长时时效后Super304H奥氏体热强钢中析出相的强化效应Strengthening effect of precipitate phase in Super304H austenitic heat-resistant steel after long-term aging

利用透射电子显微镜(TEM)研究Super304H奥氏体热强钢在650 ℃下不同时间(10~10000 h)时效过程中3种析出相的析出行为，并对其强化机理进行分析；同时，利用三维原子探针(3DAP)研究Super304H不锈钢在650 ℃时效1 h后富Cu相的早期析出行为。并详细分析富Cu相共格应变的强化机制。结果表明：细小弥散的富Cu相均匀且高度稳定地分布在奥氏体基体上，当650 ℃时效时间达到10000 h，球形的富Cu相依然保持在纳米级别，直径约为32 nm。在时效过程中，富Cu相与奥氏体基体始终保持完全共格的关系。Super304H不锈钢显微硬度的显著提高是由于细小弥散的富Cu相起到共格应变强化的作用，晶内较大尺寸的MX相也能够通过钉扎位错起到一定的强化作用；晶界上呈链状分布的M₂₃C₆相亦具有辅助强化作用。

The precipitation behavior of three precipitate phases in Super304H austenitic heat-resistant steel during long time aging (10-10000 h) at 650 ℃ was investigated by transmission electron microscopy (TEM), and the relevant strengthening mechanism was analyzed. Three dimensional atom probe (3DAP) was used to study the early stage of precipitation behavior of Cu-rich phase of Super304H aged at 650 ℃ for 1 h after solution treatment at high temperature. The coherency strain strengthening mechanism of Cu-rich phase has been investigated in detail. The results show that the dispersed fine Cu-rich precipitates exhibit spherical morphology and keep highly stable in austenite matrix, which have the size of about 32 nm in diameter, even after aging at 650 ℃ for 10000 h. The coherent relationship between Cu-rich phase and matrix is preserved during the whole aging process. Due to the coherency strain strengthening effect of Cu-rich phase, the microhardness of Super304H steel increases significantly; simultaneously, the MX phase can also pin the dislocations to induce the additional strengthening effect. Moreover, the chain-like M₂₃C₆ phase precipitated at grain boundaries can also contribute to the strengthening effect for Super304H steel.

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