High-temperature tensile properties of 316H stainless steel welded joints during long-term thermal exposure

Abstract

The microstructure and tensile properties of TIG-welded 316H joints after aging at 600 °C for up to 2000 hours were investigated. In base metal (BM), M23C6 carbides precipitated along grain boundaries after 500 hours and coarsened, while in weld metal (WM), δ-ferrite decomposed into M23C6 within 100 hours. The faster aging response in WM is due to welding-induced dislocations. At 600 °C, yield strength remained stable for both regions. BM elongation increased slightly within 500 hours, then dropped by 15.9% after 2000 hours, whereas WM elongation fell sharply by about 25% in the first 100 hours and then stabilized. The BM’s initial increase is attributed to residual stress relaxation, and its later decrease to grain-boundary carbide networks; the WM’s rapid loss results from δ-ferrite decomposition. Fracture surfaces confirmed that WM retained dimple characteristics longer, indicating better ductility retention. These findings highlight the critical role of initial microstructure in determining high-temperature tensile degradation.