Effect of Residual Impurities on Hydrogen Assisted Cracking in High-Strength Steels.
Final rept. 8 Dec 76-7 Dec 77,
PENNSYLVANIA UNIV PHILADELPHIA DEPT OF METALLURGY AND MATERIALS SCIENCE
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Intergranular embrittlement in 4340-type high strength steels yield strength approximately equal to 200 ksi have been studied both at room temperature and 77 K. The toughness trough which is the manifestation of one-step temper embrittlement was absent in a high purity steel at room temperature, but it appeared in the 77 K tests. The room temperature test produced no intergranular fracture, but some intergranular facets were found in the 77 K specimens. For commercial steels, the toughness trough occurred in both the room temperature and the 77 K tests. Intergranular fracture in the high purity steel can be produced at room temperature by charging cathodically with hydrogen in sulfuric acid solution. Hydrogen-assisted cracking in the high purity steel showed a high K sub th value approximately equal to 72 ksi sq root in in 1 atm H2 at room temperature, which is about a factor of three greater than that observed in any commercial steels. Hence, in this type of steel the resistance to hydrogen-induced cracking can be greatly increased by bringing the impurity effects under control. Author
- Metallurgy and Metallography