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2018 Vol.28, Issue 9 Preview Page
Effect of Isothermal Heat Treatment on the Microstructure and Mechanical Properties of Medium-Carbon Bainitic Steels

등온 열처리에 따른 중탄소 베이나이트강의 미세조직과 기계적 특성

Ji-Min Lee
,
Sang-In Lee
,
Hyeon-Seok Lim
,
Byoungchul Hwang†
이 지민
,
이 상인
,
임 현석
,
황 병철†
Department of Materials Science and Engineering Seoul National University of Science and Technology, Seoul 01811, Republic of Korea
서울과학기술대학교 신소재공학과
†Corresponding author E-Mail : bhwang@seoultech.ac.kr (B. Hwang, Seoul Nat’l Univ.)
September 2018. pp. 522-527
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Abstract

This study investigates the effects of isothermal holding temperature and time on the microstructure, hardness and Charpy impact properties of medium-carbon bainitic steel specimens. Medium-carbon steel specimens with different bainitic microstructures are fabricated by varying the isothermal conditions and their microstructures are characterized using OM, SEM and EBSD analysis. Hardness and Charpy impact tests are also performed to examine the correlation of microstructure and mechanical properties. The microstructural analysis results reveal that granular bainite, bainitic ferrite, lath martensite and retained austenite form differently in the specimens. The volume fraction of granular bainite and bainitic ferrite increases as the isothermal holding temperature increases, which decreases the hardness of specimens isothermally heat-treated at 300 °C or higher. The specimens isothermally heat-treated at 250 °C exhibit the highest hardness due to the formation of lath martensite, irrespective of isothermal holding time. The Charpy impact test results indicate that increasing isothermal holding time improves the impact toughness because of the increase in volume fraction of granular bainite and bainitic ferrite, which have a relatively soft microstructure compared to lath martensite for specimens isothermally heat-treated at 250 °C and 300 °C.

Keywords
medium carbon
bainitic steels
isothermal heat treatment
microstructure
mechanical properties
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Information
  • Publisher :Materials Research Society of Korea
  • Publisher(Ko) :한국재료학회
  • Journal Title :Korean Journal of Materials Research
  • Journal Title(Ko) :한국재료학회지
  • Volume : 28
  • No :9
  • Pages :522-527
  • Received Date : 2018-08-04
  • Revised Date : 2018-09-01
  • Accepted Date : 2018-09-05
  • DOI :https://doi.org/10.3740/MRSK.2018.28.9.522
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