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Meysam Ranjbar,Reza Miresmaeili,Mohammad Reza Naimi‑Jamal,Majid Mirzaei 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
This study investigated the influence of microstructure on the mechanical properties and fracture toughness of API X65pipeline steel in the presence of hydrogen. In this study, electrochemical method was used for hydrogen charging and indentationtechnique was applied to obtain the fracture toughness. The results showed that in the presence of hydrogen, elongation(EL%), reduction of area (RA), ductile fracture percentage, and fracture toughness of all microstructures decreased. Themicrostructure of martensite (M) + bainite (B) + ferrite (F), had the highest hydrogen trapping and uptake (Capp) as 8.58 × 10–6 mol cm−3 and the lowest apparent hydrogen diffusivity (Dapp) as 5.68 × 10−10 m2 s−1; thus, the maximum decrements of33% in fracture toughness, 40% in ductile fracture percentage, 47% in RA, and 35% in EL% were observed. However, themicrostructure of ferrite (F) + degenerated perlite (DP) + martensite-austenite micro constituent (M/A), where the lowestvalue of 5.85 × 10–6 mol cm−3 for Cappand the highest value of 8.5 × 10–10 m2 s−1 for Dapphad the minimum decrements as2% in fracture toughness, 10% in ductile fracture percentage, 4% in RA, and 7% in El%. According to the obtained results,depending on the type of microstructures, hydrogen-induced work softening or hardening were observed by decreasing orincreasing the yield stress respectively.
Mina Dehghan,Reza Miresmaeili,Mohsen Askari‑Paykani,Hamid Reza Shahverdi 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5
A novel severe plastic deformation is carried out on a medium Mn advanced high strength steel (AHSS) at both room andcryogenic temperatures which is called surface mechanical impact treatment (SMIT). After characterization, utilizing thedesign of experiment (DOE) program, it is obtained that how the SMIT parameters including time, voltage, and, shot diameteraffect the tensile test results of SMITed samples at room temperature (RT-SMITed). Microhardness profiles of SMITedsamples at cryogenic temperature (CT-SMITed) show more increase in microhardness than RT-SMITed ones up to thecenter of specimens. Additionally, the yield strength of CT-SMITed and RT-SMITed samples increases by 84% and 28% onaverage, respectively. The formation of mechanical twins, slip bands and, rhombic blocks improve both the microhardnessand yield strength of treated samples. The ultimate tensile strength (UTS) of all treated specimens decreases sharply (35%in RT-SMITed and 32% in CT-SMITed samples). According to DOE results, UTS has a negative correlation with voltageand based on fracture surface images, brittle fracture configurations increases with increasing voltage. The reason for thisobservation could be the precracks formed due to the deformation of detected MnS precipitates and the possibility of themartensite phase cracking during the SMIT process.
Behzad Parvaresh,Reza Salehan,Reza Miresmaeili 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.1
Wire arc additive manufacturing (WAAM) has several industrial applications because of its advantages over other additivemanufacturing methods. In this study, two stainless steel 347 walls, namely as-deposited (AD) wall, and inter-layer coldworked (CW) wall, were prepared using the WAAM method to investigate the isotropy of their mechanical properties andwear properties in vertical and horizontal directions. For the AD wall, the mean yield strength, ultimate strength, and elongationof horizontal samples were 410 MPa, 620 MPa, and 47%, respectively. In comparison, these values for the vertical (V)samples were 402 MPa, 590 MPa, and 49%, respectively. For the CW wall, the mean yield strength, ultimate strength, andelongation of horizontal samples were 815 MPa, 876 MPa, and 26%, respectively, while those of vertical samples were 722MPa, 824 MPa, and 25%, respectively. The CW wall’s tensile test results indicated that inter-layer cold working intensifiedthe anisotropy of tensile properties in both vertical and horizontal directions. Microstructural investigation revealed thatinter-layer cold working and the heat resulted from subsequent layers deposition in the CW wall recrystallized the layersand reduced the grain size. Additionally, wear test results demonstrated that inter-layer cold working increased hardness andthus wear-resistance of the samples and reduced their friction. The results showed that the coefficient of friction (COF) andwear rates of the samples are not highly dependent on their direction.
Milad Rostami,Reza Miresmaeili,Asghar Heydari Astaraee 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.4
Nanostructured materials exhibit superior properties with respect to their bulk counterpart. Recently, a new processingmethod for surface nanostructuring of metallic materials called surface mechanical impact treatment (SMIT) was developed. In this study, the surface microstructural features due to the refinement process of AISI 316L stainless steel by means ofSMIT and subsequent mechanical performance were investigated. The effects of SMIT processing parameters, i.e. ball sizeand treatment duration, were studied in terms of microstructural evolutions using X-ray diffraction, transmission electronmicroscopy, optical microscopy, and field emission scanning electron microscopy analyses, and mechanical propertiesthrough hardness and tensile tests. A gradient nanostructured surface layer was successfully formed on the surface of thetreated samples. The mean grain size was measured to be ~ 20 nm in the topmost surface layer and increased with increasingdepth. Microstructural examinations showed that the twins and their intersections (rhombic blocks) formed in the surfacelayers. It was found that the mechanical performance of the treated samples is effectively enhanced. The surface hardnessof the treated samples increased about 3 times while the yield strength of the samples increased with increasing SMIT timeand size of the ball up to 2.5 times. The grain refinement mechanisms, mechanical properties, and fracture behavior weresubsequently analyzed and discussed.
Behzad Parvaresh,Hossein Aliyari,Reza Miresmaeili,Mina Dehghan,Mohsen Mohammadi 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.11
Metal additive manufacturing is a method of producing metallic parts layer-by-layer. Some drawbacks, including anisotropyin mechanical properties, detrimental residual stresses, and the presence of columnar grain structures can affect the qualityand performance of additively manufactured metallic parts. Therefore, different industrial sectors have employed intuitiveancillary processes to improve the quality of additively manufactured parts. Of particular interest is in-situ ancillary processesthat are more applicable than other procedures due to their utmost importance to reduce manufacturing cycle time. In thisreview article, after introducing various metal additive manufacturing technologies, some of the common alloys utilized inthose processes were discussed. With an eye toward improving the quality of additively manufactured components, the focusof the review was then shifted toward the effects of building direction, processing parameters, and Alloying compositionModification on microstructure and mechanical properties. The efficacy of ancillary processes such as metalworking, in-situheat treatment, and in-situ thermo hydrogen process in reducing defects and improving physical and mechanical propertieswas then presented.