Microstructural Evolution In The Processes Of Simulated Welding Thermal Cycle And High Temperature Deformation Of 2205 Duplex Stainless Steel

The influence of welding thermal cycle and high temperature deformation on the microstructure and properties of 2205 DSS is extremely significant. In high temperature conditions, whether simulated welding thermal cycle or high temperature compression, the two-phase equilibrium of DSS can be easily destroyed, and intermetallic phases such as o phase, carbides, nitrides and reformed austenite will precipitate during the process of high temperature, this will reduce the mechanical properties.Therefore, it is of great significance to study the influence of high temperature on the microstructure transformation and properties of DSS in theory and practice.In this paper we applied simulated welding thermal cycle of different heat input and high temperature compression to 2205 DSS, and studied the influence of heat input on the microstructures and properties of 2205 DSS, analyzed the formation mechanism of Widmanstatten austenite. Meanwhile in order to investigate the high temperature deformation mechanism, we analyzed the influence of different deformation temperature and strain on the microstructure evolution process of DSS. The main results are as follows:1. Under the condition of different thermal simulation heat input, four different types of austenite were observed. With the increasing of the heat input, the microstructure occur changes significantly. three different morphologies of newly formed austenite were observed in the coarsened ferrite matrix, and GBA gradually transformed into IWA or GA.2. With the increasing of heat input, the austenite content increased to 45.24% at heat input 61.78kJ/cm from 17.11% at heat input 6.18kJ/cm. Room temperature impact test shows that the impact property of DSS 2205 is the best when the heat input was 61.78kJ/cm in this paper.3. The samples’microstructures under different heat input changed significantly. The formation and decomposition of Widmanstatten austenite have a great influence on properties of 2205 DSS. The study found that when the heat input was 25.22kJ/cm, the Widmanstatten austenite had begun to decompose, and the decomposition is thought to be related to distribution of alloying elements between the two phase. When the heat input is come to 61.78kJ/cm, the Widmanstatten austenite is almost disappeared, most austenite was refined and equiaxed.4. TEM revealed that a phase precipitated in the phase boundary of austenite and ferrite when the heat input rose to 43.69kJ/cm, observed. While Cr2N and M23C6 precipitation were observed when heat input were 61.78kJ/cm.5. The phase transformation of ferrite to austenite was the dominant transformation when deformation temperature was low, which could be shown as relative increase of austenite content; Along with the increasing of deformation temperature, phase transformation from austenite to ferrite played a dominant role, which could be shown as relative increase of ferrite content.6. In this paper we studied the influence of different deformation temperature, strain rate and deformation degree on microstructures. And the main softening mechanism of DSS 2205 during hot deformation were dynamic recovery and dynamic recrystallization of ferrite and the forming of substructure, twin and motion of dislocation gathering in austenite.