Method for determining liquid core formation temperature of steel material based on thermal simulation experiment

Abstract

This invention discloses a method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments, relating to the field of steel metallurgy technology. The method includes the following steps: performing thermodynamic calculations based on the steel material composition to obtain a reference value for the liquid core temperature; heating the steel material to the reference value and holding it at that temperature; adjusting the reference value if leakage occurs during heating; cooling the steel material and preparing a metallographic sample if no leakage occurs; obtaining the liquid core area based on the metallographic sample; adjusting the reference value if the liquid core area percentage is not within the standard range; repeating the heating experiment; and determining the liquid core formation temperature when the liquid core area percentage is within the standard range. This invention is applied to steel production rolling research and can provide a reliable basis for the development and optimization of liquid core rolling processes.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for determining the liquid core formation temperature of iron and steel materials based on thermal simulation experiments. Background Technology

[0002] Semi-solid processing technology was developed in the 1970s and applied to the production of low-melting-point materials such as aluminum alloys, magnesium alloys, and lead alloys. This process integrates continuous casting and hot rolling, offering advantages such as high efficiency, energy saving, refined and uniform microstructure of finished products, and good mechanical efficiency. In steel production, the CSP (Continuous Casting Process) was used to resolve the conflict between the different thickness requirements of continuously cast billets in continuous casting and continuous rolling. The use of light reduction at the end of solidification of the continuously cast billet aims to improve the problems of center segregation and porosity. As the dimensions of continuously cast billets have become wider and thicker, the developed heavy reduction technology also aims to improve the internal quality of the billet. Generally, reduction begins when the billet still has a partially liquid core and continues until the billet is completely solidified.

[0003] With advancements in technology and equipment, increasing rolling temperatures above the solidus line of continuously cast billets to develop liquid core rolling technology has become a new focus. Liquid core rolling utilizes the high temperature of molten steel to raise the rolling temperature, significantly improving production efficiency and thermal energy utilization. It also leverages the advantages of semi-solid forming in improving elemental segregation and microstructure density. Furthermore, changes in inclusion deformation behavior during rolling are expected to reduce steel defects. However, a method for calculating the required liquid core temperature for rolling is currently lacking. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments, thereby resolving the issues present in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments, comprising the following steps:

[0006] Thermodynamic calculations were performed based on the composition of the steel material to obtain a reference value for the liquid core temperature.

[0007] The steel material is heated to the reference temperature of the liquid core and held at that temperature. When no steel leakage occurs, the steel material is cooled and a metallographic sample is prepared. The liquid core area is obtained based on the metallographic sample. When the proportion of the liquid core area is not within the standard range, the reference temperature of the liquid core is adjusted and the heating experiment is repeated until the proportion of the liquid core area is within the standard range. The heating temperature is the liquid core formation temperature.

[0008] Preferably, the method for performing thermodynamic calculations includes: performing compositional analysis on the steel material to obtain the steel material composition, inputting the steel material composition into the thermodynamic software FactSage to calculate the solidus temperature of the steel, and using a value 15°C lower than the solidus temperature as the reference value for the liquid core temperature.

[0009] Preferably, during the heating process of steel materials, the heating rate of the high-temperature zone above 1200℃ is controlled to be no higher than 5℃ / s, and after reaching the liquid core temperature reference value, the constant temperature time is controlled to be no higher than 5s.

[0010] Preferably, the method for determining the steel leakage phenomenon includes: when the strength of the solid shell of the steel material cannot support the weight of the liquid core, and the molten steel flows out, it is determined to be steel leakage.

[0011] Preferably, when steel leakage occurs during the heating process, the liquid core temperature reference value is adjusted. The method for adjusting the liquid core temperature reference value includes reducing the liquid core temperature reference value by 10°C.

[0012] Preferably, the conditions for cooling steel materials are: when the liquid core temperature reference value is in the high-temperature zone above 1200℃, the cooling rate is not less than 20℃ / s, and when the liquid core temperature reference value is below 1200℃, the cooling rate is not less than 5℃ / s.

[0013] Preferably, the method for obtaining the liquid core area includes: cutting the steel material vertically at the center along its length, polishing and dendrite-etching the cross section, and defining the area in the center of the steel material where the dendrite morphology changes significantly as the liquid core area, and calculating the liquid core area through the liquid core area.

[0014] Preferably, the method for determining whether the liquid core area ratio is within the standard range and adjusting the liquid core temperature reference value includes: when the ratio of the liquid core area to the cross-sectional area is less than 0.05, the liquid core temperature reference value is increased by 2°C; when the ratio of the liquid core area to the cross-sectional area is greater than 0.7, the liquid core temperature reference value is decreased by 2°C; when the ratio of the liquid core area to the cross-sectional area is greater than or equal to 0.05 and less than or equal to 0.7, the heating temperature is the liquid core formation temperature.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects:

[0016] This invention can provide a research method for the liquid core pressing technology currently used in steel metallurgical production, provide a reliable basis for the research and optimization of liquid core rolling process, and promote the creation and development of new liquid core rolling technologies for steel materials.

[0017] In the process of heating steel materials, this invention controls the heating rate of the high-temperature zone above 1200℃ to no more than 5℃ / s, ensuring the synchronization between the actual temperature of the sample after reaching the high-temperature zone and the temperature set in the heating program; after reaching the liquid core temperature reference value, the constant temperature time is controlled to no more than 5s, which can prevent the liquid core area from becoming too large due to excessive constant temperature time and causing steel leakage.

[0018] The conditions for cooling steel materials according to this invention are as follows: when the liquid core temperature reference value is above 1200℃, the cooling rate is not less than 20℃ / s; when the liquid core temperature reference value is below 1200℃, the cooling rate is not less than 5℃ / s. This cooling rate setting ensures that the sample can be cooled as quickly as possible, provided the equipment conditions permit, preventing compositional changes in inclusions within the sample at high temperatures.

[0019] This invention defines the heating temperature as the liquid core formation temperature when the ratio of the liquid core area to the cross-sectional area is greater than or equal to 0.05 and less than or equal to 0.7. This ratio range ensures sufficient liquid phase for liquid core rolling studies, while the solid shell thickness is sufficient to support the weight of the liquid core without leakage. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0024] Example 1

[0025] like Figure 1 As shown, this invention includes three key steps: temperature reference value calculation, sample heating and melting and steel leakage detection, and liquid core temperature correction. The specific implementation method is as follows:

[0026] Step 1: Perform compositional analysis on the steel sample, inputting the steel composition into the thermodynamic software FactSage to calculate the solidus temperature T of the steel. SBased on experience, an initial temperature control reference T is set at 15°C below the theoretically calculated solidus temperature. C =T S -15;

[0027] Step 2: Heat the steel sample from room temperature, with the heating rate in the high-temperature zone above 1200℃ not exceeding 5℃ / s, until it reaches T. C The isothermal time should not exceed 5 seconds to form a liquid core inside the sample. During the experiment, if the solid shell strength of the steel sample cannot support the weight of the liquid core, and the molten steel flows out, it is considered a steel leakage. The liquid core temperature T is set accordingly. C The setting value is adjusted to T. C =T C -10, otherwise proceed to the next step;

[0028] Step 3: Transfer the sample from T C Cool to room temperature, with a cooling rate of no less than 20℃ / s for high-temperature regions above 1200℃ and no less than 5℃ / s for regions below 1200℃. Cut the cooled sample perpendicularly from the center along its length. Polish and dendrite erosion are performed on the cross-section. The region where the dendrite morphology in the center of the sample changes significantly is identified as the liquid core. If this region SL is equal to the total cross-sectional area S... T The ratio of S L / S T <0.05 or S L / S T If the value is greater than 0.7, then the liquid core temperature T will be... C The set value is increased or decreased by 2°C, and the process returns to step 2. Otherwise, the thickness of the liquid core and the blank shell is considered to be appropriate, and the temperature value is output as the liquid core formation temperature result.

[0029] Example 2

[0030] Taking the liquid core rolling of heavy rail steel as an example, the specific embodiments of the present invention will be further described. This example is a further illustration of the present invention, and not a limitation on the scope of the invention.

[0031] The measured composition of the steel is shown in the table below:

[0032] ％ 0.76 0.61 0.95 0.046 0.02 0.0040 0.006 0.0004 0.00012 0.0009

[0033] The continuously cast billet was machined into a smooth sample with dimensions of 160mm × 10mm × 50mm and a thickness of 10mm. The steel composition was input into FactSage 7.0, and the solidus temperature of this heavy rail steel was calculated to be 1358℃. A pure heating experiment was conducted using 1343℃ as the initial temperature. The sample was placed horizontally, with its thickness direction perpendicular to the horizontal plane. Both ends of the sample were clamped along its length. The gas pressure in the furnace containing the sample was 5 × 10⁻⁶. -3mbar. An electric current was applied to the sample, and resistance heating was used to raise the sample temperature. Cooling water was circulated through copper clamps at both ends to cool the sample. Heat was transferred from the sample surface to the furnace wall via radiation. A thermocouple was connected to the center of the sample along its length, and its readings were used to control the temperature. The sample was heated from room temperature to 1343°C at a rate of 5°C / s, during which steel leakage occurred. A new sample was taken, and the above operation was repeated, with the maximum heating temperature set at 1333°C (a decrease of 10°C), and steel leakage still occurred. Another new steel sample was taken, and the above operation was repeated, with the maximum heating temperature set at 1323°C (a decrease of 10°C), and no steel leakage or significant sample deformation was observed. The power was then cut off, and the sample was kept water-cooled at both ends. The average rate of cooling to 1200°C exceeded 20°C / s, and the rate of cooling to room temperature was no less than 5°C / s. The sample was then cut perpendicularly at its center along its length, and dendritic etching was performed on the polished section using a saturated picric acid aqueous solution. The dendrites in the original sample were arranged in parallel along the vertical direction, while the dendrites in the center of the heated sample showed a significant deflection in growth direction, and the area of ​​the deflected region accounted for about 50% of the total cross-sectional area. It was believed that the liquid core had been formed and the shell thickness was appropriate. 1323℃ was taken as the target control temperature for the formation of the liquid core.

[0034] The above are merely preferred embodiments of this application, but the scope of protection of this application 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 application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments, characterized in that, Includes the following steps: Thermodynamic calculations were performed based on the composition of the steel material to obtain a reference value for the liquid core temperature. The steel material is heated to the reference value of the liquid core temperature and held at that temperature. When no steel leakage occurs, the steel material is cooled and a metallographic sample is prepared. The liquid core area is obtained based on the metallographic sample. When the proportion of the liquid core area is not within the standard range, the reference value of the liquid core temperature is adjusted and the heating experiment is repeated until the proportion of the liquid core area is within the standard range. The heating temperature is the liquid core formation temperature. During the heating process of steel materials, the heating rate of the high-temperature zone above 1200℃ is controlled to be no higher than 5℃ / s, and after the temperature reaches the reference value of the liquid core, the constant temperature time is controlled to be no higher than 5s. The conditions for cooling steel materials are as follows: when the liquid core temperature reference value is in the high temperature zone above 1200℃, the cooling rate shall not be less than 20℃ / s; when the liquid core temperature reference value is below 1200℃, the cooling rate shall not be less than 5℃ / s. The method for obtaining the liquid core area includes: cutting the steel material perpendicularly at the center along its length, polishing and dendrite erosion of the cross section, and defining the area in the center of the steel material where the dendrite morphology changes significantly as the liquid core area, and calculating the liquid core area through the liquid core area; The methods for determining whether the liquid core area ratio is within the standard range and adjusting the liquid core temperature reference value include: when the ratio of the liquid core area to the cross-sectional area is less than 0.05, the liquid core temperature reference value is increased by 2℃; when the ratio of the liquid core area to the cross-sectional area is greater than 0.7, the liquid core temperature reference value is decreased by 2℃; when the ratio of the liquid core area to the cross-sectional area is greater than or equal to 0.05 and less than or equal to 0.7, the heating temperature is the liquid core formation temperature.

2. The method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments according to claim 1, characterized in that, The method for performing thermodynamic calculations includes: performing compositional analysis on the steel material to obtain the steel material composition, inputting the steel material composition into the thermodynamic software FactSage to calculate the solidus temperature of the steel, and using a value 15°C lower than the solidus temperature as the reference value for the liquid core temperature.

3. The method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments according to claim 1, characterized in that, The method for determining the steel leakage phenomenon includes: when the strength of the solid shell of the steel material cannot support the weight of the liquid core, the molten steel flows out, which is determined to be steel leakage.

4. The method for determining the liquid core formation temperature of steel materials based on thermal simulation experiments according to claim 1, characterized in that, The method further includes: If steel leakage occurs during the heating process, the liquid core temperature reference value should be adjusted. The method for adjusting the liquid core temperature reference value includes reducing the liquid core temperature reference value by 10°C.

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