International Journal of iron and steel society of Iran
Volume:19 Issue: 2, Summer and Autumn 2022

CK45 steel is medium carbon steel that has a wide range of applications in the production of widely used parts such as shafts, gears, axles, crankshafts, forging, rails, etc. Austenitizing is the first step in most heat treatment processes for steel. Revealing austenite grain boundaries is very important because the austenite grains have a significant influence on steels properties. Because no research has been done on the detection of prior-austenite grain boundaries of CK45 steel, our main aim in this paper is revealing the prior-austenite grains of this steel. We investigated two methods of chemical etching and oxidation etching to reveal prior-austenite grains boundaries of CK45 steel. Samples of CK45 with different structures(martensite, bainite, ferrite-perlite) steel were examined, and the optical microscopic images showed that the boundaries of the austenite grains were well visible with oxidation etching while with the chemical etching method, only the structure of the steels was determined.

Steel melting treatment powders always play an important role in reducing steel inclusions. These types of powders can be used in steel smelting production processes for all types of low-alloy and high-alloy steels. The composition of these powders are generally CaO-Al2O3-SiO2. Adding CaF2 values gives special properties to this type of refining powders. In this study, four types of refining powders with 3 to 6% of CaF2 were melted in induction furnace under high temperature and The surface of NiCrMoV low-alloy steel was impregnated by melting this sample of refining powders. The contact angle between the sample of melted refining powders and the surface of NiCrMoV steel was determined using Image Analysis (IA) and using Statistical Package for the Social Sciences (SPSS) was analyzed. The results showed increasing the percentage CaF2 about %6 in refining powder of CaO-Al2O3-SiO2 reduces the connecting angle of melting of refining powders on NiCrMoV steel about 60%.

The present study aimed to present a phenomenological and empirically-based constitutive model to predict flow behavior of a 304 stainless steel. Hot compression tests performed at temperatures of 9501100 °C and strain rates of 0.0050.5 s−1 up to the strain of 1. Classical hyperbolic sine equations with different parameters were used to derive functions for the yield stress and critical stress at the onset of dynamic recrystallization as well as the saturation stress of dynamic recovery as functions of the Zener-Hollomon parameter. Three regimes were considered to develop flow curves comprising the linear trend up to yield stress, recovery-dominant region based on the Estrin and Mecking model, and the recovery-recrystallization zone from the critical stress extends toward the steady state stress. Avrami-type equation was supposed for the kinetics of recrystallization and validated by the evolved microstructures at strain 1. Results comprised the Arrhenius expressions for the yield, saturation, and the steady state stresses, in addition of the equations for the critical and inflection strains as well as the exponent of Avrami-type kinetics for the recrystallization, the six parameters that the model is based on those relations via strain, strain rate, and temperature. Finally, the flow curves predicted by the model satisfactorily coincided with the experimental ones, confirmed that the proposed model can give an almost accurate estimation of the flow stress of 304 stainless steel.

Tundish, as a continuous metallurgical operator, provides steel for continuous casting molds with optimum flow rates, constant temperatures, uniform chemical compositions and low porosity. Basically, the cleanliness of the molten steel entering the mold is affected by the type of flow pattern and the performance of the tundish in flotation and removal of non-metallic impurities. In this paper, the fluid flow and heat transfer in a tundish in 2 cases, without an obstacle and with an obstacle, turbo-stop, which is installed at its bottom and across the melt input is simulated using the Ansys Fluent at melt heights of 0.5, 0.65, and 0.75 m. Results show that the formation of the secondary circulating flow inside the obstacle is the most important reason for the input melt velocity reduction. Increasing the melt height leads to a more uniform and less turbulent flow. Furthermore, increasing the melt height from 0.5 m to 0.75 m leads to %3 reduction of the average flow velocity. The highest heat transfer loss is from the top surface of the tundish and therefore, the most temperature gradient exists at the top surface of the melt. The flow movement paths from the tundish input show that the melt flow velocity towards the sides of the tundish is increased with the melt height inside it. Furthermore, higher melt height causes the formation of higher stagnant melt volume inside the tundish, which negatively influences the inclusion absorption by the slag.

Due to technological advances and the growing need to repair parts at low cost, the gas metal arc welding (GMAW) method has become increasingly popular among industrialists. The response surface methodology (RSM) and model validity were measured with standard statistical measures. In this research, the input parameters including; welding speed (mm/min), voltage (V), and wire feed rate (cm/min), have been selected as input parameters. Mini-tab software was utilized to carry out modeling and optimization using RSM. On heat resistance steel (SUH 310S) using the RSM method, 17 experimental experiments were designed with three center points. According to the signal-to-noise ratio (S/N), the effective parameters of mechanical properties and hardness are wire feed rate, voltage, and welding speed, respectively. The results showed that the analysis of variance (ANOVA) with the desirability model obtained 0.953. Optimum levels for each input variable were analyzed in terms of mechanical properties and welding hardness. Finally, the optimum levels obtained are welding speed of 250 mm/min, wire feed rate of 210 cm/min, and voltage of 17 volts.

Improving the level of quality of products and services provided by companies is the first and main factor of development to get a major market share. In this regard, the failure mode and effects analysis are an effective method to improve the quality and reduce waste in products. To eliminate the existing defects, especially protrusion of the melt from the casting parts, the analysis of potential failure modes based on the multiplication of three numbers of intensity, occurrence and detect was used. The results of the study showed that to reduce the melting run out defect, the most important potential for failure is the lack of skills and experience of personnel in assembly, inadequate quality of raw materials, non-compliance with continuous casting with a risk priority number of 300,400,450, respectively. Continuous training, preparation of a checklist for input items and controlling the molding continuity reduced waste run outs defect by 70%.

Cracking tubes as the main part of an olefin unit, are exposed to very harsh working conditions at both outer and inner surfaces, associated with major microstructural changes during service. Carburization, oxidation, alloying elements depletion, carbide coarsening, and secondary carbide formations are common phenomena, expected to take place in cracking tubes. This research tries to experimentally investigate the implications of cracking service exposure on microstructure and mechanical properties of the service-exposed HP-MA cracking tubes. In this regard, two tube samples after 20000 and 45000 h service at approximately 900 °C were selected. Microstructure degradation at the inner and outer surfaces of the tubes and their mid-thickness were investigated with optical and electron microscopes. By microstructural characteristics of both tube samples, it was concluded that in the 45,000-hour sample, which was more exposed to carbon, the number of secondary carbides formed on the outer surface was higher. Hardness variation across the thickness was also measured for both tubes and according to the results, in total thickness of the 45,000-hour sample, the hardness was more than the 20,000-hour specimen.

Milling is one of the most important operational stages in steel and copper processing. Liners and lifters are used inside mill to extend their life and to enhance the grinding and crushing efficiency. The wear of lifters is influenced by a range of parameters such as: media charge level and mill speed. In this work, the researcher used a pilot mill of 1m diameter and 0.5m length to investigate the influences of ball filling and the mill speed on the impact wear of lifters under wet condition. The contribution of impact wear and abrasive wear from the total wear was investigated with new mechanical test method. A copper ore smaller than one inch was used to prepare slurry at 60% solids concentration of mass and slurry filling U=1. The ball filling is 10%, 20% and 30% of mill volume at different mill speeds from 60% to 100% of the critical speed. It was found that while there is an increase in ball filling the wear impact decreases. The wear rate was maximum when the mill speed varied between 80% and 90% of the critical speed. To find out the role of impact on the wear, a mechanism was devised and installed on the pilot mill to prevent the cascade motion.

The instability point of a material is one of the most important factors when choosing a material, as it could be a good representation of its formability. In this study, the instability of functionally graded materials (FGM) was investigated. An algorithm is proposed for predicting the instability of functionally graded low-carbon steel with gradient work hardening exponent (n) and strength coefficient (K). The investigated work hardening exponent and strength coefficient of the FGM vary through the cross-section as a function of radius. Numerical methods like the Simpson rule of integration were utilized to solve the equations. The mathematical and experimental results are compared, and it can be seen that the algorithm has a reliable consistency with the experimental results. The presented analysis shows that the instability of the functionally graded low-carbon steel can be predicted using the calculation of the average strain hardening exponent. The calculated average work hardening exponent (n ̅) was 0.1095 and 0.1657 for the 550 °C and 650 °C annealed samples, respectively. The instability of more complicated FGMs can be predicted with the present algorithm.

Interdependence of markets may cause fluctuations in one market to positively or negatively affect another market. Therefore, investigating the behavior of fluctuations in financial markets and their causes in financial asset pricing processes, implementation of global risk hedging strategies and asset portfolio preference decision-making is of great importance. Given the importance of this issue, the current research aims to model energy and steel price volatility and experimentally test the spillover of fluctuations between markets using the GARCH BEKK model, during a 10-year period of 2013-2022. The data of the current research were extracted from daily data from the World Data Bank, Coin and Currency Information Site, and Economic and Financial Data Bank; then, using the Dickey-Fuller and Phillips-Perron tests, the significance of the data was evaluated. After that, the spillover effect of fluctuations between the markets was tested using the univariate GARCH and GARCH BEKK tests. The results of the first hypothesis indicate that the energy market has turbulence during the study period. As a result of the second hypothesis, it was found that the effect of turbulence exists in the price of steel during the study period. Finally, the result of the third hypothesis showed that there is an overflow of fluctuations from the price of oil and gas to the price of steel.