Abstract
The application of direct quenching after hot rolling of plates is being employed in the production of ultra-high-strength hot rolled plates. When heavy gauge plates are produced, the complexity involve in achieving high cooling rates in the plate core is increased and the formation of undesirable soft phases within martensite is common. In the current paper, both direct quenching and conventional quenching (DQ and CQ) processing routes were reproduced by dilatometry tests and continuous cooling transformation (CCT) diagrams were built for four different high-strength boron steels. The results indicate that the addition of Mo and Nb-Mo suppresses the ferritic region and considerably shifts the CCT diagram to lower transformation temperatures. The combination of DQ strategy and the Mo-alloying concept provides the best option to ensure hardenability and the formation of a fully martensitic microstructure, and to avoid the presence of soft phases in the center of thick plates.
Highlights
The practice of direct quenching (DQ) after hot rolling is gaining importance in industry in the production of high-strength plates.[1]
The DQ process avoids the re-austenitization step that is usual for the conventional quenching (CQ) procedure, enabling significant energy savings to be made, and leading to economic benefits and productivity improvements.[2,3,4]
DQ strategy is based on the application of fast cooling immediately after a thermomechanically controlled hot rolling process
Summary
The practice of direct quenching (DQ) after hot rolling is gaining importance in industry in the production of high-strength plates.[1] The DQ process avoids the re-austenitization step that is usual for the conventional quenching (CQ) procedure, enabling significant energy savings to be made, and leading to economic benefits and productivity improvements.[2,3,4] In CQ, the rolled material is cooled down to room temperature and reheated before being quenched. DQ strategy is based on the application of fast cooling immediately after a thermomechanically controlled hot rolling process. This is an efficient process used to improve the strength and toughness of steels by pancaking the austenite below the recrystallization stop (Received March 18, 2021; accepted June 18, 2021). Residence time in the cooling device may be excessively long in the case of thicker
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