Search results

The purpose of this paper is to enhance the corrosion resistance of Cr-Mn austenitic stainless steel (ASS) via low temperature salt bath nitriding and to replace the convectional Cr-Ni ASS with newly developed enhanced corrosion resistive Cr-Mn ASS.

The low temperature salt bath nitriding was performed on Cr-Mn ASS at 450°C for 3 h in potassium nitrate salt bath.

The present paper compares the corrosion resistance of salt bath nitrided Cr-Mn ASS with convectional Cr-Ni ASSs (316 L and 304 L ASSs) in 3.5 per cent NaCl by electrochemical techniques. The electrochemical impedance spectroscopy result shows the increase in film resistance and potentiodynamic polarization results show the enhanced corrosion resistance of nitrided Cr-Mn ASS, which is almost equivalent to that of 316 L and 304 L ASSs. This is attributed to the formation of nitrogen supersaturated dense nitride layer. The present results therefore suggest that the nitrided Cr-Mn ASS may replace costly convectional Cr-Ni ASSs for commercial and industrial applications.

Ever-increasing price of nickel (Ni) is driving the industries to use Ni-free or low-Ni austenitic stainless steels (ASSs). But its corrosion resistance is relatively poor as compared to conventional Cr-Ni ASSs. However, its corrosion resistance can be improved by nitriding. The low temperature salt bath nitriding of Cr-Mn ASS and its electrochemical behavior in 3.5 per cent NaCl has not been studied. The present research paper is beneficial for industries to use low cost Cr-Mn, enhance its corrosion resistance and replace the use of costly conventional Cr-Ni ASSs.

Low nickel austenitic stainless steel (ASS) has attracted much attention worldwide because of its economical price. This study aims to investigate the effect of different corrosive environments on the corrosion behavior of chrome-manganese (Cr-Mn) ASS. The tests were carried out as a function of H₂SO₄ concentrations, temperature and addition of ammonium thiocyanate (NH₄SCN) (0.01 M). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of Cr-Mn ASS. It was observed that with increasing H₂SO₄ concentration, temperature and with the addition of NH₄SCN solution, icorr, icrit and ipassive values increased. EIS data show decreasing charge transfer resistance value with increasing concentration and temperature. Higher corrosion rate with increasing temperature and concentration of H₂SO₄ is related to the anions (SO₄²⁻), which is responsible for reducing the stability of passive films. With the presence of 0.01 M NH₄SCN thiocyanate (SCN⁻ anion), there is a higher dilution of the passive film resulting in a higher corrosion rate. Energy-dispersive spectroscopy (EDS) analysis reveals the adsorption of sulfur on the surface in NH₄SCN containing a solution. The significant presence of counter ions and the adsorbed sulfur species on the steel surface play a vital role in corrosion behavior.

All the experiments were performed on a 3 mm thick sheet of Cr-Mn ASS (202 ASS) in hot rolled condition. The samples were then annealed at 1,050°C for 1 h, followed by water quenching. For microstructural examination, they were electrochemically etched in 10 Wt.% oxalic acid solution at 1 amp for 90 s. A computer-controlled Potentiostat (Biologic VMP-300) was used. After the cell was set up, the working electrode (WE) was electrostatically cleaned at −1 V vs saturated calomel electrode (SCE) for 30 s to remove the air-formed film. Then, WE were allowed to attain stable open circuit potential (OCP) for 1 h, following by the EIS test and potentiodynamic polarization test. The polarization test was started from a cathodic potential (−1.2 V vs SCE) and continued up to an anodic potential (1.6 V vs SCE) a scan rate of 0.1667 mV/s. EIS experiment was conducted on the same instrument by using a sinusoidal AC signal of 10 mV in a frequency range of 1,000,000 to 0.01 Hz at OCP.

Potentiodynamic polarization graph shows that with the increase in sulphuric acid concentration. Increasing temperature from 20°C to 80°C in 0.5 M H₂SO₄ solution increases the corrosion rate (icorr) of Cr-Mn ASS. On the addition of 0.01 M NH₄SCN to the sulfuric acid solution (0.1, 0.5 and 1 M) the corrosion rate increases drastically almost four to five times. EDS and XRD analysis shows the presence of sulfur over the oxide film and preferential site for dissolution of Cr and Mn at the steel surface when NH₄SCN is added to the sulfuric acid solution.

A study on the corrosion behavior of Cr-Mn ASS is scanty according to the author’s knowledge. Therefore, the present study will investigate the corrosion behavior of Cr-Mn ASS on SO₄⁻² anions, temperature and the addition of SCN⁻ ion in sulfuric acid.

The purpose of the study is to evaluate Cr-Mn ASS weld using different heat inputs for its microstructure, mechanical properties and electrochemical behavior. The microstructural examination used optical and scanning electron microscopy. It was observed that ferrite content decreases with increasing heat input. The length of dendrites, inter-dendritic space and volume of lathy ferrite increase with increasing heat input. The increasing heat input caused grain coarsening near the fusion boundary and produced wider heat-affected zone (HAZ). It also decreases hardness and tensile strength. This is attributed to formation of more δ ferrite in the weld. The electrochemical evaluation suggested that the δ ferrite helps in improving the pitting potential in 3.5 per cent NaCl solution saturated with CO₂. Whereas in 0.5-M H2SO4 + 0.003-M NaF solution, higher passivation current density was observed because of dissolution of dferrite. The interphase corrosion resistance decreased with increasing heat input.

The Cr-Mn austenitic stainless steel or low-nickel ASS was procured in form of 3-mm sheets in rolled condition. The tungsten inert gas welding was performed at three different heat inputs (100 A, 120 A and 140 A), argon as shielding gas with a flow rate of 15 L/min. Different welded regions were observed using optical microscope and scanning electron microscope. Electrochemicals test were performed in solutions containing 3.5 per cent NaCl with saturated CO₂ solution and 0.5 M sulfuric acid + 0.003 M NaF at a scan rate of 0.1667 mV/s at room temperature (30 °C ± 1 °C) using a potentiostat.

The test steel Cr-Mn ASS is suitable with the selected electrode (308 L) and it produces no defects. Vermicular ferrite and lathy ferrite form in welds of various heat inputs. The increase in heat input reduces the formation of lathy ferrite. The width of HAZ and un-mixed zone increases with increase in heat input. The weld zone of low heat input (LHI) has the highest hardness and tensile strength because of higher δ ferrite content and small grain size in the weld zone. The hardness at high heat input (HHI) is found to be lowest because of grain coarsening in the weld. With increase in δ ferrite, the pitting resistance increases. In 0.5-M sulfuric acid + 0.003-M NaF, the increase in ferrite content reduces the passivation current density. Interphase corrosion resistance increases with increase in δ ferrite content as higher per cent degree of sensitization was observed in LHI welds as compared to medium heat input and HHI welds.

This work focuses on welding of ASS by tungsten inert gas welding at different heat inputs. Welding is a critical process for joining metals in most of the fabrication industries and proper heat input is required for getting desired microstructure in the weld metal. This would highly affect the strength and corrosion behavior of the alloy. This paper would give an understanding of how the change in heat input by tungsten inert gas welding affects the microstructural and corrosion behavior in the weld metal.

The purpose of this study is to investigate the effect of prior cold work after annealing and thermal ageing on intergranular corrosion or sensitization of Cr-Mn austenitic stainless steel (ASS) is necessary. Such a study is particularly important because ASS are mostly used and welded in mill-annealed condition, which is equivalent to fully annealed material with some cold worked (CW).

The effect of 15% CW of 202 ASS were investigated using microstructural (optical microscope), mechanical (grain size and hardness) and electrochemical methods (double loop electrochemical reactivation [DLEPR]) followed by thermal ageing (800°C, 900°C and 1000°C).

X-ray diffraction analysis shows the presence of martensite in CW samples. The increase in martensite formation (800°C and 900°C) can be observed with the variation of thermal ageing (TA) duration (1, 2 and 3 h). However, there was decreased in the formation of martensite at the temperature of 1000°C because of martensitic reversal. The DLEPR test result shows higher degree of sensitization (DOS) for 800°C and 900°C but for 1000°C, there was re-homogenization of samples which leads to lower DOS (thermal ageing for 1, 2 and 3 h).

For 300 series steel, there are various literature available for the effect of cold work on mechanical properties and DOS. However, no one has investigated the effect of cold work and thermal ageing on the sensitization of 202 Cr-Mn ASS.

The purpose of this study is to improve the anticorrosion performance of low nickel stainless steel (AISI 201) in 3.5% NaCl by electroactive polyimide/copper oxide (EPI/CuO) composites coating.

Electroactive polyimide/copper oxide (EPI/CuO) composites were prepared by oxidative coupling polymerization followed by thermal imidization method.

The functional and structural properties of composites were characterized by X-ray diffraction, Fourier transmission infra-red and ultra violet-visible spectroscopy and the surface topography was characterized by field emission scanning electron microscope analysis and anticorrosion performance in 3.5 Wt.% NaCl was evaluated by electrochemical techniques. The obtained results of electrochemical techniques measurement indicated that the composites coated samples give better corrosion protection against attacking electrolyte.

The ever-increasing price of nickel (Ni) is driving the industries to use low-Ni austenitic stainless steels (ASSs). However, it exhibits relatively poor corrosion resistance as compared with conventional Cr-Ni ASSs. Nonetheless, its corrosion resistance can be enhanced by polymeric (electroactive polyimide [EPI]) coating. CuO particles exhibit the hydrophobic properties and can be used as inorganic filler to incorporate in EPI to further enhance the corrosion protection. The present research paper is beneficial for industries to use low-cost AISI 201, enhance its corrosion resistance and replace the use of costly conventional Cr-Ni ASSs.

The purpose of this study is on AISI 409 M ferritic stainless steel (FSS) which is developing a preferred choice for railway carriages, storage tanks and reactors in chemical plants. The intergranular corrosion behavior of welded SS 409 M has been studied in H₂SO₄ solution (0.5 M) with the addition of NH₄SCN (0.01 M) with different heat input. As this study is very important in context of various chemical and petrochemical industries.

The microstructure, mechanical properties and intergranular corrosion properties of AISI 409 M FSS using shielded metal arc welding were investigated. Shielded metal arc welding with different welding current values are used to change the heat input in the joints resulted in the microstructural variations. The microstructure of the welded steel was carefully inspected along the width of the heat-affected zone (HAZ) and the transverse-section of the thin plate.

The width of heat affected zone (3.1,4.2 and 5.8 mm) increases on increasing the welding heat input. Due to change in grain size (grain coarsening) as HAZ increased. From the microstructure, it was observed that the large grain growth which is dendritic and the structure become finer to increase in welding heat input. For lower heat input, the maximum microhardness value (388HV) was observed compared with medium (351 HV) and higher heat input (344 HV), which is caused by a rapid cooling rate and the depleted area of chromium (Cr) and nickel (Ni). The increase in weld heat input decreases tensile strength, i.e. 465 MPa, 440 MPa and 418 MPa for low, medium and high heat input, respectively. This is because of grain coarsening and chromium carbide precipitation in sensitized zone and wider HAZ. The degree of sensitization increases (27.04%, 31.86% and 36.08%) to increase welding heat input because of chromium carbide deposition at the grain boundaries. The results revealed that the higher degree of sensitization and the difference in intergranular corrosion behavior under high heat input are related to the grain growth in the HAZ and the weld zone.

The study is based on intergranular corrosion behavior of welded SS 409 M in H2SO4 solution (0.5 M) with the addition of NH4SCN (0.01 M) with different heat input which is rarely found in literature.

This paper aims to study the effect of number of welding passes on microstructure, mechanical and corrosion properties of 409 M ferritic stainless steel. Shielded metal arc welding (SMAW) process is used to weld two metal sheets of 409 M having 3 mm thickness as bead-on-plate with single, double and triple passes. Microstructures were observed at transverse section with the help of optical microscope and with increasing number of passes grain growth, and the width of heat-affected zone (HAZ) increases. The results of tensile tests revealed that as number of passes increases, there is reduction in tensile strength and ductility. Double loop electrochemical potentiokinetic reactivation (DL-EPR) test revealed that as number of passes increases, the degree of sensitization increases. This is due to the deposition of chromium carbides at the grain boundaries and the associated depletion of chromium.

Three welded plates of single, double and triple pass were welded by SMAW process. From three welded plates (single, double and triple passes), samples for microstructural examination were cut in transverse direction (perpendicular to welding direction) with the help of wire-cut electrical discharge machine (EDM). The welded plates were sliced using wire-cut EDM along transverse direction for preparing optical microscopy, tensile testing, microhardness and DL-EPR testing specimens.

From the microstructure, it was observed that the large grain growth, which is dendritic, and the structure become finer to increase in number of welding passes. As number of passes increases, the width of HAZ increases because of the higher temperature at the welded zone. The tensile strength decreases to increase the number of welding passes because of grain coarsening and chromium carbide precipitation in sensitized zone and wider HAZ. The maximum microhardness value was observed for single-pass weld as compared to double- and triple-pass welds because of the fast cooling rate. The degree of sensitization increases to increase the number of passes because of chromium carbide deposition at the grain boundaries.

The authors declare that the manuscript is original and not published elsewhere, and there is no conflict of interest to publish this manuscript.