مجله مهندسی متالورژی
پیاپی 54 (تابستان 1394)

Electrospark deposition method has been used for creating an intermediate layer on the IN738LC superalloy for subsequent laser welding or laser cladding. With using proper Electrospark deposition parameters a crack free or at least less crack susceptible layer can be formed by same filler metal on this alloy. ESD layer has unique microstructure consists of columnar gamma phase. Because of very rapid cooling rate involved in electrospark deposition method, the layer with very low elemental segregation can be obtained. Having fine grain microstructure in comparison to as cast base metal, ESD layer is more crack resistance. Laser remelted ESD layer is dense and the ESD defects like lack of fusion between layers and porosity are eliminated in laser remelted layer. Hardness results show lower hardness value for remelted laser area in comparison with ESD layer. Furthermore, no solidification or liquation crack found in remelted layer.

In the present study, the effect of addition of potassium permanganate on the cladding microstructure obtained from the simultaneous synthesis of chromium from chromium oxide and molybdenum from molybdenum trioxide, were studied. For this purpose, a paste of blended powders containing chromium oxide, molybdenum trioxide, nickel, urea and aluminum with various amounts of potassium permanganate was applied on the surface of AISI 304 stainless steel substrates and welded using GTAW process. Cross section of the cladded samples have been investigated using optical microscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The results revealed that the morphology of the claddings in the center of the weld is lathy ferritic in austenite matrix and in the interface of the substrate and cladding, the morphology was changed to skeletal ferritic. By increasing potassium permanganate in the cladding powders, the final microstructure of the cladding has been finer and the amount of ferrite in the weld metal has been increased. Furthermore, the results showed that the addition of potassium permanganate to the cladding powders would result in increasing the chromium content and subsequently decreasing the molybdenum content of the weld pool, without any significant changes in the manganese content of it.

This research focused on formation of Delta Ferrite Phase in AISI 431 Martensitic Stainless Steel by dilatometric instrument. The paper aims to determine an optimum temperature and soaking time according to the morphology and percentage of Delta phase, in order to have a better prediction of the steel’s mechanical and thermo-mechanical properties. Heating treatments were performed under temperatures from 1050 °C to 1250 °C and two time periods, 5 and 10 minutes. The dilatometric curves results show that temperature of Martensitic start transformation decreases with increasing of soaking temperature and time. The content of delta ferrite phase decreases when temperature is below of 1100 °C then increases to 14 percent of volume fraction and morphology of this phase is lathy ferrite that changes to vormecular or island shape by increasing of temperature.

cold rolling and annealing of structures with a high percent of Martensite are the new subgroups of advanced thermomechanical processes that are known as Martensite process. In this study, an alloying steel with the Nominal composition of Fe-5Ni-10Cr-8Mn (weight percent), was casted InaVacuum Arc Remeltingfurnace and after homogenizing, was placed under two steps cold rolling (until 50 %) and two steps of annealing after rolling (in different temperatures). XRD, hardness and tensile tests and EBSDinvestigation was done on samples. Results show that two step rolling and annealing at 600 for 1 hour is the most optimize state for receiving to ultra fine grained structure / nanostructure. Also, residual austenite that caused during two phase annealing in this alloy, is mechanically unstable and this phase is transferred to Martensite phase during loading and is shown TRIP property. Tensile strength of this steel is 1050 MPa under optimal state and the percent of elongation of this steel is about 28 %. This elongation creates before necking.

In this research synthesis and creating of Fe-TiC coating on plain carbon steel using ilmenite and laser alloying process was investigated. Two composition with the molar ratio of graphite to ilmenite 4:1 and 6:1 was investigated. The sample with molar ratio 6:1, were activated for 100h. Blended powder were mixed with amount of glue and pasted on AISI 1018 surface. Then laser surface alloying was done. The Result showed in un-milled sample ilmenite not reduction to TiC but in activated sample ilmenite reduction to Fe and TiC. The results showed that TiC were formed via in situ reaction between ilmenite and graphite in the molten pool during laser alloying process. The morphologies of TiC were of spherical shape; and the titanium carbides were distributed uniformly in the composite coating. Compared to the substrate, the hardness of the coatings reinforced by TiC particles were significantly enhanced.

This paper aims to evaluate the properties of tubular materials by hydraulic bulge tests combined with an analytical model. A setup is built for these tests and stainless steel type 316 tubes are used as specimens. Five specimens are tested in five different internal pressures and the tube thickness and bulge height are measured at the pole for each tube. A digitizer is used to measure the profile of the free bulge region and the result profiles are estimated by using Spline for each specimen. Using this profile and calculating its radius of curvature, and from above experimental data, one effective stress and effective strain can be derived for each specimen by the analytical method. Using these data points and the least square method, the constants of the effective stress-effective strain relation based on Ludwik equation for stainless steel type 316 tubular materials can be achieved. The flow stresses of the tubular materials by this approach are compared with those obtained by the tensile test. The samples are cut from the same tube used in bulge test. The finite element simulation of hydraulic bulge forming is carried out, using mechanical behavior of tubular materials and flow stresses obtained by the above-mentioned approach. The simulation results of forming pressures versus bulge heights and pole thicknesses are compared with the experimental results to validate the approach proposed in this paper.

Residual stresses, that are inherent in thermal spray coatings as in tungsten carbide cobalt thermal coatings, can be useful or damaging for efficiency and life of specimen relate to their state. The present investigation has been done in order to determine the residual stresses through thickness in WC-12Co thermal spray coating from HVOF Process. These stresses were determined in surface of coating and through the thickness in 50, 150, 230 and 300 µm depths. Residual stresses were obtained tensile in 50 µm depth and compressive for surface of coating and other depths. It was observed that by approaching to the interface, further 50 µm, the magnitudes of stresses increase because the peening and thermal mismatch stresses dominant the quenching stresses. The average residual stress through coating thickness was calculated -157.1 MPa and compressive that is useful for the efficiency of specimen.