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Development of a method for corrosion fatigue life prediction of structurally loaded bearing steels
2001 (English)In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 57, no 5, 404-412 p.Article in journal (Refereed) Published
Abstract [en]

In this study a simplified method to predict corrosion fatigue properties for the Cr-alloyed bearing steel 100CrMnMo8 is proposed. With this method corrosion pits are assumed to act as defects, which could initiate fatigue cracks. A linear elastic fracture mechanics (LEFM) model was used to evaluate the critical corrosion pit size when mechanical fatigue crack propagation occurred. The unknown parameters in the prediction model were corrosion pit growth rate and the threshold stress intensity factor (DeltaK(th)) for fatigue crack growth. In this study corrosion pit growth rate was determined for 100CrMnMo8 in a chloride-containing water solution by aid of a statistical method. Corrosion pit growth rate was found to be approximately proportional to the square root of time. The time dependence of corrosion pit growth Zed also to the conclusion that characterization of corrosion fatigue strength must be made with respect to both exposure time in a corrosive environment and the number of cycles to a runout level. DeltaK(th) fatigue crack growth was estimated from interrupted rotating bending fatigue tests in the corrosive environment in question. Since only the corrosion pit growth rate and DeltaK(th), are needed as input in the proposed corrosion fatigue prediction model, much effort can be saved since this can reduce the amount of fatigue testing. Corrosion pit growth rate can be determined on unloaded test coupons In the desired environment. Hence, for materials selection, exposure tests followed by a corrosion pit size analysis can indicate the corrosion fatigue performance in a given environment.

Place, publisher, year, edition, pages
2001. Vol. 57, no 5, 404-412 p.
Keyword [en]
corrosion fatigue, life prediction, localized corrosion, steel
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24408ISI: 000176356300003OAI: oai:DiVA.org:kth-24408DiVA: diva2:349518
Note
QC 20100907Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Fatigue strength of engineering materials: the influence of environment and porosity
Open this publication in new window or tab >>Fatigue strength of engineering materials: the influence of environment and porosity
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The objective of this work was to use LEFM in order to assess the detrimental influence of surrounding chloride-containing environments for stainless steels, hardened steel as well as for a cast aluminium alloy. An additional aim was also to use LEFM to assess the influence of porosity on the fatigue properties for different commercial cast aluminium alloys and manufacturing methods. The environmental influence on fatigue performance was mainly evaluated from fatigue crack growth measurements using compact tension (CT) specimens. In addition, fatigue performance in the high cycle regime was studied using spot welded specimens and smooth specimens.

Corrosion fatigue tests for stainless steels were performed in different chloride-containing aqueous solutions and compared to the behaviour in air. Variables, which have been investigated, included temperature, redox potential and fatigue test frequency. The environmental influence on fatigue performance has also been compared to localised corrosion properties. Fatigue crack propagation rates were found to be higher in 3% NaCl than in air for all stainless steels investigated. The highest alloyed austenitic steel, 654SMO, showed the least influence of the environment. For duplex stainless steels the environment enhanced fatigue crack propagation rate to a higher degree than for austenitic stainless steels. This is explained by a material-dependent corrosion fatigue mechanism.

In the high cycle regime, fatigue properties for spot welded stainless steels specimens were found to be decreased between 30%-40% due to the presence of 3% NaCl. For the hardened steel 100CrMnMo8 a fracture mechanics approach was employed for prediction of corrosion fatigue properties. In this model corrosion pit growth rate and the threshold stress intensity factor for fatigue crack propagation are needed as input parameters.

For the high pressure die cast aluminium alloy the environmental influence of fatigue initiation through pre-exposure of smooth specimens was studied. Depending on environment used for pre-exposure, fatigue strength was found to be reduced by up to 50 % compared to the fatigue strength in air. Fatigue strength reduction was clearly associated to corrosion pits in the aluminium material. A fracture mechanics model was further successfully used to predict the environmental influence.

The influence of porosity on the fatigue strength for the cast aluminium alloys tested has been described by a Kitagawa diagram. In design, the Kitagawa diagram can be used to predict the largest allowable pore size if the load situation in the component is known. The size of the porosity could either be evaluated directly from x-ray images or from metallographic prepared cross-sections using a method of extreme value analysis

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 29 p.
Series
Trita-IIP, ISSN 1650-1888 ; 06:09
Keyword
Stainless steel, cast aluminium, hardened steels, fatigue, corrosion, crack propagation, spot weld, porosity
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4195 (URN)
Public defence
2006-12-08, Brinellsalen M311, KTH, Brinellvägen 68, Stockhollm, 10:00
Opponent
Supervisors
Note
QC 20100907Available from: 2006-11-29 Created: 2006-11-29 Last updated: 2010-09-07Bibliographically approved

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