshaft manufacturing very difficult. The crankshaft, the main stress-bearing part of the engine, is mainly made of 34CrNiMo6 steel. Its common fatigue failure is metal fatigue failure, namely bending fatigue failure and torsional fatigue failure, most of which are bending fatigue failures; among them, bending fatigue failure first occurs at the connecting rod journal (crank pin) or the main journal fillet, and then develops to the crank arm; torsional fatigue cracks occur in poorly processed oil holes or fillets, and then develop in the direction of the axis.

[0003] Moreover, since the crankshaft operates in various harsh environments such as severe cold and scorching heat, and the natural environment is inconvenient for transportation and installation and maintenance, its reliability and service life are much higher than those of general machinery, especially the fatigue strength, low-temperature toughness and other performance requirements of the material are extremely strict; therefore, it is particularly important to strengthen the research on steel for marine ship engine crankshafts.

[0004] CN115058658A discloses a crankshaft, a crankshaft steel and a preparation method thereof, which are composed of the following chemical components in mass fraction: C: 0.39-0.45%; Si: 0.17-0.37%; Mn: 0.6-0.8%; Cr: 1.05-1.20%, Mo: 0.18-0.25%, V: 0.05-0.12%, Al: 0.015-0.040%, T.[O]≤0.0015%, P≤0.015%, S≤0.015%; Ni≤0.1%, Cu≤0.1%, N: 0.0050-0.0070%, and the remainder is Fe and unavoidable impurities; however, its room temperature impact energy is 68-70J, and the impact energy at a low temperature of -40°C is obviously much lower, and the degree of segregation of the cross section is not studied, which cannot meet the requirements of offshore ship generators for crankshafts.

[0005] CN111101056A discloses a crankshaft steel and a method for manufacturing a crankshaft, wherein the crankshaft steel includes 0.37wt% to 0.42wt% carbon (C), 0.55wt% to 0.70wt% silicon (Si), 1.45wt% to 1.65wt% manganese (Mn), 0.025wt% or less (excluding 0wt%) phosphorus (P), 0.020wt% to 0.035wt% sulfur (S), 0.15wt% to 0.30wt% chromium (Cr), 0.035wt% to 0.055% vanadium (V), and the remainder is iron and other inevitable impurities; its tensile strength is above 900MPa, and its yield strength is above 600MPa; there is still a lot of room for improvement, and the impact work at a low temperature of -40°C has not been studied, and the cross-sectional segregation phenomenon has not been improved.

[0006] Therefore, people are in urgent need of developing a continuous casting round billet with high strength and high low temperature toughness and a preparation method thereof, which can refine the grain structure in the steel, significantly improve the cross-sectional component segregation phenomenon, and meet the requirements of marine engine crankshafts. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a continuous casting round billet and a preparation method and application thereof, wherein specific contents of Nb and V elements are doped into the continuous casting round billet, and the content ratio of elements such as C, Mn, Cr, Mo, and Ni are optimized, thereby improving the tensile strength and low-temperature toughness, refining the steel grain structure, and improving the cross-sectional component segregation phenomenon; and the preparation process is simple and controllable; the continuous casting round billet can meet the requirements of crankshafts for generators for marine ships.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a continuous casting round billet, which comprises the following components: C: 0.30-0.38wt%, Mn: 0.50-0.80wt%, Cr: 1.30-1.70wt%, Mo: 0.15-0.30wt%, Ni: 1.30-1.70wt%, Nb: 0.05-0.10wt%, V: 0.05-0.08wt%, Si≤0.40wt%, P≤0.030wt%, S≤0.030wt% and the balance Fe.

[0010] The content of each element can be selected as follows: C: 0.30-0.38wt%, for example, 0.30wt%, 0.32wt%, 0.34wt%, 0.36wt% or 0.38wt%; Mn: 0.50-0.80wt%, for example, 0.50wt%, 0.55wt%, 0.60wt%, 0.65wt%, 0.70wt%, 0.75wt% or 0.80wt%; Cr: 1.30-1.70wt%, for example, 1 .30wt%, 1.40wt%, 1.50wt%, 1.60wt% or 1.70wt%; Mo: 0.15-0.30wt%, for example, 0.15wt%, 0.18wt%, 0.20wt%, 0.23wt%, 0.25wt%, 0.28wt% or 0.30wt%; Ni: 1.30-1.70wt%, for example, 1.30wt%, 1.35wt%, 1.40wt%, 1.45wt%, 1.50wt%, 1.60wt% or 1.70wt%; 55wt%, 1.60wt%, 1.65wt% or 1.70wt%, etc.; Nb: 0.05-0.10wt%, for example, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt% or 0.10wt%, etc.; V: 0.05-0.08wt%, for example, 0.05wt%, 0.055wt%, 0.06wt%, 0.065wt%, 0.070wt%, 0.075wt% or 0.08wt%, etc. ; Si≤0.40wt%, for example, it can be 0.40wt%, 0.35wt%, 0.30wt%, 0.25wt% or 0.20wt%, etc.; P≤0.030wt%, for example, it can be 0.030wt%, 0.025wt%, 0.020wt%, 0.015wt% or 0.010wt%, etc.; S≤0.030wt%, for example, it can be 0.030wt%, 0.025wt%, 0.020wt%, 0.015wt% or 0.010wt%, etc.

[0011] The present invention optimizes the contents of elements such as C, Mn, Cr, Mo and Ni in the chemical composition of the continuous casting round billet, and adds specific contents of Nb and V elements to inhibit the deformation recrystallization of austenite and prevent the growth of its grains, and achieves the refinement and precipitation strengthening effects of steel through the strain-induced precipitation of their carbonitrides. The composite elements work together to refine the grain structure of the continuous casting round billet and improve the internal component segregation of the continuous casting round billet; at the same time, the tensile strength, yield strength and impact work of the continuous casting round billet at -40°C (KV2) are improved, meeting the requirements of generator crankshafts for marine ships.

[0012] Preferably, the C content in the continuous casting round billet is 0.34-0.36wt%.

[0013] Preferably, the Mn content in the continuous casting round billet is 0.70-0.78wt%.

[0014] Preferably, the Cr content in the continuous casting round billet is 1.62-1.70wt%.

[0015] Preferably, the content of Mo in the continuous casting round billet is 0.23-0.28wt%.

[0016] Preferably, the Ni content in the continuous casting round billet is 1.60-1.65wt%.

[0017] Preferably, the Si content in the continuous casting round billet is 0.30-0.35wt%.

[0018] Preferably, the P content in the continuous casting round billet is ≤0.010wt%.

[0019] Preferably, the S content in the continuous casting round billet is ≤0.005wt%.

[0020] Preferably, the Nb content in the continuous casting round billet is 0.07-0.09wt%.

[0021] Preferably, the V content in the continuous casting round billet is 0.05-0.07wt%.

[0022] The present invention further preferably has a doped Nb content of 0.07-0.09wt%, and preferably has a V content of 0.05-0.07wt%, which is beneficial to improving the tensile strength and yield strength of the continuous casting round billet; if the doped Nb or V content is too low, the continuous casting round billet performance will be poor; if the doped Nb or V content is too high, the Nb or V precipitation phase will precipitate at the grain boundary and weaken the grain boundary, and the continuous casting round billet will have a risk of cracking and a high cost.

[0023] In a second aspect, the present invention provides a method for preparing the continuously cast round billet as described in the first aspect, the preparation method comprising: continuously casting and cooling molten steel in sequence to obtain the continuously cast round billet.

[0024] The continuous casting round billet of the present invention can be obtained by directly continuous casting molten steel and then cooling it. By regulating the element composition of the molten steel and the parameters of the continuous casting process, a high-strength and tough continuous casting round billet is successfully prepared, and at the same time, the grain structure is refined and the cross-sectional component segregation phenomenon is improved. The preparation process is simple and controllable, and the cost is low.

[0025] The method for preparing the molten steel comprises: selecting a steel ingot raw material according to the element composition ratio of the continuous casting round billet described in the first aspect, and sequentially subjecting the steel ingot raw material to KR desulfurization, converter smelting, ladle refining and vacuum refining to obtain the molten steel.

[0026] Preferably, the continuous casting is carried out in a continuous casting machine.

[0027] Preferably, the pulling speed during the continuous casting is 0.20-0.24 m / min, for example, it can be 0.20 m / min, 0.21 m / min, 0.22 m / min, 0.23 m / min or 0.24 m / min.

[0028] Preferably, the superheat during continuous casting is 15-25°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C or 25°C.

[0029] It is worth mentioning that superheat refers to the difference between the pouring temperature of molten steel during the process and the liquidus temperature.

[0030] The present invention further preferably sets the pulling speed during continuous casting to 0.20-0.24 m / min and the superheat to 15-25°C, which is beneficial to improving the quality of the obtained continuously cast round billet; if the superheat during continuous casting is too low, it will cause cracks on the surface of the continuously cast round billet and even cause casting interruption; if the superheat during continuous casting is too high, it will cause steel leakage, thereby forcing the pulling speed to be reduced to avoid steel leakage, but the output will decrease, and the continuously cast round billet may even develop into columnar crystals, thereby causing central segregation and looseness of the continuously cast round billet.

[0031] Preferably, the current of electromagnetic stirring of the crystallizer in the continuous casting machine is 190-210A, for example, it can be 190A, 195A, 200A, 205A or 210A.

[0032] Preferably, the frequency of the electromagnetic stirring of the crystallizer is 1.5-2 Hz, for example, 1.5 Hz, 1.6 Hz, 1.7 Hz, 1.8 Hz, 1.9 Hz or 2 Hz.

[0033] The present invention further preferably sets the current of the electromagnetic stirring of the crystallizer in the continuous casting machine to 190-210A and the frequency to 1.5-2Hz; this is beneficial to improving the component segregation from the subcutaneous layer to the edge of the columnar crystal of the continuously cast round billet; if the current or frequency of the electromagnetic stirring of the crystallizer is too low, it will cause the density of the central area of ​​the continuously cast round billet to gradually decrease, and the carbon segregation in the center of the continuously cast round billet to gradually increase; if the current or frequency of the electromagnetic stirring of the crystallizer is too high, it will cause the inclusion of protective slag, which will increase the inclusion content and increase the energy consumption.

[0034] Preferably, the current of the terminal electromagnetic stirring in the continuous casting machine is 850-950A, for example, it can be 850A, 860A, 870A, 880A, 890A, 900A, 910A, 920A, 930A, 940A or 950A.

[0035] Preferably, the frequency of the terminal electromagnetic stirring is 5-7 Hz, for example, 5 Hz, 5.5 Hz, 6 Hz, 6.5 Hz or 7 Hz.

[0036] The present invention further prefers that the current of the terminal electromagnetic stirring in the continuous casting machine is 850-950A and the frequency is 5-7Hz; this is beneficial to improving the composition segregation in the equiaxed crystal region of the continuous casting round billet; if the current or frequency of the terminal electromagnetic stirring is too low, the effect of improving the central looseness or segregation is not obvious; if the current or frequency of the terminal electromagnetic stirring is too high, a white bright band will appear in the continuous casting round billet.

[0037] Preferably, the cooling method includes slow cooling in a pit.

[0038] Preferably, the pit entry temperature for slow cooling is ≥500°C, for example, it may be 500°C, 550°C, 600°C, 650°C or 700°C.

[0039] Preferably, the time for slow cooling in the pit is ≥120h, for example, it can be 120h, 130h or 150h.

[0040] Preferably, the exit temperature of the slow cooling in the pit is ≤200°C, for example, it can be 200°C, 180°C, 150°C or 120°C.

[0041] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0042] The molten steel is continuously cast in a continuous casting machine, the pulling speed during continuous casting is 0.20-0.24 m / min, the superheat is 15-25°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 190-210A, the frequency is 1.5-2Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 850-950A, and the frequency is 5-7Hz; then, the molten steel is cooled by slow cooling in a pit, the pit entry temperature of the slow cooling in the pit is ≥500°C, the time is ≥120h, and the pit exit temperature is ≤200°C, so as to finally obtain the continuously cast round billet.

[0043] In a third aspect, the present invention provides an application of the continuously cast round billet described in the first aspect, wherein the continuously cast round billet is used to prepare a crankshaft, preferably a crankshaft for a marine ship engine.

[0044] The continuously cast round billet provided by the present invention can be used to prepare the crankshaft of the marine ship engine, and its strength and toughness can meet the requirements of the operation of the marine ship engine and has a long service life.

[0045] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The continuous casting round billet provided by the present invention optimizes the content ratio of C, Mn, Cr, Mo and Ni elements, and adds specific contents of Nb and V elements for composite strengthening. The combined effect of the elements strengthens the strength and toughness of the obtained continuous casting round billet, refines the grain structure and improves the cross-sectional segregation phenomenon. The tensile strength is preferably as high as 1076MPa or more, the yield strength is preferably as high as 766MPa or more, and the impact energy at -40°C (KV2) is preferably as high as 62J or more. At the same time, the cross-sectional component segregation phenomenon is improved, and the cross-sectional carbon segregation extreme value is ≤0.035%.

[0048] (2) The present invention provides a method for preparing a continuously cast round billet. The method controls the pulling speed, superheat, current and frequency of electromagnetic stirring of the crystallizer, and current and frequency of electromagnetic stirring at the end during continuous casting, so that the prepared continuously cast round billet has high strength and high toughness, and effectively improves the cross-sectional segregation phenomenon, which can meet the requirements of the use environment and life of the crankshaft of a generator for marine ships. In addition, the method has simple procedures, easy-to-control conditions and low cost.

[0049] (3) Application of the continuous casting round billet provided by the present invention. The continuous casting round billet can be used to prepare the crankshaft of the marine ship engine, which can meet the requirements of being used in a low temperature environment of -40°C, has high strength and toughness, and a long service life. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] The specific implementation method of the present invention provides a continuous casting round billet and a preparation method and application thereof, wherein the continuous casting round billet comprises the following components:

[0052] C: 0.30~0.38wt%, Mn: 0.50~0.80wt%, Cr: 1.30~1.70wt%, Mo: 0.15~0.30wt%, Ni: 1.30~1.7 0wt%, Nb: 0.05~0.10wt%, V: 0.05~0.08wt%, Si≤0.40wt%, P≤0.030wt%, S≤0.030wt% and the balance Fe.

[0053] 1. Implementation

[0054] Example 1

[0055] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.35wt%, Mn: 0.74wt%, Cr: 1.66wt%, Mo: 0.255wt%, Ni: 1.625wt%, Nb: 0.08wt%, V: 0.065wt%, Si: 0.325wt%, P: 0.009wt%, S: 0.004wt% and the balance Fe.

[0056] The preparation method comprises the following steps:

[0057] The molten steel is continuously cast in a continuous casting machine, wherein the pulling speed during continuous casting is 0.21 m / min, the superheat is 20°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 200A, the frequency is 1.75 Hz, and the current of the terminal electromagnetic stirring in the continuous casting machine is 900A, and the frequency is 6 Hz; then the molten steel is cooled by slow cooling in a pit, wherein the pit temperature of the slow cooling in the pit is 500°C, the time is 150h, and the pit exit temperature is 200°C, and finally the continuously cast round billet is obtained;

[0058] The cross-sectional segregation extreme difference (excluding the center point) of the continuous casting round billet obtained in this embodiment is 0.030%.

[0059] Example 2

[0060] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.34wt%, Mn: 0.70wt%, Cr: 1.62wt%, Mo: 0.23wt%, Ni: 1.60wt%, Nb: 0.07wt%, V: 0.06wt%, Si: 0.30wt%, P: 0.008wt%, S: 0.003wt% and the balance Fe.

[0061] The preparation method comprises the following steps:

[0062] The molten steel is continuously cast in a continuous casting machine, wherein the pulling speed during continuous casting is 0.20 m / min, the superheat is 15° C., the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 190 A, the frequency is 1.5 Hz, and the current of the terminal electromagnetic stirring in the continuous casting machine is 850 A, the frequency is 5 Hz; then, the molten steel is cooled by slow cooling in a pit, the pit temperature of the slow cooling in the pit is 600° C., the time is 120 h, and the pit exit temperature is 180° C., and finally the continuously cast round billet is obtained;

[0063] The cross-sectional segregation extreme difference (excluding the center point) of the continuous casting round billet obtained in this embodiment is 0.035%.

[0064] Example 3

[0065] The present embodiment provides a continuous casting round billet and a preparation method thereof, wherein the continuous casting round billet comprises the following components: C: 0.36wt%, Mn: 0.78wt%, Cr: 1.70wt%, Mo: 0.28wt%, Ni: 1.65wt%, Nb: 0.10wt%, V: 0.08wt%, Si: 0.35wt%, P: 0.010wt%, S: 0.005wt% and the remainder Fe.

[0066] The preparation method comprises the following steps:

[0067] The molten steel is continuously cast in a continuous casting machine, wherein the pulling speed during continuous casting is 0.24 m / min, the superheat is 25° C., the current of electromagnetic stirring of the crystallizer in the continuous casting machine is 210 A, the frequency is 2 Hz, and the current of electromagnetic stirring at the end of the continuous casting machine is 950 A, the frequency is 7 Hz; then, the molten steel is cooled by slow cooling in a pit, the pit temperature of the slow cooling in the pit is 550° C., the time is 130 h, and the pit exit temperature is 150° C., and finally the continuously cast round billet is obtained;

[0068] The cross-sectional segregation extreme difference (excluding the center point) of the continuous casting round billet obtained in this embodiment is 0.032%.

[0069] Example 4

[0070] This embodiment provides a continuous casting round billet and a preparation method thereof. Except that the current of the terminal electromagnetic stirring in the continuous casting machine is 840A, the rest is the same as that in Embodiment 1.

[0071] Example 5

[0072] This embodiment provides a continuous casting round billet and a preparation method thereof. Except that the current of the terminal electromagnetic stirring in the continuous casting machine is 960A, the rest is the same as that in Embodiment 1.

[0073] Examples 6 to 12 and Comparative Examples 1 to 10 adjust the element composition and content ratio on the basis of Example 1, and the rest are the same as Example 1. The element composition and content ratio are shown in Table 1, the content of the unadjusted component is the same as that of Example 1, and the content of the adjusted component is adjusted correspondingly to the Fe content.

[0074] Table 1

[0075] project C (wt%) Mn (wt%) Cr(wt%) Mo (wt%) Ni(wt%) Nb(wt%) V(wt%) Example 1 0.35 0.74 1.66 0.255 1.625 0.08 0.065 Example 6 0.30 0.74 1.66 0.255 1.625 0.08 0.065 Example 7 0.35 0.50 1.66 0.255 1.625 0.08 0.065 Example 8 0.35 0.74 1.30 0.255 1.625 0.08 0.065 Example 9 0.35 0.74 1.66 0.15 1.625 0.08 0.065 Example 10 0.35 0.74 1.66 0.255 1.30 0.08 0.065 Embodiment 11 0.35 0.74 1.66 0.255 1.625 0.10 0.065 Example 12 0.35 0.74 1.66 0.255 1.625 0.08 0.08 Comparative Example 1 0.28 0.74 1.66 0.255 1.625 0.08 0.065 Comparative Example 2 0.35 0.48 1.66 0.255 1.625 0.08 0.065 Comparative Example 3 0.35 0.74 1.25 0.255 1.625 0.08 0.065 Comparative Example 4 0.35 0.74 1.66 0.32 1.625 0.08 0.065 Comparative Example 5 0.35 0.74 1.66 0.255 1.45 0.08 0.065 Comparative Example 6 0.35 0.74 1.66 0.255 1.625 0.03 0.065 Comparative Example 7 0.35 0.74 1.66 0.255 1.625 0.08 0.04 Comparative Example 8 0.35 0.74 1.66 0.255 1.625 / 0.065 Comparative Example 9 0.35 0.74 1.66 0.255 1.625 0.08 / Comparative Example 10 0.35 0.74 1.66 0.255 1.625 / /

[0076] Wherein “ / ” indicates that the continuous casting round billet does not contain the corresponding element.

[0077] 3. Test and its results

[0078] The tensile strength, yield strength, impact energy (-40°C) and extreme value of carbon segregation in cross section (taking Φ600mm specification as an example) of the continuous casting round billet provided in the above embodiments and comparative examples were tested and calculated, and the results are shown in Table 2.

[0079] Table 2

[0080]

[0081]

[0082] From Table 2, we can see that:

[0083] (1) It can be seen from Examples 1 to 3 that the present invention optimizes the content of elements such as C, Mn, Cr, Mo and Ni in the continuous casting round billet and dopes Nb and V elements at specific contents. The elements work together to improve the impact toughness of the continuous casting round billet, the tensile strength is increased to more than 1076 MPa, the yield strength is increased to more than 766 MPa, and the impact energy is as high as more than 62 J at -40°C.

[0084] (2) Based on Example 1 and Examples 4 to 5, it can be seen that since the current of the terminal electromagnetic stirring in the continuous casting machine in Examples 4 and 5 is too low or too high, the strength and toughness of the continuously cast round billet are reduced; therefore, it can be seen that the present invention further improves the strength and toughness of the continuously cast round billet by further optimizing the current of the terminal electromagnetic stirring in the continuous casting machine during the continuous casting process to 850 to 950A, and at the same time, the impact energy at -40°C is also improved.

[0085] (3) Based on Example 1 and Examples 6 to 12, it can be seen that the present invention further preferably has the contents of C, Mn, Cr, Mo and Ni within a specific range, and doped with Nb and V elements within a preferred content range. The combined effect of each element further improves the strength and toughness of the resulting continuous casting round billet.

[0086] (4) Combining Example 1 with Comparative Examples 1 to 10, it can be seen that the tensile strength and yield strength of the continuously cast round billets in Comparative Examples 1 to 8 are reduced, and the impact energy at -40°C is also greatly reduced; the continuously cast round billets in Comparative Examples 9 to 10 are not doped with Nb and / or V elements, and various properties of the obtained continuously cast round billets are greatly reduced; it can be seen that the present invention greatly improves the strength and toughness of the continuously cast round billets by optimizing the element components and content ratios of the continuously cast round billets, and synergistically doping with specific contents of Nb and V elements, and can meet the requirements of the use environment and service life of offshore wind power gear steel.

[0087] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A continuous casting round billet, characterized in that: The continuous casting round billet comprises the following components: C: 0.30~0.38wt%, Mn: 0.50~0.80wt%, Cr: 1.30~1.70wt%, Mo: 0.15~0.30wt%, Ni: 1.30~1.7 0wt%, Nb: 0.05~0.10wt%, V: 0.05~0.08wt%, Si≤0.40wt%, P≤0.030wt%, S≤0.030wt% and the balance Fe.

2. The continuous casting round billet according to claim 1, characterized in that: The C content in the continuous casting round billet is 0.34-0.36wt%; Preferably, the content of Mn in the continuous casting round billet is 0.70-0.78wt%; Preferably, the Cr content in the continuous casting round billet is 1.62-1.70wt%; Preferably, the content of Mo in the continuous casting round billet is 0.23-0.28wt%; Preferably, the content of Ni in the continuous casting round billet is 1.60-1.65wt%; Preferably, the Si content in the continuous casting round billet is 0.30-0.35wt%; Preferably, the content of P in the continuous casting round billet is ≤0.010wt%; Preferably, the S content in the continuous casting round billet is ≤0.005wt%.

3. The continuous casting round billet according to claim 1 or 2, characterized in that: The Nb content in the continuous casting round billet is 0.07-0.09wt%; Preferably, the V content in the continuous casting round billet is 0.05-0.07wt%.

4. A method for preparing a continuous casting round billet according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The molten steel is continuously cast and cooled in sequence to obtain the continuously cast round billet.

5. The preparation method according to claim 4, characterized in that: The continuous casting is carried out in a continuous casting machine; Preferably, the pulling speed during continuous casting is 0.20-0.24 m / min; Preferably, the superheat degree during continuous casting is 15-25°C.

6. The preparation method according to claim 5, characterized in that: The current of electromagnetic stirring of the crystallizer in the continuous casting machine is 190-210A; Preferably, the frequency of the electromagnetic stirring of the crystallizer is 1.5-2 Hz.

7. The preparation method according to claim 5 or 6, characterized in that: The current of the terminal electromagnetic stirring in the continuous casting machine is 850-950A; Preferably, the frequency of the terminal electromagnetic stirring is 5 to 7 Hz.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The cooling method includes slow cooling in a pit; Preferably, the pit entry temperature for slow cooling is ≥500°C; Preferably, the slow cooling time in the pit is ≥120h; Preferably, the exit temperature of the slow cooling in the pit is ≤200°C.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The preparation method comprises the following steps: The molten steel is continuously cast in a continuous casting machine, the pulling speed during continuous casting is 0.20-0.24 m / min, the superheat is 15-25°C, the current of the electromagnetic stirring of the crystallizer in the continuous casting machine is 190-210A, the frequency is 1.5-2Hz, the current of the terminal electromagnetic stirring in the continuous casting machine is 850-950A, and the frequency is 5-7Hz; then, the molten steel is cooled by slow cooling in a pit, the pit entry temperature of the slow cooling in the pit is ≥500°C, the time is ≥120h, and the pit exit temperature is ≤200°C, so as to finally obtain the continuously cast round billet.

10. An application of the continuous casting round billet according to any one of claims 1 to 3, characterized in that: The continuously cast round billet is used for producing a crankshaft, preferably a crankshaft for a marine ship engine.

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