A mechanistic study of transgranular stress corrosion cracking of type 304 stainless steel
- PDF / 3,128,203 Bytes
- 9 Pages / 597 x 774 pts Page_size
- 0 Downloads / 221 Views
I.
INTRODUCTION
O V E R the years, substantial research effort has been devoted to the understanding of the mechanisms of transgranular stress corrosion cracking (TGSCC) of austenitic stainless steels in chloride-containing environments because of the serious problems this phenomenon can cause in service. As yet, no one model for this form of environment-induced cracking has gained general acceptance. One reason for this lack of agreement has been the conflicting nature of some phenomenological aspects of the cracking process. The crystallographic nature of crack propagation is an important clue to the underlying mechanism and was recently reviewed for face-centered cubic (fcc) metals and alloys. ]11For austenitic stainless steels, the cracking planes reported are {100}, {110}, {211}, and {210}. The apparent discrepancy in the reported cracking planes among various workers is a hindrance to formulating a single mechanism of cracking; however, it can also be attributed to the limits in the experimental techniques available for determining crack plane orientations on the microscale in some of the earlier studies. It has become increasingly clear from recent detailed workt2,31 that {100} is the predominant cracking plane in austenitic stainless steels. Crack propagation has been shown to be discontinuoust4-7~ and fractographic features on mating fracture surfaces are found to be matching and interlocking, t2,s~ All of these physical crack propagation features suggest that cracking occurs by a microcleavage process. The way in which the environment induces cleavage in an otherwise ductile material, however, is not clear. Historically, anodic dissolution has received detailed analyses as a possible mechanism for TGSCC. A mechanism
S. JANI, Graduate Student, M. MAREK, Professor, and R.F. HOCHMAN, Professor, are with the School of Materials Engineering, Georgia Institute of Technology, Atlanta, GA. 30332 E.I. MELETIS, Associate Professor, is with the Materials Engineering Program, Mechanical Engineering Department, Louisiana State University, Baton Rouge, LA 70803. Manuscript submitted March 18, 1988. METALLURGICAL TRANSACTIONS A
based on enhanced surface mobility has recently been proposed. 191 The present research is an extension of a previous study by Meletis and Hochmant21 in which the crystallographic characteristics of TGSCC of 304L stainless steel in MgCI2 were investigated. They found that cracking occurred primarily on {100} planes, with some secondary cracking occurring on {110} planes. In the present research, the main effort was directed toward characterizing the damage substructure of the 304L specimens tested in the previous study,t2] with a view to furthering understanding of the TGSCC phenomenon. Based on the results of this study, a new "hydrogen-induced cleavage" model is proposed.
II.
EXPERIMENTAL
Cylindrical single crystals of AISI 304L stainless steel were tested for TGSCC in 45 wt pct MgC12 at 155 ~ as described previously, t21 The testing was conducted on 5-mm-diameter tension specimens under
Data Loading...
