Evaluation method of high-strength corrosion-resistant steel

Abstract

The invention discloses an evaluation method of high-strength corrosion-resistant steel. The evaluation method comprises the steps of sample preparation, mechanical property testing, hardness testing, corrosion resistance testing, electrochemical testing, microstructure analysis, metallographic analysis and transmission electron microscope analysis. And comprehensively evaluating. The invention aims to provide the evaluation method for the high-strength corrosion-resistant steel, the method can comprehensively consider multiple factors such as the strength, the corrosion resistance and the microstructure of the high-strength corrosion-resistant steel, the performance of the high-strength corrosion-resistant steel is comprehensively and accurately evaluated, meanwhile, the test period is shortened, the test cost is reduced, and the test efficiency is improved. And a scientific basis is provided for research, development, production and application of the high-strength corrosion-resistant steel.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel performance evaluation, and particularly relates to a method for evaluating high-strength corrosion-resistant steel. Background Art

[0002] With the rapid development of modern industry, high-strength corrosion-resistant steel has been widely used in many fields such as construction, bridges, ocean engineering, and chemical engineering. High-strength corrosion-resistant steel not only needs to have high strength to meet the requirements of structural load-bearing, but also needs to have good corrosion resistance to ensure long-term stable use in harsh environments.

[0003] Currently, the evaluation of high-strength corrosion-resistant steel mainly focuses on the testing of single properties. For example, the evaluation of strength usually adopts methods such as tensile tests, and the evaluation of corrosion resistance mostly uses salt spray tests, immersion tests, etc. However, these traditional evaluation methods have certain limitations. On the one hand, the testing of single properties cannot comprehensively reflect the comprehensive performance of high-strength corrosion-resistant steel in actual use. In actual working conditions, steel often bears the action of mechanical loads and corrosive media simultaneously, and the good performance of a single property does not guarantee its reliability in complex environments. On the other hand, the existing evaluation methods do not study deeply enough the relationship between the microstructure and properties of steel, making it difficult to understand the reasons for the change of steel properties essentially, and thus unable to provide more effective guidance for the research and improvement of steel.

[0004] In addition, traditional evaluation methods also have deficiencies in terms of testing cycle and cost. Some corrosion resistance tests, such as long-term immersion tests or natural environment exposure tests, require a large amount of time and resources, which is a great obstacle to the rapid screening and development of new high-strength corrosion-resistant steel. Therefore, it is of great practical significance to develop a method that can comprehensively, accurately, and quickly evaluate the comprehensive performance of high-strength corrosion-resistant steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating high-strength corrosion-resistant steel, which can comprehensively consider multiple factors such as the strength, corrosion resistance, and microstructure of high-strength corrosion-resistant steel, comprehensively and accurately evaluate its performance, while shortening the testing cycle and reducing the testing cost, and providing a scientific basis for the research, production, and application of high-strength corrosion-resistant steel.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for evaluating high-strength corrosion-resistant steel of the present invention includes:

[0008] Sample preparation:

[0009] Cut multiple samples with dimensions of 100mm×50mm×5mm from a batch of cold-heading steels for high-strength and corrosion-resistant bolts to be evaluated. Among them, select 4 pieces to be processed into standard tensile specimens with dimensions meeting the requirements of GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; select another 4 pieces for surface grinding and polishing treatment as corrosion-resistant performance test samples; select 2 pieces to be prepared into metallographic specimens and perform grinding, polishing and etching treatments according to the standard process of metallographic sample preparation; finally, select 1 piece to be prepared into a transmission electron microscope specimen through mechanical thinning and ion thinning treatment steps;

[0010] Mechanical property testing:

[0011] Tensile test: Install the prepared tensile specimen on an electronic universal tensile testing machine, set the test temperature to room temperature, and the tensile speed to 4 - 6mm / min; conduct a tensile test according to the standard test method and record the load-displacement curve of the specimen; after the test, calculate the mechanical property indexes of yield strength, tensile strength and elongation after fracture based on the curve;

[0012] Hardness test: Use a Rockwell hardness tester to test the hardness of the sample, measure the hardness values at 5 points in different parts of the sample, and take the average value as the hardness of the sample;

[0013] Corrosion-resistant performance testing:

[0014] Simulated corrosion environment test: Select a neutral salt spray environment as the simulated corrosion environment, put the polished corrosion-resistant performance test sample into a salt spray test chamber, and conduct the test according to the standard of GB / T10125-2021 "Artificial atmosphere corrosion test - Salt spray test";

[0015] Electrochemical test: Use the sample as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode to form a three-electrode system; conduct potentiodynamic polarization curve test and electrochemical impedance spectroscopy test in a 3.5% mass fraction NaCl solution;

[0016] Microstructure analysis:

[0017] Metallographic analysis: Observe the metallographic specimen under a metallographic microscope at a magnification of 500 times;

[0018] Transmission electron microscope analysis: Observe the transmission electron microscope specimen under a transmission electron microscope at a magnification of 50000 times;

[0019] Comprehensive evaluation:

[0020] Establish a comprehensive evaluation model, and quantify the mechanical property indexes, corrosion resistance property indexes and microstructure indexes; according to the importance degree of different property indexes in actual use, assign corresponding weights; among them: the weight of the mechanical property index is 0.4, the weight of the corrosion resistance property index is 0.4, and the weight of the microstructure index is 0.2;

[0021] Score each index, and then calculate the comprehensive performance score according to the weights.

[0022] Further, in the corrosion resistance performance test, the test temperature is controlled at 35°C ± 2°C, and the salt spray deposition rate is 1.0 mL / (h·80 cm 2 ) - 2.0 mL / (h·80 cm 2 ).

[0023] Further, when the test proceeds to 72 hours, 144 hours, 216 hours and 288 hours, take out the samples respectively, observe the corrosion situation on the surface, and record the color, morphology and distribution of the corrosion products.

[0024] Further, for the electrochemical test: the scanning speed of the potentiodynamic polarization curve test is 1 mV / s, and the potential scanning range is ±250 mV relative to the open circuit potential.

[0025] Further, the frequency range of the electrochemical impedance spectroscopy test is 10 5 Hz - 10- 2 Hz, and the excitation signal is a sine wave with an amplitude of 10 mV.

[0026] Further, this evaluation method has good operability and repeatability.

[0027] Further, standard test equipment and test methods are adopted for each test method, and the test results are reliable, which can provide a scientific and objective evaluation basis for the production and application of high-strength corrosion-resistant steel.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are:

[0029] The evaluation method of the present invention comprehensively considers various factors such as the mechanical properties, corrosion resistance properties and microstructure of high-strength corrosion-resistant steel, can comprehensively and accurately reflect the performance of the steel in actual use, and overcomes the limitations of traditional single-property tests.

[0030] By adopting the method combining the simulated corrosion environment test and the electrochemical test, the corrosion resistance properties and corrosion mechanism of the steel can be understood more deeply, and more targeted guidance can be provided for the optimization of the corrosion resistance properties of the steel.

[0031] Microstructural analysis can essentially reveal the relationship between the properties of steel and its microstructure, providing a theoretical basis for the research and development and improvement of steel. At the same time, combined with the comprehensive evaluation model, it can quickly and accurately compare and screen the properties of different steels, shortening the R & D cycle and reducing the R & D cost.

[0032] The evaluation method of the present invention has good operability and repeatability. Standard test equipment and test methods are used for each test method, and the test results are reliable, which can provide a scientific and objective evaluation basis for the production and application of high-strength corrosion-resistant steel. Specific embodiments

[0033] The present invention will be further described in detail below with reference to the embodiments:

[0034] The purpose of the present invention is to provide an evaluation method for high-strength corrosion-resistant steel. Specifically, for a cold-heading steel for high-strength and corrosion-resistant bolts, we conduct an evaluation on it.

[0035] Sample preparation:

[0036] Cut multiple samples with dimensions of 100mm×50mm×5mm from a batch of cold-heading steel for high-strength and corrosion-resistant bolts to be evaluated. Among them, 4 pieces are processed into standard tensile specimens, and the dimensions meet the requirements of GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; another 4 pieces are subjected to surface grinding and polishing treatments as corrosion resistance test samples; 2 more pieces are prepared into metallographic specimens and are ground, polished and etched according to the standard process of metallographic sample preparation; finally, 1 piece is prepared into a transmission electron microscope specimen through mechanical thinning and ion thinning and other treatment steps.

[0037] Mechanical property testing:

[0038] Tensile test: Install the prepared tensile specimen on an electronic universal tensile testing machine, set the test temperature to room temperature (20°C ± 2°C), and the tensile speed to 5mm / min. Conduct the tensile test according to the standard test method and record the load-displacement curve of the specimen. After the test, calculate mechanical property indexes such as yield strength, tensile strength and elongation after fracture according to the curve. Through testing, the yield strength of this cold-heading steel for high-strength and corrosion-resistant bolts is 1540MPa, the tensile strength is 1716MPa, and the elongation after fracture is 19%.

[0039] Hardness test: Use a Rockwell hardness tester to test the hardness of the sample, measure the hardness values at 5 points in different parts of the sample, and take the average value as the hardness of the sample. The measurement results show that the Rockwell hardness of this sample is HRC48.

[0040] Corrosion resistance testing:

[0041] Simulated Corrosion Environment Test: Select a neutral salt spray environment as the simulated corrosion environment. Place the polished corrosion resistance test sample into a salt spray test chamber and conduct the test according to the standard of GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test temperature is controlled at 35°C ± 2°C, and the salt spray deposition rate is 1.0 mL / (h·80 cm 2 ) - 2.0 mL / (h·80 cm 2 ). When the test proceeds to 72 hours, 144 hours, 216 hours, and 288 hours, take out the samples respectively, observe the corrosion situation on the surface, and record the color, morphology, and distribution of the corrosion products, etc. After 288 hours of the test, it is found that a small amount of corrosion products are generated on the surface of the sample, mainly concentrated at the edges of the sample and some small defects.

[0042] Electrochemical Test: Use the sample as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode to form a three-electrode system. Conduct potentiodynamic polarization curve test and electrochemical impedance spectroscopy test in 3.5% (mass fraction) NaCl solution. The scanning rate of the potentiodynamic polarization curve test is 1 mV / s, and the potential scanning range is ±250 mV relative to the open circuit potential. The frequency range of the electrochemical impedance spectroscopy test is 10 5 Hz - 10 -2 Hz, and the excitation signal is a sine wave with an amplitude of 10 mV. Through the potentiodynamic polarization curve test, the corrosion potential of the sample is -0.5 V (vs. SCE), and the corrosion current density is 1.0×10 - 6 A / cm 2 ; through the analysis of the electrochemical impedance spectroscopy test, the charge transfer resistance of the sample is 1500 Ω·cm 2 , indicating that it has good corrosion resistance.

[0043] Microstructural Analysis:

[0044] Metallographic Analysis: Place the metallographic specimen under a metallographic microscope for observation with a magnification of 500 times. It can be seen that the grain size of the steel is relatively uniform, the average grain size is about 10 μm, and the grain morphology is equiaxed. The phase composition of the steel is mainly ferrite and pearlite, the number of inclusions is small and the distribution is relatively uniform, mainly small oxide inclusions.

[0045] Transmission Electron Microscopy Analysis: Place the transmission electron microscopy specimen under a transmission electron microscope for observation with a magnification of 50000 times. The presence of dislocations can be observed, the dislocation density is moderate, and the grain boundaries are clear. At the same time, some fine second-phase particles are found, with a size of about 10 nm - 50 nm, uniformly distributed in the matrix, and these second-phase particles may have a certain impact on the strength and corrosion resistance of the steel.

[0046] Comprehensive evaluation:

[0047] A comprehensive evaluation model is established, and the mechanical property indexes (yield strength, tensile strength, elongation after fracture, hardness), corrosion resistance indexes (corrosion potential, corrosion current density, charge transfer resistance) and microstructure indexes (grain size, phase composition, inclusion situation, dislocation density, second-phase particle situation) are quantified. According to the importance of different performance indexes in actual use, corresponding weights are assigned. For example, the weight of mechanical property indexes is 0.4, the weight of corrosion resistance indexes is 0.4, and the weight of microstructure indexes is 0.2.

[0048] Each index is scored, and then the comprehensive performance score is calculated according to the weights. After calculation, this cold heading steel for high-strength and corrosion-resistant bolts has good comprehensive performance.

[0049] The embodiments described above are only used to describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An evaluation method for a high-strength corrosion-resistant steel, characterized in that Including: Sample preparation: Cut multiple samples with dimensions of 100mm×50mm×5mm from a batch of cold-heading steel for high-strength and corrosion-resistant bolts to be evaluated; among them, select 4 pieces to be processed into standard tensile specimens with dimensions meeting the requirements of GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; select another 4 pieces for surface grinding and polishing treatment as corrosion resistance test samples; select 2 pieces to be prepared into metallographic specimens and carry out grinding, polishing and etching treatments according to the standard process of metallographic sample preparation; finally, select 1 piece to be prepared into a transmission electron microscope specimen through mechanical thinning and ion thinning treatment steps; Mechanical property testing: Tensile test: Install the prepared tensile specimen on an electronic universal tensile testing machine, set the test temperature at room temperature, and the tensile speed at 4-6mm / min; conduct the tensile test according to the standard test method, and record the load-displacement curve of the specimen; after the test, calculate the mechanical property indexes of yield strength, tensile strength and elongation after fracture according to the curve; Hardness test: Use a Rockwell hardness tester to test the hardness of the sample, measure the hardness values at 5 points in different parts of the sample, and take the average value as the hardness of the sample; Corrosion resistance testing: Simulated corrosion environment test: Select a neutral salt spray environment as the simulated corrosion environment, put the polished corrosion resistance test sample into a salt spray test chamber, and conduct the test according to the standard of GB / T10125-2021 "Artificial atmosphere corrosion test - Salt spray test"; Electrochemical test: Use the sample as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode to form a three-electrode system; conduct potentiodynamic polarization curve test and electrochemical impedance spectroscopy test in a 3.5% (mass fraction) NaCl solution; Microstructure analysis: Metallographic analysis: Observe the metallographic specimen under a metallographic microscope with a magnification of 500 times; Transmission electron microscope analysis: Observe the transmission electron microscope specimen under a transmission electron microscope with a magnification of 50,000 times; Comprehensive evaluation: Establish a comprehensive evaluation model, and quantitatively process the mechanical property indexes, corrosion resistance indexes and microstructure indexes; according to the importance of different performance indexes in actual use, assign corresponding weights; among them: the weight of mechanical property indexes is 0.4, the weight of corrosion resistance indexes is 0.4, and the weight of microstructure indexes is 0.2; Score each index, and then calculate the comprehensive performance score according to the weight.

2. The evaluation method of the high-strength corrosion-resistant steel according to claim 1, characterized in that In the corrosion resistance test, the test temperature is controlled at 35°C ± 2°C, and the salt spray deposition rate is 1.0 mL / (h·80 cm 2 ) - 2.0 mL / (h·80 cm 2 ).

3. The evaluation method of the high-strength corrosion-resistant steel according to claim 2, characterized in that, When the test reaches 72 hours, 144 hours, 216 hours and 288 hours, take out the samples respectively, observe the corrosion situation on the surface, and record the color, morphology and distribution of the corrosion products.

4. The evaluation method of the high-strength corrosion-resistant steel according to claim 1, characterized in that The said electrochemical test: The scanning speed of the potentiodynamic polarization curve test is 1mV / s, and the potential scanning range is ±250mV relative to the open circuit potential.

5. The evaluation method of the high-strength corrosion-resistant steel according to claim 4, characterized in that, The frequency range of the electrochemical impedance spectroscopy test is from 10 5 Hz to 10- 2 Hz, and the excitation signal is a sine wave with an amplitude of 10 mV.

6. The evaluation method of the high-strength corrosion-resistant steel according to claim 1, characterized in that, This evaluation method has good operability and repeatability.

7. The evaluation method of the high-strength corrosion-resistant steel according to claim 1, characterized in that, Each test method adopts standard test equipment and test methods, and the test results are reliable, which can provide a scientific and objective evaluation basis for the production and application of high-strength corrosion-resistant steel.