La-Ce协同处理U71Mn重轨钢夹杂物改性及强韧化研究-中国材料进展

文章信息/Info

Title:: La–Ce Synergic Inclusion Control and Strengthening Toughening of U71Mn Heavy Rail Steel

作者:: 杨希明; 任磊; 杨吉春; 张新房; 1内蒙古科技大学稀土产业学院，内蒙古包头 014017 2轻稀土资源绿色提取与高效利用教育部重点实验室（内蒙古科技大学），稀土产业学院，包头 014017

Author(s):: Yang Ximing ; Ren Lei ; Yang Jichun ; Zhang Xinfang; 1.School of Rare Earth Industry, Inner Mongolia University of Science and Technology (IMUST), Baotou 014010, China 2.Key Laboratory of Green Extraction & Efficient Utilization of Light Rare-Earth Resources (Inner Mongolia University of Science and Technology), Ministry of Education, Baotou 014010, China

Keywords:: Rare earth ; Inclusions ; Modification ; U71Mn heavy rail steel ; Thermodynamics ; MnS

摘要:: 稀土元素作为改性剂，在微合金化、改性夹杂物、改善组织、细化晶粒等方面具有高能效性。为提高重轨钢的综合力学性能以及服役性能，适用于复杂的铁路工况，本研究采用真空感应炉冶炼了不同La–Ce混合稀土含量梯度的U71Mn重轨钢，通过FactSage、SEM、全自动夹杂物分析软件对夹杂物演变规律进行分析表征，并测试维氏显微硬度、室温与低温冲击性能及拉伸性能，同时开展断口形貌分析。结果表明：稀土加入使夹杂体系由“MnS、硅酸盐主导”转变为“(La,Ce)2O2S主导”，基于球化改性作用，夹杂物形貌由不规则状演化为球形或椭球形；在扫描视场内的夹杂物数量逐级减少，且力学性能随稀土含量递增而协同提升：显微硬度由278 HV增至287 HV与294 HV；屈服强度由538 MPa增至582 MPa与610 MPa，抗拉强度由907 MPa增至948 MPa与978 MPa；断后延伸率由8.0%增至11.7%与19.1%。在室温、?20 ℃及?40 ℃下的冲击功分别最高提升至7.6 J、7.4 J与6.8 J，相对未加稀土样品最大增幅达52%与112.5%。显微硬度离散系数先增后降，约260 ppm条件下达到最低（≈4.8%），表明组织与性能实现更佳均质化。

Abstract:: Rare-earth (RE) elements exhibit high potency as micro-alloying modifiers capable of refining grains, tailoring inclusions and optimizing microstructures. To upgrade the integrated mechanical reliability and service performance of heavy-rail steels under demanding railway conditions, U71Mn steel with graded La–Ce additions was melted in a vacuum induction furnace. Inclusion evolution was quantified by FactSage thermodynamic calculations, SEM and automatic inclusion analysis, while Vickers micro-hardness, tensile properties and Charpy impact energy at 20 °C, –20 °C and –40 °C were measured and correlated with fractography. RE addition shifted the inclusion population from MnS and silicate to (La,Ce)?O?S dominance; irregular inclusions were spheroidised, their number density progressively decreased, and mechanical properties improved monotonically with RE content. Micro-hardness rose from 278 HV to 287 HV and 294 HV; yield strength increased from 538 MPa to 582 MPa and 610 MPa;tensile strength from 907 MPa to 948 MPa and 978 MPa; uniform elongation from 8.0 % to 11.7 % and 19.1 %. Impact energies at 20 °C, –20 °C and –40 °C peaked at 7.6 J, 7.4 J and 6.8 J, respectively, corresponding to maximum gains of 52 % and 112.5 % over the RE-free base. The micro-hardness scatter coefficient first increased then decreased, reaching a minimum of ≈4.8 % at ~260 ppm RE, evidencing enhanced microstructural and property homogeneity.