Abstract
Metallurgical concepts for new ultra-high strength martensitic steels have been developed through direct quenching after hot rolling. In addition to the chemical composition, the hot rolling, quenching, and annealing parameters need to be optimized to fulfill the requirements for the demanding applications for which these steels are used. It is also shown that the welding behavior is influenced by the choice of alloying concept. Typical applications also require a high fatigue resistance, especially of formed components. For that reason, a dedicated set-up was developed that allows differentiation between materials, which is illustrated through the effect of inclusions on the fatigue performance of a bent test piece.
Highlights
For many years, the production of martensitic flat steel products has been done through austenitizing and quenching, often followed by a tempering treatment
Direct quenching processes have been developed for hot strip mills to produce ultra-high strength martensitic grades
The second class is martensitic strip steels developed for structural applications, e.g., trailers, chassis parts, and lifting equipment
Summary
The production of martensitic flat steel products has been done through austenitizing and quenching, often followed by a tempering treatment. These steels were typically rolled on a plate mill. Direct quenching processes have been developed for hot strip mills to produce ultra-high strength martensitic grades. There exist two main classes of low carbon martensitic strip steels. The second class is martensitic strip steels developed for structural applications, e.g., trailers, chassis parts, and lifting equipment. This paper discusses the main metallurgical principles that need to be understood to develop low carbon martensitic strip steels via direct quenching. The test that was developed shows the importance of an optimized metallurgical concept, e.g., the need for a low amount of inclusions
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