• Title/Summary/Keyword: Multiple tempering

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Effect of Multiple Tempering on Microstructure and Mechanical Properties of AISI 4340 Steel (반복 템퍼링이 AISI 4340 강의 미세조직과 기계적 특성에 미치는 영향)

  • Jungbin Park;Junhyub Jeon;Juheon Lee;Seung Bae Son;Seok-Jae Lee;Jae-Gil Jung
    • Journal of the Korean Society for Heat Treatment
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    • v.36 no.1
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    • pp.7-14
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    • 2023
  • We investigated the effect of multiple tempering on the microstructure and mechanical properties of AISI 4340 steel. The austenitized and quenched AISI 4340 steels were tempered at 550, 600, and 650℃ for 1, 2, and 4 h by single-tempering (ST). The multiple tempering was conducted for 4 h by double-tempering (DT, 2 h + 2 h), and quadruple-tempering (QT, 1 h + 1 h + 1 h + 1 h). As tempering temperature increases, yield strength and ultimate tensile strength decrease and elongation increases due to recovery and recrystallization of martensite and coarsening of carbides. At 550℃, as the number of tempering cycles increases, the yield strength and tensile strength decrease at the expense of fracture elongation. At 600 and 650℃, the yield strength and tensile strength increase with increasing the number of tempering cycles while fracture elongation maintains similar values. The multiple tempering at the same tempering time of 4 h improves the modulus of toughness at all tempering temperatures, which is presumed to be due to the change in carbide precipitation behavior by multiple tempering.

Effect of Tempering Treatment on Mechanical Properties of Ausformed Martensite in Fe-30% Ni-0.35%C Alloy (Fe-30%Ni-0.35%C 합금에서 Ausformed Martensite의 기계적 성질에 미치는 Tempering처리의 영향)

  • Lee, E.K.;Lee, K.B.;Kim, H.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.7 no.1
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    • pp.44-52
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    • 1994
  • In order to investigate the effect of tempring treatment on the mechanical properties of ausformed martensite in Fe-30%Ni-0.35%C alloy, the hardness, yield strength and elongation were examined by tensile test. 1. The strength of deformed austenite in Fe-30%Ni-0.35%C alloy was increased due to the work hardening induced from the dislocation density increased during deformation. The strength of ausformed martensite was increased because of defects inherited from deformed austenite by martensitic transformation. 2. The ductility of ausformed martensite was shown a nearly constant values independent of deformation degrees because of the interaction of multiple factors such as increased retained austenite, formation of void and decrement of twin in ausformed martensite. 3. The strength of ausformed martensite by tempering treatment was shown a little decrement up to $340^{\circ}C$, especially showed remarkable softening resistance in higher deformation degrees. 4. Virgin martensite and ausformed martensite were shown a maximum yield strength by clustering in tempering at $100^{\circ}C$ and above $100^{\circ}C$, yield strength was very small decreased due to the decrement of solute carbon by the destruction of clustering. 5. The decomposition of retained austenite was not shown up to $450^{\circ}C$ in ausformed martensite with tempering treatment, and the matrix was rapidly softening because of the decomposition of martensite and the formation of reversed austenite with tempering above $400^{\circ}C$.

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The Influence of Stress Relieving on Microstructures and Mechanical Properties of Weld Metal in 60kg/mm2 Quenched and Tempered High Strength Steel (응력제거 열처리가 60kg/mm2급 조질 고장력강의 용접부 미세조직과 기계적 특성에 미치는 영향)

  • Kim, O.S.;Chung, I.S.;Park, K.C.
    • Journal of the Korean Society for Heat Treatment
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    • v.6 no.3
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    • pp.144-151
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    • 1993
  • For the purpose of studying the influence of stress relieving on microstructures and mechanical properties of weld metal, manual arc welding, onepole and twopole submerged arc welding were accomplished on $60kg/mm^2$ quenched and tempered high strength steel. After stress relieving, a lot of carbides were precipitated, developed and subsequently coarsened at the grain boundaries and within matrix due tn multiple tempering effect in manual arc welding, resulting in deterioated toughness. Meanwhile pearlite and cementite films were spheroidized and shortened in submerged arc welding, resulting in improved considerable toughness. It was observed that main effect of stress relieving was to reduce solut supersaturation by nucleation and growth of carbide precipitates, and stress relieving led to some reduction in the yield and tensile strenath but did not significantly affect elongation.

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Roles of YehZ, a Putative Osmoprotectant Transporter, in Tempering Growth of Salmonella enterica serovar Typhimurium

  • Kim, Seul I;Ryu, Sangryeol;Yoon, Hyunjin
    • Journal of Microbiology and Biotechnology
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    • v.23 no.11
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    • pp.1560-1568
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    • 2013
  • Salmonella, a main cause of foodborne diseases, encounters a variety of environmental stresses and overcomes the stresses by multiple resistance strategies. One of the general responses to hyperosmotic stress is to import or produce compatible solutes so that cells maintain fluid balance and protect proteins and lipids from denaturation. The ProP and ProU systems are the main transport systems for compatible solutes. The OsmU system, recently identified as a third osmoprotectant transport system, debilitates excessive growth as well by reducing production of trehalose. We studied a fourth putative osmoprotectant transport system, YehZYXW, with high sequence similarity with the OsmU system. A Salmonella strain lacking YehZ, a predicted substrate-binding protein, did not suffer from hyperosmolarity but rather grew more rapidly than the wild type regardless of glycine betaine, an osmoprotectant, suggesting that the YehZYXW system controls bacterial growth irrespective of transporting glycine betaine. However, the growth advantage of ${\Delta}yehZ$ was not attributable to an increase in OtsBA-mediated trehalose production, which is responsible for the outcompetition of the ${\Delta}osmU$ strain. Overexpressed YehZ in trans was capable of deaccelerating bacterial growth vice versa, supporting a role of YehZ in dampening growth. The expression of yehZ was increased in response to nutrient starvation, acidic pH, and the presence of glycine betaine under hyperosmotic stress. Identifying substrates for YehZ will help decipher the role of the YehZYXW system in regulating bacterial growth in response to environmental cues.