High-strength low-carbon steel and preparation method and application thereof

Abstract

The invention discloses high-strength low-carbon steel and a preparation method and application thereof, and belongs to the technical field of metallurgy. The low-carbon steel is prepared from the following components in percentage by mass: 0.06 percent to 0.08 percent of C, 0.022 percent to 0.025 percent of Si, 0.78 percent to 0.86 percent of Mn, 0.013 percent to 0.015 percent of P, 0.002 percent to 0.005 percent of S, 0.0017 percent to 0.0020 percent of V, 0.027 percent to 0.035 percent of Alt, 0.015 percent to 0.03 percent of Nb, 0.01 percent to 0.03 percent of Ti and the balance of Fe and inevitable impurities. According to the scheme, through selection of low-carbon steel components and design of preparation conditions, the strength and toughness of the obtained material are greatly improved compared with those of traditional low-carbon steel, the material is suitable for high-speed stamping conditions in follow-up machining, stamping fracture is easy, a stamping die is not excessively abraded, it can be guaranteed that after stamping, the residual stress of raw materials is small, and the product flatness is high; and the application performance of the obtained product is also improved, and the processing quality and the production efficiency are improved.

Description

Technical Field

[0001] This application relates to a high-strength low-carbon steel, its preparation method and application, and belongs to the field of metallurgical technology. Background Technology

[0002] Low-carbon and ultra-low-carbon steels not only have low carbon content (typically below 0.1% by mass) but also low alloy element content, resulting in simple manufacturing processes and significant cost advantages. Furthermore, (ultra)low-carbon steels possess good plasticity, toughness, and formability, making them easy to process through cold rolling, hot rolling, stamping, welding, and other techniques. They are widely used in vehicles, ships, bridges, construction, machinery, oil and gas pipelines, and aerospace.

[0003] Tapered roller bearings are an indispensable key component in the machinery industry. They can withstand large radial loads and unidirectional axial loads simultaneously, and are suitable for rotating parts that need to withstand heavy loads, impact loads, or require high rigidity. They are widely used in industries such as automobiles, heavy machinery and construction machinery, industrial transmission and gearboxes, metallurgy, wind power, and railways.

[0004] Tapered roller bearings consist of rollers and a cage. The cage manufacturing process includes blanking, stretching, and punching. High-speed stamping is frequently involved in cage production, with blanking frequencies reaching up to 420 times per minute. This excessive speed leads to high residual stress, warping, and dimensional errors in the stamped product. Low-carbon steel, due to its good plasticity and toughness, is less prone to fracture during stamping, resulting in increased defect rates and material waste. Furthermore, the insufficient strength of traditional low-carbon steel significantly limits its application in tapered roller bearings.

[0005] Existing technologies improve the problem of stamping fracture by adjusting the content of various components in low-carbon steel or improving the preparation process of low-carbon steel to increase the strength of the material and reduce its plasticity and toughness. However, the above improvements to low-carbon steel not only significantly increase the raw material cost or production cost, but also lead to a deterioration in the material's machinability while increasing its strength. After stamping and stretching the tapered roller bearing cage, dent defects are generated, reducing the product qualification rate. At the same time, as the strength of low-carbon steel increases, its hardness also increases, which makes the material more difficult to stamp, increases die wear, and reduces die life. On the other hand, it also leads to insufficient impact toughness of the final product under application conditions.

[0006] Therefore, how to improve the strength of low-carbon steel while ensuring its machinability and performance is a technical problem that urgently needs to be solved when using low-carbon steel as a cage material for tapered roller bearings. Summary of the Invention

[0007] To address the aforementioned issues, a high-strength low-carbon steel, its preparation method, and its application are provided. The resulting low-carbon steel material is not only easy to break during stamping and does not cause excessive wear on the stamping die, but also has a high product qualification rate and maintains good impact toughness after stamping.

[0008] According to one aspect of this application, a high-strength low-carbon steel is provided, comprising, by mass percentage: C 0.06-0.08%, Si 0.022-0.025%, Mn 0.78-0.86%, P 0.013-0.015%, S 0.002-0.005%, V 0.0017-0.0020%, Alt 0.027-0.035%, Nb 0.015-0.03%, Ti 0.01-0.03%, with the balance being Fe and unavoidable impurities.

[0009] Carbon (C) significantly improves the strength and hardness of low-carbon steel through solid solution strengthening and the formation of carbides with other elements; however, excessively high C content is detrimental to the toughness and machinability of the steel. Manganese (Mn) not only plays a role in solid solution strengthening and improving the strength of low-carbon steel, but also enhances its hardenability, improves its hot working properties, helps refine grains, and strengthens its toughness. Simultaneously, Mn can combine with sulfur (S) to form MnS, improving machinability while preventing the formation of brittle FeS and avoiding hot brittleness. A small amount of aluminum in the material can combine with oxygen, purifying the molten steel. Furthermore, the compounds formed with Nb, Ti, V, and C pin austenite grain boundaries, inhibiting grain growth and refining the grains, thereby improving the resistance to brittle fracture and toughness of low-carbon steel, and enhancing its machinability.

[0010] Preferably, the content ratio of C to Mn is 1:(13-14).

[0011] By controlling the content of C and Mn to a relatively low level, the phase transformation temperature is lowered, promoting the transformation of austenite into finer ferrite grains. This allows for a balanced control of the strength, hardness, and toughness of low-carbon steel. This ensures that the low-carbon steel is flat after stamping without causing excessive wear on the stamping die or cracking due to excessive brittleness. Insufficient content of either element results in significantly insufficient strength and toughness in the low-carbon steel. Excessive carbon content increases the overall strength of the low-carbon steel, but also increases brittleness, leading to a risk of stamping cracks. Excessive manganese content causes central segregation of manganese in the steel, resulting in a sharp decrease in the overall strength and toughness of the material, thus compromising the machinability of the low-carbon steel and making it impossible to obtain qualified products.

[0012] Preferably, the content ratio of C to Ti is 1:(0.125-0.3).

[0013] Ti can change the morphology of MnS, transforming it from elongated strips into finer, evenly distributed spherical particles, thereby significantly improving the impact toughness of steel; however, insufficient Ti content will result in a poor improvement effect.

[0014] Preferably, the high-strength low-carbon steel has a yield strength of 341-452 MPa, a tensile strength of 453-537 MPa, a grain size ≥ 9, and an elongation of 26-34%.

[0015] In this design, the yield strength and tensile strength of low-carbon steel can balance the usage requirements and processing performance of the bearing cage. While fully improving the strength of low-carbon steel, it ensures the strong impact toughness and overload safety of the ferritic steel bearing cage. Grain size determines the coarseness of the microstructure at room temperature, thus determining the strength and toughness of low-carbon steel. High grain size indicates smaller grain diameter, resulting in higher strength and toughness of low-carbon steel. Excessive or insufficient elongation will cause wear on the mold; therefore, the elongation needs to be controlled within a suitable range.

[0016] Preferably, the ratio between the yield strength and tensile strength of the high-strength low-carbon steel is 0.77-0.80.

[0017] Within this range of ratios, the yield strength and tensile strength can achieve a balance between the machinability of tapered roller bearing cages, including stamping ease and cracking risk, and usage requirements.

[0018] Preferably, the pearlite content in the high-strength low-carbon steel is 2-2.7%.

[0019] This design, through the design of element types and contents, ensures that the matrix of low-carbon steel is predominantly ferrite with 2.0-2.7% pearlite, giving the low-carbon steel both high strength and good toughness. The dispersed distribution of ferrite in the steel ensures a uniform improvement in performance, reduces localized stress, and consequently lowers the risk of cracking. It also reduces internal stress and processing distortion, improving the yield rate of stamped and stretched products and preventing processing defects such as dents, wrinkles, and cracks. Furthermore, it ensures the usability of the processed products, providing high strength while also guaranteeing impact toughness and overload resistance.

[0020] According to another aspect of this application, a method for preparing the high-strength low-carbon steel described in any of the above claims is provided, comprising the following steps:

[0021] S1. Low-carbon steel raw materials are added to a smelting furnace and smelted to obtain molten steel;

[0022] S2. Continuously cast the molten steel to obtain a steel billet;

[0023] S3. Hot-roll the obtained steel billet;

[0024] S4. High-strength low-carbon steel is obtained by water cooling the hot-rolled steel billet.

[0025] By controlling the content of each element in low-carbon steel, the austenite transformation temperature is lowered, and the billet can obtain refined grains without undergoing complex rolling and temperature control procedures, thereby improving the overall strength and density of low-carbon steel. Furthermore, by controlling the annealing temperature, the elongated grains are refined, recrystallization occurs between grains, grain size is controlled, dislocations are partially fused, and carbides are precipitated, which strengthens the steel and improves the density of the material's microstructure and overall strength. In this process, the precipitation of carbides improves the mechanical strength of the material.

[0026] Preferably, the melting in step S1 is carried out at a temperature of 1350-1480°C.

[0027] Preferably, the final rolling temperature of the hot rolling in step S3 is 820-880℃, and the hot rolling is followed by water cooling to 45℃.

[0028] According to another aspect of this application, the application of the high-strength low-carbon steel described in any of the preceding claims or the high-strength low-carbon steel prepared by any of the preceding claims is provided for use in tapered roller bearing cages.

[0029] The beneficial effects of this application include, but are not limited to:

[0030] 1. The high-strength low-carbon steel according to this application controls the content of solid solutions in low-carbon steel by controlling the content of elements such as C, Si, Mn, P, S, V, Alt, Nb, and Ti, and affects the microstructure of low-carbon steel. This maximizes the strength of low-carbon steel while ensuring the processing performance of the steel. It is beneficial for stamping fracture and avoids die wear. The resulting stamped products have no dents in the tear band and the stamped ring is flat and without warping. At the same time, the resulting products have high impact toughness and overload safety, reducing production losses and improving product qualification rate.

[0031] 2. The high-strength low-carbon steel according to this application, by controlling the type and content of elements, reduces the phase transformation temperature and promotes the transformation of austenite into finer ferrite grains, which can balance and control the relationship between the strength, hardness and toughness of low-carbon steel without the need for complex preparation processes, thus saving the production cost of high-strength low-carbon steel. Attached Figure Description

[0032] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0033] Figure 1This is a metallographic diagram of the high-strength low-carbon steel involved in Embodiment 3 of this application.

[0034] Figure 2 This is a metallographic diagram of the high-strength low-carbon steel involved in Comparative Example 1 of this application. Detailed Implementation

[0035] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only.

[0037] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0038] Example 1

[0039] This embodiment relates to a high-strength low-carbon steel, the preparation method of which is as follows:

[0040] S1. Add the low-carbon steel raw material to the melting furnace and melt it at 1350℃ to obtain molten steel;

[0041] S2. Continuously cast the molten steel to obtain a 200mm steel billet;

[0042] S3. The obtained steel billet is hot-rolled at 820℃;

[0043] S4. High-strength low-carbon steel is obtained by water cooling the hot-rolled steel billet at a rate of 25℃ / min.

[0044] The components of low-carbon steel are:

[0045] C 0.06%, Si 0.022%, Mn 0.78%, P 0.013%, S 0.002%, V 0.0017%, Alt 0.027%, Nb 0.015%, Ti 0.03%, balance Fe and unavoidable impurities.

[0046] Example 2

[0047] This embodiment relates to a high-strength low-carbon steel, the preparation method of which is as follows:

[0048] S1. Add the low-carbon steel raw material to the melting furnace and melt it at 1480℃ to obtain molten steel;

[0049] S2. Continuously cast the molten steel to obtain a 200mm steel billet;

[0050] S3. The obtained steel billet is hot-rolled at 880℃;

[0051] S4. High-strength low-carbon steel is obtained by water cooling the hot-rolled steel billet at a rate of 25℃ / min.

[0052] The components of low-carbon steel are:

[0053] C 0.08%, Si 0.025%, Mn 0.86%, P 0.015%, S 0.005%, V 0.0020%, Alt 0.035%, Nb 0.03%, Ti 0.03%, balance Fe and unavoidable impurities.

[0054] Example 3

[0055] This embodiment relates to a high-strength low-carbon steel, the preparation method of which is as follows:

[0056] S1. Add the low-carbon steel raw material to the melting furnace and melt it at 1420℃ to obtain molten steel;

[0057] S2. Continuously cast the molten steel to obtain a 200mm steel billet;

[0058] S3. The obtained steel billet is hot-rolled at 860℃;

[0059] S4. High-strength low-carbon steel is obtained by water cooling the hot-rolled steel billet at a rate of 25℃ / min.

[0060] The components of low-carbon steel are:

[0061] C 0.07%, Si 0.024%, Mn 0.8%, P 0.015%, S 0.003%, V 0.0020%, Alt 0.03%, Nb 0.02%, Ti 0.01%, balance Fe and unavoidable impurities.

[0062] Example 4

[0063] The difference between this embodiment and Embodiment 3 is that the content of C is 0.06% and the content of Mn is 0.78%.

[0064] Example 5

[0065] The difference between this embodiment and Embodiment 3 is that the content of C is 0.08% and the content of Mn is 0.86%.

[0066] Example 6

[0067] The difference between this embodiment and Embodiment 3 is that the Ti content is 0.03%.

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 3 is that the content of C is 0.10%.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 3 is that the Mn content is 1.5%.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 3 is that Ti is not added.

[0074] Example

[0075] The low-carbon steels obtained in the above embodiments and comparative examples were subjected to performance tests, and the test results are shown in Table 1. Blanking refers to placing the material in inner and outer dies and applying hydraulic force to break the material, then examining the blanked cross-section.

[0076] Table 1

[0077]

[0078]

[0079] Figure 1 The image shows the metallographic structure of the high-strength low-carbon steel involved in Example 3. Figure 2 The metallographic diagram of the high-strength low-carbon steel involved in Comparative Example 1 is shown below. Figure 1 and 2 The comparison shows that an increase in carbon content leads to an increase in pearlite content, while also forming tear bands in the microstructure, resulting in decreased microstructure uniformity and consequently, a decrease in mechanical properties. The materials in Examples 1-6 all have a grain size ≥ 9 and a pearlite content of 2.0-2.7%, which endows low-carbon steel with higher strength and toughness.

[0080] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0081] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A high-strength, low-carbon steel, characterized in that, It contains the following components by mass percentage: C 0.06-0.08%, Si 0.022-0.025, Mn 0.78-0.86%, P 0.013-0.015%, S 0.002-0.005%, V 0.0017-0.0020%, Alt 0.027-0.035%, Nb 0.015-0.03%, Ti 0.01-0.03%, balance being Fe and unavoidable impurities.

2. The high-strength low-carbon steel according to claim 1, characterized in that, The content ratio of C to Mn is 1:(13-14).

3. The high-strength low-carbon steel according to claim 1, characterized in that, The content ratio of C to Ti is 1:(0.125-0.3).

4. The high-strength low-carbon steel according to claim 1, characterized in that, The high-strength low-carbon steel has a yield strength of 341-452 MPa, a tensile strength of 453-537 MPa, and an elongation of 26-34%.

5. The high-strength low-carbon steel according to claim 1, characterized in that, The pearlite content in the high-strength low-carbon steel is 2.0-2.7%.

6. The method for preparing high-strength low-carbon steel according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Low-carbon steel raw materials are added to a smelting furnace and smelted to obtain molten steel; S2. Continuously cast the molten steel to obtain a steel billet; S3. Hot-roll the obtained steel billet; S4. High-strength low-carbon steel is obtained by water cooling the hot-rolled steel billet.

7. The method for preparing high-strength low-carbon steel according to claim 6, characterized in that, The melting process in step S1 is carried out at a temperature of 1350-1480℃.

8. The method for preparing high-strength low-carbon steel according to claim 6, characterized in that, The final rolling temperature of hot rolling in step S3 is 820-880℃, and the temperature is cooled to 45℃ by water cooling after hot rolling.

9. The application of the high-strength low-carbon steel according to any one of claims 1 to 5 or the high-strength low-carbon steel prepared by the preparation method according to any one of claims 6 to 8, characterized in that, Used for cages of tapered roller bearings.

Images