Novel Production of Light Gauge Hot-Rolled Retained Austenite Steel

摘要

The current invention provides method to produce retained austenite (RA) bearing sheet steels at light gauges directly from hot rolling or hot-rolling plus annealing without the need for subsequent cold rolling. One production method is to take advantages of additional advancements in flat-rolled steel casting and hot rolling capabilities, for example in the advent of endless strip processing and advanced runout cooling systems, to allow for the production of martensitic and bainitic hot strip in light gauges. Subsequent annealing may then be employed to produce the desired RA-bearing sheet steel. The second production method to directly produce hot rolled light gauge RA-bearing steel is enabled by advanced hot rolling, cooling, and induction reheating capabilities, in a two-stage quench and austemper process to produce the desired microstructure and properties. An example is shown in the schematic below. The target microstructures are produced by interrupting quench from austenite just below the Ms temperatures (～10-20% martensite by volume) and induction reheating into the lower regime of the bainite formation range. Carbide-free bainite formation at reduced temperatures (400 - 500 ℃) is required to prevent excess austenite decomposition to ferrite/carbide structures, which is accelerated by the pre-existence of martensite to aid in nucleation, and a significant fraction {～10%+ by volume) of austenite may be retained.