CN111500928B

CN111500928B - Low-temperature high-toughness high-temperature high-strength and high-hardenability hot die steel and preparation technology thereof

Info

Publication number: CN111500928B
Application number: CN202010338181.4A
Authority: CN
Inventors: 黄进峰; 张津; 赵超; 张�诚
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2020-04-26
Filing date: 2020-04-26
Publication date: 2021-06-18
Anticipated expiration: 2040-04-26
Also published as: CN111500928A

Abstract

The invention belongs to the field of die steel, and particularly relates to low-temperature low-toughness high-temperature high-strength high-hardenability hot die steel which comprises the following components: c: 0.15-0.35%, Si: 0.40-0.90%, Mn: less than or equal to 0.80 percent, Cr: 1.50-2.40%, Ni: 2.50 to 4.50 percent of Mo, 1.00 to 1.60 percent of Mo, 0.10 to 0.40 percent of V, 0.20 to 0.90 percent of W, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of matrix Fe and inevitable impurities, wherein the mass percent is the above percentage. After quenching and tempering, the low-temperature impact energy of the V-shaped hole at the temperature of-40 ℃ of the material can reach more than 30J, the high-temperature strength at the temperature of 700 ℃ can reach more than 380MPa, the hardenability can reach more than 200mm, and the internal and external uniformity of the structure is ensured. The material of the invention can be suitable for hot working dies requiring special working conditions of low temperature, high toughness, high temperature, high strength and high hardenability.

Description

Low-temperature high-toughness high-temperature high-strength and high-hardenability hot die steel and preparation technology thereof

Technical Field

The invention belongs to the technical field of die steel, and particularly relates to low-temperature high-toughness high-temperature high-strength high-hardenability hot die steel and a preparation technology thereof.

Background

Hot work die steel is mainly classified into a hot forming die, a hot extrusion die and a pressure casting die, and these dies are subjected to rapid cooling and rapid heating temperature changes in addition to high temperature and high load under actual conditions, so that thermal fatigue cracks are easily caused, and the service life of the hot work die steel is directly influenced by the level of thermal fatigue resistance (document 1). Literature research has shown (literature 2) that increasing the high temperature strength and toughness of a material can increase the fatigue resistance of the material and thus increase the fatigue life, since high strength can reduce the plastic strain amplitude per thermal cycle and better toughness relaxes local stress concentration; further, it is considered that (document 3), the fatigue crack initiation of the die steel can be delayed by the high strength and the thermal fatigue crack propagation can be delayed by the high ductility. In addition, the temperature in winter of many areas can be as low as-40 ℃, and the-40 ℃ low-temperature toughness of the material needs to be improved to ensure that the service of the die material is safer. In addition, the size of a plurality of large hot-work die products is larger, so that the hot-work die steel needs high hardenability to ensure that the internal and external structure properties of the die are consistent. In summary, the following new requirements are proposed to improve the service life of hot-work die steel: the high-temperature strength at 700 ℃ needs to be improved to 350MPa, the impact energy of a V-shaped hole at minus 40 ℃ needs to be more than 30J, and the hardenability reaches the level of the existing traditional hot-work die steel.

The hot traditional die steel is mainly divided into three types: high alloy hot die steel, medium alloy hot die steel and low alloy hot die steel. The document (document 4) reports that high-alloy hot-work die steel 3Cr2W8V has a tensile strength of 415MPa at a high temperature of 700 ℃; the high-temperature tensile strength of the medium-high alloy hot-work die steel H13 at the high temperature of 700 ℃ is 292 MPa; the low-alloy hot-work die steel 5CrMnMoSiV steel has the tensile strength of 137MPa at the high temperature of 700 ℃. The room temperature impact toughness of the 3Cr2W8V and H13 materials are respectively 13J and 21J, and the room temperature impact toughness of the 5CrMnMoSiV steel is 34.7J. Thus, the-40 ℃ low temperature impact toughness of the three materials will be lower than their room temperature, typically only 1/2-1/3 at room temperature. In conclusion, the existing hot work die steel cannot meet the requirements of high toughness at low temperature and high strength at high temperature at the same time.

With the development of economy and industry, the service conditions of the die are increasingly harsh, and meanwhile, in order to ensure that the hot-work die steel can be safely used in extremely cold regions, the modern manufacturing industry puts higher requirements on the high-temperature strength, the low-temperature toughness and the hardenability of the die. Therefore, hot die steel having high toughness at low temperature, high strength at high temperature and high hardenability at high temperature is required.

Document 1: the research status and development trend of the thermal fatigue performance of hot work die steel [ J ] metal heat treatment [ 2008(12): 1-6).

Document 2: differences in thermal fatigue mechanism and thermal fatigue resistance of Liujianhong, 3Cr2W8V, 4Cr5MoSiVl steels [ J ] proceedings of the institute of Engineers, Anhui, 1988(2):1-9.

Document 3: liu Jianhong. Hot work die steel 3Cr2W8V4Cr5MoSiV1 thermal fatigue mechanism research [ D ].1987.

Document 4: zhuzongyuan, China hot work die steel performance data set (II) [ J ] mechanical engineering material, 2001(3).

Disclosure of Invention

Technical problem to be solved by the invention

Aiming at the defects of the prior art, the safety of the hot work die steel in service in a low-temperature environment adopts a multi-component strengthening principle, and the invention provides the hot die steel with low temperature, high toughness, high strength and high hardenability.

Means for solving the technical problem

In order to solve the problems, the invention provides a low-alloy hot die steel with low-temperature high toughness, high-temperature high strength and high hardenability, which comprises the following components: c: 0.15-0.35%, Si: 0.40-0.90%, Mn: less than or equal to 0.80 percent, Cr: 1.50-2.40%, Ni: 2.50 to 4.50 percent of Mo, 1.00 to 1.60 percent of Mo, 0.10 to 0.40 percent of V, 0.20 to 0.90 percent of W, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and the balance of matrix Fe and inevitable impurities, wherein the mass percent is the above percentage.

In one embodiment, in addition to the above main components, 0.01 to 0.03% of Zr, 0.10 to 0.50% of Co, 0.001 to 0.005% of B, 0.01 to 0.05% of Nb, or 0.01 to 0.10% of Re may be added in terms of mass ratio.

According to a second aspect of the present invention, there is provided a method of manufacturing the above hot die steel, comprising the steps of: (1) smelting process; (2) homogenizing annealing and forging; (3) annealing process after forging; (4) and (5) hardening and tempering.

In one embodiment, the smelting process comprises the following steps of smelting by an electric furnace, external refining, vacuum degassing (EAF + LF + VD) and slag remelting (ESR), wherein the components in the smelting process are as defined in claim 1 or 2.

In one embodiment, in the smelting process, the burnt rare earth still needs to be supplemented in the electroslag remelting process, and the content is ensured to be more than 0.01 percent.

In one embodiment, in the homogenizing annealing and forging process, the steel ingot in the step (1) is heated for at least 5 hours to 1200-; when forging and cogging, the forging and drawing temperature is 1050 and 1130 ℃, the final forging temperature is more than or equal to 850 ℃, the upsetting and drawing length is 1-3 times, and the upsetting ratio is more than 2.

In one embodiment, in the homogenizing annealing and forging process, after forging and cogging, the high-precision forming of the bar can be performed by GFM precision forging, the forming of other modules can be performed by a hydraulic hammer or an oil press, the GFM precision forging heating temperature is 900-; the heating temperature for forming the hydraulic hammer or the oil press is 1150-1200 ℃, the initial forging temperature is 1130-1160 ℃, and the final forging temperature is not less than 850 ℃.

In one embodiment, in the annealing process after forging, the forge piece in the step (2) is immediately put into a furnace, heated to 850-900 ℃ at a heating rate of not more than 100 ℃/h, then kept at the temperature for 6-8h, and then taken out of the furnace to be cooled to below 500 ℃ to obtain the prefabricated piece.

In one embodiment, in the quenching and tempering step, the prefabricated part in the step (3) is quenched and tempered, wherein the quenching process comprises the steps of heating the prefabricated part to 920-.

In one embodiment, tempering may be performed twice, the temperature is selected based on the desired mechanical properties of the final product, the performance parameters of the product are then tested, and the temperature and time for the second tempering are determined based on the test results.

The invention has the advantages of

Compared with the existing hot die steel, the material of the invention adopts low alloy components, the high-temperature strength of the material reaches the high-temperature strength of medium-high carbon hot die steel, the low-temperature toughness at minus 40 ℃ reaches the low-temperature toughness of low-carbon hot die steel, and the hardenability of the material is also excellent.

Further features of the present invention will become apparent from the following description of exemplary embodiments.

Drawings

FIG. 1 shows the microstructure of the quenched and tempered steel of the present invention.

Detailed Description

One embodiment of the present disclosure will be specifically described below, but the present disclosure is not limited thereto.

The specific principle is as follows:

1. the invention adopts low alloy element chemical components in component design, forms dispersed carbide by depending on alloy elements such as Cr, Mo, W, V and the like and C, and can ensure the high-temperature strength of the material by keeping good orientation relation with a matrix, and the strength of the material depends on the common reinforcement of W/Mo. The high temperature strength of the material of the present invention is shown in Table 2.

2. Because the carbon content of the material is low and the Ni content is high, the structure after the quenching and tempering treatment is lath martensite instead of acicular martensite, and the low-temperature toughness is good. Meanwhile, rare earth, Mn, Si and other alloy elements are added to improve the purification of the material, so that the toughness of the material is improved, and the specific-40 ℃ low-temperature toughness data is shown in Table 3.

3. The hardenability of the material can be obviously improved by adding a proper amount of W, Mo, Ni, Cr, Mn and other alloy elements into the material, and the specific hardenability data is shown in Table 4.

The actions and the ranges of the contents of the respective constituent elements of the steel of the present invention will be further described below, and in the following description, the amounts of the elements added are expressed in mass ratio (%):

c: carbon is the most basic element in steel and determines the hardness and strength of the martensite after quenching. The low-carbon steel has a quenching structure of dislocation martensite, not only has high toughness, but also has certain plastic deformation capacity, and can reduce the formation of quenching cracks. When the carbon content is low, poor hardenability and insufficient strength are caused, so that the carbon content needs to be controlled to exceed 0.15%, and when the carbon content exceeds 0.35%, acicular martensite is formed after quenching, stress is large, and low-temperature toughness is reduced, so that the carbon content is designed as follows: 0.15-0.35%.

Ni: the nickel can improve the hardenability and low-temperature toughness of the steel, and when Ni is combined with Cr, W and Mo elements, the hardenability can be improved, so that the large-section steel can obtain better strength and plasticity matching after quenching and tempering. When the Ni content is less than 2.5%, the material has insufficient low-temperature toughness at-40 ℃, but the addition of Ni in excess of 4.5% causes precipitation of carbides along austenite grain boundaries upon quenching, adversely affecting the corrosion resistance of the steel. Therefore, the Ni content is designed as follows: 2.50-4.50%.

Cr: chromium is a medium carbide former, and of all the carbides, chromium carbide is the finest one, which is uniformly distributed in the steel volume, and therefore has high strength, hardness, yield point and high wear resistance. When Cr is more than 2.4%, the toughness and precipitated phases can be adversely affected, especially the low-temperature toughness; when the content of Cr is less than 1.5%, the corrosion resistance and oxidation resistance of the material are affected, so that the ratio of Cr: 1.50-2.40%.

Mo: the molybdenum has good effect of refining crystal grains, improves the strength of the steel without reducing the plasticity, and can improve the impact toughness of the steel. And the hardenability can be obviously improved by combining with Cr and Ni. However, when the Mo content is less than 1.0%, the grain size is large, and when the Mo content is more than 1.6%, a ferrite delta phase or other brittle phases are easy to appear, so that the low-temperature toughness at-40 ℃ is less than 30J, and therefore, the Mo content is selected to be 1.00-1.60%.

V: vanadium is a strong carbide forming element, the stability of carbide of the vanadium can be improved, austenite grains are effectively prevented from growing large, a refined martensite structure is obtained after quenching, the tempering toughness is improved, researches show that the toughness is adversely affected when the content of V is more than 1%, hardenability is adversely affected when the content of V is too high, and the depth of a hardening-through layer in an end quenching test is less than 200 mm. In order to ensure the toughness and hardenability of the material, the content of V is designed as follows: 0.10-0.40%.

W: tungsten not only improves the hardenability of the material, but also improves the heat strength, heat stability and high-temperature strength of the steel. The method comprises the steps of improving the red hardness of a steel matrix through solid solution and forming special carbide (M)₂C, MC) plays a role in secondary hardening. Tungsten and molybdenumThe heat stability of the steel can be improved by matching, Mo is an alloy element easy to oxidize, the oxidation and volatilization of Mo can be inhibited by adding tungsten, but when the content of tungsten exceeds 1.0 percent, the heat strength can not be obviously improved, and the low-temperature toughness of the steel can be reduced, so that the content of W in the steel is controlled to be 0.20-0.90 percent.

Zr: zirconium is a powerful deoxidizing and denitrifying element in the steelmaking process, and a small amount of Zr is added to combine with oxygen and nitrogen in the smelting process to form oxides and nitrides which are distributed in a fine and dispersed mode in a matrix, so that the grain structure can be refined. Zr element can be combined with impurity element S to generate sulfide, so that the hot brittleness of the steel is prevented. Therefore, in order to obtain a finer and purer structure steel, the Zr content can be controlled as follows: 0.01 to 0.04 percent.

Si: can be used as a reducing agent and a deoxidizing agent in the steelmaking process, can improve the annealing, normalizing and quenching temperatures, and can improve the hardenability in the hypoeutectoid steel. Moreover, the silicon can obviously improve the elastic limit, yield point and tensile strength of the steel, and simultaneously, the content of the silicon is improved, so that a carbide-free bainite structure consisting of lath-shaped ferrite and residual austenite films among laths of the lath-shaped ferrite can be obtained in the transformation process of the structure, and the structure has high strength, high hardness and higher low-temperature impact toughness, so that the content of the silicon is 0.40-0.90 percent.

Mn: under a proper amount, the manganese content is increased, so that the strength and the hardness of the steel can be improved, the effects of deoxidation and desulfurization are achieved, a part of nickel can be replaced, the hardenability of the material is improved, and the material cost is reduced. However, the Mn content is too high, the corrosion ability and weldability deteriorate, so that the Mn content does not exceed 0.80%.

Re: the rare earth can control the form of sulfide in steel, and simultaneously deoxidize and desulfurize, thereby improving the transverse performance and the low-temperature toughness. It also has a dispersion hardening effect in low-sulfur steels. Therefore, 0.01-0.03% of Re can be added to deoxidize, desulfurize and purify the steel liquid and improve the toughness of the steel.

Co: cobalt can form a continuous solid solution with iron as well as nickel and manganese, can hinder and delay the precipitation and aggregation of other alloy carbides in the tempering process, and can obviously improve the heat strength of the material, but cobalt element reduces the hardenability of martensitic steel, so excessive addition is not suitable, so the design amount is as follows: 0.10-0.50%.

B: in a certain range, the hardenability of boron is extremely strong, but the hardenability is not greatly improved after the hardenability exceeds 0.005 percent; the steel plays a role in strengthening grain boundaries in steel, and the high-temperature strength of the material can be remarkably improved, so the design amount is as follows: 0.001-0.005%.

S, P As impurity elements, all have great adverse effects on the toughness of the material. Therefore, the S, P content should be reduced, so the S, P content is controlled to be less than 0.02%.

Fe: as a matrix element, scrap steel and pure iron can be determined and selected according to the specific use condition of the barrel, the requirements of purity and the like.

The invention is key improvement from the aspect of component content and process, and the components are as follows: m is formed by the composite action of elements such as Cr, Mo, W, V and the like₂C. MC type alloy carbide, which can keep the coherent orientation relation with the matrix to high temperature, thereby obtaining high temperature and high strength; the low-carbon high-Ni design is adopted to form a lath martensite structure so as to obtain low-temperature high toughness, and alloy elements such as rare earth, Mn, Si and the like are added to improve the material purification, so that the toughness of the material can be further improved; proper amounts of W, Mo, Ni, Cr, Mn and other elements are used to ensure hardenability. The process is as follows: aiming at the characteristics of the large-size steel ingot of the steel, the annealing and tempering processes (temperature and time) after forging are adjusted, so that the steel ingot can obtain the best performance matching.

Through the key improvement, the problem that the low-temperature high-impact toughness and the high-temperature high strength of hot die steel are difficult to combine in the prior art is solved, the hardenability can reach the level of H13 steel, and the hot die steel is suitable for preparing large dies.

The invention provides low-alloy hot die steel with low temperature, high toughness, high temperature, high strength and high hardenability, and the specific preparation process comprises the following steps:

(1) smelting by processes of an electric furnace, external refining, vacuum degassing (EAF, LF and VD), slag remelting (ESR) and the like, wherein the smelting comprises the following components in percentage by mass:

c: 0.15-0.35%, Si: 0.40-0.90%, Mn: less than or equal to 0.80 percent, Cr: 1.50-2.450%, Ni: 2.50 to 4.50 percent of Mo, 1.00 to 1.60 percent of Mo, 0.10 to 0.40 percent of V, 0.20 to 0.90 percent of W, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, and Zr: 0.01-0.03%, Co 0.10-0.50%, B0.001-0.005%, Nb 0.01-0.03%, Re: 0.01-0.10 percent, and the balance of matrix Fe. The burnt rare earth still needs to be supplemented in the electroslag remelting process, and the content is ensured to be more than 0.01 percent, because the rare earth is easy to volatilize in the electroslag remelting process.

(2) Homogenizing annealing and forging process:

heating the steel ingot in the step (1) for at least 5h, raising the temperature to 1250-. Then GFM finish forging or other forging forming is carried out according to the requirement. The precision forging heating temperature is 900-1050 ℃, the initial forging temperature is 850-950 ℃, and the final forging temperature is more than or equal to 800 ℃; the heating temperature for forming the hydraulic hammer or the oil press is 1150-1200 ℃, the initial forging temperature is 1130-1160 ℃, and the final forging temperature is not less than 850 ℃.

(3) Annealing process after forging: and (3) immediately feeding the steel ingot subjected to the finish forging in the step (2) into a furnace, heating to 850-870 ℃ at a heating rate of not more than 100 ℃/h, then preserving heat for 6-8h, then cooling the steel ingot to below 500 ℃, discharging the steel ingot out of the furnace, and carrying out heap cooling.

(4) And (3) quenching and tempering: and (3) quenching and tempering the prefabricated steel ingot in the step (3), wherein the quenching process comprises the steps of heating the material to 920-980 ℃, then carrying out heat preservation for 1-6h, then carrying out water cooling or oil cooling to ensure that the temperature of the material is about 50-150 ℃, then immediately carrying out tempering for one to two times, selecting the tempering temperature according to the mechanical property required by the final product, for example, tempering at 580 ℃ for 4-10 h, then testing the hardness and toughness and the like, and determining the second tempering temperature and time according to the test result.

Examples

The present invention is described in more detail by way of examples, but the present invention is not limited to the following examples. Unless otherwise specified, "part" means "part by mass".

The specific alloy element compositions of examples 1 to 6 are shown in Table 1.

A preparation method of low-temperature high-toughness high-temperature high-strength and high-hardenability hot die steel comprises the following specific steps:

(1) the formulations were prepared according to the chemical compositions of examples 1-6 in Table 1. Composition (I)

(2) Carrying out electric furnace-refining (LF + VD) and slag remelting on the materials prepared in the material preparation (1) and other processes for smelting.

(3) Heating the electroslag ingot obtained in the step (2) for at least 5h, heating to 1260 ℃, preserving heat for 8h, then cooling to 1200 ℃ for cogging and forging, wherein an oil press is adopted for cogging, the initial forging temperature is 1200 ℃, the final forging temperature is 850 ℃, upsetting is repeatedly carried out for 1 time, and the upsetting ratio is more than 2. After cogging, the material is heated to 1160-850 ℃ at a speed of 100 ℃/h in a furnace, then heat preservation is carried out for 1h, then a precision forging machine is adopted for material forming, the initial forging temperature is 1160 ℃, and the final forging temperature is 800 ℃.

(5) And (4) immediately putting the steel ingot subjected to the finish forging in the step (4) into a furnace, heating to 860 ℃ at a heating rate of not more than 100 ℃/h, then preserving heat for 6h, then cooling the steel ingot in the furnace to below 500 ℃, discharging the steel ingot out of the furnace, and carrying out heap cooling.

(6) And (3) quenching and tempering the prefabricated steel ingot in the step (5), wherein the quenching process comprises the steps of heating the material to 930-.

And (3) performance testing: the mechanical properties and hardenability of the low-temperature high-toughness high-temperature high-strength and high-hardenability hot die steels of examples 1-6 were tested, and the materials of comparative examples 1, 2 and 3 were H13 steel, 5CrMnMoSiV and 3Cr2W8V steel, respectively. Wherein hardenability was tested using examples 1 and 4 and compared to H13 steel. The relevant test standards and specific test data are shown in tables 3-4 below:

(1) the following examples and comparative examples were tested according to HB 5278-.

(2) The high-temperature tensile mechanical property test method refers to GB/T4338-2006, and the tensile strength and the yield strength at 700 ℃ are tested. The room temperature tensile mechanical property test method refers to GB/T228.1-2010.

(3) Hardenability reference end-quench test method ASTM A255-02.

From a comparison of tables 3-4, the following conclusions can be drawn:

(1) table 3 shows that the high-temperature strength of the material of the invention at 700 ℃ is higher than that of H13 and 5CrMnMoSiV hot-work die steel, and some examples are even higher than that of high-alloy hot-work die steel 3Cr2W8V steel, which indicates that the steel of the invention has excellent high-temperature strength. The normal temperature impact toughness of the material of the invention is higher than that of the comparative examples 1, 2 and 3, the impact toughness at 40 ℃ below zero of the material of examples 1 to 3 of the invention is even higher than that of the hot die steel of the three comparative examples, and the low temperature toughness of the material of the invention is much higher than that of the comparative examples because the low temperature toughness of the material is usually much lower than that of the normal temperature. The room temperature tensile strength of the steel can be adjusted in the range of 1200-1600 MPa by adjusting the heat treatment process according to the working condition requirement, and meanwhile, the high temperature strength is ensured to be basically kept stable.

(2) As can be seen from Table 4, the hardness of the material with the upper and lower limit components of the invention decreases to a considerable extent with increasing distance from the end quenching surface, which shows that the hardenability of the material of the invention can reach the level of H13 steel.

TABLE 1 specific ingredient Table for each example

Note: (1) example 1 and example 2 the upper and lower limits of the composition of the material of the invention were investigated in comparison.

(2) Examples 3, 4 and 5 comparative studies of the Cr, Mo and Ni elements of the inventive materials were carried out.

(3) Examples 2, 3 and 5 the V and W elements of the inventive material were investigated in comparison.

(4) Example 2 and example 6 compare and study the trace elements Re, Nb, Zr, Co and B added in the material of the invention.

TABLE 2 Heat treatment Process for inventive steels

TABLE 3 TABLE of tensile strength at room temperature, high temperature and Low temperature impact energy for each example and comparative example

Note: the data of-40 ℃ low temperature impact toughness of comparative examples 1, 2 and 3 are not found, but the room temperature toughness is lower than that of the material of the invention.

TABLE 4 table of end quench hardenability of examples and comparative examples

Note: the hardness of the material of the invention decreases by an amount equivalent to that of H13 steel as the distance from the end quenching surface increases.

Industrial applicability

The material of the invention can be suitable for special working conditions requiring low temperature, high toughness, high temperature, high strength and high hardenability, and has good industrial practicability.

The present invention is not limited to the above embodiments, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The utility model provides a have low temperature high tenacity, high temperature high strength and high hardenability hot die steel which characterized in that: the hot die steel comprises the following components: c: 0.15-0.35%, Si: 0.40-0.90%, Mn: less than or equal to 0.80 percent, Cr: 1.50-2.40%, Ni: 2.50-4.50%, Mo 1.00-1.60%, V0.10-0.40%, W0.20-0.90%, P is less than or equal to 0.02%, S is less than or equal to 0.02%, Zr: 0.01-0.03%, Co: 0.10-0.50%, B: 0.001-0.005%, Nb: 0.01-0.05%, RE: 0.01-0.10 percent, and the balance of matrix Fe and inevitable impurities, wherein the mass percent is the above percent.

2. A method of producing hot die steel as claimed in claim 1, comprising the steps of:

(1) smelting process;

(2) homogenizing annealing and forging;

(3) annealing process after forging;

(4) and (5) hardening and tempering.

3. The method for producing hot die steel as claimed in claim 2, wherein the smelting is carried out by an electric furnace, external refining, vacuum degassing and electroslag remelting, and the contents of the respective components in percentage by mass in the smelting are as defined in claim 1.

4. The method for producing hot die steel as claimed in claim 3, wherein in the smelting process, the burnt rare earth is still required to be supplemented in the electroslag remelting process, and the content is ensured to be more than 0.01%.

5. The method for preparing hot die steel as claimed in claim 2, wherein in the homogenizing annealing and forging process, the steel ingot in the step (1) is heated for at least 5h to 1200-1250 ℃, and is kept warm for 15-25h, and then is cooled to the heating temperature 1130-1200 ℃, and is kept warm for 2-3 h; when forging and cogging, the forging and drawing temperature is 1050 and 1130 ℃, the final forging temperature is more than or equal to 850 ℃, the upsetting and drawing length is 1-3 times, and the upsetting ratio is more than 2.

6. The method for preparing hot die steel as claimed in claim 2, wherein in the homogenizing annealing and forging process, after forging and cogging, the high-precision forming of the bar material can be performed by GFM precision forging, the forming of other modules can be performed by hydraulic hammer or oil press, the heating temperature of GFM precision forging is 900-; the heating temperature for forming the hydraulic hammer or the oil press is 1150-1200 ℃, the initial forging temperature is 1130-1160 ℃, and the final forging temperature is not less than 850 ℃.

7. The preparation method of the hot die steel as claimed in claim 2, wherein in the annealing process after forging, the forge piece in the step (2) is immediately put into a furnace, heated to 850-900 ℃ at a heating rate of not more than 100 ℃/h, then kept warm for 6-8h, and then taken out of the furnace to be cooled to below 500 ℃ to obtain a prefabricated piece.