Solidification microstructure formation in HK40 and HH40 alloys

Xian-fei Ding^1,2，Dong-fang Liu^3,4，Pei-liang Guo¹，Yun-rong Zheng³，Qiang Feng^2,3

1. National Center for Materials Service Safety, University of Science and Technology Beijing2. Beijing Key Laboratory of Special Melting and Preparation of High-end Metal, University of Science and Technology Beijing3. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing4. Melting and Casting Center, Beijing Institute of Aeronautical Materials

摘 要：The microstructure formation processes in HK40 and HH40 alloys were investigated through JmatP ro calculations and quenching performed during directional solidification. The phase transition routes of HK40 and HH40 alloys were determined as L → L + γ→ L + γ + M₇C₃ →γ + M₇C₃ →γ + M₇C₃ + M₂₃C₆→γ + M₂₃C₆ and L → L + δ→ L + δ + γ→ L + δ + γ + M₂₃C₆→δ + γ + M₂₃C₆, respectively. The solidification mode was determined to be the austenitic mode（A mode） in HK40 alloy and the ferritic–austenitic solidification mode（FA mode） in HH40 alloy. In HK40 alloy, eutectic carbides directly precipitate in a liquid and coarsen during cooling. The primary γ dendrites grow at the 60° angle to each other. On the other hand, in HH40 alloy, residual δ forms because of the incomplete transformation from δ to γ. Cr₂₃C₆ carbide is produced in solid delta ferrite δ but not directly in liquid HH40 alloy. Because of carbide formation in the solid phase and no rapid growth of the dendrite in a non-preferential direction, HH40 alloy is more resistant to cast defect formation than HK40 alloy.

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