Effects of Zirconium on the Structure and Mechanical Properties of High-Strength Low-Alloy Steels under Quenched or Tempered Conditions

The effects of zirconium (Zr) on the microstructure, inclusions, Vickers hardness, impact toughness, and tensile properties of quenched and tempered high-strength low-alloy (HSLA) steels are investigated. The results show that the addition of Zr is beneficial to the refinement of the grain size of HSLA steels under the two heat treatment conditions. When the Zr content is 0.2 wt%, the average grain size of the steel is the smallest. The main inclusions in Zr-containing HSLA steels are Zr-O and Zr-O-Mn-S, and the distribution of inclusions in HSLA steels is the most uniform when the Zr content is 0.04 wt%. The addition of an appropriate amount of Zr improves the Vickers hardness of HSLA steels under two heat treatment conditions. In terms of impact toughness, the increase of Zr content is beneficial to improving the room-temperature impact energy of HSLA steels under two heat treatment conditions, but the improvement of the impact properties of tempered HSLA steels is limited. For tensile properties, the addition of 0.04 wt% Zr is beneficial to increasing the strength of quenched or tempered HSLA steels.