Effect of the Heat Treatment on the Corrosion Resistance of Duplex Stainless Steels

Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.     

pH与温度对2205DSS在盐卤中的孔蚀行为影响研究

利用电化学方法、交流阻抗技术、失重法及金相显微术研究了pH与温度变化对2205DSS在盐卤中耐孔蚀行为的影响.结果表明：随着卤水pH值的增大,2205DSS耐孔蚀性能先略微增强、然后减弱;根据实际制盐工艺条件,卤水的pH值应适当控制在8.7或8.8以内;随温度升高,2205DSS基体抵抗孔蚀能力明显下降;试样在盐卤水介质中的电极反应是不可逆的,其腐蚀反应既受活化极化控制,又受溶液扩散控制.     

Corrosion behavior of 2205 stainless steel in simulated flue gas condensate with different chloride concentrations in a waste incineration power plant

The effect of Cl⁻ on the initial corrosion behavior of 2205 duplex stainless steel (2205 DSS) in simulated flue gas condensate from a waste incineration power plant was investigated using Mott–Schottky plot, micro-area electrochemical methods, and microscopic surface morphology observation. The results show that at 150°C, the carrier concentration of the 2205 DSS passive film was maintained at a small value and changed little when the Cl⁻ concentration is less than 25 g/L, indicating that it has good pitting resistance. When the Cl⁻ concentration reaches 30 g/L and above, the carrier concentration of the passive film increases remarkably, and pitting corrosion appears on the 2205 DSS surface. At 180°C, there is no obvious pitting on the surface when the Cl⁻ concentration is not more than 15 g/L. When the Cl⁻ concentration is 20 g/L or above, the carrier concentration of the passive film significantly increases, and pitting corrosion appears on the surface. When the Cl⁻ concentration reaches 30 g/L, the carrier concentration of the passive film increases sharply. The passive film on a 2205 DSS surface is seriously damaged and accompanied by the occurrence of uniform corrosion.     

硫酸盐还原菌作用下2205双相不锈钢在3.5%NaCl溶液中应力腐蚀开裂行为研究

采用动电位极化技术、慢应变速率拉伸实验(SSRT)以及扫描电子显微镜(SEM)等方法研究了硫酸盐还原菌(SRB)新陈代谢对2205双相不锈钢(DSS)在3.5%(质量分数)NaCl溶液中的应力腐蚀开裂(SCC)行为的影响。结果表明,与无菌溶液中相比,SRB的存在促进了2205DSS的阳极溶解过程,诱发了点蚀,为SCC萌生提供了裂纹源。2205DSS的SCC敏感性与SRB活性浓度呈正相关,在稳定生长期SRB活性浓度最大,此时2205DSS的SCC敏感性最大。2205DSS在含SRB的3.5%NaCl溶液中发生的SCC机理为阳极溶解和氢脆混合控制机制。SRB作用下,2205DSS中铁素体相表现为穿晶解理特征,奥氏体相表现为韧性撕裂的特征,铁素体相具有更高的SCC敏感性。     

Pitting corrosion of intermetallic compound Ni3(Si,Ti) with 2 at% Mo in sodium chloride solutions

The pitting corrosion of Ni₃(Si,Ti) with 2 at% Mo consisting of a single intermetallic compound Ni₃(Si,Ti) phase of L1₂ structure and a two phase mixture of L1₂ and fcc nickel solid solution was investigated as functions of test temperature and chloride concentration in sodium chloride solutions by using a potential step method and compared with that of intermetallic compound, Ni₃(Si,Ti). The pitting potential obtained for the Ni₃(Si,Ti) with 2 at% Mo decreased with increasing chloride concentration and test temperature. A critical chloride concentration below which no pitting corrosion took place was found to exist and to decrease with increasing test temperature. The specific pitting potential at the critical chloride concentration also decreased with increasing test temperature. The pitting potential of Ni₃(Si,Ti) with 2 at% Mo was higher than pure nickel, but lower than that of Ni₃(Si,Ti). A critical chloride concentration was found to be lower than that of Ni₃(Si,Ti), whereas the specific pitting potentials at the critical chloride concentration was found to be higher than that of Ni₃(Si,Ti). Pitting corrosion occurred in the two phase mixture region.     

点缺陷模型在2205双相不锈钢中的应用

采用电化学极化曲线和电化学阻抗技术对2205双相不锈钢在0.1%、1.0%及3.5%（质量分数,%）三种不同浓度的NaCl溶液中的腐蚀性能进行测试,采用点缺陷模型(PDM)对测试结果进行建模与分析。研究结果表明,2205双相不锈钢随着溶液浓度的升高抗点蚀能力下降,这是由于在钝化膜的生长过程中,氧离子缺陷产生于金属/膜界面,消耗于膜/溶液界面,而金属离子缺陷产生于膜/溶液界面,消耗于金属/膜界面;氧离子缺陷的迁移导致钝化膜的生长,而金属离子缺陷的迁移使得钝化膜发生溶解。同时,根据PDM模型理论并从金属相角度出发对2205不锈钢建立钝化膜溶解模型,可知2205双相不锈钢奥氏体相γ上的钝化膜可能比铁素体相α优先发生溶解。     

Microstructure and stress corrosion cracking in simulated heat-affected zones of duplex stainless steels

The effects of nitrogen content and the cooling rate on the reformation of austenite in the Gleeble simulated heat-affected zone (HAZ) of 2205 duplex stainless steels (DSSs) were investigated. The variation of stress corrosion cracking (SCC) behavior in the HAZ of 40 wt% CaCl₂ solution at 100 °C was also studied. Grain boundary austenite (GBA), Widmanstatten austenite (WA), intergranular austenite (IGA) and partially transformed austenite (PTA) were present in the HAZ. The types and amounts of these reformed austenites varied with the cooling rate and nitrogen content in the DSS. U-bend tests revealed that pitting corrosion and selective dissolution might assist the crack initiation, while the types and amounts of reformed austenite in the HAZ affected the mode of crack propagation. The presence of GBA was found to promote the occurrence of intergranular stress corrosion cracking. WA, IGA and PTA were found to exhibit a beneficial effect on SCC resistance by deviating the crack propagation path.     

2205双相不锈钢在酸性H2S环境下的应力腐蚀行为及开裂机理研究

_{摘要:采用C型环实验研究了2205双相不锈钢在饱和H2S环境下的应力腐蚀行为及开裂机理。研究结果表明,2205双相不锈钢在NACE标准A溶液中有良好的抗应力腐蚀能力。通过OM}、_{SEM、EDS及电化学手段分析得出2205双相不锈钢的应力腐蚀开裂经历了表面点蚀,蚀坑形成,H2S解离,H原子吸附并从蚀坑位置扩散进入金属基体,在金属基体中聚集,通过氢致开裂机制导致裂纹萌生,并逐渐扩展。}     

Statistical analysis of metastable pitting events on carbon steel

Abstract

The metastable pitting behaviour of galvanically coupled and potentiostatically controlled A516–70 carbon steel in a chloride containing solution has been statistically analysed. It is shown that the pitting activity, indicated by the pit initiation rate, depends on immersion time, applied potential, and chloride concentration. There is a strong correlation among the pitting events at a high pitting activity, where the metastable pitting events follow non-Poissonian behaviour and a previous pit has an influence on subsequent pitting events. When the pitting activity decreases, the correlation decreases and approaches the Poisson distribution.     

Pitting corrosion of thixoformed,rheocast and gravity cast A356-T6 alloy in chloride media

Abstract

In the research work presented here, the pitting behaviour of thixoformed A356-T6 alloy, with different reheating temperatures, was evaluated and compared with the pitting behaviour of rheocast and gravity cast A356-T6 alloys with the same composition. To study the pitting behaviour, linear sweep voltammetric tests were performed on thixoformed, rheocast and gravity cast A356-T6 alloys in a 3·5%NaCl solution. A simulation method was also used to identify local galvanic corrosion current density between local galvanic couples. Results obtained show that the resistance to pitting corrosion of thixoformed samples formed at 590°C was higher than that of the samples formed at 600°C as well as rheocast and gravity cast samples. The improvement in the pitting corrosion resistance due to the thixoforming process is attributed to morphological aspects of the silicon phase as well as the area effect as related to galvanic corrosion between the silicon particles and the eutectic aluminium phase.     

Pitting corrosion of intermetallic compound Ni3(Si,Ti) in sodium chloride solutions

The pitting corrosion of intermetallic compound Ni₃(Si,Ti) was investigated as functions of test temperature and chloride concentration in sodium chloride solutions by using a potential step method. In addition, the pitting corrosion of solution-annealed austenitic stainless steel type 304 and pure nickel was also studied under the same experimental condition for comparison. The pitting potential obtained for the intermetallic compound decreased with increasing chloride concentration and test temperature. A critical chloride concentration below which no pitting corrosion took place was found to exist and to decrease with increasing test temperature. The specific pitting potential at the critical chloride concentration also decreased with increasing test temperature. In addition, the pitting potential at various constant chloride concentrations above the critical chloride concentration decreased with increasing test temperature. The pitting potential of Ni₃(Si,Ti) was higher than pure nickel, but lower than that of type 304.     

2205和316L不锈钢在氢氟酸中的电化学腐蚀行为

通过动电位极化和电化学阻抗方法考察了2205双相不锈钢和316L不锈钢在5%(体积分数)HF溶液中的电化学行为,借助Mott-Schokkty曲线分析了两种不锈钢表面钝化膜的半导体特性。结果表明：两种不锈钢在氢氟酸溶液中都能发生钝化,且2205双相不锈钢的钝化区间范围更宽,维钝电流密度更低。2205双相不锈钢表面钝化膜表现出更高的钝化膜电阻和电荷转移电阻,其抗氢氟酸腐蚀性能优于316L不锈钢,这主要与2205双相不锈钢中的Mo和Cr含量高、表面钝化膜缺陷少、钝化膜易修复等因素有关。     

Examples of metal and resin processing using high power diode lasers

In this work, the pitting corrosion resistance of welding duplex stainless steel 2205 was studied. Joints were made using the GMAW process with different fillers: duplex ER 2209 and two austenitic fillers (ER 316LSi and ER 308LSi). The microstructure obtained with the duplex ER 2209 filler is similar to the duplex 2205 base material, but the joints produced with the austenitic fillers cause a decrease of the α/γ phase ratio. In order to evaluate the influence of the filler on the weld, the pitting corrosion resistance was determined by means of an electrochemical critical pitting temperature test, and the mechanical properties by the hardness test. The phase imbalance produced for the different fillers causes variation of the pitting corrosion resistance and the mechanical properties. The variation in the mechanical properties of the material was also studied by means of hardness tests.     

Effects of alloying elements on the mechanical properties and corrosion behaviors of 2205 duplex stainless steels

The effects of alloying elements on the microstructure, mechanical properties, and corrosion behaviors of duplex stainless steels (DSSs) have been investigated in this study. Experimental alloys were prepared by varying the concentrations of the constituent elements in DSSs. Hot ductility test, tensile test, charpy impact test, and corrosion test were performed to evaluate the properties of the experimental alloys. The results showed that the extent of edge cracking of DSSs increased with the increasing value of the crack sensitivity index (CSI). The higher the hot ductility index (HDI) was, the better the hot ductility of DSSs achieved. Austenite (γ) stabilizer generally caused a decrease in the strength and an increase in the charpy impact absorbed energy of the stainless steel. On the contrary, ferrite (α) former exerted its beneficial effect on the strength but became detrimental to the toughness of DSSs. The presences of sulfur and boron also caused a decrease in the impact energy, but nitrogen and carbon hardly affected the toughness within the concentration range tested in this study. The value of pitting nucleation potential (E _np ) of different nitrogen contents in 3.5 wt.% NaCl solution at room temperature was almost the same, but the value of pitting protection potential (E _pp ) among these alloys was increased with increasing the content of nitrogen. The susceptibility to stress corrosion cracking (SCC) of DSSs was high when tested in boiling 45 wt.% MgCl₂ solution. On the other hand, the time to failure of the experimental steels in 40 wt.% CaCl₂ solution at 100 °C was longer than that in MgCl₂ solution. Nitrogen could affect the SCC behavior of DSSs in CaCl₂ solution through the combinative effects by varying the pitting resistance and the slip step dissolution. An optimum nitrogen (N) content of 0.15 wt.% was found where the highest SCC resistance could be obtained. Although γ phase exhibited better resistance to SCC, cracks were found to penetrate through α and γ grains or to propagate along the α/γ interface. As a result, a mixed transgranular plus intergranular mode of fracture surface was observed.     

双相不锈钢焊接接头的耐腐蚀性能

根据母材临界点蚀温度(CPT)的试验结果,利用小试样的腐蚀实验方法研究了奥氏体-铁素体双相不锈钢焊接接头的耐点蚀性能.结果表明,手工电弧焊工艺过程对双相不锈钢材料的耐点蚀性能具有显著的影响,点蚀优先发生在焊缝金属或焊接热影响区中.双相不锈钢材料的耐点蚀性能与材料本身奥氏体和铁素体相比例有关.腐蚀试样的表面状态(粗糙程度)对母材金属的耐点蚀性能有明显的影响.表面越粗糙,耐点蚀性能越差,临界点蚀温度越低.     

Condensed phase corrosion of P91 and DSS 2205 steels at advanced oxygen-fired pressurized fluidized bed combustion plants

To achieve the targets of high energy efficiency and reduced CO₂ emission, advanced oxygen-fired pressurized fluidized bed combustion technology is being developed. The generated flue gas condensates are very corrosive, but very limited information is available to select appropriate alloys for the cost-effective construction and long-term safe operation of flue gas components. Thus, this study investigated the corrosion performance of P91 and DSS 2205 steels in the simulated condensates at 60°C–150°C. The dominant reactions on the two steels were considerable oxide formation and high chemical dissolution of the formed oxides instead of localized pitting. The increase in temperature leads to an exponential increase in the long-term corrosion rates of the steels. Benefited from its high Cr and Mo contents, DSS 2205 steel exhibited much better corrosion resistance, and the formed surface scales consisted of inner Fe-enriched and outer Cr-enriched oxides in which Cr₂O₃ was transformed into Cr(OH)₃ with the increase in temperature. The corrosion products on P91 steel consisted of inner Cr–Fr–Mo oxides and outer Fe-enriched oxides, which were porous and unable to protect the steel.     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

Effect of halide anions and temperature on initiation of pitting in Cr–Mn–N and Cr–Ni steels

Abstract

The pitting corrosion of Cr₁₈Mn₁₂N and Cr₁₈Ni₉ steels in halide solutions (F^?, Cl^?, Br^? and I^?) has been investigated. The study involved cyclic potentiodynamic polarisation tests with subsequent examination of the specimens by both optical and scanning electron microscopy. Values of the critical concentrations of halide ions, [X^?]_cr, beyond which pitting occurs, as well as breakdown potentials for pitting in chloride solution, have been established. In addition, the effect of the temperature over the range of 5–80°C on the critical chloride ion concentration [Cl^?]_cr has been investigated and it has been found that temperature has a negligible effect beyond 40°C.     

Effect of selective dissolution on fatigue crack initiation in 2205 duplex stainless steel

The effect of selective dissolution on fatigue crack initiation of 2205 duplex stainless steel (DSS) was investigated in this study. In mixed sulfuric and hydrochloric acid aqueous solution, there existed two distinctly separated anodic peaks in the active-to-passive transition region of the polarization curve. Either ferritic or austenitic phase was selectively dissolved at each characteristic anodic peak potential. Under sinusoidal cyclic loading condition, however, selective dissolution did not assist fatigue crack initiation instead resulting in the elimination of stress concentration site in the selectively dissolving phase. As a consequence, under selective dissolution condition, fatigue crack initiated in the phase while its dissolution rate was lower with respect to the other constituent phase in the duplex stainless steel. The microstructural evolution of the corrosion fatigue crack initiation in 2205 DSS in the mixed sulfuric and hydrochloric acid solution is highlighted in this investigation.     

Effect of velocity and elevated temperature on pitting of Al 6013-20SiCp composite in 3·5 wt-%NaCl

Abstract

This paper presents new data on the effect of temperature and velocity on the pitting potential E_p, corrosion potential E_corr, and pitting morphology of O, F, and T4 tempers of alloy 6013-20SiC_p in 3·5 wt-%NaCl in the temperature range 30–130°C and at velocities of 0·5–1·0 m S_?1. The pitting potential of tempers T4 and O tended to increase with increasing temperature and flow velocity, but the pitting potential of temper F showed the opposite behaviour. Temper T4 of the alloy showed the best resistance to pitting. Alloy 6013-20SiC_p in temper T4 is therefore considered to be suitable for application in chloride containing environments.