editor@iaset.us www.iaset.us HEAT TREATMENT EFFECT ON MICROALLOYED LOW CARBON STEEL WITH DIFFERENT BORON CONTENT M. EL-SHENNAWY 1 , A. I. FARAHAT 2 , M. I. MASOUD 3 , & A. I. ABDEL-AZIZ 4 1 Mechanical Engineering Department, Faculty of Engineering, Helwan University, Helwan, Cairo, Egypt 2 Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo, Egypt 3,4 Industrial Engineering Department, Faculty of Engineering, Fayoum University, Fayoum, Egypt ABSTRACT The effect of different boron contents (between 3 and 70 ppm) on the metallurgical and mechanical properties of thermo mechanically carbon steel had been investigated. Three alloys were cast with different boron content. The alloys were subjected to thermo mechanical processing at temperature of 1200˚C and then quenched by air, oil or water as various quenching medium. Mechanical characteristics of those alloys were investigated through hardness and tensile tests at room temperature. Metallographic investigation was carried out using optical and scanning electron microscopes. Results revealed an improvement of the hot ductility of steels at increasing boron content. Ductility at 700, 900 and 1000 o C was higher than that at 800 o C, where boron microalloyed steels exhibit a region of ductility loss (hard region). Likewise, dynamic recrystallization only occurred at 900 and 1000 o C. The fracture surfaces of the tested steels showed ductile failure mode for all specimens except those with hard region the failure mode was ductile-brittle. Results are discussed in terms of dynamic recrystallization and boron segregation towards austenite grain boundaries, which may retard the formation of pro-eutectoid ferrite and increase grain boundary cohesion. KEYWORDS: Boron Steel, Heat Treatment, Micro-Alloyed, Low Carbon Steel, Boron Effect, Metallurgical Properties, Mechanical Properties INTRODUCTION Adding boron to low alloy steel promotes bainite or martensite formation due to the suppression of austenite transformation which improves the strength and hardenability of the steel [1-8]. Increasing hardenability of steels by adding boron occurs by retarding the heterogeneous nucleation of ferrite at the austenite grain surface [9-10]. If the boron concentration is excessive, a boron carbide constituent, identified as Fe 23 (B,C) 6 forms at the austenite grain boundaries of wrought steels [6]. Boron effect is entirely different in low and high carbon steel, plain and alloyed steel, with low and high soaking temperature, and more significantly with low and high cooling condition. In recent thermo-mechanical simulation study [11-15], the effectiveness of boron on hardenability has been found to be strongly dependent on soaking temperature and cooling condition, rather below a critical cooling rate boron has soften the low carbon aluminum killed steel. The presence of the intergranular Fe 23 (B,C) 6 constituent was found to not only decrease boron's hardenability effect but also seriously affect the notched toughness of steel. For example, when boron contents exceeded a value of 0.0025% in low carbon steel, both hardenability and toughness deteriorated due to the formation of this brittle boron International Journal of Mechanical Engineering (IJME) ISSN(P): 2319-2240; ISSN(E): 2319-2259 Vol. 5, Issue 4, Jun - Jul 2016; 9-20 © IASET