Preparation method of microalloyed steel

Abstract

The invention relates to a preparation method of microalloyed steel, and belongs to the technical field of metallurgy. The preparation method of the microalloyed steel comprises the following steps: S1, heating the microalloyed steel; s2, after heating is completed, the microalloyed steel is cooled; and S3, after cooling is completed, compression deformation is conducted on the microalloyed steel, and water quenching is conducted to 20-40 DEG C. According to the preparation method, the total dependent variable required in actual production is achieved through a single-pass compression process with a certain deformation quantity, meanwhile, heat preservation treatment is performed, the traditional test procedure is simplified, and the preparation method has a good application prospect in research on the precipitation mode of the deformation quantity on austenite grains and second-phase particles and the interaction effect of the second-phase particles and recrystallization. Through the preparation method, possible results can be tested with low cost and high efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for preparing microalloyed steel. Background Art

[0002] With the development of society, the demand for steel materials is increasing, and different industries have put forward different requirements for the various properties of steel materials. As the main structural material in modern industry, infrastructure and other industries, the performance of steel materials plays a vital role in promoting industrial development and building safety. Advanced ultra-high strength and high toughness micro-alloy steel is a new generation of high-strength structural materials. Large-scale structural steel represented by thick plates and heavy steel has the advantages of low production cost, high strength, good low-temperature impact toughness, corrosion resistance, high weldability, and fatigue resistance. It is widely used in large-scale engineering construction fields such as marine engineering, shipbuilding, and construction industries. However, during the rolling process of large / thick structural steel, due to its large size, the production efficiency is low, the deformation penetration is difficult, and the rolling force increases, making it difficult to achieve large reduction and low-temperature rolling. At the same time, in order to retain the high-temperature deformation structure, during the rapid cooling after rolling, the uniformity of the structure and mechanical properties of the large-size rolled piece will be deteriorated due to the large cooling rate.

[0003] In order to adapt to the diversity of my country's geographical climate, there are still many technical difficulties in developing steel for high-altitude cold areas and large-scale structural steel that have not been overcome. It is difficult to meet the development needs of rail transportation, energy mining, construction and other industries in high-altitude cold areas, and it also affects my country's international competitiveness in participating in the construction of comprehensive projects in high-altitude cold areas. Therefore, developing high-performance, stable large-scale structural steel that can serve in low-temperature environments and mastering its preparation and processing technology have important academic and engineering value for increasing product diversity, promoting infrastructure construction, and enhancing international competitiveness.

[0004] As we all know, the only effective way to improve the tensile strength and low-temperature impact toughness of materials at the same time is to strengthen the grains through fine grains. There are two ways to achieve microstructure refinement: one is to refine the grain size through phase transformation; the original grains are cut by the nucleation and growth of the new phase at the grain boundary and in the grain of the old phase, and the equivalent radius and equivalent area of ​​the original grains of the old phase are reduced, thereby achieving the purpose of refining the grain size. The second is to induce recrystallization to refine the grain size; during the rolling deformation process of steel materials, new undistorted grains will be generated from the deformed organization at a certain temperature, so that the number of grain boundaries and the number of grains in the same volume increase, thereby achieving grain refinement.

[0005] By combining phase transformation to refine the grain size with recrystallization to refine the grain size, the microstructure of large / thick structural steel can be refined to the greatest extent to obtain a good match of strength and toughness. However, the realization of this idea requires the obstruction of the grains by the second phase particles, so studying the precipitation form of the second phase particles and their obstruction to the grains is the fundamental to achieve microstructure refinement.

[0006] For example, Chinese invention patent CN112522489A discloses a method for achieving microstructure refinement by strengthening phase transformation using ultrafine austenite, which is coordinated with the rolling schedule by optimizing the design of Ti / Nb microalloying and inducing dynamic recrystallization during the finishing rolling process to obtain ultrafine austenite, so as to prepare the microstructure for subsequent phase transformation and grain size refinement. The grain boundaries of ultrafine austenite obtained by dynamic recrystallization during the finishing rolling process can provide abundant non-uniform nucleation sites for ferrite phase transformation, thereby increasing the nucleation rate of new phases and achieving microstructure refinement; however, this method does not evaluate the precipitation form of second phase particles under different strains, as well as the interaction between second phase particles and recrystallization, and the process is complicated. Summary of the invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the problems of limited compression ratio, difficulty in low temperature deformation and poor uniformity of microalloyed steel in the prior art.

[0008] In order to solve the above technical problems, the present invention provides a method for preparing microalloyed steel, explores the influence of different single-pass hot compression deformation amounts on the precipitation of second phase particles and austenite grains in microalloyed steel; the hindering effect of different holding times on austenite recrystallization, and at the same time, can evaluate the effect of the precipitation form of the second phase particles on recrystallization at low cost, which can provide certain support for actual industrial production.

[0009] The object of the present invention is to provide a method for preparing microalloyed steel, comprising the following steps:

[0010] S1. heating the microalloyed steel;

[0011] S2, cooling the microalloyed steel after the heating is completed;

[0012] S3. After cooling, the microalloyed steel is compressed and deformed, and water quenched to 20℃-40℃.

[0013] In one embodiment of the present invention, in S1, the chemical composition of the microalloyed steel and its mass percentage are: carbon 0.1%-0.2%, manganese 1.4%-1.5%, titanium 0.01%-0.02%, niobium 0.02-0.05%, nitrogen 0.002%-0.004%, and the balance is iron and other inevitable impurities.

[0014] In one embodiment of the present invention, in S1, the chemical composition of the microalloyed steel and its mass percentage are: carbon 0.12%, manganese 1.47%, titanium 0.011%, niobium 0.044%, nitrogen 0.0022%, and the balance is iron and other inevitable impurities.

[0015] In one embodiment of the present invention, in S1, the heating is performed at a rate of 10°C / min-20°C / min to 1150°C-1200°C, and the heating is maintained for 55min-65min.

[0016] In one embodiment of the present invention, in S1, the heating is performed at a rate of 20°C / min to 1150°C and kept at that temperature for 60 minutes.

[0017] In one embodiment of the present invention, in S2, the cooling is performed at a rate of 10°C / min-20°C / min to 840°C-980°C, and the temperature is kept at this temperature for 3min-5min.

[0018] In one embodiment of the present invention, in S2, the cooling is performed at a rate of 20°C / min to 950°C and kept at that temperature for 5 minutes.

[0019] In one embodiment of the present invention, in S3, the deformation amount of the compressive deformation is 30%-50%.

[0020] In one embodiment of the present invention, in S3, the compression deformation process is a single-pass compression process.

[0021] In one embodiment of the present invention, in S3, the insulation time of the compression deformation is 10 min-20 min.

[0022] The technical solution of the present invention has the following advantages over the prior art:

[0023] (1) The preparation method described in the present invention achieves the total strain required in actual production through a single-pass compression process with a certain deformation amount, and simultaneously performs heat preservation treatment, thereby simplifying the traditional test process. For studying the effects of deformation on austenite grains, the precipitation mode of second phase particles, and the interaction between second phase particles and recrystallization, the preparation method can be used to test possible results at low cost and high efficiency.

[0024] (2) The preparation method described in the present invention adopts a wide range of strain rates and deformation amounts to avoid the influence of variable temperature multi-pass deformation on the precipitation of second-phase particles, and eliminates the influence of pass strain accumulation on the precipitation mode of second-phase particles. This is very beneficial for studying the interaction between second-phase particles and recrystallization. There is no influence of strain accumulation on recrystallization, and the influence of strain accumulation and different deformation temperature gradients is eliminated. By controlling the differences between variable parameters, comparing the precipitation form of second-phase particles under different variables and the hindering effect on the growth of recrystallized grains, it is of great significance to study the precipitation of second-phase particles under different temperatures, deformation amounts, and incubation times. It has a good theoretical support to improve and clarify the influencing factors of the precipitation dynamics of second-phase particles and the hindering effect on the static / dynamic recrystallization of austenite grains at high temperatures, and lay a theoretical foundation for further microalloying to regulate the microstructure refinement of large / thick structural steels.

[0025] (3) The chemical composition Ti / N of the microalloyed steel used in the preparation method of the present invention is close to its atomic mass ratio, so the Ti-containing second phase particles formed are all TiN particles. The microalloying element Nb usually forms NbC particles in alloy steel, and its formation temperature is lower than that of TiN particles. It can significantly hinder the dynamic / static recrystallization of austenite grains and has a significant effect on the microstructure refinement of large / thick microalloyed steel. However, the precipitation form of NbC particles strongly depends on the dislocation density, precipitation temperature and incubation time contained in the alloy steel. Small and dispersed NbC particles have the best pinning effect. How to control the morphology, size and precipitation amount of NbC particles is the key to regulating the microstructure of alloy steel by Nb microalloying. How to quickly and dispersely precipitate NbC particles requires research on its precipitation kinetics. Since the mean nucleation temperature and time required for the second phase particles are relatively high, the second phase particles are easily coarsened at a higher temperature, and the pinning effect is lost. The time required for heterogeneous nucleation is short and the energy is low. Inducing heterogeneous nucleation of NbC particles is an effective method to accelerate the precipitation kinetics of NbC particles. By increasing the nucleation points and reducing the energy required for nucleation to increase the nucleation rate of NbC particles, increasing the dislocation density and the heterogeneous nucleation interface of NbC can greatly increase the nucleation rate. In large / thick structural steels, since the total deformation is limited and the increase in dislocation density depends on the application of deformation, under the premise of limited total deformation, considering the existing TiN particles, epitaxial growth is carried out to ensure that large / thick structural steels are limited in compression ratio. When the compression ratio is limited, enough NbC particles are precipitated on the surface of TiN particles, thereby playing a role in pinning the austenite grain boundaries. However, when performing composite precipitation, it strongly depends on the number and size of the pre-existing TiN particles, the size between adjacent TiN particles, and the diffusion rate of Nb atoms. In order to verify the effectiveness of this method, before realizing this idea, we first applied different strain amounts (total strain) in a single pass at the same deformation temperature to study the precipitation form of second phase particles in microalloyed steel under different deformation amounts, as well as the hindering effect of austenite grain growth and recrystallization, to provide guidance for subsequent theoretical and practical production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a flow chart of the preparation of microalloyed steel according to Example 1 of the present invention;

[0028] Figure 2 The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Example 1 of the present invention;

[0029] Figure 3The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Example 2 of the present invention;

[0030] Figure 4 The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Comparative Example 2 of the present invention;

[0031] Figure 5 The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Comparative Example 5 of the present invention;

[0032] Figure 6 The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Comparative Example 3 of the present invention;

[0033] Figure 7 The SEM and EDS spectra of the second phase particles of the microalloyed steel after being treated in Comparative Example 6 of the present invention;

[0034] Figure 8 The austenite grain structure after hot compression and heat preservation in Example 1 of the present invention;

[0035] Fig. 9 The austenite grain structure after hot compression and heat preservation in Example 2 of the present invention;

[0036] Fig.10 The austenite grain structure of comparative example 1 of the present invention after hot compression without heat preservation;

[0037] Fig.11 This is the austenite grain structure of comparative example 4 of the present invention after hot compression without heat preservation. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0039] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0040] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0041] In the present invention, unless otherwise specified, if no specific conditions are specified in the examples, the experiments were carried out according to conventional conditions or conditions recommended by the manufacturer.

[0042] In the present invention, unless otherwise specified, all reagents or instruments used without indicating the manufacturer are conventional products that can be purchased from the market.

[0043] In the present invention, unless otherwise specified, the chemical components of the microalloyed steel in the embodiments are as follows in percentage by mass: carbon 0.12%, manganese 1.47%, titanium 0.011%, niobium 0.044%, nitrogen 0.0022%, and the balance is iron and other inevitable impurities.

[0044] Example 1

[0045] Reference Figure 1 As shown, the preparation method of the microalloyed steel of this embodiment specifically comprises the following steps:

[0046] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0047] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0048] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 30% (3.6 mm) and the temperature is kept for 10 minutes, and then water quenched to room temperature.

[0049] Comparative Example 1 is basically the same as Example 1, except that the temperature is not kept after compression deformation.

[0050] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0051] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0052] S3. Compression deformation is performed through a single-pass compression process, with the hot compression deformation amount being 30% (3.6 mm), and then water quenching to room temperature.

[0053] Comparative Example 2 is basically the same as Example 1, except that the holding time after compression deformation is 1 min.

[0054] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0055] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0056] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 30% (3.6 mm) and the temperature is kept for 1 minute, and then water quenched to room temperature.

[0057] Comparative Example 3 is basically the same as Example 1, except that the chemical composition of the microalloyed steel is as follows by mass percentage: carbon 0.21%, manganese 1.56%, niobium 0.053%, nitrogen 0.0025%, and the balance is iron and other unavoidable impurities.

[0058] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0059] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0060] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 30% (3.6 mm) and the temperature is kept for 10 minutes, and then water quenched to room temperature.

[0061] Example 2

[0062] The preparation method of the microalloyed steel of this embodiment specifically comprises the following steps:

[0063] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0064] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0065] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 50% (6 mm) and the temperature is kept for 10 minutes, and then water quenched to room temperature.

[0066] Comparative Example 4 is basically the same as Example 2, except that the temperature is not kept after compression deformation.

[0067] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0068] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0069] S3. Compression deformation is performed through a single-pass compression process, with the hot compression deformation amount being 50% (6 mm), and then water quenching to room temperature.

[0070] Comparative Example 5 is basically the same as Example 2, except that the holding time after compression deformation is 1 min.

[0071] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0072] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0073] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 50% (6 mm) and the temperature is kept for 1 minute, and then water quenched to room temperature.

[0074] Comparative Example 6 is basically the same as Example 2, except that the chemical composition of the microalloyed steel is as follows by mass percentage: carbon 0.21%, manganese 1.56%, niobium 0.053%, nitrogen 0.0025%, and the balance is iron and other unavoidable impurities.

[0075] S1. Cut the microalloyed steel forged sample into 10 mm × 10 mm × 12 mm, heat it to 1150 ° C at a heating rate of 20 ° C / min and keep it for 60 min, so that the second phase precipitated in the forged state is dissolved back into the matrix;

[0076] S2, then cool to 950°C at a rate of 20°C / min and keep at this temperature for 5 min;

[0077] S3. Compression deformation is performed through a single-pass compression process, the hot compression deformation is 50% (6 mm) and the temperature is kept for 10 minutes, and then water quenched to room temperature.

[0078] Test Case

[0079] Using the conventional metallographic sample preparation process, the samples treated in Examples 1-2 and Comparative Examples 1-6 were electrolytically corroded using a 5% perchloric acid acetic acid solution, and then the distribution of the second phase particles was observed and analyzed using a scanning electron microscope; a supersaturated picric acid distilled water solution was used to perform a corrosion experiment on the original austenite, and then the austenite grains were counted using NanoMeasure software.

[0080] (1) The SEM and EDS spectra of the second phase particles of the samples treated in Examples 1-2 and Comparative Examples 1 and 4 are as follows: Figure 2-Figure 7 As shown in Table 1:

[0081] Table 1

[0082] Sample Precipitation form Austenite grain size / μm Example 1 Composite precipitation 5.65 Example 2 Composite precipitation + strain induced precipitation 5.86 Comparative Example 1 none 6.65 Comparative Example 4 none 5.9

[0083] from Figure 2-Figure 7 As can be seen from Table 1, the samples of Comparative Examples 1 and 3 after treatment (no heat preservation after compression deformation) all maintain the distribution state of the second phase particles in the solid solution state, and only the TiN particles are in the precipitation state. Due to the good thermal stability of TiN particles, they can still stably exist in the test steel when they are kept at 1150℃ for 60min. Under the same variable vector condition, since the process of non-spontaneous nucleation is dominated by element diffusion, whether it is at the dislocation or on the surface of the existing second phase particles, it is necessary to incubate nucleation and grow at a certain temperature. This process is related to the diffusion activation energy, diffusion coefficient, distance to the nucleation position and the insulation time (diffusion time along the dislocation diffusion channel, time for the second phase particles to diffuse) of the nucleation elements of the second phase particles at different temperatures. However, due to the fast speed of thermal deformation, the time experienced at high temperature is short, and it has been water-cooled to room temperature before precipitation. Therefore, when the insulation time is 0s, there are only unsolidified TiN particles in the matrix without any precipitation phase. This has nothing to do with the size of the deformation, but is mainly related to the insulation time.

[0084] In the case of small deformation (30%, 3.6mm), after 1 minute of compression deformation and heat preservation, the second phase particles after compression are compositely precipitated in the form of TiN+NbC. The size of the composite precipitate phase is about 80nm, and no separate NbC precipitate phase is found, which is quite different from the sample without heat preservation. In the process of heat preservation for 1 minute with small deformation, Nb element can diffuse and nucleate along the dislocation diffusion channel to the dislocation node and the surface of TiN particles. Since the interface energy required for diffusion and nucleation on the surface of TiN particles is small, the required energy fluctuation and concentration fluctuation are low, it is easier to form a composite precipitate phase. The number of particles will increase accordingly with the extension of the heat preservation time, and coarsening will also occur. However, due to the low dislocation density at a lower deformation, the distance between adjacent dislocations is large, resulting in a large diffusion distance of Nb element to adjacent position dislocations along the dislocation diffusion channel, and the matrix cannot replenish Nb element in time, so that the heterogeneous nucleation at the dislocation is suppressed. In the case of nucleation on the surface of existing TiN particles, Nb elements preferentially nucleate in the close-packed direction of TiN particles. At the same time, the shearing effect of the matrix on the newly formed NbC particles decreases, and the interface energy between TiN and the newly formed NbC particles decreases, which can accelerate the nucleation of NbC particles on the surface of TiN particles. Therefore, in the case of small deformation, most NbC particles rely on TiN particles for composite precipitation. Therefore, in the case of small deformation, due to the low dislocation density, the second phase particles are more inclined to attach to the pre-existing TiN particles for epitaxial precipitation. In the case of large deformation (50%, 5mm), due to the large deformation, the dislocation density is higher than that of the small deformation sample, and the distance between adjacent dislocation junctions and dislocation diffusion channels is closer. The driving force for nucleation is mainly provided by the chemical potential concentration gradient, followed by the interface energy required for nucleation and the shear force of the matrix. In the sample with large deformation, Nb element diffuses to the surface of existing TiN particles along the dislocation diffusion channel at a higher temperature. Since the energy required for nucleation at the dislocation junction is much higher than that for nucleation on the surface of existing TiN particles, the resistance to nucleation on the surface of TiN particles is also less than that at the dislocation junction. Therefore, in a short time of heat preservation (1min, comparative example 5), NbC particles are nucleated preferentially over the surface of the pre-existing TiN particles, after the surface of the TiN particles is consumed by the NbC particles. Due to its large compression ratio, with the extension of the heat preservation time (10min, embodiment 2), NbC particles can be separately nucleated and precipitated at the dislocation junction, and the number and density of the second phase particles are significantly increased. The nucleation mode of the second phase particles coexists with the epitaxial composite precipitation mechanism and the strain induced precipitation mechanism. From the perspective of inhibiting austenite recrystallization, the rapidly precipitated composite second phase particles can play a good role in hindering the static recrystallization of austenite, and retaining high-density dislocations makes the plastic strain not consumed by the static recrystallization during the heat preservation process.Properly increasing the holding time can precipitate more second-phase particles, and the precipitation mode is composite precipitation + strain-induced precipitation, which can theoretically play the best effect of hindering grain growth. Therefore, regardless of the large deformation (50%) or small deformation (30%), the second-phase particles of the matrix of the sample that has not been held are high-temperature stable TiN particles. Although the nucleation of the second-phase particles is closely related to the dislocation density, it can be seen that the nucleation of the second-phase particles is mainly dominated by diffusion, so a certain diffusion time is required for the second-phase particles to nucleate and grow.

[0085] The samples of Comparative Examples 3 and 6 (without Ti element) are similar in Nb element. Since there is no TiN particle to provide nucleation interface, the nucleation of NbC particles is also heterogeneous nucleation at the dislocation under the same deformation amount, which is very different from the precipitation mode containing TiN. The observed NbC particle size is about 100nm. Since there is no TiN particle to provide heterogeneous nucleation interface, the fine NbC particles that heterogeneously nucleate at the dislocation undergo Oswald ripening and become larger during the heat preservation process. Therefore, the application of this method confirms that under the condition of small deformation amount, the introduction of TiN particles can shorten the precipitation time and number of NbC particles and accelerate their precipitation kinetics. Therefore, the embodiment is a low-cost, high-efficiency observation of the precipitation form of the second phase particles in microalloyed steel and the effective amplification of the study of its precipitation kinetics, which is more intuitive and close to the actual production process.

[0086] (2) Austenite grain size and characterization of samples after treatment in Examples 1-2 and Comparative Examples 1 and 4 Figure 8-Figure 11 As shown in Table 1. Figure 8-Figure 11 It can be seen from Table 1 that under a larger thermal compression deformation, the austenite grain size obtained by a single compression is smaller. When the total thermal compression deformation is 50%, the austenite grain size is 5.9 μm ( Fig.10 ), which is smaller than the austenite grain size of 6.65 μm ( Fig.11 ). A larger thermal compression deformation can introduce more dislocations under the same compression process parameters, providing diffusion channels and nucleation points for the rapid nucleation of second-phase particles. At the same time, due to the larger deformation, the sample has a larger deformation storage energy, which allows dynamic recrystallization to occur in a shorter time. However, since the total thermal compression deformation of 30% is small, the dislocation density is lower than 50% of the total thermal compression deformation, resulting in less deformation storage energy, which in turn causes a longer recrystallization time. Under the subsequent same temperature and time insulation, only a small number of grains undergo recrystallization and grain growth ( Fig. 9 The total thermal compression deformation of 50% has a larger deformation storage energy, which can cause rapid recrystallization and grain growth ( Figure 8), which is the main reason why the grain size of the sample is not much different after heat preservation and when it is hot compressed without heat preservation. Due to the existence of second phase particles, the grain size after heat preservation is still slightly lower than the grain size of the compressed sample, indicating that under large deformation, the second phase particles precipitated by composite precipitation and strain induced precipitation can play a good role in hindering grain growth. In the sample with a total hot compression deformation of 30%, fine recrystallized grains can be observed after heat preservation, but they have not grown, indicating that the composite second phase particles can play a good role in hindering the growth of second phase particles.

[0087] In summary, when preparing microalloyed steel, under certain compression ratio conditions, the control of recrystallization can be achieved through strain accumulation, thereby achieving microstructure refinement. By introducing microalloying elements, the precipitation of fine second phase particles has a good inhibitory effect on the recrystallization of austenite grains, and is also conducive to strain accumulation, avoiding recrystallization that causes strain consumption and eventually the appearance of mixed crystals.

[0088] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing microalloyed steel, characterized in that: The following steps are involved: S1. heating the microalloyed steel; S2, cooling the microalloyed steel after the heating is completed; S3. After cooling, the microalloyed steel is compressed and deformed, and water quenched to 20℃-40℃.

2. The method for preparing microalloyed steel according to claim 1, characterized in that: In S1, the chemical composition and mass percentage of the microalloyed steel are: carbon 0.1%-0.2%, manganese 1.4%-1.5%, titanium 0.01%-0.02%, niobium 0.02-0.05%, nitrogen 0.002%-0.004%, and the balance is iron and other inevitable impurities.

3. The method for preparing microalloyed steel according to claim 2, characterized in that: In S1, the chemical composition and mass percentage of the microalloyed steel are: 0.12% carbon, 1.47% manganese, 0.011% titanium, 0.044% niobium, 0.0022% nitrogen, and the balance is iron and other inevitable impurities.

4. The method for preparing microalloyed steel according to claim 1, characterized in that: In S1, the heating is carried out at a rate of 10°C / min-20°C / min to 1150°C-1200°C, and the temperature is kept at this temperature for 55min-65min.

5. The method for preparing microalloyed steel according to claim 4, characterized in that: In S1, the heating is performed at a rate of 20°C / min to 1150°C and the temperature is kept for 60 minutes.

6. The method for preparing microalloyed steel according to claim 1, characterized in that: In S2, the cooling is performed at a rate of 10°C / min-20°C / min to 840°C-980°C, and the temperature is kept for 3min-5min.

7. The method for preparing microalloyed steel according to claim 6, characterized in that: In S2, the cooling is performed at a rate of 20°C / min to 950°C and the temperature is kept for 5 minutes.

8. The method for preparing microalloyed steel according to claim 1, characterized in that: In S3, the deformation amount of the compressive deformation is 30%-50%.

9. The method for preparing microalloyed steel according to claim 1, characterized in that: In S3, the compression deformation process is a single-pass compression process.

10. The method for preparing microalloyed steel according to claim 1, characterized in that: In S3, the insulation time of the compression deformation is 10 min-20 min.

Images