Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Effect of Hot Forging and Heat Treatment on the Microstructure and Mechanical Properties of Cr Steel

Cr강의 미세조직과 파괴인성에 미치는 열간단조 및 열처리 공정의 영향

  • Lee, Dong Jun (Materials Deformation Department, Korea Institute of Materials Science (KIMS)) ;
  • Kwon, Yong-Nam (Materials Deformation Department, Korea Institute of Materials Science (KIMS)) ;
  • Kim, Min Suk (Materials Deformation Department, Korea Institute of Materials Science (KIMS)) ;
  • Ku, Ga Eun (Materials Deformation Department, Korea Institute of Materials Science (KIMS)) ;
  • Heo, Sang Hyun (Research Institute Attached) ;
  • Kim, Nam Yong (Research Institute Attached) ;
  • Lee, Jin-Mo (Research Institute Attached)
  • 이동준 (재료연구소 소재성형연구실) ;
  • 권용남 (재료연구소 소재성형연구실) ;
  • 김민석 (재료연구소 소재성형연구실) ;
  • 구가은 (재료연구소 소재성형연구실) ;
  • 허상현 ((주)태웅 기업부설연구소) ;
  • 김남용 ((주)태웅 기업부설연구소) ;
  • 이진모 ((주)태웅 기업부설연구소)
  • Received : 2017.09.11
  • Accepted : 2017.12.27
  • Published : 2018.03.31
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Abstract

In this study, the effects of hot forging and heat treatment (quenching and tempering) of cast Cr alloy steel on the microstructures and mechanical properties were investigated. The hot forging was performed at a compressive ratio 0.5 at $1,250^{\circ}C$. The heat treatment process was quenching ($860^{\circ}C$ for 2 hours and water quenching) and tempering ($655^{\circ}C$ for 2 hours and air cooling). The microstructures of the hot forged specimen showed bainite, pearlite and ferrite mixed phases with high tensile strength, but showed low fracture toughness. The heat treated specimens after hot forging showed tempered martensite microstructure and high fracture toughness but relatively low yield and tensile strengths. After tensile and fracture toughness tests, the cast and the hot forged specimens both showed cleavage fracture surfaces, which occurred between lamellar structures. However, the heat treated specimen had a ductile fracture surface with dimple shaped fractures. From these results, we could conclude that the high fracture toughness was caused not by the cleavage fracture mode in the pearlite and bainite phases, but delayed fracture due to a ductile fracture mode in the tempered martensite phase.

Keywords

References

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