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Microstructure Transformation on Pre-Quenched and Ultrafast-Tempered High-Strength Multiphase Steels
Yonggang Zhao1,2,3, Zijie Xiang4, Yuanbiao Tan5,6
1College of Materials and Metallurgy, Guizhou University, Guiyang 550025, China. 18786109880@163.com.
Materials (Basel, Switzerland)
|January 30, 2019
Summary
Researchers developed high-strength multiphase steels using ultrafast tempering. Optimized heat treatment yielded superior strength by controlling martensite nucleation and tempering, minimizing pearlite formation.
Area of Science:
- Materials Science
- Metallurgy
- Physical Chemistry
Background:
- High-carbon pearlitic steels are foundational materials.
- Developing advanced high-strength steels requires novel heat treatment strategies.
- Understanding microstructure evolution is key to optimizing mechanical properties.
Purpose of the Study:
- To prepare high-strength multiphase steels via pre-quenching and ultrafast tempering.
- To investigate the influence of quenching temperature on martensite nucleation and microstructure.
- To elucidate the transformation mechanisms and softening processes in tempered steels.
Main Methods:
- Preparation of high-carbon pearlitic steels (0.81% C).
- Application of pre-quenching and ultrafast tempering heat treatments.
- Microstructural analysis using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM).
Main Results:
- Increasing quenching temperature (120–190 °C) promoted autocatalytic nucleation of martensite variants.
- Tempered nodules and multiphase structures exhibited symmetrical morphologies.
- Optimal heat treatment (120 °C quench, 200 °C/s heating to 600 °C, 60 s isothermal hold) resulted in highest strength and lowest pearlite fraction.
- Microhardness softening involves reverse martensitic transformation, cementite nucleation, austenite transformation, and carbide coarsening.
Conclusions:
- Ultrafast tempering is effective for creating high-strength multiphase steels.
- A model was developed to explain the martensite to multiphase microstructure transformation.
- Heat treatment parameters critically influence microstructure, strength, and softening mechanisms.
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