Corrosion behaviour of a dissimilar joint TIG weld between austenitic AISI 316L and ferritic AISI 444 stainless steels

The AISI 444 stainless steel (SS) has become an option to substitute the AISI 316L SS because of its low cost and satisfactory corrosion resistance. However, the use of AISI 444 alloy tubes in heat exchangers causes the welding of a dissimilar joint. The aim of this study was evaluate the corrosion resistance of the tube-to-tubesheet welded by a TIG process composed of AISI 316L and AISI 444. Preparation of samples was executed through replication of tube-to-tubesheet joints. In order to test the corrosion resistance of the welded joint, the following tests were applied: sensitisation, mass loss from room temperature up to 90 °C and electrochemical corrosion tests in 0.5 mol/L HCl and 0.5 mol/L H₂SO₄ electrolytes. The results have shown that the dissimilar joint suffers galvanic corrosion with increased degradation of the heat-affected zone of the AISI 444 tube. Nevertheless, the mechanisms of localised corrosion (pit and intergranular) were more active in the AISI 316L alloy. It is concluded that the dissimilar joint showed better corrosion resistance than the welded joint composed solely of AISI 316L at temperatures up to 70 °C, as the conditions observed in this work.     

Effects of low-temperature aging on AISI 444 steel

The consequences of aging at 400 and 475 °C on the mechanical properties, corrosion resistance, and magnetic properties of the ferritic stainless steel (SS) AISI 444 were investigated. Age hardening was measured as a function of aging time at both temperatures and was found to be more intense at 475 °C. The localized corrosion susceptibility increased, while the impact toughness decreased with aging time. These two effects were also more important at 475 °C. Unlike duplex SSs, AISI 444 did not present any variation in coercive force or Curie temperature with aging time. The effects on the Mössbauer spectra were also determined and analyzed.     

Corrosion Behavior of AISI 316L Stainless Steel and ODS FeAl Aluminide in Eutectic Li2CO3–K2CO3 Molten Carbonates under Flowing CO2–O2 Gas Mixtures

A kinetics study on AISI 316L stainless steel and ODS(Oxide-Dispersion-Strenghtened) FeAl iron aluminide was conducted concerningits corrosion behavior in moltenLi₂CO₃-K₂CO₃ eutectic at 650°C in flowingCO₂-O₂ gas mixtures. The corrosion resistance of FeAl ODS wasdemonstrated to be significantly superior to that of austenitic AISI 316Lsteel under all gas conditions tested in this work. At low CO₂partial pressure (PCO₂=0.3 atm) the corrosion rate of bothalloys decreased with time due to the formation of a protective oxidelayer. In dry CO₂ gas, corrosion of AISI steel proceeded at anear-linear rate, indicative of a surface-controlled reaction. FeAl corrodedinitially following parabolic behavior, but, on further reaction, exhibitedsome weight loss. A similar behavior was also observed in a67CO₂-33O₂ gas mixture. Corrosion of FeAl in highCO₂ gas has been postulated to initiate by acidic fluxing ofyttria particles. The attack then develops as pitting and leads to furtherreaction by general corrosion as a consequence of the formation ofactive-passive electrochemical cells between the interior of pits and theexternal surface. The weight loss of AISI 316L in67CO₂-33O₂ gas can be ascribed to the high oxidizing power ofthe gas causing a continuous dissolution of theCr₂O₃ layer into a soluble chromate.     

Corrosion and wear behaviors of boronized AISI 316L stainless steel

In this study, the effects of a boronizing treatment on the corrosion and wear behaviors of AISI 316L austenitic stainless steel (AISI 316L) were examined. The corrosion behavior of the boronized samples was studied via electrochemical methods in a simulation body fluid (SBF) and the wear behavior was examined using the ball-on-disk wear method. It was observed that the boride layer that formed on the AISI 316L surface had a flat and smooth morphology. Furthermore, X-ray diffraction analyses show that the boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB, and Ni₂B phases. Boride layer thickness increased with an increasing boronizing temperature and time. The boronizing treatment also increased the surface hardness of the AISI 316L. Although there was no positive effect of the coating on the corrosion resistance in the SBF medium. Furthermore, a decrease in the friction coefficient was recorded for the boronized AISI 316L. As the boronizing temperature increased, the wear rate decreased in both dry and wet mediums. As a result, the boronizing treatment contributed positively to the wear resistance by increasing the surface hardness and by decreasing the friction coefficient of the AISI 316L.     

AISI 316L奥氏体不锈钢低温离子-气体渗碳工艺优化

目的将低温离子-气体乙炔渗碳应用于AISI 316L奥氏体不锈钢表面硬化处理,同时探讨其硬化处理的最优工艺参数及优化效果。方法采用离子轰击去除不锈钢表面钝化膜并活化其表面,再进行低温气体乙炔渗碳,实验过程使用脉冲式供气循环处理方式。进行温度梯度实验,寻找渗碳处理的临界温度。并采用正交试验法设计3因素3水平共9组实验,分析气体比例、离子轰击时间、保温压强3个因素对渗碳层硬度和厚度产生的影响,以期得到不锈钢低温离子-气体乙炔渗碳优化工艺。通过对经过最优化工艺处理过后的不锈钢硬化层组织、成分、厚度、硬度、耐磨性、耐蚀性能的研究分析,验证此工艺对AISI 316L奥氏体不锈钢硬化处理的适用性。结果处理温度为540℃时渗碳层有碳的铬化物析出;离子轰击时间对渗碳层硬度影响最大,保温压强对硬化层厚度影响最明显。在硬化处理温度为520℃,V(H2)∶V(C2H2)=1∶1,渗碳压强为-0.02 MPa,离子轰击时间为20 min时,316L奥氏体不锈钢离子-气体乙炔渗碳效果最优。经优化工艺处理后不锈钢硬化层厚度达到30μm左右,表面硬度达到838HV0.05,耐蚀性和耐磨性能等都显著提高。结论低温离子-气体乙炔渗碳硬化处理适用于AISI 316L奥氏体不锈钢,其处理最合适温度为520℃。经优化工艺处理后的不锈钢具有较高的硬度、厚度,良好的硬度梯度,高耐蚀性能及高耐磨性能。     

Study of plasma nitriding and nitrocarburising of AISI 430F stainless steel for high hardness and corrosion resistance

ABSTRACT

In order to improve both the hardness and corrosion resistance properties of AISI 430F stainless steel, plasma nitriding (PN) and nitrocarburising processes were carried out at different temperatures ranging from 350 to 500°C for 4?h. After PN, the nitrided layer was found to be thicker compared to that obtained by plasma nitrocarburising process. There was an increase in microhardness values by a factor of six to seven compared to the plasma nitrided and nitrocarburised specimens respectively, treated at 500°C. The electrochemical corrosion behaviour of the plasma nitrided and nitrocarburised AISI 430F specimens show that the plasma nitrided and nitrocarburised specimens treated at 400°C for 4?h showed better corrosion resistance and higher surface hardness than the untreated AISI 430F stainless steel specimens. This is mainly attributed to the presence of nitrogen in the modified layer existing as a solid solution in the ferrite phase.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Inhibitoren der Korrosion 28 (1). 2-Aminopyrimidin (2-AP) als an Inhibitor der the Korrosion des Kupfers in Salzlösungen unter Sauerstoff

Inhibiors of corrosion 28 (1). 2-Aminopyrimidine (2-AP) as an inhibior of the corrosion of copper in salt solutions under oxygen 2-Aminopyrimidine is at present the best inhibitor known for the corrosion of copper, as measured under controlled conditions. A protective coating is created on the copper in conjunction with Cu¹⁺ ion as these form leave the surface. The coating at the surface was studied on variation of: (a) the concentration of 2-AP and Cu²⁺ ions, (b) the rate of agitation of the liquid medium and (c) the type of anion present in the corrosive medium. Some insight into the nature of the coating process was obtained via a rest-potential/time measurements, current voltage curves, polarisation/resistance curves and experiments interrupted in the course of the corrosion, all carried out with/without 2-AP and with/without added Cu²⁺ ions.     

Effect of weld metal chemistry on stress corrosion cracking behavior of AISI 444 ferritic stainless steel weldments in boiling chloride solution

The influence of the weld metal chemistry on the susceptibility of AISI 444 ferritic stainless steel (FSS) weldment to stress corrosion cracking (SCC) in hot chloride was investigated by constant load tests and metallographic examination. Two types of filler metal of austenitic stainless steel (E316L and E309L) were used in order to produce fusion zones of different chemical compositions. The SCC test results showed that the interface between the fusion zone (FZ) and the heat affected zone (HAZ) was the most susceptible region to SCC. Results also showed that the AISI 444 stainless steel weldment with E309L weld metal presented the best SSC resistance. Microstructural examinations indicated that the cracks initiated in the weld metal and propagated to the HAZ of the AISI 444 FSS, where the fracture occurred and it was observed a considerable amount of precipitates. Additionally, the higher SCC resistance of the AISI 444 FSS weldment with E309L weld metal may be attributed to the presence of a discontinuous delta‐ferrite network in its microstructure, which acted as a barrier to cracks propagation from the fusion zone to the HAZ/fusion zone interface of AISI 444 FSS. Fractrography analyses showed that the transgranular quasi‐cleavage fracture mode was predominant in the AISI 444 weldment with E316L weld metal and the mixed fracture mode was the predominant in the AISI 444 weldment with E309L weld metal.     

Optimization and control of drilling burr formation of AISI 304L and AISI 4118 based on drilling burr control charts

Control charts for drilling burr formation for stainless, AISI 304L, and low alloy steel, AISI 4118, were developed. Split point twist drills are used for the experiments of this work. A Drilling Burr Control Chart, based on experimental data, is a tool for prediction and control of drilling burrs. Burr classification was carried out based on the geometric characteristics, burr formation mechanisms and sizes of the burrs. New parameters consisting of cutting condition variables and drill diameter were developed, and used to show unique distributions of the burr types. Burr types and the resultant burr size showed great dependence on the new parameters regardless of the drill diameters. Through the chart, burr type can be predicted with given cutting conditions. Also cutting conditions that are believed to create preferred burr types can be selected.     

Corrosion inhibition of mild steel by amphoteric surfactants derived from aspartic acid

The inhibition of mild steel corrosion/in 0.5 M HCl solution by amphoteric surfactants (which contain both an anionic and a cationic moiety in the same molecule) of general formula: (R alkyl group of C_{10, 11, 12, 13, 15 and 17}) is shown to confirm Langmuir's adsorption isotherms. At a given concentration of surfactants, the inhibiting action increases with the increase of carbon chain length. The influence of both inductive and steric hindrance effects of methylene groups in –R on the inhibition efficiency has also been mentioned.     

Effects of hydrogen on formation of passive films on AISI 310 stainless steel

Abstract

The amount of oxide and the thickness of passive films on AISI 310 stainless steel pre-charged with hydrogen were found to be smaller than those on the uncharged samples. It is believed that one of the causes of the higher susceptibility to corrosion of stainless steels containing hydrogen is that the dissolved hydrogen degrades the passive film formed on the stainless steel. Evidence has also been obtained that passivity is associated with the oxides at the inner region of the passive film.     

Investigation of corrosion behaviors at different solutions of boronized AISI 316L stainless steel

In this study, corrosion behaviors of boronized and non-boronized AISI 316L stainless steel (AISI 316L SS) were investigated with Tafel extrapolation and linear polarization methods in different solutions (1 mol dm^?3 HCl, 1 mol dm^?3 NaOH and 0.9% NaCl) and in different immersion times. AISI 316L SS were boronized by using pack boronizing method for 2 and 6 hours at 800 and 900°C within commercial Ekabor®-2 powder. Surface morphologies and phase analyses of boride layers on the surface of AISI 316L SS were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. SEM-EDS analyses show that boride layer on AISI 316L SS surface had a flat and smooth morphology. It was detected by XRD analyses that boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB and Ni₂B phases. Boride layer thickness increases with increased boronizing temperature and time. The corrosion experiments show that boride layer significantly increased the corrosion resistance of the AISI 316L SS in 1 mol dm^?3 HCl solution. While no positive effect of the boride layer was observed in the other solutions the corrosion resistance of the borid layer on AISI 316L SS was increased in all solution with the increase of the waiting periods.     

The effect of annealing on the corrosion behaviour of 444 stainless steel for drinking water applications

In this study, the corrosion behaviour of annealed and not annealed AISI 444 ferritic stainless steel in tap water with and without addition of selected concentrations of chloride ions was investigated. Cyclic potentiodynamic macro (large area) and micro (small area) polarization measurements (CPP), salt spray test, SEM and EDS analysis were employed to evaluate the pitting and crevice corrosion susceptibility of annealed and not annealed AISI 444. The results obtained indicate that annealing does not improve the resistance to pitting and crevice corrosion. Moreover, micro CPP indicates local susceptibility to pitting on both annealed and not annealed materials; such susceptibility was not evident from macropolarization tests.     

On the corrosion mechanism of AISI 204Cu stainless steel in chlorinated alkaline media

Electrochemical techniques (CV, SECM, CPT) and surface analysis techniques (EDX, SEM) have been employed to assess the corrosion behaviour of the AISI 204Cu stainless steel. The behaviour of this steel has been compared with that of AISI 304 and AISI 434 stainless steels in chlorinated alkaline media. All samples performed well at room temperature under potentiodynamic polarisation up to a chloride to hydroxyl ratio of 10. At this ratio the AISI 204Cu and the AISI 434 steels presented pitting potential at +0.47 V vs. SCE and +0.31 V vs. SCE, respectively. Moreover, the critical pitting temperature was higher for the AISI 204Cu steel than for the AISI 434 steel, respectively 58 °C and 28 °C.In terms of corrosion performance of the AISI 204Cu stainless steel can be classified better than the AISI 434 steel and worse than the AISI 304 steel.Local electrochemical and chemical examinations allowed evidencing the local activity of some pits over long period, and to conclude that the improved corrosion performance of the low nickel alloy AISI 204Cu stainless steel should be ascribed to copper cementation at active corrosion sites.     

Correlation between microstructure and corrosion behavior in an AISI 316L steel pipeline exposed for 100,700 h at 640°C in a petrochemical plant

The microstructure and electrochemical properties of 316L stainless steel were investigated after two conditions: aged at 640°C for 100,700 h and solution annealed at 1050°C for 2 h. While the aged samples were obtained from a pipe of a petrochemical reactor plant that was in service, the solution annealing was carried out in a conventional laboratory furnace. After aging, the precipitates present in decreasing order of quantity were sigma, Laves phase, and M₂₃C₆. After solution annealing, the microstructure was full austenitic. These results were in agreement with equilibria phase simulation with Thermo-Calc software. Intergranular corrosion susceptibility, evaluated by means of the single loop electrochemical potentiokinetic reactivation technique and Practice A of ASTM 262, indicated a preponderant role for the sigma precipitate. The pitting potential (E_pit) was evaluated through potentiodynamic polarization curves in 0.6 M NaCl and electrochemical impedance spectroscopy was performed at the corrosion potential to complement the information about the corrosion resistance.     

Susceptibility of highly alloyed austenitic stainless steels to caustic stress corrosion cracking

Slow Strain Rate tests (5 × 10⁻⁶ to 4 × 10⁻⁸ s⁻¹) in 300 g/L sodium hydroxide at 200°C were conducted on highly alloyed austenitic stainless steels with various nickel and chromium concentrations: N08904 (20Cr‐25Ni‐4Mo), N8825 (22.5Cr‐40Ni‐3Mo), N08028 (27Cr‐30Ni‐3.5Mo), R20033 (32.5Cr‐31Ni‐1.5Mo). Stress Corrosion Cracking (SCC) resistance of studied alloys increases in the following order: N08904 → N8825 → N08028 → R20033 in accordance with increasing chromium content. The SCC susceptibility indexes decrease gradually with decreasing of strain rate. In materials exhibiting higher SCC resistance, tests should be conducted at very low strain rates ( < 2 × 10⁻⁷ s⁻¹) to observe indications of SCC. When sulphide ions are added the R20033 steel exhibiting an excellent corrosion behaviour in pure caustic solution, becomes highly susceptible to SCC, even at = 5 × 10⁻⁶ s⁻¹.     

4‐Chloro‐benzoic acid [1,2,4]triazol‐1‐ylmethyl ester as an effective inhibitor of mild steel corrosion in HCl solution

4‐Chloro‐benzoic acid [1,2,4]triazol‐1‐ylmethyl ester (CBT) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscope (SEM). The results showed that CBT is an excellent inhibitor for mild steel in acid medium and its inhibition efficiency (IE%) is up to 90.2% at a concentration of 10^?3 M at 298 K. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Potentiodynamic polarization studies clearly reveal that CBT acts essentially as mixed‐type inhibitor. Thermodynamic parameters such as adsorption heat ( ), adsorption entropy ( ), and adsorption free energy ( ) were obtained and discussed from experimental data of the temperature studies of the inhibition process at four temperatures ranging from 298 to 333 K. Kinetic parameters activation such as , , , and pre‐exponential factor have been calculated and discussed. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. The values of the free energy of adsorption indicated that the adsorption of CBT molecule was a spontaneous process, and was typical of chemisorption.     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO₃) solutions at 50°C using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS‐4 solution, chloride (Cl^?) and/or sulfate ( ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I_corr, was maximum in 0.01 M NaHCO₃ and with additions of ions. Higher or lower solution concentrations or additions of Cl^? alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO₃. Higher or lower solution concentrations of additions of Cl^? or decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO₃ solution, but it was minimum with the addition of Cl^? or ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO₃ solutions seems to be hydrogen‐assisted anodic dissolution.     

Fatigue behaviour of low temperature carburised AISI 316L austenitic stainless steel

Low temperature carburising (LTC) was applied to AISI316L austenitic stainless steel and its effect on microstructure and fatigue behaviour was investigated. LTC treatment enhances surface hardness and wear resistance of the steel without reducing its corrosion resistance. Surface hardness up to 1150 Vickers was achieved in the carburised layer, thanks to the formation of the so-called “S-phase”, a carbon-supersaturated austenite phase. The XRD evaluation of treated material verified expanded austenite with no evidence of carbide precipitation. Rotating bending fatigue tests showed that the low temperature carburising treatment enhances the fatigue strength of the 316L steel by 40% with respect to the untreated material due to the high residual stresses present in the treated layer. A major temperature increase was found testing the LTC specimens, with a peak value at the end of the test up to 600 °C. By air cooling the LTC specimens during the tests, a further increase of fatigue strength up to 70% was achieved with respect to the untreated material. Fatigue cracks in the surface-treated specimens always nucleated near the boundary between the carburised case and the core.