CN115045977A

CN115045977A - Medium-carbon bearing steel for flexible gear of robot harmonic speed reducer and production method thereof

Info

Publication number: CN115045977A
Application number: CN202210584327.2A
Authority: CN
Inventors: 刘烨; 尹青; 颉军定; 桂煜琳; 吴小林; 白云
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2022-05-26
Filing date: 2022-05-26
Publication date: 2022-09-13

Abstract

The invention relates to medium carbon bearing steel for a flexible gear of a harmonic speed reducer of a robot and a production method thereof, and the medium carbon bearing steel comprises the following chemical components: c: 0.36 to 0.43%, Si: 0.15 to 0.35%, Mn: 0.60-0.90%, Cr: 0.60-1.00%, S is less than or equal to 0.015%, P is less than or equal to 0.025%, Ni: 1.60-2.00%, Cu is less than or equal to 0.25%, Mo: 0.15-0.35%, less than or equal to 0.0010% of Ca, less than or equal to 0.003% of Ti, less than or equal to 0.0010% of O, less than or equal to 0.01% of As, less than or equal to 0.015% of Sn, less than or equal to 0.005% of Sb, and the balance of Fe and inevitable impurities. The production process comprises the steps of molten iron pretreatment, converter smelting, LF refining, RH refining, large-section CCM continuous casting billet, continuous casting billet slow cooling, continuous rolling, rolled material slow cooling, softening annealing and finishing, and the steel has high mechanical property, high purity and high tissue uniformity and meets the requirements of the steel for the flexible gear of the harmonic reducer of the robot.

Description

Medium carbon bearing steel for flexible gear of harmonic speed reducer of robot and production method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to medium carbon bearing steel for a flexible gear of a harmonic speed reducer of a robot and a production method thereof.

Background

The rising cost of labor and the accelerating aging of population have brought tremendous pressure to traditional manufacturing companies in recent years, and some companies have begun to upgrade intelligence to replace traditional manufacturing approaches to increase production efficiency and reduce costs. The intelligent robot industry has become a development direction of global manufacturing industry and has been developed vigorously.

There are three major core components in the intelligent robot: the device comprises a motion controller, a servo drive motor and a precision speed reducer, wherein the precision speed reducer is the most critical, and the manufacturing cost accounts for more than 35%. According to different transmission modes, the precision speed reducer is generally divided into an RV speed reducer and a harmonic speed reducer, wherein the harmonic speed reducer has the advantages of compact structure, light weight, small volume, high transmission efficiency, high transmission precision and the like, and is the most competitive precision speed reducer for the robot with the highest technical content at present.

The harmonic reducer is composed of four basic components: the flexible bearing is assembled on the wave generator to enable the flexible gear to generate controllable elastic deformation and to be meshed with the rigid gear to transmit power. When the wave generator rotates, the meshing state of the flexible gear and the rigid gear is also changed, so that each part of the flexible gear needs to bear various alternating stresses for a long time, and extremely strict requirements are provided for the precision and the performance of the flexible gear. The flexible gear is used as a key part of the harmonic speed reducer, and the fatigue life of the flexible gear generally determines the service life of the harmonic speed reducer. In summary, the flexible gear component of the harmonic reducer needs to be prepared from a special material with high purity, high tissue uniformity and long fatigue life.

At present, the flexible gear material of the harmonic reducer is monopolized by foreign enterprises, and the research and development of the material at home are blank. The core part materials of the harmonic speed reducer are imported for a long time, so that the production cost of the domestic intelligent robot is greatly improved, and the development of the intelligent robot industry in China is severely restricted.

At present, the flexible gear material of the harmonic reducer is mainly made of steel produced by a die casting process. The steel produced by the die casting process has certain advantages in the aspect of tissue uniformity, but has the obvious disadvantages of very low production efficiency, yield and productivity, very high energy consumption and production cost and the like. Therefore, the company develops and produces the steel for the flexible gear of the harmonic speed reducer with the advanced level in the world by adopting the vacuum degassing continuous casting and rolling process and improving key quality indexes such as purity of steel, oxygen content and residual harmful element content, steel structure uniformity and the like, thereby promoting the localization of key materials of the speed reducer of the robot.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for manufacturing bearing steel with high mechanical property, high structure uniformity and high purity aiming at the prior art. The invention reasonably designs chemical components, optimizes, researches and controls key procedures on the basis of producing high-purity bearing steel at present, ensures that steel has high mechanical property, high tissue uniformity and high purity, and meets the use performance of the steel for the flexible gear of the harmonic robot speed reducer.

The steel required by the invention has higher strength, certain toughness and impact resistance, and the specific requirements on mechanical properties are shown in the following table 1. In order to ensure the high strength of steel, the invention requires that the grain size is more than or equal to grade 6 and mixed crystal structure can not be generated.

TABLE 1

The invention requires the steel to have higher structure uniformity, so the steel has strict requirements on the macroscopic structure, the central porosity is required to be less than or equal to 1.0 grade, the general porosity is required to be less than or equal to 1.0 grade, the ingot type segregation is required to be less than or equal to 1.0 grade, the central segregation is required to be less than or equal to 1.5 grade, and shrinkage cavities, bubbles, cracks, inclusions, layering, peeling and white spots are not allowed to appear; secondly, in order to ensure the microstructure uniformity of steel, the invention requires that the grade of the banded structure does not exceed 2.

In order to meet the requirement that the flexible gear has longer service life and therefore requires higher purity of steel, the invention provides strict requirements for microscopic inclusions. Because the B-type and D-type inclusions belong to brittle inclusions, the hardness is high, and deformation cannot occur under the action of stress. Therefore, during the use process of the flexible gear, stress concentration is easily generated near the brittle inclusions, so that cracks are generated, the flexible gear fails in advance, and the larger the size of the inclusions is, the greater the damage is; the A-type and C-type inclusions belong to plastic inclusions, so that the ductility is high, and the damage to the service life of the flexible gear is small. The invention requires to test microscopic nonmetallic inclusions according to a GB/T10561A method, and the specific requirements for the rating of the microscopic nonmetallic inclusions are shown in the following table 2.

TABLE 2

The technical scheme adopted by the invention for solving the problems is as follows: the utility model provides a bearing steel for harmonic speed reducer machine flexbile gear of robot, the chemical composition is: c: 0.36 to 0.43%, Si: 0.15 to 0.35%, Mn: 0.60-0.90%, Cr: 0.60-1.00%, S is less than or equal to 0.015%, P is less than or equal to 0.025%, Ni: 1.60-2.00%, Cu is less than or equal to 0.25%, Mo: 0.15-0.35%, less than or equal to 0.0010% of Ca, less than or equal to 0.003% of Ti, less than or equal to 0.0010% of O, less than or equal to 0.01% of As, less than or equal to 0.015% of Sn, less than or equal to 0.005% of Sb, and the balance of Fe and inevitable impurities.

The bearing steel for the flexible gear of the harmonic speed reducer of the robot has the following chemical component design basis:

1) determination of the C content

Carbon content is one of the most important elements affecting part hardness and strength. The carbon content is increased, and the hardness and strength of the steel can be improved. However, too high a carbon content reduces the plasticity and toughness of the steel. The steel for the flexible gear of the harmonic robot speed reducer has high strength and certain toughness and impact resistance. The content of C in the invention is 0.36-0.43%.

2) Determination of the Si content

Silicon is a deoxidizing element in steel and increases the strength of steel in the form of solid solution strengthening. It can reduce the diffusion speed of carbon element in ferrite, and can make the carbide separated out in the course of tempering be not easily aggregated, and can raise the tempering stability of steel. In addition, silicon can reduce oxidation during friction heating, thereby improving the wear resistance of the steel. However, too high a silicon content leads to a decrease in toughness of the steel, and too high a silicon content increases the heat sensitivity, cracking and decarburization tendency of the steel. The Si content of the invention is 0.15-0.35%.

3) Determination of Mn content

Manganese has the function of solid solution strengthening to steel, and improves the strength of steel. Manganese is a deoxidizing and desulfurizing element in steel, and can form MnS inclusion with sulfur element in the steel smelting process, so that the cutting is easy to break, and the machinability of steel is ensured. However, the cracking sensitivity of the steel is increased by excessively high manganese content. The Mn content of the invention is controlled to be 0.60-0.90%.

4) Determination of the Cr content

Chromium is a strong carbide former and can improve the strength and wear resistance of steel. However, too high a chromium content may reduce the impact toughness of the steel. The range of the Cr content of the present invention is determined to be 0.60 to 1.00%.

5) Determination of Ni content

Nickel element can increase the hardenability of steel and can significantly improve its impact toughness, but nickel is also a precious metal, and too high a content increases costs. The Ni content of the invention is controlled to be 1.60-2.00%.

6) Determination of Mo content

The molybdenum element has the main functions of improving hardenability and mechanical properties of steel, and particularly has the effect of improving toughness. And the ductile-brittle transition temperature of the steel can be reduced, and the temper brittleness of the steel is inhibited. However, since molybdenum is a noble metal and the addition amount is too high, the manufacturing cost is increased, and thus the control range of the Mo content is determined to be 0.15 to 0.35% in the present invention.

7) Determination of Ca content

The calcium content increases the number and size of the spot-like oxides in the steel, and since the spot-like oxides have high hardness and poor plasticity, they do not deform when the steel deforms, and easily form voids at the interface, deteriorating the properties of the steel. The range of the Ca content of the invention is determined to be less than or equal to 0.001 percent.

8) Determination of the Ti content

Titanium element and N element are combined to form titanium nitride inclusion, which also belongs to brittle inclusion, has high hardness and sharp angle shape, and has great influence on the service life of the flexible gear, so the invention requires that Ti is less than or equal to 0.0030 percent

9) Determination of the O content

The oxygen exists in the steel in the form of oxide inclusions, and under the action of stress, the oxide cannot deform, stress concentration is generated nearby, cracks are further generated, and the service life of the flexible gear is too low. The invention requires that the oxygen content in the steel material cannot exceed 0.0010%.

10) P, S determination of content

The P element causes element segregation when the steel is solidified, and the P element is dissolved in ferrite to distort and coarsen crystal grains and increase cold brittleness, so that the P is determined to be less than or equal to 0.025 percent; s element is easy to cause hot brittleness of steel, ductility and toughness of the steel are reduced, and formed sulfide also destroys continuity of the steel, so that S is determined to be less than or equal to 0.015%.

11) Determination of As, Sn, Sb content

As, Sn, Sb and other trace elements belong to low-melting-point nonferrous metals, and exist in steel to cause the appearance of soft spots and uneven hardness on the surface of a part, so that the elements are regarded As harmful elements in the steel, and the content ranges of the elements are determined to be that As is less than or equal to 0.01 percent, Sn is less than or equal to 0.015 percent and Sb is less than or equal to 0.005 percent.

Another purpose of the application is to provide a production method of bearing steel for a flexible gear of a harmonic speed reducer of a robot, wherein a blank is smelted in a continuous casting mode, and the production and manufacturing process comprises molten iron pretreatment, top and bottom combined blown converter BOF-ladle refining furnace LF-vacuum circulating degassing furnace RH-large-section CCM continuous casting billet, continuous casting billet slow cooling, continuous rolling, rolled material slow cooling, softening annealing and finishing, and the specific process steps are as follows:

(1) smelting molten steel: smelting raw materials are sequentially subjected to KR pretreatment, converter smelting, LF refining and RH vacuum degassing to obtain pure molten steel according with chemical components. Molten steel smelting needs to be performed with molten iron pretreatment to obtain clean molten iron, so that the content of harmful element P is reduced; when oxygen blowing smelting is carried out in a converter, molten iron is converted into molten steel, the content of P is further reduced, the tapping end point C is controlled to be 0.10-0.25%, the end point P is controlled to be less than or equal to 0.025%, the quality of waste steel is strictly controlled, the content of residual element Cu is reduced, the Cu brittleness phenomenon of steel is avoided, a slag stopping control process is carried out before tapping, and the problem that the content of harmful elements As, Sn, Pb and Sb is higher in the prior art is solved; the tapping temperature of the converter is controlled to be 1620-1700 ℃, the temperature of the steel entering the LF refining furnace is ensured to be more than 1500 ℃, low Ti, low Ca alloy and high-quality refractory material are added in the LF refining process, the content of harmful elements Ti and Ca is controlled, a high-performance synthetic slag slagging and deoxidizing technology is adopted, the LF refining time is controlled to be more than 30min, the long-time inclusion removing process of a steel ladle is ensured, and non-metallic inclusions are enabled to float upwards fully; during RH vacuum degassing, ensuring that the furnace reaches sufficient vacuum degree, maintaining sufficient cycle treatment time, removing the content of harmful gas in steel, further removing nonmetallic inclusions by controlling the content of O, and ensuring the purity of steel;

(2) continuous casting: the large-section whole-process protection pouring is adopted, so that the secondary oxidation of molten steel is avoided; the large-section continuous casting billet with the size of 390mm multiplied by 510mm and above is adopted, so that the compression ratio of steel is more than 20, and the compactness and the macrostructure uniformity of the material are ensured; by adopting a tundish induction heating technology, the casting temperature of continuous casting is more than or equal to 1500 ℃, and the casting is carried out at a low superheat degree, the superheat degree is less than or equal to 25 ℃, so that the macrosegregation of a continuous casting billet is effectively improved; the casting blank microsegregation brought to the continuous casting blank by high alloy content is effectively improved by adopting a soft reduction process and combining an electromagnetic stirring technology, so that the material meets high uniformity, the growth of a columnar crystal area can be effectively inhibited, a central equiaxial crystal area is enlarged, and the structure crystal grains are finer; the continuous casting drawing speed is controlled to be 0.40-0.50m/min, so that the continuous casting process is stable, and the fluctuation of the liquid level is small;

(3) slow cooling of the continuous casting billet: and (3) performing pit annealing on the continuous casting blank, wherein the pit annealing temperature is higher than 650 ℃, and the pit annealing time is longer than 48 hours, so that the phenomenon that the steel cracks due to the change of thermal stress and structural stress on the surface and the inside of the steel is avoided. (ii) a

(4) Continuous rolling: the method adopts a high-temperature heating process, the continuous casting blank is heated to 1210-1260 ℃ in a heating furnace in a neutral or weak oxidizing atmosphere, heat preservation is fully carried out according to the size of the continuous casting blank, the total heating time is more than 3 hours, the full austenitizing recrystallization of the material is ensured, the steel has higher and uniform structure grain size, and the high uniformity of the material structure is ensured. After a casting blank is taken out of a furnace, removing phosphorus by high-pressure water, rolling at the temperature of 1000-1150 ℃, wherein the final rolling temperature is not less than 950 ℃, rolling into a round bar through three procedures of rough rolling, intermediate rolling and finish rolling, wherein the diameter range of the finished bar is 20-100 mm, the total compression ratio is not less than 20, the compression ratio of rough rolling is not less than 8, the compression ratio of intermediate rolling is not less than 5, and the finish rolling ensures the dimensional precision of the finished steel product;

(5) slow cooling of rolled stock: pit-leaving slow cooling is carried out on the rolled bar at the temperature of 480 ℃ or above, the slow cooling time is more than 60 hours, the pit-leaving temperature is less than 200 ℃, and in order to prevent coarse grains, the slow cooling is also beneficial to eliminating the residual stress on the surface of the steel;

(6) softening and annealing: softening and annealing the rolled bar within 24 hours after pit forming, wherein the softening and annealing temperature is 650-750 ℃, the heat preservation time is more than or equal to 7 hours, then the rolled bar is cooled to 500 ℃ along with the furnace, taken out of the furnace and air-cooled to room temperature, and the purpose of softening and annealing is as follows: in order to meet the requirement of a user on machining process of finished steel products, the hardness of the finished steel products is reduced, and the hardness of the steel products after softening and annealing is less than or equal to 269 HBW;

(7) and (3) finishing: the method comprises the finishing procedures of straightening, chamfering, nondestructive inspection and the like, wherein 100% of all products need to be subjected to nondestructive inspection, and the surface and internal quality of the products is ensured.

Compared with the prior art, the invention has the advantages that:

(1) iron is pretreated by molten iron in molten steel smelting, and the content of harmful element P is controlled;

(2) clean scrap steel is added in converter smelting, the quality of the scrap steel is strictly controlled, the content of residual element Cu is reduced, and the phenomenon of Cu brittleness caused by overhigh content of Cu is avoided; the slag-stopping control process is carried out before converter tapping, so that the problem of higher contents of harmful elements As, Sn, Pb and Sb in the prior art is solved;

(3) in the LF refining process, low-Ti and low-Ca alloy and high-quality refractory materials are selected, so that the content of harmful elements Ti and Ca in molten steel is reduced; the high-performance synthetic slag slagging and deoxidizing technology is adopted, the LF time is ensured to be more than or equal to 30min, impurities are ensured to be fully floated and removed along with slag, and the quantity and size of the impurities are effectively controlled;

(4) the content of O, H in the steel is reduced to an extremely low level by adopting an RH vacuum circulation degassing technology, and the content of gas elements in the steel is effectively controlled, so that the number of inclusions is further reduced, and the requirement of high purity of the steel is ensured. Through detection, the indexes of the product, such as the number, the size, the O content and the like, of the inclusions all reach the world leading level;

(5) the continuous casting adopts a tundish induction heating technology, the casting temperature of the continuous casting is more than or equal to 1500 ℃, the casting is carried out by adopting low superheat degree, the superheat degree is less than or equal to 25 ℃, and the macrosegregation of the continuous casting billet is effectively improved; the large-section continuous casting billet with the size of 390mm multiplied by 510mm and above is adopted, so that the compression ratio of steel is more than 20, and the compactness and the macrostructure uniformity of the material are ensured; the continuous casting drawing speed is controlled to be 0.40-0.50m/min, so that the continuous casting process is stable, and the fluctuation of the liquid level is small;

(6) in order to meet the high mechanical property of a flexible gear of a harmonic reducer, the medium carbon bearing steel reduces the carbon content, increases the contents of Cr, Ni and Mo alloy elements, and the high alloy element content can bring serious microsegregation to a continuous casting billet;

(7) the continuous rolling process adopts a high-temperature heating process, the heating temperature is controlled to be 1210-1260 ℃, the total heating time is more than 3 hours, the full austenitizing recrystallization of the material is ensured, the steel has higher and uniform tissue grain size, and the high uniformity of the material tissue is ensured.

(8) The bearing steel for the flexible gear of the harmonic speed reducer of the robot, which is produced by the invention, meets the following index requirements:

microscopic inclusions are detected according to a GB/T10561A method, the B fine system is less than or equal to 1.0 grade, the B coarse system is less than or equal to 0.5 grade, the D fine system is less than or equal to 1.0 grade, the D coarse system is less than or equal to 0.5 grade, and the DS system is less than or equal to 1.0 grade; the macrostructure requires that the center porosity is less than or equal to 1.0 grade, the general porosity is less than or equal to 1.0 grade, the ingot type segregation is less than or equal to 1.0 grade, the center segregation is less than or equal to 1.5 grade, and shrinkage cavities, bubbles, cracks, inclusions, layering, peeling and white spots are not allowed to occur. The metallographic structure after annealing has no band-shaped structure throughout the field of view.

Drawings

FIG. 1 shows the annealed structure (at 1/2R) of the product of example 1;

FIG. 2 shows the annealed structure (at 1/2R) of the product of example 2;

FIG. 3 shows the annealed structure (at 1/2R) of a comparative example (produced by die casting).

Detailed Description

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

The manufacturing process of the medium carbon bearing steel for the flexible gear of the harmonic reducer of the robot comprises the steps of molten iron pretreatment, top and bottom combined blown converter BOF, ladle refining furnace LF, vacuum circulating degassing furnace RH, large-section CCM continuous casting slab, continuous casting slab slow cooling, continuous rolling, rolled material slow cooling, softening annealing and finishing.

Specifically, high-quality molten iron, scrap steel and raw and auxiliary materials are selected during smelting, and a high-quality deoxidizer and a refractory material are selected. The tapping end point C of the converter is respectively controlled to be 0.10-0.25%, the end point P is controlled to be less than or equal to 0.025%, and the tapping temperature is 1620-1700 ℃. The casting temperature of continuous casting is more than or equal to 1500 ℃, the superheat degree is controlled within less than or equal to 25 ℃, and the drawing speed is controlled within 0.40-0.50 m/min. And (3) pit slow cooling the produced continuous casting slab, wherein the pit temperature is higher than 650 ℃, the pit slow cooling time is longer than 48 hours, and the pit discharging temperature is lower than 300 ℃. After the slow cooling is finished, the continuous casting slab is sent into a heating furnace with neutral or weak oxidizing atmosphere to be heated and rolled into a material, and the processes of steel rolling heating, rolling and cooling are shown in the following table 3. The rolled material needs to be put into a pit for slow cooling, the pit entering temperature is more than or equal to 480 ℃, the pit forming temperature is less than or equal to 300 ℃, the slow cooling time is more than or equal to 60 hours, the soft annealing treatment is carried out in 24 hours after slow cooling and pit discharging, the soft annealing temperature is 650 plus 750 ℃, the heat preservation time is more than or equal to 5 hours, and then the rolled material is cooled to 400 ℃ along with the furnace and then is taken out of the furnace for air cooling to the room temperature. And then, carrying out subsequent straightening and flaw detection on the bar to obtain a target bar finished product.

TABLE 3 rolled steel heating, rolling and cooling process

The chemical compositions (wt%) of the various examples of the present invention and (for comparison) the molded harmonic reducer flexspline materials currently used in the market are shown in table 4.

TABLE 4

	C	Si	Mn	P	S	Cr	Cu	Ni
									Example 1	0.39	0.24	0.77	0.021	0.006	0.8	0.02	1.71
Example 2	0.39	0.28	0.79	0.018	0.007	0.8	0.02	1.72
									Comparative example	0.41	0.23	0.81	0.019	0.008	0.8	0.18	1.61

TABLE 4

	Mo	As	Sn	Sb	Ca	Ti	O
								Example 1	0.23	0.0038	0.0015	0.0013	0.0002	0.0012	0.00041
Example 2	0.23	0.0038	0.0017	0.0013	0.0004	0.0012	0.00045
								Comparative example	0.16	0.0040	0.0087	0.0013	0.0003	0.0018	0.00133

From the aspect of composition, the chemical composition of the flexible gear material of the conventional harmonic reducer is optimized to a certain extent, the plasticity of the finished steel is reserved by reducing the content of C, and the strength and the impact toughness of the steel are improved by increasing the content of Ni and Mo. The content of residual element Cu is reduced by smelting in a converter and strictly controlling the quality of scrap steel, the phenomenon of Cu brittleness caused by overhigh content of Cu is avoided, the content of Sn is effectively reduced by carrying out a slag-stopping control process before tapping in the converter, and the content of Cu and Sn in the steel products of the invention is far less than that of die casting materials. Because LF refining adopts low-Ti and low-Ca alloy, the Ti content of the invention is far lower than that of die casting materials. The LF refining adopts a high-performance synthetic slag slagging and deoxidizing technology, an RH vacuum circulation degassing and a continuous casting whole-process protection pouring technology, the O content of the invention is obviously superior to that of a die casting material, and the quality of a real object reaches the international leading level.

The mechanical property data of the examples of the invention and the comparative examples are shown in Table 5.

TABLE 5

From the view of mechanical properties, the strength and the plasticity of the steel material are equivalent to those of die casting materials, the use requirements of the flexible gear of the harmonic reducer are met, and the reduction of the C content and the increase of the Ni and Mo contents do not obviously reduce the strength and the plasticity. The impact energy of the invention is much higher than that of die casting materials, which shows that the impact toughness can be improved by adding Ni and Mo, and the continuous casting process adopts a soft reduction and electromagnetic stirring process and the continuous rolling process adopts a high-temperature heating process, so that the structure can be effectively and uniformly organized and the crystal grains can be refined. Because the invention adopts softening annealing treatment, the hardness after annealing is obviously less than that of the die casting material, which is more beneficial to the machining of users.

The grain size rating results of the steels of the examples and comparative examples of the present invention are shown in Table 6.

TABLE 6

	Grain size/grade
		Example 1	8.5
Example 2	8
		Comparative example	7

According to the grain size result, the grain size rating result of the steel is obviously higher than that of a die casting material because the continuous casting process adopts a soft reduction combined electromagnetic stirring process and the continuous rolling adopts a high-temperature heating process, and the grain size rating result reaches the international advanced level.

The low power data for the inventive and comparative examples are shown in Table 7.

TABLE 7

	Center porosity	Generally loose	Ingot type segregation	Centre segregation
					Example 1	1.0	1.0	1.0	0
Example 2	1.0	1.0	1.0	0
					Comparative example	1.0	1.0	1.0	0

The low-power quality of the steel material of the invention is equivalent to that of a die casting material.

The results of the evaluation of the microscopic nonmetallic inclusions of the steels of the examples of the present invention and the comparative examples are shown in Table 8.

TABLE 8

Because the LF refining of the invention adopts a high-performance synthetic slag slagging and deoxidizing technology, an RH vacuum circulation degassing technology and a continuous casting whole-process protective pouring technology, the O content of the steel is far lower than that of a die casting material, the quantity and the size of the inclusions of the invention are further far smaller than those of the die casting material, and particularly on the indexes of B fine and DS brittle inclusions which can cause the flexible wheel material to fail in advance, the inclusion control level reaches the international advanced level.

The annealing structure view of the product of the example 1 at 1/2R is shown in figure 1, the annealing structure view of the product of the example 2 at 1/2R is shown in figure 2, and the annealing structure view of the product of the comparative example 1/2R is shown in figure 3.

The continuous casting process of the invention adopts the combination of soft reduction and electromagnetic stirring process, so that the microsegregation of the material can be obviously improved, the strip distribution of the banded structure of the annealed material is uniform, the bandwidth is narrower and is obviously smaller than that of the die casting material, and the steel of the invention does not find the banded structure penetrating through the field of view, and the banded structure is superior to the die casting material.

In summary, the bearing steel for the harmonic reducer flexspline and the production method thereof provided by the invention have the advantages that the overall idea of improving the purity of steel is adopted, the process routes of high efficiency, high capacity and low cost of vacuum degassing, continuous casting and rolling are adopted, and the key processes are optimized, researched and controlled, so that the steel can obtain higher purity and higher tissue uniformity on the basis of meeting the mechanical property of the steel. The competitiveness of the product in China is obviously enhanced on the aspects of production efficiency, production cost and product quality stability.

Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that modifications and variations of the present invention are possible to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The utility model provides a harmonic speed reducer of robot flexible gear is with well carbon bearing steel which characterized in that: the steel comprises the following chemical components: c: 0.36 to 0.43%, Si: 0.15 to 0.35%, Mn: 0.60-0.90%, Cr: 0.60-1.00%, S is less than or equal to 0.015%, P is less than or equal to 0.025%, Ni: 1.60-2.00%, Cu is less than or equal to 0.25%, Mo: 0.15-0.35%, less than or equal to 0.0010% of Ca, less than or equal to 0.003% of Ti, less than or equal to 0.0010% of O, less than or equal to 0.01% of As, less than or equal to 0.015% of Sn, less than or equal to 0.005% of Sb, and the balance of Fe and inevitable impurities.

2. The medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 1, characterized in that: the grain size of the steel is more than or equal to grade 6, and mixed crystal structure does not exist; the method of gold GB/T10561A is adopted to detect that the B fine system, the B coarse system, the D fine system, the D coarse system and the DS system of the microscopic nonmetallic inclusion are respectively less than or equal to 1.5 grade, less than or equal to 1.0 grade and less than or equal to 1.0 grade; GB/T1979 is adopted to grade the macrostructure of steel, and the requirements are that the central porosity is less than or equal to 1.5 grade, the general porosity is less than or equal to 1.0 grade, the ingot type segregation is less than or equal to 1.0 grade, and the central segregation is less than or equal to 1.5 grade; the yield strength is required to be more than or equal to 980MPa, the tensile strength is required to be more than or equal to 980MPa, the elongation is more than or equal to 12%, the reduction of area is more than or equal to 55%, the normal-temperature impact property AKV is more than or equal to 78J, the annealing hardness is less than or equal to 269HBW, and the metallographic structure after annealing does not have a strip-shaped structure penetrating through a view field.

3. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 1, characterized by comprising the following steps: the method comprises the following steps:

(1) smelting molten steel;

(2) a large-section CCM continuous casting billet;

(3) slowly cooling the continuous casting blank, wherein the temperature of a lower pit is higher than 650 ℃, and the slowly cooling time of the lower pit is ensured to be longer than 48 hours;

(4) continuous rolling;

(5) slow cooling of rolled stock: pit-removing slow cooling is carried out on the rolled bar at the temperature of 480 ℃ or above, the slow cooling time is more than 60 hours, the pit-removing temperature is less than 200 ℃, and the bar is softened and annealed within 24 hours after pit-removing;

(6) softening and annealing: the softening annealing temperature is 650-750 ℃, the heat preservation time is more than or equal to 7h, and then the temperature is cooled to 500 ℃ along with the furnace, and then the furnace is taken out for air cooling to the room temperature;

(7) and finishing, including finishing procedures such as straightening, chamfering, nondestructive inspection and the like, wherein 100% of all products need to be subjected to nondestructive inspection, so that the surface and internal quality of the products is ensured.

4. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 3, characterized by comprising the following steps: and (1) sequentially carrying out KR pretreatment on smelting raw materials through molten iron, smelting in an electric furnace or a converter, LF refining and RH or VD vacuum degassing.

5. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 4, characterized by comprising the following steps: the content of harmful element P is reduced by pretreating molten iron in molten steel smelting; when oxygen blowing smelting is carried out in a converter, the tapping end point C is controlled to be 0.10-0.25%, the end point P is controlled to be less than or equal to 0.025%, the quality of scrap steel is strictly controlled, and slag blocking control is carried out before tapping; controlling the tapping temperature of the converter at 1620-1700 ℃, ensuring the temperature of the steel entering the LF refining furnace to be more than 1500 ℃, adding low Ti and low Ca alloy and high-quality refractory materials in the LF refining process, adopting a high-performance synthetic slag slagging and deoxidizing technology, and controlling the LF refining time to be more than 30 min; and during RH vacuum degassing, ensuring that the furnace reaches sufficient vacuum degree, and maintaining sufficient circulating treatment time to remove the content of harmful gases in the steel.

6. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 3, characterized by comprising the following steps: the step (2) adopts a large-section continuous casting billet with the size of 390mm multiplied by 510mm and above, and the compression ratio of steel is more than 20; adopting a tundish induction heating technology, wherein the casting temperature of continuous casting is more than or equal to 1500 ℃, and the superheat degree is less than or equal to 25 ℃ for casting with low superheat degree; a soft reduction process is combined with an electromagnetic stirring technology; the continuous casting speed is controlled to be 0.40-0.50 m/min.

7. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 3, characterized by comprising the following steps: and (4) heating the continuous casting slab to 1210-1260 ℃ in a heating furnace in a neutral or weak oxidizing atmosphere by adopting a high-temperature heating process, wherein the total heating time is more than 3 hours.

8. The manufacturing method of the medium carbon bearing steel for the flexible gear of the robot harmonic reducer according to claim 7, characterized in that: after a casting blank is taken out of a furnace, removing phosphorus through high-pressure water, then, starting rolling at the temperature of 1000 plus 1150 ℃, wherein the final rolling temperature is more than or equal to 950 ℃, rolling the casting blank into a round bar through three processes of rough rolling, intermediate rolling and finish rolling, wherein the diameter range of the finished bar is 20-100 mm, the total compression ratio is more than or equal to 20, the compression ratio of rough rolling is more than or equal to 8, the compression ratio of intermediate rolling is more than or equal to 5, and the finish rolling ensures the size precision of the finished steel.