表面技术2023，Vol.52Issue(12)：399-407,9.DOI:10.16490/j.cnki.issn.1001-3660.2023.12.034
环境介质对ASTM A572 Gr65钢疲劳行为的影响
Effect of Environmental Factors on Fatigue Behavior of ASTM A572 Gr65 Steel
摘要
Abstract
In the actual service environment,the low alloy and high strength structural steel will be affected by the cyclic alternating load and corrosion damage caused by the corrosive medium,so that the service time of structural steel will be significantly shortened.The work aims to study the fatigue strength and fracture mechanism of ASTM A572 Gr65 low alloy high strength structural steel under different environments.According to the standard,ASTM A572 Gr65 structural steel was made into standard samples with a length of 52 mm.Rotary bending fatigue tests were carried out on QBWP-6000 rotary bending fatigue test machine under the environment of laboratory,deionized water and 3.5%NaCl solution,and the loading frequency was 100 Hz.The fixed stress ratio of the rotary bending fatigue testing machine was R=-1.When the sample failure or loading times reached 107 times,the test was stopped and the fatigue test value was recorded.In origin software,the experimental values under different strength were fitted to obtain the fatigue strength under this environment,and the fatigue strength of structural steel under different environments was compared.The sample was cut with wire cutting and the cross section was polished,and corroded with 4%nitrate alcohol solution.The microstructure of the fracture was observed by metallography microscope(CX40M)and scanning electron microscope(ZEISS Gemini 300).The energy spectrum of each corrosion fatigue fracture was collected by energy spectrometer,and the components were analyzed.Then,the changes of microhardness values near the fracture were measured by microhardness tester(ZHVST-1000C)to explore the fatigue failure mechanism under different environments. The fatigue strength of ASTM A572 Gr65 steel in the laboratory environment was 380 MPa,but the fatigue strength under deionized water and NaCl solution was 280 MPa and 80 MPa,which decreased by 26.3%and 78.9%,respectively.After fatigue failure,the grain of the sample near the fracture was obviously refined and some of the grains were elongated,while the microstructure of the base material far away from the fracture was uniform.The microhardness value near the fracture increased by about 10.4HV0.5 due to dislocation movement.With the increase of distance,the hardness value gradually tended to be the hardness value of the base material,and the change distance was about 6 mm.After the addition of deionized water and NaCl solution,a galvanic cell was formed on the surface of structural steel in fatigue test.The area with high stress is the anode,and the place with low stress is the galvanic cell cathode,which accelerated the formation of corrosion pits.Due to the loss of electrons,the anode of the galvanic cell generated Fe2+,which is oxidized into Fe3+ and initial oxide FeOOH with the dissolved oxygen in the air at the cathode,and most of them exist in the depression.In the case of NaCl solution corrosion,the main composition of the precipitate is β-FeOOH formed by hydrolysis of Fe3+.Compared with that under the laboratory environment,the fatigue fracture surface partition is not obvious,there are oxidation corrosion products and secondary cracks on the fracture surface,and the transient fault zone is transferred to the middle position of the specimen fracture,indicating that the crack propagation is carried out from all directions simultaneously.After addition of medium,corrosion pits are formed on the surface of structural steel due to electrochemical action and stress concentration leads to many microcracks under the action of continuous rotating load.In the laboratory environment,the single crack source will be transformed into multiple crack sources.In addition,the hydrogen embrittlement at the crack tip will accelerate the formation of fatigue cracks and damage fracture.关键词
ASTM A572 Gr65低合金结构钢/旋转弯曲疲劳/氧化腐蚀/去离子水/NaCl水溶液/疲劳强度Key words
ASTM A572 Gr65 low alloy structural steel/rotary bending fatigue/oxidation and corrosion/deionized water/NaCl solution/fatigue strength分类
矿业与冶金引用本文复制引用
胡张翊,张红霞,闫志峰,雷鹏飞,赵庆鲁,魏湛橙..环境介质对ASTM A572 Gr65钢疲劳行为的影响[J].表面技术,2023,52(12):399-407,9.基金项目
山西省自然科学基金(RD2000001936)Natural Science Foundation of Shanxi Province(RD2000001936) （RD2000001936）
