Ihsan-ul-Haq Toor

Manganese Effects on Repassivation Kinetics and SCC Susceptibility of High Mn–N Austenitic Stainless Steel Alloys

Effects of Mn on the localized corrosion, repassivation kinetics, and stress corrosion cracking (SCC) of high Mn-N stainless steels (SSs) were examined in chloride solutions and compared with those of type 304 SS. The resistance to pitting corrosion of high Mn-N SSs decreased with an increase in Mn content at the expense of Ni. Repassivation kinetics of the high Mn-N SSs was analyzed by the relationship between the current density i(t) and the charge density q(t) that has flown from the scratch; passive film initially nucleated according to the place exchange model and then grew according to the high-field ion conduction model in which log i(t) vs 1/q(t) has a linear relationship with a slope (cBV). The repassivation rate of the alloys, analyzed by the (cBV) value, was decreased with an increase in the Mn content. The resistance to SCC of the alloys measured in 25% MgCl 2 was in good agreement with that predicted, based on their repassivation rate. The deleterious effects of Mn on the localized and stress corrosion of the alloys appear to be associated with an increase in number and size of nonmetallic inclusions such as (Mn, Cr) oxides with Mn content.

Effects of Si on the Repassivation Kinetics and SCC Susceptibility of Stainless Steels

Effects of Si on the repassivation kinetics and stress corrosion cracking (SCC) of alloy 304Si were examined by a scratch electrode technique and slow strain rate test in chloride solutions and compared with those of other stainless steels (SSs), 304 and 316L. Repassivation kinetics of these alloys and Fe-20Cr-xSi (x = 0-2) alloy were analyzed in terms of the current density, i(t), flowing from the scratch as a function of the charge density, q(t), that has flowed from the scratch. Passive film initially nucleated and grew according to the place exchange model, and then grew according to a high-field ion-conduction model in which log i(t) has a linear relationship with 1/q(t) with a slope of cBV. The repassivation rate of Fe-20Cr-xSi (x = 0-2) alloys, evaluated by the cBV value, increased with an increase in Si content. Furthermore, repassivation rate decreased on the order of 304Si, 316L, and 304. The resistance to SCC of the SSs (304Si, 304, and 316L) measured in 35 wt % MgCl 2 solution at 120°C was in good agreement with those predicted based on the repassivation kinetics. The beneficial effects of Si on SCC of 304Si SS appears to be associated with the enrichment of Si in the passive film.

Solid Particle Erosion Downstream of an Orifice

The paper deals with solid particle erosion downstream of a sharp-edged orifice commonly found in many chemical processing industries. The orifice is installed in a pipe that is long enough to ensure fully developed turbulent flow in both upstream and downstream directions. Both the k-e model and the Lagrangian particle-tracking technique were used for predicting solid particle trajectories. Gambit 2.2 was used to construct the computational grid and the commercial Fluent 12.1 code was used to perform the calculations. The available erosion correlations were used for determination of erosion characteristics considering carbon steel and aluminum pipes. The investigation was carried out for a flow restricting orifice of fixed geometry and pipe flow velocities in the range 1–4 m/s using solid particle of diameters 50–500 μm. The results indicated two critical erosion regions downstream of the orifice: the first is in the immediate neighborhood of the orifice plate and the second is in the flow reattachment zone. The results showed also a strong dependence of erosion on both particle size and flow velocity.

Effect of Sintering Holding Time on the Corrosion Properties of Nano-Structured Fe-18Cr-2Si Alloy Prepared by SPS

Spark plasma sintering (SPS) was used to synthesize Nano-structured Fe-18Cr-2Si alloy with Fe-18Cr2Si ball milled powders. SPS was carried out in vacuum at three different holding time (5, 10 and 15min) at a fixed sintering temperature (1100 °C) and applied pressure (50MPa). Potentiodynamic Polarization (PDP), Linear Polarization (LPR) and Electrochemical Impedance Spectroscopy (EIS) were used to study the effect of sintering time on the electrochemical properties of nanostructured alloy in deaerated 0.2M NaCl and 0.5M H2SO4 solutions respectively. Corrosion resistance measured in terms of corrosion potential (Ecorr), pitting potential (Epit) and passive current density (ip) was found to be increased with an increase in holding time. Density of the samples was measured by Archimedes’ method and results showed the highest density for the specimen sintered for 15 min at 1100 0 C.

Effect of Mn Content and Solution Annealing Temperature on the Corrosion Resistance of Stainless Steel Alloys

The corrosion behavior of two specially designed austenitic stainless steels (SSs) having different Nickel (Ni) and Manganese (Mn) contents was investigated. Prior to electrochemical tests, SS alloys were solution-annealed at two different temperatures, that is, at 1030°C for 2 h and 1050°C for 0.5 h. Potentiodynamic polarization (PD) tests were carried out in chloride and acidic chloride, whereas linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) was performed in 0.5 M NaCl solution at room temperature. SEM/EDS investigations were carried out to study the microstructure and types of inclusions present in these alloys. Experimental results suggested that the alloy with highest Ni content and annealed at 1050°C/0.5 hr has the highest corrosion resistance.

Corrosion resistance of laser treated titanium alloy with B4C particles at the surface

Abstract Laser treatment of pre-prepared titanium alloy surface is carried out and electrochemical response of the treated surface is analyzed. B4C particles are located in a carbon film at the workpiece surface prior to the laser treatment process. Morphological and metallurgical changes are examined in the laser treated layer using analytical tools. Potentiodynamic tests are carried out to assess the corrosion rate of the treated surface. It is found that the laser treated surface is free from large-scale asperities such as large size cracks and cavities. Laser treatment significantly improved the corrosion resistance of the surface. The presence of B4C particles contributes to microhardness enhancement at the treated surface; however, the particles do not demonstrate any adverse effect on the corrosion resistance of the surface.

Evaluation of corrosion performance of two Mn-containing stainless steel alloys

Abstract 300 series austenitic stainless steels (SSs) are widely used as structural materials in various corrosive environments because of their excellent corrosion resistance and good mechanical properties. However, due to the rapid increase in Ni cost over the last few years, there have been attempts to develop cheap SSs while still maintaining their relatively high corrosion resistance. The possible replacements for Ni (a gamma stabilizer) in SSs are Mn, N and Cu etc. In this paper, the effect of Mn addition on the corrosion properties of two SS alloys, i. e. 202M2 and 202M4, is discussed and results are compared with those of 304 SS alloy. Results of different tests showed that overall corrosion resistance properties (measured in terms of pitting potential (Epit), metastable pitting events density and time to failure etc.) decreased with an increase in Mn content of the alloys.

Mott–Schottky analysis of passive films on Cu containing Fe–20Cr–xCu (x = 0, 4) alloys

Abstract Effect of copper on the defect density of Fe–20Cr–xCu (x = 0, 4) stainless steel alloys was investigated in deaerated pH 8·5 borate buffer solution at room temperature using Mott–Schottky analysis. Mott–Schottky analysis revealed that the addition of copper increased the acceptor density (NA, VCr−3), i.e. decreased the Cr+3 content of the passive film. Also the donor densities, shallow donor (ND1, VO+2) and deep donor (ND2, VCr+6), of the passive films formed were increased. XPS analysis confirmed the decrease in Cr content and enrichment of copper in the passive film of Cu containing alloys, which ultimately dictated their lower corrosion resistance, i.e. decreased film protectiveness and stability.

Laser treatment of high strength low alloy steel and electrochemical response of the surface

Purpose – The purpose of the present study is to report the results of the laser treatment of high-strength low-alloy (HSLA) steel surface and corrosion response of the treated surface that was carried out. Metallurgical and morphological changes in the laser-treated layer are also examined. Laser treatment of the alloy surface improves the surface properties; however, development of high thermal stress field in the treated layer can exceed the yielding limit of the alloy lowers, particularly, the corrosion resistance of the resulting surface. Design/methodology/approach – Pre-prepared workpiece surfaces are laser-treated and electrochemically tested in an electrolytic solution. Corrosion rate of the resulting surface is analyzed and pit sites are examined. Findings – It is found that the presence of nitride compounds and fine grains acts like as a self-protective layer at the laser-treated surface while lowering the corrosion resistance. Consequently, laser gas-assisted treatment provides a positive effe...

Comparison of Corrosion Behavior of Electrochemically Deposited Nano-Cobalt-Coated Ni Sheet

Corrosion behavior of nano-coblat-coated Ni sheet was compared with pure Ni and 20% Fe-Ni alloy sheet using potentiodynamic polarization and linear polarization technique in 0.1 M NaCl solution at room temperature. Results showed that corrosion resistance properties of nano-Co-coated Ni sheet were almost same as that of pure Ni sheet, however corrosion resistance of 20% Fe-Ni sheet was decreased significantly. Pitting potential of 20% Fe-Ni sheet was subsequently decreased as compared to pure Ni sheet as well as nano-cobalt-coated Ni sheet. SEM/EDS analysis of the corroded surfaces showed that both pure Ni and nano-coblat-coated Ni sheet did not show any appreciable corrosion however significant corrosion was observed in the case of 20% Fe-Ni sheet.