THE EFFECT OF MOLYBDENUM ON THE CORROSION PERFORMANCE OF STAINLESS STEEL IN CHLORIDE-CONTAMINATED AND CARBONATED CONCRETE (EUROCORR 2012, paper 1177)
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Due to the increase application of stainless steels as reinforcement in concrete structures, understanding the behavior of these alloys in media that simulate concrete pore water or in the concrete itself is extremely important for the selection of the most suitable alloy. This paper is a contribution to the understanding of the role of Mo in the corrosion resistance in concrete structures contaminated with chloride ions after carbonation. In order to study the role of Mo, samples of ferritic, austenitic and duplex stainless steels were produced in laboratory with controlled levels of Mo. These samples were prepared based on the chemical composition of commercial stainless steels. The samples were immersed in simulated carbonated and noncarbonated concrete pore solutions, both with the addition of 3.5% of sodium chloride. Samples of these steels were also embedded in concrete that was later carbonated and exposed to saline solution. The performance of the steels in concrete was verified through corrosion potential monitoring (several months) followed by electrochemical experiments (anodic polarization). Finally, the optical and electronic microscopy techniques were used to characterize the corrosion attacked surfaces. Devido ao aumento na utilização de aços inoxidáveis como armadura em estruturas de concreto, o estudo do comportamento dessas ligas, em meios que simulam a água dos poros de concreto ou no próprio concreto, é de extrema importância para a seleção da liga mais adequada. Este trabalho é uma contribuição para a compreensão do papel de molibdênio (Mo) na resistência à corrosão em estruturas de concreto contaminado com íons de cloreto após a sua carbonatação. Para o estudo do papel do Mo, amostras de aços inoxidáveis ferríticos, austeníticos e dúplex foram produzidas em laboratório com níveis controlados de Mo. As amostras foram preparadas com base na composição química dos aços inoxidáveis comerciais. As amostras foram imersas em soluções simuladas de poros de concreto carbonatado e não carbonatado, ambas com adição de 3,5 % de cloreto de sódio. Amostras destes aços foram também incorporadas em corpos de prova de concreto que foi posteriormente carbonatado e exposto a solução salina. O desempenho dos aços inoxidáveis em concreto foi verificado por meio do monitoramento do potencial de corrosão (vários meses), seguido por experimentos eletroquímicos (polarização anódica). Finalmente, as técnicas de microscopia óptica e eletrônica foram utilizadas para caracterizar as superfícies das amostras atacadas (corrosão). MESQUITA, T.J; PANOSSIAN, Z; ARAUJO, A.; SANTOS, C.A.L; SANTOS, J.V. S.; NOGUEIRA, R.P. The effect of molybdenum on the corrosion performance of stainless steel in chloride contaminated concrete. In: EUROPEAN COROSION CONGRESS, 2012, Turquia. Proceedings... Turquia: EUROCORR 2012.
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THE EFFECT OF MOLYBDENUM ON THE CORROSION PERFORMANCE OF STAINLESS STEEL IN CHLORIDE-CONTAMINATED AND CARBONATED CONCRETE (EUROCORR 2012, paper 1177)
- 1. The effect of molybdenum on the corrosion performance of stainless steel in chloride- contaminated and carbonated concrete The effect of molybdenum on the corrosion performance of stainless steel in chloride- contaminated and carbonated concrete Thiago José MESQUITA Zehbour PANOSSIAN, Adriana DE ARAUJO, Celia A. LINO DOS SANTOS, Ricardo P. NOGUEIRA, Eric CHAUVEAU and Marc MANTEL September 12th 2012
- 2. OutlineOutline 1. Introduction : Importance of studying Mo addition on SS for alkaline media application 2. Mo effect on pit corrosion of SS in alkaline media Industrial approach – Preliminary Studies 3. Mo effect on crevice corrosion in concrete Laboratory approach 4. Conclusion 1/21
- 3. Why is it important to study the role of Molybdenum addition on alkaline Media? Why is it important to study the role of Molybdenum addition on alkaline Media? Scarce literature with a focus on the Mo effect on the alkaline media Unexpected results about austenitic SS corrosion resistance Optimization of new lean duplex SS compositions Many applications for alkaline environments: - Concrete Reinforcement - Petrochemical - Chemical - Food processing - Paper and Alkaline industries - etc … 2/21
- 4. Objective of this studyObjective of this study - To investigate the role of Mo on localized corrosion resistance of different stainless steel types under alkaline conditions such as chloride-contaminated and carbonated concrete. 3/21
- 5. Industrial SS composition Industrial Material Elements (wt. %) C Si Mn Ni Cr Mo Cu N Co S * PREn Austenitic 304L 0.02 0.49 0.60 11.12 18.29 0.21 0.31 0.03 0.00 9 19.46 316L 0.01 0.49 0.73 11.08 16.89 2.17 0.48 0.03 0.25 10 24.53 Ferritic 430 0.01 0.31 0.30 0.29 16.16 0.05 0.10 0.03 0.02 5 16.80 434 0.03 0.39 0.39 0.45 16.17 0.92 0.12 0.05 0.03 23 20.01 Duplex 2304 0.02 0.41 1.09 4.02 22.30 0.28 0.30 0.15 0.13 4 25.62 2205 0.02 0.4 1.61 5.45 22.91 2.78 0.22 0.15 0.07 3 34.48 Pitting Resistance Equivalent number (PREn) = %Cr + 3.3 %Mo + 16 %N (empirical formula) -Mo is not the only varying element (Ni and Cr) 4/21 γ structure γ + α structure α structure *ppm
- 6. An absence of positive effect of Mo on pitting corrosion resistance of austenitic stainless steels was confirmed in alkaline media [1, 2] [1] Chauveau E., et al,. MEDACHS 08, International Conference in Coastal and Marine Environments, 2008. [2] T. J. Mesquita, et al. Materials Chem. And Phis., 126 (2011) 602. higher values mean better steel stability Addition of Mo in industrial Austenitic SSAddition of Mo in industrial Austenitic SS ΔEpit = Epit(316)-Epit(304) In alkaline environments AISI 304 becomes slightly more resistant than AISI 316 ∆Epit < 0 5/21
- 7. Addition of Mo in industrial Duplex SSAddition of Mo in industrial Duplex SS + No effect for austenitic SS (γ)Positive effect for duplex (α+γ) SS Is there a Mo role on the ferrite phase (α)? Oxygen evolution Oxygen evolution Oxygen evolutionMo increases Epit in all conditions (Mo) (Mo) (Mo) 6/21
- 8. Addition of Mo in industrial Ferritic SSAddition of Mo in industrial Ferritic SS Positive effect with only 0.8 % of Mo (Mo) (Mo) (Mo) 7/21
- 9. Conclusion of industrial SS approachConclusion of industrial SS approach 8/21 The austenitic SS presented an anomalous behavoir in alkaline conditions Mo has a clear positive effect in ferritic and duplex SS even in alkaline media.
- 10. Highly defined composition SS (Laboratory alloys) for concrete experiments The only difference between the SS of each type is the Mo CONTENTSPREn = %Cr + 3.3 %Mo + 16 %N *ppm αα+γγ 9/21
- 11. Experimental MethodologyExperimental Methodology 1- Stainless steel (SS) sample preparation 2- SS sample preparation being embedded in concrete 3- Two steps of Concrete Carbonation (at 25o C, at 65% of relative humidity and at 2% of CO2) 4- Partial immersion of the reinforced concrete samples in saline solution (35 g/L of NaCl) 10/21 After the 2nd step, the pH was 10
- 12. Experimental MethodologyExperimental Methodology 5- Ecorr monitoring of reinforced concrete samples during their immersion in the chloride solution 6- Electrochemical Experiments of reinforced concrete samples 11/21
- 13. Ecorr monitoring resultsEcorr monitoring results Austenitic SSAustenitic SS Strong decrease of Ecorr 12/21 Average Ecorr With Mo ~ -150mV With out Mo ~ -320mV
- 14. Ecorr monitoring resultsEcorr monitoring results Ferritic SSFerritic SS Strong decrease of Ecorr 13/21 Average Ecorr With Mo ~ -200mV With out Mo ~ -500mV
- 15. Ecorr monitoring resultsEcorr monitoring results Duplex SSDuplex SS Strong decrease of Ecorr 14/21 Average Ecorr With Mo ~ -50mV With out Mo ~ -220mV
- 16. Austenitic SSAustenitic SS Mo effect 15/21 Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution
- 17. Austenitic SSAustenitic SS 16/21 Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution
- 18. Polarization ExperimntsPolarization Experimnts Ferritic SSFerritic SS Mo effect General corrosion 17/21 Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution
- 19. Ferritic SSFerritic SS 18/21 Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution
- 20. Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution Duplex SSDuplex SS Mo effect No corrosion 19/21
- 21. Duplex SSDuplex SS 20/21 Polarization Experiments after aging in NaCl solutionPolarization Experiments after aging in NaCl solution
- 22. ConclusionConclusion Addition of 3% of Mo increased the crevice corrosion resistance for all laboratory SS families even for the austenitic ones which presented anomalous results in the synthetic carbonated pore concrete solution (pH 10). The 23Cr4.6Ni3Mo (EN 1.4462) duplex stainless steel presented the highest corrosion resistance among all studied materials under the studied aggressive concrete condition. Almost all of the samples presented crevice corrosion in the metal/resin interface. Therefore, the experimental methodology should be improved in order to avoid the crevice corrosion and in order to study only the pitting corrosion. 21/21
- 23. Many thanks for your attention e-mail address: thiago.mesquita@ugitech.com
Notes de l'éditeur
- Good afternoon everyone, Today, I ’ m going to show you my thesis works about the SS. I developed these works in CIFRE project support by UGITECH, IMOA and LEPMI laboratory from the Grenoble INP.
- I divided this presentation in several steps. Firstly, In the introduction, I will briefly explain you the beginning of these studies and the importance of Mo for alkaline applications. Secondly, I will show you the my firsts results about the Mo effect on pit nucleation and propagation.. In this step, we made a preliminary study using industrial heats and the we decided to work with Laboratory heats. In Third step, the Mo effect on the pitting repassivation are going to be discussed. For this discussion, the results from tribocorrosion measurements and the addition of molybdates in the chloride solution were done. Finally, the Mo role on the passiavtion of SS was investigated by XPS measuremnts and EIS analysis.
- To Start with, i would like to explain why we decided to study the role of moly addition on alkaline media. In the pictures for example, we can see the construction of … with 14462 DSS.
- As i said before, we don’t have much information about the mo mechacnism in alkaline media. On the other hand, many authors studied its behaviors in acidic and neutral conditions. And one p mechanism of Mo for the conditions was proposed by Pardo et al. In pardo mechanism, the pitting attack was divided in 3 steps. Firstly the pits nucleates on the MnS inclusion.in the second step, we have de formation of H which will decrease even more the pH inside of the pit. And finally the dissolved Mo will forme a MoO3 on the pit wall helping then the pit repassivation. So, from this mechanism we can conclude that Mo ( lire!!!! ) IN these contexts, the objective of my thesis is (lire!!!!)
- To our preliminaiies studies, we used industrial materials provides by UGITECH. So, we chose 3 different families of stainless steels and for each family, we chose 2 grades. One with Mo and another without. An important point that must be emphazed here is that the Mo content was not the difference in the composition industrial grades. The austenitic and duplex materials present also small difference in the Cr and Ni contents, Moreover the sample preparation of the industrial SS was complicated because of the cilindrical form. As we work with draw wires, we had to polish the external surface and put a epoxy resign to limitate the working electrolde. Sometime, a crevesse corrosion occured the interface between resgin and the material
- The first result of my thesis was the confirmation of the anomalous behaviors of Mo for austenitic SS in alkaline media. In these histograms, we can see the pit potential of the 304 and 316 in several pH. In order to directly analyse the Mo effect on the pitting corrosion resistance of these materials,we ‘ ve calculed the difference between Epit potential for 316 and 304. In tghis curve then we can clealy see the decrease of the positive effect of Mo with the pH increase.
- On the other hand, for the DSS the Mo addition was positive in all pH as you can be observed in these polarization curves. The 2205 did not present corrosion attack under any circunstance whereas the 2304 did. These results associated with the results presented before for the austenitic grades, bring up the idea of a higher influence of Mo on the ferrite phase than the austenite phase of the DSS. Therefore, we analysed the pure ferritic SS. And the results showed a positive effect of Mo for these materials as illustrated in the polariezation curves for the 430 and 434 SS. So even if ithe addition of Mo was only 0.9 % for ferritic SS, its increases the pitting corrosion ,
- On the other hand, for the DSS the Mo addition was positive in all pH as you can be observed in these polarization curves. The 2205 did not present corrosion attack under any circunstance whereas the 2304 did. These results associated with the results presented before for the austenitic grades, bring up the idea of a higher influence of Mo on the ferrite phase than the austenite phase of the DSS. Therefore, we analysed the pure ferritic SS. And the results showed a positive effect of Mo for these materials as illustrated in the polariezation curves for the 430 and 434 SS. So even if ithe addition of Mo was only 0.9 % for ferritic SS, its increases the pitting corrosion ,
- On the other hand, for the DSS the Mo addition was positive in all pH as you can be observed in these polarization curves. The 2205 did not present corrosion attack under any circunstance whereas the 2304 did. These results associated with the results presented before for the austenitic grades, bring up the idea of a higher influence of Mo on the ferrite phase than the austenite phase of the DSS. Therefore, we analysed the pure ferritic SS. And the results showed a positive effect of Mo for these materials as illustrated in the polariezation curves for the 430 and 434 SS. So even if ithe addition of Mo was only 0.9 % for ferritic SS, its increases the pitting corrosion ,
- As I said before, the industrial material presented small difference on their crand Ni chemical composition. So that, we decided to work with lab alloys, with a well defined composition. In table, you can see the composition of our new samples. So, 4 austenitic SS with (0, 1, 2 and 3 % of Mo), 2 ferritic SS with 0 and 3% Mo and 2 duplex with 0 and 3% were produced. Thus, with these heats, we had no composition an d metalurgical differences, and moreover, the specimen preparation were much easier. As we passed from the wire to disk.
- So, with these laboratory samples, we start our studies about their crevice corrosion resistance. As you can see here, we prepared the samples with electric contact for electrochemical measurements and we isolate this electric contact with a acrylic resin. In a second step the samples were embedded in concrete and then we start the contamination of our concrete. A Carbonation of the concrete was done in order to decrease its pH and after the samples were partial immersed in a saline solution, to contaminate the concrete with Cl ions.
- So, to investigate the crevice corrosion of the samples, a monitoring of he corrosion potential was done and also electrochemical experiments.
- Now I going to show you the results we got from those experiments; In this picture, we can see the evolution of the corrosion potential for 10 different samples of the austenitic SS with 3% Mo. So for this material we can see a stable evolution of the corrosion potential. However, when we look at the same results for the austenitic SS with out Mo, we observe a small decrease of the corrosion potential after the first carbonation of the concrete and a high decrease of the corrosion potential after the second carbonation. This strong deacrease can be associated with a depassivation of the ss surface and then with the corrosion attack. Now, if we compare the average corrosion potential values, we can clear see the positive effect of Mo for the austenitic as its presence increased the corrosion potential
- The results were found out for ferritic SS…. but
- Finally the corrosion potential monitoring of the duplex SS showed a high passivation of the of this material in the presence of Mo as you can see in this Figure the corrosion potential increase after the second carbonation. On other hand, in the absence of Mo, a strong decrease of the corrosion potential was observed.
- Thanks very much for your attention!!! And if have any questions…