Microprecipitation in boron-containing high-carbon steels

Abstract

Abstract. The dissolution and precipitation of boron have been studied in a high-carbon steel. Boron was found in different states: boron oxides, boron carbonitrides and iron-borocarbides Fe23(B,C)6. The dissolution of ironborocarbides in austenite is complete at 1100 ~ and precipitation along 7 grain boundaries of this boron-bearing phase was observed after water-quenching from high austenitizing temperature. Therefore, boron precipitates along 7 grain boundaries before pearlite nucleation.Key words: boron, carbon steel, borocarbides.Boron is an important microalloying element in steels because even small quantities can have a strong effect. This effect has been studied mainly in low-carbon steels in which it is well known that boron retards the nucleation of ferrite and bainite and thereby increases hardenability [1,2]. It is generally agreed that the effect of boron on hardenability results from a segregation of boron atoms at grain boundaries which lowers the strain energy in these regions and thereby retards the formation of high temperature transformation products I-3]. Nevertheless, boron steels tend to retain a reputation for inconsistency and there is still a lack of knowledge about the mechanisms by which boron imparts these remarkable improvements in mechanical properties of steels.In general, the boron treatment of hardenable steels is restricted to compositions containing up to about 0.4~o C because it was shown that as the carbon content increases the effect of boron is reduced and above certain critical levels of carbon, boron has a detrimental effect on hardenability [4]. Accordingly, very few studies have been carried out concerning high-carbon steels.The present investigation was initiated on the basis that a knowledge of the behaviour of boron in high-carbon steels might provide interesting information for understanding the mechanism by which minute percentages of boron improve the hardenability of steels and more generally to clarify various aspects of the boron

Effect of boron on the continuous cooling transformation kinetics in a low carbon advanced ultra-high strength steel (A-UHSS)

“…These results can also be related with a precipitation hardening effect. Supersaturated B can precipitate as ironboride, Fe 2 B and/or iron-borocarbide, Fe 23 (B, C) 6 , during the cooling, as it is shown by Linier et al [10].…”

Effect of direct quenching on the microstructure and mechanical properties of the lean-chemistry HSLA-100 steel plates

“…The expected solvus temperature of borocarbides is around 1100 • C. According to Valle et al [35], borocarbides can form either during rolling or cooling after hot-rolling. Borocarbides can also be present in DQT samples as indicated by Lanier et al [36] and Taylor [37] in their works with similar kind of steels. The existence of hard and brittle borocarbides at grain boundary locations is detrimental and must have been responsible for its low temperature impact toughness properties.…”

Stability of 41 metal–boron systems at 0GPa and 30GPa from first principles

“…A lot of recent work has been dedicated to related transition-metal borides, such as WB 3 /WB 4 [28][29][30][31][32] and the Mo-B system [33][34][35] . The chemical inertness and low volatility of metal borides have also allowed for their commercial use as refractory materials 36 , thermionic emitters 37,38 , and steel strengthening agents 39 . It is worth noting that the strongest permanent magnets include a small amount of boron in a complex Nd-Dy-Fe-B compound 40 .…”