• Title/Summary/Keyword: Pearlitic steel

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Modeling Microstructural Changes in Steel Wire Drawing (펄라이트 강 선재 인발에서 미세조직 변화 모델링)

  • Yoon, S.H.;Lee, Y.S.;Nam, W.J.;Park, K.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.10a
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    • pp.271-272
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    • 2008
  • This paper is concerned with the prediction of micro structural changes of pearlitic steel wire during clod drawing. The most important microstructural aspects are ferrite/cementite interlamellar spacing, cementite shape and thickness, since those are crucial factors to determine the mechanical strength of pearlitic steel. In this study, a couple of new algorithms to predict the above microstructural changes are developed based on the deformation histories of macro material points obtained from finite element simulations for pearlitic steel wire drawing. Some predictions are shown. The special features of the algorithms developed in this study are discussed in details.

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Effect of Pro-eutectoid Ferrite and Cementite-spheroidization on the Sliding Wear Resistance of Carbon Steels (탄소강의 초석페라이트와 시멘타이트 구상화가 미끄럼마멸 거동에 미치는 영향 분석)

  • Hur, H.L.;Gwon, H.;Kim, M.G.;Kim, Y.S.
    • Transactions of Materials Processing
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    • v.23 no.6
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    • pp.345-350
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    • 2014
  • The current study elucidates the effects of cementite spheroidization and pro-eutectoid ferrite on the sliding wear resistance in medium carbon (0.45wt%C) and high carbon (1wt%C) steels. Both steels were initially heat treated to obtain a fully pearlite or ferrite + pearlite microstructure. Spheroidizing heat treatments were performed on both steels to spheroidize the pearlitic cementite. Sliding wear tests were conducted using a pin-on-disk wear tester with the steel specimens as the disk and an alumina ($Al_2O_3$) ball as the pin. The sliding wear tests were carried out at room temperature in air with humidity of $40{\pm}2%$. Adapted sliding distance and applied load was 300m and 100N, respectively. Sliding speed was 0.1m/s and the wear-track radius was 9 mm. Worn surfaces and cross-sections of the wear track were examined using an SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. Hardness and sliding-wear resistance of both steel decreased with increased spheroidization of the cementite. The decrease was more significant in the fully pearlitic steel (1wt%C steel). The steel with the pro-eutectoid ferrite showed relatively higher wear resistance compared to the spheroidized pearlitic steel.

Microstructure and Wear Properties of Oxide Dispersion Strengthened Steel Powder Added Steel-Based Composite Material for Automotive Part (산화물 분산 강화 강 분말이 첨가된 자동차 부품용 철계 복합 소재의 미세조직 및 마모 특성)

  • Kim, Young-Kyun;Park, Jong-Kwan;Lee, Kee-Ahn
    • Journal of Powder Materials
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    • v.25 no.1
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    • pp.36-42
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    • 2018
  • In order to expand the application of oxide dispersion-strengthened (ODS) steel, a composite material is manufactured by adding mechanically alloyed ODS steel powder to conventional steel and investigated in terms of microstructure and wear properties. For comparison, a commercial automobile part material is also tested. Initial microstructural observations confirm that the composite material with added ODS steel contains i) a pearlitic Fe matrix area and ii) an area with Cr-based carbides and ODS steel particles in the form of a $Fe-Fe_3C$ structure. In the commercial material, various hard Co-, Fe-Mo-, and Cr-based particles are present in a pearlitic Fe matrix. Wear testing using the VSR engine simulation wear test confirms that the seatface widths of the composite material with added ODS steel and the commercial material are increased by 24% and 47%, respectively, with wear depths of 0.05 mm and 0.1 mm, respectively. The ODS steel-added composite material shows better wear resistance. Post-wear-testing surface and cross-sectional observations show that particles in the commercial material easily fall off, while the ODS steel-added material has an even, smooth wear surface.

Resistance to Hydrogen Embrittlement of Ultra-high Strength Pearlitic Bolt (펄라이트 조직을 갖는 초고강도 볼트의 수소취성 저항성)

  • Ahjeong Lyu;Young-Kook Lee
    • Journal of the Korean Society for Heat Treatment
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    • v.36 no.1
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    • pp.15-21
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    • 2023
  • Recently, ultra-high strength bolts have been developed for weight lightening of a vehicle and fuel efficiency. However, some amount of diffusible H is absorbed into the bolt during its manufacturing process so that H embrittlement (HE) often occurs particularly in high strength bolts with a tempered martensitic microstructure. This brings attention to ultra-high strength pearlitic bolts with a high resistance to HE. Therefore, in this study the HE resistance of the 1.6 GPa grade pearlitic bolt was evaluated through tightening tests and slow strain rate tests (SSRTs), and fracture surfaces of failed bolts were comparatively observed. A critical H content for the tightening test turned out to be ~0.23-0.35 mass ppm. The bolt with a diffusible H content of ~0.35 mass ppm was fractured during the tightening test, showing a quasi-cleavage fracture surface, indicating the occurrence of HE. In addition, the bolt underwent premature elastic failure during the SSRT. This implies that the HE resistance of high strength bolts can be evaluated by both tightening test and SSRT.

The Relationship between Microstructures and Mechanical Properties in Cold-drawn and Annealed Pearlitic Steel Wire (신선 가공한 펄라이트 강선의 어닐링시 미세 조직의 변화와 기계적 성질과의 관계)

  • Park, D.B.;Gang, U.G.;Nam, W.J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.159-163
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    • 2006
  • The effects of annealing temperature and time on mechanical properties and microstructures were studied in cold drawn pearlitic steel wires containing 0.84wt% Si. Annealing was performed from $200^{\circ}C$ to $450^{\circ}C$ with different time of 30sec, 1min, 15min and 1hr. The increase of tensile strength at low temperature was related with strain ageing. The decrease of tensile strength at high annealing temperature was related with spherodization of cementite and the occurrence of recovery of the lamellar ferrite in the pearlite. The improvement of ductility was connected with spherodization of cementite plate in pearlite and recovery process by reduction of high dislocation density at short time annealing temperature of $400^{\circ}C$.

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Effect of Prior Structure on Torsional Fatigue Strength of Induction Surface Hardened Medium Carbon Steel (고주파 표면경화된 중탄소강의 비틀림 피로강도에 미치는 초기조직의 영향)

  • Kim, Heung-Jip;Chung, In-Sang
    • Journal of the Korean Society for Heat Treatment
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    • v.11 no.4
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    • pp.247-257
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    • 1998
  • In order to evaluate the relation between prior structure and fatigue strength on a induction surface hardened medium carbon steel(SAE1050M) for automotive drive shafts, torsional fatigue test were conducted with various cases of different hardened depths and applied loads. Prior structures of the steel such as pearlite, fine pearlite and spheroidal pearlite were prepared by conventional nomalizing, tempering after quenching and spheroidized annealing, respectively. Maximum torsional fatigue strength can be obtained when the case depth is 18~25% diameter of the bar in each prior structure. The effect of case depth on the torsional fatigue strength was different depending on applied load to specimen, but the most good fatigue life was shown in the case of pearlitic structure when the case depth was 4.0~5.5mm(18~25% of bar diameter). Among three different prior structures, energy consumption, to obtain high strength or to get the same case depth, was the most saved in the case of pearlitic structure.

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The Effects of Drawing Strain and Annealing Condition on Mechanical Properties of High Strength Steel Wires (고강도강선의 신선 가공할 및 열처리 조건이 기계적 성질에 미치는 영향)

  • Lee, J.W.;Lee, Y.S.;Park, K.T.;Nam, W.J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.10a
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    • pp.138-141
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    • 2008
  • The effects of annealing temperature and time on mechanical properties and microstructures were investigated in cold drawn pearlitic steel wires. During annealing, the increment of the tensile strength at low temperatures found to be due to age hardening, while the decrease in the tensile strength at high temperatures was attributed to age softening, involving the spheroidization of lamellar cementite and recovery of lamellar ferrite. Since tensile strength and the occurrence of the delamination would be closely related to the dissolution of cementite, the lower annealing temperature and the increase of drawing strain caused the higher tensile strength and the easier occurrence of the delamination in cold drawn pearlitic steel wires.

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The Effects of Microstrucutral Parameters on Bending Fatigue Properties of Heavily Drawn Pearlitic Steel Filaments used for Automotive Tires (타이어 보강용 고 탄소강 미세 강선의 굽힘 피로 성질에 미치는 미세 조직의 영향)

  • Yang Y. S.;Lim S. H.;Ban D. Y.;Park C. G.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.10a
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    • pp.193-197
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    • 2005
  • Influences of microstructure on high-cycle fatigue (HCF) limit of high carbon $(>0.7wt.\;\%)$ steel filaments used for tires have been investigated. A series of the fatigue tests was carried out depending on carbon content by using Hunter-type tester at a frequency of 60 Hz at a tension/compression stress of 900 to 1500 MPa. Microstructural changes of the filaments were identified in the lateral direction by using transmission electron microscopy (TEM). It was found that the mechanical properties, such as fatigue limit and tensile strength, were improved with increasing carbon content, which was mainly attributed to decreased lamellar spacing and cementite thickness. However, the fatigue ratio, which is defined as the ratio of the fatigue limit to the tensile strength, was reduced in a higher carbon range of 0.8 to $0.9\;wt.\%$, while the fatigue ratio was nearly constant in a lower carbon range of 0.7 to $0.8\;wt.\%$. Overall mechanical properties of the filaments, depending on carbon content, have been discussed in terms of the microstructural parameter change of lamellar spacing and cementite thickness. In addition, the variation of cementite morphology on the fatigue crack propagation of high carbon $(0.9wt.\;\%)$ filaments will be discussed.

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The ]Relationship between Strain Ageing And Delamination Occurrence of Drawn Steel Wires (신선가공 고탄소 강선에서의 시효현상과 딜라미네이션 발생간의 상관관계 고찰)

  • Lee, J.W.;Lee, J.C.;Gang, U.G.;Lee, Y.S.;Park, K.T.;Nam, W.J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.231-234
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    • 2009
  • The effects of annealing temperature and time on mechanical properties and microstructures were already investigated in cold drawn pearlitic steel wires. During annealing, the increment of the tensile strength at low temperatures found to be due to age hardening, while the decrease in the tensile strength at high temperatures was attributed to age softening, involving the spheroidization of lamellar cementite and recovery of lamellar ferrite. Since Between increase of tensile strength and the occurrence of the delamination would be closely related to the dissolution of cementite, the increase of drawing strain by lower annealing temperature caused the between higher tensile strength and the easier occurrence of the delamination in cold drawn pearlitic steel wires.

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