The paper intends a study of the propagation speed for cracks of the da/dN kind, into an Austen steel employed at the refrigerating plants from the chemical industry. The testing was made with flat test of the CT model, with a lateral notch, the stress being an eccentric stretch. The cycles were of the positive oscillatory kind, with the asymmetry coefficients R=0.1, R=0.3 and R=0.5, and the test was made at normal temperature. The crack lengths a and the corresponding cycles numbers N were noted. With the help of some numerical computation programs were determined dK, the stress intensity factor, and da/dN, the crack's propagation rate. In the end were traced the graphs of the variating da/dN, in connection with the defect's length a, respectively with the dK index, for the three asymmetry coefficients.