Effect of Niobium Content on the Microstructure and Mechanical Properties of Simulated Coarse-Grained Heat-Affected Zone (CGHAZ) of High-Strength Low-Alloy (HSLA) Steels

The effect of Nb-content and heat input rate on the mechanical properties and microstructure of simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steel (HSLA) was investigated. While using a low heat input (20 kJ/cm), the toughness of simulated CGHAZ was improved by increasing the Nb-content. The maximum toughness was obtained when the Nb-content was 0.110 wt.% and the heat input was 20 kJ/cm. The samples made at this condition had fine martensite/austenite (M/A-constituent), acicular ferrite and refined austenite grains. As the heat input was increased to 200 kJ/cm, the toughness of simulated CGHAZ was significantly decreased irrespective of the Nb-content because of the formation of coarse austenite grains, low angle grain boundaries, and massive M/A-constituents.