Abstract
To study the applicability of fracture mechanics to stress corrosion cracking of SUS 304 stainless steel in 42% MgCl2 solution (143°C), three different types of tests i.e, K increasing, constant and decreasing type have been performed. It was made clear that crack propagation rate, da/dt was well characterized by K value in almost the same way in spite of the difference of testing types. Namely, the corelation curve between da/dt and K value could be divided roughly into two regions, regions I and II. In region I, da/dt was approximately proportional to the square of K value and in region II, after discontenious dropping of da/dt, da/dt increased again with K increasing. In addition, it was confirmed from the result of K decreasing type test that threshold stress intensity factor for stress corrosion cracking, Krsaa was nealy equal to 10 kg mm-3/2 in this combination of environment and material. From the observation of crack appearance, it was made clear that crack grew along single path in region I but it branched almost into two cracks in region II, so that the dropping of da/dt in region II would be caused by decreasing of K value with crack branching.
