Steel for automobile retainer and manufacturing method thereof

Abstract

The invention discloses steel for an automobile retainer and a manufacturing method of the steel. The steel for the automobile retainer comprises the following chemical components in percentage by mass: 0.23 to 0.26 percent of C, 0.30 to 0.40 percent of Si, 1.60 to 1.90 percent of Mn, 0.10 to 0.30 percent of Cr, less than or equal to 0.012 percent of P, 0.028 to 0.033 percent of S, 0.030 to 0.045 percent of Ti, less than or equal to 0.0015 percent of O and the balance of Fe and inevitable impurities. The manufacturing method comprises the process steps of primary smelting in a converter, refining, continuous casting, rolling, cooling after rolling and the like. The steel for the automobile retainer manufactured by the method has excellent performances in the aspects of hardness uniformity, banded structure control, austenite grain size, sulfur content dispersion difference and the like, and can meet the use requirements of the automobile retainer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of special steel smelting, and particularly relates to a steel for automobile retainer and a manufacturing method thereof. BACKGROUND

[0002] The automobile retainer firstly plays a separating role in the automobile, which separates the rolling bodies at equal distances, makes the rolling bodies evenly distributed in the bearing, prevents the rolling bodies from colliding and rubbing with each other, reduces the abrasion, and thus guarantees the stability and precision of the bearing in the running process. Secondly, the automobile retainer plays a guiding role of the rolling bodies, guides the rolling bodies to roll on the correct track, and prevents the rolling bodies from deviating from the track to cause jamming or abnormal abrasion. Finally, the automobile retainer can play a supporting and fixing role, provides support for the rolling bodies, and makes the rolling bodies maintain stable positions in the bearing. The automobile will experience various road conditions and dynamic loads in the running process, and the retainer can ensure that the rolling bodies will not be displaced or deformed due to external forces. The automobile retainer bears the frictional force between the rolling bodies, the inner and outer rings of the bearing, the impact force from the road surface, and the centrifugal force generated by the rolling bodies in the running process. Therefore, the steel for the automobile retainer must have good hardness uniformity, good band structure uniformity, excellent austenite grain size, and excellent sulfur content uniformity to ensure that the manufactured retainer has excellent and uniform strength, toughness, stable and long fatigue life. SUMMARY

[0003] The present application solves the technical problem of the prior art, provides a steel for automobile retainer and a manufacturing method thereof, and ensures that the manufactured retainer has excellent and uniform strength, toughness, stable and long fatigue life.

[0004] The technical scheme adopted by the present application to solve the above problems is as follows: a steel for automobile retainer, the chemical composition of the steel according to the present application is as follows: C: 0.23-0.26%, Si: 0.30-0.40%, Mn: 1.60-1.90%, Cr: 0.10-0.30%, P: ≤0.012%, S: 0.028-0.033%, Ti: 0.030-0.045%, O ≤0.0015%, and the balance is Fe and inevitable impurities.

[0005] The main role of each chemical element of the steel according to the present application and the design basis are as follows: C: Carbon content plays a crucial role in the cage steel, with the increase of carbon content in the steel, the hardness and strength of the cage will continue to rise, but the toughness of the cage will gradually decline; Carbon content is an important element that affects the banded structure of steel, and appropriate carbon elements in steel can increase the content of pearlite structure of hot-rolled steel, inhibit the generation of ferrite structure in steel, and by controlling the carbon content of the steel in a narrow range, the banded structure grade range of the steel can be effectively controlled. Therefore, the selected range of carbon content is C: 0.23-0.26%.

[0006] Si: A small amount of ferrosilicon alloy is added to the molten steel in the early refining stage, and by controlling the addition depth of ferrosilicon alloy, the efficiency of silicon deoxidation is improved to reduce the content of silicon in the steel. Too much silicon in the steel will cause intergranular oxidation during the heat treatment process of the steel, which will significantly reduce the fatigue life of the cage. Therefore, the selected range of silicon content is Si: 0.30-0.40%.

[0007] Mn: Manganese can significantly improve the ability of the steel of the present application to form martensite structure from the surface to the inside after quenching, and adding sufficient manganese element in the steel of the present application can ensure that the cage has excellent strength, thereby improving the wear resistance and carrying capacity of the cage. Therefore, the selected range of manganese content is 1.60-1.90%.

[0008] Cr: The role of chromium in the steel of the present application is basically the same as that of manganese, but since the price of chromium iron alloy is significantly higher than that of manganese iron alloy, in order to reduce production cost, a large amount of manganese element is added in the steel of the present application to replace the role of chromium element, and only a small amount of chromium element is added in the steel of the present application. Therefore, the selected range of chromium content is Cr: 0.10-0.30%.

[0009] P: The automobile cage must have sufficient toughness, and the phosphorus content in the steel must be controlled within a lower range, and the converter dephosphorization process of the steel of the present application is optimized to effectively improve the converter dephosphorization efficiency. The phosphorus content in the steel of the present application is controlled to be ≤0.012%.

[0010] S: In order to improve the stability of the cutting performance of the steel of the present application, a certain content of sulfur element needs to be added in the steel, and the sulfur element in the steel is controlled within a relatively narrow range, so that the cutting machining performance can be accurately controlled, which can not only ensure stable chip breaking effect and improve machining efficiency, but also can prevent problems such as hot brittleness caused by excessive sulfur content, so that the cutting machining process is more stable and reliable. The sulfur element in the steel is controlled within a relatively narrow range, which can ensure more stable during heat treatment and is not prone to uneven performance changes caused by fluctuations in sulfur, so that the automobile retainer can obtain more uniform mechanical properties and improve the quality stability of the product. The present application realizes accurate and stable control of the sulfur element by optimizing the feeding mode of the sulfur line in the refining process. The sulfur content in the steel of the present application is controlled to S: 0.028-0.033%.

[0011] Ti: The titanium element is added in the early stage of refining, and by optimizing the argon stirring mode and the adding mode of the titanium element, only a small amount of titanium-iron wire needs to be fed to achieve high-efficiency deoxidation, and the titanium element can be uniformly distributed in the steel. The carbon element combines with carbon to form uniformly distributed titanium carbide. These small and uniformly distributed pinning materials can effectively prevent grain growth during heat treatment. Therefore, the selected range of titanium element in the present application is Ti: 0.030-0.045%.

[0012] O: Oxygen can form oxide inclusions with other elements in the steel. These inclusions in the steel are tiny defects that can cause stress concentration. When stressed, these parts are prone to become the starting point of cracks, resulting in a decrease in the strength of the steel. The steel of the present application optimizes the argon stirring mode in the early stage of refining, optimizes the feeding mode of the titanium-iron wire, and optimizes the adding mode of the silicon-iron alloy. Only a small amount of titanium-iron wire and silicon-iron alloy needs to be added to achieve high-efficiency deoxidation. The oxygen content of the steel of the present application is controlled within the range of O≤0.0015%.

[0013] The above-mentioned steel for automobile retainer and manufacturing method thereof comprises the following process steps: (1) Adopting converter initial refining, adding lime in the converter dephosphorization process to improve the slag basicity, the slag basicity (CaO / SiO2) is controlled between 3.5-4.5; adding appropriate amount of fluorite to improve the fluidity of the slag, the proportion of fluorite in the slag is 3-5%; adding magnesium oxide to improve the stability of the slag, the proportion of magnesium oxide in the slag is 6%-8%. Adopting moderate oxygen supply intensity to gently stir the molten pool, the oxygen supply intensity is 2.5-3.5 m³ / (t·min), the distance between the oxygen lance and the molten pool slag layer is adjusted to 0.9-1.2 m, and the angle between the oxygen lance blowing oxygen and the slag layer is controlled to 8-12°, which is convenient for forming an oxidizing, fluid and stable slag, so as to improve the converter dephosphorization efficiency and achieve the purpose of deep dephosphorization. After the converter deep dephosphorization, the phosphorus content of the molten steel is ≤0.012%.

[0014] (2) In the early stage of refining, multi-hole bottom blowing and high-flow argon gas stirring are adopted. The argon gas holes at the bottom of the refining furnace are distributed along the circumference. The number of argon gas holes is 7-9, the distance between adjacent argon gas holes is 50-60cm, and the argon gas flow rate of the refining furnace is 70-80L / min. This avoids mutual interference between adjacent bubble flows and ensures uniform stirring of molten steel in the furnace. In the early refining stage, ferrotitanium wire with a diameter of φ3-5mm is fed into the furnace along the center of the bubble flow at a feeding speed of 12-15m / min. This ensures rapid melting of the ferrotitanium wire in the molten steel, rapid diffusion of titanium, and uniform distribution of titanium within the molten steel. Titanium combines with oxygen in the molten steel to form TiO2, which rises to the slag layer with argon agitation, serving as an initial deoxidizer. Next, ferrosilicon alloy is added to the molten steel at a depth of 1.5-2m to ensure complete melting before it rises to the molten steel. Silicon combines with oxygen in the molten steel to form SiO2, which also rises to the slag layer with argon agitation, serving as a secondary deoxidizer. Then, ferromanganese and ferrochrome alloys are added sequentially to the molten steel. Finally, sulfur wire is fed into the molten steel in 3-5 batches, with a 20-30s interval between each batch to ensure uniform diffusion of sulfur.

[0015] (3) The refined molten steel is hoisted to the continuous casting platform for casting. The crystallizer adopts a rotary stirring mode. The stirring speed of the molten steel in the crystallizer is 90-95 r / min, and the flow velocity of the molten steel inside the crystallizer is 0.4-1.1 m / s. The specific water volume in the secondary cooling zone of the continuous casting is 0.8-1.0 L / kg, the total hardness of the secondary cooling water is controlled at 100-150 mg / L, and the cooling intensity of the surface of the continuous casting billet in the secondary cooling zone is 50-70℃ / S. The electromagnetic force of the end electromagnetic stirring is controlled at 800-1000 N to make the element distribution in the central area of ​​the billet uniform.

[0016] (4) The continuously cast billet is heated in the heating furnace. The temperature of the preheating section of the heating furnace is 600-900℃, and the billet heating rate is 15-20℃ / min; the temperature of the heating section is 880-1100℃, and the billet heating rate is 20-25℃ / min; the temperature of the soaking section is 1080-1200℃, and the billet heating rate is 5-10℃ / min. After the continuously cast billet exits the heating furnace, it is rolled. The rough rolling speed is 0.7-1.0m / s, and the rough rolling temperature is 1080-1150℃; the intermediate rolling speed is 1.8-2.5m / s, and the intermediate rolling temperature is 1010-1070℃; the final rolling temperature is 4-7m / s, and the final rolling temperature is 930-970℃. After rolling, the steel is placed on a cooling bed at a temperature of 780-850℃. Two parallel supports are used for passing the steel, with a distance of 25-50mm between them. Simultaneously, an insulation cover is placed over the steel, and the insulation time is 15-20 minutes. After insulation, the steel is air-cooled to room temperature.

[0017] The steel for automotive cages manufactured using the method of this invention has the following characteristics: the hardness of the hot-rolled bars is 160-190 HBW, and the hardness variation within the same heat number and batch is ≤15 HBW; the banded structure of the hot-rolled bars is grade 1.0-2.5, and the banded structure variation within the same heat number and batch is ≤0.5; the austenite grain size of the hot-rolled bars after holding at 960℃ for 4 hours is grade 6-8; and the sulfur content variation of the finished steel within the same heat number and batch is ≤0.003%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: In terms of composition design, low carbon and low phosphorus are adopted, and the sulfur content is precisely controlled within a narrow range to reduce its segregation. A small amount of titanium is added and its uniform distribution is ensured. Through reasonable smelting, continuous casting, rolling and post-rolling cooling processes, the hardness and dispersion, banded structure and dispersion, high-temperature austenite grain size and sulfur content dispersion of hot-rolled bars are effectively controlled.

[0019] During the initial smelting in the converter, by optimizing parameters such as slag composition and oxygen supply, high-performance slag is formed, improving dephosphorization efficiency and achieving deep dephosphorization, so that the phosphorus content of molten steel is ≤0.012%.

[0020] During the refining process, multi-hole bottom blowing and high-flow-rate argon gas stirring are used to ensure uniform molten steel. Through reasonable wire feeding and material addition methods, deoxidation and uniform distribution of alloying elements and sulfur elements are achieved.

[0021] During continuous casting, the elements in the central region of the billet are evenly distributed through crystallizer stirring, secondary cooling zone parameter control, and end electromagnetic stirring.

[0022] The rolling and post-rolling cooling processes are reasonable, ensuring the uniformity of steel properties.

[0023] The final product exhibits excellent performance in terms of hardness, banded structure, austenite grain size, and sulfur content variation, meeting the requirements for automotive cages and filling a gap in the domestic market. Detailed Implementation

[0024] The technical solution of the present invention will be described in more detail below with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the present invention.

[0025] Example 1 and Example 2 The manufacturing method for automotive cage steel used in the two embodiments is as follows: 100t converter → 100t refining → continuous casting into square billets (240mm×240mm) → continuous casting billets are heated in a heating furnace → rolling → slow cooling after rolling, producing two batches of automotive cage steel.

[0026] In the converter primary smelting process, lime was added during dephosphorization, and the slag basicity (CaO / SiO2) was controlled at 3.53 (Example 1) and 4.47 (Example 2), respectively. Fluorite was added, with the fluorite content in the slag being 3% (Example 1) and 5% (Example 2), respectively. Magnesium oxide was added, with the magnesium oxide content in the slag being 6% (Example 1) and 8% (Example 2), respectively. Medium oxygen supply intensity was used for stirring, with oxygen supply intensities of 2.5 m³ / (t·min) (Example 1) and 3.5 m³ / (t·min) (Example 2). The distance between the oxygen lance and the slag layer in the molten pool was 0.9 m (Example 1) and 1.2 m (Example 2), respectively, and the oxygen lance blowing angle to the slag layer was 8° (Example 1) and 12° (Example 2), respectively. After deep dephosphorization in the converter, the phosphorus content of the molten steel was 0.011% (Example 1) and 0.008% (Example 2), respectively.

[0027] Refining: In the early stage of refining, a multi-hole bottom blowing system with high-flow-rate argon gas stirring was used. The number of argon gas holes was 7 (Example 1) and 9 (Example 2), with a spacing of 50 cm (Example 1) and 60 cm (Example 2) between adjacent argon gas holes, and an argon gas flow rate of 70.3 L / min (Example 1) and 99.9 L / min (Example 2). Titanium iron wire with diameters of φ3 mm (Example 1) and φ5 mm (Example 2) was fed along the center of the bubble flow at feeding speeds of 12 m / min (Example 1) and 15 m / min (Example 2). Subsequently, ferrosilicon alloy was added to depths of 1.5 m (Example 1) and 2 m (Example 2). Then, ferromanganese and ferrochrome alloys were added sequentially. Finally, sulfur wire was fed in 3 times (Example 1) and 5 times (Example 2), with intervals of 20 s (Example 1) and 30 s (Example 2), respectively.

[0028] Continuous casting: The clockwise stirring speed of the molten steel in the crystallizer was 90 r / min (Example 1) and 95 r / min (Example 2), respectively; the internal molten steel flow velocity was 0.4 m / s (Example 1) and 1.1 m / s (Example 2), respectively; the specific water volume in the secondary cooling zone of the continuous casting was 0.8 L / kg (Example 1) and 1.0 L / kg (Example 2), respectively; the total hardness of the secondary cooling water was 103 mg / L (Example 1) and 148 mg / L (Example 2), respectively; the surface cooling intensity of the continuously cast billet was 51℃ / S (Example 1) and 69℃ / S (Example 2), respectively; and the electromagnetic force of the end electromagnetic stirring was 802 N (Example 1) and 998 N (Example 2), respectively.

[0029] Rolling: The continuously cast billet is fed into the heating furnace. The preheating zone temperatures are 602-889℃ (Example 1) and 620-900℃ (Example 2), with heating rates of 15℃ / min (Example 1) and 20℃ / min (Example 2), respectively. The heating zone temperatures are 889-1090℃ (Example 1) and 900-1097℃ (Example 2), with heating rates of 20℃ / min (Example 1) and 25℃ / min (Example 2), respectively. The soaking zone temperatures are 1090-1181℃ (Example 1) and 1097-1199℃ (Example 2), with heating rates of 5℃ / min (Example 1) and 10℃ / min (Example 2), respectively. After exiting the heating furnace, the continuously cast billets were rolled at roughing speeds of 0.73 m / s (Example 1) and 0.99 m / s (Example 2), and roughing temperatures of 1086℃ (Example 1) and 1149℃ (Example 2). The intermediate rolling speeds were 1.81 m / s (Example 1) and 2.47 m / s (Example 2), and intermediate rolling temperatures of 1015℃ (Example 1) and 1069℃ (Example 2). The final rolling speeds were 4 m / s (Example 1) and 7 m / s (Example 2), and the final rolling temperatures were 932℃ (Example 1) and 969℃ (Example 2).

[0030] Post-rolling cooling: After rolling, the steel is placed on a cooling bed at temperatures of 783℃ (Example 1) and 850℃ (Example 2), respectively. The steel is passed through a double-bracket parallel arrangement with a spacing of 25mm (Example 1) and 50mm (Example 2), respectively. An insulation cover is then added, and the insulation time is 15min (Example 1) and 20min (Example 2), respectively. After that, the steel is air-cooled to room temperature.

[0031] The smelting composition of the steels obtained in Examples 1 and 2 is shown in Table 1.

[0032] Table 1. Smelting composition (wt%)

[0033] The hardness of the hot-rolled bars obtained in Examples 1 and 2 differs from that of bars from the same heat number and batch, as shown in Table 2.

[0034] Table 2 Hardness and dispersion of hot-rolled bars

[0035] The difference between the strip structure of the hot-rolled bars obtained in Examples 1 and 2 and the strip structure of the same furnace number and batch is shown in Table 3.

[0036] Table 3. Strip structure and dispersion of hot-rolled bars

[0037] After being held at 960°C for 4 hours, the hot-rolled bars obtained in Examples 1 and 2 had austenite grains of grade 6.5 (Example 1) and grade 8.0 (Example 2), respectively.

[0038] The sulfur content and dispersion of the hot-rolled bars obtained in Examples 1 and 2 are shown in Table 4.

[0039] Table 4. Spectral composition and dispersion of sulfur in hot-rolled bars (wt%)

[0040] This invention relates to a steel for automotive cages, characterized by a low-carbon, low-phosphorus composition and precise addition of sulfur. The sulfur content is controlled within a narrow range during refining, and sulfur segregation is controlled during steelmaking. A small amount of titanium (Ti) is added to ensure uniform distribution of Ti within the steel. By employing optimized smelting, continuous casting, rolling, and post-rolling cooling processes, this invention improves the uniformity of hardness and banded microstructure in hot-rolled bars, ensuring fine and uniform high-temperature austenite grain size and effectively controlling the dispersion of sulfur content in the steel. The final product is a steel for automotive cages, characterized by: a hot-rolled bar hardness of 160-190 HBW, with a hardness variation of ≤15 HBW within the same heat and batch; a banded microstructure of grade 1.0-2.5, with a banded microstructure variation of ≤0.5 within the same heat and batch; austenite grain size of grade 6-8 after holding at 960℃ for 4 hours; and a sulfur content variation of ≤0.003% within the same heat and batch. This steel for automotive cages fills a domestic gap.

Claims

1. A steel for an automobile retainer, characterized in that the chemical composition of the steel is, in terms of weight percentage: C: 0.23-0.26%, Si: 0.30-0.40%, Mn: 1.60-1.90%, Cr: 0.10-0.30%, P: ≤0.012%, S: 0.028-0.033%, Ti: 0.030-0.045%, O ≤0.0015%, and the balance being Fe and inevitable impurities.

2. A method of producing the steel for automotive retainers according to claim 1, characterized by, The method comprises the following steps: (1) Converter initial smelting: adding lime in the converter dephosphorization process to control the slag basicity between 3.5-4.5; adding fluorite to make the fluorite proportion in the slag 3-5%; adding magnesium oxide to make the magnesium oxide proportion in the slag 6%-8%, and the phosphorus content of the molten steel after deep dephosphorization in the converter is ≤0.012%; (2) Refining: in the early stage of refining, adopt porous bottom blowing and large flow argon stirring, feed titanium-iron wire along the center of the bubble flow into the furnace, the titanium-iron wire diameter is φ3-5mm, and the wire feeding speed is 12-15m / min; then add ferrosilicon alloy into the molten steel, the depth of the ferrosilicon alloy added into the molten steel is 1.5-2m; then add manganese iron and chromium iron alloy in sequence; finally, feed sulfur line into the molten steel, the sulfur line is fed in 3-5 times, and after each feeding, continue to feed after 20-30s interval; (3) Continuous casting: the molten steel after refining is hoisted to the continuous casting platform for casting; (4) Rolling: the continuous casting billet is heated in the heating furnace, the temperature of the preheating section of the heating furnace is 600-900℃, the billet heating speed is 15-20℃ / min; the temperature of the heating section is 880-1100℃, the billet heating speed is 20-25℃ / min; the temperature of the soaking section is 1080-1200℃, the billet heating speed is 5-10℃ / min, and the continuous casting billet is rolled after coming out of the heating furnace; (5) Cooling after rolling: the steel is placed on the cooling bed after rolling, and the temperature of the cooling bed for rod is 780-850℃; at the same time, the steel is covered with a heat preservation cover, the heat preservation time of the heat preservation cover is 15-20min, and then air cooling to room temperature.

3. The method of manufacturing a steel for a vehicle retainer according to claim 2, characterized by: In step (1), moderate oxygen supply intensity is used for gentle stirring of the molten pool, the oxygen supply intensity is 2.5-3.5m³ / (t·min), the distance between the oxygen lance and the slag layer of the molten pool is adjusted to 0.9-1.2m, and the angle between the oxygen lance blowing and the slag layer is controlled to 8-12°.

4. The method of manufacturing a steel for a retainer of an automobile according to claim 2, characterized by: In step (2), the argon holes at the bottom of the refining furnace are distributed along the circumference, the number of argon holes is 7-9, the distance between adjacent argon holes is 50-60cm, and the argon flow of the refining furnace is 70-80L / min.

5. The method of manufacturing a steel for a retainer of an automobile according to claim 2, characterized by: In step (3), the mold adopts rotary stirring mode, the clockwise stirring speed of the mold molten steel is 90-95r / min, the flow speed of the molten steel in the mold is 0.4-1.1m / s; the specific water consumption of the secondary cooling zone of the continuous casting is 0.8-1.0L / kg, the total hardness of the secondary cooling water is controlled to 100-150mg / L, the cooling intensity of the continuous casting billet surface in the secondary cooling zone is 50-70℃ / S; and the electromagnetic force of the end electromagnetic stirring is controlled to 800-1000N.

6. The method of manufacturing a steel for a retainer of an automobile according to claim 2, characterized by: The rough rolling speed in step (4) is 0.7-1.0 m / s, the rough rolling temperature is 1080-1150℃; the medium rolling speed is 1.8-2.5 m / s, the medium rolling temperature is 1010-1070℃; the final rolling speed is 4-7 m / s, and the final rolling temperature is 930-970℃.

7. The method of manufacturing a steel for a retainer of an automobile according to claim 2, characterized by: In step (5), the double-branch parallel overpassing is adopted, and the distance between the steel materials is 25-50 mm.

8. A method of manufacturing a steel for a gear of a smart machine tool according to claim 2, characterized by: The hardness of the prepared hot-rolled rod is 160-190 HBW, the hardness dispersion difference of the same furnace number and same batch steel is less than or equal to 15 HBW; the banded structure of the hot-rolled rod is 1.0-2.5 levels, the banded structure dispersion difference of the same furnace number and same batch steel is less than or equal to 0.5 levels; the austenite grain after the hot-rolled rod is kept at 960℃ for 4 hours is 6-8 levels; and the sulfur content dispersion difference of the same furnace number and same batch steel finished product is less than or equal to 0.003%.

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