2507超级双相不锈钢中第二相的析出行为

利用OM、SEM和EBSD等研究了经1100 ℃保温30 min固溶的热轧超级双相不锈钢(SDSS)2507在不同时效温度(750~1000 ℃)及时间(1~240 min)下的第二相析出行为。结果表明,固溶态SDSS 2507的微观组织主要是铁素体和奥氏体。在750～1000 ℃时效处理后有σ相和χ相析出。时效温度较低时,χ相从铁素体相析出且稳定存在。随着时效温度的升高,σ相主要通过α→σ+γ₂共析反应生成,随着时效时间的延长,组织中亚稳态χ相溶解并促进σ相析出。另外,时效温度也会影响第二相形貌:高温时效时(＞950 ℃),析出相形貌主要为片状σ相和γ₂相,低温时效时析出物主要呈颗粒状。由第二相析出行为及第二相的TTT曲线可知,热轧变形使SDSS 2507第二相形核的孕育期缩短,析出速度提高,析出敏感温度约为950 ℃。

Precipitation behavior of second phase in super duplex stainless steel 2507

Second phase precipitation behavior of solid solution treated (1100 ℃×30 min) super duplex stainless steel 2507 hot raled plate after aging at different temperatures (750-1000 ℃) and time (1-240 min) was investigated by using OM, SEM and EBSD. The results show that the microstructure of the tested steel is composed of austenite and ferrite after solution treatment, while after aging at 750-1000 ℃, σ phase and χ phase are detected and identified. When the aging temperature is lower, χ phase precipitates from ferrite phase and exists stably. With aging temperature increasing, the σ phase is formed mainly by the reaction α→σ+γ₂. In addition, with the longer holding time, the metastable χ phase dissolves and promotes σ phase precipitation. Additionally, the aging temperature influences the morphology of the precipitates. At higher aging temperatures (＞950 ℃), the morphology of precipitated phase is mainly sheet σ and γ₂, while at lower aging temperatures, the granular σ phase and χ phase are mainly observed. According to the precipitation behavior and the calculation of TTT diagram of the precipitates, it can be seen that hot rolling deformation shortens the nucleation incubation period of the second phases in the SDSS 2507, increases the precipitation rate, and the precipitation sensitive temperature is about 950 ℃.