Cojocaru Elisabeta Mirela, Raducanu Doina, Nocivin Anna, Cojocaru Vasile Danut
Materials Science and Engineering Faculty, University POLITEHNICA of Bucharest, 060042 Bucharest, Romania.
University OVIDIUS of Constanta, 900527 Constanta, Romania.
J Adv Res. 2020 Nov 14;30:53-61. doi: 10.1016/j.jare.2020.11.005. eCollection 2021 May.
Super-Duplex Stainless Steeles (SDSS) proved an excellent potential for its use in many chemical and offshore applications due to their both high mechanical properties and a high corrosion resistance in chloride ion solutions.
This study evaluates the influence of ageing treatment temperature and duration on σ-phase precipitation and mechanical properties of UNS S32750 SDSS alloy.
The influence of ageing treatment on microstructural features was analysed by SEM-EBSD (Scanning Electron Microscopy - Electron Backscatter Diffraction) technique, while on mechanical properties by tensile and impact testing techniques.
The obtained results show that for the short duration ageing treatments the σ-phase nucleates, within the δ-phase matrix, at the δ/γ grains boundary by the δ → σ precipitation, while for long duration ageing treatments the σ-phase nucleates, within the δ-phase matrix, at the δ/δ grains boundary, or in other favourable nucleation sites, due to the eutectoid decomposition δ → σ + γ. Experimental data showed that at low temperatures, i.e. 780 °C, in order to induce the precipitation of σ-phase, the minimum incubation time is situated close to 20 min, and that increasing treatment temperature decreases the minimum incubation time, with at 850 °C and 920 °C the σ-phase being firstly detected at 5 min. The σ-phase precipitation shows the highest precipitation kinetics at 850 °C, when the maximum weight-fraction is obtained for each treatment duration when compared with ageing treatments performed at 780 °C and 920 °C.
All presented data brings valuable insight into the σ-phase precipitation phenomena and its influence on UNS S32750 SDSS alloy's exhibited mechanical properties and, also, can provide researchers and industrial steel processors a guide regarding the selection of optimal ageing treatment parameters to avoid/minimise the embrittlement induced by the precipitation of deleterious σ-phase.
超级双相不锈钢（SDSS）因其具有高机械性能以及在氯离子溶液中具有高耐腐蚀性，在许多化工和海洋应用中展现出优异的应用潜力。
本研究评估时效处理温度和持续时间对UNS S32750 SDSS合金中σ相析出及力学性能的影响。
通过扫描电子显微镜-电子背散射衍射（SEM-EBSD）技术分析时效处理对微观结构特征的影响，通过拉伸和冲击试验技术分析对力学性能的影响。
所得结果表明，对于短时间时效处理，σ相在δ相基体中，通过δ→σ析出，在δ/γ晶粒边界形核；而对于长时间时效处理，由于共析分解δ→σ+γ，σ相在δ相基体中，在δ/δ晶粒边界或其他有利形核位置形核。实验数据表明，在低温（即780℃）下，为诱导σ相析出，最短孕育时间接近20分钟，且提高处理温度会缩短最短孕育时间，在850℃和920℃时，σ相在5分钟时首次被检测到。与在780℃和920℃进行的时效处理相比，σ相析出在850℃时表现出最高的析出动力学，此时在每个处理持续时间下均获得最大重量分数。
所有呈现的数据为σ相析出现象及其对UNS S32750 SDSS合金所表现出的力学性能的影响提供了有价值的见解，并且还可以为研究人员和工业钢铁加工商提供有关选择最佳时效处理参数的指导，以避免/最小化由有害σ相析出引起的脆化。
