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Sensitization of high-nitrogen austenitic stainless steels by dichromium nitride precipitation.

Simmons JW; Atteridge DG; Rawers JC

Corrosion 1994 Jul; 50(7):491-501

https://doi.org/10.5006/1.3294349

10012427

High-nitrogen (N) stainless steels (SS) are receiving increased attention because of their strength advantages over carbon (C)-alloyed materials, but they have been found susceptible to dichromium nitride (Cr2N) precipitation during thermal exposure between approx. 600 degrees C and 1,050 degrees C. Sensitization susceptibility of a high-N, low-C austenitic SS by Cr2N precipitation at 700 degrees C and 900 degrees C was determined using the single-loop electrochemical potentiokinetic reactivation (EPR) test. High-N SS was found susceptible to sensitization caused by grain boundary (GB) precipitation of Cr2N, with the degree of sensitization increasing systematically with aging time at 700 degrees C. Sensitization of high-N materials did not require the concomitant precipitation of chromium (Cr)-rich metal carbide (M23C6). Materials aged at 900 degrees C were not sensitized, although the rate of precipitation was greater than at 700 degrees C. This indicated the minimum Cr level in the Cr-depleted zone of the matrix associated with nitride precipitation at 900 degrees C was higher than required to produce attack in the EPR test. Prior deformation accelerated Cr2N precipitation and sensitization kinetics at 700 degrees C, in accordance with previous research on C-based alloys. Sensitization development and deformation effects in high-N austenitic SS as a result of Cr-rich Cr2N precipitation were qualitatively analogous to sensitization phenomena ascribed to Cr-rich M23C6 precipitation in C-based alloys. Results indicated high-N, low-C SS was susceptible to intergranular corrosion (IGC) and/or intergranular stress corrosion cracking (IGSCC) as a result of sensitization after thermal exposure to a temperature regime at which Cr2N precipitation occurs.

Stainless steel; Metal alloys; Electrochemical properties; Thermal effects; Temperature effects; Materials testing

CORRAK

19940701

Journal Article

1994

OP 169-94

7

0010-9312

ALRC

Corrosion

OR