Microstructure and Obdurability Improvement Mechanisms of the La‐Microalloyed H13 Steel

Abstract

Rare earth microalloying is one of the most important methods to improve the mechanical properties of die steels. This paper investigates the relationships among addition of La, microstructure, and mechanical properties of H13 steel. The influences of following factors on obdurability improvement of La‐microalloyed H13 steel, such as grain refinement, deoxidization and desulphurization, grain boundary. and precipitations, have been studied. The results indicate that with the increase of La content in the range of 0–0.45 wt%, the primary dendritic spacing and average grain size of as‐cast samples decrease at the beginning and then increase. The tensile strength, yield strengthand impact toughnessof hot‐forged samples after quenching and tempering treatments increase at the beginning and then decrease with the increase of La content. The mechanical test results indicate that with 0.03 wt% La content, the obdurability of hot–forged H13 steel after quenching and tempering treatments increases obviously. As compared with La‐free H13 steel, the and of hot‐forged H13 steel containing 0.03 wt% La increase by 5.0% and 4.6%, increases by 67.8% from 29.0 to 48.7 J·cm−2. La‐microalloyed effect is attributed to grain refinement, La2O2S precipitations and dislocation density of H13 steel.