Industry perspective on ultrafine grained steels

Abstract

Steels with ultrafine grain sizes have been the subject of major international research efforts. The step change sought from the 'ultrafine' 1 μm grain projects has now largely been back-tracked to focus on 'very fine' 2–3 μm grains. Particularly, this research has concentrated on dual phase and multiphase steels, thus merging with the ongoing developments that continued the advance of established products, though giving such developments a dramatic boost. In single phase material, refinement to 1 μm grains inherently reduces the ductility, but some applications are being designed around such properties. Moreover, poor ductility from a tensile test need not mean inadequate formability for high strength automotive sheet. For various applications, established steels remain more cost-effective, but 'very fine' grained steels have now become a standard item already selling in large tonnages. The production technology developed under these 'ultrafine grain' projects is also now used to produce plain carbon/carbon–manganese steels with grain sizes that were previously the preserve of microalloyed steels.

Keywords:

• STEEL
• ULTRAFINE GRAIN SIZE
• DUAL PHASE STEELS
• MECHANICAL PROPERTIES
• FORMABILITY