1. The hot stamping die steel material is characterized by comprising the following chemical components in percentage by mass: 0.47-0.51% of C; 0.25-0.30% of Si; 0.25-0.30% of Mn; 4.20-4.50% of Cr; 2.90-3.10% of Mo; v is 0.50-0.60%; 0.01-0.03% of Al; the balance being Fe and unavoidable impurities.

2. The hot stamping die steel material and the manufacturing method thereof as claimed in claim 1, wherein the components are as follows by mass percent: 0.47-0.49% of C; 0.25 to 0.27 percent of Si; 0.29-0.30% of Mn; 4.27-4.32% of Cr; 2.97-3.0% of Mo; v is 0.52-0.55%; 0.016-0.022% of Al; the balance being Fe and unavoidable impurities.

3. A method of manufacturing a hot stamping die steel material as claimed in any one of claims 1-2, characterized by comprising the steps of:

step S1: proportioning according to a preset percentage, smelting by using an electric furnace, and obtaining an electrode blank through vacuum refining;

step S2: electroslag remelting is carried out, and electroslag ingots with uniform components are smelted;

step S3: performing stress relief annealing on the electroslag ingot;

step S4: then placing the electroslag ingot into a heating furnace for forging and forming;

step S5: spheroidizing annealing after forging;

step S6: and finally, performing high-temperature quenching and three-time high-temperature tempering to obtain the hot stamping die steel material.

4. The method for manufacturing a steel material for a hot stamping die according to claim 3, wherein the step S1 is performed by using an eccentric arc furnace for smelting, wherein the alkalinity CaO/SiO in the arc furnace smelting process is controlled to be 3%, and the intermediate frequency furnace chemical alloy is added into a refining furnace for external refining, vacuum degassing and electrode blank injection.

5. The method for manufacturing a steel material for a hot stamping die as claimed in claim 3, wherein the step S2 employs CaF₂-Al₂O₃Carrying out electroslag remelting on a ternary slag system consisting of 244 pre-melted slag under the protection of argon; during electroslag, one electrode blank is used for electroslag and one electrode is used for electroslagThe filling ratio of the slag ingot is controlled to be 0.60-0.75, and the height-diameter ratio of the electroslag ingot is controlled to be 2.0-2.3.

6. The method for manufacturing the steel material for the hot stamping die as claimed in claim 3, wherein the step S3 is that the heat preservation time is calculated according to the diameter and the heat preservation time is calculated according to the heat preservation time of 1.5h per 100mm at 780-850 ℃, the flue gate is closed after the heat preservation is finished, the steel material is cooled for 10h along with the furnace, then the furnace is cooled to 100-150 ℃ at 15-30 ℃/h, and then the steel material is taken out of the furnace and air-cooled.

7. The method for manufacturing a steel material for a hot stamping die as claimed in claim 3, wherein the step S4 includes placing the electroslag ingot into a heating furnace with a furnace temperature of 400-450 ℃ for forging and forming, heating to 850 + -20 ℃ at a rate of 60-80 ℃/h, maintaining the temperature for 5-8 h, heating to 1250-1270 ℃ at a rate of 120-150 ℃/h, maintaining the temperature for 20-30 h, cooling to 1230 + -10 ℃ before forging, and forging by a multidirectional forging method, wherein the final forging temperature is not lower than 800 ℃.

8. The method for manufacturing a steel material for a hot stamping die as claimed in claim 3, wherein the step S5 is air-cooled to a surface temperature of 500-550 ℃ after forging, then heated to 830-860 ℃ at a speed of 60-80 ℃/h, kept warm for 10-15 h, furnace-cooled to 200 ℃ at 15-30 ℃, and then discharged for air-cooling.

9. The method for manufacturing the steel material for the hot stamping die as claimed in claim 3, wherein the step S6 includes heating to 1050-1080 ℃ for quenching, oil cooling to 50-80 ℃, and high temperature tempering at 580-610 ℃ for three times to obtain the steel material for the hot stamping die.

Background

With the increasing energy crisis and environmental problems, the lightening of automobiles has become an inevitable way for the sustainable development of the automobile industry in the world. The vehicle body is highly strengthened, the weight of the vehicle body can be reduced, the safety can be improved, and the best way for realizing the light weight of the vehicle body and improving the collision safety is provided.

In order to meet the requirement of strengthening development of the height of the vehicle, advanced high-strength steel and advanced part forming processes are carried out. When the strength of the high-strength steel reaches over 1000MPa, if the high-strength parts are produced by adopting the traditional cold stamping forming process, the technical problems of poor forming performance of the high-strength steel, serious part resilience, poor dimensional accuracy, short service life of a forming die and the like are difficult to avoid. The hot stamping forming technology can solve the problem of difficult cold stamping forming of the traditional high-strength steel and can obtain formed parts with ultrahigh strength and high precision.

The hot stamping forming is to heat the steel plate to about 900 ℃ for austenitizing, then quickly send the steel plate into a die with a cooling system for stamping forming and quenching, and the steel plate structure is transformed from austenite to martensite, thereby obtaining the ultra-high strength part. In the stamping process, the die is in direct contact with the blank, the surface of the cavity is rapidly heated by high-temperature metal, and the surface layer of the cavity generates compressive stress, so that the die material is required to have high heat strength and heat stability. When the stamping part is taken out, the temperature of the die is suddenly reduced, thermal fatigue is easily generated, and the die material is required to have good high-temperature fatigue resistance. The dies are also subjected to extreme impact loads during service, and therefore, the dies also have excellent toughness. In addition, the dies can exhibit galling during the stamping process, which requires the hot stamping die material to have sufficient hardness.

The materials which are popular at present are DIEVAR and Cr7V, and the service life is up to 30 ten thousand times. Although the thermal fatigue performance and the toughness of the DIEVAR are good, the wear resistance and the thermal conductivity are still poor; CR7V has good wear resistance but poor thermal fatigue and thermal conductivity. Therefore, there is a need for an improved hot stamping die steel material and a manufacturing method thereof, which provides a hot stamping die specific steel with good combination of wear resistance and thermal conductivity.

Disclosure of Invention

The invention aims to provide a hot stamping die steel material and a manufacturing method thereof, which can obtain the hot stamping die steel material with excellent impact toughness, tempering stability and high quenching hardness.

The invention provides a hot stamping die steel material and a manufacturing method thereof, aiming at solving the technical problems, wherein the hot stamping die steel material comprises the following chemical components in percentage by mass: 0.47-0.51% of C; 0.25-0.30% of Si; 0.25-0.30% of Mn; 4.20-4.50% of Cr; 2.90-3.10% of Mo; v is 0.50-0.60%; 0.01-0.03% of Al0.01; the balance being Fe and unavoidable impurities.

Further, the components are as follows according to the mass percentage: 0.47-0.49% of C; 0.25 to 0.27 percent of Si; 0.29-0.30% of Mn; 4.27-4.32% of Cr; 2.97-3.0% of Mo; v is 0.52-0.55%; 0.016-0.022% of Al; the balance being Fe and unavoidable impurities.

The invention also provides a manufacturing method of the hot stamping die steel material for solving the technical problems, which comprises the following steps: step S1: proportioning according to a preset percentage, smelting by using an electric furnace, and obtaining an electrode blank through vacuum refining; step S2: electroslag remelting is carried out, and electroslag ingots with uniform components are smelted; step S3: performing stress relief annealing on the electroslag ingot; step S4: then placing the electroslag ingot into a heating furnace for forging and forming; step S5: spheroidizing annealing after forging; step S6: and finally, performing high-temperature quenching and three-time high-temperature tempering to obtain the hot stamping die steel material.

Further, in the step S1, an eccentric arc furnace is adopted for smelting, the alkalinity CaO/SiO in the arc furnace smelting process is controlled to be 3%, the intermediate frequency furnace chemical alloy is added into a refining furnace, external refining is performed, vacuum degassing is performed, and an electrode blank is poured.

Further, the step S2 adopts CaF₂-Al₂O₃Carrying out electroslag remelting on a ternary slag system consisting of 244 pre-melted slag under the protection of argon; during electroslag, one electrode blank is used for electroslag and one electroslag ingot is used, the filling ratio is controlled to be 0.60-0.75, and the height-diameter ratio of the electroslag ingot is controlled to be 2.0-2.3.

Further, step S3 is to calculate the heat preservation time according to the diameter and heat preservation time of 1.5h per 100mm at 780-850 ℃, close the flue gate after finishing heat preservation and cool the flue gate for 10h along with the furnace, cool the flue gate to 100-150 ℃ at 15-30 ℃/h, and then take the flue out of the furnace for air cooling.

Further, in the step S4, the electroslag ingot is placed into a heating furnace with the furnace temperature of 400-450 ℃ for forging forming, the heating is carried out at 60-80 ℃/h to 850 +/-20 ℃ for heat preservation for 5-8 h, then the heating is carried out at 120-150 ℃/h to 1250-1270 ℃ for heat preservation for 20-30 h, the temperature is reduced to 1230 +/-10 ℃ before forging, the forging is carried out by adopting a multi-directional forging mode, and the final forging temperature is not lower than 800 ℃.

Further, after the forging in the step S5, air cooling is carried out until the surface temperature is 500-550 ℃, then heating is carried out until the surface temperature is 830-860 ℃ at the speed of 60-80 ℃/h, heat preservation is carried out for 10-15 h, then furnace cooling is carried out at 15-30 ℃ until the temperature is 200 ℃, and then discharging and air cooling are carried out.

Further, the step S6 includes heating to 1050-1080 ℃ for quenching, oil cooling to 50-80 ℃, and performing high temperature tempering at 580-610 ℃ for three times to obtain the hot stamping die steel material.

Compared with the prior art, the invention has the following beneficial effects: according to the hot stamping die steel material and the manufacturing method thereof, on the aspect of component design, according to the characteristics of high thermal conductivity and high wear resistance required by hot stamping, the influence of each alloy element on the material characteristics is analyzed, the component content of each element is scientifically designed, the content of chromium, manganese and silicon is reduced, and the content of carbon, molybdenum and vanadium is properly increased, so that the hot stamping die steel material with excellent impact toughness, tempering stability and high quenching hardness is obtained.

Detailed Description

The present invention will be further described with reference to the following examples.

The hot stamping die steel material provided by the invention mainly comprises the following elements in percentage by mass: 0.47-0.51% of C; 0.25-0.30% of Si; 0.25-0.30% of Mn; 4.20-4.50% of Cr; 2.90-3.10% of Mo; v is 0.50-0.60%; 0.01-0.03% of Al; the balance Fe and other unavoidable impurities.

The invention relates to a long-life hot stamping die steel material, which is characterized in that the contents of chromium, manganese and silicon elements are reduced and the contents of carbon, molybdenum and vanadium are properly increased in component design. According to the characteristics of high thermal conductivity and high wear resistance required by hot stamping, the component contents of various elements are scientifically designed by analyzing the influence of various alloy elements on the material characteristics.

Carbon is an essential element for ensuring the hardness of the material, and increasing the hardness of the material by appropriately increasing the carbon content is the most economical design criterion. On the basis of the traditional heat-strength steel 4Cr5MoSiV1, in order to further improve the red hardness and the heat-conducting property, the Mo content is improved to 3 percent from 1.10 to 1.75 percent; in order to ensure the thermal fatigue performance of the material, the high dispersion of the carbide of the material must be ensured, the appearance of large-particle carbide is prevented, the high-temperature carbide particles of the material are required to be rounded, the formation of a large amount of V-series carbide is prevented, and the content of V is reduced from 0.80-1.20% to 0.55%; silicon promotes dendritic crystals of steel ingots to be developed, steel segregation is aggravated, and fatigue performance is influenced, but the Si is controlled to be 0.27% in consideration of deoxidation requirements; the chromium forms M6C, the carbide is unstable in use and can be refined in production, but the carbide can be coarsened after being used for a period of time, the matrix is poor in carbon due to absorption of surrounding carbon, the hardness is reduced, the fatigue life is influenced, and the rust resistance of the material is reduced due to too low chromium. Therefore, the Cr content should be properly reduced from 4.75-5.50% to below 4.5%; manganese not only promotes the precipitation of MnS inclusions in the steel but also increases the tendency of the steel to overheat, but it helps deoxidation, so that Mn is controlled to 0.30%.

The chemical compositions of various steels in examples 1-3 are shown in Table 1:

table 1 examples 1-3 chemical compositions

The invention discloses a long-life hot stamping die steel material which is prepared by the following steps:

(1) smelting an electrode blank: the material is prepared according to the chemical components of the steel material of the long-life hot stamping die, an eccentric arc furnace is adopted for smelting, an intermediate frequency furnace is adopted for melting alloy, the alloy is added into a refining furnace, the alloy is refined outside the furnace, and an electrode blank is poured.

(2) Electroslag remelting: adopts a ternary slag system (CaF)₂-Al₂O₃-244 pre-melted slag) electroslag remelting, argon gas is adopted to protect the electroslag, and hydrogen increase, oxygen increase and nitrogen increase in the process are reduced. Electroslag adopts an electrode blank electroslag and an electroslag ingot, electroslag is not alternated, the filling ratio is controlled to be 0.60-0.75, and the height-diameter ratio of the electroslag ingot is controlled to be 2.0-2.3;

(3) and (3) stress relief annealing of the electroslag ingot: performing stress relief annealing on the electroslag ingot in a gas furnace, calculating the heat preservation time according to the diameter and the heat preservation time of 1.5h per 100mm at 780-850 ℃, closing a flue gate after the heat preservation is finished, cooling for 10h along with the furnace, then discharging the electroslag ingot from the furnace to 100-150 ℃ at the furnace cooling rate of 15-30 ℃/h, and air cooling

(4) Heating and forging: grinding the surface of the electroslag ingot, putting the electroslag ingot into a heating furnace with the furnace temperature of 400-450 ℃, heating to 850 +/-20 ℃ at the speed of 60-80 ℃/h, preserving heat for 5-8 h, then heating to 1250-1270 ℃ at the speed of 120-150 ℃/h, preserving heat for 20-30 h, cooling to 1230 +/-10 ℃ after heat preservation, forging by adopting a multidirectional forging mode, wherein the final forging temperature is not lower than 800 ℃.

(5) And (3) after-forging treatment: air cooling to 500-550 ℃ of surface temperature after forging, then heating to 830-860 ℃ at the speed of 60-80 ℃/h, preserving heat for 10-15 h, then furnace cooling to 500 ℃ at the speed of 15-30 ℃/h, discharging and stacking for cooling.

(6) Quenching and high-temperature tempering: heating to 1050-1080 ℃ for quenching, cooling oil to 50-80 ℃, and carrying out high-temperature tempering at 580-610 ℃ for three times to obtain the hot stamping die steel with excellent impact toughness, tempering stability and high thermal conductivity.

The mechanical properties of examples 1-3 are shown in Table 2 below:

table 2 mechanical properties of examples 1-3 the service life of examples 1-3 is shown in table 3 below:

application case	Service life (thousands times)
		B-column die for certain brand SUV (sports utility vehicle)	56
Front and rear anti-collision beam of certain brand car	61
		Certain brand SUV A post lower plate	53

TABLE 3 service life cases of examples 1-3

Although the present invention has been described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.