International Journal of iron and steel society of Iran
Volume:19 Issue: 1, Winter and Spring 2022

Nowadays, clean liquid steel is crucial for improving castability, increasing production efficiency, and generating high-quality, customer-satisfying products. This research studied the influence of aluminum deoxidation process on the inclusion content in steel products. The image analysis technique and the calculation of inclusion volume fraction were used to assess the cleanliness of steel products. A total of 37 heats of typical medium carbon Al killed steel with aluminum contents in the 0.015-0.040 wt.% range were put to the test. The findings revealed that at least 70% of the total aluminum utilized in the tapping and ladle furnace (LF) must be added during the tapping process in order to produce a clean steel product with an inclusion volume fraction of less than 0.023%. Moreover, aluminum granules need to be added once throughout the LF process during the first 15 minutes of the process. In order to adjust the aluminum content in the liquid steel, the aluminum wire must be fed all at once at the last minute of the LF process.

In the surface mechanical attrition treatment (SMAT) process, the material surface layer is peened with a high-velocity number of carbon steel shot particles. Various parameters such as the distance of the peening gun to the impacted surface can affect the material's surface mechanical properties in the SMAT process. In this paper, the molecular dynamics (MD) approach has been used to study the effect of particle distance from the impacted surface on mechanical and physical behavior of AZ31 after the SMAT process. For this purpose, Universal Force Field (UFF) and Embedded Atom Model (EAM) force field have been utilized for atomic interactions. Based on the molecular simulation results, residual stress, hardness, and temperature of the atomic surface layer have been obtained for various distances. The simulation results demonstrated that reducing the particle distance in the SMAT process increases residual stress and surface layer hardness. Numerically, the maximum residual stress value of 268 MPa has been obtained for a distance of 5 nm in the SMAT molecular simulation results.

The geometric shape of the sponge iron (direct reduced iron, DRI) particles used in the induction furnace is very influential on the steel making process. In this paper, the effect of geometric deformation of DRI from spherical (regular shape) to other shapes on the final product quality and performance of induction furnaces is investigated. The results showed that the typical spherical shape of DRI melts over time and consumes more energy due to the air gap between its particles. More extended periods cause more oxidation and, consequently, more iron loss and lower iron production rates. In the crushed DRI, due to rapid melting, oxidation is much less and with a high iron grade (94.9%) in steel, more molten weight, and a higher iron production rate (1.94 g/s) than other samples. Other geometric shapes, such as cylinders and cones, cannot be used industrially due to their high manufacturing costs, despite having mediocre results.

This paper has been concerned to investigate in details the effect of tempering heat treatment on mechanical properties of 35CHGSA heat treatable low alloy steel under ferrite–martensite dual-phase (DP) microstructures. For this aim, two sets of ferrite–martensite DP samples containing 6% volume fraction of ferrite have been developed using step-quench heat treatment processes at 720°C for 5 min holding times with the subsequent water quenching after being austenitized at 900°C for 15 min. In comparison to first set of fresh ferrite–martensite DP samples (marked FDP), the finalized tempering heat treatment has been carried out at 500°C for 60 min only for the second set of tempered ferrite–martensite DP (marked TDP) samples in order to optimize the strength–ductility combination. Light and electron microscopes have been used in conjunction with hardness and tensile tests to assess the structure–property relationships of FDP and TDP heat-treated samples. The experimental results demonstrate that the mechanical properties of FDP heat-treated samples are significantly increased after tempering heat treatment. The product of tensile strength multiple total elongation has been significantly increased from 2.4 (FDP) to 15.8% GPa (TDP). Moreover, the absorbed impact energy is sharply increased from 3.5 to 12 J cm-2 corresponding to the FDP and TDP marked samples, respectively. These results are rationalized to the fact that the tempering heat treatment modifies the individual mechanical behavior of ferrite and martensite microphases through influencing the ferrite and martensite hardening variations.

An improved model for fatigue life evaluation of a steel thin-wall tubular specimen based on critical plane theory is presented. This new fatigue model incorporates the crack initiation phase in the life prediction model. The total fatigue life is a combination of both crack initiation and crack propagation lives. The initial crack length is not applied priory, but is calculated within the model. The crack initiation life is evaluated using a critical plane approach base on a modified Smith-Watson-Topper and the Fatemi-Socie criteria. The fatigue lives obtained from the proposed model are validated by experimental results for a thin-wall tubular specimen. Both critical plane criteria gave similar fatigue lives, with the Fatemi-Socie criteria giving a slightly more accurate initiation life. Without consideration of the crack initiation phase, the model absolute error is high. The proposed model indicates that a correct determination of the fatigue life requires consideration of the crack initiation phase.

Austenitic stainless steels are widely used in different industries because of their attractive mechanical properties as well as their reasonable corrosion resistance. While different works have been focused on the severe plastic deformation of austenitic stainless steels, recrystallization kinetics of these alloys after the imposition of severe plastic deformation is remained less studied. The aim of this work is to study the recrystallization kinetic of austenitic stainless steels 316L after the imposition of severe plastic deformation using equal channel angular pressing. For this purpose, the alloy is processed by 0, 1, 2, and 4 passes of the mentioned process at 310 ºC by route BC. Afterwards the processed specimens are subjected to annealing at 800 ºC for a duration of 9 to 30 min. During these procedure, the kinetic of recrystallization is studied using the optical microscopy while the optical microscopy results are analyzed by the MIP5 image analyzing software. Also, the volume fraction of recrystallization is interpreted using the JMAK model. Results show that the exponent of recrystallization duration in the JMAK model is between 3 and 4. The mechanism probably involving these phenomena are discussed.

Recently, laser powder bed fusion (LPBF) technology as an important additive manufacturing (AM) technique has attracted the attention researchers. It uses a laser source to melt metal powder in layers in order to build parts. In this study, electrochemical and surface properties of 316L stainless steel manufactured by rolling and laser powder bed fusion (LPBF) were investigated in 0.1 M H2SO4 solution. In order to examine the corrosion behavior of stainless steel in acidic medium, electrochemical methods, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and characterization methods such as field emission scanning electron microscopy (FESEM), and x-ray photoelectron spectroscopy (XPS), were used. As a result of the electrochemical tests, the charge transfer resistance of stainless steel fabricated by LPBF increased about 8 times and Ecorr shifted about +40 mV compared to the rolled stainless steel. LPBF produced samples had higher corrosion resistance due to the fine cellular and spherical inclusion microstructure formed during fabrication process.