Thermodynamic aspects of carbon redistribution during ageing and tempering of Fe–Ni–C alloys

Abstract

Carbon redistribution is known to occur during martensite ageing. The two associated processes most discussed in the literature are spinodal decomposition and carbon segregation to defects. In order to elucidate the topic, the ageing and tempering of two Fe-Ni-C alloys have been characterised by means of atom probe tomography and synchrotron radiation diffraction. Upon ageing at room temperature, carbon redistribution is clearly observed, where the process of carbon segregation to defects appears to be most likely to occur. Nevertheless, the possibility of spinodal decomposition is not entirely discarded, and the current work presents a series of discussion points that challenge our current understanding of the thermodynamic of ferrite in steels. ARTICLE HISTORY

Non-equilibrium metal oxides via reconversion chemistry in lithium-ion batteries

“…The most commonly occupied interstitial site in bcc-Fe is the distorted octahedral site, such as is occupied by X = C or N in the Fe-X martensite alloys [29][30][31] . These sites are located at the centres of the faces and edges of the bcc unit cell (Fig.…”

In-situ analysis of redistribution of carbon and nitrogen during tempering of low interstitial martensitic stainless steel

“…Generally, it is not possible to distinguish unequivocally between the contributions of changes in interstitial content in solid solution and changes in internal stresses on the evolution of the austenite and martensite unit cell volumes. In martensite, the change in tetragonality of the unit cell with C and N content [14] is a widely applied relation to determine the interstitial content [9,15,16]. In the present system, the martensite unit cell must be regarded as cubic, because of the low total interstitial (C + N) content [14].…”

Theoretical Aspects of Spinodal Decomposition in Fe-C

“…However, a clear distinction must be made between the two. As discussed in previous studies by the current authors, [3,4] both defect segregation and spinodal decomposition are strongly related to the thermodynamic description of the ferrite phase.…”

“…This line of reasoning is supported by the experimental work carried out earlier by the authors. [4] The carbon redistribution during the room-temperature aging of two Fe-Ni-C alloys was studied in the context of spinodal decomposition vs carbon segregation to defects. In the experimental work, the quenched and aged alloys were characterized using atom probe tomography and synchrotron radiation X-ray diffraction, but there was no evidence for the presence of the Fe 16 C 2 structure.…”