Transformation during the isothermal deformation of low-carbon Nb-B steels
- McGill Univ., Montreal, Quebec (Canada). Dept. of Metallurgical Engineering
The transformation behavior during isothermal deformation of four steels containing different microalloying additions was investigated by means of the ``strain-rate change`` technique. The flow curves obtained at temperatures ranging from 620 C to 850 C, and the associated microstructures, indicate that the transformation in the Mo-Nb-B and Mo-B steels is of the austenite-to-bainite type. Here, dramatic increases in flow stress are observed at low temperatures. By contrast, the transformation in the Nb-15B and Nb-64B steels is basically of the austenite-to-ferrite type; in these two grades, the flow stress increases observed are attributable to strengthening by NbC precipitation. Large intergranular and intragranular Fe{sub 23}(C,B){sub 6} particles were found in the Nb-64B steel samples deformed to {var_epsilon} = 0.1 after holding for 60 seconds at 80 C. These large precipitates are considered to be responsible for accelerating the transformation in the Nb-64B steel by reducing the concentration of boron atoms available for boundary segregation and by acting as nucleation sites for the formation of polygonal ferrite. The flow curves of the Mo-Nb-B steel exhibit distinct serrations, indicating that a displacive mechanism is involved in the {gamma}-to-{Beta} transformation.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 616263
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 29, Issue 5; Other Information: PBD: May 1998
- Country of Publication:
- United States
- Language:
- English
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