Effect of Niobium Alloying on the Corrosion Fatigue Properties of the Cr-Co-Ni-Mo Series of Ultra-high Strength Stainless Steels

Abstract

In order to investigate the stress corrosion cracking behavior of ultra-high strength stainless steel， the influence of Nb microalloying on the corrosion fatigue properties of Cr-Co-Ni-Mo series ultra-high strength stainless steel was studied by OM， XRD， TEM and other testing methods in combination with corrosion fatigue test. The results show that the steel has stress corrosion sensitivity in 3.5% NaCl solution， and the stress corrosion cracking mechanism of the steel was a mixed mechanism involving hydrogen embrittlement and anodic dissolution. Niobium alloying improved the corrosion fatigue performance of the steel， that is， the corrosion fatigue strength of steel increases from 440 MPa to 495 MPa after adding 0.11% Nb. The main reason is that niobium alloying refined the grain size of steel， promoted the precipitation of irreversible hydrogen trap of NbC in steel， and increased the amount of prior austenite grain boundaries， the proportion of low-angle grain boundaries， the number of Σ3 grain boundaries， and the volume fraction of austenite in steel.

Keywords

• ultra-high strength stainless steels； erosion fatigue； mechanism of stress corrosion cracking； nbc； austenite