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A recent military hardware development program at Kaiser Electroprecision required the use of 220 ksi, 4330 V steel for a light weight, high reliability aircraft hydraulic component. The need for stringent control and prevention of hydrogen embrittlement was identified as a major program responsibility since both chrome and electroless nickel plating were employed in these components. An effort to use existing military procedures to set up a hydrogen embrittlement (HEM) test program to pull plated tension specimens was met with much frustration. It was found that a time-consuming 200-h pull test was specified in most cases for HEM tension specimens. The procedures were also found to contain a torturous and somewhat ambiguous path of logic upon which the requirements and methods regarding pull specimens were delineated.
The problem was handled in part by instituting an accelerated acceptance method for testing HEM specimens. This method involved pulling a single HEM tension bar, representing each lot of plated parts, in a seven-step load test to fracture over an 8-h period. The loads were based on a percentage of the predetermined fracture load, and each load state was held for 1 h. This technique enabled a relatively quick verification of the absence of embrittlement in the parts. It also provided the assurance that parts could be moved to subsequent processing without waiting the two- to five-week period often associated with the “standard” 200-h tests.
hydrogen embrittlement test, 8-hour test, stepped loading test
Dreher, Robert V.
Manager—Project Engineering, Kaiser Electroprecision, Irvine, CA