Abstract
In order to investigate the influence of vanadium microalloying on deformation-induced pearlite transformation (DIPT) of eutectoid steel, thermomechanical simulation tests were carried out in this study. The following four compositions of vanadium microalloying were applied in the tests: vanadium free in Steel A, vanadium content of 0.1 mass% in Steel B, vanadium content of 0.27 mass% in Steel C, and vanadium content of 0.1 mass% with the addition of 0.02 mass% N in Steel D. The dissolution of vanadium and precipitation of vanadium carbides, nitrides, or carbonitrides and the effect of vanadium microalloying on the fraction and morphology of deformation-induced pearlite for different magnitudes of strain were examined, and the mechanism of the effect was elucidated. The results revealed that DIPT could be significantly improved by vanadium microalloying with the addition of N but decreased and postponed without the addition of N because vanadium nitrides or carbonitrides were precipitated in austenite under a small strain and facilitated the nucleation of pearlite both along the boundary of austenite grain (AG pearlite) and intragranular (IG pearlite). Moreover, transformation kinetics of DIPT was fitted and compared. The results further revealed that the rate of DIPT in vanadium-microalloyed steel with the addition of N was twice as fast as that in the vanadium-free steel. In order to ensure the complete spheroidization of lamellar cementites in vanadium-microalloyed steel, a comparison of the morphology of cementites revealed that a greater magnitude of strain was required.
Highlights
High carbon steels with a fully pearlitic microstructure are widely applied in rail steels, spring steels, wire ropes, tire reinforcement, and high-strength bars because of their high strength, excellent wear resistance, and fatigue failure resistance [1,2,3,4]
The applications of high carbon steels are limited in precision instruments, tools, and small parts because of their susceptibility to brittle behavior
The objective of this study is to examine the dissolution of vanadium and precipitation of vanadium carbides, nitrides or carbonitrides in eutectoid steel and to determine the effect of vanadium microalloying on deformation-induced pearlite transformation (DIPT) such as the fraction and the morphology of deformation-induced pearlite for different magnitudes of strains, and to elucidate the mechanism of the effect
Summary
High carbon steels with a fully pearlitic microstructure are widely applied in rail steels, spring steels, wire ropes, tire reinforcement, and high-strength bars because of their high strength, excellent wear resistance, and fatigue failure resistance [1,2,3,4]. The applications of high carbon steels are limited in precision instruments, tools, and small parts because of their susceptibility to brittle behavior. In order to overcome this limitation, the lamellar pearlitic microstructure in hot rolled products should be converted to spheroidized cementite particles because high carbon steels present better machinability and ductility under spheroidized conditions. The spheroidization of cementite has been widely studied in the past. Such spheroidization was developed by annealing and it could be accelerated by the process of cold working before annealing, thermomechanical. More than a decade ago, researchers reported that the spheroidization time could be significantly reduced by the process of heavy deformation slightly below A1 temperature and dynamic spheroidizing (DSX) was realized
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