Use of the Instrumented Bolt and Constant Displacement Bolt-Loaded Specimen to Measure In Situ Hydrogen Crack Growth in High Strength Steels.

摘要

Aggressive environments experienced by large caliber gun tubes during processing and firing have lead to a great deal of investigation on the hydrogen-induced cracking susceptibility of high strength steels. The constant displacement bolt-loaded specimen has been used to determine the hydrogen crack growth rates and threshold stress intensity of AF1410 - both conventionally and isothermally heat treated - and AerMet 100. Additionally, the severe susceptibility of high strength steels has necessitated the application and modification of a low cost, highly reliable, in situ crack measurement method, called the instrumented bolt. The instrumented bolt consists of a full bridge, strain-gaged stainless steel bolt coupled to an automatic data acquisition system. New expressions have been developed for use with the instrumented bolt and bolt-loaded specimen to relate load to crack growth. Our study determined that Stage II crack growth rates for the AF1410 were 1.1E (exp -2) and 2.3E(exp -2) mm/s for conventional and isothermal AF1410, respectively. Threshold stress intensity levels for AF1410 were 16.0 and 13.7 MPa m(exp 1/2), respectively. Stage II crack growth rates for AerMet 100 were 2.4E(exp -2) mm/s, while the threshold stress intensity was 14.1 MPa m(exp 1/2).