PR-255-006 - 2004 Adv High Strength Sheet Steels for Auto Applications

Quenching and Partitioning Response of a Si-Added TRIP Sheet Steel

A. M. Streicher, J. G. Speer, D. K. Matlock and B.

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Mechanical property results are presented for sub-sized sheet tensile samples of a 0.19C-1.59Mn-1.63Si TRIP steel composition, heat-treated by a recently developed process, quenching and partitioning (Q&P). The Q&P process was proposed to produce steels with controlled volume fractions of carbon-enriched retained austenite at room temperature. For Q&P processing, sheet steel samples were heated to form austenite (either completely or partially), followed by quenching to a temperature between Ms and Mf to create controlled amounts of martensite, followed by a thermal treatment to partition carbon into the remaining austenite. All processing occurred isothermally in molten salt or in low-melting point metallic baths. The ability to create new sheet microstructures using Q&P is investigated, and the mechanical property results are compared to data for other high strength sheet products. The results suggest that Q&P is able to extend the strength of TRIP steels to higher levels than obtained by conventional processing.

Keywords: quenching and partitioning (Q&P), retained austenite, martensite, mechanical properties, TRIP, highstrength steel