Influence of Mo alloying on pitting corrosion of stainless steels used as concrete reinforcement

Abstract

Corrosion of reinforcement steels, induced by chloride ions penetrating into the concrete, is the main cause of early damage, loss of serviceability and safety of reinforced concrete structures, which can be even more severe in the presence of concomitant concrete carbonation. In order to prevent reinforcement steel corrosion in highly aggressive alkaline environments, the use of stainless steels is becoming increasingly popular in coastal and marine constructions. Although widely used as an increasing corrosion resistance element in acidic environments, the influence of Mo addition on pitting corrosion resistance of stainless steels is not very clear in these conditions. Understanding Mo mechanism on corrosion resistance in alkaline media is hence of major importance, particularly for new lean grades with low Nickel and Molybdenum contents which presents a good balance between the properties required in these applications and the final cost of the material. In this work we will show the effect of Mo addition on pitting corrosion properties of austenitic, ferritic and duplex SS. A comparison between Mo content steels (alloys: 1.4404, 1.4113 and 1.4462) and very low molybdenum contents steels (alloys: 1.4301, 1.4016 and 1.4362) is done considering their pitting corrosion resistance (pitting potential E pit ) in different corrosion conditions. The results are discussed with respect to the influence of Mo addition on pitting behaviors for the different stainless steel rebar families in several aggressive media mainly in synthetic, chlorinated and carbonated solution reproducing the real concrete pore environments (pH10 solution with carbonates and chlorides ions). Keywords

Study of plasma nitriding and nitrocarburizing for higher corrosion resistance and hardness of 2205 duplex stainless steel

“…The reason why the ferrite phase did not pit can be attributed to the fact that it is rich in Cr and Mo (Table1). Our observation that ferrite is resistance to pitting is also supported by Mesquita et.al [37] in a similar study on this steel.…”

Study of plasma nitriding and nitrocarburizing for higher corrosion resistance and hardness of 2205 duplex stainless steel

“…The reason why the ferrite phase did not pit can be attributed to the fact that it is rich in Cr and Mo (Table1). Our observation that ferrite is resistance to pitting is also supported by Mesquita et.al [37] in a similar study on this steel.…”

Cyclic Polarization of Corrugated Austenitic Stainless Steel Rebars in Acid Rain: Effect of Fly Ash, pH and Steel Type

“…However, in strongly alkaline conditions, Mo is highly unstable, exhibiting a dissolution rate that is more than one order of magnitude higher than that in a neutral solution [68]. The result of the inferior passivity of 316L at pH ≈ 12.5 is compatible with the works of Mesquita et al [45] and Refaey et al [69]; the former noted the negative influence of Mo on the pitting resistance of 316L at pH = 12.5, whereas the latter measured a lower pitting potential for 316L than 304L, at pH = 12. The work of Ai et al [3] also agrees with this, as addressed in the Introduction.…”

“…Indeed, the facilitation of high general corrosion rates of austenitic and duplex stainless steels in strongly caustic electrolytes by molybdenum (due to its active corrosion to MoO 4 2− ) has previously been demonstrated [73,74]. Similarly, the low passive currents exhibited by 304L as compared to 316L at pH ≈ 12.5 (Table 2 and Figure 4b) are justified by the absence of Mo in 304L, since, as aforementioned in Section 3.1.3, Mo has a negative influence on the passivity of the steel [22,45,69].…”

Corrosion resistance of chromium‐steel and stainless steel reinforcement in concrete

“…Molybdenum has proven to increase the resistance of reinforcing steel to pit formation, reduce the corrosion rate, encourage the repassivation process and further decrease the pit propagation when molybdenum oxides form on the pit walls. [19,20,29] In any case, no evidence was found in the current study that associates a lower corrosion resistance with 304 steel in alkaline media.…”

Study of plasma nitriding and nitrocarburizing for higher corrosion resistance and hardness of 2205 duplex stainless steel

“…The reason why the ferrite phase did not pit can be attributed to the fact that it is rich in Cr and Mo (Table1). Our observation that ferrite is resistance to pitting is also supported by Mesquita et.al [37] in a similar study on this steel.…”

Cyclic Polarization of Corrugated Austenitic Stainless Steel Rebars in Acid Rain: Effect of Fly Ash, pH and Steel Type

“…However, in strongly alkaline conditions, Mo is highly unstable, exhibiting a dissolution rate that is more than one order of magnitude higher than that in a neutral solution [68]. The result of the inferior passivity of 316L at pH ≈ 12.5 is compatible with the works of Mesquita et al [45] and Refaey et al [69]; the former noted the negative influence of Mo on the pitting resistance of 316L at pH = 12.5, whereas the latter measured a lower pitting potential for 316L than 304L, at pH = 12. The work of Ai et al [3] also agrees with this, as addressed in the Introduction.…”

“…Indeed, the facilitation of high general corrosion rates of austenitic and duplex stainless steels in strongly caustic electrolytes by molybdenum (due to its active corrosion to MoO 4 2− ) has previously been demonstrated [73,74]. Similarly, the low passive currents exhibited by 304L as compared to 316L at pH ≈ 12.5 (Table 2 and Figure 4b) are justified by the absence of Mo in 304L, since, as aforementioned in Section 3.1.3, Mo has a negative influence on the passivity of the steel [22,45,69].…”

Corrosion resistance of chromium‐steel and stainless steel reinforcement in concrete

“…Molybdenum has proven to increase the resistance of reinforcing steel to pit formation, reduce the corrosion rate, encourage the repassivation process and further decrease the pit propagation when molybdenum oxides form on the pit walls. [19,20,29] In any case, no evidence was found in the current study that associates a lower corrosion resistance with 304 steel in alkaline media.…”

Study of plasma nitriding and nitrocarburizing for higher corrosion resistance and hardness of 2205 duplex stainless steel

“…The reason why the ferrite phase did not pit can be attributed to the fact that it is rich in Cr and Mo (Table1). Our observation that ferrite is resistance to pitting is also supported by Mesquita et.al [37] in a similar study on this steel.…”

Cyclic Polarization of Corrugated Austenitic Stainless Steel Rebars in Acid Rain: Effect of Fly Ash, pH and Steel Type

“…However, in strongly alkaline conditions, Mo is highly unstable, exhibiting a dissolution rate that is more than one order of magnitude higher than that in a neutral solution [68]. The result of the inferior passivity of 316L at pH ≈ 12.5 is compatible with the works of Mesquita et al [45] and Refaey et al [69]; the former noted the negative influence of Mo on the pitting resistance of 316L at pH = 12.5, whereas the latter measured a lower pitting potential for 316L than 304L, at pH = 12. The work of Ai et al [3] also agrees with this, as addressed in the Introduction.…”

“…Indeed, the facilitation of high general corrosion rates of austenitic and duplex stainless steels in strongly caustic electrolytes by molybdenum (due to its active corrosion to MoO 4 2− ) has previously been demonstrated [73,74]. Similarly, the low passive currents exhibited by 304L as compared to 316L at pH ≈ 12.5 (Table 2 and Figure 4b) are justified by the absence of Mo in 304L, since, as aforementioned in Section 3.1.3, Mo has a negative influence on the passivity of the steel [22,45,69].…”

Corrosion resistance of chromium‐steel and stainless steel reinforcement in concrete

“…Molybdenum has proven to increase the resistance of reinforcing steel to pit formation, reduce the corrosion rate, encourage the repassivation process and further decrease the pit propagation when molybdenum oxides form on the pit walls. [19,20,29] In any case, no evidence was found in the current study that associates a lower corrosion resistance with 304 steel in alkaline media.…”