Carbon content-tuned martensite transformation in low-alloy TRIP steels

Abstract

Ultrahigh strength and good ductility are obtained for two low-alloy transformation-induced-plasticity steels fabricated by the quenching and partitioning (Q&P) processing, respectively. Compared to 0.19 wt.% C steel in which γ → α′-martensite transformation is the dominant mechanism under deformation, the relatively high C content of austenite in 0.47 wt.% C steel is responsible for the transformation from γ to ε-martensite, suggesting that the transformation is not solely determined by the stacking fault energy. The study shows that during the Q&P process, strong and ductile steels with specific transformation procedures can be obtained by adjusting volume fraction and carbon content of the retained austenite.

Future Trends on Displacive Stress and Strain Induced Transformations in Steels

“…The appearance of the metastable phases named in this section as a product of SIT/DIT mainly depends on the chemical composition of the steel and on the deformation temperature. Hence, whereas the formation of stress or strain induced α is very common in many different microstructures [23,25,35,[49][50][51][52][53][54][55][56], ε is mainly found in austenitic steels [23,25,39,48,52], although it has been sporadically detected in multiphase steels [47]. The formation of α B has not been reported, to the authors' knowledge, at room temperature, although it has been found in fully austenitized steels [35] and in multiphase steels [1,3,57] deformed at high temperatures.…”

“…ε-martensite has been mainly studied in high manganese steels or in austenitic steels (>12 wt. %) [39][40][41][42][43][44][45][46], although it has also been observed in a low fraction in low-alloy steels [47]. Its nucleation occurs from randomly spaced overlapping γ stacking faults formed at grain boundaries [39] and, in many occasions, it is an intermediate phase during the α -martensite, i.e., the martensitic transformation follows the sequence γ→ ε →α [48].…”

“…Whereas Figure 1c is an example of a direct γ →α transformation observed while straining a 304 stainless steel at −32 • C, Figure 1d is an example of a γ→ ε →α transformation in a 304L steel deformed at −196 • C, as in the micrograph one can see a α embryo on a band of ε. In multiphase structures, the transformation process is usually γ →α , where the transformation γ→ ε is only sporadically reported [47].…”

Influence of Carbon on the Microstructure Evolution and Hardness of Fe–13Cr–xC (x = 0–0.7 wt.%) Stainless Steel

“…Due to its remarkable effects on the solidification mode [ 7 , 8 , 9 ], the relative stability of austenite [ 10 ] and ferrite [ 11 ], and the M s temperature [ 12 , 13 , 14 ], carbon plays an important role in the microstructure evolution of stainless steels. The noticeable effect of carbon on the microstructure formation after welding of stainless steels, for instance, can be implied from its large coefficient in the existing empirical equations for the calculation of the Ni equivalent in Schaeffler diagrams [ 15 ].…”

Diseño de aleación de alta entropía de alto desempeño mecánico en condiciones de bajas y altas temperaturas para aplicaciones energéticas y aeroespaciales.

“…La tercera generación de aceros Q&P AHSS pretende aumentar la ductilidad conservando parcialmente una elevada resistencia mecánica [295]. Producto de su composición química (véase en tabla 1), el acero Q&P-Nb investigado presenta el mecanismo TRIP debido a la energía de falla por apilamiento (SFE por sus siglas en inglés) característica de este refuerzo (véase la Figura 16.A).…”