Cold-drawn pearlitic steel wires exhibit the highest strength amongst steel products for commercially use. The microstructure and the mechanical properties of wires are influenced by the drawing and ...post-drawing aging process. The transition of lamellar structure, e.g. cementite fragmentation, dissolution and re-precipitation, ferrite refinement, by drawing and recovery and recrystallisation by aging are summarised. In addition, the corresponding changes in mechanical properties, e.g. yield strength, delamination, hydrogen embrittlement and fatigue are summarised.
Martensitic steels of Fe-0.1%C-2%Mn-1.6%Mo and Fe-0.1%C-2%Mn-0.2%V alloys were subjected to tempering at 873 K to investigate the hydrogen trapping of Mo and V carbides. We analyzed the alloy ...carbides in detail via atomic-resolution scanning transmission electron microscopy and atom probe tomography, and evaluated hydrogen trapping energy via ab initio calculations. The hydrogen content of the Mo-added steel tempered for 1.8 ks increased from that of the quenched Mo-added steel, and the hydrogen content monotonically decreased as the tempering time increased. The hydrogen content of the V-added steels increased during tempering up to 7.2 ks and then remained almost constant. A plate-shaped B1-type Mo carbide with a chemical composition of MoC0.50 precipitated in the Mo-added steel tempered for 3.6 ks. Needle-shaped HCP Mo2C precipitated and the B1-type Mo carbide decreased in the Mo-added steel tempered for 14.4 ks. A plate-shaped B1-type V carbide with a chemical composition of VC0.75 precipitated in the V-added steel tempered for 14.4 ks. We found a positive correlation between the hydrogen content and the product of the interface area and the carbon vacancy fraction of the B1-type alloy carbide. The hydrogen trapping energy of the carbon vacancy at the interface between BCC-Fe and the B1-type Mo carbide was higher than that of the interstitial sites in BCC-Fe. These results suggest that the main trapping site in the tempered Mo-added steel was the carbon vacancy at the interface of B1-type MoC0.50, not HCP Mo2C.
To investigate the hydrogen trapping effect of the combined addition of V to Mo-added steel, 0.1C-2Mn-1.6Mo mass% steel (Steel A) and 0.1C-2Mn-1.6Mo-0.2V mass% steel (Steel B) were prepared, ...quenched, and tempered at 873 K. The hydrogen trapping effect was investigated by thermal desorption hydrogen analysis of hydrogen-charged specimens, and Steel B showed a higher hydrogen trapping capacity than Steel A. According to thermodynamic equilibrium calculations, hydrogen trapping site of Steel A and B after tempering were predicted as M2C carbides. However, according to TEM observation of these specimens, not only coarse M2C but fine MC carbides precipitated in Steel A, and only fine MC precipitated in Steel B. Chemical composition of these precipitates were investigated by the three-dimensional atom probe analysis. MC of both Steel A and B show a composition close to MC0.5, in which Mo is the primary element in metal sites. It was found that the carbon-site vacancy (C vacancy) ratio of MoC0.5 in the present work is higher than that of V4C3 (VC0.75). The hydrogen trapping capacity showed a good correlation with the product of the area of Fe–MC interface and the C vacancy ratio in MC. The reason of the higher hydrogen trapping capacity of Steel B than that of Steel A is considered as below. 1) The combined addition of V to Mo assisted the precipitation of MC instead of coarse M2C. 2) C vacancies in MC were increased by the partitioning of Mo into MC, and the vacancies acted as hydrogen trapping sites.
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.
To investigate the effect of the combined addition of V to Mo-added steel on the hydrogen trapping behavior, 0.1C-2Mn-1.6Mo mass% steel (Steel A) and 0.1C-2Mn-1.6Mo-0.2V mass% steel (Steel B) were ...prepared, quenched, and tempered at 873 K for 0.5 to 10 hours. The thermal desorption analysis of hydrogen-charged specimens confirmed that Steel B showed a higher hydrogen trapping capacity than Steel A. According to thermodynamic equilibrium calculations, it was predicted that only M2C precipitated in Steel A and B after tempering at 873 K. However, according to TEM observation of specimens tempered for 4 hours, coarse M2C and fine MC precipitated in Steel A, whereas only fine MC precipitated in Steel B. Based on the three-dimensional atom probe analysis, MC of both Steel A and B show a composition close to MC0.5, in which Mo is the primary element in metal sites. It was found that the carbon-site vacancy (C vacancy) ratio of MC in the present work is higher than that of V4C3 (VC0.75). The hydrogen trapping capacity showed a good correlation with the product of the area of interface of MC and the C vacancy ratio in MC. The reason of the higher hydrogen trapping capacity of Steel B than that of Steel A is considered to be below; 1) The combined addition of V suppressed the precipitation of M2C and increased the amount of MC. 2) C vacancies in MC which act as hydrogen trapping sites increased by the partitioning of Mo into MC.
Martensitic steels of Fe-0.1%C-2%Mn-1.6%Mo alloy and Fe-0.1%C-2%Mn-0.2%V alloy were subjected to tempering at 873 K to investigate hydrogen trapping of Mo carbides and V carbides. We carried out the ...detail analysis of the alloy carbides by atomic-resolution scanning transmission electron microscopy and atom probe tomography, and the evaluation of hydrogen trapping energy by ab initio calculation. The hydrogen content of the Mo added steel tempered for 1.8 ks increases from that of the quenched Mo added steel and the hydrogen content monotonically decreases as the tempering time increases. The hydrogen content of the V added steels increases during the tempering to 7.2 ks and then keeps almost constant. Plate-shaped B1-type Mo carbide with a chemical composition of MoC0.50 is precipitated in the Mo added steel tempered for 3.6 ks. Needle-shaped HCP Mo2C is precipitated and the B1-type Mo carbide decreases in the Mo added steel tempered for 14.4 ks. Plate-shaped B1-type V carbides with a chemical composition of VC0.75 is precipitated in the V added steel tempered for 14.4 ks. We found the positive correlation between the hydrogen content and the product of the interface area and the carbon vacancy fraction of B1-type alloy carbide. The hydrogen trapping energy of the carbon vacancy at the interface between BCC-Fe and B1-type Mo carbide is higher than that of the interstitial sites in BCC-Fe. These results suggest that the main trapping site in the tempered Mo added steel is the carbon vacancy at the interface of B1-type MoC0.50, not HCP Mo2C.
Abnormal hepatic insulin signaling is a cause or consequence of hepatic steatosis. DPP-4 inhibitors might be protective against fatty liver. We previously reported that the systemic inhibition of ...insulin receptor (IR) and IGF-1 receptor (IGF1R) by the administration of OSI-906 (linsitinib), a dual IR/IGF1R inhibitor, induced glucose intolerance, hepatic steatosis, and lipoatrophy in mice. In the present study, we investigated the effects of a DPP-4 inhibitor, linagliptin, on hepatic steatosis in OSI-906-treated mice. Unlike high-fat diet-induced hepatic steatosis, OSI-906-induced hepatic steatosis is not characterized by elevations in inflammatory responses or oxidative stress levels. Linagliptin improved OSI-906-induced hepatic steatosis via an insulin-signaling-independent pathway, without altering glucose levels, free fatty acid levels, gluconeogenic gene expressions in the liver, or visceral fat atrophy. Hepatic quantitative proteomic and phosphoproteomic analyses revealed that perilipin-2 (PLIN2), major urinary protein 20 (MUP20), cytochrome P450 2b10 (CYP2B10), and nicotinamide N-methyltransferase (NNMT) are possibly involved in the process of the amelioration of hepatic steatosis by linagliptin. Thus, linagliptin improved hepatic steatosis induced by IR and IGF1R inhibition via a previously unknown mechanism that did not involve gluconeogenesis, lipogenesis, or inflammation, suggesting the non-canonical actions of DPP-4 inhibitors in the treatment of hepatic steatosis under insulin-resistant conditions.
Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. Many studies have been conducted on the mechanism of hydrogen embrittlement. Because the elucidation of ...the state of hydrogen is important to understand the mechanism, the states of hydrogen in the steels investigated were controlled. In the present study, 0.35 mass% C and 0.8 mass% C steels annealed in the hydrogen atmosphere followed by quenching from the austenite region together with drawn pearlitic steel of 0.8 mass% C were used to analyze the state of the hydrogen contributing to the emission peak, in particular, at about 300°C in the Thermal Desorption Analysis (TDA) curve. The peak at 300°C was significant for quenched 0.8 mass% C steel with low Ms temperature; however, the peak decreased with aging at room temperature. However, in 0.35 mass% C steel with high Ms temperature, the peak at 300°C was no longer observed. Moreover, in the hydrogen charged as drawn 0.8 mass% pearlitic steel, the peak at 300°C did not change with aging at room temperature because of no significant carbon in solid solution, while the peak at 100°C decreased with the increase in aging time. Taking into account the competitive phenomenon of hydrogen trapping at the dislocation core and C segregation to dislocations during room temperature aging or during quenching from Ms temperature, it was concluded that the hydrogen peak at about 300°C is hydrogen trapped in the dislocation core, while the other hydrogen peak at 100°C is attributed to the hydrogen trapped by the stress field generated by dislocation.
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