Sensitization and Intergranular Corrosion Behavior of High Nitrogen Type 304LN Stainless Steels for Reprocessing and Waste Management Applications

High nitrogen 304LN stainless steels (SS) intended for chloride and nitric acid environments in spent nuclear fuel reprocessing and waste management applications were evaluated for their sensitization and intergranular corrosion (IGC) resistance. For this purpose, high nitrogen (0.132 pct, 0.193 pct and 0.406 pct) containing, impurity-controlled, vanadium-added 304LN SS alloys were developed. For comparison, 304L SS, which is currently used in reprocessing plants, was also studied. These stainless steels were subjected to heat treatment at 948 K (675 °C) for various durations ranging from 1 to 1000 hours and tested for susceptibility to IGC as per ASTM A262 Practice A and E tests. The degree of sensitization was estimated with the double loop electrochemical potentiokinetic reactivation technique. The increase in nitrogen content resulted in higher hardness and finer grain size. Based on the detailed microstructural and corrosion studies, it was determined that an addition of 0.132 pct and 0.193 pct nitrogen showed better IGC resistance and an additional increase in nitrogen resulted in deterioration resulting from chromium nitride precipitation, which was confirmed by electrochemical phase separation and X-ray diffraction studies. The onset of desensitization was faster for the alloy with 0.132 pct nitrogen as well as 0.406 pct nitrogen because of the lower nitrogen content in the former case and the finer grain size in the latter case. The higher hardness and superior IGC resistance of 0.132 pct and 0.193 pct nitrogen containing Type 304LN SS suggests the suitability of this alloy for nitric acid- and chloride-containing environments of reprocessing and waste management plants.     

高Ta钛合金在沸腾硝酸中的腐蚀行为

对高Ta含量钛合金Ti-32Ta在8 mol/L沸腾硝酸溶液中进行了全浸腐蚀实验,研究了Ti-32Ta合金在沸腾硝酸中的腐蚀行为。采用扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线衍射光电子能谱(XPS)等分析方法对钛合金腐蚀表面的钝化膜进行了成分、组织结构及合金价态分析。结果表明:Ti-32Ta合金在沸腾硝酸溶液中呈现均匀腐蚀行为,在介质中通入一定流量的新鲜空气对合金稳定腐蚀阶段的腐蚀速率影响不大。与Ti-6Ta合金相比,Ti-32Ta合金腐蚀后形成的钝化膜更薄更致密,耐蚀性能更好。两种合金腐蚀钝化膜中Ti和Ta的价态组成相同,Ti-32Ta合金腐蚀表面Ta及Ta2O5的含量高于Ti-6Ta合金腐蚀表面。     

Development and application of nitrogen-alloyed austenitic stainless steels in Baosteel

In recent years,nitrogen-alloyed stainless steels have been a research hotspot in the field of stainless steel product and technology. Nitrogen-alloyed austenitic stainless steels developed by Baosteel and their applications are introduced. These steels are nitrogen-controlled products 304 N and 316 LN,nitrogen containing economical products BN series and high-nitrogen stainless steel( HNS) series. The results show that the presence of nitrogen can significantly improve the strength and corrosion resistance of steel produced. By nitrogen alloying,economical austenitic stainless steels w ith considerably less nickel than 304 can be obtained; the corrosion resistances of these steels are almost the same as 304. Furthermore,by a scientific approach of nitrogen alloying,high-nitrogen steel of0. 8% nitrogen content is fabricated under the non-pressurized conditions,and the pitting potential of this steel is 1. 0 V. At present,nitrogen-alloyed steels developed by Baosteel are w idely utilized in the manufacture of cryogenic storage containers,transportation containers,and many household w ares.     

Effect of Microstructure of 304L SS and Thermal Aging of 304L SS Weld on the Corrosion Behavior in Simulated High Level Waste

The effect of oxidizing ions present in simulated high level liquid waste (HLW) on the corrosion behaviour of solution annealed, sensitized 304L SS and 304L SS weld was investigated by potentiodynamic anodic polarization technique. Potentiodynamic anodic polarization studies showed a higher passivation current density and increased corrosion potential (E_corr) in simulated HLW when compared to 3 M HNO₃ in all the specimen mentioned above. In addition, the effect of microstructure of thermally aged 304L SS weld on the corrosion behavior was investigated in simulated HLW medium. Thermal ageing of 304L SS weld was carried out at 1023 K/100 h. Optical microscopy confirmed step microstructure for solution annealed and ditch microstructure for the sensitized specimens. The weld region was found to possess delta-ferrite distributed in austenite matrix. Thermal ageing resulted in fragmentation/dissolution of delta-ferrite and transformation of delta-ferrite to carbides and sigma phases. The thermally aged 304L SS weld specimen showed only a marginal decrease in corrosion resistance in simulated HLW when compared to the 304L SS weld.     

稀土和铬对铁基自熔合金涂层耐蚀性的影响

本研究着眼于考察稀土和合金成分对铁基自熔合金涂层的耐蚀性的影响,对不同成分的合金涂层进行了三酸一盐的浸蚀试验。结果表明在硫酸和硝酸溶液中,稀土的添加对合金涂层的耐蚀性有利,但在盐酸和氯化钠溶液中,稀土的添加对合金涂层耐蚀性无益。铬含量高的铁基自熔合金涂层在硝酸溶液中有优良的耐蚀性,但在硫酸和盐酸中的耐蚀性不如铬含量低的铁基自熔合金涂层。文中分析了不同合金在试验中的不同表现的原因,进而为铁基自熔合金的进一步工业应用提供有用的信息。     

304不锈钢在模拟压水堆一回路水中高温电化学腐蚀行为

通过模拟压水堆一回路水环境,研究了氯离子浓度和溶解氧对304不锈钢高温电化学腐蚀行为的影响.动电位极化曲线结果表明,氯离子浓度主要影响高电位下的二次钝化效应,低电位下影响效果不明显,结合X射线光电子能谱对氧化膜元素成分的分析发现二次钝化效应与氧化膜中Fe/Cr元素含量比密切相关.电化学阻抗谱和扫描电镜结果表明,随着氯离子浓度增加,氧化膜阻抗逐渐降低,表面外层氧化物颗粒和间隙逐渐增大,耐腐蚀性能降低.随着溶解氧含量的升高,304自腐蚀电位逐渐升高,钝化电流密度降低,钝化区间缩小,表面氧化膜阻抗逐渐增加.      

High corrosion resistance 21%Cr-0.4%Cu ferritic stainless steel contributing to resource conservation

With prices for metal resources such as nickel and molybdenum soaring,there is a heightened sense of crisis concerning resource scarcity.While Type304,the most common stainless steel,offers excellent corrosion resistance,its price is affected significantly by the cost of nickel because of its 8%nickel content.The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required.JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel,the world’s first ferritic stainless steel,which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum,two rare metals.The newly developed steel contains 21%chromium with the addition of 0.4% copper.The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition.Copper addition enriches the chromium content in passive films after field exposure.Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304,including commercial kitchenware,building materials and industrial machinery.The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.     

Corrosion Behavior of Sensitized 304 SS in Nitric Acid Medium Containing Oxidizing Ions

The corrosion behavior of 304 stainless steel (SS) in the as-received and sensitized conditions has been investigated at room temperature and at 60 °C in the presence of oxidizing ions in 6 and 8 M nitric acid media. Corrosion of 304 SS in nitric acid was far more severe in sensitized condition than in as-received condition. Further, decrease in corrosion resistance was observed with increase in the temperature of nitric acid. The corrosion potential shifted to noble direction with increase in the concentration of nitric acid and the potential shifted further to transpassive potential at 60 °C. Increase in corrosion potential towards transpassive domain led to severe intergranualar attack. Impedance spectra showed two time constant which could be attributed to the redox reaction on the surface of oxide film. However, the effect of oxidizing metal ions was not prominent.     

合金元素对316LN不锈钢的力学性能和点蚀性能的影响

研究了N、Cr、Mo和Ni四种合金元素含量的变化对核电主管道用固溶态316LN不锈钢的晶粒尺寸以及常规力学性能和点蚀性能的影响.随着N含量的升高,316LN的晶粒明显细化,其在固溶处理过程中晶粒长大趋势也减小.N含量的升高可改善316LN的力学性能和耐点蚀性能,但是当N质量分数达到0.20%时,其耐点蚀性能又开始变差.晶粒细化对316LN强度的影响远小于N含量对316LN强度的影响.Cr及Ni含量对316LN的晶粒尺寸及抗拉强度、屈服强度等力学性能影响不大;Cr含量增加可轻微改善316LN的抗点蚀能力,Ni元素对316LN的耐点蚀性能影响不大,但可增大钝态的腐蚀速度从而不利于钝化膜的稳定.随Mo含量增加,316LN的晶粒尺寸略有减小,强度增大,延伸率显著降低,耐点蚀能力改善.      

硫酸介质中铸造奥氏体不锈钢的腐蚀磨损行为

研究了几种铸造奥氏体不锈钢在含有Ｃｌ－的硫酸介质中的点蚀规律,测定了腐蚀磨损率、摩擦因数和表面钝化膜破坏后的修复时间。实验结果表明,高铬、镍、铜不锈钢有较高的耐蚀性,但其腐蚀磨损失重却高于一般的１８－８型不锈钢     

Comparative Evaluation of Low Nickel and Nickel Free Lean Duplex Stainless Steels with 316L in a Variety of Corrosive Media

For many applications duplex stainless steels with their superior strength coupled with lower raw material cost have emerged as an attractive alternative to austenitic stainless steels. With emphasis on conservation of scarce resources like nickel and molybdenum there is continuing endeavour to develop essentially molybdenum free lean duplex stainless steels with low nickel content such as 2304 (23Cr–4Ni), 2202 (22Cr–2Ni), 2101 (21Cr–1.5Ni). This paper compares the corrosion behaviour of a low nickel duplex (21Cr–1.5Ni) and a nickel free duplex (21Cr–1.5Cu) with 316L stainless steel in several corrosive media. All the three alloys exhibit similar excellent corrosion resistance under boiling conditions in less aggressive organic acids such as 20 % acetic acid, 25 % lactic acid, 25 % citric acid. However, in stronger organic acids such as 5 % formic acid, 5 % oxalic acid, and mixture of formic and acetic acid, the duplex grades exhibit superior corrosion resistance. This edge over 316L continues on addition of chloride ions in these acids. In boiling 50 % nitric acid solution, the corrosion resistance of these nickel free and low nickel duplex is slightly better than 316L grade. Since 304L grade is generally used in nitric acid plants, tests were also conducted on 304L and these duplex grades were found to be more resistant. Similarly in 50 % phosphoric acid also, the duplex grades exhibit superior corrosion resistance compared to 316L grade. Alloying with nickel and molybdenum is known to give rise to significant improvement in corrosion resistance in this acid. However, even in the absence of these elements, the beneficial effect of higher chromium content is evident. Of all the inorganic acids, sulfuric acid is used in largest volume in the industries. Boiling tests in dilute 1 and 5 % H₂SO₄ indicate that nickel free copper bearing duplex is more resistant than low nickel duplex grade and vastly superior to 316L Thus nickel-free and low-nickel duplex stainless steels offer a very attractive combination of high corrosion resistance coupled with cost effectiveness in a wide variety of corrosive media.     

The effect of varying ruthenium content on the corrosion behaviour of two cathodically modified superferritic stainless steels

The corrosion behaviour of two superferritic stainless steels, both containing varying amounts of ruthenium, was evaluated and compared in a 10% sulphuric acid solution. It was found that small additions of ruthenium increased the corrosion resistance in both types of alloys dramatically. Apart from raising the corrosion potential of the base alloys, the cathodic Tafel slopes were also decreased with an increasing amount of ruthenium in each alloy type. The amount of ruthenium for an optimum increase in the corrosion resistance was found to be 0.16% for both types of alloy.     

幕墙连接件用铸态中氮奥氏体不锈钢的力学性能和耐蚀性

试验用新型铸态超低碳低镍中氮奥氏体不锈钢022Cr20Mn10Ni6N(%:0.023～0.027C、9.86～9.95Mn、19.24～20.09Cr、5.41～5.42Ni、0.27～0.34N)由15 kg中频感应炉冶炼,并试验研究了铸态022Cr20Mn10Ni6N钢与铸态304钢(%:0.076C、1.87Mn、18.02Cr、8.64Ni)的组织,力学性能和耐蚀性。结果表明,新型铸态不锈钢的力学性能、耐点蚀性能、耐弱酸弱碱均匀腐蚀性能明显优于铸态304不锈钢,新型铸态不锈钢022Cr20Mn10Ni6N中性盐雾耐蚀性和304钢相当,可满足大气环境玻璃幕墙金属连接件的应用要求。     

Hot corrosion of Fe-10Cr-18Ni-5Mn-5Al-Si-N steels in molten sulfate deposits

The effect of Na₂SO₄ coating on the corrosion behaviour of 5 steel alloys as well as two commercial alloys - type 304 stainless steel and Inconel 690 - were tested in air at 900 °C under atmospheric pressure. Corroded samples were analysed by XRD, SEM and EDX. A newly developed alloy (No. 5) having the composition Fe-10.4Cr-15.43Ni-5.52Mn-5.52AI-1.5Si showed almost comparable corrosion resistance with Inconel 690. Stainless steel 304 failed catastrophically. Other newly developed alloys (no. 1-4) showed intermediate resistance. The results have been interpreted in the light of the nature of scales formed and on the premise that Na₂SO₄ decomposes to give S^2- ions which delay the formation of an internal protective film.     

439超纯铁素体不锈钢耐蚀性评价

通过盐雾试验、电化学试验和FeCl3点腐蚀试验,并结合扫描电镜,对比研究了439超纯铁素体不锈钢和430普通铁素体不锈钢的耐腐蚀性能。结果表明,碳、氮间隙元素极低的439超纯铁素体不锈钢耐点蚀性能明显优于430普通铁素体不锈钢,虽然430钝化膜修复能力较强,但点腐蚀速率也较快;430不锈钢具有严重的晶间腐蚀敏感性,同样,430普通不锈钢在干湿加速盐雾试验中发生了严重腐蚀,439超纯铁素体不锈钢在上述腐蚀试验中均表现出轻微的腐蚀。可见在430普通不锈钢基础上降低碳、氮间隙元素含量,同时加入钛稳定化元素,使其耐腐蚀性能大幅提高。     

Effects of Carbon on the Corrosion Behaviour in Fe‐18Cr‐10Mn‐N‐C Stainless Steels

The effects of carbon on general and pitting corrosion behaviour of Fe‐18Cr‐10Mn‐(0.33～0.44)N‐(0～0.38)C alloys were investigated using potentiodynamic tests. Carbon made the nitrogen‐bearing alloys inert and thus promoted general corrosion resistance. These results were supported by experimental findings, such as elevated corrosion potential, reduced active dissolution rate, lowered passive potential and accelerated hydrogen evolution rate in sulphuric acid solution. The resistance to pitting corrosion in chloride solution was also enhanced by the addition of carbon, which was attributed to the improvement of the stability of the passive film. XPS analysis revealed that the cationic fraction of chromium in the passive film was increased and hence the protection ability of the film was improved by the carbon addition.     

Influence of thermal aging on the intergranular corrosion resistance of types 304LN and 316LN stainless steels

Intergranular corrosion (IGC) resistance of types 304LN and 316LN stainless steels (SS) thermally aged at 823, 873, and 923 K for various durations was assessed by ASTM A262 practice A test (electrolytic etch test) and electrochemical potentiodynamic reactivation (EPR) test. The results indicated that the type 316LN SS has significantly improved IGC resistance compared to 304LN SS. Based on the results of these tests, time-temperature-sensitization (TTS) diagrams were developed for both alloys. The secondary precipitates formed during thermal aging treatments were electrochemically extracted and analyzed by X-ray diffraction (XRD) to determine the types of precipitates formed during the aging treatments. The results indicated that the precipitates were mostly of M₂₃C₆ carbides.     

Corrosion-Resistant Ti-<Emphasis Type="Italic">x</Emphasis>Nb-<Emphasis Type="Italic">x</Emphasis>Zr Alloys for Nitric Acid Applications in Spent Nuclear Fuel Reprocessing Plants

This article reports the development, microstructure, and corrosion behavior of two new alloys such as Ti-4Nb-4Zr and Ti-2Nb-2Zr in boiling nitric acid environment. The corrosion test was carried out in the liquid, vapor, and condensate phases of 11.5 M nitric acid, and the potentiodynamic anodic polarization studies were performed at room temperature for both alloys. The samples subjected to three-phase corrosion testing were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX). As Ti-2Nb-2Zr alloy exhibited inferior corrosion behavior in comparison to Ti-4Nb-4Zr in all three phases, weldability and heat treatment studies were carried out only on Ti-4Nb-4Zr alloy. The weldability of the new alloy was evaluated using tungsten inert gas (TIG) welding processes, and the welded specimen was thereafter tested for its corrosion behavior in all three phases. The results of the present investigation revealed that the newly developed near alpha Ti-4Nb-4Zr alloy possessed superior corrosion resistance in all three phases and excellent weldability compared to conventional alloys used for nitric acid application in spent nuclear reprocessing plants. Further, the corrosion resistance of the beta heat-treated Ti-4Nb-4Zr alloy was superior when compared to the sample heat treated in the alpha + beta phase.     

硅对含强氧化性离子沸腾硝酸中奥氏体不锈钢耐蚀性的影响

 超低碳Cr Ni奥氏体不锈钢在含强氧化性离子的硝酸溶液中会发生过钝化腐蚀和晶间腐蚀,而高硅不锈钢在强氧化性浓硝酸中具有优良的耐蚀性。笔者以高纯级000Cr25Ni20和00Cr14Ni14Si4钢作为对比材料,发现在纯稀硝酸中000Cr25Ni20钢具有更优良的耐蚀性,在不同含量的40%沸腾硝酸溶液中,00Cr14Ni14Si4钢可有效抑制过钝化腐蚀,而且不发生晶间腐蚀。     

New Economical 19Cr Duplex Stainless Steels

New economical duplex stainless steels (DSSs) containing 19Cr-6Mn-xNi-1.0Mo-0.5W-0.5Cu-0.2N (x = 0.5 to 2.0) were developed, and the microstructure, impact property, and corrosion resistance of the alloys were studied. The ferrite content increases with the solution treatment temperature, but decreases with an increase in nickel. The sigma phase is not found precipitating in the alloys treated with solution from 1023 K to 1523 K (750 °C to 1250 °C). The low-temperature impact energy of the experimental alloys increases first and then decreases rapidly with an increase in nickel, which is mainly due to the martensite transformation with an increase in austenite. The alloys have a better mechanical property and pitting corrosion resistance than AISI 304. Among the designed DSS alloys, 19Cr-6Mn-1.3Ni-1.0Mo-0.5W-0.5Cu-0.2N is found to be an optimum alloy with proper phase proportion, a better combination of mechanical strength and elongation, and higher pitting corrosion resistance compared with those of the other alloys.