مجله مهندسی متالورژی
پیاپی 65 (بهار 1396)

Because of high strength, hardness and chemical stability of titanium carbide (TiC), it is known as an ideal material for manufacturing the different types of composite. In this study, surface of hot work H13 tool steel was composited with TiC particles using pulsed Nd:YAG laser process. Hardness of the composited surfaces was measured with a Vickers microhardness tester. Characterization of the composited area was done using scanning electron microscope (SEM) which equipped to energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscope (FESEM) and X-ray diffraction technique. In order to investigation of tribological behavior of non-treated and composited samples, pin-on-disk test was employed. Characterization results showed a composited zone without any crack and porosity, with appropriate incorporation and uniform distribution of TiC particles in the matrix. The results of tribological test illustrated that incorporation of TiC particles with their initial morphology and high hardness and strength, not only decrease the friction coefficient, but also improve the wear resistance of composited surfaces in compare with H13 non-composited surfaces.

The current research is an attempt to study the effect of a novel severe plastic deformation technique called "repetitive corrugation and straightening by rolling" (RCSR) and subsequent annealing on the microstructure and mechanical properties of AISI type 304 austenitic stainless steel. In this study, RCSR process was carried out at 200 °C on the 304 austenitic stainless steel (above Md30 temperature) in order to avoid the formation of martensite phase when a high density of dislocations was introduced into the austenite phase. Thereafter, annealing treatment was applied in order to refine the microstructure of 304 stainless steel. In order to determine the beginning and the end of recrystallization temperature of deformed samples, dilatometer tests were used. The specimens were examined by optical microscopy (OM), tensile and micro-hardness tests. The results indicate that by increasing the cycles of RCSR process, more mechanical twins are induced, the hardness and in particular, the yield stress of specimens have been increased.

The aim of current research was to examine the microstructure and mechanical properties of Aluminium matrix hybrid nano-composite reinforced with carbon nanotube (CNT) and silicon carbide whisker (SiCW) prepared by hot pressing. Hybrid nano-composites were fabricated with different amount of CNT and SiCW (0-5 weight percent) in equal proportion. In order to distribute the reinforcements, Al powder and the reinforcements were mixed in a planetary ball mill with a speed of 120 rpm for one hour, and then compressed samples were produced under the pressure of 500 MPa at 550ºC for 45 minutes. Followed by composite fabrication, Vickers microhardness and compressive strength test were performed and microstructural observations were undertaken using field emission scanning electron microscopy (FESEM). The results showed that by increasing the amount of reinforcements up to 1 percent, mechanical properties of nano-composites increase; while, by increasing the amount of reinforcements from 1 to 5 percent, mechanical properties of nano-composites decrease due to the agglomeration of CNTs and non-uniform dispersion of SiCW.

Austenitic stainless steel to carbon steel dissimilar joint is used in petrochemical, oil & gas and shipbuilding applications. In this study, the AC current and pulsed current was compare and the effect of current type on the microstructure and mechanical behavior of dissimilar joint of AISI 321 stainless steel to ASTM A57CL1 were studied. For this purpose, the GTAW process and ER 308L filler metal with diameter of 1.8 mm and argon protect gas were used. In order to study the microstructure and fracture surface of weld samples, optical microscope and scanning electron microscope (SEM) were used. In addition to investigate of mechanical properties of joint, the tensile, impact and hardness tests were used. The results showed that all samples were fractured from ASTM A537CL1 steel with a ductile manner during the tension test. In pulsed current technique the heat input decrease about 11 percent compare to continue current welding. The weld metal impact energy of pulsed and continues current were 200 J and 145 J respectively. The SEM micrographs of Charpy fracture surface of the weld metals were ductile manner but the dimples and Cavities of pulsed technique were finer than continues technique.

In this research, under intercritical heat treatment cycles (Austenitising at 850°C for 1 hour, Then transferring each sample to the furnace at temperatures of 770, 760 and 750°C for 15 minutes, transferring to the salt bath of 360°C for 15 minutes and finally cooling down to room temperature in air) of the AISI 4140 steel, samples of ferritic-bainitic dual phase structures with several percentages of bainite were attained. Then the mechanical properties of the samples have been studied by mechanical tests. Results show that by increasing the bainite volume fraction, the yield strength and the ultimate tensile strength are increased while the ductility and Impact energy is decreased. by investigating the fracture surfaces of the samples by SEM, it was seen that the mode of fracture in dual phase steels is like a mixture of brittle and ductile fractures, and manganese sulfide impurity particles are the places of the nucleation, growth and propagation of cracks and also with increasing the volume fraction of bainite, the ratio of brittle fracture to ductile fracture increases.

Casting as a branch of steel industry plays a basic and strategic role in producing industrial parts in upstream and high priority fields of the technology in country. The survey results of science, technology and innovation in this industry shows that suitable and codified strategic plans and the lack of precise purpose for development are the most important weakness of this industry.
This study tries to suggest a comprehensive, suitable, practical and updated model for strategic planning of steel casting factories. Also each of the strategic planning steps and of Balanced Scorecard developed with use fuzzy Analytic Hierarchy Process (Fuzzy-AHP) for prioritize the goals of the organization to determine priority actions and projects are the most important results in this study.
The suggested method is studied in a selected steel casting factory. In the strategic objectives prioritization part, the same organization managers’ recommendations were put in interval comparison matrixes, adjustability and fuzzy hierarchical analysis were conducted through Excel software and the results of the formulation of this strategy within the framework of the proposed model was tested and validated. The proposed model can be a suitable model for the strategic management of the operating or being established organizations in the steel casting industry.