Ferrite (δ) in two-phase austenite–ferrite Fe–Cr–Ni alloys decomposes into Mo- and Cr-rich phases like sigma (σ) and chi (χ), when aged in the temperature range of 873–1273 K (600–1000 °C). The precipitation of these phases for a particular Fe-Cr-Ni alloy has an adverse effect on its mechanical properties and corrosion resistance. In the present work, precipitation behavior of UNS S32205 duplex stainless steel (a Fe–Cr–Ni alloy) during controlled cooling and heating (isothermal aging) has been studied in the temperature range of 973–1073 K (700–800 °C). Scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and energy-dispersive spectrometer (EDS) attached to SEM were used to characterize the microstructures. The effect of precipitation of σ and χ phases on the micro-hardness was also studied. The precipitation sequence for 1023 K (750 °C), when cooled from 12,000 to 5 °C/min, was δ → carbides → χ → σ, while for 1073 K (800 °C), it was found to be δ → χ → σ. The Mo-enriched metastable χ phase nucleates at the initial stage of aging which then transforms to stable σ precipitates. The amount of σ and χ phases increased with temperature and aging time, but temperature was found to have a dominant role than the cooling rate due to higher diffusion of solute atoms at high temperatures. EBSD studies did not show any orientation relationship between parent δ ferrite and σ phase.

两相奥氏体-铁素体Fe-Cr-Ni合金中的铁素体（δ）分解成富Mo和Cr的相，例如σ（σ）和chi（χ），在873–1273 K（600–1000°C）的温度范围内老化。对于特定的Fe-Cr-Ni合金，这些相的沉淀对其机械性能和耐腐蚀性具有不利影响。在目前的工作中，已经研究了在973–1073 K（700–800°C）温度范围内，UNS S32205双相不锈钢（Fe–Cr–Ni合金）在受控的冷却和加热（等温时效）过程中的析出行为。 。扫描电子显微镜（SEM），X射线衍射（XRD），电子背散射衍射（EBSD）和附着在SEM上的能量色散光谱仪（EDS）用于表征微观结构。σ和χ沉淀的影响还研究了相的显微硬度。将1023 K（750°C）从12,000 / min冷却至5°C / min时的沉淀顺序为δ  →碳化物→  χ  →  σ，而1073 K（800°C）的沉淀顺序为δ  →  χ。  →  σ。富钼的亚稳态χ相在时效的初始阶段成核，然后转变为稳定的σ沉淀。σ和χ的量相随温度和老化时间的增加而增加，但是由于高温下溶质原子的扩散程度较高，因此发现温度起着比冷却速率更重要的作用。EBSD研究未显示母体δ铁氧体与σ相之间的任何取向关系。