Medium Mn steels are promising candidates for the third-generation advanced high strength steels. However, it shows a distinct limit of mechanical property under conventional hot-rolling and intercritical annealing procedures. Aiming at improving the combination of strength, ductility and toughness, the present study proposed a multi-alloyed design principle together with a direct intercritical rolling process. The results show that the microstructure of the hot rolled steel consisted of wide delta ferrite, lath martensite, twinned-martensite and coarse retained austenite with a low stability, corresponding to a product of strength and elongation (PSE) of 24.0 GPa% and an impact toughness of 13.8 J/cm 2 at −40 °C. In contrast, the intercritical rolling produced a laminated microstructure containing thin delta ferrite, submicron recrystallized ferrite and retained austenite. The PSE and impact toughness at −40 °C simultaneously increased to 46.1 GPa% and 46.7 J/cm 2 , respectively, which was also much higher than the hot rolled steel subjected to low temperature and high temperature annealing. The significant enhancement of mechanical property was mainly attributed to the highest content and optimal stability of retained austenite caused by the submicron grain size, high density of dislocations, granular morphology, and elemental enrichment. The optimized austenite stability provided persistent transformation-induced plasticity (TRIP) effect for work hardening and damage resistance. Moreover, the nano-sized VC precipitates in the intercritical rolled steel played a significant role in reaching an ultrahigh yield strength of ∼1 GPa. This study not only provides a very simple pathway to improve the mechanical property of medium Mn steel, but also sheds light on the design and development of high-performance materials. 

Tailoring retained austenite and mechanical property improvement in Al–Si–V containing medium Mn steel via direct intercritical rolling

2.3 GPa cryogenic strength through thermal-induced and deformation-induced body-centered cubic martensite in a novel ferrous medium entropy alloy

Making low-alloyed steel strong and tough by designing a dual-phase layered structure

Maraging steel with ultra-high strength and good ductility is usually achieved via semi-coherent nanometer-sized precipitates and a dual-phase structure. In this work, we studied the effect of solution treatment parameters on the microstructural evolution and the mechanical properties of cobalt-free maraging steel, with high strength (1852 MPa) and satisfactory tensile elongation (11.5%) at room temperature was obtained. The nano-scaled precipitates in the martensite matrix were analyzed, in which the η-Ni3(Ti, Mo) precipitates were distributed in width of 7.1 nm and length of 19 nm. It was found that the needle-like Ni3Ti phase plays a predominant role in enhancing the strength of the maraging steel, while the ductility can be attributed to the nano laminated austenite structure, which could effectively prevent the propagation of microcracks in the martensite matrix. A heterogeneous microstructure of precipitates was formed in the martensite matrix. Besides, the size and number density of precipitates could be regulated by tuning the solution treatment conditions, in which a finer size and a larger number of precipitates could be gained by annealing at a high temperature for a short time. 

Synergistic enhancement of strength and ductility of cobalt-free maraging steel via nanometer-scaled microstructures

Triply periodic minimal surfaces (TPMS) allow the production of structural components with high mechanical strength and energy absorption capacity and significantly reduce material consumption during manufacturing. The fabrication provided by laser powder bed fusion expands the manufacture of TPMS by allowing the obtention of high-performance components. Thus, this study investigated the compression responses of as-built and aged (480 °C for 3 h) maraging steel 300 primitive scaffolds under compressive loading in different directions (0° and 90°). Compressive tests and failure analysis showed that the maraging steel specimens subjected to aging treatment had approximately 56% improved yield and 20% collapse strength, in comparison to the as-built specimens, due to the austenite reversion and intermetallic precipitates within the martensitic structure. Also, a non-linear correlation of energy absorption capacity with strain was observed during the compression of the TPMS. It was also well evidenced that mechanical performance and energy absorption capacity depends on post heat treatment and loading direction, which can contribute to an improved design strategy of TPMS devices produced by laser powder bed fusion.

Compression and energy absorption of maraging steel primitive scaffolds produced by powder bed fusion

Ultrafine-grained dual-phase maraging steel with high strength and excellent cryogenic toughness

Fe–10Cr–10Ni cryogenic maraging steel is one of the key candidate materials applied in harsh cryogenic condition due to its high strength and good cryogenic toughness. In this study, the effect of aging temperature on its microstructure and mechanical properties was systematically studied based on austenite reversion and nano-precipitation. It shows that a desirable combination of high strength (834 MPa, 25 °C) and excellent cryogenic impact toughness (164 J, −196 °C) can be obtained by aging treatment at 500 °C. Multi-scale characterizations were conducted to reveal the microstructure characteristics of the steel. It was found that obvious film-like reversed austenite nucleate and grow at the high-angle grain boundaries of martensite matrix in the steel aged at 500 °C, whereas the higher aging temperature resulted in a larger content of blocky reversed austenite in martensite blocks. Austenite reversion mechanism was proposed based on the double-spherical-cap model and diffusion kinetics of Ni element. Besides, it was found that the precipitation sites of Ti-rich particles are not only distributed in matrix but also located at the dislocations, and they were identified as the clusters of Ni3Ti precipitates. Finally, the origin of the above cryogenic toughness includes the transformation-induced plasticity (TRIP) effect from the soft film-like austenite, higher density of high angle grain boundaries of martensite and fine nanoscale precipitates. Moreover, the precipitation strengthening from the clusters of Ni3Ti precipitates contributes to the high strength of the steel aged at 500 °C.

Effect of aging temperature on the austenite reversion and mechanical properties of a Fe–10Cr–10Ni cryogenic maraging steel

The evolution of heterogeneous microstructure and mechanical properties of a 12Cr–10Ni–Mo–Ti maraging steel was investigated at different aging temperatures. As the aging temperature increases, more reversed austenite forms with the recovery of martensite matrix. When aging temperature is up to 560 °C, more lath-like reversed austenite coalesces together and leads to the formation of martensite and austenite dual-phase microstructure. Fine η-Ni3(Ti, Al) particles initially precipitate at 440 °C and grow up with increased aging temperature. Notably, it was found that η-precipitates can be encompassed in reversed austenite at 500 °C. Thermodynamic calculations further verify the austenite reversion, and nanoprecipitation can occur independently of each other though there is competition of Ni element. However, it leads to the coarsening and dissolution of η-precipitates as the aging temperature further increases. The desirable heterogeneous microstructure of the aged martensite matrix, soft reversed austenite and stable η-precipitates at 500 °C contributes to a high yield strength (~ 1 GPa, 25 °C; ~ 1.4 GPa, -196 °C) and a reasonable cryogenic impact toughness (~ 60 J, − 196 °C), which is mainly ascribed to the precipitation strengthening of η-precipitates, transformation-induced plasticity (TRIP) toughening effect from the lath-like reversed austenite and the increased misorientation toward high-angle grain boundary.

Effect of aging temperature on the heterogeneous microstructure and mechanical properties of a 12Cr–10Ni–Mo–Ti maraging steel for cryogenic applications

Dongping Ma

Papers

Ultrafine-grained dual-phase maraging steel with high strength and excellent cryogenic toughness

Effect of aging temperature on the austenite reversion and mechanical properties of a Fe–10Cr–10Ni cryogenic maraging steel

Effect of aging temperature on the heterogeneous microstructure and mechanical properties of a 12Cr–10Ni–Mo–Ti maraging steel for cryogenic applications