Deformation mechanism of a strong and ductile maraging steel investigated using in-situ X-ray synchrotron diffraction

• Published in: International journal of plasticity 2023-06, Vol.165, p.103612, Article 103612
• Main Authors: Li, Hu, Liu, Yong, Zhao, Weijiang, Liu, Bin, Tominaga, Aki, Shobu, Takehisa, Wei, Daixiu
• Format: Article
• Language: English
• Subjects: Dislocation density; Dual-phase; Maraging steel; Nanometer-scaled precipitates; Stress-induced martensitic transformation
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2023.103612

•Developed a cobalt-free maraging steel with high strength of 1700 MPa, which can be attributed to the precipitation of nanometer-scaled η-Ni3Ti and Laves-Fe2Mo precipitates.•It was found that stress-induced martensite transformation and dislocation movement were jointed to mediate the plastic deformation.•The nanometer-sized precipitates were found to lead stress-induced martensitic transformation occurring above 876 MPa in the aged steel.•In-situ X-ray synchrotron studies have verified the stress partition and lattice strain of the “hard” martensite phase higher than that of the “soft” austenite phase on loading. This work aims at revealing the deformation mechanism of a newly developed Fe-18Ni-5Mo-2Cr-1.2Ti-0.6 V maraging steel with high strength and good ductility via in-situ synchrotron X-ray diffraction and transmission electron microscopy. High-density dislocation and nanometer-scaled precipitates were found in the lath martensite. Dislocation density decreased sharply in the as-solution-annealed steel (AS-steel), leading to massive austenite transformed into martensite on loading. Deformation results in massive dislocation proliferation, and lattice strain linear increase in aged steel (AG-steel). It was verified that even high dislocation density in AS-steel cannot be preserved after deformation due to the lack of pinning effect of dislocation slip. The plastic deformation of the crystals in AG-steel is attributed to the interaction between the nanometer-scaled Ni3(Ti, Mo) precipitates and the dislocations, obeying the Orowan mechanism. The pre-formed martensite in the AG-steel was transformed into a fresh orthogonal phase when the applied stress was above ∼876 MPa. The hard lath martensite can bear a higher level of applied stress during deformation; however, the lattice strain of austenite is much lower than that of martensite. Stress-induced martensitic transformation and dislocations proliferation were jointed to mediate the plastic deformation. And thus, the AG-steel exhibits a high work hardening rate, high strength of up to ∼1700 MPa, and an elongation of more than 11.7%. [Display omitted]