International Journal of iron and steel society of Iran
Volume:16 Issue: 2, Summer and Autumn 2019

In this study, the effect of cladded tungsten carbide layer upon HSS - M2 tool steel on microstructure, hardness, and wear behavior has been studied in two cases without using the middle layer and using the middle layer of nickel. Tungsten Carbide cladded on HSS - M2 tool steel by Arc Weld ( SMAW ). The ASTM-G65 wear test was used to determine its application for use in the mineral industry. The results show that the formation of M6C ( tungsten - rich carbide) is deposited layer, as well as tungsten carbide with the formation of a composite layer on the base metal surface, increases the wear resistance up to 60% and the hardness up to 150% compared to the uncoated sample. Comparing the results in terms of the use or non-use of the middle nickel layer indicates the improvement of wear behavior in conditions without using middle nickel layers.

Since the sub-axis of machine tool spindles subjected to fatigue loading, the effects of different surface heat treatments on fatigue behavior of 16MnCr5 steel have been investigated in the current work. After the test specimens were prepared from the steel, the surface heat treatments; carburizing, carbonitriding and a practical type of treatment involving the first nitriding then carburizing was done on samples. Fatigue tests of the rotational bending type performed on samples. In addition, microhardness and microstructural evaluations were used to analysis the achieved results from the fatigue tests. The fatigue fracture surfaces were evaluated by scanning electron microscopy (SEM). The results showed that the fatigue strength of the samples has been improved considerably by applying surface heat treatments. Also, the initiation region of the fatigue crack from the sample's surface has been transmitted to the interface of the hardened layer and the base metal in surface-treated steels. Also reduction in the number of crack initiation places in the treated samples is specified compared to raw samples.

The objective of the current study is to determine the fatigue limit of a clean and high-performance material named as HSLA-100 steel and to compare the obtained fatigue limit with that of theoretically predicted fatigue limit by statistics of extreme value (SEV) method. Also, the size of inclusions located at the site of fatigue crack nucleation on the fracture surface of the fatigue test specimens is compared with the results of extreme value distribution of the inclusions as well as with that of analysis of inclusions found on the polished specimen. The fatigue cracks were initiated from globular inclusions in all fatigue test specimens. Analyzing the fatigue results showed that the SEV method can conservatively predict the planar fatigue limit of HSLA-100 steel. Also, the largest inclusion size predicted by (SEV) method was larger than that of what was observed at the fatigue crack initiation site as well as metallographic studies of polished specimens.

Intensified environmental regulations have posed numerous challenges in the disposal of industrial wastes. The steel industry is one of the biggest production industries, with a considerable amount of daily wastes. Production of glass-ceramic from the steel industry waters is one of the proper solutions for this problem. In this study, the application utilization of different wastes (such as blast-furnace slag, converter slag, and dust) as the raw material for glass-ceramic production was evaluated. After mixing the precursors, the mixture was melted at 1450℃. The obtained melt was cooled down at 10°C/min cooling rate in metallic molds, and the glass was derived. Ceramic phases were grown by application of isothermal heat treatment periods up-to 6 h, at 750, 800, 850, and 900℃. The mean length of the ceramic phases was measured after each heat treatment period by scanning electron microscopy. It was shown that crystal growth followed a parabolic kinetic model. The activation energy of crystallization was also determined as 129 kJ/mol in the temperature range of 750-900°C.

In the present research, the effect of the homogenization process and annealing temperature were investigated for the 1.4470 ferritic-austenitic stainless steel in the as-cast condition. In this regard, microstructural evolutions, hardness, and impact energy of the steel was evaluated with different heat treatment conditions. The results show that the minimum volume fraction of austenite phase (about 42%) was formed in as-cast condition; while the maximum content of austenite phase can be achieved by annealing at 1010 °C for 45 min. without the homogenizing process (about 56%). Moreover, a good combination of impact energy and hardness was obtained by homogenizing at 1120°C/45 min. and subsequent annealing at 1010°C/15 min. followed by oil quenching. In this condition, the same volume fraction of the ferrite and austenite phase has been formed in the microstructure. and subsequent annealing at 1010°C/15 min. followed by oil quenching. In this condition, the same volume fraction of the ferrite and austenite phase has been formed in the microstructure.

Ferritic stainless steels are used in high- temperature applications like solid oxide fuel cells. Application of steels in these conditions will expose them to severe thermal cycles. Therefore, it is essential to protect them at high temperatures. One of the most effective methods for increasing the life of these components against oxidation is the application of composite and ceramic coatings. In the present study, Ni-Co-TiO2 composite coating was deposited on AISI 430 steel substrate by electroplating to investigate the oxidation behavior at operating conditions of solid oxide fuel cells. To observe the morphology, scanning electron microscopy (SEM) and to determine the phases, X-ray diffraction (XRD) was used. For investigating the oxidation behavior of steel isothermal and cyclic oxidation tests were performed at 800 °C on the samples. Results showed that in isothermal and cyclic oxidation tests, due to the formation of Ni-Co spinels, coated samples showed less weight gain than uncoated samples. Spinel prevented outward Cr diffusion which improved the oxidation resistance of AISI 430 steel.

In this research, St37 and 316L steel sheets were welded using friction stir welding (FSW) process and effective parameters such as the rotational speed, linear speed of the tool, pin diameter, and their appropriate values were studied. The microstructure, hardness, and strength of the different welding regions were investigated. It was observed that in the stir zone (SZ), a mechanical operation takes place which causes grain refinement up to 10-20 times and improves the mechanical properties of the joint. The thermo-mechanically affected zone (TMAZ) is less affected and causes the refinement of the structure. In the heat-affected zone (HAZ), no mechanical operation was performed but in some parts, the grain size was larger and more stretched than the grains of the base metal. SEM microscopic images of the weld metal showed alternating onion rings and layers consisting of poor and rich alloying elements due to the non-equilibrium cooling rate of the melt.