The impacts of M/A constituents decomposition and complex precipitation on mechanical properties of high-strength weathering steel subjected to tempering treatment

• DOI: 10.1016/j.jmrt.2023.01.136
• Publication Date: 2023-01-31T08:14:03Z
• Authors: Liyang Zhao; Qiuming Wang; Genhao Shi; Bing Hu; Shibiao Wang; Mingliang Qiao; Qingfeng Wang; Riping Liu
• Keywords: Tempering; Weathering steel; Precipitation hardening

The impact of microstructure evolution on the mechanical properties a typical 500 MPa-grade weathering steel produced by an identical thermo-mechanical control process and different tempering treatments at 450–650 °C were thoroughly investigated mainly using scanning electron microscopy (SEM) equip with backscatter diffraction (EBSD), high-resolution transmission (HRTEM), X-ray diffractometer (XRD). Results indicated that as-rolled consists granular bainitic ferrite (GBF) considerable amount martensite/austenite (M/A) constituents, exhibiting unsatisfied properties. As temperature increased from 450 to 550 650 °C, massive twin-type M/A constituents decomposed preferentially into carbides following sequence Fe3C→(Cr, Mn, Fe)3C→(Cr, Fe)3C + (Cr, Mn)23C6, small fine lath-type remained. matrix recovered laths merged, dislocation density decreased proportion high-angle grain boundary (HAGB) increased. Nanoscale (Ti, Nb)C ε-Cu particles also precipitated simultaneously, leading increase yield strength. strain hardening capacity hence tensile strength reduced resulting decomposition constituents. Moreover, toughness was first enhanced 450–600 decreasing content increasing HAGBs proportion, then deteriorated due precipitation necklace-like M23C6 boundaries. An optimum property combination achieved via 550–600 °C.