ASTM A262 Research Articles

Effect of Ultrasonic Shot Peening on Microstructure and Corrosion Properties of GTA-Welded 304L Stainless Steel

Austenitic stainless steels used in structural applications suffer from stress corrosion cracking due to residual stresses during welding. Much research is being conducted to prevent the stress corrosion cracking of austenitic steels by inducing compressive residual stresses. One method is ultrasonic shot peening (USP), which is used to apply compressive stress by modifying the mechanical properties of the material’s surface. In this study, 304L stainless steel was butt-welded by gas tungsten arc welding (GTAW) and subsequently subjected to compressive residual stress to a depth of 1 mm from the surface by a USP treatment. The influence of USP on microstructural changes in the base metal, the HAZ and weldment, and the corrosion properties was analyzed. A microstructural analysis was conducted using SEM-EDS, XRD, and EBSD methods alongside residual stress measurements. The surface and cross-sectional corrosion behavior was evaluated and analyzed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) measurements, a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, and an ASTM A262 Pr. C test. The surface was deformed and roughened by the USP. The deformed areas formed crevices, and the inside of the crevices contained some cracks. The crevices and internal cracks caused pitting, which reduced the resistance of the passivation film. The cross-section was subjected to compressive residual stress to a depth of 1 mm from the surface, and the outermost area of the cross-section had fine grain refinement, forming a solid passivation film that improved the corrosion resistance.

Evaluate Effect of Pulsed Current Gas Tungsten Arc Welding Process Parameter on Intergranular Corrosion of SS304L Weld

Austenitic stainless steel (ASS) is the most common type of stainless steel which offers excellent weldability and mechanical properties. ASS is being used for various applications i.e. automotive, oil and gas and chemical industries in which the welding process plays a prominent role. Welding process selection is the main factor that emphasizes mechanical and corrosion resistance properties in various aggressive environments. There are various corrosion occurs in ASS but intergranular corrosion (IGC) forms during welding at elevated temperatures. IGC mainly occurs at grain boundaries of structure and resulting chromium depletion due to precipitation of chromium carbide at the grain boundary. In present work pulsed current gas tungsten arc welding (PCGTAW) process was used to investigate intergranular corrosion by oxalic acid test as per ASTM A262 Practice A. Experiments performed based on Taguchi L9 using design of experiments and corrosion rates are evaluated at base metal, heat affected zone and weld zone. This work is aimed to optimize process parameters followed by regression analysis to IGC susceptibility in the weldment. In this investigation, it has been found from ANOVA and main effects plots that peak current and base current are the most significant parameters in the PCGTAW process. The results of the corrosion test revealed that heat affected zone is more susceptible to IGC. At the end, it has been observed that the optimum value of peak current, base current and frequency based on regression analysis are 100 A, 50 A and 6 Hz respectively.

Influence of Welding Energy on Intergranular and Pitting Corrosion Susceptibility of UNS S32205 Duplex Stainless-steel Joints

This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Effect of heat treatment on microstructure and mechanical properties of boron containing Ti-Stabilized AISI-321 steel for nuclear power plant application

Effect of boron on microstructure and its influence on elevated temperature properties of titanium stabilized AISI 321 steel was studied. A comparative study on mechanical properties of AISI 321 steels with and without boron addition is done. Both steels were worked to get appropriate reduction using forging-rolling process followed by solution annealing (SA) and stabilizing treatment (ST) at the appropriate temperature. Optical micrographs revealed uniform distribution of precipitates in steel. The precipitate count for Ti-stabilized AISI 321 steel with 30 ppm boron (TB30) was higher than Ti-stabilized AISI 321 steel (TB1) in which TiN and TiCN precipitates were observed. In addition to this, for TB30 steel containing boron precipitates of Fe2B and Cr2B were also observed. Precipitates refined the austenite matrix and provided yield strength stability to the AISI 321 steels. Boron addition in TB30 steel improved YS and UTS of AISI 321 steel with a marginal loss in ductility. SA and ST, TB30 steel exhibited best mechanical properties at room and elevated temperature (350 °C). Further, quantification of intergranular corrosion was done by sensitization of samples at 675⁰C for one hour and evaluated as per ASTM A262 specification practice A and practice E. Addition of nearly 30 PPM boron is highly beneficial in titanium stabilized AISI 321 steel that led to increased resistance to sensitization (both according to practice A and practice E) and improved the microstructural stability at elevated temperature resulting a reduction in intergranular corrosion and improved the elevated temperature mechanical properties. Thus, SA and ST, TB30 steels showed superior results as compared to TB1 steel. Study shows that TB30 steel is more suitable material to replace the cooling water inlet and outlet tubes of VVER type nuclear reactor.

The Effect of Severe Plastic Deformation on the Corrosion Resistance of AISI Type 304L Stainless Steel

The AISI type 304L stainless steel (SS) was solution annealed at 1050 °C and cryo-rolled at liquid nitrogen (L-N2) temperature (77 K) under severe plastic deformation (SPD). The thickness reduction through cryo-rolling plastic deformation was carried out up to 90% (designated as CR-90) of initial thickness. The cryo-rolling during rolling at liquid N2 temperature (77 K), resulted in transformation induced plastic deformation of the austenite γ-phase into α’- martensite phase. The phase transformation was characterized by x-ray diffraction (XRD) and saturation magnetization (Ms) measurement. The microstructure was measured by using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD peak positions confirmed the martensite (α’) phase formation. Saturation magnetization (Ms) value of the cryo-rolled specimens shows increasing linearity with cryo-rolling, and transformed to bct martensite (α’). The measured corrosion rate of the cryo-rolled specimens as per ASTM A-262 practice-C test (Huey test) ranges from 6.6 mpy or 0.167 mm/yr (CR 0) to 12.9 mpy or 0.328 mm/yr (CR 90), indicating the effects of severe deformation of strain-induced martensite with the cryo-rolling. Further, the role of severe deformation of strain-induced martensite with the cryo-rolling on AISI type 304L SS and also influence on the corrosion resistance are investigated in detail. The deformation microstructure roles, i.e., the phases and volume percentage induced by the different percentage of the cryo-rolling that influences the corrosion resistance properties and corresponding corrosion resistance in nitric acid have been investigated.

A study on corrosion behavior of stainless steel dissimilar alloy weld joints (321 & 347)

In this work dissimilar weld is obtained between SS 321 and SS 347 through robot guided MIG welding process. The Weldments are subjected to intergranular Corrosion test as per ASTM A262 and studied. Particularly considering the applications in wide range such as chemical storage, exhaust manifolds of automobiles and aircraft, where the surfaces are subjected to corrosive environment is taken for investigation. The specimens were welded with two different electrode wires ER 321 and ER 347. The results found that at 140A welding current and with ER347 there are no intergranular cracks and fissures found. The ER 347 is found to be the best suited electrode when compared to ER321 for welding these dissimilar joints.

Rejuvenation of Inside Surface of Intergranular Corrosion-Damaged Type 304 Stainless Steel Tube through Laser Surface Melting

The present paper describes an experimental study aimed at rejuvenation of internal surface of intergranular corrosion-damaged type 304 stainless steel tube through laser surface melting. In the present investigation, effectiveness of laser surface melting technique was experimentally demonstrated on the inside surface of type 304 SS tubular specimens, which is often the requirement in most of the industrial applications as the process fluid flows through tubes/pipes. The results of the study demonstrated that laser surface melting treatment of inner surface of intergranular corrosion-damaged type 304 stainless steel not only erased previous IGC damage, but also restored its degree of sensitization close to that of untreated condition. Laser surface-melted specimens successfully passed ASTM A262 practice E test, thereby not displaying susceptibility to intergranular corrosion. However, subsequent exposure to susceptible temperature (973 K) brought about enhancement in IGC susceptibility of laser rejuvenated surface of 304 stainless steel tube. As a logical extension of the experimental corrosion study, a laser beam maneuvering system was designed to carry out in situ laser surface melting treatment on the internal surface of tubular components. To the authors’ best knowledge, this type of laser beam maneuvering system has been designed first time to carry out laser surface melting for repair of intergranular corrosion inside the tubular parts. The results are important for rejuvenation of IGC-damaged in-service austenitic stainless steel components.

Failure Analysis on the Leakage of Methanator

The leakage of a methanator that made by 304H was analyzed. Near the lugs of the reactor, two cracks without any ductility were found in the hoop direction. From the cross-sectional view of the reactor pipe, more cracks were observed. The cracks were all initiated from OD and propagated to ID along the grain boundaries. “ASTM A262 method A” examination showed the microstructure of the cracked region had been sensitized seriously. And on the surface of the intergranular fracture, high content of sulfur was detected. These phenomena indicate the 304H reactor had suffered the intergranular stress corrosion cracking (IGSCC). According to the analysis reports on the rain pollution at the site, the most possible source of the corrosive medium should be $${\text{SO}}_{4}^{2 - }$$ from acid rain. The root cause of the IGSCC should be the insufficient consideration during design that only the strength in high-temperature service was considered, but the possibility of corrosion during downtime in the open-air environment was neglected.

Susceptibility to the intergranular attack in austenitic stainless steels

Intergranular corrosion is very dangerous local corrosion form that often leads to the dislodgment of individual grains and to the intensive negative influence on the mechanical properties of the material. The susceptibility of the austenitic stainless steels to the intergranular corrosion is connected with their exposition in the temperature range of 500-800 °C (“critical temperatures”) and with consequent slow cooling in the air which leads to the precipitation of chromium-rich carbides at the grain boundaries. This process consumes chromium from a narrow band along the grain boundaries and the steel becomes to be sensitized and susceptible to the intergranular corrosion in aggressive environments. This article deals with the susceptibility to the intergranular corrosion of three austenitic stainless steels (AISI 304, 316L, 316Ti). Both “as received” and improperly heat treated specimens (sensitization for 10 hours at 650 °C, cooling in the air) were tested by ASTM A262 standard method, A and E practices. Optical microscopy and SEM analysis were used for the assessment of the obtained results.

Pitting Corrosion Studies on Fusion Zone of Shielded Metal Arc Welded Type 316LN Stainless Steel Weldments

During welding of 316L stainless steel (SS), heat-affected zone (HAZ) is susceptible to sensitisation and fusion zone is susceptible to pitting corrosion in stainless steel welds. High-nitrogen electrodes with 0.045–0.055 wt% C and with different Cr contents were used for welding of prototype fast breeder reactor components. As-welded and thermally aged (823 K for 2 h) weldments of type 316LN SS with different N contents made by arc welding were studied for localised corrosion. ASTM A262 Practice A and E tests and double-loop electrochemical potentiokinetic reactivation studies on as-welded and thermally aged specimens revealed the absence of sensitisation in the HAZ and in fusion zone. However, pitting potential of the weldments was found to vary with the concentration of N + Cr + Mo in fusion zone and found to be lower in the thermally aged samples. The correlation between weld microstructure, alloying elements and pitting corrosion behaviour has been discussed.

Microstructure, Mechanical and Corrosion Behaviour of Weld Overlay Cladding of DMR 249A steel with AISI 308L

Abstract Medium strength low alloy steel is an attractive material for naval and defence applications for its excellent mechanical properties. DMR 249A is extensively used for application of ship building for its superior mechanical properties but owes poor corrosion resistance. In order to overcome the corrosion problem, Weld overlay cladding is used as an effective technique which improves the strength and corrosion resistance but also helps in manufacturing lightweight structures. Aim is to combat the corrosion by weld overlay surface coating using conventional arc welding process and observe the dilution. In the current study, Weld overlay cladding on medium strength low alloy steel (DMR 249A) of 50mm thick is done using manual metal arc welding process (MMAW) with corrosion resistant austenitic stainless steel (308L) electrode. Two layers of coating were done one over the other (each 2mm thick). Weld overlay clads were characterized for metallographic studies to observe the microstructure changes using image analyzer attached to optical microscopy and scanning electron microscopy (SEM). Mechanical testing were carried out using micro vickers hardness tester andductility bend test using Universal Testing Machine (UTM). Pitting corrosion behaviour is determined by the potentio-dynamic polarization tests in acidic chloride environment. Inter Granular Corrosion (IGC) was performed in boiling copper sulphate solution as per ASTM A-262 for 15 hours duration. The present investigation established that microstructure studies revealed increase in δ-ferrite in the weld overlay cladding. Superior mechanical properties are observed in second overlay coating compared to first overlay coating and base metal. Pitting potential in second overlay coating is observed to be more positive when compared with first overlay coating due to increase in chromium content. IGC studies showed that first overlay coating with AISI 308L observed to be more sensitized and having more weight loss which tends to be highly susceptible than second layer coating. It is attributed to the formation of high amount of delta ferrite.

Effect of Manufacturing Process on the Corrosion Properties of 304L Stainless Steel Pipe with 8-inch Diameter

Austenitic stainless steels used in nuclear power plants mainly use pipes made of seamless pipes, which depend on imports. The manufacturing process and high cost are some of the problems associated with seamless pipes. Therefore, in this study, the corrosion characteristics of the seamless pipe and the SAW pipe were assessed to determine the safety and reliability of the SAW pipe in a bid to replace the seamless pipe. Microstructure was analyzed using an optical microscope and the degree of hardness was measured using a Rockwell B scale. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. Anodic polarization test was performed in deaerated 1% NaCl solution at 30 ℃ and the U-bend method was used to evaluate the SCC resistance in 0.01 M Na2S4O6 at 340 ℃ and 40% NaOH solution at 290 ℃. Weld metal of the SAW pipe specimen showed relatively high degree of sensitization and intergranular corrosion rate. However, annealing to SAW pipes improved the corrosion properties in comparison to that of the seamless pipe.

Evaluation of inter-granular corrosion susceptibility in 316LN austenitic stainless steel weldments

The inter-granular corrosion resistance of 316LN austenitic stainless steel welding joints for an ITER Correction Coil case in the as-welded and post weld heat treatment (PWHT) condition were systematically investigated. Measurements were performed in accordance with the standard ASTM A262 and via double loop electrochemical potentiokinetic reactivation. The pitting corrosion resistance was determined for specimens immersed in sodium chloride solutions. In addition, the effect of microstructural characteristics on the corrosion resistance was analyzed. The results revealed that the dendrite size in the weldment slightly increased after PWHT. Moreover, the corrosion test results showed that the inter-granular corrosion resistance of the PWHT joint is significantly lower than that of the other specimens due to the element segregation in the weldments. However, all the specimens exhibite excellent pitting corrosion resistance, as indicated by the potentiodynamic polarization curves.

Argon Shrouded Plasma Spraying of Tantalum over Titanium for Corrosion Protection in Fluorinated Nitric Acid Media

Argon shrouded plasma spraying (ASPS) was used to deposit a Ta coating on commercially pure Ti (CP-Ti) under inert argon, for dissolver vessel application in the aqueous spent fuels reprocessing plant with high plutonium content. Oxidation during plasma spraying was minimized by shrouding argon system. Porosity and oxide content were controlled by optimizing the spraying parameters, to obtain a uniform and dense Ta coating. The Ta particle temperature and velocity were optimized by judiciously controlling the spray parameters, using a spray diagnostic charge-coupled device camera. The corrosion resistance of the Ta coatings developed by ASPS was investigated by electrochemical studies in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF. Similarly, the durability of the ASPS Ta coating/substrate was evaluated as per ASTM A262 Practice-C test in boiling nitric acid and fluorinated nitric acid for 240 h. The ASPS Ta coating exhibited higher corrosion resistance than the CP-Ti substrate, as evident from electrochemical studies, and low corrosion rate with excellent coating stability in boiling nitric, and fluorinated nitric acid. The results of the present study revealed that tantalum coating by ASPS is a promising strategy for improving the corrosion resistance in the highly corrosive reprocessing environment.

Effect of Heat Treatment on the Corrosion Properties of Seamless 304L Stainless Steel Pipe

Austenitic stainless steels have been widely used for various systems of nuclear power plants. Among these stainless steels, small pipes with diameter less than 14 inch have been produced in the form of seamless pipe. Annealing and cooling process during the manufacturing process can affect corrosion properties of seamless stainless steels. Therefore, 12 inch-diameter of as-received 304L stainless steel pipe was annealed and aged in this study. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. U-bend method in an autoclave was used to evaluate the SCC resistance in 0.01 M Na 2 S 4 O 6 or 40% NaOH solution at 340 °C. As-received specimen showed relatively high degree of sensitization and intergranular corrosion rate. Carbon segregation was also observed near grain boundaries. Annealing treatment could give the dissolution of segregated carbon into the matrix. Aging treatment could induce segregation of carbon and finally form carbides. Microstructural analysis confirmed that high intergranular corrosion rate of the as-received seamless pipe was due to micro-galvanic corrosion between carbon segregation and grains.

SURFACE MODIFICATION OF 316L STAINLESS STEEL BY PLASMA-ASSISTED LOW TEMPERATURE CARBURIZING PROCESS

This paper aims at improving the hardness and wear resistance of Austenitic 316L Stainless Steel (SS) by Plasma-assisted Low Temperature Carburizing (PLTC) process. The process has been employed in austenitic 316L SS for achieving carbon supersaturated phase, the so-called “S Phase”. The microstructure of the treated specimens was characterized by Optical microscopy, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The results showed evidences of expanded austenite phase and formation of “S phase” at a temperature of 460[Formula: see text]C with 10% of methane (CH[Formula: see text] and 90% of hydrogen (H[Formula: see text] at a pressure of 1mbar for a time period of 20[Formula: see text]h. The hardness of the specimen was evaluated as 1030[Formula: see text]HV using Vickers microhardness setup. The wear behavior of plasma treated specimen was studied using pin on disc test at ambient condition and the results are discussed. Wear rate in PLTC 316L SS was observed to be low when compared with the wear rate of the untreated 316L SS specimen. The PLTC 316L SS specimen is subjected to ASTM A262 oxalic acid etch test to study the intergranular corrosion behavior. The “step” formation was observed in the SEM micrographs which reveal the retention of corrosion resistance in the specimen.

Influence of Cold Work on Sensitization Kinetics and Evaluation of Degree of Sensitization in Type 316LN Stainless Steels

The sensitization behavior of Type 316LN stainless steel (SS) with varying nitrogen content (0.07 wt% and 0.22 wt%) in 0% to 25% cold worked (CW) as well as in the as-received condition was evaluated. Time-temperature-sensitization diagrams were established for the cold worked Type 316LN SS (nitrogen content: 0.07 wt% and 0.22 wt%), using ASTM A262 Practice-E test. The time required for sensitization (ts) was found to decrease and critical cooling rates (CCR) increased up to 10% CW in the alloy with 0.07 wt% N. At higher CW, ts increased and CCR decreased. Similarly, ts decreased and CCR increased up to 15% CW in the alloy with 0.22 wt% N and at higher CW, ts increased and CCR decreased. To understand the sensitization behavior of Type 316LN SS with varying nitrogen content during thermal aging at 923 K for various durations, nondestructive electrochemical techniques like double loop electrochemical potentiokinetic reactivation (DL-EPR) technique and electrochemical reactivation technique (ERT) were adopt...

Effect of Nitrogen Addition on the Intergranular Corrosion of 304L Stainless Steel in Nitric Acid Medium

Critical components in reprocessing plants like continuous dissolver and centrifugal extractor demand austenitic stainless steels (SS) with good corrosion resistance coupled with high wear resistance in nitric acid medium. High nitrogen containing, impurity controlled, and vanadium-added 304LN1 (0.132% N), 304LN2 (0.193% N), and 304LN3 (0.406% N) SS with improved hardness were developed and corrosion studies were performed as per ASTM A262 Practice-A & C test and double loop electrochemical potentiokinetic reactivation test. The 304LN stainless steels were evaluated in forged, hot rolled, and hot rolled + heat treated conditions (948 K: 1, 10, 25, 50, 100, 260 h; 1,223 K: 1 h; 1,323 K: 1 h; and 1,473 K: 1 h). The study revealed good corrosion resistance for 304LN1 and 304LN2 SS as per ASTM A262 Practice-C test in sensitized condition (948 K/1 h). The degree of sensitization (DOS) and corrosion rates of high nitrogen 304L SS increased during sensitization heat treatment (948 K) done up to a certain aging d...

Correlation between microstructure and intergranular corrosion behavior of low delta-ferrite content AISI 316L aged in the range 550–700 °C

Abstract The microstructure and the phase identification of austenitic stainless steel AISI 316L with low δ-ferrite content (δ ≤ 1%) and aged for up to 80 000 h at temperatures ranging from 550 to 700 °C were investigated by using an optical microscope (OM), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Local changes of chromium content, resulting from nucleation and growth of chromium-rich phases during aging, were quantitatively assessed by energy dispersive X-ray spectroscopy (EDX) in the scanning transmission electron microscope (STEM). The intergranular corrosion behavior (IGC) of annealed and aged specimens was evaluated using the double loop electrochemical potentiokinetic reactivation (DL-EPR) and completed by IGC morphologies according to the ASTM A262 practice A standard. The results showed that δ-ferrite decomposed gradually into M 23 C 6 at 550 °C and decomposed totally into intermetallic phases (σ, η, χ, and R) and into secondary austenite (γ r ) at temperatures equal to or higher than 650 °C. Similarly γ-austenite decomposed into M 23 C 6 carbide at 550 °C and into intermetallic phases such as η and σ in addition to carbide, at higher temperatures. The time-temperature-sensitization diagram (TTS) was established and used to calculate the critical cooling rate (CCR) that prevents IGC sensitization. The analysis of IGC results leads to the conclusion that sensitization-desensitization is still controlled by the characteristics of chromium-depleted area surrounding austenite grain boundary regions. No significant effect of remained δ-ferrite and derived components on the corrosion behavior of AISI 316 L containing 1% of δ-ferrite.

Alloy for resistance to polythionic acid stress corrosion cracking for hydroprocessing applications

In certain process units, such as hydrocracking, soda ash washing (neutralization) of austenitic stainless steel is required during turnarounds to mitigate the potential for polythionic acid stress corrosion cracking (PTA SCC). Soda ash washing can be a costly and time consuming endeavor for the refiner. This paper introduces a grade of austenitic stainless steel, a proprietary version of Type 347LN, that does not sensitize with long-term exposure to elevated temperature, thus rendering it immune to PTA SCC. ASTM A262 Practice A corrosion test results will be presented for samples isothermally aged at 565°C for a duration of up to 10,000h. These data will be compared to samples of conventional Type 347, Type 321, and Type 304H similarly aged. Photomicrographs will be shown that demonstrate the lack of grain boundary sensitization, and also the lack of grain boundary ditching in the oxalic acid test. Replica analysis of a heater tube from commercial service at 460°C average tube wall temperature for 12years showing no evidence of sensitization or grain boundary precipitation will also be presented.