• Title, Summary, Keyword: austenite

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Effect of Retained and Reversed Austenite on the Damping Capacity in High Manganese Stainless Steel (고 Mn 스테인리스강의 감쇠능에 미치는 잔류 및 역변태 오스테나이트의 영향)

  • Kim, Y.H.;Lee, S.H.;Kim, S.G.;Kang, C.Y.
    • Korean Journal of Materials Research
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    • v.25 no.1
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    • pp.9-15
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    • 2015
  • The effect of retained and reversed austenite on the damping capacity in high manganese stainless steel with two phases of martensite and austenite was studied. The two phase structure of martensite and retained austenite was obtained by deformation for various degrees of deformation, and a two phase structure of martensite and reverse austenite was obtained by reverse annealing treatment for various temperatures after 70 % cold rolling. With the increase in the degree of deformation, the retained austenite and damping capacity rapidly decreased, with an increase in the reverse annealing temperature, the reversed austenite and damping capacity rapidly increased. With the volume fraction of the retained and reverse austenite, the damping capacity increased rapidly. At same volume of retained and reversed austenite, the damping capacity of the reversed austenite was higher than the retained austenite. Thus, the damping capacity was affected greatly by the reversed austenite.

Effect of Reversed Austenite on the Damping Capacity of Austenitic Stainless Steel (오스테나이트계 스테인리스강의 감쇠능에 미치는 역변태 오스테나이트의 영향)

  • Kim, Young-Hwa;Sung, Ji-Hyun;Kang, Chang-Yong
    • Journal of the Korea Society For Power System Engineering
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    • v.19 no.1
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    • pp.70-75
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    • 2015
  • The influence of reversed austenite on the damping capacity in austenitic stainless steel with two phase of martensite and reversed austenite was investigated. The two phases of deformation induced martensite and reversed austenite was obtained by an reverse annealing treatment at $500^{\circ}C{\sim}700^{\circ}C$ for various time after 70% cold rolling. With an increase of the reverse annealing treatment temperature and time, volume fraction of reversed austenite was rapidly increased. With an increase of volume fraction of reveresd austenite, damping capacity was rapidly increased. At same volume of reveresd austenite, damping capacity of reversed austenite obtained by reverse annealing treatment at $700^{\circ}C$ for various time was higher then reveresd austenite obtained by reverse annealing treatment at $500^{\circ}C{\sim}700^{\circ}C$ for 10min. Thus, the damping capacity was affected greatly by reversed austenite obtained by annealing treatment at $700^{\circ}C$ for various time.

Effect of Austenite on the Pitting Corrosion of 202 Stainless Steel with Two Phases of Austenite and Martensite (오스테나이트와 마르텐사이트 2상 조직을 갖는 202 스테인리스강의 공식에 미치는 오스테나이트의 영향)

  • Kim, Jong-Sig;Kim, Young-Hwa;Kim, Hee-Won;Koo, Jeong-Yeup;Sung, Ji-Hyun;Kang, Chang-Yong
    • Journal of the Korea Society For Power System Engineering
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    • v.20 no.1
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    • pp.36-41
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    • 2016
  • Effects of austenite on the pitting corrosion in 202 stainless steel with two phase of austenite and martensite were investigated through the electrochemical polarization test. Two phases structures of martensite and austenite were obtained by reversed annealing treatment at the range of $500^{\circ}C-700^{\circ}C$ for 10min. in 70% cold-rolled 202 stainless steel. Volume fraction of reversed austenite has increased rapidly with an increase of annealing temperature. Pitting corrosion has arisen mainly on martensite phase in 202 stainless steel with two phases of austenite and martensite. Pitting current density has decreased with an increase of volume fraction of austenite. Consequently, pitting corrosion at martensite has occurred largely with an increase of volume fraction of austenite. Pitting corrosion was affected by volume fraction of austenite.

Austenite Stability of Nanocrystalline FeMnNiC Alloy (나노결정 FeMnNiC합금의 오스테나이트 안정성)

  • Oh, Seung-Jin;Jeon, Junhyub;Shon, In-Jin;Lee, Seok-Jae
    • Journal of Korean Powder Metallurgy Institute
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    • v.26 no.5
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    • pp.389-394
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    • 2019
  • In the present study, we have investigated the effect of sintering process conditions on the stability of the austenite phase in the nanocrystalline Fe-5wt.%Mn-0.2wt.%C alloy. The stability and volume fraction of the austenite phase are the key factors that determine the mechanical properties of FeMnC alloys, because strain-induced austenite-martensite transformation occurs under the application of an external stress at room temperature. Nanocrystalline Fe-5wt.%Mn-0.2wt.%C samples are fabricated using the spark plasma sintering method. The stability of the austenite phase in the sintered samples is evaluated by X-ray diffraction analysis and hardness test. The volume fraction of austenite at room temperature increases as the sample is held for 10 min at the sintering temperature, because of carbon diffusion in austenite. Moreover, water quenching effectively prevents the formation of cementite during cooling, resulting in a higher volume fraction of austenite. Furthermore, it is found that the hardness is influenced by both the austenite carbon content and volume fraction.

A Study on the Retained Austenite and Tensile Properties of TRIP Type High Strength Steel Sheet with Cu (Cu 함유 TRIP형 고장력 강판의 잔류오스테나이트 및 인장특성에 관한 연구)

  • Kang, C.Y.;Kim, H.J.;Kim, H.G.;Sung, J.H.;Moon, W.J.
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.3
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    • pp.231-239
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    • 1999
  • Volume fraction and morphology of retained austenite, tensile properties of TRIP type high strength steel sheet with Fe-C-Si-Mn-Cu chemical composition have been investigated. The retained austenite of granular, bar and film type existing in specimen was obtained after intercritical annealing and austempering. The granular type retained austenite increased with increase of intercritical annealing and austempering temperature. With increase of intercritical annealing temperature, retained austenite and carbon contents increased. Maximum contents of retained austenite was obtained by austempering at $400^{\circ}C$. The maximum tensile strength was obtained by austempering at $450^{\circ}C$ and maximum elongation was obtained at $400^{\circ}C$. T.S${\times}$E.L value increased with increase of retained austenite contents due to the elongation strongly controlled by contents of retained austenite, but tensile strength was affected with various factors such as bainitic structure etc.

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Effect of Reverse Transformation Treatment on the Formation of Retained Austenite in 01.5%C-6%Mn Steels (0.15%C-6%Mn강의 잔류오스테나이트 생성에 미치는 역변태 열처리의 영향)

  • Hong, H.;Lee, O.Y.;Lee, K.B.
    • Journal of the Korean Society for Heat Treatment
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    • v.11 no.1
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    • pp.35-45
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    • 1998
  • The effects of alloying elements and the conditions of reverse transformation studied treatment on the formation of retained austenite in 0.15C-6%Mn-(Ti, Nb) steels has been studied. The addition of Ti and Nb to 0.15C-6%Mn steel shows no effect on the formation of retained austenite. In case of reverse transformation treatment at various temperatures, the shape of retained austenite was lath type, growing toward the longitudinal and thickness direction with increasing the heat treatment temperatures. The retained austenite formed by the reverse transformation treatment at higher temperature has a lot of stacking faults induced by the internal stress. The retained austenite was stabilized chemically by enrichment of C and Mn in the vicinity of a untransformed austenite and the chemical stability of retained austenite was decreased with increasing the heat treatment temperature and the holding time. It was effective to heat treat at $650^{\circ}C$ in order to obtain over 30vol.% of retained austenite, but more desirable to heat treat at $625^{\circ}C$ for a long time, considering the amount and quality of retained austenite.

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Tensile Properties of High Mn Austenitic Stainless Steel with Two Phases of Martensite and Austenite (마르텐사이트와 오스테나이트의 2상 조직을 갖는 고 Mn 오스테나이트계 스테인리스강의 인장성질)

  • Kim, Young-Hwa;Kang, Chang-Yong
    • Journal of Ocean Engineering and Technology
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    • v.27 no.4
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    • pp.9-13
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    • 2013
  • The tensile properties of high manganese austenitic stainless steel with the two phase structures of deformation-induced martensite and reversed austenite were studied. Reversed austenite with an ultra-fine grain size of less than $0.3{\mu}m$ was obtained by reversion treatment. The two phases structures of deformation-induced martensite and reversed austenite were obtained by an annealing treatment in the range of $500^{\circ}C-700^{\circ}C$ for various times in 70% cold- rolled high-manganese austenitic stainless steel. The volume fraction of the reversed austenite increased rapidly with increases in the annealing temperature and time. In the stainless steel with the two phases of austenite and martensite, the strength decreased rapidly, while the elongation increased slowly and then rapidly increased with an increase in the volume fraction of the reversed austenite. Therefore, the strength and elongation were strongly controlled by the volume fraction of reversed austenite. A good combination of high strength and elongation could be obtained by the mixed structure of reversed austenite and deformation-induced martensite.

Effects of Microstructure on Ductility of Medium Carbon Spring Steels (중탄소 스프링강의 연성에 미치는 미세조직의 영향)

  • Lee, Hyun-Kwuon;Lee, Sang-Woo
    • Journal of the Korean Society for Heat Treatment
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    • v.22 no.2
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    • pp.80-87
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    • 2009
  • Effects of retained austenite contents on ductility of medium carbon spring steels according to steel alloy compositions and heat treatment conditions were studied. Contents of retained austenite varied with steel compositions and heat treatment conditions, and some retained austenite were found to transform to martensite on stress. Reduction of area (RA) increased with contents of retained austenite, then saturated through its maximum, and subsequently decreased. Increase in RA with retained austenite contents could be due to crack blunting effect by retained austenite on stress, however, more contents of martensite transformed from retained austenite in its higher contents could cause decrease in RA.

A Study on the Melting Morphology of Graphite in Cast Iron

  • Lim, Chang-Hee;Ra, Hyung-Yong
    • Journal of Korea Foundry Society
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    • v.5 no.4
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    • pp.243-257
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    • 1985
  • Many authors have studied the solidification process of cast iron and the effect of grain boundaries in austenite shell on the growth of spheroidal graphite. But, the studies on the melting morphology of cast iron are rare and the effect of grain boundaries in austenite shell on the melting procedure of spheroidal graphite cast iron is unknown. Therefore, in this work, the melting procedure of cast iron and the role of grain boundaries in austenite shell on the melting of spheroidal graphite have been studied. The main results are summarized as follows. 1. In white cast iron containing silicon, melting initiates at the interface between austenite matrix and temper carbon which was decomposed from $Fe_3C$ during heating. 2. In gray cast iron, melting initiates at the boundary of eutectic cell where elements with low melting temperature are condensed. The dissolution of kish graphite is difficult. 3. In spheroidal graphite cast iron containing little phosphor, melting initiates at the outer region of austenite shell in which silicon is condensed. In this case, grain boundaries in austenite shell give little effect on the melting procedure of spheroidal graphite. 4. In spheroidal graphite cast iron containing phosphor above 0.3 wt%, its melting phenomena are changed with heating rate due to the existence of steadite. In this case, it can be concluded that liquid phase of steadite, which segregated on outer region of austenite shell, moves to spheroidal graphite-austenite interface along the grain boundaries in austenite shell.

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Effect of Prior Deformation and Cyclic Transformation on the Mechanical Properties in Fe-30 Ni-0.24C Alloy (Fe-30 Ni-0.24C합금에서 역변태 오스테나이트의 기계적 성질에 미치는 이전가공도 및 역변태 Cycle수의 영향)

  • Kim, H.S.;Lee, K.B.;Hong, S.K.
    • Journal of the Korean Society for Heat Treatment
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    • v.3 no.4
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    • pp.1-9
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    • 1990
  • In this study, the ausformed martensite cooled to $-196^{\circ}C$ with various deformation degrees in Fe-30%Ni-0.24%C alloy was transformed to reversed austenite at $500^{\circ}C$ by cyclic reverse martensitic transformation. The effects of prior deformation and the number of cyclic reverse transformation on the microstructure and the mechanical properities of reversed anstensite were investigated. Experimental results showed that the strength of reversed austenite was higher than that of original austenite. This is due to higher dislocation density and grain refining. The reversed austenite formed from ausformed martensite was highly strengthened by prior deformation. This strengthening effect of reversed austenite is attributed to higher dislocation density than grain fefining. The yield strength of reversed austenite below 30% prior deformation, but above 30% prior deformation the strength of reversed austenite is lower than that of deformed austenite. This is due to partly disappearance of strain hardening effect at higher deformation degree by reverse transformation. The strength of reversed austenite is increased with the number of cyclic transformation. Especially, it is principally strengthened by the first cyclic transformation and shows higher increase in yield strength than that of ultimate tensile strength.

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