Sharif Digital Repository

The introduction of multi phase steels in recent years resulted in a considerable increase in development of some industries such as automobiles. By inducing soft and hard phases together, these steels could bring better mechanical properties than classical ones. Recent studies on 4340 ferritic- bainitic and ferritic- martensitic dual phase steels, indicate that 34 volume percent ferrite with hard phase, has the best combination of strength, toughness and fatigue properties. In present research, by proper heat treatment on a 4340 steel, it is tried to prepare specimens ferritic- bainitic- martensitic triple phase steels with 34 volume percent of ferrite and different percents of martensite.... 

In this research, transient liquid phase (TLP) bonding of FSX-414 superalloy was investigated using MBF-80 interlayer. The bonding was performed at different temperatures (1050-1200oC) for various times (1-120min). Also, different gap sizes were studied using the interlayer with various thicknesses (25-100µm). Homogenizing treatment was performed at different temperatures (1175-1225oC) and times (1-6h) for the samples with complete isothermal solidification. The microstructure of the samples were studied using the optical, scanning electron and transmission electron microscopes. Also, XRD, SEM/EDS, SEM/WDS and TEM/EDS analyses were used to analyse the observed phases at the joints. To... 

In the research transient liquid phase bonding of AL6061-SiC composite was performed using copper as interlayer. The joining praocess was performed in various tetemperatures (560c and 580c and 600c) And times (6 and 8 hours). Optimum Joining condition was determined by using optical and of the joint, micro hardness test was performed from the bonding zone to the bulk of the base composite. The fatigue endurance limit of Al6061-SiC composite was determined by several fatigue tests and TLP bonded samples were loaded under achieved endurance limit stress. Finally fatigue fracture surface of both base composite and TLP bonded samples were studied by using of scanning electronic microscope  

During the last few years researchers have drawn much attention to HSLA steels because of the application of these steels in many industries. Ferrite-martensite dual phase(DP) steels are one of the most common HSLA steels which are currently used. Combination of these two phases provides good strength along with good ductility. Joining and welding of these steels has always been an important challenge. The aim of this study is to examine applicability of TLP method for joining and dual phase processing of this steels at the same time. Microstructural and mechanical examination of the bonded specimens showed that isothermal solidification occurred during holding for 50 min at the... 

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... 

Dual Phase ferritic-martensitic steels are kind of high strength low alloy steels (HASLA) which are widely used in industry because of their strength and formability. Since welding of dual phase steels in conventional welding methods causes structural change and Subsequently alters mechanical properties of both weld zone and heat affected zone(HAZ), additional operations which are not commercially viable is needed to achieve a dual phase structure in structurally changed regions. In this study, transient liquid phase (TLP) bonding method is used during dual phasing process in order to preserve dual phase ferritic-martensitic structure and avoid extra heat treatment. Applied pressure during... 

Interlayer composition as one of the most important factors of TLP bonding could affect bonding region composition and microstructure that both of them govern the mechanical properties of the joint. Due to the risk of substrate microstructure degradation , welding of dual phase steel needs more cautions. TLP bonding ideally acquires joints having more similar microstructure to substrate. Moreover , using this method could avoid the change of base metal microstructure when heat treatment of carbon steel is postponed until after bonding. Fe-based , Ni-based and commercially pure Cu are three different composition has been studied in this work. The bonded samples were investigated by optic and... 

Stainless steels have many applications in different industries like chemistry, medicine and food production. So for using these alloys it is necessary to join them with appropriate method. In this research, microstructure-mechanical properties relationship of 304LC austenitic stainless steel transient liquid phase bonded using a Co-based interlayer was investigated. For this purpose, bonding was conducted at 1180 ℃ for different holding times. Microstructure of the joints was evaluated by optical microscopy (OM) and Scanning Electron Microscopy (SEM). The results showed that isothermal solidification (IS) was completed within 1800s and no intermetallic compound was formed in the joint area... 

Stainless steels have many applications in different industries. Therefore, it was always a main concern to find an appropriate joining method for using these materials in complex structures. In the present investigation, AISI 304 stainless steel was successfully joined by transient liquid phase (TLP) bonding, using a MBF-30 interlayer. The joining process was carried out at 1150 ℃ temperature and for different bonding times. Also joints with complete isothermal solidification were homogenized at 950 ℃ for different holding times. Microstructure and compositional changes of the joints were studied using optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive... 

Transient liquid phase bonding of AISI 304 was carried out in a vaccum furnace using a Ni-based interlayer. The effect of bonding time on microstructure and mechanical properties of joints at temperature of 1150 ⁰C was investigated. The results showed that isothermal solidification was completed within 20 min and eutectic phase disappeared across the joint region. The joints with complete isothermal solidification were homogenised for 180 min at temperature of 950 ⁰C. The results of shear test showed that the average shear strength of homogenised samples was about 83% thet of the base metal at the same heat treatment cycle. Corrosion behavior of the TLP bonded and base metal was studied at... 

In this study, low carbon steels were joined with TLP bonding method; using a Fe based interlayer. Transient Liquid Phase bonding is a diffusional process in which as tempreture rises a melting point depressant element difuses in to the base metal and as a result the interlayer will isothermally solidify. Due to the fact that Ferrite grain size can effect the amount of diffusion which is taking place, in this study the effect of this variable on the isothermal solidification time was investigated using steels with different initial grain sizes. Microstructural studies indicated that as the mean grain size increases the time needed for the isothermal solidification to complete increases.... 

In this study, the effect of the Cu interlayer thickness was studied on St52 steel. Specimens with different thickness of the interlayer, were subjected to 1150 °C at different times. Isothermal solidification was completed for the thickness of the 50 μm, 30 μm, and 10 μm in 30, 25 and 20 minutes. Afterwards, homogenizing and dual-phase heat treatment were used for 75 minutes at 730°C. Optical microscopy and SEM were used to analyze the microstructure of the joints. Mechanical properties of the joints, including micro hardness of different parts of the joint and also shear strength of the joint zone were studied. The results show that after homogenizing treatment, microstructure and harness... 

Cooling sandwich panels are one of the components of the heat exchangers used to cool the components of the sandwich panels . One of the applications of TLP Bonding for steel can be called cooling sandwich panels. In this research , TLP of 304 Stainless Steel , using Fe-base interlayer at 1200 C has been investigated . Cross section of bonded samples were examined by optical and scanning electron microscopes. Microscopy results revealed that 2h is sufficient for completion of isothermal solidification and there is no eutectic compound at bonding zone . Bonding in this condition resulted in the free precipitates in the diffusion affected area. By analyzing eutectic phase in bonding areas at... 

AISI 4340 steel bars were austenitized at 900°C for 1 hour followed by heating at 740°C (ferrite and austenite region) for 100 min and quenching into a salt bath at 300°C for different times followed by quenching into water to obtain triple phase microstructures with 34 Vol.% ferrite and various martensite (or bainite) contents. Presence of three phases in adjacent of each other confirmed by metallographic analysis and TEM technique. Volume fraction of different phases was measured by image analyser. The results of optical microscopy showed that by increasing VM, morphology of martensite varies from uniform distribution of small spherical network particles to large blocky islands with... 

In this study, low carbon plain steels joined with TLP bonding method using Fe-44Ni-7B-4Mo interlayer, The bonding parameters (holding time, temperature) have been changed to find optimum conditions of TLP bonding. Microstructure and properties of joints have also been investigated. Dual phase processing of the used steel has been carried out during joints homogenization. Microstructural studies with scanning electron microscope and optical microscope showed that isothermal solidification completed at holding for 50 minutes at the bonding temperature of 1180℃. These parameters are taken as optimum conditions of TLP bonding. Microstructure of the isothermally solidified zone (joint region)... 

After World War II, steel bearings containing copper element have been developed by the Navy of the United States of America with the HSLA-100 brand. Since 1890 and in order to manufacture tanks and tools for the body of navy equipment, the steel HY 80 was used instead of HSLA-100. Because of the high carbon content, the welding properties of the HY 80 are low. Furthermore, increasing of hardness and decreasing of toughness in the heat-affected zone generated during the welding process lead to susceptibility of this alloy to hydrogen cracking and brittle fracture. Therefore, in order to minimize the cost of welding, low-alloy high strength steel (HSLA) is used which contain copper. Reducing... 

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... 

The studied steel was AISI 4340 steel. In order to obtain dual-phase steel with a volume fraction of 60, 66 and 75% bainite, samples were heated in the α+γ region at temperatures of 730, 735 and 740 oC for 120 minutes and then to create lower and upper morphology of bainite, samples were transferred directly to salt bath at different target temperatures (300 oC and 400 oC) and kept 60 minutes. Also, to produce a Martemper microstructure, the full martensitic sample was tempered at 260 oC for 90 minutes. Tensile and hardness tests revealed that with the increasing volume fraction of lower bainite, yield strength, tensile strength, and hardness increased from 986 to 1211 MP, 1185 to 1519, and... 

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... 

The repair and production of Ni-based and Co-based superalloy parts have high importance in Oil and Gas, and Aerospace industries. Due to this issue, Transient Liquid Phase bonding is one of the most reliable welding methods for repair parts and fabricating new parts.In the present study, creep properties of similar transient liquid phase bonding of FSX-414 Co-based superalloy has been investigated and compared with creep properties of the un-bonded base metal. Firstly, the optimum condition of the bonding process was resulted from microstructural observations from different bonding conditions. Then, cylindrical samples for the aim of creep test specimens were fabricated in two different...