Abstract:A nuclear reactor pressure vessel steel was submitted to different quenching and tempering heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested and submitted to metallographic and fractographic survey. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical performance of the thermally embrittled microstructures. A well defined correlation was determined between the elastic-plastic fracture tou… Show more
“…In the case of sterile samples, the interior region of the fracture presented a more planar surface with a significant decline in microvoids content. Such microstructure is classified as mixed and brittle mode fracture . SRB‐inoculated samples precharged at 1 mA cm −2 demonstrated fractures similar to those obtained at lower current density.…”
Section: Resultssupporting
confidence: 51%
“…These features are characteristic of a high toughness material and typical for the fracture surfaces of 2205 DSS tested in air . Microscopic observations of above‐mentioned fractures revealed nucleation, growth, and coalescence of microvoids mechanism, wherein a complex grid of fine voids or void sheets around the big dimples can be observed (Figure a,b). This double type size distribution of microvoids (large, deep and very small microvoids depicted as 1 and 2 in Figure a, respectively) indicates the role of constituent austenite and ferrite phases in the cracking process of 2205 DSS.…”
The paper presents the results of a laboratory investigation of the microbiologically assisted hydrogen‐induced stress cracking (HISC) of 2,205 duplex stainless steel (DSS). The testing of susceptibility toward HISC was performed with two different methods. Precharged in sulfate‐reducing bacteria (SRB), inoculated medium samples were subjected to slow strain‐rate testing in artificial seawater. In situ constant load tests were performed directly in SRB‐inoculated medium under hydrogen charging at 70% of the ultimate tensile strength. Samples tested in the biotic (SRB) conditions showed a considerable loss of ductility as compared to those tested in sterile conditions. Quantitative characteristics of fracture surfaces indicated increased susceptibility to HISC of biotic samples, therefore, suggesting a role of SRB in promoting hydrogen damage of DSS.
“…In the case of sterile samples, the interior region of the fracture presented a more planar surface with a significant decline in microvoids content. Such microstructure is classified as mixed and brittle mode fracture . SRB‐inoculated samples precharged at 1 mA cm −2 demonstrated fractures similar to those obtained at lower current density.…”
Section: Resultssupporting
confidence: 51%
“…These features are characteristic of a high toughness material and typical for the fracture surfaces of 2205 DSS tested in air . Microscopic observations of above‐mentioned fractures revealed nucleation, growth, and coalescence of microvoids mechanism, wherein a complex grid of fine voids or void sheets around the big dimples can be observed (Figure a,b). This double type size distribution of microvoids (large, deep and very small microvoids depicted as 1 and 2 in Figure a, respectively) indicates the role of constituent austenite and ferrite phases in the cracking process of 2205 DSS.…”
The paper presents the results of a laboratory investigation of the microbiologically assisted hydrogen‐induced stress cracking (HISC) of 2,205 duplex stainless steel (DSS). The testing of susceptibility toward HISC was performed with two different methods. Precharged in sulfate‐reducing bacteria (SRB), inoculated medium samples were subjected to slow strain‐rate testing in artificial seawater. In situ constant load tests were performed directly in SRB‐inoculated medium under hydrogen charging at 70% of the ultimate tensile strength. Samples tested in the biotic (SRB) conditions showed a considerable loss of ductility as compared to those tested in sterile conditions. Quantitative characteristics of fracture surfaces indicated increased susceptibility to HISC of biotic samples, therefore, suggesting a role of SRB in promoting hydrogen damage of DSS.
“…Based on the microstructure analysis and plasticity behavior of materials, dimples can be of deep conical shape or quite shallow and this would affect the consolidation of microvoids by shear along slip bands. [61][62][63] For sample SFP due to the influence of heat treatment the size of dimples increases and at the end of the holes, small voids are visible. The generation of this morphology could be associated with small austenite grain and smooth austenite-ferrite grain boundary.…”
The present investigation studies the impact of post-weld heat treatment (PWHT) on the microstructure and mechanical characteristics of joints made by gas tungsten arc welding between duplex stainless steel and super-duplex stainless steel specimens. The PWHT process was considered at 1100 °C for 10 minutes followed by water quenching on UNS S32304 and UNS S32750 materials. Scanning electron microscopy, optical microscopy, X-ray diffractometry (XRD), and energy dispersive X-ray analyses have been applied in microstructure evolution, including recognizing local chemical contents and elemental distribution. To analyze the mechanical characteristics of samples, tensile and hardness tests were performed. It was shown that after applying PWHT, the morphology of the austenite varied becoming mostly intergranular/spheroidal in shape, accompanied by an improvement in the percentages of austenite. This investigation indicates the PWHT results in restoring an equal percentage of both phases. The phase percentages, based on both ASTM E1245 and ASTM E562, show a good agreement between the austenite and ferrite phases of weld materials. According to XRD, the phases are mainly ferrite and austenite with different lattice parameters with no evidence of unwanted intermetallic phases. It was concluded that the PWHT process plays a crucial role in the ductility of joint specimens due to the phase balance between austenite and ferrite.
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