Corrosion Fatigue Crack Initiation Research Articles

Modelling of corrosion fatigue crack initiation on martensitic stainless steel in high cycle fatigue regime

This paper presents an analytical model for assessing the corrosion fatigue crack initiation life on a martensitic stainless steel X12CrNiMoV12-3 in high cycle fatigue regime (between 105 and 107 cycles). Based on in-situ electrochemical measurements during corrosion fatigue tests in NaCl aqueous solution, the corrosion fatigue crack initiation mechanism was identified. Two main stages were investigated: (i) the fracture of the passive film by slip bands and (ii) the free dissolution of the metal developing fatigue crack initiation from a critical corrosion defect. The depassivation stress threshold corresponds to the median fatigue strength at 107 cycles for fatigue corrosion tests. For an applied stress range less than this threshold, the depassivation phenomenon was not observed at 107 cycles and no crack initiation occurred. The proposed model takes into account the depassivation process induced by the slip bands emergence at the specimen surface and the corrosion rate under cyclic loading. The experimental results are compared to the proposed model taking into account mechanical and electrochemical material parameters.

Corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater

In the present paper, the corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater were studied by stress-controlled fatigue tests and a series of subsequent characterizations on the fracture surface, microstructure and secondary cracks. Results show that the corrosion fatigue crack initiation and initial propagation mechanism evolves with elevated peak stress level in simulated seawater. When peak stress is far below the proof stress, cracks preferentially initiate at the parent austenite grain boundaries (PAGBs) with 68.4% probability and at the ferrite lath boundaries (FLBs) with 31.6% probability. Meanwhile, the cracks also preferentially propagate along the PAGBs and FLBs. Upon the peak stress close to or above the proof stress, cracks turn to initiate from the emerging corrosion pits and propagate without zigzag detour but by splitting the ferrite laths which transversely block its propagation way.

Prediction of corrosion fatigue crack initiation behavior of A7N01P-T4 aluminum alloy welded joints

Through investigating the corrosion fatigue crack initiation behavior of A7N01P-T4 aluminum alloy welded joints in 3.5 wt.% NaCl solution, corrosion fatigue crack initiation life is formulated as [Formula: see text] and the mechanism of corrosion fatigue crack initiation is proposed. SEM and TEM tests revealed that several corrosion fatigue cracks formed asynchronously and the first crack does not necessarily develop into the leading crack. The uneven reticular dislocations produced by fatigue loading are prone to piling up and tangling near the grain boundaries or the second phases and form the “high dislocation-density region” (HDDR), which acts as an anode in microbatteries and dissolved to form small crack. Thus the etching pits, HDDR near the grain boundaries and second phases are confirmed as the main causes inducing the initiation of fatigue crack.

High-Cycle Microscopic Severe Corrosion Fatigue Behavior and Life Prediction of 25CrMo Steel Used in Railway Axles

The effects of environmental media on the corrosion fatigue fracture behavior of 25CrMo steel were investigated. The media include air, and 3.5 wt % and 5.0 wt % NaCl solutions. Experimental results indicate that the media induces the initiation of corrosion fatigue cracks at multiple sites. The multi-cracking sites cause changes in the crack growth directions, the crack growth rate during the coupling action of the media, and the stress amplitude. The coupling effects are important for engineering applications and research. The probability and predictions of the corrosion fatigue characteristic life can be estimated using the three-parameter Weibull distribution function.

Dorf Ketal acquires Indian catalyst firm Filtra

This paper presents an analytical model for assessing the corrosion fatigue crack initiation life on a martensitic stainless steel X12CrNiMoV12-3 in high cycle fatigue regime (between 105 and 107 cycles). Based on in-situ electrochemical measurements during corrosion fatigue tests in NaCl aqueous solution, the corrosion fatigue crack initiation mechanism was identified. Two main stages were investigated: (i) the fracture of the passive film by slip bands and (ii) the free dissolution of the metal developing fatigue crack initiation from a critical corrosion defect. The depassivation stress threshold corresponds to the median fatigue strength at 107 cycles for fatigue corrosion tests. For an applied stress range less than this threshold, the depassivation phenomenon was not observed at 107 cycles and no crack initiation occurred. The proposed model takes into account the depassivation process induced by the slip bands emergence at the specimen surface and the corrosion rate under cyclic loading. The experimental results are compared to the proposed model taking into account mechanical and electrochemical material parameters.

Corrosion-fatigue properties of plasma-based low-energy nitrogen ion implanted AISI 304 L austenitic stainless steel in borate buffer solution

Abstract AISI 304 L austenitic stainless steel was modified by using the plasma-based low-energy nitrogen ion implantation (PBLEII) at a process temperature of 400 °C for a processing time of 4 h in order to improve the corrosion-fatigue resistance of the austenitic stainless steel. A single high-nitrogen face-centered-cubic phase (γN) layer with a maximal nitrogen concentration of about 25 at.% was formed on the nitrogen-modified austenitic stainless steel. Compared with the original austenitic stainless steel, the γN phase layer on the austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with a pH value of 8.4. The corrosion-fatigue properties of the γN phase layer on the austenitic stainless steel were examined by the push–pull fatigue experiments with a ratio R of tensile and compression of − 1 in the borate buffer solution. The γN phase layer has an increased corrosion-fatigue strength up to 230 MPa from 180 MPa of the original austenitic stainless steel with an apparent increase of about 28%. The corrosion-fatigue crack initiation in the γN phase layer was found as a controllable stage in the fracture process at the interface between the γN phase layer and the austenitic stainless steel matrix with the arc corrosion-fatigue source. Some tiny corrosion-fatigue striations were obtained on the corrosion-fracture surfaces of the γN phase layer. The high density of slip bands and dislocations in the γN phase layer was able to prevent the crack initiation and propagation, leading to improvement of the corrosion-fatigue properties in the borate buffer solution.

The influence of metallurgical factors on corrosion fatigue strength of stainless steels

Corrosion fatigue strength of stainless steels is controlled by tangled interaction among environmental, mechanical and metallurgical factors. In order to estimate corrosion fatigue strength it is indispensable to understand the role of an each influencing factor. The aim of this paper is to present briefly surveyed results on metallurgical factors on corrosion fatigue strength of stainless steels such as austenitic, martensitic and duplex stainless steels mainly based upon author’s experimental results. The targeted dominant metallurgical factors focussed upon are chemical compositions, heat treatment, manufacturing process and microstructures.The emphasis is placed upon effect of Molybdenum content on corrosion fatigue strength of austenitic stainless steels in 3%NaCl aqueous solution, tempering temperature on corrosion fatigue strength of 13% Chromium stainless steel in 3%NaCl aqueous solution and volume percent ferrite on corrosion fatigue strength of duplex stainless steel in potassium alum aqueous solution. The surface and fracture surface observation by optical and scanning electron microscopy revealed that corrosion pit formed at corrosion fatigue crack initiation area. In light of relatively smaller effect of corrosive environment on corrosion fatigue crack propagation rate it can be surmised that corrosion fatigue strength of stainless steels is governed by crack initiation process. It can be concluded that corrosion fatigue strength of stainless steels is strongly influenced by metallurgical factors such as chemical compositions, heat treatment, manufacturing process and microstructures.The information obtained in this survey directly lead to prevention of corrosion fatigue failure in stainless steels made components, selection of stainless steels in corrosive environments and development of corrosion resistant stainless steels.

Effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel in high temperature water

The effect of oxidation behavior on the corrosion fatigue crack initiation and propagation of 316LN austenitic stainless steel (SS) in 320°C water and air environments was investigated by corrosion fatigue cracking test system, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The experimental results indicated that the cracks were found to be initiated at first 20% of fatigue life of the specimens tested in 320°C water, while only a few cracks were found until fracture when tested in 320°C air. The crack propagation rates of the specimens tested in 320°C water were obviously faster than those tested in 320°C air especially at lower strain amplitude of ±0.5%. This can be attributed to the oxidation behavior of the 316LN SS specimens tested in 320°C water was more serious than those tested in 320°C air. The compositions were more complex of the oxide films formed in 320°C water than those tested in 320°C air, which lead to crack initiation easier in the former. Moreover, the 320°C water made the mechanical properties of the oxide films worse, resulting in a faster fatigue crack propagation rate at crack tip.

Ultrasonic Corrosion Fatigue Behaviorof Duplex Stainless Steel

Ultrasonic Corrosion Fatigue Tests were Conducted for SUS329J3L in Air and 3%NaCl Aqueous Solution. Reduction of Giga-Cycle Corrosion Fatigue Strength was 12.5%. Corrosion Pit was Observed on Corrosion Fatigue Crack Initiation Area. Striation was Predominantly Observed on Crack Propagation Area both in Air and 3% Nacl Aqueous Solution. it can be Concluded that the Reduction of Corrosion Fatigue Strength of SUS329J3L is due to the Corrosion Pit Formation at Corrosion Fatigue Crack Initiation Area.

Effect of corrosion on the high cycle fatigue strength of martensitic stainless steel X12CrNiMoV12-3

This paper addresses the effects of corrosion on the high cycle fatigue (HCF) strength of a high mechanical strength martensitic stainless steel (X12CrNiMoV12-3) that is used in aeronautic applications. HCF tests (between 105 and 107cycles) were carried out in two environments: (i) in air and (ii) in an aqueous solution (pH=6) of 0.1M NaCl+0.044M Na2SO4 at a loading frequency of 120Hz. Surface crack initiation is observed in air, whereas in solution, the crack initiated at corrosion defects. The decrease observed in the corrosion fatigue strength of specimens at 107cycles was 33% of that of similar specimens tested in air. The electrochemical behaviour of the passive film was investigated during fatigue testing in a NaCl aqueous solution by monitoring the free potential and through electrochemical impedance spectroscopy (EIS). Based on fractography analysis and the EIS tests results, fatigue crack initiation mechanisms in air and in the NaCl aqueous solution were identified. A scenario for fatigue crack initiation is proposed based on the physical evidence. Local passive film ruptures are the cause of the corrosion fatigue crack initiation. The film is broken by material strain from the applied cyclic stress during fatigue testing, causing increased local corrosive attack. This effect has been shown at 10Hz and 120Hz because the characteristic time for repassivation for the steel is very low compared to the period of the cyclic loading.

Study on the mechanism of high-cycle corrosion fatigue crack initiation in X80 steel

Corrosion fatigue experiments on X80 steel in 3.5% NaCl solution were conducted on a researcher-developed cantilever-bending corrosion fatigue testing machine. The morphology of corrosion pits and the change in the surrounding microstructure were carefully examined using SEM and TEM, and the stress field was simulated using the finite-element method. The results show that the corrosion fatigue crack initiation is due to not only the corrosion pits’ stress concentration effects but also the adhering corrosion products. Corrosion products formed on the surface of slip bands, and the action of corrosion products on fatigue crack initiation was explained using physical models.

OS2124 各種ステンレス鋼のギガサイクル腐食疲労挙動

Giga-cycle corrosion fatigue behavior of 12 Cr martensitic stainless steels in NaCl and NaOH aqueous solution were summarized mainly on the basis of the author's experimental results. Then giga-cycle corrosion fatigue behavior of austenitic stainless steels such as SUS304,SUS304N2, SUS316, 2.5%Cr containing steel and YUS270 super stainless steel are demonstrated on the basis of the author's recent experimental results. Giga-cycle corrosion fatigue behavior of SUS329 duplex stainless steel is touched on briefly. The reduction of giga-cycle corrosion fatigue strength of stainless steels is depending on the kind of stainless steel. It can be concluded that the reduction of corrosion fatigue strength of martensitic, austenitic and duplex stainless steels is due to the corrosion pit formation at corrosion fatigue crack initiation area.

Corrosion–Fatigue Life Prediction for 2024-T62 Aluminum Alloy Using Damage Mechanics-Based Approach

An approach based on the continuum damage mechanics was applied to predict corrosion–fatigue crack initiation life of 2024-T62 aluminum alloy. A fatigue test in air, a pre-corrosion–fatigue test, and a corrosion–fatigue test on smooth standard specimens were performed. The fatigue lives are strongly reduced by the corrosive environment of 5 wt.% NaCl continuous salt spray compared with non-corroded specimens. Damage evolution models for fatigue in air and pre-corrosion–fatigue of smooth specimens were established, which forms the basis for solving the corrosion–fatigue problem. Finally, the method of corrosion–fatigue life prediction was presented. The predictions comply with the experimental data.

OS0612 高強度ステンレス鋼の超音波腐食疲労挙動(OS6-3 材質および熱処理の影響,OS-6 金属材料の超高サイクル疲労と信頼性評価)

Ultrasonic corrosion fatigue tests were conducted for high strength stainless steels such as YUS270, SUS304N2 and SUS329 in 3%NaCl aqueous solution. The reduction of corrosion fatigue strength at 10^9 cycles for YUS270 and SUS304N2 was not observed at all, while the reduction of giga-cycle corrosion fatigue strength was 12.5% for SUS329. Corrosion pit was observed on corrosion fatigue crack initiation area. Striation was predominantly observed on crack propagation area both in air and in 3% NaCl aqueous solution. It can be concluded that the reduction of corrosion fatigue strength of 2.5%Mo containing high strength austenitic stainless steels is due to the corrosion pit formation at corrosion fatigue crack initiation area.

Corrosion fatigue crack initiation behavior of stainless steels

Corrosion fatigue crack initiation behavior of various kinds of stainless steels is reviewed mainly on the basis of the author’s experimental results. The role of corrosion pit in the corrosion fatigue crack initiation process of martensitic, ferritic, austenitic, duplex and precipitation-hardening stainless steels is briefly summarized. The recent investigation of an electrochemical noise measurement method is demonstrated for 12%Cr martensitic stainless steel and 2.5%Mo containing high strength austenitic stainless steels. Finally a couple of future problems to be solved in corrosion fatigue crack initiation are touched on briefly.

Sensitivity to Fatigue Cracks Initiation of Symmetrical <110>Tilt Grain Boundaries in Pure Copper Bicrystals in 1M NaNO<sub>2</sub> Solution

Sensitivity to corrosion fatigue (CF) crack initiation has been investigated in a series of pure copper bicrystals with a symmetrical <110>-tilt grain boundary. Tests were performed by axial tension-compression tests in 1M NaNO2 solutions. The small-angle tilt bicrystals fractured in both intergranular and transgranular manners accompanied by a large amount of plastic strain to fracture while the large-angle bicrystals fractured in almost intergranular manner with a smaller plastic strain. Susceptibility to CF cracks increases with increasing misorientation. It seems that effect of grain boundaries structures, i.e., Σ-values is small in this experiment. Stress concentration generated by the pile-up of trapped dislocations at the grain boundary could account for the high susceptibility of the intergranular cracks in large-angle grain boundaries

Assessment of the dynamics of corrosion fatigue crack initiation applying recurrence plots to the analysis of electrochemical noise data

Electrochemical current oscillations generated during the early stages of corrosion fatigue damage (CFD) were analysed applying recurrence plots. “This novel analysis tool allowed us to assess changes in the dynamics of the CFD process, differentiating pure electrochemical process like of pitting corrosion (PC) from the corrosion fatigue crack formation and initial growth”. The dynamics of CFD initiation was characterized by determining changes in the selected recurrence quantification analysis (RQA) parameter: the percentage of determinism (% D). A significant contribution of this work is that it was possible to separate through changes in % D as a function of the number of cycles ( N), the electrochemical process of pitting corrosion from the corrosion fatigue crack initiation and growth, which has a random nature and involved low values of % D of around 5%. A subsequent augment of the % D to values from 75% to 95% with the increase of N could be related to the short fatigue crack arrest. The increment of % D indicates that the electrochemical pitting corrosion process was the predominant contribution to the current oscillations.

해수환경중 부식피로균열 발생수명 평가에 관한 연구

With regard to corrosion fatigue crack initiation life (Nc), it has been treated ambiguously for the member which doesn't have stress concentration area. In this research, in order to clarify the corrosion fatigue crack initiation life (Nc), corrosion fatigue tests were carried out. Reasonable and universal corrosion fatigue crack initiation life (Nc) was defined and corrosion fatigue crack initiation/propagation model was suggested also. As the fatigue crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM was conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the followings were obtained. When there is no clear stress concentration point which seems to fall into a corrosion fatigue crack initiation life, the significance of the definition and suggestion of the moment of the reasonable and universal corrosion fatigue crack initiation life (Nc), at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and propagates in earnest, has been clarified.

Corrosion fatigue crack initiation in 12% chromium stainless steel

Characteristics of corrosion fatigue failures of steam turbine blades derived from failure analysis are summarized. Then corrosion fatigue variables on corrosion fatigue strength of 12% chromium stainless steel are briefly reviewed. The paper emphasizes initiation and growth of corrosion pits in the corrosion fatigue crack initiation process. A recent investigation of the early stages of corrosion pit initiation by use of electrochemical noise measurement is demonstrated. Finally, some recommendations are given how to clarify the corrosion fatigue crack initiation process.

Effect of selective dissolution on fatigue crack initiation in 2205 duplex stainless steel

The effect of selective dissolution on fatigue crack initiation of 2205 duplex stainless steel (DSS) was investigated in this study. In mixed sulfuric and hydrochloric acid aqueous solution, there existed two distinctly separated anodic peaks in the active-to-passive transition region of the polarization curve. Either ferritic or austenitic phase was selectively dissolved at each characteristic anodic peak potential. Under sinusoidal cyclic loading condition, however, selective dissolution did not assist fatigue crack initiation instead resulting in the elimination of stress concentration site in the selectively dissolving phase. As a consequence, under selective dissolution condition, fatigue crack initiated in the phase while its dissolution rate was lower with respect to the other constituent phase in the duplex stainless steel. The microstructural evolution of the corrosion fatigue crack initiation in 2205 DSS in the mixed sulfuric and hydrochloric acid solution is highlighted in this investigation.