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• The two-dimensional temperature field of the tensile process was investigated based on Digital Image Correlation (DIC) technology and cooling heat transfer model. • The reconstructed temperature field is in good agreement with the temperature rise in the tensile process. • The observed trend of increased martensite production is consistent with the simulated predictions. To better understand the tensile fracture behavior and temperature variation during the tension testing of the 316LN at cryogenic temperatures, a two-dimensional temperature field solution method is developed based on two-dimensional strain field measured by the digital image correlation technology combined with the Taylor Quinney coefficient model and the intrinsic model of strain-induced martensitic phase transformation. The method allows for visualization of the strain field and temperature variation of the 316LN austenitic stainless steel at cryogenic temperature. By numerical simulation, the localized temperature elevation of the 316LN is determined to be 13.3 K during the tensile test at 77 K, which is in good agreement with the experimental result of 10.2 K. This model reconstructed the two-dimensional temperature field variation throughout the entire tensile test, which is beneficial for facilitating the analysis of the mutual relation between the mechanical properties and microstructural evolution of the 316LN and other metastable austenitic stainless steels in cryogenic temperatures. [ABSTRACT FROM AUTHOR]

• The sound welded joint was obtained with Ni interlayer for 316L/Cu dissimilar laser welding joint. • No welding defects and spherical particles were formed in the fusion zone. • The average tensile strength of dissimilar welded joint is 408 MPa at 77 K. To improve the quality of welded joints between copper and 316L stainless steel, laser welding with Ni interlayer was carried out. A sound welded joint was obtained and the microstructures as well as mechanical properties were investigated. Results indicate that no welding defects or spherical particles were formed in the fusion zone. The microstructures in the fusion zone were characterized as dendritic grains, and no macroscopic segregation was observed. The welded joint failed at copper base material with an average tensile strength of 408 MPa at 77 K, and ductile fracture mode with dimples on the fracture surface were presented. Moreover, the addition of Ni interlayer prevents formation of welding defects and spherical particles and improves mechanical properties of the joint. [ABSTRACT FROM AUTHOR]

• Mechanical properties of 316LN stainless steel with cryogenic pre-strain were studied at different temperatures (RT, 77 K and 4.2 K). • The pre-strained samples stretched at cryogenic temperature obtain higher mechanical strength. • The samples stretched at 77 K possess higher elongation and hardness than RT and 4.2 K, the mechanism was explained. • The results are attributed to the changes in dislocation density and martensite transformation due to temperature and cryogenic pre-strain. The 316LN stainless steel (SS) used for TF conduits in the ITER must undergo a series of pre-deformation during the fabrication. In order to investigate the variation of mechanical properties of 316LN SS with different temperature and cryogenic pre-strain, the cryogenic pre-strained samples with 0%, 15%, 25%, and 35% pre-strain were prepared and stretched at room temperature (RT), 77 K and 4.2 K, respectively. The yield strength (YS), ultimate tensile strength (UTS), elongation and microhardness of the samples were measured. Besides, the Scanning Electronic Microscopy (SEM) and Transmission Electronic Microscopy (TEM) were applied to observe the microstructure of 316LN SS. The magnetic measurements for the samples were carried out to investigate the volume percent of phase transformation. The results indicate that the YS, UTS and microhardness of 316LN SS are improved by means of cryogenic pre-strain and the decrease of elongation of pre-strained samples is different at different temperatures. All 316LN samples show the ductile fracture. The dislocation of samples promotes by cryogenic pre-strain and hinders by cryogenic temperatures. The martensitic transformation occurs after all pre-strained samples were stretched. The volume percent of α' martensite is minimal at RT and increases dramatically at cryogenic temperatures (77 K and 4.2 K). The combination of dislocation density and martensitic transformation results in changes in the 316LN SS mechanical properties. [ABSTRACT FROM AUTHOR]