Yielding Behaviour of Martensite in Steel

The Effect of Tempering on the Microstructure and Mechanical Properties of a Novel 0.4C Press-Hardening Steel

“…A plateau for the elongation was reached at 400 • C as the martensite strength decrease was already substantial. Hutchinson et al [5,6] have discussed the yielding phenomena in martensitic steels, noting that uniform elongation may increase with increasing strength level, i.e., tempered samples have decreased uniform elongation as was also seen in the current study. They argued that the relaxation of internal stresses was the main cause for earlier instability that subsequently led to the decrease of uniform elongation.…”

“…They argued that the relaxation of internal stresses was the main cause for earlier instability that subsequently led to the decrease of uniform elongation. Also, Hutchinson et al [5,6] studied the increase of yield strength caused by low-temperature tempering, which could be also explained by the relaxation of internal stresses. The quenched martensite has very high internal stresses, which are decreased by the tempering.…”

“…These features comprise the fine and complex structure of the martensite phase that can be altered by chemical composition and processing. Carbon atoms segregated in the structure, prior austenite grain size, dislocation density, different precipitates, and retained austenite together contribute to the superior strength and hardness of martensite, with carbon responsible for the main contribution [1][2][3][4][5][6][7][8]. Furthermore, the highest hardness and strength levels are often achieved by expensive, heavy alloying, or by the utilization of time-consuming heat treatments in order to meet requirements related to usability and toughness.…”

Effect of Tempering on the Bainitic Microstructure Evolution Correlated with the Hardness in a Low-Alloy Medium-Carbon Steel

“…The dislocation density may be overestimated at the start due to other contributions affecting the FWHM used to calculate the dislocation density. For example, Hutchinson et al [44,45] have shown that peak broadening in martensite also can be related to internal stresses and not only to dislocation density. The same principles could also be valid for bainite and could thus explain the relatively high dislocation densities calculated in bainitic steels.…”

“…The same principles could also be valid for bainite and could thus explain the relatively high dislocation densities calculated in bainitic steels. [44,45] However, the equations previously used to estimate the dislocation density in bainite have not taken other contributions, such as stresses, into account, thus assuming that the changes in FWHM originate from the dislocation density only. So in order to use previously derived equations and make a fair comparison of the amount of dislocations, the calculation in this work has been conducted in the same way.…”