Low-oxygen rare earth steels

Rare earth (RE) addition to steels to produce RE steels has been widely applied when aiming to improve steel properties. However, RE steels have exhibited extremely variable mechanical performances, which has become a bottleneck in the past few decades for their production, utilization and related study. Here in this work, we discovered that the property variation of RE steels stems from the presence of oxygen-based inclusions. We proposed a dual low-oxygen technology, and keeping low levels of oxygen content in steel melts and particularly in the raw RE materials, which have long been ignored, to achieve impressively stable and favourable RE effects. The fatigue life is greatly improved by only parts-per-million-level RE addition, with a 40-fold improvement for the tension–compression fatigue life and a 40% enhancement of the rolling contact fatigue life. We find that RE appears to act by lowering the carbon diffusion rate and by retarding ferrite nucleation at the austenite grain boundaries. Our study reveals that only under very low-oxygen conditions can RE perform a vital role in purifying, modifying and micro-alloying steels, to improve the performance of RE steels.向钢材中添加稀土（Rare earth, RE）以制备稀土钢，已被广泛应用于改善钢材性能的场景中。然而，稀土钢的力学性能表现出极强的离散性，近几十年来这一问题已成为制约其生产、应用及相关研究的瓶颈。本研究发现，稀土钢的性能波动源于含氧夹杂物的存在。我们提出了双低氧技术，即严格控制钢液尤其是长期被忽视的稀土原材料中的氧含量至较低水平，从而实现了稳定且优异的稀土改性效果。仅需添加ppm级别的稀土，即可大幅提升疲劳寿命：拉压疲劳寿命提升40倍，滚动接触疲劳寿命提升40%。研究表明，稀土可通过降低碳扩散速率、阻滞奥氏体晶界处的铁素体形核发挥作用。本研究揭示，唯有在极低氧含量条件下，稀土方能在钢材净化、改性与微合金化进程中发挥关键作用，进而优化稀土钢的综合性能。