FATIGUE CRACK GROWTH IN MARTENSITIC 2 1/4 CR-1MO STEEL AT ELEVATED TEMPERATURES. PDF Download

Author: C. A. Hippsley
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description

Author: O. P. Keifer
Publisher:
ISBN:
Category :
Languages : en
Pages : 114

View

Book Description
Environmental effects in elevated temperature fatigue have been extensively studied and reported in the literature for 2 1/4 Cr-1 Mo steel. The results of cycles to failure (lumped initiation and propagation life) verses strain range have shown drastic reductions in fatigue life with a dwell period at compressive strains in each loading cycle. This thesis has separately examined the crack initiation and propagation stages for several specimens tested in air at 538 deg C without dwell and a single specimen with a five minute compressive dwell. With dwell, the crack initiation stage was severely reduced (by a factor greater than eleven) relative to testing without dwell. The results clearly indicate that oxide cracking is a precursor to crack initiation in the substrate. It is concluded that the fatigue life of this alloy must be estimated based on the crack propagation characteristics alone, since crack initiation can be expected very clearly (i.e., first few cycles) for any practical environment. Originator supplied keywords include: Fatigue, oxide cracking, 2 1/4 Cr - Mo Steel.

Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 704

View

Book Description

Author: C. A. Hippsley
Publisher:
ISBN:
Category :
Languages : en
Pages : 46

View

Book Description
Micromechanisms of high-temperature crack growth in martensitic 2 1/4 Cr-1Mo steel have been studied in vacuum, under static loading at 500 C. Detailed metallographic and fractographic measurements have been combined with Scanning Auger Microscopy and crack growth resistance curves to characterize the micro-mechanisms of failure. At low Stress intensities, the mode of crack growth is high-temperature, brittle intergranular fracture (HTBIGF) and is controlled by the dynamic segregation of sulphur to crack-tip regions. Crack advance appears to occur by discrete jumps when a critical concentration of sulphur is achieved over the jump distance. Keyword: Great Britain.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
Environmental effects in elevated temperature fatigue have been extensively studied and reported in the literature for 2 1/4 Cr-1 Mo steel. The results of cycles to failure (lumped initiation and propagation life) verses strain range have shown drastic reductions in fatigue life with a dwell period at compressive strains in each loading cycle. This thesis has separately examined the crack initiation and propagation stages for several specimens tested in air at 538 deg C without dwell and a single specimen with a five minute compressive dwell. With dwell, the crack initiation stage was severely reduced (by a factor greater than eleven) relative to testing without dwell. The results clearly indicate that oxide cracking is a precursor to crack initiation in the substrate. It is concluded that the fatigue life of this alloy must be estimated based on the crack propagation characteristics alone, since crack initiation can be expected very clearly (i.e., first few cycles) for any practical environment. Originator supplied keywords include: Fatigue, oxide cracking, 2 1/4 Cr - Mo Steel.

Author: G. S. Sangdahl
Publisher: ASTM International
ISBN:
Category : Chromium-molybdenum steel
Languages : en
Pages : 482

View

Book Description

Author: Pierre G. Vining
Publisher:
ISBN:
Category :
Languages : en
Pages : 138

View

Book Description
The microstructural changes and fatigue crack growth rates induced by elevated temperature push-pull fatigue and creep fatigue tests in 2 1/4 Cr - 1 Mo steel have been examined using optical and electron microscopy techniques. The only microstructural change noted was the development of dislocation substructures in the proeutectoid ferrite. Creep fatigue tests with a single maximum strain hold period per cycle created a cellular substructure whose size was solely dependent on the carbide interparticle spacing. Temperature and strain range effects were noted on the dislocation densities in the maxtrix which were generally consistent with work reported in the literature. As there were no resolvable changes in the carbides in the ferrite, it was concluded that there must be some change in the microstructure on a finer scale, such as the early stages of M0-C-Mo cluster formation, which might explain the cyclic hardening/cyclic softening response of the alloy. The fatigue crack growth rate of the alloy was strongly dominated by the hold periods imposed during the loading cycle. A single 0.1 hr. hold period doubled the fatigue crack growth rate obtained for a continuously cycled test and two hold periods per loading cycle gave a four fold increase over the continuously cycled crack growth rate.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
The microstructural changes and fatigue crack growth rates induced by elevated temperature push-pull fatigue and creep fatigue tests in 2 1/4 Cr - 1 Mo steel have been examined using optical and electron microscopy techniques. The only microstructural change noted was the development of dislocation substructures in the proeutectoid ferrite. Creep fatigue tests with a single maximum strain hold period per cycle created a cellular substructure whose size was solely dependent on the carbide interparticle spacing. Temperature and strain range effects were noted on the dislocation densities in the maxtrix which were generally consistent with work reported in the literature. As there were no resolvable changes in the carbides in the ferrite, it was concluded that there must be some change in the microstructure on a finer scale, such as the early stages of M0-C-Mo cluster formation, which might explain the cyclic hardening/cyclic softening response of the alloy. The fatigue crack growth rate of the alloy was strongly dominated by the hold periods imposed during the loading cycle. A single 0.1 hr. hold period doubled the fatigue crack growth rate obtained for a continuously cycled test and two hold periods per loading cycle gave a four fold increase over the continuously cycled crack growth rate.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
The fatigue crack propagation of 2 1/4 Cr-1 Mo steel was examined in air over a wide range of experimental conditions. The fatigue crack growth rate was found to: generally increase monotonically with increasing temperature from 172/sup 0/ to 866/sup 0/K, except in the range where dynamic strain aging occurs, near 644/sup 0/K; increase with decreasing frequency at room temperatures above 783/sup 0/K - this frequency dependence was not observed below 783/sup 0/K; and increase with increases in mean stress. The results were evaluated, and a simple empirical model was developed to yield estimates of average and upper limit crack growth rates as a function of temperature, frequency, and effective stress intensity. However, the model is not applicable in the low region where threshold effects become important since insufficient data were available in that range.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
The influence of gaseous environment is examined on fatigue crack propagation behavior in steels. Specifically, a fully martensitic 300-M ultrahigh strength steel and a fully bainitic 2-1/4Cr-1Mo lower strength steel are investigated in environments of ambient temperature moist air and low pressure dehumidified hydrogen and argon gases over a wide range of growth rates from 10−8 to 10−2 mm/cycle, with particular emphasis given to behavior near the crack propagation threshold .delta.K0. It is found that two distinct growth rate regimes exist where hydrogen can markedly accelerate crack propagation rates compared to air, (1) at near-threshold levels below (5 x 10−6 mm/cycle) and (2) at higher growth rates, typically around 10−5 mm/cycle above a critical maximum stress intensity K/sub max//sup T/. Hydrogen-assisted crack propagation at higher growth rates is attributed to a hydrogen embrittlement mechanism, with K/sub max//sup T/ nominally equal to K/sub Iscc/ (the sustained load stress corrosion threshold) in high strength steels, and far below K/sub Iscc/ in the strain-rate sensitive lower strength steels. Hydrogen-assisted crack propagation at near-threshold levels is attributed to a new mechanism involving fretting-oxide-induced crack closure generated in moist (or oxygenated) environments. The absence of hydrogen embrittlement mechanisms at near-threshold levels is supported by tests showing that .delta.K0 values in dry gaseous argon are similar to .delta.K0 values in hydrogen. The potential ramifications of these results are examined in detail.