Method for corroding austenite grain size of 34Mn6 continuous casting round billet

Abstract

The invention discloses a method for corroding the austenite grain size of a 34Mn6 continuous casting round billet, which comprises the following steps: 1) selecting five samples made of 34Mn6; 2) performing austenitizing process treatment on the sample, and performing heat treatment of quenching at 1150 + / -10 DEG C, heat preservation, water quenching and air cooling to room temperature; (3) chamfering and rough grinding are carried out, oxide scale is removed, and polishing is carried out; (4) the austenite grain size is corroded through a chemical corrosion method; 5) in a constant-temperature water bath at 45 DEG C, adding a proper amount of washing agent into the corrosive agent, putting the sample into the corrosive agent, and corroding for 28-32 minutes; (6) cleaning with clean water and slightly wiping; (7) observing; and (8) determining the average grain size of the austenite by adopting image analysis and an intercept point method. After the optimized technical scheme is implemented, the corroded austenite grain boundary is clearer than before.

Description

Technical Field

[0001] The invention belongs to the technical field of austenite corrosion methods, and in particular relates to a method for corroding austenite grain size of 34Mn6 continuous casting round billet. Background Art

[0002] Austenite grain size, as a key indicator for evaluating austenite grain size, has a profound and direct impact on the performance of phase transformation products during cooling. In the field of steel manufacturing, the control of austenite grain size is particularly important when producing 34Mn6 large-section continuous casting round billets. This parameter is not only directly related to the final mechanical properties, toughness and fatigue resistance of the product, but also has a profound impact on the overall efficiency and effect of the heating process of the ring heating furnace. Based on in-depth research on the basic science of C-Mn steel materials, especially the growth law and organizational homogenization characteristics of the original austenite under specific conditions, the purpose is to develop a more economical and efficient heating process system. The core of this system is to achieve fine control of austenite grains by precisely controlling the temperature curve and time parameters during the heating process. Summary of the invention

[0003] The purpose of the present invention is to provide a method for corroding the austenite grain size of 34Mn6 continuous casting round billet. The corrosive agent and the corrosion conditions (heating temperature, holding time) are re-optimized and formulated by using a multi-factor variable test, and the corroded austenite grain boundary is clearer than before. Based on the original austenite growth law and organizational homogenization research of the material, the heating process of seamless steel pipe round billet can be guided, and the heating temperature and heating time distribution principle of each section in the furnace can be formed, so that the billet can be perforated and rolled in the optimal plastic zone, and the high-temperature organization of the billet can be controlled, which is conducive to improving the microstructural stability and uniformity of the product, and is the basis for ensuring the performance of hot-rolled products and the stable and uniform deformation of alloy steel.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for corroding austenite grain size of 34Mn6 continuous casting round billet, comprising the following steps:

[0006] 1) Select 34Mn6 as the material, the blank shape is Φ200mm section, and make austenite grain size and structure observation samples, a total of 5 samples;

[0007] 2) The sample is subjected to austenitizing process, quenched at 1150±10℃, heat-insulated, water-quenched, and air-cooled to room temperature;

[0008] 3) The heat-treated samples are first chamfered and roughly ground on a grinding machine to remove the iron oxide scale, and then finely ground and polished step by step on a metallographic polishing machine;

[0009] 4) Use chemical corrosion method to corrode the austenite grain size. The corrosion liquid composition is as follows: hydrofluoric acid 0.01-0.05%, cupric chloride 0.005-0.06%, nitric acid 0.10-0.45%, alcohol 0-5%, and the rest is distilled water;

[0010] 5) Take out a certain amount of the prepared corrosion solution and pour it into a beaker, then put the sample into the beaker with the observation side facing down, then place the beaker in a constant temperature water bath at 45°C, add an appropriate amount of detergent to the corrosive agent, put the sample in for corrosion, and the corrosion time is 28-32 minutes;

[0011] 6) Wash the observation surface of the corroded sample with clean water, and then gently wipe off the film product on the surface of the sample with a polishing flannel. Do not wipe too hard to avoid eliminating the corroded grain boundaries;

[0012] 7) Observe the sample using a metallographic microscope and take 100x magnification photos of the austenite grain boundaries;

[0013] 8) The average austenite grain size was determined by image analysis and intercept method.

[0014] Furthermore, the sample size is 20 mm × 20 mm × 15 mm.

[0015] Furthermore, in the step 2), the 5 samples were quenched at 1150° C., kept warm for 10 min, 20 min, 30 min, 40 min, and 60 min, respectively, quenched in water, and air-cooled to room temperature.

[0016] Furthermore, in step 5), 20 mL of the prepared corrosion solution is taken out and poured into a beaker.

[0017] Furthermore, the corrosion time is 30 min.

[0018] Furthermore, the metallographic microscope used was Axio observer, Zeiss, Germany.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] The present invention adopts multi-factor variable test to re-optimize and formulate the corrosive agent and corrosion conditions (heating temperature, holding time). Based on the original austenite growth law and organization homogenization research of the material, it can guide the heating process of seamless steel pipe round billet, form the heating temperature and heating time distribution principle of each section in the furnace, make the billet perforated and rolled in the best plastic zone, control the high temperature organization of the billet, which is conducive to improving the microstructure stability and uniformity of the product, and is the basis for ensuring the performance of hot-rolled products and stable and uniform deformation of alloy steel.

[0021] After implementing the optimized technical solution, the austenite grain boundaries corroded are clearer and more distinct than before. Figure 3 The images in the figure clearly show the continuity and integrity of the grain boundaries, providing a basis for subsequent grain size analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 This is a photo of grain size corrosion at room temperature;

[0024] Figure 2 This is a photo of grain size corrosion in a 60°C water bath;

[0025] Figure 3 This is a photo of grain size corrosion in a 45°C water bath;

[0026] Figure 4 This is the grain size corrosion photo of sample 1#;

[0027] Figure 5 This is the grain size corrosion photo of sample 2#

[0028] Figure 6 This is the grain corrosion photo of sample 3#

[0029] Figure 7 This is the grain size corrosion photo of sample 4#

[0030] Figure 8 This is the grain size corrosion photo of the 5# sample;

[0031] Fig. 9 is the average grain size at different holding times. DETAILED DESCRIPTION

[0032] 1. Comparative Example 1

[0033] ① Take out 20mL of the prepared corrosion solution and pour it into a beaker, then put the sample into the beaker with the observation side facing down, and then place it at room temperature for corrosion. The corrosion time is 30min, 60min, 90min, and 120min respectively;

[0034] A series of corrosion tests were designed and performed at room temperature to explore the effect of different corrosion times on the appearance of austenite grain boundaries in the specimens. Specifically, the test set four time points - 30 minutes, 60 minutes, 90 minutes and 120 minutes, and observed the changes in austenite grain boundaries of the specimens after these time points. However, at the first three observation points (i.e., after 30 minutes, 60 minutes, and 90 minutes), no obvious corrosion grain boundaries were successfully observed, indicating that the corrosion conditions used could not effectively reveal the fine structure of the grain boundaries in a shorter period of time.

[0035] After the corrosion time was extended to 120 minutes, a faint grain boundary outline was captured on the surface of the sample, but this outline was fuzzy and unclear. Figure 1 This phenomenon not only reveals the inefficiency of the current technical solution, that is, it is too time-consuming, but more importantly, it cannot provide clear and accurate grain boundary images, which constitutes a major obstacle to the subsequent accurate measurement of grain size.

[0036] Figure 1 The intuitive display shows that under the longest corrosion time, the effect of grain boundary appearance is far from ideal, which will undoubtedly affect the scientificity and accuracy of grain size analysis. Therefore, in order to improve the test efficiency and ensure the reliability of data, the existing technical solutions need to be optimized.

[0037] ② Take out 20mL of the prepared corrosion solution and pour it into a beaker, then put the sample into the beaker with the observation side facing down, then place the beaker in a constant temperature water bath at 60℃, put the sample in for corrosion, and set the corrosion time to 10min, 20min, and 30min respectively;

[0038] The grain size corrosion was carried out in a constant temperature water bath at 60°C. After 10 minutes of corrosion, the austenite grain boundaries of the sample were observed. The corrosion grain boundaries could be observed, but the corrosion degree was too deep, such as Figure 2 shown.

[0039] from Figure 2 It was observed that although the corrosion treatment successfully highlighted the austenite grain boundaries, the excessive temperature and corrosion intensity also corroded part of the matrix structure of the sample. This excessive corrosion phenomenon not only interfered with the clear identification of the grain boundaries themselves, but also directly had an adverse effect on the subsequent precise measurement and statistical analysis of the grain size, which in turn may affect the accuracy and reliability of the overall test results.

[0040] ③ Take out 20mL of the prepared corrosion solution and pour it into a beaker, then put the sample into the beaker with the observation side facing down, then place the beaker in a constant temperature water bath at 45℃, add an appropriate amount of detergent to the corrosive agent, put the sample in for corrosion, and the corrosion time is 30min;

[0041] Targeted optimization and improvement were carried out for the technical solution of Comparative Example 2, aiming to further improve the clarity and efficiency of the corrosion effect. Specifically, the original water bath temperature was lowered and set to a milder 45°C constant temperature environment for corrosion testing. This adjustment was based on in-depth experimental analysis and theoretical discussion, aiming to find a balance point that can promote the clear appearance of austenite grain boundaries and effectively avoid excessive corrosion.

[0042] After implementing the optimized technical solution, the austenite grain boundaries corroded are clearer and more distinct than before. Figure 3 The images in the figure clearly show the continuity and integrity of the grain boundaries, providing a basis for subsequent grain size analysis.

[0043] It can be seen that adjusting the water bath temperature to 45°C and conducting corrosion tests under constant temperature water bath conditions is a feasible and effective technical optimization measure. This technical solution not only successfully solved the problems of poor corrosion effect and long time consumption in the original solution, but also demonstrated good operability and implementation effect.

[0044] 2. Comparative Proportion of the Same Technical Solution

[0045] Five groups of tests were designed. The test scheme is shown in Table 1. The samples were quenched at 1150℃ and heat treated with different holding times. The original austenite grain morphology at each holding time is shown in Table 1. Figure 4-Figure 8 .

[0046] For the corroded austenite grain boundaries, the average austenite grain size was determined by image analysis and intercept method, such as Fig. 9 shown.

[0047] Table 1 Experimental plan

[0048] Sample No. Quenching temperature / ℃ Insulation time / min 1# 1150 10 2# 1150 20 3# 1150 30 4# 1150 40 5# 1150 60

[0049] Depend on Fig. 9 It can be seen that when the quenching temperature is 1150℃, as the holding time increases, the grains grow faster and the average austenite grain size increases from 144μm to 198μm.

[0050] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for corroding austenite grain size of 34Mn6 continuous casting round billet, characterized in that: The steps include: 1) Select 34Mn6 as the material, the blank shape is Φ200mm section, and make austenite grain size and structure observation samples, a total of 5 samples; 2) The sample is subjected to austenitizing process, quenched at 1150±10℃, heat-insulated, water-quenched, and air-cooled to room temperature; 3) The heat-treated samples are first chamfered and roughly ground on a grinding machine to remove the iron oxide scale, and then finely ground and polished step by step on a metallographic polishing machine; 4) Use chemical corrosion method to corrode the austenite grain size. The corrosion liquid composition is as follows: hydrofluoric acid 0.01-0.05%, cupric chloride 0.005-0.06%, nitric acid 0.10-0.45%, alcohol 0-5%, and the rest is distilled water; 5) Take out a certain amount of the prepared corrosion solution and pour it into a beaker, then put the sample into the beaker with the observation side facing down, then place the beaker in a constant temperature water bath at 45°C, add an appropriate amount of detergent to the corrosive agent, put the sample in for corrosion, and the corrosion time is 28-32 minutes; 6) Wash the observation surface of the corroded sample with clean water, and then gently wipe off the film product on the surface of the sample with a polishing flannel. Do not wipe too hard to avoid eliminating the corroded grain boundaries; 7) Observe the sample using a metallographic microscope and take 100x magnification photos of the austenite grain boundaries; 8) The average austenite grain size was determined by image analysis and intercept method.

2. The method for corroding austenite grain size of 34Mn6 continuous casting round billet according to claim 1, characterized in that: The sample size is 20mm×20mm×15mm.

3. The method for corroding austenite grain size of 34Mn6 continuous casting round billet according to claim 1, characterized in that: In the step 2), the heat treatment is performed by quenching at 1150° C., keeping the five samples warm for 10 min, 20 min, 30 min, 40 min, and 60 min, quenching with water, and air cooling to room temperature.

4. The method for corroding austenite grain size of 34Mn6 continuous casting round billet according to claim 1, characterized in that: In the step 5), 20 mL of the prepared corrosion solution is taken out and poured into a beaker.

5. The method for corroding austenite grain size of 34Mn6 continuous casting round billet according to claim 1, characterized in that: The corrosion time is 30 minutes.

6. The method for corroding austenite grain size of 34Mn6 continuous casting round billet according to claim 1, characterized in that: The metallographic microscope used was Axio observer, Zeiss, Germany.

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