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2022 Vol. 40 No. 3
Published: 2022-06-15
1
ZHANG Guocai,XIE Xiaorong
Experimental study on detection depth of alternating
current fluorescent magnetic powder
Magnetic powder detection is an important method to detect the welding seam and its raw materials of ferromagnetic pressure equipment as well as the surface and near surface defects of machined parts. To investigate the difference of magnetic powder detection depth when three types of alternating currents (including sine wave, square wave, and triangular wave) were used at different frequencies, the experimental detection system of artificial slot and variable frequency alternating current magnetic yoke with different buried depths was designed and manufactured. The difference of detection depth of three kinds of variable frequency alternating current electromagnetic powder was explored under the same fluorescent magnetic powder detection conditions. The results showed that compared to the sine wave and triangular wave, the square wave had a deeper detection depth and higher detection sensitivity during the detection of nonopen defects near surface with certain burial depth. Therefore, the square wave alternating current could be used as a useful complement to exciting current for magnetic powder detection.
2022 Vol. 40 (3): 1-8 [
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9
LIU Yanjie,YU Tongxin,SHU Jintao,LIU Yi,FAN Liuming,AN Tanglin
Research of high-throughput hardness tester
In order to shorten the development cycle of new materials and reduce the R&D cost, a high-throughput hardness tester with 32 stations was developed by designing the related machine control system and software based on the characteristics and mechanism of hardness test, thus realizing the high-throughput characterization of mechanical properties of materials. The automatic dotting, automatic recording and automatic switching of samples could be realized in hardness testing. The testing time of the developed high-throughput hardness tester was only 1/3 of the common manual hardness tester, which significantly enhanced the characterization rate of material property. The developed high-throughput hardness tester was applied for the testing of standard samples with different hardness, stainless samples, and high-entropy alloy samples. The results showed that the high-throughput tester hardness was suited for the material with hardness greater than 200HV (∽19 HRC). The indication error and indication repeatability were -0.2HRC and 0.764HRC, respectively. The measuring accuracy could meet the requirements of hardness tester, and the measuring results were reliable.
2022 Vol. 40 (3): 9-12 [
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13
YU Daojun,YANG Yanhui,CHEN Ruojin
Research on fatigue testing and processing
methods of data reliability
In engineering testing, researchers usually pay much attention to the specific fatigue life or fatigue limit of materials. However, the reliability and accuracy analysis of fatigue test data should be also brought to the forefront. In the study, the axial tension and compression fatigue tests of 40Cr steel were performed, and the results were analyzed statistically. The data processing methods were mainly studied, including the method of discriminating and rejecting suspicious data, the data normality testing, the influence of the quantity of sample on the test results, the comparison and analysis of fatigue test data of different states of sample processing and different testing machines. The results showed that the data processing by statistical method could reduce the influence of various interference factors in fatigue testing and effectively improve the reliability of fatigue testing results.
2022 Vol. 40 (3): 13-17 [
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18
ZHAO Gang
Application of EBSD technology on microstructure
characterization of X80 grith welding heat affected zone
The optical microscopy (OM), scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) technology were used to systematically characterized and contrastively analyzed the size, distribution, morphology and crystallographic characteristics of the M/A constituent microstructure in the intercritical coarse grain zone of X80 grith heat affected zone. The results showed that the M/A constituent was distributed along the parent austenite grain boundary in the form of island chain in the intercritical coarse grain zone of X80 grith heat affected zone. The island chain M/A constituent was surrounded by the high angle grain boundary, and a stress field generated around it. The OM and SEM could only present the size, distribution and morphology of this M/A constituent in matrix. In contrast, the use of the grain boundary map and band slope map of EBSD could further characterize the interface information and stress field distribution of this island-type M/A constituent. Moreover, compared with the inverse pole figure map and band contrast map of EBSD, the band slope map was more suitable for the characterization of the M/A island chain structure distributed along grain boundaries.
2022 Vol. 40 (3): 18-22 [
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23
YANG Dong，LI Chao
Analysis of microstructure and property of welded joint on S355NL
hot rolled H-shaped steel with resistance to low temperature
SMAW welding process tests of S355NL European standard HE1000B large size hot rolled H-typed steel with resistance to low temperature were carried out. The microstructure and property of welded joint were tested and analyzed. The results showed that the tensile strength of welded joint of S355NL hot rolled H-typed steel was higher than 514 MPa. The average value of impact absorbing energy at -40 ℃ was more than 83 J. The hardness in heat affected zone was less than 209HV10. The microstructure was composed of ferrite, pearlite and granular bainite with different morphologies. All these properties could meet the requirements of the standard.
2022 Vol. 40 (3): 23-26 [
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27
GU Xiurui，ZHANG Peng，SUN Xiaoran，SUN Jianghua
Display method of original austenite grain
boundary of 18Ni maraging steel
The etchants with different composition and concentration were prepared at room temperature. The display method of original austenite grain boundary of 18Ni maraging steel after treatment by chemical etching at different temperatures was studied using optical microscope(Zeiss).The experimental results showed that only the metallographic microstructure of 18Ni maraging steel could be obtained when the etchant with strong corrosivity and high concentration was adopted. However, as 4% (volume fraction) nitric acid alcohol solution was used for chemical etching, the original austenite grain boundaries of the 18Ni maraging steel samples could be clearly observed after solution and air cooling at 800-925 ℃. Moreover, the grain size grades could be evaluated accurately.
2022 Vol. 40 (3): 27-30 [
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31
YU Lei,YANG Chun,LIU Ming,XIE Jinpeng,ZHONG Zhenqian,ZHANG Zhuo
Formation analysis of white spot imperfections on
cold rolling 1Cr18Ni9Ti stainless steel pipes
Many white spot imperfections were observed on the inner surface of 1Cr18Ni9Ti stainless-steel pipes produced by cold rolling process, so that the products could not be delivered normally. In order to confirm the reasons for the formation of white spots, the surface morphology, metallographic structure, grain size and micro area composition of this batch of steel pipes were analyzed and detected using scanning electron microscopy + energy disperse spectroscopy, metallographic microscope, and laser-induced breakdown spectroscopy. The results showed that the surface carburization occurred on both inner and outer surface of the pipe, and the carburization in white spot imperfection was much more serious than other areas. The severe intergranular corrosion was caused during pickling and passivating. Many grains on the surface were dropped off, deteriorating the roughness on partial surface, and forming white spot imperfections. The inadequate degreasing on pipe surface caused carburization in heat treatment process, which was the major reason for white spot imperfections.
2022 Vol. 40 (3): 31-34 [
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35
JIN Xinyan，BI Wenzhen，WANG Li
Application of grain characteristic in analysis of
surface defects on automotive steel sheets
A variety of surface defects on continuous annealed or galvanized automotive steel sheets such as scratches, dents, coating pinhole, stamping orange peel, stamping streak and streaky mark were studied. The crystalline grains located in defects were observed by scanning electron microscope(SEM) and optical microscope(OM), and four types of grain characteristics were found including fine grains, coarse grains, non-recrystallized grains, and deformed grains. The results indicated that the grain characteristics at the defect position could be utilized to further determine the defect origination and reduce the scope of inspection. For the scratches or dents originated from the continuous annealing line, the local deformed grains indicated that the defect may originate in the cooling section. The local coarse grains suggested a strain-induced secondary recrystallization occurred in the ends of heating section or in the beginning of soaking section. The local fine grains meant that the defect probably occurred in the heating section, cleaning section or it might be brought by the as received cold rolled steel sheet.
2022 Vol. 40 (3): 35-44 [
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45
GUO Feng
Cause analysis of layered fracture in tensile test of Q550D steel
The microstructure analysis of typical layered fracture in tensile test of low alloy high strength steel Q550D was conducted by means of optical microscope(OM) and scanning electron microscopy(SEM). The results showed that the microstructure was composed of bainite, ferrite and granular carbide with certain zonal distribution. In the process of tensile deformation of sample, the dislocation pileup located at large carbide particles led to the origination of microcracks and pores. When the necking down formation occurred on the sample, the crack propagation was caused due to the tensile stress which perpendicular to the tensile axis. The zonal distribution of microstructure further promoted the crack propagation, and the macroscopic layered fracture was finally formed.
2022 Vol. 40 (3): 45-48 [
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49
WEN Yongyue
Cause analysis of unqualified elongation of
track shoe and improvement measures
After heat treatment of 25MnB track shoe, the sample with unqualified elongation was comprehensively analyzed. The chemical composition was detected using direct reading spectrometer. The gas composition including N, H and O was detected using oxygen-nitrogen-hydrogen analyzer. The metallographic structure and non-metallic inclusion levels were inspected using metallographic microscope. The fracture analysis of sample was conducted using scanning electron microscopy(SEM). It was found that the cooling rate of track shoe was slow in the core of grouser, leading to the formation of nonuniform structure. Moreover, the presence of ferrite led to the unqualified elongation. By changing the cooling water nozzle to increase the cooling water flow rate, the cooling rate of track shoe quenching was accelerated. Thereby the generated tempered martensite with uniform structure was formed, and the elongation of track shoe could meet the requirements of the enterprise standard.
2022 Vol. 40 (3): 49-53 [
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54
WANG Yanfeng，XIE Bo,LV Qing,ZHANG Weihao,FENG Yan2,BAO Nan
Combing of current standard of high carbon chromium bearing steel and comparison of GCr15 standards
The current standards for high carbon chromium bearing steel were combed. The standard number, name, category, application scope and standard system category were listed. Meanwhile, the internal control standard of high carbon chromium bearing steel (GCr15 and GCr15PGI) with similar grade and composition was selected for the comparison with GB/T 18254-2016 and ISO 683-17 taking a steel enterprise as an example. It explained the requirements of different standards on carbides, inclusion, and chemical composition of GCr15 and other bearing steel with similar composition. It was found that the requirements of GB/T 18254-2016 were stricter than ISO 683-17, and internal control standard of enterprise had further requirements based on GB/T 18254-2016.
2022 Vol. 40 (3): 54-61 [
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62
ZHU Guifeng,ZHENG Ziqin,JIAO Zhongbin,LIANG Jingheng,LI Shuai,WANG Yan
Study on maximum allowable tube voltage for
AZ ceramic X-ray digital radiography
Digital radiography (DR) detection technology was used to detect the AZ ceramic pieces (toughening of Al2O3 by ZrO2) with thickness of 6, 8, 10, 12 mm, respectively. The maximum allowable tube voltage was studied by analyzing the indexes including image resolution ratio, sensitivity, and normalized signal to noise ratio. The results showed that when the exposure requirement was not less than 0.5 mA·s, the maximum allowable tube voltage of 6, 8, 10 and 12 mm-thickness AZ ceramic by DR detection was 80, 95, 105 and 115 kV, respectively. For the digital array detector, the increase of signal to noise ratio caused by the increase of tube voltage had a greater influence on the sensitivity than the decrease of contrast. Under the premise that the tube voltage could penetrate the workpiece, the detection sensitivity would not change significantly with the increase of tube voltage. When the tube voltage was below 190 kV and the normalized signal to noise ratio was greater than 120, the image quality meeting the B-level detection technology of GB/T 35388—2017 standard could be obtained.
2022 Vol. 40 (3): 62-67 [
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68
Xiaoyang,LIU Lanzhou,ZHAO Renwei,LI Chunjian
Discussion on direct current electric potential
difference method in GB/T 21143-2014
Direct current electric potential difference (DCEPD) method is one of recommended methods in GB/T 21143-2014 for the determination of quasistatic fracture toughness. In some cases, it can be used for the auxiliary measurement of sample which is inconvenient to be tested by the common compliance method. To verify the actual effect of DCEPD method in fracture toughness measurement, the fracture toughness of sample was tested according to the DCEPD method specified in standard, and the measuring results were compared with the compliance method. It was found that the Method 1 in GB/T 21143—2014 (i.e., indirect measurement method) was more convenient and accurate to measure the length of cracks, and the results were consistent with those obtained by the compliance method. For the Method 2 (i.e., direct measurement method), it was not easy to control the measurement accuracy of cracks in actual test, and both the accuracy and convenience were inferior to the Method 1.
2022 Vol. 40 (3): 68-71 [
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