Schematic of the thermomechanical schedule performed in the plane strain compression machine.
Schematics of the mechanical property sample extraction from the plane strain compression sample.
(a) Engineering tensile curves obtained for all of the Fast Cooling Temperatures (FCTs). Tensile curves measured before (FCT) and after induction heat treatment (FCT-HT) have been included. (b) Evolution of yield strength and tensile strength as a function of the Fast Cooling Temperature (samples obtained before and after induction treatment).
Evaluation of the effect of the induction heat treatment and the FCT on the yield/tensile strength ratio.
FEGSEM (field-emission gun scanning electron microscopy) micrographs corresponding to every Fast Cooling Temperature and both (a–c) FCT and (d–f) FCT-HT samples: (a,d) FCT790, (b,e) FCT720 and (c,f) FCT650.
FEGSEM micrographs (higher magnifications) corresponding to every Fast Cooling Temperature and both (a–c) FCT and (d–f) FCT-HT samples: (a,d) FCT790, (b,e) FCT720 and (c,f) FCT650.
Image quality and inverse pole figure (IPF) maps corresponding to the samples without induction heat treatment: (a) FCT790 and (b) FCT650.
Grain boundary maps (red lines between 2° and 15°, black lines > 15°) corresponding to the samples obtained before (FCT in (a,c,e)) and after induction treatment (FCT-HT in (b,d,f)) and under different conditions: (a,b) FCT790 and (c,d) FCT720 and (e,f) FCT650.
(a) Influence of the Fast Cooling Temperature and the induction heat treatment on the average unit size, using different threshold misorientation criteria: low angle (2°) and high angle (15°) boundaries. (b) Effect of FCT on the on Dc20%/D15°.
Grain boundary length per unit area as a function of the FCT. Results concerning high and low angle grain boundaries (HAGB and LAGB) are included.
Kernel maps corresponding to the samples obtained before (FCT in (a,c,e)) and after induction treatment (FCT-HT in (b,d,f)) at different conditions: (a,b) FCT790 and (c,d) FCT720 and (e,f) FCT650.
Influence of Fast Cooling Temperatures and induction heat treatment on dislocation density.
Thin foil TEM micrographs for the samples without induction treatment: (a) FCT790 and (b) FCT650. (c) Influence of the Fast Cooling Temperature on the precipitate size distribution (representing accumulated frequency).
Thin foil TEM micrographs for the entire range of Fast Cooling Temperatures and both (a,c,e) FCT and (b,d,f) FCT-HT conditions: (a,b) FCT790, (c,d) FCT720 and (e,f) FCT650.
Mean precipitate sizes (Dppt) as a function of FCT. Measurements carried out in the FCT and FCT-HT samples have been included.
Individual strengthening contributions (grain size, dislocations, MA islands, precipitation and composition) for every microstructure (ferrite, ferrite/bainite and bainite, for FCT790, FCT720 and FCT650, respectively) and the samples obtained before (FCT) and after (FCT-HT) induction heat treatment.
Comparison between Charpy curves corresponding to FCT650, FCT650-HT, FCT790 and FCT790-HT: (a) absorbed energy and (b) ductile fraction as a function of the test temperature.
) Comparison between experimental and calculated DBTT values predicted by Equation (2). The data reported by Isasti et al. [17
] and Larzabal et al. [5
] have been included in the graph. (b
) Estimated contributions (solid solution, secondary phases, dislocation + precipitation, grain size and heterogeneity) to the DBTT for every condition and comparison with experimental values.
Relative contribution of each metallurgical parameter (grain size, solid solution, dislocations, martensite/austenite (MA) fraction, MA size, heterogeneity and precipitation) on both strength and toughness properties. FCT and FCT-HT conditions are compared for both types of microstructures: (a) ferritic in FCT790 and (b) bainitic in FCT650.
Chemical compositions of the steels (weight percent).
Yield strength (YS), tensile strength (TS), elongation (%), and area reduction (%) values for the all of the conditions: FCT650, FCT650-HT, FCT720, FCT720-HT, FCT790, and FCT790-HT.
|Condition||Yield Strength (MPa)||Tensile Strength (MPa)||Elongation (%)||Area Reduction (%)|
|FCT650||495 ± 3||667 ± 3||25 ± 2||79 ± 0|
|FCT650-HT||632 ± 1||738 ± 2||22 ± 0||76 ± 0|
|FCT720||525 ± 1||707 ± 3||19 ± 1||79 ± 1|
|FCT720-HT||654 ± 4||758 ± 1||27 ± 0||80 ± 1|
|FCT790||544 ± 0||676 ± 0||20 ± 0||77 ± 0|
|FCT790-HT||646 ± 3||739 ± 4||25 ± 1||80 ± 1|