“…The observation done from Fig. 7c and d was previously done by Kim et al [38], who found that α'-martensite formation under a nanoindent occurs in form of several blocks with different variants. These authors postulated that a sequential transformation takes places, with the resulting increase of misorientation and change of stress field when each new block is created.…”
Section: U N C O R R E C T E D P R O O F Jj Roa Et Al Materials Scsupporting
Metastable austenitic stainless steels, and in particular the TRansformation Induced Plasticity steels, rely on a phase transformation from a ductile austenite to a slightly harder martensite. These materials under fatigue testing conditions at the macrometric length scale can induce a softening or hardening effect as a function of the underlying deformation feature activated. Thus, given the interaction of single grains in polycrystalline materials, the collective response to macroscopic fatigue testing is not trivial to interpret. Within this context, small scale tests are required to obtain a more in detail understanding of the fatigue properties at the local level of those materials. In this regard, cyclic nanoindentation tests represent a suitable technique to give insight on the local fatigue of metastable stainless steels for a certain crystallographic orientation. In this experimental work, the influence of the testing mode (loading and/or displacement control mode) on the fatigue behavior of <111> austenitic grains as a function of their micromechanical properties as well as their deformation features was investigated in detail. It was found that the experiments done under loading control mode could be compared to conventional low cycle fatigue tests. In contrast when experiments were performed under displacement control mode they may be compared to high cycle fatigue tests. Furthermore, the microstructural observation by transmission electron microscopy allowed to observe the formation of shear bands. This phenomenon preceded the apparition of martensitic laths during the cyclic indentation process.
“…The observation done from Fig. 7c and d was previously done by Kim et al [38], who found that α'-martensite formation under a nanoindent occurs in form of several blocks with different variants. These authors postulated that a sequential transformation takes places, with the resulting increase of misorientation and change of stress field when each new block is created.…”
Section: U N C O R R E C T E D P R O O F Jj Roa Et Al Materials Scsupporting
Metastable austenitic stainless steels, and in particular the TRansformation Induced Plasticity steels, rely on a phase transformation from a ductile austenite to a slightly harder martensite. These materials under fatigue testing conditions at the macrometric length scale can induce a softening or hardening effect as a function of the underlying deformation feature activated. Thus, given the interaction of single grains in polycrystalline materials, the collective response to macroscopic fatigue testing is not trivial to interpret. Within this context, small scale tests are required to obtain a more in detail understanding of the fatigue properties at the local level of those materials. In this regard, cyclic nanoindentation tests represent a suitable technique to give insight on the local fatigue of metastable stainless steels for a certain crystallographic orientation. In this experimental work, the influence of the testing mode (loading and/or displacement control mode) on the fatigue behavior of <111> austenitic grains as a function of their micromechanical properties as well as their deformation features was investigated in detail. It was found that the experiments done under loading control mode could be compared to conventional low cycle fatigue tests. In contrast when experiments were performed under displacement control mode they may be compared to high cycle fatigue tests. Furthermore, the microstructural observation by transmission electron microscopy allowed to observe the formation of shear bands. This phenomenon preceded the apparition of martensitic laths during the cyclic indentation process.
“…Nevertheless, not all the pop-ins shown in the P – h curve represents the formation of martensite beneath the indenter. By fitting the elastic part of the P – h curve using the Hertzian solution, it is generally found that deviation of the P – h curve from the Hertzian solution is accompanied by a pop-in ( Figure 10 ), which could represent the incipient plasticity or nucleation of dislocation [ 150 ]. The second pop-in could be induced by the formation of martensite beneath the indenter because the deformation mode is changed [ 149 , 151 ].…”
In this review, we separate the different governing factors on austenite stability into intrinsic and extrinsic factors, depending on the domain defined by austenite grain boundaries. The different measuring techniques on the effectiveness of the governing factors in affecting the austenite stability are discussed. On the basis of the austenite stability, a new alloy design strategy that involves the competition between the intrinsic and extrinsic factors to control the transformation-induced plasticity (TRIP) effect to realize the stronger the more ductile steel is proposed. The present review may provide new insights into the development of novel thermal-mechanical processing to advance the mechanical properties of steels for industrial applications.
The automobile industry is presently focusing on processing of advanced steels with superior strength-ductility combination and lesser weight as compared to conventional high-strength steels. Advanced high-strength steels are a new class of materials to meet the need of high specific strength while maintaining the high formability required for processing, and that too at reasonably low cost. First and second generation of advanced high-strength steels suffered from some limitations. First generation had high strength but low formability while second generation possessed both strength and ductility but was not cost effective. Amongst the different types of advanced high-strength steels grades, dual-phase steels, transformation-induced plasticity steels, and complex phase steels are considered as very good options for being extended into third generation advanced high-strength steels. The present review presents the various processing routes for these grades developed and discussed by different authors. A novel processing route known as quenching and partitioning route is also discussed. The review also discusses the resulting microstructures and mechanical properties achieved under various processing conditions. Finally, the key findings with regards to further research required for the processing of advanced high-strength steels of third generation have been discussed.
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