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2024 Vol. 42 No. 1
Published: 2024-02-15
Test and Research
Measuring Technology
Defect Analysis
Subject Discussion
Test and Research
1
NIU Tong, ZHANG Na, XIONG Xilin
Corrosion behavior characterization of 7050 aluminum alloy based on in-situ observation and machine learning
The in-situ observation of corrosion behavior of T7451 and as-cast 7050 aluminum alloys in 3.5% NaCl solution was performed. The corrosion morphology feature and precipitated phase composition were analyzed by scanning electron microscopy (SEM), and the relationship between grain orientation and corrosion behavior was analyzed statistically by combining with EBSD. Based on 196 pieces of historical literature data, the importance ranking of corrosion behavior characteristics were conducted by Pearson correlation screening and Backforward algorithm. It was found that the corrosion behavior of 7050 aluminum alloy started around the precipitated phase, and the corrosion depth and range increased with time, which was accompanied with crack initiation. Among them, the precipitated phases were most distributed in the crystal faces of <112>, <114> and <324>. Potentiodynamic scan showed that the self-corrosion current density increased with the precipitated phase density. In addition, the importance ranking of SEM and machine learning showed that Cu, Ti, Fe and Mg all appeared in the precipitated phase, and their influence on the corrosion behavior was most significant. This study could effectively guide the corrosion resistance design of aluminum alloys.
2024 Vol. 42 (1): 1-7 [
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HAN Qing, JING Fengwei, XU Wenlong, WANG Jiangwei, WANG Peng
Deformation resistance model and experimental analysis of Q235 steel
Gleeble-2000 thermal simulation test machine was used to conduct the isothermal thermocompression deformation tests on Q235 steel. In order to ensure the accuracy of test data and the rationality of experiments, the selection of insulation time and repeatability tests were carried out. The insulation time was reasonably determined and the instrument accuracy was verified. The effects of different deformation conditions (deformation temperature, deformation degree, and deformation rate) on deformation resistance were investigated. The deformation resistance model was reasonably selected, and the model parameters were regressed using the experimental data. Through on-site data verification, the established mathematical model for deformation resistance exhibited good prediction accuracy.
2024 Vol. 42 (1): 8-13 [
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NIE Xianghui, YANG Zhoujin, ZHANG Jilong, ZHANG Hui, REN Tao
In-situ tensile test of HFW weld under scanning electron microscope
The in-situ tensile tests of HFW weld were conducted under scanning electron microscope (SEM) to observe the morphology changes at different positions. During the test, the deformation of sample mainly occurred in the heat affected zone. A large number of slip and necking deformation were generated in the heat affected zone. The nucleation of cracks occurred in the heat affected zone and expanded perpendicular to the tensile direction until to fracture. The fracture of HFW weld sample belonged to ductile fracture, and the main cracks were transgranular type. The formation process included the elastic elongation of sample, intragranular slip deformation, necking deformation, slip step formation and sample cracking. Under the interaction of slip deformation and necking, the slip deformation was accumulated continuously, which was the main reason for crack generation and specimen fracture.
2024 Vol. 42 (1): 14-21 [
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LIU Ajiao, YAO Huiqin, WANG Jingzhong, CHEN Xiaoshan
Discussion about continuous cooling transformation behavior of Q345qNH weathering bridge steel
The Q345qNH weathering bridge steel was investigated. The phase transition temperature and time of Q345qNH weathering bridge steel containing Nb and V at different cooling rates were measured using Formastor-FⅡ phase transformation tester. The metallographic microstructure, hardness and transformation process were analyzed, and the continuous cooling transformation (CCT) curve of Q345qNH steel was created. The results showed that the microstructure of tested steel was mainly composed of pearlite and ferrite when the cooling rate was 0.3-2 ℃/s. As the cooling rate was 2-3 ℃/s, the microstructure was composed of uniform pearlite + ferrite + a small amount of granular bainite. When the cooling rate was 3-20 ℃/s, the microstructure of tested steel was mainly composed of uniform ferrite matrix + uniform granular bainite. When the cooling rate was further increased to 20-50 ℃/s, the lath bainite appeared in the microstructure, but the ferrite and granular bainite were dominant. The relationship between hardness and microstructure could be divided into three stages: the stage of ferrite refined crystalline strengthening, the stage of granular bainite incremental strengthening, and the stage of bainite strip morphology strengthening.
2024 Vol. 42 (1): 22-27 [
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LIU Yang, LU Qianqian, GU Hairong, MA Cong, CHEN Zhong, TIAN Zhijun
Effect of coiling temperature on microstructure and properties of 800 MPa-level high hole expansion steel
The microstructure, mechanical property and hole expansion property of 800 MPa-level hot-rolled acid-pickled hole expansion steel at different coiling temperatures were analyzed by optical microscope, scanning electron microscope, tensile tester and hole punching expansion tester. The results showed that the microstructure was mainly composed of ferrite + bainite when the coiling temperature was 450-600 ℃. With the increase of coiling temperature, the ferrite grains increased, while the volume fraction of bainite decreased gradually. The yield strength and tensile strength of the material were improved, the elongation had no significant change, and the hole expansion rate was reduced obviously. With overall consideration, when the coiling temperature was 450-500 ℃, the tensile strength was higher than 780 MPa, and the hole expansion rate was above 50%.
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Measuring Technology
32
LI Chunhui, ZHANG Congyi, WANG Shuo, CHEN Jieming, LIU Pan, ZHANG Xinyao
Determination of phase transformation point of TA24 alloy by composition calculating method and differential scanning calorimetry
The β transformation temperatures of 11 pieces of TA24 near α titanium alloy samples in 4 specifications were measured by composition calculating method and differential scanning calorimetry. In the composition calculating method, the β transformation temperature of titanium alloy was determined according to the contribution rate of alloying elements and impurity elements to the phase transformation temperature. In the differential scanning calorimetry, the β transformation temperature was measured based on the heat change of titanium alloy during phase transition. The results showed that under the condition of 95% confidence, the deviation between methods was (-1.3±5.8) ℃, and the absolute value of deviation was (2.4 ± 3.9) ℃. The measurement results of composition calculating method and differential scanning calorimetry method were consistent, and the deviation was between -6.9 ℃ and 2.4 ℃, which were both less than the allowable deviation (±8 ℃) of two parallel tests in the laboratory specified by HB 6623.1-1992 and HB 6623.2-1992. The composition calculating method could be used as a convenient and effective method to quickly predict the β transformation temperature of TA24 titanium alloy.
2024 Vol. 42 (1): 32-36 [
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Defect Analysis
37
SUN Qian, XU Ruiliang, YIN Haiyuan, LI Cheng, ZHU Gaofeng, LIU Shanshan
Cause analysis of crack in flash butt welding of low alloy steel square pipe
Aiming at the transverse welding crack problem of Q355B steel strip (thickness of 7.5 mm) during the preparation of square pipe by welding, the composition analysis, mechanical property inspection and metallographic structure inspection were conducted. The results showed that the structure of base metal steel strip was composed of ferrite + pearlite + very small amount of bainite, which could meet the standard requirements. The crack initiation position of the square tube was in the heat-affected zone of the weld. The metal grains were distorted at the end of crack, which belonged to the extension morphology after stress crack tearing. The microstructure was the Widmannstatten structure with extremely poor plastic toughness, and there were large-size cluster inclusions at the weld which severely cut the continuity of the matrix. After comprehensive analysis, it was believed that the high welding power and too fast cooling speed led to the formation of coarse Widmannstatten structure at the weld, which seriously reduced the ductility and toughness. Combined with the impurity discharge of inclusions such as Si and Mn oxides in the weld pool, the continuity of the weld was destroyed. Under the action of tensile stress in the subsequent correction process, the crack extension was formed, which was the main reason to cause transverse cracks after welding. Such kind of problems could be avoided by optimizing the flash butt welding process and reasonably controlling the austenite grain size in the weld.
2024 Vol. 42 (1): 37-43 [
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ZHANG Mengjiu, XIE Aijun, PANG Ningning, WANG Xuzhen, WANG Kui, WANG Junjie
Effect of grain boundary oxidation on fatigue strength of 50CrV4 chain plate
50CrV4 is a high-quality Cr-Mn-V series alloy spring steel. After isothermal quenching and tempering heat treatment, the duplex structure of lower bainite + tempered martensite + a small amount of retained austenite + dispersed granular carbide can be obtained. After heat treatment, the automotive timing toothed chain plate made of 50CrV4 strip steel can ensure high fatigue strength, and meanwhile, possess good wear resistance. However, due to the existence of Cr, Mn and V in 50CrV4, the undercooled austenite of 50CrV4 is relatively stable. During hot rolling, the cooling cannot be too fast, otherwise the martensite and bainite are prone to occur, leading to cracking in the process of coiling. Therefore, the residence time in the high temperature zone is relatively long, and there is inevitably grain boundary oxidation at different levels. 50CrV4 strips with different grain boundary oxidation levels were studied. The grain boundary oxidation depth was detected. Then the strips were punched to chain plates, which were prepared to the finished chains under same heat treatment conditions. The tension and fatigue strength of chains were measured, and the effects of different degrees of grain boundary oxidation were obtained. Through comparative analysis, it was found that the longitudinal grain boundary oxidation could cause the decrease of tensile strength and fatigue strength. Moreover, the transverse grain boundary oxidation had a severer impact on the tensile strength than the longitudinal grain boundary oxidation. The fatigue strength of the chains would be seriously reduced.
2024 Vol. 42 (1): 44-49 [
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50
GUO Wenjing
Analysis of bending cracking of Q235B steel plate and control measures
The problem of serious cracking was observed during bending test of Q235B hot-rolled coil produced by one factory. The cracking position and non-cracking position of steel plate were compared and analyzed by means of optical microscope, scanning electron microscope and energy disperse spectroscopy. The results showed that there were obvious inclusions in the material, which could induce the formation of cracks. Moreover, the content of manganese sulfide inclusions in the material was high. After adjusting the production process and controlling the content of manganese sulfide inclusions, the problem of bending cracking could be significantly improved. The recurrence of this problem was avoided.
2024 Vol. 42 (1): 50-53 [
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WANG Shiru, LI Jiandong, CHEN Yihui, SU Daiping
Cause analysis of pipe explosion of boiler superheater
The pipe explosion of superheater pipeline for a boiler in one self-owned power plant occurred. The exploded pipes and adjacent sections were analyzed by macroscopic inspection, chemical composition, hardness test and metallographic inspection. The results showed that the cracking was due to the long-term high temperature operation of pipes. In addition, the exploded pipes were subjected to overtemperature before explosion. The strength of steel was reduced sharply at high temperature, leading to significant plastic deformation of the pipes. Due to the expansion of the diameter and the thinning of the wall, the rupture and bursting of pipes occurred. The adjacent pipe sections were composed of massive ferrite and carbide particles with only a few traces of bainite range. After the aggregation and growth of carbides, most of them were granularly distributed at grain boundaries and within grains. The metallographic test results showed that the spheroidization grade of the material was 4, and the material had already entered the last stage of life.
2024 Vol. 42 (1): 54-57 [
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Subject Discussion
58
ZHA Yanqing, PAN Shenglin, JIANG Yixin, ZHANG Xiu, FENG Yahui, LI Haimin
Discussion on attribute identification of one case of imported copper-containing solid waste
In recent years, there have been some cases of smuggling imported copper-containing waste using the name of copper concentrate. The traditional detection methods have certain limitations in the identification of such materials. In this paper, the attribute identification of one batch of imported copper-containing solid waste using the declared name of copper concentrate was studied by means of X-ray diffraction spectroscopy (XRD), X-ray fluorescence spectrometry (XRF), ultra depth of field microscopy, and scanning electron microscopy. The source of the samples was determined, which provided a scientific basis for the customs supervision and resource utilization.
2024 Vol. 42 (1): 58-62 [
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