Microstructure refinement of structural steel in China

Abstract

In Oct. 1998 Chinese government opened national program: "Fundamental Research on New Generation of Iron and Steel Materials in China" (N.G. Steels). The progress of on-going project has been briefly reported in this paper. In order to get microstructure refinement in structural steels, the following 5 ways have been studied: For Ferrite+Pearlite microstructure in plain carbon steels and low-alloy steels, (1) Purified steel-making→Fully equiaxed continuous casting→Rough-mill with higher Zener-Hollman parameter (γDRX refinement)→Finishing-mill rolling by Deformation Induce Ferrite Transformation (DIFT) technology. (2) For thin-slab continuous casting and rolling (CSP) process, ultra-fine sulfides (20-60 nm) and oxides (5-20 nm) controlling technology. (3) For Low Carbon Bainite (and Ultra Low Carbon Bainite) microstructure (LCB/ULCB) in microalloyed steels, combination of Deformation Induced Precipitation (DIP) and subsequent middle temperature phase transformation controlling. For quench-temperated martensite microstructure in alloy structural steels: (4) Ultra-fine γ grains by innovated heat treatment and alloy design; (5) Carbide-free bainite/martensite microstructure with retained γ films along lath/sub-lath boundaries.