Microstructure and partitioning behavior characteristics in low carbon steels treated by hot-rolling direct quenching and dynamical partitioning processes
In this work, a new process and composition design are proposed for “quenching and partitioning” or Q&P treatment. Three low carbon steels were treated by hot-rolling direct quenching and dynamical partitioning processes (DQ&P). The effects of proeutectoid ferrite and carbon concentration on microstructure evolution and mechanical properties were investigated. The present work obtained DQ&P prototype steels with good mechanical properties and established a new notion on compositions for Q&P processing. Microstructures were characterized by means of electro probe microanalyzer (EPMA), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD), especially the morphology and size of retained austenite. Mechanical properties were measured by uniaxial tensile tests. The results indicated that introducing proeutectoid ferrite can increase the volume fraction of retained austenite and thus improve mechanical properties. TEM observation showed that retained austenite included the film-like inter-lath austenite and blocky austenite located in martensite/ferrite interfaces or surrounded by ferrites. It was interesting that when the carbon concentration is as low as ~ 0.078%, the film-like inter-lath untransformed austenite cannot be stabilized to room temperature and almost all of them transformed into twin martensite. The blocky retained austenite strengthened the interfaces and transformed into twin martensite during the tensile deformation process. The PSEs of specimens all exceeded 20 GPa.%. - Highlights: •This study focused on a new process: Q&P process applying dynamical partitioning. •Ferrite can increase the volume fraction of retained austenite. •The film-like austenite and the blocky austenite were observed. •The low carbon steels treated by new process reached PSEs higher than 20 GPa.%.
- OSTI ID:
- 22689653
- Journal Information:
- Materials Characterization, Journal Name: Materials Characterization Vol. 121; ISSN 1044-5803; ISSN MACHEX
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AUSTENITE
BACKSCATTERING
CARBON
CARBON STEELS
CONCENTRATION RATIO
ELECTRON DIFFRACTION
ELECTRON MICROPROBE ANALYSIS
FERRITE
FERRITES
MARTENSITE
MECHANICAL PROPERTIES
MICROSTRUCTURE
MORPHOLOGY
PARTITION
QUENCHING
ROLLING
SCANNING ELECTRON MICROSCOPY
TEMPERATURE RANGE 0273-0400 K
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION