Forming process of cold extrusion part

Abstract

The invention discloses a forming process of a cold extrusion part, which comprises a rough blank manufacturing step, and the rough blank manufacturing step comprises the following steps: heating steel to 1000-1050 DEG C, and carrying out die forging and punching to form a die forging blank; the die forging blank is immediately immersed in the normalizing liquid, the liquid is discharged when the die forging blank is cooled to 580-680 DEG C, and the die forging blank is transferred to an isothermal normalizing furnace for isothermal normalizing; and the die forging blank obtained after isothermal normalizing is immediately put into a spheroidizing annealing furnace, heat preservation is conducted for 13-15 h at the temperature of Ac1 + 10-30 DEG C, then the die forging blank is cooled to Ar1-20-30 DEG C along with the furnace, heat preservation is conducted for 16-20 h, then the die forging blank is discharged out of the furnace and air-cooled, and a rough blank used for rough turning is obtained. The rough blank manufacturing step is short in time consumption, flaky carbides in original flaky pearlite can be spheroidized and converted into spherical carbide particles, spherical pearlite with granular carbides dispersed and distributed on a ferrite matrix is formed, the hardness of the rough blank is remarkably reduced to 135-145 HB, and therefore the cold machining deformation capacity of the rough blank is improved, and subsequent cold extrusion forming is facilitated.

Description

Technical Field

[0001] The invention relates to the field of gear manufacturing, and in particular to a forming process for cold extrusion parts. Background Art

[0002] At present, most automotive gear products are still produced by cutting methods such as gear hobbing, gear shaping, and gear shaving, which have low production efficiency. For example, the gear making process of a small diameter gear takes 10 to 20 minutes, and the material utilization rate is also low (generally, the material utilization rate is only 30% to 40%). A large amount of precious metal becomes chips, and a lot of energy is wasted.

[0003] The production of gears using cold extrusion technology can not only greatly improve production efficiency, but also significantly save materials and achieve the precision required for automotive gears. Compared with the cutting method, the production efficiency of the cold extrusion method can generally reach 10 to 20 pieces / min, which can save 20% to 30% of materials and reduce the total production cost of gears by 10% to 20%.

[0004] Automobile gears mainly include three types: spur gears, helical gears and bevel gears. The production process of heavy-duty gearbox cylindrical gears using cold extrusion technology is: hot-rolled round steel blanking → pre-forging → normalizing → spheroidizing annealing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low-temperature tempering → gear grinding → surface phosphating → finished parts. Spheroidizing annealing is an indispensable heat treatment process before cold extrusion in the precision plastic forming process of carburizing steel gears. The appropriate spheroidizing annealing process can not only adjust the microstructure of the carburizing steel gear blank, but also greatly reduce the hardness of the gear blank, thereby reducing the deformation resistance in the subsequent cold extrusion forming process, protecting the cold extrusion die and extending the service life of the die.

[0005] The current spheroidizing annealing process for cold extruded parts is: (750-780)℃×(13-15)h→(660-710)℃×(16-20)h→cooled to (200-400)℃ and taken out of the furnace. After the gear blank is final forged at above 970℃, the external force is removed after the forging is stopped. The gear blank will undergo static recrystallization under the action of high temperature, and the local grains will grow secondary and cause mixed crystals. In addition, during the air cooling (generally using the stack cooling method), due to the different cooling rates of different parts of the same workpiece, secondary band segregation and even abnormal structures such as bainite will appear, making the uniformity of the structure and hardness of the gear blank poor. After the gear blank is forged and stacked, it is directly spheroidized and annealed without the homogenization heat treatment, which will produce uneven tissue inheritance. After spheroidizing annealing, the gear blank (the current production furnace load is generally more than 20 tons) is cooled to 400℃ and then taken out of the furnace. This cooling stage takes more than 80 hours, occupies a large production capacity, and has low production efficiency. Summary of the invention

[0006] The invention provides a forming process for cold extruded parts. The rough blank manufacturing step in the forming process is time-saving, and the lamellar carbides in the original lamellar pearlite can be spheroidized and converted into spherical carbide particles, so as to form spherical pearlite with granular carbides dispersed on a ferrite matrix, and the hardness of the rough blank is significantly reduced to 135-145HB, thereby improving the cold processing deformation capacity of the rough blank and facilitating subsequent cold extrusion forming.

[0007] The technical solution provided by the present invention is as follows:

[0008] The present invention provides a forming process for a cold extruded part, comprising a rough blank manufacturing step, wherein the rough blank manufacturing step comprises:

[0009] The steel is heated to 1000-1050°C, and die-forged and punched to form a die-forged billet;

[0010] Immerse the die forging billet in normalizing liquid immediately, remove it from the liquid when it cools to 580-680℃ and transfer it to an isothermal normalizing furnace for isothermal normalizing;

[0011] The die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace, kept at Ac1+10~30℃ for 13~15h, then cooled with the furnace to Ar1-20~30℃, kept for 16~20h, then taken out of the furnace and air-cooled to obtain a rough billet for rough turning.

[0012] Compared with the prior art, the present invention increases the furnace exit temperature of the die forging billet after spheroidizing annealing, can significantly shorten the furnace cooling time, greatly shorten the rough billet manufacturing step time, and the hardness of the rough billet can be reduced to a hardness (135-145HB) that is less damaging to the cold extrusion die. The present invention reduces the occupation of the spheroidizing annealing furnace by the die forging billet, saves a lot of energy consumption, thereby reducing production costs, and has broad application prospects.

[0013] The present invention immediately immerses the die forging billet in the normalizing liquid and cools it to 580-680°C, which can shorten the cooling time between the final forging temperature and the normalizing temperature. The temperature of the normalizing liquid is 580-680°C, and immersing the die forging billet in the 580-680°C normalizing liquid can avoid defects caused by the die forging billet being rapidly cooled.

[0014] In some embodiments of the present invention, the initial forging temperature of the die forging punching is 980-1030° C., and the final forging temperature is 950-970° C. Compared with the prior art, the present invention reduces the final forging temperature, which can prevent the die forging blank from static recrystallization under high temperature, and the secondary growth of local grains to cause mixed crystals.

[0015] In some embodiments of the present invention, the isothermal normalizing is: isothermal holding at 550-650°C for 1-3 hours. Isothermal normalizing is carried out in an isothermal normalizing furnace, and then transferred to a spheroidizing annealing furnace for isothermal spheroidization. The isothermal normalizing furnace can be quickly transferred out to facilitate isothermal normalizing treatment of the next batch of die forging billets.

[0016] In some embodiments of the present invention, the time of cooling with the furnace is 4 to 6 hours. The present invention increases the temperature of the second insulation stage in the spheroidizing annealing furnace and air cools the furnace at this temperature, which can shorten the time of cooling with the furnace to 4 to 6 hours.

[0017] In some embodiments of the present invention, the die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace and heated to Ac1+10-30°C within 2-5 hours. In the present invention, the die forging billet after isothermal normalizing is not air-cooled to room temperature, but the die forging billet after isothermal normalizing is directly placed in a spheroidizing annealing furnace immediately, which can make full use of the heat of the die forging billet after normalizing, omit the air cooling time, and shorten the heating time.

[0018] In some embodiments of the present invention, Ac1+10-30° C. is 750-760° C. At this temperature, spheroidized graphite can be quickly formed in the die forging billet, thereby improving the processing performance of the die forging billet.

[0019] In some embodiments of the present invention, Ar1-20-30° C. is 680-700° C. At this temperature, more spheroidized graphite can be formed in the die forging billet, thereby improving the processing performance of the die forging billet.

[0020] In some embodiments of the present invention, the steel is one of Cr-Nb carburizing steel, SCM420H carburizing steel, and 20CrMnTiH carburizing steel. These steels are suitable for manufacturing gears, especially heavy-duty gearbox cylindrical gears.

[0021] In some embodiments of the present invention, the cold-extruded part is a gear.

[0022] In some embodiments of the present invention, after the rough blank manufacturing step, the rough blank used for rough turning is subjected to rough turning, polymer lubrication, cold extrusion, finish turning, carburizing heat treatment, intermediate cold treatment, secondary heating, quenching, low temperature tempering, finishing processing, and surface phosphating in sequence to obtain a finished cold extruded part.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] (1) The rapid spheroidizing annealing process for carburized steel gear blanks provided by the present invention eliminates the uneven structure formed during the air cooling process of the existing gear blank forging by isothermal normalizing with forging residual heat, and refines the austenite grains to obtain a fine pearlite + ferrite structure, thereby preparing the structure for the subsequent spheroidizing annealing process.

[0025] (2) The present invention makes full use of the waste heat of the gear blank, directly heats the isothermal gear blank to Ac1+(10-30)°C, keeps it warm for 13-15 hours, cools it down with the furnace for (4-6) hours to Ar1-(20-30)°C, keeps it warm for 16-20 hours, and then directly takes it out of the furnace for air cooling, thus saving a lot of energy and greatly shortening the time for reheating and cooling the gear blank with the furnace.

[0026] (3) After isothermal spheroidizing treatment, there is no need to cool the furnace to a lower temperature before taking it out of the furnace. It can be applied to almost all carburized steel gear blanks, which can greatly shorten the process cycle of gear blank spheroidizing annealing, improve production efficiency, reduce equipment resource occupation, save a lot of energy consumption, thereby reducing production costs, and has broad application prospects. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range. Similarly, any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0029] It should be noted that, in the description of this article, unless otherwise specified, "above", "below" are inclusive numbers, and the meaning of "multiple" in "one or more" is two or more. Relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0030] In the description of this specification, the description with reference to the terms "any embodiment / method", "one embodiment / method", "some embodiments / methods", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments / methods or examples. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.

[0031] The term "Ac1" of the present invention refers to the starting temperature of transformation from pearlite to austenite during heating, and the temperature above "Ac1" is the austenitizing temperature; the term "Ar1" refers to the starting temperature of transformation from austenite to pearlite during cooling.

[0032] The above summary of the invention of the present invention is not intended to describe each disclosed embodiment or each implementation in the present invention. The following description more specifically illustrates exemplary embodiments. These embodiments can be used in various combinations. In each embodiment, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0033] As mentioned above, in order to reduce the deformation resistance of steel during cold extrusion, reduce its damage to the cold extrusion die, and extend the service life of the die, the rough blank is usually spheroidized annealed before cold extrusion to adjust the microstructure of the rough blank to reduce the hardness of the rough blank. In the prior art, the spheroidizing annealing process of the rough blank is: (750-780)℃×(13-15)h→(660-710)℃×(16-20)h→cooling to (200-400)℃→out of the furnace. Since the cooling stage with the furnace takes more than 80 hours and occupies a large production capacity, the production efficiency of the forming process of cold extruded parts is relatively low.

[0034] In order to solve the problem of low production efficiency of the forming process of cold extruded parts, the present invention provides a forming process of cold extruded parts, including a rough blank manufacturing step, wherein the rough blank manufacturing step includes:

[0035] The steel is heated to 1000-1050°C, and die-forged and punched to form a die-forged billet;

[0036] Immerse the die forging billet in normalizing liquid immediately, remove it from the liquid when it cools to 580-680℃ and transfer it to an isothermal normalizing furnace for isothermal normalizing;

[0037] The die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace, kept at Ac1+10~30℃ for 13~15h, then cooled with the furnace to Ar1-20~30℃, kept for 16~20h, then taken out of the furnace and air-cooled to obtain a rough billet for rough turning.

[0038] The present invention immerses the die forging billet in normalizing liquid immediately after forming and cools it to 580-680°C, then normalizes it isothermally, and then heats the die forging billet after isothermal normalizing to Ac1+10-30°C for insulation, cools it to Ar1-20-30°C with the furnace, and then air-cools it out of the furnace. The present invention immerses the die forging billet in normalizing liquid immediately and cools it to 580-680°C, which can shorten the cooling time between the final forging temperature and the normalizing temperature. The temperature of the normalizing liquid is 580-680°C, and immersing the die forging billet in the 580-680°C normalizing liquid can avoid defects caused by rapid cooling of the die forging billet. Compared with the prior art, the present invention increases the out-of-furnace temperature of the die forging billet after spheroidizing annealing, which can greatly shorten the cooling time with the furnace, greatly shorten the time of the rough billet manufacturing step, and the hardness of the rough billet can be reduced to a hardness (135-145HB) that is less damaging to the cold extrusion die. The present invention reduces the occupation of the spheroidizing annealing furnace by the die forging billet, saves a large amount of energy consumption, thereby reducing production costs and has broad application prospects.

[0039] After the die forging billet is pile-cooled, spheroidizing annealing is directly performed without performing a heat treatment for homogenizing the structure, which will produce uneven tissue inheritance. The present invention performs isothermal normalizing on the die forging billet so that the metallographic structure of the die forging billet is fully transformed into uniform ferrite + pearlite, and the grain size is uniform without obvious banded structure. In some embodiments of the present invention, the isothermal normalizing is: isothermal insulation at 550-650°C for 1-3h. In the prior art, isothermal normalizing and spheroidizing annealing are performed in the same isothermal normalizing furnace. Since the spheroidizing annealing cycle is long, the isothermal normalizing furnace takes a long time, and the die forging billet has a long waiting time. Generally, it can only wait to enter the isothermal normalizing furnace for normalizing after cooling to a lower temperature. The isothermal normalizing of the present invention is carried out in an isothermal normalizing furnace, and then transferred to a spheroidizing annealing furnace for isothermal spheroidization, so that the isothermal normalizing furnace can be quickly transferred out, which is convenient for isothermal normalizing treatment of the next batch of die forging billets. Therefore, the present invention can immerse the die forging billet in normalizing liquid immediately after it is formed, and when it is cooled to 580-680°C, the liquid is taken out and transferred to an isothermal normalizing furnace for isothermal normalizing, thereby shortening the time from final forging to entering the isothermal normalizing furnace, as well as the cooling time between heating to the normalizing temperature.

[0040] Compared with ordinary normalizing, isothermal normalizing is easy to control the formation of non-equilibrium structure (such as bainite) because its organizational transformation is completed at a constant temperature, making the hardness more uniform, obtaining a more ideal microstructure, improving machining accuracy, reducing machining deformation, extending the life of machining tools, reducing the final heat treatment deformation and cracking tendency, and ensuring the final heat treatment quality. The present invention immerses the die forging billet in a normalizing liquid immediately after it is formed and cools it to 580-680°C, and then isothermal normalizing it, which can fully utilize the heat after the die forging billet is forged.

[0041] After the die forging billet is final forged at a temperature above 970°C, the external force is removed after the forging is stopped. The die forging billet will undergo static recrystallization under the action of high temperature, and the local grains will grow secondary to cause mixed crystals. In addition, during air cooling (generally using a pile cooling method), due to the different cooling rates of different parts of the same die forging billet, secondary band segregation and even abnormal structures such as bainite will occur, resulting in poor uniformity of the structure and hardness of the die forging billet. The present invention controls the initial forging temperature of the die forging punching to 980-1030°C and the final forging temperature to 950-970°C, which can eliminate the above problems.

[0042] In some embodiments of the present invention, the time of cooling with the furnace is 4 to 6 hours. The present invention increases the temperature of the second stage of the spheroidizing annealing furnace and air cools the steel out of the furnace at this temperature, which can shorten the time of cooling with the furnace to 4 to 6 hours without affecting the structure and hardness of the rough blank.

[0043] In some embodiments of the present invention, the die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace and heated to Ac1+10-30°C within 2-5 hours. In the present invention, the die forging billet after isothermal normalizing is not air-cooled to room temperature, but the die forging billet after isothermal normalizing is directly placed in a spheroidizing annealing furnace immediately, which can make full use of the heat of the die forging billet after normalizing, omit the air cooling time, and shorten the heating time.

[0044] In some embodiments of the present invention, Ac1+10-30° C. is 750-760° C. At this temperature, spheroidized graphite can be quickly formed in the die forging billet, thereby improving the processing performance of the die forging billet.

[0045] In some embodiments of the present invention, Ar1-20~30℃ is 680~700℃. After the present invention is kept at Ac1+10~30℃, it is cooled to 680~700℃ with the furnace, and can be taken out of the furnace after keeping it for 16~20h. Compared with the prior art, it is taken out of the furnace at a lower temperature, which greatly shortens the cooling time of the die forging billet with the furnace.

[0046] The forming process of the cold extruded parts of the present invention can be applied to almost all carburizing steels. In some embodiments, the steel is one of Cr-Nb carburizing steel, SCM420H carburizing steel, and 20CrMnTiH carburizing steel. Among them, by mass percentage, SCM420H carburizing steel includes: C 0.21%, Si 0.26%, Mn 0.67%, P 0.015%, S 0.022%, Cr1.05%, Mo 0.23%, Al 0.031%, and the rest is Fe and inevitable impurities; 20CrMnTiH carburizing steel includes: C0.20%, Si 0.23%, Mn 0.98%, P 0.019%, S 0.025%, Cr 1.21%, Ti 0.043%, Al0.019%, and the rest is Fe and inevitable impurities; Cr-Nb carburizing steel includes: C 0.16%, Si 0.23%, Mn0.58%, P0.019%, S 0.024%, Cr 1.09%, Nb 0.043%, Al 0.051%, B 0.0019%, Cu 0.17%, N 0.011%, and the rest Fe and inevitable impurities. These steel materials are only representative examples of the present invention and do not limit the types of steel materials of the present invention.

[0047] In some embodiments of the present invention, after the rough blank manufacturing step, the rough blank used for rough turning is subjected to rough turning, polymer lubrication, cold extrusion, finish turning, carburizing heat treatment, intermediate cold treatment, secondary heating, quenching, low temperature tempering, finishing processing, and surface phosphating in sequence to obtain a finished cold extruded part.

[0048] In some embodiments of the present invention, the cold extruded part is a gear. The production process of the gear is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → gear grinding → surface phosphating → finished product. Preferably, the gear is a heavy-duty gearbox cylindrical gear.

[0049] Example

[0050] The technical scheme of the present invention is described in detail by way of examples below. If the manufacturer's brand or preparation method is not specified, the raw materials, equipment or solvents used are all common raw materials, equipment or solvents on the market. Unless otherwise specified, the raw materials of the same name used in the following examples and comparative examples are all the same raw materials.

[0051] Example 1

[0052] The round steel bar material used in this embodiment is SCM420H carburizing steel. Calculated by mass percentage, the chemical composition of SCM420H carburizing steel includes: C 0.21%, Si 0.26%, Mn 0.67%, P 0.015%, S 0.022%, Cr 1.05%, Mo0.23%, Al 0.031%, and the rest is Fe and unavoidable impurities.

[0053] This embodiment provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0054] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0055] (2) SCM420H gear blank forging: The carburized hot-rolled round steel is heated to 1050°C after cutting, and then formed into a gear blank after die forging and punching. The initial forging temperature is controlled at 1020°C and the final forging temperature is controlled at 970°C.

[0056] (3) Isothermal normalizing with residual forging heat: The red-hot gear blank after final forging is directly immersed in a 680°C normalizing liquid, cooled to 680°C and then quickly transferred to an isothermal normalizing furnace for 3 hours at 650°C, so that the metallographic structure of the gear blank is fully transformed into uniform ferrite + pearlite, with uniform grain size and no obvious banded structure.

[0057] (4) Isothermal waste heat rapid spheroidizing annealing: The gear blank after isothermal normalizing is quickly transferred to the spheroidizing annealing furnace. The loading capacity of the gear blank in the isothermal normalizing furnace is 25 tons. Using the waste heat of the gear blank after isothermal normalization, the gear blank is heated to 760℃ for 2h, kept at this temperature for 15h, cooled with the furnace for 4h to 700℃, kept at this temperature for 20h, and then directly taken out of the furnace for air cooling to obtain the rough blank for rough turning.

[0058] The time required for the heat treatment process of step (3) and step (4) is: 3h+2h+15h+4h+20h=44h.

[0059] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 130~140HB.

[0060] Example 2

[0061] The round steel bar material used in this embodiment is 20CrMnTiH carburizing steel. The chemical composition of 20CrMnTiH carburizing steel includes, by mass percentage, C 0.20%, Si 0.23%, Mn 0.98%, P 0.019%, S 0.025%, Cr 1.21%, Ti 0.043%, Al 0.019%, and the rest is Fe and unavoidable impurities.

[0062] This embodiment provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0063] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0064] (2) 20CrMnTiH gear blank forging: The carburized steel hot-rolled round steel is heated to 1020℃ after cutting, and is formed into a gear blank after die forging and punching. The initial forging temperature is controlled at 980℃ and the final forging temperature is controlled at 950℃.

[0065] (3) Isothermal normalizing with residual forging heat: The red-hot gear blank after final forging is directly immersed in a 580°C normalizing liquid, cooled to 580°C and then quickly transferred to an isothermal normalizing furnace for 1 hour at 550°C to fully transform the metallographic structure of the gear blank into uniform ferrite + pearlite with uniform grain size and no obvious banded structure.

[0066] (4) Isothermal waste heat rapid spheroidizing annealing: The cooled gear blank is placed in a spheroidizing annealing furnace with a loading capacity of 21 tons. The gear blank is heated to 750°C for 4 hours using the waste heat after isothermal treatment, kept at this temperature for 13 hours, cooled with the furnace for 6 hours to 680°C, kept at this temperature for 18 hours, and then directly removed from the furnace for air cooling to obtain a rough blank for rough turning.

[0067] The time required for the heat treatment process of step (3) and step (4) is: 1h+4h+13h+6h+18h=42h.

[0068] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 125~135HB.

[0069] Example 3

[0070] The round steel bar material used in this embodiment is Cr-Nb carburizing steel. The chemical composition of Cr-Nb carburizing steel includes, by mass percentage, C 0.16%, Si 0.23%, Mn 0.58%, P0.019%, S 0.024%, Cr 1.09%, Nb0.043%, Al 0.051%, B 0.0019%, Cu 0.17%, N 0.011%, and the rest is Fe and unavoidable impurities.

[0071] This embodiment provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0072] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0073] (2) Forging of Cr-Nb carburizing steel gear blanks: The carburizing steel hot-rolled round steel is heated to 1035°C after cutting, and then formed into gear blanks after die forging and punching. The initial forging temperature is controlled at 1000°C and the final forging temperature is controlled at 960°C.

[0074] (3) Isothermal normalizing with residual heat from forging: The red-hot gear blank after final forging is directly immersed in a 620°C normalizing liquid, cooled to 620°C and then quickly transferred to an isothermal normalizing furnace and kept at 600°C for 1 hour to fully transform the metallographic structure of the gear blank into uniform ferrite + pearlite with uniform grain size and no obvious banded structure.

[0075] (4) Isothermal waste heat rapid spheroidizing annealing: The cooled gear blank is placed in a spheroidizing annealing furnace with a loading capacity of 30 tons. The gear blank is heated to 760°C for 5 hours using the waste heat after isothermal treatment, kept at this temperature for 14 hours, cooled with the furnace to 690°C for 5 hours, kept at this temperature for 16 hours, and then directly removed from the furnace for air cooling to obtain a rough blank for rough turning.

[0076] The time required for the heat treatment process of step (3) and step (4) is: 1h+5h+14h+5h+16h=41h.

[0077] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 105~115HB.

[0078] Comparative Example 1

[0079] The round steel bar material used in this comparative example is SCM420H carburizing steel. Calculated by mass percentage, the chemical composition of SCM420H carburizing steel includes: C 0.21%, Si 0.26%, Mn 0.67%, P 0.015%, S 0.022%, Cr 1.05%, Mo0.23%, Al 0.031%, and the rest is Fe and unavoidable impurities.

[0080] This comparative example provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → gear grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0081] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0082] (2) SCM420H gear blank forging: The carburized hot-rolled round steel is heated to 1050°C after cutting, and then formed into a gear blank after die forging and punching. The initial forging temperature is controlled at 1020°C and the final forging temperature is controlled at 970°C.

[0083] (3) Air cooling after forging: The red-hot tooth blank after final forging is placed in the air to cool naturally to room temperature.

[0084] (4) Spheroidizing annealing: The cooled gear blank is placed in a spheroidizing annealing furnace with a loading capacity of 25 tons. The gear blank is heated to 760°C for 8 hours, kept at this temperature for 15 hours, cooled with the furnace to 700°C for 4 hours, kept at this temperature for 20 hours, then cooled with the furnace to 400°C for 85 hours, and then air-cooled out of the furnace to obtain a rough blank for rough turning.

[0085] The time required for the heat treatment process of step (3) and step (4) is: 8h+15h+4h+20h+85h=132h.

[0086] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 135~145HB.

[0087] Comparative Example 2

[0088] The round steel bar material used in this comparative example is 20CrMnTiH carburizing steel. Calculated by mass percentage, the chemical composition of 20CrMnTiH carburizing steel includes: C 0.20%, Si 0.23%, Mn 0.98%, P 0.019%, S 0.025%, Cr 1.21%, Ti 0.043%, Al 0.019%, and the rest is Fe and unavoidable impurities.

[0089] This comparative example provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → gear grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0090] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0091] (2) 20CrMnTiH gear blank forging: The carburized steel hot-rolled round steel is heated to 1020℃ after cutting, and is formed into a gear blank after die forging and punching. The initial forging temperature is controlled at 980℃ and the final forging temperature is controlled at 950℃.

[0092] (3) Isothermal normalizing with residual forging heat: The gear blank after final forging is placed in the air to cool naturally to room temperature.

[0093] (4) Isothermal residual heat rapid spheroidizing annealing: The cooled gear blank is placed in a spheroidizing annealing furnace with a loading capacity of 21 tons. The gear blank is heated to 750°C for 7 hours, kept at this temperature for 13 hours, cooled with the furnace to 680°C for 6 hours, kept at this temperature for 18 hours, and then cooled with the furnace to 400°C for 82 hours before being air-cooled to obtain a rough blank for rough turning.

[0094] The time required for the heat treatment process of step (3) and step (4) is: 7h+13h+6h+18h+82h=126h.

[0095] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 130~140HB.

[0096] Comparative Example 3

[0097] The round steel bar material used in this comparative example is Cr-Nb series carburizing steel. Calculated by mass percentage, the chemical composition of Cr-Nb series carburizing steel includes: C 0.16%, Si 0.23%, Mn 0.58%, P0.019%, S 0.024%, Cr 1.09%, Nb0.043%, Al 0.051%, B 0.0019%, Cu 0.17%, N 0.011%, and the rest is Fe and unavoidable impurities.

[0098] This comparative example provides a cold extrusion heavy-duty gearbox cylindrical gear forming process. The production process of heavy-duty gearbox cylindrical gears is: rough blank manufacturing → rough turning → polymer lubrication → cold extrusion tooth shape → fine turning chamfering → carburizing heat treatment → intermediate cold treatment → secondary heating → quenching → low temperature tempering → gear grinding → surface phosphating → finished product. The specific process flow of the rough blank manufacturing steps is:

[0099] (1) Round steel cutting: The round steel bar with a specification of Φ110 mm is cut into 205 mm sections by a CNC round steel cutting machine to ensure that the cutting size is accurate, the end surface of the section is high in flatness, and there is no burr, so as to obtain carburized steel hot-rolled round steel.

[0100] (2) Forging of Cr-Nb carburizing steel gear blanks: The carburizing steel hot-rolled round steel is heated to 1250℃ after cutting, and then formed into gear blanks after die forging and punching. The initial forging temperature is controlled at 1200℃ and the final forging temperature is controlled at 1050℃.

[0101] (3) Forging waste heat austenitization and insulation: The red-hot forging billet after final forging is quickly transferred to the mesh belt furnace for insulation using the forging waste heat. The temperature of the mesh belt furnace is set to 950°C and the insulation time is 110 min to fully austenitize the forging billet.

[0102] (4) Intermediate cooling: The austenitized forging blank is placed in the intermediate cooling zone and rapidly cooled to 620°C. The cooling time is controlled to 10 min to avoid the appearance of proeutectoid ferrite in the forging blank.

[0103] (5) Three-stage isothermal spheroidizing annealing: The first stage: the forging billet after intermediate cooling treatment is immediately transferred to the isothermal furnace, and the loading capacity of the gear billet is 30 tons. The isothermal temperature is controlled at 620℃, and the isothermal time is 2h; the second stage: the forging billet after the first stage isothermal treatment is heated to 770℃ for 4h, and the isothermal time is 2h; the third stage: the forging billet after the second stage isothermal treatment is cooled in the furnace for 6h to 680℃, and the isothermal time is 5h. After cooling in the furnace for 65h to 500℃, it is taken out of the furnace and air-cooled to room temperature to obtain the rough billet for rough turning.

[0104] The time required for the heat treatment process of step (3), step (4) and step (5) is: 2h+2h+4h+2h+6h+5h+65h=86h.

[0105] The metallographic structure of the rough blank is spheroidized cementite + ferrite, and the cross-sectional hardness is 112~123HB.

[0106] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A forming process for cold extruded parts, characterized in that: The method comprises a rough blank manufacturing step, wherein the rough blank manufacturing step comprises: The steel is heated to 1000-1050°C, and die-forged and punched to form a die-forged billet; Immerse the die forging billet immediately in the normalizing liquid, cool it to 580-680℃, remove it from the liquid and transfer it to an isothermal normalizing furnace for isothermal normalizing; The die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace, kept at Ac1+10~30℃ for 13~15h, then cooled with the furnace to Ar1-20~30℃, kept for 16~20h, then taken out of the furnace and air-cooled to obtain a rough billet for rough turning.

2. The forming process of cold extruded parts according to claim 1, characterized in that: The initial forging temperature of die forging punching is 980~1030℃, and the final forging temperature is 950~970℃.

3. The forming process of cold extruded parts according to claim 1, characterized in that: The isothermal normalizing is: isothermal insulation at 550-650° C. for 1-3 hours.

4. The forming process of cold extruded parts according to claim 1, characterized in that: The time for furnace cooling is 4 to 6 hours.

5. The forming process of cold extruded parts according to claim 1, characterized in that: The die forging billet after isothermal normalizing is immediately placed in a spheroidizing annealing furnace and heated to Ac1+10~30℃ within 2~5h.

6. The forming process of cold extruded parts according to claim 1, characterized in that: Ac1+10~30℃ is 750~760℃.

7. The forming process of cold extruded parts according to claim 1, characterized in that: Ar1-20~30℃ is 680~700℃.

8. The forming process of cold extruded parts according to claim 1, characterized in that: The steel material is one of Cr-Nb carburizing steel, SCM420H carburizing steel and 20CrMnTiH carburizing steel.

9. The forming process of cold extruded parts according to claim 1, characterized in that: The cold extruded part is a gear.

10. The forming process of cold extruded parts according to claim 1, characterized in that: After the rough blank manufacturing step, the rough blank used for rough turning is subjected to rough turning, polymer lubrication, cold extrusion, finish turning, carburizing heat treatment, intermediate cold treatment, secondary heating, quenching, low temperature tempering, finishing processing, and surface phosphating in sequence to obtain a finished cold extruded part.