Journal of the Korean Society for Heat Treatment (열처리공학회지)

The Korean Society for Heat Treatment (한국열처리공학회)
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Calculation of Jominy Hardenability Curve of Low Alloy Steels from TTT/CCT data

TTT/CCT 데이터를 이용한 저합금강의 죠미니 경화능 곡선 계산

  • Jung, Minsu (Heat Treatment R&D Group, Korea Institute of Industrial Technology) ;
  • Son, YoonHo (YuJin SMC Co.)
  • 정민수 (한국생산기술연구원 열처리그룹) ;
  • 손윤호 ((주) 유진에스엠씨)
  • Received : 2019.01.09
  • Accepted : 2019.01.24
  • Published : 2019.01.31
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Abstract

Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

Keywords

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Fig. 1. A block diagram showing a procedure to obtain Jominy hardenability curve corresponding to specific input conditions.

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Fig. 2. A schematic diagram of Jominy test: (a) simulation; (b) experiment.

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Fig. 3. A calculated TTT diagram denoting the domain of each phase of SCM415 low alloy steel.

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Fig. 4. Transformation lines as a function of transformed amount of a specific phase (upper) and symmetric phase fraction curve for transformed amount as a function of reaction time at a specific temperature.

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Fig. 5. (a) TTT diagram and (b) CCT diagram of 16MnCr5 Carburizing low alloy steel.

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Fig. 7. (Left) Changes in phase fractions of various phases in 16MnCr5 steel. (Right) Hardness changes as a function of distance from the end of Jominy bar. Note that all symbols were referred from Fig. 3 showing CCT diagram of 16MnCr5 steel.

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Fig. 9. Changes in phase fractions of martensite (red), bainite (blue) as a function of average cooling time between 800°C and 500°C in Jominy bar of 50CrMo4 steel (dot for JMatPro, solid for this study, and symbol for experimental CCT data).

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Fig. 6. Changes in phase fractions of martensite (red), bainite (blue), and ferrite (olive) as a function of cooling time between 800°C and 500°C in Jominy bar of 16MnCr5 steel (dot for JMatPro, solid for this study, and symbol for experimental CCT data).

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Fig. 8. Comparison of experimental cooling data from CCT diagram shown in Fig. 5 and calculated cooling curve at jominy distance of 13 mm.

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Fig. 10. (Left) Changes in phase fractions of various phases in 50CrMo4 steel. (Right) Hardness changes as a function of distance from the end of Jomiiny bar. Note that all symbols were referred from Fig. 3 showing CCT diagram of 50CrMo4 steel.

Table 1. Values for major parameters in Kirkaldy’s formula

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Table 2. Composition of low alloy steel and heat treating conditions used in the calculation

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