Corrosion Fatigue Crack Propagation Behavior of 2205 Duplex Stainless Steel in Aqueous Medium
Key words: duplex stainless steel ; deionized water ; 3.5%NaCl solution ; corrosion fatigue ; crack growth
Due to the diversity of material-environment systems and the interaction of environment and cyclic loads, the corrosive fatigue behavior of metallic materials is very complicated. In the complex environment of the marine and nuclear power industry, corrosion fatigue of equipment materials is one of the major failure modes [1,2,3]. In corrosion fatigue, the crack propagation life accounts for 90% of the total fatigue life of corrosion . Studying the fatigue crack propagation behavior of metallic materials in aqueous solution is of great significance for its safe use. 2205 Duplex Stainless Steel (DSS) has gained more and more applications in shipbuilding and transportation due to its excellent corrosion resistance, high strength and economical practicality . At present, research on duplex stainless steels mainly focuses on the corrosion resistance [6,7], heat treatment process and heat treatment on the corrosion performance [8,9,10,11,12,13] and its weldability, weld performance The study [14,15,16,17] and so on, the study of corrosion fatigue behavior of duplex stainless steel is still rare . In this paper, the 2205 DSS specimens were subjected to fatigue crack growth experiments in air, deionized water and 3.5% (mass fraction) NaCl solution environments. The influence of the media environment on the fatigue crack propagation behavior and the fracture mechanism were studied.
3 Analysis and Discussion
Hydrogen-induced cracking is the main reason for the weakening of duplex stainless steel materials in aqueous media [19,20,21]. The fatigue crack propagation of 2205DSS materials in aqueous solution is mainly related to the hydrogen embrittlement of the ferrite phase . In aqueous solution, the cyclic load causes the passivation film on the surface of the sample to crack, and the bare metal can act as a dissolution reaction at the anode. The crack wall can be used as a cathode for hydrogen evolution reaction. The electrochemical reaction is shown in (1)~(3). When the adsorbed hydrogen Hads diffused to the crack tip reaches a critical concentration, the crack tip metal cracks while leaving Fe-containing oxide on the crack surface. This process is repeated and fatigue cracks expand forward.
Anode reaction M→Mz++ze−M→Mz++ze-(1)
Hydrolysis reaction Mz++pH2O→M(OH)z−pp+pH+Mz++pH2O→M(OH)pz-p+pH+(2)
Cathodic reaction H++e−→HadsH++e-→Hads Hads+Hads→H2Hads+Hads→H2(3)
Among them, M represents the major element of the stainless steel matrix Fe, Cr or Ni.
The difference in crack propagation ability between 2205 DSS materials in two aqueous solutions is related to the driving force for crack propagation. The two phases of the duplex stainless steel have inconsistent deformation capabilities and are liable to cause local stress concentration at the phase boundary, generate defects and develop into small secondary cracks, resulting in an increase in the effective crack length, as shown in FIG. 5 . If the crack growth driving force Es is expressed as:
Among them, ED is the total energy required for crack propagation, the initial length of the main crack is L0, and the crack length caused by the secondary crack increases to ΔL. Compared with the deionized water, the Cl-containing medium has stronger corrosion effect, and it is easy to induce a large number of defects and form more secondary cracks at the front end of the main crack, so that the effective crack length is longer and the driving force for crack propagation is smaller. The fatigue crack growth driving force of the 2205DSS material in 3.5% NaCl solution is lower than that in the deionized water medium, and the expansion speed is slower, which is consistent with the data obtained by the Paris formula.
The difference in media environment caused the fracture mechanism of the 2205 DSS specimen to change. In the 3.5% NaCl solution, Cl- induced more defects in the front of the main crack, resulting in secondary cracks, resulting in a number of small tearing edges; whereas in deionized water, only the leading end of the main crack formed a coarse in the destabilization zone. Ridge-like torn edges.
Aqueous solution environment significantly improved the fatigue crack growth rate of 2205 DSS, and reduced its fatigue life. The order of fatigue crack propagation rate was: (da/dN)deionized water>(da/dN)NaCl>(da/dN)atmosphere, fatigue crack growth life sequence For: Natmosphere>NNaCl>Ndeionized water. The two phases have uncoordinated deformability and are prone to stress concentration at the phase boundary, resulting in secondary small cracks and increasing the effective crack length. Compared with deionized water, Cl-has stronger corrosion effect, and can induce more defects and develop secondary cracks at the front of the main crack, so that the effective crack length is longer and the driving force for crack propagation is smaller.
The authors have declared that no competing interests exist.
Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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