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.
The intrinsic mechanism of the thermotolerance of Kluyveromyces marxianus was investigated by comparison of its physiological and metabolic properties at high and low temperatures. After glucose ...consumption, the conversion of ethanol to acetic acid became gradually prominent only at a high temperature (45°C) and eventually caused a decline in viability, which was prevented by exogenous glutathione. Distinct levels of reactive oxygen species (ROS), glutathione, and NADPH suggest a greater accumulation of ROS and enhanced ROS-scavenging activity at a high temperature. Fusion and fission forms of mitochondria were dominantly observed at 30°C and 45°C, respectively. Consistent results were obtained by temperature upshift experiments, including transcriptomic and enzymatic analyses, suggesting a change of metabolic flow from glycolysis to the pentose phosphate pathway. The results of this study suggest that K. marxianus survives at a high temperature by scavenging ROS via metabolic change for a period until a critical concentration of acetate is reached.
Kluyveromyces marxianus, a thermotolerant yeast, can grow well at temperatures over 45°C, unlike Kluyveromyces lactis, which belongs to the same genus, or Saccharomyces cerevisiae, which is a closely related yeast. K. marxianus may thus bear an intrinsic mechanism to survive at high temperatures. This study revealed the thermotolerant mechanism of the yeast, including ROS scavenging with NADPH, which is generated by changes in metabolic flow.
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.
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.
Work hardening of pearlite and bainite during drawing of high-carbon steel wires was studied by using stress-strain curves of drawn wires and making a detailed observation of their microstructure. ...The study revealed the following relationship between flow stress and strain in high-carbon steel wires. Flow stress σ is represented by a weighted average of the strengths of ferrite and cementite. The amount of work hardening Δσ is represented by an equation corresponding to exp(Bε) where B is a constant that depends on the initial microstructure of the steel wire and ε is the strain. When the initial microstructure of steel wire is made up entirely of a pearlite lamellar structure, the value of B is 0.5. When the initial microstructure contains some bainite, the value of B is lower than 0.5. Finally the flow stress was formulated as a function of carbon content, supercooling degree, and ε. The calculated maximum flow stress showed good correlation with the measured flow stress of 0.8 % C and 0.2%Cr-0.92%C steel wires during drawing.
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.
Fatigue Strength of an Ultra-low Carbon Steel GOTOH, Shoji; NISHIDA, Seiki; USHIODA, Kohsaku ...
Journal of the Society of Materials Engineering for Resources of Japan,
1996/08/31, Letnik:
9, Številka:
1
Journal Article
Odprti dostop
In order to study the effects of surface pickling in acid solution and test atmosphere on the fatigue strength of an ultra-low carbon steel (Interstitial free steel), the reversed bending fatigue ...tests were carried out under a bending stress range of 140-340MPa in air and Ar atmospheres. The results obtained were as follows. (1) The fatigue life for the test in air strongly depended on the time of pickling in the acid solution. The life increased as the pickling time increased, however it did not depend on the pickling time for a time span of less than 10minute. The fatigue life for a10minute pickling time increased with decrease in bending stress and a fatigue threshold existed at around120MPa. (2) The fatigue fracture surface showed that thecrack propagation process is dominated bx the formation of ductile fatigue striations and that the crack growth mechanism is a mixed mode of transgranular and intergranular. (3) However, the crack growth process was mostly intergranular in surface region and gradually changed to transgranular in the interior region. (4) The tendency of intergranular in the surface region was more distinguished in the longer pickling time and/or in air atmosphere. (5) The micromechanism of intergranular was believed to be related to a combination of hydrogen atoms dissolved during the pickling and, oxygen atoms penetrating from the test atmosphere at the crack front in the grain boundary region.
Outline of trend in development of steel bar and wire rod products is guided. There is a certain tendency towards better function or higher strength of steel products, fewer manufacturing process ...from customers' needs with increasing importance of global environment preservation. To satisfy these requirements, Nippon Steel has been keeping on supplying new products of high performance. Authors introduce several examples of developed bars and wire rods of special steel, high carbon steel wires and the latest nano-level materials characterization techniques which support microstructure control of these products.
The optimum patenting conditions for hypereutectoid steel to obtain a high drawability and a high work hardening rate were studied by metallographic examinations and laboratory drawing. Based on the ...present results, higher strength steel wire with small diameter has been manufactured on a production basis. 1) Provided that an appropriate cooling rate corresponding to carbon content is secured, the precipitation of thick proeutectoid cementite can be prevented. 2) In the practical patenting temperature range, the cementite plate thickness as well as the pearlite lamellar spacing decreases as the carbon content increases. 3) The work hardening rate during drawing and the delamination resistance are enhanced through elimination of the upper bainite in pearlite. 4) The maximum strength of 0.04 mm wire manufactured from 0.96%C-0.2%Si-0.3%Mn-0.2%Cr steel without delamination occurrence has reached to as high as 5.70 GPa.
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