Oxalic Acid Etch Test Research Articles

Effect of thermomechanical processing via rotary swaging on grain boundary character distribution and intergranular corrosion in 304 austenitic stainless steel

In the present work, the thermomechanical processing consisting of rotary swaging deformation and annealing treatment was performed to optimize the grain boundary character distribution (GBCD) of 304 austenitic stainless steel. To systematically investigate the effect of GBCD evolution on intergranular corrosion (IGC), double loop electrochemical potentiokinetic reactivation and electrolytic oxalic acid etch tests were employed. The experimental results show that the fraction of low-Σ coincident site lattice (CSL) boundaries increased from 58.1% to 74.0% for the specimen swaged to 0.06 true strain and then annealed at 1050 °C for 5 min duration. By characterizing the evolution of GBCD as a function of strain level in terms of low-Σ CSL boundaries fraction, average twin-related domain (TRD) size, average number of grain per TRD and fractal dimension of the maximum random boundary connectivity, the grain boundary engineering (GBE) microstructure was realized by the occurrence of prolific multiple twinning events during strain-induced boundary migration while static recrystallization has a detrimental effect on optimizing GBCD for the prolific of new strain-free grains with random boundaries. The IGC resistance of the GBE-treated 304 austenitic stainless steel is enhanced by inhibiting the nucleation and propagation of IGC cracks, resulting from the increase in the fraction of low-Σ CSL boundaries, especially Σ3 boundaries and the disruption of random boundary network connectivity.

Investigation on thermo-mechanical processing and intergranular corrosion of TP347H stainless steel

The grain boundary character distributions of TP347H stainless steel after different thermo-mechanical processes in terms of grain boundary engineering (GBE) were investigated by EBSD. DL-EPR and electrolytic oxalic acid etch tests were carried out to evaluate the improvement of GBE treatment on intergranular corrosion. The low-Σ CSL grain boundary proportion of the TP347H can be increased to about 90% through a single-step thermo-mechanical treatment consisted of a slight tensile deformation (3%) and subsequent annealing process at 1150°C for 1 h. Compared with conventional TP347H, the optimum GBE microstructure suppressed intergranular corrosion due to the high proportion of low-Σ CSL grain boundaries, particularly the twin (Σ3) boundaries which is almost immune to intergranular corrosion.

Effect of Sensitizing Treatment on the Microstructure and Susceptibility to Intergranular Corrosion of High-Nitrogen Austenitic Stainless Steel

This experiment investigated the effect of different sensitizing treatment times (2–48 h) at 800 °C on the microstructure and intergranular corrosion of high-nitrogen austenitic stainless steel by using scanning electron microscopy, energy-dispersive spectroscopy, double loop electrochemical potentiokinetic reactivation, and an oxalic acid etch test. The results indicate that with increasing sensitizing time, the austenite grains grew significantly and the carbide quantity began to increase at the grain boundary. The lamellar pearlite-like Cr2N was precipitated when the specimens were aged at 800 °C for 12 h. DL-EPR testing showed that IGC susceptibility of high-nitrogen austenitic stainless steel is mainly caused by the precipitation of carbide and increases when sensitization time is increased from 2 to 48 h.

Enhancement in intergranular corrosion resistance of the stabilised ultra-pure 430LX ferritic stainless steel by tin addition

ABSTRACTThe intergranular corrosion (IGC) susceptibility of the Ti–Nb-stabilised ultra-pure 430LX FSSs with 0–0.47 wt-% tin addition was investigated using double loop electrochemical potentiokinetic reactivation (DL-EPR) and oxalic acid etch tests. The result of DL-EPR test reveals that IGC resistance increases with the increase in tin content. The specimens with different contents of tin exhibit the same microstructural evolution based on oxalic acid etch test. M23C6 precipitates form along grain boundaries, inducing Cr-depleted zones and finally resulting in the susceptibility to IGC. Tin addition gives rise to the formation of SnO2 on the FSSs surface, thus inhibiting the attack of corrosive ions towards Cr-depleted zones.

Studies on Intergranular Corrosion Characteristics of Cast Duplex Stainless Steel Stabilized with Niobium

Abstract To study intergranular corrosion (IGC) characteristics, two cast grades of duplex stainless steels, 5A and 5A stabilized with niobium, were produced in a vacuum induction melting furnace. The samples were tested under three different heat-treatment conditions that were selected using a property diagram generated through the TCFE8 database of the Thermo-Calc® software (Thermo-Calc Software, Solna, Sweden). A Feritscope FMP30® (Fischer Technology, Inc., Windsor, CT) was used to measure the ferrite phase content in the samples and compared with that specified in the property diagram. Metallurgical characteristics were analyzed through optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Each heat-treated sample possessed a distinct texture due to the formation of various intermetallic phases in the alloy. The corrosion behavior of the samples was studied using an oxalic acid etch test. Double-loop electrochemical potentiokinetic reactivation and sulfuric acid tests were conducted on the niobium-stabilized samples, and the results demonstrated that the samples possess superior resistance to corrosion compared to those not stabilized with niobium. The addition of niobium produced a mixture of niobium compounds that suppressed the chromium depletion and reduced the degree of sensitization. This study demonstrated the potential of using niobium as a stabilizer in the duplex stainless steel alloy to considerably reduce IGC.

Intergranular corrosion behavior and mechanism of the stabilized ultra-pure 430LX ferritic stainless steel

Intergranular corrosion (IGC) behavior of the stabilized ultra-pure 430LX ferritic stainless steel (FSS) was investigated by using double loop electrochemical potentiokinetic reactivation (DL-EPR) and oxalic acid etch tests to measure the susceptibility of specimens given a two-step heat treatment. The results reveal that IGC occurs in the specimens aged at the temperature range of 600–750 °C for a short time. The aging time that is required to cause IGC decreases with the increase of aging temperature. A longer aging treatment can reduce the susceptibility to IGC. The microstructural observation shows that M23C6 precipitates form along the grain boundaries, leading to the formation of Cr-depleted zones. The presence of Cr-depleted zones results in the susceptibility to IGC. However, the atoms of stabilizing elements replace chromium atoms to form MC precipitates after long-time aging treatment, resulting in the chromium replenishment of Cr-depleted zones and the reduction of the susceptibility to IGC.

Contradictory Results from Single Loop Electrochemical Potentiokinetic Reactivation Test and Oxalic Acid Test for Intergranular Corrosion in 304L Stainless Steels Attributed to Si Grain-Boundary Segregation

The intergranular corrosion susceptibility of AISI 304L stainless steel can be measured in the field using the single loop electrochemical potentiokinetic reactivation test. However, the present work questions the reliability of the test, with nominally the same as-received samples given a wide range of degrees of sensitization, enough for opposite conclusions and potentially false positive results. More worryingly, when comparing the results to the oxalic acid etch test, a false negative result of the SL-EPR test was obtained on some heat-treated samples. This could entail serious repercussions and justifies a thorough investigation into this issue. The most likely explanation for the unexpected behavior of one batch of 304L, is its moderate silicon enrichment at 0.4 wt%. As long as the stainless steel does not exceed the passive region, as is the case for the SL-EPR test, the moderate silicon additions help suppress intergranular corrosion, but in the strongly oxidizing environment of the oxalic acid test the stainless steel becomes transpassive and the silicon results in accelerated corrosion of the grain boundaries.

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.

Synthesis and Comparative Study on Intergranular Corrosion Characteristics of Stabilized 5A Grade Cast Duplex Stainless Steel

Abstract In this paper, stabilization using zirconium and niobium was investigated to reduce the effect of intergranular corrosion (IGC) in 5A grade cast duplex stainless steel. Computational thermodynamic software was used to determine the various heat treatment temperatures according to phase precipitation. Resistance to IGC was investigated by oxalic acid etch test and double-loop electrochemical potentiokinetic reactivation (DL-EPR) technique. The surface of the specimens was observed using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry to evaluate the presence of various intermetallic phases prone to IGC. Oxalic acid etch test response has indicated the susceptibility, whereas the DL-EPR test has provided the degree of sensitization. The results revealed that zirconium-stabilized samples are more susceptible to IGC compared to the niobium samples. Earlier formation of niobium compounds led to the reduction of intergranular attack in the niobium-stabilized samples.

Comparative Study on Intergranular Corrosion Characteristics of Cast Duplex Stainless Steel Stabilized with Zirconium

Intergranular corrosion of duplex stainless steel is a major concern in high corrosive environments. Interstitial stabilization of alloy is a possible technique for susceptibility to intergranular corrosion. In this paper, zirconium addition was made to 5A grade cast duplex stainless steel in order to achieve the stabilization. Addition of zirconium forms a mixture of zirconium carbides and nitrides which suppress the chromium depletion and thus increase the intergranular corrosion resistance. The metallurgical characterization was carried out on the specimens by means of optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffractometry. Corrosion behavior investigation using oxalic acid etch test and double-loop electrochemical potentiokinetic reactivation technique results underline the superior corrosion-resistant property of zirconium-added cast duplex stainless steel.

Investigation of Susceptibility to Intergranular Corrosion of Tin-Added Austenitic Stainless Steel

The intergranular corrosion (IGC) character of tin-added B316LX and the influence of tin addition on IGC susceptibility were investigated by DL-EPR, oxalic acid etch test and transmission electron microscopy. IGC susceptibility of B316LX is mainly caused by the precipitation of M 23C6 carbide and intermetallic Laves phase. DL-EPR test is unsuitable to evaluate the IGC susceptibility of B316LX with long-time sensitization, because more carbides and intermetallic phases are formed at grain boundaries and inside the grains, which induce more severe IGC and pits attacks. Tin addition increases the IGC susceptibility, maybe due to diffusion of tin toward grain boundaries.

원자력발전소용 316 스테인리스강 배관의 부식특성에 미치는 유도가열벤딩공정의 영향

Recently, the application of bending products has been increased since the industries such as automobile, aerospace, ships, and plants greatly need the usage of pipes. For facility fabrication, bending process is one of key technologies for pipings. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. Because of local heating and compressive strain, detrimental phases may be precipitated and microstructural change can be induced. This work focused on the effect of induction heat bending process on the properties of ASME SA312 TP316 stainless steel. Evaluation was done on the base metal and the bended areas before and after heat treatment. Microstructure analysis, intergranular corrosion test including Huey test, double loop electropotentiokinetic reactivation test, oxalic acid etch test, and anodic polarization test were performed. On the base of microstructural analysis, grain boundaries in bended extrados area were zagged by bending process, but there were no precipitates in grain and grain boundary and the intergranular corrosion rate was similar to that of base metal. However, pitting potentials of bended area were lower than that of the base metal and zagged boundaries was one of the pitting initiation sites. By re-annealing treatment, grain boundary was recovered and pitting potential was similar to that of the base metal.

Weld decay failure of a UNS S31603 stainless steel storage tank

A brine storage tank was reported to have visible and severe localized corrosion 1year after installation. The material used for this tank was UNS S31603 stainless steel. The corrosion was mainly noticeable at various points/areas along the welded joint, and there was also some pitting on the base metal at the bottom of the tank. Corrosion was also found at the welded joint at the hatch wall. Indications of severe corrosion that resulted in deep metal loss were found at some points along the welded joint. The results of an oxalic acid etch test in the heat-affected zone (HAZ) showed the interdendritic ditches, which are considered to be prone to intergranular corrosion/weld decay. The results of a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test and 3D multiscale images were in agreement with the results of an oxalic acid etch test that indicated the intergranular corrosion susceptibility of the HAZ. The base metal, in contrast, did not show any intergranular corrosion.

Mechanical properties and sensitization on clad steel welding design

We have investigated the traits of clad metals in hot-rolled clad steel plates, including the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516), under various specific circumstances regarding post heat treatment, multilayered welds, and thick or repeated welds for repair. For evaluations, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by Micro Vickers hardness, tensile, and etching tests, and the results were compared with those of EPR tests. Clad steel plates were butt-welded using SAW + SMAW, and with the time of heat treatment as the variable, heat treatment was conducted at 625°C, for 80, 160, 320, 640, and 1280 minutes. Then, the change in corrosion resistance was evaluated in these specimens. With carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro-hardness gradually increased and decreased after 640 min. The elongation and contraction of the area also increased gradually. The oxalic acid etch test and EPR test on STS316, a clad metal, showed STEP structure and no sensitization. From the test results on multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. The purpose of this study was to suggest some considerations for developing on-site techniques to evaluate the sensitization of stainless steels.

열간압연 클래드강의 맞대기용접부 내식성 및 용접성 평가

We have investigated the traits of clad metals in hot-rolled clad steel plates, including the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516), under various specific circumstances regarding post heat treatment, multilayered welds, and thick or repeated welds for repair. For evaluations, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by micro vickers hardness, tensile, and etching tests the results were compared with those of EPR tests. The clad steel plates were butt-welded using FCAW and SAW with the time of heat treatment as the variable, a that was conducted at <TEX>$625^{\circ}C$</TEX>, for 80, 160, 320, 640, and 1280 min. Then, the change in corrosion resistance was evaluated in these specimens. With carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro-hardness gradually increased and decreased after 640 min. The elongation and contraction of the area also increased gradually. The oxalic acid etch test and EPR test on STS316 and the clad metal showed STEP structure and no sensitization. From the test results on multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. The purpose of this study was to suggest some considerations for developing on-site techniques to evaluate the sensitization of stainless steels.

용접 공정 디자인에 따른 클래드강의 기계적 성질 변화

In this study, we investigated the traits of the clad metals used in hot-rolled clad steel plates. We examined the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516) under the specific circumstances of post heat treatment and whether a weld was multilayered and thick or repeated because of repairs. The test conditions were as follows. The clad steel plates were butt-welded using FCAW/SAW, and the heat treatment was conducted at <TEX>$625^{\circ}C$</TEX>, for 80, 160, 320, 640, or 1280 min. The change in the corrosion resistance was evaluated in these specimens. In the case of the carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro- hardness gradually increased and then decreased after 640 min. The elongation and contraction of the area increased gradually. An oxalic acid etch test and EPR test on STS316, a clad metal, showed a STEP structure and no sensitization. From the test results for the multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. In summary, the purpose of this study was to suggest some considerations when developing on-site techniques and evaluate the sensitization of stainless steels.

RETRACTED ARTICLE: Comparison of mechanical properties and sensitization of clad steel weld zone with FCAW

This study aims at developing on-site techniques to evaluate the sensitization of stainless steels. Sensitization and mechanical properties of clad metals in hot-rolled clad steel plates, STS 316 steel plate and carbon steel (A516), are investigated at the specific conditions of post heat treatment and welds which are multiple-layers-thick or are repeated for repair. Sectioned weldments and external surfaces are investigated to reveal the degree of sensitization by evaluating Micro Vickers hardness test, tensile test and etching. The results are compared with those of EPR tests. As test conditions, clad steel plates are butt-welded by FCAW + SMAW, and heat treatments are conducted at a temperature of 625°C for 80, 160, 320, 640 and 1280 minutes, using the time of heat treatment as a variable. The change of corrosion resistance is also evaluated for these specimens. As the heat treatment time increases in case of carbon steel (A516), the annealing effect causes the tensile strength to decrease. The micro-hardness gradually increased, and decreased after 640 min. Elongation and contraction of the area also increased gradually. After oxalic acid etch tests and EPR tests on STS316, clad metal shows STEP structure with no sensitization. It can be concluded that there is no effect on the corrosion resistance of clad metals by use of the test results on multi-layered and repair welds.

UNS N08810 합금의 입계부식손상과 원인 분석

Corrosion failure of petrochemical facilities is one of the difficulties in maintenance, since operating conditions of crude oil production, storage, and refinement are very aggressive. UNS N08810, which has been used for crude oil transportation pipes and storage tanks in petrochemical industries, shows good resistance to general corrosion and localized corrosion in several environments. Among its environments, UNS N08810 showed better corrosion resistance in fuel gas containing sulfuric acid and phosphoric acid and sulfur. However, ductility and toughness at high temperature over about <TEX>$500^{\circ}C$</TEX> were greatly reduced due to microstructural change. In general, welding process is the representative method to join the parts in industrial components. Because the alloy by welding can be sensitized and corroded, the manufacturing process should be controlled. In this work, UNS N08810 was used and heat treatment conditions including solution and stabilization treatments were controlled. Oxalic acid etch test by ASTM A262 Practice A was done to evaluate the qualitative sensitization in room temperature. Huey test by ASTM A262 Practice C was done to evaluate the intergranular corrosion rate in boiling 65% <TEX>$HNO_3$</TEX> solution. Also, the microstructure by thermal history was analyzed. Experimental alloy showed high intergranular corrosion rate and its corrosion mechanism was elucidated.

Structural analysis and intergranular corrosion tests of AISI 316L steel

Pure AISI 316L steel is investigated after solution heat treatment (1050 degrees C/H(2)O) and structural sensitization (650 degrees C). Two quite different intergranular corrosion tests are used to determine the degree of structural sensitization due to the precipitation of secondary phases along the grain boundaries (mainly the M(23)C(6) and sigma-phase): the oxalic acid etch test and the electrochemical potentio-kinetic reactivation test. Generally, the dissolution of chromium-rich carbides (M(23)C(6)) is provoked by oxalic acid etch tests, whereas the chromium-depleted zones, in the vicinity of chromium-rich carbides (M(23)C(6)), are attacked by electrochemical potentio-kinetic reactivation tests. Both intergranular corrosion tests are used to determine the maximum degree of structural sensitization. Thus structural analysis by carbon replicas reveals the Laves phase, and both the M(23)C(6) and (Cr,Mo)(x)(Fe,Ni)(y) phases. The results of intergranular corrosion tests are related to the findings of the structural analysis.

EBSD investigation of intergranular corrosion attack on low interstitial stainless steel

AbstractGrain boundary effect on corrosion behaviour of low interstitial AISI 316LN austenitic stainless steel after homogenization and heat treatment at 700 and 800°C was investigated by means of Electron Backscattered Diffraction (EBSD) technique. Rapid oxalic acid etch test (ASTM A262‐ practice A) was used to determine steel susceptibility to intergranular corrosion. An attempt to quantify oxalic acid etch test results was also made.Beneficial effect of low carbon and nitrogen content on grain boundary precipitation and corrosion was observed. No changes neither in grain orientations nor in grain boundary types between sensitised and non‐sensitised steel states using orientation measurements were recorded. Twin boundaries were found in all samples with highest amount and only small occurrence changes. CSL categorizations showed only little increase of special boundary fractions with increasing time and temperature of heat treatment. Irrespective to annealing conditions a continued network of random boundaries was retained. Additionally, based on misorientation measurement of 50 grooved grain boundaries, a tendency for preferred attack of high angle boundaries (30–55°) was noted.