Strategies for Mitigation of Hydrogen Environment Assisted Cracking of High Strength Steels

摘要

Modem ultra high strength alloy steels (UHSS) have been developed with outstanding combinations of strength and fracture toughness. Such steels are characterized by high purity and nanoscale strengthening clusters/coherent precipitates in a complex precipitation hardened, martensitic microstructure. However, the performance of such steels is degraded dramatically by internal hydrogen embrittlement (IHE) and hydrogen environment embrittlement (HEE). Thus, the development of an UHSS that is immune to hydrogen embrittlement is of seminal importance. The issues that hinder understanding of IHE/HEE center on the capability to first understand fracture process zone damage mechanisms, and second to quantify and ultimately predict crack tip hydrogen concentrations relative to critical concentrations that trigger fracture. Mitigation of the hydrogen-cracking resistance of modem UHSS requires reduction in hydrogen uptake and/or modification of critical hydrogen concentrations for a given material by improving the intrinsic tolerance to dissolved and trapped hydrogen. Strategies for controlling and/or mitigating HEE and IHE of UHSS include control of intrinsic intergranular susceptibility governed by hydrogen- segregated impurity interactions and metallurgical alteration of H trap states. Another strategy is to exploit the strong electrochemical potential dependency of HEE cracking by using tailored cathodic protection schemes. Lastly, coatings can be designed to release ions that% reduce H production and/or block H uptake at crack tips. A combination of a responsive coating that provides a tailored- low level of cathodic protection and active corrosion inhibition, as well as control of metallurgical purity and H trap states, provides a necessary- couple strategy to mitigate HEE of modem high strength steels.