文献翻译-钢制压力容器在高温腐蚀性铝酸溶液中的应力腐蚀裂纹研究

英文文献 1 英文原文 Stress Corrosion Cracking of Pressure Vessel Steels in High-Temperature Caustic Aluminate Solutions SUE LIU, ZIYONG ZHU, HUI GUAN, and WEI KE Stress corrosion cracking (SCC) behavior of three kinds of low alloy pressure vessel steels in high temperature (200 to 300 ) caustic aluminate (AlO2-) solutions has been studied by slow strain rate tests (SSRT). The results indicate that these pressure vessel steels are susceptible to SCC in caustic alnminate solution and that the SCC susceptibility increases with increasing temperature between 200 to 300 Sulfide content and stringered sulfide inclusions severely and anisotropically affect the caustic SCC of these low alloy steels. The inclusions in the rare-earth-treated steel are predominantly globular rare-earth sulfides or oxysulfides, resulting in improved transverse properties. The effect of inclusions on SCC behavior correlates with the projected area of inclusions per unit volume at the crack tip, Av, on the plane perpendicular to the tensile direction. The susceptibility to SCC increases with increasing A v. I. INTRODUCTION LOW alloy pressure vessel steels are the common structural materials for welded reaction vessels (e.g., digesters, precipitators, and evaporators) in the Bayer process for extraction of alumina from hydrated oxide ores (e.g., bauxite). These low alloy reaction vessels are in contact with high temperature concentrated caustic alnminate solutions and frequently suffer from stress corrosion cracking (SCC) during service. 1,2 Although SCC of steels in simple NaOH solutions has been the subject of numerous studies, f3,41 little work has been done in caustic aluminate solutions at 92 oc.t5,61 To purify alumina from lower quality ores, the extracting temperature has been elevated. However, there are no data on SCC susceptibility of steels used in the alumina industry at higher temperatures. The objective of the present work is to study the SCC behavior of low alloy pressure vessel steels with different sulfur contents in an imitative Bayer process at 200 to 300 Over the past few years, a number of research works 7,8,9 have shown that nonmetallic sulfide inclusions can cause environmentally assisted cracking to occur in high-temperature water related primarily to Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) environments. The effect of MnS inclusions on caustic SCC property is also discussed in this article to give recommendations for improving SCC resistance of materials used in the alumina industry. II. EXPERIMENTAL PROCEDURE Studies were conducted on three kinds of low alloy steels: 16MnR, A48CPR, and rare-earth-treated 16MnRE. The pressure vessel quality rolling steel plates used in this work were 50-mm thick and were annealed at 650 The chemical compositions and mechanical properties of these steels were similar (Tables I and II), although the sulfur contents were very different. The cylindrical tensile specimens were 24 mm in gage length and 5 mm in diameter with threads at each end to fit tensile grips. Two kinds of tensile test pieces were sectioned from the steel plates parallel (L specimen) and perpendicular (T specimen) to the rolling direction to investigate specimen orientation effects. All specimens were polished with a 1000 grit emery paper and then cleaned with alcohol and acetone before testing. The test environment imitated the industrial Bayer process, and the temperature was varied from 200 to 300 The initial molal (M) concentration (Table III) in imitative Bayer solutions (IBS) was 7.42M NaOH, 1.32M A1203 3H20, and some impurities: carbonate, sulfate, and chloride. The test solution was prepared from distilled water and analytical grade chemicals. The resulting concentrations of anions are based on stoichiometric formation of aluminate species (AlOe-) according to Eq. 1: OHAIOAIH22232 4The slow strain rate tests were performed on an SERT-5000DP-9L machine in a static autoclave at an initial strain rate of 3.3*10-6/s. To protect the autoclave from caustic solution, a loose-fitting nickel liner, which held the corrosive media, was placed within it. A small amount of water was injected into the crevice between the autoclave and the liner to improve heat transfer and to prevent the formation of a concentrated caustic solution in this crevice. After sealing, the system was overpressured with 2.0 MPa nitrogen to prevent boiling and to minimize the transfer of corrosive media to the crevice. At the start of each test, specimens were initially loaded to 50 MPa and then strained to fracture. The tensile specimens were at the natural corrosion potential during straining. The results obtained in IBS were compared with those in an inert environment of 2.0 MPa nitrogen. The time to failure (TTF), the percent reduction of crosssectional area (pet ROA), and the elongation (E) were the main parameters used to evaluate SCC susceptibility. One-half of the specimen was mounted with epoxy resin, ground, and given a final metallographic polish to observe the secondary cracks along the gage length by optical microscopy. Table I. Analyses of Composition (Weight Percent) Steels C Si Mn P S Al Cu Mo Ni RE 16MnR 0.16 0.47 1.53 0.014 0.018 - 0.055 - - - A48CPR 0.175 0.34 1.35 0.012 0.006 - - 0.045 0.058 - 16MnRE 0.16 0.40 1.38 0.018 0.009 - - - - 0.020 Table II. Mechanical Properties of Steels Impact Strength（ J/cm , by Charpy Test） 25 260 Steels Ultimate Strengt（ MPA ） Yield Strength（ MPA ） Elongation （ Pct） L Specimen T Specimen L Specimen T Specimen 16MnR 530.0 350.0 32.0 159 172 77 75 97 142 169 85 81 76 A48CPR 528.9 316.1 31.6 209 187 298 231 258 240 233 317 272 16MnRE 535.0 338.0 32.5 169 172 172 156 129 122 Table III. Composition of IBS (M) NaOH Al2O3 3H2O Na2CO3 Na2SO4 NaCl 7.42 1.32 0.3 0.14 0.14 Ill. RESULTS A. The Effect of Temperature on Caustic SCC Behavior Figure 1 shows the effect of temperature on SCC behavior for L specimens of 16MnR steel in IBS at 260 The pct ROA is reduced by the corrosive solution as compared with that in nitrogen. Also the TTF, pct ROA, and E of specimens in IBS decrease with increasing test temperature. The results indicate that 16MnR steel is susceptible to SCC in IBS and that the susceptibility increases with an increase in temperature from 200 to 300 B. Comparison of SCC Susceptibility between 16MnR, A48CPR, and 16MnRE Steels The pet ROA data of L specimens for both steels shown in Figure 2 are the average values of duplicate specimens in each test condition, and the results can be reproduced as follows. For A48CPR steel, the pct ROA data are 66.0 and 64.2 at 260 and 63.6 and 61.1 at 280 For 16MnR steel, the pct ROA data (as shown in Figure 1) are 57.2 and 55.0 at 260 and 49.6 and 47.0 at 280 The results (Figure 2) of L specimens for both steels indicate that A48CPR steel is also susceptible to SCC under the test conditions and that the susceptibility may increase slightly with increasing temperature from 260 to 280 The L specimens of 16MnR steel are inferior to those of A48CPR steel. The effects of specimen orientation on SCC behavior ar shown in Figure 3. The T specimens of 16MnR steel ar obviously more susceptible to SCC than its L specimens However, the SCC behavior for A48CPR steel of T specmens is similar to the L specimens. The SCC resistanc for the T specimen of rare-earth-treated steel 16MnRE improved, and the extent of anisotropy of 16MnRE decreases as compared with 16MnR. The large number of cracks observed on an L specimen of 16MnR steel after testing in IBS at 280 is shown in Figure 4. The cracking path of a typical specimen is shown in Figure 5. The cracks predominantly propagated in intergranular path, but there are also some transgranular cracks. IV. DISCUSSION Caustic SCC of low alloy pressure vessel steels in IBS at elevated temperatures is predominately intergranular (Figure 5) as at 92 The SCC susceptibility increases at high temperatures between 200 and 300 (Figures1 and 2). In comparison to the conventional (25 Pourbaix diagram, the most noticeable change at higher temperature diagrams is the larger area of stability for the HFeOi ion. An association between caustic cracking and the formation of HFeO2 ion has been previously suggested, vq Simultaneously, the reaction rate of the anodic and cathodic reactions increases at the elevated temperature. The orientation effect on SCC behavior (Figure 3) is considered to be related to inclusions in the steels. The volume fraction, shape, and distribution of manganese sulfide inclusions in 16MnR and A48CPR steels are very different,as shown in Figures 6(a) and (b). The volume fraction of inclusions in 16MnR steel is greater than in A48CPR steel because the sulfur content is higher. The inclusions in A48CPR steel are globular and well distributed, whereas those in 16MnR steel are predominantly elongated and in bands parallel to the rolling direction. The SCC process is the brittle or quasibrittle fracture of a material under the conjoint actions of stress and corrosive environments. The detrimental effects of nonmetallic inclusions on the mechanical properties of steels are now well established, tg Considering the mechanical fracture aspect during the SCC process, the effect of inclusion on SCC behavior correlates with the total projected area, Aw, of inclusions per unit volume at the crack tip on the plane perpendicular to the tensile direction, i. The crack propagation rate is accelerated by cracking in or around the inclusions near the crack tip and is more severe with increasing A w. If the shape of inclusion is assumed to be triaxial ellipsoids (Figure 7), it is possible to calculate the magnitude of A vi in the following equation: Avi=6Vv/(di) 2 where Vv is the volume fraction of inclusion and di is the average dimensions of inclusion in the tensile direction, i.There are more inclusions in 16MnR steel than in A48CPR steel. The value of Vv for 16MnR steel is therefore larger. But the average dimension of the elongated inclusions on the longitudinal section, for L specimens of 16MnR steel is also larger. However, the value of Aw on the plane perpendicular to the tensile direction, for the L specimen, is similar for both steels. So the difference in SCC susceptibility of L specimens between 16MnR and A48CPR steels is slight (Figure 2). The results indicate that the amount and shape of inclusion have no significant effect on the SCC behavior for L specimens. However, the shape and distribution of inclusion in steels severely affect the transverse properties such as the impact strength of Charpy tests (Table II) and SCC susceptibility (Figure 3). Even though a steel contains the same amount of inclusion, in a given steel, the volume fracture of inclusion should be the same, but the inclusion length dimension di and A w on the different fracture plane may be different according to the shape of inclusion. Because inclusions in 16MnR steel are stringered bands parallel to the rolling direction, the average length dimension of inclusions in the longitudinal direction, is much larger than that in the transverse direction, d2, and the average projected area on the transverse plane for the longitudinal specimen, Aw, is correspondingly smaller than that on the longitudinal plane for the transverse specimen, A v2. The elongated inclusionsin the 16MnR steel cause anisotropy in its SCC resistance(Figure 3). In comparison with the 16MnR steel, the value of Art is equal to that of At2 for globular inclusions in the A48CPR steel, so the SCC behavior is isotropic. On the other hand, SCC is also an electrochemical process. The pre-existing active-path theories tl31 have been applied primarily to intergranular cracking of ductile alloys in aqueous environments and relate the propagation process to the preferential dissolution of chemically active regions in the grain boundaries. The recent investigations indicate that the MnS inclusions dissolve readily in high-temperature water, presumably forming HS- and H2S. These species strongly affect the crack growth rate during SCC or corrosion fatigue processesYl In areas containing a dense distribution of elongated MnS inclusions, the crack tip can propagate much faster than in the surrounding area. So inclusions in steels have an influence on SCC behavior. The results of rare-earth-treated steel 16MnRE under the same test conditions further confirmed the inclusion effect. The inclusions in 16MnRE steels are predominately globular rare-earth sulfides or oxysulfides (Figure 6(c) which are hard particles and difficult to be deformed and elon- gated. The SCC results shown in Figures 3 and 8 indicate that the ratio of pct ROA for T specimens, ROA(T), to that for L specimens, ROA(L), increases in comparison with that for 16MnR steel. The transverse SCC resistance obviously improves with inclusion shape, controlled by adding rare-earth elements in the low alloy steel 16MnR. But there are still a few stringered inclusions (Figure 6(c) in 16MnRE, so the transverse SCC resistance of 16MnRE is not as good as that of A48CPR. Nevertheless, it is hoped that 16MnRE steel can have the same SCC resistance as that of A48CPR used in the alumina industry by controlling the amount of rare-earth elements added and the rolling process. V. CONCLUSIONS 1. Both 16MnR and A48CPR steels exhibit caustic SCC susceptibility in the IBS. The SCC susceptibility of 16MnR steel increases with increasing temperature from 200 to 300 2. The volume fraction, shape, and distribution of inclusions in steels affect the caustic SCC of low alloy pressure vessel steels, especially in steels with stringered sulfide inclusions where the transverse SCC resistance is severely reduced. Adding rare-earth elements to the steel improves transverse SCC resistance by controlling the shape and dis tribution of inclusions. 3. The effects of inclusion on SCC behavior correlate with the projected area of inclusions at the crack tip, Av, on the plane perpendicular to the tensile direction. The SCC susceptibility increases with A v. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Contract No. 59271049) and the State Key Laboratory of Corrosion and Protection, Academia Sinica. REFERENCES 1. Caustic Stress Corrosion Symposium, Alcan Jamaica Company (Aljam), Mandeville, Jamaica, Mar. 1982. 2. V.I. Artemev, V.I. Seregin, E.P. Zholoboya, and V.P. Belyaev: Zashch. Met., 1979, vol. 15, p. 62-65. 3. M.F. Maday, A. Mignone, and A. Borello: Corrosion, 1989, vol. 45, pp. 273-82. 4. D. Singbeil and D. Tromans: Metall. Trans. A, 1982, vol. 13A, pp. 1091-98. 5. Huy Ha Le and Edward Ghali: Corros. Sci., 1990, vol. 30, pp. 117- 34. 6. R. Sriram and D. Tromans: Corrosion, 1985, vol. 41, pp. 381-85. 7. F.P. Ford: Proc. 2nd Int. Atomic Energy Agency Specialists Meeting on Subcritical Crack Growth, Sendai, Japan, May 15-17, 1985, W.H. Cullen, ed., NUREG CP-0067, vol. 2, pp. 3-72. 8. H. Hanninen, K. Torronen, M. Kemppainen, and S. Salonen: Corros. Sci., 1983, vol. 23 (6), pp. 663-79. 9. J.H. Bulloch: Proc. 3rd lnt. Symp. on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors, TMS, Warrendale, PA, 1988, pp. 261-68. 10. H.E. Townsend: Corros. Sci., 1970, vol. 10, pp. 343-58. 11. M.J. Humphries and R.N. Parkins: Syrup. Fundamental Aspects of Stress-Corrosion Cracking, The Ohio State University, Columbus, OH, Sept. 11 15, 1967, R.W. Stache, A.J. Forty, and D. Van Rooyen, eds., NACE, Houston, TX, 1969, pp. 384-95. 12. W.A. Spitzig: Metall. Trans. A, 1984, vol. 15A, pp. 1259-64. 13. Shinobu Matsushima, Yasuyuki Katada, Shunji Sato, and Norio Nagata: Corrosion Control, Proc. 7th Asian-Pacific Corrosion Control Conf., International Academic Publisher, Beijing, 1991, pp. 112-17 2 译文 钢制压力容器 在高温腐蚀性铝酸溶液中的应力腐蚀裂纹研究 刘舒 朱自勇 关慧 魏柯 通过慢应变速率（ SSRT）的测试，对三种低合金压力容器用钢在高温（ 200 -300）腐蚀性铝酸（ AlO2-）溶液中的应力腐蚀开裂（ SCC）情况进行了研究。结果表明，这类压力容器钢在该类溶液中 SCC 较敏感，并随温度升高SCC 会加剧。另外，硫化物及其它杂质的混入也会引起钢的腐蚀。稀土处理过的钢中主要含球状的硫化稀土和硫氧化合稀土，这就导致其加大了横向断裂特性，包括在延伸区域应力腐蚀断裂点 Av，也就是在垂直与平面的伸长方向，随着 Av 值的变大，应力腐蚀特性较为明显。 一引言 低合金钢是比较常见的焊接反应容器的材料（例如沼气池， 除尘器，蒸发器等） ，通过贝尔反应从含氧的水合物中将 AlO2-提取出来。这类低合金反应容器与具腐蚀性的高温铝酸溶液接触并立刻出现腐蚀现象。在此期间，钢材在纯 NaOH 溶液中的应力腐蚀已经有过大量的研究，在 92腐蚀性铝酸溶液中也做了小规模的实验。为了将氧化铝从杂质矿石中提取出来，提取时的温度大大高于 92。然而，很难预知 SCC 的敏感性在更高温度下的铝酸盐工业中的情况。目前的主要工作就是研究低合金压力容器用钢与不同硫化物模拟在 200 - 300时的贝尔反应情形下的应力腐蚀断裂。在过去的几年里，大量的研究工作表明，能引起非金属硫化物在沸水中对容器的腐蚀，主要与反应器和压水器的环境有关，包括含腐蚀性的 MnS 的影响，这一点在本文也将提到，并介绍抗SCC 材料在铝酸盐工业中的应用。 二实验步骤 三种低合金钢处理方式的研究 :16MnR 钢， A48CPR ，稀土处理过的16MnRE 。进行试验的压力容器轧制钢板厚 50 毫米， 650 退火处理。这类钢材的化学成分和力学性能（表一和表二）较为相似，但硫的含量大不相同。取可伸长的圆柱形样本原长 24 毫米，直径 5 毫米，且均带螺纹便于装紧。从钢材的横断面和纵断面方向分别切割，这种张力实验研究样本的向性能力，所有样本用硬度为 1000 的砂轮抛光并且测试前用酒精和丙酮液清洗。 测试环境模仿工业上的贝尔过程，温度持续在 200 到 300之间 。初始摩尔（ M）浓度（表三）类似贝尔溶液： 7.42M 的 NaOH， 1.32M 的 Al2O3 3H2O，并含有杂质碳酸盐、硫酸盐、氯化物。待测液由蒸馏水和分析化学药物组成。此化学反应根据反应前后负离子（ AlO2-）浓度相等得到公式 ： 1OHAIOAIH232 4在一个 SERT- 5000DP-9L 型机器中进行试验，应变速率为 3.3 *10-6 /秒。为避免腐蚀性溶液腐蚀反应容器，内置一个装有抗腐蚀介质的密合式镍垫片。将少量的水注入反应容器和垫片之间的缝隙，以提高传热和防止缝隙中形成腐蚀性的浓碱溶液。密封后，该系统充入 2.0 MPa 氮，以防止沸腾并最大限度地减小缝隙的腐蚀。在每次试验之前，样本先被加压到 50MPa，然后将裂缝张紧。受拉样本在被拉时处于自然腐蚀的状态。在 IBS 情况下获得的结果与在 2.0 MPa 氮的情况下作比较。其失效期（ TTF） ，伸缩率（ pct ROA） ，伸长率（ E ）是用来评价 SCC 敏感性的主要参数。其中一半的样本加上环氧树脂，并做最后的磨光处理，使其有金属光泽，观察沿断面方向的二次断裂。 表一 分析成分（重量百分比） 钢材 C Si Mn P S Al Cu Mo Ni RE 16MnR 0.16 0.47 1.53 0.014 0.018 - 0.0