Ferritic Corrosion Research Articles

The corrosion behavior of low carbon steel (AISI 1010) influenced by grain size through microstructural mechanical

Low-carbon steel (AISI 1010) is the predominant material used in industrial food processing equipment. Such equipment is vulnerable to the corrosive environment produced by various production stages. Different processes, such as sulphonation and carbonation, are used in the processing of sugar in the sugar industry, creating a corrosive atmosphere. The corrosion behavior of low carbon steel (AISI 1010) is strongly influenced by grain size variations, which in turn affect the microstructural mechanical properties of the material. The mechanical behavior and performance of metallic materials, including their corrosion resistance, is determined by grain size which is an important parameter for this phenomena. The impact of low-carbon steel (AISI 1010) microstructure on corrosion behavior is discussed in this work. Heat treatment produces two different types of microstructure from the same material, which are then analyzed. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) have both been used to study characteristics including morphology and content. By supplying an appropriate corrosive medium, the corrosion performance of several microstructures of low-carbon steel (AISI 1010) was assessed, and corrosion rates were calculated using weight-loss and electrochemical techniques. Results show that the creation of a protective coating with a higher charge transfer resistance is caused by the adsorption process. The variety in phases and grain sizes may contribute to the corrosion stability of different microstructures, and as a result, the corrosion rate lowers as average grain sizes are reduced. Employing the galvanic effect, pearlite increases the rate of ferrite corrosion. The study's findings support the notion that quenching low-carbon steel (AISI 1010) results in a finer grain structure and greater corrosion resistance.

Effect of joint-extrusion-force on the plasticity of beam oscillation fiber laser welded X2CrTiNb18 ferritic corrosion resisting steels

The effect of extrusion force on the microstructure and plasticity of the X2CrTiNb18 ferritic corrosion resisting steels joints which were welded by beam oscillation laser welding was studied. The cross section profile of welded joint beam oscillating fiber laser welding & extrusion (OLW&E) was similar to that of the beam oscillation laser welding (OLW), but the weld width of OLW&E was slightly narrow. The differences of microstructure between them were very obvious. In the OLW&E weld zone (WZ), on the one hand, the quantity of small grains increased obviously, and on the other hand they grew in a staggered state. In the plastic forming process, the deformation compatibility of welded joints was significantly improved, and its plasticity was increased by 21%.

Corrosion Behavior of Ancient White Cast Iron Artifacts from Marine Excavations at Atmospheric Condition

A large number of iron pot artifacts were excavated from the “Nanhai I” shipwreck. The rapid embrittlement and pulverization of these objects (that have a good matrix) in the atmospheric environment is worthy of attention. Metallographic analysis showed that the material of the iron pots was hypereutectic white cast iron. Micro-CT observations revealed that there were numerous microcracks and fissures within the seemingly well-preserved iron. These fissures increased and enlarged with prolonged exposure to air. Scanning electron microscopy exhibited that the microcracks were initially created at the “concave surface” formed by the ferrite corrosion, and the cementite was gradually torn by the local accumulation of large internal stresses. Micro-Raman proved that the structure of rust was varied and complex during the generation and development of fissures. The dimension of corrosion products could expand and contract in mutual transformation, forming local internal stress and promoting the expansion of microcracks. This work proposed a reasonable mechanism for the rapid embrittlement and pulverization in the atmospheric environment of such hypereutectic white cast iron artifacts out of the sea, which provided a scientific reference for future protection.

Galvanic corrosion of X80 pipeline steel double‐sided submerged arc welded joints in simulated near‐neutral soil solution

AbstractThe corrosion behaviors of double‐sided submerged arc welded joints in X80 pipeline steel with or without coupling were studied in simulated near‐neutral soil solution. The galvanic effect in the welded joint was evaluated by corrosion morphology, corrosion depth, and electrochemical measurements. When the weld metal (WM), heat affected zone (HAZ) and base metal (BM) samples were immersed in the solution isolated, pitting holes occurred around the martensite/austenite constituents in the weld metal and base metal samples, which was mainly due to the preferential corrosion of ferrite. However, no pitting holes occurred in the heat affected zone due to small specific surface area induced by the coarse martensite/austenite constituents. Polarization curves results showed that the corrosion current density of coupled base metal was 5 times larger than that of isolated base metal and the corrosion current density of isolated heat affected zone was three times larger than that of coupled heat affected zone after 48 h immersion. The corrosion current density of coupled heat affected zone was one order of magnitude lower than that of coupled weld metal and base metal. When the welded joint was exposed to an aggressive environment, the base metal samples were determined to be the most anodic zone while the heat affected zone was the most cathodic zone. The weld metal underwent little galvanic interaction, as its corrosion potential was close to the coupled potential. In addition, the galvanic effect among the welded joints decreased with the prolong of immersion time.

Effect of Varying H2S Content on High-Temperature Corrosion of Ferritic and Austenitic Alloys in a\xa0Simulated Pyrolysis Process of Post-Consumer Plastics

The alloys K90941 and N08811 were tested under conditions simulating a pyrolysis process of post-consumer plastics. Impurities in the plastic feedstock like chlorine containing materials or organic components yield HCl and H2S respectively during the cracking process. The reactor material must be able to withstand these harsh corrosive conditions.In lab-scale test equipment, process conditions of the reactor zone of the pyrolysis process were simulated at temperatures of 420 °C and 580 °C for 72 h. The gas atmosphere consisted of either 200 ppm or 20000 ppm H2S and 3.8 vol% HCl, 1.9 vol% CO2, 0.3 vol% CO, 2.8 vol% H2, bal. N2. After the corrosion experiments, the samples were analyzed by metallography, SEM/EDX, and XRD. Additionally, the mass loss was evaluated. Results show that the ferritic K90941 is more aggressively attacked than the austenitic N08811 and that for both materials the mass loss rises with increasing H2S content in the gas atmosphere and increasing temperature.

Correlative EBSD and SKPFM characterisation of microstructure development to assist determination of corrosion propensity in grade 2205 duplex stainless steel

Correlative electron backscatter diffraction (EBSD) and scanning Kelvin probe force microscopy (SKPFM) analysis has been carried out to characterise microstructure development and associated corrosion behaviour of as-received and 750 °C heat-treated grade 2205 duplex stainless steel. High-resolution EBSD analysis revealed the presence of σ- and χ-phase, secondary austenite, Cr2N, and CrN after ageing treatment. SKPFM Volta potential measurements confirmed the formation of discrete reactive sites, indicating local corrosion propensity in the microstructure. Cr2N, σ-phase, and inter-granular χ-phase had the largest net cathodic activity, followed by CrN and intra-granular χ-phase showing medium electrochemical activity, with ferrite and austenite (including secondary austenite) showing net anodic activity. Corrosion screening confirmed selective corrosion of ferrite in the as-received and 750 °C-aged conditions with the corrosion propensity of secondary phases staying in-line with SKPFM observations. Stress corrosion micro-cracks were also observed and are discussed in light of microstructure corrosion propensity.

Silicon Effects on the Corrosion of Ferritic and Austenitic Chromia Forming Alloys in Wet and Dry CO2

Model alloys of Fe-9Cr, Fe-20Cr and Fe-20Ni-20Cr (wt.%) with Si (0.1, 0.2 and 0.5%) were reacted isothermally in dry Ar-20CO2 gas at 818 oC. Silicon-free Fe-9Cr formed thick scales of FeO and FeCr2O4, Fe-20Cr formed thin scales of Cr2O3 alone, and Fe-20Ni-20Cr formed Fe3O4, FeCr2O4 and FeNi3. Silicon additions suppressed formation of iron oxides on Fe-9Cr and Fe-20Cr-20Ni, and dramatically slowed oxidation of all alloys. Scales on 0.2Si-alloys consisted of an outer layer of Cr2O3 and an inner layer of amorphous SiO2. Internal precipitation of chromium-rich carbides took place in all undoped alloys, but was suppressed in Si-bearing alloys. Wagner’s theory of alloy depletion is shown to provide a successful description of these phenomena. Addition of water vapour to the gas makes it much more corrosive. All silicon-free alloys underwent breakaway corrosion, developing thick iron-rich oxide scales and internal carbide precipitates. Silicon additions to Fe-9Cr had no detectable effect on reaction in wet gas, but were beneficial in the higher chromium alloys. Silicon additions substantially improved both oxidation and carburisation resistance in wet CO2, by forming a layer of silica beneath the chromia scale. In both wet and dry gases, the silica layer acted as a barrier to carbon entry, and slowed outward metal diffusion, thus slowing scaling rates. Silicon-bearing austenitic alloys underwent scale spallation on cooling from reaction in wet gas, but not after reaction in dry CO2. No spallation was observed for ferritic alloys after reaction in either wet or dry CO2. The contributions of thermal and growth stresses to spallation, and of growth stresses to the onset of breakaway are discussed.

Acoustic Emission Response of 316LN Welded Joint during Intergranular Corrosion

The acoustic emission (AE) response of 316LN welded joint during intergranular corrosion (IGC) was investigated in this study. The boiling nitric acid method was chosen to provide the IGC environment and AE signals were detected by Macro-SAMOS AE testing system. The metallographic structures and AE results were studied and analyzed in detail. The results show that the IGC process of 316LN welded joint can generate many AE signals and the AE activity is high. The AE amplitude is below 35dB and mainly ranges from 25dB to 34dB. Two types of AE signals are obtained and both the frequency peaks are 50 kHz. It is believed that grain boundary corrosion, ferrite corrosion and separation of grains are the possible AE sources.

Testing of pigmented coatings on thermal sensitised stainless steel

Purpose – The purpose of this paper is to verify the capability of pigmented coatings to mitigate the effects of thermal sensitisation of 430 stainless steel.Design/methodology/approach – Experimental weld joints of non‐stabilised ferritic corrosion resistant steel type AISI 430 were prepared. Protective coatings in several variants were applied to a number of weldments, subsequently subject to corrosion tests in SO2 and NaCl. The anticorrosive efficiency of the coatings was evaluated by means of normative visual assessment and metallographic analysis of the mechanism and depth of corrosion damage.Findings – Anticorrosive efficiency of the tested coatings was experimentally established under conditions where differences were identified in structural changes caused by welding, or resulting from mechanical damage to the coating. Differences in the progress of corrosion damage caused by phase changes in the heat‐affected zone were established.Practical implications – Tests of anticorrosive efficiency of coat...

Effect of inclusions on very high cycle behaviour in a ferritic corrosion resisting steel

The number of structural components which must operate frequently at repeated loading higher as N ≈ 106 – 107 cycles increases. This fact is serious problem in engineering practice. Fatigue lifetime in the ultra high cycle region (108 < N< 1011 cycles) is therefore studied very intensively with the aim to correctly select the structural material. The paper is devoted to an experimental examination of the fatigue lifetime of X12Cr13 corrosion resisting steel used in the power industry. The high frequency fatigue testing (frequency f ≈ 20 kHz, temperature T = 20 ± 10°C, sinus push-pull loading with load ratio R= -1) was used with the aim to obtain experimental data in the high cycle and ultra high cycle region (from N ≈ 106 to N ≈ 1011 cycles). The obtained S–N curve revealed a continuous downward slope without any indication for plateau region, whereby surface (in the region 106 < N< 109 cycles) and subsurface (N > 109 cycles) fatigue crack initiation occurs in the used range of loading amplitudes. The inclusions of type Al4Ca and Al2Ca were the places of subsurface crack initiation; their role is discussed with regard on the fatigue lifetime of the X12Cr13 steel with ferritic matrix. Obtained results confirm that occurrence of those inclusions must be taken in consideration in application of the X12Cr13 steel for very high cycle service in power industry.

X-ray micro- fluorescence, diffraction and absorption spectroscopy for local structure investigation of a radioactive zinc ferrite deposit

X-ray micro- fluorescence (μXRF), diffraction (μXRD) and absorption spectroscopy (μXAS) techniques have been used to investigate the micro-crystalline and chemical structure of a radioactive zinc ferrite corrosion deposit phase formed on a zirconium dioxide substrate. Micro- fluorescence provides structural information based on the elemental distribution analysis, μXRD allows the determination of lattice parameters of crystalline compounds while μXAS yields data related to the atomic environment, such as coordination number and the distances to the nearest neighbours. The μXAS and the μXRD results are compared including a discussion of precision and accuracy of both techniques.

Corrosion study of an austenitic steel in Pb–17Li under magnetic field and rotating flow

The liquid alloy Pb–17Li has been proposed as breeder material in the water-cooled blankets for fusion reactors. During operation, structural materials such as austenitic and martensitic steels exposed to Pb–17Li are subject to corrosion. The strong magnetic fields anticipated in fusion reactors may have a significant influence on the corrosion processes. This paper reports corrosion data from tests carried out in liquid Pb–17Li at 480 °C up to 350 h without and applying a 0.2 T magnetic field. The flow of Pb–17Li was simulated using a specific device with a rotating disk constituting the 316 L austenitic steel specimen. After the tests, a ferritic corrosion layer at the surface of all the specimens has been observed. The thickness of the layer depends on the hydrodynamic of the flow, which is modified by the magnetic field. An explanation of the effect of a magnetic field is being offered.

Corrosion and deposition of ferrous alloys in molten lead–bismuth

This paper reports corrosion and deposition data from tests carried out with liquid eutectic lead–bismuth (Pb–55 at.% Bi) filled steel tubes (austenitic and martensitic) under a thermal gradient (500–280 °C) for 3000 h. For the austenitic steel, the surface exposed to Pb–55Bi exhibited a ferritic corrosion layer depleted in nickel and chromium at temperature above 450 °C. In the temperature range 450–360 °C, deposits composed of iron and chromium were found. There is a temperature effect on composition with a change from iron-rich to chromium-rich with decreasing temperature. For the martensitic steel, a corrosion without corrosion layer was observed above 480 °C. Only one type of deposit consisting of 98Fe–2Cr was found in the 400–480 °C temperature range.

On the kinetics of chromium electrodeposition on copper electrodes

In a previous work, we observed that, during cyclic potentiodynamic curves of cathodic polarisation (from 0.00 to −1.25 V/SCE, 5 mV s −1) in chromic acid solution of industrial composition, ARMCO iron undergoes a pitting corrosion, while carbon steels undergo a selective ferritic corrosion. Blisters of pure iron were also observed on ARMCO iron electrodes surface. These occurrences suggest a direct participation of the metal substrate to the overall reaction of reduction of the chromic acid to chromium metal. Therefore, the chemical nature of the electrode metal has been changed, in order to prove that the chromium reduction goes on through an ECE mechanism involving a fast chemical reaction between unstable intermediate chromium products and the metal substrate. Cathodic potentiodynamic polarisation curves were performed on copper electrodes and the scans were stopped at four different potentials (−0.90, −1.00, −1.10 and −1.25 V/SCE). The copper surface undergoes a severe corrosion in all the experimental conditions. The morphology of the attack depends on the polarisation potential and on the presence of additives in solution, like iron sulphate.

The effect of copper on passivity and corrosion behaviour of ferritic and ferritic–austenitic stainless steels

The paper presents investigations of the influence of copper as an alloying element on the structure and on the passive behaviour of ferritic Fe–18%Cr and duplex ferritic–austenitic Fe–24%Cr–6%Ni–3%Mo cast alloys. Copper dissolved in the solid solution (austenite) does not show detrimental effect on the stability of a passive film. The solubility of copper in ferrite is lower than in austenite and therefore the ε-phase can be precipitated during thermal treatment (500–600°C). Ferritic alloy containing high copper content (1.58%Cu) shows precipitation of the ε-phase already in cast form (without sensitisation). In duplex ferritic–austenitic steels, the precipitation of the ε-phase in ferrite occurs during the sensitisation in a temperature range 500–600°C. The presence of the ε-phase stimulates pitting corrosion of ferrite. Electrochemical measurements of the passive behaviour of investigated materials show that the alloys containing precipitates of the the ε-phase undergo pitting corrosion in 1 M H2SO4–1 M NaCl. Thermal treatment dissolving the ε-phase increases the resistance of alloys to local attack. Our experiments show that the increase of copper content in ferritic alloys increases also the tendency to chromium segregation at grain boundaries and thus the tendency to intergranular corrosion of cast alloys.

Selective surface preoxidation to inhibit the corrosion of AISI type 316L stainless steel by liquid Pb17Li

This paper describes the formation of a ternary oxide coating on 316L stainless steel from the reaction of Pb17Li with the preoxidized surface of steel specimens. The preoxidized surfaces were prepared by heating 316L stainless steel specimens to 800°C in a controlled H 2/H 2O atmosphere (ratio 1000:1). The oxide layer before reaction with the Pb17Li was characterized as Mn 1.5Cr 1.5P 4. Analysis after reaction with Pb17Li indicated a LiMn 2O 4 structure with some of the manganese sites occupied by chromium. 316L specimens prepared with different oxide layer thicknesses, along with uncoated specimens, were corroded in the isothermal hot legs of two Pb17Li filled thermal convection loops. Post-test analysis of the specimens indicated that the oxide coated specimens had, on average, a thinner ferritic corrosion layer than the uncoated specimens. The coated specimens also showed areas with no ferritic corrosion layer.

The effect of oxygen impurities on the behaviour of type 316 stainless steel in Pb-17Li

Corrosion tests carried out in Pb-17Li, with and without added oxygen, have shown that oxygen enhances the corrosion of 316 steel by increasing the depth of the ferritic corrosion layer and the extent of chromium depletion within the layer. Tests using Pb-Li alloys with compositions between Pb-17Li and Pb-11Li and in pure Pb showed no change in the depth of the ferritic zone with composition of the alloys but a significant increase for pure Pb. Measurements of the solubility of nickel in Pb-17Li and Pb-10Li showed the solubility to be similar for both compositions and to be much less than that previously measured in pure Pb. The solubility may be expressed by the equations: log10S(wppm) = 4.832−981,2/T(K) for Pb-17Li, log10S(wppm) = 5.148−1162/T(K) for Pb-10Li.The increase in ferrite zone formation, in the presence of oxygen, cannot, therefore, be due to increased Ni solubility caused by a change in composition of the alloy. A study of the reactions of oxides with Pb-17Li has shown that Cr may interact with oxygen to form the ternary oxide LiCrO2.

Zum kohlenstoffaustausch zwischen stabilisierten austenitischen stählen und flüssigem natrium

We have measured the carbon-concentration profiles in the surface zones of specimens of stabilized austenitic steels after exposure to liquid sodium of 700°C in a sodium circuit. Under the conditions of the tests the specimens were carburized. However, the carbon content of the ferritic corrosion layers decreased to values the initial values. They corresponded to the carbon activity of the sodium.

Stress Corrosion of Ferritic and Martensitic Stainless Steels in Saline Solutions

Abstract The influence of strength level and test temperature on SCC of 410 stainless steel in a NaCl solution poisoned with Na2S has been determined and compared with the behavior of 430 stainless...

Vacuum melting developments

This paper reports corrosion and deposition data from tests carried out with liquid eutectic lead–bismuth (Pb–55 at.% Bi) filled steel tubes (austenitic and martensitic) under a thermal gradient (500–280 °C) for 3000 h. For the austenitic steel, the surface exposed to Pb–55Bi exhibited a ferritic corrosion layer depleted in nickel and chromium at temperature above 450 °C. In the temperature range 450–360 °C, deposits composed of iron and chromium were found. There is a temperature effect on composition with a change from iron-rich to chromium-rich with decreasing temperature. For the martensitic steel, a corrosion without corrosion layer was observed above 480 °C. Only one type of deposit consisting of 98Fe–2Cr was found in the 400–480 °C temperature range.