A lightweight, high-strength, annealing-free bolt base material and a preparation method thereof

Abstract

The invention discloses a lightweight high-strength annealing-free bolt base material and a preparation method thereof. The bolt base material has the following chemical components in weight percentage: C 0.28-0.32wt%, Si 0.18-0.25wt%, Mn 21.0-23.0wt%, Al 6.5-7.0wt%, B 0.0074-0.0087wt%, Ti 0.80-0.95wt%, P≤0.010wt%, S≤0.010wt%, and the rest is Fe and unavoidable impurities. The preparation method is to add refined scrap steel, pure aluminum, electrolytic manganese, graphite, scrap steel, refined slag powder, FeB17 and FeTi30 as raw materials into a vacuum medium frequency induction melting furnace for smelting and casting, and finally heat treat the casting after being taken out of the furnace; wherein, the heat treatment is fast forging by using a 1200℃-950℃ fast forging process, the obtained forging is placed in a water tank for quenching and solid solution at a cooling rate of ≥50℃ / s to room temperature, and finally the forged parent material is placed in a 350℃ insulation box protected by argon gas for 10h annealing. The bolt parent material prepared by the present invention has low density and high strength, and the cold-forged bolt has excellent mechanical and physical properties without the need for a heat treatment process.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and particularly relates to a lightweight and high-strength non-annealed bolt base material and a preparation method thereof. Background Art

[0002] In recent years, the experimental research and application scope of lightweight and high-strength non-annealed special bolt materials at home and abroad have been gradually expanding. Lightweight and high-strength non-annealed special bolts have broad application potential in fields such as aviation, automobiles, nuclear power, thermal power, and hydropower. In particular, fields such as aviation and automobiles have put forward higher requirements for the lightweight and high strength of materials. Timely carrying out the research and development and industrialization of the production and application of such advanced steel new materials is of great significance for improving the research and development technology level in the field of advanced steel new materials and obtaining core competitive advantages in this field. There have been reports on the research and production of low-density high-strength and tough steels in existing patents and papers, but it is difficult to use the strength and toughness matching for cold-heading formed non-annealed bolts. For example, Chinese Patent CN103820735A discloses an ultra-high-strength C-Al-Mn-Si series low-density steel and a preparation method thereof. The mass percentage of the chemical composition is: C: 0.28 - 1.15%, Al: 3.0 - 12.0%, Mn: 6.9 - 27.60%, Si: 0.01 - 2.0%, Cr: 0.01 - 0.80%, Ni: 0.01 - 0.60%, Mo: 0.01 - 0.30%, V: 0.001 - 0.10%, Nb: 0.001 - 0.06%, Ti: 0.001 - 0.02%, and the rest are Fe and inevitable impurities. Its tensile strength ≥ 800 MPa, and the density ≤ 7.4 g / cm 3 ³. This patent only considers achieving the strengthening effect of precipitation phase through Nb, V, Ti carbide precipitation elements, and the effect is relatively single. It is difficult to balance the strength and plasticity-toughness. On the basis of ensuring strength, the plasticity-toughness will be poor. In addition, a low-density cold-rolled steel sheet for automobiles and a preparation method disclosed in Chinese Patent CN104674109A. The mass percentage of the chemical composition of this density cold-rolled steel sheet for automobiles is: 0.65% - 0.75% C, 14.0% - 19.0% Mn, 7.0% - 10.5% Al, P < 0.003%, S < 0.002%, and the balance is Fe and inevitable impurities. Its density is 6.65 - 7.05 g / cm 3 ³, and the product of strength and plasticity > 40 GPa·%. It is obtained through smelting, forging, hot rolling deformation, solution treatment, cold rolling deformation, and annealing treatment. Since this patent does not add other alloying elements to regulate the grain boundary precipitates, the experimental steel does not reach the lowest density value under this Al range, and at the same time, it fails to meet the optimal plasticity-toughness under this composition condition.

[0003] The present invention aims to provide a material with a density of about 7.2 g / cm 3, a special non-annealed bolt base material with a tensile strength of over 900 MPa. The cold-headed bolts do not require an annealing heat treatment process and possess excellent mechanical and physical properties. Summary of the Invention

[0004] The first object of the present invention is to provide a lightweight and high-strength non-annealed bolt base material, and the second object of the present invention is to provide a preparation method for the lightweight and high-strength non-annealed bolt base material.

[0005] The first object of the present invention is achieved as follows. A lightweight and high-strength non-annealed bolt base material has the following chemical components by weight percentage: C 0.28 - 0.32 wt%, Si 0.18 - 0.25 wt%, Mn 21.0 - 23.0 wt%, Al 6.5 - 7.0 wt%, B 0.0074 - 0.0087 wt%, Ti 0.80 - 0.95 wt%, P ≤ 0.010 wt%, S ≤ 0.010 wt%, and the rest is Fe and inevitable impurities; the bolt base material has the following process mechanical properties: the yield strength ReL is 910 - 950 MPa, the reduction of area Z is 51 - 55%, and the density is 7.11 - 7.23 g / cm 3 .

[0006] The second object of the present invention is achieved as follows. The preparation method for the lightweight and high-strength non-annealed bolt base material is to add refined scrap steel, pure aluminum, electrolytic manganese, graphite, scrap steel, refining slag powder, FeB17, and FeTi30 as raw materials into a vacuum medium-frequency induction melting furnace for melting and casting, and finally perform heat treatment on the castings after they are taken out of the furnace;

[0007] Among them, the heat treatment is to perform quick forging using a quick forging process at 1200°C - 950°C, quench and solutionize the obtained forgings in a water bath at a cooling rate of ≥50°C / s to room temperature, and finally place the forged base material in an argon-protected insulation box at 350°C for 10 h for annealing treatment.

[0008] The beneficial effects of the present invention are as follows:

[0009] (1) The raw materials of the lightweight and high-strength non-annealed bolt base material of the present invention reduce the density of the steel through the lower atomic coefficient of aluminum element, rationally allocate lightweight elements such as Al, C, and Si, as well as strengthening elements such as Ti and Mn, effectively reducing the density of the steel, while ensuring that the test steel has a high strength, preventing performance mutations caused by overuse of aluminum during material heat treatment, and taking into account plasticity and toughness, so that the steel has good comprehensive mechanical properties.

[0010] (2) In the raw materials of the light-weight, high-strength and non-annealed bolt base material of the present invention, a relatively high Mn content is utilized. Based on the precipitation strengthening mechanism, solid solution strengthening is achieved to improve the mechanical properties of the material. Carbides precipitate at grain boundaries to reduce the grain size and increase the yield strength of the material. C and Mn strength elements are used to compensate for the amount of K carbides (i.e., (Fe, Mn)3AlC phase) formed during the γ→α phase transformation caused by excessive use of aluminum, hinder the generation trend of k carbides, improve the precipitation of grain boundary carbides, and promote the coordination of the strength, plasticity and toughness of the light-weight, high-strength and non-annealed bolt base material.

[0011] (3) The preparation of the bolt base material of the present invention adopts a rapid forging process at 1200°C - 950°C to uniformly fragment and refine the grains. After 950°C, the precipitation of carbides at the austenite grain boundaries restricts the growth of austenite grains. Water quenching is carried out at a rate of ≥50°C / s for rapid cooling to ensure that the grains are fine and uniform. The austenite grain size is small, and it has a relatively high plastic elongation strength and tensile strength. The forged base material is placed in an argon-protected incubator at 350°C for 10 h for annealing treatment. Bolts formed by cold heading the base material can obtain light-weight, high-strength and non-annealed bolts with relatively uniform structure, relatively fine and uniform grains, and relatively small internal stress without further annealing treatment. Specific embodiments

[0012] The following further illustrates the present invention in conjunction with embodiments, but the present invention is not limited in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0013] A light-weight, high-strength and non-annealed bolt base material of the present invention has the following chemical components by weight percentage: C 0.28 - 0.32 wt%, Si 0.18 - 0.25 wt%, Mn 21.0 - 23.0 wt%, Al 6.5 - 7.0 wt%, B 0.0074 - 0.0087 wt%, Ti 0.80 - 0.95 wt%, P≤0.010 wt%, S≤0.010 wt%, and the rest are Fe and inevitable impurities; the bolt base material has the following process mechanical properties: yield strength ReL is 910 - 950 MPa, reduction of area Z is 51 - 55%, and density is 7.11 - 7.23 g / cm 3 。

[0014] The present invention also provides a preparation method of the light-weight, high-strength and non-annealed bolt base material, which is to add refined scrap steel, pure aluminum, electrolytic manganese, graphite, scrap steel, refining slag powder, FeB17 and FeTi30 as raw materials into a vacuum medium frequency induction melting furnace for melting and casting, and finally perform heat treatment on the castings after they are taken out of the furnace;

[0015] Among them, the heat treatment is carried out by rapid forging with a process of 1200°C - 950°C. The obtained forging is put into a water tank and quenched and solutionized at a cooling rate of ≥50°C / s until room temperature. Finally, the forged base material is put into a 350°C incubator with argon protection and annealed for 10h.

[0016] The raw material amounts added to a 10kg vacuum medium frequency induction melting furnace are as follows: refined scrap steel 5.9 - 6.1kg, electrolytic manganese 1.89 - 1.91kg, pure aluminum 0.63 - 0.65kg, 98 carbon powder 0.015 - 0.017kg, FeB17 0.013 - 0.015kg, FeTi30 0.032 - 0.034kg, refining slag powder 0.5kg.

[0017] The raw materials are charged into the 10kg vacuum medium frequency induction melting furnace in the following order: high-quality refined scrap steel at the bottom → pure aluminum → electrolytic manganese → graphite → scrap steel → refining slag powder. Charge FeB17 and FeTi30 into the alloy material tank in the melting furnace.

[0018] The chemical composition of the high-quality refined scrap steel is C 0.22wt%, Si 0.33wt%, Mn 1.34wt%, Ti 0.002%, P 0.010wt%, S ≤ 0.004wt%, and the rest is Fe and inevitable impurities;

[0019] The chemical composition of the electrolytic manganese is: Mn 99.8wt%, P 0.002wt%, S ≤ 0.010wt%, and the rest is Fe and inevitable impurities;

[0020] The Al content of the pure aluminum is 99.5wt%, and the rest is inevitable impurities;

[0021] The chemical composition of the refining slag powder is CaO 55wt%, SiO 2 33wt%, Al 2 O 3 18wt%, and the rest is inevitable impurities.

[0022] The melting conditions are as follows: at a vacuum degree of about 4×10 -3Start the power supply of the melting furnace for heating at Pa, and control the heating and temperature rising curve according to the following requirements: 20°C - 200°C → 60 min, temperature rising speed 3°C / min; keep the temperature at 200°C for 30 min; 200°C - 600°C → 30 min, temperature rising speed 13.3°C / min; keep the temperature at 600°C for 30 min; 600 - 1570°C → 60 min, temperature rising speed 16.2°C / min; keep the temperature at 1570°C for 10 min; after keeping the temperature at 1570°C for 10 min, add ferro-titanium FeTi30 and ferro-boron FeB17 alloys, continue to keep the temperature and carry out electromagnetic stirring for 5 min, electromagnetic stirring parameters: current 140 A, frequency 1500 Hz, keep electromagnetic stirring, cut off the power and cool down to 1410 - 1420°C for casting.

[0023] After casting is completed, turn off the power supply of the melting furnace, let the melting furnace cool naturally under vacuum conditions, break the vacuum inside the melting furnace when the lining temperature cools below 200°C, and take out the cast steel.

[0024] Before the casting is taken out of the furnace, first cut off the riser of the casting blank, mill 3 mm on the surface to remove surface slag inclusions, and slowly heat it to 1200°C at a temperature rising speed of 25 - 35°C / h under argon protection, keep the temperature for more than 4 h and make the blank completely uniform before taking it out of the furnace.

[0025] The power capacity of the vacuum medium-frequency induction melting furnace is 100 kW, the rated power supply is 220 v, the frequency is 1500 - 2500 HZ, the number of phases is 3 phases, and the cold-state ultimate vacuum degree is 6.67×10 -3 Pa, the crucible molten steel capacity is 10 kg, and the rated temperature is 1600°C. The melting furnace has a vacuum casting position, and after melting is completed, the casting can be cast under vacuum conditions inside the furnace.

[0026] Example 1

[0027] A. Confirm the process conditions: Use a vacuum medium-frequency induction melting furnace for melting. The melting furnace has a vacuum casting position, and after melting is completed, the casting can be cast under vacuum conditions inside the furnace. The power capacity is 100 kW, the rated power supply is 220 v, the frequency is 1500 - 2500 HZ, the number of phases is 3 phases, and the cold-state ultimate vacuum degree is 6.67×10 -3 Pa, the crucible capacity is 10 kg (molten steel), and the rated temperature is 1600°C.

[0028] B. Vacuum Melting and Vacuum Casting: Calculated based on producing an 8 kg ingot with 8.9 kg of actual molten steel, charge 6.0 kg of high-quality refined scrap steel (chemical composition: C 0.22 wt%, Si 0.33 wt%, Mn 1.34 wt%, Ti 0.002%, P 0.010 wt%, S ≤ 0.004 wt%, the rest is Fe and inevitable impurities), 1.90 kg of electrolytic manganese (chemical composition: Mn 99.8 wt%, P 0.002 wt%, S ≤ 0.010 wt%, the rest is Fe and inevitable impurities), 0.64 kg of pure aluminum (chemical composition: Al 99.5 wt%, the rest is inevitable impurities), 0.016 kg of 98% carbon powder (chemical composition: C 98.0 wt%, the rest is inevitable impurities), and 0.5 kg of refining slag powder (composition: CaO 55 wt%, SiO2 33 wt%, Al2O3 18 wt%, the rest is inevitable impurities) into a 10 kg vacuum medium-frequency induction melting furnace in the following order: bottom refining slag powder → high-quality refined scrap steel → pure aluminum → electrolytic manganese → graphite → scrap steel → refining slag powder. Load 0.014 kg of ferrosilicon boron FeB17 and 0.33 kg of ferrotitanium FeTi30 into the alloy material tank in the melting furnace.

[0029] Cover the melting furnace lid, start the vacuum pump to evacuate, and start the power supply of the melting furnace to heat when the vacuum degree reaches about 4.2×10 -3 Pa. Control the heating and temperature-rising curve according to the following requirements: 20°C - 200°C → 54 min, temperature-rising speed 3.3°C / min; keep the temperature at 200°C for 35 min; 200°C - 600°C → 32 min, temperature-rising speed 12.5°C / min; keep the temperature at 600°C for 30 min; 600 - 1570°C → 59 min, temperature-rising speed 16.5°C / min; keep the temperature at 1570°C for 11 min. Then add ferrotitanium FeTi30 and ferrosilicon boron FeB17 alloys, continue to keep the temperature and carry out electromagnetic stirring for 5 min. Electromagnetic stirring parameters: current 140 A, frequency 1500 Hz. Cut off the power supply and cool down while maintaining electromagnetic stirring, and observe the temperature drop to 1418°C.

[0030] C. Vacuum Casting: When the temperature drops to 1418°C, slowly pour the molten steel into the in-furnace mold within 17 s. After casting is completed, turn off the power supply of the melting furnace, let the melting furnace cool naturally in a vacuum state. When the furnace lining temperature cools below 180°C, break the vacuum inside the melting furnace and take out the cast steel.

[0031] D, Heat treatment: Cut off the riser from the casting blank, mill 3 mm on the surface to remove surface slag inclusions, and slowly heat it to 1202 °C at a heating rate of 28 °C / h under argon protection. Keep it warm for more than 4 h until the blank is completely uniform, then take it out of the furnace. Forge the casting into the required bolt base material for cold heading forming with a quick forging machine. When the temperature reaches 953 °C, put the forging into a water tank and quench and solutionize it to room temperature at a cooling rate of 58 °C / s. Put the forged base material into an argon-protected insulation box at 350 °C and keep it warm for 10 h, then air-cool it to room temperature. Obtain a 900 MPa grade high-strength and lightweight non-annealed bolt base material, and its chemical composition is as follows: C 0.30 wt%, Si 0.21 wt%, Mn 22.0 wt%, Al 6.8 wt%, B 0.0080 wt%, Ti 0.89 wt%, P≤0.007 wt%, S≤0.005 wt%, and the rest are Fe and inevitable impurities. It has the following process mechanical properties: ReL is 924 MPa, Z is 51.8%, and the density of the steel is 7.18 g / cm 3 .

[0032] Example 2

[0033] A. Confirm process conditions: Use a vacuum intermediate frequency induction melting furnace for melting. The melting furnace has a vacuum casting position and can cast the casting in a vacuum state inside the furnace after melting. The power capacity is 100 kW, the rated power supply is 220 v, the frequency is 1500 - 2500 HZ, the number of phases is 3 phases, the cold-state ultimate vacuum degree is 6.67×10 -3 Pa, the crucible capacity is 10 kg (molten steel), and the rated temperature is 1600 °C.

[0034] B. Vacuum melting and vacuum casting: Calculate according to the production of 8 kg ingots and 8.83 kg of actual molten steel. Use 5.9 kg of high-quality refined scrap steel (chemical composition: C 0.22 wt%, Si 0.33 wt%, Mn 1.34 wt%, Ti 0.002%, P 0.010 wt%, S≤0.004 wt%, and the rest are Fe and inevitable impurities), 1.91 kg of electrolytic manganese (chemical composition: Mn 99.8 wt%, P 0.002 wt%, S≤0.010 wt%, and the rest are Fe and inevitable impurities), 0.65 kg of pure aluminum (chemical composition: Al 99.5 wt%, and the rest are inevitable impurities), 0.017 kg of 98 carbon powder (chemical composition: C 98.0 wt%, and the rest are inevitable impurities), and 0.5 kg of refining slag powder (composition: CaO 55 wt%, SiO 2 33 wt%, Al2O 318 wt%, and the rest are inevitable impurities) are charged into a 10 kg vacuum medium frequency induction melting furnace in the order of bottom refining slag powder → high-quality refined scrap steel → pure aluminum → electrolytic manganese → graphite → scrap steel → refining slag powder. 0.015 kg of ferroboron FeB17 and 0.034 kg of ferrotitanium FeTi30 are loaded into the alloy material tank in the melting furnace. Cover the melting furnace lid, start the vacuum pump to evacuate, and start the power supply of the melting furnace to heat when the vacuum degree is about 4×10 -3 Pa. The heating and temperature rising curve is controlled according to the following requirements: 20°C - 200°C → 60 min, the heating rate is 3.5°C / min; keep warm at 200°C for 30 min; 200°C - 600°C → 31 min, the heating rate is 13.0°C / min; keep warm at 600°C for 30 min; 600 - 1570°C → 59 min, the heating rate is 16.5°C / min; keep warm at 1570°C for 11 min, then add ferrotitanium FeTi30 and ferroboron FeB17 alloys, continue to keep warm and carry out electromagnetic stirring for 6 min, the electromagnetic stirring parameters: current 140 A, frequency 1500 Hz, cut off the power and cool down while maintaining electromagnetic stirring, and observe the temperature dropping to 1410°C.

[0035] C. Vacuum casting: When the temperature drops to 1410°C, slowly pour the molten steel into the mold in the furnace within 15 s. After casting is completed, turn off the power supply of the melting furnace, let the melting furnace cool naturally in a vacuum state, break the vacuum in the melting furnace when the furnace lining temperature cools below 185°C, and take out the cast steel.

[0036] D. Heat treatment: Cut off the riser of the cast blank, mill the surface by 3 mm to remove surface slag inclusions, slowly heat it to 1200°C at a heating rate of 25°C / h under argon protection, keep warm for 4.5 h and make the blank completely uniform, then take it out of the furnace, forge the cast into the required cold heading formed bolt base material with a forging machine. When the temperature reaches 952°C, put the forging into a water tank and quench and solutionize it to room temperature at a cooling rate of 54°C / s. Put the forged base material into an argon-protected insulation box at 350°C and keep it warm for 10 h, then air cool it to room temperature to obtain a 900 MPa grade high-strength lightweight non-annealed bolt base material, and its chemical composition is as follows: C 0.31 wt%, Si 0.21 wt%, Mn 22.3 wt%, Al 7.0 wt%, B 0.0087 wt%, Ti 0.924 wt%, P 0.007 wt%, S 0.005 wt%, and the rest are Fe and inevitable impurities. It has the following process mechanical properties: ReL is 931 MPa, Z is 53.0%, and the density of the steel is 7.23 g / cm 3 .

[0037] Example 3

[0038] A. Confirm process conditions: Use a vacuum intermediate frequency induction melting furnace for melting. The melting furnace has a vacuum casting position, and after melting, the casting can be cast in a vacuum state inside the furnace. The power supply capacity is 100 kW, the rated power supply is 220 v, the frequency is 1500 - 2500 HZ, the number of phases is 3 phases, the cold state ultimate vacuum degree is 6.67×10 -3 Pa, the crucible capacity is 10 kg (molten steel), and the rated temperature is 1600 °C.

[0039] B. Vacuum melting and vacuum casting: Calculated based on producing an 8 kg ingot and 8.97 kg of actual molten steel, put 6.1 kg of high-quality refined scrap steel (chemical composition: C 0.22 wt%, Si 0.33 wt%, Mn 1.34 wt%, Ti 0.002%, P 0.010 wt%, S ≤ 0.004 wt%, the rest is Fe and inevitable impurities), 1.89 kg of electrolytic manganese (chemical composition: Mn 99.8 wt%, P 0.002 wt%, S ≤ 0.010 wt%, the rest is Fe and inevitable impurities), 0.63 kg of pure aluminum (chemical composition: Al 99.5 wt%, the rest is inevitable impurities), 0.015 kg of 98 carbon powder (chemical composition: C 98.0 wt%, the rest is inevitable impurities), 0.5 kg of refining slag powder (composition: CaO 55 wt%, SiO 2 33 wt%, Al2O 3 18 wt%, the rest is inevitable impurities) into the 10 kg vacuum intermediate frequency induction melting furnace in the following order: bottom refining slag powder → high-quality refined scrap steel → pure aluminum → electrolytic manganese → graphite → scrap steel → refining slag powder, and put 0.013 kg of ferroboron FeB17 and 0.032 kg of ferrotitanium FeTi30 into the alloy material tank in the melting furnace.

[0040] Cover the melting furnace lid, start the vacuum pump to pump vacuum, start the power supply of the melting furnace to heat when the vacuum degree is about 4×10 -3 Pa. Control the heating and temperature rising curve according to the following requirements: 20 °C - 200 °C → 60 min, the temperature rising speed is 3 °C / min; keep the temperature at 200 °C for 30 min; 200 °C - 600 °C → 30 min, the temperature rising speed is 13.3 °C / min; keep the temperature at 600 °C for 30 min; 600 - 1570 °C → 60 min, the temperature rising speed is 16.2 °C / min; keep the temperature at 1570 °C for 11 min, then add ferrotitanium FeTi30 and ferroboron FeB17 alloys, continue to keep the temperature and carry out electromagnetic stirring for 5 min, the electromagnetic stirring parameters: current 140 A, frequency 1500 Hz, cut off the power and cool down while keeping electromagnetic stirring, and observe the temperature to drop to 1415 °C.

[0041] C. Vacuum casting: When the temperature drops to 1420 °C, slowly pour the molten steel into the in-furnace mold within 20 s. After casting is completed, turn off the power supply of the melting furnace, and let the melting furnace cool naturally under vacuum. When the temperature of the furnace lining drops below 200 °C, break the vacuum inside the melting furnace and take out the cast steel.

[0042] D. Heat treatment: Cut off the riser from the casting blank, mill 3 mm from the surface to remove surface slag inclusions. Slowly heat it to 1200 °C at a heating rate of 35 °C / h under argon protection, hold for 4 h until the blank is completely uniform, then take it out of the furnace. Use a forging machine to forge the casting into the bolt base material required for cold heading forming. When the temperature reaches 955 °C, put the forging into a water tank and quench and solutionize it to room temperature at a cooling rate of 58 °C / s. Put the forged base material into an argon-protected incubator at 350 °C and hold for 10 h, then air-cool to room temperature. Obtain the base material for lightweight and high-strength non-annealed bolts, and obtain the 900 MPa grade high-strength lightweight non-annealed bolt base material. Its chemical composition is as follows: C 0.29 wt%, Si 0.21 wt%, Mn 21.7 wt%, Al 6.6 wt%, B 0.0074 wt%, Ti 0.856 wt%, P 0.007 wt%, S 0.005 wt%, and the rest is Fe and unavoidable impurities. It has the following process mechanical properties: ReL is 912 MPa, Z is 51.0%, and the density of the steel is 7.11 g / cm 3 .

Claims

1. A lightweight, high-strength, anneal-free bolt base material, characterized in that: The bolt base material has the following chemical composition in weight percentage: C 0.28-0.32wt%, Si 0.18-0.25wt%, Mn 21.0-23.0wt%, Al 6.5-7.0wt%, B0.0074-0.0087wt%, Ti 0.80-0.95wt%, P≤0.010wt%, S≤0.010wt%, and the rest is Fe and unavoidable impurities; the bolt base material has the following process mechanical properties: yield strength ReL is 910-950MPa, cross-sectional shrinkage Z is 51-55%, and density is 7.11-7.23g / cm 3 .

2. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 1, characterized in that: The method is to add refined scrap steel, pure aluminum, electrolytic manganese, graphite, scrap steel, refined slag powder, FeB17 and FeTi30 as raw materials into a vacuum medium frequency induction melting furnace for smelting and casting, and finally heat treat the castings after being taken out of the furnace; wherein, the heat treatment is fast forging by using a 1200℃~950℃ fast forging process, and the obtained forgings are placed in a water tank for quenching and solution treatment at a cooling rate of ≥50℃ / s to room temperature, and finally the forged parent material is placed in a 350℃ insulation box protected by argon gas for 10h annealing treatment.

3. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: The amounts of raw materials added to the 10kg vacuum medium frequency induction melting furnace are as follows: 5.9~6.1kg of refined scrap steel, 1.89~1.91kg of electrolytic manganese, 0.63~0.65kg of pure aluminum, 0.015~0.017kg of 98 carbon powder, 0.013~0.015kg of FeB17, 0.032~0.034kg of FeTi30, and 0.5kg of refined slag powder.

4. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: The raw materials are fed into a 10kg vacuum medium frequency induction melting furnace in the following order: high-quality refined scrap steel at the bottom → pure aluminum → electrolytic manganese → graphite → scrap steel → refined slag powder, and ferroboron FeB17 and ferrotitanium FeTi30 are loaded into the alloy material trough in the melting furnace.

5. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: The chemical composition of the refined scrap steel is C 0.22wt%, Si 0.33wt%, Mn 1.34wt%, Ti 0.002%, P 0.010wt%, S≤0.004wt%, and the rest is Fe and inevitable impurities; The chemical composition of the electrolytic manganese is: Mn 99.8wt%, P 0.002wt%, S≤0.010wt%, and the rest is Fe and inevitable impurities; The Al content of the pure aluminum is 99.5wt%, and the rest is inevitable impurities; The chemical composition of the refined slag powder is CaO 55wt%, SiO2 33wt%, Al2O3 18wt%, and the rest are inevitable impurities.

6. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: The melting conditions are as follows: at a vacuum degree of 4×10 -3 Pa, start the smelting furnace power heating, and the heating temperature rise curve is controlled according to the following requirements: 20℃~200℃→60min, heating rate 3℃ / min; 200℃ insulation for 30min; 200℃~600℃→30min, heating rate 13.3℃ / min; 600℃ insulation for 30min; 600~1570℃→60min, heating rate 16.2℃ / min; 1570℃ insulation for 10min; after 1570℃ insulation for 10min, add titanium iron FeTi30 and boron iron FeB17 alloy, continue to keep warm and electromagnetically stir for 5min, electromagnetic stirring parameters: current 140A, frequency 1500Hz, maintain electromagnetic stirring, turn off the power and cool down to 1410~1420℃ for casting.

7. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: After casting is completed, turn off the power of the melting furnace and let the melting furnace cool naturally under vacuum. When the temperature of the furnace lining cools to below 200°C, break the vacuum in the melting furnace and take out the casting steel.

8. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: Before the casting is taken out of the furnace, the riser of the casting blank is first cut off, the surface is milled off 3mm, the surface slag is removed, and it is slowly heated to 1200℃ at a heating rate of 25~35℃ / h under argon protection. It is kept warm for more than 4h and the blank is completely uniform before being taken out of the furnace.

9. The method for preparing the lightweight high-strength annealing-free bolt base material according to claim 2, characterized in that: The power capacity of the vacuum medium frequency induction melting furnace is 100kW, the rated power is 220V, the frequency is 1500~2500Hz, the phase number is 3, and the cold state limit vacuum is 6.67×10 -3 Pa, the crucible steel liquid capacity is 10kg, and the rated temperature is 1600℃; the melting furnace is equipped with a vacuum casting position, and castings can be cast under vacuum in the furnace after melting is completed.