Structural Product Quality Improvements Through the Microniobium Steelmaking Alloy Approach

by Steven G Jansto

Publisher - CBMM-Reference Metals Company, USA

Category - General Novel

The MicroNiobium® Alloy Approach has been applied in carbon steels exceeding 0.20% carbon such as AISI1050 grade automotive and AISI1080 long product steel applications. Developed applications involve automotive fasteners, seismic resistant rebar and pre stressed concrete wire rod. The MicroNiobium Alloy Approach mechanism is described and correlated to a variety of medium and high carbon steel grades and applications. The application of the MicroNiobium Alloy Approach in over 0.20% carbon steels enhances the metallurgical properties, consistency and processability of the hot rolled product. Such process and product metallurgical improvements relate to the Nb-pinning effect of the austenite grain boundaries in Nb- microalloyed steels exceeding 0.20%C steels. The key operational attribute is the micro-addition of Nb in higher carbon steels which mechanistically pins the austenite grain boundary during the reheat furnace process, thereby minimizing abnormal grain growth in the billet or slab prior to rolling. Typically abnormal grain growth occurs when thermal fluctuations and furnace abnormalities exist in actual reheat furnace operations. This abnormal grain growth leads to inhomogeneous ferrite grains in the final hot rolled product and subsequent variations and reductions in mechanical property performance such as fatigue, fracture toughness and yield-to-tensile properties. Additional evolving development opportunities and applications span pressure vessels, automotive coil springs, eutectoid rail steels, alloy tool and die steels, and tyre rod.

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