scholarly journals Effect of Heat-Treatment Upon the Fatigue-Crack Growth Behavior of Alloy 718 Weldments—Part I: Macroscopic Behavior

1985 ◽  
Vol 107 (1) ◽  
pp. 34-40 ◽  
Author(s):  
L. A. James ◽  
W. J. Mills
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Crack Growth Behavior ◽  
Alloy 718 ◽  
Gas Tungsten Arc ◽  
Increasing Temperature ◽  
Crack Growth Rates

Gas-tungsten-arc weldments in Alloy 718 were studied in fatigue-crack growth tests conducted at five temperatures over the range 24–649°C. In general, crack growth rates increased with increasing temperature, and weldments given the “conventional” post-weld heat-treatment generally exhibited crack growth rates that were higher than for weldments given the “modified” (INEL) heat-treatment. Limited testing in the as-welded condition revealed crack growth rates significantly lower than observed for the heat-treated cases, and this was attributed to residual stresses. Three different heats of filler wire were utilized, and no heat-to-heat variations were noted.

Fatigue Crack Growth Behavior of Four Structural Alloys in High Temperature High Purity Oxygenated Water

1979 ◽  
Vol 101 (3) ◽  
pp. 191-198 ◽  
Author(s):  
D. A. Hale ◽  
C. W. Jewett ◽  
J. N. Kass
Keyword(s):  
Fatigue Crack ◽  
High Temperature ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Oxygenated Water ◽  
Crack Growth Rates

The fatigue crack growth behavior of four structural alloys was studied and the effects of high temperature (288°C), high purity oxygenated water, cycle frequency, and mean stress were evaluated. The results for carbon and low alloy steel show that while crack growth rates are affected by the water environment, modified ASME code procedures result in conservative predictions of growth. Often, higher crack growth rates are found for shallow cracks than for deep cracks. For stainless steels and Inconel the measured growth rates in water were similar to data obtained in air over the range of cycle frequencies studied.

Fatigue crack growth of 42CrMo4 and 41Cr4 steels under different heat treatment conditions

2018 ◽  
Vol 9 (3) ◽  
pp. 326-336 ◽  
Author(s):  
Grzegorz Lesiuk ◽  
Monika Maria Duda ◽  
José Correia ◽  
Abilio M.P. de Jesus ◽  
Rui Calçada
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Microstructural Properties ◽  
Content Type ◽  
Paris Law ◽  
Crack Growth Rates

Purpose For nowadays construction purposes, it is necessary to define the life cycle of elements with defects. As steels 42CrMo4 and 41Cr4 are typical materials used for elements working under fatigue loading conditions, it is worth to know how they will behave after different heat treatment. Additionally, typical mechanical properties of material (hardness, tensile strength, etc.) are not defining material’s fatigue resistance. Therefore, it is worth to compare, except mechanical properties, microstructure of the samples after heat treatment as well. The paper aims to discuss these issues. Design/methodology/approach Samples of normalized 42CrMo4 (and 41Cr4) steel were heat treated under three different conditions. All heat treatments were designed in order to change microstructural properties of the material. Fatigue tests were carried out according to ASTM E647-15 standard using compact tension specimens. Later on, based on obtained results, coefficients C and m of Paris’ Law for all specimens were estimated. Similar procedure was performed for 41Cr4 steel after quenching and tempering in different temperatures. Findings The influence of heat treatment on the fatigue crack growth rates (42CrMo4, 41Cr4 steel) has been confirmed. The higher fatigue crack growth rates were observed for lower tempering temperatures. Originality/value This study is associated with influence of microstructural properties of the material on its’ fatigue fracture. The kinetic fatigue fracture diagrams have been constructed. For each type of material (and its heat treatment), the Paris law constants were determined.

scholarly journals Measuring Fatigue Crack Growth Behavior of Ferritic Steels Near Threshold in High Pressure Hydrogen Gas

2020 ◽  
Author(s):  
Joseph Ronevich ◽  
Chris San Marchi ◽  
Kevin A. Nibur ◽  
Paolo Bortot ◽  
Gianluca Bassanini ◽  
...  
Keyword(s):  
High Pressure ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Pressure Vessels ◽  
Hydrogen Gas ◽  
Crack Growth Behavior ◽  
Crack Growth Rates ◽  
Pressure Hydrogen

Abstract Following the ASME codes, the design of pipelines and pressure vessels for transportation or storage of high-pressure hydrogen gas requires measurements of fatigue crack growth rates at design pressure. However, performing tests in high pressure hydrogen gas can be very costly as only a few laboratories have the unique capabilities. Recently, Code Case 2938 was accepted in ASME Boiler and Pressure Vessel Code (BPVC) VIII-3 allowing for design curves to be used in lieu of performing fatigue crack growth rate (da/dN vs. ΔK) and fracture threshold (KIH) testing in hydrogen gas. The design curves were based on data generated at 100 MPa H2 on SA-372 and SA-723 grade steels; however, the data used to generate the design curves are limited to measurements of ΔK values greater than 6 MPa m1/2. The design curves can be extrapolated to lower ΔK (< 6 MPa m1/2), but the threshold stress intensity factor (ΔKth) has not been measured in hydrogen gas. In this work, decreasing ΔK tests were performed at select hydrogen pressures to explore threshold (ΔKth) for ferritic-based structural steels (e.g. pipelines and pressure vessels). The results were compared to decreasing ΔK tests in air, showing that the fatigue crack growth rates in hydrogen gas appear to yield similar or even slightly lower da/dN values compared to the curves in air at low ΔK values when tests were performed at stress ratios of 0.5 and 0.7. Correction for crack closure was implemented, which resulted in better agreement with the design curves and provide an upper bound throughout the entire ΔK range, even as the crack growth rates approach ΔKth. This work gives further evidence of the utility of the design curves described in Code Case 2938 of the ASME BPVC VIII-3 for construction of high pressure hydrogen vessels.

scholarly journals Effect of Heat-Treatment Upon the Fatigue-Crack Growth Behavior of Alloy 718 Weldments—Part II: Microscopic Behavior

1985 ◽  
Vol 107 (1) ◽  
pp. 41-47 ◽  
Author(s):  
W. J. Mills ◽  
L. A. James
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Alloy 718 ◽  
Fatigue Crack Growth Behavior ◽  
Heat Treated

The microstructural features that influenced the fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination revealed that operative fatigue mechanisms were dependent on microstructure, temperature and stress intensity factor. All specimens exhibited three basic fracture surface morphologies at temperatures up to 538°C: crystallographic faceting at low stress intensity range (ΔK) levels, striation formation at intermediate values, and dimples coupled with striations in the highest ΔK regime. At 649°C, extensive amounts of intergranular cracking were observed. Laves and δ particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused an overall acceleration in crack growth rates at intermediate and high ΔK levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material were attributed to compressive residual stresses introduced by the welding process.

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