Effect of Cooling Rates on the Porosity Healing at Joint Interface of 35CrMo Steel after Unidirectional Hot Pressing

doi:10.3901/JME.2021.10.169

Abstract

Abstract: The 35CrMo forging steel is selected as the sample to study the microstructural feature of the joint interface after addictive forging simulation. Based on the dynamic recrystallization of deformed austenite related to hot compressive bonding, the relationship between different cooling rates and the porosity healing degree at joint interface is investigated through unidirectional hot pressing experiments. The solid-state transformation mechanism clearly shows that the ferrite-pearlite phase transformation induced by slow cooling can form lattice continuity by growing across the joint interface, thereby enhancing the healing degree effectively. Conversely, the martensitic transformation caused by rapid cooling cannot form lattice continuity across the joint interface, hence having no contribution to the healing degree. The preliminary calculation according to thermodynamics and kinetics together shows that the growth rate of ferrite in early stage is similar to that of austenite recrystallization, but its lower driving force leads to the low nucleation rate and gradually decreased growth rate, which may be responsible for its relatively weak healing ability compared to the dynamic recrystallization.

Key words: 35CrMo steel, joint interface, solid state transformation, additive forging, porosity healing

CLC Number:

TG156

ZENG Zhen, ZHANG Kun, GUO Zhenghong, GU Jianfeng. Effect of Cooling Rates on the Porosity Healing at Joint Interface of 35CrMo Steel after Unidirectional Hot Pressing[J]. Journal of Mechanical Engineering, 2021, 57(10): 169-177.

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