CN110129678A - An economical fine-grained high-strength toughness hot work die steel and its preparation method - Google Patents

Abstract

The invention relates to an economical fine-grained high-strength toughness hot work die steel GBL64 and a preparation method thereof, belonging to the technical field of alloy steel manufacture. The composition formula includes the following elements by weight percentage: C: 0.25% to 0.40%; Si: 0.15% to 1.2%; Mn: 0.2% to 0.9%; Cr: 3% to 6%; Mo: 1.0% to 3.5%; W: 0.6% to 2.2%, the balance being iron. The preparation method includes: smelting, electroslag remelting, high-temperature homogenization, upsetting, elongation, stress relief annealing, superfine treatment, and quenching and tempering treatment. The obtained economical hot work die steel has a grain size as fine as about 0.5-3.5 μm, and has excellent strength and toughness, high temperature friction and wear performance, thermal strength, thermal stability, thermal fatigue performance and high thermal conductivity.

Description

An economical fine-grained high-strength toughness hot work die steel and its preparation method

technical field

The invention relates to an economical fine-grained high-strength toughness hot work die steel GBL64 and a preparation method thereof, belonging to the technical field of alloy steel manufacture.

Background technique

AISI H13 steel is one of the most widely used mold steels in the current mold industry. The high-temperature friction and wear properties, high-temperature thermal strength, thermal stability, thermal fatigue performance and thermal conductivity of this product still cannot meet the current high-strength steel hot stamping requirements. conditions, gradually unable to meet the needs of the mold industry, and related alternative products such as high-strength 1.2367, 8418/DIEVAR, 3Cr2W8V are suitable for die-casting dies, QRO90, HTCS-130 and DHA-THERMO are used for hot stamping dies, 5CrNiMo is used for die-casting and hot Forging dies, but each has its own disadvantages, such as QRO90, 1.2367, 5CrNiMo and 3Cr2W8V have insufficient toughness, 8418/DIEVAR has insufficient thermal force, and although HTCS-130 has high thermal conductivity, its thermal strength is very low.

In order to comprehensively improve the life of the mold, the general idea in the industry is to optimize the alloy composition and assist the relatively harsh production equipment and process conditions, but two problems have not been solved: (1) The expensive V element has not yet found a suitable replacement, because VC plays the role of secondary hardening in H13 series steel; (2) Composition optimization generally requires more stringent production equipment conditions, making it impossible for special steel enterprises with low and medium production capacity to produce similar products.

The general idea of alloying is to reduce chromium content to improve thermal conductivity, and increase manganese content to improve wear resistance. However, chromium element is the core element of Cr5 series die steel, and reducing chromium will make it difficult to guarantee oxidation resistance and corrosion resistance; Increasing manganese has the risk of increasing manganese segregation in large modules. In addition, the current hot work die steel is still dominated by free forging of large modules, assisted by the ultra-fine process. The combination of the two can obtain the ultra-fine precipitated structure, but the essential grain size that determines the impact toughness and comprehensive performance is still not clear. controlled. In addition, on the basis of grain refinement, whether high-strength and thermal stability can be improved at the same time, and good impact toughness can be maintained is a major problem that plagues current mold material researchers.

Existing solutions are:

(1) The patent document whose publication number is CN109518084A discloses a high thermal conductivity containing Al, Nb nitriding hot work die steel and its preparation method. Based on the alloy composition of 4Cr5MoSiV1 steel, the proportion of C, Cr, Mo and V is adjusted, and Al and Nb are added. 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 4Cr5MoSiV1 steel, high thermal conductivity and nitriding, excellent wear resistance and tempering resistance. However, the heating of Al is easy to form Al ₂ O ₃ in molten steel and increase inclusions. In addition, the range of Nb content is too large, and the effect of adding Nb on grain refinement is still not obvious.

(2) The patent document whose publication number is CN109136765A proposes a kind of hot work die steel composition, also discloses a kind of preparation method of hot work die steel, including batching, smelting, pouring, electroslag remelting; high temperature diffusion annealing, Multi-directional forging heat treatment; preliminary heat treatment; final heat treatment. The prepared steel has the advantages of high thermal stability, thermal strength and good toughness, and meets the high temperature performance requirements of current mold manufacturing for its materials. The special feature of this invention is that the content of Mo is increased to 3.2%, which improves the thermal strength and thermal conductivity, but the content of V is still high and the cost increases.

(3) The patent document with the publication number CN109023153A proposes a kind of in-situ trace nano-TiC particle toughening forging hot work die steel, and proposes the relevant composition formula; the process is to use nano-TiC particles in the forging hot work die steel As a structure regulator and strengthening agent of ordinary carbon steel, it can improve its toughness and plasticity. But the addition of Ti element is easy to form TiN, which will obviously reduce the impact toughness of steel.

(4) The patent document with publication number CN108950413A proposes a mold steel material and its preparation method and application. The method adds trace Ti elements, optimizes the smelting process, and adopts solid solution treatment, spheroidizing annealing treatment, quenching treatment, and tempering treatment to heat-treat the prepared hot-working die steel, and obtains a new type of hot-working die steel material by smelting. . The invention uses titanium microalloying and subsequent heat treatment technology to significantly reduce the thermal fatigue damage factor of the treated hot work die steel, and greatly improve its thermal fatigue resistance. But the addition of Ti element is easy to form TiN, which will obviously reduce the impact toughness of steel.

(5) The patent document with the publication number CN109280849A proposes a high-performance hot work die steel composition and its manufacturing process. V to 0.10 to 0.30%. The invention adopts the alloying idea of reducing V and increasing W, which improves the wear resistance and reduces the cost, but the low Cr content makes the hot workability of the steel not very good.

(6) The patent document whose publication number is CN109321826A proposes a high manganese and low chromium type hot work die steel alloy composition and its preparation method, adding Ni to 0.80-3.00%, which improves the hardenability of the die steel. The invention is a high-manganese and low-chromium hot work die steel. The increase of Mn will improve the wear resistance, but it will also significantly increase the segregation of Mn elements, resulting in a significant decrease in impact energy and thermal fatigue performance.

(7) The patent document with the publication number CN108265232A adopts a three-pronged approach of optimizing raw material formula, optimizing smelting process, and optimizing heat treatment process, combining the high stability of H13, further improving thermal fatigue resistance, tempering resistance, heat strength Toughness, significantly improving the service life of the mold. However, the invention does not disclose the alloy composition ratio, so it is difficult to judge its performance.

(8) The patent document with the publication number CN107974637A proposes a hot work die steel alloy composition formula, which uses a high Mo content of 2.80% to 3.20% to improve the thermal strength and impact toughness of the die steel. This invention adopts the idea of high carbon and high Mo alloy, but there is still no better V alternative, and the cost of die steel is still high.

(9) The patent document with the publication number CN108220815A proposes a composition formula of high thermal strength and high impact toughness hot work die steel for hot forging, adopting high C 0.40-0.50%, low Cr: 3.00-3.80%, and adding Rare earth elements 0.002 to 0.008%. In this invention, by adding rare earths to purify grain boundaries, the impact toughness will be improved, but there is still no clear plan and steps for adding rare earths.

(10) The patent document with publication number CN107974632A proposes a composition formula of austenitic hot work die steel and a preparation method thereof. The steel makes full use of the austenite forming elements Mn and C to expand the austenite phase region to obtain a stable austenite structure; uses the directional solidification electroslag process to control the behavior of carbides and inclusions in the electroslag ingot; utilizes appropriate heat treatment process to control grain size and carbide decomposition and precipitation behavior. Although the single austenitic hot work die steel prepared by the invention can fully improve the heat resistance and heat strength of the die steel, it cannot be applied to the general heat treatment process of H13 steel in the current market, making it more difficult to popularize. Another is that the yield strength of austenite is not as good as that of martensite.

(11) The patent document whose publication number is CN108070794A, the invention proposes a composition formula of high wear-resistant hot work die steel and its preparation method, the steel adds 1.8-2.5% of nano-tungsten carbide and reduces molybdenum to 0.8-1.0%, And adding 0.06-0.1% of cerium oxide can fully improve the thermal strength, grain size and tissue purity of hot work die steel. The addition of ceramic composite powder in this invention will help improve the wear resistance of die steel, but the formula elements of this patent are too complex and diverse, making production more difficult.

(12) The patent document whose publication number is CN107904510A proposes a high-performance hot work die steel alloy composition and its preparation method, adding Y 0.01-0.03%, Ir 0.02-0.05% and Sr 0.01-0.03% to purify hot work die steel of steel. The invention adds rare earth elements such as Y and Ir to improve the high temperature strength of the die steel, and the control of the metallurgical properties of the rare earth is a major problem in the production of the steel.

(13) The patent document with the publication number CN107400838A, which proposes a high wear resistance hot work die steel and its preparation method. The hot work die steel reduces chromium to 1.0-1.5% by adding carbon fiber composite material 0.7-1.0% %, add nickel 1.0-1.5% and tungsten 0.1-0.2% to achieve the purpose of improving hardenability and heat strength. This invention needs to add carbon fiber, the cost is higher, Ni is also more, the cost is increased, and the cracking tendency is increased.

(14) The patent document with the publication number CN107557667A, which proposes a high-performance hot-work die steel for large die-casting dies and its manufacturing process. In order to realize the production of die-casting dies with large cross-sections, a low C of 0.20% to 0.30% is proposed , adding W0.10% to 0.20%, and Nb 0.02% to 0.04% to achieve the purpose of high toughness and high thermal strength. The thermal strength of the die steel can be improved by adding a small amount of W and Nb, but the content of W is low, and the grain refinement effect of Nb is limited.

(15) The patent document with publication number CN107699789A proposes a high-toughness, high-thermal-stability ZW866 hot work die steel for die-casting. The idea is to add a certain amount of Nb 0.005%-0.08% to improve the grain size and improve the overall performance the goal of. The addition of a small amount of Nb element makes it more difficult to control the high-temperature thermal processing process, otherwise it will be difficult to achieve the effect of grain refinement.

Therefore, it is necessary to improve the existing technology to obtain an economical fine-grained high-strength toughness hot work die steel GBL64, which reduces costs and facilitates processing.

Contents of the invention

The purpose of the present invention is to provide an economical fine-grained high-strength toughness hot work die steel GBL64.

Another object of the present invention is to provide a method for preparing the above-mentioned economical fine-grained high-strength and tough hot work die steel.

The invention provides an economical fine-grained high-strength toughness hot work die steel GBL64, the composition formula of which includes the following elements by weight percentage: C: 0.25%-0.40%; Si: 0.15%-1.2%; Mn: 0.2%-0.9% ; Cr: 3% to 6%; Mo: 1.0% to 3.5%; W: 0.6% to 2.2%, the balance is iron, and trace unavoidable residual elements S, P, N, O, H.

Among them, S, P, N, O, H are impurities with acceptable content.

More preferably, the formula includes the following elements by weight percentage:

C: 0.28% ~ 0.40%; Si: 0.20% ~ 1.05%; Mn: 0.25% ~ 0.85%; Cr: 3.5% ~ 5.5%; Mo: 1.2% ~ 3.4%; W: 0.8% ~ 2%, the balance For iron, and trace residual elements S, P, N, O, H. Among them, S, P, N, O, H are impurities with acceptable content.

In a preferred embodiment of the present invention, formula comprises the following elements by weight percentage:

C: 0.28%; Si:, 1.05%; Mn: 0.85%; Cr: 3.6%; Mo: 2.2%; W: 2%, the balance is iron, and trace residual elements S, P, N, O, H. Among them, S, P, N, O and H are impurities with acceptable content, and the content is 1-200ppm respectively.

The above-mentioned die steel is named GBL64, the G code is called "Gong" which means Shanghai University of Engineering Technology, the BL code is called "Billon" which means Bilong Mold Material Technology (Nantong) Co., Ltd., and 64 is the serial number of the steel.

The preparation method of the above-mentioned economical fine-grained high-strength and tough hot work die steel adopts the following process and steps:

1) Smelting: Put the ingredients into the electric arc furnace for smelting. After the smelted alloy composition reaches the target, control the temperature of the molten steel to 1520-1540°C and cast it into a mold to form an electrode steel rod. After demolding, remove the scale and pits on the surface of the electrode rod defect;

2) Electroslag remelting: Electroslag remelting is carried out on the electrode rod, so that the molten steel is slowly crystallized and solidified into a round steel ingot after being filtered by the slag system;

3) High-temperature homogenization: heat the round steel ingot to 1230-1265°C, hold the temperature for (0.2-0.4)×D hours, where D is the diameter of the steel ingot (cm), so that the components in the steel can diffuse evenly, and then cool to forging Temperature 1180±10℃;

4) Upsetting: Upsetting the 1180°C±10°C steel ingot along the height direction of the steel ingot on the press to 40% to 50% of the height, then finishing, returning to the furnace and heating at 1180°C±10°C for 2-4 hours; and then The second upsetting, finishing, returning to the furnace at 1180°C±10°C for 2 to 4 hours, and then performing the third upsetting, finishing, and always keeping the final forging temperature above 870°C;

5) Elongation: Elongate and forge the steel ingot after repeated upsetting three times to the final size to obtain a module, keep the final forging temperature at 870°C-900°C, and cool the pit to about 350±10°C after elongation;

6) Stress relief annealing: heat the module to 850±10°C and anneal for 10 to 16 hours to eliminate stress, and then cool with the furnace;

7) Ultrafine treatment: heat the module to 1060-1100°C and keep it warm for (0.2-0.25)×d hours, where d is the effective size of the forging in cm, water quenching to room temperature; then heat up to 860±10°C for isothermal (0.4-0.6) ×d hours, d is the effective size of the forging in cm; then furnace cooled to 740±10°C, isothermal (0.9～1.2)×d hours, d is the effective size of the forging in cm, and then cooled to room temperature with the furnace; when the forging is a round bar, The effective size is its diameter; when the forging is a plate, the effective size is its thickness;

8) Quenching and tempering treatment: heat the module to 1060±10°C for 1.5 to 2.5 hours, vacuum air quench to room temperature, temper at 560±10°C for 9 to 11 hours, air cool to room temperature, and temper at 600±10°C for 9 hours ~11 hours, out of the oven and air-cooled.

Preferably, in step 3) during high-temperature homogenization, the round steel ingot is heated to 1230-1265° C., and the holding time is (0.3-0.4)×D hours, where D is the diameter of the steel ingot (cm), so that the components in the steel can be diffused evenly. Then cool to the forging temperature of 1180±10°C.

Preferably, during step 7) ultra-fine treatment, heat the module to 1060-1100°C and keep it warm for (0.2-0.25)×d hours, where d is the effective size of the forging in cm, quench it to room temperature; then heat up to 860±10°C for isothermal (0.4～0.5)×d hours, d is the effective size of the forging in cm; then furnace cooled to 740°C, isothermal (0.9～1)×d hours, d is the effective size of the forging in cm, and then cooled to room temperature with the furnace.

In step 2), after electroslag remelting and metallurgical slag system filtration are used to remove most of the impure impurities in the electrode rod, the molten steel slowly crystallizes and solidifies to form a round steel ingot.

Some terms involved in the present invention are explained below.

Electrode rod: the base metal used for electroslag remelting, which is casted after being smelted in an electric arc furnace.

Electroslag remelting: A method of smelting using the resistance heat generated when an electric current passes through the slag as a heat source. Its purpose is to increase the purity of the metal and improve the crystallization of the ingot.

Steel ingot: The molten steel is poured into the mold through the ladle and solidified to form a steel ingot of a certain shape.

High-temperature homogenization: It is a heat treatment process that eliminates or reduces the inhomogeneity of the intragranular composition and the structural state that deviates from the balance under the actual crystallization conditions by diffusion at high temperature, and improves the process performance and serviceability of the alloy material.

Segregation: The phenomenon that the constituent elements in the alloy are unevenly distributed during crystallization.

Upsetting: A forging process that reduces the height of the billet and increases the cross-section. Improve the transverse mechanical properties of forgings and reduce anisotropy; repeated upsetting and elongation to break up carbides in alloy tool steel and make them evenly distributed.

Elongation: Refers to any forging process that reduces the cross-sectional area and increases the length.

Superfine: A heat treatment process adopted by alloy steel with carbide precipitation behavior to facilitate processing and ensure subsequent good toughness. This process heats the steel to the austenitizing temperature, then slowly cold cuts with the furnace The fine dispersed alloy carbides are uniformly precipitated and slowly grow into spherical shapes. Then cool down to room temperature with the furnace. The ultra-fine steel has good dimensional stability and machinability, and the impact toughness is better after subsequent quenching and tempering.

W and Mo are effective elements for comprehensively improving wear resistance, high temperature heat strength and thermal conductivity, and the dispersed precipitation of WC can prevent grain coarsening. The present invention adds molybdenum and tungsten on the basis of 4Cr5MoSiV1 steel composition to form fine Dispersed WC wear-resistant precipitates, which are densely pinned around the fine grains, hinder the growth of grains, and remove the relatively expensive V element, replacing VC with WC strengthening; therefore, this type of economical Type fine-grained hot work die steel will have lower cost than H13 and 8418 steel, better wear resistance, high temperature thermal strength and toughness and thermal conductivity.

The economical hot work die steel GBL64 of the invention has a grain size as small as about 0.5-3.5 μm, and has excellent strength and toughness, high temperature friction and wear performance, thermal strength, thermal stability, thermal fatigue performance and high thermal conductivity.

The beneficial effects of the present invention are:

(1) The impact toughness of the economical steel GBL64 of the invention exceeds the excellent level of H13, not only has excellent high-temperature friction and wear properties, high-temperature heat strength, thermal stability, and thermal fatigue properties, but also some solid-solution Mo and W elements will be significantly improved Thermal conductivity.

(2) Since the refinement of the grain size is realized from the perspective of composition, it will be beneficial to realize the stable trial production of the inventive steel in conventional large-scale production.

(3) The present invention maintains the grain size of the elevated hot work die steel above ASTM grade 8, the hardness ranges from 42 to 48HRC, and the impact energy of the 7×10×55 unnotched pattern is greater than 300J.

Description of drawings

Fig. 1 is the 1000 times metallographic structure diagram of embodiment 1 mold steel

Figure 2 is a test comparison chart of the thermal stability of die steel and H13 steel in Example 1 tempered at 600°C

Fig. 3 is the test comparison chart of the friction and wear coefficient of the mold steel and H13 steel in Example 1

Fig. 4 is the comparison diagram of the thermal conductivity of the mold steel and H13 steel in embodiment 1

Detailed ways

The technical solution of the present invention will be described below in conjunction with specific embodiments.

Example 1

The composition formula of economical fine-grained high-strength and tough hot stamping die steel GBL64 contains the following elements by weight percentage:

C: 0.28%; Si: 1.05%; Mn: 0.85%; Cr: 3.6%; Mo: 2.2%; W: 2%; Fe and trace residual elements S, P, N, O, H are the balance.

In the present embodiment, the technological process and steps of GBL64 steel are as follows:

1) Smelting: Put the ingredients into the electric arc furnace according to the ratio and melt them. After the metallurgical components meet the requirements, control the temperature to about 1520-1540°C and cast them into Electrode rods, remove defects such as scale and pits after demoulding the electrode rods.

2) Electroslag remelting: The electrode rod is subjected to electroslag remelting and refining, and most of the impure impurities in the electrode rod are removed by filtering through the metallurgical slag system, and then the molten steel slowly crystallizes and solidifies into a 1 ton round steel ingot (about 320mm in diameter).

3) High-temperature homogenization: heat 1 ton of steel ingot to 1245±10°C, keep it warm for 11 hours, then slowly cool to 1180±10°C to prepare for forging.

4) Upsetting: Upsetting the 1180°C steel ingot along the height direction of the steel ingot to a height of 45%, then finishing (that is, using a press to flatten the irregular edges), returning to the furnace and heating at 1180±10°C for 3 hours, and then performing the second step Second upsetting, finishing, return to the furnace at 1180±10°C for 3 hours, and then carry out third upsetting, finishing, and keep the final forging temperature above 870°C.

5) Drawing length: forging and drawing the steel ingot after repeated upsetting three times to the final size of 165mm×520mm×1550mm (thickness×width×length), the effective size is 165mm, and the final forging temperature is kept above 870°C. Cool to about 350°C.

6) Stress-relief annealing: heat the module to 850±10°C for 10 hours to anneal for stress relief, and then cold cut with the furnace.

7) Ultrafine treatment: heat the module to 1060±10°C for 3.5 hours, water quench to room temperature, then raise the temperature to 860±10°C for 7 hours, then furnace cool to 740±10°C, hold for 15 hours, and then Furnace cool to room temperature.

8) Quenching and tempering treatment: heat the module to 1060±10°C for 2 hours, vacuum air quench to room temperature, temper at 560°C for 10 hours, air-cool to room temperature, temper at 600±10°C for 10 hours, and air cool out of the furnace.

The metallographic structure diagram (1000 times) of the obtained die steel is shown in Fig. 1 . The grain size is as fine as about 0.5-3.5 μm, ASTM grade 8 or above.

Performance Testing

The performance test of the above-mentioned GBL64 steel is as follows:

(1) The hardness after quenching and tempering is 43HRC;

(2) The impact energy of the unnotched 7×10×55 pattern is greater than 300J;

The impact energy of U-shaped notch is 30J

(3) Thermal stability: The expression of thermal stability here is: GBL64 steel is kept at 600°C for different times, and the downward trend of its hardness is the judgment of thermal stability. At the same time, a comparative test of thermal stability was carried out with H13 steel. The composition comparison is shown in Table 1 (wt.%), and the thermal stability data comparison is shown in Table 2 (unit: HRC) and Figure 2.

(4) GBL64 steel and H13 steel were tested for friction and wear coefficients, and the results are shown in Figure 3.

(5) The thermal conductivity of GBL64 steel and H13 steel was tested with a laser thermal conductivity meter, and the results of thermal conductivity changing with temperature are shown in Figure 4.

Table 1 Comparison of H13 and GBL64 steel composition

steel number 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 2 Hardness comparison of H13 and GBL64 steels tempered at 600℃ for different times

steel number 5h 10h 15h 20h 25 hours 30h 35h 40h H13 46 45 42 39 37 36 34 28 GBL64 47 44 44 40 39 38 36 36

Claims (8)

1. a kind of economical fine grain high-toughness hot working die steel, which is characterized in that its component prescription includes following weight percent Element: C:0.25%~0.40%；Si:0.15%~1.2%；Mn:0.2%~0.9%；Cr:3%~6%；Mo:1.0% ~3.5%；W:0.6%~2.2%, surplus are iron and micro residue element S, P, N, O, H.

2. economical fine grain high-toughness hot working die steel according to claim 1, which is characterized in that formula includes following heavy Measure the element of percentage:

C:0.28%~0.35%；Si:0.20%~1.05%；Mn:0.25%~0.85%；Cr:3.5%~5.5%；Mo: 1.2%~3.4%；W:0.8%~2%, surplus are iron and micro residue element S, P, N, O, H.

3. economical fine grain high-toughness hot working die steel according to claim 1, which is characterized in that formula includes following heavy Measure the element of percentage:

C:0.28%；Si:1.05%；Mn:0.85%；Cr:3.6%；Mo:2.2%；W:2%, surplus are iron and micro residual Remaining element S, P, N, O, H.

4. described in any item economical fine grain high-toughness hot working die steels according to claim 1~3, which is characterized in that wherein, S, P, N, O, H are the acceptable impurity of content.

5. the preparation method of economical fine grain high-toughness hot working die steel according to any one of claims 1 to 4, feature It is, step includes:

1) melting: being put into melting in electric arc furnaces for ingredient, after molten alloy ingredient touches the mark, by molten steel temperature control to 1520- 1540 DEG C are cast to formation electrode rod iron, clearing electrode stick surface scale and pit defect after demoulding in mold；

2) electroslag remelting: electrode bar carries out electroslag remelting, makes the molten steel of melting after slag system filters, slow crystallization and freezing is at circle Steel ingot；

3) high temperature homogenization: round steel ingot is heated to 1230-1265 DEG C, soaking time is (0.2~0.4) × D hours, and D is Steel ingot diameter dimension cm, keeps component diffusion in steel uniform, is subsequently cooled to 1180 ± 10 DEG C of forging temperature；

4) jumping-up: by 1180 DEG C of ± 10 DEG C of steel ingots on press along steel ingot short transverse carry out jumping-up to 40%~50% height, Then heating 2-4 hours is melted down in finishing；Second of jumping-up is carried out again, and finishing melts down heat preservation 2-4 hours, then carries out third time upsetting Slightly, finishing remains 870 DEG C of final forging temperature or more；

5) it pulls out: the steel ingot three times repeatedly after jumping-up being pulled out and forged to final size obtains module, keep finish-forging temperature 870 DEG C~920 DEG C or more of degree, hole is cooled to 350 ± 10 DEG C after pulling；

6) stress relief annealing: module is heated to 850 ± 10 DEG C of annealing 10-16 hours, eliminates stress, then furnace cooling；

7) ultra fine: being heated to 1060~1100 DEG C for module and keep the temperature (0.2~0.3) × d hours, and d is the effective ruler of forging Very little cm, water quenching to room temperature；860 ± 10 DEG C of isothermals (0.4~0.6) × d hours are then heated to, d is forging effective dimensions cm；With After be furnace-cooled to 740 ± 10 DEG C, isothermal (0.9~1.2) × d hours, d is forging effective dimensions cm, then with being furnace-cooled to room temperature；

8) modifier treatment: being heated to 1060 ± 10 DEG C for module and keep the temperature 1.5~2.5 hours, vacuum air-quenching to room temperature, and 560 ± 10 DEG C tempering 9~11 hours, after being air-cooled to room temperature, 600 ± 10 DEG C be tempered 9~11 hours, come out of the stove air-cooled.

6. the preparation method of economical fine grain high-toughness hot working die steel according to claim 5, which is characterized in that step 3) round steel ingot is heated to 1230~1265 DEG C when high temperature homogenization, soaking time is (0.3~0.4) × D hours, and D is steel Ingot diameter dimension (cm), keeps component diffusion in steel uniform, is subsequently cooled to 1180 ± 10 DEG C of forging temperature.

7. the preparation method of economical fine grain high-toughness hot working die steel according to claim 5, which is characterized in that step 7) when ultra fine, module is heated to 1060~1100 DEG C and keeps the temperature (0.2~0.25) × d hours, d is forging effective dimensions Cm, water quenching to room temperature；860 ± 10 DEG C of isothermals (0.4~0.5) × d hours are then heated to, d is forging effective dimensions cm；Then It is furnace-cooled to 740 DEG C, isothermal (0.9~1) × d hours, d is forging effective dimensions cm, then with being furnace-cooled to room temperature.

8. the preparation method of economical fine grain high-toughness hot working die steel according to claim 5, which is characterized in that step 2) sand pit is embedded to after electroslag remelting to be cooled to room temperature.