Delayed Cracking of Metastable Austenitic Stainless Steels after Deep Drawing

In metastable austenitic stainless steels, strain-induced martensitic transformation during plastic deformation enhances work hardening of the material, increasing its strength and in some cases also ductility.1,2) The presence of α’-martensite, however, may increase the susceptibility of these materials to hydrogen embrittlement phenomena, for example delayed cracking.3–6) Delayed cracking can occur in metastable austenitic stainless steels after forming operations like deep drawing. Cracks may appear in successfully formed components after hours, days or even weeks from forming. Delayed cracking is related to coexistence of internal hydrogen, strain-induced α’-martensite and tensile residual stresses. The initiation and advance of cracks is controlled by hydrogen diffusion to regions of high tensile stress. Small average concentration of hydrogen absorbed in the material during its manufacturing process is sufficient to cause delayed cracking.7) Hydrogen may enter steel from water contained in the raw materials or in the furnace gases, during pickling in mineral acids or cathodic electrolytical Delayed Cracking of Metastable Austenitic Stainless Steels after Deep Drawing