Air-cooled bainite steel based on phase change latent heat platform temperature regulation and preparation method thereof

Abstract

The application relates to the technical field of steel metallurgical processing, in particular to air-cooled bainite steel based on phase change latent heat platform temperature regulation and a preparation method thereof.The alloying elements and mass percentages in the air-cooled bainite steel are as follows: C: 0.15-0.43%, Mn: 2.0-2.4%, Si: 0.8-1.8%, Cr: 0-0.8%, Mo: 0-0.3%, V: 0-0.1%, and the rest is Fe.The efficient and accurate utilization of alloying elements is realized, the addition amount of excessive valuable alloying elements is avoided, the phase change latent heat platform temperature and the duration are controlled, the accurate control of the bainite organization content is realized, and the performance stability of the air-cooled bainite steel is improved.

Description

An air-cooled bainitic steel based on temperature control of latent heat plateau in phase transformation and its preparation method Technical Field

[0001] This application relates to the field of iron and steel metallurgical processing technology, and more specifically, it relates to an air-cooled bainitic steel based on temperature control of the latent heat platform of phase transformation and its preparation method. Background Technology

[0002] my country has a strong demand for high-strength and high-toughness steel materials in high-end equipment manufacturing and key engineering projects. Currently, commercially available ultra-high-strength steel (strength ≥ 1200 MPa) is mostly tempered martensite or sorbite, typically produced using a quenching and tempering process. This process is complex and requires additional high-temperature tempering. Against this backdrop, air-cooled bainitic steel has attracted widespread attention due to its simplicity, energy efficiency, and lack of need for additional heat treatment. For example, patent publications CN113388774A ("Hot-rolled air-cooled bainitic high-toughness and high-strength steel plate with tensile strength ≥ 1300 MPa and its manufacturing method") and CN1477226A ("Medium-low carbon manganese-based air-cooled bainitic steel") disclose the composition and manufacturing method of air-cooled bainitic steel.

[0003] However, as is well known, traditional air-cooled bainitic steel relies on natural cooling without the need for additional cooling media. This inevitably makes it susceptible to the influence of ambient temperature and the dimensions of the steel components, leading to performance instability. Furthermore, traditional air-cooled bainitic steel employs a multi-element alloying design to avoid the formation of high-temperature ferrite, resulting in a high and complex total alloy content. For example, the "multi-element microalloyed air-cooled bainitic steel" with patent publication number CN1189542A contains microalloying elements such as boron, nitrogen, and reticulum (RE), all of which are difficult to smelt. These existing technological drawbacks significantly limit the industrial manufacturing and application of air-cooled bainitic steel. Summary of the Invention

[0004] This disclosure provides a method for preparing air-cooled bainitic steel based on temperature control of the latent heat platform of phase transformation, in order to solve the technical problems of unstable performance and complex alloying elements in traditional air-cooled bainitic steel.

[0005] In a first aspect, this disclosure provides an air-cooled bainitic steel based on temperature control of a phase transformation latent heat platform, wherein the alloying elements and their mass percentages in the air-cooled bainitic steel are C: 0.15-0.43%, Mn: 2.0-2.4%, Si: 0.8-1.8%, Cr: 0-0.8%, Mo: 0-0.3%, V: 0-0.1%, and the remainder is Fe.

[0006] Based on the control of the latent heat of bainitic phase transformation, a simple alloying of elements is used to achieve the formation of a stable carbide-free bainitic / martensite dual-phase structure under natural cooling conditions. This method does not require the addition of expensive alloying elements and avoids traditional quenching and tempering or salt bath isothermal treatment, thus simplifying the process and achieving the beneficial effects of saving resources, reducing energy consumption, and reducing CO2 emissions.

[0007] Secondly, this disclosure provides a method for preparing air-cooled bainitic steel based on temperature control of the latent heat platform of phase transformation, comprising the following steps:

[0008] (1) The air-cooled bainitic steel is made into steel parts, austenitized and then naturally cooled. The latent heat plateau temperature of phase transformation during the natural cooling process is controlled to be 300-450℃ and the duration is 2-15 minutes.

[0009] (2) The steel part is allowed to form a carbide-free bainite / martensite multiphase structure after being naturally cooled to room temperature.

[0010] Based on the theory of latent heat of bainitic phase transformation, this application focuses on the coupled influence of alloying elements, steel dimensions, and ambient temperature on the latent heat plateau temperature of air-cooled bainitic steel during natural cooling. It proposes a compositional design using a blend of Mn-Si-Cr as the main elements, supplemented by Cr, Mo, and V. This design allows the latent heat plateau temperature to be controlled at 300-450℃ for 2-15 minutes, enabling the steel to form a carbide-free bainitic / martensite dual-phase structure under natural cooling conditions. This achieves efficient and precise utilization of alloying elements, avoiding excessive addition of precious alloying elements. Simultaneously, controlling the latent heat plateau temperature and duration allows for precise control of the bainite content, improving the performance stability of air-cooled bainitic steel.

[0011] Preferably, in step (1), the latent heat platform temperature of the phase transformation is obtained by naturally cooling the steel part after austenitization, measuring the cooling curve of the steel part during the natural cooling process, and using finite element simulation calculation based on the kinetic curve of the bainitic phase transformation and the latent heat value of the phase transformation.

[0012] Preferably, the cooling curve of the steel component is measured using a non-contact infrared thermometry method or a contact thermocouple method.

[0013] Preferably, the latent heat of phase transformation of the bainitic phase transformation is determined by differential scanning calorimetry.

[0014] Preferably, in step (2), the content of carbide-free bainite in the carbide-free bainite / martensite multiphase structure is 20-60%.

[0015] In summary, this application has the following beneficial effects:

[0016] 1. Because this application is based on the control of the latent heat of bainite phase transformation, it adopts a simple alloy element compounding to achieve the formation of a stable carbide-free bainite / martensite multiphase structure under natural cooling conditions. It does not add expensive alloy elements and avoids traditional quenching and tempering or salt bath isothermal treatment, which simplifies the process and has the beneficial effects of saving resources, reducing energy consumption and reducing CO2 emissions.

[0017] 2. The air-cooled bainitic steel prepared in this application forms a stable carbide-free bainitic / martensite multiphase structure in steel parts of different specifications over a wide range of cooling rates. The bainite content is controllable, which solves the technical problem of unstable microstructure and properties of traditional air-cooled bainitic steel.

[0018] 3. The air-cooled bainitic steel obtained by this application has a tensile strength of 1200-2000MPa, a yield strength of 900-1800MPa, an elongation of 10-20%, an impact toughness AKV of 40-120J, and a fatigue strength of 650-1080MPa. Its comprehensive performance is superior to that of traditional martensitic steel, and it has broad application prospects.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of protection of this disclosure. Attached Figure Description

[0020] 1. Figure 1 is a schematic diagram of the preparation method of air-cooled bainitic steel based on temperature control of latent heat platform of phase transformation in this application;

[0021] 2. Figure 2 is the natural cooling curve of the air-cooled bainitic fine-rolled threaded steel bar of Embodiment 2 of this application, obtained by finite element simulation.

[0022] 3. Figure 3 is the natural cooling curve of the air-cooled bainitic wear-resistant steel plate of Embodiment 3 of this application, measured by non-contact infrared method;

[0023] 4. Figure 4 shows the carbide-free bainitic / martensite multiphase microstructure of the air-cooled bainitic wear-resistant steel plate of Example 3 of this application. Detailed Implementation

[0024] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0025] Example

[0026] Example 1

[0027] A method for preparing air-cooled bainitic steel based on temperature control of the latent heat plateau of phase transformation, comprising:

[0028] The alloying elements and their mass percentages in the air-cooled bainitic steel are C: 0.15%, Mn: 2.0%, Si: 1.5%, Cr: 0.8%, Mo: 0.3%, V: 0.1%, with the remainder being Fe. The steel is rolled into heavy-duty drill rods, austenitized, and then naturally cooled. During the natural cooling process, the latent heat plateau temperature of the phase transformation is 380℃, and the duration is 6 minutes. After naturally cooling to room temperature, a carbide-free bainitic / martensite multiphase structure is formed.

[0029] Example 2

[0030] A method for preparing air-cooled bainitic steel based on temperature control of the latent heat plateau of phase transformation, comprising:

[0031] The alloying elements and their mass percentages in the air-cooled bainitic steel are C: 0.25%, Mn: 2.4%, Si: 1.8%, Cr: 0.5%, Mo: 0.25%, V: 0.08%, with the remainder being Fe. The steel is rolled into precision threaded steel bars, austenitized, and then naturally cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process is 400℃, and the duration is 10 minutes. After natural cooling to room temperature, a carbide-free bainitic / martensite multiphase structure is formed.

[0032] Example 3

[0033] A method for preparing air-cooled bainitic steel based on temperature control of the latent heat plateau of phase transformation, comprising:

[0034] The alloying elements and their mass percentages in the air-cooled bainitic steel are C: 0.30%, Mn: 2.2%, Si: 1.5%, Cr: 0.5%, Mo: 0.1%, V: 0.06%, with the remainder being Fe. The steel is rolled into wear-resistant steel plates, austenitized, and then naturally cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process is 320℃, and the duration is 2 minutes. After natural cooling to room temperature, a carbide-free bainitic / martensite multiphase structure is formed.

[0035] Example 4

[0036] A method for preparing air-cooled bainitic steel based on temperature control of the latent heat plateau of phase transformation, comprising:

[0037] The alloying elements and their mass percentages in the air-cooled bainitic steel are C: 0.42%, Mn: 2.3%, Si: 1.7%, Cr: 0.5%, Mo: 0%, V: 0.04%, with the remainder being Fe. The steel is cast into wear-resistant cast steel, austenitized, and then naturally cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process is 300℃, and the duration is 10 minutes. After natural cooling to room temperature, a carbide-free bainitic / martensite multiphase structure is formed.

[0038] Using a universal tensile testing machine, impact testing machine, and bending fatigue testing machine, and employing standard tensile, impact, and fatigue specimens, the mechanical properties of the specimens in each embodiment were determined according to the provisions of national standards GB / T228.1-2021, GB / T229-2020, and GB / T4337-2015. The performance range is shown in Table 1.

[0039] Comparative Example

[0040] Comparative Example 1

[0041] The steel containing the components of Example 1 was rolled into a heavy-duty drill rod, austenitized, and then forced to air-cool. During the natural cooling process, the latent heat plateau temperature of the phase transformation was 280°C and the duration was 2 minutes. After natural cooling to room temperature, a coarse fused bainite / martensite multiphase structure was formed.

[0042] Comparative Example 2

[0043] The steel containing the components of Example 2 was rolled into precision threaded steel bars, austenitized, and then slowly air-cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process was 460°C, and the duration was 20 minutes. After natural cooling to room temperature, a coarse granular bainite / martensite multiphase structure was formed.

[0044] Comparative Example 3

[0045] Unlike Example 3, Comparative Example 3 has a Mn content of 3.0%; the steel is rolled into a wear-resistant steel plate, austenitized and then naturally cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process is 300°C and the duration is 2 minutes; after natural cooling to room temperature, a martensitic structure is formed.

[0046] Comparative Example 4

[0047] Unlike Example 4, Comparative Example 4 has a Mo content of 0.5%; the steel was cast into wear-resistant cast steel, austenitized and then naturally cooled. The latent heat plateau temperature of the phase transformation during the natural cooling process was 250°C and lasted for 1 minute; after natural cooling to room temperature, a martensitic structure was formed.

[0048] Table 1 Mechanical properties of each embodiment and comparative example

[0049]

[0050]

[0051] The above description is merely an exemplary embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing air-cooled bainitic steel based on temperature control of the latent heat plateau of phase transformation, characterized in that, The alloying elements and their mass percentages in the air-cooled bainitic steel are: C: 0.15-0.43%, Mn: 2.0-2.4%, Si: 1.5-1.8%, Cr: 0.5-0.8%. Mo: 0.1-0.3%, V: 0.04-0.1%, the remainder being Fe; the preparation method of the air-cooled bainitic steel includes the following steps: (1) the air-cooled bainitic steel is made into a steel part, austenitized and then naturally cooled, and the latent heat plateau temperature of the phase transformation is controlled at 300-450℃ during the natural cooling process, and the duration is 2-15 minutes; the latent heat plateau temperature of the phase transformation is obtained by naturally cooling the steel part after austenitization, measuring the cooling curve of the steel part during the natural cooling process, and using finite element simulation calculation based on the kinetic curve of the bainitic phase transformation and the latent heat value of the phase transformation; (2) the steel part is naturally cooled to room temperature to form a carbide-free bainitic / martensite multiphase structure; the content of carbide-free bainite in the carbide-free bainitic / martensite multiphase structure is 20-60%.

2. The method for preparing air-cooled bainitic steel based on temperature control of the latent heat platform of phase transformation according to claim 1, characterized in that, The cooling curve of the steel component is measured using a non-contact infrared thermometry method or a contact thermocouple method.

3. The method for preparing air-cooled bainitic steel based on temperature control of the latent heat platform of phase transformation according to claim 1, characterized in that, The latent heat of phase transformation of the bainitic phase transformation was determined by differential scanning calorimetry.

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