Effect of martensitic transformation on cryogenic thermal conductivity and specific heat capacity of S30408 austenitic stainless steel

Abstract

Austenitic stainless steel S30408 is widely used in cryogenic equipment manufacturing due to its excellent cryogenic mechanical properties. However, the influence of martensitic transformation induced by plastic deformation and cryogenic environments during processing or service on its thermophysical properties remains unclear. In this study, room-temperature tensile deformation (0 %, 5 %, 12 %, 20 %, and 30 % plastic strains) and liquid nitrogen aging treatments were employed to induce varying martensite phase contents (0 %–36.6 %). The mechanisms of martensitic transformation on the cryogenic thermal conductivity and specific heat capacity of S30408 were systematically investigated. Using steady-state axial heat flow and relaxation calorimetry methods, the variations in thermal conductivity and specific heat capacity within the 20 K–300 K temperature range were measured. Results indicate that increased martensite content leads to a significant rise in lattice defects (slip bands, twins), enhanced electron–phonon scattering, and consequently, a marked reduction in both thermal conductivity and specific heat capacity. Within the 20 K–300 K temperature range, the thermal conductivity and specific heat capacity of samples with 30 % plastic deformation (36.6 % martensite content) decreased by an average of 27 % and 20 %, respectively, compared to undeformed samples. Further analysis revealed a linear negative correlation between thermophysical properties (thermal conductivity and specific heat capacity) and martensite content at specific temperatures (20 K, 77 K, 110 K, 300 K), with phase transformation exerting a more pronounced influence on thermophysical properties at the relatively higher temperature range within the low-temperature zone. This study elucidates the regulatory mechanism of martensitic transformation on the cryogenic thermophysical properties of austenitic stainless steel, providing critical data support for thermal performance design and service safety evaluation of cryogenic equipment.