Sharif Digital Repository

Al-6wt%Mg alloy has been enormously exploited in aerospace industry. Since for production of this alloy in the form of sheets of different thickness, the cold rolling process is used, thus to understand the final mechanical properties of the rolled alloy products, their work hardening should be examined. Also, one of the important phenomena that occurs in cold state of the alloy is dynamic strain-aging (DSA), which can cause serrations in realistic stress-strain curve. The aforementioned issue is discussed in the current study. Therefore, the work-hardening values for the mentioned alloy during and after rolling is determined, and then compared with the experimental studies. The results of... 

St52 was heated at 745°C for 70 minutes and then quenched into a salt bath at 400°C. To obtain different volume fraction of bainite and martensite with constant volume fraction of ferrite (67%), samples were quenched into water after different times. Presence of three phases of ferrite, bainite and martensite was proved by optical microscope and hardness test. Different volume fractions were measured by image analysis. Optical microscope results showed that with increasing of martensite up to 9.4%, morphology of martensite is a uniform distribution of small and sphere particles. These samples then were cold worked at various degrees. Tensile test and hardness test show that increasing the... 

Cold roll forming is a process for manufacturing of long sheet metal products with constant cross sections. The base of this process is bending and formation of plastic deformation in sheet. In this process, bending operation occurs in several forming stations. The purpose of this project is estimation of the distance between stations in roll forming. This work is based on determination of deformation length. In this study, first, the researches done in the roll forming is expressed. Then, a relation for estimation of deformation length has been derived that could be used in different stages of roll forming. Compared with other works, the work hardening effect has been considered in the... 

This study investigates effect of cold roll prior to inter-critical annealing on microstructure and mechanical properties of ferrite-martensite dual phase steel. Samples were heated to 850oC for 1h followed by oil quench, then the steel sheet were cold rolled by 0%,10%,15% and 20% reduction in thickness, Then an inter-critical annealing(750oC,120min) was performed to generate a ferrite-martensite microstructure. Microstructural study showed that increase in applied Cold roll, leading to increase volume fraction of martensite and decrease in ferrite grain size. Mechanical properties of dual phase steel were tested by Tensile test, impact test and micro-hardness Test. Results shows that... 

Many Investigations have been carried out on high work hardening, strengthening and secondary hardening of MP35N superalloy. In this study, behavior of MP35N under uniaxial hot compression at 600 °C with true strain of 0.05, 0.10, 0.16 and 0.22 was investigated. After calculating on stress- true strain curve, work hardening rate versus strain come out. Serrated flow has been seen in all mentioned strains. In TEM investigation on these samples, dislocations array with extended faults and micro twinning have been seen. According to Suzuki mechanism with solute partitioning and diffusion of solute, stacking fault extended. Uninterrupted separations and combinations of partial dislocations lead... 

Hadfield’s manganese steel, nominally Fe–1.2%C–13%Mn, is an alloy with inherent toughness, work-hardening characteristics and excellent resistance to some types of adhesive and abrasive wear. However, due to its low yield strength, it may be deformed markedly before its work-hardening become effective. There have been many studies on increasing strenght by alloying manganese steel, but the effects some other alloying additions such as 1 to 2 percent Al, Cr, W, V despite increase strenght and wear resistance at the low stress abrasive condition, decrease work-hardening characteristics and wear resistance at the high stress abrasive condition. The aim of present work, is to modify... 

Hadfiled steel was invented by Sir Robert Hadfield in 1882. Different types of this steel have been used widely in cement industry, mining, drilling and railroad ways due to its high toughness, high work hardening capacity and excellent wear resistance. Since the wear life of machineries and parts used in such industries is short and costly, time consuming service of the wear parts, there have been a lot of interest to increase wear resistance of austenitic manganese steels in recent years. In this study a new type of austenitic manganese steels with high carbon-high vanadium and high tungsten content has been introduced and effect of carbon, vanadium and tungsten on microstructure, micro... 

In this study, the effect of martensite volume fraction on the wear behaviour of 4340 steel with triple-phase steel microstructure with a constant volume fraction of 34% ferrite was investigated. Using the Holman equation, it was found that triple-phase steel with different martensite volume fraction has two stages of work hardening. By increasing martensite volume fraction, yield strength and ultimate tensile strength and work hardening exponent of first and second stages increase and the elongation decreased. To perform the wear test, the pin on disc apparatus was used according to the ASTM G99 standard, and the test was done at two forces of 10 and 50 N at a fixed distance of 400 m. The... 

Design of thick-walled spherical and cylindrical vessels as fluids containers of high gradient thermal loading is a challenging issue. Using these tanks in high pressure and temperature gradient, particularly in chemical industries, needs to use new methods in design. Elasto-Plastic solution for thick-walled hollow spherical and cylindrical tanks made of FG materials subjected to internal pressure and temperature loading is presented. The power law modeling is used for through-the-thickness variation of mechanical properties. This method is using the new advanced materials with high pressure and thermal strength in fabricating these vessels. One of these materials is functionally graded (FG)... 

AEREX350 is a wrought Ni-Co base superalloy which was first developed as a fastener alloy and is a member of MP family of alloys which are thermo-mechanically processed. Due to chemical composition of AEREX350, the alloy benefits from precipitation hardening and solid solution strengthening as well as cold working and can be used in higher temperatures. To investigate the effect of deformation during precipitation, solution-treated samples was underwent hot compression test up to strain of 0.5 at range 650-800˚C, range of γ΄ formation. It is seen that work-hardening and deformation mechanism of high temperature deformation is slip and as a result its structure is dislocation but in room... 

This study investigates effect of cold roll prior to inter-critical annealing on microstructure and mechanical properties of ferrite-martensite dual phase steel. Samples were heated to 850oC for 1h followed by oil quench, then the steel sheet were cold rolled by 0%,10%,15% and 20% reduction in thickness, Then an inter-critical annealing(750oC,120min) was performed to generate a ferrite-martensite microstructure. Microstructural study showed that increase in applied Cold roll, leading to increase volume fraction of martensite and decrease in ferrite grain size. Mechanical properties of dual phase steel were tested by Tensile test, impact test and micro-hardness Test. Results shows that...