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.

在旨在改善钢性能时，在钢中添加稀土 (RE) 以生产稀土钢已得到广泛应用。然而，稀土钢表现出极其多变的力学性能，这已成为过去几十年其生产、利用和相关研究的瓶颈。在这项工作中，我们发现稀土钢的性能变化源于氧基夹杂物的存在。我们提出了双重低氧技术，将钢水，特别是稀土原料中一直被忽视的低氧含量保持在低水平，以达到令人印象深刻的稳定和良好的稀土效果。仅添加百万分之一级别的稀土，疲劳寿命大大提高，拉伸-压缩疲劳寿命提高了 40 倍，滚动接触疲劳寿命提高了 40%。我们发现稀土似乎通过降低碳扩散速率和延缓奥氏体晶界处的铁素体成核来起作用。我们的研究表明，只有在极低氧条件下，稀土才能在钢的净化、改性和微合金化方面发挥重要作用，从而提高稀土钢的性能。