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RISS 인기검색어
- 검색키워드
- 저자 : Seyed Ebrahim Vahdat (검색결과 4 건)
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Seyed Ebrahim Vahdat,Said Nategh,Shamsoddin Mirdamadi 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
Microstructure of an alloy has a significant effect on mechanical properties. Deep cryogenic treatment extends life of tool steels because of microstructure changes. In this research, effects of microstructural parameters were studied on tensile toughness of a medium carbon-low alloy tool steel. The results showed that the maximum population density of sub-micron sized secondary carbide was obtained after 36 h of soaking time. Also, amount of secondary carbides increased with soaking or tempering times from 2.18 vol% to 12.87 vol%. In addition, high population density and high content of secondary carbides were responsible for tensile toughness enhancement. Therefore, the best results (12-35% improvement in tensile toughness) were obtained for a specimen, which underwent a full treatment cycle consisting of heating, water quenching, soaking at -196ºC for 36 or 48 h and tempering at 200ºC for 1 or 2 h, respectively.
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Effect of Deep Cryogenic Processing on Tensile Toughness of 45WCrV7 Steel
Seyed Ebrahim Vahdat 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.3
Toughness is an important property for being used in steels in engineering applications. In this research, tensile toughnessof 45WCrV7 steel was measured and calculated in 10 different processing conditions. The results of tensile test showed thattwo samples had maximum tensile toughness. Microstructural studies demonstrated that the required condition for high tensiletoughness was simultaneous increase in two microstructural factors named content and population density of the secondarycarbides because a matrix which was poor of carbon and alloying elements was softened and thus increased total tensiletoughness.
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Repairing the Surface Grooves of St37 Structural Steel Using Flame Spray Welding
Fariborz Amiri,Keyvan Seyedi Niaki,Seyed Ebrahim Vahdat 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.18 No.12
In today’s industry, preventive measures for the preservation and repair of devices and equipment are extremely important. Various welding methods are used for repairing the surface crack of metal pieces in order to improve their mechanical properties and increase their useful life. In the present study, the performance of flame spray welding using pure iron powder is evaluated in repairing the surface grooves of St37 structural steel. First, five groups of specimen (one control group and four grooved steel groups with 0.5 mm groove tip, 10 mm length and 0.5, 0.8, 1 and 1.3 mm groove depths) were prepared. Then, the repair was performed. The results showed that after repairing the surface groove via flame spray welding using pure iron powder, the tensile strength and yield strength of the repaired specimens with the groove depths of 0.5 and 0.8 mm were achieved to control ones, but the elongation was decreased, which was still acceptable for engineering applications (module of toughness of 74.2 MJ) for the repaired specimen with the groove depth of 0.5 mm.
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Effect of Pressure and DCT on Microstructure and Strength of Diffusion Bonds of PLCS-HSLAS
Navab Khosravi,Keyvan Seyedi Niaki,Dariusz Lukowiec,Mirka Pawlyta,Seyed Ebrahim Vahdat 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.9
In the present study, eight pairs of samples were used in four groups for diffusion bonds of plain low carbon steel (PLCS) to high strength low alloy steel (HSLAS) so that, diffusion bonding was performed on two groups without pressure and two groups with the pressure of 2 MPa. Then, the groups alternatively underwent deep cryogenic treatment at -196°C (DCT) for 10 h; finally, all the groups were tempered at 150°C for 1 h. The results show under the non-pressure conditions, DCT had a positive effect on the bond strength because population density of carbide increased from 1400000 to 2300000 mm-2. While under the pressure conditions, the DCT led to 59% decrease in the bond strength because discontinuity on the bond metal increased from 7 to 15 percent. In addition, in the absence of DCT, applying pressure during diffusion bonding caused the strength of the bond to increase 25.8%, the reason of which could be attributed to the increase in the bond length from 160 to 220 μm, or the larger bond metal. It is found that discontinuity in bond metal, population density of carbides and bond's length are three main factors to affect the bond strength. The role of discontinuity in bond metal is negative while the others are positive. Finally, to increase bond strength just one of these two operations (pressure during diffusion bonding or DCT after diffusion bonding) must be used.
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