Kaynar Mgcl2 Çözeltilerinde çift fazlı paslanmaz çeliklerin gerilmeli korozyon çatlaması
Stress corrosion cracking of duplex stainless in boiling Mgcl2 solution
- Tez No: 39501
- Danışmanlar: DOÇ.DR. MUSTAFA ÜRGEN
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 120
Özet
100x10x1 mm respectively. The polished specimens were bended by using tensile test machine. Decoration experiments were conducted in the same manner as the unstressed ones. Before studying the decorated U bend specimens with SEM, specimens were separated into three different regions depending on the amount of deformation that took place during bending. The top of U-bend which has most severe deformation was called as“O”region. Other regions were named as OA and AB. OA region is the neighbouring region of O, which was subjected to less deformation. AB region was the region in which deformation was negligible. The results of the experiments that were conducted by using unstressed and stressed (U bend specimens) AISI 304, Zeron 100, Sumitomo and Zeron 25 stainless steel specimens are summarized below: 1. On decorated unstressed specimens, the defects and weak points on the passive film can be determined by using modified decoration technique. The differences in the amount of active sites between the two phases in DSS can be easily determined. The metals or alloys that have more defective passive film were found to be not always more susceptible to localized corrosion. Because alloying elements, especially N in DSS, have very important effect on localized corrosion of metals or alloys. Altough austenite phase in Zeron 100 is more heavily decorated with gold pitting wasn't observed in this phase since N improves pitting resistance of austenite phase. 2. In DSS pitting can take place either in the ferrite or austenit phase depending on the steel composition and the environment. For DSS with high nitrogen content in chloride environments, preferential pitting is observed in the ferrite phase and austenite/ferrite interface DSS with low nitrogen content preferential pitting takes place in austenite phase and austenite/ferrite interface. 3. It was observed that decoration density of ferrite and austenite phases in both Zeron 100 and Sumitomo type DSS increased with increasing deformation. The number of active sites that will be preferentially decorated increases with increasing plastic deformation. The decoration density on both austenite and ferrite phases increases with plastic deformation. 4. In %42 boiling MgCİ2 solutions Zeron 100 type duplex stainless steels showed better resistance to stress corrosion cracking than Sumitomo type duplex stainless steel which is in accordance with the decoration experiment results. 5. Corrosion tunnels were observed in ferrite phase of Zeron 100, austenite phase of Sumitomo and partly in ferrite phase of Sumitomo.
Özet (Çeviri)
examined successfuly by Scanning Electron Microscopy (SEM) instead of TEM. in this study three types duplex stainless steels that have different chromium, molybdenum and nitrogen content were used. The duplex stainless steel with trade name Zeron 100 is a süper DSS vvhich has a high nitrogen and molybdenum content. The other two DSS are low grade DSS with trade names of Zeron 25 and Sumitomo which have lovver nitrogen and molybdenum contents when compared to Zeron 100. Before decoration experiments specimens were wet abraded with SiC grinding paper to 1200 grit and then polished mechanically and than degreased ultrasonically in ether 50 % and alcohol 50 % solution for 15 minutes and dried. The samples to be decorated were introduced into 42 % boiling MgCl2 solution. After holding the specimens for two minutes in this solution 300 jj.lt decoration solution was added. it was vvaited for 30 seconds for decoration to take piace. Thus, the samples were subjected to 42 % MgCl2 solution containing 0.14 gr/lt gold ions for 30 seconds. After the decoration the samples were immediately taken out, dipped in höt vvater and distilled water and then dried after vvashing with methanol. Decorated specimens were examined by Scanning Electron Microscope, SEM, (Jeol T330). in order to test the performance of the modified decoration technigue on U bend specimens decoration experiments were conducted with U bend AISI 304 type austenitic stainless steels. The results of these experiments shovved that traces of slip produced by plastic deformation are preferentially decorated by gold ions and corrosion tunnels were clearly visible. These observations were in accordance with the results of Nielsen's study which showed that modified decoration technique can also be applied successfuly for marking the active sites on U bend stainless steels. After this verification of the modified decoration technique, experiments with DSS were started. The first group experiments were performed by using unstressed Zeron 100, Sumitomo and Zeron 25 type duplex stainless steels specimens. The dfmensions of these samples were approximately 20x15x15 mm. The modified decoration technigue was applied to determine weak and film free sites on DSS in 42 % boiling MgCl2 solutions. The second groups experiments were applied to U-bend specimens by using Zeron 100 and Sumitomo type DSS. in this experiments decoration technique was applied to determine SCC initiation sites in 42 % boiling MgCl2 solutions. Zeron 100 and Sumitomo type duplex stainless steel specimens that were used for U bend test had dimensions of 120x19x2 mm. and ix100x10x1 mm respectively. The polished specimens were bended by using tensile test machine. Decoration experiments were conducted in the same manner as the unstressed ones. Before studying the decorated U bend specimens with SEM, specimens were separated into three different regions depending on the amount of deformation that took place during bending. The top of U-bend which has most severe deformation was called as“O”region. Other regions were named as OA and AB. OA region is the neighbouring region of O, which was subjected to less deformation. AB region was the region in which deformation was negligible. The results of the experiments that were conducted by using unstressed and stressed (U bend specimens) AISI 304, Zeron 100, Sumitomo and Zeron 25 stainless steel specimens are summarized below: 1. On decorated unstressed specimens, the defects and weak points on the passive film can be determined by using modified decoration technique. The differences in the amount of active sites between the two phases in DSS can be easily determined. The metals or alloys that have more defective passive film were found to be not always more susceptible to localized corrosion. Because alloying elements, especially N in DSS, have very important effect on localized corrosion of metals or alloys. Altough austenite phase in Zeron 100 is more heavily decorated with gold pitting wasn't observed in this phase since N improves pitting resistance of austenite phase. 2. In DSS pitting can take place either in the ferrite or austenit phase depending on the steel composition and the environment. For DSS with high nitrogen content in chloride environments, preferential pitting is observed in the ferrite phase and austenite/ferrite interface DSS with low nitrogen content preferential pitting takes place in austenite phase and austenite/ferrite interface. 3. It was observed that decoration density of ferrite and austenite phases in both Zeron 100 and Sumitomo type DSS increased with increasing deformation. The number of active sites that will be preferentially decorated increases with increasing plastic deformation. The decoration density on both austenite and ferrite phases increases with plastic deformation. 4. In %42 boiling MgCİ2 solutions Zeron 100 type duplex stainless steels showed better resistance to stress corrosion cracking than Sumitomo type duplex stainless steel which is in accordance with the decoration experiment results. 5. Corrosion tunnels were observed in ferrite phase of Zeron 100, austenite phase of Sumitomo and partly in ferrite phase of Sumitomo.examined successfuly by Scanning Electron Microscopy (SEM) instead of TEM. in this study three types duplex stainless steels that have different chromium, molybdenum and nitrogen content were used. The duplex stainless steel with trade name Zeron 100 is a süper DSS vvhich has a high nitrogen and molybdenum content. The other two DSS are low grade DSS with trade names of Zeron 25 and Sumitomo which have lovver nitrogen and molybdenum contents when compared to Zeron 100. Before decoration experiments specimens were wet abraded with SiC grinding paper to 1200 grit and then polished mechanically and than degreased ultrasonically in ether 50 % and alcohol 50 % solution for 15 minutes and dried. The samples to be decorated were introduced into 42 % boiling MgCl2 solution. After holding the specimens for two minutes in this solution 300 jj.lt decoration solution was added. it was vvaited for 30 seconds for decoration to take piace. Thus, the samples were subjected to 42 % MgCl2 solution containing 0.14 gr/lt gold ions for 30 seconds. After the decoration the samples were immediately taken out, dipped in höt vvater and distilled water and then dried after vvashing with methanol. Decorated specimens were examined by Scanning Electron Microscope, SEM, (Jeol T330). in order to test the performance of the modified decoration technigue on U bend specimens decoration experiments were conducted with U bend AISI 304 type austenitic stainless steels. The results of these experiments shovved that traces of slip produced by plastic deformation are preferentially decorated by gold ions and corrosion tunnels were clearly visible. These observations were in accordance with the results of Nielsen's study which showed that modified decoration technique can also be applied successfuly for marking the active sites on U bend stainless steels. After this verification of the modified decoration technique, experiments with DSS were started. The first group experiments were performed by using unstressed Zeron 100, Sumitomo and Zeron 25 type duplex stainless steels specimens. The dfmensions of these samples were approximately 20x15x15 mm. The modified decoration technigue was applied to determine weak and film free sites on DSS in 42 % boiling MgCl2 solutions. The second groups experiments were applied to U-bend specimens by using Zeron 100 and Sumitomo type DSS. in this experiments decoration technique was applied to determine SCC initiation sites in 42 % boiling MgCl2 solutions. Zeron 100 and Sumitomo type duplex stainless steel specimens that were used for U bend test had dimensions of 120x19x2 mm. and ixexamined successfuly by Scanning Electron Microscopy (SEM) instead of TEM. in this study three types duplex stainless steels that have different chromium, molybdenum and nitrogen content were used. The duplex stainless steel with trade name Zeron 100 is a süper DSS vvhich has a high nitrogen and molybdenum content. The other two DSS are low grade DSS with trade names of Zeron 25 and Sumitomo which have lovver nitrogen and molybdenum contents when compared to Zeron 100. Before decoration experiments specimens were wet abraded with SiC grinding paper to 1200 grit and then polished mechanically and than degreased ultrasonically in ether 50 % and alcohol 50 % solution for 15 minutes and dried. The samples to be decorated were introduced into 42 % boiling MgCl2 solution. After holding the specimens for two minutes in this solution 300 jj.lt decoration solution was added. it was vvaited for 30 seconds for decoration to take piace. Thus, the samples were subjected to 42 % MgCl2 solution containing 0.14 gr/lt gold ions for 30 seconds. After the decoration the samples were immediately taken out, dipped in höt vvater and distilled water and then dried after vvashing with methanol. Decorated specimens were examined by Scanning Electron Microscope, SEM, (Jeol T330). in order to test the performance of the modified decoration technigue on U bend specimens decoration experiments were conducted with U bend AISI 304 type austenitic stainless steels. The results of these experiments shovved that traces of slip produced by plastic deformation are preferentially decorated by gold ions and corrosion tunnels were clearly visible. These observations were in accordance with the results of Nielsen's study which showed that modified decoration technique can also be applied successfuly for marking the active sites on U bend stainless steels. After this verification of the modified decoration technique, experiments with DSS were started. The first group experiments were performed by using unstressed Zeron 100, Sumitomo and Zeron 25 type duplex stainless steels specimens. The dfmensions of these samples were approximately 20x15x15 mm. The modified decoration technigue was applied to determine weak and film free sites on DSS in 42 % boiling MgCl2 solutions. The second groups experiments were applied to U-bend specimens by using Zeron 100 and Sumitomo type DSS. in this experiments decoration technique was applied to determine SCC initiation sites in 42 % boiling MgCl2 solutions. Zeron 100 and Sumitomo type duplex stainless steel specimens that were used for U bend test had dimensions of 120x19x2 mm. and ixSince wavy slip lines were formed in the ferrite phase of Zeron 100, corrosion tunnels were not on certain crystallographic planes like austenitic stainless steels. 6. In both Zeron 100 and Sumitomo, crack mode changed from transgranular to intergranular with increasing deformation. Intergranular cracking was observed in the most severely stressed“O”region. X!
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