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Microstructure Characterization of Reversed Transformation in Cryogenically Rolled 22MnB5
Shengjie Yao1, Long Chen1, Guannan Chu1
1School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264-209, China.
Materials (Basel, Switzerland)
|April 12, 2020
Summary
Asymmetric cryogenic rolling refines austenite grains, enhancing hot stamping. This method improves strength and ductility in ultra-high-strength steel parts by controlling grain evolution during heat treatment.
Area of Science:
- Materials Science
- Metallurgy
- Manufacturing Processes
Background:
- Hot stamping produces high-strength automotive parts but faces challenges with cost, energy efficiency, and reduced ductility.
- Ultra-high-strength parts often exhibit limitations in ductility and toughness.
- Refining austenite grains is a key strategy to enhance the strength of hot stamped components.
Purpose of the Study:
- To investigate the evolution of reversed austenite transformation in asymmetrically cryogenically rolled steel.
- To control austenite grain size for improved hot stamping performance.
- To explore asymmetric rolling as a method to enhance the properties of hot stamped parts.
Main Methods:
- Asymmetric cryogenic rolling at liquid nitrogen temperature (LNT).
- Thermomechanical simulation and salt bath heat treatment.
- Microstructural characterization using transmission electron microscopy (TEM) and scanning electron microscopy (SEM).
Main Results:
- Asymmetric rolling significantly inhibits ferrite recrystallization during reheating compared to symmetric rolling.
- Asymmetric prerolling promotes the nucleation of inner austenite grains.
- The reversed transformation dynamics are accelerated by asymmetric prerolling, leading to finer austenite grains.
Conclusions:
- Asymmetric cryogenic rolling offers a novel approach to refine parent austenite grains before press hardening.
- This technique can enhance the hot stamping process by enabling partial fast reheating.
- The findings suggest a new strategy for improving the strength, ductility, and toughness of hot stamped ultra-high-strength parts.
