阅读说明：本技术 一种超高强度、高韧性合金钢的制备方法 (Preparation method of ultrahigh-strength and high-toughness alloy steel ) 是由 韩顺 厉勇 王春旭 刘振宝 李建新 庞学东 于 2021-06-29 设计创作，主要内容包括：本发明公开了一种超高强度、高韧性合金钢的制备方法,属于金属材料技术领域,解决了现有的双真空冶炼法成本较高,现有的单真空冶炼法得到的钢锭经常容易存在径向偏析和环状花样等问题。上述制备方法包括炉外精炼和真空自耗重熔冶炼,真空自耗重熔冶炼过程中控制平均熔速为3.8～6.2kg/min,并采用氦气冷却,控制氦气流量230～300L/min；钢的成分按质量百分比计,包括C：0.07％～0.13％,Mn：0.4％～0.70％,Ni：3.0％～3.5％,Si：0.15％～0.35％,Cr：1.0％～1.40％,Mo：0.08％～0.15％,Nb：0.01％-0.05％,P≤0.015％,S≤0.015％,Cu：≤0.35％,B：≤0.001％,O≤0.0015％,N≤0.0025％。本发明的制备方法能够制得超纯净的钢,钢的低倍组织中径向偏析级别A级别,环状花样A级别,强韧性匹配良好。(The invention discloses a preparation method of ultrahigh-strength and high-toughness alloy steel, belongs to the technical field of metal materials, and solves the problems that the cost of the existing double-vacuum smelting method is high, and the steel ingot obtained by the existing single-vacuum smelting method often has radial segregation, annular patterns and the like easily. The preparation method comprises external refining and vacuum consumable remelting smelting, wherein the average melting speed is controlled to be 3.8-6.2 kg/min in the vacuum consumable remelting smelting process, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min; the steel comprises the following components in percentage by mass: 0.07-0.13%, Mn: 0.4% -0.70%, Ni: 3.0% -3.5%, Si: 0.15-0.35%, Cr: 1.0% -1.40%, Mo: 0.08-0.15%, Nb: 0.01-0.05%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Cu: less than or equal to 0.35 percent, B: less than or equal to 0.001 percent, less than or equal to 0.0015 percent of O and less than or equal to 0.0025 percent of N. The preparation method can prepare the ultra-pure steel, and the steel has a radial segregation grade A and an annular pattern grade A in a macrostructure, and has good obdurability matching.)

1. The preparation method of the alloy steel with ultrahigh strength and high toughness is characterized by comprising external refining and vacuum consumable remelting smelting, wherein the average melting speed is controlled to be 3.8-6.2 kg/min in the vacuum consumable remelting smelting process, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min; the steel comprises the following components in percentage by mass: 0.07-0.13%, Mn: 0.4% -0.70%, Ni: 3.0% -3.5%, Si: 0.15-0.35%, Cr: 1.0% -1.40%, Mo: 0.08-0.15%, Nb: 0.01-0.05%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Cu: less than or equal to 0.35 percent, B: less than or equal to 0.001 percent, less than or equal to 0.0015 percent of O and less than or equal to 0.0025 percent of N.

2. The method of claim 1, comprising:

step S1, smelting in an electric furnace; tapping conditions of electric furnace smelting are as follows: p is less than or equal to 0.003 percent;

step S2, LF process; tapping conditions of the LF process are as follows: less than or equal to 0.001 percent of S, and 0.06 to 0.08 percent of Al is added;

step S3, VD refining; and (3) entering VD temperature: more than or equal to 1650 ℃; the vacuum degree is less than or equal to 67Pa during vacuum pumping, and the vacuum degree is maintained for more than or equal to 10 minutes; after the vacuumizing is finished, adjusting the Ar gas flow to 15-30L/min for soft blowing, and forbidding exposing the steel liquid level during the soft blowing, wherein the soft blowing retention time is more than or equal to 15 minutes; pouring at 1560-1590 ℃ under the protection of Ar gas to obtain an electrode;

step S4, annealing the electrode;

s5, carrying out vacuum consumable remelting and smelting to obtain a steel ingot; in the vacuum consumable remelting smelting process, the average melting speed in the stable smelting stage is 3.8-6.2 Kg/min, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min;

and step S6, annealing the steel ingot.

3. The method as claimed in claim 2, wherein in step S1, the raw material is selected from returned steel, pig iron and scrap steel, and the oxidation is carried out at T.gtoreq.1530 ℃.

4. The method according to claim 2, wherein in the step S4, the electrode annealing includes: heating the electrode to 670-700 ℃ at a heating rate of less than 100 ℃/h, and keeping the temperature for more than 25 h; then furnace cooling is carried out at a cooling rate of below 50 ℃/h to below 400 ℃, and discharging and air cooling are carried out.

5. The method according to claim 2, wherein in the step S6, the ingot annealing includes: heating to 660-700 ℃ at a heating rate of less than 100 ℃/h, preserving heat for more than 25h, cooling to below 400 ℃ in a cooling furnace at a cooling rate of less than 50 ℃/h, discharging and air cooling.

6. The method according to any one of claims 2 to 5, wherein the ingot after annealing in step S6 has a non-metallic inclusion A, B, D type of fine inclusions of 0.5 or less, a radial segregation level A level in a macrostructure, an annular pattern A level, and a grain size level of 5 or more.

7. The method of manufacturing according to claim 2, further comprising:

step S7, forging a steel ingot; the initial forging temperature in the forging process is 1200-1250 ℃, the heating temperature of the returned blank in the forging process is controlled to be 1000-1120 ℃, and the final forging temperature is controlled to be 850-;

step S8, annealing the bar; annealing the forged bar;

step S9, bar heat treatment: the heat treatment includes normalizing, quenching and tempering.

8. The method according to claim 7, wherein in step S7, the billet is heated to the forging starting temperature by a step heating method; the step heating method comprises:

heating in the first stage: heating to 580-620 ℃, and preserving heat for 2-3 h;

heating in the second stage: heating to 800-900 ℃, and preserving heat for 2-3 h;

heating in the third stage: heating to 1200-1250 ℃, and preserving heat for 2-4 h.

9. The method according to claim 8, wherein in step S7, the heating rate of each stage of heating is less than or equal to 100 ℃/h.

10. The method for preparing the alloy material of claims 7 to 9, wherein in the step S8, the annealing process comprises: heating to 870-890 ℃ at the speed of less than or equal to 100 ℃/h, preserving heat for 6-8 h, and air cooling to less than or equal to 100 ℃; heating to 670-690 ℃ at the speed of less than or equal to 100 ℃/h, keeping the temperature for more than or equal to 25h, then cooling to less than or equal to 300 ℃ at the speed of less than or equal to 30 ℃/h, and discharging.

Technical Field

The invention belongs to the technical field of metal materials, and particularly relates to a preparation method of alloy steel with ultrahigh strength and high toughness.

Background

With the rapid development of aerospace technology in China, the aerospace craft has extremely high requirements on the strength, toughness and the like of parts such as a transmission shaft of the aerospace craft in the high-speed long-time cruising flight process. Therefore, the raw materials of parts such as the current aviation transmission shaft and the like are generally manufactured by a double-vacuum smelting method (vacuum smelting and vacuum consumable remelting), but the double-vacuum smelting method has higher cost and poorer economy; at present, how to reduce the cost on the premise of ensuring the product quality becomes one of the problems to be solved urgently by steel enterprises. At present, some researches on preparation methods of parts such as aviation transmission shafts and the like relate to single vacuum smelting (namely external refining and vacuum consumable remelting), however, the current single vacuum smelting method is not mature, the obtained steel ingot often easily has radial segregation and annular patterns, and the defects of the steel ingot can directly cause the mechanical properties of the finished product after heat treatment.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a method for preparing an ultra-high strength, high toughness alloy steel, which can solve at least one of the following technical problems: (1) the existing double vacuum smelting method has higher cost; (2) the steel ingot obtained by the existing single vacuum smelting method often has the defects of radial segregation, annular patterns, more inclusions and the like; (3) the steel ingot obtained by the existing single vacuum smelting method has higher O, N content.

The purpose of the invention is mainly realized by the following technical scheme:

the invention provides a preparation method of ultrahigh-strength and high-toughness alloy steel, which comprises external refining and vacuum consumable remelting smelting, wherein the average melting speed is controlled to be 3.8-6.2 kg/min in the vacuum consumable remelting smelting process, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min; the steel comprises the following components in percentage by mass: 0.07-0.13%, Mn: 0.4% -0.70%, Ni: 3.0% -3.5%, Si: 0.15-0.35%, Cr: 1.0% -1.40%, Mo: 0.08-0.15%, Nb: 0.01-0.05%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Cu: less than or equal to 0.35 percent, B: less than or equal to 0.001 percent, less than or equal to 0.0015 percent of O and less than or equal to 0.0025 percent of N.

Further, the preparation method comprises the following steps:

step S1, smelting in an electric furnace; tapping conditions of electric furnace smelting are as follows: p is less than or equal to 0.003 percent;

step S2, LF process; tapping conditions of the LF process are as follows: less than or equal to 0.001 percent of S, and 0.06 to 0.08 percent of Al (namely the mass of the added Al accounts for 0.06 to 0.08 percent of the mass of the molten steel);

step S3, VD refining; and (3) entering VD temperature: more than or equal to 1650 ℃; the vacuum degree is less than or equal to 67Pa during vacuum pumping, and the vacuum degree is maintained for more than or equal to 10 minutes; after the vacuumizing is finished, adjusting the Ar gas flow to 15-30L/min for soft blowing, and forbidding exposing the steel liquid level during the soft blowing, wherein the soft blowing retention time is more than or equal to 15 minutes; pouring at 1560-1590 ℃ under the protection of Ar gas to obtain an electrode;

step S4, annealing the electrode;

s5, carrying out vacuum consumable remelting and smelting to obtain a steel ingot; in the vacuum consumable remelting smelting process, the average melting speed in the stable smelting stage is 3.8-6.2 Kg/min, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min;

and step S6, annealing the steel ingot.

Further, in the step S1, the raw material can be composed of return steel, pig iron and scrap steel, and the oxidation is carried out at T ≥ 1530 ℃ in the oxidation period; the tapping temperature is more than or equal to 1650 ℃.

Further, in step S4, the electrode annealing includes: heating the electrode to 670-700 ℃ at a heating rate of less than 100 ℃/h, and keeping the temperature for more than 25 h; then furnace cooling is carried out at a cooling rate of below 50 ℃/h to below 400 ℃, and discharging and air cooling are carried out.

Further, in step S6, the annealing the steel ingot includes: heating to 660-700 ℃ at a heating rate of less than 100 ℃/h, preserving heat for more than 25h, cooling to below 400 ℃ in a cooling furnace at a cooling rate of less than 50 ℃/h, discharging and air cooling.

Further, in step S6, the annealed steel ingot includes, by mass, C: 0.07-0.13%, Mn: 0.4% -0.70%, Ni: 3.0% -3.5%, Si: 0.15-0.35%, Cr: 1.0% -1.40%, Mo: 0.08-0.15%, Nb: 0.01-0.05%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Cu: less than or equal to 0.35 percent, B: less than or equal to 0.001 percent, less than or equal to 0.0015 percent of O and less than or equal to 0.0025 percent of N.

Further, in the steel ingot after annealing in step S6, the non-metallic inclusions A, B, D-type fine inclusions are not more than 0.5 grade, the radial segregation grade in the macrostructure is a grade, the annular pattern grade is a grade, and the grain size grade is not less than 5 grade.

Further, the method also comprises the following steps:

step S7, forging a steel ingot; the initial forging temperature in the forging process is 1200-1250 ℃, the heating temperature of the returned blank in the forging process is controlled to be 1000-1120 ℃, and the final forging temperature is controlled to be 850-;

step S8, annealing the bar; annealing the forged bar;

step S9, bar heat treatment: the heat treatment includes normalizing, quenching and tempering.

Further, in step S7, the billet is heated to the forging starting temperature by a step heating method; the step heating method comprises:

heating in the first stage: heating to 580-620 ℃, and preserving heat for 2-3 h;

heating in the second stage: heating to 800-900 ℃, and preserving heat for 2-3 h;

heating in the third stage: heating to 1200-1250 ℃, and preserving heat for 2-4 h.

Further, in the step S7, the heating speed of each stage of heating is below 100 ℃/h.

Further, in step S8, the annealing process includes: heating to 870-890 ℃ at the speed of less than or equal to 100 ℃/h, preserving heat for 6-8 h, and air cooling to less than or equal to 100 ℃; heating to 670-690 ℃ at the speed of less than or equal to 100 ℃/h, keeping the temperature for more than or equal to 25h, then cooling to less than or equal to 300 ℃ at the speed of less than or equal to 30 ℃/h, and discharging.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

a) according to the preparation method of the ultrahigh-strength and high-toughness alloy steel, metal Nb is added for microalloying treatment, so that the effects of grain refinement and strength improvement are achieved.

b) The invention strictly controls the melting speed of vacuum consumable remelting, overcomes the defect of low-power annular patterns of low-alloy structural steel, and has a radial segregation grade A grade and an annular pattern grade A in a low-power structure.

c) The preparation method can obtain ultra-low gas and ultra-pure steel, wherein O is less than or equal to 0.0015 percent, N is less than or equal to 0.0025 percent, the non-metallic inclusion A, B, D type fine system inclusion is less than 0.5 grade, the other types of inclusions are not included, and the grain size grade is more than 5 grade.

d) The steel prepared by the method has excellent comprehensive properties after heat treatment, including tensile strength sigma_bNot less than 1200MPa, yield strength sigma_0.2Not less than 940MPa, elongation delta₄Not less than 15%, reduction of area psi not less than 59%, fracture toughness K_JIC≥200MPa﹒m^1/2(ii) a Has higher strength and impact toughness, and further improves the materialThe service life of the material.

e) Compared with the existing double-vacuum smelting method, the method of the invention has the advantages that the cost is reduced by 20-40%, and the economic benefit is obvious.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description.

Drawings

The drawings are only for purposes of illustrating the particular invention and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout the figures.

FIG. 1 is a schematic view of the heating process of the step heating method in example 1.

Detailed Description

The existing raw materials of parts such as an aviation transmission shaft and the like are generally manufactured by a double-vacuum smelting method (vacuum smelting and vacuum consumable remelting), but the double-vacuum smelting method has higher cost and poorer economy; some researches on preparation methods of parts such as aviation transmission shafts and the like relate to single vacuum smelting (namely external refining and vacuum consumable remelting), however, the existing single vacuum smelting method is not mature, the obtained steel ingot often has radial segregation and annular patterns easily, and the defects of the steel ingot can directly cause the mechanical properties of the finished product after heat treatment. Therefore, how to reduce the cost on the premise of ensuring the product quality becomes one of the problems to be solved urgently by steel enterprises. Through long-term intensive research, the inventor of the invention realizes the precise control of chemical components, the ultralow gas content and the lower inclusion content of steel and the reduction of radial segregation and annular patterns by precisely controlling the steps of the production process; ensuring that the steel has excellent and stable mechanical properties.

The invention provides a preparation method of ultrahigh-strength and high-toughness alloy steel, which comprises external refining and vacuum consumable remelting smelting, wherein the average melting speed is controlled to be 3.8-6.2 kg/min in the vacuum consumable remelting smelting process, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min; ensuring that O is less than or equal to 0.0015 percent, N is less than or equal to 0.0025 percent and non-metallic inclusion A, B, D type fine system inclusion is below 0.5 grade in a steel ingot.

Specifically, the preparation method of the ultrahigh-strength and high-toughness alloy steel comprises the following steps:

step S1, electric furnace smelting: determining the proportion of the raw materials according to the content of each component in the component proportion and smelting the raw materials; tapping conditions are as follows: p is less than or equal to 0.003 percent;

step S2, LF process: feeding Al in the LF furnace according to 0.20 percent of the mass of the molten steel, deoxidizing by adopting Si-C powder or SiC, keeping the white slag time to be more than or equal to 30min, adjusting chemical components according to a full analysis result, adding Nb according to the calculation of 0.02 percent, and tapping conditions: less than or equal to 0.001 percent of S, and 0.06 to 0.08 percent of Al is fed (namely the mass of the added Al accounts for 0.06 to 0.08 percent of the mass of the molten steel);

step S3, VD refining: slagging off before canning, and entering VD temperature: more than or equal to 1650 ℃; the vacuum degree is less than or equal to 67Pa during vacuum pumping, and the vacuum degree is maintained for more than or equal to 10 minutes; after the vacuumizing is finished, adjusting the Ar gas flow to 15-30L/min for soft blowing, and forbidding exposing the steel liquid level during the soft blowing, wherein the soft blowing retention time is more than or equal to 15 minutes; pouring at 1560-1590 ℃, and performing Ar gas protection pouring to obtain an electrode;

step S4, electrode annealing: heating the electrode to 670-700 ℃ at a heating rate of less than 100 ℃/h, and keeping the temperature for more than or equal to 25 h; then furnace cooling is carried out at a cooling rate of below 50 ℃/h to below 400 ℃, and discharging and air cooling are carried out;

s5, carrying out vacuum consumable remelting and smelting to obtain a steel ingot; in the vacuum consumable remelting smelting process, the average melting speed in the stable smelting stage is 3.8-6.2 Kg/min, helium is adopted for cooling, and the flow of the helium is controlled to be 230-300L/min;

step S6, annealing steel ingots: heating to 660-700 ℃ at a speed of less than or equal to 100 ℃/h, keeping the temperature for more than or equal to 25h, cooling to below 400 ℃ at a speed of less than or equal to 50 ℃/h, discharging and air cooling;

step S7, forging steel ingot: in the forging process, the heating temperature of the returned blank is controlled to be 1000-1120 ℃, the temperature is kept for 2-2.5 h, then forging is carried out, and the final forging temperature is controlled to be 850-930 ℃;

step S8, bar annealing: directly conveying the forged bar into a heat treatment furnace in a red mode for annealing;

step S9, bar heat treatment: the heat treatment includes normalizing, quenching and tempering.

Specifically, in step S1, the raw material may be returned steel, pig iron, scrap steel, etc., and the P is removed early in the melting period; in the oxidation period, the temperature T is more than or equal to 1530 ℃ for oxidation, oxygen blowing and batch addition of ore and lime are carried out according to the temperature and the condition of P, uniform and violent boiling is achieved, slag flows automatically, and slag materials are added in a proper amount. Tapping conditions are as follows: the lower limit of C is less than or equal to, P is less than or equal to 0.003 percent, and the temperature is more than or equal to 1650 ℃.

Specifically, in step S4, the purpose of electrode annealing is to fully release internal stress of the electrode, reduce electrode hardness, reduce fluctuation in the consumable remelting process, and ensure stability of the consumable process. Considering that the internal and external stresses are increased due to the too high temperature rise speed, surface cracks are easy to generate, the temperature rise speed is too low, the electrode annealing efficiency is too low, and the economical efficiency is poor. Therefore, the temperature rise rate is controlled to be less than 100 ℃/h, and exemplarily, the temperature rise rate is 80-100 ℃/h, such as 80 ℃/h, 85 ℃/h, 90 ℃/h, 95 ℃/h and 100 ℃/h.

Specifically, in step S4, it is considered that the hardness of the electrode decreases slightly when the heat-insulating time is too short, and the hardness does not decrease continuously when the heat-insulating time is too long, so that the annealing efficiency is low and the economical efficiency is poor; therefore, the heat preservation time is controlled to be more than or equal to 25 hours; for example, the heat preservation time is 25-30 h.

Specifically, in step S4, hardness after annealing is comprehensively ensured in consideration of furnace cooling speed and annealing time, and stress removal is ensured, so that the cooling speed is too fast, the hardness is reduced less, cracking is easy, and too slow economy is poor; therefore, the furnace cooling speed is controlled to be less than or equal to 50 ℃/h. Exemplarily, the furnace cooling speed is 30-50 ℃/h.

Specifically, in step S4, the hardness of the electrode is not changed and the internal stress is not changed after the electrode is discharged at 400 ℃ or lower, so that the electrode is cooled to 400 ℃ or lower and discharged for air cooling.

Specifically, in step S5, it is considered that radial segregation and coarse dendrites are likely to occur when the average melting rate is too high, and that an annular pattern is generated when the melting rate is too low because the molten pool is too shallow. Therefore, the average melting rate is controlled to be 3.8 to 6.2 kg/min.

Specifically, in step S5, it is considered that a circular pattern macrostructure is likely to appear due to an excessive flow of helium gas; too small a radial segregation and dendrites occur; therefore, the flow rate of the helium gas is controlled to be 230 to 300L/min.

Specifically, in step S6, if the temperature rise rate is too fast, internal and external stresses may increase, surface cracks may easily occur, the temperature rise rate is too small, the annealing efficiency is too slow, and the economy is poor; therefore, the temperature rise rate is controlled to be less than 100 ℃/h, and exemplarily, the temperature rise rate is 80-100 ℃/h, such as 80 ℃/h, 85 ℃/h, 90 ℃/h, 95 ℃/h and 100 ℃/h.

Specifically, in step S6, the heat-insulating time is controlled to be not less than 25 hours. For example, the heat preservation time is 25-30 h.

Specifically, in step S6, it is considered that the furnace cooling rate is too high, cracking is likely to occur, and the furnace cooling rate is too slow and the economical efficiency is poor; therefore, the furnace cooling speed is controlled to be less than or equal to 50 ℃/h. Exemplarily, the furnace cooling speed is 25-50 ℃/h.

Specifically, in step S6, the furnace is cooled to 400 ℃ or lower, and the product is discharged and air-cooled.

In step S6, the annealed steel ingot includes, by mass, C: 0.07-0.13%, Mn: 0.4% -0.70%, Ni: 3.0% -3.5%, Si: 0.15-0.35%, Cr: 1.0% -1.40%, Mo: 0.08-0.15%, Nb: 0.01-0.05%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, Cu: less than or equal to 0.35 percent, B: less than or equal to 0.001 percent, less than or equal to 0.0015 percent of O, and less than or equal to 0.0025 percent of N; the non-metallic inclusion A, B, D fine inclusion is below 0.5 grade, the radial segregation grade in the macrostructure is A grade, the annular pattern is A grade, and the grain size grade is above 5 grade (the austenite grain size of the steel is tested according to the GB/T6394 carburization method).

Specifically, in step S7, the blank needs to be heated to the forging starting temperature before forging, the forging starting temperature is 1200-1250 ℃, considering that the heating speed is too fast in the heating process of forging, the heating is not uniform, and cracks are easily generated, so that the blank is heated by adopting a step heating method, specifically, the step heating method comprises:

heating in the first stage: heating to 580-620 ℃ at a heating speed of less than 100 ℃/h (for example, 50-100 ℃/h), and keeping the temperature for 2-3 h;

heating in the second stage: heating to 800-900 ℃ at a heating speed of less than 100 ℃/h (for example, 50-100 ℃/h), and keeping the temperature for 2-3 h;

heating in the third stage: heating to 1200-1250 ℃ at a heating rate of less than 100 ℃/h (for example, 70-100 ℃/h), and keeping the temperature for 2-4 h.

Specifically, when the blank is heated by the step heating method, the heating speed of each stage is controlled to be below 100 ℃/h, so that the uniformity of steel ingot heating can be ensured, the internal and external temperatures of the steel ingot are consistent after the temperature is reached, and the internal stress generated by heating is reduced; isothermal treatment is divided into 3 stages, the isothermal temperature of the first stage is 580-620 ℃ and is lower than A_C1Wires, which can be uniformly organized, in preparation for austenitization; the isothermal temperature of the second stage is 800-900 ℃ and is higher than A_C3And finally, heating to the forging temperature of 1200-1250 ℃, and then starting forging.

Specifically, in the step S7, the forging is divided into 3 times of heating, 1 heading and 1 pulling per heating, and the heating is performed gradually to perform cooling forging, wherein the 1 st time of heating is performed for cogging forging, dendrites are crushed per heating, the dendrites are uniformly and thoroughly crushed by 3 times of heating, and finally the dendrites are elongated to a suitable size of the bar by 1 time of heating to refine the structure.

Specifically, in step S8, the annealing process includes: heating to 870-890 ℃ at the speed of less than or equal to 100 ℃/h, preserving heat for 6-8 h, and air cooling to less than or equal to 100 ℃; heating to 670-690 ℃ at the speed of less than or equal to 100 ℃/h, keeping the temperature for more than or equal to 25h, then cooling to less than or equal to 300 ℃ at the speed of less than or equal to 30 ℃/h, and discharging.

Specifically, in step S9, the heat treatment of the bar material specifically includes:

s901, normalizing at the normalizing temperature of 921-928 ℃, preserving heat for 55-65 min, and air cooling;

s902, quenching, wherein the quenching temperature is 810-825 ℃, the temperature is kept for 55-65 min, and oil cooling is carried out;

s903, tempering at the tempering temperature of 144-156 ℃, preserving heat for 170-185 min, and air cooling;

specifically, in step S9, the structure of the heat-treated bar is a tempered martensite structure with a high dislocation density, the grain size of the prior austenite reaches 5 grades or more, part of the epsilon carbide is precipitated in the structure, and the toughness of the material is well matched.

Specifically, in step S9, the mechanical properties of the bar after heat treatment are as follows: tensile Strength σ_bNot less than 1200MPa, yield strength sigma_0.2Not less than 940MPa, elongation delta₄Not less than 15%, reduction of area psi not less than 59%, fracture toughness K_JIC≥200MPa﹒m^{1 /2}。

Compared with the prior art, the preparation method of the alloy steel with ultrahigh strength and high toughness provided by the invention has the advantages that the metal Nb is added for microalloying treatment, and the effects of grain refinement and strength improvement are achieved.

The invention strictly controls the melting speed of vacuum consumable remelting, overcomes the defect of low-power annular patterns of low-alloy structural steel, and has a radial segregation grade A grade and an annular pattern grade A in a low-power structure.

The preparation method can obtain ultra-low gas and ultra-pure steel, wherein O is less than or equal to 0.0015 percent, N is less than or equal to 0.0025 percent, the non-metallic inclusion A, B, D type fine system inclusion is less than 0.5 grade, the other types of inclusions are not included, and the grain size grade is more than 5 grade.

The steel prepared by the method has excellent comprehensive properties after heat treatment, including tensile strength sigma_bNot less than 1200MPa, yield strength sigma_0.2Not less than 940MPa, elongation delta₄Not less than 15%, reduction of area psi not less than 59%, fracture toughness K_JIC≥200MPa﹒m^1/2(ii) a Has higher strength and impact toughness, and further prolongs the service life of the material.

The advantages of the steel according to the invention with regard to the precise control of the composition and process parameters will be shown in the following in the specific examples and comparative examples.

Example 1

The embodiment provides a preparation method of ultrahigh-strength and high-toughness alloy steel. The method comprises the following steps:

(1) electric furnace smelting: the raw materials are composed of return steel, pig iron, scrap steel and the like, and P is removed in the early stage of the melting period. And (3) oxidation period: oxidizing at 1605 deg.C, blowing oxygen and adding ore and lime in batches according to temperature and P condition to make them uniformly and fiercely boil, automatically flowing slag and adding appropriate amount of slag. 0.05 percent of C, 0.003 percent of P, the temperature is 1675 ℃, and tapping is carried out.

(2) An LF process: the LF in place is fed with Al according to 0.20 percent. Deoxidizing by using SiC, keeping white slag for 40min, adjusting chemical components according to a full analysis result, adding 0.02% of Nb, feeding 0.07% of Al after 0.001% of S, and tapping.

(3) And (3) VD refining process: slagging off before canning, and entering VD temperature: 1680 deg.C. The vacuum degree was 67Pa during the evacuation and the time was 10 minutes. After the vacuum pumping is finished, the Ar gas flow is adjusted to 20L/min for soft blowing, and the exposed steel liquid level is forbidden during the soft blowing. The soft blow hold time was 16 minutes. And (4) pouring at 1580 ℃ under the protection of Ar gas to obtain the electrode.

(4) And (3) annealing the electrode, namely heating to 680 ℃ at a speed of 100 ℃/h, preserving heat for 25h, then cooling to 350 ℃ at a speed of 50 ℃/h, discharging and air cooling.

(5) Smelting in a vacuum consumable electrode furnace: the average melting speed of the vacuum consumable electrode furnace in the normal melting stage is 6.0kg/min, the specification of the remelted steel ingot is phi 660mm, helium is adopted for cooling in the melting process of the vacuum consumable electrode furnace, and the flow rate of the helium is controlled to be 240L/min; and (5) after the steel ingot is demoulded, the steel ingot is put into a pit and slowly cooled for 56 hours, and then annealing is carried out. The annealing process is carried out by heating to 680 ℃ at 100 ℃/h, keeping the temperature for 25h, then cooling to 400 ℃ at 50 ℃/h, discharging, air cooling, polishing the surface of the steel ingot, and then forging the steel ingot.

(6) Forging and processing; heating the steel ingot in a heating furnace at a speed of 100 ℃/h to 600 ℃, and preserving heat for 2 h; heating at 100 deg.C/h, and maintaining at 850 deg.C for 2 h; the forging is started again by raising the temperature to 1210 ℃ at 100 ℃/h and keeping the temperature for 3 h. Forging a steel ingot by adopting 1 upsetting and 1 drawing, cogging to a phi 680mm circle, then returning and heating, keeping the temperature at 1120 ℃ for 2.5 hours, then forging, discharging the steel ingot by adopting 1 upsetting and 1 drawing, cogging to a 550mm square, returning, heating at 1020 ℃, directly discharging the steel ingot by adopting a third fire, and producing the steel ingot with the specification of phi 200mm, wherein the final forging temperature is 890 ℃. Directly conveying the forged bar into a heat treatment furnace in a red mode for annealing; the annealing treatment process comprises the following steps: heating to 890 ℃ at the speed of 100 ℃/h, preserving the heat for 6h, and cooling to 100 ℃ in air; heating to 680 ℃ at the speed of 100 ℃/h, preserving heat for 26h, then furnace-cooling to 300 ℃ at the speed of 30 ℃/h, and discharging.

(7) Heat treatment of bars: the heat treatment includes normalizing, quenching and tempering. Normalizing at 927 deg.C, maintaining for 60min, and air cooling; quenching temperature is 816 ℃, heat preservation is carried out for 60min, and oil cooling is carried out; tempering at 150 deg.C, maintaining for 180min, and air cooling.

Example 2

The embodiment provides a preparation method of ultrahigh-strength and high-toughness alloy steel. The method comprises the following steps:

(1) electric furnace smelting: the raw materials are composed of return steel, pig iron, scrap steel and the like, and P is removed in the early stage of the melting period. And (3) oxidation period: oxidizing at 1610 ℃, blowing oxygen and adding ores and lime in batches according to the conditions of temperature and P to achieve uniform and violent boiling, automatically flowing slag and adding slag materials in proper amount. 0.05 percent of C, 0.003 percent of P, the temperature is 1675 ℃, and tapping is carried out.

(2) An LF process: the LF in place is fed with Al according to 0.20 percent. Deoxidizing by using SiC, keeping white slag for 40min, adjusting chemical components according to a full analysis result, adding 0.02% of Nb, feeding 0.07% of Al after 0.001% of S, and tapping.

(3) And (3) VD refining process: slagging off before canning, and entering VD temperature: 1680 deg.C. The vacuum degree was 67Pa during the evacuation and the time was 10 minutes. After the vacuum pumping is finished, the Ar gas flow is adjusted to 20L/min for soft blowing, and the exposed steel liquid level is forbidden during the soft blowing. The soft blow hold time was 17 minutes. And (4) pouring at 1585 ℃ under the protection of Ar gas to obtain the electrode.

(4) And (3) electrode annealing, namely heating to 680 ℃ at a speed of 95 ℃/h, preserving heat for 25h, then furnace cooling to 355 ℃ at a speed of 50 ℃/h, discharging and air cooling.

(5) Smelting in a vacuum consumable electrode furnace: the average melting speed of the vacuum consumable electrode furnace in the normal melting stage is 5.8kg/min, the specification of the remelted steel ingot is phi 660mm, helium is adopted for cooling in the melting process of the vacuum consumable electrode furnace, and the flow rate of the helium is controlled to be 235L/min; and (5) after the steel ingot is demoulded, the steel ingot is put into a pit and slowly cooled for 56 hours, and then annealing is carried out. The annealing process is carried out by heating to 680 ℃ at 100 ℃/h, keeping the temperature for 25h, then cooling to 400 ℃ at 50 ℃/h, discharging, air cooling, polishing the surface of the steel ingot, and then forging the steel ingot.

(6) Forging and processing; heating the steel ingot in a heating furnace at a speed of 100 ℃/h to 600 ℃, and preserving heat for 2 h; heating at 100 deg.C/h, and maintaining at 850 deg.C for 2 h; the forging is started again by raising the temperature to 1210 ℃ at 100 ℃/h and keeping the temperature for 3 h. Forging a steel ingot by adopting 1 upsetting and 1 drawing, cogging to a phi 680mm circle, then returning to the furnace for heating, keeping the temperature at 1120 ℃ for 2.5 hours, then forging, discharging from the furnace by adopting 1 upsetting and 1 drawing, cogging to a 550mm square, returning to the furnace by adopting a second fire, heating at 1020 ℃, directly discharging from the furnace by adopting a third fire, and producing a bar with the specification of phi 200mm, wherein the final forging temperature is 895 ℃. Directly conveying the forged bar into a heat treatment furnace in a red mode for annealing; the annealing treatment process comprises the following steps: heating to 870 ℃ at the speed of 100 ℃/h, preserving heat for 8h, and cooling in air to 100 ℃; heating to 670 ℃ at the speed of 100 ℃/h, keeping the temperature for 26h, then furnace-cooling to 300 ℃ at the speed of 30 ℃/h, and discharging.

(7) Heat treatment of bars: the heat treatment includes normalizing, quenching and tempering. Normalizing at 925 deg.C, keeping the temperature for 60min, and air cooling; quenching temperature is 815 ℃, heat preservation is carried out for 60min, and oil cooling is carried out; tempering at 150 deg.C, maintaining for 180min, and air cooling.

Example 3

The embodiment provides a preparation method of ultrahigh-strength and high-toughness alloy steel. The method comprises the following steps:

(1) electric furnace smelting: the raw materials are composed of return steel, pig iron, scrap steel and the like, and P is removed in the early stage of the melting period. And (3) oxidation period: oxidizing at 1605 deg.C, blowing oxygen and adding ore and lime in batches according to temperature and P condition to make them uniformly and fiercely boil, automatically flowing slag and adding appropriate amount of slag. 0.05 percent of C, 0.003 percent of P, the temperature is 1670 ℃, and tapping is carried out.

(2) An LF process: the LF in place is fed with Al according to 0.20 percent. Deoxidizing by using SiC, keeping white slag for 40min, adjusting chemical components according to a full analysis result, adding 0.02% of Nb, feeding 0.07% of Al after 0.001% of S, and tapping.

(3) And (3) VD refining process: slagging off before canning, and entering VD temperature: 1680 deg.C. The vacuum degree was 67Pa during the evacuation and the pressure was maintained for 15 minutes. After the vacuum pumping is finished, the Ar gas flow is adjusted to 20L/min for soft blowing, and the exposed steel liquid level is forbidden during the soft blowing. The soft blow hold time was 16 minutes. And (4) pouring at 1580 ℃ under the protection of Ar gas to obtain the electrode.

(4) And (3) annealing the electrode, namely heating to 680 ℃ at a speed of 100 ℃/h, preserving heat for 25h, then cooling to 360 ℃ at a speed of 50 ℃/h, discharging and air cooling.

(5) Smelting in a vacuum consumable electrode furnace: the average melting speed of the vacuum consumable electrode furnace in the normal melting stage is 6.0kg/min, the specification of the remelted steel ingot is phi 660mm, helium is adopted for cooling in the melting process of the vacuum consumable electrode furnace, and the flow rate of the helium is controlled to be 245L/min; and (5) after the steel ingot is demoulded, the steel ingot is put into a pit and slowly cooled for 56 hours, and then annealing is carried out. The annealing process is carried out by heating to 680 ℃ at 100 ℃/h, keeping the temperature for 26h, cooling to 400 ℃ at 48 ℃/h, discharging, air cooling, polishing the surface of the steel ingot, and forging the steel ingot.

(6) Forging and processing; heating the steel ingot in a heating furnace at a speed of 100 ℃/h to 600 ℃, and preserving heat for 2.5 h; heating at 100 deg.C/h, and maintaining at 850 deg.C for 2 h; the forging is started again by raising the temperature to 1210 ℃ at 100 ℃/h and keeping the temperature for 3 h. Forging a steel ingot by adopting 1 upsetting and 1 drawing, cogging to a phi 680mm circle, then returning and heating, keeping the temperature at 1120 ℃ for 2.5 hours, then forging, discharging the steel ingot by adopting 1 upsetting and 1 drawing, cogging to a 550mm square, returning, heating at 1020 ℃, directly discharging the steel ingot by adopting a third fire, and producing the steel ingot with the specification of phi 200mm, wherein the final forging temperature is 890 ℃. Directly conveying the forged bar into a heat treatment furnace in a red mode for annealing; the annealing treatment process comprises the following steps: heating to 870 ℃ at the speed of 90 ℃/h, preserving heat for 8h, and cooling in air to 100 ℃; heating to 670 ℃ at the speed of 90 ℃/h, keeping the temperature for 27h, then furnace-cooling to 280 ℃ at the speed of 25 ℃/h, and discharging.

(7) Heat treatment of bars: the heat treatment includes normalizing, quenching and tempering. Normalizing at 925 deg.C, keeping the temperature for 60min, and air cooling; quenching temperature is 816 ℃, heat preservation is carried out for 60min, and oil cooling is carried out; tempering at 150 deg.C, maintaining for 180min, and air cooling.

Comparative example 1

The comparative example provides a method of preparing an alloy steel. The method comprises the following steps:

(1) electric furnace smelting: the raw materials are composed of return steel, pig iron, scrap steel and the like, and P is removed in the early stage of the melting period. And (3) oxidation period: oxidizing at 1605 deg.C, blowing oxygen and adding ore and lime in batches according to temperature and P condition to make them uniformly and fiercely boil, automatically flowing slag and adding appropriate amount of slag. 0.05 percent of C, 0.003 percent of P, the temperature is 1675 ℃, and tapping is carried out.

(2) An LF process: the LF in place is fed with Al according to 0.20 percent. Deoxidizing by using SiC, keeping white slag for 40min, adjusting chemical components according to a full analysis result, adding 0.02% of Nb, feeding 0.07% of Al after 0.001% of S, and tapping.

(3) And (3) VD refining process: slagging off before canning, and entering VD temperature: 1680 deg.C. The vacuum degree was 67Pa during the evacuation and the time was 10 minutes. After the vacuum pumping is finished, the Ar gas flow is adjusted to 20L/min for soft blowing, and the exposed steel liquid level is forbidden during the soft blowing. The soft blow hold time was 16 minutes. And (4) pouring at 1580 ℃ under the protection of Ar gas to obtain the electrode.

(4) And (3) annealing the electrode, namely heating to 680 ℃ at a speed of 100 ℃/h, preserving heat for 25h, then cooling to 350 ℃ at a speed of 50 ℃/h, discharging and air cooling.

(5) Smelting in a vacuum consumable electrode furnace: the average melting speed of the vacuum consumable electrode furnace in the normal melting stage is 8kg/min, the specification of the remelted steel ingot is phi 660mm, helium is adopted for cooling in the melting process of the vacuum consumable electrode furnace, and the flow rate of the helium is controlled to be 200 ml/min. And (5) after the steel ingot is demoulded, the steel ingot is put into a pit and slowly cooled for 56 hours, and then annealing is carried out. The annealing process is carried out by heating to 680 ℃ at 100 ℃/h, keeping the temperature for 25h, then cooling to 400 ℃ at 50 ℃/h, discharging, air cooling, polishing the surface of the steel ingot, and then forging the steel ingot.

(6) Forging and processing; heating the steel ingot in a heating furnace at a speed of 100 ℃/h to 600 ℃, and preserving heat for 2 h; heating at 100 deg.C/h, and maintaining at 850 deg.C for 2 h; the forging is started again by raising the temperature to 1210 ℃ at 100 ℃/h and keeping the temperature for 3 h. Forging a steel ingot by adopting 1 upsetting and 1 drawing, cogging to a phi 680mm circle, then returning and heating, keeping the temperature at 1120 ℃ for 2.5 hours, then forging, discharging the steel ingot by adopting 1 upsetting and 1 drawing, cogging to a 550mm square, returning, heating at 1020 ℃, directly discharging the steel ingot by adopting a third fire, and producing the steel ingot with the specification of phi 200mm, wherein the final forging temperature is 890 ℃. Directly conveying the forged bar into a heat treatment furnace in a red mode for annealing; the annealing treatment process comprises the following steps: heating to 890 ℃ at the speed of 100 ℃/h, preserving the heat for 6h, and cooling to 100 ℃ in air; heating to 680 ℃ at the speed of 100 ℃/h, preserving heat for 26h, then furnace-cooling to 300 ℃ at the speed of 30 ℃/h, and discharging.

(7) Heat treatment of bars: the heat treatment includes normalizing, quenching and tempering. Normalizing at 927 deg.C, and maintaining for 60 min; quenching temperature is 816 ℃, and heat preservation is carried out for 60 min; tempering temperature is 150 ℃, and heat preservation is carried out for 180 min.

The chemical compositions of the steels of examples 1 to 3 and comparative example 1 are shown in Table 1, and the test results of examples 1 to 3 and comparative example 1 are shown in tables 2 and 4.

Table 1 chemical composition wt% of examples and comparative examples

Serial number	C	Mn	Si	S	P	Ni	Cr	Mo	Nb	Cu	B	O	N
														Example 1	0.115	0.58	0.22	0.001	0.001	3.15	1.20	0.09	0.020	0.08	0.0004	0.0008	0.0018
Example 2	0.109	0.62	0.24	0.001	0.001	3.12	1.19	0.10	0.025	0.09	0.0004	0.0009	0.0020
														Example 3	0.112	0.52	0.25	0.001	0.001	3.11	1.25	0.09	0.028	0.08	0.0004	0.0008	0.0019
Comparative example 1	0.110	0.58	0.22	0.001	0.001	3.12	1.25	0.10	0.022	0.09	0.0004	0.0009	0.0022

TABLE 2 non-metallic inclusions of examples and comparative examples

The specification requirements for the non-metallic inclusions are shown in table 3 below.

TABLE 3 technical Specification requirements for non-metallic inclusions

Note: in the table, a-A + B + C is less than or equal to 3, i.e. the sum of the numbers of a of A, B and C cannot be more than 3; B-A + B + C is less than or equal to 8, namely the sum of the numbers of B of A, B and C cannot be more than 8.

TABLE 4 macroscopic, grain size and Properties of the examples and comparative examples

TABLE 4 Low power and Performance continuation of the examples and comparative examples

Comparing examples 1-3 with comparative example 1, it can be seen that the steels prepared by the method for preparing ultra-high strength, high toughness alloy steels according to the present invention are acceptable in terms of macrostructure, and have excellent overall properties, such as tensile strength σ_bNot less than 1203MPa, yield strength sigma_0.2Not less than 1041MPa, elongation delta₄Not less than 15%, reduction of area psi not less than 69%, fracture toughness K_JIC≥277MPa﹒m^1/2. Whereas the macrostructure of comparative example 1 was not qualified and radial segregation was severe.

Compared with the existing double-vacuum smelting method, the cost of the preparation method of the invention is reduced by 20-40%, and the economic benefit is obvious.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.