Method for improving grain size and mechanical properties of AF1410 steel free forging workpiece

Abstract

The application provides a method for improving grain size and mechanical properties of AF1410 steel free forging, and belongs to the technical field of alloy preparation. The method for improving grain size and mechanical properties of AF1410 steel free forging is characterized by increasing high-temperature diffusion pre-pulling and improving diffusion temperature, and further improving the uniformity of the structure through four-pulling and four-pulling, so as to provide a good structure basis for the uniformity of the grain size in the later stage. The deformation amount of the final fire is further controlled to be greater than or equal to 50-55%, the final forging temperature is reduced, the pack forging technology is adopted, and the mixed grain size caused by the non-uniformity of the temperature is prevented. Through the forging process method, the grain size level is greatly improved, and the grain size of the edge, 1 / 2 radius and center of the cross section at any position is all above grade 8 and is very uniform. In addition, the improvement of the grain size and the uniformity also improves the mechanical properties, reduces the difference between the longitudinal and transverse impact toughness, and the ratio of the transverse impact toughness to the longitudinal impact toughness is improved from the original 0.76 to 0.95.

Description

Technical Field

[0001] This invention belongs to the field of alloy preparation technology, specifically relating to a method for improving the grain size and mechanical properties of AF1410 steel free forgings. Background Technology

[0002] AF1410 (16Co14Ni10Cr2MoE) steel is a new type of low-carbon, high-alloy, secondary-hardening, ultra-high-strength material with excellent fatigue resistance and crack propagation resistance. It is widely used in major load-bearing structural components of aerospace. Compared with other commonly used high-strength steels, its yield strength and tensile strength reach over 1500MPa and 1600MPa respectively, but its thermal conductivity is only 1 / 3 to 1 / 4 that of other high-strength steels, making it a typical difficult-to-machine material.

[0003] The grain size of AF1410 steel directly affects its properties, with a significant impact on fatigue life. Current processing methods for controlling the grain size of this steel primarily focus on die forging, and reports on this are relatively scarce. However, research on controlling the grain size and improving the mechanical properties of free forgings of this steel on presses remains unexplored.

[0004] In production, the grain size of the free forgings of this steel is mainly adjusted by multiple normal tempering after forging. This method has low production efficiency and high cost. If the forging process is not properly controlled, it is difficult to achieve the ideal effect even after multiple normal temperings. For example, if there are mixed grains or coarse grains, the impact toughness and fracture toughness values ​​will not meet the standards, and there may even be large differences in longitudinal and transverse properties, which will reduce the service life of the product.

[0005] Therefore, there is an urgent need to provide a method that can improve the grain size of AF1410 steel, enhance its mechanical properties, and significantly reduce costs. Summary of the Invention

[0006] The present invention aims to solve the aforementioned technical problems by providing a method for improving the grain size and mechanical properties of AF1410 (16Co14Ni10Cr2MoE) steel free forgings. The technical objective of this invention is twofold: firstly, to address the issue of low grain size in free forgings produced by existing AF1410 steel processing techniques; and secondly, to address the problem of low mechanical properties in free forgings of AF1410 steel.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for improving the grain size and mechanical properties of AF1410 steel free forgings, comprising the following steps:

[0009] (1) Heat AF1410 steel ingots to 1150-1180℃, adjust the height-to-diameter ratio to 1.8-2.2 by upsetting and drawing, and then put them into the furnace for high-temperature diffusion;

[0010] (2) Adjust the high-temperature homogenization temperature to 1230-1250℃ and keep it warm for 30-50 hours;

[0011] (3) After high temperature diffusion, the temperature is reduced to 1150-1180℃, and the temperature is held for 2-3 hours before forging. The forging is carried out using the four-pile and four-drawing billet opening technology.

[0012] (4) First upsetting and drawing, upsetting ratio 2-2.2, drawing rectangle deformation 45-55%, final forging temperature ≥900℃;

[0013] (5) Second upsetting and drawing, heating temperature 1150-1180℃, holding time calculated as 0.3-0.4*H (thickness) min, upsetting ratio 2-2.2, drawing rectangle deformation 45-55%, final forging temperature ≥900℃;

[0014] (6) Third forging: heating temperature 1060-1080℃, holding time calculated as 0.3-0.4*H (thickness) min, forging ratio 2-2.2, forging rectangle deformation 45-55%, final forging temperature ≥850℃;

[0015] (7) Fourth forging: heating temperature 1060-1080℃, holding time calculated as 0.3-0.4*H (thickness) min, upsetting ratio 2-2.2, elongated deformation 45-55%, final forging temperature ≥850℃;

[0016] (8) Open the intermediate billet, heating temperature 1020-1030℃, holding time calculated as 0.3-0.4*H (thickness) min, drawing deformation 50-55%, final forging temperature ≥850℃;

[0017] (9) Forging into a finished product, which is then obtained.

[0018] The processing method provided by this invention, on the one hand, increases the pre-drilling and raising of the high-temperature diffusion temperature, further enhancing the high-temperature homogenization effect; on the other hand, the four-drilling and four-raising process further improves the uniformity of the microstructure, providing a good microstructure foundation for the uniformity of the grain size in the later stage. Through the forging process method provided by this invention, the grain size level of AF1410 steel is greatly improved, and the grain size at the edge, half radius, and center of any cross-section is all above grade 8 and very uniform. Furthermore, through the above forging method, while improving the grain size and uniformity of AF1410 steel, the mechanical properties are also significantly improved, reducing the difference in impact toughness between the longitudinal and transverse directions, and increasing the impact toughness ratio from 0.76 to 0.95.

[0019] Furthermore, the elemental composition of the AF1410 steel ingot, by weight percentage, is as follows: C 0.15-0.19%, Co 13.50-14.50%, Ni 9.50-10.50%, Cr 1.80-2.20%, Mo 0.90-1.10%, Si≤0.10%, Mn≤0.10%, S≤0.005%, P≤0.008%, P+S≤0.010%, Al≤0.015%, Ti≤0.015%, O≤0.0020%, N≤0.0015%, with the balance being Fe.

[0020] Furthermore, during the forging process, the heating temperature is controlled at 1020-1030℃, and the holding time is 0.2*H (thickness) min.

[0021] Furthermore, during forging, after heating and holding, the resulting billet is taken out of the furnace, wrapped in high-temperature resistant insulation cotton, and then fired again in the furnace for 0.2-0.3 * H (thickness) min before being taken out of the furnace to forge the finished product.

[0022] Furthermore, during forging, the final forging deformation is controlled to be ≥50-55%. This invention reduces the final forging temperature and employs a sleeve forging technique, further preventing grain size mixing caused by temperature inhomogeneity.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) The method of the present invention improves the grain size of AF1410 steel to grade 8-10, and the grain size of the edge, 1 / 2 radius and center of the cross section at any position is very uniform, without mixed grains and coarse grains.

[0025] (2) The method of the present invention improves the mechanical properties of AF1410 steel, reduces the difference in impact toughness between the transverse and longitudinal directions, and the impact toughness ratio can be increased to 0.95.

[0026] (3) The method of the present invention is simple, low in cost, and suitable for widespread application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0028] Example 1

[0029] This invention provides an AF1410 (16Co14Ni10Cr2MoE) steel, the elemental composition of which is shown in Table 1 below:

[0030] Table 1. Elemental Composition of AF1410 (16Co14Ni10Cr2MoE) Steel

[0031] element C Co Ni Cr Mo Si Mn S Sample 1 0.15 14.20 9.90 1.90 0.90 0.08 0.08 0.0015 Sample 2 0.16 14.00 10.00 2.0 1.00 0.05 0.05 0.0010 Sample 3 0.17 13.90 10.10 2.10 1.10 0.02 0.02 0.0008 element P P+S Al Ti O N Fe Sample 1 0.006 0.0075 0.010 0.010 0.0012 0.0015 margin Sample 2 0.005 0.0060 0.008 0.008 0.008 0.0012 margin Sample 3 0.004 0.0048 0.005 0.003 0.0006 0.0008 margin

[0032] Sample 1 from Table 1 above was taken as AF1410 steel material, and its preparation method adopted the following process flow: 6T vacuum induction furnace (casting electrode rod) → vacuum self-consumption furnace (remelting 3T ingot).

[0033] During the forging process, the free forging steel ingot obtained by the above process is subjected to the following forging treatment:

[0034] 1. The steel ingot is heated to 1150℃, and after being pulled and adjusted to a height-to-diameter ratio of 1.8, it is put into the furnace for high-temperature diffusion. The purpose is to break up the as-cast dendrites, shorten the secondary dendrite spacing, and reduce the atomic diffusion distance to achieve a better diffusion effect.

[0035] 2. High-temperature homogenization: Increase the high-temperature homogenization temperature to 1230℃ and hold for 30 hours;

[0036] 3. After high-temperature diffusion, the temperature is reduced to 1150℃, and after holding at that temperature for 2 hours, forging begins, using a four-pronged forging and four-pulling technique.

[0037] 4. First forging (first upsetting and drawing), upsetting ratio 2, drawing rectangle deformation 45%; final forging temperature 900℃;

[0038] 5. Second forging (second upsetting and drawing): heating temperature 1150℃, holding time calculated as 0.3*H (thickness) min, upsetting ratio 2, drawing rectangle deformation 45%; final forging temperature 900℃.

[0039] 6. Third forging (third drawing): heating temperature 1060℃, holding time calculated as 0.3*H (thickness) min, upsetting ratio 2, drawing rectangle deformation 45%; final forging temperature 850℃.

[0040] 7. Fourth forging (fourth upsetting and drawing): heating temperature 1060℃, holding time calculated as 0.3*H (thickness) min, upsetting ratio 2, drawing rectangle deformation 45%; final forging temperature 850℃.

[0041] 8. Fifth forging (intermediate billet): heating temperature 1020℃, holding time calculated as 0.3*H (thickness) min, elongation deformation 50%, final forging temperature 850℃.

[0042] 9. For the sixth heat (forged product), the heating temperature is 1020℃, and after holding at that temperature for 0.2*H (thickness) min, the billet is taken out of the furnace, wrapped with high-temperature resistant insulation cotton, and then fired again for 0.2*H (thickness) min before being taken out of the furnace as the forged product. The deformation amount of the final heat is 50%.

[0043] Example 2

[0044] Sample 2 from Table 1 was selected as the AF1410 steel material, and its preparation method adopted the following process flow: 6T vacuum induction furnace (casting electrode rod) → vacuum self-consumption furnace (remelting 6T ingot).

[0045] During the forging process, the free forging steel ingot obtained by the above process is subjected to the following forging treatment:

[0046] 1. The steel ingot is heated to 1180℃, and after being pulled and adjusted to a height-to-diameter ratio of 2.2, it is put into the furnace for high-temperature diffusion. The purpose is to break up the as-cast dendrites, shorten the secondary dendrite spacing, and reduce the atomic diffusion distance to achieve a better diffusion effect.

[0047] 2. High-temperature homogenization: Increase the high-temperature homogenization temperature to 1250℃ and hold for 50 hours;

[0048] 3. After high-temperature diffusion, the temperature is reduced to 1180℃, and after holding at that temperature for 3 hours, forging begins, using a four-pronged forging and four-pulling technique.

[0049] 4. First forging (first upsetting and drawing): Upsetting ratio 2.2, drawing rectangle deformation 55%; final forging temperature 920℃;

[0050] 5. Second forging (second upsetting and drawing): heating temperature 1180℃, holding time calculated as 0.4*H (thickness) min, upsetting ratio 2.2, drawing rectangle deformation 55%; final forging temperature 920℃.

[0051] 6. Third forging (third drawing): heating temperature 1080℃, holding time calculated as 0.4*H (thickness) min, upsetting ratio 2.2, drawing rectangle deformation 55%; final forging temperature 870℃.

[0052] 7. Fourth forging (fourth upsetting and drawing): heating temperature 1080℃, holding time calculated as 0.4*H (thickness) min, upsetting ratio 2.2, drawing rectangle deformation 55%; final forging temperature 870℃.

[0053] 8. Fifth forging (intermediate billet): heating temperature 1030℃, holding time calculated as 0.4*H (thickness) min, elongation deformation 55%, final forging temperature 870℃.

[0054] 9. The sixth heat (forged product): heating temperature 1030℃, holding temperature for 0.2*H (thickness) min, the billet is taken out of the furnace, wrapped with high temperature resistant insulation cotton, and then fired in the furnace for another 0.3*H (thickness) min before being taken out as the forged product. The deformation amount of the final heat is 55%.

[0055] Example 3

[0056] Sample 1 from Table 1 above was taken as AF1410 steel material, and its preparation method adopted the following process flow: 6T vacuum induction furnace (casting electrode rod) → vacuum self-consumption furnace (remelting 3T ingot or 6T ingot).

[0057] During the forging process, the free forging steel ingot obtained by the above process is subjected to the following forging treatment:

[0058] 1. The steel ingot is heated to 1170℃, and after being pulled and adjusted to a height-to-diameter ratio of 2.0, it is put into the furnace for high-temperature diffusion. The purpose is to break up the cast dendrites, shorten the secondary dendrite spacing, and reduce the atomic diffusion distance to achieve a better diffusion effect.

[0059] 2. High-temperature homogenization: Increase the high-temperature homogenization temperature to 1240℃ and hold for 40 hours;

[0060] 3. After high-temperature diffusion, the temperature is reduced to 1160℃ and held for 2.5 hours before forging, using a four-pronged forging and four-pulling technique.

[0061] 4. First forging (first upsetting and drawing), upsetting ratio 2.1, drawing rectangle deformation 50%; final forging temperature 910℃;

[0062] 5. Second forging (second upsetting and drawing): heating temperature 1160℃, holding time calculated as 0.35*H (thickness) min, upsetting ratio 2.1, drawing of rectangular shape deformation 50%; final forging temperature 910℃.

[0063] 6. Third forging (third upsetting and drawing): heating temperature 1070℃, holding time calculated as 0.35*H (thickness) min, upsetting ratio 2.1, drawing of rectangular shape deformation 50%; final forging temperature 860℃.

[0064] 7. Fourth forging (fourth upsetting and drawing): heating temperature 1070℃, holding time calculated as 0.35*H (thickness) min, upsetting ratio 2.1, drawing rectangle deformation 50%; final forging temperature 860℃.

[0065] 8. Fifth forging (intermediate billet): heating temperature 1025℃, holding time calculated as 0.35*H (thickness) min, elongation deformation 52%, final forging temperature 860℃.

[0066] 9. The sixth heat (forged product): heating temperature 1025℃, holding temperature for 0.2*H (thickness) min, the billet is taken out of the furnace, wrapped with high temperature resistant insulation cotton, and then fired again for 0.25*H (thickness) min before being taken out of the furnace as the forged product. The deformation amount of the final heat is 52%.

[0067] Comparative Example 1

[0068] The forging process according to the processing method of Example 1 is as follows:

[0069] 1. Direct diffusion of steel ingots, diffusion temperature 1200℃, holding time 30h;

[0070] 2. After the steel ingot undergoes two upsetting and two drawing processes, an intermediate billet is produced (heating temperature 1150℃);

[0071] 3. The forging temperature of the finished product is 1100℃, and the final deformation is 40%.

[0072] Comparative Example 2

[0073] The forging process according to the processing method of Example 2 is as follows:

[0074] 1. Direct diffusion of steel ingots, diffusion temperature 1200℃, holding time 50h;

[0075] 2. After the steel ingot undergoes two upsetting and two drawing processes, an intermediate billet is produced (heating temperature 1180℃);

[0076] 3. The finished product forging heating temperature is 1100℃, and the final deformation is 45%.

[0077] Comparative Example 3

[0078] The forging process according to the processing method of Example 3 is as follows:

[0079] 1. Direct diffusion of steel ingots, diffusion temperature 1200℃, holding time 40h;

[0080] 2. After the steel ingot undergoes two upsetting and two drawing processes, an intermediate billet is produced (heating temperature 1170℃);

[0081] 3. The finished product forging heating temperature is 1100℃, and the final deformation is 42%.

[0082] Test case

[0083] The properties of the steel ingots obtained in the examples and comparative examples were tested. Performance was tested by sampling the finished products, and the results are shown in Tables 2 and 3 below:

[0084] Table 2 Grain size information

[0085] process Grain size requirement ≥ 6 levels illustrate Example 1 Level 9 Uniform grain size in cross section Example 2 Level 9 Uniform grain size in cross section Example 3 Level 10 Uniform grain size in cross section Comparative Example 1 Level 6 Coarse grains are present in some parts of the cross section. Comparative Example 2 Level 7 Coarse grains are present in some parts of the cross section. Comparative Example 3 Level 7 Coarse grains are present in some parts of the cross section.

[0086] Table 3 Performance Status

[0087]

[0088]

Claims

1. A method for improving the grain size and mechanical properties of AF1410 steel free forgings, characterized in that, Includes the following steps: (1) Heat the AF1410 steel ingot to 1150-1180°C, adjust the height-to-diameter ratio to 1.8-2.2 by upsetting and then put it into the furnace for high-temperature diffusion; (2) Adjust the high-temperature homogenization temperature to 1230-1250°C and keep it warm for 30-50 hours; (3) After high-temperature diffusion, the temperature is reduced to 1150-1180°C, and the temperature is held for 2-3 hours before forging. The forging is carried out using the four-pile and four-drawing billet opening technology. (4) First upsetting and drawing, upsetting ratio 2-2.2, drawing rectangle deformation 45-55%, final forging temperature ≥900°C; (5) Second upsetting and drawing, heating temperature 1150-1180°C, holding time calculated as 0.3-0.4*H (thickness) min, upsetting ratio 2-2.2, drawing rectangle deformation amount 45-55%, final forging temperature ≥900°C; (6) Third upsetting and drawing, heating temperature 1060-1080°C, holding time calculated as 0.3-0.4*H (thickness) min, upsetting ratio 2-2.2, drawing rectangle deformation 45-55%, final forging temperature ≥850°C; (7) Fourth forging: heating temperature 1060-1080°C, holding time calculated as 0.3-0.4*H (thickness) min, upsetting ratio 2-2.2, rectangular deformation 45-55%, final forging temperature ≥850°C; (8) Open the intermediate billet, heat the temperature to 1020-1030°C, hold for 0.3-0.4*H (thickness) min, draw out the deformation amount to 50-55%, and finish forging temperature ≥850°C; (9) Forging the finished product, control the heating temperature to 1020-1030°C and the holding time to 0.2*H (thickness) min. After heating and holding, take the obtained billet out of the furnace, wrap it with high temperature resistant insulation cotton, and return it to the furnace for another 0.2-0.3*H (thickness) min before taking it out of the furnace to forge the finished product. Control the final deformation amount to ≥50-55% to obtain the finished product.

2. The method according to claim 1, characterized in that, The elemental composition of the AF1410 steel ingot, by weight percentage, is: C 0.15-0.19%, Co 13.50-14.50%, Ni 9.50-10.50%, Cr 1.80-2.20%, Mo 0.90-1.10%, Si ≤0.10%, Mn ≤0.10%, S ≤0.005%, P ≤0.008%, P+S ≤0.010%, Al ≤0.015%, Ti ≤0.015%, O ≤0.0020%, N ≤0.0015%, with the balance being Fe.

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