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Vol.56, No.3, 221 ~ 227, 2018
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| Title |
| Effect of Hot Forging and Heat Treatment on the Microstructure and Mechanical Properties of Cr Steel |
| 이동준 Dong Jun Lee , 권용남 Yong-nam Kwon , 김민석 Min Suk Kim , 구가은 Ga Eun Ku , 허상현 Sang Hyun Heo , 김남용 Nam Yong Kim , 이진모 Jin-mo Lee |
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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 ℃. The heat treatment process was quenching (860 ℃ for 2 hours and water quenching) and tempering (655 ℃ 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.
(Received September 11, 2017; Accepted December 27, 2017) |
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| Key Words |
| Cr steel, heat treatment, fracture toughness, microstructure, tempered martensite |
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