Controlling austenite grain size is an effective method to improve mechanical properties of alloy steels. This article shows that La addition can effectively restrain the growth of austenite grains in H13 steel and make the grain size distribution more uniform. When holding at 1050 °C from 10 to 180 minutes, the average austenite grain of La-microalloyed H13 steel increases by 35.7 pct, while that of La-free H13 steel increases by 66.7 pct. With the extension of austenitizing time, the decrease in the strength and the plasticity of tempered La-microalloyed H13 steel is considerably less than those of tempered La-free H13 steel. Austenitized at 1050 °C for 180 minutes, the tensile strength and the elongation to failure of the tempered La-microalloyed steel are 1895 MPa and 9.3 pct, respectively. The addition of La increases the amount of undissolved carbide V₈C₇ and refines the carbide, and La₂O₂S particles with high melting point are detected. Because of the combined effect of these fine dispersed second-phase particles, the pinning effect on grain boundary migration increases, and the grain growth is restrained. Some martensitic substructures transform from twin configuration to dislocation configuration because of La addition, and the lath bundles of martensite are refined. As a result, the strength and the toughness of the steel are improved.

控制奥氏体晶粒尺寸是改善合金钢机械性能的有效方法。本文表明，添加La可以有效抑制H13钢中奥氏体晶粒的生长，并使晶粒尺寸分布更加均匀。当在1050°C下保持10至180分钟时，La微合金H13钢的平均奥氏体晶粒增加35.7 pct，而不含La的H13钢的平均奥氏体晶粒增加66.7 pct。随着奥氏体化时间的延长，回火的La微合金化H13钢的强度和可塑性的降低远小于无回火的H13钢。在1050°C进行了180分钟的奥氏体化，回火的La微合金钢的抗拉强度和断裂伸长率分别为1895 MPa和9.3 pct。₈ Ç ₇和提炼的碳化物，和La ₂ ö ₂检测到具有高熔点S的颗粒。由于这些细分散的第二相颗粒的组合作用，对晶界迁移的钉扎效应增加，并且抑制了晶粒的生长。由于添加了La，一些马氏体的亚结构从孪晶构型转变为位错构型，并细化了马氏体的板条束。结果，提高了钢的强度和韧性。