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2014 Vol. 32 No. 2
Published: 2014-04-15
Test and Research
Measuring Technology
Defect Analysis
Subject Discussion
Test and Research
1
ZHANG Zhan-pu,NIU Xu-fei
Annealing Process and Annealing Microstructure of HYRH12 Steel
The different annealing processes and annealing microstructure of HYRH12 steel were discussed, the abnormal microstructure of roll blank with spheroidizing annealing was analyzed. The annealing microstructure was contrasted with NADCA#207 standard.
2014 Vol. 32 (2): 1-5 [
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6
SUN Ying,YUAN Xu
Research of the Cleanness of Ultra-High Strength Steels Produced by Different Metallurgy Processes
The cleanness of ultra-high strength steels produced by vacuum arc remelting (VAR) and electroslag remelting (ESR) were analyzed. The content of nonmetallic inclusion element and the types, volume fraction and characteristic parameters of nonmetallic inclusions were obtained by chemical analysis, phase analysis, quantitative metallography and SEM .The results show that the content of S, P, O and N of VAR steel were lower than ESR steel. The mean free paths of the larger stripy MnS in ESR steel were relatively small. The mean free paths of the fine spherical MnS in VAR steel were relatively large. The cleanness of VAR steel was higher than ESR steel based on the fact of nonmetallic inclusion element and nonmetallic inclusions.
2014 Vol. 32 (2): 6-9 [
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10
TIAN Hao,FU Zhi-bin,JIANG Jin-xing,LI Jun,FAN Lei,WANG Qing-feng
Measurement and Analysis of SHCCT Curve for X90 Pipeline Steel
For revealing the effect of t8/5 on microstructure and hardness of X90 pipeline steel in welding heat affected zone (HAZ) , the thermal cycles process at different t8/5 (10～300 s) were simulated by a Gleeble-3500 simulator. The SHCCT curve was established through analysis of thermal expansion curve and microstructure. For each sample, the microstructure was observed by optical microscopy (OM) and transmission electron microscope (TEM), and the vickers hardness was measured. The results show that with the t8/5 decreasing, the starting and finishing temperatures for phase transition in HAZ of experimental steel decreased. The dominated microstructure changed gradually from the granular bainite (GB) to the lath bainite (LB). The prior austenite grain and bainitic ferrite were obviously refined. The variation in the microstructure of HAZ caused an increasing hardness value. The t8/5 of 10～20 s is recommended for the girth welding of this steel.
2014 Vol. 32 (2): 10-14 [
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15
WU Qing-song,ZHU Hong-chuan,WANG Li-xin,LEI Ze-hong
Discussion on Testing Method for Secondary Working Embrittlement of Steel Sheets
By using IF steel and high strength IF steel as testing materials，some problems in current secondary working embrittlement testing were discussed. It is noticed that die clearance affects the authenticity of testing results, and coaxiality seriously affects the validity of testing results. However there are no requirements about die clearance and coaxiality between cup sample and hammer in current standard.
2014 Vol. 32 (2): 15-17 [
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18
WANG Ai-min,CHEN Hao-wei,BAI Guang-hou,XU Rong-chang
Determination and Analysis of Annealing Process of Cored Welding Ribbon Steel
The grains of flux cored wire strip after cold rolling is deformed seriously, which affects the performance of the steel. According to the special requirements for properties of cold rolled strip in production of flux-cored wire the annealing process of cold rolled strip was formulated, the microstructure and mechanical properties of the rolled strip after annealing were studied. Result shows that the microstructure of the strip steel after annealing was uniform equiaxed grains, the yield strength was more than 180 MPa, elongation was greater than 43% and the average hardening index was 0.23, which could fully meet the requirements of flux-cored wire production.
2014 Vol. 32 (2): 18-21 [
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22
HE Xi-kou,LIU Zheng-dong,LIN Zhao-jie
Effect of Aluminum on CCT Curve of 508-3 RPV Steel
The phase transformation temperatures of two comparative tested steels with different Al content were measured by using Formastor-FⅡphase transformation instrument. Subsequently, the microstructure of the samples at different cooling rate was observed by optical microscopy, and the hardness was tested in a Vickers hardness tester. According to the test results, the complete CCT curve was drawn. The results show that Al could lower the critical cooling rate of the martensite transformation and start temperature of bainite transformation, and delay the ferrite/pearlite transformation. The CCT curve of 508-3 steel with high Al content shifted to the right so that the hardenability of 508-3 steel was increased.
2014 Vol. 32 (2): 22-24 [
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Measuring Technology
25
MA Feng-chun
Recognition Method of Slab Surface Defect Based on KPCA
Existed kernel methods were introduced and studied, and a new kernel function was presented and applied to feature extraction of slab surface defects. SVM was used to classify the images. Experimental results show that the feature extracted by new kernel function gets the highest classification rate of 91.55%.
2014 Vol. 32 (2): 25-27 [
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28
KANG Hao,HAN Zong-tao,ZHAO Xian-ming,WU Di
A Method of Measuring the Average Pearlite Interlamellar Spacing in Steel Using Electron Probe Microanalysis
Taking the typical pearlitic steel U75V as an example, a method of measuring the average pearlitic interlamellar spacing in steel by electron probe microanalysis (EPMA) was introduced. Choosing the scanning path as perpendicular to pearlite interlamellar as possible, the curve of C content alternated as “wave trough” and “wave crest”. The distance between two "wave trough" or two "ware crest" is one pearlitic interlamellar spacing. The method is direct, simple, and the measurement of pearlite interlamellar spacing is close to the true value.
2014 Vol. 32 (2): 28-30 [
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Defect Analysis
31
YANG Jian-ping,QIN Xiao-mei,ZHAO Ya-juan,TIAN Li,LI Xue-jie
Analysis on Cracking of the Tensile Specimen Surface of NM400 Sear-Resistant Steel
To the problem of cracking of the tensile specimen surface of NM400 wear-resistant steel after tensile deformation, the fracture, surface cracks and microstructure were investigated by optical microscopy, electron scanning microscopy and energy spectroscopy. The results show that the surface cracking resulted from the process between rolling and quenching, which may be the cooling process on the cooling bed after rolling or flame cutting process. Some inclusions distributed at grain boundary weakening the boundary, and under the effect of internal stress, the inclusions became cracking source. During the subsequent process of quenching, the crack appears the high temperature oxidation and slight decarburization.
2014 Vol. 32 (2): 31-35 [
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36
YANG Jin-ling,PENG Qi-chun
Analysis of Surface Linear Defects of Cold-Rolled Galvanized Strip
Linear defect is one of the common defects of galvanized strip. The formation mechanism of linear defect is analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results indicate that Al2O3 inclusion and mold powder involve in ingot in steel-making process, resulting in scratches or rough spots on surface of cold rolled strip. Linear defects are formed at the places of scratches or cracks during hot dip galvanizing. Corresponding measures are put forward to reduce defects after comprehensive consideration of steelmaking, rolling and galvanized process.
2014 Vol. 32 (2): 36-39 [
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GONG Min-li
Failure Analysis on Fracture of 20CrMnTi Cam Shaft
During the experiment in the host plant, big and small key slot of 20CrMnTi cam shaft were fractured. Chemical analysis on fracture position of cam shaft, optical microscopy and scanning electron microscopy analysis on the microstructure and crack shape, hardness test of the cam shaft big key slot cross section and small key slot cross section were carried out. The results show that the chemical composition, microstructure and hardness are all in accordance with the requirements of the related technical standard. Big crack originated from the slot bottom, accumulated and led to final fracture. Obvious wear occurred at the position of conical degree, indicating the maximum loading there. Small crack originated from the slot bottom and no significant expansion area occured, so it belongs to the instantaneous fracture. At both of the keyway bottoms there are no obvious chamfer, which increases the tendency of stress concentration, and thus results into the fracture of cam shaft.
2014 Vol. 32 (2): 44-46 [
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47
ZHANG Yun-xiang,LIU Ping-yuan,PENG Qi-chun,WANG Qin,GUI Zhou,LI Wei
Analysis on Tensile Fracture With Centerline De-Lamination Defect of Ti-Bearing High Strengthen Steel Strip
Serious centerline de-lamination fractures appeared in hot rolled strip of high-strength structural steel HG70C during tensile test. Specimens under different stress levels were designed for comparison with normal specimen. The formation of centerline cracks of the test specimens was studies by optical microscopy and scanning electron microscopy with energy dispersive spectroscopy. Progressive failure for centerline lamination fracture was analyzed; furthermore the cracking mechanism of de-lamination tensile fracture was described. The results indicated that the pearlite colonies of centerline segregation banding were not the main reason of centerline lamellar fracture. The micro-crack was observed around the inclusions which existed in abundance in the center area. With increasing tensile stress, the micro-cracks coalesced, eventually extended to lamellar cleavage fracture.
2014 Vol. 32 (2): 47-50 [
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51
DUAN Yuan-fu,WANG Li-hui
Analysis of Gland Crack
To the problem of gland cracks, the fracture was analyzed by chemical composition analysis, hardness test, metallographic examination, scanning electron microscopy analysis and other measure. The results show that the gland tissue is abnormal and there are a large number of small sulfides in raw material. The cause of cracking is transformation of temper brittleness by analyzing production process and fracture morphology.
2014 Vol. 32 (2): 51-53 [
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Subject Discussion
54
YU Zhao-bin，WU Qian-ying，YANG Lei-gang，YANG Xin-sheng，ZHU Tie-zhu
Improvement of Material Testing Machine for New National Standard
The realization about the 《Metallic Materials-Tensile Testing-Part1:Method of Test at Room Temperature》 was introduced such as the zero setting, the method of clamping, test rate and control methods setting. Based on the deep understanding of the new standard, the functions of a test machine developed by a international company were expounded. The new function of strain rate control realized the authentic strain rate control that many other test machines can’t realize. The test results show that the strain rate control of the test machine was very accurate and stable.
2014 Vol. 32 (2): 54-56 [
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57
ZHAO Wen-chong
Fault Maintainance of Cup Wheel Automatic Grinding Machine in HS-200BZ Laboratory
A HS-200BZ laboratory cup wheel automatic grinding machine is used, and its grinding wheel as well as horizontal movement works normally, but the grinding head cannot move up and down. The upper and lower feed machinery part works normal without jamming, but with active electricity the stepping motor does not work. By checking the electric control part, it can be found that there is no 55V AC power supply for stepping motor driver (MS-2HO-90M), and the power supply transformer output of 55V voltage is normal. Fianlly, it is confirmed that the break of UF11 fuse in protection section occurs. After the replacement and the trial operation , the grinding machine works normally.
2014 Vol. 32 (2): 57-60 [
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