With the increasing use of thick-section quenched and tempered steels for nuclear and chemical reactors, there is a definite need for information on the properties of some of the newer low-alloy high-strength steels when given such thick-section heat treatment.Of particular interest are yield and tensile strengths attainable, the notch toughness to be expected, the plastic fatigue strengths available and the kinds of microstructure that appear to be characteristic of these thicknesses.In the program reported here, four quenched and tempered heavy-section steels-A212 Grade B, A533 Grade B, A542 and A543 - were studied in the simulated 6-in. thick and 12-in. thick quenched, tempered and stress-relieved condition.Specimens taken from these simulated heavy sections were evaluated to provide a characterization of the properties and structure of heavy-section, heat-treated, low-alloy steels.