Method for improving high-temperature thermoplasticity of steel for building structure

Abstract

The invention discloses a method for improving high-temperature thermoplasticity of steel for a building structure, and belongs to the technical field of building materials. The method comprises the following steps that the strain rate is controlled, specifically, in the high-temperature machining process of the steel for the building structure, the strain rate is accurately controlled according to different machining temperature intervals, and in the machining temperature interval of 600-900 DEG C, the strain rate not lower than 10 s <-1 > is adopted; the strain rate is not lower than 5s <-1 > in the processing temperature interval of 1000-1200 DEG C; the processing temperature is 1000-1200 DEG C, and the processing time is 3-5 minutes; after machining is completed, the workpiece is rapidly cooled to the room temperature at the cooling speed not lower than 20 DEG C / s; in the steel smelting process, the content of microalloy elements is reasonably controlled. The invention aims to improve the plasticity and processability of the steel for the building structure at high temperature, reduce the crack risk of the steel in the high-temperature processing process and guarantee the safety and stability of the building structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a method for improving the high-temperature plasticity of building structure steel. BACKGROUND

[0002] With the development of the construction industry, steel structure buildings have attracted widespread attention due to their energy-saving and environmentally friendly characteristics and recyclable use. High-performance building structure steel is increasingly widely used in steel structure buildings. However, the high-temperature plasticity of such steel is affected by various factors, such as carbonitride precipitates, decomposed ferrite, and fracture dynamic secondary crystallization, which can cause cracks and other problems during high-temperature processing, affecting the performance of the steel and the safety of the building structure. At present, there is a lack of effective solutions to these problems, making it difficult to meet the demand for high-performance steel in the construction industry. SUMMARY

[0003] The purpose of the present application is to provide a method for improving the high-temperature plasticity of building structure steel, which reduces the negative impact of carbonitride precipitation, ferrite decomposition, and fracture dynamic secondary crystallization on the plasticity of the steel by controlling the strain rate and optimizing the processing temperature, thereby improving the plasticity and processing performance of the building structure steel at high temperatures, reducing the risk of cracks during high-temperature processing of the steel, and ensuring the safety and stability of the building structure.

[0004] To solve the above technical problems, the present application adopts the following technical solutions:

[0005] The present application provides a method for improving the high-temperature plasticity of building structure steel, comprising the following steps:

[0006] (1) Control the strain rate: during the high-temperature processing of building structure steel, the strain rate is precisely controlled according to different processing temperature intervals. In the processing temperature interval of 600-900℃, the strain rate is not less than 10s -1 ; in the processing temperature interval of 1000-1200℃, the strain rate is not less than 5s -1 ;

[0007] (2) Process in the range of 1000-1200℃, and strictly control the processing time in combination with the strain rate, with the processing time controlled in the range of 3-5 minutes; after processing, rapidly cool to room temperature at a cooling speed of not less than 20℃ / s;

[0008] (3) In the steel smelting process, the content of micro-alloying elements is reasonably controlled, including Nb, V, and Ti; under the premise of meeting the performance requirements of the steel, the content of Nb is controlled in the range of 0.03%-0.035%, the content of V is controlled in the range of 0.035%-0.04%, and the content of Ti is controlled in the range of 0.015%-0.02%.

[0009] Furthermore, the strain rate is controlled by a high-precision strain rate control system, which can monitor and dynamically adjust the strain rate in real time to ensure that it is stable within a set range.

[0010] Furthermore, the high-precision strain rate control system includes a data acquisition module, a data analysis module and a control execution module; the data acquisition module is used to collect strain data during the processing process in real time; the data analysis module analyzes and processes the collected data and compares it with the preset strain rate; the control execution module dynamically adjusts the operating parameters of the processing equipment according to the comparison results to ensure that the strain rate is stable within the set range and the deviation does not exceed ±0.5s -1 .

[0011] Furthermore, in step (2), a high-precision temperature sensor and an automated temperature control system are used to accurately control the heating and cooling process of the steel, so that the steel quickly passes through the temperature range where a large amount of carbonitrides precipitate.

[0012] Furthermore, the high-precision temperature sensor and automatic temperature control system monitor the temperature of various parts of the steel in real time through multiple groups of temperature sensors. The automatic temperature control system accurately controls the temperature change of the steel by adjusting the power and flow parameters of the heating and cooling equipment based on the monitoring data, so that the steel passes through the temperature range where a large amount of carbonitrides precipitate at a speed of not less than 20°C / s during the heating and cooling process.

[0013] Furthermore, the method of adding rare earth elements is to add the rare earth elements in the form of an alloy to the molten steel through a quantitative addition device, and to use an electromagnetic stirring device during the addition process to uniformly distribute the rare earth elements in the molten steel. The stirring intensity of the electromagnetic stirring device is 2-5A, and the stirring time is 5-10 minutes.

[0014] Furthermore, the structural steel is a high-performance structural steel with a basic chemical composition by mass of: C: 0.12-0.18%, Si: 0.3-0.4%, Mn: 1.5-1.7%, P ≤ 0.02%, S ≤ 0.003%. Alloying elements and rare earth elements are added to this basic composition.

[0015] Furthermore, in the step (2), the mixture is rapidly cooled to room temperature at a cooling rate of 28-32°C / s (preferably 30°C / s).

[0016] Compared with the prior art, the present invention has the following beneficial technical effects:

[0017] (1) By controlling the strain rate, the precipitation of ferrite at the grain boundaries and the stress concentration phenomenon are effectively suppressed, and the thermoplasticity of the steel is significantly improved in the temperature range of 600℃-900℃, reducing the risk of cracks. (2) By optimizing the processing temperature, the large-scale precipitation of carbonitrides at the grain boundaries is avoided. The thermoplasticity improvement characteristics in the temperature range of 1000℃-1200℃ are utilized to improve the processing quality of the steel and ensure the performance stability of the steel used in building structures during high-temperature processing. (3) By adjusting the chemical composition, the precipitation amount of microalloying element carbonitrides is reduced, the bonding force between the grains is enhanced, and the high-temperature thermoplasticity of the steel is further improved, making the steel used in building structures more stable and reliable during high-temperature processing, thereby improving the safety and durability of the building structure. DETAILED DESCRIPTION

[0018] A method for improving the high-temperature thermoplasticity of steel used in building structures, the specific technical solution is as follows:

[0019] Control the strain rate: During the high temperature processing of building structure steel, select the appropriate strain rate according to the processing temperature range. When the processing temperature is between 600℃ and 900℃, use a higher strain rate, such as not less than 10s -1 A higher strain rate can shorten the deformation time, inhibit the large amount of ferrite precipitation, avoid the decrease of intergranular bonding force due to the precipitation of ferrite at the grain boundary, thereby reducing stress concentration and improving the thermoplasticity of steel in this temperature range. When the processing temperature is between 1000℃ and 1200℃, the strain rate can be adjusted appropriately, but it must be ensured to be no less than a certain threshold (such as 5s -1 ) to utilize the effect of higher strain rate to refine grains, prevent structural cracks from expanding, and maintain good thermoplasticity of steel.

[0020] Optimize processing temperature: Accurately control the processing temperature of building structure steel, and try to avoid temperature ranges where plasticity dips are likely to occur. For building structure steel containing microalloying elements (Nb, V, Ti, etc.), it is necessary to avoid staying in the temperature range where carbonitrides precipitate in large quantities for a long time. According to the experimental results, the heating and cooling processes are controlled so that the steel passes quickly through the temperature range that may cause large amounts of carbonitrides to precipitate at the grain boundaries, reducing the generation of voids and cracks at the grain boundaries. Reasonably select the starting and ending temperatures for processing. When processing in the range of 1000℃-1200℃, make full use of the fact that the thermoplasticity of steel in this temperature range improves with increasing temperature to improve processing quality. However, it should be noted that when the temperature exceeds 1000℃, a long stretching time at a low strain rate may lead to intensified grain boundary melting. Therefore, the processing time should be considered in combination with the strain rate.

[0021] Adjusting the chemical composition: Optimize the chemical composition of structural steel and rationally control the content of microalloying elements (Nb, V, Ti). While meeting the steel's strength and other performance requirements, appropriately reduce the amount of microalloying elements added to reduce the precipitation of carbonitrides and their damage to grain boundary bonding, thereby improving the steel's high-temperature thermoplasticity. Adding trace amounts of rare earth elements improves the steel's microstructure, strengthens the bonding between grains, and increases the steel's ability to resist cracking during thermoplastic deformation. For example, adding an appropriate amount of rare earth elements can refine the grains, reduce the precipitation of ferrite at grain boundaries, and enhance the steel's high-temperature thermoplasticity.

[0022] The following is a further detailed description of a method for improving the high-temperature thermoplasticity of steel for building structures according to the present invention.

[0023] Example: This example is a preferred example among various implementations of the present invention.

[0024] A method of improving the high-temperature thermoplasticity of steel for building structures in this embodiment includes: material preparation, heating and strain rate control, processing temperature optimization, and chemical composition adjustment.

[0025] High-performance building structural steel with a specific chemical composition was selected as the processing material. Its basic chemical composition (mass fraction wt.%) is: C 0.14, Si 0.36, Mn 1.59, P 0.017, S 0.002, and contains micro-alloying elements V 0.040, Nb 0.046, Ti 0.02, and the rest is Fe and impurities.

[0026] Steel samples were fabricated into standard hot-drawn round bars with M10 standard threads machined on both ends. The processing was simulated using a thermal simulator, shielded by argon gas. The samples were heated to 1250°C at a heating rate of 5°C / s and held at that temperature for 0.5 hours to achieve complete austenite homogenization. The samples were then cooled to the target processing temperature range at a cooling rate of 5°C / s.

[0027] 600℃-900℃ processing stage: When the temperature is cooled to 750℃, according to the strain rate control requirements, -1 The strain rate of the test machine is used to ensure that the strain rate is stable within the set value ±0.5s. -1 This high strain rate shortens the deformation time, effectively suppresses the large-scale precipitation of ferrite, and avoids the problems of decreased bonding strength and stress concentration caused by excessive ferrite at the grain boundaries.

[0028] 1000℃-1200℃ processing stage: cool another part of the sample to 1100℃ and use 5s -1The strain rate is used to process the steel. This ensures a stable process. The higher strain rate refines the grains and enhances the steel's ability to resist crack growth.

[0029] Throughout the heating and cooling process, high-precision temperature sensors and an automated temperature control system are used to precisely control temperature fluctuations. When cooling from 1250°C, the cooling medium flow and temperature are optimized to rapidly move the billet through the temperature range where carbonitrides are most likely to precipitate in large quantities, reducing the amount of carbonitride precipitation at grain boundaries. When processing at 1100°C, the processing time is strictly controlled to 3-5 minutes. After processing, the steel is rapidly cooled to room temperature at a cooling rate of 30°C / s to prevent intensified melting at grain boundaries and ensure the thermoplastic stability of the steel.

[0030] After processing, the performance test of the sample was carried out. The cross-sectional shrinkage of the sample reached more than 80%, the ferrite precipitation at the grain boundary was significantly reduced, and the grains were refined and uniform.

[0031] Example 1:

[0032] A batch of high-performance building structure steel samples (whose basic chemical composition mass fraction wt.% is: C0.14, Si0.36, Mn 1.59, P 0.017, S 0.002, and contains micro-alloying elements V 0.040, Nb0.046, Ti 0.02, and the rest is Fe and impurities) were selected and processed at a temperature of 700℃ and a strain rate of 10s -1 Perform high temperature stretching.

[0033] The sample was rapidly heated to 1100°C and maintained at this temperature for a short time for processing, and then rapidly cooled at a cooling rate of 30°C / s to avoid staying in the temperature range where carbonitrides are easily precipitated.

[0034] Add 0.01% rare earth elements to the steel and appropriately reduce the content of Nb elements to 0.03%;

[0035] The processed samples were tested for reduction of area and microstructure. The results showed that the reduction of area reached 85%, a 10% improvement compared to samples not treated with this method. Microstructural observation revealed a significant reduction in ferrite precipitation at grain boundaries, resulting in grain refinement and effective improvement in the steel's high-temperature plasticity.

[0036] Example 2:

[0037] When the processing temperature is 800℃, the strain rate is 12s -1 Another batch of high-performance building structure steel samples identical to those in Example 1 were processed.

[0038] The sample was heated to 1050°C, processed at this temperature, and then rapidly cooled.

[0039] 0.02% of rare earth elements is added while the content of V element is controlled at 0.035%.

[0040] It is tested that the reduction of area of the sample reaches 88%, the grains in the microstructure are uniform and small, and the grain boundaries are clear, which further verifies the effectiveness of the method for improving the high-temperature hot plasticity of the steel.

[0041] Comparative Example 1:

[0042] At the processing temperature of 700℃, a lower strain rate of 10 -3 s -1 The sample of the high-performance building structure steel is processed, and other processing conditions are the same as those in Example 1.

[0043] The test results show that the reduction of area of the sample is only 65%, which is significantly lower than that in Example 1. Microstructure observation shows that a large amount of ferrite is precipitated at the grain boundaries, and there is obvious stress concentration phenomenon, which indicates that the low strain rate is not conducive to improving the high-temperature hot plasticity of the steel.

[0044] Comparative Example 2:

[0045] When the sample of the high-performance building structure steel is processed, the temperature range in which the carbonitride is easy to precipitate is slowly heated and cooled (slow heating is to heat from room temperature to 1100℃ at a rate of 1℃ / s and keep for 2h, and slow cooling is to cool from 1100℃ to room temperature at a rate of 1℃ / s), and the strain rate and chemical composition are adjusted the same as in Example 1.

[0046] The reduction of area of the sample is 70%, which is lower than that in Example 1. More cavities and cracks appear at the grain boundaries in the microstructure, which indicates that the unoptimized processing temperature will seriously affect the high-temperature hot plasticity of the steel.

[0047] Through the comparison of the examples and the comparative examples, it can be obviously seen that the method of the present application can effectively improve the high-temperature hot plasticity of the building structure steel, and improve the processing performance and quality of the steel.

[0048] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for improving the high-temperature thermoplasticity of steel for building structures, characterized in that: The following steps are involved: (1) Control the strain rate: During the high-temperature processing of steel used in building structures, the strain rate is accurately controlled according to different processing temperature ranges. In the processing temperature range of 600℃-900℃, the strain rate is not less than 10s -1 The strain rate is not less than 5s in the processing temperature range of 1000℃-1200℃. -1 ; (2) Processing is performed within the range of 1000°C to 1200°C, and the processing time is strictly controlled in combination with the strain rate, and the processing time is controlled within 3-5 minutes; after processing, the processing is quickly cooled to room temperature at a cooling rate of not less than 20°C / s; (3) During the steel smelting process, the content of microalloying elements including Nb, V, and Ti is reasonably controlled; on the premise of meeting the performance requirements such as steel strength, the Nb content is controlled within 0.03%-0.035%, the V content is controlled within 0.035%-0.04%, and the Ti content is controlled within 0.015%-0.02%.

2. The method for improving high-temperature thermoplasticity of steel for building structures according to claim 1, characterized in that: The strain rate is controlled by a high-precision strain rate control system, which can monitor and dynamically adjust the strain rate in real time to ensure that it remains stable within a set range.

3. The method for improving high temperature thermoplasticity of steel for building structures according to claim 2, characterized in that: The high-precision strain rate control system includes a data acquisition module, a data analysis module and a control execution module; the data acquisition module is used to collect strain data during the processing process in real time; the data analysis module analyzes and processes the collected data and compares it with the preset strain rate; The control execution module dynamically adjusts the operating parameters of the processing equipment according to the comparison results to ensure that the strain rate is stable within the set range and the deviation does not exceed ±0.5s -1 .

4. The method for improving high-temperature thermoplasticity of steel for building structures according to claim 1, characterized in that: In the step (2), a high-precision temperature sensor and an automated temperature control system are used to accurately control the heating and cooling processes of the steel, so that the steel quickly passes through the temperature range where a large amount of carbonitrides precipitate.

5. The method for improving high temperature thermoplasticity of steel for building structures according to claim 4, characterized in that: The high-precision temperature sensors and automated temperature control system monitor the temperature of various parts of the steel in real time through multiple groups of temperature sensors. The automated temperature control system adjusts the power and flow parameters of the heating and cooling equipment based on the monitoring data to accurately control the temperature change of the steel, so that the steel passes through the temperature range where a large amount of carbonitrides precipitate at a speed of not less than 20°C / s during the heating and cooling process.

6. The method for improving high temperature thermoplasticity of steel for building structures according to claim 1, characterized in that: The method of adding rare earth elements is to add rare earth elements in the form of alloy to the molten steel through quantitative addition equipment, and use an electromagnetic stirring device to evenly distribute the rare earth elements in the molten steel during the addition process. The stirring intensity of the electromagnetic stirring device is 2-5A and the stirring time is 5-10 minutes.

7. The method for improving high temperature thermoplasticity of steel for building structures according to claim 1, characterized in that: The building structure steel is high-performance building structure steel, and its basic chemical composition by mass percentage is: C: 0.12-0.18%, Si: 0.3-0.4%, Mn: 1.5-1.7%, P≤0.02%, S≤0.003%.

8. The method for improving high-temperature thermoplasticity of steel for building structures according to claim 1, characterized in that: In the step (2), the mixture is rapidly cooled to room temperature at a cooling rate of 28-32°C / s.