Effect of Cold Work on Stress Corrosion Crachking Behavior of Types 304 and 316 Stainless Steels

- Dec 08, 2016-

It is well known that cold work has an influence on the stress corrosion cracking (SSC) behavior of austenitic stainless steels. A study on the effect of prestraining in uniaxial tension on the stress corrosion behavior of 304 and 316 stainless steels in MgCl2 at 154℃ has led to the following results and conclusion:

(1)     In tests carried out at a stress of 112 MPa for 316 stainless steel the time for fracture decreased with cold work, passed through a minimum, increasing again beyond the minimum giving a 'U' shaped curve, while for 304 stainless steel there was no systematic variation in time for fracture with cold work.

(2)     In tests carried out at stresses corresponding to 40 pct of the yield strength for each cold work condition, for both 304 and 316 stainless steels, the time for fracture decreased with increasing cold work.

(3)     For both steels at all stresses, stress corrosion cracking initiated in the transgranular mode; the fracture mode changed to intergranular in the case of 316 stainless steel for all the test conditions with the final separation occurring by ductile dimple mode. In the case of 304 stainless steel, a transgranular to intergranular transition occurred only in specimens that had been cold worked to very high levels (26 pct and 56 pct). There was a general tendency for an increase in the intergranular fracture area with level of cold work and applied stress.

(4)     In the initial transgranular cracking region typical wellknown fan patterns were observed. The direction of fans was generally found to coincide with the direction of macroscopic crack propagation. The density of fans increased with prior cold work, though at very high degrees of deformation fan patterns became less obvious due to extensive tangling of dislocations.