Abstract
The characteristics and formation mechanisms of intragranular acicular ferrite (IAF) in steel with MgO nanoparticle additions were systematically investigated for different isothermal heat-treatment temperatures, and its influence on mechanical properties was also clarified. The results indicate that the inclusions were finely dispersed and refined after adding MgO nanoparticles. In addition, with decreasing heat-treatment temperature, the microstructure changed from grain boundary ferrite (GBF) and polygonal ferrite (PF) to intragranular acicular ferrite. Moreover, the steel with MgO additions had excellent mechanical properties in the temperature range of 973 to 823 K and an average Charpy absorbed energies value of around 174 J at 873 K due to the significant refinement of the microstructure and nucleation of intragranular acicular ferrite.
Highlights
With the development of a new generation of steel materials, the cleanliness of steel has been significantly improved [1,2,3]
Takamura et al [6] and Mizoguchi et al [7] proposed a new concept of oxide metallurgy, which uses small-sized inclusions and precipitates particles as nucleation sites of intragranular acicular ferrite (IAF) or pins austenite grains to improve the final properties of steel
Further research and applications of this technique have shown that nonmetallic inclusions induce the formation of IAF, which becomes the core point [8]
Summary
With the development of a new generation of steel materials, the cleanliness of steel has been significantly improved [1,2,3]. Takamura et al [6] and Mizoguchi et al [7] proposed a new concept of oxide metallurgy, which uses small-sized inclusions and precipitates particles as nucleation sites of intragranular acicular ferrite (IAF) or pins austenite grains to improve the final properties of steel. Further research and applications of this technique have shown that nonmetallic inclusions induce the formation of IAF, which becomes the core point [8]. Up to now, these inclusions have been formed either by an internal precipitation method or by an external addition method [9]. Numerous studies have focused on the internal precipitation method, which mainly forms oxide inclusions through strong deoxidizer and alloying elements such as
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