Abstract
It is known that precipitates that are present in austenite can influence its subsequent transformation behaviour. This investigation deals specifically with the role of nickel aluminide precipitates on the rate of the bainite reaction, in recent alloys intended for applications at about 400∘C. It is demonstrated that the aluminides lead to an increase in the nucleation kinetics of the bainite. Furthermore, their presence increases the total quantity of bainite that forms, thus helping to reduce the scale of the austenite retained in the final microstructure. There is therefore, an increase in the fracture and impact toughnesses without sacrificing the strength. Diffraction experiments show that the retained austenite is optimally stable during the tensile test of the alloy containing NiAl.
Highlights
The driving force for the bainite transformation is affected by the solute content of the parent austenite
The aluminium addition is essential for NiAl precipitation, and greatly retards the precipitation of cementite [18,19,20,21], which would in turn cause the austenite to decompose
Since the sheaf length does not change significantly in the presence or absence of NiAl, it can be concluded that NiAl promotes the heterogeneous nucleation of bainite
Summary
The driving force for the bainite transformation is affected by the solute content of the parent austenite. The effect of elements that are in solid solution is essentially on the relative thermodynamic stabilities of the austenite and ferrite. In steels where there is a substantial concentration of nickel and aluminium, it is possible during heat treatments at temperatures above 500 ∘C to precipitate NiAl in the austenite [11,12,13]. We recently have developed such a steel for elevated temperature service, in which bainite is generated at a sufficiently high temperature where NiAl may precipitate [13,17]. Stability at high temperatures is achieved by alloying with a large concentration of nickel which has the well-known austenite stabilising effect, and allows reversion to austenite if the temperature is sufficiently high [17]. The transformed steel is subjected to mechanical tests to establish a structure-property relationships
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
