When 3:30 PM - 5:00 PM Sep 11, 2008
Where Johnson Rooms, Lurie Engineering Center
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Paraequilibrium Carburization of Austenitic Stainless Steels: Interstitial Hardening Taken to a New Level

Arthur H. Heuer, Case Western Reserve University (Van Vlack Lecture)

Carburization of austenitic stainless steels at low temperatures, i.e. under paraequilibrium conditions, leads to massive increase in surface hardness (Rockwell C values of 70.5 or higher) without carbide formation. This "superhardness" is due to a "colossal" supersaturation of carbon interstitials (single phase austenite containing 10-20 at % carbon) and results in ~100x improvement in wear resistance, with essentially no loss in ductility of carburized components. Furthermore, the carbon concentration profile resulting from the LTCSS (Low Temperature Colossal Super Saturation) gas phase carburization process leads to residual surface compressive stresses ≥ 2 GPa, which arise because the uncarburized core constrains the ~3% lattice expansion that would otherwise arise from the massive concentration of interstitial carbon. These residual compressive stresses dramatically improve the fatigue resistance. In particular, fatigue lifetimes are increased by up to ~100x, and the endurance limit is nearly doubled. Finally, and most significantly, the corrosion resistance of 316L stainless steel in seawater is greatly enhanced—in crevice corrosion tests, for example, carburized 316L outperforms Ni-base alloys such as IN625.

Extensions of LTCSS technology to ferritic and duplex stainless steels and to Ni-base alloys will also be described.

The Van Vlack Lecture Series was established in honor of L. H. Van Vlack, to provide a distinguished lecture series from the outstanding leaders in the field of Materials Science and Engineering

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