Abstract
Residual stress can be easily generated during material processing and affect the performance of structural components. Phase stress distribution in austenitic-ferritic duplex stainless steels (DSSs) is complicated due to the different material properties between the two phases. In this study, residual phase stress distribution along the thickness direction of centrifugally cast DSS hollow cylinder was measured by pulsed neutron diffraction with the time-of-flight (TOF) method. The triaxial phase stress distribution along the thickness direction shows that the phase stress of austenitic phase is generally in tension and higher than that of ferrite phase. From the outer surface to the inner surface, the macro-stress distributes from −400 MPa to 200 MPa. The mechanism of macro-stress formation was deduced by taking into consideration the thermal shrinkage behavior during the cooling process of water quench after the solution heat treatment. Furthermore, the lattice strain and phase stress evolution under the uniaxial tensile loading was evaluated by in-situ neutron diffraction measurement. The results indicated that the magnitude of phase stress could be affected by plastic working as well. All these measurements were conducted at Japan Proton Accelerator Research Complex (J-PARC).
Highlights
Austenitic-ferritic duplex stainless steels (DSSs) are widely applied to the seawater equipment and line pipes due to their high corrosion resistance and high mechanical properties
Following the material process of “centrifugal cast→solution heat treatment (SHT) at 1100 ◦C for 3 h→water quench (WQ)”, the hollow cylinders were machine-finished from the original dimensions to φ 150 mm × 200 mm with a wall thickness of 16 mm for residual stress measurement, which were designated as sample set TP16
The results showed that no obvious segregation occurred during centrifugal cast in this case, indicating that, in terms of chemical composition distribution, the lattice structure should not change along the thickness direction of the hollow cylinders
Summary
Austenitic-ferritic duplex stainless steels (DSSs) are widely applied to the seawater equipment and line pipes due to their high corrosion resistance and high mechanical properties. Harjo et al have discussed the thermal residual elastic strains in ferrite-austenite Fe–Cr–Ni alloys with different phase volume fractions and found that the thermal residual stress of γ phase tended to increase with its decreasing phase volume fraction [7,8]. They have discovered that the partitioned plastic strain in γ phase is larger than that in α phase under tensile loading according to the dislocation density analysis [9]. Some results in this article are summarized based on the author’s previous publications in Japanese [13,14]
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