Preparation method of wheel hub bearing without macrosegregation

Abstract

The invention discloses a preparation method of a hub bearing without macrosegregation, and relates to the technical field of metal material processing, the preparation method comprises the following steps: step S101, converter smelting and external refining are carried out on molten steel to make the components of the molten steel reach preset values; s102, the molten steel is subjected to continuous casting to form a continuous casting blank, the superheat degree of the continuous casting molten steel is controlled to be 20-35 DEG C, and the cooling water amount of a crystallizer is larger than 0.5 L / kg; s103, the continuous casting billet is heated; s104, the continuous casting billet is subjected to water descaling, then the continuous casting billet is rolled, and hot-rolled round steel is formed; and S105, the hot-rolled round steel is subjected to induction heating to 1200-1250 DEG C, die forging is conducted, and controlled cooling is conducted to the room temperature after die forging. The hub bearing produced through the method is uniform in macroscopic component and structure and free of macrosegregation, and failure of the contact position of the hub bearing and a rolling body caused by ingot segregation can be effectively avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material processing, and particularly to a preparation method for a hub bearing without macrosegregation. Background Art

[0002] The hub bearing is a key component connecting the axle and the vehicle body of high-end cars, etc. The bearing ring is a hollow rotating part, integrated with the axle, and is usually made of medium-carbon non-quenched and tempered steel such as C56E2. After forging and controlled cooling, the surface of the position in contact with the rolling element is induction hardened to improve hardness and wear resistance. When forging the hub bearing, the ingot segregation of the raw material often flows to the position in contact with the rolling element, and the deformation amount at this position is small, making it particularly prone to problems such as coarse grains, resulting in unqualified quality of the hub bearing. Redistributing the forging deformation amount requires redesigning the die, which involves significant changes. If macrosegregation such as ingot segregation can be eliminated from the perspective of raw material production, the degree of coarse grains at the position in contact with the rolling element can be significantly reduced, which is of great significance for improving the quality of the hub bearing.

[0003] Ingot segregation is caused by the enrichment of solute elements in the molten steel at the front of the columnar crystal growth during the continuous casting of steel billets. Currently, generally, means such as reducing the superheat of continuous casting and increasing electromagnetic stirring are used to dilute and evenly distribute the enriched solute elements to reduce the degree of ingot segregation. However, the solidification of molten steel during continuous casting is unstable, and it is difficult to achieve uniform consistency in each cross-section throughout the continuous casting process, with high control difficulty; and this method cannot completely eliminate ingot segregation, and for components such as hub bearings that are very sensitive to ingot segregation, the improvement effect is limited. Therefore, there is an urgent need for a method that can eliminate ingot segregation and thus avoid the failure of the position where the hub bearing contacts the rolling element. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a preparation method for a hub bearing without macrosegregation.

[0005] To solve the above technical problems, the technical solution of the present invention is as follows: A preparation method for a hub bearing without macrosegregation, comprising the following steps: Step S101: Carry out converter smelting and secondary refining on molten steel to make the composition of the molten steel reach a preset value; Step S102: Continuously cast the molten steel into a continuous casting billet, and control the superheat of the continuous casting molten steel to be 20 - 35 °C, and the cooling water volume of the mold is greater than 0.5 L / kg; Step S103: Heat the continuous casting billet; Step S104: Remove scale from the continuous casting billet with water, and then roll the continuous casting billet to form a hot-rolled round steel; Step S105: Inductively heat the hot-rolled round steel to 1200 - 1250 °C, perform die forging to make a forged blank of the hub bearing, and control the cooling to room temperature after die forging.

[0006] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: in the step S102, while controlling the superheat of the continuous casting molten steel to be 20 - 35 °C and the cooling water volume of the mold to be greater than 0.5 L / kg, it further includes: Control the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min.

[0007] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: while controlling the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min, it further includes: Obtain the long side and the short side of the cross-section of the continuous casting billet; Control the cooling rate of the long side of the continuous casting billet in the mold to be k times the cooling rate of the short side, and k = the length of the short side of the cross-section of the continuous casting billet / the length of the long side of the cross-section of the continuous casting billet.

[0008] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: in the step S103, heating the continuous casting billet includes: Control the temperature of the heating section to be 1150 - 1170 °C, keep warm for 1 - 2 h, the temperature of the soaking section is 1130 - 1150 °C, and keep warm for 30 - 60 min.

[0009] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: in the step S104, rolling the continuous casting billet includes: Control the starting rolling temperature to be 1100 - 1120 °C, and the final rolling temperature to be 800 - 830 °C.

[0010] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: in the step S104, rolling the continuous casting billet to form hot-rolled round steel includes: Use a reversing mill to perform blooming on the continuous casting billet, and alternately roll two adjacent sides of the continuous casting billet during the blooming process; After blooming is completed, use a horizontal-vertical alternating continuous rolling mill to continuously roll the continuous casting billet until finished round steel is formed.

[0011] As a preferred embodiment of the method for preparing a hub bearing without macrosegregation according to the present invention, wherein: when performing die forging on the hot-rolled round steel in the step S105, it further includes: Perform center punching on the hot-rolled round steel.

[0012] The beneficial effects of the present invention are: (1) The hot-rolled round steel prepared by the present invention has no ingot shape segregation, but obvious center segregation. The ingot shape segregation is grade 0, and the center segregation is grade 0.5 - 1.5. The diameter of the center segregation is not more than 5 mm. The hub bearing obtained after forging and punching has no macroscopic segregation such as ingot shape segregation and center segregation.

[0013] (2) The present invention controls the superheat of the continuous casting molten steel to be 20 - 35 °C, avoiding serious enrichment of solute atoms caused by too high superheat, and also avoiding too fast solidification of the molten steel when the mold is strongly water-cooled due to too low superheat, which cannot make the columnar crystals fully grow to the center of the continuous casting billet, that is, an equiaxed crystal zone is generated, and then ingot shape segregation that cannot be removed appears.

[0014] (3) The present invention controls the cooling water volume of the mold to be greater than 0.5 L / kg, uses strong water-cooling to promote the growth of columnar crystals, and pushes the solute elements to the center of the continuous casting billet as much as possible. At the same time, the drawing speed of the continuous casting billet is controlled to be 0.3 - 0.5 m / min. The drawing speed is slower, making the water-cooling time of the continuous casting billet longer, ensuring that no equiaxed crystal zone appears, and thus no ingot shape segregation appears. In addition, the cooling rates of the long side and the short side of the continuous casting billet are controlled to ensure the shape and size of the center segregation area.

[0015] (4) The present invention removes the center segregation by means of forging and punching process, and thus obtains a hub bearing without macroscopic segregation, ensuring the tissue uniformity and the quality after induction hardening. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic diagram of the macrostructure morphology after the cross-section of the rolled piece prepared in Example 1 is corroded with 50% hot hydrochloric acid for 20 min; Figure 2 It is a schematic diagram of the cross-sectional and longitudinal microstructures of the center position of the rolled piece prepared in Example 1 corroded with 4% nitric acid alcohol; Figure 3 It is a schematic diagram of the macrostructure morphology after the cross-section of the rolled piece prepared in Comparative Example 1 is corroded with 50% hot hydrochloric acid for 20 min; Figure 4 It is a schematic diagram of the macrostructure morphology of the longitudinal section of the hub bearing prepared in Comparative Example 1. Detailed Embodiments

[0018] To make the content of the present invention more clearly understood, the present invention will be further described in detail below according to the detailed embodiments and in combination with the drawings.

[0019] The present application provides a preparation method for a hub bearing without macrosegregation, comprising the following steps: Step S101: Carry out converter smelting and secondary refining on molten steel to make the composition of the molten steel reach a preset value.

[0020] Step S102: Continuously cast the molten steel into a continuous casting billet, and control the superheat of the continuously cast molten steel to be 20 - 35°C, the cooling water volume of the mold to be greater than 0.5 L / kg, and the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min.

[0021] Specifically, control the superheat of the continuously cast molten steel to be 20 - 35°C. If the superheat is too high, serious enrichment of solute atoms will occur, and it cannot be ensured that the center segregation diameter of the rolled material is not greater than 5 mm, and then it will be washed away; if the superheat is too low, the molten steel will solidify too fast during the strong water cooling of the mold, and the columnar crystals cannot grow fully to the center of the continuous casting billet, that is, an equiaxed crystal zone will be generated, and then ingot-shaped segregation that cannot be removed will appear.

[0022] Control the cooling water volume of the mold to be greater than 0.5 L / kg, use strong water cooling to promote the growth of columnar crystals, and push the solute elements towards the center of the continuous casting billet as much as possible.

[0023] Control the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min. The drawing speed is slower, so that the water cooling time of the continuous casting billet is longer, ensuring that no equiaxed crystal zone appears, and then no ingot-shaped segregation appears.

[0024] It should be noted that when controlling the drawing speed of the continuous casting billet, it is necessary to first obtain the cross-sectional dimensions of the continuous casting billet, the length and width of the cross-section of the continuous casting billet, that is, a × b. Then, control the cooling rate of the long side of the continuous casting billet in the mold to be k times the cooling rate of the wide side, that is, control the cooling rate of side a of the continuous casting billet in the mold to be b / a times the cooling rate of side b, ensuring that the columnar crystal zones on the four sides of the continuous casting billet grow to the center of the cross-section of the continuous casting billet at the end of the mold, thereby controlling the shape and size of the center segregation.

[0025] Step S103: Heat the continuous casting billet.

[0026] Specifically, when heating the continuous casting billet, control the temperature of the heating section to be 1150 - 1170°C, keep it warm for 1 - 2 h, and the temperature of the soaking section to be 1130 - 1150°C, keep it warm for 30 - 60 min. On the premise that the continuous casting billet is heated through as much as possible and rolled before rolling, try to shorten the high-temperature holding time to reduce the outward diffusion of alloy elements in the center segregation.

[0027] Step S104: Carry out water descaling on the continuous casting billet, and then roll the continuous casting billet to form hot-rolled round steel.

[0028] Specifically, when rolling the continuous casting billet, control the starting rolling temperature to be 1100 - 1120°C and the final rolling temperature to be 800 - 830°C.

[0029] It should be noted that in the above hot rolling process, first, a reversing mill is used for blooming. During blooming, adjacent two sides are alternately rolled, and it is not allowed to roll one side for multiple passes and then turn the steel to roll the other side. After blooming, a horizontal-vertical alternating continuous rolling mill is used for continuous rolling to the finished round steel. During rolling, the single-pass reduction of adjacent two sides should be kept at a relatively equal level as much as possible to prevent eccentricity in the center segregation area, so that it will not fall into the hole during forging punching, and macro-segregation will occur in the hub bearing.

[0030] Step S105: Induction heat the hot-rolled round steel to 1200 - 1250 °C, perform die forging, and then control the cooling to room temperature after die forging.

[0031] Specifically, induction heating shortens the heating time and avoids the diffusion of alloying elements in the center segregation. Controlling the cooling after die forging ensures the microstructure and mechanical properties of the hub bearing blank.

[0032] In addition, center punching is required in the hub bearing die forging process to facilitate connection with the axle. In this application, the center segregation is removed by means of the punching process, and thus a hub bearing without macro-segregation is obtained, ensuring the tissue uniformity and the quality after induction hardening.

[0033] The above preparation method will be further described below through examples and comparative examples.

[0034] Example 1: This example provides a preparation method for a hub bearing without macro-segregation, which specifically includes the following steps: Step S101: The molten steel undergoes converter steelmaking and secondary refining until the composition reaches the target value.

[0035] Step S102: Continuously cast the molten steel into a continuous casting billet. The superheat of the continuous casting molten steel is 35 °C, the cooling water volume in the mold is 1 L / kg, and the drawing speed of the continuous casting billet is 0.4 m / min; the cooling rate of the short side of the continuous casting billet in the mold is about 1.5 times that of the long side, ensuring that the columnar crystal zones on the four sides of the continuous casting billet grow to the center of the cross-section of the continuous casting billet at the end of the mold. In this example, the size of the cross-section of the continuous casting billet is 320 mm × 480 mm.

[0036] Step S103: The continuous casting billet is fed into a heating furnace for heating. The temperature in the heating section is 1160 °C and it is held for 2 h, and the temperature in the soaking section is 1150 °C and it is held for 60 min.

[0037] Step S104: After descaling the continuous casting billet by water, rolling is started. The starting rolling temperature is 1120 °C, and the final rolling temperature is 830 °C to obtain a hot-rolled round steel. First, a reversing mill is used for blooming. During blooming, adjacent two sides are alternately rolled, and it is not allowed to roll one side for multiple passes and then turn the steel to roll the other side. After blooming, a horizontal-vertical alternating continuous rolling mill is used for continuous rolling to the finished round steel.

[0038] Step S105: After cutting the hot-rolled round steel, it is induction-heated to 1250 °C and then subjected to die forging. After die forging, it is cooled to room temperature under controlled conditions.

[0039] The produced hot-rolled round steel has no ingot-shaped segregation, with an ingot-shaped segregation grade of 0 and a central segregation grade of 1.5. The diameter of the central segregation is approximately 5 mm. The finally prepared hub bearing has no macroscopic segregation such as ingot-shaped segregation and central segregation.

[0040] The macrostructure of the cross-section of the hot-rolled round steel after being corroded with 50% hot hydrochloric acid for 20 min is shown in Figure 1 , after cutting, the cross-sectional and longitudinal microstructures of the central position after being corroded with 4% nitric acid alcohol are shown in Figure 2 . Obvious central segregation can be seen in the round steel. There is a black line about 3 mm wide at the segregation area, which is generated near the impurity elements. The central segregation and the black line are removed when punching the center hole during forging. The segregation grade of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1.

[0041] Comparative Example 1: This comparative example provides a method for preparing a hub bearing without macroscopic segregation, which specifically includes the following steps: Step S101: The molten steel undergoes converter steelmaking and secondary refining until the composition reaches the target value.

[0042] Step S102: The molten steel is continuously cast into a continuous casting billet. The superheat of the continuous casting molten steel is 15 °C, the cooling water volume in the mold is 0.4 L / kg, and the drawing speed of the continuous casting billet is 0.8 m / min; the cooling rate on the short side of the continuous casting billet in the mold is about 1.1 times that on the long side.

[0043] Step S103: The continuous casting billet is fed into a heating furnace for heating. The temperature in the heating section is 1160 °C and it is held for 4 h, and the temperature in the soaking section is 1150 °C and it is held for 2 h.

[0044] Step S104: After descaling the continuous casting billet with water, rolling is started. The starting rolling temperature is 1100 - 1120 °C, and the final rolling temperature is 800 - 830 °C to form hot-rolled round steel. First, a reversing mill is used for blooming, and a horizontal-vertical alternating continuous rolling mill is used for continuous rolling to the finished round steel.

[0045] Step S105: After cutting the hot-rolled round steel, it is induction-heated to 1250 °C and then subjected to die forging. After die forging, it is cooled to room temperature under controlled conditions.

[0046] The macrostructures of the cross-section of the hot-rolled round steel and the longitudinal section of the hub bearing after being corroded with 50% hot hydrochloric acid for 20 min are shown in Figure 3 and Figure 4。Due to the use of traditional continuous casting process control and the reduction of ingot segregation, obvious ingot segregation can still be seen in the round steel. The ingot segregation level is 1.0, and the ingot segregation remains on the hub bearing after forging, as shown by the black arrow. These ingot segregations will promote the further growth of austenite grains at this position. The segregation level of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1.

[0047] Comparative Example 2: The difference between this comparative example and Example 1 is only that: the cooling rate on the short side of the continuous casting billet in the mold is about 1 time that on the long side.

[0048] The segregation level of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1. Since the cooling rates on the short side and the long side of the continuous casting billet are the same, the columnar crystals growing on the long side meet preferentially. The columnar crystals on the short side meet the preferentially solidified columnar crystals on the long side before they meet, resulting in a segregation band parallel to the long side. The two ends of this segregation band cannot be removed during forging and remain in the hub bearing, resulting in coarse grains.

[0049] Comparative Example 3: The difference between this comparative example and Example 1 is only that: the continuous casting billet is heated in a heating furnace, the heating section temperature is 1160 °C and the holding time is 4 h, and the soaking section temperature is 1150 °C and the holding time is 3 h.

[0050] The segregation level of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1. Since the heating time of the continuous casting billet is relatively long, the central segregation diffuses outward, resulting in incomplete removal during forging and causing coarse grains in the unremoved part.

[0051] Comparative Example 4: The difference between this comparative example and Example 1 is only that: first, a reversing mill is used for blooming. After the long side is continuously pressed down with a large deformation amount in 2 passes, the short side is then pressed down in 1 pass after flipping the steel, and this is repeated.

[0052] The segregation level of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1. Due to two-pass continuous rolling, the central segregation is elliptical, and the long axis of the ellipse is extremely long. The two ends of the long axis cannot be removed during forging, resulting in coarse grains.

[0053] Example 2: This example provides a method for preparing a hub bearing without macroscopic segregation, which specifically includes the following steps: Step S101: The molten steel undergoes converter steelmaking and secondary refining, and the composition reaches the target value.

[0054] Step S102: Continuously cast the molten steel into a continuous casting billet. The superheat of the continuous casting molten steel is 20 °C, the cooling water volume in the mold is 0.6 L / kg, and the drawing speed of the continuous casting billet is 0.5 m / min. The cooling rate of the short side of the continuous casting billet in the mold is about 1.56 times that of the long side, ensuring that the columnar crystal zones on the four surfaces of the continuous casting billet grow to the center of the cross-section of the continuous casting billet at the end of the mold. In this embodiment, the size of the cross-section of the continuous casting billet is 160 mm × 250 mm.

[0055] Step S103: Heat the continuous casting billet in a heating furnace. The temperature in the heating section is 1150 °C and keep it for 1 h, and the temperature in the soaking section is 1130 °C and keep it for 30 min.

[0056] Step S104: After descaling the continuous casting billet with water, start rolling. The starting rolling temperature is 1100 °C, and the final rolling temperature is 800 °C to form hot-rolled round steel. First, use a reversing mill for blooming. For blooming, two adjacent sides need to be alternately rolled, and it is not allowed to roll one side multiple times and then turn the steel to roll the other side. After blooming, use a horizontal-vertical alternating continuous rolling mill for continuous rolling to the finished round steel.

[0057] Step S105: After cutting the hot-rolled round steel, use induction heating to 1200 °C and perform die forging, and then control the cooling to room temperature.

[0058] The obtained hot-rolled round steel has no ingot-shaped segregation, the ingot-shaped segregation is grade 0, and there is center segregation of grade 0.5. The diameter of the center segregation is about 3 mm. The finally prepared hub bearing has no macroscopic segregation such as ingot-shaped segregation and center segregation. The segregation grade of the round steel and the austenite grain size at the contact position between the hub bearing and the rolling element are shown in Table 1.

[0059]

[0060] Table 1 Segregation grade of round steel and austenite grain size at the contact position between hub bearing and rolling element As can be seen from Table 1, compared with the hub bearings produced by the traditional process, the entire hub bearing produced by this application has uniform composition and structure macroscopically, without macroscopic segregation, and in particular, it can avoid the failure at the contact position with the rolling element caused by ingot-shaped segregation.

[0061] In addition to the above embodiments, the present invention may also have other implementation manners; all technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A preparation method of a hub bearing without macrosegregation, characterized in that: It includes the following steps: Step S101: Carry out converter smelting and secondary refining on the molten steel to make the composition of the molten steel reach the preset value; Step S102: Continuously cast the molten steel into a continuous casting billet, and control the superheat of the continuous casting molten steel to be 20 - 35 °C, and the cooling water volume of the mold is greater than 0.5 L / kg; Step S103: Heat the continuous casting billet; Step S104: Remove scale from the continuous casting billet by water, and then roll the continuous casting billet to form a hot-rolled round steel; Step S105: Induction heat the hot-rolled round steel to 1200 - 1250 °C, carry out die forging to make a forged blank for hub bearings, and control the cooling to room temperature after die forging.

2. The preparation method of the hub bearing without macrosegregation according to claim 1, characterized in that: In the said step S102, while controlling the superheat of the continuous casting molten steel to be 20 - 35 °C and the cooling water volume of the mold to be greater than 0.5 L / kg, it also includes: Controlling the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min.

3. The preparation method of the hub bearing without macroscopic segregation according to claim 2, characterized in that: While controlling the drawing speed of the continuous casting billet to be 0.3 - 0.5 m / min, it also includes: Obtaining the long side and the short side of the cross-section of the continuous casting billet; Controlling the cooling rate of the long side of the continuous casting billet in the mold to be k times the cooling rate of the short side, and k = the length of the short side of the cross-section of the continuous casting billet / the length of the long side of the cross-section of the continuous casting billet.

4. The preparation method of the hub bearing without macrosegregation according to claim 1, characterized in that: In the said step S103, heating the continuous casting billet includes: Controlling the temperature of the heating section to be 1150 - 1170 °C, holding for 1 - 2 h, and the temperature of the soaking section to be 1130 - 1150 °C, holding for 30 - 60 min.

5. The preparation method of the hub bearing without macroscopic segregation according to claim 1, characterized in that: In step S104, rolling the continuous casting billet includes: Controlling the starting rolling temperature to be 1100 - 1120 °C and the final rolling temperature to be 800 - 830 °C.

6. The preparation method of the hub bearing without macroscopic segregation according to claim 1, characterized in that: In the said step S104, rolling the continuous casting billet to form a hot-rolled round steel includes: Using a reversing mill to roll the continuous casting billet for blooming, and alternately rolling two adjacent sides of the continuous casting billet during the blooming process; After completing blooming, using a horizontal-vertical alternating continuous rolling mill to continuously roll the continuous casting billet until a finished round steel is formed.

7. The preparation method of the hub bearing without macroscopic segregation according to claim 1, characterized in that: In the said step S105, when carrying out die forging on the hot-rolled round steel, it also includes: Centrally punching the forged blank for hub bearings.

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