Sharif Digital Repository

The X80 high-strength low-alloy microalloyed steel was procured as a hot rolled plate with accelerated cooling. The four-wire tandem submerged arc welding process, with different heat input, was used to generate a welded microstructure. The effects of real and Gleeble simulated double pass thermal cycles on the properties of the heated and reheated coarse grained heat affected zones (CGHAZ) in X80 microalloyed pipeline steel has been investigated. The thermal simulated process for heated region involved heating the X80 steel specimens to the peak temperature of 1400 °C, with different cooling rates. The influence of the second peak temperature during real and simulated welding hass been... 

Nanocrystalline steel was developed by severe cold-rolling and subsequent annealing of HSLA steel with an original microstructure of lath martensite. Specimens are austenitized at 1000 ºC for 30 min followed by quenching in brine. The quenched specimens are cold rolled with 80% to 90 % reduction and then annealed at temperatures from 400 to 700ºC for 10 to 120 min.The specimens annealed at temperature 500oC for 60 min showed the multiphased ultrafine structure composed of equiaxed ultrafine ferrite grains with the mean grain size of 180 nm, nano-carbides distributed uniformly and blocks of tempered martensite. The produced nanostructured steel exhibited a yield stress and UTS, of 1280 MPa... 

Repair welding is one of the important maintenance processes that include build-up welding and surfacing.In this study, investigation of repair welding parameters has been conducted to achieve desired microstructure with the appropriate toughness and minimum residual stress.In this research, local post-weld heat treatment has been performed by Tungsten electrode arc on weld zone. Performing this process with optimum parameters leads to the best heat cycle with the tempered Martensite microstructure. Residual stress of the sample will be reduced. HAZ coarse grains will be refined to finer grains which result in to improved toughness and reduced hardness to the acceptable limit.
Results... 

In the present study the production of ferrite-martensite dual-phase (DP) Steel was investigated during the bonding process by transient liquid phase method. The effect of martensite morphologies on mechanical properties of bonding zone were also studied. To make the bonding process and DP steel production heat treatment cycle simultaneously, the step in which the isothermal solidification completed, bonding process, was done simultaneously with austenitising of the steel. Homogenizing of the bond zone, was also done with DP steel making at the intercritical temperature. The St52 steel was utilized for producing DP steel and for bonding process, iron base interlayer with melting point of... 

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... 

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... 

Austenitic stainless steels have extensive and special mechanical properties because of austenite to α΄-martensite transformation due to plastic work. Obtaining a process path that provides maximum strength and flexibility and minimum α΄-martensite content (α΄-martensite increases corrosion current) in these steels is important in the industry. Applying the aging process after applying plastic strain (single-stage aging) results in an increase in strength of up to 200 MPa and an increase in hardness of up to 60 Vickers. However, single-stage aging does not cause significant changes in the amount of α΄-martensite in steel and in the temperature range of 400 to 500 ° C, it causes a slight... 

In austenitic stainless steel types 304 and 316, due to the instability of the austenite phase, the martensite phase is formed by plastic deformation below the Md temperature. In this research, the cold rolling of 304L austenitic stainless steel and the transformation of austenite to strain-induced martensite and its effect on mechanical properties, especially wear, were studied. In this way, the samples were rolled in two modes and four passes in each mode. In the first case, the samples were cooled between each pass in water as a cooling liquid, and in the second case, the samples were cooled in each pass without using water and by air. Next, tests such as hardness measurement, uniaxial...