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1
Content available Fatigue and Corrosion Fatigue of 18Ni Maraging Steel
Yongmei Zhu, Junjie Chen, Wenxian Tang, Weicheng Cui, Xiaorong Wang, Fang Wang, Baoji Yin
Archives of Metallurgy and Materials
|
2021
|
Vol. 66, iss. 2
381--390
EN
This study focused on the fatigue and corrosion fatigue of maraging steel 18Ni (250). The 18Ni (250) samples were tested for axial fatigue in air and 3.5% NaCl solution. The effects of loading frequency and stress ratio on the fatigue strength of 18Ni (250) were studied. in air, the loading frequency was 10 Hz, and the stress ratio was 0.5. however, three loading methods were used in the 3.5% NaCl solution: (i) the loading frequency of 1 Hz and stress ratio of 0.5; (ii) the loading frequency of 1 Hz and stress ratio 0.1, and (iii) the loading frequency 5 Hz and stress ratio 0.5. The corrosion fatigue strength of samples in the 3.5% NaCl solution was 63.3% lower than that of the samples in air. The fractures in the samples were observed after the test.
2
Content available Fatigue and Corrosion Fatigue of 18Ni Maraging Steel
Yongmei Zhu, Junjie Chen, Wenxian Tang, Weicheng Cui, Xiaorong Wang, Fang Wang, Baoji Yin
Archives of Metallurgy and Materials
|
2021
|
Vol. 66, iss. 1
321--330
EN
This study focused on the fatigue and corrosion fatigue of maraging steel 18Ni (250). The 18Ni (250) samples were tested for axial fatigue in air and 3.5% NaCl solution. The effects of loading frequency and stress ratio on the fatigue strength of 18Ni (250) were studied. In air, the loading frequency was 10 Hz, and the stress ratio was 0.5. However, three loading methods were used in the 3.5% NaCl solution: (i) the loading frequency of 1 Hz and stress ratio of 0.5; (ii) the loading frequency of 1 Hz and stress ratio 0.1, and (iii) the loading frequency 5 Hz and stress ratio 0.5. The corrosion fatigue strength of samples in the 3.5% NaCl solution was 63.3% lower than that of the samples in air. The fractures in the samples were observed after the test.
3
Content available Comparing of High-Cycle Fatigue Lifetimes in Un-corroded and Corroded Piston Aluminum Alloys in Diesel Engine Applications
Azadi M., Aroo H., Azadi M., Parast M. S. A.
Archives of Foundry Engineering
|
2021
|
Vol. 21, iss. 1
89--94
EN
Diesel engine components in the combustion chamber have been exposed to cyclic loadings under environmental effects, including high temperatures and corrosive fluids. Therefore, knowing the corrosion-fatigue behavior of materials is essential for designer engineers. In this article, pure fatigue and corrosion-fatigue behaviors of the piston aluminum alloy have been experimentally investigated. For such an objective, as-cast and pre-corrosive standard samples were tested by the rotary bending fatigue machine, under 4 stress levels. Some specimens were exposed to the corrosive fluid with 0.00235 % of the sulfuric acid for 100 and 200 hours. The results showed higher weight losses for 200 hours immersion times. As another result, it could be concluded that the lifetime decreased in pre-corrosive samples for both 100 and 200 hours of the immersion time, compared to that of as-cast specimens. However, such a lifetime reduction was more significant for 200 hours of the immersion time, especially within the high-cycle fatigue regime (or lower stress levels). Under high stress levels, both pre-corrosive sample types had almost similar behaviors. The field-emission scanning electron microscopy images of specimen fracture surfaces indicated that the brittle region of the fractured surface was larger for specimens after the 200 hours of corrosion-fatigue testing than the other specimen.
4
Content available Influence of loads in the process of laying on the resource of sea pipelines
Poberezhnyi L., Tregubenko S., Poberezhna L., Hrytsanchuk A., Stanetsky A.
Archives of Materials Science and Engineering
|
2019
|
Vol. 96, nr 2
63--72
EN
Purpose: In the process of laying on the bottom of the sea material of the pipeline undergoes single-cycle alternating load. The purpose of the work is to determine the effect of pre-operational loads on the resource of marine pipelines. Design/methodology/approach: The influence of the method of construction of pipelines on their stress-strain state is analysed. According to the real modes of packing of sea pipelines, the loading regime is programmed and the laboratory modelling of the pipelaying process by the S-method has been programmed. Findings: According to the results of one-cycle shift load were obtained characteristics of the hysteresis loop. It is proposed to simplify the mathematical description of the hysteresis loop of the pipeline laying cycle in the given form. It was shown that the preload during the construction process negatively affects the durability of the pipeline material due to the exhaustion of its plasticity resource, reducing it to 70%. Research limitations/implications: In the future, investigations into the effect of overloading and overloading during the repair of pipeline sections on their durability and on the safe exploitation of resources should be continued. Practical implications: The developed method of estimation of influence of preoperational loads in the process of pipeline laying on its safe exploitation resource is used in gas-extraction enterprises. Originality/value: To forecast the deformation behaviour of the pipeline material in the laying cycle, it is efficient to use diagrams of a sign-changing single-cycle bend, which were built considering the creep. The fatigue life capability of a steel pipeline depends on the history of the pipeline load in the laying cycle. Ratio σ*0.2c / σ* 0.2t and εyc / ε yt can use as power and deformation criteria for evaluating Bauschinger effect. It is suggested that fatigue damage is determined by the width of the hysteresis loop.
5
Content available Corrosion fatigue crack propagation rate characteristics for weldable ship and offshore steels with regard to the influence of loading frequency and saltwater temperature
Jakubowski M.
Polish Maritime Research
|
2017
|
nr 1
88--99
EN
After Vosikovsky (1975), the corrosion fatigue crack growth rate (CFCGR) characteristics have been divided into three regions. The region-III rates are very close to mechanical fatigue crack growth rates. CFCGR formulae, including the long-crack length effect (in region I only), the loading frequency effect (in region II only), and the saltwater temperature effect, have been proposed. It has been assumed that CFCGR is proportional to f –k, where f is the loading frequency and k is a constant. The averaged k-value for all steels of yield stress (YS) below 500 MPa, usually with ferrite-pearlite microstructures, is higher than that for YS > 500 MPa, usually with quenched and tempered microstructures. The temperature effect does not appear in region I below room temperature. In the remaining cases, that is, in region I for elevated temperatures and in region II for both low and elevated temperatures, the CFCGR increases with increasing temperature. Under a potential of –0.8 V, a long-crack-length effect, qualitatively similar to analogous effect for free corrosion conditions, appears.
6
Content available Corrosion Fatigue Crack Growth Studies on Pressure Vessel and Piping Steels in Water Environment
Mathew N. M., Vishnuvardhan S., Raghava G., Santhi A. S.
Archives of Metallurgy and Materials
|
2017
|
Vol. 62, iss. 3
1857--1862
EN
Corrosion fatigue crack growth studies were conducted on eccentrically-loaded single edge notch tension specimens made of SA 333 Gr. 6 and SA 516 Gr. 70 carbon steels in water environment. The experiments were conducted using a ±250 kN capacity Universal Testing Machine under constant amplitude sinusoidal loading at a test frequency of 0.50 Hz and stress ratio of 0.1. The fabrication of test specimens and the experiments were carried out based on ASTM E 647 and ASTM E 1820. The crack initiation and growth were monitored and images were captured by using a digital camera at regular intervals of fatigue cycles. By using these images, the length of crack was measured. The tests were terminated when the uncracked portion of the specimens was insufficient to take further load. Crack growth rate and stress intensity factor range values were evaluated at incremental values of loading cycles and crack length. Using the crack growth rate vs. stress intensity factor range plots, best fit curves following power law in the form of Paris’ equation were obtained.
7
Content available remote Effect of some metallurgical variables on the corrosion fatigue behavior of α-brass in sodium nitrite solution
Youssef G. I., Khorshed L. A., Ashour E. A.
Ochrona przed Korozją
|
2016
|
nr 10
378--383
EN
The corrosion fatigue behavior of three metallurgical conditions of α-brass (as- received, cold- rolled and annealed) in 1 M NaNO2 solution under free corrosion potential and under a constant applied anodic potential of 300 mVNHE (Normal Hydrogen Electrode) was investigated by applying the reverse bending technique at 70 cycle /min. The fatigue life and fatigue strength of α-brass in 1 M NaNO2 solution under free corrosion is considerably shorter than that obtained in air, while under applied anodic potential value 300 mVNHE a further reduction in fatigue life was obtained. The longest fatigue life is that corresponding to the cold- rolled followed by the fatigue life of the as- received and finally the fatigue life to the annealed specimens. The same order was also obtained in sodium nitrite solution at the free corrosion condition as well as under the applied anodic potential. The fracture mode of the fatigued specimens changed from transgranular in air to mixed inter-and transgranular in nitrite solution for the as- received and cold- rolled. Annealed specimens show a mixed mode in both air and nitrite solution. The conjoint action of film rupture and adsorption models is the operating mechanism of corrosion fatigue of brass in nitrite solution.
PL
Za pomocą metody odwróconego zginania wykonanej z zastosowaniem 70 cykli gięcia na minutę, badano korozję zmęczeniową w 1 M NaNO2 przy wolnym potencjale korozyjnym i stałym przyłożonym potencjale anodowym równym 300 VSEW (Standardowa Elektroda Wodorowa). Trwałość i wytrzymałość zmęczeniowa α-mosiądzu w roztworze 1 M Na-NO2 przy wolnej korozji jest znacznie niższa niż przy wystawieniu go na działanie powietrza, a po przyłożeniu potencjału anodowego 300 mVNHE, żywotność zmęczeniowa spada jeszcze bardziej. Najdłuższą żywotność zmęczeniową osiągnięto w przypadku α-mosiądzu walcowanego na zimno, mniejszą dla odmiany w stanie wyjściowym, a najniższą w przypadku próbek odprężonych. Tę samą kolejność uzyskano dla próbek poddanym działaniu roztworu azotynu sodu w warunkach wolnej korozji jak również w przypadku próbek z przyłożonym potencjałem anody. Charakter pęknięć próbek w stanie wyjściowym i walcowanych na zimno był śródkrystaliczny w przypadku wystawienia na działanie powietrza i mieszany między- oraz śródkrystaliczny po ekspozycji w roztworze azotynowym. W odprężonych próbkach występowały oba rodzaje pęknięć zarówno po wystawieniu ich na działanie powietrza jak i roztworu azotynowego. Mechanizmem roboczym zmęczenia korozyjnego mosiądzu w roztworze azotynu sodu jest połączone działanie modeli adsorpcji i pękania powłoki.
8
Zmęczenie korozyjne przyczyną awarii rurociągów energetycznych
Gajewski M., Furmańczyk P., Barwicki L.
Energetyka
|
2014
|
nr 11
652--655
PL
W pracy przedstawiono mechanizm anodowego rozpuszczania żelaza i powstawania pęknięć powodowanych zmęczeniem korozyjnym. Omówiono dwa charakterystyczne przypadki zmęczenia korozyjnego rurociągu pary wtórnej ze stali 10H2M oraz króćca rury międzywalczakowej kotła ze stali K18. Przeprowadzone badania potwierdziły istotną rolę ogniwa galwanicznego w procesie pękania.
EN
The paper presents the mechanism of anodic dissolution of iron and the formation of cracks caused by corrosion fatigue. Discusses two typical cases of corrosion fatigue secondary steam pipe made of 10H2M steel and pipe nipple of boiler made of K18 type steel. The study confirmed the important role of galvanic cell in the process of cracking.
9
Content available remote Corrosion and corrosion fatigue behaviour of Al-bronze in LiBr solutions
Youssef G. I., Shehata M. F., Meleigy A. E., Warraky A. A., Aziz A. M. A.
Ochrona przed Korozją
|
2013
|
nr 2
34--38
EN
The corrosion behaviour of Al-bronze in LiBr solution was investigated by means of solution analysis, potentiodynamic cyclic polarization, and surface examination. It was found that the dissolution of the alloy at lower concentrations of LiBr (0.25 M) was mainly general due to the formation of CuBr and/or Cu2O. By increasing the concentration of LiBr (≥ 0.5 M) the predominant species were CuO, Cu(OH)2 and CuBr2 • 3Cu(OH)2, CuLiO phase in addition to Al2O3, which is more passive, while the corrosion form was mainly pitting. The corrosion fatigue results proved that both the fatigue life and fatigue strength deteriorated as the LiBr concentration increased. Phractographic examinations revealed a shift of fracture mode from transgranular in air to a mixed mode of transgranular and intergranular with an increasing percentage of intergranular as the LiBr concentration increased. The above results indicate that the failure was due to the action of a mechanochemical mechanism.
PL
Właściwości korozyjne brązu aluminiowego w roztworze LiBr badano za pomocą analizy roztworu, cyklicznej polaryzacji potencjodynamicznej i analizy powierzchni. Stwierdzono, że przy mniejszym stężeniu roztworu LiBr (0,25 M) roztwarzanie stopu zachodzi z wytworzeniem głównie CuBr i/lub Cu2O. Zwiększenie stężenia Libr (≥ 0,5 M) powoduje korozję wżerową na skutek utworzenia się pasywnej warstwy składającej się przede wszystkim z CuO, Cu(OH)2, CuBr2 • 3Cu(OH)2 i fazy CuLiO. Badania zmęczeniowe wykazały, że zarówno trwałość, jak i wytrzymałość zmęczeniowa zmniejszają się ze wzrostem stężenia LiBr. Badania fraktograficzne ujawniły zmianę rodzaju pęknięć z śródkrystalicznych w powietrzu na mieszane śródkrystaliczne i międzykrystaliczne, aż do międzykrystalicznych, w miarę wzrostu stężenia LiBr. Wyniki badań wskazują na mechanochemiczny mechanizm powstawania pęknięć.
10
Content available Low - cycle fatigue of Al-Mg alloy joints
Czechowski M.
Journal of KONES
|
2012
|
Vol. 19, No. 2
103-108
EN
This article presents the results of the low-cycle fatigue tests of AW-5059 Alustar alloy. Gas metallic welding in argon arc shield was used. Metallographic analysis of bonds showed a proper structural construction MIG welded 5059 aluminum alloy. The low-cycle fatigue tests were carried out in the air and artificial seawater (3.5% water solution NaCl), with stable amplitude of stress value. The stresses were changed in the symmetric cycle (the stress ratio was R = -1) with constant strain rate of 5mm/min and the frequencies oscillating between 0.08-0.2 Hz. During the tests the following parameters was observed: number of cycles until the specimen's destruction, upper and lower extreme values of force and strain for the selected cycles, duration-time of the test and frequency. Analysis of specimens fracture surfaces was performed with scanning electron microscope (SEM) Philips XL30. In case of the specimens exposed in 3,5% water solution NaCl the fatigue durability is lower than the durability of specimens tested in the air. The article depicts the changes in total strain amplitude Iac [mm] depending on number of cycles [N] obtained in the tests with ia=const and the low-cycle fatigue resistance for the welded Alustar alloy. Original value are received results of the low-cycle fatigue tests of AW-5059 Alustar alloy welded by MIG
11
Prędkość propagacji pęknięć zmęczeniowych w stali austenityczno-ferrytycznej - wpływ wodoru i mikrostruktury
Marciniak S., Głowacka A., Pakieła Z., Świątnicki W.
Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne
|
2007
|
Z. 4
84-85
PL
W pracy przedstawiono badania prędkości propagacji pęknięć zmęczeniowych w stali austenityczno-ferrytycznej X2CrNiMN23-5-3 w powietrzu i w warunkach katodowego nasycania wodorem. Badania prowadzono na próbkach w dwóch stanach mikrostrukturalnych: po walcowaniu na gorąco oraz po dodatkowej obróbce cieplnej. Stal po obróbce plastycznej na gorąco cechowała się drobnoziarnistą strukturą i silnym ukierunkowaniem obszarów ferrytu i austenitu w kierunku walcowania. Obróbka cieplna spowodowała rozrost ziaren obu faz oraz zanik anizotropii mikrostrukturalnej. Wykazano, że przy małej częstotliwości obciążeń, prędkość propagacji pęknięć zmęczeniowych jest znacznie większa w środowisku wydzielającym wodór w porównaniu do prób prowadzonych w powietrzu. W próbce po walcowaniu, prędkość propagacji pęknięć zmęczeniowych w środowisku wydzielającym wodór zależy od kierunku przyłożonych obciążeń względem kierunku walcowania. Ta anizotropia prędkości propagacji pęknięć zmęczeniowych nie występuje w próbkach po obróbce cieplnej. Oznacza to, że czynniki mikrostrukturalne mają większy wpływ na propagację pęknięć zmęczeniowych w środowisku wydzielającym wodór w porównaniu do prób realizowanych w powietrzu.
EN
The investigations of fatigue crack propagation rate in austenitic-ferritic steel have been described. Fatigue tests have been performed in air and during cathodic hydrogen charging from aqueous solutions. Two various kinds of steel specimens have been tested: one of them issued from hot rolling, and the other one additionally annealed at high temperature. The hot rolled specimens had fine-grained microstructure and were composed of austenite and ferrite plates elongated in the rolling direction. The subsequent annealing induced the grain growth of both phases leading to more isotropic phase morphology. It has been shown, that at low loading frequency, the fatigue crack growth occurs at higher rate in hydrogen generating solution than in air. In the hot rolled samples the fatigue crack growth rate during hydrogen charging depended on the direction of loading, with respect to the rolling direction. This anisotropy of crack growth rate was absent in the annealed specimens. It means that microstructural factors have greater influence on the fatigue crack growth rate in hydrogen generating solution than that in air.
12
Content available remote Pękanie korozyjno-zmęczeniowe. Koncepcja modelu zużywania
Stachowiak A., Zwierzycki W.
Tribologia
|
2007
|
nr 3-4
237-244
PL
W artykule przedstawiono koncepcję matematycznego modelowania procesu zużywania determinowanego pękaniem korozyjno-zmęczeniowym. Scharakteryzowano główne założenia modelu oraz jego zasadnicze moduły: - moduł wyznaczania pola naprężeń i przemieszczeń u czoła pęknięcia (metoda elementów brzegowych), - moduł prognozowania zmian warunków elektrochemicznych w obszarze mikroszczeliny.
EN
In this paper the new concept of the corrosive - mechanical wear calculation was presented. The new alghoritmus, based on the crack propagation theory was elaborated as well. Authors of this paper have been engaged for a number years in working out methods of wear calculation of sliding pairs running in electrolytes (it proceeds corrosive - mechanical type of wear then). In earlier research, authors formulated the computational algorithm, in which procedures of calculation of mechanical and corrosive (electrochemical) components from Lazarev's model were used. Own modules permitting calculation of the corrosive current value and parameters of the surface roughness (resulted from transformation process of the technological surface layer in the operating surface layer) were utilized also in this algorithm. This model was tentatively verified by experimental data. Currently, authors work on the second, alternative calculation model of corrosive - mechanical wear supported on the interpretation of the formation process of particles - wear products based on the crack mechanics. The conception of calculation and empirical characteristics obtaining indispensable to their conducting was formulated in this paper.
13
Influence of corrosion environments on materials and strength of structures:new approaches and practical applications.
Dmytrakh I.
Prace Naukowe Instytutu Materiałoznawstwa i Mechaniki Technicznej Politechniki Wrocławskiej. Konferencje
|
2007
|
Vol. 65, nr 11
13-35
EN
The presented lecture highlights the mechanical, physical and corrosion aspects of the environmentally assisted fracture of structural metallic materials. The methods and testing equipment for corrosion crack growth studies and electrochemical measurements within cracks are described. The relationship between electrochemical state and stress-strain state of pre-fracture zone was derived on the base of received experimental data for the number systems "material-environment". The new method for determining of corrosion fatigue crack growth rate diagrams is presented with taken into account an electrochemical situation in the crack tip. It has been proven that such diagrams reflect the extreme influence of the environment factor on material corrosion fatigue fracture processes and may be recommended as the base for a remaining lifetime calculation of the structure elements that are exploited under environmental conditions. The engineering applications of presented approaches and methods for expert assessment of technical state of heat-and-power engineering pipelines are considered and the examples of calculations of residual life of some structural elements are given with taken into account of the actual data of metal properties and operating conditions of equipment.
14
Zmęczenie korozyjne stali austenityczno-ferrytycznej w warunkach nasycania wodorem
Głowacka A., Wysocka O., Miśkiewicz M., Pakieła Z., Świątnicki W.
Zeszyty Naukowe. Mechanika / Politechnika Opolska
|
2005
|
z. 82
305-314
PL
W pracy przedstawiono badania prędkości propagacji pęknięć zmęczeniowych w stali austenityczno-ferrytycznej 00H22N5M3 w powietrzu i w warunkach katodowego nasycania wodorem. Wykazano, że w środowisku wydzielającym wodór, na prędkość propagacji pęknięć zmęczeniowych wpływa z jednej strony częstotliwość obciążeń, a z drugiej anizotropia mikrostrukturalna stali.
EN
The fatigue crack propagation investigations have been performed in austenitic-ferritic duplex stainless steel in air and during cathodic hydrogen charging. It was shown that the crack propagation during hydrogen charging was influenced by the frequency of loading and also by the microstructural anisotropy of the steel.
15
Content available Prediction of corrosion fatigue crack propagation life for welded joints under cathodic potentials
Jakubowski M.
Polish Maritime Research
|
2005
|
nr 2
17-20
EN
Enhancement of corrosion fatigue crack growth rates by cathodic protection is observed below the optimum applied potential of the protection. An empirical formula for the effect of the protective potential below -0.8 V (Ag/AgCl2) on the crack growth rates for some classes of shipbuilding steels tested in salt water has been derived for medium and high value ranges of the stress intensity factor. For the lower value range the formula reflects a relatively steep decrease of the crack growth rates (against the same values in air) along with decreasing the stress intensity factor range. A simple formula for the corrosion fatigue crack propagation life under cathodic potential has been derived for fillet welded joints in bending by integrating the corrosion fatigue kinetic characteristics. The new formula for the stress intensity factor range has been used for the bent joint. The predicted "S-Np" curves have been compared with experimental data, taken from literature, for two different values of both applied potential and the plate thickness. The predicted curves correspond approximately to lower bounds of the test results. The presented procedure can be applied to joints of higher strength steels (of the yield strength ay = 315 and 355 MPa) fatigued at any applied cathodic potential below -0.8 V under sea loading of (0.05+0.2 Hz) frequency at (0+0.2) stress ratios.
16
Content available remote Corrosion fatigue of GMA welded Al-Mg alloy
Czechowski M.
Advances in Materials Science
|
2004
|
Vol. 4, nr 1(5)
16-24
EN
This article presents the results of the low-cycle fatigue tests of AW-5059 Alustar alloy. Gas metallic welding in argon arc shield was used. The low-cycle fatigue tests were carried out in the air and 3.5% water solution NaCl, with stable amplitude of the stress value. The stresses were changed in the symmetric cycle (the stress ratio was R = -1) with constant strain rate of 5 mm/min and the frequencies oscillating between 0,08÷0,2 Hz. During the tests the following was observed: number of cycles until the specimen's destruction, upper and lower extreme values of force and strain for the selected cycles, duration time of the test and frequency. In case of the specimens exposed in 3,5% water solution NaCl the fatigue durability is lower than the durability of the specimens tested in the air. The article depicts the changes in the total strain amplitude epsilon[ac] [mm] depending on the number of cycles [N] obtained in the tests with sigma[a] = const and the low-cycle fatigue resistance for the welded Alustar alloy.
17
Corrosion fatigue crack rate in nodular cast iron
Mazur M.
Inżynieria Materiałowa
|
2003
|
R. XXIV, nr 6
688-689
EN
The fatigue corrosion cracking tests of nodular ferrite-pearlite cast iron in 3% NaCl water solution were performed. Corrosion cracks rate were calculated from Paris-Erdogan equation. Crack rate increments for standard tests was the smallest, but for partially immersed by aerated environment was the highest. The three stage of corrosion fatigue crack propagation were observed. In the last stage the corrosion crack propagation rate decreased due to the well known "glucing" process of the graphite particles that made difficult to washing them out the crack front, thus the resistance of nodular cast iron to fatigue corrosion increased. The cycling changes of "m" parameter once again confirmed the interaction of propagating crack with the randomly graphite particle distributed in ferrite-pearlite matrix.
PL
W pracy przedstawiono wyniki badań zmęczeniowych żeliwa sferoidalnego przeprowadzonych na powietrzu oraz w wodnych roztworach NaCl różniących się charakterem przepływu. Badania prędkości wzrostu pęknięć zmęczeniowych wykonano zgodnie z metodami mechaniki pękania wyznaczając prędkość pękania ze wzoru Parisa-Erdogana. Interpretacja graficzna wyników badań pozwoliła wyodrębnić kilka zakresów prędkości pękania odpowiadającym kolejnym etapom wzrostu pęknięć, a tym samym ocenić wpływ ośrodka korozyjnego na prędkość ich rozwoju. Stwierdzono także, że stała "m" ze wzoru Parisa-Erdogana podlega cyklicznym zmianom, będącym efektem wzajemnych oddziaływań cząstek grafitu z frontem pęknięcia.
18
Content available remote Hydrogen-enhanced stress corrosion cracking and corrosion fatigue of HSLA steels in sea-water
Ćwiek J.
Advances in Materials Science
|
2003
|
Vol. 3, nr 1(3)
5--17
EN
Hydrogen degradation of extra high strength weldable steels bas been evaluated under static and cyclic tensile loads in sea-water at room temperature. Two quenched and tempered steel grades and their submerged arc welded (SAW) and shielded metal arc welded (SMAW) joints were examined. Slow strain rate tests (SSRT) on cylindrical smooth specimens, in air and artificial sea-water were performed. Tests in sea-water were conducted under cathodic polarisation with constant current densities. Relative values of: fracture energy, time to failure, elongation, reduction in area and tensile strength were chosen as measures of hydrogen degradation. Low-cycle corrosion fatigue tests were performed on cylindrical smooth specimens. Sinusoidal wave form uniaxial tension loading under strain control was carried out. Fracture modes were investigated with the use of a scanning electron microscope (SEM). Polarisation curves in artificial sea-water for brie metals with the potentiostatic method were obtained. Additionally, polarisation curves for selected areas of welded joints were established with the use of a microcell and the potentiodynamic method. Hydrogen permeation through brie metal, heat affected zone (HAZ), and weld metal were measured by means of conventional Devanathan-Stachurski method. Hydrogen diffusivity and content of diffusible hydrogen were established. Observed decrease of relative values of degradation parameters with the increase of current density exhibits a certain minimum. The loss of plasticity was as high as 70-90% for brie metals and welded joints. Further increase of current density does not cause higher degradation. Significant reduction of a fatigue life time (40-50%) due to hydrogen absorption was also observed.
19
Content available remote Corrosion fatigue in power devices.
Gajewski M.
Zagadnienia Eksploatacji Maszyn
|
2002
|
Vol. 37, nr 2
43-52
EN
Corrosion resistance, to a large extent, decides about the life of fittings, pumps, pipelines and other devices in power and chemical industry. The effective fight against corrosion depends on full understanding of the phenomenon character as well as the factors, which cause its initiation and propagation. The paper presents the mechanism of corrosion fatigue resulting from iron anodic dissolution in galvanic cells. Investigations into a piping damaged fragment confirmed the nature of the mechanism. Numerous galvanic cells occuring on the internal surface of the pipeline originated due to the simultaneous action of changing mechanical loads and corrosive environment. The resultant iron anodic dissolution pits were the sites of stress concentration and micro-cracks nucleation. Micro-cracks enlargement proceeded due to the action of a galvanic cell, which was steel operating in the pit, with the anode located at the micro-crack front. Observations of the pipeline surface internal morphology and numerous pits as well as the microanalysis of corrosion products chemical composition confirmed the character of the process.
PL
W przemyśle energetycznym i chemicznym o trwałości armatury, pomp, systemów rurociągów i innych urządzeń decyduje w istotnym stopniu ich odporność na korozję. Skuteczna walka z korozją zależy od dokładności rozpoznania charakteru tego zjawiska oraz czynników powodujących jego inicjację i rozwój. W pracy przedstawiono mechanizm zmęczenia korozyjnego będącego skutkiem anodowego rozpuszczania żelaza w mikroogniwach galwanicznych i potwierdzono go badaniami zniszczonego fragmentu rurociągu. Do powstania licznych mikroogniw galwanicznych na powierzchni badanego rurociągu doszło wskutek jednoczesnego działania zmiennych obciążeń mechanicznych i środowiska korozyjnego. Powstające w rezultacie anodowego rozpuszczania żelaza-wżery, były miejscami koncentracji naprężeń oraz zarodkowania mikropęknięć. Powiększaniu się mikropęknięć sprzyjało oddziaływanie mikroogniwa galwanicznego, które nadal funkcjonowało w powstającej szczelinie, przy czym anoda usytuowana była na czole mikropęknięcia. Potwierdziły to obserwacje morfologii wewnętrznej powierzchni rurociągu i licznych szczelin oraz mikroanalizy składu chemicznego produktów korozji.
20
Wpływ laserowej obróbki na zmęczenie korozyjne stali węglowych i nierdzewnych.
Pokhmurska H., Mucha Z., Kalita W., Hoffman J., Kaminski O.
Inżynieria Materiałowa
|
2000
|
R. XXI, nr 6
397-399
PL
W pracy przedstawiono wyniki badań wpływu laserowego hartowania na wytrzymałość zmęczeniową oraz korozyjno-zmęczeniową stali węglowej i stopowej. Próbki o kształcie cylindrycznym o średnicy 5 mm i długości powierzchni roboczej 30 mm były wykonane ze stali ferrytyczno-perlitycznej 20, o wysokiej wytrzymałości 28X2MFBD i stali nierdzewnej martenzytycznej 20X13. Hartowanie próbek przeprowadzono przy pomocy lasera CO2 o działaniu ciągłym i maksymalnej mocy 2,5 kW. Próbki były obciążone przez czyste zginanie z rotacją o częstości 50 Hz. Przeprowadzono analizę wytrzymałości zmęczeniowej i korozyjno-zmęczeniowej na podstawie krzywych Wohlera. Wpływ laserowej obróbki na wytrzymałość zmęczeniową stali węglowej i stopowej jest odmienny. Dla stali węglowej graniczna wytrzymałość zmęczeniowa w powietrzu obniża się z 500 MPa do 300 MPa z powodu pojawiania się strukturalnych koncentratorów i praktycznie nie ma wpływu na korozyjno-zmęczeniowe charakterystyki.
EN
In the present paper we report the results of laser hardening influence on the corrosion fatigue of carbon and stainless steels. Cylindrical samples with the diameter of working part equal to 5 mm have been made from carbon pearlite-ferrite 20, high-strength 28X2MFBD and stainless martensite 20X13 steels. The process of hardening was carried out using CO2 2,5kW continuous wave laser. The type of loading was pure bending with rotation of 50 Hz frequency. Fatigue curves have been taken with simultaneous metallographic analysis of corrosion-fatigue crack initiation and propagation. Influence of laser treatment on fatigue behaviour of low carbon and stainless steels is different. For carbon steel laser treatment decreases the fatigue limit in the air from 500 MPa to 300 MPa due to structural concentrator appearance and practically doesn't influence the corrosion fatigue characteristics.
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