Optimizing Microalloy Addition to Produce 460 MPa Grade Steel in Thick Normalized Plate Commercially

To develop a high strength yield strength (YS) of minimum 460 MPa and high‐impact toughness (Min. 27 J at −50 °C) steel in thick normalized plate (>50 mm thickness), three different types of steel are prepared with varying nitrogen (90–150 ppm), vanadium (0.1–0.15 wt%), and niobium (0.03 wt%) levels. The cast steels are hot rolled and normalized at 900 °C. The microstructures are characterized by optical microscopy, scanning electron microscopy, electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM) to correlate with the tensile properties. The complex mechanism of precipitate dissolution, grain boundary pinning, and reprecipitation is involved in the case of vanadium precipitation in the normalized steel. The increase in nitrogen content from 90 to 150 ppm seems to have no positive effect on strength in the normalized condition. The strengthening is calculated for both as‐rolled and normalized conditions, and the highest precipitation strengthening is observed in 0.15V–90N in the as‐rolled state, and the highest grain size strengthening and precipitation strengthening are observed for 0.1V–0.03Nb–100N steel in the normalized state. Based on the above laboratory‐based study, a successful commercial heat is processed, and ≈450 MPa YS and 110 J (−50 °C) are observed in the hot‐rolled and normalized plate.