Paper Title
Evaluation of Toughness of High Strength Low Alloy (HSLA) Steels as a Function of Carbon Content

Abstract
The influence of carbon content on the microstructure and toughness of HSLA steel at room temperature was investigated based on experimental work and literature. It was revealed that increasing the carbon content in from 0.06 to 0.14 wt-% is detrimental to toughness, giving higher impact transition temperature. The deterioration of toughness was correlated to undesired changes in the microstructure, which showed an increase in pearlite volume fraction at the expense of ferrite. At high carbon content, cementite of pearlite was found to grow more rapidly to form continuous plates which act as preferred sites for crack nucleation and propagation. In addition, the lamellar spacing of the pearlite increased as a function of carbon content, which in turn gave worse toughness. The presence of high carbon content and carbide forming elements in the chemical composition was more detrimental to toughness due to the formation of thick carbides around the grain boundaries. These carbides act as a path for crack propagation, which makes it easy for cracks to cohere, leading to inter granular fracture. Keywords - HSLA steel, Carbon, Brittleness, Toughness, Impact Transition Temperature (ITT).