GH4698 fine bar structure homogenization control method

Abstract

The invention discloses a GH4698 thin bar structure homogenization control method, and belongs to the technical field of alloy machining. The problem that the grain structure of an existing GH4698 alloy fine bar is not uniform is solved. The invention provides a GH4698 thin bar structure homogenization control method. The control method comprises the following steps that 1, a cast ingot is prepared, and homogenization diffusion annealing treatment is conducted on the cast ingot; 2, the cast ingot obtained in the step 1 is subjected to forging, cogging and rolling, and a bar blank is obtained; 3, the bar blank obtained in the step 2 is subjected to secondary homogenization treatment; and 4, the bar obtained after secondary homogenization treatment is subjected to finish rolling treatment, and the GH4698 thin bar is obtained. The GH4698 alloy fine bar prepared by the control method disclosed by the invention is good in grain structure uniformity.

Description

Technical Field

[0001] This invention relates to the field of alloy processing technology, and in particular to a method for controlling the homogenization of the microstructure of GH4698 fine bars. Background Technology

[0002] GH4698 nickel-based superalloy exhibits excellent high-temperature strength, creep strength, and oxidation resistance in high-temperature and corrosive environments, and is widely used in petrochemical, energy, and automotive industries. Fine bars of GH4698 alloy are primarily used in the manufacture of various components and structural parts for aerospace vehicles. Most of these structural parts operate under harsh conditions of high temperature, steam corrosion, and alternating loads. Therefore, aerospace manufacturing companies have extremely stringent quality requirements for GH4698 alloy fine bars: in addition to meeting specific performance specifications, the microstructure must be uniform, with no large grains exceeding grade 0.

[0003] However, domestically produced GH4698 alloy fine bars often exhibit uneven grain structure and contain some large grains of grade 0 and 00, making it difficult to meet the procurement needs of domestic aerospace manufacturing companies. The pass rate of fine bars supplied by metallurgical plants has consistently been low, only 40-50%, resulting in a significant waste of human and material resources. Therefore, resolving the problem of uneven grain structure in GH4698 alloy fine bars and eliminating grade 0 and 00 large grains is urgent and of great significance to the supply chain and related industries of this alloy. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for controlling the uniformity of the microstructure of GH4698 fine bars, in order to solve the problem of non-uniform grain structure of existing GH4698 alloy fine bars.

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

[0006] This invention provides a method for controlling the homogenization of the microstructure of GH4698 fine rods, comprising the following steps:

[0007] Step 1: Prepare the ingot and perform homogenization diffusion annealing on the ingot;

[0008] Step 2: Forge and roll the ingot obtained in Step 1 to obtain bar billet;

[0009] Step 3: Perform a secondary homogenization treatment on the bar billet obtained in Step 2;

[0010] Step 4: Perform precision rolling on the bar after the secondary homogenization treatment to obtain GH4698 thin bar.

[0011] Further, in step 4, the initial rolling size of the bar billet is Φ14-120mm. After being fully heated at 1070-1120℃, it is rolled out of the furnace and the final rolling size is Φ5-30mm. After rolling, it is air-cooled to obtain GH4698 thin bars.

[0012] Furthermore, in step 4, multi-pass reversing continuous rolling is used when rolling the bar billet.

[0013] Furthermore, in step 4, the multi-pass reversing continuous rolling is changed to a ten-pass reversing continuous rolling;

[0014] The first rolling pass has a deformation of 5-20%, and the second rolling pass is performed immediately after the first rolling pass is completed.

[0015] The second pass involves rotating the bar by 90° and rolling it based on the first pass. The rolling deformation is 5-20%. The third pass is performed immediately after the first pass.

[0016] Furthermore, in step 4, the third pass involves rotating the bar by 90° and rolling it based on the second pass, with a rolling deformation of 5-20%. Immediately after rolling, the fourth pass is performed.

[0017] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass. The rolling deformation is 5-20%. The fifth pass is performed immediately after the third pass.

[0018] Furthermore, in step 4, the fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass, with a rolling deformation of 5-20%. Immediately after rolling, the sixth pass is performed.

[0019] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass. The rolling deformation is 5-20%. The seventh pass is performed immediately after the fifth pass.

[0020] Furthermore, in step 4, the seventh pass involves rotating the bar by 90° and rolling it based on the sixth pass, with a rolling deformation of 5-20%. Immediately after rolling, the eighth pass is performed.

[0021] Furthermore, in step 4, the eighth pass involves rotating the bar by 90° and rolling it based on the seventh pass. The rolling deformation is 5-20%, and the ninth pass is performed immediately after the rolling is completed.

[0022] Furthermore, in step 4, the ninth pass involves rotating the bar by 90° and rolling it based on the eighth pass, with a rolling deformation of 5-20%. The tenth pass is performed immediately after the rolling is completed.

[0023] Furthermore, in step 4, the tenth pass involves rotating the bar by 90° and rolling it based on the ninth pass. The rolling deformation is 5-20%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bars with a diameter of Φ5-30mm.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] (1) The multi-pass continuous directional fine rolling of the present invention can improve the uniformity of grains and obtain a more uniform grain size.

[0026] (2) The average grain size of the GH4698 fine rod prepared by the control method of the present invention is 3.5-4.5, and there are no abnormally large grains such as grade 0 and grade 00 grains.

[0027] 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 through the embodiments described and the accompanying drawings, which are particularly pointed out. Attached Figure Description

[0028] 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.

[0029] Figure 1a A schematic diagram of the grain morphology of GH4698-Φ9.0mm rods produced by existing processes (I) (average grain size grade 3.7, some coarser than grade 00);

[0030] Figure 1b Schematic diagram of grain morphology of GH4698-Φ9.0mm rod produced by existing process (II) (average grain size grade 3.7, some coarser than grade 00);

[0031] Figure 2 A schematic diagram showing the driving forces and influencing factors of grain growth;

[0032] Figure 3a The grain morphology of bars rolled from billets that have undergone secondary homogenization treatment;

[0033] Figure 3b The grain morphology of bars rolled from billets that have not undergone secondary homogenization treatment;

[0034] Figure 4 A schematic diagram of the morphology of black dot-shaped carbides in a transmission image;

[0035] Figure 5a This is a schematic diagram of the grain morphology of the continuously oriented multi-pass precision rolled bar after standard heat treatment according to the present invention.

[0036] Figure 5b This is a schematic diagram of the grain morphology of bars after standard heat treatment, where the deformation amount per pass is not controlled and the bars are not rolled in the reverse direction using existing processes.

[0037] Figure 6a This is a schematic diagram of the grain morphology after special treatment following precision rolling;

[0038] Figure 6b This is a schematic diagram of the grain morphology after precision rolling without any special treatment.

[0039] Figure 7 A schematic diagram (I) of the grain morphology of small-sized GH4698 alloy bars produced by the preparation method of the present invention;

[0040] Figure 8 A schematic diagram (II) of the grain morphology of small-sized GH4698 alloy bars produced by the preparation method of the present invention;

[0041] Figure 9 A schematic diagram (III) of the grain morphology of small-sized GH4698 alloy bars produced by the preparation method of the present invention;

[0042] Figure 10 A schematic diagram (IV) of the grain morphology of small-sized GH4698 alloy bars produced using the preparation method of the present invention.

[0043] Figure 11 This is a schematic flowchart of the method for controlling the uniformity of microstructure in GH4698 fine rods according to the present invention. Detailed Implementation

[0044] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention 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.

[0045] This invention provides a method for controlling the homogenization of the microstructure of GH4698 fine rods, comprising the following processes:

[0046] Step 1: Prepare the ingot and perform homogenization diffusion annealing on the ingot;

[0047] Step 2: Forge and roll the ingot obtained in Step 1 to obtain bar billet;

[0048] Step 3: Perform a secondary homogenization treatment on the bar billet obtained in Step 2;

[0049] Step 4: Perform precision rolling on the bar after the secondary homogenization treatment to obtain GH4698 thin bar.

[0050] In step 1 above, an ingot is obtained through dual purification smelting using vacuum induction and vacuum consumable electrode refining (VIM+VAR). The ingot size is Φ150~700mm in diameter. The specific process is as follows: based on the design composition of GH4698 fine rods, raw materials except for C and Mg are added to the melting crucible. After the vacuum degree is ≤0.1Pa, high-temperature melting is carried out, with electromagnetic stirring during the high-temperature melting process. Degassing is performed during the refining process. To prevent the formation of a large number of inclusions that affect the ingot quality later, N, O, S, and P must be controlled below 0.0030wt.% during degassing. A rough consumable electrode is finally obtained. After stress-relief annealing, surface treatment, and head and tail removal, a fine consumable electrode is prepared.

[0051] In the vacuum consumable remelting process of step 1 above, the prepared consumable electrode is welded, aligned, loaded into the furnace and vacuumed. When the vacuum degree is ≤0.1Pa, the set process parameters are input for melting. Electromagnetic stirring is required during the vacuum consumable remelting process. After melting, the electrode is cooled and removed from the furnace to obtain a consumable ingot with a diameter of Φ150~700mm.

[0052] This invention employs a vacuum induction + vacuum consumable smelting process for melting, resulting in a faster alloy solidification rate, more uniform alloy composition distribution, less segregation, lower inclusion content, and cleaner degassing, thus obtaining GH4698 fine bars with good microstructure and compositional uniformity.

[0053] In step 1 above, the prepared ingot is subjected to homogenization diffusion annealing treatment; the specific process includes: homogenization diffusion treatment in a chamber furnace, the ingot is heated with the furnace or heated to a warm charge furnace, the holding temperature is 1160-1200℃, and the holding time is 20-60h.

[0054] During homogenization diffusion annealing, annealing within the range of 1160-1200℃ enables carbides and segregating elements in the bar alloy to diffuse more quickly. If the temperature is too low (<1160℃), the diffusion of alloying elements is slow, significantly increasing time and production costs, and the diffusion effect of segregating elements is greatly reduced, which is detrimental to the homogenization of the alloy structure. If the temperature is too high (>1200℃), the alloy is prone to overheating, grain boundary embrittlement, adversely affecting the hot working of the bar, and even leading to the scrapping of the bar billet. If the holding time is too short (<20h), the diffusion of alloying elements is incomplete, resulting in uneven microstructure and inability to effectively control grain uniformity; if the holding time is too long (>60h), production costs increase, the grain boundaries of the bar are prone to overheating, leading to grain boundary embrittlement and easily causing the scrapping of the bar billet.

[0055] Step 2: Forge and roll the ingot obtained in Step 1 to obtain bar billet;

[0056] In step 2 above, rolling is carried out on a transverse rolling mill, wherein the heating temperature is 1130~1180℃, the holding time depends on the size of the ingot, and rolling is performed after sufficient holding. The final diameter of the rolled bar billet is Φ14-120mm.

[0057] In step 2 above, when the ingot size is within the range of Φ150-700mm, the heating and holding temperature is 1130~1180℃, and the holding time is 2~20h. If the holding temperature is too low (<1130℃), the ingot will be difficult to heat through and is prone to forging cracks; if the holding temperature is too high (>1180℃), the ingot is prone to overheating, reducing the hot working window and being unfavorable for billet forging. Similarly, if the holding time is too short (<2h), the ingot will be difficult to heat through and is prone to forging cracks; if the holding time is too long (>20h), it will lead to increased production costs, and the ingot is prone to overheating, grain boundary embrittlement, and reduced hot working window, which is unfavorable for billet forging.

[0058] Step 3: Perform a secondary homogenization treatment on the bar billet obtained in Step 2;

[0059] In step 3 above, the bar billet rolled in step 4 undergoes a second homogenization treatment and is processed in a chamber furnace. The bar billet is heated in the furnace or charged into the furnace at a certain temperature. The holding temperature is 1160-1200℃ and the holding time is 8-40h. After holding, it is air-cooled.

[0060] In step 3 above, for bar billets with a diameter of Φ14-120mm, homogenization diffusion treatment within the range of 1160-1200℃ allows carbides and segregating elements in the bar alloy to diffuse more quickly. If the temperature is too low (<1160℃), the diffusion of alloying elements is slow, significantly increasing time and production costs, and the diffusion effect of segregating elements will be greatly reduced, which is not conducive to the homogenization of the alloy structure. If the temperature is too high (>1200℃), the alloy is prone to overheating, grain boundary embrittlement, adversely affecting the hot working of the bar, and even leading to the scrapping of the bar billet. If the holding time is too low (<8h), the diffusion of alloying elements is incomplete, resulting in uneven structure and inability to effectively control grain uniformity; if the holding time is too high (>40h), production costs increase, the grain boundaries of the bar are prone to overheating, leading to grain boundary embrittlement, and easily causing the scrapping of the bar billet.

[0061] Step 4: Perform precision rolling on the bar after the secondary homogenization treatment to obtain GH4698 thin bar.

[0062] The bar material processed in step 3 is precision rolled on a transverse rolling mill. The initial rolling size is Φ14-120mm. After being fully heated at 1070-1120℃, it is rolled out of the furnace and the final rolling size is Φ5-30mm. After rolling, it is air-cooled.

[0063] The grain structure of the bars rolled in the temperature range of 1070-1120℃ is relatively uniform, which can promote the GH4698 alloy to obtain a more uniform grain structure after rolling. If the rolling temperature is too low (<1070℃), it will be difficult to deform the bars and the deformation of the bars will be irregular. If the rolling temperature is too high (>1120℃), the bars will be overheated and the grains of the rolled bars will be coarse, which is not conducive to grain refinement and affects the alloy properties.

[0064] To achieve coordinated and uniform deformation throughout the rolling process and prevent areas of excessively high or low distortion energy caused by uneven deformation in certain regions, this invention employs multi-pass continuous rolling with reversing direction during bar rolling. Each pass involves a deformation of 5-20%, with adjacent passes reversing direction by 90°. The initial rolled bar diameter is Φ14-120mm. After sufficient heat treatment at 1070-1120℃, it is removed for rolling, undergoing a total of 10 passes, with each pass reversing direction by 90° and a deformation of 5-20% per pass, as detailed below:

[0065] The first rolling pass has a deformation of 5-20%, and the second rolling pass is performed immediately after the first rolling pass is completed.

[0066] The second pass involves rotating the bar by 90° and rolling it based on the first pass. The rolling deformation is 5-20%. The third pass is performed immediately after the first pass.

[0067] The third pass involves rotating the bar by 90° and rolling it based on the second pass. The rolling deformation is 5-20%. The fourth pass is performed immediately after the second pass.

[0068] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass. The rolling deformation is 5-20%. The fifth pass is performed immediately after the third pass.

[0069] The fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 5-20%. The sixth pass is performed immediately after the rolling is completed.

[0070] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass. The rolling deformation is 5-20%. The seventh pass is performed immediately after the fifth pass.

[0071] In the seventh pass, the bar is rotated 90° and rolled based on the sixth pass, with a rolling deformation of 5-20%. The eighth pass is rolled immediately after the sixth pass.

[0072] The eighth pass involves rotating the bar by 90° and rolling it based on the seventh pass. The rolling deformation is 5-20%. The ninth pass is performed immediately after the seventh pass.

[0073] In the ninth pass, the bar is rotated 90° and rolled based on the eighth pass, with a rolling deformation of 5-20%. The tenth pass is rolled immediately after the eighth pass.

[0074] In the tenth pass, the bar is rotated 90° and rolled based on the ninth pass, with a rolling deformation of 5-20%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bars with a diameter of Φ5-30mm.

[0075] It should be emphasized that, after rolling, in order to further improve the homogenization of the microstructure of GH4698 fine bars, the homogenization control method of the present invention for GH4698 fine bars also includes step 5. Step 5: Perform special heat treatment on the fine bars after finishing rolling; wherein, the special heat treatment process includes: after the heat treatment furnace reaches the temperature, loading the rolled bars into the furnace, holding the temperature at 1100-1200℃ for 2-30 minutes, and after the holding time is completed, removing the bars and air cooling them.

[0076] This special heat treatment process employs a unique heat treatment on the bar stock, creating a special recrystallization environment to increase the recrystallization nucleation rate while limiting excessive grain growth. Ultimately, it achieves uniform recrystallization of the bar stock, eliminating the uneven recrystallization caused by uneven energy storage due to deformation after rolling, thus ensuring a uniform grain structure. If the holding temperature is too low (<1100℃), uniform recrystallization cannot be achieved, resulting in a uniform grain structure; if the holding temperature is too high (>1200℃), the grains will grow rapidly, eventually resulting in large grains of grade 0 and 00, also failing to achieve a uniform grain structure. If the holding time is too short (<2min), the bar stock cannot achieve complete uniform recrystallization, failing to completely eliminate uneven energy storage due to deformation after rolling, ultimately failing to achieve a uniform grain structure; if the holding time is too long (>30min), the recrystallized grains will grow excessively, failing to achieve a uniform grain structure with smaller grain size.

[0077] It should be noted that, after special heat treatment, in order to further improve the homogenization of the microstructure of GH4698 fine bars, the homogenization control method of GH4698 fine bars of the present invention further includes step 6, which involves heat treating the fine bars after special heat treatment.

[0078] Step 6: Heat treat the bar obtained in Step 5 and inspect the microstructure and properties of the bar.

[0079] In step 6 above, the heat treatment process includes a first solution treatment, a second solution treatment, and an aging treatment, which are as follows: First solution treatment: (1100-1120)℃×8h, air cooling; Second solution treatment: 1000℃±10℃×4h, air cooling; Aging treatment: 775℃±10℃×16h, air cooling.

[0080] In step 6 above, the heat treatment process specifically includes the following sub-steps:

[0081] Step 61: Raise the furnace temperature to 1100-1120℃, put in the bar stock, keep it at the temperature for 8 hours, and then take it out and air cool it.

[0082] Step 62: Raise the furnace temperature to 1000℃, put in the bar, keep it at the temperature for 4 hours, and then take it out and air cool it.

[0083] Step 63: Raise the furnace temperature to 765-785℃, put in the bar stock, keep it at that temperature for 16 hours, then take it out and air cool it.

[0084] GH4698 fine rods (Φ5-30mm) prepared using existing technologies generally suffer from excessively large grain size and localized abnormal grain growth, exhibiting coarse grains of grade 0 and 00, severe mixed grains, and significant grain inhomogeneity, as shown in Figure 1. Compared to existing technologies, the grain structure of GH4698 fine rods prepared using the control method of this invention is as follows: Figure 7 As shown, the average grain size is 3.0-5.0, with no abnormally large grains such as grade 0 or grade 00 grains.

[0085] It should be noted that the specifications of the above-mentioned GH4698 fine rods are in diameter Φ5~30mm. The composition of the GH4698 fine rods by weight percentage includes: C: 0.030~0.080wt%, Si: ≤0.50wt%, Mn: ≤0.40wt%, Cr: 13.0~16.0wt%, Mo: 2.80~3.20wt%, Al: 1.45~1.80wt%, Ti: 2.35~2.75wt%, Fe: ≤2.00wt%, Nb: 1.80~2.20wt%, Mg: ≤0.0080wt%, Ce: ≤0.0050wt%, Zr: ≤0.050wt%, B: ≤0.015wt%, with the balance being Ni and unavoidable impurities.

[0086] In the composition of the aforementioned GH4698 alloy small-diameter bars, carbon (C) is a grain boundary strengthening element. It has extremely low solubility in the γ phase, often segregating at grain boundaries and acting as an interstitial element to fill the gaps in these regions, slowing diffusion and thus reducing the tendency for grain boundary cracking. C can also form carbides to pin dislocations, playing a precipitation strengthening role in the alloy. Too low a C content will reduce the strengthening effect, while too high a content will form continuous, network-like carbides at grain boundaries, which is detrimental to the alloy's mechanical properties. Therefore, the C content in this invention is 0.030–0.080 wt%.

[0087] In the composition of the above-mentioned small-diameter bars of GH4698 alloy, Si can improve the casting performance and corrosion resistance of GH4698 alloy, and can also improve the fluidity and surface finish of the alloy; however, if the Si content is too high, it will reduce the toughness of GH4698 alloy and lead to increased brittleness. Therefore, the Si content is controlled within the range of ≤0.50wt%.

[0088] In the composition of the above-mentioned small-diameter bars of GH4698 alloy, Mn can improve the hardness and strength of GH4698 alloy, and can also improve the weldability and machinability of the alloy. However, if the Mn content is too high, manganese compounds will be formed, which will reduce the toughness of the alloy. Therefore, the Mn content is controlled to be ≤0.40wt%.

[0089] In the composition of the aforementioned GH4698 alloy small-diameter bars, the role of Mo is as follows: Mo is a large-sized element that is difficult to dissolve in the matrix. Its atomic radius differs significantly from that of Ni, thus exhibiting a significant solid solution strengthening effect on the matrix. Mo atoms can dissolve in the matrix in large quantities, making it the element that contributes most to solid solution strengthening in the GH4698 alloy; therefore, a relatively high Mo content is added. However, excessive Mo addition can affect the alloy's machinability and easily precipitate a harmful μ phase, impacting the alloy's service life. Therefore, the Mo content is controlled at 2.8–3.2 wt%.

[0090] In the composition of the above-mentioned small-diameter bars of GH4698 alloy, the roles of Al and Ti are as follows: Al and Ti form Ni3(Al,Ti) and TiC particles in the GH4698 alloy, respectively. Ni3(Al,Ti) and TiC particles can play a precipitation strengthening role, thereby improving the strength of the alloy. However, if the content of Al and Ti is too high, it will lead to supersaturation precipitation in the alloy, thereby reducing the hot working performance of the alloy and even causing forging cracks. Therefore, the range of Al and Ti is controlled as follows: Al: 1.45~1.80wt%, Ti: 2.35~2.75wt%.

[0091] In the composition of the above-mentioned small-sized bars of GH4698 alloy, Fe can reduce costs, and Fe, as a substitute solid solution atom in GH4698 alloy, can hinder dislocation movement and play a solid solution strengthening role, which is beneficial to improving yield strength. However, too much Fe will reduce the alloy's oxidation and corrosion resistance. Therefore, Fe is controlled at ≤2.00wt%.

[0092] In the composition of the aforementioned GH4698 alloy small-diameter bars, Nb can promote the precipitation of NbC carbides to improve the alloy strength, and Nb can also promote the precipitation of the γ(Ni3Nb) phase, thereby increasing the alloy strength. However, excessive Nb content will reduce the hot workability of the GH4698 alloy; therefore, the Nb content is controlled within the range of 1.80–2.20 wt%.

[0093] In the composition of the above-mentioned GH4698 alloy small-diameter bars, Mg and Ce, as trace alloying elements, mainly play the role of purifying grain boundaries and improving the plasticity of the alloy. However, these trace alloying elements cannot be added in excess, otherwise it will lead to excessively clean alloy grain boundaries, or even Mg and Ce segregation along the grain boundaries, causing grain boundary embrittlement, thereby greatly reducing the high-temperature plasticity of the alloy. Therefore, the content ranges of Mg and Ce are ≤0.0080wt% and ≤0.0050wt%, respectively.

[0094] In the composition of the aforementioned GH4698 alloy small-diameter bars, zirconium tends to segregate at grain boundaries, acting as a grain boundary strengthening element. Adding Zr to the GH4698 alloy further enhances the grain boundary strengthening effect and can also inhibit the diffusion of grain boundary elements, delaying the initiation of grain boundary cracks. However, Zr is expensive, and excessive Zr content reduces the corrosion resistance of the nickel alloy; therefore, the Zr content is ≤0.050 wt%.

[0095] In the composition of the aforementioned GH4698 alloy small-diameter bars, boron (B) is one of the two most important grain boundary strengthening elements in nickel-based alloys. Its solubility in the γ phase is extremely low, and it tends to segregate at grain boundaries, acting as interstitial elements to fill the gaps in these regions, slowing diffusion and thus reducing the tendency for grain boundary cracking. B can significantly improve the high-temperature creep rupture performance of GH4698 alloy. Furthermore, B can also slow down the M-phase cracking at grain boundaries. 23 The coarsening rate of C6 increases the number of intragranular carbides and improves the hot strength of GH4698 alloy. However, excessive B content will cause the precipitation of borides, affecting the hot working and mechanical properties of the alloy. Therefore, the B content should be ≤0.015wt%.

[0096] To further improve the uniformity of the grain structure of GH4698 alloy small-diameter bars, the composition of the above-mentioned GH4698 alloy small-diameter bars by weight percentage includes: C: 0.050~0.080wt%, Si: ≤0.35wt%, Mn: ≤0.40wt%, Cr: 14.0~16.0wt%, Mo: 2.90~3.20wt%, Al: 1.45~1.70wt%, Ti: 2.55~2.75wt%, Fe: 0.46~1.50wt%, Nb: 1.90~2.20wt%, Mg: 0.0020~0.0080wt%, Ce: 0.0020~0.0050wt%, Zr: 0.030~0.050wt%, B: 0.0030~0.010wt%, with the balance being Ni and unavoidable impurities.

[0097] To further improve the uniformity of the grain structure of GH4698 alloy small-diameter bars, the above-mentioned GH4698 alloy small-diameter bars, by weight percentage, consist of: 0.050wt%, Si: 0.35wt%, Mn: 0.10wt%, Cr: 14.7wt%, Mo: 2.95wt%, Al: 1.47wt%, Ti: 2.65wt%, Fe: 0.75wt%, Nb: 1.96wt%, Mg: 0.0040wt%, Ce: 0.0020wt%, Zr: 0.0030wt%, B: 0.0050wt%, with the balance being Ni and unavoidable impurities.

[0098] To further improve the uniformity of the grain structure of GH4698 alloy small-diameter bars, the composition of the above-mentioned GH4698 alloy small-diameter bars by weight percentage is as follows: C: 0.055wt%, Si: 0.23wt%, Mn: 0.15wt%, Cr: 15.40wt%, Mo: 2.92wt%, Al: 1.48wt%, Ti: 2.68wt%, Fe: 0.49wt%, Nb: 2.01wt%, Mg: 0.0030wt%, Ce: 0.0030wt%, Zr: 0.050wt%, B: 0.010wt%, with the balance being Ni and unavoidable impurities.

[0099] Furthermore, the composition of the above-mentioned GH4698 alloy small-diameter bars, by weight percentage, is C: 0.062wt%, Si: 0.26wt%, Mn: 0.33wt%, Cr: 14.1wt%, Mo: 3.01wt%, Al: 1.55wt%, Ti: 2.69wt%, Fe: 0.67wt%, Nb: 2.09wt%, Mg: 0.0020wt%, Ce: 0.0030wt%, Zr: 0.040wt%, B: 0.0040wt%, with the balance being Ni and unavoidable impurities.

[0100] To further improve the uniformity of the grain structure of GH4698 alloy small-diameter bars, the composition of the above-mentioned GH4698 alloy small-diameter bars by weight percentage is as follows: C: 0.080wt%, Si: 0.35wt%, Mn: 0.40wt%, Cr: 16.0wt%, Mo: 3.2wt%, Al: 1.7wt%, Ti: 2.75wt%, Fe: 1.5wt%, Nb: 2.2wt%, Mg: 0.0070wt%, Ce: 0.0040wt%, Zr: 0.050wt%, B: 0.015wt%, with the balance being Ni and unavoidable impurities.

[0101] It is important to emphasize that in the method for controlling the homogenization of the microstructure of GH4698 fine bars in this invention, given that the standard heat treatment regime for GH4698 alloy is (1100-1120)℃ × 8h, the influence of microstructure and composition inhomogeneity on grain growth will continuously amplify with increasing heating time during such high-temperature and long-duration heat treatment. Regarding the evolution behavior and mechanism of post-rolled grains during the solution treatment process, the key processes determining the final grain size are the deformation-driven recrystallization process and the interfacial energy-driven grain growth process, such as... Figure 2 As shown. For hot-rolled thin bars (Φ5~30mm), before solution treatment, the distribution of the second phase, compositional uniformity, and the magnitude and distribution of deformation energy storage in the microstructure serve as the starting point for recrystallization and have a significant impact on the grain morphology after heat treatment. To ensure a uniform grain structure and avoid abnormally excessive grain growth, it is necessary to ensure the uniformity of the microstructure and composition as much as possible before rolling the alloy bars. Therefore, this invention performs a secondary homogenization treatment on the billet alloy before rolling to further homogenize the microstructure and composition, facilitating coordinated and uniform deformation of each part during the subsequent rolling process.

[0102] It is also important to emphasize that in the method for controlling the homogenization of the microstructure of GH4698 fine bars, during the solution treatment process at (1100-1120)℃ for 8 hours, a recrystallization process occurs first, followed by a grain growth process. The nucleation rate, nucleation location, grain size distribution, grain orientation distribution, and grain boundary state after recrystallization serve as the starting point for grain growth. To ensure uniform grain size distribution and relatively harmonious grain boundary state, it is necessary to ensure uniform deformation of all parts during rolling to prevent regions with excessively high or low distortion energy due to uneven deformation in some areas. Therefore, this invention employs multi-pass continuous rolling with reversing direction during bar rolling, with a deformation amount of 5-20% per pass.

[0103] It needs to be emphasized again that in the method for controlling the homogenization of the microstructure of GH4698 fine bars, the ultimate cause of excessive grain growth is the difference in energy storage during rolling deformation, which leads to differences in the grain nucleation and incubation period, resulting in uneven growth. Therefore, this invention employs a special post-rolling heat treatment to create a recrystallization environment to increase the recrystallization nucleation rate. Simultaneously, by limiting the time, grain growth under high superheat conditions is restricted, ultimately achieving uniform recrystallization of the bar and eliminating the uneven recrystallization caused by uneven energy storage during the initial post-rolling deformation. In the subsequent grain growth process of solution treatment at (1100-1120)℃ for 8 hours, interfacial energy is the driving force for grain growth; therefore, the initial grain size and uniformity have a significant impact on the grain growth process.

[0104] Example 1

[0105] To more clearly illustrate the beneficial effects of the fine rolling process of this invention, this embodiment uses a comparison to illustrate the influence of fine rolling using the present invention and fine rolling without the present invention on the microstructure of the bar stock.

[0106] This invention employs multi-pass continuous rolling with reversing direction during bar rolling, with a deformation of 5-20% per pass and a 90° reversal between adjacent passes. The initial rolled bar diameter is Φ14mm, which is then held at 1080℃ for 1 hour before being rolled again. A total of 10 passes are performed, with each pass reversing direction by 90° and a deformation of 5-20% per pass. The specific process includes the following:

[0107] The first rolling pass has a deformation of 12%, and the second rolling pass is performed immediately after the first rolling pass is completed.

[0108] The second pass involves rotating the bar by 90° and rolling it based on the first pass, with a rolling deformation of 10%. The third pass is performed immediately after the first pass is completed.

[0109] The third pass involves rotating the bar by 90° and rolling it based on the second pass, with a rolling deformation of 14%. The fourth pass is performed immediately after the second pass.

[0110] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass, with a rolling deformation of 11%. The fifth pass is performed immediately after the rolling is completed.

[0111] The fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 8%. The sixth pass is performed immediately after the rolling is completed.

[0112] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass. The rolling deformation is 7%. The seventh pass is performed immediately after the fifth pass.

[0113] In the seventh pass, the bar is rotated 90° and rolled based on the sixth pass, with a rolling deformation of 12%. The eighth pass is rolled immediately after the sixth pass.

[0114] The eighth pass involves rotating the bar by 90° and rolling it based on the seventh pass. The rolling deformation is 10%. The ninth pass is performed immediately after the seventh pass.

[0115] In the ninth pass, the bar is rotated 90° and rolled based on the eighth pass, with a rolling deformation of 8%. The tenth pass is rolled immediately after the eighth pass.

[0116] In the tenth pass, the bar is rotated 90° and rolled based on the ninth pass, with a rolling deformation of 5%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bar with a diameter of Φ5mm.

[0117] After precision rolling, the final bar diameter is Φ5mm. The grain morphology of the rolled bar after pretreatment and standard heat treatment ((1100-1120)℃×8h, AC+1000℃±10℃×4h, 775℃±10℃×16h, AC) is as follows: Figure 5a As shown, the existing process does not control the deformation amount in each pass and the grain morphology of the bar after standard heat treatment without reversal rolling is as follows. Figure 5b As shown.

[0118] Depend on Figure 5a It is evident that the grain size obtained by the multi-pass continuous directional fine rolling of this invention is relatively uniform, while the grains obtained by the original rough rolling process (existing process) are prone to large, coarse grains along the edges, such as... Figure 5b As indicated by the markings above the dashed line.

[0119] It should be noted that the multi-pass continuous directional fine rolling of the present invention can improve the uniformity of grains, with an improvement rate of 70-80%. In order to further improve the difference in grain nucleation and incubation period caused by the difference in energy storage during rolling deformation, and reduce the impact of uneven grain growth caused by this situation, the present invention adopts a special heat treatment after rolling to create a recrystallization environment to increase the recrystallization nucleation rate, while limiting the grain growth under high superheat environment by limiting the time.

[0120] Specifically, the rolled Φ5-30mm bars undergo special heat treatment, are placed in a warm charging furnace, and held at 1100-1200℃ for 2-30 minutes. The results are as follows. Figure 6a and Figure 6b As shown, Figure 6a The grain morphology of a Φ12mm bar after precision rolling, special heat treatment, and then standard heat treatment. Figure 6b The grain morphology refers to the same bar material after standard heat treatment without any special heat treatment. For example... Figure 6a and Figure 6b As shown, although the bars have all undergone continuous multi-pass precision rolling with changing direction, due to Figure 6a After undergoing a special heat treatment process followed by standard heat treatment, its grain morphology becomes finer and more uniform, with an average grain size of 4.0-4.5 grade; while Figure 6b The bars, without undergoing special heat treatment and directly subjected to standard heat treatment, have relatively coarse grains, with an average grain size of 3.0-3.5, and some grade 0 grains are present. Figure 6b As shown by the dashed line.

[0121] Example 2

[0122] This embodiment investigates the effect of a secondary homogenization process on the microstructure uniformity of GH4698 thin bars before rolling. Two bars with a diameter of Φ50mm were subjected to secondary homogenization. Group A bars underwent secondary homogenization at 1180℃ for 30 hours, while Group B bars did not. The bars were rolled into thin bars with a diameter of Φ12mm, and the rolled grain and second-phase morphology were observed. The results are as follows: Figure 3a and Figure 3b As shown, among which, by Figure 3a It is evident that the grain surface of the bar rolled from the homogenized billet is relatively clean, with very few dot-like carbide structures; Figure 3b As shown, the surface of the grains in the rolled bar from the non-homogenized billet contains many black dot-like carbides. Transmission analysis reveals that these carbides have a macroscopic morphology of TiC particles, such as... Figure 4 As shown.

[0123] Example 3

[0124] This embodiment provides a method for controlling the homogenization of the microstructure of GH4698 fine rods, including the following steps:

[0125] Step 1: Optimize and determine the internal control composition range, that is, determine the composition range of GH4698 fine rods; the composition of GH4698 fine rods, by weight percentage, includes: 0.050wt%, Si: 0.35wt%, Mn: 0.10wt%, Cr: 14.7wt%, Mo: 2.95wt%, Al: 1.47wt%, Ti: 2.65wt%, Fe: 0.75wt%, Nb: 1.96wt%, Mg: 0.0040wt%, Ce: 0.0020wt%, Zr: 0.040wt%, B: 0.0050wt%, with the balance being Ni and unavoidable impurities.

[0126] Step 2: Obtain an ingot by dual purification smelting using vacuum induction + vacuum self-consumption (VIM+VAR), with an ingot size of Φ200mm in diameter;

[0127] Step 3: Perform homogenization diffusion annealing on the ingot obtained in Step 2;

[0128] The homogenization and diffusion treatment is carried out in a chamber furnace. The ingot is heated with the furnace or heated to a warm temperature. The holding temperature is 1170℃ and the holding time is 30h.

[0129] Step 4: Forging and rolling of consumable ingots to obtain bar billets;

[0130] In step 4 above, rolling is carried out on a transverse rolling mill, wherein the heating temperature is 1140℃, the holding time is 50h, and after sufficient holding, rolling is performed, and the final rolled bar billet diameter is Φ40mm.

[0131] Step 5: Perform a secondary homogenization treatment on the bar billet obtained in Step 4;

[0132] In step 5 above, the bar billet rolled in step 4 undergoes a second homogenization treatment and is processed in a chamber furnace. The bar billet is heated in the furnace or charged into the furnace at a certain temperature. The holding temperature is 1170℃ and the holding time is 12h. After holding, it is air-cooled.

[0133] Step 6: Perform precision rolling on the bars after the secondary homogenization treatment;

[0134] The bar material processed in step 5 is precision rolled on a transverse rolling mill with an initial rolling size of Φ40mm. After being fully heated at 1070℃, it is rolled out of the furnace to a final size of Φ13.7mm. After rolling, it is air-cooled.

[0135] In step 6 above, the present invention employs multi-pass continuous rolling with reversing direction during bar rolling, with a deformation of 5-20% per pass and a 90° reversal between adjacent passes. The initial rolled bar diameter is Φ40mm, which is then fully heated at 1070℃ before being rolled again. A total of 10 passes are rolled, with a 90° reversal in each pass and a deformation of 5-20% per pass, as detailed below:

[0136] The first rolling pass has a deformation amount of 10%, and the second rolling pass is carried out immediately after the first rolling pass is completed.

[0137] The second pass involves rotating the bar by 90° and rolling it based on the first pass, with a rolling deformation of 8%. The third pass is performed immediately after the first pass is completed.

[0138] The third pass involves rotating the bar by 90° and rolling it based on the second pass, with a rolling deformation of 14%. The fourth pass is performed immediately after the second pass.

[0139] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass, with a rolling deformation of 10%. The fifth pass is performed immediately after the rolling is completed.

[0140] The fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 9%. The sixth pass is performed immediately after the rolling is completed.

[0141] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass, with a rolling deformation of 8%. The seventh pass is performed immediately after the rolling is completed.

[0142] In the seventh pass, the bar is rotated 90° and rolled based on the sixth pass, with a rolling deformation of 17%. The eighth pass is rolled immediately after the sixth pass.

[0143] The eighth pass involves rotating the bar by 90° and rolling it based on the seventh pass. The rolling deformation is 8%. The ninth pass is performed immediately after the seventh pass.

[0144] In the ninth pass, the bar is rotated 90° and rolled based on the eighth pass, with a rolling deformation of 12%. The tenth pass is rolled immediately after the eighth pass.

[0145] In the tenth pass, the bar is rotated 90° and rolled based on the ninth pass, with a rolling deformation of 5%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bar with a diameter of Φ13.7mm.

[0146] In this embodiment, a GH4698 fine rod with a diameter of Φ13.7 mm was prepared. The grain structure of the GH4698 fine rod is as follows: Figure 8 As shown, the average grain size is 3.5-4.5, and there are no abnormally large grains such as grade 0 or grade 00 grains.

[0147] Example 4

[0148] This embodiment provides a method for controlling the homogenization of the microstructure of GH4698 fine rods, including the following steps:

[0149] Step 1: Optimize and determine the internal control composition range, that is, determine the composition range of GH4698 fine rods; the composition of the above GH4698 fine rods by weight percentage is as follows: C: 0.055wt%, Si: 0.23wt%, Mn: 0.15wt%, Cr: 15.40wt%, Mo: 2.92wt%, Al: 1.58wt%, Ti: 2.68wt%, Fe: 0.49wt%, Nb: 2.01wt%, Mg: 0.0030wt%, Ce: 0.0030wt%, Zr: 0.050wt%, B: 0.010wt%, with the balance being Ni and unavoidable impurities.

[0150] Step 2: Obtain an ingot by dual purification smelting using vacuum induction + vacuum self-consumption (VIM+VAR), with an ingot size of Φ350mm in diameter;

[0151] Step 3: Perform homogenization diffusion annealing on the ingot obtained in Step 2;

[0152] The homogenization and diffusion treatment is carried out in a chamber furnace. The ingot is heated with the furnace or charged into the furnace at a warm temperature. The holding temperature is 1180℃ and the holding time is 40h.

[0153] Step 4: Forging and rolling of consumable ingots to obtain bar billets;

[0154] In step 4 above, rolling is carried out on a transverse rolling mill, wherein the heating temperature is 1160℃, the holding time is 10h, and after sufficient holding, rolling is performed, and the final rolled bar billet diameter is Φ90mm.

[0155] Step 5: Perform a secondary homogenization treatment on the bar billet obtained in Step 4;

[0156] In step 5 above, the bar billet rolled in step 4 undergoes a second homogenization treatment and is processed in a chamber furnace. The bar billet is heated in the furnace or charged into the furnace at a certain temperature. The holding temperature is 1180℃ and the holding time is 20h. After holding, it is air-cooled.

[0157] Step 6: Perform precision rolling on the bars after the secondary homogenization treatment;

[0158] The bar material processed in step 5 is precision rolled on a transverse rolling mill with an initial rolling size of Φ90mm. After being fully heated at 1090℃, it is rolled out of the furnace to a final size of Φ22.5mm. After rolling, it is air-cooled.

[0159] In step 6 above, the present invention employs multi-pass continuous rolling with reversing direction during bar rolling, with a deformation of 5-20% per pass and a 90° reversal between adjacent passes. The initial rolled bar diameter is Φ90mm, which is then fully held at 1070-1120℃ before being rolled again. A total of 10 passes are performed, with a 90° reversal in direction per pass and a deformation of 5-20% per pass, as detailed below:

[0160] The first rolling pass has a deformation of 12%, and the second rolling pass is performed immediately after the first rolling pass is completed.

[0161] The second pass involves rotating the bar by 90° and rolling it based on the first pass, with a rolling deformation of 12%. The third pass is performed immediately after the first pass.

[0162] The third pass involves rotating the bar by 90° and rolling it based on the second pass, with a rolling deformation of 16%. The fourth pass is performed immediately after the second pass.

[0163] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass, with a rolling deformation of 13%. The fifth pass is performed immediately after the rolling is completed.

[0164] The fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 10%. The sixth pass is performed immediately after the rolling is completed.

[0165] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass, with a rolling deformation of 9%. The seventh pass is performed immediately after the rolling is completed.

[0166] In the seventh pass, the bar is rotated 90° and rolled based on the sixth pass, with a rolling deformation of 18%. The eighth pass is rolled immediately after the sixth pass.

[0167] In the eighth pass, the bar is rotated 90° and rolled based on the seventh pass, with a rolling deformation of 14%. The ninth pass is rolled immediately after the seventh pass.

[0168] In the ninth pass, the bar is rotated 90° and rolled based on the eighth pass, with a rolling deformation of 15%. The tenth pass is rolled immediately after the eighth pass.

[0169] In the tenth pass, the bar is rotated 90° and rolled based on the ninth pass, with a rolling deformation of 10%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bar with a diameter of Φ22.5mm.

[0170] In this embodiment, a GH4698 thin rod with a diameter of Φ22.5 mm was prepared. The grain structure of the GH4698 thin rod is as follows: Figure 9 As shown, the average grain size is 3.5-4.5, and there are no abnormally large grains such as grade 0 or grade 00 grains.

[0171] Example 5

[0172] This embodiment provides a method for controlling the homogenization of the microstructure of GH4698 fine rods, including the following steps:

[0173] Step 1: Optimize and determine the internal control composition range, that is, determine the composition range of GH4698 fine rods; GH4698 fine rods, by weight percentage, C: 0.062wt%, Si: 0.22wt%, Mn: 0.13wt%, Cr: 15.1wt%, Mo: 3.01wt%, Al: 1.75wt%, Ti: 2.69wt%, Fe: 0.67wt%, Nb: 2.09wt%, Mg: 0.0020wt%, Ce: 0.0030wt%, Zr: 0.020wt%, B: 0.015wt%, with the balance being Ni and unavoidable impurities.

[0174] Step 2: Obtain an ingot by dual purification smelting using vacuum induction + vacuum self-consumption (VIM+VAR), with an ingot size of Φ600mm in diameter;

[0175] Step 3: Perform homogenization diffusion annealing on the ingot obtained in Step 2;

[0176] The homogenization and diffusion treatment is carried out in a chamber furnace. The ingot is heated with the furnace or heated to a warm temperature. The holding temperature is 1200℃ and the holding time is 50h.

[0177] Step 4: Forging and rolling of consumable ingots to obtain bar billets;

[0178] In step 4 above, rolling is carried out on a transverse rolling mill, wherein the heating temperature is 1170℃, the holding time is 18h, and the rolling is carried out after sufficient holding time. The final diameter of the rolled bar billet is Φ120mm.

[0179] Step 5: Perform a secondary homogenization treatment on the bar billet obtained in Step 4;

[0180] In step 5 above, the bar billet rolled in step 4 undergoes a second homogenization treatment and is processed in a chamber furnace. The bar billet is heated in the furnace or charged into the furnace at a certain temperature. The holding temperature is 1190℃ and the holding time is 35h. After holding, it is air-cooled.

[0181] Step 6: Perform precision rolling on the bars after the secondary homogenization treatment;

[0182] The bar material processed in step 5 is precision rolled on a transverse rolling mill with an initial rolling size of Φ120mm. After being fully heated at 1120℃, it is rolled out of the furnace to a final size of Φ30mm. After rolling, it is air-cooled.

[0183] In step 6 above, the present invention employs multi-pass continuous rolling with reversing direction during bar rolling, with a deformation of 5-20% per pass and a 90° reversal between adjacent passes. The initial rolled bar diameter is Φ120mm, which is then fully held at 1120℃ before being rolled, with a total of 10 passes, each with a 90° reversal direction and a deformation of 5-20% per pass, as detailed below:

[0184] The first rolling pass has a deformation of 16%, and the second rolling pass is performed immediately after the first rolling pass is completed.

[0185] The second pass involves rotating the bar by 90° and rolling it based on the first pass, with a rolling deformation of 14%. The third pass is performed immediately after the first pass.

[0186] The third pass involves rotating the bar by 90° and rolling it based on the second pass, with a rolling deformation of 18%. The fourth pass is performed immediately after the second pass.

[0187] The fourth pass involves rotating the bar by 90° and rolling it based on the third pass, with a rolling deformation of 13%. The fifth pass is performed immediately after the rolling is completed.

[0188] The fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 11%. The sixth pass is performed immediately after the rolling is completed.

[0189] The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass, with a rolling deformation of 9%. The seventh pass is performed immediately after the rolling is completed.

[0190] In the seventh pass, the bar is rotated 90° and rolled based on the sixth pass, with a rolling deformation of 18%. The eighth pass is rolled immediately after the sixth pass.

[0191] In the eighth pass, the bar is rotated 90° and rolled based on the seventh pass, with a rolling deformation of 14%. The ninth pass is rolled immediately after the seventh pass.

[0192] In the ninth pass, the bar is rotated 90° and rolled based on the eighth pass, with a rolling deformation of 6%. The tenth pass is rolled immediately after the eighth pass.

[0193] In the tenth pass, the bar is rotated 90° and rolled based on the ninth pass, with a rolling deformation of 10%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bar with a diameter of Φ30mm.

[0194] Step 7: Perform special heat treatment on the thin bars rolled in Step 6;

[0195] The special heat treatment process includes: after the heat treatment furnace reaches the required temperature, the rolled bars are loaded into the furnace, the holding temperature is 1200℃, the holding time is 3 minutes, and after the holding time is completed, they are taken out and air-cooled.

[0196] Step 8: Heat treat the bar obtained in Step 7 and inspect the microstructure and properties of the bar.

[0197] In step 8 above, the heat treatment process includes a first solution treatment, a second solution treatment, and an aging treatment, which are as follows: First solution treatment: 1120℃×8h, air cooling; Second solution treatment: 1000℃±10℃×4h, air cooling; Aging treatment: 775℃±10℃×16h, air cooling.

[0198] In step 8 above, the heat treatment process specifically includes the following sub-steps:

[0199] Step 81: Raise the furnace temperature to 1120℃, put in the bar stock, keep it at that temperature for 8 hours, then take it out and air cool it.

[0200] Step 82: Raise the furnace temperature to 1000℃, put in the bar, keep it at the temperature for 4 hours, and then take it out and air cool it.

[0201] Step 83: Raise the furnace temperature to 785℃, put in the bar stock, keep it at that temperature for 16 hours, then take it out and air cool it.

[0202] In this embodiment, a GH4698 thin rod with a diameter of Φ30mm was finally prepared. The grain structure of the GH4698 thin rod is as follows: Figure 10 As shown, the average grain size is 3.5-4.5, and there are no abnormally large grains such as grade 0 or grade 00 grains.

[0203] 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 controlling the uniformity of microstructure in GH4698 fine rods, characterized in that, Includes the following steps: Step 1: Prepare the ingot and perform homogenization diffusion annealing on the ingot; Step 2: Forge and roll the ingot obtained in Step 1 to obtain bar billet; Step 3: Perform a secondary homogenization treatment on the bar billet obtained in Step 2; Step 4: Perform precision rolling on the bar after the secondary homogenization treatment to obtain GH4698 alloy thin bars with uniform microstructure.

2. The method for controlling the homogenization of microstructure in GH4698 fine rods according to claim 1, characterized in that, In step 4, the initial rolling size of the bar billet is Φ14-120mm. After being fully heated at 1070-1120℃, it is rolled out of the furnace and the final rolling size is Φ5-30mm. After rolling, it is air-cooled to obtain GH4698 thin bars.

3. The method for controlling the homogenization of the microstructure of GH4698 fine rods according to claim 2, characterized in that, In step 4, the bar billet is rolled using a multi-pass reversing continuous rolling process.

4. The method for controlling the homogenization of the microstructure of GH4698 fine rods according to claim 3, characterized in that, In step 4, the multi-pass reversing continuous rolling is a ten-pass reversing continuous rolling. The first rolling pass has a deformation of 5-20%, and the second rolling pass is performed immediately after the first rolling pass is completed. The second pass involves rotating the bar by 90° and rolling it based on the first pass. The rolling deformation is 5-20%. The third pass is performed immediately after the first pass.

5. The method for controlling the homogenization of the microstructure of GH4698 fine rods according to claim 4, characterized in that, In step 4, the third pass involves rotating the bar by 90° and rolling it based on the second pass. The rolling deformation is 5-20%. The fourth pass is performed immediately after the rolling is completed. The fourth pass involves rotating the bar by 90° and rolling it based on the third pass. The rolling deformation is 5-20%. The fifth pass is performed immediately after the third pass.

6. The method for controlling the homogenization of the microstructure of GH4698 fine rods according to claim 5, characterized in that, In step 4, the fifth pass involves rotating the bar by 90° and rolling it based on the fourth pass. The rolling deformation is 5-20%. The sixth pass is performed immediately after the rolling is completed. The sixth pass involves rotating the bar by 90° and rolling it based on the fifth pass. The rolling deformation is 5-20%. The seventh pass is performed immediately after the fifth pass.

7. The method for controlling the homogenization of microstructure in GH4698 fine rods according to claim 6, characterized in that, In step 4, the seventh pass involves rotating the bar by 90° and rolling it based on the sixth pass. The rolling deformation is 5-20%. Immediately after rolling, the eighth pass is performed.

8. The method for controlling the homogenization of microstructure in GH4698 fine rods according to claim 7, characterized in that, In step 4, the eighth pass involves rotating the bar by 90° and rolling it based on the seventh pass. The rolling deformation is 5-20%. Immediately after rolling, the ninth pass is performed.

9. The method for controlling the homogenization of the microstructure of GH4698 fine rods according to claim 8, characterized in that, In step 4, the ninth pass involves rotating the bar by 90° and rolling it based on the eighth pass. The rolling deformation is 5-20%. Immediately after rolling, the tenth pass is performed.

10. The method for controlling the homogenization of the microstructure of GH4 698 fine rods according to claim 9, characterized in that, In step 4, the tenth pass involves rotating the bar by 90° and rolling it based on the ninth pass. The rolling deformation is 5-20%. After rolling, the bar is air-cooled to finally obtain GH4698 thin bars with a diameter of Φ5-30mm.

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