Effect of cold working on the microstructure and mechanical properties of jacket for future fusion reactors

• Revealing the evolution of mechanical properties in the CHSN01 jacket under 0–20% cold working. • Samples with 5% cold working achieved excellent strength-ductility balance at 4.2 K (YS > 1500 MPa, EL > 30%, K IC > 200 MPa·m 1/2 ). • Moderate work hardening can enhance strength, but excessive deformation leads to embrittlement. • Provides key data and theoretical support for future fusion jacket processing optimization. The jacket layer of superconducting magnets in tokamak fusion reactors must withstand extreme electromagnetic-thermal–mechanical loads. China has developed a modified version of Nitronic-50 (N50) austenitic stainless steel, designated as CHSN01 (Cryogenic High-Strength No. 1). Cold working (CW) deformation is a critical process for optimizing the mechanical properties of CHSN01 jacket pipes, though excessive deformation may introduce embrittlement risks. This study systematically investigates the mechanical behavior of the CHSN01 jacket under varying CW degrees (0%, 5%, 10%, 20%) by precisely controlling the deformation of the jacket’s inner diameter. Tensile, fracture toughness, and fatigue tests were conducted at 300 K, 77 K, and 4.2 K. The research identifies the optimal CW deformation (5%) for enhancing the CHSN01 jacket’s mechanical performance in fusion magnets, achieving an optimal strength-ductility balance at 4.2 K (YS ＞ 1500 MPa; EL ＞ 30%; K IC ＞ 200 MPa·m 1/2 ). Insufficient CW deformation fails to achieve the desired strengthening effect, while excessive CW may lead to the jacket becoming brittle, potentially shortening the jacket’s service life. Additionally, microstructural features were analyzed using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The deformation microstructure indicated that an exceptional strength-ductility balance was obtained through the formation of high-density dislocation structures and deformation twins at moderate deformation levels, providing critical data and theoretical insights for optimizing processing techniques in fusion reactor jacket materials.