CN110129678B - Economical fine-grain high-toughness hot-work die steel and preparation method thereof - Google Patents
Economical fine-grain high-toughness hot-work die steel and preparation method thereof Download PDFInfo
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Abstract
The invention relates to economical fine-grain high-toughness hot-work die steel GBL64 and a preparation method thereof, belonging to the technical field of alloy steel manufacture. The formula of the material comprises the following elements in percentage by weight: c: 0.25 to 0.40 percent; si: 0.15% -1.2%; mn: 0.2 to 0.9 percent; cr: 3% -6%; mo: 1.0% -3.5%; w: 0.6 to 2.2 percent of iron and the balance of iron. The preparation method comprises the following steps: smelting, electroslag remelting, high-temperature homogenization, upsetting, drawing, stress relief annealing, superfine treatment and thermal refining. The obtained economic hot-work die steel has the grain size as small as 0.5-3.5 microns, and has excellent strength and toughness, high-temperature frictional wear performance, heat strength, heat stability, thermal fatigue performance and high heat conductivity.
Description
Technical Field
The invention relates to economical fine-grain high-toughness hot-work die steel GBL64 and a preparation method thereof, belonging to the technical field of alloy steel manufacture.
Background
The AISI H13 steel is one of the most widely used die steels in the current die industry, the high-temperature friction wear performance, the high-temperature heat strength, the heat stability, the thermal fatigue performance and the heat conductivity of the product still can not meet the harsh conditions of the current high-strength steel hot stamping and can not meet the requirements of the die industry gradually, and related substitute products such as 1.2367, 8418/DIEVAR and 3Cr2W8V with high toughness are suitable for die-casting dies, QRO90, HTCS-130 and DHA-THERMO are used for hot stamping dies, and 5CrNiMo is used for die-casting and hot die forging dies, but have disadvantages, such as insufficient toughness of QRO90, 1.2367, 5CrNiMo and 3Cr2W8V, insufficient heat strength of 8418/DIEVAR, and HTCS-130 has high heat conductivity but low heat strength.
For comprehensively prolonging the service life of the die, the common idea in the industry is to optimize alloy components and assist in relatively harsh production equipment and process conditions, but still not solve two problems: (1) the expensive V element still does not find a suitable substitute, because VC plays a role in secondary hardening in H13 series steel; (2) the general requirements for component optimization are strict, so that special steel enterprises with medium and low production capacity cannot produce similar products.
The common alloying idea is to reduce the chromium content to improve the thermal conductivity and increase the manganese content to improve the wear resistance, however, the chromium element is the core element of the Cr5 series die steel, and the oxidation resistance and the corrosion resistance are difficult to ensure by reducing the chromium; increasing the manganese element increases the risk of segregation of the manganese element of the large module. In addition, the current hot-work die steel mainly adopts free forging of large modules and assists in an ultrafine process, and the ultrafine precipitation structure can be obtained only by combining the large modules and the ultrafine process, but the intrinsic grain size determining the impact toughness and the comprehensive performance is not controlled yet. In addition, on the basis of grain refinement, whether the strength and the thermal stability can be improved at the same time, and good impact toughness can be maintained is a great problem which troubles the current mould material researchers.
The existing solutions are:
(1) patent document CN109518084A discloses a nitriding hot work die steel containing Al and Nb with high thermal conductivity and a preparation method thereof. Based on the 4Cr5MoSiV1 steel alloy components, the proportion of C to Cr, Mo and V is adjusted, Al and Nb are added, and the alloy content is 1.5-2.0% less than that of 4Cr5MoSiV1 steel. The steel of the invention has low cost, toughness equivalent to that of 4Cr5MoSiV1 steel, high thermal conductivity and nitriding property, and excellent wear resistance and tempering resistance. However, Al is easily formed in molten steel by heating Al2O3And the inclusion is increased, and in addition, the range of the Nb content is too large, so that the grain refining effect of the Nb addition is still not obvious.
(2) The patent document with publication number CN109136765A provides a hot die steel composition, and also discloses a preparation method of the hot die steel, which comprises the steps of batching, smelting, casting and electroslag remelting; high-temperature diffusion annealing and multidirectional forging hot working; performing preliminary heat treatment; and (4) final heat treatment. The prepared steel has the advantages of high thermal stability, high heat strength, good toughness and the like, and meets the high-temperature performance requirements of the current die manufacturing on the material. The invention is characterized in that the Mo content is increased to 3.2%, the heat intensity and the heat conductivity are improved, but the V content is still higher, and the cost is increased.
(3) The patent document with publication number CN109023153A provides an in-situ micro nano TiC particle strengthening and toughening forging hot-work die steel, and provides related component formulas; the process is to use nano TiC particles as a tissue regulator and a reinforcer of common carbon steel in forging hot work die steel to improve the toughness and the plasticity of the hot work die steel. However, TiN is easily formed by adding Ti, and the impact toughness of the steel is obviously reduced.
(4) Patent document CN108950413A proposes a die steel material and a preparation method and application thereof. The method comprises the steps of adding trace Ti element, optimizing a smelting process, carrying out heat treatment on the prepared hot work die steel by adopting solution treatment, spheroidizing annealing treatment, quenching treatment and tempering treatment, and smelting to obtain the novel hot work die steel material. The invention adopts titanium micro-alloying and subsequent heat treatment technology to remarkably reduce the thermal fatigue damage factor of the treated hot die steel and greatly improve the thermal fatigue resistance of the hot die steel. However, TiN is easily formed by adding Ti, and the impact toughness of the steel is obviously reduced.
(5) The patent document with publication number CN109280849A provides a high-performance hot-work die steel component and a manufacturing process thereof, wherein the low-carbon C is 0.20-0.30%, the Cr is reduced to 3.10-4.00%, the W is added by 0.50-1.00%, and the V is reduced to 0.10-0.30%. The invention adopts the alloying idea of reducing V and increasing W, thereby well improving the wear resistance and reducing the cost, but the Cr content is lower, so that the hot working performance of the steel grade is not too good.
(6) The patent document with publication number CN109321826A provides a high-manganese low-chromium hot-work die steel alloy component and a preparation method thereof, Ni is added to 0.80-3.00%, and the hardenability of the die steel is improved. The high-manganese low-chromium hot-work die steel provided by the invention has the advantages that the wear resistance is improved by increasing Mn, but the Mn element segregation is also obviously increased, so that the impact energy and the cold and hot fatigue performance are obviously reduced.
(7) The patent document with publication number CN108265232A adopts three steps of optimizing raw material formula, optimizing smelting process and optimizing heat treatment process, combines the high stability of H13, further improves the thermal fatigue resistance, the tempering resistance and the thermal strength and toughness, and obviously prolongs the service life of the die. However, the invention does not disclose the composition ratio of the alloy, so that the performance is difficult to judge.
(8) The patent document with publication number CN107974637A provides a hot work die steel alloy component formula, which adopts high Mo content of 2.80% -3.20%, and improves the heat strength and impact toughness of the die steel. The invention adopts the idea of high-carbon and high-Mo alloy, but still has no better V substitution scheme, and the cost of the die steel is still higher.
(9) The patent document with publication number CN108220815A provides a formula of a hot work die steel with high heat resistance and high impact toughness for hot forging, wherein the formula comprises 0.40-0.50% of high C, 3.00-3.80% of low Cr and 0.002-0.008% of rare earth elements. According to the invention, the rare earth is added to purify the grain boundary, so that the impact toughness is improved, but a rare earth adding method has no clear scheme or step.
(10) The patent document with publication number CN107974632A provides a formula of components of austenitic hot work die steel and a preparation method thereof. The steel fully utilizes austenite forming elements Mn and C to enlarge an austenite phase region so as to obtain a stable austenite structure; controlling the behavior of carbides and inclusions in the electroslag ingot by utilizing a directional solidification electroslag process; the grain size and the decomposition and precipitation behavior of carbides are controlled by a suitable heat treatment process. The single austenitic structure hot-work die steel prepared by the method can fully improve the heat resistance and the heat strength of the die steel, but cannot be applied to the H13 steel heat treatment process commonly used in the current market, so that the popularization difficulty is increased, and the yield strength of the austenitic structure is not good as that of the martensitic structure.
(11) The invention discloses a high-wear-resistance hot-work die steel and a preparation method thereof, and the high-wear-resistance hot-work die steel is disclosed in the patent document with the publication number of CN108070794A, wherein 1.8-2.5% of nano tungsten carbide is added into the steel, molybdenum is reduced to 0.8-1.0%, and 0.06-0.1% of cerium oxide is added into the steel, so that the heat strength, the grain size and the tissue purity of the hot-work die steel are fully improved. The ceramic composite powder is added to the die steel, so that the wear resistance of the die steel is improved, but the formula elements of the die steel are complex and various, and the production difficulty is increased.
(12) The patent document with publication number CN107904510A proposes a high-performance hot-work die steel alloy composition and a preparation method thereof, and the steel quality of purified hot-work die steel is added with Y0.01-0.03%, Ir 0.02-0.05% and Sr 0.01-0.03%. According to the invention, rare earth elements such as Y and Ir are added to improve the high-temperature strength of the die steel, and the control of the metallurgical properties of the rare earth is a great problem in the production of the die steel.
(13) The invention discloses a high-wear-resistance hot-work die steel and a preparation method thereof, and the high-wear-resistance hot-work die steel is prepared by adding 0.7-1.0% of carbon fiber composite material to reduce chromium to 1.0-1.5%, and adding 1.0-1.5% of nickel and 0.1-0.2% of tungsten to achieve the purposes of improving hardenability and heat strength. The invention needs to add carbon fiber, has higher cost, more Ni, increased cost and increased cracking tendency.
(14) The invention discloses a high-performance hot-working die steel for a large die-casting die and a manufacturing process thereof, and aims to realize the production of a large-section die-casting die by providing 0.20-0.30% of low C, 0.10-0.20% of added W and 0.02-0.04% of added Nb and realize the aims of high toughness and high heat strength. The heat strength of the die steel is improved by adding small amounts of W and Nb, but the content of W is low, and the grain refining effect of Nb is limited.
(15) The patent document with publication number CN107699789A provides a hot-work die steel for die casting of ZW866 with high toughness and high thermal stability, and the idea is to add a certain amount of Nb 0.005% -0.08%, improve the grain size and realize the purpose of improving the comprehensive performance. The addition of trace Nb element increases the control difficulty of the high-temperature hot working process, otherwise the effect of grain refinement is difficult to achieve.
Therefore, it is necessary to improve the prior art to obtain an economical fine-grained high-toughness hot-work die steel GBL64, which is low in cost and convenient to process.
Disclosure of Invention
The invention aims to provide economical fine-grain high-toughness hot-work die steel GBL 64.
The invention also aims to provide a preparation method of the economical fine-grain high-strength-and-toughness hot-work die steel.
The invention provides economical fine-grain high-toughness hot-work die steel GBL64, which comprises the following elements in percentage by weight: c: 0.25 to 0.40 percent; si: 0.15% -1.2%; mn: 0.2 to 0.9 percent; cr: 3% -6%; mo: 1.0% -3.5%; w: 0.6 to 2.2 percent of iron and the balance of trace unavoidable residual elements S, P, N, O, H.
Wherein S, P, N, O, H is an impurity with acceptable content.
More preferably, the formula comprises the following elements in percentage by weight:
c: 0.28 to 0.40 percent; si: 0.20 to 1.05 percent; mn: 0.25 to 0.85 percent; cr: 3.5% -5.5%; mo: 1.2% -3.4%; w: 0.8-2%, the balance of iron and S, P, N, O, H% trace residual elements. Wherein S, P, N, O, H is an impurity with acceptable content.
In a preferred embodiment of the invention, the formulation comprises the following elements in percentage by weight:
c: 0.28 percent; si: 1.05 percent; mn: 0.85 percent; cr: 3.6 percent; mo: 2.2 percent; w: 2%, the balance being iron, and trace residual elements S, P, N, O, H. Wherein S, P, N, O, H is an impurity with acceptable content, and the content is 1-200 ppm respectively.
The above mold steel is named as GBL64, G is named as "Gong", i.e. Shanghai engineering and technology university, BL is named as "Bi Long", i.e. Bi Long mold materials science and technology (Nantong) Co., Ltd., and 64 is the serial number of steel.
The preparation method of the economical fine-grain high-strength and high-toughness hot-work die steel adopts the following technical processes and steps:
1) smelting: the ingredients are put into an electric arc furnace for smelting, after the components of the smelted alloy reach the index, the molten steel is cast into a mold to form an electrode steel bar at the temperature of 1520-;
2) electroslag remelting: carrying out electroslag remelting on the electrode rod, filtering molten steel by a slag system, and slowly crystallizing and solidifying the molten steel into a circular steel ingot;
3) high-temperature homogenization: heating the round steel ingot to 1230-1265 ℃, keeping the temperature for (0.2-0.4) multiplied by D hours, wherein D is the diameter size (cm) of the steel ingot, enabling the components in the steel to be uniformly diffused, and then cooling to 1180 +/-10 ℃ of forging temperature;
4) upsetting: upsetting a steel ingot at 1180 +/-10 ℃ on a press along the height direction of the steel ingot to 40-50% of the height, then finishing, and heating for 2-4 hours at 1180 +/-10 ℃ in a return furnace; then carrying out second upsetting and finishing, returning to a furnace at 1180 +/-10 ℃ and preserving heat for 2-4 hours, and then carrying out third upsetting and finishing, wherein the final forging temperature is always kept above 870 ℃;
5) drawing out: drawing and forging the steel ingot subjected to the three-time repeated upsetting to the final size to obtain a module, keeping the finish forging temperature of 870-900 ℃, and cooling a pit to about 350 +/-10 ℃ after drawing;
6) stress relief annealing: heating the module to 850 +/-10 ℃, annealing for 10-16 hours, eliminating stress, and then cooling along with the furnace;
7) ultra-fining treatment: heating the module to 1060-1100 ℃, keeping the temperature for (0.2-0.25) x d hours, wherein d is the effective size cm of the forge piece, and water-quenching the module to room temperature; then heating to 860 +/-10 ℃ and keeping the temperature constant (0.4-0.6) x d hours, wherein d is the effective size cm of the forge piece; then furnace cooling is carried out to 740 +/-10 ℃, isothermal (0.9-1.2) x d hours are carried out, d is the effective size cm of the forge piece, and then furnace cooling is carried out to room temperature; when the forging piece is a round bar, the effective size is the diameter of the forging piece; when the forged piece is a plate, the effective size is the thickness of the forged piece;
8) quenching and tempering: heating the module to 1060 +/-10 ℃ and preserving heat for 1.5-2.5 hours, carrying out vacuum gas quenching to room temperature, tempering for 9-11 hours at 560 +/-10 ℃, air cooling to room temperature, tempering for 9-11 hours at 600 +/-10 ℃, and discharging for air cooling.
Preferably, in the step 3), during high-temperature homogenization, the circular steel ingot is heated to 1230-1265 ℃, the heat preservation time is (0.3-0.4) multiplied by D hours, D is the diameter size (cm) of the steel ingot, so that the components in the steel are uniformly diffused, and then the steel ingot is cooled to the forging temperature of 1180 +/-10 ℃.
Preferably, in the step 7), during the superfine treatment, the module is heated to 1060-1100 ℃ and is kept warm (0.2-0.25) for d hours, wherein d is the effective size cm of the forged piece, and water quenching is carried out to room temperature; then heating to 860 +/-10 ℃ and keeping the temperature constant (0.4-0.5) x d hours, wherein d is the effective size cm of the forge piece; and then, cooling the forging blank in the furnace to 740 ℃, keeping the temperature constant (0.9-1) x d hours, wherein d is the effective size cm of the forging, and then cooling the forging blank in the furnace to room temperature.
In the step 2), after most impure impurities in the electrode bar are removed through electroslag remelting and metallurgical slag system filtration, the molten steel is slowly crystallized and solidified to form a circular steel ingot.
Some terms to which the present invention relates are explained as follows.
Electrode bar: the base material for electroslag remelting is cast and formed after being smelted by an electric arc furnace.
Electroslag remelting: a method for melting by using resistance heat generated when an electric current is passed through slag as a heat source. The purpose is to improve the purity of metal and improve ingot casting crystallization.
Steel ingot: the molten steel is poured into a casting mould through a ladle and is solidified to form a steel ingot with a certain shape.
High-temperature homogenization: and (3) a heat treatment process for eliminating or reducing the structural state that the intragranular components are not uniform and deviate from balance under the actual crystallization condition by diffusion at high temperature, and improving the processing performance and the service performance of the alloy material.
Segregation: the distribution of each component element in the alloy is not uniform when the alloy is crystallized.
Upsetting: a forging step in which the height of the billet is reduced and the cross section is increased. The transverse mechanical property of the forge piece is improved, and the anisotropy is reduced; repeated upsetting and stretching are carried out to break up carbide in the alloy tool steel so as to ensure that the carbide is uniformly distributed.
Drawing out: all that is referred to is the forging process in which the cross-sectional area is reduced and the length is increased.
Ultra-fining: the alloy steel with carbide precipitation behavior is a heat treatment process which is convenient for processing and ensures good toughness, and the process heats steel to austenitizing temperature, namely, the steel is slowly cold cut along with a furnace, so that fine dispersion alloy carbide is uniformly precipitated and slowly grows into a ball shape. Then furnace cold cutting to room temperature. The steel after the superfine modification has good dimensional stability and machining performance, and the impact toughness is better after the subsequent quenching and tempering.
W, Mo is an effective element for comprehensively improving the wear resistance, high-temperature heat strength and heat conductivity, and the dispersion precipitation of WC can prevent the coarsening of crystal grains, the invention adds molybdenum and tungsten on the basis of 4Cr5MoSiV1 steel components to form a fine dispersed WC wear-resistant precipitation phase, the precipitation phase is intensively pinned around the fine crystal grains to prevent the growth of the crystal grains, and V element with relatively high cost is removed, and the strengthening of WC is used for replacing VC; therefore, the economical fine-grained hot-work die steel has lower cost, better wear resistance, high-temperature hot strength and toughness and better thermal conductivity than H13 and 8418 steel.
The grain size of the economical hot-work die steel GBL64 is as fine as about 0.5-3.5 mu m, and the economical hot-work die steel has excellent obdurability, high-temperature frictional wear performance, heat strength, heat stability, thermal fatigue performance and high heat conductivity.
The invention has the beneficial effects that:
(1) the impact toughness of the economical steel GBL64 exceeds the excellent level of H13, and the economical steel GBL64 has excellent high-temperature frictional wear performance, high-temperature heat strength, heat stability and thermal fatigue performance, and the heat conductivity of partial solid solution Mo and W elements is obviously improved.
(2) The grain size is refined from the component angle, so that the stable trial production of the steel is realized in the conventional large-scale production.
(3) The invention keeps the grain size of the hot work die steel to be improved to be more than ASTM 8 grade, the hardness is 42-48HRC range, and the impact energy of 7 multiplied by 10 multiplied by 55 unnotched style is more than 300J.
Drawings
FIG. 1 is a 1000-fold metallographic structure chart of die steel of example 1
FIG. 2 is a graph comparing the thermal stability of 600 ℃ tempered steel of example 1 die steel and H13 steel
FIG. 3 is a graph comparing the frictional wear coefficients of the die steel and H13 steel of example 1
FIG. 4 is a graph comparing the thermal conductivity of the die steel of example 1 and H13 steel
Detailed Description
The technical solution of the present invention will be described below with reference to specific examples.
Example 1
The economic fine-grain high-strength-and-toughness hot stamping die steel GBL64 comprises the following elements in percentage by weight:
c: 0.28 percent; si: 1.05 percent; mn: 0.85 percent; cr: 3.6 percent; mo: 2.2 percent; w: 2 percent; fe and trace residual element S, P, N, O, H as the balance.
In this example, the process and steps of GBL64 steel are as follows:
1) smelting: the ingredients are put into an electric arc furnace according to the proportion for smelting, and the alloy is cast into the product after the metallurgical components reach the requirements and the temperature is controlled to be about 1520-
And removing the defects of oxide skin, pits and the like after the electrode bar is demoulded.
2) Electroslag remelting: the electrode bar is subjected to electroslag remelting refining, most impure impurities in the electrode bar are removed through metallurgical slag system filtration, and then molten steel is slowly crystallized and solidified into 1 ton of circular steel ingot (the diameter is about 320 mm).
3) High-temperature homogenization: heating 1 ton steel ingot to 1245 +/-10 ℃, preserving heat for 11 hours, and then slowly cooling to 1180 +/-10 ℃ to prepare forging processing.
4) Upsetting: upsetting a 1180 ℃ steel ingot to 45% of the height along the height direction of the steel ingot, finishing (namely, flattening irregular edges by using a press), returning to 1180 +/-10 ℃ for heating for 3 hours, then carrying out second upsetting and finishing, returning to 1180 +/-10 ℃ for preserving heat for 3 hours, then carrying out third upsetting and finishing, and keeping the final forging temperature above 870 ℃.
5) Drawing out: and forging and drawing the steel ingot subjected to three times of repeated upsetting to obtain a final size of 165mm multiplied by 520mm multiplied by 1550mm (thickness multiplied by width multiplied by length), an effective size of 165mm, keeping the final forging temperature above 870 ℃, and cooling a pit to about 350 ℃ after drawing.
6) Stress relief annealing: and heating the module to 850 +/-10 ℃, annealing for 10 hours, eliminating stress, and then carrying out furnace cold cutting.
7) Ultra-fining treatment: heating the module to 1060 +/-10 ℃ and preserving heat for 3.5 hours, quenching the module to room temperature by water, then heating the module to 860 +/-10 ℃ and carrying out isothermal treatment for 7 hours, then cooling the module to 740 +/-10 ℃ in a furnace, carrying out isothermal treatment for 15 hours, and then cooling the module to room temperature along with the furnace.
8) Quenching and tempering: heating the module to 1060 +/-10 ℃ and preserving heat for 2 hours, carrying out vacuum gas quenching to room temperature, tempering for 10 hours at 560 ℃, air-cooling to room temperature, tempering for 10 hours at 600 +/-10 ℃, discharging and air-cooling.
The metallographic structure of the obtained die steel (1000 times) is shown in FIG. 1. The grain size is as fine as about 0.5 to 3.5 μm, ASTM grade 8 or more.
Performance testing
The GBL64 steel is subjected to performance tests, and the results are as follows:
(1) the hardness after hardening and tempering is 43 HRC;
(2) the impact energy of the unnotched 7 multiplied by 10 multiplied by 55 pattern is more than 300J;
impact energy of opening U-shaped notch 30J
(3) Thermal stability: the expression of thermostability here is: the GBL64 steel is kept at 600 ℃ for different times, and the hardness of the steel decreases to judge the heat stability. At the same time, comparative tests for thermal stability were carried out with H13 steel. The compositional comparisons are shown in table 1 (wt.%), and the thermal stability data are shown in table 2 (unit: HRC) and figure 2.
(4) The GBL64 steel and the H13 steel were subjected to a friction wear coefficient test, and the results are shown in FIG. 3.
(5) The GBL64 steel and the H13 steel were tested for thermal conductivity using a laser thermal conductivity meter, and the results of thermal conductivity as a function of temperature are shown in FIG. 4.
TABLE 1 comparison of the compositions of H13 and GBL64 steels
| Steel grade | C | Si | Mn | Cr | Mo | W | S | P |
| H13 | 0.42 | 1.05 | 0.85 | 5.2 | 1.25 | 0 | 0.002 | 0.006 |
| GBL64 | 0.28 | 1.05 | 0.85 | 3.6 | 2.2 | 2 | 0.002 | 0.009 |
TABLE 2600 ℃ hardness comparison of H13 and GBL64 steels for different tempering times
| |
5h | | |
|
|
30h | |
40h | |
| H13 | |||||||||
| 46 | 45 | 42 | 39 | 37 | 36 | 34 | 28 | ||
| GBL64 | 47 | 44 | 44 | 40 | 39 | 38 | 36 | 36 |
Claims (5)
1. The economical fine-grain high-strength-toughness hot-work die steel is characterized by comprising the following elements in percentage by weight: c: 0.25 to 0.40 percent; si: 0.15% -1.2%; mn: 0.2 to 0.9 percent; cr: 3% -6%; mo: 1.0% -3.5%; w: 0.6% -2.2%, the balance being iron, and trace residual elements S, P, N, O, H, wherein S, P, N, O, H is impurities with acceptable content; the preparation method comprises the following steps:
1) smelting: the ingredients are put into an electric arc furnace for smelting, after the components of the smelted alloy reach the index, the molten steel is cast into a mold to form an electrode steel bar at the temperature of 1520-;
2) electroslag remelting: carrying out electroslag remelting on the electrode rod, filtering molten steel by a slag system, and slowly crystallizing and solidifying the molten steel into a circular steel ingot;
3) high-temperature homogenization: heating the round steel ingot to 1230-1265 ℃, keeping the temperature for (0.2-0.4) multiplied by D hours, wherein D is the diameter size cm of the steel ingot, enabling the components in the steel to be uniformly diffused, and then cooling to 1180 +/-10 ℃ of forging temperature;
4) upsetting: upsetting a steel ingot at 1180 +/-10 ℃ on a press along the height direction of the steel ingot to 40-50% of the height, finishing, and returning to the furnace and heating for 2-4 hours; then carrying out second upsetting, finishing, returning to the furnace and preserving heat for 2-4 hours, and then carrying out third upsetting and finishing, wherein the final forging temperature is kept above 870 ℃ all the time;
5) drawing out: drawing and forging the steel ingot subjected to three times of repeated upsetting to the final size to obtain a module, keeping the finish forging temperature above 870 ℃, and cooling a pit to 350 +/-10 ℃ after drawing;
6) stress relief annealing: heating the module to 850 +/-10 ℃, annealing for 10-16 hours, eliminating stress, and then cooling along with the furnace;
7) ultra-fining treatment: heating the module to 1060-1100 ℃, preserving heat for (0.2-0.3) x d hours, wherein d is the effective size cm of the forge piece, and water quenching to room temperature; then heating to 860 +/-10 ℃ and keeping the temperature constant (0.4-0.6) x d hours, wherein d is the effective size cm of the forge piece; then furnace cooling is carried out to 740 +/-10 ℃, isothermal (0.9-1.2) x d hours are carried out, d is the effective size cm of the forge piece, and then furnace cooling is carried out to room temperature;
8) quenching and tempering: heating the module to 1060 +/-10 ℃ and preserving heat for 1.5-2.5 hours, carrying out vacuum gas quenching to room temperature, tempering for 9-11 hours at 560 +/-10 ℃, air cooling to room temperature, tempering for 9-11 hours at 600 +/-10 ℃, and discharging for air cooling.
2. The economical fine-grain high-strength-toughness hot-work die steel as claimed in claim 1, wherein the composition formula comprises the following elements by weight percent: c: 0.28 percent; si: 1.05 percent; mn: 0.85 percent; cr: 3.6 percent; mo: 2.2 percent; w: 2%, balance iron, and trace residual elements S, P, N, O, H, wherein S, P, N, O, H is impurities of acceptable content.
3. The economical fine-grained high-strength-toughness hot-work die steel as claimed in claim 1, wherein the circular ingot is heated to 1230-1265 ℃ during the high-temperature homogenization in step 3), the heat preservation time is (0.3-0.4) x D hours, D is the diameter size cm of the ingot, so that the components in the steel are uniformly diffused, and then the steel is cooled to the forging temperature 1180 +/-10 ℃.
4. The economical fine-grained high-strength-toughness hot-work die steel as claimed in claim 1, wherein in the step 7) of ultra-fining treatment, the die block is heated to 1060-1100 ℃ for heat preservation (0.2-0.25) x d hours, d is the effective size cm of the forged piece, and water quenching is carried out to room temperature; then heating to 860 +/-10 ℃ and keeping the temperature constant (0.4-0.5) x d hours, wherein d is the effective size cm of the forge piece; and then, cooling the forging blank in the furnace to 740 ℃, keeping the temperature constant (0.9-1) x d hours, wherein d is the effective size cm of the forging, and then cooling the forging blank in the furnace to room temperature.
5. The economical fine-grained high-strength-toughness hot-work die steel as claimed in claim 1, wherein the steel is embedded in a sand pit and cooled to room temperature after electroslag remelting in step 2).
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