A large-size hot work die steel forging, a preparation method and application thereof

Abstract

The present application relates to alloy material casting technical field, specifically relates to a kind of large specification hot working die steel forgings and its preparation method and application.The percentage of the chemical composition of the large specification hot working die steel forgings meets the requirements of 0.60%≤Si+Mo≤0.72%;1.75%≤Mn+Cr+V≤1.98%.The present application sets reasonable chemical composition, provides good conditions and basis for the material performance and forging of large specification hot working die steel forgings, and successfully obtains a kind of large specification hot working die steel forgings with excellent performance and high yield rate by combining simple preparation process.The technical scheme of the present application effectively solves the problems of complex preparation process, harsh conditions and low yield rate of 55NiCrMoV7 die steel large forgings in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy material casting, in particular to a large-size hot work die steel forging and a preparation method and application thereof. BACKGROUND

[0002] 55NiCrMoV7 steel belongs to hot work die steel, the Cr element content of the steel is relatively high, has high hardenability, heat crack resistance, fatigue resistance and impact resistance and other characteristics, is widely used in the manufacturing field of hot stamping die of heavy machinery, marine equipment, special vehicle manufacturing and the like. The use environment of 55NiCrMoV7 die steel is extremely harsh, directly contacts with hot blank during working, which requires that it not only overcomes thermal fatigue stress formed by cold and hot alternation, but also bears high strength impact load, therefore, the quality requirements must meet: first, has good wear resistance and thermal stability; second, has high high-temperature strength and good toughness; third, has relatively uniform structure and performance distribution.

[0003] Due to the size and weight characteristics of large 55NiCrMoV7 die steel forgings, when the existing technology is used to prepare large 55NiCrMoV7 die steel forgings, internal defects and surface defects of the forgings are prone to occur, which leads to the failure and cracking of the forgings. Based on this, developing a preparation technology of 55NiCrMoV7 die steel large forgings has practical significance for widening the application field of 55NiCrMoV7 die steel.

[0004] At present, the solution method for solving the defects of 55NiCrMoV7 die steel large forgings is mostly through optimizing the forging process, such as controlling the forging temperature, deformation speed and deformation degree, and preheating the forgings, so as to achieve uniform deformation of the metal and reduce the purpose of cracks. However, such operation not only needs very fine control of temperature and time, but also needs to go through multiple forging processes, the process is complex and the conditions are harsh, and the yield of the obtained large forgings is only about 65%.

[0005] Based on this, developing a preparation process of 55NiCrMoV7 die steel large forgings with simple process and high yield has practical significance for the application of 55NiCrMoV7 die steel. SUMMARY

[0006] In view of the problems of complex preparation process, strict conditions and low yield of the 55NiCrMoV7 die steel large forging in the prior art, the application provides a large-size hot work die steel forging and a preparation method and application thereof. The application sets reasonable chemical components, provides good conditions and foundation for the material performance and forging of the large-size hot work die steel forging, and successfully prepares a large-size hot work die steel forging with excellent performance and high yield by combining with a simple preparation process, thereby effectively solving the above problems of the 55NiCrMoV7 die steel large forging and providing a new design idea for the preparation of the 55NiCrMoV7 die steel large forging.

[0007] To achieve the above-mentioned application purposes, the application provides the following technical solutions:

[0008] The application provides a large-size hot work die steel forging, and the mass percentage of the chemical components of the large-size hot work die steel forging is as follows: C: 0.52%-0.58%, Si: 0.15%-0.35%, Mn: 0.70%-0.90%, Cr: 0.85%-1.15%, Ni: 1.55%-1.72%, Mo: 0.38%-0.49%, V: 0.05%-0.12%, S: ≤0.01%, P: ≤0.02% and the balance of Fe and inevitable impurities; and 0.60%≤[Si]+[Mo]≤0.72% and 1.75%≤[Mn]+[Cr]+[V]≤1.98%, wherein [Si] represents the content of Si in the large-size hot work die steel forging, [Mo] represents the content of Mo in the large-size hot work die steel forging, [Mn] represents the content of Mn in the large-size hot work die steel forging, [Cr] represents the content of Cr in the large-size hot work die steel forging, and [V] represents the content of V in the large-size hot work die steel forging.

[0009] Compared with the prior art, the application sets reasonable chemical components, and provides good conditions and foundation for the material performance and forging of the large-size hot work die steel forging. The application limits the mass percentages of Si and Mo, thereby improving the high-temperature oxidation resistance, mechanical strength and temper resistance of the large-size hot work die steel forging, improving the ductile-brittle transition temperature of the large-size hot work die steel forging, and significantly improving the hardness of the large-size forging to avoid internal cracking. By limiting the mass percentages of Mn, Cr and V, on the one hand, the hardening depth of the large-size forging is improved, the thermal brittleness is reduced, the forgeability and plasticity of the forging are improved; on the other hand, the hot strength of the large-size forging is improved, the elongation and the area reduction are reduced, the surface defects of the forging are avoided, meanwhile, the addition of V can strengthen the grain boundary and intergranular of the large-size forging, improve the hardness and mechanical strength of the forging, and also can be used as a grain refiner to reduce the grain size, thereby improving the toughness of the large-size forging and reducing the forging cracking phenomenon.

[0010] The second aspect of the present application provides a preparation method of the large-size hot work die steel forging, comprising the following steps:

[0011] Step one, the returned material is analyzed for chemical composition, and new material is dosed according to the requirements of chemical composition;

[0012] Step two, the returned material is melted, when the returned material is melted by 70wt%-80wt%, new material is added, melted, to obtain mixed molten steel; the mixed molten steel is refined at 1530℃-1580℃ under a vacuum degree of 1Pa-2Pa to obtain refined molten steel; the elements of the refined molten steel are adjusted at 1550℃-1570℃ to obtain standard molten steel;

[0013] Step three, the standard molten steel is cast under inert atmosphere, cooled to 1000℃-1100℃ to obtain alloy ingot; the alloy ingot is heated to 1330℃-1350℃ for high-temperature homogenization treatment, cooled to 1210℃-1260℃ for insulation, and sequentially subjected to twice piercet forging to obtain first alloy forging;

[0014] Step four, the first alloy forging is cooled to 780℃-840℃ for insulation, and after oil cooling, is subjected to tempering treatment at 615℃-700℃ to obtain second alloy forging; the second alloy forging is heated to 910℃-960℃ for normalizing treatment, and air-cooled to obtain large-size hot work die steel forging.

[0015] Compared with the prior art, the present application successfully prepares large-size hot work die steel forging with excellent performance through refining, high-temperature homogenization treatment, piercet forging, tempering treatment and normalizing treatment. Using returned material as the main raw material greatly reduces the inclusion content in the metal raw material, avoids internal defects caused by excessive impurities in the forging, and further reduces the aggregation of carbides, refines the internal organization, effectively solves the cracking problem caused by uneven internal stress, and combines high-temperature homogenization treatment. After twice piercet forging, the overall organization of the forging is homogenized, which is beneficial to subsequent heat treatment to fully forge the core and maximize the elimination of internal stress. Tempering treatment and normalizing treatment can effectively remove internal stress of the forging, improve the stability of the organization, and prevent cracking of the large-size forging.

[0016] Preferably, in step one, the chemical composition of the return material has the following mass percentage: C: 0.50%-0.58%, Si: 0.15%-0.30%, Mn: 0.70%-0.80%, Cr: 0.95%-1.15%, Ni: 1.55%-1.72%, Mo: 0.38%-0.42%, V: 0.05%-0.10%, S: ≤0.03%, P: ≤0.03%, and the balance of Fe and inevitable impurities.

[0017] Preferably, in step two, the holding time of the refining is 2h-4h.

[0018] Preferably, in step three, the holding time of the high-temperature homogenization treatment is 1h-2h.

[0019] Preferably, in step three, the holding time is 20min-30min.

[0020] Preferably, in step three, the deformation of the first upsetting forging is 25%-30%, and the deformation of the second upsetting forging is 30%-35%.

[0021] Preferably, in the high-temperature homogenization treatment, the temperature is raised to 1330℃-1350℃ by programmed heating, and the heating rate is 25℃ / min-30℃ / min.

[0022] Preferably, in step four, the temperature is lowered to 780℃-840℃ by programmed cooling, and the cooling rate is 20℃ / min-25℃ / min.

[0023] Preferably, in step four, the holding time is 40min-60min.

[0024] Preferably, in step four, the tempering treatment is five times, and the specific operation includes the following steps: the first tempering temperature is 615℃-625℃, the first tempering holding time is 25min-40min; the second tempering temperature is 635℃-645℃, the second tempering holding time is 25min-40min; the third tempering temperature is 655℃-665℃, the third tempering holding time is 25min-40min; the fourth tempering temperature is 675℃-685℃, the fourth tempering holding time is 25min-40min; the fifth tempering temperature is 690℃-700℃, and the fifth tempering holding time is 25min-40min.

[0025] The multiple temperature and multiple tempering can effectively eliminate the internal stress of the forging and improve the organization stability of the large-scale forging.

[0026] Preferably, in the fourth step, the normalizing treatment is five times of normalizing treatment, and the specific operation comprises the following steps: the first normalizing temperature is 910-920 DEG C, the first normalizing holding time is 15-20 min; the second normalizing temperature is 921-930 DEG C, the second normalizing holding time is 15-20 min; the third normalizing temperature is 931-940 DEG C, the third normalizing holding time is 15-20 min; the fourth normalizing temperature is 941-950 DEG C, the fourth normalizing holding time is 15-20 min; the fifth normalizing temperature is 951-960 DEG C, and the fifth normalizing holding time is 15-20 min.

[0027] The gradient normalizing treatment can form a certain temperature gradient in the forging, so that the large-size forging has good mechanical properties and anti-cracking performance.

[0028] The third aspect of the present application provides a large-size hot work die steel forging or a large-size hot work die steel forging prepared by the preparation method thereof in the field of developing new hot stamping die materials.

[0029] In summary, the present application uses 55NiCrMoV7 die steel return material as the main raw material, and through limiting the mass percentage of chemical components and the preparation process, a large-size hot work die steel forging with excellent performance is obtained, the preparation process of the large-size hot work die steel forging is simple, the operation is simple and convenient, and the finished product rate is high, and the problems of complex preparation process, strict conditions and low finished product rate of the 55NiCrMoV7 die steel large forging in the prior art are effectively solved. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] Embodiment 1

[0032] The present embodiment provides a large-size hot work die steel forging, which specifically comprises the following contents:

[0033] The mass percentage of the chemical components of the large-size hot work die steel forging is: C: 0.54%, Si: 0.27%, Mn: 0.83%, Cr: 0.94%, Ni: 1.64%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and inevitable impurities;

[0034] The preparation method of the large-size hot work die steel forging comprises the following steps:

[0035] Step one, the returned material is analyzed for chemical composition, and new material is dosed according to the requirements of the chemical composition; wherein the mass percentage of the chemical composition of the returned material is: C: 0.54%, Si: 0.26%, Mn: 0.78%, Cr: 0.94%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and unavoidable impurities;

[0036] Step two, the returned material is melted, when the returned material is melted by 75wt%, new material is added, melted, to obtain a mixed molten steel; the mixed molten steel is refined at 1560℃ under a vacuum degree of 1Pa for 3h to obtain a refined molten steel; at 1560℃, the refined molten steel is supplemented with metal material according to the design ratio, and the elements of the refined molten steel are adjusted to reach the composition content of the large-size hot work die steel forging to obtain a standard molten steel;

[0037] Step three, the standard molten steel is cast under an inert atmosphere, cooled to 1065℃ to obtain an alloy ingot; the alloy ingot is heated to 1340℃ at a heating rate of 25℃ / min for high-temperature homogenization treatment for 1.5h, cooled to 1240℃ for 25min, and sequentially subjected to two times of piercet forging, wherein the first piercet forging has a forging deformation of 25%, and the second piercet forging has a forging deformation of 35% to obtain a first alloy forging;

[0038] Step four, the first alloy forging is gradiently cooled to 800℃ at a cooling rate of 20℃ / min, and after being taken out of the furnace and oil-cooled, is tempered at 615℃-700℃ to obtain a second alloy forging; the second alloy forging is heated to 910℃-960℃ for normalizing treatment, and air-cooled to obtain a large-size hot work die steel forging.

[0039] The specific operation of the tempering treatment comprises the following steps:

[0040]

[0041] The specific operation of the normalizing treatment comprises the following steps:

[0042]

[0043] Example 2

[0044] The embodiment provides a large-size hot work die steel forging, and specifically comprises the following contents:

[0045] The mass percentage of the chemical composition of the large-size hot work die steel forging is: C: 0.55%, Si: 0.27%, Mn: 0.76%, Cr: 0.85%, Ni: 1.72%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and inevitable impurities;

[0046] The preparation method of the large-size hot work die steel forging comprises the following steps:

[0047] Step one, the returned material is analyzed for chemical composition, and new material is dosed according to the chemical composition requirements; wherein the mass percentage of the chemical composition of the returned material is: C: 0.55%, Si: 0.26%, Mn: 0.76%, Cr: 0.85%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and inevitable impurities;

[0048] Step two, the returned material is melted, when the returned material is melted by 80wt%, new material is added, melted, to obtain a mixed molten steel; the mixed molten steel is refined at 1560℃ under a vacuum degree of 2Pa for 3h to obtain a refined molten steel; at 1570℃, the refined molten steel is supplemented with metal materials according to the design ratio, and the elements of the refined molten steel are adjusted to reach the composition content of the large-size hot work die steel forging, to obtain a standard molten steel;

[0049] Step three, the standard molten steel is cast under an inert atmosphere, cooled to 1000℃, to obtain an alloy ingot; the alloy ingot is heated to 1330℃ at a heating rate of 30℃ / min for high-temperature homogenization treatment for 2h, cooled to 1210℃ for 30min, and sequentially subjected to two times of piercet forging, wherein the first piercet forging has a forging deformation of 30%, and the second piercet forging has a forging deformation of 30%, to obtain a first alloy forging;

[0050] Step four, the first alloy forging is gradiently cooled to 800℃ at a cooling rate of 20℃ / min, and after being taken out of the furnace and oil-cooled, is tempered at 615-700℃ to obtain a second alloy forging; the second alloy forging is heated to 910-960℃ for normalizing treatment, and air-cooled to obtain the large-size hot work die steel forging.

[0051] The specific operation of the tempering treatment comprises the following steps:

[0052]

[0053] The specific operation of the normalizing treatment comprises the following steps:

[0054]

[0055] Embodiment 3

[0056] The embodiment provides a large-size hot work die steel forging, and particularly relates to the following contents:

[0057] The mass percentage of the chemical components of the large-size hot work die steel forging is as follows: C: 0.54%, Si: 0.27%, Mn: 0.83%, Cr: 0.94%, Ni: 1.64%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and inevitable impurities;

[0058] The preparation method of the large-size hot work die steel forging comprises the following steps:

[0059] In step one, the returned material is subjected to chemical component analysis, and new material is dosed according to the chemical component requirements; the mass percentage of the chemical components of the returned material is as follows: C: 0.54%, Si: 0.16%, Mn: 0.83%, Cr: 0.94%, Ni: 1.55%, Mo: 0.41%, V: 0.11%, S: 0.01%, P: 0.015%, and the balance of Fe and inevitable impurities;

[0060] In step two, the returned material is subjected to melting, new material is added when the returned material is melted by 75wt%, and then the mixed molten steel is obtained; the mixed molten steel is subjected to refining at 1550 DEG C under a vacuum degree of 2Pa for 3h, and the refined molten steel is obtained; the refined molten steel is supplemented with metal material at a design ratio at 1565 DEG C, and the elements of the refined molten steel are adjusted so as to reach the component content of the large-size hot work die steel forging, and the standard molten steel is obtained;

[0061] In step three, the standard molten steel is subjected to casting under an inert atmosphere, and the alloy ingot is obtained by cooling to 1065 DEG C; the alloy ingot is subjected to high-temperature homogenization treatment at a temperature increasing rate of 30 DEG C / min to 1340 DEG C for 1.5h, and then cooled to 1235 DEG C for 25min; the alloy ingot is subjected to two times of piercet forging in sequence, wherein the first piercet forging has a forging deformation of 25%, and the second piercet forging has a forging deformation of 35%, and the first alloy forging is obtained.

[0062] In step four, the first alloy forging is subjected to gradient cooling at a temperature decreasing rate of 20 DEG C / min to 800 DEG C, and then subjected to tempering treatment at 615 DEG C-700 DEG C after oil cooling, and the second alloy forging is obtained; the second alloy forging is subjected to normalizing treatment at 910 DEG C-960 DEG C, and then air-cooled, and the large-size hot work die steel forging is obtained.

[0063] The specific operation of the tempering treatment includes the following steps:

[0064]

[0065] The specific operation of the normalizing treatment includes the following steps:

[0066]

[0067] Example 4

[0068] The embodiment provides a large-size hot work die steel forging, which is different from the embodiment 1 in that the gradient tempering treatment is modified into tempering treatment at 660 DEG C for 2.5 h, and specifically includes the following contents:

[0069] The mass percentage content of the chemical components of the large-size hot work die steel forging is as follows: C: 0.54%, Si: 0.27%, Mn: 0.83%, Cr: 0.94%, Ni: 1.64%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and inevitable impurities;

[0070] The preparation method of the large-size hot work die steel forging includes the following steps:

[0071] In step one, the returned material is analyzed in terms of chemical components, and new material is prepared according to the requirements of the chemical components; wherein the mass percentage content of the chemical components of the returned material is as follows: C: 0.54%, Si: 0.26%, Mn: 0.78%, Cr: 0.94%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and inevitable impurities;

[0072] In step two, the returned material is melted, and when the returned material is melted by 75 wt%, new material is added and melted to obtain mixed liquid steel; the mixed liquid steel is refined at 1560 DEG C under a vacuum degree of 1 Pa for 3 h to obtain refined liquid steel; at 1560 DEG C, metal material is added to the refined liquid steel according to a designed proportion, and elements of the refined liquid steel are adjusted so as to reach the component content of the large-size hot work die steel forging, thereby obtaining standard liquid steel;

[0073] In step three, the standard liquid steel is cast under an inert atmosphere, and is cooled to 1065 DEG C to obtain an alloy ingot; the alloy ingot is heated to 1340 DEG C at a heating rate of 25 DEG C / min, and is subjected to high-temperature homogenization treatment for 1.5 h, and is cooled to 1240 DEG C for 25 min of insulation, and is subjected to two times of piercet forging in sequence, wherein the first piercet forging has a forging deformation of 25%, and the second piercet forging has a forging deformation of 35%, thereby obtaining a first alloy forging.

[0074] Step four, the first alloy forging gradient is cooled to 800℃ at a cooling rate of 20℃ / min, and then tempered at 660℃ for 2.5h after oil cooling, to obtain a second alloy forging; the second alloy forging is heated to 910-960℃ for normalizing treatment, and then air cooled to obtain a large-size hot work die steel forging.

[0075] The specific operation of the normalizing treatment includes the following steps:

[0076]

[0077] Example 5

[0078] The present example provides a large-size hot work die steel forging, which is different from example 1 in that the gradient normalizing treatment is replaced by normalizing treatment at 935℃ for 100min, and specifically includes the following contents:

[0079] The mass percentage of the chemical composition of the large-size hot work die steel forging is: C: 0.54%, Si: 0.27%, Mn: 0.83%, Cr: 0.94%, Ni: 1.64%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and unavoidable impurities;

[0080] The preparation method of the large-size hot work die steel forging includes the following steps:

[0081] Step one, the returned material is analyzed for chemical composition, and new material is dosed according to the requirements of the chemical composition; wherein the mass percentage of the chemical composition of the returned material is: C: 0.54%, Si: 0.26%, Mn: 0.78%, Cr: 0.94%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and unavoidable impurities;

[0082] Step two, the returned material is melted, and when the returned material is melted by 75wt%, new material is added for melting to obtain a mixed steel liquid; the mixed steel liquid is refined at 1560℃ under a vacuum degree of 1Pa for 3h to obtain a refined steel liquid; at 1560℃, the refined steel liquid is supplemented with metal materials according to the designed ratio, and the elements of the refined steel liquid are adjusted to reach the component content of the large-size hot work die steel forging to obtain a standard steel liquid;

[0083] Step three, casting the standard steel liquid under inert atmosphere, cooling to 1065 DEG C, obtaining alloy ingot; heating the alloy ingot to 1340 DEG C at a heating rate of 25 DEG C / min, carrying out high temperature homogenization treatment for 1.5h, cooling to 1240 DEG C, carrying out insulation for 25min, sequentially carrying out two times of piercet forging, wherein the first piercet forging has a forging deformation of 25%, the second piercet forging has a forging deformation of 35%, obtaining first alloy forge piece;

[0084] Step four, gradiently cooling the first alloy forge piece to 800 DEG C at a cooling rate of 20 DEG C / min, carrying out insulation, carrying out tempering treatment at 615 DEG C-700 DEG C after oil cooling, obtaining second alloy forge piece; heating the second alloy forge piece to 935 DEG C, carrying out normalizing treatment for 100min, air cooling, obtaining large-size hot work die steel forge piece.

[0085] The tempering treatment includes the following steps:

[0086]

[0087] Comparative example 1

[0088] The present comparative example provides a large-size hot work die steel forge piece, which is different from example 1 in that the Si+Mo is 0.8%, and specifically includes the following contents:

[0089] The large-size hot work die steel forge piece has the following mass percentage of chemical components: C: 0.54%, Si: 0.28%, Mn: 0.83%, Cr: 0.94%, Ni: 1.64%, Mo: 0.52%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and inevitable impurities.

[0090] The preparation method of the large-size hot work die steel forge piece includes the following steps:

[0091] Step one, carrying out chemical component analysis on the return material, and carrying out new material batching according to the chemical component requirement; wherein the return material has the following mass percentage of chemical components: C: 0.54%, Si: 0.26%, Mn: 0.78%, Cr: 0.94%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and inevitable impurities.

[0092] Step two, melting the return material, when the return material is melted by 75wt%, adding new material, melting, obtaining a mixed molten steel; refining the mixed molten steel at 1560℃ under a vacuum degree of 1Pa for 3h, obtaining a refined molten steel; supplementing metal material into the refined molten steel according to a designed ratio at 1560℃, adjusting the elements of the refined molten steel to reach the component content of the large-size hot work die steel forging, obtaining a standard molten steel;

[0093] Step three, casting the standard molten steel under an inert atmosphere, cooling to 1065℃, obtaining an alloy ingot; high-temperature homogenizing the alloy ingot at a heating rate of 25℃ / min to 1340℃ for 1.5h, cooling to 1240℃ for 25min, sequentially performing two times of open-die forging, wherein the first open-die forging has a forging deformation of 25%, and the second open-die forging has a forging deformation of 35%, obtaining a first alloy forging;

[0094] Step four, gradiently cooling the first alloy forging to 800℃ at a cooling rate of 20℃ / min, holding, after oil cooling, performing tempering treatment at 615℃-700℃, obtaining a second alloy forging; heating the second alloy forging to 910℃-960℃, performing normalizing treatment, air cooling, obtaining the large-size hot work die steel forging.

[0095] The tempering treatment specifically includes the following steps:

[0096]

[0097] The normalizing treatment specifically includes the following steps:

[0098]

[0099] Comparative Example 2

[0100] This comparative example provides a large-size hot work die steel forging, which is different from Example 1 in that Mn+Cr+V is 2.06%, specifically including the following contents:

[0101] The mass percentage content of the chemical components of the large-size hot work die steel forging is: C: 0.54%, Si: 0.27%, Mn: 0.85%, Cr: 1.10%, Ni: 1.64%, Mo: 0.41%, V: 0.11%, S: 0.006%, P: 0.008%, and the balance of Fe and unavoidable impurities;

[0102] The preparation method of the large-size hot work die steel forging includes the following steps:

[0103] Step one, the return material is analyzed for chemical composition, and new material is dosed according to the chemical composition requirements; wherein the mass percentage of the chemical composition of the return material is: C: 0.54%, Si: 0.26%, Mn: 0.78%, Cr: 0.94%, Ni: 1.63%, Mo: 0.40%, V: 0.08%, S: 0.011%, P: 0.013%, and the balance of Fe and inevitable impurities;

[0104] Step two, the return material is melted, when the return material is melted by 75wt%, new material is added, melted, to obtain mixed molten steel; the mixed molten steel is refined at 1560℃ under a vacuum degree of 1Pa for 3h to obtain refined molten steel; at 1560℃, metal material is added to the refined molten steel according to the design ratio, and the elements of the refined molten steel are adjusted to reach the composition content of the large-size hot work die steel forging, to obtain standard molten steel;

[0105] Step three, the standard molten steel is cast under an inert atmosphere, cooled to 1065℃ to obtain an alloy ingot; the alloy ingot is heated to 1340℃ at a heating rate of 25℃ / min for high-temperature homogenization treatment for 1.5h, cooled to 1240℃ for 25min, and sequentially subjected to two times of piercet forging, wherein the first piercet forging has a forging deformation of 25%, and the second piercet forging has a forging deformation of 35%, to obtain a first alloy forging;

[0106] Step four, the first alloy forging is gradiently cooled to 800℃ at a cooling rate of 20℃ / min, and then tempered at 615-700℃ after oil cooling to obtain a second alloy forging; the second alloy forging is heated to 910-960℃ for normalizing treatment, and then air-cooled to obtain a large-size hot work die steel forging.

[0107] The specific operation of the tempering treatment includes the following steps:

[0108]

[0109] The specific operation of the normalizing treatment includes the following steps:

[0110]

[0111] In order to further embody the technical effect of the present application, the large-size hot work die steel forgings obtained in Examples 1-5 and Comparative Examples 1-2 are subjected to relevant performance tests, specifically including the following contents: 1000 forgings are prepared, and the yield rate thereof (with no cracks on the surface and no internal cracks in ultrasonic flaw detection as the finished product standard) is counted; room temperature tensile test is tested according to the national standard GB / T228.1-2010; the hardness of the sample is tested by using an HRC-150 Rockwell hardness tester; impact test is tested according to the NADCA#207-90 standard, and the obtained test results are shown in Table 1.

[0112] Table 1 Performance test results of the large-size hot work die steel forgings obtained in Examples 1-5 and Comparative Examples 1-2

[0113]

[0114] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of making a large size hot work die steel forging, characterized by: The method comprises the following steps: Step one, chemical composition analysis is performed on the returned material, and new material is dosed according to the chemical composition requirements; Step two, the returned material is melted, when the returned material is melted by 70wt%-80wt%, new material is added and melted to obtain mixed molten steel; the mixed molten steel is refined at 1530℃-1580℃ under a vacuum degree of 1Pa-2Pa to obtain refined molten steel; the elements of the refined molten steel are adjusted at 1550℃-1570℃ to obtain standard molten steel; Step three, the standard molten steel is cast under an inert atmosphere, cooled to 1000℃-1100℃ to obtain an alloy ingot; the alloy ingot is heated to 1330℃-1350℃ for high-temperature homogenization treatment, cooled to 1210℃-1260℃ for insulation, and sequentially subjected to two times of piercet forging to obtain a first alloy forge piece; Step four, the first alloy forge piece is cooled to 780℃-840℃ for insulation, and after oil cooling, is subjected to tempering treatment at 615℃-700℃ to obtain a second alloy forge piece; the second alloy forge piece is heated to 910℃-960℃ for normalizing treatment, and air-cooled to obtain a large-size hot-working die steel forge piece; In step four, the tempering treatment is five times of tempering treatment, and the specific operation comprises the following steps: the first time of tempering is at 615℃-625℃, the first time of tempering insulation is for 25min-40min; the second time of tempering is at 635℃-645℃, the second time of tempering insulation is for 25min-40min; the third time of tempering is at 655℃-665℃, the third time of tempering insulation is for 25min-40min; the fourth time of tempering is at 675℃-685℃, the fourth time of tempering insulation is for 25min-40min; the fifth time of tempering is at 690℃-700℃, the fifth time of tempering insulation is for 25min-40min; In step four, the normalizing treatment is five times of normalizing treatment, and the specific operation comprises the following steps: the first time of normalizing is at 910℃-920℃, the first time of normalizing insulation is for 15min-20min; the second time of normalizing is at 921℃-930℃, the second time of normalizing insulation is for 15min-20min; the third time of normalizing is at 931℃-940℃, the third time of normalizing insulation is for 15min-20min; the fourth time of normalizing is at 941℃-950℃, the fourth time of normalizing insulation is for 15min-20min; the fifth time of normalizing is at 951℃-960℃, the fifth time of normalizing insulation is for 15min-20min; The mass percentage of the chemical composition of the large-size hot work die steel forging is: C: 0.52%-0.58%, Si: 0.15%-0.35%, Mn: 0.70%-0.90%, Cr: 0.85%-1.15%, Ni: 1.55%-1.72%, Mo: 0.38%-0.49%, V: 0.05%-0.12%, S: ≤0.01%, P: ≤0.02%, and the balance of Fe and inevitable impurities; and 0.60%≤[Si]+[Mo]≤0.72%; 1.75%≤[Mn]+[Cr]+[V]≤1.98%, wherein [Si] represents the content of Si in the large-size hot work die steel forging, [Mo] represents the content of Mo in the large-size hot work die steel forging, [Mn] represents the content of Mn in the large-size hot work die steel forging, [Cr] represents the content of Cr in the large-size hot work die steel forging, and [V] represents the content of V in the large-size hot work die steel forging.

2. The method of making a large size hot work die steel forging of claim 1, wherein: In step one, the mass percentage of the chemical composition of the return material is: C: 0.50%-0.58%, Si: 0.15%-0.30%, Mn: 0.70%-0.80%, Cr: 0.95%-1.15%, Ni: 1.55%-1.72%, Mo: 0.38%-0.42%, V: 0.05%-0.10%, S: ≤0.03%, P: ≤0.03%, and the balance of Fe and inevitable impurities.

3. The method of making a large size hot work die steel forging of claim 1, wherein: In step two, the holding time of the refining is 2h-4h; and / or In step three, the holding time of the high-temperature homogenization treatment is 1h-2h; and / or In step three, the holding time is 20min-30min; and / or In step three, the forging deformation of the first drawing and upsetting forging is 25%-30%, and the forging deformation of the second drawing and upsetting forging is 30%-35%.

4. The method of making a large size hot work die steel forging of claim 1 or 3, wherein: In the high-temperature homogenization treatment, the temperature is raised to 1330℃-1350℃ by programmed heating, and the heating rate is 25℃ / min-30℃ / min.

5. The method of making a large size hot work die steel forging of claim 1, wherein: In step four, the temperature is lowered to 780℃-840℃ by programmed cooling, and the cooling rate is 20℃ / min-25℃ / min; and / or In step four, the holding time is 40min-60min.

6. Application of the large-size hot work die steel forging prepared by the preparation method of the large-size hot work die steel forging according to any one of claims 1-5 in the field of developing hot stamping die materials.

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