Metastable austenitic stainless steels, particularly low-Ni grades, are susceptible to delayed cracking after forming operations. Delayed cracking, or internal hydrogen embrittlement, is affected by several factors, including solute hydrogen, strain-induced martensitic transformation, residual stresses and chemical composition of the steel. In this study, metastable austenitic stainless steel grades, namely AISI 301 and AISI 204Cu, were tested under constant tensile loading in order to obtain deeper understanding on the role of internal (“metallurgical”) hydrogen on enhanced susceptibility to delayed cracking. Internal hydrogen concentration and its re-distribution in the course of loading and phase transformation were measured and analyzed using the thermal desorption method. The strain-induced phase transformation of the steel results in remarkable changes in the hydrogen thermal desorption spectra: the complex peak of hydrogen desorption from austenite observed before straining shifts to the lower temperatures after forming a sufficient amount of α’-martensite in the steel. The results demonstrate that the strain-induced transformation of austenite to α’-martensite results in an enhanced hydrogen transport in the steels, and support the concept that local accumulation of a critical hydrogen content is necessary to induce delayed cracking of the metastable austenitic stainless steels.