Punching die for bearing ring production and machining treatment technology of punching die

Abstract

The invention discloses a punching die for bearing ring production and a machining process of the punching die. And the punching die is prepared by processing a 4Cr5MoSiWV1-Nb steel alloy bar with niobium in gradient distribution. The alloy bar comprises the following chemical components in percentage by weight: 0.32%-0.45% of carbon, 4.75%-5.50% of chromium, 0.35%-0.50% of manganese, 0.80%-1.20% of silicon, 1.10%-1.55% of molybdenum, 0.50%-1.00% of tungsten, 0.80%-1.20% of vanadium, less than or equal to 0.03% of sulfur, less than or equal to 0.03% of phosphorus and niobium with the content in gradient change from the surface to the center of the alloy bar, the niobium content in the center of the alloy bar is 0, the niobium content in the surface is 0.10%-0.20%, and the balance of iron and inevitable impurities. The punching die prepared from the alloy bar is high in surface fatigue resistance, small in abrasion and long in service life.

Description

Technical Field

[0001] The present invention relates to the technical field of bearing processing equipment, and particularly relates to an alloy bar, a punching die processed and prepared from the alloy bar, a processing technology of the punching die, and an application of the punching die in manufacturing a punching die for a bearing ring forging processed by hot deformation. Background Art

[0002] The ring is an important component of a bearing. The ring is generally produced by a process flow of induction heating, blanking, upsetting, forming, bottom cutting, punching, and sizing. Forming is a process of punching a hole with a skin on the upset blank using a punching die, and the operation is carried out on a press.

[0003] 4Cr5MoSiV1 steel (H13) is a hot work die steel, and its composition (by weight percentage) mainly includes: carbon 0.32% - 0.45%, chromium 4.75% - 5.50%, manganese 0.35% - 0.50%, silicon 0.80% - 1.20%, molybdenum 1.10% - 1.55%, vanadium 0.80% - 1.20%, sulfur ≤ 0.03%, phosphorus ≤ 0.03%, and the rest is iron and inevitable impurities. 4Cr5MoSiV1 steel (H13) has high hardenability and toughness, excellent thermal cracking resistance, and small heat treatment deformation, but its wear resistance is generally average. 4Cr5MoSiV1 steel (H13) is widely used in manufacturing forging dies, hot extrusion dies, die casting dies for alloys such as copper and aluminum, etc. Bearing enterprises often use 4Cr5MoSiV1 steel (H13) to manufacture punching dies for bearing rings. When punching, the temperature of the blank is above 800°C, and the temperature is transferred to the punching die, causing the punching die to be heated passively. After the punching die leaves the blank, the temperature drops rapidly. Therefore, the punching die is always in an alternating process of heating expansion - cooling contraction during work, resulting in fatigue cracks such as turtle cracks or reticular cracks on the surface of the punching die. In addition, when punching, the blank is deformed under the extrusion of the punching die, so the blank will strongly rub the surface of the punching die, and the blank is softened at high temperature and easily adheres to the surface of the punching die, and these behaviors all aggravate the surface wear of the punching die. The interaction of surface fatigue and surface wear causes the surface of the punching die to fail after working for a short time and needs to be replaced, which not only wastes expensive die steel materials, but also interrupts the production rhythm and reduces production efficiency, bringing great economic losses to the enterprise.

[0004] The patent specification with the publication number CN115505850A discloses an alloy material, a punching die and a processing technology. The chemical composition of the alloy material by weight percentage is as follows: carbon 0.36% - 0.42%, chromium 5.05% - 5.25%, manganese 0.40% - 0.50%, silicon 1.05% - 1.15%, molybdenum 1.35% - 1.50%, vanadium 0.95% - 1.05%, niobium 0.06% - 0.12%, rare earth yttrium 0.006% - 0.012%, rare earth terbium 0.06% - 0.12%, sulfur ≤ 0.002%, phosphorus ≤ 0.015%, and the rest is iron and inevitable impurities; in the alloy material, the weight of rare earth yttrium is 10% of the weight of niobium, and the weights of rare earth terbium and niobium are equal. The punching die is processed from the alloy material as the raw material. Based on the composition of the original H13 steel, by adding niobium (containing 0.06% - 0.12% niobium by weight percentage), the molten steel is effectively purified, the hardness of the steel is improved, ensuring that the punching die has high hardness and wear resistance. At the same time, the grains are refined, the coarsening of carbides is inhibited, the number of inclusions is reduced, and the inclusions are spherical, improving the comprehensive mechanical properties of the steel, especially the thermal fatigue resistance. However, in this patent technology, niobium is uniformly incorporated into the matrix phase of the alloy material, resulting in a relatively large consumption of niobium and increasing the material cost. In addition, the uniform doping of the matrix phase also brings an adverse result that the internal and external mechanical properties are the same, unable to meet the composite requirements of high toughness inside and high wear resistance on the surface of the punching die. When the niobium content is low, although the overall strength and toughness of the material can be improved, the surface hardness cannot meet the high wear resistance requirements of the punching die; when the niobium content is high, the overall hardness of the material is high, but the strength and toughness decrease, and the punching die is prone to punching fracture. Summary of the Invention

[0005] The present invention provides an alloy rod, a punching die processed and prepared from the alloy rod, and a processing technology for the punching die. The punching die prepared using the alloy rod has high surface fatigue resistance, small wear, and long service life. Using the alloy rod to manufacture punching dies has important application value in the field of bearing processing.

[0006] The specific technical solutions are as follows:

[0007] [1] A 4Cr5MoSiWV1-Nb steel alloy bar with a gradient distribution of niobium, the chemical composition by weight percentage is: carbon 0.32% - 0.45% (such as 0.40% etc.), chromium 4.75% - 5.50% (such as 5.00% etc.), manganese 0.35% - 0.50% (such as 0.40% etc.), silicon 0.80% - 1.20% (such as 1.00% etc.), molybdenum 1.10% - 1.55% (such as 1.30% etc.), tungsten 0.50% - 1.00% (such as 0.90% etc.), vanadium 0.80% - 1.20% (such as 1.00% etc.), sulfur ≤ 0.03%, phosphorus ≤ 0.03%, and niobium with a content that varies in a gradient from the surface to the center of the alloy bar, and the niobium content at the center of the alloy bar is 0, the niobium content at the surface is 0.10% - 0.20% (such as 0.14%, 0.15%, 0.16% etc.), preferably 0.14% - 0.16%, further preferably 0.15%, the niobium decreases from the surface to the center, showing a gradient distribution, and the rest is iron and inevitable impurities.

[0008] The diameter of the 4Cr5MoSiWV1-Nb steel alloy bar with a gradient distribution of niobium can be 40 - 100 mm, such as 65 mm etc.

[0009] In some embodiments, the 4Cr5MoSiWV1-Nb steel alloy bar with a gradient distribution of niobium is prepared by casting: spray a layer of niobium iron powder on the inner surface of the mold, and through a stepped gating system, make the molten alloy liquid fill the mold from bottom to top to avoid turbulence of the alloy liquid inside the mold; preheat the mold to 200 - 500 °C, such as 400 °C etc. before pouring.

[0010] The present invention requires that the alloy bar has high surface hardness and good internal toughness. For this reason, the present invention designs the pouring temperature to be 100 - 300 °C higher than the melting point of 4Cr5MoSiWV1, uses the waste heat of the molten metal to melt the niobium iron alloy powder sprayed on the inner surface of the mold, and allows niobium to diffuse inward; to ensure the melting of niobium, the lowest melting temperature of the alloy powder is achieved through the weight ratio of niobium to iron; at the same time, preheat the mold to 200 - 500 °C, such as 400 °C etc. before pouring, slow down the chilling effect of the mold, extend the residence time of the casting in the high-temperature zone, and promote the inward diffusion of niobium. Through the synergistic effect of the pouring temperature, the design of the niobium iron alloy powder, and the preheating of the mold, an alloy bar material with a gradient distribution of niobium is obtained, and then a composite alloy bar with different internal and external mechanical properties is obtained. If these three factors cannot be organically coordinated, then, on the one hand, the niobium iron powder is not completely melted, and on the other hand, the melted niobium is unevenly distributed, seriously segregated on the surface, becoming a crack source, reducing the surface toughness and fatigue life. At the same time, very little niobium diffuses towards the center of the alloy bar, and it is impossible to effectively improve the core properties. As a result, the punching die further obtained is prone to failure during application.

[0011] In some embodiments, zircon sand is used for molding.

[0012] In some preferred examples, the mass ratio of niobium to iron in the ferroniobium powder is 10:90, which has a low melting temperature.

[0013] In some embodiments, the mass of the sprayed ferroniobium powder is 0.05% to 2.50% of the mass of the poured alloy liquid, such as 0.50%, 1.00%, 1.50%, etc.

[0014] In some embodiments, the chemical components in the alloy liquid are by weight percentage: carbon 0.32% to 0.45% (such as 0.40%, etc.), chromium 4.75% to 5.50% (such as 5.00%, etc.), manganese 0.35% to 0.50% (such as 0.40%, etc.), silicon 0.80% to 1.20% (such as 1.00%, etc.), molybdenum 1.10% to 1.55% (such as 1.30%, etc.), tungsten 0.50% to 1.00% (such as 0.90%, etc.), vanadium 0.80% to 1.20% (such as 1.00%, etc.), sulfur ≤ 0.03%, phosphorus ≤ 0.03%, and the rest is iron and inevitable impurities.

[0015] In some preferred examples, the pouring temperature is 100 - 300 °C higher than the melting point of 4Cr5MoSiWV1, being 1600 - 1800 °C, such as 1750 °C, etc.

[0016] [2] A punching die prepared by processing a 4Cr5MoSiWV1-Nb steel alloy rod with a niobium gradient distribution as described in [1].

[0017] [3] The processing technology of the punching die according to [2], including:

[0018] Preparing a 4Cr5MoSiWV1-Nb steel alloy rod with a niobium gradient distribution by casting: spraying a layer of ferroniobium powder on the inner surface of the mold, and enabling the molten alloy liquid to fill the mold from bottom to top through a stepped gating system to avoid turbulence of the alloy liquid inside the mold; preheating the mold to 200 - 500 °C, such as 400 °C, etc., before pouring;

[0019] The 4Cr5MoSiWV1-Nb steel alloy rod with a niobium gradient distribution is first subjected to spheroidizing annealing treatment, then machined into the target structure and size, then quenched, and then tempered, and cooled to obtain the punching die.

[0020] In some embodiments, zircon sand is used for molding.

[0021] In some preferred examples, the mass ratio of niobium to iron in the ferroniobium powder is 10:90, which has a low melting temperature.

[0022] In some embodiments, the mass of the sprayed niobium iron powder is 0.05% to 2.50% of the mass of the poured alloy liquid, such as 0.50%, 1.00%, 1.50%, etc.

[0023] In some embodiments, the chemical components in the alloy liquid are by weight percentage: carbon 0.32% to 0.45% (such as 0.40%, etc.), chromium 4.75% to 5.50% (such as 5.00%, etc.), manganese 0.35% to 0.50% (such as 0.40%, etc.), silicon 0.80% to 1.20% (such as 1.00%, etc.), molybdenum 1.10% to 1.55% (such as 1.30%, etc.), tungsten 0.50% to 1.00% (such as 0.90%, etc.), vanadium 0.80% to 1.20% (such as 1.00%, etc.), sulfur ≤ 0.03%, phosphorus ≤ 0.03%, and the balance is iron and unavoidable impurities.

[0024] In some preferred examples, the pouring temperature is 100 - 300 °C higher than the melting point of 4Cr5MoSiWV1, being 1600 - 1800 °C, such as 1750 °C, etc.

[0025] In some embodiments, the spheroidizing annealing treatment specifically includes: heating to 840 - 900 °C, such as 860 ± 10 °C, etc., holding for 120 - 240 min, such as 180 - 200 min, etc., furnace cooling to 700 - 750 °C, such as 730 ± 10 °C, etc., holding for 120 - 240 min, such as 180 - 200 min, etc., and then furnace cooling to 480 - 500 °C and taking out of the furnace for air cooling.

[0026] In some embodiments, the quenching specifically includes: preheating to 800 - 850 °C, such as 830 ± 5 °C, etc., holding for 20 - 60 min, such as 20 - 25 min, 30 min, etc., then heating to 1000 - 1100 °C, such as 1050 ± 5 °C, etc., holding for 10 - 100 min, such as 15 - 20 min, etc., and quenching in oil.

[0027] In some embodiments, the tempering treatment specifically includes: performing high-temperature tempering twice, each tempering temperature being 450 - 600 °C, such as 560 ± 10 °C, etc., each tempering time being 20 - 300 min, such as 120 - 125 min, etc., and oil cooling.

[0028] [4] Application of the 4Cr5MoSiWV1-Nb steel alloy bar with a niobium gradient distribution according to [1] or the punching die according to [2] in manufacturing a punching die for a bearing ring forging processed by hot deformation.

[0029] Exemplarily, the alloy bar of the present invention can be used to manufacture a punching die for bearing ring forgings, heat-treat it according to the designed process, install the manufactured punching die on a press, and produce bearing ring blanks (for example, with an inner hole diameter of 60 mm), and record the service life of the punching die.

[0030] The present invention can obtain a punching die with low cost, high surface fatigue resistance, small wear, and long service life.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] Since the temperature of the bearing blank is above 800 °C, the heat of the blank is conducted to the punching die, causing it to heat up. Therefore, high requirements are imposed on the high-temperature mechanical properties of the punching die. Compared with 4Cr5MoSiV1, 4Cr5MoSiWV1-Nb has an increased tungsten element, which improves the high-temperature strength, red hardness, and anti-tempering softening ability of the punching die, and is particularly suitable for the high-temperature working conditions of punching bearing blanks with the punching die. Since tungsten forms stable carbides with carbon, the wear of the punching die at high temperatures can be significantly reduced. Tungsten can also inhibit grain growth and improve the toughness of the punching die. In addition, during the tempering process, the carbides of tungsten can interact synergistically with the carbides of niobium to enhance the precipitation strengthening effect, which helps to improve the high-temperature strength and creep resistance of the steel, and is significantly better than the single use effect of tungsten or niobium.

[0033] The 4Cr5MoSiWV1-Nb alloy bar with a niobium gradient distribution is prepared by casting. Niobium iron powder is sprayed on the inner surface of the mold as a niobium source. The pouring temperature of 4Cr5MoSiWV1 is 1600-1800 °C. A higher pouring temperature can melt the niobium iron powder attached to the inner wall of the mold, thereby increasing the niobium content on the surface of the alloy bar. When the mass content of niobium in the niobium iron powder is 10%, its melting point is the lowest and it is easy to melt. If pure niobium powder is directly used, because niobium has a high melting point, it cannot be completely melted. A stepped gating system is adopted to make the molten metal fill the mold slowly and smoothly from bottom to top, avoiding turbulence of the molten metal inside the mold, so that the melted niobium can be concentrated on the surface layer of the alloy bar. The mold is preheated before pouring, and the solidification and cooling time of the alloy bar at high temperature is extended, which can ensure the diffusion of niobium to the center of the alloy bar and form a gradient distribution.

[0034] The beneficial effects brought by the niobium gradient distribution to the 4Cr5MoSiWV1-Nb alloy bar are as follows:

[0035] Effect 1: Niobium is a strong carbide-forming element. During the high-temperature austenitization process, it can inhibit grain boundary migration. The high niobium content on the surface of the alloy bar can significantly refine the surface grains, hinder the propagation of surface cracks, and improve the thermal fatigue resistance of the punching die at high temperatures, which is particularly suitable for the use conditions of punching dies with high impact and high cyclic thermal loads.

[0036] Function 2: The high niobium content on the surface of the alloy bar increases the amount of niobium carbide on the surface after tempering. Niobium carbide can synergistically interact with the carbides of vanadium, molybdenum, and tungsten, significantly increasing the surface hardness, effectively solving the problem of insufficient hardness of H13 steel, and significantly enhancing the wear resistance of the punching die during long-term high-temperature service. The same effect cannot be achieved with only the carbides of niobium, vanadium, molybdenum or vanadium, molybdenum, and tungsten.

[0037] Function 3: Niobium is a rare and precious metal with a high price. Gradient distribution of niobium from the surface to the center, with the highest surface concentration, can meet the requirements for the surface mechanical properties of the punching die; a small amount of niobium inside can improve the strength and toughness of the internal material. Compared with the uniform use of niobium, the gradient use of niobium can reduce the niobium usage by 30% - 50% or even more, effectively balancing the performance improvement and material cost. Specific implementation method

[0038] The following combines specific embodiments to further elaborate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operation methods without specific conditions noted in the following embodiments are usually in accordance with conventional conditions or in accordance with the conditions recommended by the manufacturer.

[0039] Embodiment 1:

[0040] A 4Cr5MoSiWV1-Nb alloy bar for a punching die of a bearing ring forging, comprising the following substances by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤ 0.03%, phosphorus ≤ 0.03%; the niobium content in the center is 0, the surface niobium content is 0.15%, and the niobium content shows a gradient distribution from the surface to the center; the rest is iron and inevitable impurities.

[0041] The above 4Cr5MoSiWV1-Nb alloy bar with a niobium gradient distribution is prepared by casting. Use zircon sand for molding, and spray a layer of niobium iron powder (niobium: iron mass ratio = 10:90) on the inner surface of the mold. The mass of the sprayed niobium iron powder is 1.00% of the mass of the poured alloy liquid. The chemical components in the alloy liquid are by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤ 0.03%, phosphorus ≤ 0.03%, and the rest is iron and inevitable impurities. Through a stepped gating system, the molten metal is filled into the mold slowly and smoothly from bottom to top to avoid turbulence of the molten metal inside the mold. The pouring temperature is 1750 °C. The mold is preheated to 400 °C before pouring. The diameter of the bar is 65 mm.

[0042] The 4Cr5MoSiWV1-Nb alloy rod with a niobium gradient distribution is first subjected to spheroidizing annealing, heated to 860 ± 10 °C and held for 180 min; furnace-cooled to 730 ± 10 °C and held for 180 min; furnace-cooled to 500 °C and then air-cooled after being taken out of the furnace.

[0043] The alloy rod is machined into a punching die with a conventional structure and size.

[0044] The punching die is quenched, preheated to 830 °C and held for 20 min; then heated to 1050 °C and held for 15 min, followed by oil quenching. Then it is subjected to high-temperature tempering twice, with the tempering temperature being 560 ± 10 °C and the tempering time being 120 min, and then oil-cooled.

[0045] The punching die is installed on a stamping machine to produce bearing ring blanks (inner hole diameter 60 mm). After continuous production for 64 h, the surface fails and needs to be replaced.

[0046] Comparative Example 1:

[0047] The difference from Example 1 is only that commercial 4Cr5MoSiV1 steel is used. The chemical composition of commercial 4Cr5MoSiV1 steel by weight percentage is: carbon 0.32% - 0.45%, chromium 4.75% - 5.50%, manganese 0.35% - 0.50%, silicon 0.80% - 1.20%, molybdenum 1.10% - 1.55%, vanadium 0.80% - 1.20%, sulfur ≤ 0.03%, phosphorus ≤ 0.03%; the rest is iron and unavoidable impurities.

[0048] A punching die is made using a commercial 4Cr5MoSiV1 steel alloy rod. A punching die of the same specification is manufactured using the same process as in Example 1 and production is carried out under the same conditions. After continuous production for 11 h, the surface fails and needs to be replaced.

[0049] Comparative Example 2:

[0050] The difference from Example 1 is only that the prepared 4Cr5MoSiWV1 alloy rod has no niobium, that is, niobium iron powder is not sprayed on the inner surface of the casting mold.

[0051] A punching die of the same specification is manufactured using the same process as in Example 1 and production is carried out under the same conditions. After continuous production for 32 h, it fractures.

[0052] Comparative Example 3:

[0053] The difference from Example 1 is only that it is cast with 4Cr5MoSiV1 without tungsten, that is, the chemical components in the alloy liquid are by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, vanadium 1.00%, sulfur ≤0.03%, phosphorus ≤0.03%, and the rest is iron and inevitable impurities. 4Cr5MoSiV1-Nb with a niobium gradient distribution is prepared.

[0054] The punching die with the same specifications is manufactured by the same process as in Example 1 and production is carried out under the same conditions. It fractures after continuous production for 29 h.

[0055] From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that the present invention simultaneously introduces tungsten and a niobium with a gradient distribution. The two cooperate with each other, significantly improving the surface fatigue resistance of the punching die, reducing wear, and extending the service life, which is significantly extended from no more than 32 h to 64 h.

[0056] Example 2:

[0057] A 4Cr5MoSiWV1-Nb alloy rod for a punching die of a bearing ring forging includes the following substances by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤0.03%, phosphorus ≤0.03%; the niobium content at the center is 0, the niobium content on the surface is 0.10%, and the niobium content shows a gradient distribution from the surface to the center; the rest is iron and inevitable impurities.

[0058] The 4Cr5MoSiWV1-Nb alloy rod with a niobium gradient distribution is prepared by the same casting process as in Example 1, but the amount of sprayed niobium iron powder is 0.67% of the mass of the cast alloy liquid.

[0059] The punching die with the same specifications is manufactured by the same process as in Example 1 and production is carried out under the same conditions. The surface fails after continuous production for 52 h and needs to be replaced.

[0060] Example 3:

[0061] A 4Cr5MoSiWV1-Nb alloy rod for a punching die of a bearing ring forging includes the following substances by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤0.03%, phosphorus ≤0.03%; the niobium content at the center is 0, the niobium content on the surface is 0.20%, and the niobium content shows a gradient distribution from the surface to the center; the rest is iron and inevitable impurities.

[0062] The 4Cr5MoSiWV1-Nb alloy rod with a niobium gradient distribution was prepared by the same casting process as in Example 1, but the amount of sprayed niobium iron powder was 1.33% of the mass of the poured alloy liquid.

[0063] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 59 h, the surface failed and needed to be replaced.

[0064] Comparative Example 4:

[0065] A 4Cr5MoSiWV1-Nb alloy rod for a punching die of a bearing ring forging includes the following substances by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤0.03%, phosphorus ≤0.03%; the niobium content at the center is 0, the niobium content on the surface is 0.05%, and the niobium content from the surface to the center shows a gradient distribution; the rest is iron and unavoidable impurities.

[0066] The 4Cr5MoSiWV1-Nb alloy rod with a niobium gradient distribution was prepared by the same casting process as in Example 1, but the amount of sprayed niobium iron powder was 0.33% of the mass of the poured alloy liquid.

[0067] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 39 h, the surface failed and needed to be replaced.

[0068] Comparative Example 5:

[0069] A 4Cr5MoSiWV1-Nb alloy rod for a punching die of a bearing ring forging includes the following substances by weight percentage: carbon 0.40%, chromium 5.00%, manganese 0.40%, silicon 1.00%, molybdenum 1.30%, tungsten 0.90%, vanadium 1.00%, sulfur ≤0.03%, phosphorus ≤0.03%; the niobium content at the center is 0, the niobium content on the surface is 0.30%, and the niobium content from the surface to the center shows a gradient distribution; the rest is iron and unavoidable impurities.

[0070] The 4Cr5MoSiWV1-Nb alloy rod with a niobium gradient distribution was prepared by the same casting process as in Example 1, but the amount of sprayed niobium iron powder was 2.00% of the mass of the poured alloy liquid.

[0071] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 13 h, the surface failed and needed to be replaced. The reason is that excessive niobium causes niobium carbide to aggregate and grow at the grain boundaries, becoming the crack source, and the coarse niobium carbide also causes stress concentration.

[0072] Comparative Example 6:

[0073] The 4Cr5MoSiWV1-Nb alloy rod was prepared by the same casting process as in Example 3, but the mold was not preheated before pouring.

[0074] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 8 hours, the surface failed and needed to be replaced. Inspection found that there was still some unmolten niobium iron powder on the surface layer of the alloy rod, and the distribution of niobium incorporated into the surface layer of the alloy rod was also uneven.

[0075] Comparative Example 7:

[0076] The 4Cr5MoSiWV1-Nb alloy rod was prepared by the same casting process as in Example 3, but the pouring temperature was 1550 °C.

[0077] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 7 hours, the surface failed and needed to be replaced. Inspection found that there was still some unmolten niobium iron powder, and not only was the niobium content in the surface layer of the alloy rod low, but it was also severely aggregated and not fully dispersed.

[0078] Comparative Example 8:

[0079] The 4Cr5MoSiWV1-Nb alloy rod was prepared by the same casting process as in Example 3, but the mass ratio of niobium to iron in the niobium iron powder was 20:80.

[0080] The punching die of the same specification was manufactured by the same process as in Example 1, and production was carried out under the same conditions. After continuous production for 5 hours, the surface failed and needed to be replaced. Inspection found that most of the niobium iron powder did not melt, and the niobium content in the surface layer of the alloy rod was very low and segregated. The reason is that the melting point of the niobium iron powder with a mass ratio of niobium to iron of 20:80 is about 200 °C higher than that of the niobium iron powder with a mass ratio of 10:90.

[0081] The comparison between Example 3 and Comparative Examples 6-8 shows that it is necessary to comprehensively coordinate processes such as pouring temperature, niobium iron alloy powder design, and mold preheating in order to achieve full melting and uniform diffusion of niobium in the alloy rod.

[0082] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A 4Cr5MoSiWV1-Nb steel alloy rod with a niobium gradient distribution, characterized in that: The chemical composition is calculated by weight as follows: carbon 0.32% to 0.45%, chromium 4.75% to 5.50%, manganese 0.35% to 0.50%, silicon 0.80% to 1.20%, molybdenum 1.10% to 1.55%, tungsten 0.50% to 1.00%, vanadium 0.80% to 1.20%, sulfur ≤0.03%, phosphorus ≤0.03%, and niobium whose content changes gradually from the surface to the center of the alloy rod, and the niobium content in the center of the alloy rod is 0, and the niobium content on the surface is 0.10% to 0.20%, preferably 0.14% to 0.16%, and more preferably 0.15%, and the rest is iron and unavoidable impurities.

2. The 4Cr5MoSiWV1-Nb steel alloy rod with niobium gradient distribution according to claim 1, characterized in that: The diameter of the 4Cr5MoSiWV1-Nb steel alloy rod with niobium gradient distribution is 40-100 mm.

3. A punching die produced by processing the 4Cr5MoSiWV1-Nb steel alloy rod with niobium gradient distribution as claimed in claim 1 or 2.

4. The processing technology of the punching die according to claim 3 is characterized in that: include: A 4Cr5MoSiWV1-Nb steel alloy rod with a niobium gradient distribution is prepared by casting: a layer of ferroniobium powder is sprayed on the inner surface of a casting mold, wherein the mass ratio of niobium to iron in the ferroniobium powder is 10:90, and a molten alloy liquid is filled into the casting mold from bottom to top through a stepped pouring system to avoid turbulence of the alloy liquid inside the casting mold; the pouring temperature is 1600-1800° C., and the casting mold is preheated to 200-500° C. before pouring; The 4Cr5MoSiWV1-Nb steel alloy rod with niobium gradient distribution is firstly subjected to spheroidizing annealing treatment, then machined into a target structure and size, then quenched, then tempered, and cooled to obtain the punching die.

5. The processing process according to claim 4, characterized in that: The mass of the sprayed ferroniobium powder is 0.05% to 2.50% of the mass of the cast alloy liquid.

6. The processing technology according to claim 4, characterized in that: The chemical components in the alloy liquid are as follows by weight: carbon 0.32%-0.45%, chromium 4.75%-5.50%, manganese 0.35%-0.50%, silicon 0.80%-1.20%, molybdenum 1.10%-1.55%, tungsten 0.50%-1.00%, vanadium 0.80%-1.20%, sulfur ≤0.03%, phosphorus ≤0.03%, and the rest are iron and unavoidable impurities.

7. The processing process according to claim 4, characterized in that: The spheroidizing annealing treatment specifically includes: heating to 840-900° C., keeping the temperature for 120-240 minutes, furnace cooling to 700-750° C., keeping the temperature for 120-240 minutes, furnace cooling to 480-500° C., and air cooling after exiting the furnace.

8. The processing technology according to claim 4, characterized in that: The quenching specifically includes: preheating to 800-850° C., keeping warm for 20-60 minutes, then heating to 1000-1100° C., keeping warm for 10-100 minutes, and oil cooling quenching.

9. The processing process according to claim 4, characterized in that: The tempering treatment specifically includes: performing high temperature tempering twice, each tempering temperature is 450-600° C., each tempering time is 20-300 minutes, and oil cooling.

10. Use of the 4Cr5MoSiWV1-Nb steel alloy rod with niobium gradient distribution according to claim 1 or 2 or the punching die according to claim 3 in manufacturing a punching die for a bearing ring forging through hot deformation processing.