Applications of rapid thermal processing to advanced high strength sheet steel developments

Abstract

Rapid thermal processing strategies, i.e. thermal histories that involve high heating rates, short times at peak temperatures, and subsequent rapid cooling by quenching, and that typically require significantly shorter total processing times than are utilized in conventional sheet steel processing, are reviewed to illustrate potential benefits and challenges for the production of new advanced high strength steel grades. A fundamental framework based on conventional induction heat treating often applied to rapidly selectively harden surfaces of steel components is highlighted to provide a basic structure for assessment of rapid thermal processing of sheet steels. Four sheet steel product groups were considered. These include dual-phase (DP) steels, quenched and partitioned (Q&P) steels, flash processed steels, and press hardened steels. In comparison to conventionally heat-treated steels, rapid processing of steels resulting in multi-constituent microstructures consisting of ferrite and martensite (DP) and also containing retained austenite (Q&P) result in enhanced strength-ductility combinations primarily due to microstructural refinement. Results indicate that flash processed and press hardening steels, both with primarily martensitic microstructures, exhibit properties largely similar to conventional quenched and low-temperature-tempered steels.