Effect of Alloying Elements on Propagation Rate of Stress Corrosion Cracking and K_ISCC of Austenitic Stainless Steels in Boiling in MgCl₂ Solutions

Abstract

The effect of alloying elements on the propagation rate of stress corrosion cracking and threshold stress intensity factor for stress corrosion cracking (K_ISCC) of austenitic stainless steels has been investigated in boiling MgCl₂ solutions. The fracture surface was investigated fractographically by scanning electron microscopy. The results obtained are as follows:
(1) K_ISCC was about 3 MPa\sqrtm (10 kgf/mm^3⁄2) for SUS 304 stainless steels containing below about 0.020 mass%P and decreased with increasing the amount of phosphorus above 0.020 mass% in boiling 45%MgCl₂ solution.
The propagation rate of stress corrosion cracking increased with the increase in phosphorus content.
(2) The increase molybdenum and nitrogen content decreased K_ISCC and increased the propagation of stress corrosion cracking in boiling 42% and 40%MgCl₂ solutions, respectively.
(3) Sulfur in the composition range of 0.008∼0.038 mass% had no significant influence on K_ISCC and the propagation rate of stress corrosion cracking in boiling 45%MgCl₂ solution.
(4) It was found that the fracture surface of SCC was transgranular and composed of {100} and {110} planes, which was determined by the morphology of etch pits.