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B-alloyed tool steels - thermodynamic calculation and metallographic characterization of the effect of the alloying elements Mn and Mo in the quaternary system Fe-C-B-Cr

B合金工具钢。四元系Fe-C-B-Cr中合金元素Mn和Mo影响的热力学计算和金相表征

基本信息

批准号：
232707733
负责人：
Professor Dr.-Ing. Arne Röttger
金额：
--
依托单位：
Lehrstuhl für Neue Fertigungstechnologien und Werkstoffe (FUW)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2012
资助国家：
德国
起止时间：
2011-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/232707733?language=en
关键词：
alloyed tool steels thermodynamic calculation

项目摘要

As a hard-phase forming alloying element, boron is a cost-effective possibility to improve the tribological performance of tool steels. Targeted stabilization of boride phases is used to uncouple martensitic hardening (promoted by carbon) from hard phase formation. In particular, borides of M2B type (Fe2B, Cr2B, (Fe,Cr)2B) feature higher hardness and fracture toughness than the carbide of type M7C3. These Cr-rich M7C3 carbides are used as hard phase in conventional tool steel concepts. Results gathered in the first funding period show that high B/(B+C)-ratios promote the formation of M2B type borides. In addition, the alloying element Cr further stabilizes the M2B phase and improves its micro-mechanical properties like hardness and fracture toughness. With respect to the solidification sequence in the system Fe-C-B and Fe-Cr-C-B, carboborides of M3(C,B) or M23(C,B)6 type are formed besides the M2B type boride. The formation of these softer carboborides is associated by a consumption of the elements C and Cr. This counteracts a martentisic hardenability of the metal matrix by C depletion and decreases the hardness of M2B phase due to decreased solute Cr-content inside the M2B phase. Preliminary test as well as literature data indicate that the elements Mn and Mo further stabilize the M2B type phase, while avoiding the formation of undesirable carboborides in the systems Fe-C-B and Fe-Cr-C-B.However, characterization and understanding of the effects of the alloying elements Mo and Mn in the systems Fe-C-B and Fe-Cr-C-B remains an area of research interest. Regarding the development of tool steels, focus of the investigations is placed on solidification sequence, resulting microstructure and phase composition, phase transformation in solid-state and micro-mechanical properties of the formed hard phases. Within the scope of the renewal proposal, thermodynamic calculation and metallographic characterization of laboratory melts are simultaneously used to uncover the interdependencies of the elements Cr and Mn or Mo in the underlying mechanisms. Furthermore, the effect of the element B on secondary-hardening precipitations is of high interest. Commonly, secondary-hardening carbides are formed by the alloying elements Mo, Cr, V and C during tempering a quenched tool steel in the secondary hardening regime. It will be investigated, whether the low solubility of boron and its simultaneously high diffusivity in the metal matrix enable the formation of secondary-hardening borides or carboborides. Results will be used to deduce an alloying concept for a B-alloyed tool steel. Using this concept, an alloy featuring preferably spherolitic M2B borides, which are embedded inside a martensitic metal matrix should be developed. Finally, tribological properties of this alloy are characterized to enable comparability with a conventional Fe-Cr-C based reference alloy.

作为一种硬相形成合金元素，硼是一种具有成本效益的改善工具钢摩擦学性能的可能性。硼化物相的目标稳定化用于将马氏体硬化（由碳促进）与硬质相形成分开。特别地，M2 B型硼化物（Fe 2B、Cr 2B、（Fe，Cr）2B）具有比M7 C3型碳化物更高的硬度和断裂韧性。这些富Cr的M7 C3碳化物在常规工具钢概念中用作硬质相。在第一资助期收集的结果表明，高B/（B+C）比促进M2 B型硼化物的形成。此外，合金元素Cr进一步稳定了M2 B相，并改善了其显微机械性能，如硬度和断裂韧性。对于Fe-C-B和Fe-Cr-C-B系统中的凝固序列，除了M2 B型硼化物之外，还形成M3（C，B）或M23（C，B）6型的碳硼化物。这些较软的碳硼化物的形成与元素C和Cr的消耗有关。这抵消了金属基体的马氏体可硬化性，这是由于C耗尽，并且由于M2 B相内溶质Cr含量降低而降低了M2 B相的硬度。初步试验以及文献数据表明，元素Mn和Mo进一步稳定M2 B型相，同时避免在Fe-C-B和Fe-Cr-C-B系统中形成不期望的碳硼化物。然而，表征和理解合金元素Mo和Mn在Fe-C-B和Fe-Cr-C-B系统中的作用仍然是研究兴趣的领域。关于工具钢的发展，研究的重点放在凝固序列，产生的显微组织和相组成，固态相变和形成的硬质相的微观力学性能。在更新建议的范围内，实验室熔体的热力学计算和金相表征同时用于揭示元素Cr和Mn或Mo在潜在机制中的相互依赖性。此外，元素B对二次硬化沉淀的影响也是非常令人感兴趣的。通常，二次硬化碳化物由合金元素Mo、Cr、V和C在二次硬化状态下回火淬火工具钢期间形成。将研究硼的低溶解度及其同时在金属基体中的高扩散性是否能够形成二次硬化硼化物或碳硼化物。结果将被用来推导出一个合金化的概念，硼合金化工具钢。使用该概念，应当开发优选地以嵌入马氏体金属基质内的球状M2 B硼化物为特征的合金。最后，该合金的摩擦学性能的特点，使可比性与传统的Fe-Cr-C基参考合金。