Effect of Nb Content on Mechanical Properties and Microstructure of High Strength Low Alloy Steel

This research investigates the influence of Nb content on the mechanical properties and microstructure of high strength low alloy (HSLA) steel. The results show that compared with Nb-free steel, there is a significant improvement in yield strength, tensile strength, and impact absorption energy within the temperature range of – 60 to 20 ℃ when the content of Nb is not higher than 0.17%. In addition, Nb-added HSLA steels demonstrate good impact toughness stability as the impact temperature decreases within the range of Nb content. However, when the Nb content is excessively high, due to the growth of grain size and the precipitation of large-sized Nb carbides, the low-temperature toughness is compromised. Considering strength, toughness, and alloy cost comprehensively, the optimal performance is achieved when the Nb content is 0.04%. This is primarily attributed to its fine and uniform microstructure, along with the presence of nanosized Nb carbides (50–70 nm).