ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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 , Volume 56 Issue 2 Previous Issue
 Select Corrosion Behavior of X80 Steel Welded Joint in Simulated Natural Gas Condensate Solutions CHEN Fang,LI Yadong,YANG Jian,TANG Xiao,LI Yan Acta Metall Sin, 2020, 56 (2): 137-147.  DOI: 10.11900/0412.1961.2019.00237 Abstract   HTML   PDF (10336KB) ( 156 ) Carbon steels are widely used as transportation pipelines in oil and gas fields and welding is one of the main ways of connecting pipeline steel. The welded joints are easily corroded due to the difference in composition, structure and properties of the various components. The effect of content of HAc, Cl-, ethylene glycol (MEG) and temperature (T) on the corrosion behavior of welded joint of X80 steel in a simulated natural gas condensate saturated with CO2 was studied by the orthogonal experimental design, weight loss experiment and electrochemical experiment. It is demonstrated that the corrosion rate of the welded joint is significantly higher than that of the base metal because of the formation of macroscopic corrosion galvanic cells, and the corrosion of the weld metal as an anode region is accelerated to become a weak link of the welded joint. The significance of the four factors on the corrosion process is: c(HAc)>T $\gg$c(Cl-)>c(MEG), c(HAc) and T are the main factors affecting the corrosion behavior, and c(Cl-) and c(MEG) are secondary factors. Base metal and weld metal corrosion tendencies increase with increasing temperature. Because ferrous acetate is less protective as a corrosion product, as the c(HAc) increases, the impedance of the base metal and weld metal decreases, and the corrosion rate increases. Based on the results of orthogonal experiments, a multivariate linear regression equation was established.
 Select Microstructure, Texture and Mechanical Property ofTA32 Titanium Alloy Thick Plate CHENG Chao,CHEN Zhiyong,QIN Xushan,LIU Jianrong,WANG Qingjiang Acta Metall Sin, 2020, 56 (2): 193-202.  DOI: 10.11900/0412.1961.2019.00226 Abstract   HTML   PDF (28271KB) ( 218 ) TA32 alloy is a new near α titanium alloy designed by optimizing the alloy elements ratio based on a series of elements Ti-Al-Sn-Zr-Mo-Si-Nb-Ta which has less β-stabilizing elements. This alloy has an excellent match of heat resistance and heat stability at 550 ℃, and good short-term mechanical properties at 600~650 ℃. TA32 titanium alloy thick plate can be applied to the key components in high temperature service of the hypersonic vehicle. Due to the low deformation degree of thick plate during rolling process, the heterogeneity of microstructure, texture and mechanical properties of the thick plate increases. In order to provide theoretical basis and experimental basis for the subsequent optimization of mechanical properties of TA32 titanium alloy thick plate, the microstructure, texture and mechanical properties of this alloy with a thickness of 60 mm are investigated in this work. Results show that the microstructure of the as-received material is mainly composed of lamellar α grains with few retained thin β layers, and the microstructure difference is not obvious from the surface to the center along the thickness direction of the plate no matter of the RD (rolling direction)-ND (normal direction) plane or the TD (transverse direction)-ND plane. Moreover, the rolling streamline can be obviously observed on the two planes. The morphology of α grains of the alloys presents either straight or wavy depending on their orientations with respect to the principal rolling directions. XRD results show that the as-received material has a typical T-type texture with c-axis of α phase approximately parallel to TD. At the same time, the <$10\bar{1}0$> poles are parallel to RD while <$10\bar{1}1$> poles present random distribution. As the c-axis gradually deviates from the TD of the surface to the center along the thickness direction of the plate, the Schmidt factors gradually increase, which is one of the main reasons for the gradual decrease of tensile strength; and the decrease of fraction of intragranular substructure from the surface to the center along the thickness direction is another important factor. The tensile properties have no obvious difference along the TD and RD at the same thickness position of the as-received material, but slightly worse along the ND. In addition, the influences of microstructure and texture on tensile properties are further clarified by adding two sets of heat treatment experiments (920 ℃, 30 min, AC+600 ℃, 5 h, AC; 950 ℃, 30 min, AC+600 ℃, 5 h, AC). The results show that the texture is the main factor affecting the tensile strength of TA32 titanium alloy plate at different positions under the condition of no obvious difference in microstructure. After double annealing, microstructure difference is the main factor affecting tensile strength.