Abstract
The specimens of C – Mn – Si - steel wire rod 5.5 mm in diameter with 0.005% B and without B additions from Moldova Steel Works had been studied. It was been established by crystallographic-geometrical analysis, that the boron atoms could be allocate in B – alloyed a – Fe only in the positions of a sub-interstitial solid solution. By study a static strain aging (SSA) and a dynamic strain aging (DSA) specimens of wire rod by C – Mn – Si - steel with B and without B (both with multi-phase (ferrite- martensite (bainite)-pearlite) microstructures) more expressed decreasing of strengthening properties and higher characteristics of ductility had been determined for C – Mn – Si - steel specimens with B. These results could be explained by “de - nitrogenous” and “de - carbonaceous” mechanisms, when boron atoms from a – Fe sub-interstitial solid solution by producing wire rod and by its strain aging thermal treatment with temperatures 150 - 450 °С generate boron- nitrogenous and boron - carbonaceous – nitrogenous precipitations. By realizing these mechanisms nitrogen and carbon atoms are partly excluded from the dislocation pinning’s process. This, in fact, explains to inhibit the development of strain aging (SSA and DSA) in boron- micro-alloyed C – Mn – Si - steel.
Highlights
The specimens of C – Mn – Si - steel wire rod 5.5 mm in diameter with 0.005% B and without B additions from Moldova Steel Works had been studied
Even though numerous studies have been conducted in this field, many issues connected with the influence of B - micro-additions, in particular, on mechanical properties of low-alloyed steel wire rod during strain aging has remained uninvestigated at all making this research very important
As shown by the microstructure analysis, hot-rolled C – Mn – Si - steel wire rod with and without B additions originally had a multi-phase microstructure consisting of a polygonal ferrite matrix (ferrite grain size dFG = 15 – 17 μm, No 10 (ASTM)) with evenly distributed pearlite and martensite islands (Figure 1)
Summary
It was showed in (Frank & Kirkcaldy, 1998; Yalamanchili, Nelson, Power, & Lanham, 2001; Parusov., Sychkov, Zhigarev, & Perchatkin, 2004), that metal-roll of boron – micro-alloyed low – carbon and low-alloyed steels was characterized by a high level of ductility and deformability. Data of the X-ray structure analysis were showed (Shevelev, 1966), that a crystalline lattice parameter ɑ of the B – alloyed α - Fe had a lower value, than such in α – Fe without B As it in (Shevelev, 1966) was stated the boron atoms could be allocate only in the positions of a sub-interstitial solid solution in B – alloyed α – Fe. A thermodynamically steady solid solution was found out (Brown, Garnish, & Honeycombe, 1974) in boron alloyed α – Fe by the method of autoradiography. On the one part, leads to adverse implications, such as loss of ductility and toughness and certain instability of properties of steels over time (Babich, Gul, & Dolzhenkov, 1972) To mitigate these effects technological solutions and methods are being studied with the aim to inhibit the development of strain aging processes in steels. Even though numerous studies have been conducted in this field, many issues connected with the influence of B - micro-additions, in particular, on mechanical properties of low-alloyed steel wire rod during strain aging has remained uninvestigated at all making this research very important
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