EFFECT OF STRAIN RATE AND REFORMED AUSTENITE ON MECHANICAL PROPERTIES OF AISI 415 STAINLESS STEEL

Hydraulic turbine blades are exposed to cyclic loading which favors formation and propagation of fatigue cracks. Due to different in-service loading regimes, the crack tip is subjected to a range of strain rates. The present study proposes an experimental investigation of the mechanical properties of a 13%Cr-4%Ni martensitic stainless steel at strain rates (ε ̇) ranging from 4.7E-6s-1 to 6E-2s-1. The ε ̇ was chosen to simulate plastic deformation rate at the crack tip for load cycles frequency ranging from 0.3 to 35 Hz. Two heat treatments were applied to the alloy to obtain a martensitic microstructure containing 2% and 20% of reformed austenite (RA). For the sample containing 2% of RA, increasing ε ̇ resulted in a difference in yield strength (σ_y) and ultimate tensile strength (UTS) of 10% and 7%, respectively. As for the sample containing 20% of RA, an increase in the RA content had no significant effect on the σ_y strain rate sensitivity. On the other hand, it reduced the UTS strain rate sensitivity to 1%. These results indicate that σ_y is strain rate sensitive for both tested microstructure. Results also show that presence of RA increased 23% the uniform elongation as compared to microstructure containing
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