18Mn-12Cr-1.7Ni非磁性鋼の強化法

概要

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Nonmagnetic drill collars for oil wells should be rigid enough to sustain the intense load higher than 70kgf/mm2.The following two methods proved to be effective for enhancing the proof stress of austenitic steel bearing 18% Mn, 12% Cr and 1.7% Ni, one of candidate materials for such an application.(1) Niobium additionThe modification through Nb addition up to 0.15% yields the finer grain size and so the increment of 0.2% proof stress for the bars solution-treated at 1000°C. The steel with 0.15% Nb attains 48kgf/mm2 surpassing the 0.2% proof stress of Nb-free one by 11kgf/mm2.(2) Hot-cold WorkA heavy working is ready at 800°C, where the strain hardening remains moderate.The hot-cold working more than 30% guarantees the 0.15% Nb steel the 0.2% proof stress exceeding 70kgf/mm2.The high strength steel obtained above fullfils the requirements for drill collars, prominent ductility and depressed permeability.
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