高張力４３４０鋼ＳＣＣ破面近傍の残留応力分布に及ぼす電極電位の影響

Abstract

Stress corrosion cracking tests were conducted by using the compact tension (CT) specimens of 200°C tempered AISI 4340 steel in a 3.5% NaCl solution environment under various electrode potentials. The distribution of the residual stress beneath the fracture surface was measured with the X-ray diffraction technique. The fracture surface and the crack morphology were also observed by scanning electron microscopy. The Effect of electrode potential on the growth kinetics of stress corrosion cracking was discussed on the bases of the results of X-ray observation and scanning microfractography. The results obtained are summarized as follows:(1) The residual stress measured on the fracture surface was tension under cathodic potential. It decreased with increasing potential, and changed to compression under anodic potential.(2) The relation between the plastic zone depth ωy and the stress intensity factor K can be approximated by the following fracture mechanics equation:ωy=α(K/σY)2where σY is the yield strength. The α value was 0.084 under the free corrosion condition and 0.053 under the cathodic polarization condition.