Preparation method of large-size fine-grain bar

Abstract

The invention provides a preparation method of a large-size fine-grain bar, which comprises the following steps: S1, weighing metal Cr, Ni, Mo, Al, W, Co, Ti, Zr, graphite C and nickel-boron raw materials, adding the raw materials into a smelting furnace, smelting, vacuumizing, refining and pouring after the raw materials are molten to obtain an electrode bar, then the electrode bar is sequentially subjected to electroslag remelting and vacuum consumable remelting, and a consumable ingot is obtained; s2, the alloy ingot is subjected to high-temperature homogenization diffusion annealing, and a low-segregation cast ingot is obtained; s3, the cast ingot is heated before forging, and then a bar billet is obtained through forging; and S4, the bar blank is turned to obtain the fine-grain bar with the final specification. According to the method, the fine grain forging process of upsetting and drawing cogging and drawing is adopted, metallurgical defects such as black spots and white spots are not found on the obtained bar in a low magnification mode, abnormal inclusion aggregation is avoided, obvious harmful TCP phase precipitation is not found through microscopic structure analysis of the obtained bar, the structure is uniform, and the grain size is larger than 8 grades.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloys, and in particular to a method for preparing large-size fine-grained rods. Background Art

[0002] GH4720Li alloy is a nickel-based age-hardened high-temperature alloy with excellent high-temperature mechanical properties, fatigue resistance, creep resistance, and good corrosion resistance and oxidation resistance. In order to improve the high-temperature stability and strength of the alloy, too many alloying elements are added to the alloy, such as Cr, Co, Mo, W, Al, Ti, etc. Due to the high degree of alloying of GH4720Li high-temperature alloy, the alloy is prone to serious element segregation, poor plasticity and easy cracking during the preparation process, especially when preparing large-sized fine-grained bars, which is more difficult. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing large-sized fine-grained rods. Through triple purification smelting, homogenization diffusion and fine-grained forging processes, large-sized low-segregation fine-grained rods of GH4720Li alloy are prepared. The obtained rods have a uniform grain size of ≥8 at each position and excellent room temperature tensile properties.

[0004] The technical solution adopted by the present invention is:

[0005] A method for preparing large-size fine-grained rods, comprising the following steps:

[0006] Step S1, according to mass percentage, the large-size fine-grained rod includes the following elements: C 0.01-0.02, Cr15.5-16.5, Ti 5.05-5.25, Al 2.45-2.60, W 1.20-1.40, Co 14.5-15.5, Mo 2.75-3.25, Zr 0.025-0.050, B 0.01~0.02, the balance is Ni and inevitable impurities from smelting, the above total is 100%, the content of the inevitable impurities is S≤0.001, P≤0.015, Mn≤0.15, Fe≤0.5, Si≤0.2, O≤0.002, N≤0.0032, metal Cr, Ni, Mo, Al, W, Co, Ti, Zr, graphite C and nickel-boron raw materials are weighed according to the above elements, and the above raw materials are added into a smelting furnace for smelting and vacuuming, after the raw materials are melted, they are refined and cast in sequence to obtain electrode rods, and then the electrode rods are subjected to electroslag remelting and vacuum consumable remelting in sequence to obtain ingots;

[0007] Step S2, subjecting the alloy ingot obtained in step S1 to high temperature homogenization diffusion annealing to obtain an ingot with low segregation;

[0008] Step S3, tumbling the circumferential surface of the ingot obtained in step S2, and heating the tumbled ingot in a heating furnace before forging, and then forging to obtain a rod blank;

[0009] Step S4, polishing the bar blank obtained in step S3 to obtain a fine-grained bar of specified specifications.

[0010] Preferably, in the method for preparing large-sized fine-grained rods, the large-sized fine-grained rods in step S1 include the following elements: C 0.012-0.018%, Cr 15.7-16.1%, Ti 5.05-5.15%, Al 2.45-2.55%, W1.20-1.40%, Co 14.50-15.00%, Mo 2.95-3.15%, Zr0.03-0.04%, B 0.014-0.016%, S≤0.001%, O≤0.002%, N≤0.0032%, and Ni as the balance.

[0011] Preferably, in the method for preparing large-size fine-grained rods, the melting temperature in step S1 is 1430-1460°C, the refining temperature is 1500-1530°C, and the pouring temperature is 1465-1485°C.

[0012] Preferably, in the method for preparing large-size fine-grained rods, the slag system of electroslag remelting in step S1 includes CaF2, Al2O3, CaO, MgO, and TiO2, and the weight ratio of CaF2, Al2O3, CaO, MgO, and TiO2 is 50:20:20:5:3.

[0013] Preferably, in the method for preparing large-size fine-grained rods, the vacuum degree of vacuum consumable remelting in step S1 is less than 1.0 Pa, and the steady-state melting rate is 3.0-3.3 kg / min.

[0014] Preferably, in the method for preparing large-size fine-grained rods, the high-temperature homogenization diffusion annealing temperature in step S2 is 1210-1230° C., and the holding time is 70-100 h.

[0015] Preferably, in the method for preparing large-size fine-grained rods, the heating before forging in step S3 is specifically as follows: first heating to 750±10°C for preheating, then heating to the forging temperature and keeping the temperature for ≥8h.

[0016] Preferably, in the method for preparing large-size fine-grained bars, the forging in step S3 is specifically as follows: the forging in step S3 is specifically as follows: four upsetting passes are used to open the blank, and then four upsetting passes are performed to lengthen the blank to the forged size to obtain the bar blank, each upsetting pass includes heating, upsetting, heating and lengthening steps, and during the upsetting process, the average deformation of each upsetting pass is controlled to be 40% to 50%, the heating temperature of each pass is controlled to be 1130 to 1150°C, and the holding time is 120 to 24 0min; during drawing, the heating temperature is controlled at 1130-1150°C for the first drawing pass, and the heating temperature is controlled at 1110-1130°C for the second to third drawing passes, the deformation amount of each drawing pass is controlled to be 40%-50%, and the holding time is 120-240min. The last pass is for deformation and rounding steps, the heating temperature is controlled at 1110-1130°C, the deformation amount is controlled to be 20%-30%, and the holding time is 120-240min.

[0017] Preferably, in the method for preparing large-size fine-grained rods, the surface roughness of the rods after polishing is controlled to be ≤1.6 μm in step S4.

[0018] Advantages of the present invention:

[0019] (1) The preparation method of large-scale fine-grained rods of the present invention optimizes the alloy composition range and the homogenization diffusion process, reduces the element segregation of the ingot, and the residual segregation index of the main element of the consumable ingot after adjustment is less than 0.1;

[0020] (2) The preparation method of the large-size fine-grained rod of the present invention adopts a fine-grained forging process of upsetting and drawing the blank + drawing and elongation. The obtained rod has no metallurgical defects such as black spots and white spots at low magnification, no abnormal inclusion aggregation, and no obvious harmful TCP phase precipitation is found in the microstructure analysis of the obtained rod. The structure is uniform and the grain size is greater than level 8.

[0021] (3) The preparation method of the large-sized fine-grained rod of the present invention controls the deformation temperature, holding time and deformation amount during the upsetting process to prepare the large-sized fine-grained rod of GH4720Li alloy with excellent performance. The tensile strength at 650°C can reach more than 1350MPa, and the yield strength can reach more than 1025MPa.

[0022] (4) The preparation method of large-sized fine-grained rods of the present invention solves for the first time the problems of easy segregation and elongated crystals that are easy to occur in large-sized rods. Its organizational uniformity and mechanical properties reach the level of small-sized rods, meeting the application requirements of large-sized fine-grained GH4720Li alloy rods for aircraft engine turbine disks. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a grain size test diagram of Example 1 of the present invention.

[0024] Figure 2 This is a grain size test diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] A method for preparing large-size fine-grained rods comprises the following steps:

[0028] Step S1, according to mass percentage, the large-size fine-grained rod includes the following elements: C 0.01-0.02, Cr15.5-16.5, Ti 5.05-5.25, Al 2.45-2.60, W 1.20-1.40, Co 14.5-15.5, Mo 2.75-3.25, Zr 0.025-0.050, B 0.01~0.02, the balance is Ni and inevitable impurities from smelting, the above total is 100%, the content of the inevitable impurities is S≤0.001, P≤0.015, Mn≤0.15, Fe≤0.5, Si≤0.2, O≤0.002, N≤0.0032, according to the above elements, metal Cr, Ni, Mo, Al, W, Co, Ti, Zr, graphite C and nickel-boron raw materials are weighed, and the above raw materials are added into a smelting furnace for smelting and vacuuming, and the raw materials are refined and cast in turn after melting to obtain electrode rods, the melting temperature is 1450℃, the refining temperature is 1515℃, and the casting temperature is 1480℃. ℃; then the bottom of the electrode rod is welded to the dummy electrode and placed in an electroslag remelting furnace to obtain a consumable electrode after arcing, steady state, and hot capping. The slag system selected for electroslag remelting includes CaF2, Al2O3, CaO, MgO, and TiO2. The weight ratio of CaF2, Al2O3, CaO, MgO, and TiO2 is 50:20:20:5:3. Then the bottom of the consumable electrode rod is welded to the dummy electrode and placed in a vacuum consumable remelting furnace for vacuum consumable remelting. After arcing, steady state, and hot capping, an ingot is obtained after vacuum consumable remelting. During the vacuum consumable remelting process, the vacuum degree is less than 1.0Pa, and the steady-state melting rate is 3.05-3.2kg / min;

[0029] Step S2, subjecting the ingot obtained in step S1 to high temperature homogenization diffusion annealing to obtain an ingot with low segregation, wherein the high temperature homogenization diffusion annealing temperature is 1220° C. and the holding time is 72 hours;

[0030] Step S3, rolling the circumferential surface of the ingot obtained in step S3, and heating the rolled ingot before forging in a heating furnace, wherein the heating before forging is as follows: firstly heating the temperature to 750±10°C for preheating, then heating the temperature to the forging temperature and keeping the temperature for 8 hours, and then forging to obtain a rod blank;

[0031] The forging is specifically as follows: four upsetting passes are used for blanking, and finally four upsetting passes are performed to the forged size to obtain the bar blank, each upsetting pass includes heating, upsetting, heating and upsetting steps, and during the upsetting process, the average deformation of each upsetting pass is controlled to be 43%, the heating temperature of each pass is controlled to be 1130°C, and the holding time is 240min; during the drawing, the heating temperature of the first drawing pass is controlled to be 1130°C, and the heating temperature of the second to third drawing passes is controlled to be 1120°C, the deformation of each drawing pass is controlled to be 42%, and the holding time is 240min, and the last pass is a deformation and rounding step, the heating temperature is controlled to be 1120°C, the deformation is controlled to be 23%, and the holding time is 240min;

[0032] Step S4, polishing the bar blank obtained in step S2 until there is no crack on the surface, and the surface roughness of the polished alloy bar is ≤1.6 μm to obtain a fine-grained bar with a specification of Φ200 mm.

[0033] Example 2

[0034] A method for preparing large-size fine-grained rods comprises the following steps:

[0035] Step S1, according to mass percentage, the large-size fine-grained rod includes the following elements: C 0.01-0.02, Cr15.5-16.5, Ti 5.05-5.25, Al 2.45-2.60, W 1.20-1.40, Co 14.5-15.5, Mo 2.75-3.25, Zr 0.025-0.050, B 0.01~0.02, the balance is Ni and inevitable impurities from smelting, the above total is 100%, the content of the inevitable impurities is S≤0.001, P≤0.015, Mn≤0.15, Fe≤0.5, Si≤0.2, O≤0.002, N≤0.0032, according to the above elements, metal Cr, Ni, Mo, Al, W, Co, Ti, Zr, graphite C and nickel-boron raw materials are weighed, and the above raw materials are added into the smelting furnace for smelting and vacuuming, and the raw materials are refined in sequence after melting. and pouring to obtain an electrode rod, and then the electrode rod is sequentially subjected to electroslag remelting and vacuum consumable remelting to obtain an ingot; the melting temperature is 1455°C, the refining temperature is 1510°C, and the pouring temperature is 1485°C; the slag system of the electroslag remelting includes CaF2, Al2O3, CaO, MgO, and TiO2, and the weight ratio of CaF2, Al2O3, CaO, MgO, and TiO2 is 50:20:20:5:3; the vacuum degree of the vacuum consumable remelting is <1.0Pa, and the steady-state melting rate is 3.05-3.2kg / min;

[0036] Step S2, subjecting the ingot obtained in step S1 to high temperature homogenization diffusion annealing to obtain an ingot with low segregation, wherein the high temperature homogenization diffusion annealing temperature is 1220° C. and the holding time is 80 hours;

[0037] Step S3, rolling the consumable ingot obtained in step S2 on the circumferential surface, the rolling temperature is 1140°C, the deformation is 5%, and the rolled consumable ingot is heated before forging in a heating furnace, the pre-forging heating is specifically: firstly heating to 750±10°C for preheating, then heating to the forging temperature and keeping the temperature for 8 hours, and then forging to obtain the rod;

[0038] The forging is specifically as follows: the consumable ingot after heating before forging is first surface-rolled, then four upsetting passes are used for blanking, and finally four upsetting passes are performed to the forged size to obtain a bar blank, each upsetting pass includes heating, upsetting, heating and upsetting steps, and during the upsetting process, the average deformation of each upsetting pass is controlled to be 41.5%, the heating temperature of each pass is controlled to be 1140°C, and the holding time is 240min; during the drawing, the heating temperature is controlled to be 1130°C during the first drawing pass, and the heating temperature is controlled to be 1120°C during the second to third drawing passes, the deformation of each drawing pass is controlled to be 45.5%, and the holding time is 240min, and the last pass is a deformation and rounding step, the heating temperature is controlled to be 1120°C, the deformation is controlled to be 27.5%, and the holding time is 240min;

[0039] Step S4, polishing the bar blank obtained in step S3 until there is no crack on the surface, and the surface roughness of the polished alloy bar is ≤1.6 μm to obtain a fine-grained bar with a specification of Φ200 mm.

[0040] The chemical composition of the GH4720Li alloy rod in Example 1-2 is shown in Table 1.

[0041] Table 1

[0042] element standard Control scope Example 1 Example 2 C 0.01～0.02 0.012～0.018 0.018 0.018 Cr 15.5～16.5 15.70～16.10 15.72 15.78 Ti 4.75～5.25 4.95～5.15 5.10 5.07 Al 2.25～2.75 2.35～2.55 2.51 2.46 W 1.00～1.50 1.20～1.40 1.25 1.24 Co 14.0～15.5 14.50～15.00 14.85 14.82 Mo 2.75～3.25 2.95～3.15 3.01 3.03 Zr 0.025～0.05 0.03～0.04 0.038 0.03 B 0.01～0.02 0.014～0.016 0.014 0.015 S ≤0.001 / ≤0.0005 ≤0.0005 P ≤0.015 / 0.0039 0.0038 Mn ≤0.15 / ≤0.01 ≤0.01 Fe ≤0.5 / 0.04 0.035 Si ≤0.2 / ≤0.01 ≤0.01 O ≤0.002 / 0.0003 0.0005 N ≤0.0032 / ≤0.0005 ≤0.0005 Ni Remain Remain Remain Remain

[0043] The grain size and strength test of GH4720Li alloy rod in Example 1-2 are shown in Table 2. Figure 1 This is the grain size test diagram of Example 1, Figure 2 This is the grain size test diagram of Example 2.

[0044] Table 2

[0045]

[0046] From Table 1, Table 2, Figure 1 and Figure 2 It can be concluded that the large-size fine-grained rods of GH4720Li alloy prepared by the present invention meet the commonly used industry standards, have good indicators, and are highly competitive in the market.

[0047] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing large-size fine-grained rods, characterized in that: The following steps are involved: Step S1, according to mass percentage, the large-size fine-grained rod includes the following elements: C 0.01-0.02, Cr 15.5-16.5, Ti 5.05-5.25, Al 2.45-2.60, W 1.20-1.40, Co 14.5-15.5, Mo 2.75-3.25, Zr0.025-0.050, B 0.01-0.02, the remainder is Ni and inevitable impurities from smelting, the total of the above is 100%, the content of the inevitable impurities is S ≤0.001, P≤0.015, Mn≤0.15, Fe≤0.5, Si≤0.2, O≤0.002, N≤0.0032, weigh metal Cr, Ni, Mo, Al, W, Co, Ti, Zr, graphite C and nickel-boron raw materials according to the above elements, add the above raw materials into a smelting furnace for smelting and vacuuming, after the raw materials are melted, refine and cast in sequence to obtain electrode rods, and then the electrode rods are sequentially subjected to electroslag remelting and vacuum consumable remelting to obtain ingots; Step S2, subjecting the ingot obtained in step S1 to high temperature homogenization diffusion annealing to obtain an ingot with low segregation; Step S3, tumbling the circumferential surface of the ingot obtained in step S2, and heating the tumbled ingot in a heating furnace before forging, and then forging to obtain a rod blank; Step S4, polishing the bar blank obtained in step S3 to obtain a fine-grained bar of specified specifications.

2. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: The large-size fine-grained rod in step S1 includes the following elements: C 0.012~0.018%, Cr 15.7~16.1%, Ti 5.05~5.15%, Al 2.45~2.55%, W 1.20~1.40%, Co 14.50~15.00%, Mo 2.95~3.15%, Zr 0.03~0.04%, B0.014~0.016%, S≤0.001%, O≤ 0.002%, N≤0.0032%, Ni is the balance.

3. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: In step S1, the melting temperature is 1430-1460°C, the refining temperature is 1500-1530°C, and the pouring temperature is 1465-1485°C.

4. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: The slag system of the electroslag remelting in step S1 includes CaF2, Al2O3, CaO, MgO, and TiO2, and the weight ratio of CaF2, Al2O3, CaO, MgO, and TiO2 is 50:20:20:5:

3.

5. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: The vacuum degree of the vacuum consumable remelting in step S1 is less than 1.0 Pa, and the steady-state melting rate is 3.0-3.3 kg / min.

6. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: In step S2, the high temperature homogenization diffusion annealing temperature is 1210-1230° C., and the holding time is 70-100 hours.

7. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: The heating before forging in step S3 is specifically as follows: firstly heating to 750±10°C for preheating, then heating to forging temperature and keeping the temperature for ≥8h.

8. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: The forging in step S3 is specifically as follows: the consumable ingot after pre-forging heating is opened by four upsetting and drawing, and then drawn to the forged size by four upsetting and drawing, each upsetting and drawing includes heating, upsetting, heating and drawing steps, and the average deformation of each upsetting is controlled to be 40% to 50% during the upsetting process, and the heating temperature of each pass is controlled to be 1130 to 1150°C, and the holding time is 120 to 240 minutes; during the drawing, the first pass The heating temperature is controlled at 1130-1150°C during drawing, and the heating temperature is controlled at 1110-1130°C during the 2nd-3rd drawing. The deformation amount of each drawing pass is controlled at 40%-50%, and the holding time is 120-240min. The last pass is for deformation and rounding steps, and the heating temperature is controlled at 1110-1130°C, the deformation amount is controlled at 20%-30%, and the holding time is 120-240min.

9. The method for preparing large-size fine-grained rods according to claim 1, characterized in that: In step S4, the surface roughness of the rod after polishing is controlled to be ≤1.6 μm.

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