Alloy Qualification for Producing Quench and Tempered Plate Steels with Extra‐Heavy Gage

The present study analyzes the impact of the alloy design on hardenability to produce extra‐heavy‐gage steel plates exceeding 100 mm thickness with a minimum yield strength of 690 MPa. Such plates are critical for infrastructure and offshore applications. The typical production route employs conventional quenching after plate rolling. Core cooling rates due to heavy plate gage can be low (≈2 K s −1 ). To ensure sufficient core strength and avoid soft phases, through‐thickness hardenability is an important alloy design criterion. This study investigates the individual effects and potential synergies of molybdenum, nickel, and boron on hardenability and transformation behavior. Experimental work includes dilatometry to construct continuous cooling transformation diagrams and Jominy tests to evaluate hardenability. Results indicate that 0.5% molybdenum with nickel content between 0.5% and 1.0% can achieve the desired strength level in the center of very heavy‐gaged plates. Molybdenum is the key alloying element for achieving high hardenability across different cooling rates. Nickel supports molybdenum‐based hardenability particularly at low cooling rates. Boron microalloying lowers transformation‐start temperatures below 550 °C, promoting homogeneity and suppressing ferrite formation. These findings allow to define a suitable alloy concept for achieving high as‐quenched hardness depending on the plate thickness and related core cooling rate.