Effects of Local Heat Input Conditions on the Thermophysical Properties of Super Duplex Stainless Steels (SDSS)

The properties of the super duplex stainless steels (SDSS) are strongly affected by the thermal history imposed by welding procedures. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this paper, we newly proposed a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure that combine the effects of temperature and phase changes during welding. We applied inverse method to fit the thermophysical parameters based on measured data. The model was verified by comparing measured and predicted temperature profiles using thermocouples located within the heat affected zone. Thus, an inverse method was implemented to obtain the parameters fitting for the grain growth evolution compatible with the final microstructure and grain size measured using SEM images and stereological techniques. We demonstrated that very small amount of non-equilibrium deleterious phases and nanosized precipitated are expected during the welding procedures depending upon the local conditions of temperature, compositions and alloying dilution evolutions.

超级双相不锈钢（Super Duplex Stainless Steels, SDSS）的性能受焊接工艺施加的热历史影响显著。其可控双相微观组织由铁素体与奥氏体构成，兼具优异的力学强度与耐腐蚀性，同时拥有较低的热膨胀系数和较高的热导率。本文首次提出一种模型，可在综合焊接过程中温度与相变共同影响的前提下，同时预测焊接件的热历史以及焊接过程中形成的局部力学性能。本研究采用逆方法，基于实测数据拟合热物理参数。通过使用位于热影响区的热电偶采集的温度分布实测值与模型预测值进行对比，完成了模型验证。为此，本研究进一步采用逆方法获取适配晶粒长大演化的参数，该参数与通过扫描电子显微镜（SEM）图像及体视学技术测得的最终微观组织和晶粒尺寸相匹配。研究表明，根据温度、成分及合金稀释演化的局部工况，焊接过程中预计会生成极少量的非平衡有害相与纳米级析出相。