The Effect of Some Electrolytes on the Stress Corrosion Cracking of AISI 4340 Steel

The effects of solutions of 16 different electrolytes on the stress corrosion cracking (SCC) of AISI 4340 steel U-bend specimens have been studied at various concentrations and at 25, 65, and 100 C (77, 149, and 212 F). Stresses were near the yield point of the alloy. In unbuffered solutions of neutral salts, there was poor correlation between time to failure and the initial or final pH of the solution. In strongly buffered solutions, there was a strong pH dependence; the time to failure in 10% NaCl increased about 100 fold between pH 4-5 and pH 7. Susceptibility to cracking increased moderately with the concentration of KNO3 solutions, but decreased with rising concentration of NaCl solutions. The cracking rate increased by 50% per 10 C for NaCl solutions. The rate increased 85% per 10 C for KNO3 solutions. KNO2 or NaNO2, dicyclohexylammonium nitrate, some K2CrO4 solutions and all alkaline solutions with a strong reserve of base inhibited SCC by factors of 10 to 100 times as compared with cracking in distilled H2O.