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Strain aging in C-Mn-Si steel wire rod with multi-phase microstructure DOI:10.15199/28.2019.1.3

  1. INTRODUCTION Metal-roll of low-carbon steels with boron microaddition and lowalloyed steels are characterized by a high ductility and deformability [1÷3]. Mеchanical and physical properties of boron micro-alloyed low-carbon steels and low-alloyed steels are determined by specific distribution of boron atoms in the crystal lattices of γ-Fe and α-Fe (austenite and ferrite, respectively). A comparison between the sizes of the octahedral and tetrahedral voids in the crystal lattices of γ-Fe and α-Fe and the boron atomic radius showed (Tab. 1), that the boron atoms (whose size in 1.26 times surpasses the size of nitrogen atom and in 1.18 times the size of carbon atom) could be allocate in the octahedral and tetrahedral voids of austenite and ferrite. Boron is characterized by high solubility in γ-Fe and α-Fe (Tab. 2), [5]. X-ray structural analysis reveals [6] that the lattice parameter a of the α-Fe with boron addition is lower than lattice parameter of α-Fe without boron. According to Shevelev investigations [6], the boron atoms could be allocate only in the positions of a sub-interstitial solid solution in B-alloyed α-Fe. A thermodynamically stable solid solution was found out [7] in boron-alloyed α-Fe by the method of autoradiography. A Snoek peak was not detected in internal-friction measurements, indicating that boron is not in an interstitial solid solution in α-Fe. Therefore authors [7] claim, that boron generate in α-Fe a sub-interstitial solid solution, but in γ-Fe, possibly, an interstitial solid solution. However, the changing of the lattice parameter a of γ-Fe (without B and with 0.005 wt % B) at temperature interval 925÷1200°С showed (Fig. 1), that at all temperatures of this interval the lattice parameter a of the boron-alloyed γ-Fe was lower than in γ-Fe without B. In conclusion, only the sub-interstitial solid solution in &[...]

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