A method for producing bearing steel by multi-pass combined rolling with one heating instead of two heating

Abstract

The application discloses a kind of one fire instead of two fire heating multi-pass combined rolling bearing steel production method.The bearing steel production process route is: smelting→billet continuous casting→heating→multi-pass combined rolling→slow cooling, wherein multi-pass combined rolling adopts 1 set of Φ1150mm unit+3 sets of Φ850mm unit+8 sets of short stress+18 sets of rolling mill unit+3 sets of reducing diameter unit+4 sets of multi-roller reducing diameter unit for rolling, finished steel specification is Φ20mm~Φ80mm, and processing ratio is greater than or equal to 37.The process flow reduces billet slow cooling, billet cleaning and heating process, thereby reducing process transmission time and energy consumption caused by secondary heating, while ensuring that material indexes completely meet the requirements of two fire rolling, production cost is saved, production efficiency is improved, and a new production method is provided for the development of hot-rolled round steel.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and more particularly to a method for producing bearing steel by multi-pass combined rolling with a single-heating process instead of a two-heating process. Background Technology

[0002] High-carbon chromium bearing steel is the main raw material for manufacturing balls, rollers, and bearing rings. Bearings withstand immense pressure and friction during operation, requiring bearing steel with high and uniform hardness, wear resistance, and a high elastic limit. Therefore, the purity of high-carbon chromium bearing steel and the sufficient homogenization of carbides within the steel are crucial. Carbide segregation is an important indicator of the uniformity of bearing steel, typically expressed using carbide liquid segregation, carbide banding, and carbide network levels to indicate the severity of segregation. Bearing steel with severe carbide segregation will exhibit uneven wear during use, affecting its service life. Carbide improvement usually involves two-heating and high-temperature diffusion followed by rolling, which can reduce carbide aggregation, eliminate liquid carbides in GCr15 bearing steel, and reduce banded carbides. By controlling the post-rolling cooling rate, the precipitation of network carbides can be effectively reduced. However, because the billet undergoes two heating and rolling processes, the two-heating rolling process is lengthy, increasing the consumption of natural gas and coal gas, resulting in higher costs, and also reducing the yield. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention, taking into account the size characteristics of continuously cast billets and the layout characteristics of rolling lines, provides a method for producing bearing steel using a single-heating process that replaces the two-heating process with multi-pass combined rolling. This method ensures that the material properties fully meet the requirements of two-heating rolling while saving production costs and improving production efficiency, thus providing a new production process for the development of hot-rolled round steel.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A method for producing bearing steel using a single-pass heating process instead of a two-pass heating process with multiple rolling stages, wherein the bearing steel production process route is: smelting → billet continuous casting → heating → multi-pass rolling → slow cooling, wherein:

[0006] Continuous casting: Continuous casting yields a square billet with a cross-sectional size of 390mm × 480mm;

[0007] Heating: The billet is heated in a hot charging furnace for continuous casting. The furnace inlet temperature is ≥400℃, the outlet temperature is 1190~1220℃, and the total heating time is more than 11 hours.

[0008] Multi-pass combined rolling: The billet is rolled into square steel using one Ф1150mm mill with a processing ratio ≥3.0 and an aspect ratio of 0.9. The square steel obtained from the billet is then transferred to three Ф850mm mills for rolling with a processing ratio ≥1.6 and an aspect ratio of 1.0. The resulting square steel is then transferred to eight short-stress mills for rolling with a processing ratio ≥2.3 and an aspect ratio of 1.0. Finally, the steel is rolled into an 18-stand mill + three sizing mills + four multi-roll sizing mills. The finished steel has a specification of Φ20mm~Φ80mm and a processing ratio ≥37.

[0009] In the above technical solution, the smelting process is further described as follows: smelting is carried out using an electric furnace, followed by refining in an LF refining furnace and vacuum degassing in an RH refining furnace.

[0010] In the above technical solution, the heating is further described as a four-stage heating process: the preheating stage temperature is ≤600℃, the first heating stage temperature is 880~1120℃, the second heating stage temperature is 1200~1260℃, the soaking stage temperature is 1200~1230℃, the total heating time of the preheating stage and the first heating stage is ≥5 hours, and the total heating time of the second heating stage and the soaking stage is ≥6 hours.

[0011] In the above technical solution, the slow cooling process is further described as follows: the rolled steel is placed in a slow cooling pit for heat preservation, and the slow cooling time is ≥48 hours.

[0012] In the above technical solution, further, the bearing steel, by weight percentage, has the following chemical composition: C 0.95%–1.05%, Si 0.15%–0.35%, Mn 0.25%–0.45%, Cr 1.4%–1.65%, Mo ≤0.10%, Ni ≤0.25%, Cu ≤0.25%, Alt ≤0.050%, P ≤0.015%, S ≤0.010%, O ≤0.0006%, Ti ≤0.0015%, Ca ≤0.0010%, As ≤0.04%, As+Sn+Sb ≤0.075%, Pb ≤0.002%, with the balance being Fe and unavoidable impurities.

[0013] The beneficial effects of this invention are as follows:

[0014] The production method of this invention reduces the processes of slow cooling, cleaning, and heating of steel billets, reduces the time spent on process transfers and the energy consumption caused by secondary heating, saves production costs, improves production efficiency, and produces steel with a compression ratio of ≥37 and high density, providing a new production process for the development of hot-rolled round steel.

[0015] The low-magnification microstructure and carbides of the steel produced by the method of this invention conform to the GB / T18254-2016 standard for high-carbon chromium bearing steel. Attached Figure Description

[0016] Figure 1 This is a low-magnification macroscopic photograph of the pickled Φ80mm hot-rolled round steel bearing steel from Example 1.

[0017] Figure 2 The image shows the microscopic photograph of the most severe network of carbides in the Φ80mm hot-rolled round steel bearing steel of Example 1.

[0018] Figure 3 This is a micrograph of the most severe banded carbides in the Φ80mm hot-rolled round steel bearing steel of Example 1.

[0019] Figure 4 This is a micrograph of the most severe field-of-view liquid carbide precipitation in the Φ80mm hot-rolled round steel bearing steel of Example 1. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0021] Example 1

[0022] The chemical composition of the bearing steel in this embodiment, expressed as a percentage by mass, is shown in Table 1. The remainder consists of Fe and unavoidable impurities.

[0023] Table 1. Chemical composition (%) of bearing steel in Example 1

[0024]

[0025] A method for producing bearing steel using a single-pass heating process instead of a two-pass heating process with multiple rolling stages, comprising the following production route: smelting → billet continuous casting → heating → multi-pass rolling → slow cooling, wherein:

[0026] Smelting and continuous casting: The traditional production process is adopted, using electric furnace for smelting, followed by refining in LF refining furnace and RH refining furnace for vacuum degassing treatment. The continuous casting machine adopts full-process non-oxidizing protection casting technology, continuous bending, continuous straightening, solidification end heavy pressure technology, crystallizer electromagnetic stirring, and end electromagnetic stirring for continuous casting, producing continuous casting bearing steel square billets with a cross-sectional size of 390mm×480mm.

[0027] Heating: The continuously cast square billet (cross-sectional dimensions of 390mm×480mm) with a temperature not lower than 400℃ is loaded into the heating furnace for heating. The preheating section is 400~600℃, the first heating section is 1000℃, and the sum of the heating time of the preheating section and the first heating section is 5.5 hours. The temperature of the second heating section is 1230℃, the temperature of the soaking section is 1215℃, and the sum of the heating time of the second heating section and the soaking section is 6.5 hours. The total heating time is 12 hours. After the continuously cast square billet is taken out of the furnace, it is descaled by high pressure water to remove the iron oxide scale on the surface of the billet.

[0028] Multi-pass combined rolling: The continuously cast square billet enters one Danieli Ф1150mm BD billet mill for initial rolling, and is rolled into a steel billet with a cross-sectional size of 232mm×268mm. It is then transferred to three Ф850mm mills for rolling, and is rolled into a steel billet with a cross-sectional size of 200mm×195mm. Then it is transferred to eight VAI-POMINI standless short stress mills for rolling, and is rolled into a steel billet with a cross-sectional size of 131.76mm×131.76mm. Finally, it is transferred to an 18-stand high-rigidity mill group + three reduction and sizing mill groups + four KOCKS multi-roll reduction and sizing mill groups for rolling, and Φ80mm steel is obtained.

[0029] Slow cooling: The rolled Φ80mm steel is transferred into a slow cooling pit for heat preservation, and the slow cooling time is ≥48 hours.

[0030] The bearing steel of Example 1 was inspected according to the GB / 18254-2016 standard.

[0031] A low-magnification macroscopic photograph of the pickled Φ80mm hot-rolled round steel bearing steel produced in Example 1 is shown below. Figure 1 As shown, the rolled material exhibits low magnification, central porosity, segregation of 0.5 level, and no shrinkage cavities.

[0032] The results of the most severe field-of-view carbide network and carbide banding liquefaction of bearing steel Φ80mm hot-rolled round steel in Example 1 are as follows: Figure 2-4 As shown, the carbide network is grade 3, the carbide band is grade 1.5, and the carbide liquid precipitation is grade 0.

[0033] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for producing bearing steel using a single-heating process instead of a two-heating process in multiple-pass combined rolling, characterized in that: The production route for the bearing steel is as follows: smelting → continuous casting of billets → heating → multi-pass combined rolling → slow cooling, wherein: Continuous casting: Continuous casting yields a square billet with a cross-sectional size of 390mm × 480mm; Heating: The billet is heated in a hot charging furnace for continuous casting. The furnace inlet temperature is ≥400℃, the outlet temperature is 1190~1220℃, and the total heating time is more than 11 hours. Multi-pass combined rolling: A 1150mm mill is used to roll the billet into square steel with a processing ratio ≥3.0 and an aspect ratio of 0.

9. The square steel obtained from the billet is then transferred to a 3-stand 850mm mill for rolling with a processing ratio ≥1.6 and an aspect ratio of 1.

0. The resulting square steel is then transferred to an 8-stand short-stress mill for rolling with a processing ratio ≥2.3 and an aspect ratio of 1.

0. Finally, it is transferred to an 18-stand mill + 3 sizing mills + 4 multi-roll sizing mills for rolling, producing finished steel with a specification of Φ20mm~Φ80mm and a processing ratio ≥37. The bearing steel, by weight percentage, comprises: C 0.95%~1.05%, Si 0.15%~0.35%, Mn 0.25%~0.45%, Cr 1.4%~1.65%, Mo≤0.10%, Ni≤0.25%, Cu≤0.25%, Alt≤0.050%, P≤0.015%, S≤0.010%, O≤0.0006%, Ti≤0.0015%, Ca≤0.0010%, As≤0.04%, As+Sn+Sb≤0.075%, Pb≤0.002%, with the balance being Fe and unavoidable impurities.

2. The method for producing bearing steel by multi-pass combined rolling with a single-heating process replacing a two-heating process as described in claim 1, characterized in that: The smelting process is as follows: smelting is carried out using an electric furnace, followed by refining in an LF refining furnace and vacuum degassing in an RH refining furnace.

3. The method for producing bearing steel by multi-pass combined rolling with a single-fire heating process replacing a two-fire process, as described in claim 1, is characterized in that: The heating process employs a four-stage heating method: a preheating stage with a temperature ≤600℃, a heating stage 1 with a temperature of 880~1120℃, a heating stage 2 with a temperature of 1200~1260℃, and a heat spreader stage with a temperature of 1200~1230℃. The total heating time for the preheating stage and the heating stage 1 is ≥5 hours, and the total heating time for the heating stage 2 and the heat spreader stage is ≥6 hours.

4. The method for producing bearing steel by multi-pass combined rolling with a single-fire heating process replacing a two-fire process, as described in claim 1, is characterized in that: The slow cooling process is as follows: the rolled steel is placed in a slow cooling pit for heat preservation, and the slow cooling time is ≥48 hours.

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