A manufacturing method for rapidly forming a large shaft solid forging by using a continuous casting blank

Abstract

The application relates to a manufacturing method for rapidly forming a large shaft solid forging by using a continuous casting blank, and belongs to the field of large shaft forging manufacturing. The method solves at least one of the following problems existing in the traditional process of the large shaft solid forging: (1) the product qualified rate is difficult to meet a higher expected target; (2) the production cost is higher; (3) the production cycle is longer; and (4) the material utilization rate is lower. The manufacturing method comprises the following steps: S1, preparing a blank: a high-carbon alloy steel material continuous casting rod-shaped blank; S2, performing first-time heating on the continuous casting rod-shaped blank, adopting die forging extrusion, and extruding the continuous casting rod-shaped blank into an X-section shaft extrusion piece, wherein X is 1-3; and S3, if the segment number Y of the large shaft solid forging is greater than 3, heating the shaft extrusion piece, and processing the roll necks other than the X segments by using a free forging mode. Through process design and parameter control, the method improves the product qualified rate, reduces the production cost, shortens the production cycle, and improves the material utilization rate.

Description

Technical Field

[0001] This invention relates to the field of large shaft forging technology, and in particular to a method for rapidly forming large solid shaft forgings using continuously cast billets. Background Technology

[0002] Traditional processes for large solid shaft forgings typically involve obtaining ingots through vacuum smelting and casting, or, under conditions requiring high internal quality, producing blanks via electroslag remelting or other methods. Then, using a large hydraulic press or oil press, the ingot is forged freely. Generally, the ingot is first pressed into the jaws, then upset and drawn once or multiple times to compact it. Finally, it is drawn and cut to complete the manufacturing of the shaft forging. The process is as follows: Ingot / electroslag ingot → Free forging (jamming, upsetting + drawing, cutting to produce finished product).

[0003] However, the aforementioned traditional processes have shortcomings in terms of product qualification rate, production cost, production cycle, and material utilization rate. In conclusion, with the development of the equipment manufacturing industry and the continuous improvement of the green manufacturing concept, it is indeed necessary to develop new methods for manufacturing large solid shaft forgings, aiming to improve product qualification rate, reduce production costs, shorten production cycle, and increase material utilization rate. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a manufacturing method for rapidly forming large solid shaft forgings using continuous casting billets, in order to solve at least one of the following problems in the traditional process of large solid shaft forgings: (1) the product qualification rate is difficult to meet the high expected target; (2) the production cost is high; (3) the production cycle is long; (4) the material utilization rate is low.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a method for rapidly forming large solid shaft forgings using continuously cast billets, the method comprising the following steps:

[0007] S1. Prepare billet: The billet is a continuous casting bar billet made of high carbon alloy steel;

[0008] Based on the maximum diameter D1 of the large solid shaft forging to be formed and the extrusion ratio R, determine the initial diameter D0 of the billet, satisfying: D0 = D1 × R 1 / 2 R > 2;

[0009] Based on the weight M1 of the large solid shaft forging to be formed, and considering the pressure residue F during the die forging and extrusion process and the metal oxidation loss L during each heating process, determine the initial weight M0 of the billet, which satisfies: M0=M1×(1+F) / (1-L). nWhere F is 5%–10%, L is 1%–2%, and n is the number of fires;

[0010] S2. The continuously cast bar billet is heated in the first heat, and then extruded into X-segment shaft extrusion parts by die forging. The excess part is removed, and X is 1 to 3.

[0011] S3. If the number of segments Y of the large solid shaft forging to be formed is greater than 3, the X-segment shaft extrusion obtained in step S2 is heated (n-1) times, and the roll necks of the remaining (YX) segments other than the X segment are processed by free forging to obtain the large solid shaft forging.

[0012] Where n≥2, the maximum diameter of the roll neck in the remaining (YX) segments is less than D1.

[0013] Furthermore, in step S2, the main steps of the first heating process include: heating the continuously cast bar billet to T1 = 1200~1250℃ and holding it at that temperature for a holding time t1 = D0 × k1, k1 = 120min~150min / 100mm, where D0 is in mm.

[0014] Furthermore, in step S3, when the number of segments Y is 4 to 7, n = 2, that is, the X-segment shaft extrusion obtained in step S2 is subjected to a second heating.

[0015] Furthermore, in step S3, the main steps of the second heating process include: heating the X-segment shaft extrusion to T2 = 1150~1200℃ and holding it at that temperature for a holding time t2 = D1 × k2, k2 = 40min~55min / 100mm, where D1 is in mm.

[0016] Furthermore, the extrusion ratio R satisfies: 2.5≤R≤4.

[0017] Furthermore, in step S2, the forging speed is controlled between 1 mm / s and 10 mm / s, wherein the speed V1 in the initial stage of extrusion, the speed V2 in the middle stage of extrusion, and the speed V3 in the later stage of extrusion satisfy the following condition: V3 > V1 > V2.

[0018] Furthermore, the initial extrusion velocity V1 is 4 mm / s to 6 mm / s, the middle extrusion velocity V2 is 1 mm / s to 3 mm / s, and the later extrusion velocity V3 is 8 mm / s to 10 mm / s.

[0019] Furthermore, in step S1, chamfers are machined on the upper and lower end faces of the blank, wherein the chamfer on the upper end face is an arc with a radius of 130-170mm, and the chamfer on the lower end face is an arc with a radius of 80-120mm.

[0020] Furthermore, in step S2, the main steps of die forging and extrusion include: first, coating the inner surface of the die forging and extrusion mold with glass powder for lubrication; then, placing the heated billet into the mold; and then using a large press to apply pressure to the mold. The mold will transfer this pressure to the billet, so that the billet is formed under triaxial compressive stress and the interior of the billet is effectively pressed together.

[0021] Further, in step S1, the chemical composition of the high-carbon alloy steel, by mass percentage, includes: C: 0.8–0.9%, Si: 0.65–0.75%, Mn: 0.35–0.45%, P: 0.010–0.015%, S: 0.001–0.005%, Cr: 4.95–5.05%, Ni: 0.30–0.35%, Mo: 0.20–0.25%, V: 0.10–0.15%, N: 0.003–0.005%, with the balance being Fe and unavoidable impurities.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] (1) The present invention uses continuous casting billet as forging raw material, which greatly reduces manufacturing cost. The continuous casting billet is directly extruded into shaft extrusion parts with 3 sections or less by die forging. If necessary, free forging is combined to process the remaining parts with more than 3 sections. Through process design and parameter control, the product qualification rate is improved, which can meet higher expected goals, reduce production costs, shorten the production cycle, and improve material utilization.

[0024] (2) In this invention, by controlling the extrusion ratio R to be greater than 2 when calculating the initial diameter of the billet, it helps to ensure that the loose cracks in the core of the continuously cast billet can be effectively pressed together under the extrusion in the mold. This effectively solves the problem that existing continuously cast billets cannot be used to manufacture large shaft solid forgings due to core defects. The products obtained by this invention have good overall quality, especially ensuring that there are no defects in the core. Even under the condition of high internal quality requirements, the product qualification rate of this invention can reach more than 95%. Moreover, compared with the existing process, the product obtained by this invention has higher dimensional accuracy, especially the roller body with the largest diameter and the roller neck with a larger diameter.

[0025] (3) In this invention, when calculating the initial mass of the billet, by controlling the pressure residue F and the metal oxidation loss L during each heating process to be within a suitable range, it can be ensured that the expected pressure residue and oxidation loss are closer to the actual situation, thereby improving material utilization, reducing material costs, and avoiding unnecessary processing allowance waste. Compared with the traditional free forging process using die-cast steel ingots or electroslag ingots, this invention uses a near-net-shape forming method of "continuous casting billet → die forging extrusion forming" to complete the manufacturing of large shaft solid forgings with 3 or fewer sections in one heating process, which improves production efficiency and shortens the production cycle. This is because the die forging extrusion of 3 or fewer sections, including the largest diameter section, has a much shorter cycle and higher forming accuracy than the multi-heating and gradual forming of free forging. For the remaining sections exceeding 3 sections, since the defects in the core have been effectively pressed together during die forging extrusion, the overall quality of the product, especially the core, is better than that of the existing process.

[0026] (4) In some preferred embodiments, when the first heating is performed before die forging and extrusion, by selecting a suitable heating temperature and holding time, it is helpful to better eliminate the core defects of the continuously cast billet during in-die extrusion, which can promote the homogenization of the internal structure of the material, improve the material uniformity, reduce the resistance during die forging and extrusion, reduce the required forging force, and avoid excessive holding time that would cause energy waste. Overall, it further improves processing efficiency, shortens the production cycle, and reduces costs. It can also reduce the pressure residue in die forging and extrusion and the metal oxidation loss during heating while ensuring product quality and processing performance, which is conducive to improving material utilization.

[0027] (5) In some preferred embodiments, when the number of segments Y of the solid shaft forging to be formed is 4 to 7, it is only necessary to heat it in the second heating process to ensure that the parts other than the 3 segments have good processing performance during free forging. By controlling the process parameters of the second heating process, i.e., selecting appropriate heating temperature and holding time, the product quality can be guaranteed, the overall performance of the product can be improved, and the optimal balance can be achieved between production cost, production cycle and material utilization.

[0028] (6) In some preferred embodiments, during die forging, the extrusion ratio is controlled between 2.5 and 4, which can ensure that the central defects of the continuously cast billet are fully compressed by triaxial compressive stress and have the best microstructure uniformity, and can also achieve the optimal balance between forging quality, production cycle, production cost and material utilization.

[0029] (7) In some preferred embodiments, by controlling the extrusion speed within a suitable range (1 to 10 mm / s), it is possible to ensure more uniform metal flow and reduce defects when filling the die. During the die forging extrusion process, by adopting a variable extrusion speed strategy, namely, a medium speed in the early stage of extrusion, a slow speed in the middle stage of extrusion, and the fastest speed in the later stage of extrusion, it is helpful to improve product quality and overall performance, further shorten the production cycle, reduce production costs, and improve material utilization.

[0030] (8) In some preferred embodiments, by controlling the speed of different stages of die forging and extrusion to be in the appropriate range respectively, for example, the initial extrusion speed V1 is 4mm / s to 6mm / s, the middle extrusion speed V2 is 1mm / s to 3mm / s, and the later extrusion speed V3 is 8mm / s to 10mm / s, it helps to obtain the best product quality and overall performance, while achieving the optimal balance between production cycle, production cost and material utilization.

[0031] (9) In some preferred embodiments, before die forging and extrusion, by opening appropriately sized rounded chamfers on the upper and lower end faces of the prepared blank, the material utilization rate can be maximized while facilitating blank positioning and entry into the mold, reducing the extrusion of the mold gap and helping to improve the surface quality of the formed product.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 A schematic flowchart of the manufacturing method provided by the present invention;

[0035] Figure 2 This is a schematic diagram of the structure from billet to product provided in an embodiment of the present invention, wherein (a) is a billet; (b) is a 3-segment shaft extrusion; and (c) is a 5-segment shaft solid forging.

[0036] Figure 3 The images are of a continuously cast bar billet made of high-carbon alloy steel provided in the embodiments of the present invention, wherein (a) is a cross-sectional image; and (b) is an enlarged view of part A containing the core crack in (a).

[0037] Figure 4 A cross-sectional photograph of a solid shaft forging obtained by the preparation method of this embodiment of the invention;

[0038] Figure 5 The image shows a magnified section of the cross-section of a solid shaft forging obtained by the preparation method of Comparative Example 1.

[0039] Figure 6 The image shows a magnified section of the cross-section of a solid shaft forging obtained by the preparation method of Comparative Example 2 after dye penetrant testing.

[0040] Figure 7 The image shows a magnified section of the cross-section of the solid shaft forging obtained by the preparation method of Comparative Example 6 after dye penetrant testing. Detailed Implementation

[0041] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0042] Traditional processes for large solid shaft forgings have shortcomings in terms of product qualification rate, production cost, production cycle, and material utilization. During free forging, the flow direction and speed of metal are difficult to control precisely, easily leading to uneven microstructure and defects such as localized cracks. For large free forging presses, the precision and control capabilities of the equipment limit the accuracy of the dimensions and shape of large shaft forgings, especially the forming accuracy of the largest diameter roll body and the largest diameter roll neck, making it difficult to meet high expected product qualification rates. The production cost of die-cast steel ingots / electroslag ingots is high, increasing raw material costs. Free forging requires at least three heating cycles, consuming a large amount of energy and increasing production costs. The production cycle of die-cast steel ingots or electroslag ingots is long, and the production efficiency of free forging is relatively low. Each forging cycle is long, and multiple reheating cycles are required to maintain processing plasticity, increasing production time. Material utilization: Die-cast steel ingots or electroslag ingots generate many risers and trimmings during the casting process, resulting in low material utilization, typically only around 50% to 70%.

[0043] Compared to the traditional casting of large solid shaft forgings using die-cast steel ingots / electroslag ingots, continuously cast billets offer advantages such as lower cost, shorter forming cycle, and higher material utilization. However, defects such as shrinkage cavities and microcracks are prone to occur during continuous casting, resulting in poor core quality and limiting the application of continuously cast billets in high-strength applications. Currently, the application of continuously cast billets in shaft forgings is limited to hollow shaft forgings or small low-carbon alloy shaft forgings with low strength requirements. For large solid shaft forgings with high strength requirements, how to successfully manufacture products with high yield rates using continuously cast billets remains a gap in this field, presenting numerous technical challenges. For example, how to overcome core defects through reasonable process and parameter control, and how to shorten the production cycle, reduce costs, and improve material utilization while ensuring product quality in the manufacturing of large shaft forgings, are also multifaceted challenges.

[0044] Based on this, the present invention provides a method for rapidly forming large solid shaft forgings using continuously cast billets, the method comprising the following steps:

[0045] S1. Prepare billet: The billet is a continuous casting bar billet made of high carbon alloy steel;

[0046] Based on the maximum diameter D1 of the large solid shaft forging to be formed and the extrusion ratio R, determine the initial diameter D0 of the billet, satisfying: D0 = D1 × R 1 / 2 R > 2;

[0047] Based on the weight M1 of the large solid shaft forging to be formed, and considering the pressure residue F during the die forging and extrusion process and the metal oxidation loss L during each heating process, determine the initial weight M0 of the billet, which satisfies: M0=M1×(1+F) / (1-L). n Where F is 5%–10%, L is 1%–2%, and n is the number of fires;

[0048] S2. The continuously cast bar billet is heated in the first heat, and then extruded into X-segment shaft extrusion parts by die forging. The excess part is removed, and X is 1 to 3.

[0049] S3. If the number of segments Y of the large solid shaft forging to be formed is greater than 3, the X-segment shaft extrusion obtained in step S2 is heated (n-1) times, and the roll necks of the remaining (YX) segments other than the X segment are processed by free forging to obtain the large solid shaft forging.

[0050] Where n≥2, the maximum diameter of the roll neck in the remaining (YX) segments is less than D1.

[0051] Compared with existing technologies, this invention uses continuously cast billets as forging raw materials, significantly reducing manufacturing costs. It employs die forging to directly extrude the continuously cast billets into shaft-type extrusions of three or fewer segments. If necessary, free forging is combined to process the remaining segments exceeding three. Through process design and parameter control, the product qualification rate is improved, meeting higher expected targets, reducing production costs, shortening the production cycle, and increasing material utilization. Specifically, by controlling the extrusion ratio R to be greater than 2 during the initial billet diameter calculation, it helps ensure that the loose cracks in the core of the continuously cast billet can be effectively pressed together under in-die extrusion. This effectively solves the problem that existing continuously cast billets cannot be used to manufacture large solid shaft forgings due to core defects. The products obtained by this invention have good overall quality, especially ensuring a defect-free core. Even under conditions with high internal quality requirements, the product qualification rate of this invention can reach over 95%. Moreover, compared with existing processes, the dimensional accuracy of the products obtained by this invention is higher, especially for the largest diameter roll body and the larger diameter roll neck. During the initial billet mass calculation, by controlling the residual pressure F and the metal oxidation loss L during each heating cycle to be within appropriate value ranges, the pre-... The pressure residue and oxidation loss during the process are closer to the actual situation, thereby improving material utilization, reducing material costs, and avoiding unnecessary processing allowance waste. Compared with the traditional free forging process using die-cast steel ingots or electroslag ingots, this invention uses a near-net-shape forming method of "continuous casting billet → die forging extrusion forming" to complete the manufacturing of large shaft solid forgings with 3 or fewer sections in one heat, which improves production efficiency and shortens the production cycle. This is because the die forging extrusion of 3 or fewer sections, including the largest diameter section, has a much shorter cycle and higher forming accuracy than the multi-heating and gradual forming of free forging. For the remaining sections exceeding 3 sections, since the defects in the core have been effectively pressed together during die forging extrusion, the overall quality of the product, especially the core, is better than that of the existing process.

[0052] It is understood that the "large solid shaft forging" mentioned in this invention refers to a maximum diameter D1 ≥ 400 mm, for example, D1 = 450 mm. The "extrusion ratio R" refers to: R = A0 / A1, where A0 is the cross-sectional area of ​​the blank before forming, and A1 is the maximum cross-sectional area of ​​the large solid shaft forging after forming. As long as the ratio of A0 / A1 is ensured to be > 2, the extrusion ratio of other sections of the large solid shaft forging will also be greater than 2.

[0053] For example, in step S1, the diameter D0 of the "continuously cast bar billet" is ≥ 640 mm. For example, D0 is 800 mm to 1600 mm.

[0054] Specifically, in step S2, the main steps of the first heating process include: heating the continuously cast rod-shaped billet to T1 = 1200~1250℃ and holding it at that temperature for a holding time t1 = D0 × k1, where k1 = 120min~150min / 100mm, and D0 is in mm. For example, k1 = 125min / 100mm, 130min / 100mm, 135min / 100mm, 140min / 100mm, or 145min / 100mm. Before die forging and extrusion, selecting appropriate heating temperature and holding time has the following benefits in terms of eliminating core defects in continuously cast billets, improving material uniformity, processing efficiency, reducing costs, and improving material utilization: (1) Eliminating core defects: Appropriate heating temperature can promote element diffusion and recrystallization inside the metal material, which helps to eliminate core defects in continuously cast billets, such as shrinkage cavities and cracks, during die extrusion. Appropriate holding time can ensure uniform temperature inside the material, reduce internal stress concentration, and reduce the risk of cracks and pores forming during die extrusion; (2) Improving material uniformity: Appropriate heating temperature and holding time can promote the homogenization of the internal structure of the material, which helps to achieve more uniform deformation in the subsequent die forging and extrusion process. (3) Improve processing efficiency: Appropriate heating temperature and holding time can reduce the resistance in the die forging and extrusion process, reduce the required forging force, and avoid excessive holding time causing energy waste, thereby improving overall processing efficiency; (4) Reduce costs: By optimizing heating temperature and holding time, energy consumption and production time can be reduced while ensuring product quality and processing performance, thus reducing overall production costs; (5) Improve material utilization: Appropriate heating temperature and holding time can reduce the pressure residue in die forging and extrusion and the metal oxidation loss in heating while ensuring product quality and processing performance, thereby reducing processing allowance and subsequent processing requirements, thus improving material utilization.

[0055] It is understandable that the number of segments (i.e., the number of stepped diameter segments) and the variation pattern of stepped diameter in large solid shaft forgings will vary depending on specific production requirements. In actual production, the number of stepped diameter segments in shaft forgings is usually between 2 and 5, and usually does not exceed 7.

[0056] For example, the variation pattern of the step diameter can be that it decreases sequentially from the middle to both ends, such as... Figure 2 (c); or, decrease sequentially from one end to the other.

[0057] Therefore, in step S3, when the number of segments Y is 4 to 7, n = 2, that is, the X-segment shaft extrusion obtained in step S2 is subjected to a second heating. It can be seen that for most large solid shaft forgings, the method of this invention can quickly form a continuous X-segment roll body and roll neck containing the largest diameter. Compared with free forging with multiple heating stages, this greatly shortens the production cycle. The remaining roll necks can be obtained by free forging after the second heating stage. Since the remaining (YX) roll neck segments are small, free forging does not require multiple heating stages. By controlling the process parameters of the second heating stage, workability can be maintained. All roll necks can be formed with fewer heating stages, saving energy, reducing costs, and resulting in products of excellent overall quality with no core defects. Figure 4 .

[0058] Specifically, in step S3, the main steps of the second heating process include: heating the X-segment shaft extrusion to T2 = 1150~1200℃ and holding it at that temperature for a time t2 = D1 × k2, where k2 = 40 min~55 min / 100 mm, and D1 is in mm. More preferably, k2 = 40 min~50 min / 100 mm. For example, k2 = 42 min / 100 mm, 45 min / 100 mm, and 47 min / 100 mm. By selecting appropriate heating temperatures and holding times after die forging and before free forging, product quality can be guaranteed, overall performance improved, and an optimal balance can be achieved between production costs, production cycle, and material utilization. If the temperature is too high or the holding time is too long, the grains may grow excessively, leading to a decrease in the overall performance of the product (such as strength and hardness), while increasing energy consumption and production costs. It will also increase the oxidation loss on the surface of shaft extrusions, thus reducing material utilization. If the temperature is too low or the holding time is too short, the shaft extrusions will not achieve the ideal processing performance, which will increase the force required for free forging, thus lengthening the production cycle and increasing costs. At the same time, due to insufficient plasticity, the residual stress in the product may not be fully released, affecting the dimensional stability, overall quality and performance of the product.

[0059] For example, in step S1, the chemical composition of the high-carbon alloy steel, by mass percentage, includes: C: 0.8-0.9%, Si: 0.65-0.75%, Mn: 0.35-0.45%, P: 0.010-0.015%, S: 0.001-0.005%, Cr: 4.95-5.05%, Ni: 0.30-0.35%, Mo: 0.20-0.25%, V: 0.10-0.15%, N: 0.003-0.005%, with the balance being Fe and unavoidable impurities.

[0060] In some preferred embodiments, the extrusion ratio R satisfies: 2.5 ≤ R ≤ 4. Controlling the extrusion ratio between 2.5 and 4 during die forging ensures that the central defects of the continuously cast billet are fully compressed during die forging, resulting in optimal microstructure uniformity. It also achieves an optimal balance between forging quality, production cycle, production cost, and material utilization. Controlling the extrusion ratio between 2.5 and 4 is particularly suitable for the chemical composition of high-carbon alloy steel as described above. A larger extrusion ratio R results in more material being extruded during die forging, increasing the residual pressure F, reducing material utilization, increasing the required press power and energy consumption, lengthening the production cycle, and increasing costs. Examples include R = 2.8, 3.0, 3.2, 3.5, and 3.8.

[0061] In some preferred embodiments, in step S2, the forging speed is controlled between 1 mm / s and 10 mm / s, wherein the speed V1 in the initial stage of extrusion, the speed V2 in the middle stage of extrusion, and the speed V3 in the later stage of extrusion satisfy: V3 > V1 > V2. In the forging process, controlling the extrusion speed is an important means to improve product quality and achieve the optimal balance between production cycle, production cost, and material utilization. Specifically, (1) by controlling the extrusion speed within a suitable range (1 to 10 mm / s), it is possible to ensure more uniform metal flow and reduce defects such as bubbles and cracks when filling the die. If the extrusion speed is too slow, it will cause the metal to overheat, increase the risk of oxidation and heat loss, prolong the production cycle, and increase the overall cost; if the extrusion speed is too fast, it may cause uneven metal flow and filling defects, affecting product quality. (2) By adopting a variable extrusion speed strategy during the die forging process, namely, a medium speed in the early stage of extrusion, a slow speed in the middle stage of extrusion, and the fastest speed in the later stage of extrusion, it is helpful to improve product quality and overall performance, increase production efficiency, reduce production costs, and improve material utilization. For example, a medium speed in the early stage helps to start the flow of metal and perform preliminary compression of core defects; the reduced speed in the middle stage can further compact the metal, ensuring that core defects are filled and compressed more fully. Appropriate speed changes help to obtain a more uniform microstructure, which helps to improve the overall performance of the product, such as mechanical properties and dimensional stability; the rapid extrusion in the later stage can shorten the time for filling the die and improve production efficiency. By reasonably controlling the extrusion speed at different stages, production efficiency can be improved and production costs reduced as a whole while ensuring product quality.

[0062] In some possible designs, the die for forging includes an upper die column, an extrusion cylinder, and a lower die mechanism. The lower die mechanism includes a first lower die and a second lower die. The upper extrusion port of the extrusion cylinder communicates with the forming cavity inside the upper die column, and the outer wall of the upper die column is tightly slidably connected to the inner wall of the extrusion cylinder. The lower extrusion port of the extrusion cylinder communicates with the forming cavity of the first lower die or the second lower die, and the lower end of the extrusion cylinder rests on a stepped groove opened at the upper end of the first lower die or the second lower die. Exemplarily, the forming process of the billet in the die includes the following possibilities:

[0063] (1) When the large solid shaft forging to be formed is a single-section type, the accommodating space of the forming cavity of the upper die mechanism is 0. The blank is squeezed from the lower extrusion port of the extrusion cylinder into the cylindrical forming cavity of the lower die mechanism to form the required single-section shape.

[0064] (2) When the large solid shaft forging to be formed is a two-section type, the accommodating space of the forming cavity of the upper die mechanism is 0. The billet is squeezed from the lower extrusion port of the extrusion cylinder into the cylindrical forming cavity of the first lower die to form the shape of the first section. The first lower die is replaced with the second lower die, and the billet continues to be squeezed from the lower extrusion port of the extrusion cylinder into the cylindrical forming cavity of the second lower die to form the shape of the second section.

[0065] (3) When the large solid shaft forging to be formed is a 3-section type, the billet is extruded from the upper and lower extrusion ports of the extrusion cylinder into the cylindrical forming cavity of the upper die and the first lower die respectively and filled to form the roller necks at both ends. The first lower die is replaced with the second lower die, and the billet continues to be extruded from the lower extrusion port into the cylindrical forming cavity of the second lower die to form the middle section of the roller body.

[0066] For example, in the initial stage of extrusion, when the heated billet is placed into the extrusion cylinder of the die and the large press applies pressure to the die, the billet will be subjected to triaxial compressive stress and undergo plastic deformation in the extrusion cylinder, i.e. upsetting. After the billet has finished filling the extrusion cylinder, it enters the middle stage of extrusion. In this stage, the billet begins to be extruded from the extrusion port of the extrusion cylinder into the forming cavity to form the required shape, while continuing to be subjected to triaxial compressive stress. After the middle stage of extrusion, when the billet begins to be stably extruded from the extrusion cylinder and the extruded roll neck or roll body reaches a stable state, it reaches the later stage of extrusion.

[0067] More preferably, the speed V1 in the initial stage of extrusion is 4 mm / s to 6 mm / s, the speed V2 in the middle stage of extrusion is 1 mm / s to 3 mm / s, and the speed V3 in the later stage of extrusion is 8 mm / s to 10 mm / s, which helps to obtain the best product quality and overall performance, while achieving the optimal balance between production cycle, production cost and material utilization.

[0068] In some preferred embodiments, in step S1, chamfers are machined on the upper and lower end faces of the billet. The upper end face chamfer is an arc with a radius of 130–170 mm, and the lower end face chamfer is an arc with a radius of 80–120 mm. Using arcs of suitable radii as chamfers for the upper and lower end faces maximizes material utilization while facilitating billet positioning and entry into the mold. Furthermore, a larger chamfer on the upper end face helps reduce extrusion skin adhesion through mold gaps. The principle is as follows: In some possible designs, during the initial extrusion stage (i.e., when the billet is upset and fills the extrusion cylinder within the mold), the lower end face of the billet completes the extrusion cylinder process first. During filling, the lower blank will begin to change diameter and be extruded from the lower extrusion port of the die, regardless of whether the upper die pillar in contact with the upper end face of the blank has a cavity (if so, it can form the upper roller neck). At this time, the lower end face of the blank is almost filled, while the upper end face has a large chamfer and is not fully filled. If pressure is continued, the lower end face blank will continue to be extruded from the lower extrusion port of the die to form the roller neck, or the upper and lower end face blanks will be extruded from the upper and lower extrusion ports of the die respectively to form the upper and lower roller necks. A larger chamfer on the upper end face can make the upper end face complete filling later than the lower end face. This can effectively control the upper end face blank from being extruded from the gap between the upper die pillar and the extrusion cylinder, reducing flash at this point.

[0069] It should be noted that in step S2, the main steps of the die forging extrusion include: first, coating the inner surface of the die forging extrusion mold with glass powder for lubrication, then placing the heated billet into the mold, and then using a large press to apply pressure to the mold. The mold will transfer this pressure to the billet, so that the billet is formed under triaxial compressive stress and the interior of the billet is effectively pressed together. In particular, it can efficiently and effectively press together the loose cracks in the core of the continuously cast billet under triaxial compressive stress.

[0070] In this invention, "triaxial compressive stress" refers to the fact that during the die forging and extrusion process, the pressure on the billet is usually all-round, that is, there is pressure in three directions. For example, a bar billet will be subjected to compressive stress in the axial direction toward the interior of the billet, and will also be subjected to compressive stress in any two perpendicular directions of the radial plane toward the interior of the billet.

[0071] The method of this invention can successfully manufacture large solid shaft forgings of high-carbon alloy steel. The main evaluation index for the pass rate is based on the absence of equivalent defects larger than 2 mm in diameter inside the forgings by non-destructive testing. The pass rate of the products obtained in this embodiment can reach more than 95%. Compared with the existing methods, the production cycle is shortened by more than 30-50%, the production cost is reduced by at least 20%, and the material utilization rate is increased by at least 10-25%.

[0072] Understandably, the size of internal defects is a key evaluation indicator in the manufacturing and quality control of metal forgings. The absence of equivalent defects larger than 2mm in diameter within the forging is generally considered a high-quality expectation.

[0073] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0074] Example 1:

[0075] This embodiment provides a method for rapidly forming large solid shaft forgings using continuously cast billets, including the following steps:

[0076] S1. Prepare the blank: such as Figure 2 As shown in (a), the billet is a continuously cast bar-shaped billet made of high-carbon alloy steel. The chemical composition of the high-carbon alloy steel is shown in Table 1 below:

[0077] Table 1: Chemical composition of high-carbon alloy steel (by mass percentage)

[0078]

[0079] See Figure 2 (c) The large solid shaft forging to be formed is a 5-segment type, with the middle section being the roller body with the largest diameter, D1 = 450 mm. The diameter decreases from the middle to both ends. That is, the middle roller body with the largest diameter is taken as the first segment, and the second and third segments with diameters of 380 mm are respectively taken to the left and right ends, and the fourth and fifth segments with diameters of 280 mm. Based on its volume and density, the weight of the large solid shaft forging to be formed can be determined as M1 = 3100 kg.

[0080] (1) Determine the initial diameter D0 of the billet:

[0081] Based on the maximum diameter D1 = 450 mm of the large solid shaft forging to be formed and the extrusion ratio R = 2.4, the initial diameter of the billet D0 = D1 × R is determined. 1 / 2 =450 × 2.4 1 / 2 =700mm;

[0082] (2) Based on the residual pressure F = 10% during the die forging and extrusion process and the metal oxidation loss L = 2% during each heating process, determine the initial weight of the billet M0 = M1 × (1 + F) / (1 - L). n =3100×(1+10%) / (1-2%) 2 = 3550Kg; based on Table 1, the density of the alloy is 7.85g / cm³. 3 The initial length of the billet was calculated to be L0 = 1175 mm.

[0083] (3) Based on the alloy chemical composition and dimensions (initial diameter D0 and length L0) of the billet, a continuous casting rod billet is prepared using a vertical casting machine, and a circular arc chamfer with a radius of 150 mm is machined on the upper end face of the billet, and a circular arc chamfer with a radius of 100 mm is machined on the lower end face of the billet.

[0084] S2. The continuous casting bar billet prepared in step S1 is heated for the first time, that is, heated to T1 = 1230℃ and held for a holding time t1 = 700mm × 120min / 100mm = 14h.

[0085] Then, the continuously cast bar billet is extruded into a three-section shaft-type extrusion part using die forging, such as... Figure 2 As shown in (b), the maximum diameter of the middle section is D1 = 450 mm. Specifically, before die forging, glass powder is coated on the inner surface of the die for lubrication. Then, the heated billet is placed into the die, and a large press is used to apply pressure to the die. The die will transfer this pressure to the billet, so that the billet is formed under triaxial compressive stress and the interior of the billet is effectively compressed. The speed V1 in the initial stage of extrusion is 5 mm / s, the speed V2 in the middle stage of extrusion is 2 mm / s, and the speed V3 in the later stage of extrusion is 9 mm / s. After the die forging is completed, the residual pressure is removed by shearing with a chopping knife.

[0086] S3. The three-section shaft extrusion obtained in step S2 is subjected to a second heating process, that is, heated to 1170℃ and held for a holding time t2=450mm×40min / 100mm=3h.

[0087] Keep as Figure 2 (b) The diameter of the middle section (i.e., the first section) of the 3-section shaft extrusion shown is fixed at 450mm. Then, the roll necks of the remaining sections 2 to 5 are machined on a free forging press. The roll necks of sections 2 and 3, located to the left and right of section 1, are all pressed from 450mm to 380mm, with a forging ratio of 1.4. The diameters of sections 4 and 5, located at the left and right ends, are all pressed from 450mm to 280mm, with a forging ratio of 2.6, resulting in a 5-section solid shaft forging. Figure 2 As shown in (c).

[0088] The method described in this embodiment successfully manufactured a large, five-section solid shaft forging made of high-carbon alloy steel. The overall quality was excellent, especially the core, which was free of cracks and other defects. Figure 4 As shown, the main evaluation index for the pass rate is based on the absence of equivalent defects larger than 2 mm in diameter inside the forgings by non-destructive testing. The pass rate of the products obtained in this embodiment can reach more than 95%. Compared with the existing methods, the production cycle is shortened by at least 30% and the production cost is reduced by at least 20%.

[0089] If traditional die-cast steel ingots or electroslag ingots are used as raw materials, the material utilization rate is usually only 50% to 75%. Even at a higher rate of 65% to 75%, to form the 5-segment solid shaft forging in this embodiment, the required blank weight of die-cast steel ingots or electroslag ingots is 3100 kg / 0.75 to 3100 kg / 0.65, or approximately 4130 kg to 4770 kg. In contrast, the weight of the continuously cast blank in this embodiment, M0, is 3550 kg, which saves 580 kg to 1220 kg of material. Therefore, this embodiment saves at least 12% to 25% of raw materials compared to existing processes, thus improving material utilization.

[0090] Example 2

[0091] The difference between this embodiment and Embodiment 1 is that in step S1, the extrusion ratio R = 3.2, and the initial diameter of the billet D0 = D1 × R. 1 / 2 =450 × 3.2 1 / 2 =805mm, initial length of billet L0 =889mm, the remaining steps and parameters are similar to those in Example 1.

[0092] This embodiment uses a more preferred extrusion ratio R (2.5~4.0), and takes the absence of equivalent defects with a diameter greater than 2mm in the forgings as the main evaluation index for the pass rate based on non-destructive testing. The pass rate of the products obtained in this embodiment can reach more than 97%.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that in step S1, the extrusion ratio R = 1.9, and the initial diameter of the billet D0 = D1 × R. 1 / 2 =450 × 1.9 1 / 2 =620mm, initial length of billet L0 =1500mm, the remaining steps and parameters are similar to those in Example 1.

[0095] Because this comparative example did not use the preferred range of extrusion ratio R (R > 2) provided by the present invention, the core crack of the resulting 5-segment solid shaft forging still remained. See [link to related documentation]. Figure 5 In section B, as indicated, the forging product qualification rate decreased by at least 25% compared to Example 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that in step S2, the heat preservation time t1 = D0 × 105 min / 100 mm = 700 mm × 105 min / 100 mm = 12.25 h; the remaining steps and parameters are similar to those in Example 1.

[0098] Because this comparative example did not use the preferred range of holding time in the first heating cycle provided by the present invention (t1 = D0 × k1, k1 = 120 min ~ 150 min / 100 mm), the core crack of the resulting 5-segment solid shaft forging still remained. See [link to related documentation]. Figure 6 The section C marked in the figure was inspected by dye penetrant testing. The traces in section C that were colored were cracks. The pass rate of the forging products decreased by at least 20% compared with Example 1.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that in step S2, the heat preservation time t1 = D0 × 165 min / 100 mm = 700 mm × 165 min / 100 mm = 19.25 h; the remaining steps and parameters are similar to those in Example 1.

[0101] Because this comparative example did not use the preferred range of holding time in the first heating provided by the present invention (t1=D0×k1,k1=120min~150min / 100mm), the resulting 5-segment solid shaft forging had an increased risk of internal defects due to factors such as excessively coarse local grains. The forging product qualification rate decreased by at least 15% compared to Example 1.

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 1 is that in step S3, the heat preservation time t2 = D1 × 30 min / 100 mm = 450 mm × 30 min / 100 mm = 2.25 h; the remaining steps and parameters are similar to those in Example 1.

[0104] Because this comparative example did not use the preferred range of holding time in the second heating provided by the present invention (t2=D1×k2,k2=40min~55min / 100mm), the resulting 5-segment solid shaft forgings had an increased risk of internal defects due to local unevenness of the microstructure and thermal stress cracks, and the forging product qualification rate decreased by at least 10% compared with Example 1.

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 1 is that in step S3, the heat preservation time t2 = D1 × 60 min / 100 mm = 450 mm × 60 min / 100 mm = 4.5 h; the remaining steps and parameters are similar to those in Example 1.

[0107] Because this comparative example did not use the preferred range of holding time in the second heating provided by the present invention (t2=D1×k2,k2=40min~55min / 100mm), the resulting 5-segment solid shaft forgings had an increased risk of internal defects due to local unevenness of the microstructure and excessively coarse grains. The forging product qualification rate decreased by at least 10% compared with Example 1.

[0108] Comparative Example 6

[0109] The difference between this comparative example and Example 1 is that in step S2, the extrusion speed of the entire die forging process is 11 mm / s; the remaining steps and parameters are similar to those of Example 1.

[0110] Because this comparative example did not use the preferred range of forging speed (1 mm / s to 10 mm / s) provided by the present invention, the resulting 5-segment solid shaft forging still had residual core cracks. See [link to related documentation]. Figure 7 The section D marked in the figure was inspected by dye penetrant testing. The traces in section D that were colored were cracks. The pass rate of the forging products decreased by at least 25% compared with Example 1.

[0111] Comparative Example 7

[0112] The difference between this comparative example and Example 1 is that in step S2, the speed V1 in the initial stage of extrusion is 2 mm / s, the speed V2 in the middle stage of extrusion is 5 mm / s, and the speed V3 in the later stage of extrusion is 9 mm / s; the remaining steps and parameters are similar to those in Example 1.

[0113] Because this comparative example did not adopt the preferred relationship of different stages of forging extrusion speed (V3 > V1 > V2) provided by the present invention, the yield of forging products decreased by about 5 to 10% compared with Example 1.

[0114] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapidly forming large solid shaft forgings using continuously cast billets, characterized in that, The manufacturing method includes the following steps: S1. Prepare billet: The billet is a continuous casting bar billet made of high carbon alloy steel; Based on the maximum diameter D1 of the large solid shaft forging to be formed and the extrusion ratio R, determine the initial diameter D0 of the billet, satisfying: D0 = D1 × R 1 / 2 R > 2; Based on the weight M1 of the large solid shaft forging to be formed, and considering the pressure residue F during the die forging and extrusion process and the metal oxidation loss L during each heating process, determine the initial weight M0 of the billet, which satisfies: M0=M1×(1+F) / (1-L). n Where F is 5%–10%, L is 1%–2%, and n is the number of fires; S2. The continuously cast bar billet is heated in the first heat, and then extruded into X-segment shaft extrusion parts by die forging. The excess part is removed, and X is 1 to 3. S3. If the number of segments Y of the large solid shaft forging to be formed is greater than 3, the X-segment shaft extrusion obtained in step S2 is heated (n-1) times, and the roll necks of the remaining (YX) segments other than the X segment are processed by free forging to obtain the large solid shaft forging. Where n≥2, the maximum diameter of the roll neck in the remaining (YX) segments is less than D1.

2. The manufacturing method according to claim 1, characterized in that, In step S2, the main steps of the first heating process include: heating the continuously cast bar billet to T1 = 1200~1250℃ and holding it at that temperature for a holding time t1 = D0 × k1, k1 = 120min~150min / 100mm, where D0 is in mm.

3. The manufacturing method according to claim 1, characterized in that, In step S3, when the number of segments Y is 4 to 7, n = 2, that is, the X-segment shaft extrusion obtained in step S2 is subjected to a second heating.

4. The manufacturing method according to claim 3, characterized in that, In step S3, the main steps of the second heating process include: heating the X-segment shaft extrusion to T2 = 1150~1200℃ and holding it at that temperature for a holding time t2 = D1 × k2, k2 = 40min~55min / 100mm, where D1 is in mm.

5. The manufacturing method according to claim 1, characterized in that, The extrusion ratio R satisfies: 2.5≤R≤4.

6. The manufacturing method according to claim 1, characterized in that, In step S2, the forging speed is controlled between 1 mm / s and 10 mm / s, wherein the speed V1 in the initial stage of extrusion, the speed V2 in the middle stage of extrusion, and the speed V3 in the later stage of extrusion satisfy the following condition: V3 > V1 > V2.

7. The manufacturing method according to claim 6, characterized in that, The initial extrusion velocity V1 is 4 mm / s to 6 mm / s, the intermediate extrusion velocity V2 is 1 mm / s to 3 mm / s, and the final extrusion velocity V3 is 8 mm / s to 10 mm / s.

8. The manufacturing method according to claim 1, characterized in that, In step S1, chamfers are machined on the upper and lower end faces of the blank. The chamfer on the upper end face is an arc with a radius of 130 to 170 mm, and the chamfer on the lower end face is an arc with a radius of 80 to 120 mm.

9. The manufacturing method according to claim 1, characterized in that, In step S2, the main steps of the die forging extrusion include: first, coating the inner surface of the die forging extrusion mold with glass powder for lubrication, then placing the heated billet into the mold, and then using a large press to apply pressure to the mold. The mold will transfer this pressure to the billet, so that the billet is formed under triaxial compressive stress and the interior of the billet is effectively pressed together.

10. The manufacturing method according to claim 1, characterized in that, In step S1, the chemical composition of the high-carbon alloy steel, by mass percentage, includes: C: 0.8-0.9%, Si: 0.65-0.75%, Mn: 0.35-0.45%, P: 0.010-0.015%, S: 0.001-0.005%, Cr: 4.95-5.05%, Ni: 0.30-0.35%, Mo: 0.20-0.25%, V: 0.10-0.15%, N: 0.003-0.005%, with the balance being Fe and unavoidable impurities.

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