Brittle-to-ductile transitions and its relation to the deformability of cementite in fully pearlitic steels

Abstract

Temperature dependence of absorbed impact energy in fully pearlitic steels was investigated. Two-step brittle-to-ductile transitions were observed. The value of the activation energy associated with the first transition is comparable to that of low carbon ferritic steels, indicating that the first transition is the brittle-toductile transition of ferrite phase in pearlitic steels. It suggests that the first transition is controlled by the dislocation glide in ferrite. The value of the activation energy associated with the second transition is higher than that of the first transition. Micrographs of fracture surfaces and side surfaces after fracture tests suggest that the activation energy associated with the second transition should relate to the deformability of cementite in pearlite, that is, the second transition is controlled by the dislocation activity in cementite of pearlite.

Wear between wheel and rail: A pin-on-disc study of environmental conditions and iron oxides

“…Therefore, the wear process is supposed to be mainly two-body wear, so adhesive wear would be dominant and contribute to the considerable wear rate. Furthermore, at such an extremely low temperature, the ductility of steel will drop sharply to a fairly low level, producing what is called black brittleness in materials science [41][42][43]. During continuous sliding, the pins and discs are locally subjected to strong adhesive wear caused by micro cold welding, in which materials are temporarily transferred between the pins and discs.…”

Two Step Ductile to Brittle Transition Behavior on Ferrite + Pearlite Structure Steel Sheet

“…The absorbed energy in this study decreases from 1 270 to 630 kJ/m 2 between 323 and 253 K. More- over, between 253 and 193 K, the energy decreases gradually from 630 to 530 kJ/m 2 . Finally, the energy transition appears clearly from 193 to 173 K. The DBT in this study is observed to occur with two steps, and there is a "middle shelf " 19) between the upper and lower shelf. Moreover, the width of the middle shelf range is over 60 K. We call the transition from the upper shelf to the middle shelf as "first transition" and the transition from the middle shelf to the lower shelf as "second transition."…”

“…This model indicated the important factors that affect the relation shown in Fig. 14: the properties of structures in steel, 9,11,21) strain rate, 19) specimen thickness, 13) and shape of the notch. 13) However, the evidence for the model in this study is not sufficient.…”

“…Recently, Sirthanakorn et al 19) showed the two step DBT behavior in fully pearlitic steel wires using the impact test with several crosshead speeds. They evaluated that the value of the activation energy associated with the second transition was comparable to that associated with the typical single transition of low carbon ferritic steel.…”

Effect of Pearlite Volume Fraction on Two-step Ductile to Brittle Transition in Ferrite + Pearlite Structure Steel Sheets

“…In our previous study, 10) we had investigated the ductileto-brittle transition (DBT) with decreasing temperature in ferrite + pearlite DP structural steel sheets using a Charpy impact test with sub-size specimens. The absorbed energy showed a two-step DBT behavior with decreasing temperature 11) and the transition curve showed a clear "middle shelf" (MS) between the upper shelf (US) and lower shelf (LS). In the MS, the absorbed energy remained at the middle level, and the fracture surface (FS) was found to be a cleavage-like surface with a few dimples.…”