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The austenite reversion and co-precipitation behavior of an ultra-low carbon medium manganese quenching-partitioning-tempering steel
Acta Materialia ( IF 9.4 ) Pub Date : 2018-03-01 , DOI: 10.1016/j.actamat.2017.12.035
Yu Li , Wei Li , Wenqing Liu , Xiaodong Wang , Xueming Hua , Huibin Liu , Xuejun Jin

Abstract The multiphase microstructure evolution and mechanical properties of an ultra-low carbon medium manganese quenching-partitioning-tempering (QPT) steel have been investigated based on the nanoscale austenite reversion correlated with the co-precipitation behavior. The blocky austenite (aspect ratio 3) always formed during the tempering procedure in the alloy-enriched structures after partitioning. The adjacent co-precipitation of Ni-rich particles shells with Cu-rich precipitates was observed in quenching-tempering (QT) steels. The lower annealing temperature of QPT-1 steels resulted in a multiphase constitution of mostly film austenite, nanoscale dispersed Ni-rich precipitates and in the obvious coarsening and anisotropic growth of Cu-rich precipitates. With a high annealing temperature, QPT-2 steels showed a large percentage of blocky austenite, an entire core-shell co-precipitation structure of Ni-rich and Cu-rich precipitates in martensite and elongated Cu-rich particles in the blocky austenite. The introduction of nanoparticles in dual phase has rarely been found in ultra-low carbon steels with a low alloying degree. The co-precipitation mechanisms are closely related to the cooperative austenite reversion process, which is governed by Mn diffusion and segregation: this leads to a different element enrichment degree in dual phase. In addition, the intergranular precipitates in QT-steels result in stress concentration in the grain boundaries and a very low ductility, although with strong modulus and Orowan hardening effects. The difference of yield strength (67 MPa) in the two QPT steels mainly originate from the contribution of dispersion strengthening effect (44 MPa) under the consideration of the constituent phases. The lower mechanical stability of the blocky austenite in QPT-2 steels results in a lower uniform elongation and impact toughness.

中文翻译:

一种超低碳中锰调质钢的奥氏体回复与共沉淀行为

摘要 基于与共沉淀行为相关的纳米级奥氏体回复,研究了超低碳中锰调质(QPT)钢的多相组织演变和力学性能。块状奥氏体(纵横比 3)总是在回火过程中在分配后的合金富集组织中形成。在淬火-回火 (QT) 钢中观察到富镍颗粒壳与富铜沉淀物的相邻共沉淀。QPT-1钢的较低退火温度导致主要为膜奥氏体的多相组成,纳米级分散的富Ni析出物以及富Cu析出物的明显粗化和各向异性生长。由于退火温度高,QPT-2 钢显示出大量块状奥氏体,马氏体中富镍和富铜沉淀物的完整核壳共沉淀结构以及块状奥氏体中拉长的富铜颗粒。在合金化度低的超低碳钢中很少发现双相中纳米颗粒的引入。共沉淀机制与协同奥氏体回复过程密切相关,该过程受 Mn 扩散和偏析控制:这导致双相中不同的元素富集程度。此外,QT 钢中的晶间析出导致晶界应力集中和非常低的延展性,尽管具有很强的模量和 Orowan 硬化效应。两种QPT钢的屈服强度差异(67 MPa)主要源于考虑组成相的弥散强化效应(44 MPa)的贡献。QPT-2 钢中块状奥氏体的较低机械稳定性导致较低的均匀伸长率和冲击韧性。
更新日期:2018-03-01
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