Strengthening mechanism and precipitation behavior of advanced ultrahigh-strength titanium microalloy weathering steels for photovoltaic support

Abstract

This study developed an 800 MPa grade ultrahigh-strength titanium microalloy weathering steel for photovoltaic support with yield and tensile strengths of 869 MPa and 956 MPa, respectively, and elongation above 12%. A comprehensive analysis was conducted to reveal the strengthening mechanisms and precipitation behavior of ultrahigh-strength weathering steel. The results illuminated that grain refinement, dislocation, and precipitation strengthening contribute 70.7% of total yield strength, the main strengthening mechanism of the ultrahigh-strength weathering steel. Notably, the average size of the elliptical TiC particles was 6.9 nm, and a long-to-short axis ratio of TiC particles ranging from 1.62 to 2.03 aligned with the theoretical shape factor of 2.16. The thermodynamic calculations agree with the experimental results, and the precipitated phase can be regarded as TiC. The precipitation kinetics indicated that optimal finishing rolling and coiling temperatures (CT) are critical for obtaining many nano-sized TiC precipitates. Compared to the CT of 630 °C, 570 °C retains more dislocations, promotes the nucleation site of TiC precipitates, and slows the post-nucleation coarsening, which is the main reason for the higher precipitation and dislocation strengthening than 630 °C. The first observation of multi-atomic layer GP clusters near precipitated phases within the ultrahigh-strength titanium microalloy weathering steel was noteworthy. The GP clusters, acting as intermediate precipitates containing Ti precipitates, keep a co-lattice relationship with the iron matrix by the dislocations around the GP clusters adjusting the mismatch. The contribution of the interaction of GP clusters and dislocations to the yield strength was estimated to be ∼53 MPa.