Fully pearlitic steel was wire-drawn up to a strain of 2.2. Torsion tests were performed using two types of specimens—one was an as-drawn specimen, and the other was aged at 423 K for 3.6 ks. A ...delamination crack propagated along the longitudinal direction of the wire in the aged specimen, whereas normal fracture was exhibited perpendicular to the longitudinal direction in the as-drawn specimen during torsion tests. Backscattered electron images indicated that the cementite lamellae beneath the delamination crack had vanished, whereas, in the as-drawn specimen, the cementite lamellae beneath the normal fracture surface had rotated until the fracture. Torsion tests with different strain rates indicated an inverse strain-rate dependence of the onset of the delamination, suggesting that the plastic deformability of ferrite and existence of the thermally activated process that controls the cementite dissolution indicate the onset of the delamination. In the present study, the effect of aging and deformability of ferrite on delamination is discussed, suggesting that the delamination crack propagates as a result of the local plastic instability on the scale of several microns.
In high carbon steel, TTT nose temperature rises and upper baninte becomes easy to be formed with quantity of Si addition. Generation of upper bainite is reduced by boron addition. In this study, the ...influence of boron addition on isothermal transformation behavior in Si-added high carbon steel was clarified. By boron addition, lamellar spacing and growth rate of pearlite doesn’t change, but the nucleation of pealite is reduced. But nucleation of pearlite is promoted when Fe23(C,B)6 precipitates. In the Si-added high carbon steel, upper bainite is often formed with the generated ferrite on prior austenite grain boundary. It is inferred that boron reduces ferrite generation in grain boundary which causes upper bainite formation. It is confirmed that effective existence state of boron is grain boundary segregation.
Hydrogen absorption behavior and microstructural change of carburized JIS SCr420 steels containing different amounts of retained austenite in rolling contact fatigue were investigated. The thermal ...desorption analysis confirmed hydrogen desorption at the second-peak between 423 and 623 K after rolling contact fatigue. The hydrogen concentration at the second-peak increased with number of cycles in the rolling contact. This increment was larger when using the steel with higher amount of retained austenite before the fatigue test. It was still large even when the amount of martensitic transformation from retained austenite under cyclic stress to introduce dislocation with trapping capacity was small. The activation energies of desorption for the second-peak hydrogen were calculated to be 50.6 kJ·mol−1 for the steel with 10.4% retained austenite and 55.8 kJ·mol−1 for the steel with 4.9% retained austenite. The activation energies of cathodically charged 0.8%C steels with 10.9% and 6.0% retained austenite, simulating carburized layer before the test, were 36.2 and 42.2 kJ·mol−1, respectively. This means that the activation energy of hydrogen desorption increased during rolling contact. The absorbed hydrogen during the rolling contact fatigue was likely trapped in more stable trapping sites related to the retained austenite which were formed under cyclic stress.
Bainite in steel is an industrially useful structure. However, the controlling factor of its transformation start point is not clearly known. In this study, we measured the bainite transformation ...start temperature (Bs) in Fe–9Ni–C alloys containing 0.3–0.9 mass%C via microstructure observation of the specimens held isothermally between 600 K and 798 K. Bs existed between 758 K and 773 K in all alloys used, and was independent of carbon content. Especially, Bs was higher than T0, at which fcc and bcc of the same composition have the same free energy, at more than 0.3 mass%C. This result was completely different from that of our previous study on low carbon Fe–9Ni–C alloys, in which Bs decreased with the increase in carbon and kept the certain driving force of partitionless transformation from fcc to bcc. Bs in middle–high carbon alloys corresponded to the temperature of the intersection point between T0′, at which the driving force is 400 J/mol, and the γ/(γ + θ) phase boundary. This suggests that the nucleation and growth of bainitic ferrite in austenite containing solute carbon higher than T0′ is promoted by the precipitation of cementite in austenite.
Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The ...resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with φ5.0 mm (ε=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging.
Matrix metalloproteinase-9 (MMP-9) plays a pivotal role in cancer invasion and metastasis. Recently, experimental study has shown that MMP-9 is also implicated in early carcinogenesis. We ...hypothesized that MMP-9 polymorphisms influence the predisposition to develop renal cell carcinoma (RCC). To test the hypothesis, we determined MMP-9 C−1562T and R279Q genotypes in Japanese RCC cases (
n=179) and controls (
n=211). Furthermore, we investigated the relationship between MMP-9 polymorphisms and clinicopathological features. The distribution of C−1562T and R279Q genotypes was not significantly associated with the risk of RCC (odds ratio OR=1.14, 95% confidence interval CI=0.73–1.77 for −1562 CT/TT genotypes versus CC genotype; OR=1.29, 95% CI=0.86–1.93 for 279 RQ/QQ genotypes versus RR genotype). However, the distribution of R279Q genotypes was significantly associated with the histological grade (
P<0.01). The present results suggest that MMP9 R279Q polymorphism has influence on the malignant potential of RCC.
Hydrogen absorption behavior and microstructural change of carburized JIS SCr420 steels containing different amounts of retained austenite in rolling contact fatigue were investigated. The thermal ...desorption analysis confirmed hydrogen desorption at the second-peak between 423 and 623 K after rolling contact fatigue. The hydrogen concentration at the second-peak increased with number of cycles in the rolling contact. This increment was larger when using the steel with higher amount of retained austenite before the fatigue test. It was still large even when the amount of martensitic transformation from retained austenite under cyclic stress to introduce dislocation with trapping capacity was small. The activation energies of desorption for the second-peak hydrogen were calculated to be 50.6 kJ·mol-1 for the steel with 10.4% retained austenite and 55.8 kJ·mol-1 for the steel with 4.9% retained austenite. The activation energies of cathodically charged 0.8%C steels with 10.9% and 6.0% retained austenite, simulating carburized layer before the test, were 36.2 and 42.2 kJ·mol-1, respectively. This means that the activation energy of hydrogen desorption increased during rolling contact. The absorbed hydrogen during the rolling contact fatigue was likely trapped in more stable trapping sites related to the retained austenite which were formed under cyclic stress.
Fully pearlitic steel was wire-drawn up to a strain of 2.2. Torsion tests were performed using two types of specimens—one was an as-drawn specimen, and the other was aged at 423 K for 3.6 ks. A ...delamination crack propagated along the longitudinal direction of the wire in the aged specimen, whereas normal fracture was exhibited perpendicular to the longitudinal direction in the as-drawn specimen during torsion tests. Backscattered electron images indicated that the cementite lamellae beneath the delamination crack had vanished, whereas, in the as-drawn specimen, the cementite lamellae beneath the normal fracture surface had rotated until the fracture. Torsion tests with different strain rates indicated an inverse strain-rate dependence of the onset of the delamination, suggesting that the plastic deformability of ferrite and existence of the thermally activated process that controls the cementite dissolution indicate the onset of the delamination. In the present study, the effect of aging and deformability of ferrite on delamination is discussed, suggesting that the delamination crack propagates as a result of the local plastic instability on the scale of several microns.
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