High purity bearing steel and its applications

Abstract

The application discloses high-purity bearing steel and application thereof, and has the following components in percentage by mass: C 0.95%-1.05%, Si 0.45%-0.65%, Mn 0.45%-0.65%, Cr 1.10%-1.30%, trace Mo, Ni and Cu; impurities such as O≤0.0010%, S≤0.0080%, Ti≤0.0030% and Ca≤0.0010% are strictly controlled, the upper limit of single elements such as As, Sn, Sb, Pb and Bi is limited and the total amount is ≤0.035%, and the balance is iron. The application adopts medium-silicon manganese, low-chromium main alloy and super-low impurity control, greatly reduces MnS, TiN and oxide inclusions, suppresses residual element grain boundary segregation, balances low-sulfur steel cutting performance with trace calcium, and improves high-temperature hardness with trace molybdenum. After heat treatment, the hardness is ≥HRC61, the L10 fatigue life under 4.5GPa is 2.5-3 times higher than that of conventional GCr15, and high toughness and dimensional stability are combined. The application does not need precious alloy, the production process is mature, and is suitable for multi-roll cold rolling machine backing bearing, precision rolling machine supporting roller bearing and wind power main shaft bearing.

Description

Technical Field

[0001] This invention relates to the field of bearing steel materials technology, and more specifically, to a high-purity bearing steel and its applications. Background Technology

[0002] With the upgrading of the high-end equipment manufacturing industry, precision rolling equipment such as cold-rolled thin plate mills, multi-roll reversible cold rolling mills, and Sendzimir mills are continuously developing towards higher precision, higher speed, and longer service life. Precision rolling mill bearings need to maintain micron-level rotational accuracy under high-speed rotation conditions, while also withstanding high alternating contact stress and complex loads, which places extremely stringent requirements on the purity, fatigue performance, and microstructure uniformity of the bearing steel used as its core material.

[0003] High-carbon chromium bearing steel GCr15 is currently the most widely used general-purpose bearing steel. Its standard composition is C 0.95%~1.05%, Si 0.15%~0.35%, Mn 0.25%~0.45%, and Cr 1.40%~1.65%. After quenching and low-temperature tempering, it can obtain high and uniform hardness, excellent wear resistance and contact fatigue performance, and is widely used in the manufacture of rolling elements and rings of various general-purpose bearings.

[0004] However, under high-end operating conditions in precision rolling mill bearings, conventional GCr15 bearing steel has the following significant limitations: First, insufficient purity control. Conventionally produced GCr15 typically has an oxygen content ≥12ppm and a sulfur content ≤0.020%. Elements such as titanium and calcium lack strict control, easily leading to the formation of elongated MnS inclusions, brittle TiN inclusions, and oxide inclusions within the steel. Under high alternating contact stress, these can easily become fatigue crack initiations, significantly shortening the bearing's service life. Second, the uniformity of the microstructure needs improvement. High chromium content easily leads to uneven carbide distribution and a greater tendency to form network carbides, reducing the steel's toughness and the uniformity of large-section performance, making it difficult to meet the full-section performance requirements of large-size precision bearings. Third, a lack of systematic control over residual elements. Low-melting-point residual elements such as arsenic, tin, antimony, lead, and bismuth are prone to segregation at grain boundaries, causing hot brittleness and temper brittleness. Existing standards only set individual limits for a small number of residual elements, without considering the cumulative segregation effect, affecting the long-term reliability of the bearing.

[0005] To address the aforementioned performance shortcomings, research has been conducted in various directions, including alloying and process optimization. For example, some technical solutions improve the strength and toughness of steel by adding various precious microalloying elements such as niobium, vanadium, and zirconium, combined with a grain refinement strengthening mechanism. However, this significantly increases alloy costs, and the multi-element composite addition requires high smelting control, making large-scale production difficult. Some technical solutions introduce rare earth elements to modify inclusions and refine grains, but the yield of rare earth elements fluctuates greatly and is sensitive to smelting process parameters, making it difficult to guarantee the performance stability of industrial-scale mass production. Other technical solutions enhance the surface properties of bearing parts through processes such as strong magnetic field quenching and special aging heat treatment. However, these only optimize the post-processing stage and do not address the core issues of insufficient purity and uneven carbide distribution at the source of material composition. As a result, the overall performance improvement is limited and cannot fully meet the long life and high reliability requirements of precision rolling mill bearings.

[0006] Therefore, developing a high-purity bearing steel that does not rely on expensive alloying elements, achieves comprehensive performance improvement through composition system optimization and precise purity control, and is suitable for high-end working conditions of precision rolling mill bearings is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a high-purity bearing steel. Through systematic optimization of the main alloying element ratio, strict control of harmful impurity elements, and limitation of the total amount of residual harmful elements, the steel simultaneously possesses ultra-high purity, excellent contact fatigue life, good toughness, and machinability, meeting the stringent requirements of precision rolling mill bearings for long service life and high reliability. Another objective of the present invention is to provide specific industrial application scenarios for this bearing steel.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A high-purity bearing steel, the chemical composition of which, by mass percentage, includes: Main alloying elements: C: 0.95%~1.05%; Si: 0.45%~0.65%; Mn: 0.45%~0.65%; Cr: 1.10%~1.30%; Mo: ≤0.08%; Ni: ≤0.25%; Cu: ≤0.20%; Harmful impurity elements: O: ≤0.0010%; S: ≤0.0080%; P: ≤0.015%; Ti: ≤0.0030%; Ca: ≤0.0010%; Al: ≤0.050%; Residual harmful elements: As: ≤0.015%; Sn: ≤0.010%; Sb: ≤0.005%; Pb: ≤0.002%; Bi: ≤0.0100%; And it satisfies the following relationship: As + Sn + Sb + Pb + Bi ≤ 0.035%; the remainder is Fe and unavoidable impurities.

[0009] Furthermore, as a preferred technical solution: The oxygen content of the bearing steel is preferably ≤0.0008%; The sulfur content of the bearing steel is preferably ≤0.0050%; The titanium content of the bearing steel is preferably ≤0.0015%.

[0010] Furthermore, after oil quenching at 840±10℃ and low-temperature tempering at 160±10℃, the bearing steel has a surface hardness ≥HRC61. Using a thrust plate contact fatigue test, under a maximum contact stress of 4.5GPa, the L10 contact fatigue life is ≥7.0×10⁻⁶. 7 Second-rate.

[0011] The design principles of each component of this invention are as follows: C: Carbon is the core element that ensures the hardness, strength, and wear resistance of bearing steel. If the content is too low, sufficient martensitic hardness and carbide quantity cannot be obtained, while if it is too high, it will exacerbate the inhomogeneity of carbides. This invention controls the C content between 0.95% and 1.05%, ensuring high hardness and wear resistance while also taking into account the uniformity of the microstructure.

[0012] Si and Mn: Both silicon and manganese can improve the hardenability of steel. Silicon has the functions of solid solution strengthening and improving tempering stability, while manganese can help reduce the harm of sulfur. Compared with conventional GCr15, this invention simultaneously increases the Si and Mn content to 0.45%~0.65%, effectively enhancing the hardenability depth of large-size bearing parts, compensating for the hardenability loss caused by the reduction of chromium content, and ensuring the uniformity of performance across the entire cross-section of large cross-section workpieces.

[0013] Cr: Chromium can improve hardenability and wear resistance, and promote carbide formation, but excessive content can easily lead to carbide segregation and network carbides, reducing the toughness of steel. This invention appropriately reduces the Cr content to 1.10%–1.30%, effectively optimizing the carbide distribution morphology, reducing the tendency to form network carbides, and improving the toughness and microstructure uniformity of steel. At the same time, the combination of Si and Mn elements can still ensure sufficient hardenability and wear resistance.

[0014] Mo: Trace amounts of molybdenum can improve the hot hardness and tempering stability of steel, and suppress temper brittleness. This invention controls the Mo content to ≤0.08%, mainly through residual content in raw materials, to achieve performance gains without significantly increasing costs.

[0015] Ni and Cu: As residual alloying elements, an appropriate amount of nickel can improve the toughness of steel, while excessive copper can easily cause hot brittleness. Therefore, their upper limits are limited to avoid adverse effects.

[0016] Precise control of harmful impurity elements Oxygen forms oxide inclusions in steel, which are the main initiation source of contact fatigue cracks. The contact fatigue life of bearing steel is negatively correlated with oxygen content. This invention strictly controls the O content to ≤0.0010% (10ppm), significantly reducing the number of oxide inclusions and substantially improving contact fatigue life.

[0017] Sulfur readily forms elongated MnS inclusions, disrupting the continuity of the matrix, reducing the transverse toughness and fatigue performance of steel, and increasing material anisotropy. This invention controls the S content to ≤0.0080%, far exceeding general standard requirements, effectively reducing MnS inclusions and improving the fatigue resistance and isotropic mechanical properties of the steel.

[0018] P: Phosphorus tends to segregate at grain boundaries, causing cold brittleness and reducing the toughness of steel. Therefore, its upper limit is strictly limited.

[0019] Ti: Titanium readily forms hard, angular, brittle inclusions such as TiN and Ti(C,N), which severely compromise contact fatigue life. This invention controls the Ti content to ≤0.0030%, eliminating the fatigue hazards posed by TiN-type inclusions at the source.

[0020] Ca: Excessive calcium easily forms brittle low-melting-point calcium aluminate inclusions (Ds type), impairing the purity of the steel; however, trace amounts of calcium can form fine low-melting-point inclusions, which play a role in chip breaking and lubrication during machining, improving the machinability of low-sulfur steel. This invention precisely controls the Ca content to ≤0.0010%, balancing purity requirements with machinability.

[0021] Al: Aluminum remains as a deoxidizing element, and excessive amounts can easily form alumina inclusions, thus limiting its upper limit.

[0022] The total amount of residual harmful elements (As, Sn, Sb, Pb, and Bi) is controlled. As these are all low-melting-point residual harmful elements, they are prone to segregation at grain boundaries, causing hot brittleness and temper brittleness, and reducing the uniformity of steel performance and long-term service reliability. This invention not only limits the individual content upper limit of each element, but also innovatively controls the total amount of the five elements, requiring As+Sn+Pb+Sb+Bi≤0.035%, effectively suppressing the cumulative segregation effect of residual elements and ensuring the performance uniformity and long-term service stability of large-section bearing parts.

[0023] (III) Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: 1. Ultra-high purity level. This invention achieves ultra-low harmful element control through multi-dimensional precise management, with oxygen ≤10ppm, sulfur ≤0.008%, titanium ≤0.0030%, and calcium ≤0.0010%. At the same time, the total amount of the five residual harmful elements is limited to ≤0.035%. The number and size of long strip-shaped MnS inclusions, TiN brittle inclusions, and oxide inclusions in the steel are significantly reduced, and the overall purity reaches the international advanced level.

[0024] 2. Excellent contact fatigue life. Based on ultra-high purity and optimized composition system, the bearing steel of this invention has a significantly reduced probability of fatigue crack initiation under high alternating contact stress. The contact fatigue life of L10 is 2.5 to 3 times higher than that of conventional GCr15, which can meet the long service life requirements of precision rolling mill bearings under high speed and high load conditions.

[0025] 3. Excellent comprehensive mechanical properties. By reducing chromium content and optimizing carbide distribution, combined with ultra-low sulfur design to reduce anisotropy, the steel maintains high hardness above HRC61 and excellent wear resistance, while also possessing good toughness and transverse mechanical properties, and exhibiting excellent performance uniformity under large cross-section conditions.

[0026] 4. Excellent high-temperature dimensional stability. The presence of trace amounts of molybdenum allows the steel to maintain high hardness and structural stability even under bearing operating temperature rise conditions, inhibiting tempering softening and ensuring the dimensional and rotational accuracy of precision bearings.

[0027] 5. Balanced machinability. By precisely controlling the trace calcium content, while achieving ultra-low sulfur purity, the problem of difficult chip breaking and easy tool sticking in low-sulfur steel is effectively improved, giving the steel good cold working machinability and making it suitable for the precision machining requirements of bearing parts.

[0028] 6. Significant economic advantages. This invention does not rely on the addition of expensive alloying elements such as Nb, V, and rare earth elements. It uses composition system optimization and purity control as the core technical means, making raw material costs controllable. The preparation process can be realized by relying on existing mature smelting production lines, making it suitable for large-scale industrial production and widespread application. Detailed Implementation

[0029] The bearing steel used in both the embodiments and comparative examples of this invention employs the following preparation process: electric arc furnace primary refining → pre-deoxidation of tapped steel → deep desulfurization and composition fine-tuning in an LF refining furnace → RH vacuum degassing and trace element regulation → continuous casting under full protection → high-temperature diffusion annealing of continuously cast billets → hot rolling → spheroidizing annealing to obtain the finished steel. The finished steel is then subjected to performance testing after oil quenching at 840±10℃ and low-temperature tempering at 160±10℃.

[0030] Example 1 This embodiment describes a high-purity bearing steel suitable for backing bearings in precision cold-rolled thin plate mills. Its chemical composition, by mass percentage, is as follows: C: 1.00%, Si: 0.50%, Mn: 0.50%, Cr: 1.25%, Mo: 0.05%, Ni: 0.15%, Cu: 0.10%; Harmful element control: O: 0.0008%, S: 0.0050%, P: 0.010%, Ti: 0.0015%, Ca: 0.0005%, Al: 0.035%; Residual element control: As: 0.008%, Sn: 0.006%, Sb: 0.002%, Pb: 0.001%, Bi: 0.003%, As+Sn+Sb+Pb+Bi=0.020%, and ≤0.035%. The balance is Fe and unavoidable impurities.

[0031] Performance test results: After standard heat treatment, the surface hardness of the steel is HRC62~63; under a maximum contact stress of 4.5 GPa, the L10 contact fatigue life reaches 8.2 × 10⁻⁶. 7 Second-rate.

[0032] Application Results: The steel used in this embodiment was used to prepare high-precision multi-row assembled backing bearings for a 1400mm twelve-roll double-stand reversible cold rolling mill. After 6 months of actual operation, the bearing rings and rolling elements showed no pitting or peeling. The bearing rotation accuracy remained stable, and the thickness tolerance of the rolled product was controlled within ±0.001mm, meeting the production process requirements for high-precision cold-rolled thin plates.

[0033] Example 2 This embodiment provides a high-purity bearing steel suitable for support roll bearings of high-speed precision rolling mills. Its chemical composition by mass percentage is as follows: C: 0.98%, Si: 0.55%, Mn: 0.55%, Cr: 1.30%, Mo: 0.06%, Ni: 0.10%, Cu: 0.08%; Harmful element control: O: 0.0009%, S: 0.0060%, P: 0.012%, Ti: 0.0020%, Ca: 0.0008%, Al: 0.040%; Residual element control: As: 0.010%, Sn: 0.008%, Sb: 0.003%, Pb: 0.0015%, Bi: 0.004%, As+Sn+Pb+Sb+Bi=0.0265%, and ≤0.035%. The balance is Fe and unavoidable impurities.

[0034] Performance test results: After standard heat treatment, the surface hardness of the steel is HRC62~63; under a maximum contact stress of 4.5 GPa, the contact fatigue life of L10 reaches 7.8 × 10⁻⁶. 7 Second-rate.

[0035] Application Results: When the steel used in this embodiment is used to make support roll bearings for high-speed cold rolling mills, the overall rotational accuracy of the bearings reaches P4 level under multi-bearing assembly conditions. After 12 months of continuous and stable operation, no early failures have occurred, which significantly reduces equipment maintenance costs and downtime losses.

[0036] Comparative Example 1 This comparative example uses conventional commercial GCr15 bearing steel, whose chemical composition by mass percentage is: C 1.00%, Si 0.25%, Mn 0.30%, Cr 1.50%, P 0.020%, S 0.018%, O 0.0013%, with no strict control over titanium, calcium and residual elements.

[0037] Performance test results: After the same heat treatment process as in the example, the surface hardness of the steel was HRC60~63; under the same test conditions, the contact fatigue life of L10 was only 2.6×10⁻⁶. 7 Electron microscopy of the fracture surface revealed obvious elongated MnS inclusions and blocky TiN inclusions. Fatigue cracks were present around the inclusions, which was the main reason for the low fatigue life.

[0038] Comparative Example 2 The main alloy composition of the bearing steel in this comparative example is the same as that in Example 1, but the titanium content is not strictly controlled. The Ti content is 0.0080%, and the remaining components and preparation process are the same as in Example 1.

[0039] After undergoing the same heat treatment, the performance test results showed that the L10 contact fatigue life was 4.1 × 10⁻⁶ after a contact stress of 4.5 GPa. 7 The concentration of titanium was significantly lower than in Example 1. Electron microscopy revealed a large number of angular TiN hard inclusions in the steel, which became the preferred sites for fatigue crack initiation, verifying the key role of ultra-low titanium content control in improving contact fatigue life.

[0040] The comparison results of the above embodiments and comparative examples show that the present invention can significantly improve the contact fatigue life and overall performance of bearing steel through the synergistic effect of main alloy element optimization and multi-dimensional purity control, thus meeting the high-end service requirements of precision rolling mill bearings.

[0041] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A high-purity bearing steel, characterized in that, The chemical composition of the bearing steel, by mass percentage, includes: C: 0.95%–1.05%; Si: 0.45%~0.65%; Mn: 0.45%~0.65%; Cr：1.10%～1.30%； Mo: ≤0.08%; Ni: ≤0.25%; Cu: ≤0.20%; O：≤0.0010%； S：≤0.0080%； P：≤0.015%； Ti: ≤0.0030%; Ca: ≤0.0010%; Al：≤0.050%； As: ≤0.015%; Sn: ≤0.010%; Sb: ≤0.005%; Pb: ≤0.002%; Bi: ≤0.0100%; And it satisfies As+Sn+Sb+Pb+Bi≤0.035%; the balance is Fe and unavoidable impurities.

2. The high-purity bearing steel according to claim 1, characterized in that, The mass percentage of oxygen in the bearing steel is ≤0.0008%.

3. The high-purity bearing steel according to claim 2, characterized in that, The mass percentage of sulfur in the bearing steel is ≤0.0050%.

4. The high-purity bearing steel according to claim 3, characterized in that, The mass percentage of titanium in the bearing steel is ≤0.0015%.

5. The high-purity bearing steel according to any one of claims 1-4, characterized in that, The bearing steel, after being oil-quenched at 840±10℃ and tempered at 160±10℃, has a surface hardness ≥HRC61 as measured by GB / T 230.

1. Using a thrust plate contact fatigue test, under a maximum contact stress of 4.5GPa, the L10 contact fatigue life is ≥7.0×10⁻⁶. 7 Second-rate.

6. The application of the high-purity bearing steel according to any one of claims 1-5 in the backing bearings of precision cold-rolled thin plate mills.

7. The application according to claim 6, characterized in that, The precision cold-rolled sheet mill is a multi-roll reversible cold rolling mill.

8. The application of the high-purity bearing steel according to any one of claims 1-5 in the support roll bearings of high-speed precision rolling mills.