A test method for simulating freeze-thaw cycles of steel materials in fresh water environments

Abstract

The present application belongs to the technical field of material environment test simulation, and particularly relates to a test method for simulating freeze-thaw cycles of steel materials in fresh water environment, which comprises sample pretreatment, freeze-thaw cycles, sample characterization, spraying of simulated fresh water solution in the freeze-thaw cycles, then low-temperature freezing and ice formation, followed by high-temperature melting and drying, and repeating. The sample after the freeze-thaw cycles is characterized, and the characterization results show that the test method effectively simulates the surface icing behavior, dry-wet alternating corrosion and coupling damage mechanism in the freeze-thaw process under the temperature cycling condition in the fresh water environment, and can solve the problem that the existing test method fails to simulate the temperature periodic alternation in the fresh water environment, and fill the research gap of the freeze-thaw cycle simulation method of steel materials.

Description

Technical Field

[0001] This invention belongs to the field of material environmental testing simulation technology, specifically involving a test method for simulating the freeze-thaw cycle of steel materials in a freshwater environment. Specifically, it is a method for simulating the freeze-thaw cycle test of materials by simulating the freshwater freeze-thaw cycle environment in the laboratory. Background Technology

[0002] In freshwater environments, due to the low salinity, low conductivity, and high resistivity of freshwater, its corrosive properties are relatively weak. However, reactions may occur between cations and anions or between water molecules, damaging the oxide film on metals. The corrosion mechanism is electrochemical corrosion primarily driven by oxygen depolarization. The reaction is influenced by the solubility of alkaline substances such as calcium oxide in the steel slag and the oxygen diffusion rate. The corrosion products are relatively uniform and dense, mainly Fe3O4, α-FeOOH, and γ-FeOOH. In this environment, freeze-thaw cycles are primarily affected by physical forces; the repeated expansion forces generated by water freezing lead to increased microcracks and porosity within the material, resulting in mass loss and a decrease in strength (compressive strength).

[0003] During freeze-thaw cycles, the ambient temperature repeatedly crosses the 0°C freezing point, causing a periodic alternating wet and dry state of "freezing-thawing" on the surface of steel materials: when the temperature is above 0°C, the surface ice or frost melts into a liquid water film; when the temperature drops below 0°C, the water film refreezes back into ice. This repeated phase change process of moisture on the material surface is called a freeze-thaw cycle. Freeze-thaw cycles not only cause ice to accumulate on the steel surface, increasing structural loads and threatening service safety, but also severely affect the durability and service life of critical components due to repeated frost heave stress.

[0004] Construction steel is widely used in numerous fields such as industrial buildings, super high-rise buildings, public buildings, offshore platforms, bridges, and towers. Its quality and performance are directly related to the safety, durability, and economy of the structure, playing a fundamental supporting role in the high-quality development of the industry. Construction steel is mainly divided into two categories: steel for steel structures and steel for reinforced concrete. Steel for steel structures is widely used in key load-bearing components such as beams and columns in high-rise and super high-rise buildings, as well as large-span spatial structures such as stadiums, exhibition centers, theaters, airport terminals, and railway stations. Steel for reinforced concrete is a reinforcing material embedded in concrete to compensate for the insufficient tensile strength of concrete. It mainly includes hot-rolled steel bars, cold-rolled ribbed steel bars, prestressed steel wires, and steel strands.

[0005] Currently, simulation testing methods for freeze-thaw cycles mainly focus on steel used in construction or geological materials such as concrete and soil. Relevant testing standards (such as GB / T 50082 and ASTM C666) primarily assess the freeze-thaw resistance and structural integrity of porous materials. However, research on simulation testing methods for freeze-thaw cycles in freshwater environments is relatively limited, and a systematic and standardized testing system has not yet been established. Existing methods struggle to effectively simulate the surface icing behavior, alternating wet and dry corrosion, and their coupled damage mechanisms involved in the freeze-thaw process of steel materials.

[0006] Therefore, developing a freeze-thaw cycle simulation test method suitable for steel materials in freshwater environments, and systematically evaluating their corrosion resistance and freeze resistance under low temperature alternation and high humidity environments, is of great engineering value and practical significance for revealing the freeze-thaw damage mechanism of steel materials. Summary of the Invention

[0007] To address the problem that freeze-thaw cycles in freshwater environments cannot effectively simulate the surface icing behavior, wet-dry corrosion, and coupled damage mechanisms of steel materials during freeze-thaw cycles, this invention provides a test method for simulating freeze-thaw cycles in freshwater environments. This method includes sample pretreatment, freeze-thaw cycles, and sample characterization. During the freeze-thaw cycle, a simulated freshwater solution is sprayed, followed by low-temperature freezing, then high-temperature thawing and drying. This process is repeated, and the samples after the freeze-thaw cycles are then characterized. The characterization results show that the technical solution disclosed in this invention can effectively simulate the surface icing behavior, wet-dry corrosion, and coupled damage mechanisms of steel materials during freeze-thaw cycles under varying temperature conditions in freshwater environments.

[0008] To solve the above-mentioned technical problems, the present invention provides a test method for simulating freeze-thaw cycles of steel materials in a freshwater environment, comprising the following steps: sample pretreatment - freeze-thaw cycles - sample characterization; Sample pretreatment: Pretreatment of the sample; Freeze-thaw cycle: spraying a dilute aqueous solution - freezing at low temperature - thawing and drying at high temperature, with a cycle count of ≥1 time; Sample characterization; The desalinated water solution is a desalinated water solution with pH=6.5~8.5, chloride ion content ≤250mg / L, alkalinity 50~200mg / L, hardness 50~500mg / L, and conductivity 10~500μS / cm, selected from deionized water, tap water, natural river water, lake water, groundwater or self-made desalinated water. The spraying process is as follows: the pretreated sample is placed vertically and 2-5 ml of dilute aqueous solution is sprayed evenly using a spray bottle to simulate the environment; When the simulated environment is a freshwater environment with winter temperatures of -20 to -10℃ and summer temperatures of 20 to 30℃, the water is frozen at -10 to -20℃ for 0.5 to 2 hours and then thawed and dried at 20 to 30℃ for 0.5 to 2 hours. When the simulated environment is a freshwater environment with winter temperatures of -10~0℃ and summer temperatures of 25~35℃, the water is frozen at -10~0℃ for 0.5~2 hours and then thawed and dried at 25~35℃ for 0.5~2 hours. When the simulated environment is a freshwater environment with winter temperatures of -15 to -5°C and summer temperatures of 15 to 25°C, the product is frozen at -15 to -5°C for 0.5 to 2 hours and then thawed and dried at 15 to 25°C for 0.5 to 2 hours.

[0009] Based on the above technical solution, the sample is a steel material, selected from one of the following: shipbuilding steel, marine engineering steel, bridge steel, and construction steel.

[0010] Based on the above technical solution, the sample is selected from one of the following: shipbuilding steel A, AH32, AH36, EH36, FH36, marine engineering steel VL4-4, and bridge steel Q420qE.

[0011] Based on the above technical solution, the sample pretreatment includes processing and polishing, alkaline degreasing, hydrophobic modification, or coating. The specific processing and polishing process is as follows: the sample is processed into parallel samples with dimensions of 30~50×30~50×3~10mm. Three parallel samples are used for testing. The parallel samples are polished with sandpaper until the surface is uniform and consistent, and then degreased with alkaline solution.

[0012] Based on the above technical solution, the alkaline degreasing specifically involves using an alkaline solution with a concentration of 20~50g / L to degrease the sample after sanding, wherein the alkaline solution is selected from at least one of sodium hydroxide, sodium carbonate, trisodium phosphate, and sodium metasilicate.

[0013] Based on the above technical solution, the hydrophobic modification specifically involves: performing hydrophobic modification on the sample after degreasing treatment, wherein the modifier is selected from at least one of hydrochloric acid, ferric chloride, copper sulfate, stearic acid, ethanol, and water, and the modification conditions are immersion in the modifier for 0.5 to 6 hours; The modifier is preferably an aqueous solution of HCl / FeCl3, a stearic acid / ethanol solution, or an aqueous solution of copper sulfate.

[0014] Based on the above technical solution, the coating treatment specifically involves coating the sample after degreasing, wherein the coating is selected from at least one of metal coating, organic coating, and inorganic / composite coating, and the coating thickness is 5~200μm.

[0015] Based on the above technical solution, the sample characterization includes morphological observation, corrosion electrochemical testing, corrosion weight loss calculation, hydrophobicity characterization, and durability characterization.

[0016] Beneficial effects The technical solution disclosed in this invention pretreats steel materials, then subjectes them to freeze-thaw cycles in a freshwater environment, and then characterizes and analyzes the performance of the cyclically cycled samples. This allows for the acquisition of service characteristics or corrosion failure characteristics of steel materials under simulated freshwater freeze-thaw cycles in the laboratory. This is beneficial for the performance research of steel and surface protection materials under freshwater freeze-thaw cycles. Moreover, the test method is simple and efficient, with economic and safety advantages, and can solve the problem that existing test methods cannot evaluate the performance of steel materials under freeze-thaw cycles in a freshwater environment. Attached Figure Description

[0017] Figure 1 A schematic diagram of an experimental method for simulating freeze-thaw cycles of steel materials in a freshwater environment; Figure 2 The corrosion electrochemical linear polarization diagram is shown in Example 1. Figure 3 This is a graph showing the change of water contact angle with the freeze-thaw cycle in Example 2. Detailed Implementation

[0018] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0020] In Example 2 of this invention, the FeCl3 content of the HCl / FeCl3 aqueous solution is 10wt%, the mass ratio of HCl to FeCl3 is 1:1; the stearic acid concentration of the stearic acid / ethanol solution is 0.05mol / L; and the concentration of the copper sulfate aqueous solution is 0.05mol / L.

[0021] Example 1 A test method simulating freeze-thaw cycles of steel materials in a freshwater environment is used to conduct freeze-thaw cycle tests on shipbuilding steels AH36, EH36, and FH36 in a simulated natural river water environment in Northeast China, and to analyze the corrosion electrochemical behavior of the steel materials after the freeze-thaw cycle test. The samples used are shipbuilding steels AH36, EH36, and FH36. The samples are processed into parallel specimens with dimensions of 50×50×10mm. They are then polished sequentially with 200#, 600#, and 1000# sandpaper until the surface is uniform. Surface oil contamination is removed with an alkaline solution (40g / L sodium hydroxide / sodium bicarbonate solution, with a sodium hydroxide to sodium bicarbonate mass ratio of 1:1). After sample pretreatment, 100 freeze-thaw cycles are initiated. In each freeze-thaw cycle, the sprayed freshwater solution is natural river water (sourced from Wanshui River in Anshan City, pH 7.8, chloride ion content 150mg / L). (L, alkalinity 100 mg / L, hardness 150 mg / L, conductivity 400 μS / cm) The pretreated samples were placed vertically and sprayed with an equal volume of solution (2 mL) using a spray bottle. The parallel samples were then placed in a constant temperature test chamber with the ambient temperature set to -15°C (average winter temperature in Northeast China) for 1 hour, allowing the sprayed solution on the sample surface to freeze. Subsequently, the ambient temperature was set to 25°C (average summer temperature in Northeast China) for 0.5 hours, allowing the frozen layer on the sample surface to melt and dry. The samples were then removed, and the next freeze-thaw cycle was initiated. After 100 freeze-thaw cycles, the parallel samples were removed for corrosion electrochemical performance analysis to evaluate the corrosion electrochemical performance of steel materials under simulated freshwater freeze-thaw cycle conditions. The test results are shown below. Figure 1 The linear polarization spectra of the samples show that the polarization resistance of the three types of marine steel is relatively small after freeze-thaw cycles.

[0022] Example 2 A test method for simulating freeze-thaw cycles of steel materials in a freshwater environment is used to conduct freeze-thaw cycle tests on the superhydrophobic modified surface of Q420qE bridge steel in a simulated freshwater environment in North China, and to analyze the hydrophobic properties of the modified surface after the freeze-thaw cycle test. The samples used were Q420qE bridge steel. The samples were machined into parallel specimens measuring 40×40×5mm. They were then polished sequentially with 200#, 600#, and 1000# sandpaper until the surface was uniform. Surface oil was removed with an alkaline solution (a 30g / L sodium hydroxide and trisodium phosphate solution, with a sodium hydroxide to trisodium phosphate mass ratio of 10:1). Three different methods were used to modify the surface to be superhydrophobic (etching, deposition, or coupling). For etching, the etching modification solution was a 1:1 mass ratio of HCl / FeCl3 aqueous solution and stearic acid / ethanol solution, with an immersion modification time of 2 hours. For deposition, the deposition solution was a 1:1 mass ratio of copper sulfate aqueous solution and stearic acid / ethanol solution, with an immersion modification time of 1 hour. For coupling, the coupling modification solution was the etching modification solution and the deposition solution. The solution composition was as follows: the mass ratio of etching modification solution to deposition solution was 1:1, and the immersion modification time was 3 hours. After sample pretreatment, 20 freeze-thaw cycles were initiated. In each freeze-thaw cycle, the sprayed aqueous solution was tap water (pH 7.5, chloride ion content 150 mg / L, alkalinity 120 mg / L, hardness 200 mg / L, conductivity 200 μS / cm). The sample was placed vertically, and an equal amount of solution (3 mL) was sprayed evenly using a spray bottle. Then, parallel samples were placed in a constant temperature test chamber with the ambient temperature set to -5°C (winter temperature in North China) and the freezing time was 2 hours, causing the sprayed solution on the sample surface to freeze. Subsequently, the ambient temperature was set to 25°C (summer temperature in North China) and the thawing and drying time was 1.5 hours, allowing the frozen ice layer on the sample surface to melt and dry. The sample was then removed, and the next freeze-thaw cycle was initiated. After 50 freeze-thaw cycles, parallel samples were taken out for hydrophobicity analysis to evaluate the hydrophobicity of steel-modified surface materials under simulated freshwater freeze-thaw cycle conditions. The analysis showed that the hydrophobicity of different superhydrophobic modified surfaces exhibited different trends under freeze-thaw cycle conditions. The test results are shown in [Figure number missing]. Figure 2 .

[0023] Example 3 A test method simulating freeze-thaw cycles of steel materials in a freshwater environment is disclosed. This method is used to conduct freeze-thaw cycle tests on the epoxy coating of bridge steel Q420qE in a simulated freshwater environment in Northwest China, and to analyze the durability of the coating surface after the freeze-thaw cycle test. The test specimens used are bridge steel Q420qE. The specimens are processed into parallel specimens with dimensions of 50×50×10mm. The specimens are then polished sequentially with 200#, 600#, and 1000# sandpaper until the surface is uniform. Surface oil contamination is removed with an alkaline solution (a 30g / L solution of sodium hydroxide / trisodium phosphate / sodium metasilicate, with a mass ratio of sodium hydroxide, trisodium phosphate, and sodium metasilicate of 8:1:1). An organic epoxy coating (zinc-rich epoxy coating, 125μm thick) is then applied to the surface. After the specimen pretreatment, 50 freeze-thaw cycles are performed. During each freeze-thaw cycle, tap water (pH 7) is sprayed as the freshwater solution. 5. With a chloride ion content of 150 mg / L, alkalinity of 120 mg / L, hardness of 200 mg / L, and conductivity of 200 μS / cm, the sample was placed vertically and sprayed with an equal volume of solution (5 mL). The parallel samples were then placed in a constant temperature test chamber with the ambient temperature set to -10°C (the average winter temperature in Northwest China) for 1.5 hours, allowing the sprayed solution on the sample surface to freeze. Subsequently, the ambient temperature was set to 15°C (the average summer temperature in Northwest China) for 1 hour, allowing the frozen layer on the sample surface to melt and dry. The samples were then removed, and the next freeze-thaw cycle was initiated. After 50 freeze-thaw cycles, the parallel samples were removed for durability analysis. The calculated sample mass loss rate was only 0.15%, demonstrating that the surface organic coating possesses good durability under freeze-thaw cycle conditions. The cyclic freeze-thaw cycles did not damage the organic coating.

[0024] Comparative Example The standard GB / T 43356-2023 "Cyclic Immersion Test Method for Corrosion of Steel Bars in Salt Solution" or TB / T 2375-1993 "Cyclic Immersion Corrosion Test Method for Weathering Steel for Railways" is used to conduct cyclic corrosion tests on steel for shipbuilding, marine engineering, and bridges. The corrosion electrochemical performance, hydrophobicity, and durability performance after the test are then tested. This method can only conduct cyclic immersion tests at constant temperature and cannot simulate freeze-thaw cycles under alternating temperature conditions.

[0025] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A test method for simulating freeze-thaw cycles of steel materials in a freshwater environment, characterized in that, The steps include: sample pretreatment, freeze-thaw cycles, and sample characterization. Sample pretreatment: Pretreatment of the sample; Freeze-thaw cycle: spraying a dilute aqueous solution - freezing at low temperature - thawing and drying at high temperature, with a cycle count of ≥1 time; Sample characterization; The desalinated water solution is a desalinated water solution with pH=6.5~8.5, chloride ion content ≤250mg / L, alkalinity 50~200mg / L, hardness 50~500mg / L, and conductivity 10~500μS / cm, selected from deionized water, tap water, natural river water, lake water, groundwater or self-made desalinated water. The spraying process is as follows: the pretreated sample is placed vertically and 2-5 ml of dilute aqueous solution is sprayed evenly using a spray bottle to simulate the environment; When the simulated environment is a freshwater environment with winter temperatures of -20 to -10℃ and summer temperatures of 20 to 30℃, the water is frozen at -10 to -20℃ for 0.5 to 2 hours and then thawed and dried at 20 to 30℃ for 0.5 to 2 hours. When the simulated environment is a freshwater environment with winter temperatures of -10~0℃ and summer temperatures of 25~35℃, the water is frozen at -10~0℃ for 0.5~2 hours and then thawed and dried at 25~35℃ for 0.5~2 hours. When the simulated environment is a freshwater environment with winter temperatures of -15 to -5°C and summer temperatures of 15 to 25°C, the product is frozen at -15 to -5°C for 0.5 to 2 hours and then thawed and dried at 15 to 25°C for 0.5 to 2 hours.

2. The test method according to claim 1, characterized in that, The sample is a steel material, which is selected from one of the following: shipbuilding steel, marine engineering steel, bridge steel, and construction steel.

3. The test method according to claim 1, characterized in that, The sample pretreatment includes processing and polishing, alkaline degreasing, hydrophobic modification, or coating. The specific processing and polishing process is as follows: the sample is processed into parallel samples with dimensions of 30~50×30~50×3~10mm. Three parallel samples are used for testing. The parallel samples are polished with sandpaper until the surface is uniform and consistent, and then degreased with alkaline solution.

4. The test method according to claim 3, characterized in that, The alkaline degreasing process specifically involves using an alkaline solution with a concentration of 20-50 g / L to degrease the sample after sanding. The alkaline solution is selected from at least one of sodium hydroxide, sodium carbonate, trisodium phosphate, and sodium metasilicate.

5. The test method according to claim 3, characterized in that, The hydrophobic modification specifically involves: performing hydrophobic modification on the sample after degreasing treatment, wherein the modifier is selected from at least one of hydrochloric acid, ferric chloride, copper sulfate, stearic acid, ethanol, and water, and the modification conditions are immersion in the modifier for 0.5 to 6 hours; The modifier is preferably an aqueous solution of HCl / FeCl3, a stearic acid / ethanol solution, or an aqueous solution of copper sulfate.

6. The test method according to claim 3, characterized in that, The coating process specifically involves applying a coating to the degreasing sample. The coating is selected from at least one of metal coatings, organic coatings, and inorganic / composite coatings, and the coating thickness is 5~200μm.

7. The test method according to claim 1, characterized in that, The sample characterization includes morphological observation, corrosion electrochemical testing, corrosion weight loss calculation, hydrophobicity characterization, and durability characterization.

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