A method for evaluating hydrogen embrittlement sensitivity of high-strength chain links in simulated service environment

Abstract

This invention discloses a method for evaluating the hydrogen embrittlement sensitivity of high-strength chain links under simulated service conditions, belonging to the field of material performance testing and evaluation technology. The method first involves taking samples from the non-welded portion of the chain link and subjecting them to pre-stretch plastic strain to simulate service stress. Subsequently, coal slurry solutions of different concentrations are prepared as corrosive media to simulate a real downhole environment. Through comprehensive electrochemical polarization testing, in-situ hydrogen-filled tensile experiments at different cathode potentials, and long-term isothermal immersion corrosion experiments, multi-dimensional data such as corrosion rate, hydrogen content, mechanical property loss, and fracture morphology are systematically obtained. By comparing and analyzing the performance differences of the samples before and after pre-straining, the influence of the pre-strain rate on the hydrogen embrittlement sensitivity of the samples is quantitatively analyzed, improving the evaluation accuracy and achieving a more precise, safer, and more reliable comprehensive evaluation of the chain links under near-real service conditions.

Description

Technical Field

[0001] This invention relates to the field of material performance testing and evaluation technology, and in particular to a method for evaluating the hydrogen embrittlement sensitivity of high-strength chain links under simulated service conditions. Background Technology

[0002] In coal mining operations, scraper conveyors not only provide the running track for coal mining machines but also undertake the task of transporting coal over long distances. Their reliable operation directly impacts the efficient production of coal mining enterprises. High-strength chain links are an important component of coal scraper conveyors, primarily bearing tensile stress along their length. Due to the complex geological conditions underground, the scraper chain is also subject to corrosion from groundwater, affecting its performance.

[0003] Scraper chains are made of low-alloy high-strength steel through flash welding, followed by quenching and tempering to achieve excellent comprehensive mechanical properties, with strengths often exceeding 1200 MPa. Therefore, their hydrogen embrittlement susceptibility should be evaluated when operating in corrosive downhole environments. Traditional hydrogen embrittlement susceptibility evaluation tests are usually conducted in simulated seawater. However, in reality, scraper chains are immersed in coal slurry for extended periods during service, and artificial seawater cannot fully reflect the actual conditions. Therefore, there is an urgent need for a test method that can simulate the operation of scraper chains in a coal slurry environment to quantitatively analyze the changes in the mechanical properties of the chain links caused by corrosion-induced hydrogen. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and provide a method for evaluating the hydrogen embrittlement sensitivity of high-strength chain links under simulated service conditions. By immersing the sample in a coal slurry solution under simulated service conditions, combined with tensile testing and hydrogen content testing, the influence of the coal slurry medium on the hydrogen embrittlement sensitivity of the sample can be quantitatively analyzed, thereby improving the reliability of the evaluation.

[0005] To achieve the above-mentioned technical objectives and meet the above-mentioned technical requirements, the technical solution adopted by the present invention is as follows:

[0006] A method for evaluating the hydrogen embrittlement sensitivity of high-strength chain links under simulated service conditions includes the following steps:

[0007] Step 1: Sample Preparation and Pre-straining: In-situ hydrogen-filled tensile specimens, such as plate-shaped I-beam specimens, are cut from the non-welded portion of the high-strength chain link to be tested. Some specimens are pre-stretched on a tensile testing machine to simulate the service pre-stress state of the chain link. The strain of the pre-stretching is 1%-5%, preferably 3%. The pre-stretching rate is 1-2 mm / min, preferably 1.5 mm / min. The chain steel specimens before and after pre-straining are processed into various shapes, including thin bar specimens, thick bar specimens, cuboid specimens, and I-beam specimens, for subsequent different tests.

[0008] Step 2: Construction of Simulated Service Environment: Prepare a coal slurry corrosion solution to simulate the underground coal slurry environment; mix raw coal crushed to 200 mesh with tap water that has been left to stand, and physically stir in a mixer for 20 minutes to prepare coal slurry solutions of different concentrations, which will serve as the corrosion medium for simulating the underground service of scraper conveyor chain links; the concentration of the coal slurry solution includes one or more of 1%, 5%, 10%, 20%, 30%, 40%, and 50%;

[0009] Step 3: Electrochemical testing: Using a Princeton electrochemical workstation, the polarization curves of the samples before and after pre-strain in coal slurry solutions with different mass fractions were measured to obtain electrochemical parameters such as self-corrosion potential and self-corrosion current density.

[0010] Step 4: In-situ hydrogen charging tensile test and quantitative evaluation of hydrogen embrittlement sensitivity: Take the I-beam sample from Step 1 and conduct in-situ hydrogen charging tensile tests at different cathode hydrogen charging potentials in a coal slurry solution with a certain mass fraction (e.g., 30%). Based on the experimental results, plot the relationship between hydrogen charging potential and elongation after fracture, plastic loss rate and reduction of area, respectively, to evaluate the effect of cathode hydrogen charging on the hydrogen embrittlement sensitivity of chain steel.

[0011] Step 5, Fracture Surface and Hydrogen Content Determination: For the sample that was broken in Step 4, the fracture surface was cut off by wire cutting, and the fracture surface and side crack morphology were observed by scanning electron microscopy (SEM); at the same time, a 0.5 cm sample segment was cut from the sample, and its hydrogen content was determined by a hydrogen thermal analyzer.

[0012] Step Six: Long-Term Immersion Corrosion and Hydrogen Permeation Study: The thin rod sample, thick rod sample, and cuboid sample from Step One were subjected to a long-term immersion corrosion experiment. The immersion corrosion experiment was conducted in a 30℃ constant temperature water bath for 56 days, with the solution replenished periodically and replaced every 5 days. Samples were periodically removed before and after pre-strain for macroscopic morphology recording, corrosion rate calculation, hydrogen content determination, and cross-sectional corrosion morphology observation. Specifically, the macroscopic corrosion morphology and corrosion mass loss of the thin rod sample were recorded, and the corrosion rate was calculated. After cleaning the surface with coarse sandpaper, the hydrogen content was determined using a hydrogen thermal analyzer. The thick rod sample was cut, and circular pieces with corrosion products were cut from both ends of the sample using wire cutting. The polarization curve was measured, and the corrosion morphology of the circular rod cross-section was observed under a scanning electron microscope. A set of comparative experiments was conducted simultaneously. In this comparative experiment, the corrosion products covering the sample surface were periodically polished to explore the influence mechanism of corrosion products on the hydrogen intrusion behavior of the sample.

[0013] Step 7, Microscopic Characterization: The original microstructure of the sample obtained in Step 1 was analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The composition and structure of the corrosion products of the sample after immersion were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The microscopic corrosion morphology of the cuboid sample taken out in Step 6 was observed by scanning electron microscopy.

[0014] Step 8: Comprehensive Evaluation: Compare and analyze the experimental results of the samples before and after pre-straining, and draw a graph showing the relationship between corrosion time, corrosion rate, and hydrogen content; and combine microstructure characterization and corrosion product analysis to comprehensively evaluate the influence mechanism of hydrogen embrittlement sensitivity of chain steel before and after pre-straining in the simulated coal slurry service environment.

[0015] Compared with the traditional structure, the beneficial effects of the present invention are as follows:

[0016] 1. This method is rigorously designed, introducing coal slurry, a real-world service medium for the chain links, into the hydrogen embrittlement evaluation system, thus overcoming the shortcomings of traditional methods that use seawater, resulting in strong environmental simulation realism. By comparing and analyzing the performance differences of samples before and after pre-straining, the influence of pre-strain rate on the hydrogen embrittlement sensitivity of the samples is quantitatively analyzed, improving the evaluation accuracy and achieving a comprehensive evaluation of the chain links' safety and reliability under near-real-world service conditions.

[0017] 2. By simulating the service prestress state of the chain links through pre-stretching treatment, the effect of pre-strain on the hydrogen embrittlement sensitivity of the material was revealed, making the evaluation conditions closer to the actual stress conditions of the components and improving the reliability of the evaluation.

[0018] 3. This method integrates multiple dimensions of analysis, including electrochemical corrosion behavior, macroscopic mechanical properties, hydrogen content testing, microscopic characterization, and fracture morphology, forming a closed-loop, mutually verifying systematic evaluation system.

[0019] 4. By plotting the relationship curves between hydrogen charging potential and various plasticity indices, a quantitative evaluation of hydrogen embrittlement sensitivity was achieved, providing data support for the hydrogen embrittlement resistance design and service life prediction of high-strength chain links. Simultaneously, through long-term immersion experiments and comparative experiments, the influence mechanism of the corrosion product layer on hydrogen permeation behavior was explored in depth. Attached Figure Description

[0020] Figure 1 The polarization curves and self-corrosion parameters of the samples in coal slurry solutions of different concentrations are shown in the figure (a. polarization curve of the unstrained sample, b. polarization curve of the 3% prestrained sample, c. self-corrosion potential, d. self-corrosion current).

[0021] Figure 2 This is a flowchart of the immersion corrosion experiment of the present invention;

[0022] Figure 3This is a schematic diagram of the immersion corrosion test apparatus used in this invention;

[0023] Figure 4 A comparison of weight loss and corrosion rate of chain steel before and after 3% pre-strain in coal slurry solution at different times;

[0024] Figure 5 The graph shows the relationship between the immersion time of the unstrained sample in the coal slurry solution and the hydrogen concentration (with corrosion layer).

[0025] Figure 6 The graph shows the relationship between the immersion time of a 3% pre-strained sample in coal slurry solution and the hydrogen concentration (a and c have corrosion layers, b and d have the corrosion layers removed by grinding).

[0026] Figure 7 Elongation after fracture curves at different cathode hydrogen charging potentials;

[0027] Figure 8 Curves showing the plasticity loss rate at different cathode hydrogen charging potentials;

[0028] Figure 9 Curves showing the cross-sectional shrinkage rate under different cathode hydrogen charging potentials;

[0029] Figure 10 Hydrogen desorption curves at different cathode hydrogen charging potentials;

[0030] Figure 11 This is a graph showing the change in elongation after fracture as a function of hydrogen concentration.

[0031] Figure 12 This is a graph showing the change in plasticity loss rate with hydrogen concentration. Detailed Implementation

[0032] The present invention will be further described below.

[0033] Example: Taking high-strength chain links with a strength grade of 1200MPa used in scraper conveyors as the evaluation object, the specific steps are as follows:

[0034] 1. Sample preparation and pre-strain:

[0035] Plate-shaped I-beam tensile specimens were wire-cut from the non-welded sections of the chain links. A portion of the specimens were subjected to pre-tensioning tests on a universal tensile testing machine at a tensile rate of 1.5 mm / min. The strain was unloaded when it reached 3%. This pre-strain rate was intended to simulate the typical working stress level experienced by the chain links.

[0036] The materials before and after pre-straining were processed into the following specimens: thin rods (for corrosion weight loss and hydrogen content testing), thick rods (for cross-sectional observation and electrochemical testing), cuboids (for microscopic morphology observation), and I-shaped specimens (for in-situ tensile testing).

[0037] 2. Simulated service environment construction:

[0038] Raw coal is extracted from the mine, crushed using a pulverizer, and passed through a 200-mesh sieve.

[0039] Coal powder and tap water that has been standing for more than 24 hours are mixed in a certain mass ratio and physically stirred on a mixer for 20 minutes to prepare coal slurry solutions with concentrations of 5%, 10%, 20%, 30%, 40%, and 50%.

[0040] 3. Electrochemical testing:

[0041] Using a Princeton electrochemical workstation, the potentiodynamic polarization curves of the samples before and after pre-straining in coal slurry solutions of different concentrations were measured in a three-electrode system. The results are as follows: Figure 1 As shown, the self-corrosion current density of the sample increases significantly after pre-straining, indicating that its corrosion rate is accelerated.

[0042] 4. Quantitative evaluation of in-situ hydrogen embrittlement tensile testing and hydrogen embrittlement sensitivity:

[0043] The pre-strained I-shaped specimen was mounted on a tensile testing machine. In a 30% coal slurry solution, hydrogen was applied at cathode potentials of -700mV, -800mV, -900mV, -1000mV, -1100mV, -1200mV, -1300mV, -1400mV, and -1500mV, respectively, and the specimen was stretched at a constant rate until fracture.

[0044] Record fracture data and plot the relationship curves between hydrogen charging potential and elongation after fracture, plastic loss rate, and reduction of area (see [reference]). Figures 7-9 The results showed that as the hydrogen charging potential shifted negatively (increased hydrogen content), the plasticity of the material decreased significantly.

[0045] 5. Determination of fracture surface and hydrogen content:

[0046] After the sample was broken, it was removed and a 0.5 cm long segment was cut near the fracture with a wire cutter. The hydrogen content of the segment was then determined using a hydrogen analyzer.

[0047] The fracture surface and side crack morphology of the fracture samples were observed under a scanning electron microscope. It was found that the uncharged or high-potential samples had ductile fracture surfaces, while the low-potential (high hydrogen content) hydrogen-charged samples showed obvious intergranular cracks, exhibiting hydrogen embrittlement characteristics.

[0048] 6. Study on long-term immersion corrosion and hydrogen permeation:

[0049] Corrosion experiments were conducted by suspending thin rods, thick rods, and cuboid samples before and after pre-straining in a coal slurry solution in a 30°C constant-temperature water bath. The experimental setup is shown below. Figure 3The experiment lasted 56 days. The solution lost through evaporation was replenished daily, and the solution was completely replaced every 5 days to maintain a relatively stable concentration. The procedure is as follows: Figure 2 .

[0050] On days 1, 3, 7, 14, 28, and 56 of immersion, a set of samples (including control samples with corrosion products and those with corrosion products removed by periodic grinding) were taken out.

[0051] For the removed thin rod samples: record the macroscopic morphology, remove corrosion products, weigh them, and calculate the corrosion rate (see results). Figure 4 Then the hydrogen content was determined using a hydrogen analyzer (see results). Figure 5 , Figure 6 ).

[0052] For the extracted coarse rod sample: wire cut circular pieces with corrosion products at its ends, perform polarization curve testing, and prepare cross-sectional metallographic samples to observe the thickness and morphology of the corrosion layer under SEM.

[0053] 7. Microscopic characterization:

[0054] The microstructure of the original sample was analyzed by characterization tests such as OM, SEM, XRD and EBSD. The corrosion products after immersion for 56 days were analyzed by EDS and XRD. The micromorphology of the cuboid sample taken out in step 6 was observed by scanning electron microscopy.

[0055] 8. Overall Evaluation:

[0056] Based on the experimental results of the samples before and after pre-straining, a graph showing the relationship between corrosion time, corrosion rate, and hydrogen content was plotted (e.g., Figures 4-12 (This is used to evaluate the corrosion behavior of chain steel in coal slurry solution before and after pre-straining).

[0057] Analysis shows that pre-strain not only accelerates the corrosion rate of the material in coal slurry but also significantly promotes hydrogen intrusion and enrichment. During the same immersion time, the hydrogen content of the pre-strained sample was consistently higher than that of the un-pre-strained sample. While the corrosion product layer provides some resistance to hydrogen penetration, the microscopic defects generated by pre-straining offer more sites for hydrogen, ultimately leading to a significantly higher hydrogen embrittlement sensitivity compared to the un-pre-strained material.

[0058] The above embodiments of the present invention are merely examples to clearly illustrate the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for evaluating hydrogen embrittlement susceptibility of high-strength chain links under a simulated service environment, characterized by: Includes the following steps: Step 1: Sample preparation and pre-straining: In-situ hydrogen-filled tensile specimens are cut from the non-welded part of the high-strength chain link to be tested, and the specimens are pre-stretched. The strain of the pre-stretching strain is 1%-5%, and the stretching rate is 1-2 mm / min, to simulate the service pre-stress state of the chain link; the chain steel specimens before and after pre-straining are processed into thin bar specimens, thick bar specimens, cuboid specimens and I-beam specimens, respectively. Step 2: Construction of simulated service environment: Prepare a coal slurry corrosion solution to simulate the underground coal slurry environment; mix raw coal crushed to 200 mesh with tap water, and stir to prepare a coal slurry solution with one or more concentrations of 1%, 5%, 10%, 20%, 30%, 40%, and 50%, which will serve as the corrosion medium for simulating the underground service of the scraper conveyor chain links. Step 3: Electrochemical testing: Using an electrochemical workstation, the polarization curves of the samples before and after pre-straining in coal slurry solutions with different mass fractions were measured. Step 4: In-situ hydrogen charging tensile test and quantitative evaluation of hydrogen embrittlement sensitivity: Take the I-beam sample from Step 1 and conduct in-situ hydrogen charging tensile tests at different cathode hydrogen charging potentials in a 30% coal slurry solution; based on the experimental results, plot the relationship between hydrogen charging potential and elongation after fracture, plastic loss rate and reduction of area, respectively, to evaluate the effect of cathode hydrogen charging on the hydrogen embrittlement sensitivity of chain steel. Step 5, Fracture Surface and Hydrogen Content Determination: The fracture surface of the sample after the tensile fracture in Step 4 is cut off by wire cutting, and the fracture surface and side crack morphology are observed by scanning electron microscopy; at the same time, a sample segment is cut from the sample and its hydrogen content is determined by a hydrogen thermal analyzer. Step Six: Long-Term Immersion Corrosion and Hydrogen Permeation Study: The thin rod sample, thick rod sample, and cuboid sample from Step One were subjected to a long-term immersion corrosion experiment. The immersion corrosion experiment was conducted in a constant temperature water bath at 30℃ for 56 days, with the solution replenished periodically and replaced every 5 days. Samples were periodically removed before and after pre-strain, and the macroscopic corrosion morphology and corrosion mass loss of the thin rod sample were recorded. The corrosion rate of the sample was calculated, and its hydrogen content was measured after polishing. Circular slices with corrosion products were cut from the thick rod sample, and the polarization curves were measured and the corrosion morphology of the circular rod cross-section was observed. A set of comparative experiments was conducted simultaneously. In this comparative experiment, the corrosion products covering the sample surface were periodically polished to explore the influence mechanism of corrosion products on the hydrogen intrusion behavior of the sample. Step 7, Microscopic Characterization: The microstructure of the sample obtained in Step 1 is analyzed using one or more of the following characterization methods: optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD); corrosion products are analyzed using energy dispersive spectroscopy (EDS) and X-ray diffractometer. Observe the micro-corrosion morphology of the cuboid sample taken out in step six; Step 8: Comprehensive Evaluation: Compare and analyze the experimental results of the samples before and after pre-straining, and draw a graph showing the relationship between corrosion time, corrosion rate, and hydrogen content; and combine microstructure characterization and corrosion product analysis to comprehensively evaluate the influence mechanism of hydrogen embrittlement sensitivity of chain steel before and after pre-straining in the simulated coal slurry service environment.

2. The method for evaluating hydrogen embrittlement susceptibility of high-strength chain links under simulated service environment according to claim 1, characterized by: The strain of the pre-stretched plastic strain is 3%, and the stretching rate of the pre-stretch is 1.5 mm / min.

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