Design of an Fe--12Mn--0. 2Ti alloy steel for low temperature use
An investigation has been made to improve the low temperature mechanical properties of Fe-8 approximately 12% Mn-0.2 Ti alloy steels. A two-phase (a + ..gamma..) tempering in combination with cold-working or hot-working has been identified as an effective treatment. In an Fe-12 Mn-0.2 Ti alloy a promising combination of fracture toughness and yield strength was obtained at -196/sup 0/C. A potential application as a Ni-free cryogenic steel was thus shown for this alloy. These improvements of properties were mainly attributed to the ultra-fine grain size and to a uniform distribution of retained austenite. It was also shown that an Fe-8 Mn steel could be grain-refined by a purely thermal treatment because of its dislocated martensitic structure and absence of epsilon phase. As a result, a significant reduction of the ductile-brittle transition temperature was obtained in this alloy. The nature and origin of brittle fracture in Fe-Mn alloys were also investigated. Two embrittling regions were found in a cooling curve of an Fe-12 Mn-0.2 Ti steel which were shown to be responsible for intergranular fracture. A fast cooling through the martensite transformation temperatures results in a quench-crack type brittleness along prior ..gamma.. grain boundaries. Auger electron spectroscopy identified no segregation during solution-annealing treatment. If held too long below the transformation finish temperature, the 12 Mn steel undergoes another form of embrittlement. This phenomenon was attributed to intergranular tempered martensite embrittlement. Avoiding the embrittling zones by controlled cooling led to a high cryogenic toughness in a solution-annealed condition.
- Research Organization:
- California Univ., Berkeley (USA). Lawrence Berkeley Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 7301179
- Report Number(s):
- LBL-6603
- Country of Publication:
- United States
- Language:
- English
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