CN115181901A - High-strength-toughness hard low-temperature bainite hot-work die steel and preparation method thereof - Google Patents

Abstract

The invention discloses high-strength and high-toughness hard low-temperature bainite hot-work die steel which is characterized by comprising the following chemical components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities. In addition, the invention also discloses a preparation method of the high-strength-toughness hard low-temperature bainite hot-work die steel. The secondary tempering structure of the hot work die steel still maintains the appearance of low-temperature bainite, and carbides are precipitated in the structure, so that the hot work die steel has good thermal stability; the preparation process flow is simple and easy to implement, is beneficial to industrial production, and has high preparation efficiency.

Description

High-strength-toughness hard low-temperature bainite hot-work die steel and preparation method thereof

Technical Field

The invention relates to the technical field of die steel, in particular to high-strength-toughness hard low-temperature bainite hot-work die steel and a preparation method thereof, wherein the low-temperature bainite hot-work die steel has the tensile strength of not less than 1900 MPa, the hardness of not less than 53 HRC and the unnotched impact energy of not less than 500J, and is particularly suitable for the fields of hot forming, processing and the like.

Background

The production and manufacturing level of the mold industry in modern industry has attracted high attention of the manufacturing industry, and the level of the industry becomes one of the important marks for measuring the national manufacturing level. With the adjustment of the global economic industry structure, the world market determines that China will be developed into a large mold manufacturing country. In the world mold production value, the manufacturing proportion of Chinese molds is remarkably improved, and the use amount of mold steel is also remarkably increased.

The hot-work die steel is most widely applied in the die industry, wherein the main steel types in the hot-work die steel are H13, 3Cr2W8V and 5CrMnMo steel, and the hot-work die steel has high strength and toughness, thermal fatigue resistance, high hardenability and good wear resistance. However, compared with the imported hot-work die steel, the domestic traditional hot-work die steel has the defects of banded segregation, along-grain carbide and the like, so that the problems of poor isotropic performance, short service time and the like are caused, and the service life of the die is influenced.

In order to meet the actual production needs, many research and development units also perform a great deal of research and development work on the improvement and development of hot-work die steel, and the following descriptions are provided: patent document CN101240400B proposes a low-cost hot-work die steel, which contains C:0.38 to 0.42%, si:0.9 to 1.1%, mn:0.3 to 0.5%, W:0.9 to 1.2%, cr:4.8 to 5.8%, mo:0.45 to 0.55%, V:0.25 to 0.45 percent, the final heat treatment adopts a quenching and tempering process, the hardness of the alloy after the tempering at 570 ℃ is not more than 52 HRC, and the tensile strength is not more than 1800 MPa. The invention patent with the granted publication number of CN11748733A "an H13 hot work die steel and its preparation method" contains C:0.36 to 0.42%, si:0.18 to 0.23%, mn:0.39 to 0.46%, ni:0.06 to 0.12%, cr:4.5 to 5.00%, mo:2.20 to 2.70%, V:0.5 to 0.8 percent, and after quenching and secondary tempering treatment, the hardness of the steel after tempering is not more than 40 HRC, and the tensile strength is not more than 1400 MPa. Patent document with publication number CN 1104812A proposes a high performance hot stamping die steel and its manufacturing process, wherein the steel comprises (by mass percent) C:0.78%, si:1.00%, mn:0.40%, cr:5.50%, mo:1.60%, V:0.45 percent, and the impact energy of the hot stamping die steel at room temperature after twice tempering at 580 ℃ is more than or equal to 260J.

However, under high-temperature tempering conditions, carbides are easily precipitated and easily aggregated in hot-work die steel having a high Cr element content, thereby reducing the service life of the hot-work die steel. In addition, the appropriate addition of Ni, V and other alloy elements may be favorable to raise the toughness of hot-work die steel.

Moreover, the hot-work die steel belongs to martensite steel, and the toughness and the thermal stability of low-temperature bainite are higher than those of martensite, so that the low-temperature bainite can possibly show performance advantages when being used for the hot-work die steel, and is one of the development directions for improving the tempering performance of the die steel. Therefore, it is necessary to develop a high-toughness hard low-temperature bainite hot-work die steel with excellent comprehensive mechanical properties so as to accelerate the large-scale development, popularization and application of hot-work die steel in China.

Disclosure of Invention

In order to solve the problem that the prior art can not meet the use requirements of high toughness, strength and thermal stability on a die material, the invention provides high-toughness hard low-temperature bainite hot-work die steel and a preparation method thereof, and the comprehensive mechanical property of the hot-work die steel is improved through component design and a heat treatment process.

In order to solve the technical problems, the invention adopts the technical scheme that:

a high-strength-toughness hard low-temperature bainite hot-work die steel comprises the following chemical components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities.

The chemical component proportion satisfies: n is more than or equal to 0.16 and less than or equal to 0.26, ts is more than or equal to 266 and less than or equal to 330, tr is more than or equal to 405 and less than or equal to 525,

wherein n = (2.5 Ni-Cr + Mo)/(2Si + Mn + 1.1V)

Ts=560-306[C]-30[Mn]-12[Si] -20[Ni]-22[Cr]-12[V]+12[Mo]，

Tr=830-110[C]-50[Mn]+41.6[Si]-35[Ni]-60[Cr]-40[V]-20[Mo]。

In addition, the invention also provides a preparation method of the high-strength-toughness hard low-temperature bainite hot-work die steel, which comprises the following steps: A. smelting: feeding according to the design requirements of the composition components of steel, smelting in a vacuum induction furnace and casting into steel ingots, wherein the steel comprises the following components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities; B. hot rolling and annealing: hot rolling the steel ingot, annealing the hot-rolled sample, and finally air-cooling to room temperature; C. spheroidizing annealing: heating the sample subjected to the heat treatment in the step B to 830-870 ℃, preserving heat for 1-1.5 h, cooling to 740-770 ℃ along with a furnace, preserving heat for 2-2.5 h, finally cooling to 500 ℃ along with the furnace, and taking out of the furnace for air cooling; D. isothermal quenching treatment: heating the sample subjected to the heat treatment in the step C to 990-1050 ℃, preserving the heat for 20-30 min, then quickly putting the sample into a salt bath furnace at 280-350 ℃, quenching the sample for 1-3 h at medium temperature, and then air cooling the sample to room temperature; E. tempering treatment: and D, heating the sample subjected to the heat treatment in the step D to 555 to 565 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, air-cooling, then heating to 575 to 585 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, and air-cooling.

The technical scheme of the invention achieves the aim through the following principles and modes.

(1) On the basis of accurately understanding the content control principle of C, si, mn, cr, ni, V and Mo multi-element alloying elements of the high-strength hot-working die steel, the chemical components (in percentage by weight) of the low-temperature bainite hot-working die steel are reasonably designed and controlled.

C: the C element has stronger solid solution strengthening effect, one part of the C element is dissolved into a matrix in the hot work die steel through a heat treatment process to improve the hardness and the strength of the matrix, and the other part of the C element is combined with the alloy element to form alloy carbide to enhance the wear resistance. The preferable content range is 0.45 to 0.55.

Mn: mn has a solid solution strengthening effect and can improve the strength, hardness and hardenability of ferrite and austenite. Has stronger affinity with S element, avoids FeS from being formed at the crystal boundary, and eliminates the harmful effect of the S element. The preferable content range is 0.20 to 0.50.

Si: si is an element for promoting ferrite to form and has a solid solution strengthening effect on ferrite. Meanwhile, si is an effective element for improving the tempering resistance, the diffusion speed of carbon in ferrite is reduced, carbides separated out during tempering are not easy to gather, and the tempering stability is improved. The preferable content range is 1.20 to 1.50.

Mo: mo has solid solution strengthening effect, and Mo is dissolved in austenite to improve the hardenability of the steel. Meanwhile, mo element is combined with C element to precipitate Mo in martensite during tempering ₂ C, the main alloy element causing the secondary hardening phenomenon. In addition, mo element can prevent tempering brittleness, improve the tempering stability of the steel, enable the hot die steel to be tempered at higher temperature and improve plasticity. The preferable content range is 1.10 to 1.80.

V: in the hot work die steel, the V element has the function of refining the structure and the crystal grains of the steel, and forms VC reinforcing secondary hardening effect with the C element during tempering like the Mo element. Meanwhile, due to the thermal stability of VC, the tempering stability of the steel can be improved. The preferable content range is 0.70 to 1.30.

Cr: cr element can increase the hardenability of steel, improve the hardness and wear resistance of high-carbon steel without making the steel brittle, make the steel have good high-temperature oxidation resistance and oxidation medium corrosion resistance, and also increase the heat strength of the steel. However, the higher content of Cr can form high-chromium M with carbon in the quenching and tempering process ₂₃ C ₆ The high Cr carbide has poor thermal stability, so the invention adopts the component design of reducing the Cr content, inhibits the formation of the Cr carbide, promotes the C to be fully combined with the carbide stabilizing elements V and Mo to form MC and M with the advantages of fine size, dispersion distribution and good high-temperature stability ₂ C-type carbides, thereby improving the thermal strength and thermal fatigue resistance of the steel. The preferable content range is 2.90 to 3.50.

Ni: the Ni element has the functions of solid solution strengthening and hardenability improvement, the ferrite grains are refined, the plasticity and toughness of the hot work die steel are improved, and the combined use of the Ni element and the Cr element and the Mo element can improve the heat strength of the hot work die steel. The preferable content range is 0.8 to 1.20.

(2) Besides the need of reasonably controlling the chemical component ranges of all elements, the following innovative technical requirements must be set, and the relative addition amount of a part of key elements must be accurately regulated and controlled so as to play the key regulation and control role of the elements on the comprehensive mechanical properties of the steel, such as strength, hardness, impact toughness and the like.

(a) By regulating the relation that n is more than or equal to 0.16 and less than or equal to 0.26, the element content ratio of Ni, cr, mo, si, mn and V is required to be n = (2.5 Ni-Cr + Mo)/(2Si + Mn + 1.1V). Ni and Mn are favorable for impact toughness of the hot work die steel, and Mo, V and Si are favorable for improving tempering hardness of the hot work die steel. The reduction of Cr is beneficial to the improvement of comprehensive mechanical property.

(b) By regulating and controlling the relational expression that Ts is not less than 266 and not more than 330 and Tr is not more than 405 and not more than 525, the alloy elements of C, ni, cr, mo, si, mn and V are required to be according to the conditions that Ts =560-306[ C ] -30[ Mn ] -12[ Si ] -20[ Ni ] -22[ Cr ] -12[ V ] +12[ Mo ], tr =830-110[ C ] -50[ Mn ] +41.6[ Si ] -35[ Ni ] -60[ Cr ] -40[ V ] -20[ Mo ] "determine that the austenite → martensite initial transformation temperature Ts of the high-toughness and low-temperature hard bainite hot working die steel is controlled between 266 ℃ and 330 ℃ and the austenite → bainite initial transformation temperature Tr is controlled between 405 ℃ and 525 ℃, and the phase transition temperature interval is controlled in a lower range so as to be beneficial to inhibit nucleation of upper bainite tissue, promote the generation of the low-temperature bainite tissue, ensure the small size of the low-temperature bainite tissue, and further improve the mechanical property of the hot bainite die steel.

The invention has the beneficial effects that:

1. the structure of the high-strength and high-toughness hard low-temperature bainite hot-work die steel is mainly a low-temperature bainite structure, namely bainite ferrite and film-shaped residual austenite among ferrite laths. Wherein the low-temperature bainite structure is not less than 75%.

2. The secondary tempering structure of the high-strength and high-toughness hard low-temperature bainite hot-work die steel still keeps the low-temperature bainite morphology, and carbides are precipitated in the structure, so that the high-strength and high-toughness hard low-temperature bainite hot-work die steel has good thermal stability.

3. The unnotched impact energy of the secondary tempered sample of the high-strength-toughness hard low-temperature bainite hot-work die steel is not less than 500J, the tensile strength is not less than 1900 MPa, and the hardness is not less than 53.0 HRC.

4. The high-strength-toughness low-temperature bainite hot-work die steel alloy system is reasonable in control, the preparation process flow is simple and easy to implement, industrial production is facilitated, and the preparation efficiency is high.

The present invention will be described in detail with reference to the accompanying drawings.

Drawings

FIG. 1 is a scanning electron microscope photograph of austempered structure of the high toughness hard low temperature bainite hot work die steel prepared in example 1;

FIG. 2 is a scanning electron microscope photograph of austempered structure of the high toughness hard low temperature bainite hot work die steel prepared in example 2;

FIG. 3 is a scanning electron microscope photograph of austempered structure of the high toughness hard low temperature bainite hot work die steel prepared in example 3;

FIG. 4 is a scanning electron microscope photograph of the secondary tempered structure of the high toughness and low temperature bainite hot work die steel prepared in example 4;

FIG. 5 is a SEM image of the secondary tempered structure of the high toughness and low temperature bainite hot work die steel prepared in example 5;

FIG. 6 is a SEM image of the secondary tempered structure of the high toughness and low temperature bainite hot work die steel prepared in example 6.

Detailed Description

The invention provides high-strength and high-toughness hard low-temperature bainite hot-work die steel which comprises the following chemical components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities, wherein the hot-working die steel structure is low-temperature bainite.

Besides, the proportion of the chemical components meets the following requirements: n is more than or equal to 0.16 and less than or equal to 0.26, ts is more than or equal to 266 and less than or equal to 330, and Tr is more than or equal to 405 and less than or equal to 525.

Wherein n = (2.5 Ni-Cr + Mo)/(2Si + Mn + 1.1V)

Ts=560-306[C]-30[Mn]-12[Si] -20[Ni]-22[Cr]-12[V]+12[Mo]，

Tr=830-110[C]-50[Mn]+41.6[Si]-35[Ni]-60[Cr]-40[V]-20[Mo]。

The invention also provides a preparation method of the high-strength-toughness hard low-temperature bainite hot-work die steel, which comprises the following steps.

A. Smelting: the steel is fed according to the design requirements of the composition components of the steel, melted in a vacuum induction furnace and cast into steel ingots.

The steel comprises the following components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities. Besides, the contents of the alloy elements in percentage by weight must also satisfy: n is more than or equal to 0.16 and less than or equal to 0.26, ts is more than or equal to 266 and less than or equal to 330, and Tr is more than or equal to 405 and less than or equal to 525.

B. Hot rolling and annealing: and hot rolling the steel ingot, annealing the hot rolled sample, and finally air cooling to room temperature.

C. Spheroidizing annealing: and C, heating the sample subjected to the heat treatment in the step B to 830-870 ℃, preserving heat for 1-1.5 h, cooling to 740-770 ℃ along with a furnace, preserving heat for 2-2.5 h, finally cooling to 500 ℃ along with the furnace, and taking out of the furnace for air cooling.

D. Isothermal quenching treatment: and C, heating the sample subjected to the heat treatment in the step C to 990-1050 ℃, preserving the heat for 20-30 min, then quickly putting the sample into a salt bath furnace at 280-350 ℃, quenching the sample for 1-3 h at medium temperature, and then air cooling the sample to room temperature.

E. Tempering treatment: and D, heating the sample subjected to the heat treatment in the step D to 555 to 565 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, air-cooling, then heating to 575 to 585 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, and air-cooling.

The present invention will be described in detail with reference to specific examples.

Example 1, see figure 1, in this example.

A. The weight percentage is as follows: c0.45, si 1.20, mn 0.25, cr 2.9, mo 1.20, V0.7, ni 0.9, P0.0075 and S0.0041, the balance of Fe, calculating the feeding proportion, smelting in a vacuum high-frequency induction furnace and electroslag remelting, and then casting into a round ingot with the diameter phi of 80 mm.

B. Annealing and hot rolling: heating the steel ingot to 1150 ℃, preserving heat for 5 hours, carrying out homogenizing annealing, and cooling along with the furnace. Then, hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm; and finally, annealing treatment is carried out on the hot-rolled and cogging steel plate, the annealing heating temperature is 880 ℃, and furnace cooling is carried out after heat preservation is carried out for 1.5 hours.

C. Spheroidizing annealing: and heating the hot rolled plate blank to 860 ℃, preserving heat for 1.5 h, cooling the hot rolled plate blank to 760 ℃ along with the furnace, preserving heat for 2.5 h, finally cooling the hot rolled plate blank along with the furnace to 500 ℃, discharging the hot rolled plate blank from the furnace and air cooling the hot rolled plate blank.

D. Isothermal quenching: and (3) putting the spheroidizing annealed plate into a furnace with the temperature of 1000 ℃, preserving the heat for 20 min, then quickly putting the plate into a salt bath furnace with the temperature of 350 ℃ for moderate temperature for 1.5 h, taking the plate out of the furnace, and air-cooling the plate to the room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 1. As can be seen from fig. 1: the structure is a low-temperature bainite structure, and the volume fraction of the low-temperature bainite structure is 76%. In this example, a low temperature bainite die steel was prepared, n =0.16, ts =327 ℃, tr =511 ℃, wherein the hardness of the low temperature bainite structure was 49.3 HRC, the unnotched impact energy was not less than 500J, and the charpy U-notch impact energy (KU) ₂ ) 24J, tensile strength 1820 MPa. See table 1 for data.

Example 2, see fig. 2, in this example.

A. The weight percentages are as follows: 0.50 percent of C, 1.34 percent of Si, 0.32 percent of Mn, 3.2 percent of Cr, 1.55 percent of Mo, 0.98 percent of V, 1.00 percent of Ni, 0.0075 percent of P and 0.0035 percent of S, and the balance of Fe, calculating the feeding proportion, and casting into a round ingot with the diameter of phi 80 mm after smelting in a vacuum high-frequency induction furnace and electroslag remelting.

B. Annealing and hot rolling: heating the steel ingot to 1150 ℃, preserving heat for 5 hours, carrying out homogenizing annealing, and cooling along with the furnace. Then, hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm; and finally, annealing treatment is carried out on the hot-rolled and cogging steel plate, the annealing heating temperature is 880 ℃, and furnace cooling is carried out after heat preservation is carried out for 1.5 hours.

C. Spheroidizing annealing: and heating the hot rolled plate blank to 860 ℃, preserving heat for 1.2 h, cooling the hot rolled plate blank to 750 ℃ along with a furnace, preserving heat for 2 h, cooling the hot rolled plate blank to 500 ℃ in the furnace, and then discharging the hot rolled plate blank from the furnace for air cooling.

D. Isothermal quenching: and (3) putting the spheroidizing annealed plate into a furnace with the temperature of 1020 ℃, preserving the heat for 20 min, then quickly putting the spheroidizing annealed plate into a salt bath furnace with the temperature of 320 ℃ for 2 h at the medium temperature, then discharging the plate out of the furnace and cooling the plate to the room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 2. As can be seen from fig. 2: the structure is a low-temperature bainite structure, and the volume fraction of the structure is 80%. In this example, a low temperature bainite die steel was prepared, n =0.26, ts =298 ℃, tr =462 ℃, wherein the low temperature bainite structure hardness was 50.2 HRC, the unnotched impact energy was not less than 500J, and charpy U-notch impact energy (KU) ₂ ) 30J and 1845 MPa of tensile strength. See table 1 for data.

Example 3, see figure 3, in this example.

A. The weight percentages are as follows: c0.55, si 1.50, mn 0.48, cr 3.5, mo 1.75, V1.30, ni 1.20, P0.0055 and S0.0045, and the balance of Fe, calculating the feeding proportion, and casting into round ingots with the diameter of phi 80 mm after smelting in a vacuum high-frequency induction furnace and electroslag remelting.

B. Annealing and hot rolling: heating the steel ingot to 1150 ℃, preserving heat for 5 hours, carrying out homogenizing annealing, and cooling along with the furnace. Then, hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm; and finally, annealing treatment is carried out on the hot-rolled and cogging steel plate, the annealing heating temperature is 880 ℃, and furnace cooling is carried out after heat preservation is carried out for 1.5 hours.

C. Spheroidizing annealing: and heating the hot rolled plate blank to 840 ℃ and preserving heat for 1.2 h, cooling to 740 ℃ along with the furnace and preserving heat for 2 h, finally cooling to 500 ℃ along with the furnace, and discharging from the furnace for air cooling.

D. Isothermal quenching: and (3) placing the spheroidizing annealed plate into a furnace at 1050 ℃, preserving the heat for 20 min, then quickly placing the spheroidizing annealed plate into a salt bath furnace at 285 ℃, carrying out medium temperature for 2.5 h, taking out of the furnace, and carrying out air cooling to room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in the table1 and 3. As can be seen in fig. 3: the structure is a low-temperature bainite structure, and the volume fraction of the structure is 82%. This example prepared a low temperature bainite die steel, n =0.25, ts =265 ℃, tr =406 ℃, where the low temperature bainite structure hardness was 51.2 HRC, the unnotched impact power was not less than 500J, charpy U-notch impact power (KU) ₂ ) 40J, tensile strength 1865 MPa. See table 1 for data.

Example 4, see figure 4, in this example: the austempered sheet of example 1 was placed in a box furnace at 560 ℃ and tempered for 1 hour, taken out of the furnace and air-cooled to room temperature. Then putting the mixture into a box furnace for the second time, heating the mixture to 580 ℃, tempering the mixture for 1 hour, discharging the mixture out of the furnace, and air-cooling the mixture to room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 4. As can be seen in fig. 4: this example produced tempered bainite, precipitated carbides and globular undissolved carbide structures. The tissue hardness is 53.5 HRC, the unnotched impact energy is not less than 500J, and the Charpy U-shaped notch impact energy (KU) ₂ ) 20J, tensile strength 1920 MPa. See table 1 for data.

Example 5, see figure 5, in this example: the austempered sheet of example 2 was placed in a box furnace at 560 ℃ and tempered for 1 hour, taken out of the furnace and air-cooled to room temperature. Then putting the mixture into a box furnace for the second time, heating the mixture to 580 ℃, tempering the mixture for 1 hour, discharging the mixture out of the furnace, and air-cooling the mixture to room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 5. As can be seen in fig. 5: this example produced tempered bainite, precipitated carbides and globular undissolved carbide structures. The tissue hardness is 53.5 HRC, the unnotched impact energy is not less than 500J, and the Charpy U-shaped notch impact energy (KU) ₂ ) 28J and 1935 MPa tensile strength. See table 1 for data.

Example 6, see fig. 6, in this example: the austempered sheet of example 3 was placed in a box furnace at 560 ℃ for tempering for 1 hour, taken out of the furnace and air cooled to room temperature. Then putting the mixture into a box furnace for the second time, heating the mixture to 580 ℃ and tempering the mixture for 1 hour, discharging the mixture out of the furnace and air-cooling the mixture to room temperature.

The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 6. As can be seen in fig. 6: this example produced tempered bainite, precipitated carbides and globular undissolved carbide structures. The tissue hardness is 55.2 HRC, the unnotched impact energy is not less than 500J, and the Charpy U-shaped notch impact energy (KU) ₂ ) 30J and 1966 MPa of tensile strength. See table 1 for data.

The mechanical property results of the high-toughness and high-temperature and high-toughness bainite hot-work die steels in examples 1 to 6 are shown in the following table 1

。

In conclusion, the high-strength and high-toughness hard low-temperature bainite hot-work die steel obtained by the scheme of the invention has high preparation efficiency and excellent tempering performance.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention and not to limit it; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art will understand that: modifications of the embodiments of the invention or equivalent substitutions for parts of the technical features are possible; without departing from the spirit of the present invention, it is intended to cover all aspects of the invention as defined by the appended claims.

Claims (9)

1. The high-strength-toughness hard low-temperature bainite hot-work die steel is characterized by comprising the following chemical components in percentage by mass: 0.45 to 0.55 percent of C, 1.2 to 1.50 percent of Si, 0.20 to 0.50 percent of Mn, 2.90 to 3.50 percent of Cr, 1.10 to 1.80 percent of Mo, 0.70 to 1.30 percent of V, 0.80 to 1.20 percent of Ni, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities.

2. The high-strength-toughness low-temperature bainite hot-work die steel as claimed in claim 1, wherein the chemical components of Si, mn, cr, ni, V and Mo in the low-temperature bainite hot-work die steel in percentage by mass are in accordance with: n is more than or equal to 0.16 and less than or equal to 0.26, wherein,

n=(2.5Ni-Cr+Mo)/(2Si+Mn+1.1V)。

3. the high-strength-toughness low-temperature bainite hot-work die steel as claimed in claim 1, wherein the chemical components of C, si, mn, cr, ni, V and Mo in the low-temperature bainite hot-work die steel in percentage by mass are in accordance with: ts is more than or equal to 266 and less than or equal to 330, tr is more than or equal to 405 and less than or equal to 525, wherein,

Ts=560-306[C]-30[Mn]-12[Si] -20[Ni]-22[Cr]-12[V]+12[Mo]，

Tr=830-110[C]-50[Mn]+41.6[Si]-35[Ni]-60[Cr]-40[V]-20[Mo]。

4. the high toughness hard low temperature bainite hot work die steel according to claim 1, wherein the structure of the low temperature bainite hot work die steel is composed of a low temperature bainite structure and undissolved carbides.

5. The high toughness, hard low temperature bainite hot work die steel according to claim 4, wherein the low temperature bainite structure includes bainitic ferrite and thin film retained austenite.

6. The high strength and toughness hard low temperature bainite hot work die steel according to claim 4, wherein the content of the low temperature bainite structure is not less than 75%.

7. The high strength and toughness hard low temperature bainite hot work die steel according to any one of claims 1 to 6, wherein the tensile strength of the hot work die steel is not lower than 1900 MPa.

8. The high strength and toughness hard low temperature bainite hot work die steel according to any one of claims 1 to 6, wherein the hardness of the hot work die steel is not lower than 53.0 HRC, and the unnotched impact power is not lower than 500J.

9. A method for preparing high strength and toughness hard low-temperature bainite hot-work die steel, which is used for preparing the low-temperature bainite hot-work die steel as claimed in any one of claims 1 to 8, and is characterized by comprising the following steps:

A. smelting: feeding according to the design requirements of the components of the steel, smelting in a vacuum induction furnace and casting into steel ingots,

the steel comprises the following components in percentage by mass: c0.45 to 0.55 percent, si 1.2 to 1.50 percent, mn 0.20 to 0.50 percent, cr 2.90 to 3.50 percent, mo 1.10 to 1.80 percent, V0.70 to 1.30 percent, ni 0.80 to 1.20 percent, P <0.01 percent and S <0.005 percent, and the balance of Fe and inevitable impurities;

B. hot rolling and annealing: hot rolling the steel ingot, annealing the hot-rolled sample, and finally air-cooling to room temperature;

C. spheroidizing annealing: heating the sample subjected to the heat treatment in the step B to 830 to 870 ℃, preserving heat for 1 to 1.5 hours, cooling to 740 to 770 ℃ along with the furnace, preserving heat for 2 to 2.5 hours, finally cooling to 500 ℃ along with the furnace, and taking out the sample from the furnace for air cooling;

D. isothermal quenching treatment: heating the sample subjected to the heat treatment in the step C to 990-1050 ℃, preserving the heat for 20-30 min, then quickly putting the sample into a salt bath furnace at 280-350 ℃, quenching the sample for 1-3 h at medium temperature, and then air cooling the sample to room temperature;

E. tempering treatment: and D, heating the sample subjected to the heat treatment in the step D to 555 to 565 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, air-cooling, then heating to 575 to 585 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, and air-cooling.

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