On significance of initial microstructure in governing mechanical behavior and fracture of dual-phase steels
Yong-gang Deng1 . Hong-shuang Di1 . R. D. K. Misra2
1 State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, Liaoning, China 2 Laboratory for Excellence in Advanced Steel Research, University of Texas, El Paso, TX 79968, USA
On significance of initial microstructure in governing mechanical behavior and fracture of dual-phase steels
Yong-gang Deng1 . Hong-shuang Di1 . R. D. K. Misra2
1 State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, Liaoning, China 2 Laboratory for Excellence in Advanced Steel Research, University of Texas, El Paso, TX 79968, USA
摘要 Different initial microstructures were obtained through annealing and cold-rolling. Subsequently, steels with ferrite-pearlite (FP), ferrite-martensite (FM) and completely martensite (M) microstructure were intercritically heat treated at 780 °C for 5 minutes followed by water quenching to obtain ferrite-martensite dual-phase microstructures. We have elucidated here the significance of initial microstructure on ultimate microstructure, mechanical properties, strain hardening behavior and fracture mechanism in dual-phase steels. FP, FM and M initial microstructure yielded different martensite morphologies, notably, chain-like networked structure, fine and fibrous martensite structure, respectively. Furthermore, with increaed martensite volume fraction in the initial microstructure, the average ferrite grain size was significantly refined from 12.3 to 2.1 μm, such that yield strength and tensile strength were increased, while total elongation remained unaffected, uniform elongation and strain hardening ability were increased. A comparison of mechanical properties for different initial microstructure suggested that when the initial microstructure was completely martensite, the steel had excellent mechanical properties, UTS×UE was 122.5 J?cm-3, which was 24% greater compared to the conventional continuous annealed steels with ferrite-pearlite initial microstructure (98.8 J?cm-3). The variation in strength, elongation, strain hardening behavior and fracture mechanism of steels with different initial microstructure are discussed in relation to the ultimate microstructure.
Abstract：Different initial microstructures were obtained through annealing and cold-rolling. Subsequently, steels with ferrite-pearlite (FP), ferrite-martensite (FM) and completely martensite (M) microstructure were intercritically heat treated at 780 °C for 5 minutes followed by water quenching to obtain ferrite-martensite dual-phase microstructures. We have elucidated here the significance of initial microstructure on ultimate microstructure, mechanical properties, strain hardening behavior and fracture mechanism in dual-phase steels. FP, FM and M initial microstructure yielded different martensite morphologies, notably, chain-like networked structure, fine and fibrous martensite structure, respectively. Furthermore, with increaed martensite volume fraction in the initial microstructure, the average ferrite grain size was significantly refined from 12.3 to 2.1 μm, such that yield strength and tensile strength were increased, while total elongation remained unaffected, uniform elongation and strain hardening ability were increased. A comparison of mechanical properties for different initial microstructure suggested that when the initial microstructure was completely martensite, the steel had excellent mechanical properties, UTS×UE was 122.5 J?cm-3, which was 24% greater compared to the conventional continuous annealed steels with ferrite-pearlite initial microstructure (98.8 J?cm-3). The variation in strength, elongation, strain hardening behavior and fracture mechanism of steels with different initial microstructure are discussed in relation to the ultimate microstructure.
YONGGANG -Deng. On significance of initial microstructure in governing mechanical behavior and fracture of dual-phase steels[J]. Journal of Iron and Steel Research International, 2018, 25(9): 932-942.
2018, Vol. 25 
