Optimum Thread Rolling Process That Improves SCC Resistance

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Accelerated testing in environments aggressive for the specific material have shown that fastener threads that are rolled after strengthening heat treatments have improved resistance to SCC initiation. For example, intergranular SCC was produced in one day when machined (cut) threads of high strength steel (ASTM A193 B-7 and A354 Grade 8) were exposed to an aggressive aqueous environment containing 8 weight % boiling ammonium nitrate and stressed to about 40% of the steel's yield strength (120 ksi, 827 MPa). In similar testing conditions, fasteners that had threads rolled before heat-treatment (quench and temper) had similar susceptibility to SCC. However, threads ... continued below

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4282 Kilobytes pages

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Kephart, A.R. October 29, 2001.

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This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided by UNT Libraries Government Documents Department to Digital Library, a digital repository hosted by the UNT Libraries. It has been viewed 13 times . More information about this report can be viewed below.

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  • Lockheed Martin
    Publisher Info: Lockheed Martin Corporation, Schenectady, NY 12301 (United States)
    Place of Publication: Schenectady, New York

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Description

Accelerated testing in environments aggressive for the specific material have shown that fastener threads that are rolled after strengthening heat treatments have improved resistance to SCC initiation. For example, intergranular SCC was produced in one day when machined (cut) threads of high strength steel (ASTM A193 B-7 and A354 Grade 8) were exposed to an aggressive aqueous environment containing 8 weight % boiling ammonium nitrate and stressed to about 40% of the steel's yield strength (120 ksi, 827 MPa). In similar testing conditions, fasteners that had threads rolled before heat-treatment (quench and temper) had similar susceptibility to SCC. However, threads rolled after strengthening, exhibited no SCC after a week of exposure, even when stressed to 100% of the B-7 alloy yield strength. Similarly, intergranular SCC was produced in less than one day when machined (cut) threads of nickel-base alloys (X-750 and aged 625) were exposed to an aggressive 750 F doped steam environment (containing 100 ppm of chloride, fluoride, sulfate, nitrate and a controlled hydrogen overpressure) and stressed to about 80% of the alloy yield strength (117 ksi, 807 MPa). In similar testing conditions, threads rolled after strengthening exhibited no SCC after 50 days of exposure. This beneficial effect of the optimum thread rolling process (i.e., threads rolled after strengthening) is due to the retention of large residual compressive stresses in the thread roots (notches) which mitigate the applied notch tensile stresses resulting from joint design pre-loads. use of these material specific aggressive environments can provide an accelerated test to verify that threads were produced by the optimum thread rolling process. These tests could support fastener acceptance criteria or failure analysis of fasteners with unknown or uncertain manufacturing processes. The optimum process effects may not always be detected by more conventional methods (e.g., metallography or hardness testing).

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4282 Kilobytes pages

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OSTI as DE00821687

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  • Other Information: PBD: 29 Oct 2001

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  • Report No.: LM-01K107
  • Grant Number: AC12-00SN39357
  • DOI: 10.2172/821687 | External Link
  • Office of Scientific & Technical Information Report Number: 821687
  • Archival Resource Key: ark:/67531/metadc781924

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • October 29, 2001

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • April 28, 2016, 8:52 p.m.

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Kephart, A.R. Optimum Thread Rolling Process That Improves SCC Resistance, report, October 29, 2001; Schenectady, New York. (digital.library.unt.edu/ark:/67531/metadc781924/: accessed May 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.