A method of displaying high carbon pearlite, multiphase high silicon bainite rail head original austenite grain
By employing a water bath heating method combining low-temperature tempering and specific corrosive agents, the challenge of displaying austenitic grains in high-carbon pearlitic and multiphase high-silicon bainitic rails was solved, enabling clear grain corrosion and evaluation, and improving rail performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA BAOTOU STEEL UNION
- Filing Date
- 2026-04-10
- Publication Date
- 2026-07-31
AI Technical Summary
Existing technologies make it difficult to clearly display the original austenite grains of high-carbon pearlitic and multiphase high-silicon bainitic steel rails simultaneously. In particular, grain corrosion of multiphase high-silicon bainitic steel rails is more difficult, affecting the assessment of the rail's strength, toughness, and fatigue resistance.
After low-temperature tempering, a specific ratio of supersaturated picric acid aqueous solution, carbon tetrachloride aqueous solution and detergent was prepared as an etchant. Combined with water bath heating and mechanical polishing, the etched grains were observed under a microscope.
This method enables clear corrosion visualization of the original austenite grains in high-carbon pearlitic and multiphase high-silicon bainitic rails, improving the operability and reproducibility of grain size assessment and enhancing the strength, toughness, and fatigue resistance of the rails.
Smart Images
Figure CN122487339A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metallographic testing technology, and in particular relates to a method for displaying the original austenite grains in the rail head of high-carbon pearlite and multiphase high-silicon bainite steel rails. Background Technology
[0002] The grain size of steel rails significantly affects their strength, plasticity, toughness, and fatigue resistance, thus requiring grain size inspection. Identifying high-carbon pearlitic steel rails is a classic and challenging metallographic analysis problem because the microstructure of the rail at room temperature after hot rolling or heat treatment is pearlitic, and the original austenite grain boundaries may be "masked" or become unclear during phase transformation. Compared to pearlitic rails, bainitic rails possess higher strength, toughness, and wear resistance, but their chemical composition is complex, primarily based on a C-Si-Mn-Cr-Mo system with varying elemental contents. Due to differences in rolling and heat treatment processes, their microstructure consists of bainitic ferrite, retained austenite, and possibly a small amount of martensite, resulting in a more complex morphology. The diversity of chemical composition and microstructure in bainitic rails, especially for those with high silicon content, further increases the difficulty of corroding the original austenite grains.
[0003] However, the finer the original austenite grains, the finer the pearlite and bainite lath bundles are usually, which significantly improves the strength, toughness, fatigue resistance, and wear resistance of the rail, and ultimately improves the stability and service life of the rail.
[0004] Current methods for revealing austenite grain boundaries involve direct etching, typically using picric acid and a surfactant. Picric acid, as the primary etchant, can slightly corrode ferrite, but it tends to selectively corrode impurities or carbides concentrated at the austenite grain boundaries. The surfactant reduces the surface tension of the solution, allowing it to better wet and penetrate the "weak link" of the austenite grain boundaries, thereby disrupting the oxide film on the sample surface and making the etching more uniform and effective.
[0005] Chinese patents CN 112881247 A disclose a method for evaluating the grain size of steel rails, CN 116735437 A disclose a method for evaluating the grain size of pearlitic steel rails, and CN119643251 A disclose a corrosion method for determining the original austenitic grain size of high-carbon pearlitic steel rails. These three patents focus on the corrosion and evaluation methods for pearlitic steel rail grains; methods for corroding bainitic steel rail grains are rarely reported. In summary, none of these patents constitute a method capable of simultaneously revealing the original austenitic grain size of both high-carbon pearlitic steel rails and multiphase high-silicon bainitic steel rail heads. Summary of the Invention
[0006] The purpose of this invention is to provide a method for displaying the original austenite grains in the rail head of high-carbon pearlitic and multiphase high-silicon bainitic steel rails. For the first time, this method specifies the austenite grains of corroded steel rails from aspects such as sample preparation, corrosion reagent ratio, and sample pretreatment. It is highly operable and repeatable, and can clearly display the original austenite grain boundaries of high-carbon pearlitic and multiphase high-silicon bainitic steel rails, solving the problem of difficult corrosion of original austenite grain size. This provides convenient conditions for the research and development of new rail products and for metallographic testing personnel to study the austenite grains of rails.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] This invention discloses a method for displaying the original austenite grains in a rail head made of high-carbon pearlite and multiphase high-silicon bainite, comprising the following steps:
[0009] S1: Take transverse metallographic specimens from a designated or arbitrary position on the rail head using sawing or wire cutting methods to facilitate subsequent sample preparation;
[0010] S2: The sample taken in S1 is subjected to low-temperature tempering pretreatment. Tempering temperature: 260~320℃, tempering time: 3~5h, cooling method: furnace cooling to 50~100℃.
[0011] S3: A corrosive agent for corroding the original austenite grains of the rail. This corrosive agent consists of a supersaturated picric acid aqueous solution, a carbon tetrachloride aqueous solution, and detergent. By volume ratio, the ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent is 9.0~11.0:0.9~1.1:0.9~1.1.
[0012] S4: Grind and mechanically polish the transverse section of the sample prepared in S2, pour the corrosive liquid prepared in S3 into a glass container, place the polished surface of the sample prepared in S2 into the corrosive liquid in the glass container, and use a simple support to separate the polished surface from the bottom surface of the glass container at a distance of 2~5mm.
[0013] S5: Place the test apparatus prepared in S4 into a water bath heating device and heat for 10-15 minutes. Take out the sample, gently remove the corrosion products on the cross-section of the sample, and observe and collect the original austenite grains on the cross-section of the rail sample under a microscope.
[0014] Furthermore, the sample size is: 20~45mm long × 20~45mm wide × 20~30mm high.
[0015] Furthermore, the carbon content in high-carbon pearlitic steel rails is between 0.75 and 0.95 wt%.
[0016] Furthermore, the silicon content in multiphase high-silicon bainitic rails is between 0.9 and 1.6 wt%.
[0017] Furthermore, the tempering temperature is 300℃, the tempering time is 4 hours, and the furnace is cooled to 50℃.
[0018] Furthermore, calculated by volume ratio, the ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent is 10.0:1.0:1.0.
[0019] Furthermore, a simple stand is used to separate the polished surface from the bottom of the glassware by a distance of 5mm.
[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:
[0021] This invention provides a method for revealing the original austenite grains of high-carbon pearlitic steel rails and multiphase high-silicon bainitic steel rail heads, achieving the goal of simultaneously displaying the original austenite grains of multiple types of rails with a single etchant. High-carbon pearlitic steel rails, due to their high carbon content, are easily etched to reveal their microstructure. However, for multiphase high-silicon bainitic steel rails, silicon is a grain boundary strengthening element, making it difficult to reveal the austenite grains using traditional etching methods. This invention is the first in the industry to successfully etch the original austenite grains of multiphase high-silicon bainitic steel rails. This invention is groundbreaking, and its operation is simple, clearly revealing the austenite grains of two types of rails that are difficult to etch in the industry. It exhibits strong reproducibility and operability, making it easy to promote and use. Attached Figure Description
[0022] The present invention will be further described below with reference to the accompanying drawings.
[0023] Figure 1 Photograph of the original austenite grains in the high-carbon pearlitic steel rail head in Example 1;
[0024] Figure 2 This is a photograph of the original austenite grains in the rail head of the multiphase high-silicon bainitic steel rail in Example 2. Detailed Implementation
[0025] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.
[0026] Example 1:
[0027] A high-carbon pearlitic steel rail with a carbon content of 0.79% was selected. (1) A transverse metallographic sample was taken from any position on the rail head using wire cutting. The preferred sample size was 25mm (length) × 25mm (width) × 20mm (height). The sample was subjected to low-temperature tempering treatment. The tempering temperature was 270℃, the tempering time was 4.5h, and the cooling method was furnace cooling to 100℃. (2) A corrosive agent for corroding the original austenitic grains of the steel rail was prepared. The ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent was 10.0:1.0:1.0 by volume. (3) The transverse surface of the sample was ground and mechanically polished. The polished surface was placed in a glass container filled with corrosive liquid. A simple support was used to separate the polished surface from the bottom of the glass container by a distance of 2mm. (4) After heating the glassware in a water bath for 10 minutes, take out the sample, gently remove the corrosion products on the cross-section of the sample, observe and collect the original austenite grains on the cross-section of the rail sample under a microscope. The grain size level is 8.0.
[0028] Example 2:
[0029] A multiphase bainitic steel rail with a silicon content of 1.20% was selected. (1) A transverse metallographic sample was taken from any position on the rail head using mechanical cutting. The preferred sample size was 30mm (length) × 20mm (width) × 25mm (height). The sample was subjected to low-temperature tempering treatment. The tempering temperature was 320℃, the tempering time was 5h, and the cooling method was furnace cooling to 50℃. (2) A corrosive agent for corroding the original austenitic grains of the steel rail was prepared. The ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent was 11.0:0.9:1.1 by volume. (3) The transverse surface of the sample was ground and mechanically polished. The polished surface was placed in a glass container filled with corrosive liquid. A simple support was used to separate the polished surface from the bottom of the glass container by a distance of 5mm. (4) After heating the glassware in a water bath for 15 minutes, take out the sample, gently discard the corrosion products on the cross section of the sample, observe and collect the original austenite grains on the cross section of the rail sample under a microscope. The grain size level is 7.0.
[0030] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for displaying the original austenite grains in a rail head made of high-carbon pearlite and multiphase high-silicon bainite, characterized in that, Includes the following steps: S1: Take transverse metallographic specimens from a designated or arbitrary position on the rail head using sawing or wire cutting methods to facilitate subsequent sample preparation; S2: The sample taken in S1 is subjected to low-temperature tempering pretreatment. Tempering temperature: 260~320℃, tempering time: 3~5h, cooling method: furnace cooling to 50~100℃. S3: A corrosive agent for corroding the original austenite grains of the rail. This corrosive agent consists of a supersaturated picric acid aqueous solution, a carbon tetrachloride aqueous solution, and detergent. By volume ratio, the ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent is 9.0~11.0:0.9~1.1:0.9~1.
1. S4: Grind and mechanically polish the transverse section of the sample prepared in S2, pour the corrosive liquid prepared in S3 into a glass container, place the polished surface of the sample prepared in S2 into the corrosive liquid in the glass container, and use a simple support to separate the polished surface from the bottom surface of the glass container at a distance of 2~5mm. S5: Place the test apparatus prepared in S4 into a water bath heating device and heat for 10-15 minutes. Take out the sample, gently remove the corrosion products on the cross-section of the sample, and observe and collect the original austenite grains on the cross-section of the rail sample under a microscope.
2. The method for displaying the original austenite grains of high-carbon pearlite and multiphase high-silicon bainite steel rail heads according to claim 1, characterized in that, Sample size: 20~45mm long × 20~45mm wide × 20~30mm high.
3. The method for displaying the original austenite grains of high-carbon pearlite and multiphase high-silicon bainite steel rail heads according to claim 1, characterized in that, The carbon content in high-carbon pearlitic steel rails is between 0.75 and 0.95 wt%.
4. The method for displaying the original austenite grains of high-carbon pearlite and multiphase high-silicon bainite rail head according to claim 1, characterized in that, The silicon content in multiphase high-silicon bainitic steel rails is between 0.9 and 1.6 wt%.
5. The method for displaying the original austenite grains in the rail head of a high-carbon pearlite, multiphase high-silicon bainite steel rail according to claim 1, characterized in that, The tempering temperature is 300℃, the tempering time is 4 hours, and the furnace is cooled to 50℃.
6. The method for displaying the original austenite grains of high-carbon pearlite and multiphase high-silicon bainite rail head according to claim 1, characterized in that, Based on volume ratio, the ratio of saturated picric acid aqueous solution: carbon tetrachloride aqueous solution: detergent in the corrosive agent is 10.0:1.0:1.
0.
7. The method for displaying the original austenite grains of high-carbon pearlite and multiphase high-silicon bainite rail head according to claim 1, characterized in that, Use a simple stand to separate the polished surface from the bottom of the glassware by 5mm.