Effect of Hot Working Technology on Precipitation Behavior of Nanoscale Strengthening Phase in Ferritic Cu-rich High Strength Steel

The introduction of nanoscale Cu-rich precipitates into low carbon high strength steel can improve the weldability while ensuring its strength and toughness, but the precipitation behavior of nanoscale Cu-rich precipitates need to be controlled by appropriate hot working process. The effect of hot working process on the precipitation behavior of ferritic Cu-rich nano-precipitation strengthened high strength steel was studied by JMatPro software, optical microscope（OM） and transmission electron microscope（TEM）. The results show that the precipitates in hot-rolled ferritic Cu-rich high strength steel are mainly spherical（Nb,Ti）C with a diameter of about 15 nm. After tempering at 600 ℃, a large number of fine 9R/3R structure Cu rich phases dispersion of 5-17 nm, and a small amount of large（Fe,Cr）₃C precipitate with a size of 100-280 nm.The strengthening increment of nanoscale Cu-rich phase is about 92 MPa, which is semi-coherent with the matrix and has no adverse effects on the toughness. Therefore, the yield strength of the tempered ferritic Cu-rich high strength steel can reach639 MPa and the impact absorption energy can reach 265 J at-40 ℃.