Fe-12Ni-4Co-2Mo-.05Ti alloy for use at 77°K and below

Thesis/Dissertation · Wed Oct 01 00:00:00 EDT 1975

DOI:https://doi.org/10.2172/4166848· OSTI ID:4166848

Whitaker, Bradley Watford ^[1]

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1. Univ. of California, Berkeley, CA (United States)

A variant of the maraging class of steels is proposed for application at 77°K and below where a combination of very high strength and good toughness is required. The alloy has a composition of Fe-12Ni-4Co-2Mo-0.05Ti where low interstitial content. The as quenched and quenched and aged structures were completely martensitic with a prior austenitic grain size of 10 to 12 μm. This structure had a Y.S. of 138.5 ksi and 154 ksi before and after aging respectively. All aging was done at 444°C for 4 hours. The DBTT was shown to lie above 77°K as measured by C_v testing. Based on dilatometric studies of the α $Yields$ γ and γ → α transformation temperatures a cycling treatment consisting of reportedly heating to above the A_f temperature followed by a water quench was utilized to further reduce the prior γ grain size to approximately 4 to 6 μm. The structure was completely martensitic and possessed a Y.S. of 151 ksi at 77°K in the unaged condition with a Y.S./K_IC ratio of 1.9 while the aged structure showed a Y.S. of 162 ksi with a Y.S./K_IC ratio of 1.3. C_v testing showed the DBTT to lie between 77°K and 4.2°K. Further grain refinement was accomplished by a 2 phase decomposition procedure which resulted in a grain size of 1 to 2 μm. The structure which contained decreasing amounts of austenite with temperature (3.0 percent at R.T. to 1.0 percent at 4.2°K) showed the best combination of strength and ductility at 4.2°K. A Y.S. of 205 ksi with a Y.S./K_IC ratio of 0.84 was achieved before aging. The aged structure was brittle at 4.2°K with a Y.S. of 218 ksi and a Y.S./K_IC ratio of 0.425.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: US Energy Research and Development Administration (ERDA)
• DOE Contract Number: W-7405-ENG-48
• NSA Number: NSA-33-005965
• OSTI ID: 4166848
• Report Number(s): LBL-4152
• Resource Relation: Other Information: Thesis. Orig. Receipt Date: 30-JUN-76
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
*COBALT ALLOYS- MECHANICAL PROPERTIES
*IRON BASE ALLOYS- MECHANICAL PROPERTIES
*MOLYBDENUM ALLOYS- MECHANICAL PROPERTIES
*NICKEL ALLOYS- - MECHANICAL PROPERTIES
AGING
CHARPY TEST
DUCTILITY
GRAIN SIZE
LOW TEMPERATURE
MARTENSITE
PHASE TRANSFORMATIONS
TITANIUM ADDITIONS
ULTRALOW TEMPERATURE
YIELD STRENGTH