A heat treatment technique was applied on standard duplex stainless steel welds in order to investigate the influence of thermal treatments, e.g., multi-pass welding, on the microstructure. By using a stationary arc, a spatial steady-state temperature field ranging from liquidus to room temperature evolves within a single sample and results in a graded microstructure. The arc heat treatment was applied for 10 and 60 min respectively, and the experimental results were compared against thermodynamic calculations. Metallographic investigations revealed the formation of secondary phases within distinct zones. For the 10 min arc heat treated sample, the formation of sigma phase was observed in a temperature range of 730–1000 °C and chi phase was found above 700 °C. For the 60 min sample, sigma phase formed between 675 and 1025 °C, while chi phase formed above 600 °C. In both samples, transformation of chi phase to sigma phase as well as the formation of secondary austenite at 575–1100 °C was observed. Hardness measurements identified brittle regions, which correlated with the regions enriched in sigma phase and decomposition of ferrite. Compared to the initial microstructure, regions with secondary phases showed increased sensitization to local corrosion, when tested according to ASTM A262-Practice A.

中文翻译：

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用电弧热处理技术研究双相不锈钢焊缝的组织

为了研究热处理（例如多道次焊接）对显微组织的影响，将热处理技术应用于标准双相不锈钢焊缝。通过使用固定电弧，范围从液相线到室温的空间稳态温度场在单个样品内演化，并形成渐变的微观结构。分别进行了10分钟和60分钟的电弧热处理，并将实验结果与热力学计算进行了比较。金相研究表明在不同区域内形成了第二相。对于10分钟的电弧热处理样品，在730–1000°C的温度范围内观察到σ相的形成，而在700°C以上的温度下则发现了chi相。对于60分钟的样品，在675和1025°C之间形成σ相，高于600°C时会形成chi相。在这两个样品中，观察到在575-1100°C时chi相转变为σ相以及形成第二奥氏体。硬度测量确定了脆性区域，该区域与富含σ相和铁素体分解的区域相关。与最初的微观结构相比，当按照ASTM A262-Practice A测试时，具有次要相的区域对局部腐蚀的敏感性增强。