High-standard bearing hot-rolled ribbon steel and manufacturing method therefor

Abstract

A high-standard bearing hot-rolled ribbon steel and a manufacturing method therefor, relating to the technical field of steel production. The high-standard bearing hot-rolled ribbon steel comprises the following chemical components in percentage by mass: C: 0.95-1.06%; Si: 0.15-0.35%; Mn: 0.25-0.45%; Cr: 1.50-1.65%; Ni: 0.15-0.20%; Cu≤0.05%; Mo≤0.10%; Ti≤0.003%; As≤0.012%; Al≤0.05%; O≤0.0008%; Pb≤0.002%; P≤0.015%; S≤0.008%; and the balance being Fe and inevitable impurity elements. The obtained high-standard bearing hot-rolled ribbon steel has an inclusion rating result of coarse inclusions A+B+C+D≤1.0, fine inclusions A+B+C+D≤2.0, and carbide networks≤2.0, and meets the use requirements of high-end high-standard bearing hot-rolled ribbon steel manufacturers.

Description

A high-standard bearing hot-rolled narrow strip steel and its preparation method Technical Field

[0001] The present invention relates to the technical field of steel production, and in particular to a high-standard hot-rolled narrow strip steel for bearings and a preparation method thereof. Background Art

[0002] Bearings are a crucial component in modern mechanical equipment. Their primary function is to support rotating bodies, reduce friction during movement, and ensure rotational accuracy, playing a vital role in modern industry. Bearings are primarily made of bearing steel, which is used to manufacture balls, rollers, and bearing rings. Consequently, bearing steel is primarily available in rod and wire form. Numerous studies, papers, and patents have focused on rod and wire bearing steel, but relatively few have explored bearing steel available in the form of hot-rolled narrow strip.

[0003] Hot-rolled narrow strip bearing steel is primarily used to manufacture plane bearings and ring bearings. Plane bearings are widely used in automobiles, most commonly in engines, transmissions, drivetrains, and suspension systems. Ring bearings are primarily used in the textile industry as a key component in the winding section of ring spinning machines. Therefore, hot-rolled narrow strip bearing steel is an indispensable component of the bearing steel industry.

[0004] Bearing fatigue life is the primary performance indicator of bearing steel, and the main factors affecting bearing steel fatigue life are steel cleanliness (inclusions), carbides, and performance. Different types and sizes of inclusions have different degrees of damage to bearing steel. The larger the inclusion, the greater the damage. Under the same size conditions, hard spherical inclusions (Class B and Class D) have a higher damage index to bearing steel. Therefore, improving the cleanliness of molten steel and reducing the inclusion rating are of great significance to extending the service life of bearing steel.

[0005] As a high-carbon steel, bearing steel is very prone to forming carbides. Carbides are classified into liquid carbides, banded carbides, and network carbides based on their microstructure and distribution. Network carbides are more harmful to bearing steel and have always been a difficult problem to solve. The presence of network carbides poses two main hazards to bearing steel: ① Cracks are likely to occur during grinding of the bearing steel; ② When the network structure is severe, it is difficult to eliminate it through heat treatment. During the use of the bearing steel, network carbides act as a source of fatigue cracks, leading to fatigue failure of the bearing steel. Therefore, my country's national standard for bearing steel, GB / T 18254-2016, stipulates that the assessment level of network carbides after quenching and tempering shall not exceed 2.5. More advanced users even require network carbides to be ≤2.0.

[0006] For hot-rolled narrow strip bearing steel, there is relatively little research on improving cleanliness, reducing network carbides, and optimizing composition. Therefore, it is extremely important to explore a dedicated preparation method for high-quality, high-standard hot-rolled narrow strip bearing steel.

[0007] Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a high-standard bearing hot-rolled narrow strip steel and a preparation method thereof.

[0009] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0010] A high-standard hot-rolled narrow strip steel for bearings, whose chemical composition and mass percentage are as follows: C: 0.95-1.06%, Si: 0.15-0.35%, Mn: 0.25-0.45%, Cr: 1.50-1.65%, Ni: 0.15-0.20%, Cu: ≤0.05%, Mo: ≤0.10%, Ti: ≤0.003%, As: ≤0.012%, Al: ≤0.05%, O: ≤0.0008%, Pb: ≤0.002%, P: ≤0.015%, S: ≤0.008%, and the balance is Fe and unavoidable impurity elements.

[0011] The present invention also provides a method for preparing high-standard bearing hot-rolled narrow strip steel, comprising the following steps: electric furnace smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting → heating → rolling → cooling → curling.

[0012] As a preferred solution of the preparation method of the high-standard bearing hot-rolled narrow strip steel described in the present invention, during the electric furnace smelting process, the Ni element is added to 0.09%-0.12% in the electric furnace; the steel tapping conditions of the electric furnace smelting are C: 0.3~0.7%, P: ≤0.012%, and the temperature is greater than or equal to 1600℃.

[0013] As a preferred solution of the method for preparing high-standard bearing hot-rolled narrow strip steel according to the present invention, the order of adding materials for tapping the electric furnace during the electric furnace smelting process is: deoxidizer, alloy, pre-melted slag, and lime. The amount of the deoxidizer added is 0.5-1.2 kg / t, the amount of the pre-melted slag added is 4-7 kg / t, and the amount of the lime added is 4-6 kg / t.

[0014] As a preferred solution of the method for preparing the high-standard hot-rolled narrow strip steel for bearings of the present invention, the deoxidizer includes but is not limited to aluminum blocks and aluminum-iron alloys.

[0015] As a preferred solution of the method for preparing the high-standard hot-rolled narrow strip steel for bearings described in the present invention, during the LF furnace refining process, the initial aluminum content is ≥0.05%, the end point aluminum content is ≥0.02%, the amount of lime added is less than or equal to 3 kg / t, and the diffusion deoxidizer is less than or equal to 2.0 kg / t.

[0016] As a preferred solution of the method for preparing high-standard hot-rolled narrow strip steel for bearings according to the present invention, during the vacuum degassing process in the VD furnace, the ultimate vacuum time is greater than or equal to 15 minutes, and the static stirring time is greater than or equal to 20 minutes.

[0017] As a preferred solution of the preparation method of the high-standard bearing hot-rolled narrow strip steel described in the present invention, the heating process includes a preheating section, a heating section, a heating section, a heating section, and a soaking section. The furnace temperature of the preheating section is less than or equal to 950°C, the furnace temperature of the heating section is 700-1100°C, the furnace temperature of the heating section is 950-1150°C, the furnace temperature of the heating section is 1000-1250°C, the furnace temperature of the soaking section is 1100-1300°C, and the time in the furnace is ≥120min.

[0018] As a preferred solution of the preparation method of the high-standard bearing hot-rolled narrow strip steel described in the present invention, wherein: during the rolling process, the starting rolling temperature is 1080-1220°C, the final rolling temperature is 850-950°C, the cooling process adopts a combination of water cooling and air cooling, the temperature after water cooling is 650-750°C, and the temperature after air cooling is 620-680°C, and the temperature of the curling process is 450-600°C.

[0019] As a preferred solution of the method for preparing the high-standard bearing hot-rolled narrow strip steel of the present invention, the thickness of the hot-rolled narrow strip steel is 4.0-12 mm, and the width is 160-420 mm.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention stabilizes the O content in the molten steel by strictly controlling the C content in the steel, preventing the molten steel from being overoxidized during tapping, and reducing the generation of inclusions from the source. In addition, the stability of the O content in the molten steel also provides a guarantee for the stability of the quality of the hot-rolled narrow strip steel for bearings. The strict control of the order of adding materials in the steel tapping process further reduces the generation of inclusions in the steel tapping process, and at the same time controls the generated inclusions to be inclusions that are easy to aggregate and float, further promoting the removal of inclusions. In the refining process, by controlling the Al content and the diffusion deoxidizer, early slag formation and good slag are achieved, the S element in the molten steel is removed, and it also plays a role in absorbing inclusions and deoxidation. The control of the extreme vacuum time during the vacuum degassing process of the VD furnace creates conditions for the effective removal of H and N gases, and soft stirring promotes the floating of inclusions. A series of operations and controls in the refining process are all aimed at obtaining high-purity molten steel and reducing the rating of inclusions. The control of the temperature during heating and rolling, especially the final rolling temperature and the cooling mode of strong water cooling + air cooling after rolling, is mainly to quickly pass through the sensitive precipitation temperature range of network carbides without increasing the risk of hot-rolled narrow strip cracking and abnormal microstructure.

[0022] (2) This invention combines existing special steel smelting and rolling equipment with optimized smelting and rolling processes to achieve improved cleanliness and reduced carbide network ratings for high-quality hot-rolled narrow strip bearing steel, without requiring additional equipment or processes. This method is simple, novel, and widely applicable, providing excellent guidance for further improving product quality and developing new steel grades.

[0023] (3) The high-standard hot-rolled narrow strip steel for bearings produced by the present invention has inclusion rating results of A+B+C+D coarse series ≤1.0, A+B+C+D fine series ≤2.0, and network carbide ≤2.0, meeting the use requirements of high-end and high-standard hot-rolled narrow strip steel for bearings manufacturers. DETAILED DESCRIPTION

[0024] In order to make the contents of the present invention more clearly understood, the present invention is further described below in detail based on specific implementation methods in conjunction with the accompanying drawings.

[0025] This embodiment provides a high-standard hot-rolled narrow strip steel for bearings, whose chemical composition and mass percentage are as follows: C: 1.03%, Si: 0.20%, Mn: 0.31%, Cr: 1.58%, Ni: 0.17%, Cu: 0.03%, Mo: 0.04%, Ti: 0.001%, As: 0.007%, Al: 0.02%, O: 0.0005%, Pb: 0.001%, P: 0.008%, S: 0.003%, and the remainder is Fe and unavoidable impurity elements.

[0026] The preparation method of the above-mentioned high-standard bearing hot-rolled narrow strip steel is as follows: electric furnace smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting → heating → rolling → cooling → coiling.

[0027] During the electric furnace smelting process, one ton of nickel-iron alloy is added to the furnace. The tapping conditions are: C content: 0.38%, P content: 0.0095%, Ni content: 0.096%, and temperature: 1635°C.

[0028] It's important to note that strict control of carbon content during tapping is necessary, on the one hand, to prevent excessive oxidation of the molten steel during the tapping process, which increases inclusion formation and reduces steel cleanliness; and, on the other hand, to prevent excessive carbon content, which could result from the addition of large amounts of alloys exceeding the specified upper limit. The addition of nickel to the electric furnace is primarily intended to reduce the amount of alloy added during the tapping process, minimize temperature drop and slag formation, and improve the removal of initial inclusions. The temperature requirement is primarily intended to accelerate alloy melting and the formation of refining slag.

[0029] The order of adding materials to the electric furnace for tapping steel is: deoxidizer, alloy, pre-melted slag, and lime. The amount of deoxidizer added is 0.8 kg / t, the amount of pre-melted slag added is 6 kg / t, and the amount of lime added is 5 kg / t. In this embodiment, the deoxidizer is aluminum block or ingot.

[0030] The strict order of adding materials is primarily to prevent alloy oxidation, thereby increasing alloy yield. Al is also used to control the oxygen content in the molten steel, thereby improving its cleanliness. The amount of deoxidizer, pre-melted slag, and lime added is primarily to determine the appropriate refining slag system.

[0031] During the LF furnace refining process, the initial Al content is 0.06%. As smelting progresses, the final Al content reaches 0.02%. After treatment in the VD furnace, the Al content decreases to 0.015%. The refining process requires lime addition of 2 kg / t and diffusion deoxidizer of 1 kg / t. Diffusion deoxidizers include SiC powder and C powder. During the VD furnace vacuum degassing process, the ultimate vacuum is maintained for 20 minutes, and static stirring is performed for 30 minutes. Ca treatment and Al line addition are strictly prohibited. The static stirring time is determined according to the actual production schedule.

[0032] During the vacuum degassing process of the VD furnace, the regulation of the maximum vacuum time is mainly to ensure that the H and N elements in the molten steel can be effectively removed; the regulation of the static stirring time is to effectively remove the inclusions generated by the mixing of the steel slag in the VD process so that they can be effectively floated and removed; Ca treatment is strictly prohibited mainly to avoid the formation of spherical calcium aluminate inclusions, which are the most harmful to the service life of bearing steel; Al line addition is strictly prohibited mainly to avoid destroying the balance of the steel slag after VD treatment and prevent the production of new inclusions, which will further pollute the molten steel.

[0033] The heating process used a walking-beam furnace, consisting of a preheating section, a first heating section, a second heating section, a third heating section, and a soaking section. The preheating section temperature was 489°C, the first heating section temperature was 725°C, the second heating section temperature was 1060°C, the third heating section temperature was 1133°C, and the soaking section temperature was 1168°C. The total furnace time was 170 minutes.

[0034] During rolling, the starting temperature is 1140°C and the finishing temperature is 901°C. Post-rolling cooling is achieved using a combination of water and air cooling. The inlet temperature of the water-cooled flat chain is 745°C, and after air cooling, the temperature stabilizes at 670°C. The coiling temperature is 540°C.

[0035] The final rolling temperature is set to ensure that the deformation of the hot-rolled coil is in the austenite region, preventing deformation in the two-phase region and increasing the risk of cracking of the hot-rolled coil; on the other hand, it is also to ensure that the strong water cooling after rolling can reduce the temperature to a predetermined range, while also preventing the generation of abnormal martensite structure due to excessively rapid temperature drop. Strong water cooling + air cooling after rolling is mainly to enhance the cooling rate, quickly pass through the network carbide precipitation temperature range, and reduce the precipitation of network carbides. In addition, considering that the thickness of the high-standard bearing hot-rolled narrow strip steel is relatively thick, the surface temperature of the hot-rolled coil will first decrease and then increase after strong water cooling, so air cooling is added to the flat chain.

[0036] After rolling, the steel is either pile-cooled in a sheltered area or slowly cooled in a pit. The post-rolling pile-cooling temperature is 450°C, and the rolled product is 5.8mm thick and 263mm wide.

[0037] The above-described preparation method is now suitable for mass production. The inclusion rating results for a typical rolling mill, shown in Table 1, achieved a rating of ≤1.0 for the coarse A+B+C+D system and ≤2.0 for the fine A+B+C+D system. The rating results for the decarburized layer and network carbides, shown in Table 2, showed a network carbide rating of ≤2.0, meeting the requirements of high-end, high-standard hot-rolled narrow strip bearing manufacturers.

[0038] Table 1

[0039] Table 2

[0040] Thus, the technical solution of this application combines existing special steel smelting and rolling equipment to optimize the smelting and rolling processes, achieving the goal of improving the cleanliness of high-standard hot-rolled narrow strip bearing steel and reducing the carbide network rating, without adding additional equipment or processes. This method is simple, novel, and widely applicable, and provides excellent guidance for further improving product quality and developing new steel grades.

[0041] In addition to the above embodiments, the present invention may also have other implementation methods; any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A high-standard hot-rolled narrow strip steel for bearings, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.95-1.06%, Si: 0.15-0.35%, Mn: 0.25-0.45%, Cr: 1.50-1.65%, Ni: 0.15-0.20%, Cu: ≤0.05%, Mo: ≤0.10%, Ti: ≤0.003%, As: ≤0.012%, Al: ≤0.05%, O: ≤0.0008%, Pb: ≤0.002%, P: ≤0.015%, S: ≤0.008%, and the balance is Fe and unavoidable impurity elements.

2. A method for preparing the high-standard hot-rolled narrow strip steel for bearings according to claim 1, characterized in that: The following steps are involved: Electric furnace smelting → LF furnace refining → VD furnace vacuum degassing → continuous casting → heating → rolling → cooling → curling.

3. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: During the electric furnace smelting process, the Ni element is added to the electric furnace to 0.09%-0.12%; the steel tapping conditions of the electric furnace smelting are C: 0.3-0.7%, P: ≤0.012%, and the temperature is greater than or equal to 1600°C.

4. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: The order of adding materials for electric furnace steelmaking during the electric furnace smelting process is: deoxidizer, alloy, pre-melted slag, lime. The addition amount of the deoxidizer is: 0.5-1.2kg / t, the addition amount of the pre-melted slag is: 4-7kg / t, and the addition amount of the lime is: 4-6kg / t.

5. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 4, characterized in that: The deoxidizer includes but is not limited to aluminum block and aluminum-iron alloy.

6. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: During the LF furnace refining process, the initial aluminum content is ≥0.05%, the final aluminum content is ≥0.02%, the amount of lime added is less than or equal to 3kg / t, and the diffusion deoxidizer is less than or equal to 2.0kg / t.

7. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: During the vacuum degassing process of the VD furnace, the ultimate vacuum time is greater than or equal to 15 minutes, and the static stirring time is greater than or equal to 20 minutes.

8. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: The heating process includes a preheating section, a first heating section, a second heating section, a third heating section and a soaking section. The furnace temperature of the preheating section is less than or equal to 950°C, the furnace temperature of the first heating section is 700-1100°C, the furnace temperature of the second heating section is 950-1150°C, the furnace temperature of the third heating section is 1000-1250°C, the furnace temperature of the soaking section is 1100-1300°C, and the time in the furnace is ≥120min.

9. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: During the rolling process, the starting rolling temperature is 1080-1220°C, the final rolling temperature is 850-950°C, the cooling process adopts a combination of water cooling and air cooling, the temperature after water cooling is 650-750°C, the temperature after air cooling is 620-680°C, and the temperature of the curling process is 450-600°C.

10. The method for preparing high-standard hot-rolled narrow strip steel for bearings according to claim 2, characterized in that: The hot-rolled narrow strip steel has a thickness of 4.0-12 mm and a width of 160-420 mm.

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